FISCHER-TYPE IRON ALKYNYLCARBENE COMPLEXES - SYNTHESIS AND REACTIONS WITH 1,3-DIENES

Abstract

Five (alkynylethoxymethylene)Fe(CO)4 complexes (1a-e) are prepared through the reaction of Fe(CO)5 with alkynyllithiums (R = (n)Pr, cyclohexyl, (t)Bu, trimethylsilyl, Ph) and subsequent O-ethylation of the resulting acyl anion complexes with ethyl fluorosulfonate; while (diethoxycyclopropenyldiene)Fe(CO)4 (2) is obtained in the case of (ethoxyethynyl)lithium. In the reaction of the trimethylsilyl-substituted alkynylcarbene complex 1d with 2,3-dimethyl- 1,3-butadiene, the (eta-3-vinylcarbene)Fe-(CO)3 complex 3 is produced via [2 + 4] cycloaddition, while the reaction with cyclopentadiene leads to formation of the eta-4-vinylketene complex 4 through CO insertion at the carbene carbon, promoted by chelation of another internal carbon-carbon double bond after [2 + 4] cycloaddition.