Carbon-carbon coupling on tetrahedral iridium clusters: X-ray molecular structures and multinuclear NMR studies of the two isomeric forms of [Ir4(CO)6(m3-h2-HCCPh)(m2-h4-C4H2Ph2)(m-PPh2)2].

The reactions of [HIr4(CO)9(Ph2PC.tplbond.CPh)(m-PPh2)] (1) or [Ir4(CO)8(m3-h2-HCCPh)(m-PPh2)2] (2) with HC.tplbond.CPh gave two isomeric forms of [Ir4(CO)6(m3-h2-HCCPh)(m2-h4-C4H2Ph2)(m-PPh2)2] (3 and 4) in good yields as the only products. These compds. were characterized with anal. and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy and their mol. structures were established by x-ray diffraction studies. Compds. 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two m-PPh2 that occupy different positions in the structures of the two isomers. Both mols. contain a HC.tplbond.CPh ligand bonded in a m3-h2-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir4(CO)6(m3-h2-HCCPh){m2-h4-(H)CC(Ph)C(H)C(Ph)}(m-PPh2)2] (3) and tail-to-tail coupling, in that of [Ir4(CO)6(m3-h2-HCCPh){m2-h4-(H)CC(Ph)C(Ph)C(H)}(m-PPh2)2] (4), and which is linked to two metal atoms of the 2nd wing of the butterfly