Phosphorus–hydrogen bond cleavage on a Ph2PH-substituted μ3-thioxo dicobalt–iron cluster as a route to bridging phosphido and thiophosphine ligands

The secondary phosphine-substituted (at cobalt) mixed-metal dicobalt–iron complex [Co2Fe(μ3-S)(CO)8(PPh2H)] (1) can be prepared in good yield from the reaction of [Co2Fe(μ3-S)(CO)9] with one equivalent of Ph2PH in toluene. Also isolated in the reaction, as minor products, are the disubstituted (both at cobalt) complex [Co2Fe(μ3-S)(CO)7(PPh2H)2] (2) and the trisubstituted species [Co2Fe(μ3-S)(CO)6(PPh2H)3] (3). Thermolysis of 1 or 2 results in PH bond cleavage and the formation of the bis-phosphido-bridged species [Co2Fe(μ3-S)(μ-PPh2)2(CO)6] (4) and [Co2Fe(μ3-S)(μ-PPh2)2(CO)5(PPh2H)] (5). Complex 5 can also be prepared more directly by treatment of 4 with one equivalent of Ph2PH. The X-ray structure of the PhPMe2 analogue of 5, [Co2Fe(μ3-S)(μ-PPh2)2(CO)5(PPhMe2)] (5′), reveals the phosphine to be cobalt-bound and occupying an equatorial site. Carbonylation of 4 results in coupling of one phosphido group with the sulphur cap to give the thiophosphine-bridged complex [Co2Fe(μ3-SPPh2)(μ-PPh2)(CO)7] (6), while treatment of 1 with n-BuLi followed by RSCH2Cl (R=Me, Ph) results in the formation of the previously reported thiophosphinomethane-bridged species [Co2Fe(μ3-S)(μ-PPh2CH2SR)(CO)8] (R=Me 7a, Ph 7b). In contrast, interaction of 1 with n-BuLi followed by successive treatment with carbon disulphide and methyl iodide yields the dithiomethoxycarbonylphosphine-bridged complex [Co2Fe(μ3-S){μ-PPh2C(SMe)S}(CO)8] (8). Single crystal X-ray diffraction studies have been performed on complexes 5′ and 8.