SYNTHESIS AND CRYSTAL-STRUCTURE OF THE CONJUGATED TETRAYNE (ETA(5)-C5ME5)RE(NO)(PPH3)(C-CC-CC-CC-CSIME3) - APPLICATION OF THE CADIOT-CHODKIEWICZ COUPLING REACTION TO THE CHAIN EXTENSION OF METAL-CAPPED SP-CARBON WIRES

Sequential reactions of the butadiynyl complex (eta(5)-C5Me5)Re(No)(PP h3)(C = CC = CH) with n-BuLi, Cul, and Me3SiC = CC = CBr (THF/EtNH2, - 45 to -20 degrees C) give the 1,3,5,7-tetrayne (eta(5)-C5Me5)Re(NO)(PP h3)(C = CC = CC = CC CSiMe3) (8) in 77% yield. This involves an interm ediate ReC = CC = CCu species, and constitutes one of the first exampl es of a Cadiot-Chodkiewicz coupling in a metal coordination sphere. Th e crystal structure of 8 (monoclinic, P2(1)/n (No. 14), a=16.685(5) An gstrom, b=13.211(2) Angstrom, c=18.067(4) Angstrom, beta=109.97(2)degr ees, Z = 4) is analyzed in detail. The eight bond angles associated wi th the ReC = CC = CC = CC = CSi unit range from 175.9(8)degrees to 179 (1)degrees. Other reactions that have been used to construct polyalkyn yl sp-carbon chains, in which at least one of the two endgroups is the chiral rhenium fragment (eta(5)-C5Me5)Re(NO)(PPh3), are discussed.