Atom-transfer radical reactions catalyzed by a coordinatively unsaturated diruthenium amidinate, [(eta(5)-C5Me5)Ru(mu(2)-i-PrN=C(Me)Ni-Pr)Ru(eta(5)-C5Me5)](+)

摘要

Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4, [(eta(5)-C5Me5)Ru(mu(2)-i-PrN=C(Me)Ni-Pr)Ru(eta(5)-C(5)Me5)](+), are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl alpha-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (eta(5)-C5Me5)Ru( mu(2)-i-PrN=C(Me)Ni-Pr)Ru(eta(5)-C5Me5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF6 and NaBPh4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of alpha,alpha,gamma-trichlorinated gamma-lactam with alkenes at rt to afford the corresponding alpha-alkylated gamma-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y = PF6] and in situ-generated 4 [Y = PF6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C-Br bond of macromolecule initiators; BrCMe2CO2[O(CH2)(4)](n)-n-Bu (M-n = 3800; M-w/M-n = 1.2) initiated ATRP of MMA even at 25 degrees C to afford the poly(THF)-poly(MMA) block copolymer of M-n = 26,000 and M-w/M-n = 1.2 with the aid of 4. The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed. (c) 2005 Elsevier Ltd. All rights reserved.