Oxidative Addition of Propargyl Halides, Chloroacetonitrile, and Ethyl Chloroacetate to a Dimethylplatinum(II) Complex: Kinetic and DFT Studies
journal contributionposted on 14.04.2014, 00:00 authored by S. Jafar Hoseini, Hasan Nasrabadi, Roghayeh Hashemi Fath, Zohreh Moradi, Mehdi Rashidi
Oxidative addition reaction of propargyl halides, XCH2CCH (X = Cl, Br), with the platinum(II) complex [PtMe2(bipy)] (1), in which bipy = 2,2′-bipyridine, gave a mixture of the propargyl halide complex [PtXMe2(CH2CCH)(bipy)], (X = Cl, trans isomer 2a and cis isomer 2a′; X = Br, trans isomer 2b and cis isomer 2b′) and the allene complex [PtXMe2(CHCCH2)(bipy)], (X = Cl, trans isomer 3a and cis isomer 3a′; X = Br, trans isomer 3b and cis isomer 3b′). The reaction involving propargyl bromide followed second-order kinetics (first order in both reactants), while that involving propargyl chloride showed third-order kinetics (first order in 1, second order in ClCH2CCH) in acetone or benzene solvent. Similar reactions of chloroacetonitrile (ClCH2CN) and ethyl chloroacetate (ClCH2COOEt) reagents with complex 1 yielded [PtClMe2(CH2CN)(bipy)] (4) and [PtClMe2(CH2COOEt)(bipy)] (5), respectively, each as a mixture of cis and trans isomers, proceeding with second-order kinetics. Unpredictably, the reaction rates of complex 1 with propargyl bromide and chloroacetonitrile in benzene solvent are faster than those in acetone solvent. Consistent with our 1H NMR experimental results, DFT studies showed that the cis addition products of allene tautomers (3a′,b′) are more stable than their corresponding trans isomers (3a,b).