Phosphinamides as Tunable Ligand Precursors for the Titanium-Catalyzed Hydroaminoalkylation of Alkenes

Phosphinamides are reported as a new class of P -bridged κ 2 N, O -chelating ligand precursors for titanium-catalyzed hydroaminoalkylation reactions of alkenes and for the synthesis of new titanium complexes. To evaluate the catalytic activity in six different hydroaminoalkylation reactions, TiBn 4 is used as a catalyst precursor in combination with a ligand precursor library obtained by a systematic variation of the P- and N-bound phenyl substituents of the phosphinamides. The catalyst screening reveals the beneficial role of para -methoxy- and meta - tert -butyl-substitution on the P- and N-bound benzene rings of the phosphinamides. The combination of both substitution patterns in a single ligand precursor leads to a significant synergistic effect, which, in combination with TiBn 4, results in a highly active catalyst system for the intermolecular hydroaminoalkylation of alkenes. As a result, the reaction of 1-octene with N -methylaniline, performed with a catalyst loading of 5 mol % at 160 °C, delivers the branched hydroaminoalkylation product in 94% yield after 2 h. The same conditions can also be applied to other alkene and amine substrates. Furthermore, the synthesis of five new titanium complexes obtained from selected phosphinamide ligand precursors and Ti(NMe 2 ) 4 is described, and in each case, single-crystal X-ray diffraction confirms the expected κ 2 N, O -coordination of the ligand.