New pathways for reactions of transition-metal-propargyl complexes with Fe2(CO)9. Characterization of products derived from iron and chromium propargyls

Article abstract of DOI:10.1021/om00037a032

Reactions of the isoelectronic metal-propargyl complexes Cp(CO)₂FeCH₂C≡CPh (1) and Cp-(NO)₂CrCH₂C≡CPh (2) with Fe₂(CO)₉ were investigated. In pentane at room temperature 1 affords a binuclear metal-η⁴-allylcarbonyl product, (CO)₃Fe[η⁴-C(O)C(Ph)?C(Fe(CO) ₂Cp)?CH₂] (3), whereas in hexane, also at room temperature, 2 surprisingly yields a homobinuclear metal-μ-η²,η³-allenyl product, (CO)₃Fe(μ-η²,η³-PhC=C=CH ₂)Fe(CO)₂(NO) (4), and known CpCr(CO)₂(NO). A mechanism for the formation of 3 is proposed which is similar to that for the cycloaddition reactions of metal-propargyl complexes with neutral electrophiles. Complex 4 arises by an unprecedented complete transfer of the propargyl group as the corresponding allenyl ligand from the parent transition metal (Cr) to the substrate metal (Fe). The diyne (PhC≡CCH₂)₂ (5), which forms in the preparation of 1 and 2, reacts with Fe₂(CO)₉ to give a new bicyclic ferrole complex, (CO)₆Fe₂[PhC=C(C₂H₄)C=CPh] (6). Complexes 3, 4, and 6 were characterized by a combination of elemental analysis, mass spectrometry, and IR and ¹H and ¹³C NMR spectroscopy; the structures of 3 and 6 were determined by single-crystal X-ray analysis. Crystallographic parameters: 3 P1, a = 8.967 (2) A?, b = 9.304 (3) A?, c = 12.533 (4) A?, α = 98.02 (3)°, β = 104.84 (2)°, γ = 105.48 (3)°, Z = 2, R = 0.032, R_w = 0.032 for 4121 independent reflections with I > 3σ(I); 6 P1, a = 7.895 (1) A?, b = 9.056 (1) A?, c = 15.722 (2) A?, α = 78.27 (1)°, β = 79.84 (1)°, γ = 77.12 (1)°, Z = 2, R = 0.028, R_w = 0.028 for 3784 independent reflections with I > 3σ(I).