Pack Size
Quantity
Price
 
2.5 g
$217.00

Product data and descriptions listed are typical values, not intended to be used as specification.

  • HMIS

    2-4-0-X
  • Molecular Formula

    C8H18Ge
  • Molecular Weight (g/mol)

    186.82
  • Purity (%)

    95%
  • Boiling Point (˚C/mmHg)

    152°
  • Density (g/mL)

    1.005
  • Flash Point (˚C)

    32°C (90°F)
  • Refractive Index @ 20˚C

    1.4501

Application

Oligomerizes with butadiene in presence of NiCl2-Et2AlCl-Ph3P.1
Undergoes Diels-Alder reactions.2
Reacts with Fischer carbene complexes to form germyl enol ethers.3

Reference

1. Rafikov, S. Izv. Akad. Nauk. Ser. Khim. 1982, 920.
2. Salimgareeva, I. et al. Dokl. Nauk. 1981, 261, 118.
3. Barluenga, J. et al. Organometallics 1997, 16, 4525.

Safety

  • Packaging Under

    Nitrogen
  • Organogermane Cross-Coupling Agent

    The cross-coupling reaction is a highly useful methodology for the formation of carbon-carbon bonds. It involves two reagents, with one typically being a suitable organometallic reagent - the nucleophile - and the other a suitable organic substrate, normally an unsaturated halide, tosylate or similar - the electrophile.

    Vinyltriethylgermane; Triethylvinylgermane; Ethenyltriethylgermane; Triethyl(ethenyl)germane

  • Vinylation reagent
  • Oligomerizes with butadiene in presence of NiCl2-Et2AlCl-Ph3P
  • Undergoes Diels-Alder reactions
  • Reacts with Fischer carbene complexes to form germyl enol ethers
  • Extensive review of silicon based cross-coupling agents: Denmark, S. E. et al. "Organic Reactions, Volume 75" Denmark, S. E. ed., John Wiley and Sons, 233, 2011
  • Metal-Organic Chemistry, Articles

    Applications of Germanium Compounds – Wille et al.

    1021_Metal-Organics 4000B_Metal Organics 3000B 9/11/10 10:02 AM Page 93
    
        
    
    Gelest, Inc.
    
    Applications of Germanium Compounds
    Andrew E. Wille and Barry Arkles
    Gelest Inc.
    Germanium compounds have emerged as critically important materials in the fabrication of microelectronics,
    optics and sensors. Potential new applications in organic transformations and polymer synthesis have also been
    reported. This article highlights some of the chemistry associated with these applications. It also compares and
    contrasts the chemistry of germanium with the more widely understood chemistry of silicon. For readers with a
    deeper interest in the chemistry of germanium, comprehensive reviews provide a detailed description.1,2,3,4,5
    Metallic Germanium and Metallization Chemistry
    Germanium is a semiconductor. In fact, germanium was the first material to be fabricated into practical semiconductor devices, diodes. As a consequence, a significant body of literature relating to the electrical properties of
    germanium has developed. The mobility of holes in germanium is greater than that of silicon and of any other
    common semiconductor. The hole and electron mobilities are closer in germanium than other semiconductors,
    particularly at low temperatures. This has made germanium an attractive candidate for high performance CMOS
    technology. In high speed digital communications associated with broad-band and cell-phones, SiGe films are
    used to fabricate heterojunction bipolar transistors (HBTs). In other high speed applications SiGe films are
    deposited as molecular films which act as templates for the epitaxial deposition of silicon. The resulting lattice
    mismatch creates a strained silicon layer which exhibits enhanced electron mobility, providing improved device
    performance. SiGe technology has the potential to replace GaAs in many applications. Other electronic applications of metallic germanium and its alloys include quantum dots, amorphous films for solar energy and LEDs.6,7
    Germane, GeH4, in combination with silane, SiH4, is the most widely used germanium precursor for chemical
    vapor deposition (CVD) of SiGe films. Other precursors include methylgermane, n-butylgermane, t-butylgermane
    and diethylgermane.8
    A broader range of germanium compounds have been used to synthesize germanium nanowires including
    diphenylgermane9,10 and germanium tetraiodide11,i. Amorphous a-GeCO:H films have been deposited from
    tetramethylgermane by PECVD.12
    Bulk germanium metal, fabricated from wafers, is currently of interest in the fabrication of monolithic
    fiber-optic receivers, since germanium photodiodes perform well at 1.3-1.5 micron wavelengths.
    Germanium metal is also of utility in infrared detectors, which comprise the metal’s largest current use.
    
    Inorganic Germanium Chemistry
    Bond energies of Ge-X bonds are generally considered to be about 10% less than corresponding Si-X bonds.
    This is reflected in the somewhat lower thermal stability of germanium compounds. The electronegativities of
    germanium and silicon are 2.01 and 1.90, respectively, on the Pauling scale; their configuration energies are 11.80
    eV and 11.33 eV, respectively. While silicon is apparently more electropositive than germanium, reactivity
    indicates that polarization parameters may be more equivalent. Valence states of +2 are readily accessible for
    germanium and GeCl2, GeBr2 and GeI2 are isolable compounds. In contrast, silicon dihalides are known as reactive intermediates by studies of emission bands or trapping experiments. The chemistry of both elements proceeds
    primarily in the +4 state, although hyper-coordinate states, particularly for fluorocompounds, are known.
    Both silicon and germanium metal react with halogens and hydrogen halides to give analogous products.
    Halides of both elements react rapidly with water to give oxides and hydroxides. Germanium oxides can be
    converted back to the halides by reaction with the appropriate acid. In the case of silicon, only hydrofluoric acid
    reacts with the oxides to form fluorosilanes.
    Germanium compounds have higher optical densities than silicon compounds. This leads to the second major
    application of germanium compounds: the controlled combustion of germanium tetrachloride with silicon tetrachloride in a hydrogen-oxygen flame in chemical vapor axial deposition (CVAD) for the formation of ingots from
    which step-index fiber optics are drawn.,14,15 Tetraethoxy-germane is a liquid metal-organic precursor with a high
    vapor pressure that is well-suited for CVD of germanium oxide in optical16 and dielectric17applications. Sol-gel
    processing has also been employed as a method of preparing mixed germanium oxides. Again, tetraethoxygermane is the most widely used metal-organic precursor, but other germanium alkoxides containing methoxy and
    isopropoxy groups are used.18
    
    Reprinted from: Metal-Organics for Materials, Polymers and Synthesis © Gelest Inc., 2011
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    Organic Chemistry
    In contrast to silicon, sterically hindered organogermanium compounds in the +2 state are
    readily isolated. Examples include dicyclopentadienylgermanium, di[bis(trimethylsilyl)methyl]
    germanium and bis[bis(trimethylsilyl)amino]germanium.
    (CH3)3Si
    
    Si(CH3)3
    N Ge
    
    Ge
    
    (CH3)3Si
    
    (CH3)3Si
    H C Ge
    (CH3)3Si
    
    N
    Si(CH3)3
    
    Si(CH3)3
    C H
    Si(CH3)3
    
    The bis[bis(trimethylsilyl)amino]germanium forms poly(germanium enolates) upon reaction with
    _,`-unsaturated ketones.19
    O
    (CH3)3Si
    
    ((CH3)3Si)2N
    
    Si(CH3)3
    N Ge
    
    (CH3)3Si
    
    N
    
    Ge
    ((CH3)3Si)2N
    
    +
    Si(CH3)3
    
    O
    
    Di[bis(trimethylsilyl)amino]germanium also reversibly binds H2 and CO2 in 3-coordinate complexes.
    Germanium dihalides, GeI2 and GeCl2 and its readily prepared complexes GeCl2-etherate and GeCl2dioxanate react with alkyl and aryl halides20 to yield alkyl and aryl germanium trihalides.
    CH3CH2CH2CH2Cl
    
    + GeCl 2
    
    CH3CH2CH2CH2GeCl 3
    GeCl 3
    
    Br
    3 GeCl 2 ¥• O
    
    O
    
    +
    
    3
    
    2
    
    GeBr 3
    +
    
    Most germanium proceeds in the +4 state and is comparable to silicon. The following enumeration is
    extremely incomplete.
    Grignards and alkali metal organics will displace halides bound to germanium and silicon to give the
    organo-substituted compound.
    Germanium forms Ge-Ge bonds readily through Grignard chemistry in addition to alkali metal coupling,
    which is the most accessible route for Si-Si bond formation. While Si-Si bonds can be readily cleaved by
    Na-K in ether, Ge-Ge are cleaved only under more rigorous conditions such as the use of higher boiling
    solvents like tetrahydrofuran. In both cases multiple metal-metal bonds give photoreactive compounds.
    Organogermanium and organosilicon compounds can both be prepared by the copper catalyzed direct
    reaction of alkyl and aryl halides with the metal.
    Silicon undergoes migration from carbon to oxygen in the Brook rearrangement of _-silyl ketones.
    Germanium does not appear to undergo a similar migration.
    Doubly bonded silicon-silicon and germanium-germanium compounds have been demonstrated, but are
    not representative of large classes of chemistry for the elements.
    Perfluorinated methyl and ethyl germanes are isolable and stable. Simple trifluoromethyl(methyl)silanes
    have only recently been prepared. Other perfluorinated methyl and ethyl silanes are thermally unstable,
    decomposing above 80°.
    Repeating silicon-oxygen bonds tend to form extended linear polymers in preference to cyclic structures.
    Repeating germanium-oxygen bonds tend to form cyclic structures in preference to extended linear polymers.
    In contrast to silicon hydrides, germanium hydrides readily undergo metallation. For example, the reaction of triphenylgermane with butyl lithium followed by carbonation yields triphenylgermanecarboxylic acid.
    Like organosilanes, organogermanes can be fluorodemetallated. Additionally, organogermanes can be
    demetallated with bromine.
    
