Synthesis and structures of heterobimetallic Ir2M (MPd, Pt) sulfido clusters and their catalytic activity for regioselective addition of alcohols to internal 1-aryl-1-alkynes

The heterobimetallic trinuclear sulfido clusters [(Cp*Ir)2(μ3-S)2MCl2] (M=Pd (3), Pt (4); Cp*=η5-C5Me5) were synthesized from the dinuclear hydrogensulfido complex [Cp*IrCl(μ-SH)2IrCp*Cl] (2) and [MCl2(COD)] (COD=cycloocta-1,5-diene), while the reaction of 2 with [Pd(PPh3)4] afforded the cationic trinuclear cluster [(Cp*Ir)2(μ3-S)2PdCl(PPh3)]Cl (5). Clusters 3 and 4 reacted with PPh3 to give a series of mono and dicationic clusters including 5, while the dicationic clusters [(Cp*Ir)2(μ3-S)2M(dppe)][BPh4]2 (M=Pd (9), Pt (10); dppe=Ph2PCH2CH2PPh2) were obtained by the reaction with dppe followed by anion metathesis. The molecular structures of 5·CH2Cl2, 9·CH3COCH3, and 10·CH3COCH3 were determined by X-ray crystallography. Clusters 3 and 4 were found to catalyze the addition of alcohols to alkynes to give the corresponding acetals. Internal 1-aryl-1-alkynes were transformed by cluster 3 into the corresponding 2,2-dialkoxy-1-arylalkanes with high regioselectivity up to 99:1, while cluster 4 was a much less regioselective catalyst.