Intramolecular Stabilization of Carbene Complexes (CO)4W=C(NRR′)Si(aryl)2X (X = H, CMe=CHMe, NEt2) by Interaction of the Metal Center with the Silicon Substituent X

Abstract

The degree of intramolecular stabilization by the substituent X in the carbene complexes (CO)4W=C(NRR′)Si(aryl)2X was investigated by density functional calculations and reactivity studies. Calculations carried out for (CO)4W=C(NH2)SiH2X (X = H, Ph, Me, CMe=CHMe) or (CO)4W=C(NH2)OMe show that the agostic Si−H interaction in (CO)4W=C(NH2)SiH3 transfers as much electron density to the metal as the π−interaction of the olefinic group in (CO)4W=C(NH2)SiH2CMe=CHMe. An agostic interaction is not observed if the silicon atom is replaced by a carbon atom. Interaction of the phenyl group in (CO)4W=C(NH2)SiH2Ph is much weaker and can be described as a weak π−interaction. Owing to the agostic Si−H interaction, (CO)5W=C(NHR)SiHMes2 (R = Me, Et) does not eliminate HSiR′3 upon thermolysis, as observed in the corresponding complexes (CO)5W=C(NHR)SiR′3, but instead gives the 16-electron complex (CO)4W=C(NHR)SiHMes2. When the complexes (CO)5W=C(NMe2)SiPh2CMe=CHMe or (CO)5W=C(NHMe)SiPh2NEt2 are thermolyzed or photolyzed, CO is eliminated and either the olefinic or amino group coordinates intramolecularly to the empty coordination site. The corresponding reaction was not observed when the stable 16-electron complexes (CO)4W=C(NR2)SiPh3 were allowed to react with olefins or tertiary amines respectively. The X-ray structure analysis of (CO)4W=C(NMe2)SiPh2CMe=CHMe is reported.