Tri- and tetranuclear homo- and heterometallic clusters as precatalysts for the Pauson-Khand reaction

Tri- and tetranuclear clusters of formula C[RuCo3(CO) 12] (C = NEt4, NEt4-3; C = bmim, bmim-3; C = H, H-3), [Co4(CO)12] (4), [Co4(CO) 10(μ-dppm)] (dppm = Ph2PCH2PPh2) (5), [Co4(CO)8(μ-dppa)2] (dppa = Ph 2PNHPPh2) (6), [HFeCo3(CO) 11(PPh3)] (7), and [(PNP)PtCo2(CO)7] (PNP = dppa, 8-H; PNP = C6H13SCH2CH 2N(PPh2)2,8-S; PNP = PhN(PPh2) 2,8-Ph) were used as precatalysts in the intramolecular Pauson-Khand reaction of diethyl (allylpropargyl)malonate (1) under 8 bar of CO at 70 °C, which afforded the cyclopentenone 2. The best results with 2% precatalyst loading were obtained with NEt4-3 and bmim3, which gave isolated yields of 93 and 94%, respectively. With a 10% loading, H-3 afforded a yield of 98%. Whereas the diphosphane-substituted Co4 clusters 5 and 6 were inactive, the PtCo2 clusters 8 (at 5% loading) afforded yields ranging from 85 to 91%. The enyne-substituted clusters 9 with a butterfly RuCo3 metal core were isolated from the reaction of NEt4-3 with 1 and were characterized by ESI-MS and spectroscopic methods