Germylenes and germanium doubly bonded species in heterocyclic organogermanium chemistry. Some results from the Toulouse group. (Review)

Abstract

Germylenes, divalent germanium species, and germanium derivatives with Ge=Y double bonds (Y=C=, O, S, N-, P-) are powerful synthetic reagents in organometallic chemistry. The germylenes exhibit properties analogous to those of carbenes and have been shown to insert into various σ-bonds such as carbon-heteroelement, metal-carbon, and metal-heteroelement of heterocyclic derivatives with ring expansion. The addition of germylenes to various unsaturated compounds (dienes, orthoquinones, carbonyl compounds, imines, nitrosobenzene) leads, as a rule, to cycloadducts with low stability except for dienes and quinones. The doubly bonded germanium species are highly reactive and widely used in organometallic synthesis in various types of reactions such as: - addition (or insertion reactions) to various σ-bonds of organometallic compounds; - insertion reactions with ring expansion of small organic rings; - cycloaddition reactions with 1–2, 1–3, and 1–4 dipolar reagents.