Hydrogen bonds, coordination isomerism, and catalytic dehydrogenation of alcohols with the bifunctional iridium pincer complex ^{{{\left( {HOC{H_2}} \right)}2}}\left( {P{C{s{p^3}}}P} \right)$$ ( H O C H 2 ) 2 ( P C s p 3 P ) IrHCl (original) (raw)
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Organometallics, 1998
The reaction of fac-[IrH 2 (NCCH 3) 3 (P i Pr 3)]BF 4 (1) with potassium pyrazolate gave the binuclear 34-electron complex [Ir 2 (µ-H)(µ-Pz) 2 H 3 (NCCH 3)(P i Pr 3) 2 ] (2). The structure of 2 was determined by X-ray diffraction. An electrostatic potential calculation located three terminal hydride ligands and one hydride bridging both iridium centers. The feasibility of this arrangement was studied by EHMO calculations. The spectroscopic data for 2 show that the complex is rigid in solution on the NMR time scale. In solution, the acetonitrile ligand of 2 dissociates. The activation parameters for this dissociation process in toluene-d 8 are ∆H q) 20.9 (0.6 kcal mol-1 and ∆S q) 2.5 (1.3 e.u. Reaction of 2 with various Lewis bases (L) gives the substitution products [Ir 2 (µ-H)(µ-Pz) 2 H 3 (L)(P i Pr 3) 2 ] (L) C 2 H 4 (3), CO (4), HPz (5)). The reaction of complex 5 with C 2 H 4 yields the ethyl derivative [Ir 2 (µ-H)(µ-Pz) 2 (C 2 H 5)H 2 (HPz)(P i Pr 3) 2 ] (6); this reaction is reversible. Complexes 2 and 3 react with CHCl 3 to give CH 2 Cl 2 and the compounds [Ir 2 (µ-H)(µ-Pz) 2 H 2 (Cl)(L)(P i Pr 3) 2 ] (L) NCCH 3 (7), C 2 H 4 (8)). In the 1 H NMR spectra of 2-6, the signal of the bridging hydride ligand shows two very different J HP couplings; in contrast, for the chloride complexes 7 and 8, two equal J HP couplings are observed. NOE and T 1 measurements lead to the conclusion that in complexes 2-6 the hydride bridges the iridium centers in a nonsymmetric fashion, whereas for 7 and 8 the bridge is symmetrical. This structural feature largely influences the reactivity. Compounds 2 and 3 undergo H/D exchange under a D 2 atmosphere. Analysis of the isotopomeric mixtures of 2 reveals downfield isotopic shifts in the 31 P{ 1 H} NMR spectrum. Downfield as well as high-field shifts are found for the hydride signals in the 1 H NMR spectrum of partially deuterated 2. Further reaction of 3 with H 2 gave ethane and the dihydrogen complex [Ir 2 (µ-H)(µ-Pz) 2 H 3 (η 2-H 2)(P i Pr 3) 2 ] (9). Under a deficiency of H 2 , in toluened 8 solution, 9 undergoes H/D scrambling with the participation of the solvent. It has also been found that under H 2 complex 3 catalyzes the hydrogenation of cyclohexene.
Russian Chemical Bulletin, 2000
The protonation of complexes Cp*M(dppe)H 3 (dppe is ethylenebis(diphenylphosphine), M = Mo (1), W (2)) by a variety of fluorinated alcohols of different acid strength (FCH 2 CH 2 OH, CF 3 CH 2 OH, (CF 3 ) 2 CHOH, and (CF 3 ) 3 COH) was investigated experimentally by the variable temperature spectroscopic methods (IR, NMR) and stopped flow technique (UV Vis). The structures of the hydrogen bonded and proton transfer products were studied by DFT calcula tions. In agreement with the calculation results, the IR data suggest that the initial hydrogen bond is established with a hydride site for complex 1 and with the metal site for complex 2. However, no intermediate dihydrogen complex found theoretically was detected experimen tally on the way to the final classical tetrahydride product.
