BRIDGING ALKENYL SPECIES FROM THE PROTONATION OF DITUNGSTEN, TUNGSTEN-MOLYBDENUM AND DIMOLYBDENUM TRANSVERSE ALKYNE COMPLEXES WITH HCL AND CF3COOH - CRYSTAL-STRUCTURE OF [WMOCL(MU-(E)-HC=CHPH)(CO)(4)(ETA(5)-C5H5)(2)]

Some Group 6 transition metal complexes with bridging alkyne ligands [MM'(mu-HCCMe)(CO)(4)(eta(5)-C5H5)(2)] [MM' = W-2 1; WMo 2; Mo-2 3] and [WMo(mu-HCCPh)(CO)(4)(eta(5)-C5H5)(2)] (5) were treated with hydrogen chloride to afford respectively [MM'Cl(mu-HC=CHMe)(Co)(4)(eta(5)-C5H5)(2)] [MM'=W-2 (6); WMO (7a); Mo-2 (8)] and [WMoCl(mu-HC=CHPh)(CO)(4)(eta(5)-C5H5)(2)] (9a). Similarly, the complexes [WMo(mu-HCCMe)(CO)(4)(eta(5)-C5H5)(2)] (2) and [MM'(mu-HCCPh)(CO)(4)(eta(5)-C5H5)(2)][MM'=W-2 (4); WMo (5)] were treated with trifluoroacetic acid to give respectively [WMo(CF3COO)(mu-HC=CHMe)(CO)(4)(eta(5)-C5H5)(2)] (7b) and [MM'(CF3COO)(mu-HC=CHPh)(CO)(4)(eta(5)-C5H5)(2)][MM'=W-2 (10); WMo (9b)]. All the products 6-10 result from anti Markovnikov addition of a proton to the bridging alkyne groups in 1-5, and contain (E)-alkenyl ligands, mu-HC=CHR, sigma-bonded to one metal centre and ir-bonded to the other. The metal centre to which the alkenyl ligand is sigma-bonded in 6-10 is also coordinated by a conjugate base (Cl- or CF3COO-). In the case of 9a a single-crystal X-ray diffraction study shows that the W centre has been formally oxidised from W(+1) to W(+3), with both the alkenyl and chloro groups sigma-bonded to it, while the Mo centre is pi-coordinated by the alkenyl group and remains in oxidation state(+1).