Incorporation of Thiophene Rings into Tri- and Tetraruthenium Clusters via Cyclometalation and C−P Bond Cleavage of the Ligand Diphenyl-2-thienylphosphine

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Abstract

Diphenyl-2-thienylphosphine, Ph2PC4H3S (1), reacts with [Ru3(CO)12] in refluxing toluene to give the compound [Ru3(μ2-H)(μ3-Ph2PC4H2S)(CO)9] (2) (59%), cyclometalated at the thiophene ring, with smaller amounts of the cluster [Ru3(μ2-H)(μ3-Ph2PC4H2S)(CO)8(Ph2PC4H3S)] (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 μ3-ligand Ph2PC4H2S bound through phosphorus to one Ru atom, through a σ-Ru−C bond to another and by an η2 interaction to the third. There is a dynamic interchange between the σ and η2 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 [Ru3(CO)12] gave two tetranuclear clusters, [Ru4(μ4-PPh)(μ4-C4H2S)(CO)11] (5) by elimination of benzene and the known cluster [Ru4(μ4-PPh)(μ4-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 PPh3. Each has an approximate square of metal atoms capped on one side by μ4-PPh and on the other by μ4-thiophyne (C4H2S) or μ4-benzyne (C6H4), respectively. The C6H4 ligand is coordinated as a 6-electron donor, tilted with respect to the Ru4 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 Ru4 plane in a manner related to known alkyne clusters of the type [Ru4(μ4-PPh)(μ4-alkyne)(CO)11].

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