Comparative kinetics of axial ligation to ruthenium and iron porphyrin and phthalocyanine complexes. Relationship between spin state and cis and trans effects

Article abstract of DOI:10.1021/ic00142a027

Kinetic data for the dissociative axial substitution reactions of benzyl isocyanide (BzNC) and CO complexes of ruthenium octaethylporphyrin (OEP), tetraphenylporphyrin (TPP), and phthalocyanine (Pc) complexes are reported and compared with corresponding data for iron complexes. The relative lability of BzNC complexes containing 1-methylimidazole (CH₃Im) and 4-tert-butylpyridine (t-Bupy) is RuPc < RuP ? FePc < FeP. The porphyrin systems are inherently more labile by 3-5 kcal/mol in ΔG?. In complexes with two weak-field axial ligands, a spin change occurring along the reaction coordinate for ligand dissociation is proposed to account for an additional ～3 kcal/mol lower ΔG? only in the iron porphyrin systems. Trans effects of CO and BzNC are rationalized in terms of spin-state effects in the transition state.