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1. Bimetallic, Silylene‐Mediated Multielectron Reductions of Carbon Dioxide and Ethylene

   https://doi.org/10.1002/ange.202011489  

   Whited, Matthew T. ; Zhang, Jia ; Conley, Anna M. ; Ma, Senjie ; Janzen, Daron E. ; Kohen, Daniela ( November 2020 , Angewandte Chemie)

   A metal/ligand cooperative approach to the reduction of small molecules by metal silylene complexes (R₂Si=M) is demonstrated, whereby silicon activates the incoming substrate and mediates net two‐electron transformations by one‐electron redox processes at two metal centers. An appropriately tuned cationic pincer cobalt(I) complex, featuring a central silylene donor, reacts with CO₂to afford a bimetallic siloxane, featuring two Co^IIcenters, with liberation of CO; reaction of the silylene complex with ethylene yields a similar bimetallic product with an ethylene bridge. Experimental and computational studies suggest a plausible mechanism proceeding by [2+2] cycloaddition to the silylene complex, which is quite sensitive to the steric environment. The Co^II/Co^IIproducts are reactive to oxidation and reduction. Taken together, these findings demonstrate a strategy for metal/ligand cooperative small‐molecule activation that is well‐suited to 3dmetals.

    

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2. Bimetallic, Silylene‐Mediated Multielectron Reductions of Carbon Dioxide and Ethylene

   https://doi.org/10.1002/anie.202011489  

   Whited, Matthew T. ; Zhang, Jia ; Conley, Anna M. ; Ma, Senjie ; Janzen, Daron E. ; Kohen, Daniela ( November 2020 , Angewandte Chemie International Edition)

   A metal/ligand cooperative approach to the reduction of small molecules by metal silylene complexes (R₂Si=M) is demonstrated, whereby silicon activates the incoming substrate and mediates net two‐electron transformations by one‐electron redox processes at two metal centers. An appropriately tuned cationic pincer cobalt(I) complex, featuring a central silylene donor, reacts with CO₂to afford a bimetallic siloxane, featuring two Co^IIcenters, with liberation of CO; reaction of the silylene complex with ethylene yields a similar bimetallic product with an ethylene bridge. Experimental and computational studies suggest a plausible mechanism proceeding by [2+2] cycloaddition to the silylene complex, which is quite sensitive to the steric environment. The Co^II/Co^IIproducts are reactive to oxidation and reduction. Taken together, these findings demonstrate a strategy for metal/ligand cooperative small‐molecule activation that is well‐suited to 3dmetals.

    

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3. Mechanochemical insertion of cobalt into porphyrinoids using Co 2 (CO) 8 as a cobalt source

   https://doi.org/10.1039/D0GC01010C  

   Damunupola, Dinusha ; Chaudhri, Nivedita ; Atoyebi, Adewole O. ; Brückner, Christian ( June 2020 , Green Chemistry)

   null (Ed.)

   Cobalt porphyrinoids find broad use as catalysts or electrode materials. Traditional solution state cobalt insertion reactions into a free base porphyrinoid to generate the corresponding cobalt complex generally require fairly harsh conditions, involving the heating of the reactants in high-boiling solvents for extended period of times. We report here an alternative method of cobalt insertion: A solvent-free (at least for the insertion step) mechanochemical method using a planetary ball mill with Co 2 (CO) 8 as a cobalt source. The scope and limits of the reaction were investigated with respect to the porphyrinic substrate susceptible to the reaction conditions, the influences of different grinding aids, and bases added. While the mechanochemical method is, like other metal insertion methods into porphyrinoids, not universally suitable for all substrates tested, it is faster, milder, and greener for several others, when compared to established solution-based methods. 

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4. Hydrogenation reactions catalyzed by HN(CH 2 CH 2 PR 2 ) 2 -ligated copper complexes

   https://doi.org/10.1039/d1qi00776a  

   Ekanayake, Dewmi A. ; Chakraborty, Arundhoti ; Krause, Jeanette A. ; Guan, Hairong ( October 2021 , Inorganic Chemistry Frontiers)

   null (Ed.)

   HN(CH 2 CH 2 PR 2 ) 2 -ligated copper borohydride complexes, ( R PN H P)Cu(BH 4 ) (R = i Pr, Cy, t Bu), which can be prepared from ( R PN H P)CuBr and NaBH 4 , are capable of catalyzing the hydrogenation of aldehydes in an alcoholic solvent. More active hydrogenation catalysts are ( R PN H P)CuBr mixed with KO t Bu, allowing various aldehydes and ketones to be efficiently reduced to alcohols except those bearing a nitro, N -unprotected pyrrole, pyridine, or an ester group, or those prone to aldol condensation ( e.g. , 1-heptanal). Modifying the catalyst structure by replacing the NH group in ( i Pr PN H P)CuBr with an NMe group results in an inferior catalyst but preserves some catalytic activity. The hexanuclear copper hydride cluster, ( i Pr PN H P) 3 Cu 6 H 6 , is also competent in catalyzing the hydrogenation of aldehydes such as benzaldehyde and N -methyl-2-pyrrolecarboxaldehyde, albeit accompanied by decomposition pathways. The catalytic performance can be enhanced through the addition of a strong base or i Pr PN H P. The three catalytic systems likely share the same catalytically active species, which is proposed to be a mononuclear copper hydride ( R PN H P)CuH with the NH group bound to copper. 

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5. Thermodynamic and kinetic studies of H 2 and N 2 binding to bimetallic nickel-group 13 complexes and neutron structure of a Ni(η 2 -H 2 ) adduct

   https://doi.org/10.1039/C9SC02018G  

   Cammarota, Ryan C. ; Xie, Jing ; Burgess, Samantha A. ; Vollmer, Matthew V. ; Vogiatzis, Konstantinos D. ; Ye, Jingyun ; Linehan, John C. ; Appel, Aaron M. ; Hoffmann, Christina ; Wang, Xiaoping ; et al ( July 2019 , Chemical Science)

   Understanding H 2 binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H 2 with protons and electrons. This work reports the first thermodynamic and kinetic H 2 binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al ( 1 ), Ga ( 2 ), and In ( 3 ), and L = [N( o -(NCH 2 P i Pr 2 )C 6 H 4 ) 3 ] 3− . Thermodynamic free energies (Δ G °) and free energies of activation (Δ G ‡ ) for binding equilibria were obtained via variable-temperature 31 P NMR studies and lineshape analysis. The supporting metal exerts a large influence on the thermodynamic favorability of both H 2 and N 2 binding to Ni, with Δ G ° values for H 2 binding found to span nearly the entire range of previous reports. The non-classical H 2 adduct, (η 2 -H 2 )NiInL ( 3 -H 2 ), was structurally characterized by single-crystal neutron diffraction—the first such study for a Ni(η 2 -H 2 ) complex or any d 10 M(η 2 -H 2 ) complex. UV-Vis studies and TD-DFT calculations identified specific electronic structure perturbations of the supporting metal which poise NiML complexes for small-molecule binding. ETS-NOCV calculations indicate that H 2 binding primarily occurs via H–H σ-donation to the Ni 4p z -based LUMO, which is proposed to become energetically accessible as the Ni(0)→M( iii ) dative interaction increases for the larger M( iii ) ions. Linear free-energy relationships are discussed, with the activation barrier for H 2 binding (Δ G ‡ ) found to decrease proportionally for more thermodynamically favorable equilibria. The Δ G ° values for H 2 and N 2 binding to NiML complexes were also found to be more exergonic for the larger M( iii ) ions. 

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