SYNTHESIS OF THE NEW BINUCLEATING COMPOUND PYRAZIN-2-YL 2-PYRIDYL SULFIDE FOR STEPWISE OR DIRECT APPROACH TO ASYMMETRIC BINUCLEAR RUTHENIUM(II) COMPLEXES

Pyrazin-2-yl 2-pyridyl sulfide (pzpys) has been prepared by reaction o f 2-sulfanylpyridine with chloropyrazine. As shown by H-1 NMR spectros copy, its major isomer has two binding sites which are inequivalent, o ne chelating through the N-1-pyrazine and N-pyridine atoms, the other monodentate through the N-4 atom of the pyrazine ring. By reaction of pzpys with [RuL(2)(NO)(NO2)][PF6](2) [(L = 2,2'-bipyridine (bipy) or d i-2-pyridyl sulfide (dps)] the mononuclear complexes [RuL(2)(pzpys)(NO 2)][PF6] have been obtained in which pzpys is the monodentate. The rea ctions of pzpys with cis-[RuL(2)Cl(2)] complexes [L = bipy,1,10-phenan throline (phen) or dps] have been studied. The dps derivative reacts w ith a large excess of pzpys affording [Ru(dps)(2)(pzpys)Cl][PF6] in wh ich pzpys is monodentate. On the contrary the bipy and phen (L) deriva tives, under the same experimental conditions, undergo substitution of both chloride ligands giving as major products, [RuL(2)(pzpys)][PF6]( 2) in which pzpys is chelated. When the reactions were carried out in the presence of a stoichiometric amount of pzpys the binuclear complex es [L(2)Ru(pzpys)RuL(2)Cl][PF6](3) (L = bipy or phen) were slowly form ed. The mononuclear complexes have been used as-ligands in the reactio ns with [Ru(bipy)(2)Cl-2] giving the new binuclear species [L(2)Ru(pzp ys)RuL(2)(NO2)][PF6](3) (L = bipy or phen). The compounds have been fu lly characterized by infrared, UV/VIS, H-1 and C-13 NMR spectroscopies In acetonitrile solution [Ru(bipy)(2)(pzpys)Cl][PF6] undergoes a reve rsible Ru-II --> Ru-III electron transfer. In contrast, the one-electr on oxidation of [Ru(dps)(2)(pzpys)Cl][PF6], [Ru(bipy)(2)(pzpys)(NO2)][ PF6] and [Ru(bipy)(2)(pzpys)][PF6](2) is complicated by subsequent che mical reactions. The binuclear complex [(bipy)(2)Ru(pzpys)Ru(bipy)(2)C l][PF6](3) undergoes two consecutive one-electron oxidations (Delta E( o)' = 0.55 V), which allow the corresponding (RuRuIII)-Ru-II species t o be classified as a completely delocalized (Class III) mixed-valence compound.