SELECTIVE DIMERIZATION AND CYCLOTRIMERIZATION OF PHENYLACETYLENE WITHRHODIUM AND IRIDIUM COMPLEXES

Oligomerization of phenylacetylene is catalyzed by Rh(ClO4)(CO)(PP3)(2 ) (Rh-1), [Rh(CO)(PPh(3))(3)]ClO4 (Rh-2), [Rh(COD) L(2)]ClO4 (L(2) = ( PPh(3))(2), Rh-3; (PPh(3))(PhCN), Rh-4; (PhCN)(2), Rh-5), [Rh(C3H5)(Cl )(CO)(SbPh(3))(2)]ClO4 (Rh-6), [Ir(COD)L(2)] ClO4(L(2)=(PPh(3))(2), Ir -1; (PPh(3))(PhCN), Ir-2; (PhCN)(2), Ir-3; (AsPh(3))(PhCN), Ir-4; Ph(2 )PCH(2)CH(2)PPh(2), Ir-5; COD, Ir-6 and 2,2'-dipyridyl, Ir-7), Ir(ClO4 )(CO)(PPh(3))(2), Ir-8, [Ir(PhCN)(CO)(PPh(3))(2)]ClO4, Ir-9 to produce dimerization products, 1,3-diphenylbut-1-yn-3-ene, 1, (E)-1,4-dipheny lbut-1-yn-3-ene, 2 and (Z)-1,4-diphenylbut-1-yn-3-ene, 3, and cyclotri merization products, 1,3,5-triphenylbenzene, 4 and 1,2,4-triphenylbenz ene, 5. Product distribution of the oligomers varies depending on vari ous factors such as the nature of catalysts, reaction temperature, cou nter anions and excess ligand present in the reaction mixtures. Increa sing reaction temperature in general increases the yield of the cyclot rimerization products. Exclusive production of dimer I and trimer 4 ca n be obtained with Ir-1 at 0 degrees C and with Ir-2 in the presence o f excess PhCN (or CH3CN) at 50 degrees C, respectively. Dimer 2 (up to 81%) and trimer 5 (up to 98%) are selectively produced with Rh-l at 5 0 and 100 degrees C, respectively. Production of 3 is selectively incr eased up to 85% by using PF6- salt of [Ir(COD)(PPh(3))(2)](+) at 25 de grees C. Addition of CH3I to Rh-1 produces CH(3)PPh(3)(+)I(-) and incr eases the rate of oligomerization(disappearance of phenylacetylene). A mong the metal compounds investigated in this study, Zr-1 catalyzes mo st rapidly the oligomerization where the catalytically active species seems to contain Ir(PPh(3))(2) moiety. The stoichiometric reaction of phenylacetylene wth Ir-9 at 25 degrees C quantitatively produces hydri dophenyl-ethynyl iridium (III) complex, [Ir(H)(C=CPh)(PhCN)(CO)(PPh(3) )(2)]ClO4 (Ir-11), which seems to be an intermediate for the oligomeri zation.