Synthesis of Ortho-metallated Iridium Complex for Inter- and Intramolecular Hydroamination of Alkynes and Reductive Amination

A series of P~N ligands (o-(diphenylphosphino)(N-benzylidene)- aniline) were prepared by the acid catalyzed condensation of 2-(diphenylphosphino)- aniline with the corresponding aldehydes or ketones. Reaction of ligand La~Ld with [Ir(COD)Cl]2 provided the substitution product [(P-(LX)Ir(COD)Cl](X= a. b. c. d) (13a~13d). Treatment of 13a with AgBF4 yielded the cyclometalled iridium hydride complex [P,N,C-(P~N)Ir(COD)H]BF4 (14). Carrying out the substitution of [Ir(COD)Cl]2 with 13a under atmospheric pressure of CO resulted in the formation of [P,N,C-(P~N)IrH(CO)Cl] (15). Conversion of 3 into 4 can also be achieved by the substitution reaction of 14 with CO in presence of tetraethylammonium chloride. Moreover, treatment of 14 with triphenylphosphine and tetraethylammonium bromide under atmospheric pressure of CO resulted in the formation of [P,N,C-(P~N)Ir(CO)(PPh3)H] (16). However, carrying out the substitution of [Ir(COD)Cl]2 with Lb under atmospheric pressure of CO resulted the formation of [P,N,O-(P~N)Ir(CO)HCl] (17). Finally, treatment of 13d with NaB[3,5-C6H3(CF3)2]4 (denoted as NaBArF4) afforded [(P~N)Ir(COD)]BArF4 (18) without the formation of C-H activation product due to the steric effect.
All iridium complexes were not good catalysts for hydroamination. However, the combination of 15 with NaBArF4 provided a good catalytic system for both intra- and intermolecular hydroamination of alkynes. Further, in the presence of NaBArF4 acting as Bronsted acid, complex 15 show an excellent activity on reductive amination of aldehydes in water.