Non-covalent interactions in stoichiometric and catalytic reactions of iridium pincer complexes
Mendeleev Communications, 2019
Recent results in the chemistry of various pincer Ir iii com plexes are highlighted with the particular attention paid to the activation of Ir−Cl and Z-H bonds (Z−H = M−H, B−H, N−H, etc.) via lowenergy (noncovalent) interactions (hydrogen bonded or Lewis complexes) and the role of such interactions in the proposed mechanisms of amine-borane dehydrogena tion reaction. Elena S. Osipova received her MS at Chemistry Department of M. V. Lomonosov Moscow State University in 2014 and continued her education by admission to the PhD program at the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (in the Laboratory of Metal Hydrides) under supervision of Professors Elena Shubina and Natalia Belkova. In 2016, she completed a training in the group of Dr. Maurizio Peruzzini at the Institute of Chemistry of OrganoMetallic Compounds ICCOM-CNR (Florence, Italy). Oleg A. Filippov received his MS (1999) and PhD (2003) degrees at M. V. Lomonosov Moscow State University. Since 2002, he is a member of Laboratory of Metal Hydrides at the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences. In 2007-2008, he attended a post-doctoral training in the group of Professor Agustí Lledós at Universitat Autònoma de Barcelona (Spain). In 2017, he received Dr.Sci. degree being currently a senior researcher in the Laboratory of Metal Hydrides at A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, specializing in computational chemistry and molecular spectroscopy, and their applications to the main group element compounds and hydrides, intermolecular interactions, hydrogen bonding, and proton transfer as well as other reaction mechanisms. Elena S. Shubina graduated from M. V. Lomonosov Moscow State University and received her PhD degree there. She completed her Dr.Sci degree at the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, where she is a Professor of Chemistry and the head of the Metal Hydrides Laboratory since 2001. She was plenary, invited or keynote lecturer at European and International Conferences on organometallic, coordination and boron chemistry. She is a member of EuCheMS Division on Organometallic Chemistry. Fields of her research interest include physical organoelement chemistry, molecular spectroscopy, noncovalent interactions involving metal complexes, transition metal and main group element hydrides, and supramolecular compositions. She has published over 150 papers in Russian and international journals and several book chapters. Natalia V. Belkova graduated from M. V. Lomonosov Moscow State University and received the PhD degree at A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences. Her PhD work had been awarded by Academia Europeae award for young scientists from Russia in 1997. After two years post-doctoral fellowship at St. Jude Children's Research Hospital (Memphis, TN, USA), she returned to the A. N. Nesmeyanov Institute, where she received her Dr.Sci. degree in 2011 and became a leading researcher. In 2016, she was elected a Professor of Russian Academy of Sciences. Her research interests include hydrogen bonding and other non-covalent interactions in organometallic chemistry and their implication in mechanisms of reactions involving migration of hydrogen ions (proton transfer, hydride transfer), and structure-properties relationships for metal complexes.
Journal of Organometallic Chemistry, 2018
Organometallic ruthenium(II) complex [Ru(L 1 C ∧ N ∧ N)(PPh 3) 2 (CO)] (1) [where L 1 H 2 is (E)-N-((1H-pyrrol-2-yl)methylene)naphthalen-1-amine] [H represents dissociable proton] was synthesized via C-H bond activation using different synthetic strategies. Ruthenium hydrido carbonyl complexes [Ru(L 1 N ∧ N)(PPh 3) 2 (CO)H] (2) [where L 1 H 2 is (E)-N-((1H-pyrrol-2yl)methylene)naphthalen-1-amine] and [Ru(L 2 N ∧ N)(PPh 3) 2 (CO)H] (3) [where L 2 H 2 is (E)-N-((1H-pyrrol-2-yl)methylene)-1-phenylmethanamine] were isolated. All the complexes were characterized by UV-Vis, IR and NMR spectral studies. Molecular structures of complexes 1, 2 and 3 were authenticated using X-ray crystallography. Geometry optimization of the complexes 1-3 have been performed using Density Functional Theory (DFT) studies. Time-dependent DFT calculations were performed to better understand the electronic properties of complexes 1-3. Complex 1 was utilized as catalyst in transfer hydrogenation of ketones. On the basis of literature study, the plausible mechanisms were proposed for hydride formation and catalytic transfer hydrogenation.
Journal of the American Chemical Society, 2008
At high temperatures in toluene, [2,5-Ph2-3,4-Tol2(η 5 -C4COH)]Ru(CO)2H (3) undergoes hydrogen elimination in the presence of PPh3 to produce the ruthenium phosphine complex [2,5-Ph2-3,4-Tol2-(η 4 -C4CO)]Ru(PPh3)(CO)2 (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H 2 to give unsaturated ruthenium complex A, and trapping by PPh3 to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.