Palladium-copper-catalyzed coupling of tricarbonylchromium-complexed phenylacetylene with iodoarenes - A facile access to alkynyl-bridged Cr(CO)(3)-complexed benzenes

The palladium-copper-catalyzed coupling of the tricarbonylchromium-complexed chlorobenzene 1 with (trimethylsilyl)acetylene gives tricarb onyl{eta(6)-[(trimethylsilyl)thynyl]benzene}chromium(0) (2) in high yield. After desilylation of 2 tricarbonyl[eta(6)-(ethynylbenzene)]chromium (3) is obtained quantitatively. Using the palladium-copper-catalyzed methodology, we can readily introduce Cr(CO)(3)-complexed phenylethynyl units by a multifold coupling of 3 with iodobenzene, 1,2-, 1,3-, 1,4-di- and 1,3,5-tiiodobenzene (4a-e) or 1 to give polynuclear Cr(CO)(3)-complexed (phenylethynyl)benzenes 5a-e and doubly Cr(CO)(3)-complexed tolane 6 in good to moderate yield. The crystal structure analyses of mu(3){eta 6:eta(6):eta(6)[1,3,5-benzenetriyltris(2,1-ethylnediyl)]tris(benzene)}tris[tricarbonylchromium(0)] (5e) and mu-{eta(6):eta 6-[1,2-ethynediylbis(benzene)]}bis[tricarbonylchromium(0)] (6) reveal that the tricarbonylchromium tripods in the same molecule are arranged in antiparallel syn-eclipsed conformations. The Eglington coupling of 3 affords a doubly Cr(CO)(3)-complexed diphenylbutadiyne 7 in excellent yield.