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    Germanium hydrides and silicon hydrides react with olefins in hydrogermylation and hydrosilylation
    reactions. Both are catalyzed by platinum compounds, but catalysis is not a requirement for hydrogermylation.
    Trichlorogermane is particularly reactive and reaction products are associated with both hydrogermylation
    and dichlorogermene insertion.21
    R2CHCR2GeCl 3
    RC CR’GeCl3
    
    RGeCl 3
    R2C=CR2
    
    RX
    
    RC CR’
    HGeCl 3
    RCOCl
    
    R2O
    
    R
    
    RGeCl 3
    
    RCOGeCl 3
    R
    
    GeCl 3
    GeCl 3
    
    Cl 3Ge
    
    Germanium in Organic Synthesis
    For a variety of reasons applications of organogermanes in organic synthesis are limited, while applications
    of organosilanes in organic synthesis are well-developed. Until recently organogermanes have had relatively
    poor availability compared to organosilanes. Also, the germanium oxygen bond is somewhat more susceptible to
    hydrolysis compared to the silicon oxygen bond. Beyond these facts, the largest determinant for differences in
    applications is the higher cost of germanium compounds. Consequently, only unique applications of organogermanium compounds are likely to be of importance. Potential applications include trimethylgermylacetonitrile as
    a carbanion source, trimethylbromogermane and trimethylchlorogermane employed in the preparation of masked
    dienolates in a variety of regioselective syntheses, trichlorogermane for ether cleavage, and germanium diiodide
    and cesium trichlorogermanate for conversion of alkyl halides to alkylgermyltrihalides.
    The palladium catalyzed cross-coupling reactions of germanium compounds have been investigated.22,23,24,
    
    O
    
    Pd(0), Ar 1X
    
    GeH
    3
    
    Cs2CO3
    
    Pd(0), Ar 2X
    GeAr1
    n-Bu4NF
    3
    
    O
    Br
    
    Ar1
    
    Ar 2
    
    R
    
    N
    
    Pd catalyst
    
    +
    Ge
    
    O
    R
    
    O
    O
    
    Tri-n-butylgermane is an effective reducing agent. It reduces benzylic chlorides 70x faster than silyl
    hydrides and reduces acyl chlorides to aldehydes in the presence of Pd(0) .
    Cl
    C 6H 5
    
    C
    
    H
    H
    
    C 6H 5
    
    C
    
    H
    
    nBu
    +
    
    nBu
    
    Ge
    
    nBu
    H
    
    TiCl4
    +
    
    nBu
    CH 3O
    
    nBu
    
    Ge
    
    Cl
    
    nBu
    CH 3O
    
    Polymers and Polymerization
    The most commercially important application of germanium compounds are as catalysts in polymerization
    of polyester. Non-yellowing polyester fibers and clear polyester beverage bottles are produced by germanium
    dioxide and hydroxygermatrane catalyzed condensation of dimethyl terephthalate and selected diols.
    Copolymers have been prepared from organogermanes with polymerizeable functionality, including allyl, vinyl27
    and methacrylate28 groups.
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    REFERENCES:
    1. M. Lesbre, P. Mazerroles and J. Satge, The Organic Compounds of Germanium, Wiley, 1971
    2. S. Patai, ed. “The Chemistry of Organic Germanium, Tin and Lead Compounds, Vol. 1, Wiley, 1995
    3. Z. Rappoport, ed. “The Chemistry of Organic Germanium, Tin and Lead Compounds, Vol. 2, Wiley, 2002
    4. B. J. Aylett, Organometallic Compounds, Volume 1, Part 2, Chapman & Hall, 1979
    5. V. I. Davydov, Germanium, Gordon & Breach, 1966
    6. W. DeBoer, et al, Appl. Phys. Lett., 1991, 58, 1226.
    7. H. Kuhne et al, J. Mater. Res., 1993, 8, 131.
    8. B. Kellerman et al, J. Vac. Sci & Tech. A., 1995, 13, 1819.
    9. T. Hanrath et al, Adv. Mater., 2003, 15, 437
    10. K. Ryan et al, J. Am. Chem. Soc., 2003, 125, 6284.
    11. Y. Wu et al, Chem. Mat., 2000, 605, 12.
    12. A. Grill et al, J. Mater. Res., 2002, 17, 367.
    13. R. Maurer, US Pat. 3,737,293, 1973.
    14. J. MacChesney et al, US Pat. 4,217,027, 1980.
    15. C. Hung et al, J. Mater. Res., 1992, 7, 1870.
    16. D. Secrist et al, Bull. Am. Ceram. Soc., 1966, 45, 784.
    17. S. Fisher et al, Solid State Tech., September, 1993, 55.
    18. see specific references in the germanium compound section following this article
    19. S. Kobayashi et al, J. Am. Chem. Soc., 1992, 114, 4929.
    20. F. Riedmiller et al, Organometallics, 1999, 18, 4317
    21. W. Wolfsberger, J. Praktische Chem., 1992, 334, 453
    22. T. Nakamura et al, Org. Lett., 2002, 4, 3165
    23. M. Kosugi et al, J. Organomet. Chem., 1996, 508, 255
    24. J. Faller et al, Organometallics, 2002, 21, 5911
    25. H. Mayr et al, Angew. Chem. Int’l Ed Eng., 1992, 31, 1046.
    26. L. Geng, X. Lu, Organomet. Chem., 1989, 376, 41.
    27. S. Rafikov, Izv. Akad. Nauk. SSR, Ser. Khim., 1982, 920
    28. D. Mixon et al, J. Vac. Sci. Technol., B, 1989, 7(6), 1723
    
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    Stable Homonuclear Double and Triple Bonded Germanium Species and Their Reactions
    Elke Hoppe and Philip P. Power
    Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California
    95616, USA. E-mail: pppower@ucdavis.edu
    “Although germanium is only slightly larger than silicon, it is too large for any !-overlap and no
    multiple bonded germanium compounds are known.”1
    There was widespread agreement with this opinion until relatively recently,2 but in the last quarter
    of the 20th century and the beginning decade of the 21st the synthesis of numerous stable compounds
    that contain multiple bonds to germanium and other heavier main group elements has not only vitiated
    this statement, but has also changed our perception of bonding itself. Germanium compounds have
    played a key role in effecting this change. This is because group 14 element compounds have occupied
    a central position in the study of multiple bonding among heavier main group elements and germanium
    is the central element in group 14. In many respects its multiple bonded derivatives represent a
    transition point in the geometrical, bonding and reactivity changes that occur with increasing atomic
    number. In this article we provide a brief summary of two classes of multiple bonded germanium
    compounds. These are the germanium congeners of the double bonded olefins (digermenes) or the
    triple bonded alkynes (digermynes).
    The first multiple bonded germanium species to be isolated had their origin in the work of Lappert
    and his group in the 1970s. The original objective of their work was the preparation of stable heavier
    group 14 element carbene analogues of formula: ER2 (E = Si, Ge, Sn, or Pb; R = amido or alkyl group).
    The key element of the synthetic approach was simply to use large ligands such as the amido or alkyl
    groups -N(SiMe3)2 or -CH(SiMe3)2 to achieve stability by preventing association via ligand bridging or
    E-E bond formation. A very simple salt elimination route sufficed to isolate the first red tin and purple
    lead dialkyl species: ER2 via reaction of the lithium salt of the ligand with the metal dihalide,3 but the
    corresponding yellow germanium dialkyl :Ge{CH(SiMe3)2}2 was most conveniently obtained via the
    reaction of :Ge{N(SiMe3)2}2 with two equivalents of LiCH(SiMe3)2. 4 ,5 Like its tin counterpart:
    Ge{CH(SiMe3)2}2 existed as carbene-like monomers in solution5 and could behave as a Lewis base
    donor toward transition metals.6 However, it was later shown to have a Ge-Ge double bonded dimeric
    structure 7 of formula (Dis)2Ge=Ge(Dis)2, Dis = CH(SiMe3)2 8 (like its tin counterpart
    (Dis)2Sn=Sn(Dis)2) in the solid state.4,5,7
    
    Ge[N(SiMe3 ) 2 ]2 + 2 LiDis
    
    - 2 LiN(SiMe 3) 2
    
    Ge(Dis) 2
    
    1/
    2
    
    Dis
    Dis
    
    Ge
    
    Ge
    
    Dis
    Dis
    
    Scheme 1
    The most surprising aspect of the tin and germanium structures was that they were not planar like
    ethylene but had a trans-pyramidalized structure with local C2h symmetry at the C2E=EC2 (E = Ge or
    Sn) cores. Moreover the GeGe and SnSn bond lengths were only slightly shortened compared to single
    bonds. Synthetic and structural results like these initiated a revolution not only in main group chemistry
    but have also led to new insights in chemical bonding.9,10,11 Numerous classes of multiple bonded
    germanium compounds now exist12,13,14,15,16,17 but the scope of this review is confined to stable species
    with double or triple bonds between two germanium atoms.
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    DIGERMENES
    Syntheses of Digermenes
    Whereas the first digermene was synthesized by Lappert via a salt elimination route, several
    different synthetic approaches have since been developed. These include photochemical conversions,
    various elimination reactions as well as insertion routes which are summarized in the following
    sections.
    Photochemical Conversions
    A photochemical conversion led to the first structural characterization of a stable digermene in the
    solid state in 1984 by the group of Masamune. Photolysis of (Ar2Ge)3 (Ar = 2,6–dimethylphenyl or 2,6diethylphenyl) afforded of Ar2Ge=GeAr2 as shown in Scheme 2.18
    H3C
    
