A number of para-substituted chloro(aryl)carbenes are generated within the cavities of a series of dry alkali metal cation-exchanged zeolites (LiY, NaY, KY, RbY, and CsY) upon laser flash photolysis of the corresponding diazirine precursor. The absolute reactivity of the chloro(aryl)carbene is found to be strongly dependent on both the nature of the electron-donating and -withdrawing properties of the aryl substituent and the nature of the zeolite charge-balancing cations. The results strongly suggest that two opposing mechanisms for capture of the carbene can occur depending on whether the zeolite framework behaves as a nucleophilic reagent or an electrophilic reagent in its reaction with the carbene center. Hammett relationships for the decay of the carbene as a function of aryl substituent and zeolite counterion versus the sigma+ substituent parameter support a change in mechanism as the carbene center toggles between being electron poor and electron rich. For the electron-poor chloro(4-nitrophenyl)carbene, a framework adduct is proposed upon reaction of the nucleophilic [Si-O-Al]- bridge with the carbene center, and for the electron-rich chloro(4-methoxyphenyl)carbene, an adduct with the tight Li+ cation is proposed.
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J Am Chem Soc
January 2025
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
The remarkable efficiency with which enzymes catalyze small-molecule reactions has driven their widespread application in organic chemistry. Here, we employ automated fast-flow solid-phase synthesis to access catalytically active full-length enzymes without restrictions on the number and structure of noncanonical amino acids incorporated. We demonstrate the total syntheses of iron-dependent myoglobin (BsMb) and sperm whale myoglobin (SwMb).
View Article and Find Full Text PDFAcc Chem Res
January 2025
Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States.
ConspectusUnderstanding f element-ligand covalency is at the center of efforts to design new separations schemes for spent nuclear fuel, and is therefore of signficant fundamental and practical importance. Considerable effort has been invested into quantifying covalency in f element-ligand bonding. Over the past decade, numerous studies have employed a variety of techniques to study covalency, including XANES, EPR, and optical spectroscopies, as well as X-ray crystallography.
View Article and Find Full Text PDFChem Biol Interact
January 2025
Institute of Vascular Biology and Thrombosis Research, Center for Physiology and Pharmacology, Medical University of Vienna, Schwarzspanierstrasse 17, 1090 Vienna, Austria. Electronic address:
A series of eight gold(I) N-heterocyclic carbene (NHC) complexes [Au(IMes)(HLn)] based on 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 7-azaindole derivatives (HLn), where n = 1-8 for HL1 = 5-flouro-7-azaindole, HL2 = 5-bromo-7-azaindole, HL3 = 3-chloro-7-azaindole, HL4 = 3-iodo-7-azaindole, HL5 = 5-bromo-3-chloro-7-azaindole, HL6 = 5-bromo-3-iodo-7-azaindole, HL7 = 4-chloro-2-methyl-7-azaindole and HL8 = 7-azaindole, was prepared, characterised and studied for their in vitro anti-cancer and anti-inflammatory effects. The complexes showed significant cytotoxicity on human ovarian cancer cell lines (A2780, IC ≈ 8-19 μM and A2780R, IC ≈ 8-19 μM) and lowered toxicity in normal HaCat and MRC-5 cells. Cellular effects of the selected complexes 1 and 7 were evaluated in A2780 cells using flow cytometry.
View Article and Find Full Text PDFChemistry
January 2025
University of Oxford, Inorganic Chemistry Laboratory, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.
Combining experiment and theory, the mechanisms of H2 activation by the potassium-bridged aluminyl dimer K2[Al(NON)]2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tertbutyl-9,9-dimethylxanthene) and its monomeric K+-sequestered counterpart have been investigated. These systems show diverging reactivity towards the activation of dihydrogen, with the dimeric species undergoing formal oxidative addition of H2 at each Al centre under ambient conditions, and the monomer proving to be inert to dihydrogen addition. Noting that this K+ dependence is inconsistent with classical models of single-centre reactivity for carbene-like Al(I) species, we rationalize these observations instead by a cooperative frustrated Lewis pair (FLP)-type mechanism (for the dimer) in which the aluminium centre acts as the Lewis base and the K+ centres as Lewis acids.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
January 2025
CNRS/UCSD, Chemistry, University of California, San Diego, 5213 Pacific Hall,, Department of Chemistry, 92093-0343, La jolla, UNITED STATES.
N-Heterocyclic carbene (NHC) ligands possess the ability to stabilize metal-based nanomaterials for a broad range of applications. With respect to metal-hydride nanomaterials, however, carbenes are rare, which is surprising if one considers the importance of metal-hydride bonds across the chemical sciences. In this study, we introduce a bottom-up approach leveraging preexisting metal-metal m-center-n-electron (mc-ne) bonds to access a highly stable cyclic(alkyl)amino carbene (CAAC) copper-hydride nanocluster, [(CAAC)6Cu14H12][OTf]2 with superior stability compared to Stryker's reagent, a popular commercial phosphine-based copper hydride catalyst.
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