RESUMO

Saturated N-heterocyclic carbenes have unique ligand properties that differ even from their unsaturated analogs. While the unsaturated version has been extensively used in multidentate ligand scaffolds, the incorporation of the saturated version is less common. Here we report the straightforward synthesis of a new bis-saturated N-heterocyclic carbene ligand wherein the carbene moieties are linked by a flexible meta-xylyl unit. Carbene metal complexes of the proligand can be generated by direct metalation, transmetallation or base assisted metalation all of which lead to monodentate coordination modes of silver or iridium. Attempts at direct metalation using zirconium tetrakis-dimethylamide did not lead to complex formation but to the chloroform adduct or amide addition product. As yet, a method to generate pincer complexes from this ligand has not been found. The flexible nature of the xylyl linker as well as the higher σ-bacisity and π-acidity are postulated to contribute to these results.

RESUMO

Pincer complexes can act as catalysts in organic transformations and have potential applications in materials, medicine and biology. They exhibit robust structures and high thermal stability attributed to the tridentate coordination of the pincer ligands and the strong σ metal-carbon bond. Nickel derivatives of these ligands have shown high catalytic activities in cross-coupling reactions and other industrially relevant transformations. This work reports the crystal structures of two polymorphs of the title Ni(II) POCOP pincer complex, [Ni(C29H41N2O8P2)Cl] or [NiCl{C6H2-4-[OCOC6H4-3,5-(NO2)2]-2,6-(OP(t)Bu2)2}]. Both pincer structures exhibit the Ni(II) atom in a distorted square-planar coordination geometry with the POCOP pincer ligand coordinated in a typical tridentate manner via the two P atoms and one arene C atom via a C-Ni σ bond, giving rise to two five-membered chelate rings. The coordination sphere of the Ni(II) centre is completed by a chloride ligand. The asymmetric units of both polymorphs consist of one molecule of the pincer complex. In the first polymorph, the arene rings are nearly coplanar, with a dihedral angle between the mean planes of 27.9 (1)°, while in the second polymorph, this angle is 82.64 (1)°, which shows that the arene rings are almost perpendicular to one another. The supramolecular structure is directed by the presence of weak C-H...O=X (X = C or N) interactions, forming two- and three-dimensional chain arrangements.

Assuntos

Complexos de Coordenação/química , Níquel/química , Cristalização , Cristalografia por Raios X , Ligação de Hidrogênio , Ligantes , Modelos Moleculares

RESUMO

Crystals of the title compound were obtained as a 1:1 dimethyl sulfoxide solvate, C(20)H(16)N(2)O(2)·C(2)H(6)O. The mol-ecular conformation of the organic mol-ecule is similar to that in the previously reported unsolvated structure [Eltayeb et al. (2009 ▶). Acta Cryst. E65, o1374-o1375]. Thus, the dihedral angles formed by the benzimidazole moiety with the two benzene rings are 57.54 (4) and 76.22 (5)°, and the dihedral angle between the benzene rings is 89.23 (5)°. In the crystal, a three-dimensional network features O-H⋯O, O-H⋯N and O-H⋯S hydrogen bonds, as well as C-H⋯O and C-H⋯π inter-actions.