Interaction of alkylaluminum reagents with organotransition-metal arene complexes: Net addition of alkide, haloalkide, and dichloromethide to [(arene)2Fe]2+ cations

Article abstract of DOI:10.1021/om00037a057

AlEt₃ reacts with the hexafluorophosphate salts of Ar₂Fe²⁺ cations (Ar = arene = benzene (1a), p-xylene (1b), mesitylene (1c), pentamethylbenzene (1d), hexamethylbenzene (1e)) in dichloromethane or 1,2-dichloroethane to afford ChArFe⁺ (Ch = cyclohexadienyl) cations. The major products, the hexafluorophosphate salts of 2a-e, result from net Et^- addition to a single arene ring. The corresponding reactions with AlMe₃ in CH₂X₂ (X = Cl, Br) are more complex and afford characterizable products for 1c,e only. The unexpected major products of these reactions are the hexafluorophosphate salts of the [(6-CH₂X-Ch)ArFe]⁺ monocations 3c,e (X = Cl) and 4c,e (X = Br), derived from net addition of CH₂X, rather than the expected methide addition products, 5a-e. 1c reacts with [N(CH₂CH₂O)₃Al₂Me₃] ₂ (6), a compound that contains an octahedral aluminum methyl moiety, in dichloromethane to produce yet another ChArFe⁺ species, (η ⁵-exo-6-(dichlorpmethyl)-1,3,5-trimethylcyclohexadienyl)(η ⁶-mesitylene)iron(II) hexafluorophosphonate (7c[PF₆]), which is the result of net addition of CHCl₂^-. The methide addition monocationic product 5c[PF₆] can be prepared in low yield from AlMe₃ or 6 and 1c if benzene and 1,2-dichloroethane, respectively, are utilized as solvent. The relevance of these reactions is discussed in the general context of transition-metal activation of Ar molecules. In addition to spectroscopic characterization, several compounds were characterized by X-ray crystallography. Full crystallographic details of the CH₂Cl-Ch and CHCl₂-Ch cations 3c and 7c, respectively, are presented and discussed in the context of related ChFe compounds: 3c[PF₆], orthorhombic, Pcab, with a = 15.2496 (9) A?, b = 15.5537 (10) A?, c = 17.5146 (16) A?, Z = 8, R = 0.059, R_w = 0.058 for 2506 independent, observed (I > 2.5σ(I)), and absorption-corrected reflections; 7c[PF₆]·(CH₃)₂CO, monoclinic, P2₁/c, with a = 18.762 (3) A?, b = 8.758 (2) A?, c = 17.104 (3) A?, β = 113.40 (2)°, Z = 4, R = 0.049, R_w = 0.055 for 2051 independent, observed (I > 2.5σ(I)), and absorption-corrected reflections.