RING EXPANSION OF SPIROCYCLIC GERMANIUM(II) DI(PHOSPHANYL)METHANIDE COMPLEXES BY INSERTION OF SULFUR AND SELENIUM INTO GERMANIUM-PHOSPHORUS BONDS

Germanium in the intermolecularly stabilized germylene derivative Ge[C(PMe2)2(SiMe3)]2 (2a) is not oxidized by sulfur but the latter inserts 1 to 4 chalcogenide atoms into the Ge-P bonds of the four-membered chelate (4/4-) rings to give 4/5-, 5/5-, 5/6, and 6/6-membered spirocycles Ge[C2(SPMe2)n(Pme2)4-n(SiMe3)2] (n = 1-4: 4,5a,6,7). Only 5a and 7 could be obtained in pure form, whereas compounds 4 and 6 with odd-numbered chalcogenide atoms are only characterized in solution, where they exist in equilibrium with 2a and 5a or 5a and 7, respectively. All these molecules are fluctional in solution. 7 is also obtained from GeCl2. dioxane and Li[C(SPMe2)2(SiMe3)]. The selenium compound Ge[C(SePMe2)(Pme2)(SiMe3)]2 (5b) is obtained from 2a and grey selenium in toluene. An X-ray structure determination of 5b shows a distorted sphenoidal arrangement [approximate C2 symmetry of a spirocyclic germanium center within two five-membered rings containing a nearly linear Se - Ge - Se unit (Ge - Se 2.712/2.769(1) angstrom)]. The angle PGeP is 95.9(1)-degrees. A bonding model with a stereochemically non-active electron lone pair at the formal germanium(II) center may account for this geometry. As byproducts in the sulfurization reactions, bis(phosphanyl)methane disulfides are also observed in certain cases, from which H2C(SPMe2)2 has been isolated in pure form and characterized structurally.