Stabilization of heterodiatomic SiC through ligand donation: theoretical investigation of SiC(L)2 (L=NHC(Me) , CAAC(Me) , PMe3 ).

Quantum chemical calculations have been carried out at the BP86/TZ2P+ level for the compounds SiC(L)2 with L=NHC(Me) , CAAC(Me) , PMe3 (NHC=N-heterocyclic carbene, CAAC=cyclic (alkyl)aminocarbene). The optimized geometries exhibit a trans arrangement of the ligands L at SiC with a planar coordination when L=NHC(Me) and PMe3 , while a twisted conformation is calculated when L=CAAC(Me) . The bending angle L-Si-C is significantly more acute than the angle L-C-Si. Both angles become wider with the trend PMe3 <NHC(Me) <CAAC(Me) . The latter trend is also found for the bond dissociation energies of the reaction SiC(L)2 →SiC+2 L, which have absolute values between De =98-163 kcal mol(-1) . Calculations suggest that the compounds SiC(L)2 have a very large first and second proton affinity, which takes place at the central carbon and silicon atoms, respectively. Energy decomposition analyses indicate that the best description of the bonding situation in SiC(L)2 features a cumulenic carbon-carbon bond and a dative carbon-silicon bond LCSi←L at the center.