Metal–ligand cooperation in the trans addition of dihydrogen to a pincer Ir(i) complex: a DFT study

Abstract

DFT calculations on the hydrogenation of a (PNP)Ir(I) complex, to give the trans--rather then the cis--dihydride isomer, show that the reaction proceeds via a deprotonation/protonation of the ligand arm with concomitant dearomatization/aromatization of the pyridine core. Thus, the actual H(2) activation step occurs by an Ir(III) complex and not by the Ir(I) starting complex, as supported by experimental observations. This ligand participation allows for products that would otherwise be inaccessible. In addition, trace amounts of water, which are likely to be present in the solvent, facilitate proton transfer reaction steps.

Iridium complexes bearing a PNP ligand, favoring facile C(sp3)–H bond cleavage

“…** The Ir-P(2)-C(10) bond angle in 3 is 90.31 (18) 2 and Ir(PNP) Si *(Cl)(OTf) respectively. The Ir-P(2) distance in the iridacycle of 3 is 2.2901 (14) and is shorter as compared to the Ir-P(1) 2.3794 (13). Also consistent with this assertion, the 31 P NMR resonance for P(2) is shielded significantly to -48.31 ppm from 8.36 ppm for P (1).…”

Discovery of Environmentally Benign Catalytic Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru Complexes, Based on Metal–Ligand Cooperation

“…This Ir(III) complex can be trapped by treating the Ir(I) phenyl complex with CO, forming complex 7 (Scheme 4). This mechanism has recently been supported by DFT calculations [44][45][46]. ligand, which undergoes b-H elimination, we have realized that this process is likely to be hampered by the lack of a cis coordination site.…”

“…Among these, complexes of PNP (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) and PNN (PNN = 2-(di-tertbutylphosphinomethyl)-6-diethylaminomethyl)pyridine) ligands, exhibit diverse reactivity . Recently, we have discovered a new mode of bond activation by metalligand cooperation based on aromatization-dearomatization of pyridine-based pincer complexes [38][39][40][41][42][43][44][45] (Scheme 1). Deprotonation of a pyridylic proton of a pyridine-based pincer complex can lead to dearomatization.…”

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

“…[63] In the heterolytic activation of ammonia, the tantalum centre acts as a Lewis acid and the imido or amido moiety as the Lewis basic cooperating ligand (Scheme 4). Such cooperative tandem or bifunctional activation [65,66] through the Lewis acid/Lewis base couple formed by a metal centre and a ligated nitrogen atom, termed "1,2-NH bond addition" or the "NH effect", [67] has already been highlighted in the heterolytic splitting of H 2 [68] and is crucial to catalytic systems such as asymmetric hydrogenation of ketones. [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.…”