181422-72-0Relevant academic research and scientific papers
Steric effect of NHC ligands in Pd(II)–NHC-catalyzed non-directed C–H acetoxylation of simple arenes
Mandal, Tanmoy,Yadav, Sudha,Choudhury, Joyanta
, (2021/09/06)
Although there has been a lot of progress in oxidative arene C–H functionalization reactions catalyzed by Pd(II/IV) system, the non-directed, site-selective functionalization of arene molecules is still challenging. It has been established that ligands play a pivotal role in controlling rate- as well as selectivity-determining step in a catalytic cycle involving well-defined metal-ligand bonding. N-heterocyclic carbene (NHC) ligands have had a tremendous contribution in the recent extraordinary success of achieving high reactivity and excellent selectivity in many catalytic processes including cross-coupling and olefin-metathesis reactions. However, the immense potential of these NHC ligands in improving site-selectivity of non-directed catalytic C–H functionalization reactions of simple arenes is yet to be realized, where overriding the electronic bias on deciding selectivity is a burdensome task. The presented work demonstrated an initiative step in this regard. Herein, a series of well-defined discrete [Pd(NHCR′R)(py)I2] complexes with systematically varied degree of spatial congestion at the Pd centre, exerted through the R and R’ substituents on the NHC ligand, were explored in controlling the activity as well as the site-selectivity of non-directed acetoxylation of representative monosubstituted and disubstituted simple arenes (such as toluene, iodobenzene and bromobenzene, naphthalene and 1,2-dichlorobenzene). The resulting best yields were found to be 75% for toluene and 65% for bromobenzene with [Pd(NHCMePh)(py)I2], 75% for iodobenzene and 79% for naphthalene with [Pd(NHCMeMe)(py)I2], and 41% for 1,2-dichlorobenzene with [Pd(NHCCyCy)(py)I2]. Most importantly, with increasing the bulkiness of the NHC ligand in the complexes, the selectivity of the distal C-acetoxylated products in comparison to the proximal ones, was enhanced to a great extent in all cases. Considering the vast library of NHC ligands, this study underscores the future opportunity to develop more strategies to improve the activity and the crucial site-selectivity of C–H functionalization reactions in simple as well as complex organic molecules.
A more sustainable and efficient access to IMes·HCl and IPr·HCl by ball-milling
Beillard, Audrey,Bantreil, Xavier,Métro, Thomas-Xavier,Martinez, Jean,Lamaty, Frédéric
supporting information, p. 964 - 968 (2018/03/13)
Herein is described a mechanochemical one-pot two-step procedure giving access to various NHC (N-heterocyclic carbene) precursors. This original approach enabled the production of the widely used IPr·HCl, IMes·HCl, Io-Tol·HCl and ICy·HCl in much better yields than conventional solvent-based procedures, while the environmental impact was drastically reduced.
Facile and scalable synthesis of imidazolium halides using dimethylmethyleneammonium salts as ring closing reagents
Mistryukov, Electron A.
, p. 258 - 259 (2007/10/03)
An efficient procedure is proposed for the synthesis of 1,3-dialkylimidazolium salts starting from 1,4-diaza-1,3-dienes and methyleneammonium salts.
Process for preparing heterocyclic carbenes
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, (2008/06/13)
PCT No. PCT/EP97/01296 Sec. 371 Date Nov. 2, 1998 Sec. 102(e) Date Nov. 2, 1998 PCT Filed Mar. 14, 1997 PCT Pub. No. WO97/34875 PCT Pub. Date Sep. 25, 1997A process for preparing heterocyclic carbenes of the in which R1, R2, R3 and R4 are individually sat
