CATALYZED DIMERIZATION OF A DIQUINOETHYLENE AND FORMATION OF DIQUINOETHYLENE-RHODIUM COMPLEXES

Dimerization of diquinoethylene (dqe) 3a to tetraquinocyclobutane 4 is catalyzed by the nickel complexes Ni-(PPh3)2(CO)2 and Ni(diphos)(CO)2, and also by a mixture of Ni(COD)2 and triphenylphosphine. Triphenylphosphine alone catalyzes the same dimerization but more slowly. With tris(triphenylphosphine)chlororhodium, compounds 3a and 3b form complexes Rh(Ph3P)2(dqe). Single-crystal X-ray diffraction of the Rh(PPh3)2Cl(dqe) complex from 3a shows that the central double bond of the cumulene system is bonded to the rhodium; the diquinoethylene moiety is almost planar but is significantly bent at the central carbon atoms. © 1979, American Chemical Society. All rights reserved.