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 MCl2 (MCl2 = NiCl2, (COD)PdCl2, (COD)PtCl2, 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 NaBH4 provides (PNP)MH (8). (PNP)MH (8) compounds react with CDCl3 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 LnM0 (Ln = (COD)2, (PPh3)4, (PBut3)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 LnM0 starting material. Thermolysis of (PNP)MMe (9, M = Ni, Pd, Pt) in the presence of excess PPh3 does not lead to N−C reductive elimination, thus indicating irreversibility of the N−C oxidative addition.