Siliciumhaltige carben-komplexe XIII. Darstellung und eigenschaften der 16-elektronen carben-komplexe (CO) 4MC(NR 2)SiR′ 3 (M = Cr, Mo, W)

Abstract

Dialkylaminocarbene complexes (CO) 5MC(NR 2)SiR′ 3 ( 1– 3) (M = Cr, Mo, W; SiR′ 3 = SiPh 3, SiPh 2Me, SiPhMe 2; NR 2 = NMe 2, NMeEt, NC 4H 8, NC 5H 10) are obtained by reaction of (CO) 5MC(OEt)SiR′ 3 with HNR 2. If the sterically more demanding amines HNEt 2, HNBu nMe or HN(CH 2Ph)Me are used, monoalkylamino-substituted carbene complexes (CO) 5MC(NHR)SiR′ 3 are formed instead, owing to cleavage of one of the organic substituents at nitrogen. However, diethylamino-substituted carbene complexes can be synthetized by reaction of the anionic complexes Li[(CO) 5MC(NEt)SiR′ 3] with Et 3O + and show no unusual chemical behaviour. The anionic complexes are prepared by deprotonation of (CO) 5MC(NHEt)SiR′ 3. On heating the pentacarbonyl complexes 1– 3 to 100–150°C, in the case of some of the chromium and molybdenum complexes already during their synthesis, a cis-CO ligand is lost to give the stable 16-electron carbene complexes (CO) 4MC(NR 2)SiR′ 3 ( 8– 10). An X-ray structure analysis of (CO) 4WC(NC 5H 10)SiPh 3 ( 8d) reveals that the empty coordination site that results is screened by a phenyl substituent and that relaxation of the steric strain induced by the bulky carbene ligand, seems to be the driving force for the formation of the 16-electron species. In solution the 16-electron complexes 8– 10 are fluxional. In a CO atmosphere the complexes 8– 10 are retransformed quantitatively into the pentacarbonyl complexes 1– 3. Reaction of (CO) 4WC(NMe 2)SiPh 3 ( 8a) with methyl isonitrile or phosphines exclusively yields cis-substituted (CO) 4LWC(NMe 2)SiPh 3 (L = MeNC, PR 3).