Synthesis and Reactivity of an Iridium(I) Acetonyl PNP Complex. Experimental and Computational Study of Metal−Ligand Cooperation in H−H and C−H Bond Activation via Reversible Ligand Dearomatization

Abstract

The complex (PNP)IrI(CH2COCH3) 2 (PNP = 2,6-bis((di-tert-butylphosphino)methyl)pyridine) was prepared by reaction of the dearomatized, electron-rich complex (PNP*)IrI(COE) (1; PNP* = deprotonated PNP, COE = cyclooctene) with acetone. Upon treatment with CO, complex 2 undergoes a surprising elimination of acetone to form the dearomatized species (PNP*)IrI(CO) (4), involving proton migration from the ligand “arm” to the acetonyl moiety. DFT studies reveal that this process occurs via the square-pyramidal intermediate 2+CO, formed upon CO coordination to 2, in which the acetonyl moiety is located at the apical position prior to proton migration. Reaction of 2 with H2 (D2) indicates an equilibrium between complex 2 and the nonaromatic (PNP*)IrIII(H)(CH2COCH3) complex 2b, which is the species that actually activates H2 to exclusively form the trans-dihydride (PNP)IrIII(H)2(CH2COCH3) (5a) and activates D2 to form the trans-hydride−deuteride 5b with benzylic-D incorporation, as also corroborated by DFT studies. Interestingly, benzene C−H activation by complex 2 results in formation of the complex (PNP)IrI(C6H5) (6a) and elimination of acetone. DFT studies show that the benzene C−H bond is actually activated by the dearomatized “bare” (PNP*)IrI intermediate 2c, formed upon acetone elimination from 2.

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

“…The dearomatized Ir(I) complex 2, readily obtained by deprotonation of the cationic Ir(I) complex 1, activates the sp 2 C-H of benzene [18] and the sp 3 C-H of acetone [21] to form complexes 3 with concomitant aromatization of the pyridine ring (scheme 3). This process proceeds via an Ir(III) intermediate 4 which was generated and characterized spectroscopically at −70 • C by deprotonation of the cationic complex 5.…”

Computational Mechanistic Studies on Reactions of Transition Metal Complexes with Noninnocent Pincer Ligands: Aromatization–Dearomatization or Not

“…33 These reactions involve the X-H (X=H, C, O, N, and B) activations, [34][35][36][37][38][39][40][41] dehydrogenative coupling reactions, [42][43][44][45][46][47][48] and hydrogenation reactions. [49][50][51][52][53][54][55][56] In addition, a theoretical study about the ruthenium acridine complex was also reported.…”

“…Possible pathways via the formation of 21 are unfavorable because the formation of 21 has a barrier of 26.4 kcal/mol and 21 is higher than 18 by 10.4 kcal/mol. Scheme 7: Proposed mechanism for the reactions of complex 18 and CO in benzene with the M06 by Milstein and coworkers (values are free energies) 36. …”

Optimum bifunctionality in a 2-(2-pyridyl-2-ol)-1,10-phenanthroline based ruthenium complex for transfer hydrogenation of ketones and nitriles: impact of the number of 2-hydroxypyridine fragments

“…7,8 Remarkably, bio-inspired complexes have emerged as a privileged class of compounds in organometallic chemistry. Inspired by the pioneering work in this field of Noyori, [11][12][13][14] Shvo,15,16 Morris, [17][18][19][20][21] and Milstein, [22][23][24][25] new generations of bifunctional catalysts have been developed. Inspired by the pioneering work in this field of Noyori, [11][12][13][14] Shvo,15,16 Morris, [17][18][19][20][21] and Milstein, [22][23][24][25] new generations of bifunctional catalysts have been developed.…”