Reactions of [Mo2(μ-RC2R)(CO)4Cp2] (R = CO2Me, Cp = η-C5H5) with P2Ph4, PPh2H and R1SH (R1 = Et, Pri, C6H4Me-p or But):: stabilisation of μ-vinyl complexes by chelating substituents

The dimolybdenum alkyne complex [Mo-2(mu-C2R2)(CO)(4)Cp-2] 1 (R=CO2Me; Cp=eta-C5H5) reacts with P2Ph4 to afford three major products, which have been identified as the phosphido-bridged vinyl complexes cis- and trans-[Mo-2(mu-CR=CHR)(mu-PPh2)(CO)(2)Cp-2] (two separable isomers, 2 and 3 respectively) and [Mo-2(mu-CR=CRCHO)(mu-PPh2)(CO)(2)Cp-2] 4. The crystal structure of 3 has been determined and shows that the CO2Me group attached to the beta-carbon of the vinyl ligand is co-ordinated to one metal atom through the carbonyl group, thus forming a five-membered chelate ring. The reaction of 1 with PPh2H in refluxing toluene gave the same three complexes, whereas treatment of 1 with PPh2H at room temperature in the presence of trimethylamine N-oxide afforded the monosubstituted complex [Mo-2(mu-C2R2)(CO)(3)(PPh2H)Cp-2] 6 together with a small amount of 4; thermolysis of 6 also yields 2, 3 and 4. Treatment of 1 with thiols (RSH)-S-1 (R-1=Et, Pr-i or C6H4Me-p) afforded the complexes [Mo-2(mu-CR=CHR)(mu-SR1)(CO)(2)Cp-2] 7a-7c which are analogous to 3; the structure of the complex with R-1=Pr-i has been determined. In contrast, treatment of 1 with (BuSH)-S-t affords the unusual complex [Mo-2(mu-S)(2)(mu-RCH=CHR)Cp-2] 8 in which the alkyne ligand has been hydrogenated to an alkene which is bonded in an eta(2) manner to one metal atom and through both CO2Me groups to the other. The complexes [Mo-2(mu-CH=CHR)(mu-SR1)(CO)(2)Cp-2] 10, derived from the methyl propiolate complex [Mo-2(mu-HC2R)(CO)(4)Cp-2], are also described.