    Ar2
    Ge
    Ar2Ge
    
    h
    
    Ar2Ge
    
    GeAr2
    
    GeAr2
    
    C2H5
    ,
    
    Ar =
    H3C
    
    C2H5
    
    Scheme 2: Photochemical route to digermenes
    The Ge-Ge bond length was found to be 2.213(2) Å which is considerably shorter than the single
    bond distance of 2.44 Å and the coordination of the Ge atoms displayed pyramidal distortion in which
    the germanium was displaced by 0.15 Å from the plane formed by the two ipso-carbons and the other
    germanium. Similar structural data were found for tetrakis(2,4,6-triisopropylphenyl)digermene 19
    (GeGe = 2.213(1) Å) whereas the tetrakis(mesityl)digermene,20 which was synthesized by the same
    route in 2007, shows a slightly longer Ge-Ge distance of 2.2856(8) Å. These structures had a greater
    pyramidal distortion (pyramidal displacement = 0.42 Å) than the corresponding disilenes with the same
    ligands (e.g. Mes2Si=SiMes2, Mes = -C6H2-2,4,6-Me3: displacement = 0.22 Å)21 but a smaller one than
    distannenes such (Dis)2Sn=Sn(Dis)2 (displacement = 0.61 Å)7.
    Reductive Elimination Synthetic Routes
    Reductive elimination reactions are a well established method for synthesis of multiple bonded
    germanium species. These are usually effected by dehalogenation or salt elimination reactions.
    Masamune and co-workers used lithium naphthalenide as a reducing agent for dichloro(2,6diisopropylphenyl)mesitylgermane (Dipp(Mes)GeCl2), Dipp = C6H3-2,6-iPr2. Under elimination of
    lithium chloride the product was formed as two isomers with the Z isomer being more stable than the E
    isomer but only the Z variant crystallized upon concentration of a solution of the reaction mixture.22
    The GeGe bond length is 2.301(1) Å. It was shown by kinetic studies that isomerization proceeds in a
    staightforward way via rotation around the GeGe bond axis and not through a thermal dissociationrecombination mechanism.
    2 Dipp(Mes)GeCl2
    
    Li naphthalenide
    
    Dipp(Mes)Ge
    
    Ge(Mes)Dipp
    
    E and Z isomers
    
    Scheme 3
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    Reduction of dichlorobis(diisopropylmethylsilyl)germane with a sodium dispersion afforded the
    tetrakis(trialkylsilyl)digermene. As shown by the group of Kira23 the trialkyl substituents enforce a
    nearly planar geometry around the GeGe bond and no twisting is observed. The distance between the
    two germanium atoms is 2.268(1) and 2.266(1) Å, respectively, and is thus shorter than in
    Dis2GeGeDis2 (2.3458(7) Å)7 or Dipp(Mes)GeGe(Mes)Dipp (2.3011(9) Å)22.
    
    2 (R 3Si)2 GeCl2
    
    2 Na
    
    (R3 Si) 2 Ge
    
    Ge(SiR3 )2
    
    Scheme 4
    The use of lithium naphthalenide as reducing agent for Tbt(Mes)GeCl2 (Tbt = C6H2-2,4,6[CH(SiMe3)2]3) by Tokitoh and coworkers afforded MesTbtGeGeMesTbt.The GeGe bond length
    (2.416(3) Å) in this compound is considerably longer than GeGe double bond lengths of other reported
    digermenes with carbon substituents and is very close to a normal GeGe single bond of GeGe = 2.44 Å
    in elemental germanium. Elongation of the GeGe double bond is consistent with the very large size of
    the substituents. Considerable geometrical distortion, which also involves twisting of the geometry
    around the GeGe axis, was also observed.24
    2 Tbt(Mes)GeCl 2
    
    Li naphthalenide
    
    Tbt(Mes)Ge
    
    Ge(Mes)Tbt
    
    Scheme 5
    Reaction of a tetrachloro digermane with 1,1-dilithiosilane R2SiLi2 (R = SiMetBu2) afforded a
    heavier group 14 element cyclopropene along with a linear digermene via salt elimination.25,26 The
    GeGe double bond in the three membered ring is a relatively short one (2.2429(5) Å).
    
    RCl2GeGeCl2R
    
    R2
    E
    
    R2ELi2 (xs)
    - 2 LiCl
    
    RGe
    
    GeR
    
    +
    
    R2E
    
    ER2
    
    E = Si, Ge
    
    Scheme 6
    The use of terphenyl groups (Ar' = C6H3-2,6(C6H3-2,6-íPr2)2 or Ar* = C6H3-2,4,6(C6H3-2,6-iPr3)2) as
    sterically encumbering ligands enabled halogeno substituted digermenes to be isolated. These species,
    which are in equilibrium with the corresponding monomeric germylenes, allow further digermenes to
    be readily synthesized by replacement of the chlorines.27 The chlorines can be substituted by methyl,
    ethyl or phenyl groups in a salt elimination reaction with the corresponding lithium reagents. In
    contrast the analogous terphenyl tin (II) chlorides display trans-bridged structures with no tin-tin
    bond.27 Corresponding dihydrodigermenes can be easily obtained via reaction of the chloro derivatives
    with LiB(s-Bu3)H.28 The product has crystallographic 2/m symmetry in which the C-Ge-Ge-C array is
    incorporated in the mirror plane with a Ge-Ge distance of 2.3724(9) Å. The GeGe bond length is longer
    than average (see below in Table 1) probably as a result of steric effects.
    
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    2 LiAr
    - 2 LiCl
    
    2 :GeCl2 (dioxane)
    
    ArClGe
    
    2 ArGeCl
    
    GeClAr
    
    Ar = Ar', Ar*
    
    Ph
    Ge
    
    H
    
    Ar'
    
    .
    
    2 LiPh Et2O
    
    Ge
    
    2 Ar'GeCl
    
    Ar'
    Ph
    
    2 Li(BsBu3H)
    
    Ge
    Ar'
    
    2 RMgBr
    R = Me, Et
    R
    Ge
    Ar'
    
    Ar'
    
    Ge
    
    H
    
    Ar'
    
    Ge
    
    R
    
    Scheme 7
    Reaction of the cationic tricyclic species (GeSitBu3)3+ (with a B(ArF)4- counter anion; ArF = -C6F5)
    with potassium halide afforded the halogen-substituted cyclotrigermene.29 The GeGe double bond
    (2.2743(8) Å) and the GeGe single bonds (2.4191(9) and 2.4200(9) Å) are relatively short. These
    effects are explained by introduction of an electronegative group at the endocyclic sp3 germanium atom
    and accordingly with the ?*-aromaticity concept.29
    SitBu3
    
    Sit Bu3
    
    Ge
    Ge
    t
    
    +
    
    B(Arf)4
    
    Ge
    
    Ge
    
    KX
    -KB(Arf)4
    
    Ge
    
    Sit Bu3
    
    Bu3Si
    
    X
    
    Ge
    
    t
    
    Sit Bu3
    
    Bu3Si
    
    Scheme 8
    Weidenbruch and co-workers showed that tetragermanium 1,3-butadiene could lead to digermene
    when it is reacted with 2-methoxyphenyl isocyanate. 30 During the reaction an initial germylene
    cleavage occurs. The four membered ring is planar but it is not clear if the neighboring GeGe and CN
    double bonds are conjugated. The digermene also formed in this reaction Tripp2GeGeTripp2 (Tripp =
    C6H2-2,4,6-iPr3) had been obtained previously.19,31,32 The GeGe bond lengths in this molecule were
    reported to be 2.2894(6) and 2.2635(15) Å, respectively.
    RGe
    NC
    
    N
    OMe
    +
    
    Scheme 9
    
    100
    
    RGe
    R2Ge
    
    GeR
    GeR2
    
    GeR
    GeR2
    OMe
    +
    
    R2Ge
    
    GeR2
    
        
    
    Gelest, Inc.
    
    Synthesis via Insertion Reactions
    Another interesting approach for the synthesis of ring species containing GeGe double bonds was
    described by Sekiguchi's group. Reaction of a three membered ring with GeCl2.dioxane to afford an
    insertion reaction and a four membered ring product as shown by.33
    t Bu MeSi
    2
    
    E
    E'
    t
    
    t
    
    SiMet Bu2
    + GeCl2 dioxane
    
    Si
    
    Ge
    
    Ge
    
    Si
    
    Si
    
    Cl
    t Bu MeSi
    2
    
    SiMet Bu2
    
    Bu2MeSi
    
    SiMet Bu2
    
    Bu2MeSi
    
    E = Ge, E' = Si
    E = Si, E' = Ge
    
    Cl
    
    SiMet Bu2
    
    Scheme 10
    PROPERTIES
    Digermenes are usually colored diamagnetic compounds with the n+ " n- or n " p electronic
    transitions as the chromophore. Digermenes can dissociate to germylene monomers in solution when
    the substituents are sufficiently large. Whereas disilenes are usually dimeric in solid state as well as in
    solution. About half of the digermenes dissociate into monomers in solution whereas almost all
    distannenes are dissociated when dissolved. They can act as electrophilic compounds.
    Structural aspects and bonding
    
    Ge
    
    Ge
    
    Ge
    
    Scheme 11
    In contrast to olefins which usually have planar structures, digermenes typically display
    considerable distortion from this ideal. These distortions can be defined with use of a number of
    different parameters that include not only the length of the double bond between germanium atoms, but
    also the angular parameters ? and ? illustrated above in Scheme 11. Instead of ? also the geometrical
    displacement of the germanium atom above the plane of the connected atoms can be used to describe
    the molecular geometry accurately.
    The strength of the double bond between the two germanium atoms is relatively low. This, and the
    observed geometry can be interpreted as a double donor-acceptor bond or, alternatively, by the valence
    bond representation.7
    
    101
    
        
    
    Gelest, Inc.
    
