Reactivity of triruthenium thiophyne and furyne clusters: competitive S–C and P–C bond cleavage reactions and the generation of highly unsymmetrical alkyne ligands

Abstract

The synthesis and reactivity of the thiophyne and furyne clusters [Ru₃(CO)₇(μ-dppm)(μ₃-η²-C₄H₂E){μ-P(C₄H₃E)₂}(μ-H)] (E = S, O) is reported. Addition of P(C₄H₃E)₃ to [Ru₃(CO)₁₀(μ-dppm)] (1) at room temperature in the presence of Me₃NO gives simple substitution products [Ru₃(CO)₉(μ-dppm){P(C₄H₃E)₃}] (E = S, 2; E = O, 3). Mild thermolysis in the presence of further Me₃NO affords the thiophyne and furyne complexes [Ru₃(CO)₇(μ-dppm)(μ₃-η²-C₄H₂E){μ-P(C₄H₃E)₂}(μ-H)] (E = S, 4; E = O, 6) resulting from both carbon-hydrogen and carbon-phosphorus bond activation. In each the C₄H₂E (E = S, O) ligand donates 4-electrons to the cluster and the rings are tilted with respect to the μ-dppm and the phosphido-bridged open triruthenium unit. Heating 4 at 80 °C leads to the formation of the ring-opened cluster [Ru₃(CO)₅(μ-CO)(μ-dppm)(μ₃-η³-SC₄H₃){μ-P(C₄H₃S)₂}] (5) resulting from carbon-sulfur bond scission and carbon-hydrogen bond formation and containing a ring-opened μ₃-η³-1-thia-1,3-butadiene ligand. In contrast, a similar thermolysis of 3 affords the phosphinidene cluster [Ru₃(CO)₇(μ-dppm)(μ₃-η²-C₄H₂O){μ₃-P(C₄H₃O)}] (7) resulting from a second phosphorus-carbon bond cleavage and (presumably) elimination of furan. Treatment of 4 and 6 with PPh₃ affords the simple phosphine-substituted products [Ru₃(CO)₆(PPh₃)(μ-dppm)(μ₃-η²-C₄H₂E){μ-P(C₄H₃E)₂}(μ-H)] (E = S, 8; E = O, 9). Both thiophyne and furyne clusters 4 and 6 readily react with hydrogen bromide to give [Ru₃(CO)₆Br(μ-Br)(μ-dppm)(μ₃-η²-η¹-C₄H₂E){μ-P(C₄H₃E)₂}(μ-H)] (E = S, 10; E = O, 11) containing both terminal and bridging bromides. Here the alkynes bind in a highly unsymmetrical manner with one carbon acting as a bridging alkylidene and the second as a terminally bonded Fisher carbene. As far as we are aware, this binding mode has only previously been noted in ynamine complexes or those with metals in different oxidation states. The crystal structures of seven of these new triruthenium clusters have been carried out, allowing a detailed analysis of the relative orientations of coordinated ligands.