The addition of isonitriles to [{M(CO)2(η-C5H5)}2](M = Mo or W). Syntheses and properties of [M2(µ-η2-CNR)(CO)4(η-C5H5)2](M = Mo or W, R = Me or But) and [{Mo(CNR)(CO)2(η-C5H5)}2](R = Me or But). X-Ray crystal structures of [Mo2(µ-η2-CNBut)(CO)4(η-C5H5)2] and [{Mo(CNBut)(CO)2(η-C5H5)}2]

Abstract

Addition of CNR (R = Me or Bu^t) to the MM complex [{M(CO)₂(η-C₅H₅)}₂](M = Mo or W) results in addition of one isonitrile across the MM bond and the formation of [M₂(µ-η²-CNR)(CO)₄(η-C₅H₅)₂]. The Bu^t molybdenum derivative crystallises as black platey needles [orthorhombic, a= 31.75(3), b= 8.171(11), c= 15.722(17)Å; R converged to 0.0357 for 1 775 independent reflections for which I/σ(I) > 3.0]. The molecule consists of two Mo(CO)₂(η-C₅H₅) groups linked by a Mo–Mo single bond and bridged by the CNBu^t group in a µ-η² four-electron donor fashion. The bonding is viewed as donation of the carbon long pair to one molybdenum atom and donation of CN π-electron density to the second. Prolonged reaction times of [Mo₂(µ-η²-CNR)(CO)₄(η-C₅H₅)₂] with excess CNR results in cleavage of the CN–Mo π-donor interaction and formation of the symmetrically disubstituted complex [{Mo(CNR)(CO)₂(η-C₅H₅)}₂]. The Bu^t derivative crystallises as dark red prisms [monoclinic, a= 10.354(7), b= 11.672(5), c= 10.793(5)Å, β= 103.68(4)°; R converged to 0.0519 for 1 102 independent reflections for which I/σ(I) > 3.0]. The molecule consists of two Mo(CNBu^t)(CO)₂(η-C₅H₅) groups linked through a Mo–Mo single bond with a crystallographically imposed centre of symmetry midway along the Mo–Mo bond. Decarbonylation by thermolysis of this compound results in the formation of [Mo₂(CNBu^t)(µ-η²-CNBu^t)(CO)₃(η-C₅H₅)₂], containing one terminal and one bridging isonitrile. Reductive cleavage of [{Mo(CNR)(CO)₂(η-C₅H₅)}₂] with sodium amalgam gives the anions [Mo(CNR)(CO)₂(η-C₅H₅)]^– which react with SnPh₃Cl to give the tin complexes [Mo(SnPh₃)(CNR)(CO)₂(η-C₅H₅)], as mixtures of cis and trans isomers.