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1. Transition-metal-mediated reduction and reversible double-cyclization of cyanuric triazide to an asymmetric bitetrazolate involving cleavage of the six-membered aromatic ring

   https://doi.org/10.1039/d0sc04949b  

   Vaddypally, Shivaiah; Kiselev, Vitaly G.; Byrne, Alex N.; Goldsmith, C. Franklin; Zdilla, Michael J. (February 2021, Chemical Science)

   null (Ed.)

   Cyanuric triazide reacts with several transition metal precursors, extruding one equivalent of N 2 and reducing the putative diazidotriazeneylnitrene species by two electrons, which rearranges to N -(1′ H -[1,5′-bitetrazol]-5-yl)methanediiminate (biTzI 2− ) dianionic ligand, which ligates the metal and dimerizes, and is isolated from pyridine as [M(biTzI)] 2 Py 6 (M = Mn, Fe, Zn, Cu, Ni). Reagent scope, product analysis, and quantum chemical calculations were combined to elucidate the mechanism of formation as a two-electron reduction preceding ligand rearrangement. 

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2. Phosphine-Mediated Cleavage of Sulfur–Sulfur Bonds

   https://doi.org/10.1021/acs.organomet.2c00271  

   Tran, Phuong M.; Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Lahm, Mitchell E.; Schaefer, Henry F.; Robinson, Gregory H. (November 2022, Organometallics)
3. Carbon–fluorine bond cleavage mediated by metalloenzymes

   https://doi.org/10.1039/C9CS00740G  

   Wang, Yifan; Liu, Aimin (January 2020, Chemical Society Reviews)

   Fluorochemicals are a widely distributed class of compounds and have been utilized across a wide range of industries for decades. Given the environmental toxicity and adverse health threats of some fluorochemicals, the development of new methods for their decomposition is significant to public health. However, the carbon–fluorine (C–F) bond is among the most chemically robust bonds; consequently, the degradation of fluorinated hydrocarbons is exceptionally difficult. Here, metalloenzymes that catalyze the cleavage of this chemically challenging bond are reviewed. These enzymes include histidine-ligated heme-dependent dehaloperoxidase and tyrosine hydroxylase, thiolate-ligated heme-dependent cytochrome P450, and four nonheme oxygenases, namely, tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, 2-oxoglutarate-dependent hydroxylase, Rieske dioxygenase, and thiol dioxygenase. While much of the literature regarding the aforementioned enzymes highlights their ability to catalyze C–H bond activation and functionalization, in many cases, the C–F bond cleavage has been shown to occur on fluorinated substrates. A copper-dependent laccase-mediated system representing an unnatural radical defluorination approach is also described. Detailed discussions on the structure–function relationships and catalytic mechanisms provide insights into biocatalytic defluorination, which may inspire drug design considerations and environmental remediation of halogenated contaminants. 

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4. The bridge helix of Cas12a imparts selectivity in cis ‐DNA cleavage and regulates trans ‐DNA cleavage

   https://doi.org/10.1002/1873-3468.14051  

   Parameshwaran, Hari Priya; Babu, Kesavan; Tran, Christine; Guan, Kevin; Allen, Aleique; Kathiresan, Venkatesan; Qin, Peter Z.; Rajan, Rakhi (February 2021, FEBS Letters)

   Cas12a is an RNA‐guided DNA endonuclease of the type V‐A CRISPR‐Cas system that has evolved convergently with the type II Cas9 protein. We previously showed that proline substitutions in the bridge helix (BH) impart target DNA cleavage selectivity inStreptococcus pyogenes(Spy) Cas9. Here, we examined a BH variant of Cas12a fromFrancisella novicida(FnoCas12a^KD2P) to test mechanistic conservation. Our results show that for RNA‐guided DNA cleavage (cis‐activity), FnoCas12a^KD2Paccumulates nicked products while cleaving supercoiled DNA substrates with mismatches, with certain mismatch positions being more detrimental for linearization. FnoCas12a^KD2Palso possess reducedtrans‐single‐stranded DNA cleavage activity. These results implicate the BH in substrate selectivity in bothcis‐andtrans‐cleavages and show its conserved role in target discrimination among Cas nucleases. 

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5. Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage

   https://doi.org/10.1021/acs.inorgchem.4c01522  

   Jakhar, Vineet K; Shen, Yu-Hsuan; Yadav, Rinku; Nadif, Soufiane S; Ghiviriga, Ion; Abboud, Khalil A; Lester, Daniel W; Veige, Adam S (July 2024, Inorganic Chemistry)

   Reactions between tungsten alkylidyne [tBuOCO]W≡CtBu(THF)2 1 and sulfur containing small molecules are reported. Complex 1 reacts with CS2 to produce intermediate η2 bound CS2 complex [O2C(tBuC═)W(η2-(S,C)-CS2)(THF)] 8. Heating complex 8 provides a mixture of a monomeric tungsten sulfido complex 9 and a dimeric complex 10 in a 4:1 ratio, respectively. Heating the mixture does not perturb the ratio. Addition of excess THF in a solution of 9 and 10 (4:1) converts 10 to 9 (>96%) with concomitant loss of (CS)x. Both 9 and 10 can be selectively crystallized from the mixture. An alternative synthesis of exclusively monomeric 9 involves the reaction between 1 and PhNCS. Demonstrating ring expansion metathesis polymerization (REMP), tethered tungsten alkylidene 8 polymerizes norbornene to produce cis-selective syndiotactic cyclic polynorbornene (c-poly(NBE)). 

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