Metallaborane heteroatom incorporation reactions:: Enyne insertion into arachno-[(CO)(PMe3)2HIrB8H12]

arachno-[(CO)(PMe3)(2)HIrB8H12] (1) reacts with HC=C-C(CH3)=CH2 in xylene at 138 degrees C to afford [7-{C(CH3)CH2}-9,9,9-(CO)(PMe3)(2)-nido-9,7,8-IrC2B8H10] (2; 10%) together with traces of [5,5,5-(CO)(PMe3)(2)-mu-6,7-{CHC(CH3)CH2}-nido-5,6-IrCB8H11] (3, <1%). Compound 2 is a conventional nido 11-vertex metallacarborane with the {C2Ir} three-atom string in the open face of the cluster, whereas compound 3 is based on a nido 10-vertex {5,6-IrCB8} skeleton with C(2) of the original butyne bridging adjacent B(7) and C(6) cluster open-face positions. Compounds 2 and 3 are characterized by H-1, P-31, and B-11 NMR spectroscopy and by single-crystal X-ray diffraction analysis.