Base hydrolysis of ruthenium(II) thiophene complexes and reactions of the coordinated ligands

Abstract

This paper describes the acid/base reactivity of a series of ruthenium thiophene complexes. In the acid form the starting compounds (ring)Ru(C[sub 4]R[sub 4]S)[sup 2+] are reactive toward 2 equiv of aqueous base, first as an OH- acceptor and next as a proton donor. The first and the second conjugate bases exist in at least two isomeric forms whose interconversions we have examined. The present results are related to previous work where we showed that one C-S bond in (C[sub 5]Me[sub 5])Rh(C[sub 4]R-4S)[sup 2+] undergoes base hydrolysis by attack of 2 equiv of OH-. C-S cleavage occurs upon deprotonation of the intermediate [(C[sub 5]Me[sub 5])-Rh([eta][sup 4]-C[sub 4]R-4S-2-OH)][sup +], giving rise to a neutral acyl thiolato complex. Furthermore NMR measurements indicated that the resulting acyl thiolates were dynamic in a manner that was poorly understood. We also showed that the initial attack of (excess) base results in formation of the thiophene 1-oxide complex [(C[sub 5]Me[sub 5])Rh([eta][sup 4]-C[sub 4]R[sub 4]S-1-O)], but intermediates in the formation of this S-oxide were not observed. Our studies of related ruthenium systems have uncovered the following: (i) evidence that S-hydroxythiophene complexes are precursors to the thiophene 1-oxides and C[sub 4]R[sub 4]S-2-OH complexes, (ii) an explanation of the dynamicmore » properties of the acyl thiolates, and (iii) the stereochemical course of the protonation of the acyl thiolates. 23 refs., 2 figs.« less