Synthesis and structure of pyridine-2-thiolato ruthenium aryls bearing a pendant imine-phenol function

Abstract

The reaction of Ru(η²-RL)(PPh₃)₂(CO)Cl (1) with sodium pyridine-2-thiolate (Napyt) has afforded the complexes of the type Ru(η¹-RL)(PPh₃)₂(CO)(pyt) (3) in excellent yield (η²-RL is C₆H₂O-2-CHNC₆H₄R(p)-3-Me-5, η¹-RL is C₆H₂OH-2-CHNC₆H₄R(p)-3-Me-5 and R is Me, MeO, Cl). The reaction is irreversible and is believed to proceed via cis attack by pyt^- on an octahedral face. The type 3 species are thermodynamically more stable than the corresponding carboxylates, nitrites and nitrates. Structure determination of the solvate, 3(R=Cl)·C₆H₆·0.5C₆H₁₄ has revealed a distorted octahedral RuC₂P₂NS coordination sphere with the pairs (P, P), (C(aryl), N) and (C(carbonyl), S) defining the three trans directions. The η¹-ClL ligand metallated ortho to the phenolic oxygen occurs in the imine-phenol tautomeric form (NO, 2.639(8) Å) which is consistent with IR and ¹H NMR data. The transformation 1→3 is associated with changes in tautomeric form, hapticity and conformation (in relation to CO) of RL. The Ru(η¹-ClL) fragment excluding the pendant C₆H₄Cl(p) group is nearly coplanar (dihedral angle 6.1°) with the Ru(pyt) plane. The Ru---S distance, 2.524(1) Å, is longer than usual due to steric reasons. The type 3 complexes display a quasi-reversible Ru(III)/Ru(II) couple near 0.6 V versus SCE.