589-39-9Relevant academic research and scientific papers
A cyclometalated Ir(iii)-NHC complex as a recyclable catalyst for acceptorless dehydrogenation of alcohols to carboxylic acids
Borah, Dhrubajit,Das, Pankaj,Saha, Biswajit,Sarma, Bipul
, p. 16866 - 16876 (2020/12/18)
In this work, we have synthesized two new [C, C] cyclometalated Ir(iii)-NHC complexes, [IrCp?(C∧C:NHC)Br](1a,b), [Cp? = pentamethylcyclopentadienyl; NHC = (2-flurobenzyl)-1-(4-methoxyphenyl)-1H-imidazoline-2-ylidene (a); (2-flurobenzyl)-1-(4-formylphenyl)-1H-imidazoline-2-ylidene (b)] via intramolecular C-H bond activation. The molecular structure of complex 1a was determined by X-ray single crystal analysis. The catalytic potentials of the complexes were explored for acceptorless dehydrogenation of alcohols to carboxylic acids with concomitant hydrogen gas evolution. Under similar experimental conditions, complex 1a was found to be slightly more efficient than complex 1b. Using 0.1 mol% of complex 1a, good-to-excellent yields of carboxylic acids/carboxylates have been obtained for a wide range of alcohols, both aliphatic and aromatic, including those involving heterocycles, in a short reaction time with a low loading of catalyst. Remarkably, our method can produce benzoic acid from benzyl alcohol on a gram scale with a catalyst-to-substrate ratio as low as 1?:?5000 and exhibit a TON of 4550. Furthermore, the catalyst could be recycled at least three times without losing its activity. A mechanism has been proposed based on controlled experiments and in situ NMR study.
Iridium catalysts for acceptorless dehydrogenation of alcohols to carboxylic acids: Scope and mechanism
Cherepakhin, Valeriy,Williams, Travis J.
, p. 3754 - 3763 (2018/05/23)
We introduce iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2-PyCH2(C4H5N2))(COD)]OTf (1) or [Ir(2-PyCH2PBu2t)(COD)]OTf (2). The method provides both aliphatic and benzylic carboxylates in high yield and with outstanding functional group tolerance. We illustrate the application of this method to a diverse variety of primary alcohols, including those involving heterocycles and even free amines. Complex 2 reacts with alcohols to form the crystallographically characterized catalytic intermediates [IrH(η1,η3-C8H12)(2-PyCH2PtBu2)] (2a) and [Ir2H3(CO)(2-PyCH2PtBu2){μ-(C5H3N)CH2PtBu2}] (2c). The unexpected similarities in reactivities of 1 and 2 in this reaction, along with synthetic studies on several of our iridium intermediates, enable us to form a general proposal of the mechanisms of catalyst activation that govern the disparate reactivities of 1 and 2, respectively, in glycerol and formic acid dehydrogenation. Moreover, careful analysis of the organic intermediates in the oxidation sequence enable new insights into the role of Tishchenko and Cannizzaro reactions in the overall oxidation.
The hydroxide-promoted catalytic hydrodefluorination of fluorocarbons by ruthenium in aqueous media
Konnick, Michael M.,Bischof, Steven M.,Periana, Roy A.,Hashiguchi, Brian G.
, p. 632 - 636 (2013/05/09)
A ruthenium complex ligated by the non-innocent protic ligand 2,6-imidizoylpyridine (IPI) in aqueous potassium hydroxide media is shown to be a suitable catalyst for the C-F bond activation and subsequent hydrodefluorination (and hydrogenolysis) of a model fluorocarbon. Furthermore, the conversion of C-F bonds was enhanced upon increasing the concentration of potassium hydroxide [KOH]. A simple, non-ligated heterogeneous analogue derived from ruthenium(III) trichloride trihydrate dissolved in aqueous potassium hydroxide is shown to be an even more active catalyst, capable of hydrodefluorination of aryl fluorocarbons at room temperature and alkyl fluorocarbons under more forcing conditions. Copyright
Bioreversible Protection for the Phospho Group: Bioactivation of the Di(4-acyloxybenzyl) and Mono(4-acyloxybenzyl) Phosphoesters of Methylphosphonate and Phosphonoacetate
Mitchell, Anthony G.,Thomson, William,Nicholls, Dave,Irwin, William J.,Freeman, Sally
, p. 2345 - 2354 (2007/10/02)
The di(4-acetoxybenzyl) ester of methylphosphonate 4 (X = H, R = Me) and the di(4-acyloxybenzyl) esters of methoxycarbonylmethylphosphonate 4 (X = MeO2C, R = Me, Et, Pr, iPr, Bu or tBu) were prepared from the appropriate benzyl alcohol and phosphonic dichloride.At pD 8.0 and 37 deg C, both series of compounds hydrolyse with half-lives greater than 24 h to the corresponding mono(4-acyloxybenzyl) esters 5 (X = H or MeO2C, R = Me, Et, Pr, iPr, Bu or tBu) which were prepared by treatment of the di(4-acyloxybenzyl) esters 4 with sodium or lithium iodide.The mono(4-acyloxybenzyl) esters 5 (X = H, R = Me) and 5 (X = MeO2C, R = Me, Et, Pr, iPr or tBu) undergo chemical hydrolysis to methylphosphonate 6 (X = H), and methoxycarbonylmethylphosphonate 6 (X = MeO2C), respectively, together with 4-hydroxybenzyl alcohol and the appropriate acylate anion.The rates of hydrolysis of the mono(4-acyloxybenzyl) esters decrease as the length and steric bulk of the acyl group increases, with half-lives ranging from ca. 150 h for the acetyl analogues to 2240 h for the pivaloyl derivative.The hydrolyses of the di- and mono-(4-acyloxybenzyl) esters were catalysed by porcine liver carboxyesterase (PLCE), and in all cases the acylate anion was formed.The rate of enzymatic hydrolysis was most rapid for the 4-butanoyloxybenzyl and 4-isobutanoyloxybenzyl analogues.The methoxycarbonyl ester of the phosphonoacetate analogues was not cleaved by PLCE.The methylphosphonate generated from the reaction of 4 (X = H, R = Me) in the presence of esterase and H2(18)O, did not contain (18)O attached directly to phosphorus.These results suggest that both the chemical and enzymatical hydrolyses of themono(4-acyloxybenzyl) esters and the PLCE-catalysed hydrolyses of the di(4-acyloxybenzyl) esters proceed via hydrolysis of the acyl group to give the acylate anion and the unstable 4-hydroxybenzyl esters.The electron-donating 4-hydroxy group facilitates the cleavage of the benzyl-oxygen bond with the formation of the 4-hydroxybenzyl carbonium ion 9, which readily reacts either with water or the phosphate buffer.The 4-acyloxybenzyl phosphoesters provide the first example of a protecting group which will enable the bioactivation of phosphonate prodrugs at rates appropriate to biological systems.
