A new class of silatranes derived from nitrilotris(methylenephenylphosphinic) acid

Abstract

Reactions of a series of trichlorosilanes RSiCl₃ (R = Me, tBu, Bn, Ph, Vi, Cl) and the tris(trimethylsilyl) derivative of nitrilotris(methylenephenylphosphinic) acid (NTPA(SiMe₃)₃) proceeded with transsilylation (release of Me₃SiCl) and afforded the respective silatrane-like cage compounds of the type N(CH₂P(=O)(Ph)O)₃SiR (NTPA(SiR), R = Me, tBu, Bn, Ph, Vi, Cl). According to single-crystal X-ray diffraction analyses (for R = Me, tBu, Bn, Ph, Vi) and DFT analyses (R = Me, Cl), these compounds accommodate [4+1]-coordinate Si atoms in a capped tetrahedral coordination sphere. The environment of the N atom is trigonal pyramidal, with the lone pair pointing toward the Si atom with N⋅⋅⋅Si distances in the range of 2.7451(12) Å (R = Bn) to 2.827(5) Å (R = tBu). For R = Cl, N⋅⋅⋅Si distances were calculated at the PBE0 level to be 2.748 Å in the isolated molecule, 2.620 Å in a chloroform solvate of the type NTPA(SiCl)(HCCl₃)₃. Analyses of the Intrinsic Bond Orbitals (IBOs) and Natural Localized Molecular Orbitals (NLMOs) revealed polarization of the N-located lone pair toward Si, with only marginal orbital contribution of the Si atom in the resultant NLMO (ca. 1.4% for R = hydrocarbyl, 2.2% for R = Cl, 3.3% for R = Cl(HCCl₃)₃).