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

• Transsilylation of the tris(trimethylsilyl) derivative of nitrilotris(methylenephenylphosphinic) acid and trichlorosilanes affords phosphinate-derived silatranes with [4+1]-coordinated Si atom. • The first crystal structure of this new class of silatranes are presented. • In a mild protolysis, ethanol can liberate ethoxysilanes and can give rise to alkoxysilyl substituted derivatives of nitrilotris(methylenephenylphosphinic) acid. Reactions of a series of trichlorosilanes R SiCl 3 ( R = Me, t Bu, Bn, Ph, Vi, Cl) and the tris(trimethylsilyl) derivative of nitrilotris(methylenephenylphosphinic) acid ( NTPA(SiMe 3 ) 3 ) proceeded with transsilylation (release of Me 3 SiCl) and afforded the respective silatrane-like cage compounds of the type N(CH 2 P(=O)(Ph)O) 3 Si R ( NTPA(Si R ) , R = Me, t Bu, Bn, Ph, Vi, Cl). According to single-crystal X-ray diffraction analyses (for R = Me, t Bu, 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 = t Bu). 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)(HCCl 3 ) 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(HCCl 3 ) 3 ). Reactions of the SiMe3 derivative of nitrilotris(methylenephenylphosphinic) acid, NTPA(SiMe3)3 , and chlorosilanes R SiCl3 (e.g., R = Me) afforded a novel class of silatrane-related compounds, NTPA(Si R ) , with [4+1]-coordinated silicon atom.