The Structure of Complexes of Carbonylruthenium(II) with Octaethylporphyrin

Porphyrin complexes of ruthenium with carbon monoxide and other ligands, especially with nitrogen-containing ones, are convenient models for studying natural energy centers. An X-ray diffraction analysis of single crystals of the complexes has shown the structural features determining their properties. In the complex of carbonylruthenium(II) with β-octaethylporphyrin, the ruthenium atom is firmly held by four nitrogen porphyrin atoms, while carbon monoxide acts as an axial ligand. Ruthenium(II) porphyrinates with coordinated axial ligands form similar crystalline structures of island type in the triclinic syngony belonging to spatial group P 1. A five-coordinate ruthenium carbonyl complex of porphyrin, which is originally obtained in the reaction of β-octaethylporphyrin with triruthenium dodecacarbonyl, easily coordinates even weak ligands, such as ethanol, that easily can be exchanged by pyridine. The coordination polyhedron of the ruthenium atom can be described as a distorted tetragonal bipyramid. Comparison of the structure of ruthenium porphyrinate complexes has clearly demonstrated the peculiarities of manifestation of the trans influence of ligands. Carbon monoxide pulls the ruthenium atom out of a plane formed by four nitrogen atoms of porphyrin, causing a significant elongation (by about 10%) and the corresponding weakening of the bond of ruthenium with a trans ligand that occupies the sixth coordination position. Similarly, trans ligands affect the Ru–CO bond according to the coordination strength of the ligand. The quantum-chemical calculation of porphyrin complexes of ruthenium has been performed. The mechanism of the trans influence of ligands is illustrated by the analysis of molecular electronic wave functions by the method of natural localized orbitals. Identification of structural patterns and their relationship with the properties of complexes contributes to understanding the functioning of similar natural complexes of iron, including heme.