72918-80-0Relevant articles and documents
Reductive elimination of aryl carboxylates from acyl(aryloxy)nickel(II) and -palladium(II) complexes
Komiya, Sanshiro,Akai, Yasushi,Tanaka, Kohkichi,Yamamoto, Takakazu,Yamamoto, Akio
, p. 1130 - 1136 (2008/10/08)
Acyl(p-cyanophenoxy)nickel(II) and -palladium(II) complexes, M(COR)(OC6H4-p-CN)L2 (M = Ni, Pd; L2 = bpy, (PEt3)2), have been prepared by insertion reactions of CO into the metal-carbon bonds of the corresponding methylnickel(II) and -palladium(II) complexes. Addition of π-acids such as CO, maleic anhydride, and acrylonitrile selectively induces reductive elimination of p-cyanophenyl acetate from acylnickel(II) complexes, whereas thermolysis of the complexes mainly results in decarbonylation. In contrast, reductive elimination from the palladium analogue proceeds smoothly on thermolysis, and no apparent accelerating effect of added π-acids is observed. Kinetic studies of both reductive eliminations reveal that the former proceeds via an associative mechanism involving a five-coordinate intermediate, whereas the latter proceeds via two mechanisms, one being a dissociative pathway involving a three-coordinate species and the other being a direct reductive elimination from a four-coordinate species.
Oxidative Addition of Aryl Carboxylates to Ni(0) Complexes Involving Cleavage of the Acyl-O Bond
Yamamoto, Takakazu,Ishizu, Junichi,Kohara, Teiji,Komiya, Sanshiro,Yamamoto, Akio
, p. 3758 - 3764 (2007/10/02)
Reactions of aryl carboxylates RCOO-p-C6H4X (R=CH3, C2H5, n-C3H7; X=H, CH3, OCH3, CN) with bis(1,5-cyclooctadiene)nickel, Ni(cod)2, in the presence of phosphine ligands yield olefin (R(-H)), p-XC6H4OH, and nickel carbonyl complex(es) when the R group has a β hydrogen, whereas CH4, C2H6, nichel carbonyl complex(es), and nickel phenoxide are formed when the R group is CH3.The formation of the products is accounted for by assuming oxidative addition of the ester to nickel involving the cleavage of the acyl-O bond of RCOO-p-C6H4X followed by decarbonylation of the acylnickel complex and decomposition of the alkylnickel complex: RCOO-p-C6H4X + NiLn -> RCONiLnOC6H4X -> RNiLnOC6H4X + CO.The intermediate alkyl(phenoxo)nickel-type complex NiCH3(OC6H5) was in fact isolated in the reaction of phenyl acetate with Ni(cod)2 in the presence of 2,2'-bipyridine.The rate of the reaction is first order with respect to the concentration of the zerovalent nickel complex and the pseudo-first-order rate constant increases with with the increase in the basicity of the phosphine ligand added and with the increase of the electron-withdrawing ability of X.On the basis of these results a mechanism involving a nucleophilic attack at the carbonyl carbon by nickel is proposed.The activation parameters for the reaction of C2H5COOC6H5 with the mixture of Ni(cod)2 and PPh3 are ΔH=21+/-2 kcal/mol, ΔS=-8.8+/-2.9 eu.
