Oxidative addition of N-C and N-H bonds to zerovalent nickel, palladium, and platinum

Abstract

Reactions of chelating pincer-type PNP ligands based on the bis(ortho-phosphinoaryl)-amine substructure and containing either an N-H (PN(H)P, 1) or N-Me (PN(Me)P, 2) central moiety with group 10 complexes have been explored. Reactions with MCl 2 (MCl 2 = NiCl 2, (COD)PdCl 2, (COD)PtCl 2, COD = 1,5-cyclooctadiene) proceed readily with the loss of either HCl or MeCl and the formation of (PNP)MCl (7) where PNP is an anionic, meridional amido-PNP ligand. Alkylation of (PNP)MeCl with MeMgCl gives (PNP)MMe (9), and reaction of (PNP)MCl with excess NaBH 4 provides (PNP)MH (8). (PNP)MH (8) compounds react with CDCl 3 to regenerate (PNP)MCl (7). The transformations 7 - 8 - 7 - 9 are sluggish for M = Pt compared with M = Ni or Pd. Solid-state structures of (PNP)PdH (8b-Pd) and (PNP)-PdMe (9b-Pd) were determined. The environment about Pd in either structure is approximately square planar with a meridional amido-PNP ligand. Reactions of 1 and 2 with L nM 0 (L n = (COD) 2, (PPh 3) 4, (PBu 13)2) proceed in some cases via N-H or N-C oxidative addition to give either (PNP)MH (8) or (PNP)MMe (9). The N-H oxidative addition reactions are more facile. Both the N-H and N-Me oxidative addition reactions are kinetically inhibited by liberated phosphines from the L nM 0 starting material. Thermolysis of (PNP)MMe (9, M = Ni, Pd, Pt) in the presence of excess PPh 3 does not lead to N-C reductive elimination, thus indicating irreversibility of the N-C oxidative addition.