Synthesis of styrylcycloheptatriene derivatives via the electrophilic addition of tropylium ions to [Fe(CO)3(η4-C8H8)]: X-ray crystal structure of tricarbonyl(1–4-η-7-styrylcyclohepta-1,3,5-triene)iron

Abstract

The reaction between [Fe(CO)₃(η⁴-cot)](cot = cyclo-octatetraene) and tropylium tetrafluoroborate yields [Fe(CO)₃(η⁴-C₇H₇CHCHPh)](1), X-ray studies on which have revealed the formation of a co-ordinated styrylcycloheptatriene ligand. The C₇ ring adopts an envelope conformation (interplanar angle 138°) to which the Fe(CO)₃ fragment is η⁴ bonded on the convex face. The atoms of the styryl substituent are all coplanar, and this plane lies approximately orthogonal to the mean plane of the C₇ ring. Crystals of [Fe(CO)₃(η⁴-C₇H₇CHCHPh)] are monoclinic, with space group C2/c, and the structure has been refined to R 0.063 for 1 977 reflections to 2θ= 55°(Mo-K_α) at 293 K. The reaction between [C₇H₇]⁺ and [Fe(CO)₃(η⁴-C₈H₇Me)], giving [Fe(CO)₃{η⁴-C₇H₆(Me)CHCHPh}] in which the methyl group is located on the cycloheptatriene ring, shows that both the cot and tropylium groups undergo ring contraction during the generation of the exocyclic alkene bond of (1). Complex (1) reacts with HBF₄, giving the cycloheptadienyl complex [Fe(CO)₃(η⁵-C₇H₈CHCHPh)][BF₄], and with tetracyanoethylene to give the 1,3-cyclo-adduct, 9-σ: 2–4-η-7,7,8,8-tetracyano-5-styrylbicyclo[4.2.1]nonenediyliron.