Dimerization of Ethynylcyclopentadienylmetal Complexes

Heating of bulky ethynyltetramethylcyclopentadienylmetal complexes, RCCH (R = Me4C5Rh(cod), Me4C5Ir(cod), Me4C5Fe (C5Me4H)), in the presence of catalytic amounts of Ru(H)2(CO)(PPh3)3 afforded the corresponding butatriene, RCH=C=C=CHR. The rhodium complex was stepwise hydrogenated by Ru(H)2(CO)(PPh3)3 to give a butadiene complex, RCH=CH–CH=CHR, whose molecular structure was determined by X-ray diffraction analysis.