Rhodium and Iridium Complexes with Chelating C–C′-Imidazolylidene–Pyridylidene Ligands: Systematic Approach to Normal, Abnormal, and Remote Coordination Modes

A series of linked imidazolium–pyridinium salts ([Him-pyH]­(X)₂) have been used as imidazolylidene–pyridylidene ligand precursors for the preparation of rhodium­(III) and iridium­(III) complexes. The relative configuration of the [Him-pyH]­(X)₂ salts determines whether the coordination of the pyridylidene occurs through the normal, abnormal, or remote form. In order to obtain complexes with the imidazolylidene part of the ligand coordinated through the abnormal form, salts with the C2 position of the imidazolium blocked with a methyl group were used, although the products resulting from the C–H aliphatic activation of the methyl group or the C–C cleavage of the C2–Me bond were obtained instead. The crystallographic study of three molecules allowed us to evaluate the relative trans influence of the normal, abnormal, and remote coordination forms of the pyridylidene and also to compare it to the trans influence provided by the imidazolylidene.