(η-Benzene)bis(trimethylphosphine)iron: a useful precursor to polyene iron derivatives. Crystal structure of 2–4-η : 2′–4′-η-1,1′-bi(cyclohex-3-en-2-yl)-bis(trimethylphosphine)iron(II)

Abstract

(η-Benzene)bis(trimethylphosphine)iron reacts with 6,6-dimethylfulvene, 6-phenylfulvene, 6,6-di-phenylfulvene, cyclobutene, indene, 1,2-bis(dimethylphosphino)ethane, and 1,2-bis(diphenylphosphino) ethane giving [Fe(η⁵,η^5′-C₅H₄CMe₂CMe₂C₅H₄)], [Fe{η⁵,η^5′-C₅H₄CH(Ph)CH(Ph)C₅H₄}], [Fe(σ,η⁵-C₅H₄CPh₂)(PMe₃)₂], [Fe(η-C₄H₆)(PMe₃)₃], [Fe(η⁵-C₉H₇)(PMe₃)₂H], and [Fe(η-C₆H₆)(R₂PCH₂CH₂PR₂)](R = Me or Ph) respectively. Treatment of [Fe(η-C₆H₆)(PMe₃)₂] with buta-1,3-diene gives a mixture of [Fe(η-C₆H₆)(η-C₄H₆)] and [Fe(η-C₄H₆)₂(PMe₃)]; with cycloheptatriene a mixture of [Fe(η⁴-C₇H₈)(PMe₃)₃], [Fe(η-C₆H₆)(η⁴-C₇H₈)], and [Fe(η⁵-C₇H₇)(η⁵-C₇H₉)] is obtained. [Fe(η-C₆H₆)(PMe₃)₂] reacts with cyclohexa-1,3-diene causing an unusual coupling giving the compound [Fe(η³,η^3′-C₁₂H₁₆)(PMe₃)₂] which has been characterized by ¹H–¹H COSY, heteronuclear ¹H–¹³C shift correlation two-dimensional n.m.r. experiments and crystal structure determination. Protonation of [Fe(η³,η^3′-C₁₂H₁₆)(PMe₃)₂] gives the cation [[graphic omitted](PMe₃)₃]⁺ which contains an agostic hydrogen.