Ruthenium complexes bearing a tridentate polypyridyl ligand with non-coordinating donor atoms: Construction of a specific coordination environment involving noncovalent interactions

Abstract

We have prepared carbonyl (CO) ruthenium complexes which contained the tridentate polypyridyl type ligand (2,6-di(1,8-naphthyridin-2-yl)pyridine; dnp) with non-coordinating nitrogen atoms, for the development of specific reactions using noncovalent interactions. Similar to the aqua precursors that display intramolecular hydrogen bonds between the aqua and dnp ligands, a noncovalent interaction is formed between the terminal carbonyl ligand and non-coordinating nitrogen atoms of dnp; its strength depends on the identity of the axial ligand (triphenylphosphine or pyridine). Additionally, we investigated the reactivity of dnp-containing complexes bearing carbonyl ligands in both the equatorial and axial positions. As a result, it is suggested that the noncovalent interaction between dnp and CO ligands in positions equatorial to the dnp ligand is relatively strong, because the axial carbonyl ligand dissociates preferentially in ligand substitution reactions using organic solvents. Furthermore, in the ligand substitution reaction with a nitrile derivative, the coordination space constructed by the {Ru-dnp}2+ unit enables regulation of not only the ligand substitution reaction rate but also the identity of the donor atom. The present complex also leads to activation and cleavage of inert CCl and CBr bonds.