Cycloaddition reactions between vinylidene iron(II) complexes and alkynes: the first stable cyclobutenylidene complexes

Abstract
[(η5-C5H5)(CO)LfeCCH2]+CF3SO3 complexes react with phenylpropyne with formation of [2 + 2] cycloadducts [(η5-C5H5)(CO)Lfe[graphic omitted]H2]+CF3SO3 (structurally characterized by X-ray crystallography); addition of phenyllithium leads to a stable cyclobutenyl complex in good yield.