Mono, bis, and tris(phosphoramidate) titanium complexes: synthesis, structure, and reactivity investigations

Abstract

A series of variously substituted phosphoramidate titanium complexes bearing dimethylamido ligands are reported. Aryl-substituted ligands impart crystallinity to the systems and allow for the elucidation of the molecular structures via X-ray crystallography. Higher-substituted complexes, including a tris(phosphoramidate)mono(dimethylamido) complex, were isolated and characterized in the solid state, as well as in solution using variable temperature ¹H and ³¹P NMR spectroscopy. The steric bulk possessed by this ligand system, relative to amidate and ureate ligands, has allowed access to a mono(phosphoramidate)tris(dimethylamido) complex. The first solid-state-molecular structure of a mono-ligated 1,3-N,O chelated complex of titanium is reported and compared to the respective bis- and tris-analogues. These complexes were screened for hydroaminoalkylation activity between secondary amines and terminal alkenes and the intramolecular hydroamination of a terminal aminoalkene. Mono(phosphoramidate)tris(dimethylamido) complexes were screened in situ and found to be more active than their respective bis(N,O)-chelated analogues. The elucidation of these complexes allows for a direct comparison to other N,O-chelates of early transition metals, particularly in their hydroaminoalkylation and hydroamination reactivity.