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(η 6 -C 5 H 4 CH 2 )(η 6 -C 6 H 6 )] + , from the respective carbinol precursor [Re(η 5 -C 5 H 4 CH 2 OH)(η 6 -C 6 H 6 )]. 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(η 5 -C 5 H 4 CHO)(η 6 -C 6 H 6 )] which gave access to the carbinol complex [Re(η 5 -C 5 H 4 CH 2 OH)(η 6 -C 6 H 6 )] and the title compound, both described herein. With [Re(η 6 -C 5 H 4 CH 2 )(η 6 -C 6 H 6 )] + 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 Xray crystal structures of [Re(η 6 -C 5 H 4 CH 2 )(η 6 -C 6 H 6 )] + and postfunctionalized [Re(η 5 -C 5 H 4 CH 2 R)(η 6 -C 6 H 6 )] complexes are presented to confirm their authenticities.

Substituent Effect versus Aromaticity─A Curious Case of Fulvene Derivatives

“… 3 In coordination chemistry, pentafulvenes offer many sites for binding with metal centers, with η 2 , η 4 , η 6 , and η 5 :η 1 complexes reported in the literature, or are important reactants in the synthesis of cyclopentadienyl and carbene complexes. Among them are complexes with Ti, 4 Nb, 5 Zr, 6 and Re 7 metal centers, some with potentially interesting applications. Heptafulvene complexes are less common.…”