Complexation of a rigid multi-pyridine ligand bis(2-pyridyl)-1,8-naphthyridine (bpnp) with [Cu(2)(TFA)(4)] (TFA = trifluoroacetate) resulted in the formation of a dinuclear copper(II) complex, namely [Cu(2)(bpnp)(μ-OH)(TFA)(3)] (1). This complex has been characterized by X-ray crystallographic, spectroscopic and elemental analyses. Complex 1 is an efficient catalyst for the oxidative coupling of various 2,6-disubstituted phenols with molecular oxygen. Yields and selectivity depend on the reaction conditions employed, the best results being obtained in isopropanol or dioxane at 90 °C with yields of >99%. Mechanistic pathway of the catalysis is discussed.

N-Heterocyclic carbene gold(I) complexes [(L)AuCl] [L = 1,3-diethyl-4,5-dihydroimidazol-2-ylidene (3a); 1,3-dibenzyl-4,5-dihydroimidazol-2-ylidene (3c); 1,3-dipicolyl-4,5-dihydroimidazol-2-ylidene (3d); 1,3-diethylimidazol-2-ylidene (5a); and 1-methylthiomethyl-3-mesitylimidazol-2-ylidene (10)] react with [(PhCN)2PdCl2] to give the corresponding palladium complexes, and the reactions are promoted by the addition of triphenylphosphine. This study demonstrates that the carbene moiety can be transferred from Au(I) to Pd(II) for the first time.

Coordination of iridium(I) metal ions with a pyridinyl imidazol-2-ylidene ligand (pyNwedgeC-R) [R=Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated. The iridium carbene complexes [(C-pyNwedgeC-R)IrCl(COD)] (COD=1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes. Upon the abstraction of chloride, the chelation of pyNwedgeC becomes feasible, resulting in the formation of [C,N-(pyNwedgeC-R)Ir(COD)](BF4) (4). The coordinated COD of complex 4 can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-(pyNwedgeC-R)Ir(CO)2](BF4). The labile nature of the pyridinyl nitrogen donor is readily replaced by acetonitrile, as is evidenced by the NMR study. All iridium complexes show catalytic activity on the hydrogen-transfer reduction of carbonyl and nitro functionalities. By manipulation of the reaction conditions, the iridium-catalyzed reduction of nitroarenes can selectively provide aniline or azo compounds as the desired product.

Coordination chemistry of a pyridine imidazole-2-ylidene ligand (pyN^C) with sterically hindered substituents toward palladium(II) metal ions has been investigated. The palladium carbene complex [(C-pyN^C)Pd(g 3 -allyl)Cl] (3) is prepared via the transmetallation from the corresponding silver carbene complexes with [ClPd(g 3 -allyl)] 2 . Upon the abstraction of chloride, coordination of pyridinylnitrogen becomes feasible to form [C,N-(pyN^C)Pd(g 3 -allyl)](BF 4 ) (4). Ligand substitution reaction of 4 with triphenylphosphine results in the formation of [(C-pyN^C)Pd(PPh 3 )(g 3 -allyl)](BF 4 )], which the pyridinyl-nitrogen donor is substituted by the phosphine. This palladium complex appears to be base sensitive. Treatment of 4 with t-butoxide causes the decomposition to yield the metal nano-particles. Furthermore, de-complexation of 4 takes place under hydrogen atmosphere to generate the carbene precursor, 1-(6-mesityl-2-picolyl)-3-mesitylimidazolium salt. Nevertheless, the palladium complex 4 shows good catalytic activity on the Suzuki-Miyaura and MizorokiHeck reactions.

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