Iridium(I) Complexes Bearing a Noninnocent PNP-Pincer-Type Phosphaalkene Ligand: Catalytic Application in the Base-Free N-Alkyl ation of Amines with Alcohols

A series of Ir-I complexes [Ir(L)(PPEP*)] [L = Cl- (3), CO (4), tBuNC (5), PMe3 (6), PPh3 (7)], coordinated with a PNP-pincer-type phosphaalkene ligand bearing a dearomatized pyridine ring (PPEP*), have been prepared and their catalytic properties for the dehydration/condensation of amines with alcohols has been examined. The catalytic reactions successfully proceed under base-free conditions to give N-alkylated amines and their dehydrogenation derivatives (imines). The product selectivity is dependent on L coordinated with Ir(PPEP*). Complexes 4 and 5 that contain p-accepting ligands (CO, tBuNC) form N-alkylated amines as the major products in a closed system using a nitrogen-gas-filled Schlenk tube. In contrast, complex 7 that contain PPh3 as L produces imines as the major products under a nitrogen-gas flow. The reason for the selectivity change depending on L is discussed based on stoichiometric reactions using model compounds of presumed catalytic intermediates.