    The molecular orbital (MO) treatment of their bonding also affords valuable insights. In this
    approach the geometrical distortions are explained on the basis of mixing of anti-bonding and bonding
    levels within the molecule. This mixing is a second order Jahn-Teller (SOJT) effect25-27 which arises
    from a symmetry allowed, intramolecular mixing of an anti-bonding orbital with a bonding orbital
    (generally the HOMO (highest occupied molecular orbital) in multiple bonded species).28,29 This can
    lead to very large deformations in molecular geometry because the orbital mixing introduces nonbonding, lone pair character in a HOMO (originally a purely !-orbital) which can have a drastic effect
    on molecular shape.30 The extent of the mixing is inversely proportional to the energy separation of the
    orbitals and this is maximized in the heavier elements because the weakened bonding often permits a
    close approach (<4eV) of the molecular levels. The initial stages of the SOJT distortion and orbital
    interactions are shown in Scheme 12.
    (b3u)
    (bu)
    n+ (ag)
    
    (b1g)
    
    Ge
    
    Ge
    (b2u)
    
    Ge
    
    n- (bu)
    
    Ge
    (ag)
    
    (ag)
    D2h (planar)
    
    C2h (trans pyramidalized)
    
    Scheme 12
    The GeGe bond lengths in digermenes (Table 1) can be strongly influenced by the spatial and
    electronic properties of the coordinating ligands. However, a correlation between steric bulk around the
    germanium and its double bond length is not feasible.34,35,36 The nature of the ligands also influences
    the twisting and bending around the GeGe double bond. It can be seen from Table 1 that the GeGe
    bond lengths in digermenes vary from ca. 2.21 to 2.50 Å and have an average value of ca. 2.32 Å. Thus
    the shortest (and presumably the strongest) Ge-Ge double bonds are about 9.4 % shorter than the 2.44
    Å single bond length in elemental germanium.
    
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    Table 1
    Compound
    
    Ref.
    
    GeGe [Å]
    
    (Dis)2Ge=Ge(Dis)2
    
    37
    
    2.3458(7)
    
    (Et2C6H3) 2Ge=Ge(C6H3 Et2 )
    
    18
    
    2.212(3)
    
    Ar'HGe=GeHAr'
    
    83
    
    2.3025(3)
    
    Mes2Ge=GeMes2
    
    38
    
    2.2855(7)
    
    MesDippGe=GeMesDipp
    
    22
    
    Tripp2Ge=GeTripp2
    
    19
    
    Ar'HGe=GeHAr'
    
    28
    t
    
    trans-bending [°]
    
    twisting [°]
    
    color
    
    !max [nm]
    
    32
    
    0
    
    bright yellow
    
    not reported
    
    15
    
    11
    
    yellow
    
    263, 412
    
    45
    
    not reported
    
    orange
    
    434
    
    33.4
    
    2.9
    
    yellow
    
    not reported
    
    2.3011(9)
    
    36
    
    not reported
    
    yellow
    
    280, 412
    
    2.213(1)
    
    12.3
    
    13.7
    
    pale yellow
    
    not reported
    
    2.3724(9)
    
    20.5
    
    not reported
    
    orange
    
    not reported
    
    (N(R')C2H 4N(R')Si(R) 2Ge)2 R' = Bu
    
    39
    
    2.4541(15)
    
    41.3, 42.3
    
    not reported
    
    dark red
    
    475
    
    (N(R')C2H 4N(R')Si(R) 2Ge)2 R' = tBu,i Pr
    
    40
    
    2.4602(8), 2.4528(9)
    
    „much larger than in
    any other“
    
    63
    
    violet
    
    557
    
    Ar*MeGe=GeMeAr*
    
    27
    
    2.316(2)
    
    39.7
    
    not reported
    
    yellow-green
    
    not reported
    
    Ar*EtGe=GeEtAr*
    
    27
    
    2.347(2), 2.271(6)
    
    37.9
    
    not reported
    
    yellow
    
    not reported
    
    Ar*PhGe=GePhAr*
    
    27
    
    2.318(3)
    
    33.7
    
    not reported
    
    orange
    
    not reported
    
    Ar*ClGe=GeClAr*
    
    27
    
    2.363(2)
    
    36.8
    
    not reported
    
    orange
    
    not reported
    
    BbtBrGe=GeBrBbt
    
    41
    
    2.5088(8)
    
    44.6
    
    64.2
    
    orange
    
    449
    
    42
    
    2.2521(8)
    
    0
    
    20.4
    
    orange-yellow
    
    not reported
    
    (Me PrSi)2Ge=Ge(SiMe Pr 2)2
    
    43
    
    2.267(2), 2.270(2)
    
    5.9, 7.1
    
    0, 0
    
    yellow
    
    361, 413
    
    (iPr3Si)2Ge=Ge(SiiPr3) 2
    
    43
    
    2.2957(2)
    
    16.4
    
    0
    
    pale yellow
    
    472, 432, 367, 332, 277
    
    Ar'ClGe=GeClAr'
    
    79
    
    2.4626(4)
    
    38.8
    
    not reported
    
    orange
    
    not reported
    
    (TrippGe)2(Tripp2Ge)2 Se
    
    30
    
    2.2975(5)
    
    33.4, 35.1
    
    not reported
    
    yellow
    
    399
    
    (TrippGe)2(Tripp2Ge)2 S
    
    44
    
    2.2841(5)
    
    29.9, 35.7
    
    not reported
    
    yellow
    
    400
    
    ( Bu2Ar)2Ge=Ge(Ar Bu2)2
    
    45
    
    2.3644(4)
    
    37.2, 42.6
    
    not reported
    
    red
    
    425
    
    (Tripp)Ge=Ge(Tripp)(Tripp)Ge=Ge(Tripp)
    
    46
    
    2.3568(7), 2.3439(5)
    
    not reported
    
    not reported
    
    greenish black,
    dark blue hexane
    solution
    
    405, 560
    
    MesTbtGe=GeTbtMes
    
    24
    
    2.416(3)
    
    not reported
    
    16.5, 34.6
    
    t
    
    t
    
    ( BuMe3C6H) 2Ge=Ge(C6H BuMe 3)2
    i
    
    i
    
    t
    
    t
    
    orange, hexane hexane solution: r.t. 575
    solution: r.t. blue (germylene); low temp.
    low temp. orange
    439 (digermene)
    yellow
    
    GeGe double bonds in three-membered cycles
    (tBu3SiGe)2Ge(Cl)SitBu 3
    
    47
    
    2.2723(9)
    
    trans-bent, not
    reported
    
    not reported
    
    dark red
    
    not reported
    
    (tBu3SiGe)2Ge(Br)SitBu3
    
    47
    
    2.2742(9)
    
    cis-bent, 45.1, 10.2
    
    not reported
    
    dark red
    
    not reported
    
    ( Bu3SiGe)2Ge(I)Si Bu3
    
    47
    
    2.2720(6)
    
    cis-bent, 43.3, 8.0
    
    not reported
    
    dark red
    
    not reported
    
    (tBu3SiGe)2Ge(SitBu3)Si(SiMe 3)
    
    48
    
    2.264(2)
    
    cis-bent: 12.5, 4.4*
    
    not reported
    
    red
    
    not reported
    
    48
    
    2.2638(11)
    
    0
    
    0
    
    dark red
    
    not reported
    
    25, 26
    
    2.2429(5)
    
    51.0
    
    not reported
    
    dark red
    
    470, 403, 311, 236
    
    25, 26
    
    2.2429(5)
    
    60.5
    
    not reported
    
    dark red
    
    457, 407, 324, 234
    
    49
    
    2.241(4)
    
    not reported
    
    not reported
    
    dark red
    
    not reported
    
    49
    
    2.240(3)
    
    not reported
    
    not reported
    
    dark red
    
    not reported
    
    t
    
    t
    
    t
    
    t
    
    ( Bu3SiGe)2Ge(Si Bu3)2
    t
    
    t
    
    ( Bu2MeSiGe) 2Si(Si Bu2 Me)2
    t
    
    t
    
    ( Bu2MeSiGe) 2Ge(Si Bu2 Me)2
    (tBu3SiGe)2Ge(SitBu3)2
    t
    
    t
    
    (( Bu3Ge)Ge)2Ge(Ge Bu3)2
    
    GeGe double bonds in four-membered cycles
    ((SitBu2 Me)Ge)2(Si(Cl)SitBu2 Me)2
    
    33
    
    2.291(6)
    
    not reported
    
    not reported
    
    bright orange
    
    not reported
    
    (Ar'Ge)2(CPh)2
    
    50
    
    2.4710(8)
    
    not reported
    
    not reported
    
    dark red
    
    375
    
    * No energy minimum was found for the trans-bent form. The introduction of electropositve substituents leads to rather small trans bent angles.
    see " Ref. 43
    
    gelest.com
    
    103
    
        
    
    Gelest, Inc.
    
    REACTIVITY
    Digermenes display a wide variety of reactions. The range of such reactions is quite diverse but
    most of them can be classified as additions, coordination reactions or reductions. Products that ensue
    from the reactions of dissociated digermenes (i.e. germylenes) are not considered in this section.
    Addition Reactions
    Addition of Lewis acids or multiple bonded species such as O2, isonitriles, azides, butadiene, N2O
    and diazomethane, to double bonds are well known from the chemistry of olefins and more recently
    from the chemistry of disilenes. Addition reactions of digermenes have also been extensively studied.
    Oxygen
    Reactions of digermenes with dioxygen have been investigated by several research groups. Very
    shortly after their structures had been established, digermenes were shown to react with oxygen by a
    1,2-addition process affording 3,4-digermadioxetanes which rearrange to 2,4-digermadioxetanes with
    irradiation.51 The GeGe distance (2.441(2) Å) in the 3,4-digermadioxetane is essentially the same as a
    normal GeGe single bond length (2.44 Å).52
    R
    O
    
    O
    Ar2Ge
    
    GeAr2
    
    Ar = Dipp, C6H3Et2
    
    O2
    
    Ar2Ge
    
    O
    
    Ge
    
    GeAr2
    
    Ar
    R
    
    OH
    
    90 °C
    
    GeAr2
    
    R = H, Me
    h
    
    O
    Ar2Ge
    
    GeAr2
    O
    
    Scheme 13
    In 2003 Tokitoh and coworkers showed that exposure of solid TbtMesGe=GeTbtMes to an oxygen
    atmosphere in the absence of light led to the formation of trans-1,3,2,4-dioxadigermetanes in two
    conformational isomers. Formation of the corresponding cis isomer was not observed. Interestingly,
    when the reaction was conducted with a digermene in solution a mixture of one of the trans isomers
    and the cis isomer were formed. Most likely this can be explained by a dissociation of the digermene
    into two germylene fragments in solution which react with dioxygen.24 The Ge...Ge distances (2.653(2),
    2.660(2) and 2.691(4) Å, respectively) are much longer than typical Ge-Ge single bonds (2.457-2.463
    Å).53,54 This is in contrast to the behaviour of the analogous silicon species in which the separation can
    be even shorter than typical Si-Si single bond lengths. This can be explained by the shorter Si-O bond
    lengths which impose closer Si...Si approaches.
    
