N−H Activation of Amines and Ammonia by Ru via Metal−Ligand Cooperation

Abstract

A nonoxidative addition pathway for the activation of NH bonds of ammonia and amines by a Ru(II) complex is reported. The pincer complex 1 cleaves N-H bonds via metal-ligand cooperation involving aromatization of the pincer ligand without a change in the formal oxidation state of the metal. Electron-rich N-H bond substrates lead to reversible activation, while electron-poor substrates result in stable activation products. Isotopic labeling studies using ND(3) as well as density functional theory calculations were used to shed light on the N-H activation mechanism.

Alkene Isomerisation Catalysed by a Ruthenium PNN Pincer Complex

“…However, as indicated by Equilibria similar to that between 1/isopropanol and 3 have been demonstrated for NÀH activation of amines by [RuH(CO)-(PNP)] (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine). [54] In this case, the observation at room temperature by NMR spectroscopy of the starting material with free amine, the coordination complex or the activation of the amine NÀH bond was highly dependent on the electronic properties of the substrate. We thus decided to react compound 1 with one equivalent of the more acidic o-allyl phenol.…”

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

“…In the case of ammonia, the coordinated NH 3 complex is 6.3 kcal mol −1 more stable than the free complex, whereas the N-H-activated complex is approximately 5.2 kcal mol −1 higher in energy than the starting materials, precluding its direct spectroscopic observation, although it is reversibly formed as the H/D exchange study shows. The activated complex is accessible at room temperature even in the case of isopropylamine [28]. A rare example of amine N-H activation by Rh(I) occurs by MLC involving ligand aromatization [29].…”

Ammonia and Dinitrogen Activation by Surface Organometallic Chemistry on Silica‐Grafted Tantalum Hydrides

“…[69,70] The silica-grafted system [(ϵSiO) 2 Ta(=NH)(NH 2 )], for which we have already reported Ta=NH bifunctional activation of H 2 , would be one of the few well-established examples of such an "NH effect" for ammonia activation. [50,59,71] Such bifunctional activation, in which two functionalities cooperate in substrate activation and transformation, also appears relevant in the mechanism of formation of [(ϵSiO) 2 Ta(NH)(NH 2 )] from dinitrogen. Mechanistically, the cleavage of the NϵN triple bond by 2 is very surprising: multimetallic cooperation for N 2 cleavage has been reported in almost all previous literature, [72][73][74][75][76][77][78] including the HaberBosch catalyst [62] and the biochemical nitrogenase enzymes [79] (see Figure 7 for some selected representative examples); the only exception, besides our surface organometallic system, is the Yandulov-Schrock homogeneous catalyst, [(HIPTN) 3 N]Mo(N 2 ) {HIPT = 3,5-(2,4,6-iPr 3 C 6 H 2 ) 2 -C 6 H 3 NCH 2 CH 2 }.…”