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1. Addition of H 2 Across a Cobalt–Phosphorus Bond

   https://doi.org/10.1002/anie.201710100  

   Poitras, Andrew M. ; Knight, Sadie E. ; Bezpalko, Mark W. ; Foxman, Bruce M. ; Thomas, Christine M. ( January 2018 , Angewandte Chemie International Edition)

   Addition of H₂across the cobalt–phosphorus bond of (PPP)CoPMe₃(3) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP⁻) donor. The chlorophosphine Co^IIcomplex (PP^ClP)CoCl₂(2) can be generated through coordination of the chlorophosphine ligand (PP^ClP,1) to CoCl₂. Subsequent reduction of2with KC₈in the presence of PMe₃generates (PPP)CoPMe₃(3), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H₂to complex3cleanly affords (PP^HP)Co(H)PMe₃(4), in which H₂has ultimately been added across the metal–phosphorus bond. Complex4was characterized spectroscopically and using computational methods to predict its geometry.

    

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2. Addition of H 2 Across a Cobalt–Phosphorus Bond

   https://doi.org/10.1002/ange.201710100  

   Poitras, Andrew M. ; Knight, Sadie E. ; Bezpalko, Mark W. ; Foxman, Bruce M. ; Thomas, Christine M. ( January 2018 , Angewandte Chemie)

   Addition of H₂across the cobalt–phosphorus bond of (PPP)CoPMe₃(3) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP⁻) donor. The chlorophosphine Co^IIcomplex (PP^ClP)CoCl₂(2) can be generated through coordination of the chlorophosphine ligand (PP^ClP,1) to CoCl₂. Subsequent reduction of2with KC₈in the presence of PMe₃generates (PPP)CoPMe₃(3), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H₂to complex3cleanly affords (PP^HP)Co(H)PMe₃(4), in which H₂has ultimately been added across the metal–phosphorus bond. Complex4was characterized spectroscopically and using computational methods to predict its geometry.

    

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3. POCOP-type cobalt and nickel pincer complexes bearing an appended phosphinite group

   https://doi.org/10.1139/cjc-2020-0137  

   Li, Yingze ; Krause, Jeanette A. ; Guan, Hairong ( April 2021 , Canadian Journal of Chemistry)

   The reaction of 1,3,5-( i Pr 2 PO) 3 C 6 H 3 with Co 2 (CO) 8 leads to the isolation of a POCOP-type mononuclear pincer complex {κ P ,κ C ,κ P -2,4,6-( i Pr 2 PO) 3 C 6 H 2 }Co(CO) 2 (1) or a tetranuclear species {κ P -{κ P ,κ C ,κ P -2,4,6-( i Pr 2 PO) 3 C 6 H 2 }Co(CO) 2 } 2 Co 2 (CO) 6 (2), depending on the ligand to cobalt ratio employed. The latter compound can be an impurity during the synthesis of {2,6-( i Pr 2 PO) 2 -4-Me 2 N-C 6 H 2 }Co(CO) 2 , when the ligand precursor 5-(dimethylamino)resorcinol is contaminated with phloroglucinol due to incomplete monoamination. Similarly, the reaction of 1,3,5-( i Pr 2 PO) 3 C 6 H 3 with NiCl 2 in the presence of 4-dimethylaminopyridine provides {κ P ,κ C ,κ P -2,4,6-( i Pr 2 PO) 3 C 6 H 2 }NiCl (3) bearing an appended phosphinite group. Structures 1–3 have been studied by X-ray crystallography. 

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4. Crystal structures of phosphine-supported (η 5 -cyclopentadienyl)molybdenum(II) propionyl complexes

   https://doi.org/10.1107/S2056989021008008  

   Whited, Matthew T. ; Ball, Margaret A. ; Block, Alison ; Brewster, Benjamin A. ; Ferrer, LouLou ; Jin-Lee, Helen J. ; King, Colby J. ; North, Jamie D. ; Shelton, Inger L. ; Wilson, David G. ( September 2021 , Acta Crystallographica Section E Crystallographic Communications)

   Three cyclopentadienylmolybdenum(II) propionyl complexes featuring triarylphosphine ligands with different para substituents, namely, dicarbonyl(η 5 -cyclopentadienyl)propionyl(triphenylphosphane-κ P )molybdenum(II), [Mo(C 5 H 5 )(C 3 H 5 O)(C 18 H 15 P)(CO) 2 ], ( 1 ), dicarbonyl(η 5 -cyclopentadienyl)propionyl[tris(4-fluorophenyl)phosphane-κ P ]molybdenum(II), [Mo(C 5 H 5 )(C 3 H 5 O)(C 18 H 12 F 3 P)(CO) 2 ], ( 2 ), and dicarbonyl(η 5 -cyclopentadienyl)propionyl[tris(4-methoxyphenyl)phosphane-κ P ]molybdenum(II) dichloromethane solvate, [Mo(C 5 H 5 )(C 3 H 5 O)(C 21 H 21 O 3 P)(CO) 2 ]·CH 2 Cl 2 , ( 3 ), have been prepared from the corresponding ethyl complexes via phosphine-induced migratory insertion. These complexes exhibit four-legged piano-stool geometries with molecular structures quite similar to each other and to related acetyl complexes. The extended structures of the three complexes differ somewhat, with the para substituent of the triarylphosphine of ( 2 ) (fluoro) or ( 3 ) (methoxy) engaging in non-classical C—H...F or C—H...O hydrogen-bonding interactions. The structure of ( 3 ) exhibits modest disorder in the position of one Cl atom of the dichloromethane solvent, which was modeled with two sites showing approximately equivalent occupancies [0.532 (15) and 0.478 (15)]. 

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5. Structural and Electronic Influences on Rates of Tertpyridine−Amine Co III −H Formation During Catalytic H 2 Evolution in an Aqueous Environment

   https://doi.org/10.1002/cphc.202100295  

   DiMarco, Brian N. ; Polyansky, Dmitry E. ; Grills, David C. ; Wang, Ping ; Kuwahara, Yutaka ; Zhao, Xuan ; Fujita, Etsuko ( June 2021 , ChemPhysChem)

   In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺species results in the formation of [Co^II(κ⁴‐L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴‐L)(OH₂)]⁺, which undergoes a rate‐limiting structural rearrangement to [Co^I(κ⁵‐L)]⁺before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺formation is similar for all complexes in the series. UsingE_1/2values of various Co species and pK_avalues of [Co^III−H]²⁺estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺is unfavorable, [Co^II−H]⁺reacts with protons to produce H₂. The catalytic activity for H₂evolution tracks the hydricity of the [Co^II−H]⁺intermediate.

    

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