Siliciumhaltige Carben-Komplexe XIII. Darstellung und Eigenschaften der 16-Elektronen Carben-Komplexe (CO)4MC(NR2)SiR'3 (M = Cr, Mo, W)

Article abstract of DOI:10.1016/0022-328X(90)87286-M

Dialkylaminocarbene complexes (CO)5MC(NR2)SiR'3 (1-3) (M = Cr, Mo, W; SiR'3 = SiPh3, SiPh2Me, SiPhMe2; NR2 = NMe2, NMeEt, NC4H8, NC5H10) are obtained by reaction of (CO)5MC(OEt)SiR'3 with HNR2.If the sterically more demanding amines HNEt2, HNBuⁿMe or HN(CH2Ph)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, diethyl-amino-substituted carbene complexes can be synthetized by reaction of the anionic complexes Li<(CO)5MC(NEt)SiR'3> with Et3O⁺ 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 deg 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(NR2)SiR'3 (8-10).An X-ray structure analysis of (CO)4WC(NC5H10)SiPh3 (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(NMe2)SiPh3 (8a) with methyl isonitrile or phosphines exclusively yields cis-substituted (CO)4LWC(NMe2)SiPh3 (L = MeNC, PR3).