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

Terminal titanium imido complexes of the general formula [Ti(N^t Bu)Cl(CH(Ph₂PNR)₂)] 4 (R = Ph,ⁱ Pr,^t Bu) are reported. These compounds were synthesized from the corresponding Li adducts 3 of BIPMH (bis(iminophosphoranyl)methanide) and Mountford's complex [Ti(N^t Bu)Cl₂(Py)₃]. The crystal structures of two of the Ti complexes (R = Ph,^t Bu) and two of the Li compounds (R =ⁱ Pr,^t Bu) are reported. Dynamic solution NMR spectroscopy reveals a dynamic isomerisation process in the case of the Ti complex 4c (R =^t Bu). DFT studies showed that this dynamic process comes from steric repulsion between the imido ligand and the^t Bu 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.