Protonolysis approach to the catalytic amination of olefins with bis(phosphine)palladium(II) dialkyls
作者:Allen L. Seligson、William C. Trogler
DOI:10.1021/om00027a026
日期:1993.3
Several compounds of the general type PdR2(PR3)2, where R = alkyl and (PR3)2 = monodentate or chelating alkyl- or arylphosphines, catalyze the addition of aniline to acrylonitrile. Acrolein, methyl acrylate, and crotonitrile also act as substrates for aniline addition with Pd(CH3)2(dmpe) catalyst, where dmpe = 1,2-bis(dimethylphosphino)ethane. All the catalysts require 1 equiv of H+ cocatalyst, provided as NH3Ph+. The mechanism proposed for catalysis involves protonolysis of a Pd-R bond to form PdR(PR3)2+. This species can bind acrylonitrile and add NH2R to form PdRR'(PR3)2, with R'= -C(CN)HCH2(NH2R)+, which can be detected in solution by NMR spectroscopy. The net effect is the regeneration of a new palladium dialkyl complex and an H+ source to continue the catalytic cycle. Catalyst stabilities vary in the order 7, Pd(CH3)2(PMe3)2 < 1, Pd(CH3)2(dmpe) almost-equal-to 2, Pd(CH3)2(dppe) < 3, Pd[CH2Si(CH3)3]2(dmpe) almost-equal-to 4, Pd[CH2Si(CH3)3]2(dppe) < 5, PdMe[(t-Bu2)P(CH2)2CH(CH2)2P(t-BU)2]. Complex 5 forms a catalyst active for hundreds of turnovers with no loss of activity. Catalytic turnover rates at 30-degrees-C increase in the order 3 almost-equal-to 2 < 1 < 7 < 5. The unexpected high activity of the sterically hindered catalyst 5 is partly attributed to its crowded binding site. NMR studies show it favors coordination of acrylonitrile over aniline, in contrast to 1.