Half-sandwich nickel complexes with ring-expanded NHC ligands - synthesis, structure and catalytic activity in Kumada-Tamao-Corriu coupling.

The general synthesis of [Ni(Cp)(X)(NHC)] complexes from a nickel halide, CpLi, and a carbene solution is reported. This procedure yields unprecedented complexes with ring-expanded NHC ligands (RE-NHC) of six- (1a, 1b), seven- (1c), and eight-membered (1d) heterocycles. The NMR spectra of 1a-1d are consistent with the hindered rotation of Ni-Ccarbene and N-CMes bonds, while X-ray analyses of 1b, 1c, and 1d reveal a pronounced trans influence of the RE-NHC ligands. Complexes 1a-1e are efficient pre-catalysts in Kumada-Tamao-Corriu coupling with the maximum efficiency observed for complexes bearing the six-membered NHC.

Axial chiral metallocenes by two-fold ring-closing metathesis.

Novel doubly bridged metallocenes have been prepared by remarkably selective two-fold alkene ring-closing metathesis. The solid state structures of 3 and 5 reveal 1,2',3,4'-connectivity and screw-shaped geometry of the molecules.

Novel ruthenium(II)2 carboxylates as catalysts for alkene metathesis.

The reactions of [Ru-(=CHR)Cl2(PCy3)2] (1: R = Ph; 1a: R = -CH=CPh2) with silver salts of carboxylic acids afforded new dimeric complexes of the general formula [Ru2(=CHR)2-(R'CO2)2(mu-R'CO2)2(PCy3)2(mu-H2O)] (2: R = Ph, R' = CF3; 3: R = Ph, R' = C2F5; 4: R = -CH=CPh2, R' = CF3; 5: R = Ph, R' = C6F5; 6: R = -CH=CPh2, R' = C6F5; 7: R = -CH=CPh2, R'=CCl3) in good yields. With R' = CF3, C2F5 or CCl3 these complexes are active catalysts for metathesis of acyclic alkenes, including unsaturated fatty acid esters, as well as for ring closing metathesis. The reactivity of these complexes with bases and weak donor solvents has been studied and their half-life times in several media were determined.