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991.
992.
Marius D. R. Lutz Hongyu Zhong Nils Trapp Bill Morandi 《Helvetica chimica acta》2023,106(4):e202200199
We report the synthesis of coordinatively unsaturated cationic rhodium complexes bearing the sterically encumbered electron-rich NHC ligand IPr*OMe. The COD (1,5-cyclooctadiene) complex [Rh(IPr*OMe)(COD)]BF4 adopts a tilted, pseudo-square planar coordination geometry, where bonding to the ipso-carbon of the NHC aryl substituent was observed in the solid state. Hydrogenation of this complex afforded a metastable dihydride complex [Rh(IPr*OMe)(H)2]BF4 with an unusual internal coordination to an arene of the ligand. In the absence of a hydrogen atmosphere, spontaneous reductive elimination of H2 afforded a rhodium complex [Rh(IPr*OMe)]BF4 with a single chelating ligand that stabilizes the highly unsaturated metal by two-fold π-face donation as suggested by NMR spectroscopy and computational studies. This unusual complex might serve as a versatile precatalyst for a variety of transformations. 相似文献
993.
Dr. Hye Won Moon Dr. Feng Wang Dr. Kalishankar Bhattacharyya Dr. Oriol Planas Dr. Markus Leutzsch Dr. Nils Nöthling Dr. Alexander A. Auer Dr. Josep Cornella 《Angewandte Chemie (International ed. in English)》2023,62(49):e202313578
Organobismuth-catalyzed transfer hydrogenation has recently been disclosed as an example of low-valent Bi redox catalysis. However, its mechanistic details have remained speculative. Herein, we report experimental and computational studies that provide mechanistic insights into a Bi-catalyzed transfer hydrogenation of azoarenes using p-trifluoromethylphenol ( 4 ) and pinacolborane ( 5 ) as hydrogen sources. A kinetic analysis elucidated the rate orders in all components in the catalytic reaction and determined that 1 a (2,6-bis[N-(tert-butyl)iminomethyl]phenylbismuth) is the resting state. In the transfer hydrogenation of azobenzene using 1 a and 4 , an equilibrium between 1 a and 1 a ⋅ [OAr]2 (Ar=p-CF3−C6H4) is observed, and its thermodynamic parameters are established through variable-temperature NMR studies. Additionally, pKa-gated reactivity is observed, validating the proton-coupled nature of the transformation. The ensuing 1 a ⋅ [OAr]2 is crystallographically characterized, and shown to be rapidly reduced to 1 a in the presence of 5 . DFT calculations indicate a rate-limiting transition state in which the initial N−H bond is formed via concerted proton transfer upon nucleophilic addition of 1 a to a hydrogen-bonded adduct of azobenzene and 4 . These studies guided the discovery of a second-generation Bi catalyst, the rate-limiting transition state of which is lower in energy, leading to catalytic transfer hydrogenation at lower catalyst loadings and at cryogenic temperature. 相似文献
994.
Dr. Yue Pang Dr. Markus Leutzsch Dr. Nils Nöthling Dr. Josep Cornella 《Angewandte Chemie (International ed. in English)》2023,62(32):e202302071
Herein, we report the synthesis of a sterically distorted distibene ( [4]2 ) and its transition-metal-like reactivity towards two fundamental feedstock chemicals: H2 and ethylene. Although [4]2 exhibits an unusually long Sb=Sb distance and noticeable backbone distortion in the solid state, NMR data suggest that [4]2 remains predominantly as a dimer in solution, even at high temperatures. However, it was proposed that the elusive reactivity of [4]2 toward H2 and ethylene results from reversible dissociation of [4]2 into the transient stibinidene ( [4] ), which could be observed by NMR spectroscopic techniques. 相似文献
995.
Nils L. Ahlburg Oliver Hergert Prof. Dr. Peter G. Jones Prof. Dr. Daniel B. Werz 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202214390
A novel class of highly activated donor-acceptor cyclopropanes bearing only a single, vinylogous acceptor is presented. These strained moieties readily undergo cycloadditions with aldehydes, ketones, thioketones, nitriles, naphth-2-ols and various other substrates to yield the corresponding carbo- and heterocycles. Diastereocontrol can be achieved through the choice of catalyst (Brønsted or Lewis acid). The formation of tetrahydrofurans was shown to be highly enantiospecific when chiral cyclopropanes are employed. A series of mechanistic and kinetic experiments was conducted to elucidate a plausible catalytic cycle and to rationalize the stereochemical outcome. 相似文献