Tuning “kappticity” of tripodal ligands

Abstract

The synthesis and structural characterization of a series of tripodal tris(phosphine) ligands, containing SiMe₂ elbow groups, is described. The significant steric congestion in these ligands, due to the silylmethyl substituents, is manifest both in the solid-state structures and in the solution NMR spectra of the free ligands. Variable temperature ¹H{³¹P} NMR studies of one of the ligands, CH₃C(SiMe₂PEt₂)₃ (4b) gave an estimated barrier to rotation around the Si–C_apical bonds of approximately 10.4 kcal mol⁻¹. Octahedral κ²- and κ³-molybdenum complexes of these ligands also demonstrate the impact of the additional bulk imparted by the SiMe₂ substituents, and the high Lewis basicity of these phosphines, with subtle changes at the apical and phosphine substituents changing the overall coordination chemistry observed.