Novel 2-Mercaptopyridine−Ruthenium Complex Exhibiting Electrochemically Induced Linkage Isomerization Switched On/Off by Protolysis

A ruthenium complex [ruthenium bis(2,2‘-bipyridine)(2-mercaptopyridine)(pyridine)](PF6)2 was crystallographically characterized from
its deprotonated form and was electrochemically investigated. In
the deprotonated complex, the 2-mercaptopyridine ligand coordinates to the Ru atom only by the S atom; therefore, the N atom
of the 2-mercaptopyridine ligand can be protonated. In a CH3CN
solution, the complex shows a reversible redox couple attributed
to RuIII/II−S. The addition of a base to the CH3CN solution of the
complex gives irreversible voltammograms, implying electrochemically induced linkage isomerization between RuII−S and RuIII−N.
Analysis of the observed cyclic voltammograms gave the equilibrium and rate constants for linkage isomerization:  KIINS = 1.2 ×
1018, KIIINS = 0.64, kIINS = 5 × 10 s-1, kIISN = 4 × 10-17 s-1, kIIINS
= 0.26 s-1, and kIIISN = 0.40 s-1.