Copper(I) 1,3-R2-3,4,5,6-tetrahydropyrimidin-2-ylidenes (R = mesityl, 2-propyl):: synthesis, X-ray structures, immobilization and catalytic activity

The synthesis of novel copper (1) N-heterocyclic carbene complexes is described. Thus, reaction of CuX with 1,3-di(2-propyl)3,4,5,6-tetrahydropyrimidin-2-ylidene yields CuX(1,3-di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (X=Cl, (1a), Br (1b)); however, reaction of CuCl with 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene yields the bis-N-heterocylcic carbene complex Cu(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2)(+) CuBr2-(2). A supported version of 1, i.e. PS-DVB-CH2-OCO-CF2-CF2-CF2-COOCu(1,3-di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (3) was prepared from I and PS-DVB-CH2-OCO-CF2-CF2-CF2-COOAg. A copper loading of 4.15 mu mol/g was realized. The new compounds were used as catalysts in carbonyl hydrosilylation and cyanosilylation reactions. Excellent reactivity was observed, giving raise to turn-over numbers (TONs) of up to 100,000. Compounds 1a, 1b, and 2 have also been used as catalysts for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). A linear conversion of monomer with time was observed, however, no control over molecular weight of PMMA was observed. (c) 2005 Elsevier Ltd. All rights reserved.