Complexes of SiH22+ with carbodiphosphorane and analogues {R(PPh3)2} in unusual bonding mode (E = C, Si, Ge, Sn, Pb)

Abstract

Quantum chemical calculations at the BP86 level with various basis sets (SVP, TZVPP) were carried out for complexes of carbodiphosphorane analogues E(PPh₃)₂ with E = C, Si, Ge, Sn, Pb. The equilibrium geometries of the complexes [SiH₂²⁺–{E(PPh₃)₂}] (Si²⁺-1E) possess the carbodiphosphorane ligand 1C is slightly bonded in a tilted way to SiH₂²⁺ in the complex Si²⁺-1C, whereas the heavier group-14 ligands E(PPh₃)₂ (E = Si, Ge, Sn, Pb) in the complexes Si²⁺-1Si – Si²⁺-1Pb are strongly bonded in side-on fashions. The surprising structures SiH₂²⁺-tetrylone complexes possess a strong Si-C1 bond between the Si atom of the SiH₂²⁺ fragment and atom C1 of the phenyl group. The trend of the bond dissociation energies  (BDEs) for the Si-E bond in the Si²⁺-1E complexes is Si²⁺-1C ~ Si²⁺-1Si ~ Si²⁺-1Ge < Si²⁺-1Sn < Si²⁺-1Pb. Bonding analysis of the complexes shows that the Si-E bonds have a significant contribution from H₂Si²⁺←E(PPh₃)₂ π-donation.

Keywords: Donor-acceptor interactions; bonding analysis; density functional theory, bond dissociation energy.