A comparison of the reactions of PPh₂CH₂SR (R = Me, Ph) with alkyne-bridged dicobalt carbonyl complexes and with an iron dicobalt μ₃-thioxo carbonyl complex

The reactions of Ph₂PCH₂SR (R = Me, Ph) in toluene with the dicobalt complexes [Co₂ (μ-R¹CCR²(CO)₆] (R¹ = R² = CO₂Me and R¹ = H, R² = CO₂Me) give the monosubstituted complexes [Co₂(μ-R¹CCR²)(CO)₅PPh ₂CH₂SMe] 1 and [Co₂(μ- R¹CCR²(CO)₅PPh₂CH₂SPh] 2. On heating 1 and 2 in toluene solution, loss of CO leads to the bridged species [Co₂(μ-R¹CCR²)(μ- PPh₂CH₂SMe)(CO)₄] 3 and [Co₂ (μ -R¹CCR²)(μ-PPh₂CH₂SPh)(CO) ₄] 4. This transformation is readily reversed by treatment of 3 and 4 with CO, showing the Co-S bond in these complexes to be relatively weak. Similar reactions of Ph₂PCH₂SR (R = Me, Ph) with [Co₂Fe(μ₃-S)(CO)₉], however, give only the ligand bridged species [Co₂Fe(μ₃-S)(μ-Ph₂PCH ₂SR)(CO)₇] (R = Me 5 and R = Ph 6). Treatment of 5 and 6 with CO causes cleavage of the Co-S bond but, in contrast to 3 and 4, the ligand bridged species readily reform when the CO purge ceases. The structures of 3a and 6 have been confirmed by single-crystal X-ray analysis.