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1. Cobalt(I) Pincer Complexes as Catalysts for CO2 Hydrogenation to Formate

   https://doi.org/10.1021/acs.organomet.4c00161  

   Yao, Wenzhi; Olajide, Gbolagade; Boudreaux, Chance M; Wysocki, Megan M; Ahmed, Md Kausar; Qu, Fengrui; Szilvási, Tibor; Papish, Elizabeth T (June 2024, Organometallics)

   Carbon dioxide hydrogenation with base to generate formate salts can provide a means of storing hydrogen in an energy dense solid. However, this application requires catalytic CO2 hydrogenation, which would ideally use an earth abundant metal catalyst. In this article, six new (CNC)CoIL2 pincer complexes were synthesized and fully characterized, including single crystal X-Ray diffraction analysis on four new complexes. These complexes contain an imidazole-based (1R) N-heterocyclic carbene (NHC) ring or a benzimidazole based NHC ring (2R) in the CNC pincer. The R group is para to N on the pyridine ring and been varied from electron withdrawing (CF3) to donating (Me, OMe) substituents. The L type ligands have included CO and phosphine ligands (in PPh32 and PMe32). Thus, two known Co complexes (1, 1OMe) and six new complexes (1Me, 1CF3, 2, 2OMe, PPh32, PMe32) were studied for the CO2 hydrogenation reaction. In general, the unsubstituted CNC pincer complexes bearing two carbonyl ligands led to the highest activity. The best catalyst, 2, remains active for over 16 h and produces a turnover number of 39,800 with 20 bars of 1:1 CO2 / H2 mixture at 60 °C. A computational study of the mechanism of CO2 hydrogenation is also reported. 

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2. Generation and Stabilization of a Dinickel Catalyst in a Metal‐Organic Framework for Selective Hydrogenation Reactions

   https://doi.org/10.1002/anie.202306905  

   Guo, Qing‐Yun; Wang, Zitong; Feng, Xuanyu; Fan, Yingjie; Lin, Wenbin (July 2023, Angewandte Chemie International Edition)

   Abstract Although many monometallic active sites have been installed in metal–organic frameworks (MOFs) for catalytic reactions, there are no effective strategies to generate bimetallic catalysts in MOFs. Here we report the synthesis of a robust, efficient, and reusable MOF catalyst, MOF‐NiH, by adaptively generating and stabilizing dinickel active sites using the bipyridine groups in MOF‐253 with the formula of Al(OH)(2,2′‐bipyridine‐5,5′‐dicarboxylate) forZ‐selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β‐unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy⋅⁻)Ni^II(μ₂‐H)₂Ni^II(bpy⋅⁻) as the active catalyst. MOF‐NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution‐inaccessible Earth‐abundant bimetallic MOF catalysts for sustainable catalysis. 

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3. Cyclopentadienone Iridium Bipyridyl Complexes: Acid-Stable Transfer Hydrogenation Catalysts

   https://doi.org/10.1021/acs.organomet.3c00266  

   Marron, Daniel P.; Galvin, Conor M.; Waymouth, Robert M. (August 2023, Organometallics)

   The synthesis, structure, and reactivity of a series of cyclopentadienone and hydroxycyclopentadienyl 4,4’-dimethylbipyridine (dmbpy) iridium complexes (C5Tol2Ph2O)(dmbpy)IrCl 1, [(C5Tol2Ph2OH)(dmbpy)IrCl][OTf] 2 (C5Tol2Ph2O)(dmbpy)IrH 3, and [(C5Tol2Ph2OH)(dmbpy)IrH][OTf] 4 are described. The Ir(I) complexes 1 and 3 are active catalyst precursors for transfer hydrogenation of aldehydes, ketones, and N-heterocycles with HCO2H/Et3N under mild conditions. Model studies implicate the cationic iridium hydride, [(C5Tol2Ph2OH)(dmbpy)IrH][OTf] 4 as a key intermediate, as 4 reacts readily with acetone to generate isopropanol. Selectivity over hydrogenation of alkenes is enhanced compared to other Shvo-type catalysts, and only modest C=C hydrogenation observed when adjacent to polarizing functional groups. Catalytic hydrogenation likely proceeds by a metal-ligand bifunctional mechanism similar to related cyclopentadienone complexes 

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4. Homogeneous versus MOF-supported catalysis: A direct comparison of catalytic hydroboration at Ni tripodal P ₃ E (E = Si, Ge) complexes

   https://doi.org/10.1039/D3DT01328F  

   Barrios-Vargas, Luz Jimena; Abeynayake, Niroshani Samitri; Secrist, Carlee; Le, Nghia; Webster, Charles Edwin; Donnadieu, Bruno; Kaphan, David M; Roy, Amitava; Ibarra, Ilich A.; Montiel-Palma, Virginia (January 2023, Dalton Transactions)

   MOF NU-1000 was employed to host Ni tripodal complexes prepared from new organometallic precursors [HNi(κ4(E,P,P,P)-E(o-C 6 H 4 CH 2 PPh 2 ) 3 ], E = Si (Ni-1), Ge (Ni-2). The new heterogenous catalytic materials, Ni-1@NU-1000 and Ni-2@NU-1000 show the advantages of both homogenous and heterogeneous catalysts. They catalyze the hydroboration of aldehydes and ketones more efficiently than the homogenous Ni-1 and Ni-2, under aerobic conditions, and allowing recyclability of the catalyst. 

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5. Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

   https://doi.org/10.3390/molecules26010188  

   Buchspies, Jonathan; Rahman, Md. Mahbubur; Szostak, Michal (January 2021, Molecules)

   null (Ed.)

   The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions. 

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