Reaction of a (Salen)ruthenium(VI) Nitrido Complex with Thiols. C−H Bond Activation by (Salen)ruthenium(IV) Sulfilamido Species

The reaction of [RuVI(N)(L)(MeOH)](PF6) [1; L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion] with a stoichiometric amount of RSH in CH3CN gives the corresponding (salen)ruthenium(IV) sulfilamido species [RuIV{N(H)SR}(L)(NCCH3)](PF6) (2a, R = tBu; 2b, R = Ph). Metathesis of 2a with NaN3 in methanol affords [RuIV{N(H)StBu}(L)(N3)] (2c). 2a undergoes further reaction with 1 equiv of RSH to afford a (salen)ruthenium(III) sulfilamine species, [RuIII{N(H)2StBu}(L)(NCCH3)](PF6) (3). On the other hand, 2b reacts with 2 equiv of PhSH to give a (salen)ruthenium(III) ammine species [RuIII(NH3)(L)(NCCH3)](PF6) (4); this species can also be prepared by treatment of 1 with 3 equiv of PhSH. The X-ray structures of 2c and 4 have been determined. Kinetic studies of the reaction of 1 with excess RSH indicate the following schemes: 1 → 2a → 3 (R = tBu), 1 → 2b → 4 (R = Ph). The conversion of 1 to 2 probably involves nucleophilic attack of RSH at the nitrido ligand, followed by a proton shift. The conversions of 2a to 3 and 2b to 4 are proposed to involve rate-limiting H-atom abstraction from RSH by 2a or 2b. 2a and 2b are also able to abstract H atoms from hydrocarbons with weak C−H bonds. These reactions occur with large deuterium isotope effects; the kinetic isotope effect values for the oxidation of 9,10-dihydroanthracene, 1,4-cyclohexadiene, and fluorene by 2a are 51, 56, and 11, respectively.