1076-43-3Relevant articles and documents
Effect of solvent and ancillary ligands on the catalytic H/D exchange reactivity of Cp IrIII(L) complexes
Lehman, Matthew C.,Gary, J. Brannon,Boyle, Paul D.,Sanford, Melanie S.,Ison, Elon A.
, p. 2304 - 2310 (2013)
The reactivity of a series of Cp*lIrIII(L) complexes that contain a diverse set of ancillary ligands, L, (L = PMe3, N-heterocyclic carbene, NHC = 1,3-dimethylimidazol-2-ylidene, aqua, 4-t-butylpyridine, and 4-(2,4,6-tris-(4-t-butylphenyl)pyridinium)pyridine tetrafluoroborate) has been examined in catalytic H/D exchange reactions between C6H6 and a series of deuterated solvents (methanol-d 4, acetic acid-d4, and trifluoroacetic acid-d 1). These studies demonstrate that (1) the mechanism of catalytic H/D exchange is significantly influenced by the nature of the solvent; (2) electron-donating ligands (PMe3, NHC) promote the formation of Ir hydrides in methanol-d4, and these are critical intermediates in catalytic H/D exchange processes; and (3) weak/poorly donating ligands (4-t-butylpyridine, 4-(2,4,6-tris-(4-t-butylphenyl)pyridinium)pyridine tetrafluoroborate and aqua) can support efficient H/D exchange catalysis in acetic acid-d4.
Iridium(iii) catalyzed trifluoroacetoxylation of aromatic hydrocarbons
Bischof, Steven M.,Hashiguchi, Brian G.,Lokare, Kapil S.,Gunsalus, Niles,Yousufuddin, Mohammed,Periana, Roy A.
, p. 35639 - 35648 (2014)
A tridentate, NNC-tb (where NNC-tb = 2-(pyridin-2-yl)benzo[h]quinoline) ligated IrIII complex (NNC-tb)Ir(Ph)(4-MePy)(TFA), 11 along with analogues are very active for CH activation as evidenced by rapid catalytic H/D exchange between benzene and trifluoroacetic acid-d1 (DTFA). The complexes were examined with a variety of oxidants for the catalytic conversion of benzene to phenyltrifluoroacetate. Herein, the synthesis and characterization of (NNC-tb)Ir complexes is described along with the reactivity of these complexes towards arenes and alkanes.
Benzene C-H bond activation in carboxylic acids catalyzed by O-donor iridium(III) complexes: An experimental and density functional study
Bischof, Steven M.,Ess, Daniel H.,Meier, Steven K.,Oxgaard, Jonas,Nielsen, Robert J.,Bhalla, Gaurav,Goddard III, William A.,Periana, Roy A.
, p. 742 - 756 (2010)
The mechanism of benzene C-H bond activation by [Ir(-acac-O,O,C 3)(acac-O,O)(OAc)]2 (4) and [Ir(μ-acac-O,O,C 3)(acac-O,O)(TFA)]2 (5) complexes (acac = acetylacetonato, OAc = acetate, and TFA = trifluoroacetate) was studied experimentally and theoretically. Hydrogen-deuterium (H/D) exchange between benzene and CD 3COOD solvent catalyzed by 4 (ΔH = 28.3± 1.1 kcal/mol, ΔS = 3.9±3.0 cal K-1 mol-1) results in a monotonie increase of all benzene isotopologues, suggesting that once benzene coordinates to the iridium center, there are multiple H/D exchange events prior to benzene dissociation. B3LYP density functional theory (DFT) calculations reveal that this benzene isotopologue pattern is due to a rate-determining step that involves acetate ligand dissociation and benzene coordination, which is then followed by heterolytic C-H bond cleavage to generate an iridium-phenyl intermediate. A synthesized iridium-phenyl intermediate was also shown to be competent for H/D exchange, giving similar rates to the proposed catalytic systems. This mechanism nicely explains why hydroarylation between benzene and alkenes is suppressed in the presence of acetic acid when catalyzed by [Ir(μ-acac-O,O,C3)(acac-O,O)(acacC3)]2 (3) (Matsumoto et al. J. Am. Chem. Soc. 2000, 122, 7414). Benzene H/D exchange in CF3COOD solvent catalyzed by 5 (ΔH = 15.3 ± 3.5 kcal/mol, ΔS =-30.0 ± 5.1 cal K-1 mol-1) results in significantly elevated H/D exchange rates and the formation of only a single benzene isotopologue, (C6H5D). DFT calculations show that this is due to a change in the rate-determining step. Now equilibrium between coordinated and uncoordinated benzene precedes a single rate-determining heterolytic C-H bond cleavage step.
Coordination Chemistry of Benzene, Toluene, Cyclohexadienes, Cyclohexene, and Cyclohexane on Pt100)
Tsai, Min-Chi,Muetterties, E. L.
