An [(NHC)(NHC(EWG))RuCl2(CHPh)] complex for the efficient formation of sterically hindered olefins by ring-closing metathesis.

NHC with EWGs for RCM: Ruthenium complexes with two N-heterocyclic carbenes (NHCs), one of them substituted with electron-withdrawing groups (EWGs), are highly efficient (pre)catalysts for the synthesis of tetrasubstituted olefins and trisubstituted olefins by ring-closing metathesis reactions (RCM, see scheme).

Sulfonated N-heterocyclic carbenes for Suzuki coupling in water.

Sulfonated, water-soluble imidazolium and imidazolinium salts were synthesized and the respective Pd-complexes with N,N'-bis(2,6-dialkyl-4-SO(3)(-)-phenyl)imidazol-2-ylidene and N,N'-bis(2,6-dialkyl-4-SO(3)(-)-phenyl)-4,5-dihydroimidazol-2-ylidene ligands were applied in aqueous Suzuki coupling reactions of aryl chlorides.

Tuning the electronic properties of N-heterocyclic carbenes.

The electron-donating properties of N-heterocyclic carbenes ([N,N'-bis(2,6-dimethylphenyl)imidazol]-2-ylidene and the respective dihydro ligands) with 4,4'-R-substituted aryl rings (4,4'-R=NEt2, OC(12)H(25), Me, H, Br, S(4-tolyl), SO(4-tolyl), SO2(4-tolyl)) were studied. Twelve new N-heterocyclic carbene (NHC) ligands were synthesized as well as the respective iridium complexes [IrCl(cod)(NHC)] and [IrCl(CO)2(NHC)]. Cyclic voltammetry (DeltaE1/2) and IR (nu (CO)) can be used to measure the electron-donating properties of the carbene ligands. Modifying the 4-positions with electron-withdrawing substituents (4-R=-SO(2)Ar, DeltaE1/2=+0.92 V) results in NHC ligands with virtually the same electron-donating capacity as a trialkylphosphine in [IrCl(cod)(PCy3)] (DeltaE1/2 =+0.95 V), while [IrCl(cod)(NHC)] complexes with 4-R=NEt2 (DeltaE1/2= +0.59 V) show drastically more cathodic redox potentials and significantly enhanced donating properties.