Structural diversity in pyridine-N-functionalized carbene copper(I) complexes

The use of the versatile pyridine N-functionalized carbene ligands has allowed the isolation and structural characterization of copper(I) imidazol-2-ylidene complexes of the type ([(3-R)(1-L)imidazol-2-ylidene] CuBr}, where L = 2-picolyl, R = 2,4,6-trimethylphenyl (mesityl), 2,6-(Pr2C6H3)-C-i; L = 2-pyridyl, R = 2,6-(Pr2C6H3)-C-i. They were prepared by interaction of the corresponding imidazolium bromides with Cu2O in chlorinated solvents in the presence of molecular sieves. In the solid state the 2-picolyl derivatives crystallize as dimers or polymers depending on the crystallization conditions, while the 2-pyridyl derivative crystallizes as monomer.