A family of thioxanthato ruthenium and osmium aryls

Abstract

The title complexes of type M(RL²)(PPh₃)₂(CO)(S₂CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL¹)(PPh₃)₂(CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL² ligand in 2 is the imine-phenol tautomer of N-C₆H₄R(ρ)-4-methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic-C2 atom only while RL¹ in 1 is the iminium-phenolato tautomer chelated via carbanionic-C2 and phenolato-O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ~180° around the M-C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ~40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL²)(PPh₃)₂(CO)(O₂CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru-P bonds in 2a (R = Me) differ in length by as much as 0.06 Å. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate.