Synthesis of new alkyne-bridged ditungsten complexes [W2(CO)4(µ-HC2R)(η-C5H5)2](R = Me or Ph) and the reactions of these and related alkyne-bridged complexes with chlorodiphenylphosphine

Abstract

The new ditungsten alkyne-bridged complexes [W2(CO)4(µ-R1C2R2)(η-C5H5)2](R1= H, R2= Ph 1c or Me 1d) have been prepared. These and the related complexes with R1= R2= Ph 1a or CO2Me 1b were treated with PPh2Cl in refluxing xylene or toluene. The identity of the products depends on the nature of the R group but in general their formation involves the oxidative addition of one or more molecules of PPh2Cl to 1. From 1a two species, [W2Cl(µ-PPh2)(µ-PhC2Ph)(CO)(η-C5H5)2]2a and [W2(O)Cl(µ-PPh2)(µ-PhC2Ph)(η-C5H5)2]4a, in which the alkyne bridge remains intact were isolated, along with a paramagnetic complex, [W2Cl(µ-PPh2)2(CO)(η-C5H5)2]3a, from which the alkyne bridge has been displaced by a diphenylphosphide group. Reaction of 1b with PPh2Cl gave [W2Cl(µ-PPh2){µ-C2(CO2Me)2}(CO)(η-C5H5)2]2b, an analogue of 2a, together with two complexes involving phosphorus–carbon bond formation, [W2(µ-Cl){µ-PPh2C(CO2Me)C(CO2Me)}(CO)2(η-C5H5)2]6b and [W2Cl2(µ-PPh2){µ-PPh2CCH(CO2Me)}(η-C5H5)2]5b. The formation of 5b, involves, in addition, cleavage of a carbon–carbon bond. From 1c, both of the products, [W2Cl2(µ-PPh2){µ-PPh2CCHPh}(η-C5H5)2]5c and [W2Cl2(µ-Cl)(µ-PPh2CCHPh)(η-C5H5)2]7c, involve phosphorus–carbon bond formation. Finally from 1d the only well characterised product is a terminal oxo species, [W2O(µ-PPh2)(µ-CHCHMe)(CO)(η-C5H5)2]8d, in which a vinyl group and a phosphide fragment bridge the two metal centres. A complex related to 8d, [W2O(µ-PPh2){µ-C(CO2Me)CH(CO2Me)}(CO)(η-C5H5)2]8b, is formed on treatment of 2b with silica. Thermolysis of complex 6b results in phosphorus–carbon bond cleavage to give 2b. In contrast, photolysis of 6b gives, as the only well characterised product, paramagnetic [W2Cl(µ-Cl){µ-PPh2C(CO2Me)C(CO2Me)}(CO)(η-C5H5)2]9b. The structures of complexes 2a, 3a and 9b have been determined by X-ray crystallography.