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((NBu)-Bu-t)Cl{CH(Ph2PNR)(2)}] 4 (R = Ph, Pr-i, Bu-t) are reported. These compounds were synthesized from the corresponding Li adducts 3 of BIPMH (bis-(iminophosphoranyl)methanide) and Mountford's complex [Ti((NBu)-Bu-t)Cl-2(Py)(3)]. The crystal structures of two of the Ti complexes (R = Ph, Bu-t) and two of the Li compounds (R = Pr-i, Bu-t) are reported. Dynamic solution NMR spectroscopy reveals a dynamic isomerisation process in the case of the Ti complex 4c (R = Bu-t). DFT studies showed that this dynamic process comes from steric repulsion between the imido ligand and the Bu-t N-substituents on the BIPMH ligand. Complexes 4 were tested in allryne hydroamination; 4a (R = Ph) displayed modest catalytic activity in the reaction of aniline with phenylacetylene.