Organogermanium chemistry is the science of chemical species containing one or moreC–Ge bonds. Germanium sharesgroup 14 in the periodic table with carbon,silicon,tin andlead. Historically, organogermanes are considered asnucleophiles and the reactivity of them is between that oforganosilicon andorganotin compounds. Some organogermanes have enhanced reactivity compared with their organosilicon andorganoboron analogues in somecross-coupling reactions.[1]
In general, organogermanium chemistry is much less well-developed than the other group-14 congeners, mainly because germanium is expensive.[2]
The great majority of organogermanium compounds are tetrahedral with the formula GeR4−nXn where X = H, Cl, Br, I. Ge-C bonds are air-stable, although Ge-H bonds can undergo air-oxidation. The first organogermanium compound, tetraethylgermane, synthesized by Winkler in 1887,[3] by the reaction ofgermanium tetrachloride withdiethylzinc. More commonly, these Ge(IV) compounds are prepared by alkylation of germanium halides byorganolithium andGrignard reagents, including surfaces terminated with Ge-Cl bonds.[4] Recent work, however, has developedchlorine-free germanium processing.
Some organogermanes are prepared by nucleophilic substitution or Pd-catalyzed cross-coupling reactions.[1] Hydrogermylation provides another route to organogermanium compounds.[5]
Structure of the trigonal prismatic[GeAr]6 where Ar = 2,6-(iPr)2C6H3.[6] Color code: blue-gray = Ge, gray = C.
Akin tohydrocarbons andpolysilanes, many organogermanium compounds are known with Ge-Ge bonds. An early example is hexaphenyldigermane,(C6H5)3Ge−Ge(C6H5)3. It is prepared byWurtz coupling of the bromide:[7]
2 (C6H5)3GeBr + 2 Na → (C6H5)3Ge−Ge(C6H5)3 + 2 NaBr
Many cyclic polygermanes are known, e.g.[Ge(C6H5)2]4, [Ge(C6H5)2]5, and [Ge(C6H5)2]6.
Compounds with multiple bonds to Ge are usually highly reactive or require bulky organic substituents for their isolation. This situation follows from thedouble bond rule. Digermynes only exist for extremely bulky substituents. According toX-ray crystallography, the C–Ge≡Ge–C core of digermynes is bent. Such compounds are prepared by the reduction of bulky arylgermanium(II) halides.[9]
Compounds containing Ge=C (germenes) double bonds require bulky organic substituents for their isolation.[10] and Ge=Ge (digermylenes)[11] Other examples include the bulky derivatives of germabenzene and 1,2-digermabenzene,[12] analogues of benzene.
Germylenes (carbene analogues) and germyl free radicals have been investigated. Reaction of a Ge(II) chloride with a lithium trialkylgermanide affords a germylene:[13]
ArGeCl + LiGe(C(CH3)3)3 → ArGeGe((C(CH3)3)3 + LiCl (Ar = 2,6-(mesityl)2C6H3)
Organogermanium compounds are used in relatively few commercial applications.Isobutylgermane, a volatile colorless liquid, is used inMOVPE (Metalorganic Vapor PhaseEpitaxy) in the deposition of Gesemiconductor films.
^Akiyama Takahiko (2004). "Germanium in Organic Synthesis". In Yamamoto Hisashi; Oshima Koichiro (eds.).Main Group Metals in Organic Synthesis.ISBN3-527-30508-4.
^Buriak, Jillian M. (2002). "Organometallic Chemistry on Silicon and Germanium Surfaces".Chemical Reviews.102 (5):1271–1308.doi:10.1021/cr000064s.PMID11996538.
^Sekiguchi, Akira; Yatabe, Tetsuo; Kabuto, Chizuko; Sakurai, Hideki (1993). "Chemistry of organosilicon compounds. 303. The missing hexasilaprismane: Synthesis, x-ray analysis and photochemical reactions".Journal of the American Chemical Society.115 (13):5853–5854.doi:10.1021/ja00066a075.
^Amadoruge, Monika L.; Weinert, Charles S. (2008). "Singly Bonded Catenated Germanes: Eighty Years of Progress".Chemical Reviews.108 (10):4253–4294.doi:10.1021/cr800197r.PMID18816144.
^Setaka, Wataru; Sakamoto, Kenkichi; Kira, Mitsuo; Power, Philip P. (2001). "Synthesis and Structure of Stable Tri-tert-butylgermyl-Substituted Stannylene and Germylene".Organometallics.20 (22):4460–4462.doi:10.1021/om010591h.
