ИСТИНА

Two factors has stimulated our research: (i) high thermal, oxidative and hydrolytic stability of cyclopalladated compounds (CPCs) provides their excellent performance in achiral homogenic catalysis; (ii) the most impressive successes in enantioselective catalysis were achieved with planar chiral CPCs. As consequence, we undertook the preparation of two new planar chiral palladacycles, viz., CP-dimer with ferrocene backbone, and non-metallocenic CN-dimer based on [2.2]paracyclophane-derived ligand. Enantiopure CP-dimer (SCRpl)-1 was prepared by double asymmetric synthesis including (i) stereospecific substitution of Me2N group in the known amine (SC)-FcCH(Me)NMe2 with But2P group, following (ii) direct diastereoselective cyclopalladation of the tertiary phosphine thus formed. For preparation of the enantiopure CN-dimer (Spl)-2 we used standard approach based on the corresponding racemic dimer optical resolution with (SC)-prolinate ligand as chiral derivatizing agent. The absolute configuration of the new palladacycles was established by an X-ray diffraction study of their (SC)-prolinate precursors. The new dimers 1, 2 along with their mononuclear derivatives were tested as catalysts in Suzuki cross-coupling of bulky naphthyl reagents and Michael reactions of 2-cyclohexen-1-one with aryl boronic acids. Two known planar chiral CPCs were also used in the same reactions for comparison purpose. Previously we have shown a very high catalytic activity of the CN-dimer rac-4 in the model Suzuki reaction, allowing to perform it under mild conditions.