Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The H-1 and P-31 NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by P-31 NMR at -98 degrees C in CD2Cl2.