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  1. Photochemical electrocyclization reactions are valued for both their ability to produce structurally complex molecules and their central role in elucidating fundamental mechanistic principles of photochemistry. We present herein a highly enantioselective 6π photoelectrocyclization catalyzed by a chiral Ir(III) photosensitizer. This transformation was successfully realized by engineering a strong hydrogen-bonding interaction between a pyrazole moiety on the catalyst and a basic imidazolyl ketone on the substrate. To shed light on the origin of stereoinduction, we conducted a comprehensive investigation combining experimental and computational mechanistic studies. Results from density functional theory calculations underscore the crucial role played by the prochirality and the torquoselectivity in the electrocyclization process as well as the steric demand in the subsequent [1,4]-H shift step. Our findings not only offer valuable guidance for developing chiral photocatalysts but also serve as a significant reference for achieving high levels of enantioselectivity in the 6π photoelectrocyclization reaction. 
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    Free, publicly-accessible full text available December 4, 2024
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  5. Complex (PNP)NbCl 2 (N[ t Bu]Ar) (1) (PNP − = N[2-P i Pr 2 -4-methylphenyl] 2 ; Ar = 3,5-Me 2 C 6 H 3 ) reacts with one equiv. of NaN 3 to form a mixture of (PNPN)NbCl 2 (N[ t Bu]Ar) (2) and (PNP)NbN(N[ t Bu]Ar) (3), both of which have been spectroscopically and crystallographically characterized, including 15 N isotopic labelling studies. Complex 3 represents the first structurally characterized example of a neutral and mononuclear Nb nitride. Independent studies established 3 to form via two-electron reduction of 2, whereas oxidation of 3 by two-electrons reversed the process. Computational studies suggest the transmetallation step to produce the intermediate [(PNP)NbCl(N 3 )(N[ t Bu]Ar)] (A) which extrudes N 2 to form the phosphinimide [(PNPN)NbCl(N[ t Bu]Ar)] (B) followed by disproportionation to 2 and low-valent [(PNPN)Nb(N[ t Bu]Ar)] (C). The latter then undergoes intramolecular N-atom transfer to form the nitride moiety in 3. 
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  6. Through the application of a redox-innocent aryl diimine chelate, the discovery and utilization of a cobalt catalyst, ( Ph 2 PPr ADI)Co, that exhibits carbonyl hydrosilylation turnover frequencies of up to 330 s −1 is described. This activity is believed to be the highest ever reported for metal-catalyzed carbonyl hydrosilylation. 
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