REACTIONS OF TRANSITION-METAL SIGMA-ACETYLIDE COMPLEXES .15. CYCLOADDITION OF TRANS-1,2-BIS(METHOXYCARBONYL)-1-CYANOETHENE - STUDIES ON THE MODE OF RING-OPENING OF SIGMA-CYCLOBUTENYL COMPLEXES - X-RAY STRUCTURES OF 2 ISOMERS OF RU(C=CPHCH(CO2ME)C(CN)(CO2ME))(CO)(PPH3)(ETA-C5H5), RU(C[=C(CN)(CO2ME)]CPH=CH(CO2ME))(CO)(PPH3)(ETA-C5H5), AND RU(ETA-3-CH(CO2ME)CPHC=C(CN)(CO2ME))(CO)(ETA-C5H5)

Cycloaddition of trans-CH(CO2Me) = C(CN)(CO2Me) to Ru(C2Ph)(CO)(PPh3)(eta-C5H5) afforded two isomers of the cyclobutenyl complex Ru{C = CPhCH(CO2Me)C(CN)(CO2Me)}(CO)(PPh3)(eta-C5H5) (5a,b) formed by approach of the acetylide to each side of the olefin plane. Thermal opening of the cyclobutenyl ring occurred in conrotatory fashion in both complexes to give the same butadienyl, Ru{C[= C(CN)(CO2Me)]CPh = CH(CO2Me)}(CO)(PPh3)(eta-C5H5) (6); i.e., the sigma-bonded transition-metal-ligand substituent does not affect the course of the reaction, which is in accord with the Woodward-Hoffmann rules. Further heating of the butadienyl complex resulted in loss of PPh3 rather than CO and formation of Ru{eta(3)-CH(CO2Me)CPhC = C(CN)(CO2Me)}(CO)(eta-C5H5) (9). All four complexes were characterized by single-crystal X-ray studies: crystals of 5a are monoclinic, space group P2(1)/c, with a = 14.719 (13) angstrom, b = 11.851 (6) angstrom, c = 18.572 (13) angstrom, beta = 91.29 (4)-degrees, V = 3238.8 angstrom 3, and Z = 4; crystals of 5b are orthorhombic, space group Pna2(1), with a = 18.188 (7) angstrom, b = 18.059 (4) angstrom, c = 10.349 (5) angstrom, V = 3399.2 angstrom 3, and Z = 4; crystals of 6 are triclinic, space group P1BAR, with a = 9.227 (5) angstrom, b = 13.069 (9) angstrom, c = 15.860 (8) angstrom, alpha = 98.44 (3)-degrees, beta = 92.17 (4)-degrees, gamma = 103.91 (3)-degrees, V = 1831.0 angstrom 3, and Z = 2; crystals of 9 are monoclinic, space group P2(1)/n, with a = 9.018 (3) angstrom, b = 12.244 (2) angstrom, c = 18.060 (4) angstrom, beta = 104.56 (2)-degrees, V = 1929.9 angstrom 3, and Z = 4.