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

Abstract

The dimolybdenum alkyne complex [Mo₂(μ-C₂R₂)(CO)₄Cp₂] 1 (R = CO₂Me; Cp = η-C₅H₅) reacts with P₂Ph₄ to afford three major products, which have been identified as the phosphido-bridged vinyl complexes cis- and trans-[Mo₂(μ-CRCHR)(μ-PPh₂)(CO)₂Cp₂] (two separable isomers, 2 and 3 respectively) and [Mo₂(μ-CRCRCHO)(μ-PPh₂)(CO)₂Cp₂] 4. The crystal structure of 3 has been determined and shows that the CO₂Me group attached to the β-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 [Mo₂(μ-C₂R₂)(CO)₃(PPh₂H)Cp₂] 6 together with a small amount of 4; thermolysis of 6 also yields 2, 3 and 4. Treatment of 1 with thiols R¹SH (R¹ = Et, Prⁱ or C₆H₄Me-p) afforded the complexes [Mo₂(μ-CRCHR)(μ-SR¹)(CO)₂Cp₂] 7a–7c which are analogous to 3; the structure of the complex with R¹ = Prⁱ has been determined. In contrast, treatment of 1 with Bu^tSH affords the unusual complex [Mo₂(μ-S)₂(μ-RCHCHR)Cp₂] 8 in which the alkyne ligand has been hydrogenated to an alkene which is bonded in an η² manner to one metal atom and through both CO₂Me groups to the other. The complexes [Mo₂(μ-CHCHR)(μ-SR¹)(CO)₂Cp₂] 10, derived from the methyl propiolate complex [Mo₂(μ-HC₂R)(CO)₄Cp₂], are also described.