Generation of Stable Ruthenium(IV) Ketimido Complexes by Oxidative Addition of Oxime Esters to Ruthenium(II): Reactivity Studies Based on Electronic Properties of the Ru−N Bond.

The reaction of an oxime ester with [Ru(PPh3)3X2] proceeded smoothly at room temperature to afford a stable RuIV ketimido complex as oxidative adduct. The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed an almost linear Ru−N−C array. The electronic properties of the nitrogen atom were estimated by DFT calculations, and the results suggested double-bond character of the Ru−N bond. Kinetic studies and consideration of the substituent effect on the oxime ester led to the proposal of a reaction mechanism involving oxidative addition, which could proceed by N,O-chelating coordination to the Ru center prior to N−O bond cleavage. The obtained Ru ketimido complex could be transformed into a ruthenacycle by C−H activation by a concerted metalation-deprotonation mechanism in dichloromethane/methanol. Ru ketimido complexes with a tethered alkyne or alkene moiety underwent chloroamination of unsaturated C−C bonds followed by C−H activation, which resulted in the formation of a ruthenacycle. Considering the LUMO of an isolated Ru ketimido complex, the chloroamination should proceed by a synchronous 1,3-dipolar cycloaddition-type mechanism. Insight into the character and reactivity of Ru ketimido complexes will be helpful for developments in the catalytic transformation of oxime esters. [ABSTRACT FROM AUTHOR]