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

Treatment of the dibridged dicobalt complex [Co-2(mu -PPh2){mu-eta (1)(S) : eta (1)(C) : eta (2)(C)-SPhC(O)CR'CR}(CO)(4)] (R' = R = H 1a) with L, at a mbient temperature, affords an inseparable mixture of two mono-substituted isomeric complexes of general formula [Co-2(mu -PPh2){mu-eta (1)(S) : eta ( 1)(C) : eta (2)(C)-SPhC(O)CHCH}(CO)(3)(L)] [L = P(OMe)(3) 2a/3a, PPhMe2 2b/ 3b], differing only in the metal centre at which L is coordinated. When the reaction is performed with [Co-2(mu -PPh2){mu-eta (1)(S) : eta (1)(C) : et a (2)(C)-SPhC(O)CR'CR}(CO)(4)] [R' = Me, R = H 1b], in which R' and R are i nequivalent, a similar mixture of inseparable isomers is isolated, [Co-2(mu -PPh2){mu-eta (1)(S) : eta (1)(C) : eta (2)(C)-SPhC(O)CMeCH}(CO)(3)(L)] [L = P(OMe)(3) 4a/5a, PPhMe2 4b/5b] and, in addition, a third separable isome r, [Co-2(mu -PPh2){mu-eta (1)(S) : eta (1)(C) : eta (2)(C)-SPhC(O)CHCMe}(CO )(3)(L)] [L = P(OMe)(3), 6a, PPhMe2 6b], in which R' and R have interchange d. Addition of a further equivalent of L at elevated temperature to mixture s of 2/3 results in both carbonyl substitution and a rearrangement of the b ridging ligand assembly to give [Co-2(mu -SPh){mu-eta (1)(P) : eta (1)(C) : eta (2)(C)-PPh2CRCR'C(O)}(CO)(2)(L)(2)] [R' = R = H; L = P(OMe)(3) 7a, PPh Me2 7b] in high yield. A similar transformation is achieved on interaction of 4/5 and 6 with L leading to [Co-2(mu -SPh){mu-eta (1)(P) : eta (1)(C) : eta (2)(C)-PPh2CRCR'C(O)}(CO)(2)(L)(2)] [R' = Me, R = H; L = P(OMe)(3) 8a, PPhMe2 8b] and, in addition, [Co-2(mu -SPh){mu-eta (1)(P) : eta (1)(C) : et a (2)(C)-PPh2CR'CRC(O)}(CO)(2)(L)(2)] [R' = Me, R = H; L = P(OMe)(3) 9a, PP hMe2, 9b], in which the positions of R' and R are reversed. Reaction of 2a/ 3a with triphenylphosphine, gives the mixed phosphite-phosphine rearranged species [Co-2(mu -SPh){mu-eta (1)(P) : eta (1)(C) : eta (2)(C)-PPh2CHCHC(O) }(CO)(2){P(OMe)(3)}(PPh3)] 10 as the sole product. The facility of the brid ging ligands in 1 to undergo a range of bond-breaking (C-S and C-C) and bon d-forming (C-S, C-P and C-C) reactions induced by phosphorus donor ligand a ddition is discussed and pathways postulated. The single crystal X-ray stru ctures of 2b, 7a and 10 are described.