| Research Abstract |
The Pd/Cu-catalyzed cross-coupling reaction between sp^2 C halides and terminal acetylenes provides a useful method for synthesizing conjugated alkynes that have found application in diverse area ranging from anticancer drugs to material science. The cross coupling reaction of terminal acetylenes with aromatic bromides using standard catalytic systems, (Ph_3P)_2PdCl_2/CuI/amine, requires higher temperature, which may cause some oligomerization of acetylenes, than those of the corresponding iodides. The following optimum catalytic conditions for the coupling of aryl bromides with phenyl acetylene are obtained ; phenyl acetylene (1.5 equiv.), C_6H_5Br(1.0 equiv.), Bu_4NI(10 mol%), CuI(4 mol%), DMF/^nBuNH_2=20/1 70℃. The catalyst, (PhCN)_2PdCl_2/^tBu_3P,/CuI containing electron rich bulky phosphine, have recently been shown to be effective for the cross-coupling of aryl bromides at room temperature [S. L. Buchwald. et al, Org. Lett.,2, 1729(2000)]. The Pd-complex catalyst containing electron rich bulky phosphine such as (R_3P)_2PdCl_2,R_3P = P^tBu_2, P^tBu_2(o-C_6H_4OMe), P^tBu_2Ph, P^tBu_2(C_4H_3S) and 1,1 bis(ditertiarybutyl)phosphinoferrocene, can be also used as an alternative to the above system. From the comparison of the catalytic activities of three types of mononuclear Pd complexes, L_2PdCl_2, dinuclear Pd complexes, (R_3P)_2Pd_2Cl_4, and Chelate Pd complexes, L-LPdCl_2, we conclude that the equilibrium, L_2Pd 【tautomer】 LPd + L, for the mononuclear Pd complexes, and an aqueous solvents for the chelate phosphine complex play a role in the catalytic cycle, respectively.
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