ALKYNE INSERTIONS INTO METAL-METAL BONDS - SYNTHESIS OF HETERONUCLEAR DIMETALLATED OLEFINS BY INSERTION OF MEO(2)CC-CCO(2)ME INTO AN RE-FE SINGLE BOND

Activation of the complex CpFe(CO)(2)Re(CO)(5), 1, by Me(3)NO followed by treatment with MeO(2)CC drop CCO(2)Me yielded the Z-dimetalated olefin complex CpFe(CO)(2)[mu-(Z)-(MeO(2)C)C=C(CO(2)Me)]Re(CO)(4), 2, in 78% yield. Compound 2 was isomerized to E-isomer CpFe(CO)(2)[mu-(E)-(MeO(2)C)C=C( CO(2)Me)]Re(CO)(4), 3, 18% yield, by heating solutions in heptane solvent to reflux for 70 min. When compound 2 was treated with MeO(2)CC drop CCO(2)Me in heptane solvent at reflux, the metallacyclic complex CpFeRe(CO)(4)[mu-C(CO(2)Me)C(CO(2)Me)C(CO(2)Me)C(CO(2)Me)], 4, was formed in 59% yield. Compounds 2, 3, and 4 were characterized by single crystal x-ray diffraction analyses. Compound 2 is a Z-dimetalated olefin complex in which the carbonyl oxygen atom of one of the carboxylate groups is coordinated to the rhenium atom to form a four-membered ring. Compound 3 is an E-isomer of 2 in which the carbonyl oxygen atom of the other carboxylate group is coordinated to the rhenium atom to form a five-membered ring. In compound 4 the two alkynes are coupled to each other and to the rhenium atom to form a metallacycle that is ct-bonded to the iron atom. Crystal data for 2: space group = P2(1)/n, a = 14.010(2) Angstrom, b = 10.259(3) Angstrom, c 14.116(3) Angstrom, beta = 105.96(1)degrees, Z = 4, 2274 reflections, R = 0.023. For 3: space group = P1, a = 8.967(1) Angstrom, b = 16.106(2) Angstrom, c = 7.143(1) Angstrom, alpha 101.69(1)degrees, beta = 99.10(1)degrees, gamma = 98.30(1)degrees, Z = 2, 2581 reflections, R = 0.024. For 4: space group = P2(1)/c, a = 16.335(3) Angstrom, b = 7.622(2) Angstrom, c 19.382(4) Angstrom, beta = 96.39(2)degrees, Z = 4, 2342 reflections, R = 0.032.