The mechanism of metal-promoted alkyne cyclo-oligomerisation with isocyanides leading to cyclopentadiene derivatives. The crystal and molecular structure of [WSPri(CNBut){η2-C4(CF3)4CNBut}(η5-C5H5)] containing an η2-tetrakis(trifluoromethyl)cyclopentadienimine ligand

Reaction of t-butyl isocyanide with the two co-ordinated alkynes in [MSR′(CF3CCCF3)2(η5-C5H5)](M = Mo, R′= C6F5; M = W, R′=p-tolyl) has been shown to involve initial attack at the alkyne followed by transfer of CNBut to the metal with concomitant oxidative metallocyclisation and subsequent reductive cyclisation to give [MSR′(CNBut){η2-C4(CF3)4CNBut}(η5-C5H5)] shown by X-ray diffraction studies (M = W, R′= Pri) to contain a tetrakis(trifluoromethyl)cyclopentadienimine ligand attached only via the C–N bond to the metal.