Isomerisation and fragmentation of sulfur-containing organometallacycles on dicobalt centres induced by phosphorus donor ligands

Treatment of the dibridged dicobalt complex [Co2(μ-PPh2){μ-η1(S)∶η1(C)∶η2(C)-SPhC(O)CR′CR}(CO)4] (R′ = R = H 1a) with L, at ambient temperature, affords an inseparable mixture of two mono-substituted isomeric complexes of general formula [Co2(μ-PPh2){μ-η1(S)∶η1(C)∶η2(C)-SPhC(O)CHCH}(CO)3(L)] [L = P(OMe)32a/3a, PPhMe22b/3b], differing only in the metal centre at which L is coordinated. When the reaction is performed with [Co2(μ-PPh2){μ-η1(S)∶η1(C)∶η2(C)-SPhC(O)CR′CR}(CO)4] [R′ = Me, R = H 1b], in which R′ and R are inequivalent, a similar mixture of inseparable isomers is isolated, [Co2(μ-PPh2){μ-η1(S)∶η1(C)∶η2(C)-SPhC(O)CMeCH}(CO)3(L)] [L = P(OMe)34a/5a, PPhMe24b/5b] and, in addition, a third separable isomer, [Co2(μ-PPh2){μ-η1(S)∶η1(C)∶η2(C)-SPhC(O)CHCMe}(CO)3(L)] [L = P(OMe)3, 6a, PPhMe26b], in which R′ and R have interchanged. Addition of a further equivalent of L at elevated temperature to mixtures of 2/3 results in both carbonyl substitution and a rearrangement of the bridging ligand assembly to give [Co2(μ-SPh){μ-η1(P)∶η1(C)∶ η2(C)-PPh2CRCR′C(O)}(CO)2(L)2] [R′ = R = H; L = P(OMe)37a, PPhMe27b] in high yield. A similar transformation is achieved on interaction of 4/5 and 6 with L leading to [Co2(μ-SPh){μ-η1(P)∶η1(C)∶η2(C)-PPh2CRCR′C(O)}(CO)2(L)2] [R′ = Me, R = H; L = P(OMe)38a, PPhMe28b] and, in addition, [Co2(μ-SPh){μ-η1(P)∶η1(C)∶η2(C)-PPh2CR′CRC(O)}(CO)2(L)2] [R′ = Me, R = H; L = P(OMe)39a, PPhMe2, 9b], in which the positions of R′ and R are reversed. Reaction of 2a/3a with triphenylphosphine, gives the mixed phosphite–phosphine rearranged species [Co2(μ-SPh){μ-η1(P)∶η1(C)∶η2(C)-PPh2CHCHC(O)}(CO)2{P(OMe)3}(PPh3)] 10 as the sole product. The facility of the bridging ligands in 1 to undergo a range of bond-breaking (C–S and C–C) and bond-forming (C–S, C–P and C–C) reactions induced by phosphorus donor ligand addition is discussed and pathways postulated. The single crystal X-ray structures of 2b, 7a and 10 are described.