Synthesis and reactivity of the rhenium fulvene sandwich complex [Re(η6-C5H4CH2)(η6-C6H6)]+

Abstract

We present the synthesis of the first mixed-ring rhenium fulvene sandwich complex, [Re(η6-C5H4CH2)(η6-C6H6)]+, from the respective carbinol precursor [Re(η5-C5H4CH2OH)(η6-C6H6)]. The demanding preparation on the basis of the reactive cross-conjugated π system of the fulvene ligand restricts the synthetic accessibility for such fulvene complexes, and the only pathways elaborated originate from the respective carbinols. In contrast to related systems, a suitable rhenium-containing precursor did not exist hitherto. Recently, we described the synthesis of the mixed-aromatic complex [Re(η5-C5H4CHO)(η6-C6H6)] which gave access to the carbinol complex [Re(η5-C5H4CH2OH)(η6-C6H6)] and the title compound, both described herein. With [Re(η6-C5H4CH2)(η6-C6H6)]+ in hand, the susceptibility of the exocyclic methylidene group of the coordinated pentafulvene to nucleophilic attacks was investigated with a variety of Lewis bases (hydride, cyanide, amide, alkoxide, thiolate, and phosphine moieties). The characteristic NMR pattern and X-ray crystal structures of [Re(η6-C5H4CH2)(η6-C6H6)]+ and postfunctionalized [Re(η5-C5H4CH2R)(η6-C6H6)] complexes are presented to confirm their authenticities.