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1. Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel‐Boron Cooperativity in a PBP‐Ni Complex

   https://doi.org/10.1002/anie.202306315  

   Álvarez‐Rodríguez, Lucía; Ríos, Pablo; Laglera‐Gándara, Carlos J.; Jurado, Andrea; Fernández‐de‐Córdova, Francisco José; Gunnoe, T. Brent; Rodríguez, Amor (July 2023, Angewandte Chemie International Edition)

   Abstract The synthesis and characterization of (^tBuPBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni−C bond of (^tBuPBP)NiMe (1) is presented. An unexpected CO₂cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (^tBuPBOP)₂Ni₄(μ‐CO)₂(6). Mechanistic investigation of this reaction indicates a reductive scission of CO₂by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO₂activation reaction produces a three‐coordinate (^tBuP₂BO)Ni‐acyl intermediate (A) that leads to a (^tBuP₂BO)−Ni^Icomplex (B) via a likely radical pathway. The Ni^Ispecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (^tBuP₂BO)Ni^II(η²‐TEMPO) (7). Additionally,¹³C and¹H NMR spectroscopy analysis using¹³C‐enriched CO₂provides information about the species involved in the CO₂activation process. 

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2. Synthesis and structure of a new bulky bis(alkoxide) ligand on a terphenyl platform

   https://doi.org/10.1107/S2056989021013438  

   Kurup, Sudheer S.; Nasser, Sandra; Ward, Cassandra L.; Groysman, Stanislav (January 2022, Acta Crystallographica Section E Crystallographic Communications)

   A new sterically bulky chelating bis(alkoxide) ligand 3,3′-([1,1′:4′,1′′-terphenyl]-2,2′′-diyl)bis(2,2,4,4-tetramethylpentan-3-ol), (H 2 [OO] tBu ), was prepared in a two-step process as the dichloromethane monosolvate, C 36 H 50 O 2 ·CH 2 Cl 2 . The first step is a Suzuki–Miyaura coupling reaction between 2-bromophenylboronic acid and 1,4-diiodobenzene. The resulting 2,2′′-dibromo-1,1′:4′,1′′-terphenyl was reacted with t BuLi and hexamethylacetone to obtain the desired product. The crystal structure of H 2 [OO] tBu revealed an anti conformation of the [CPh 2 (OH)] fragments relative to the central phenyl. Furthermore, the hydroxyl groups point away from each other. Likely because of this anti – anti conformation, the attempts to synthesize first-row transition-metal complexes with H 2 [OO] tBu were not successful. 

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3. Reduction-induced CO dissociation by a [Mn(bpy)(CO) ₄ ][SbF ₆ ] complex and its relevance in electrocatalytic CO ₂ reduction

   https://doi.org/10.1039/c9dt04150h  

   Kuo, Hsin-Ya; Tignor, Steven E.; Lee, Tia S.; Ni, Danrui; Park, James Eujin; Scholes, Gregory D.; Bocarsly, Andrew B. (January 2020, Dalton Transactions)

   [Mn(bpy)(CO) 3 Br] is recognized as a benchmark electrocatalyst for CO 2 reduction to CO, with the doubly reduced [Mn(bpy)(CO) 3 ] − proposed to be the active species in the catalytic mechanism. The reaction of this intermediate with CO 2 and two protons is expected to produce the tetracarbonyl cation, [Mn(bpy)(CO) 4 ] + , thereby closing the catalytic cycle. However, this species has not been experimentally observed. In this study, [Mn(bpy)(CO) 4 ][SbF 6 ] ( 1 ) was directly synthesized and found to be an efficient electrocatalyst for the reduction of CO 2 to CO in the presence of H 2 O. Complex 1 was characterized using X-ray crystallography as well as IR and UV-Vis spectroscopy. The redox activity of 1 was determined using cyclic voltammetry and compared with that of benchmark manganese complexes, e.g. , [Mn(bpy)(CO) 3 Br] ( 2 ) and [Mn(bpy)(CO) 3 (MeCN)][PF 6 ] ( 3 ). Infrared spectroscopic analyses indicated that CO dissociation occurs after a single-electron reduction of complex 1 , producing a [Mn(bpy)(CO) 3 (MeCN)] + species. Complex 1 was experimentally verified as both a precatalyst and an on-cycle intermediate in homogeneous Mn-based electrocatalytic CO 2 reduction. 

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4. Differential impact on oral cancer cell viability for three carboxylate-stabilized rhenium(I) tricarbonyl centers supported by 2,2′-bipyridine: One-pot synthesis, a structure, and proton-catalyzed carboxylate ligand substitution

   https://doi.org/10.1016/j.ica.2024.122105  

   Buren, Lyndsey; Tumbaco, Emily; Piesco, Alyssa; Irvin, Justin; Emge, Thomas J; Weisburg, Jeffrey H; Moehring, Gregory A; Naik, Datta V (August 2024, Inorganica Chimica Acta)

   A set of six carboxylate-stabilized rhenium(I) tricarbonyl complexes supported by a 2,2’-bipyridine (bpy) ligand, Re(O2CR)(CO)3(bpy) (R = H, CH3, CHF2, R- or S CHBrCH(CH3)2, and C5H11), were prepared by acidolysis of the complex Re(OCO2C5H11)(CO)3(bpy) with the appropriate carboxylic acid and characterized by 1H and 13C-{1H} NMR and IR spectroscopy. The crystal structure of the complex, Re[R-O2CCHBrCH(CH3)2](CO)3(bpy), was determined by X-ray crystallography. Cytotoxicity results correlate positively with the Kb value of the carboxylate ligand. Apparently, the more substitutionally inert the carboxylate-stabilized complex is in a chloride-rich environment (similar to extracellular fluid) the greater the amount of cytotoxic [Re(CO)3(bpy)(H2O)]+ that forms in the cytosol. 

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5. Solar CO₂ reduction using a molecular Re(I) catalyst grafted on SiO₂ via amide and alkyl amine linkages

   https://doi.org/10.1039/d3dt03623e  

   Fenton, Thomas; Ahmad, Esraa; Li, Gonghu (February 2024, Dalton Transactions)

   Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO)3Cl where bpy is 2,2’-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO)3Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO)3Cl onto SiO2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re(I) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re(I)-OH species on SiO2. Furthermore, the amine group likely contributes to the stabilization of a surface Re(I)-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re(I) catalyst containing the alkyl amine linkage. 

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