Small Neutral Geminal Silicon/Phosphorus Frustrated Lewis Pairs

Two new silicon/phosphorus‐based frustrated Lewis pairs (FLP), F 3 SiCH 2 P t Bu 2 ( 1 ) and Cl 3 SiCH 2 P t Bu 2 ( 2 ) were prepared from lithiated di‐ tert‐ butylmethylphosphane, LiCH 2 P t Bu 2 , 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. Cl 3 SiCH 2 P t Bu 2 ( 2 ) was converted with perfluorophenyllithium and 3,5‐bis(trifluoromethyl)phenyllithium. The reaction with LiC 6 F 5 resulted in the ortho‐fluoride substitution product (C 6 F 5 ) 2 SiCH 2 (C 6 F 4 )P t Bu 2 ( 5 ), while the aryl reagent without ortho‐fluoride groups, leads to the intramolecular Lewis pair (C 8 H 3 F 6 ) 3 SiCH 2 P t Bu 2 ( 6 ). The FLP reactivity of 6 was tested.