Remarkable coordination behavior of alkyl isocyanides toward unsaturated vicinal frustrated P/B Lewis pairs

Abstract

The conjugated frustrated phosphane/borane Lewis pairs formed by 1,1-carboboration of a substituted diphenylphosphino acetylene, undergo a synergistic 1,1-addition reaction to n-butyl isocyanide with formation of new B–C and P–C bonds to the former isonitrile carbon atom. Using tert-butyl isocyanide dynamic behaviour between the isocyanide–[B] adduct and the 1,1-addition product formation was observed in solution. The different modes of isocyanide binding to the FLPs in the solid state were characterized using X-ray crystal structure analyses and comprehensive ¹¹B and ³¹P solid-state magic-angle-spinning (MAS-) NMR experiments. The free FLP, the Lewis adduct at the borane group, and the cyclic product resulting from isocyanide addition to both reaction centers, can be differentiated via¹¹B and ³¹P isotropic chemical shifts, ¹¹B nuclear electric quadrupole coupling constants, isotropic indirect ¹¹B–³¹P spin–spin coupling constants, and ¹¹B⋯³¹P internuclear distances measured by rotational echo double resonance.