6533b835fe1ef96bd129ff42

RESEARCH PRODUCT

Organometallic nucleophiles.A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium (II) and platinum (II)

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Abstract The reactions of the 2- and 4-pyridyl complexes [MX(C 5 H 4 N C n )(dppe)] and trans -[MX(C 5 H 4 N C n )(PPh 3 ) 2 ] (M  Pd, Pt; X  Cl, Br; n = 2, 4)- involving halide displacement from the organic halides XCH 2 R (X  Cl, Br; R  CN, Ph, CH  CH 2 ) by the pyridyl nitrogen have been studied kinetically by conductivity in acetone or acetonitrile at 25°C. The kinetic data fit the second-order rate law rate k 2 [XCH 2 R][complex], in agreement with an S N 2 process at saturated carbon. The higher rates are displayed by the 2-pyridylplatinum derivatives with X  Br in both the metal complex and the organic halide. The higher nucleophilic power of the 2-pyridyl complexes compared with their 4-pyridyl analogs is paralleled by a higher basicity, as reflected by a higher p K a value. In any case, the metal-containing substituent enhances considerably the reactivity and basicity of the pyridine nitrogen. The rates are scarcely influenced by the coordination geometry around the metal.