Small Neutral Geminal Silicon/Phosphorus Frustrated Lewis Pairs

Abstract

Two new silicon/phosphorus-based frustrated Lewis pairs (FLP), F3SiCH2PtBu2 (1) and Cl3SiCH2PtBu2 (2) were prepared from lithiated di-tert-butylmethylphosphane, LiCH2PtBu2, and the corresponding silicon tetrahalides. They were characterised by NMR spectroscopy and by single-crystal X-ray diffraction. A gas phase electron diffraction study of 1 identified two conformers of similar energy in the vapor. The reactivity of both, 1 and 2, towards a series of small molecules was investigated. Phenyl isocyanate was found to undergo addition reactions of its C-N unit to afford five-membered SiCPC(O)N-ring structures. Cl3SiCH2PtBu2 (2) was converted with perfluorophenyllithium and 3,5-bis(trifluoromethyl)phenyllithium. The reaction with LiC6F5 resulted in the ortho-fluoride substitution product (C6F5)2SiCH2(C6F4)PtBu2 (5), while the aryl reagent without ortho-fluoride groups, leads to the intramolecular Lewis pair (C8H3F6)3SiCH2PtBu2 (6). The FLP reactivity of 6 was tested.