Titanium imido complexes stabilised by bis(iminophosphoranyl)methanide ligands: the influence of N-substituents on solution dynamics and reactivity

Abstract

Terminal titanium imido complexes of the general formula [Ti(N^tBu)Cl{CH(Ph₂PNR)₂}] 4 (R = Ph, ⁱPr, ^tBu) are reported. These compounds were synthesized from the corresponding Li adducts 3 of BIPMH (bis(iminophosphoranyl)methanide) and Mountford's complex [Ti(N^tBu)Cl₂(Py)₃]. The crystal structures of two of the Ti complexes (R = Ph, ^tBu) and two of the Li compounds (R = ⁱPr, ^tBu) are reported. Dynamic solution NMR spectroscopy reveals a dynamic isomerisation process in the case of the Ti complex 4c (R = ^tBu). DFT studies showed that this dynamic process comes from steric repulsion between the imido ligand and the ^tBu N-substituents on the BIPMH ligand. Complexes 4 were tested in alkyne hydroamination; 4a (R = Ph) displayed modest catalytic activity in the reaction of aniline with phenylacetylene.