Oxygen Atom Transfer from a trans ‐Dioxoruthenium(VI) Complex to Nitric Oxide

In aqueous acidic solutions trans ‐ [Ru VI (L)(O) 2 ] 2+ (L=1,12‐dimethyl‐3,4:9,10‐dibenzo‐1,12‐diaza‐5,8‐dioxacyclopentadecane) is rapidly reduced by excess NO to give trans ‐[Ru(L)(NO)(OH)] 2+ . When ≤1 mol equiv NO is used, the intermediate Ru IV species, trans ‐[Ru IV (L)(O)(OH 2 )] 2+ , can be detected. The reaction of [Ru VI (L)(O) 2 ] 2+ with NO is first order with respect to [Ru VI ] and [NO], k 2 =(4.13±0.21)×10 1   M −1  s −1 at 298.0 K. Δ H ≠ and Δ S ≠ are (12.0±0.3) kcal mol −1 and −(11±1) cal mol −1  K −1 , respectively. In CH 3 CN, Δ H ≠ and Δ S ≠ have the same values as in H 2 O; this suggests that the mechanism is the same in both solvents. In CH 3 CN, the reaction of [Ru VI (L)(O) 2 ] 2+ with NO produces a blue‐green species with λ max at approximately 650 nm, which is characteristic of N 2 O 3 . N 2 O 3 is formed by coupling of NO 2 with excess NO; it is relatively stable in CH 3 CN, but undergoes rapid hydrolysis in H 2 O. A mechanism that involves oxygen atom transfer from [Ru VI (L)(O) 2 ] 2+ to NO to produce NO 2 is proposed. The kinetics of the reaction of [Ru IV (L)(O)(OH 2 )] 2+ with NO has also been investigated. In this case, the data are consistent with initial one‐electron O − transfer from Ru IV to NO to produce the nitrito species [Ru III (L)(ONO)(OH 2 )] 2+ ( k 2 >10 6   M −1  s −1 ), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)] 2+ and NO 2 − ( k 2 =54.7  M −1  s −1 ).