BASE HYDROLYSIS OF RUTHENIUM(II) THIOPHENE COMPLEXES AND REACTIONS OF THE COORDINATED LIGANDS

Described are reactions of aqueous base with dicationic thiophene complexes of the type [RU(C6R6)(C4R4S)]2+ (1) and the acid/base reactivity of these products. Attack of OH- on [Ru(C6R6)(C4R4S)]2+ (1) occurs at sulfur to give [Ru(C6R6)(C4R4S-1-OH)]+ (2H+) which was observed by H-1 NMR spectroscopy. This species displays two forms of reactivity: (i) further reaction with OH- to give the S-oxides (sulfoxides) Ru(C6R6)(C4R4S-1-O) (2) and (ii) rearrangement to give 2-hydroxythiophene-yl derivatives [Ru(C6R6)(C4R4S-2-OH)]+ (3). In solution the S-oxides rearrange to give acyl thiolate complexes such as Ru(cymene)(SC3MeH2-COMe) (4d). The acyl thiolato complexes exist in two isomeric forms which were separated in the case of 4d and are labeled 4d(kin) and 4d(therm). The conversion of 4d(kin) to 4d(therm) proceeds via a first order process with tl/2 = 4.5 h and K(eq) approximately 30. In contrast the acyls derived from tetramethylthiophene are dynamic on the NMR time scale until low temperatures. [Ru(cymene)-(MeSC3Me3COMe)]+ prepared by methylation of 4a is static. Similarly, methylation of the two isomers of 4d gave the corresponding S-methylated isomers 4d(therm)Me+ and 4d(kin)Me+ whose isomerization is catalyzed by HOTf. Solutions of H4d(therm)Me2+ react with dimethylthiophene to regenerate ld. Base hydrolysis of [Ru(arene)(C4H4S)]2+ affords a pair of isomeric formyl thiolates Ru(arene)(SC3H3CHO), which were shown not to undergo H/D exchange with aqueous base. The isomerization of the species with arene = cymene isomerized very slowly (t1/2 = 84 h) vs 4d. Basification of [Ru(C4Me4S)(C4R4S)]2+ (R4 = Me4,2,5-Me2H2) results in the addition of O2- to one ring, in the case of the mixed thiophene complex the addition occurs at the less methylated ring. The base hydrolysis reactions are reversible such that reprotonation affords the starting dicationic thiophene sandwich complexes. However it was found that protonation of 4d(therm) affords the vinyl-thiolato complex [Ru(C6R6)(mu-SCMe=CHCH2COMe)]22+ , not thiophene complex 1d. Deprotonation of this diruthenium species with KOH gives the dimetallic thioaldehyde complex [Ru(C6R6)(mu-S=CMeCH=CHCOMe)]2 which rapidly (minutes, 25-degrees-C) isomerizes to 4d(therm). Treatment of 4d(therm) with BH(OMe)3- affords one stereoisomer of Ru(cymene)(SC3MeH2CHOHMe).