Titanocene(iii) complexes with 2-phosphinoaryloxide ligands for the catalytic dehydrogenation of dimethylamine borane

Abstract

A study of the dehydrogenation of dimethylamine borane using different titanocene(III) complexes with 2-phosphinoaryloxide ligands is presented. Complexes Cp₂Ti(κ²-O, P-O-C₆H₄-PR₂) (3a: R = i-Pr, 3b: R = Ph) (Cp = η⁵-cyclopentadienyl) and Cp*₂Ti(κ¹-O-O-C₆H₄-PR₂) (5a: R = i-Pr, 5b: R = Ph) (Cp* = η⁵-pentamethylcyclopentadienyl) were prepared by reactions of the 2-phosphinophenol ligand with different titanocene sources and fully characterised. Their catalytic activity depends on the steric influence of the cyclopentadienyl ligand, the coordination mode of the 2-phosphinoaryloxide ligand and on the used solvent. Complex 3a showed a turnover number of 43.2 in the neat substrate after 24 hours. EPR investigations were used to elucidate the fate of the Ti(III) catalyst.