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

Abstract

The reaction of an oxime ester with [Ru(PPh ) X ] proceeded smoothly at room temperature to afford a stable Ru 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.

Copper-catalyzed [1,3]-nitrogen rearrangement ofO-aryl ketoximesviaoxidative addition of N–O bond in inverse electron flow

“…14 In fact, Okamoto and Ohe reported that the r value for the oxidative addition of the oxime ester N-O bond to ruthenium is +0.19 at the oxime carbon. 15 Thus, the N-O bond cleavage process in the present rearrangement reaction can be regarded as an oxidative addition with inverse electron ow. On the other hand, the inverse electron ow in oxidative addition observed in the present reaction is in good agreement with the report by Amgoune and Bourissou; the r value for the oxidative addition of para-substituted iodoarenes to cationic Au(I) complex is −1.09.…”

Activation of N–O σ Bonds with Transition Metals: a Versatile Platform for Organic Synthesis and C–N Bonds Formation

“…The same research group was indeed able to further streamline this idea and use the same class of substrates to access highly subsituted pyridines 49, [50] and the authors also suggested that a Ru-ketimido complex was a possible intermediate species (Scheme 12a), as in the case of oxime esters (Scheme 3e). [13] Further confirming the exploitability of this fact, Ohe and coworkers were able to utilize Rh and Co catalysts to access 2H-pyrroles 50 and azabicyclic cyclopropanes 51, respectively (Scheme 12a). [51] It is very intriguing how these different catalytic conditions can greatly influence the reaction outcome.…”

“…As in the case of Pombeiro's rhenium complex 8, [10] the short bond distance (1.790 Å) claimed for a significant double bond character, which was supported by natural bond orbital (NBO) analysis (Scheme 3e). [13] The group of Love isolated the Ni(II) complex 16 resulting from the oxidative addition of [(dtbpe)Ni(0)] complex (dtbpe = 1,2bis(di-tert-butylphosphino)ethane) into the N-O bond of Nadamantyl oxaziridine. This complex proved to be stable enough at -30 °C to grow crystals (Scheme 3f), but decomposed at higher temperatures.…”

Nickel-Catalyzed Transformation of Alkene-Tethered Oxime Ethers to Nitriles by a Traceless Directing Group Strategy

“…In this context, we envisioned that alkene-tethered oxime ethers would be converted into nitriles in the presence of a transition metal catalyst, proving a novel method for the catalytic synthesis of nitriles from oxime derivatives as shown in Scheme . Initially, the oxidative addition of a N–O bond or an oxime C–H bond of the alkene-tethered oxime ethers to a low valent metal center would occur via intermediate I to generate intermediate II or III . As shown in intermediate I , we speculate that the oxidative addition step might be accelerated by the directing effect of the alkene group to the metal center .…”