NiII, PdII and PtII pincer complexes of 2-(diphenylphosphanyl)-N-(2-(diphenyl-phosphanyl)benzyl)benzamide: synthesis, reactivity and catalytic studies

Abstract

In this article, the synthesis of bis(phosphine), o-Ph₂PC₆H₄C(O)N(H)CH₂C₆H₄PPh₂-o (1) (hereafter referred to as “P^CNH^CP” and its anionic form as “P^CN^CP”) and its group 10 metal chemistry and catalytic studies are described. P^CNH^CP (1) on reaction with NiCl₂(DME) and PdCl₂(COD) afforded pincer complexes, [MCl{(P^CN^CP)κ³-P,N,P}] (M = Ni, 2; Pd, 3). A similar reaction of 1 with PtCl₂(COD) yielded a chelate complex, [PtCl₂{(P^CNH^CP)κ²-P,P}] (4), which on further treatment with LiHMDS produced the 1,2-azaphospholene-phosphine complex, [PtCl(Ph){(o-P(Ph)C₆H₄CONCH₂C₆H₄PPh₂-o)κ²-P,P}] (5) via P–C/P–N bond metathesis. Passing dry HCl gas through the solution of 5 resulted in benzene elimination to form [PtCl₂{(o-P(Ph)C₆H₄CONCH₂C₆H₄PPh₂-o)κ²-P,P}] (6). Treatment of 1 with PtCl₂(COD) and Pt(Cl)(Me)(COD) in the presence of a base resulted in pincer complexes [PtX{(P^CN^CP)κ³-P,N,P}] (X = Cl, 7; Me, 8). Nickel complex 2 catalyzed the Suzuki–Miyaura cross coupling reaction between bromobenzene and phenyl boronic acid to give the corresponding biphenyls in good yield. The platinum complex 5 showed good catalytic activity towards regio- and stereoselective hydroboration of terminal alkynes. Both the catalytic reactions were performed under mild reaction conditions with a very low catalyst loading.