, p. 5067 - 5071 (1982)
The surface chemistry of benzene, toluene, cyclohexane, cyclohexene, and cyclohexadienes on Pt(100) is described.Benzene chemisorption was largely molecular although H-D exchange between chemisorbed C6H6 and C6D6 was observed at temperatures of 100 deg C and above.Toluene chemisorbed with bond breaking to give Pt-(100)-benzyl.This benzyl species (C6D5CD2) underwent H-D exchange with chemisorbed hydrogen.Exchange was more facile at the CH2 site than at aromatic C-H sites.Cyclohexane, cyclohexene, and cyclohexadienes chemisorbed on Pt(100) to form benzene with expected relative ease of dehydrogenation of cyclohexadienes >/= cyclohexene > cyclohexane.
H/D exchange processes catalyzed by an iridium-pincer complex
Iluc, Vlad M.,Fedorov, Alexey,Grubbs, Robert H.
, p. 39 - 41 (2012)
A PNP-pincer iridium dihydride performs the H/D exchange between aromatic substrates and tertiary hydrosilanes and D2O or C6D 6. Complete incorporation of deuterium into sterically accessible Car-H and Si-H bonds was observed at a moderate temperature of 80 °C.
Kinetic isotope effects in hydrogen exchange of aromatic CH bonds in benzene, fluorobenzene, and nitrogen-containing heterocycles with solution of alkali metal amide in liquid ammonia
Tupitsyn,Zatsepina
, p. 1133 - 1143 (2001)
The kinetic isotope effects in deuterium and tritium exchange in benzene, fluorobenzene, pyridine, pyridine N-oxide, and quinoline with a solution of an alkali metal amide in liquid ammonia kNH3D/kNH3T were determined, where kNH3D and kNH3T are the experimental rate constants of protodedeuteration and protodetritiation, respectively. The variation of the tritium exchange rates in benzene in going from NH3 to ND3 (kNH3T and kND3T) was evaluated. The deviation of the observed ratios kNH3D/kNH3T and kND3H/kND3T from the maximum possible values corresponding to the Swan-Shaad equation suggests the reaction mechanism in which both elementary stages, ionization of the CH acid and diffusion separation of the complex of the carbanion with the ammonia molecule, are partially limiting. A small decrease in the secondary isotope effect of the solvent, defined as kND3T/kNH3T, as compared to the theoretical maximum of 2.4, is assumed to be due to similar structures of the transition state and the equilibrium carbanion. A theoretical explanation was given for the observed dependences of the primary isotope effect of the substrate on pKa for deutero (tritio) derivatives of fluorobenzene [4D(t) NH3D/kNH3T ～ 1).
Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces
Zhang, Jing,Wang, Bingwen,Nikolla, Eranda,Medlin, J. Will
, p. 6594 - 6598 (2017)
Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO2 films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface.
H/D exchange at aromatic and heteroaromatic hydrocarbons using D 2O as the deuterium source and ruthenium dihydrogen complexes as the catalyst
Prechtl, Martin H. G.,Hoelscher, Markus,Ben-David, Yehoshoa,Theyssen, Nils,Loschen, Rebekka,Milstein, David,Leitner, Walter
, p. 2269 - 2272 (2007)
Getting heavy: At temperatures as low as 50°C, D2O can serve as a cheap and readily available deuterium source for the efficient deuteration of aromatic and heteroaromatic substrates if nonclassical ruthenium hydride complexes are used as catalysts (see scheme). DFT calculations support a catalytic cycle comprising σ-bond metathesis as the key step for the exchange processes. (Chemical Equation Presented).
MOLECULAR MECHANISMS IN THE CYCLOTRIMERIZATION OF ACETYLENE TO BENZENE ON PALLADIUM(III).
Patterson,Lambert
, p. 1266 - 1270 (1988)
Multiplexed temperature programmed reaction measurements have been used to examine mechanistic details of the acetylene yields benzene reaction on Pd(111). Results obtained from (C//2H//2 plus C//2D//2) experiments are in quantitative accord with a nondissociative reaction pathway; H/D scrambling in the reactants is not of significance, but at higher temperatures some H/D scrambling is observed between product molecules. The effects of surface crowding by unreacted acetylene on the binding and conformation of the benzene product are investigated, and it is shown that all benzene desorption is the result of the same initial reactive events. (C//2D//2 plus C//6H//6) data demonstrate that benzene desorption is not reaction-rate limited, consistent with the above conclusion.
Synthesis of Hexalithiobenzene
Baran, J. R.,Hendrickson, C.,Laude, D. A.,Lagow, R. J.
, p. 3759 - 3760 (1992)
A new synthesis for hexalithiobenzene starting with hexachlorobenzene is reported.
