Ruthenium(II) and Ruthenium(III) Complexes of p-Benziporphyrin: Merging Equatorial and Axial Organometallic Coordination.

A diamagnetic ruthenium(II) complex of 5,10,15,20-tetraphenyl-p-benziporphyrin [Ru(p-BzP)(CO)Cl] was obtained via the insertion of ruthenium into p-benziporphyrin using triruthenium(0) dodecacarbonyl [Ru(CO)] as the metal source. The procedure applying dichloro(cycloocta-1,5-diene)ruthenium(II) (polymer, [Ru(COD)Cl]) afforded the paramagnetic six-coordinate ruthenium(III) p-benziporphyrin [Ru(p-BzP)Cl]. As shown by X-ray crystallography, the p-phenylene ring in both complexes is sharply tilted out of the N plane, as reflected by the respective N (pyrrole)-C (p-phenylene) dihedral angle [Ru(p-BzP)(CO)Cl, 52.5°; Ru(p-BzP)Cl, 53.7°]. p-Phenylene is bound to the ruthenium cation in an η fashion, revealing the shortest ever Ru-C distance in the series of p-benziporphyrin complexes [Ru(p-BzP)(CO)Cl, 2.275(2) Å; Ru(p-BzP)Cl, 2.324(5) Å]. The reaction of Ru(p-BzP)(CO)Cl with ArMgCl or AlkMgCl results in the formation of diamagnetic six-coordinate ruthenium(II) p-benziporphyrin complexes containing the apically coordinated σ-alkyl or σ-aryl ligands, where the metal ion simultaneously coordinates to three carbon centers respectively accommodating η (phenylene) and σ (aryl and alkyl) modes. Reactions of σ-aryl (alkyl) carbanions with paramagnetic Ru(p-BzP)Cl have been followed by H NMR spectroscopy. The procedure afforded the six-coordinate paramagnetic ruthenium(III) p-benziporphyrin [Ru(p-BzP)(Ph)Cl], which binds one σ-aryl ligand, as reflected by the characteristic H NMR spectra spread within the +120 to -120 ppm range. Both paramagnetic complexes Ru(p-BzP)(Ph)Cl and Ru(p-BzP)(p-Tol)Cl are formed as a mixture of two stereoisomers differentiated by two nonequivalent locations of σ-aryl with respect to the puckered macrocyclic ring. The paramagnetic shifts of σ-aryls are indicative of π-spin delocalization patterns. Analysis of the contact shifts and parallel density functional theory calculations of the spin density distribution in Ru(p-BzP)Cl, Ru(p-BzP)(Ar)Cl, and Ru(p-BzP)(Alk)Cl reflect the features of the d(dd) electronic ground state.