Oxidative Addition of N−C and N−H Bonds to Zerovalent Nickel, Palladium, and Platinum

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 n M 0 (L n = (COD) 2, (PPh 3 ) 4, (PBu t 3 ) 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 n M 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.