    104
    
        
    
    Tbt
    
    Mes
    Ge
    
    Ge
    
    Mes
    
    Tbt
    
    O2
    
    Mes
    
    O
    Ge
    
    solid state
    Tbt
    
    Gelest, Inc.
    
    Ge
    O
    
    Mes
    
    Tbt
    
    solution
    
    Tbt
    Ge
    
    O2
    
    Mes
    
    Tbt
    
    Mes
    
    O
    Ge
    
    Mes
    
    +
    
    Ge
    O
    
    Tbt
    Ge
    Mes
    
    Tbt
    
    Tbt
    
    O
    Ge
    O
    
    Mes
    
    Scheme 14
    
    Exposure of digermene stabilized by 1,4-di-tert-butylbenzene ligands afforded a trigerma-1,3dioxolane product as shown by Weidenbruch's group.55
    R2
    Ge
    R2GeGeR2
    
    O
    
    O
    
    R2Ge
    
    GeR2
    
    O2
    
    Scheme 15
    The geometry of the five membered ring is nearly planar. The Ge-Ge bond length of 2.513(1) Å is
    slightly longer than a typical GeGe single bond. Earlier, Baines and coworkers had shown that the
    addition of O2 to tetramesityldigermene resulted in the formation of a 3,4-digermadioxetane with
    subsequent insertion of a germylene into the O-O single bond.56
    O
    Mes2(H)GeSiEt3
    
    Mes2
    Ge
    Mes2Ge
    
    GeMes2
    
    +
    
    Mes2Ge
    
    GeMes2
    Mes2
    Ge
    
    O
    h
    O2
    Et3SiH
    
    Mes2Ge
    
    O
    GeMes2
    
    O
    
    O
    + Mes2Ge
    
    GeMes2 +
    
    Mes2Ge
    
    O
    GeMes2
    
    O
    
    Scheme 16
    The GeGe single bond (2.504(3) Å) is slightly shorter than that in the five-membered ring reported
    by Weidenbruch. Formation of the 1,3-digermadioxetane results from rearrangement during irradiation
    of the 3,4 digermadioxetane as already shown above for Ar2GeGeAr2 by Masamune.51
    
    105
    
        
    
    Gelest, Inc.
    O
    Mes2Ge
    
    GeMes2
    O
    
    h
    O
    
    O
    
    Mes2Ge
    
    GeMes2
    
    Mes2Ge
    
    Mes2
    Ge
    O
    
    O
    Mes2Ge
    
    GeMes2
    
    Scheme 17
    Digermaoxirane was formed as part of the reaction mixture and proved to be relatively stable since
    it could be stored for several months under ambient conditions without decomposition. Nevertheless,
    attempts at a direct synthesis from digermene and m-chloroperbenzoic acid failed even though a similar
    approach had been used for the preparation of disilaoxiranes by West and coworkers.57 Instead, only
    1,3 digermadioxetane, the pentacycle and only in very small amounts the digermaoxirane were
    obtained.56
    A tetragermabuta-1,3-diene was reacted with dry air to yield in a tetraoxatetragermabicyclo[4.1.1]octane skeleton. The folded cyclodigermoxane ring can be seen as a result of a [2+4] addition of O2 to
    the terminal germanium atoms, followed by a 1,2-addition of a second O2 molecule.43
    R
    GeR
    
    RGe
    
    2 O2
    
    GeR2
    
    O
    
    GeR2
    
    R2Ge
    
    R
    O
    Ge
    Ge
    O
    
    R2Ge
    
    O
    
    Scheme 18
    Diazomethane
    MesDipGe=GeDipMes reacted with diazomethane R'HCN2 (R' = H, SiMe3) to give a
    azodigermirane in a [2+1] cycloaddition. No subsequent loss of nitrogen was observed, however.19 In
    contrast Ando and coworkers,58 obtained a digermirane in low yield as shown in Scheme 19. The
    azodigermirane features a GeGe bond with a distance of 2.4237(4) Å, which is typical for a single
    bond. A similar ring system was isolated as a product of the reaction of tetramesityldisilene with
    phenyldiazomethane.59
    CHR'
    N
    Tripp2Ge
    
    GeTripp2
    
    CHR'N2
    
    N
    TrippGe
    
    R2Ge
    
    Scheme 19
    
    106
    
    GeR2
    
    GeTripp
    
    CH2N2
    R2Ge
    
    GeR2
    
        
    
    Gelest, Inc.
    
    1,3-Butadiene
    1,3-butadienes are well known reagents in olefin chemistry, particularly in connection with DielsAlder reactions. The first use of 1,3-butadiene in digermene chemistry in 2000 by Sekiguchi involved
    an attempt to trap the digermene tBu3Si(Cl)Ge=Ge(Cl)SitBu3 which decomposes during warming above
    a temperature of -8 °C. Its reaction with isoprene and 2,3-dimethyl-1,3-butadiene, respectively,
    afforded only a single stereoisomer of the addition product.60
    t
    
    tBu Si
    3
    
    Cl
    
    Cl
    
    Ge
    
    Ge
    
    Cl
    
    t
    
    Bu3Si
    
    SitBu3
    
    Cl
    Ge
    
    - NaCl
    Cl
    
    Na
    
    Bu3Si
    Cl
    
    R
    
    Ge
    
    Ge
    
    Cl
    Sit Bu3
    
    Ge
    
    R = H, Me
    t
    
    Si Bu3
    R
    
    Scheme 20
    Stereoselective Diels-Alder reactions are extensively studied.60 The addition of 1,3-butadienes to a
    diastereotopic digermene afforded interesting results. For example it has been found that the cis-bent
    geometry around the Ge=Ge double bond of halogen substituted cyclotrigermenes has an effect on
    selectivity in the reaction with dimethyl butadiene. Thus, the dimethylbutadiene attacks the GeGe
    double bond from the side having the bulkier tBu3Si and only one stereoisomer is formed during the
    reactions. This is opposite to the selectivity of mesityl substituted cyclotrigermenes.61,62,52
    Sit Bu3
    
    Sit Bu3
    
    X
    
    Ge
    
    Ge
    Ge
    t
    
    Bu3Si
    
    X
    
    Ge
    
    t
    
    Sit Bu3
    
    Bu3Si
    
    Ge
    
    Ge
    
    Sit Bu3
    
    Scheme 21
    When Mes2Ge=GeMes2 was reacted with 1,3-butadiene, formation of mesityl(trimesitylgermyl)germacylopentene was observed. This was explained on the basis of a 1,2 shift of one mesityl group
    from one to the second germanium atom followed by trapping with the diene. A trapping reaction using
    Et3SiH led to the same result.7
    Mes
    Mes3Ge
    
    Mes2Ge
    
    GeMes2
    
    Mes3Ge
    
    Ge
    
    GeMes
    Mes
    
    Et3SiH
    Mes3Ge
    
    Ge
    SiEt3
    
    Scheme 22
    
    H
    
    11
    107
    
        
    
    Gelest, Inc.
    
    Reactions with Protic Lewis Acids and Halogen Reagents
    Reactions of digermenes with protic reagents can either lead to addition products or eliminations.
    For example, the reaction of digermenes with alcohols has been investigated by several groups.
    Masamune and coworker observed the addition of methanol to tetra(diethylphenyl)digermene
    (Ar2GeGeAr2).18 The same reactivity was found for Mes2GeGeMes2 and methanol, carbonic acids and
    chloroform, respectively. In the case of chloroform the addition involved the C-Cl bond rather than the
    C-H bond.7
    Y
    
    X
    Ar2Ge
    
    XY
    
    GeAr2
    
    Ar2Ge
    
    GeAr2
    
    X = OMe
    X = OH
    X = CHCl2
    X = OMe, OOR
    R = tBu, Mes
    
    Ar = 2,6-Et2C6H3
    Ar = 2,5-tBuC6H3
    Ar = Mes
    Ar = Mes
    
    Y=H
    Y=H
    Y = Cl
    Y=H
    
    Scheme 23
    The reaction of R2GeGeR2 (R = 2,5-tBu2C6H3) with water resulted in a digermanol.55 This is in
    contrast to reactions of (Dis)2GeGe(Dis)2 with ethanol or Tbt(Mes)GeGe(Mes)Tbt with methanol,
    respectively, which provided the corresponding alkoxides via an elimination reaction.24,63
    Interestingly, the reaction of the hexakis(tripp)tetragerma-1,3-butadiene leads not to a direct addition
    product but to a cyclic oxatetragermapentane as a result of an intial 1,2 addition of water to one of the
    GeGe double bonds followed by 1,3-hydride shift and ring formation.30
    
    RGe
    
    GeR
    
    H2O
    
    RGe
    
    GeR2
    
    R2Ge
    
    H
    
    H
    
    GeR
    
    RGe
    
    GeR2
    
    R2Ge
    
    GeR
    
    R2Ge
    
    GeR2
    O
    
    HO
    
    R = Tripp
    
    H
    
    Scheme 24
    Ring compounds featuring GeGe double bonds also react with methylene dichloride and tetrachloro
    methane at room temperature. In the case of CCl4 a 1,2-addition occurs and the resulting
    cyclodigermane can be isolated using an excess of dichloromethane the product of a ring expansion is
    obtained. For chloroform only formation of a mixture of products was obtained.25,26
    R
    
    R
    
    R
    
    E
    R
    
    Ge
    Cl
    
    Scheme 25
    108
    
    E
    
    CC l4
    Ge
    
    Cl
    R
    
    R
    
    R Ge
    
    R
    
    E = Si , Ge
    R = Si CH3(tBu)2
    
    R
    
    E
    
    CH2C l2
    GeR
    
    R
    
    Cl
    
    Ge
    R
    
    E
    
    R
    Ge
    
    Ge
    
    R
    Cl
    
    Cl
    
    R
    Cl
    Ge
    R
    
        
    
    Gelest, Inc.
    
