Incorporation of thiophene rings into tri- and tetraruthenium clusters via cyclometalation and C-P bond cleavage of the ligand diphenyl-2-thienylphosphine

Diphenyl-2-thienylphosphine, Ph(2)PC(4)H(3)S (1), reacts with [Ru-3(CO)(12)] in refluxing toluene to give the compound [Ru-3(mu(2)-H)(mu(3)-Ph(2)PC(4)H(2)S)(CO)(9)] (2) (59%), cyclometalated at the thiophene ring, with smaller amounts of the cluster [Ru-3(mu(2)-H)(mu(3)-Ph(2)PC(4)H(2)S)(CO)(8)(Ph(2)PC(4)H(3)S)] (3) (10%), which is a substituted derivative of 2 and may also be formed by substitution at 2 with ligand 1. The single-crystal X-ray structure of cluster 2 shows that it contains the mu(3)-ligand Ph(2)PC(4)H(2)S bound through phosphorus to one Ru atom, through a sigma-Ru-C bond to another and by an eta(2) interaction to the third. There is a dynamic interchange between the sigma and eta(2) interactions of the thienyl group leading to NMR coalescence and a time-averaged plane of symmetry. The corresponding process would be nondegenerate in the substituted compound 3 (X-ray structure reported) and is quenched. Thermal treatment of cluster 2 with [Ru-3(CO)(12)] gave two tetranuclear clusters, [Ru-4(mu(4)-PPh)(mu(4)-C4H2S)(CO)(11)] (5) by elimination of benzene and the known cluster [Ru-4(mu(4)-PPh)(mu(4)-C6H4)(CO)(11)] (6) by elimination of thiophene. Although compounds 5 and 6 are stoichiometrically equivalent, their single-crystal X-ray structures show that they adopt different geometries. The structure of 6 was shown to be the same as that reported previously for the compound derived from PPh(3). Each has an approximate square of metal atoms capped on one side by mu(4)-PPh and on the other by mu(4)-thiophyne (C4H2S) or mu(4)-benzyne (C6H4), respectively. The C6H4 ligand is coordinated as a 6-electron donor, tilted with respect to the Ru-4 plane, with the coordinated C-C bond parallel to an Ru-Ru edge, whereas C4H2S is coordinated as a 4-electron donor, perpendicularly and diagonally across the Ru-4 plane in a manner related to known alkyne clusters of the type [Ru-4(mu(4)-PPh)(mu(4)-alkyne)(CO)(11)].