Structure and magnetic properties of [Cp2M(μ-PEt2)]2 (M = Ti, Zr)

Abstract

The complex [Cp2Ti(μ-PEt2)]2 (1) crystallizes in the monoclinic space group P21/n with a = 16.591(3) Å, b = 8.662(2) Å, c = 37.407(2) Å, β = 102.40(1)°, Z = 8, and V = 5250(2) Å3. The Ti2P2 core of the dimeric complex is planar and the angles at Ti and P are close to 90°. The Ti … Ti separations were found to be 3.732(1) and 3.706(1) Å in the two independent molecules in the unit cell. Bulk magnetic susceptibility measurements on solid 1 show that the species is diamagnetic over the range 5–340 K. The coupling constant for the antiferromagnetic interaction between the Ti centers of 1 is found to be at least −300 cm−1. Extended Hückel Molecular Orbital calculations suggest that mixing of the frontier 1a1 orbitals of the Cp2Ti fragments with the p orbitals of the phosphide fragments affords a mechanism for super-exchange through the ligands. In THF solution, variable temperature 1H, and 31P{1H} NMR and EPR spectra for 1 are consistent with the generation of the paramagnetic monomeric species Cp2TiPEt2, 3. As well, the data suggest thermal populations of the paramagnetic triplet state of the dimer may occur to a small extent at 340 K. In contrast, the analogous Zr dimer 2 shows no evidence of dissociation or of thermal population of the triplet state at temperatures to 340 K. Key words: titanium phosphides, structures, magnetic properties.