Siliciumhaltige Carben-Komplexe. XIV. Untersuchungen zur Frage der Aciditaet der Si-H-Gruppe in Silylcarben-Komplexen (CO)5MC(XR)SiHR'2 (M = Cr, W; XR = OEt, NR2)

Article abstract of DOI:10.1016/0022-328X(93)86055-M

The very unstable carbene complexes (CO)5MC(OEt)Si(H)Mes2 (1a: M=W; 1b: M=Cr; Mes=mesityl) were prepared by reaction of M(CO)6 with Li, followed by alkylation with BF4.Corresponding complexes with smaller substituents at the silicon atom were considerably less stable.While 1a yielded the aminocarbene complexes (CO)5WC(NHR)Si(H)Mes2 upon reaction with H2NR (R=Me, Et, CH2CH=CH2, i-Pr), reaction with HNR2 was strongly influenced by steric effects.Dialkylaminocarbene complexes (CO)5WC(NR2)Si(H)Mes2 were only obtained with the sterically less demanding amines HNMe2 or HNC4H8.Complex 1b only reacted with H2NMe.The X-ray structure analysis of (CO)5WC(NC4H8)Si(H)Mes2 (2f) showed that the hydrogen atom at silicon is strongly screened and hardly accessible.Although spectroscopic data of the new complexes indicate a slight enhancement of the acidity of the Si-H group compared with R2SiH2, no deprotonation was possible using several bases.