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

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-eta(4)-allylcarbonyl product, (CO)3Fe[eta(4)-C(O)C(Ph)-C(Fe(CO)2Cp)-CH2] (3), whereas in hexane, also at room temperature, 2 surprisingly yields a homobinuclear metal-mu-eta(2),eta(3)-allenyl product, (CO)3Fe(mu-eta(2),eta(3)-PhC = C = CH2)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 H-1 and C-13 NMR spectroscopy; the structures of 3 and 6 were determined by single-crystal X-ray analysis. Crystallographic parameters: 3 P1BAR, a = 8.967 (2) angstrom, b = 9.304 (3) angstrom, c = 12.533 (4) angstrom, alpha = 98.02 (3)-degrees, beta = 104.84 (2)-degrees, gamma = 105.48 (3)-degrees, Z = 2, R = 0.032, R(w) = 0.032 for 4121 independent reflections with I > 3-sigma(I); 6 P1BAR, a = 7.895 (1) angstrom, b = 9.056 (1) angstrom, c = 15.722 (2) angstrom, alpha = 78.27 (1)-degrees, beta = 79.84 (1)-degrees, gamma = 77.12 (1)-degrees, Z = 2, R = 0.028, R(w) = 0.028 for 3784 independent reflections with I > 3-sigma(I).