Labile Rhodium(I)–N-Heterocyclic Carbene Complexes

Palacios, Laura Lucía; Giuseppe, Andrea Di; Opalinska, Anna; Castarlenas, Ricardo; Pérez‐Torrente, Jesús J.; Lahoz, Fernando J.; Oro, Luis A.

doi:10.1021/om400209m

Cited by 21 publications

(15 citation statements)

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“…On the other hand, the electron rich iridium centre in [Ir(cod){(MeIm) 2 CHCOO}] (2) promotes the activation of dihydrogen and the hydrogenation of the coordinated 1,5-cyclooctadiene to cyclooctene which has proven to be a labile ligand. 41 Thus, under the catalytic reaction conditions (H 2 O, 60 atm, PH 2 /PCO 2 : 2/1) replacement of the coe ligand in 7 by a water molecule to give the species [IrH 2 (H 2 O){(MeIm) 2 CHCOO}] (A) can be assumed. In order to shed light on the reaction mechanism, a computational study at the DFT level has been carried out.…”

Section: Hydrogenation Of Co 2 To Formate Catalyzed By [Ir(cod){(meimmentioning

confidence: 99%

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

et al. 2017

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The bis-imidazolium salt, 1,1-bis(N-methylimidazolium) acetate bromide, is a convenient precursor for the synthesis of zwitterionic iridium(I) [Ir(cod){(MeIm) 2 CHCOO}] and cationic iridium(III) [IrH(cod){(MeIm) 2 CHCOO}] + compounds (MeIm = 3-methylimidazol-2-yliden-1-yl) having a carboxylate-functionalized bis(NHC) ligand. The [Ir(cod){(MeIm) 2 CHCOO}] compound catalyzes the hydrogenation of CO 2 to formate in water using NEt 3 as base reaching turnover numbers of approximately 1500. Reactivity studies have shown that activation of the catalyst precursor involves the reaction with H 2 in a multistep process that result, under catalytic conditions, in the formation of a dihydrido iridium(III) octahedral [IrH 2 (H 2 O){(MeIm) 2 CHCOO}] species stabilized by the  3-C,C',O coordination of the ligand. DFT studies on the mechanism were carried out to elucidate two possible roles of the base. In the first one, NEt 3 neutralizes only the produced formic acid whereas in the second it assists the proton transfer in heterolytic cleavage of the H 2 molecule. Although this base-involved mechanism is more favourable exhibiting a lower energy span for the overall reaction, the energy barrier obtained from kinetic experiments suggests that both mechanisms could be operative under the experimental reaction conditions. RESULTS AND DISCUSSION Synthesis and reactivity of iridium complexes bearing a carboxylate-functionalized bis(NHC) ligand. The carboxylate-functionalized bis-(imidazolium) salt precursor was prepared according to the general synthetic method entailing the alkylation of N-alkylimidazole with a suitable functionalized alky bromide. 26 Thus, reaction of ethyl dibromoacetate with an excess of Nmethylimidazole in THF at 343 K for 72 h gave a brown slurry from which the salt 1,1'-bis(N-methylimidazolium) acetate bromide, [(MeImH) 2 CHCOO] Br (1), was obtained as a white hygroscopic solid in 79% yield after recrystallization from methanol/acetone (Scheme 1). Scheme 1. Synthesis of 1,1-bis(N-methylimidazolium) acetate bromide. ASSOCIATED CONTENT Supporting Information. NMR spectra for the new compounds and reactivity studies. Detailed information on the determination of activation parameters for the hydrogenation of CO 2. Hydrogen bonds in the molecular structure of 2. Electronic energy, enthalpy, free energy and optimized coordinates for catalytic intermediates and transition states. The Supporting Information is available free of charge on the ACS Publications website.

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Section: Hydrogenation Of Co 2 To Formate Catalyzed By [Ir(cod){(meimmentioning

confidence: 99%

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

et al. 2017

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“…This compound can be also prepared by abstraction of chloride from 2 with thallium or silver salts. Complex [ 2 ]PF 6 should be isolated quickly since it decomposes slowly in thf and undergoes a fast replacement of the olefin dvtms in acetonitrile to give [Rh(IPr)(MeCN) 3 ]PF 6 . All attempts to grow monocrystals of [ 2 ]PF 6 failed, but we succeeded by replacing the counteranion PF 6 − by BF 4 − .…”

Section: Methodsmentioning

confidence: 99%

“…Complex [2]PF 6 should be isolated quicklysince it decomposes slowly in thf and undergoes af ast replacemento ft he olefin dvtmsi nacetonitrile to give [Rh(IPr)(MeCN) 3 ]PF 6 . [12] All attempts to grow monocrystals of [2]PF 6 failed, but we succeeded by replacing the counteranionP F 6 À by BF 4 À .T he structure of the cation in [2]BF 4 is shown in Figure 3.…”

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Three‐Coordinate Rhodium Complexes in Low Oxidation States

Varela‐Izquierdo

López

Bruin

et al. 2020

Chemistry A European J

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The isolation of simultaneously low‐coordinate and low‐valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri‐coordinate rhodium(‐I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ‐Cl)(IPr)(dvtms)}2] (1, IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolyl‐2‐ylidene; dvtms=divinyltetramethyldisiloxane) with KC8 gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]+ results from their oxidation or by abstraction of chloride from 1 with silver salts. The paramagnetic Rh0 complex is a unique fully metal‐centered radical with the unpaired electron in the dz2 orbital. The Rh(‐I) complex reacts with PPh3 with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh3)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh‐Au(PPh3)] with a metal–metal bond between two d10 metal centers.

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“…In addition, a rotational process for the IPr and ethylene ligands is observed. 21 Scheme 3. Synthesis of Rh I -quinolinolate complexes 5-6.…”

Section: C{mentioning

confidence: 99%

Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(i)–N-heterocyclic carbene complexes

Palacios

Giuseppe

Artigas

et al. 2016

Catal. Sci. Technol.

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Labile Rhodium(I)–N-Heterocyclic Carbene Complexes

Cited by 21 publications

References 105 publications

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

Three‐Coordinate Rhodium Complexes in Low Oxidation States

Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(i)–N-heterocyclic carbene complexes

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Labile Rhodium(I)–N-Heterocyclic Carbene Complexes

Cited by 21 publications

References 105 publications

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO2 Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO2 Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

Three‐Coordinate Rhodium Complexes in Low Oxidation States

Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(i)–N-heterocyclic carbene complexes

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Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound

Experimental and Theoretical Mechanistic Investigation on the Catalytic CO₂ Hydrogenation to Formate by a Carboxylate-Functionalized Bis(N-heterocyclic carbene) Zwitterionic Iridium(I) Compound