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.