    Reactions with Heavier Chalcogens
    Heating of tetragerma-1,3-butadiene with excess of selenium in the presence of a small amount of
    Et3P as a chalcogen transfer reagent afforded the formation of selenatetragermacyclopentene as yellow
    crystals.30 The same reactivity is observed in the presence of elemental sulfur. Tetragerma-1,3butadiene forms with sulfur a thiotetragermacyclopentane.43 Both structures are very similar. The five
    membered ring products are almost planar. The Ge1Ge2 and Ge3Ge4 bond lengths which have an
    average value mean 2.46 Å are typical for GeGe single bonds, but the Ge2Ge3 bonds, which are
    2.2841(5) and 2.2975(5) Å are typical for a GeGe double bond.
    
    RGe
    R2Ge
    
    GeR
    
    RGe
    
    + Se
    
    GeR2
    
    GeR
    
    R2Ge
    
    (Et3P)
    
    GeR2
    Se
    
    R = Tripp
    
    1
    
    / 8 S8
    RGe
    
    GeR
    
    R2Ge
    
    GeR2
    S
    
    Scheme 26
    Photolysis of trigermirane in the presence of elemental sulfur gave two reaction products. One is the
    addition product of the formed digermene and sulfur whereas the second product can be viewed as a
    result of the head-to-tail dimerized germathione, Mes2Ge=S, intermediate that is formed by reaction of
    sulfur and the corresponding germylene.64
    Mes2
    Ge
    Mes2Ge
    
    GeMes2
    
    h
    
    GeMes2 + Mes2Ge
    
    Mes2Ge
    
    S8
    S
    Mes2Ge
    
    GeMes2
    
    + Mes2Ge
    
    S
    
    S
    Mes2Ge
    
    GeMes2
    S
    
    Scheme 27
    Reaction of digermene dihydride with PMe3 results in an isomerization reaction to afford a mixed
    valent species. In this compound the GeGe distance of 2.5304(7) Å is at the longer end of the GeGe
    single bond range.28,65
    
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    Ar'
    
    2 LiBsBu3H
    
    2 Ar'GeCl
    
    Ar'
    
    H
    Ge
    
    PMe3
    
    Ge
    
    H
    
    Ge
    Ar'
    
    Ar'
    
    PMe3
    
    Ge
    H
    
    H
    
    Scheme 28
    Reduction Reactions
    Reduction of the dihydrodigermene Ar'(H)GeGe(H)Ar' with alkaline metals (Li, Na or K) gave
    highly reactive salts M2[Ar'(H)GeGe(H)Ar'] as deep red/black crystals.66 Depending on the nature of
    the alkali metal counterions the nature of the structural type formed differed. In the potassium salt the
    [Ar'(H)GeGe(H)Ar']2- core is trans pyramidal with terminal Ge-H bonds and a long GeGe distance of
    2.6468(4) Å. In contrast in the sodium salt the [Ar'(H)GeGe(H)Ar']2- core has bridging hydrogen
    atoms, the GeGe distance with 2.5904(5) Å is long.66 On the other hand the structure of the lithium salt
    resembles that of the potassium salt, but has a much shorter GeGe distance of 2.395(2) Å. Theoretical
    calculations show that the different isomeric structures are close in energy.67
    Ar'
    
    H
    Ge
    
    Ge
    
    H
    
    Ar'
    
    M
    
    Ar'(H)GeGe(H)Ar' 2
    
    M = Li, Na, K
    
    Scheme 29
    DIGERMYNES
    These compounds are analogous to their alkyne carbon counterparts. A stable example was first
    reported in 2002 via the reduction of a digermene. Only a few examples of stable digermynes are
    currently known although they have already been shown to have a rich chemistry.
    Synthesis of digermynes
    The synthesis of dichlorobis(terphenyl)digermanes offered not only the chance for further
    substitution reactions leading to heteroleptic digermanes but also afforded an easy access route for
    germanium analogues of alkynes. The synthesis of the first stable digermyne by this route was
    described in 2002. 68 Reduction of Ar'(Cl)GeGe(Cl)Ar' with potassium furnished Ar'GeGeAr' as
    orange-red crystals. This digermyne has a planar trans bent core and is centrosymmetric. The GeGe
    distance with 2.2850(6) Å is considerably shorter than a GeGe single bond indicating considerable
    multiple-bonding character. The Ge-C(ipso) is 1.996(3) Å and the GeGeC bending angle is 128.67(8)°.
    
    Ar*ClGe
    
    Scheme 30
    
    110
    
    GeClAr*
    
    2K
    
    Ar*Ge
    
    GeAr*
    
        
    
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    A similar reaction was also reported in 2006 by Tokitoh and co-workers. 69 Starting with
    BbtBrGeGeBrBbt, Bbt = C6H2-2,6-(CH(SiMe3)2)2-4-C(SiMe3)3, a reduction with KC8 led to
    BbtGeGeBbt. For this compound two nonidentical molecules were found in the unit cell. The GeGe
    bond lengths [2.2060(7) and 2.2260(7) Å] are shorter than that in Ar'GeGeAr'. The GeGeC bending
    angles vary from 123.60(13) to 138.66(14)° and are in the same range observed for Ar'GeGeAr'
    (128.67(8)°).
    Bbt
    
    Br
    Ge
    
    Bbt
    
    KC8
    
    Ge
    
    Ge
    
    Ge
    
    Bbt
    Br
    
    Bbt
    
    Scheme 31
    Although Ar'GeGeAr' and BbtGeGeBbt are both digermynes, they show different reactivities which
    is apparently caused by the different germanium substituents. In Ar'GeGeAr' the bond order is
    decreased from idealized triply bonded to approximately two and contains some lone-pair character at
    the germanium atoms. The lower bond order may be accounted for in terms of a second-order JahnTeller effect involving the mixing of a ?* orbital and the in plane ??orbital upon trans bending of the
    linear skeleton (Scheme 32).70,71,72 The structure can also be written in several resonance forms as
    shown on the left hand side of Scheme 32. One of these has a diradicaloid character form and this is
    reflected in the reactivity of Ar'GeGeAr' as discussed below.
    
    bu ( *)
    bg ( *)
    
    Ge
    
    Ge
    
    ag (n+ )
    
    Ge
    
    Ge
    
    au ( )
    bu (n-)
    
    Ge
    
    ag ( )
    D
    
    8
    
    Ge
    
    h
    
    (linear)
    
    C2h (trans-bent)
    
    Scheme 32
    
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    Reactivity of Ar'GeGeAr'
    Ar'GeGeAr' and BbtGeGeBbt displayed different reactivities. When BbtGeGeBbt was heated in
    presence of Et3SiH with its reactive Si-H bond no reaction was observed, whereas, during addition
    reactions with water or methanol formation of the 1,1-dimethoxydigermane and 1,1dihydroxydigermane, respectively, was observed. Reaction with 2,3-dimethyl-1,3-butadiene yielded the
    product of a [4+1] addition.70
    Bbt
    Ge
    
    Ge
    Bbt
    
    Bbt
    Ge
    
    Ge
    
    Et3SiH
    
    no reaction
    
    Bbt
    2 ROH
    R = H, Me
    Bbt(H)2Ge
    
    Ge(OR)2Bbt
    
    Scheme 33
    This is in contrast to the observed reactivity of Ar'GeGeAr' and 2,3-dimethyl-1,3-butadiene. Three
    molecules of 2,3-dimethyl-1,3-butadiene react with one germylene molecule to form two
    germacyclopentenes bridged via an olefin.73 This difference in reactivity emphasizes the different
    nature of the GeGe bond in Ar*GeGeAr* versus BbtGeGeBbt.
    
