Germanium in Organic Synthesis

Because chlorotrialkylgermanes, e.g. RjGeCl [4], were not readily available commercially until recently [5], chlorogermanes had to be prepared from GeCl4 [6], the cheapest commercial source of germanium. 

Organogermanium compounds have properties between those of organosihcon and organotin compounds and this unique synthetic utility has not been extensively explored. Whereas organotin compounds prefer radical reactions, ionic reactions predominate with organosilicon compounds. Organogermanium compounds have both characteristics. 

Although compilations of organogermanium chemistry are available [7, 8], most review articles focus on the structure and reaction of the organogermanium compounds. For fhis reason I wish to address the synthetic utihty of organogermanium compounds focusing on articles pubhshed after 1990. 

Main Group Metals in Organic Synthesis. Edited by H. Yamamoto, K Oshima Copyright 2004 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30508-4 

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Limited studies of the germanium and tin hydride analogs of the silicon hydrides show that they share this ability to function as hydride sources in ionic hydrogenations however, their relatively greater reactivity toward acids appears to restrict their practical applications in organic synthesis.24,25... 

In contrast to their germanium analogues, the main applications of tin heterocycles are not concerned with their biological activity although several 1,3,2-dioxastannolane derivatives exhibit in vitro antitumor activity (88BSB873, 92H(34)549>. The two most important fields involve technical uses of 1,3,2-diheterastannolanes and their use in organic synthesis. 

This chapter will emphasize the synthesis, stabilization, spectroscopic and structural aspects, reactivity and synthetic use of these compounds. For completeness, a summary of the subject previously reviewed3-10 will be included together with recent examples from the literature. The material will be divided into three sections preparations, spectroscopic and structural studies (with some characteristic spectroscopic and structural data) and reactivity (with some applications in organic synthesis). Each part will be organized into sections dealing with a particular element in the order germanium, tin and then lead. 

Because of the high cost of germanium and the high toxicity of lead, these metal-14 elements have been little used in organic synthesis compared with tin. The use of tin compounds in syntheses has been reviewed411 207. We shall here illustrate the particular application of metal-14 anions. 

The single-bond compounds between Si, Ge, and Sn and chalcogens (S, Se, Te) are reactive and used as synthetic intermediates in the synthesis of organic compounds, organochalcogen compounds, organo-silicon, -germanium and -tin compounds, and transition metal-chalcogen complexes and clusters. 

The reactions of atoms or radicals with silicon hydrides, germanium hydrides, and tin hydrides are the key steps in formation of the metal-centered radicals [Eq. (1)]. Silyl radicals play a strategic role in diverse areas of science, from the production of silicon-containing ceramics to applications in polymers and organic synthesis.1 Tin hydrides have been widely applied in synthesis in radical chain reactions that were well established decades ago.2,3 Germanium hydrides have been less commonly employed but provide some attractive features for organic synthesis. 

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