Isomerism in Bi-π-allyl type complexes

Abstract

Reaction between Fe₂(CO)₉ and 1-phenylallene gave three isomeric complexes with the composition [PhCHCCH₂ Fe(CO)₃]₂: (A) orange cubic crystals, m.p. 191–193°(B) orange-red prismatic crystals, m.p. 188–190°; (C) dark red prismatic crystals, m.p. 131–131·5°. On the basis of infrared and n.m.r. spectra, probable structures for these three are proposed. In (A), two isolated Fe(CO)₃ moieties co-ordinate to a tetramethylene-ethene ligand whose double bond presumably participates in the co-ordination. In (B) and (C), the ligand may be regarded as a bi-π-phenylallyl to which the two Fe(CO)₃ moieties, linked by a metal–metal bond, co-ordinate to the two allyl systems. (A) isomerised to (C) at 135° in o-dichlorobenzene, providing support for the structural assignment. In contrast to the parent bi-π-allyl complex, (B) and (C) do not show temperature-dependent tn.m.r. spectra. The isomerism or tautomerism is discussed, and a reaction scheme for formation of the three complexes is proposed.