    Ar*GeGeAr*
    
    Ge
    Ar*
    Ar*
    Ge
    
    Scheme 34
    Reductions
    Digermynes can undergo further one and two step reductions with alkali metals. Experiments with
    stoichiometric quantities of alkali metal reductant (1:1 ratio of alkali metal : Ar'/Ar*GeCl) (Ar* =
    C6H3-2,6-(C6H2-2,4,6-Pri3)2) showed that the reduced mono- and dianions were produced in addition to
    the neutral species, especially if short reaction times were used.74,75 Planarity of the core trans bent
    geometry as seen in the precursors are preserved in the monoanionic radical and dianionic diradical
    compounds. No dimerization like that seen for diarylacetylenes76,77 was observed, presumably because
    of steric effects. The GeGe distances (NaAr*GeGeAr*: 2.3089(8) Å, KAr'GeGeAr': 2.3331(4) Å) are
    slightly longer than observed in the neutral (2.2850(6) Å) compound but the GeGeC angles (112.60(5)115.32(12)°) are ca. 15° narrower than in Ar'GeGeAr' (128.67(8)°). These changes are probably caused
    by an increase of the electropositive character of Ge after addition of one electron to the GeGe unit. As
    a result, the electronegativity of the ligands relative to the central element is increased so that greater
    bending is observed. The differences between the Ar' and Ar* derivatives are only minor.78
    112
    
        
    
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    Reaction of Ar'GeCl and Ar*GeCl with an excess of lithium, sodium or potassium afforded the
    doubly reduced salts.79 The alkali metal countercations are sandwiched between the flanking aryl rings
    and the structures are very similar. The GeGe distances are somewhat increased (Li: 2.455(9) Å, Na:
    2.394(1) Å, K: 2.3912(6) Å) in comparison to the monoanionic salts at 2.32 Å and the GeGeC angles
    are narrower than those in the monoanions. This is consistent with the addition of the second electron
    to the n+ orbital of Scheme 32 in the GeGe unit.79 Also the [Ar'GeGeAr']2- is isoelectronic to double
    bonded Ar'SbSbAr'80 and the GeGe bond can be considered a double one.
    Ar'GeGeAr'
    
    Ar*GeGeAr*
    
    2M
    M
    
    2M
    
    M2[Ar'GeGeAr']
    
    M = Li
    
    M[Ar'GeGeAr']
    
    M =K
    
    M2[Ar*GeGeAr*]
    
    M = Na, K
    
    M[Ar*GeGeAr*]
    
    M = Na
    
    M
    
    Scheme 35
    Reactions with Unsaturated Molecules
    Several of the reactions of Ar'GeGeAr' are suggestive of diradical character (Scheme 36-38). For
    instance, very recently it has been shown the addition of two equivalents O2 to a bis terphenyl
    digermyne yielding the unique species {Ar'Ge(#-O)2($1,$1:#2-O2)GeAr'}. In this species the two
    germanium atoms are connected via an peroxo bridge and #2-oxo groups.80 The Ge...Ge distance is
    quite short (2.4127(10) Å), although there is no GeGe bond.
    O
    Ar'GeGeAr'
    
    2 O2
    Ar'Ge
    
    O
    O
    
    GeAr'
    
    O
    
    Scheme 36
    In Scheme 37 reaction with the radical TEMPO (tetramethylpiperidineoxide) cleanly affords
    :Ge(Ar')(TEMPO). Scheme 38 shows that upon reaction with Me3SiN3 the diradicaloid Ar'Ge(#NSiMe3)Ge(Ar') is obtained. In addition the reactions of Ar'GeGeAr' with tin reagents is consistent
    with its radical character. Several of the reactions in Scheme 39 are consistent with the participation of
    radicals as exemplefied by the activation of the flanking aryl ring of an Ar' group upon reaction with
    Me3SiCCH or the one electron coupling to give a C-C bonded product upon reaction with PhCN.
    
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    The reaction of Ar'GeGeAr' with different isonitriles (Scheme 37) showed different reactivity
    depending on the nature of the isonitrile. The reaction with tBuNC afforded a 1:1 adduct in which the
    isonitrile is coordinated to one of the Ge centers.81 As a consequence the GeGe distance increased
    slightly (2.3432(8) Å) and has the nature of a double bond. The addition of a second Lewis base
    molecule was not observed with tBuNC as Lewis base but when Ar'GeGeAr' was reacted with two
    equivalents MesNC yielding a digermylene which is a characterized by a very long GeGe bond
    (2.6626(8) Å).82
    
    Ge
    
    Ge
    Ar'
    
    H
    
    Ar'
    
    O
    
    ai r
    
    N
    
    Ar'
    
    O
    Ge
    
    Ge
    Ar'
    
    NH
    
    O
    
    ON
    
    t
    
    BuNC
    
    Ar'
    
    Ge
    
    t
    
    Bu NC
    
    Ar'GeGeAr'
    
    Ge
    
    H
    O
    
    2 N2O
    
    Ge
    Ar'
    
    Ar'
    2 MesNC
    MesNC
    
    Ar'
    Ge
    
    + 2 N2
    
    O
    H
    
    2 TEMPO
    
    CNMes
    Ge
    
    Ar'
    
    2
    
    Ge
    
    O
    
    Ar'
    
    Ar'
    
    N
    
    Ge
    
    Scheme 37
    
    H
    N
    
    n
    
    Bu3Sn
    
    Ge
    
    Ge
    Ar'
    
    Ge
    Ar'
    
    SiMe3
    N
    Ge
    N
    SiMe3
    
    N
    H
    
    114
    
    SnnBu3
    
    nBu SnN
    3
    3
    
    Ar'
    
    Me3SiN3
    
    H2
    N
    
    Me3SnN3
    
    Ar'GeGeAr'
    
    Ge
    Ar'
    
    PhSCH2N3
    2 Ar'Ge(SPh)2N=CH2
    
    Scheme 38
    
    Ar'
    
    AdN3
    Ar'Ge
    
    GeAr'
    N
    Ad
    
    Ge
    N
    H2
    
    Ar
    '
    
        
    
    Ar'
    Ge
    N
    
    N
    
    N
    
    Ph
    
    N
    
    SiMe3
    
    N
    
    Ar'Ge
    
    Me3Si
    
    Ph
    
    N
    
    SiMe3
    Me3SiCHN2
    
    Ar'
    
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    GeAr'
    GeAr'
    GeAr*
    
    PhCN
    
    Ar'
    Ge
    
    Ge
    
    N
    
    N
    
    Ph
    
    PhC
    
    Ph
    
    *ArGe
    
    Ar'GeGeAr'
    
    PhNNPh
    
    Me3SiC
    
    CPh
    
    Ar'
    
    CH
    
    Ar'
    Ge
    
    iPr
    
    Ge
    SiMe3
    
    Ph
    
    Ph
    
    Ar'Ge
    
    Ge
    SiMe3
    Dipp
    
    Scheme 39
    Addition of Hydrogen
    The digermene Ar'GeGeAr' reacts spontaneously with hydrogen under ambient conditions to give,
    depending on the stoichiometry, differing quantities of germanium hydrides Ar'(H)GeGe(H)Ar',
    Ar'(H)2GeGe(H)2Ar' and ArGeH3. These compounds represent germanium hydrides with formal
    oxidation states at the Ge atom of +2, +3 and +4, respectively.83 This was the first example of a
    successful addition of hydrogen to a main group molecule at ambient conditions (25 °C and 1 atm).
    Ar'(H)GeGe(H)Ar'
    
    Ar'GeGeAr'
    
    Ar'(H2)GeGe(H2)Ar'
    
    Ar'GeH3
    
    1 H2
    
    21 %
    
    10 %
    
    9%
    
    2 H2
    
    2%
    
    85 %
    
    13 %
    
    3 H2
    
    0%
    
    65 %
    
    35 %
    
    Scheme 40
    CONCLUSIONS
    Digermenes, of which more than thirty have been isolated and characterized, can be readily
    synthesized by photochemical reactions, insertion routes and various elimination reactions. In contrast
    to olefins, however, they do not have planar structures but show in most cases a trans pyramidalized
    geometry and Ge-Ge bond lengths shorter than a single one. The germanium congeners of triple
    bonded alkynes, digermynes, have been synthesized via reduction of digermenes. These have a transbent structure in contrast to their carbon congeners and Ge-Ge bond lengths similar to the “short”
    Ge-Ge double bonds.
    115
    
        
    
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    Both digermenes and digermynes have very rich chemistries which have many differences from
    unsaturated carbon species. The most notable feature is the very high reactivity that is generally
    observed. This is exemplified by the fact that both digermenes and digermynes react directly with
    hydrogen – the first example of a reaction between hydrogen and a main group molecule under ambient
    conditions.
    ABBREVIATIONS
    
    Dis =
    
    Si(CH3)3
    Mes =
    Si(CH3)3
    Si(CH3)3
    
    Si(CH3)3
    (H3C)3Si
    
    (H3C)3Si
    Si(CH3)3
    
    Tbt =
    
    Si(CH3)3
    Si(CH3)3
    Si(CH3)3
    
    Bbt =
    
    Si(CH3)3
    (H3C)3Si
    
    (H3C)3Si
    Si(CH3)3
    
    Dipp =
    
    Tripp =
    
    Ar' =
    
    Ar* =
    
    TEMPO =
    
    Scheme 41
    
    116
    
    Si(CH3)3
    
    O N
    
        
    
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    REFERENCES
    1.
    2.
    3.
    4.
    5.
    6.
    7.
    8.
    9.
    10.
    11.
    12.
    13.
    14.
    15.
    16.
    17.
    18.
    19.
    20.
    21.
    22.
    23.
    24.
    25.
    26.
    27.
    28.
    29.
    30.
    31.
    32.
    33.
    34.
    35.
    36.
    37.
    38.
    39.
    40.
    41.
    42.
    43.
    44.
    45.
    
