Allylic oxidation of cyclohexene and indene by cis-[RuIV(bpy)2(py)(O)]2+

The kinetics of oxidation of cyclohexene, cyclohexen-1-ol, and indene by cis-[Ru-IV(bpy)(2)(py)(O)](2+) (bpy = 2,2'-bipyridine and py = pyridine) have been studied in CH3CN. The reactions are first-order in both Ru-IV=O2+ and substrate in an initial, rapid stage in which Ru(IV) is reduced to Ru(III). The rate constants are 0.16 +/- 0.01, 1.10 +/- 0.02, and 5.74 +/- 0.74 M-1 s(-1) for cyclohexene, cyclohexen-1-ol, and indene, respectively. A k(alpha,alpha'-H-4)/k(alpha,alpha'-D-4) kinetic isotope effect of 21 +/- 1 is observed for the oxidation of cyclohexene. At a 2:1 ratio of Ru-IV=O2+ to olefin, the reactions of Ru-IV=O2+ with either cyclohexene or indene give Ru-II-NCCH32+ and the 4-electron ketone products, 2-cyclohexen-1-one and indenone, respectively, as identified by GC-MS. As the ratio of cyclohexene to Ru-IV=O2+ is increased, cyclohexen-1-ol becomes an increasingly competitive product. The mechanisms of these reactions are highly complex. They involve two distinct stages and the formation and subsequent reactions of Ru-III-substrate bound intermediates.