    Rossotti, H. Diverse Atoms: Profiles of the Chemical Elements, Oxford University Press, Oxford, 1998, p. 299.
    Dasent, W. E. Nonexistent compounds, Marcel Dekker, New York, 1965, Chapter 4.
    Davidson, P.J.; Lappert, M.F. J. Chem. Soc. Chem. Commun. 1973, 317.
    Goldberg, D.E.; Harris, D. H.; Lappert, M. F.; Thomas, K. M. J. Chem. Soc. Chem. Commun. 1976, 261.
    Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc. Dalton 1976, 2268.
    Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.; Power, P. P. J. Chem. Soc. Chem. Commun.1978, 192.
    Goldberg, D. E.; Hitchcock, P. B.; Lappert, M. F.; Thomas K. M.; Thorne, A. J., Fjeldberg, T.; Haaland,
    A.; Schilling, B. E. R. J. Chem. Soc., Dalton Trans. 1986, 2387.
    For a summary of all abbreviations: see appendix.
    Kutzelnigg, W. Angew. Chem. Int. Ed. 1984, 23, 272.
    Power, P. P. Chem. Rev. 2000, 99, 3463.
    Grev, R. S. Adv. Organomet. Chem. 1991, 33, 125.
    Barnes, K. M.; Stibbs, W. G. Adv. Organomet. Chem. 1996, 39, 275.
    Escudie, J; Ranaivonjatovo, H. Adv. Organomet. Chem. 1999, 44, 114
    Tokitoh, N.; Okazaki, R., ÒThe Chemistry of Organic Germanium Tin and Lead CompoundsÒ volume 2,
    part 1, chapter 13, page 843, 2002, John Wiley & Sons, Chichester, West Sussex, England.
    Escudie, J.; Couret, C.; Ranaivonjatovo, H. Coord. Chem. Rev. 1998, 178-180, 305.
    Escudie, J.; Ranaivonjatovo, H. Organometallics 2007, 26, 1542.
    Leigh, W. J. Pure & Appl. Chem. 1999, 71, 453.
    Snow, J. T.; Murakami, S.; Masamune, S.; Williams, D. J. Tetrahedron Lett. 1984, 25, 4191.
    Schafer, A.; Saak, W.; Weidenbruch, M. Organometallics 1999, 18, 3159.
    Hurni, K. L.; Rupar, P. A.; Payne, N. C.; Baines, K. M. Organometallics 2007, 26, 5569.
    Fink, M. J.; Michalczyk, M. J.; Haller, K. J.; West, R.; J. Michl Organometallics 1984, 3, 793.
    Batcheller, S. A.; Tsumuraya, T.; Tempkin, O.; Davis, W. M.; Masamune, S. J. Am. Chem. Soc. 1990,
    112, 9394.
    Kira, M.; Iwamoto, T.; Maruyama, T.; Kabuto, C.; Sakurai, H. Organometallics 1996, 15, 3767.
    Tokitoh, N.; Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.; Takeda, N. Polyhedron 2002, 21, 563.
    Lee, V. Ya.; Yasuda, H.; Ichinohe, M.; Sekiguchi, A. Angew. Chem., Int. Ed. 2005, 44, 6378.
    Lee, V. Ya.; Yasuda, H.; Ichinohe, M.; Sekiguchi, A. J. Organomet. Chem. 2007, 692, 10.
    Stender, M.; Pu, L.; Power, P. P. Organometallics 2001, 20, 1820.
    Richards, A. F.; Phillips, A. D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 3204.
    Sekiguchi, A.; Ishida, Y.; Fukaya, N.; Ichinohe, M.; Takagi, N., Nagase, S. J. Am. Chem. Soc. 2002, 124,
    1158.
    Ramaker, G.; Saak, W.; Haase, D.; Weidenbruch, M. Organometallics 2003, 22, 5212.
    Park, J.; Batcheller, S. A.; Masamune S. J. Organomet. Chem. 1989, 367, 39.
    Ando, V.; Itoh, H.; Tsumuraya T. Organometallics 1989, 8, 2759.
    Lee, V. Y.; Takanashi, K.; Ichinohe, M.; Sekiguchi, A. J. Am. Chem. Soc. 2003, 125, 6012.
    Weidenbruch, M. Eur. J. Inorg. Chem. 1999, 373.
    Weidenbruch, M. J. Organomet. Chem. 2002, 646, 39.
    Weidenbruch, M. Organometallics 2003, 22, 4348.
    Hitchcock, P. B.; Lappert, M. F.; Miles, S. J.; Thorne, A. J. Chem. Commun. 1984, 480.
    Hurni, K. L.; Rupar, P. A.; Payne, N. C.; Baines, K. M. Organometallics 2007, 26, 5569.
    Schafer, A.; Saak, W.; Weidenbruch, M.; Marsmann, H.; Henkel, G. Chem. Ber. 1997, 130, 1733.
    Schafer, A.; Saak, W.; Weidenbruch, M. Z. Anorg. Allg. Chem. 1998, 624, 1405.
    Sasamori, T.; Sugiyama, Y.; Takeda, N.; Tokitoh, N. Organometallics 2005, 24, 3309.
    Weidenbruch, M.; Sturmann, M.; Kilian, H.; Pohl, S.; Saak, W. Chem. Ber. 1997, 130, 735.
    Kira, M.; Iwamoto, T.; Maruyama, T.; Kabuto, C.; Sakurai, H. Organometallics 1996, 15, 3767.
    Ramaker, G.; Schaefer, A.; Saak, W.; Weidenbruch, M. Organometallics 2003, 22, 1302.
    Pampuch, B.; Saak, W.; Weidenbruch, M. J. Oranomet. Chem. 2006, 691, 3540.
    117
    
        
    
    Gelest, Inc.
    
    46. Schafer, H.; Saak, W.; Weidenbruch, M. Angew. Chem., Int. Ed. 2000, 39, 3703.
    47. Sekiguchi, A.; Ishida, Y.; Fukaya, N.; Ichinohe, M.; Takagi, N.; Nagase, S. J. Am. Chem. Soc. 2002, 124,
    1158.
    48. Sekiguchi, A.; Fukaya, N.; Ichinohe, M.; Takagi, N.; Nagase, S. J. Am. Chem. Soc. 1999, 121,11587.
    49. Sekiguchi, A.; Yamazaki, H.; Kabuto, C.; Sakurai, H. J. Am. Chem. Soc. 1995, 117, 8025.
    50. Cui, C.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2004, 126, 5062.
    51. Masamune, S.; Batcheller, S. A.; Park, J.; Davis, W. M.; Yamashita, O.; Ohita, Y.; Kabe, K. J. Am.
    Chem. Soc. 1989, 111, 1888.
    52. a) Ross, L.; DrŠger, M. J. Organomet. Chem. 1980, 199, 195. b) DrŠger, M.; Ross, L. Z. Anorg. Allg.
    Chem. 1981, 476, 95. c) Jensen, W.; Jacobson, R. Cryst. Struct. Commun. 1975, 4, 299. d) Glidewell,
    C.; Liles, D. C. Acta Crystallogr. 1978, B34, 119. e) Glidewell, C.; Rankin, W. H.; Robiette, A. G.;
    Sheldrick, G. M.; Beagley, B.; Cradock, S. J. Chem. Soc. A 1970, 315.
    53. Ross., L.; DrŠger, M. J. Organomet. Chem. 1980, 199, 195.
    54. DrŠger, M.; Ross, L. Z. Anorg. Allg. Chem. 1981, 476, 95.
    55. Pampuch, B.; Saak, W.; Weidenbruch, M. J. Organomet. Chem. 2006, 691, 3540.
    56. Samuel, A. S.; Jennings, M. C.; Baines, K. M. J. Organomet. Chem. 2001, 636, 130.
    57. Millevolte, A. J.; Powell, D. R.; Johnson, S. G.; West, R. Organometallics 1992, 11, 1091.
    58. Ando, W.; Tsumuraya, T. Organometallics 1988, 7, 1882.
    59. Piana, H.; Schubert, U. J. Organomet. Chem. 1988, 348, C19.
    60. Inchinohe, M.; Sekiyama, S.; Fukaya, N.; Sekiguchi, A. J. Am. Chem. Soc. 2000, 122, 6781.
    61. Woodward, R. B.; Hoffmann, R. Conservation of Orbital Symmetry, 1970 Academic Press.
    62. Xidos, J. D.; Gosse, T. L.; Burke, E. D.; Poirier, R. A.; Burnell, D. J. J. Am. Chem. Soc. 2001, 123, 5482.
    63. Fukaya, N.; Ichinohe, M.; Sekiguchi A. Angew. Chem. Int. Ed. 2000, 39, 3881.
    64. Lappert, M. F.; Miles, S. J.; Atwood, J. L.; Zaworotko, M. J.; Carty, A. J. J. Organometal. Chem. 1981,
    212, C4.
    65. Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988, 7, 2015.
    66. Rivard, E., Power, P. P. Dalton Trans. 2008, 4336.
    67. Richards, A. F.; Brynda, M.; Power, P. P. J. Am. Chem. Soc. 2004, 126, 10530.
    68. Trinquier, G. J. Am. Chem. Soc. 1991, 113, 144.
    69. Stender, M. Philips, A. D. Wright, R. J.; Power, P. P. Angew. Chem. Int. Ed. 2002, 41, 1785.
    70. Sugiyama, Y.; Sasamori, T.; Hosoi, Y.; Furukawa, Y.; Takagi, N.; Nagase, S.; Tokitoh, N. J. Am. Chem.
    Soc. 2006, 128, 1023.
    71. Bader, R. F. W. Can. J. Chem. 1962, 40, 1164.
    72. Grev, R. S. Adv. Organomet. Chem. 1991, 33, 125.
    73. Allen, T. L.; Fink, W. H.; Power, P. P. Dalton Trans. 2000, 407.
    74. Stender, M.; Philips, A. D.; Power, P. P. Chem. Commun. 2002, 1312.
    75. Twamley, B.; Haubrich, S. T.; Power, P. P. Adv. Organomet. Chem. 1999, 441.
    76. Clyburne, J. A. C.; McMullen, N. Coord. Chem. Rev. 2000, 210, 73.
    77. Schlenk, W.; German, E. Justus Liebigs Ann. Chem. 1928, 463, 71
    78. Smith, L. I.; Hoehn, H. H. J. Am. Chem. Soc. 1941, 61, 1184.
    79. Pu, L.; Phillips, A. D.; Richards, A. F.; Stender, M.; Simons, R. S.; Olmstead, M. M.; Power, P. P. J. Am.
    Chem. Soc. 2003, 125, 11626.
    80. Pu, L.; Senge, M. O.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1998, 120, 12682.
    81. Twamley, B.; Sofield, C. D.; Olmstead, M. M.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc. 1999,
    121, 3357.
    82. Wang, X.; Peng, Y.; Olmstead, M. M.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc. 2009, 131, 14164.
    83. Spikes, G. H.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 12232.
    84. Spikes, G. H.; Power, P. P. Chem. Commun. 2007, 85.
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