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1. Improved Synthesis of Chiral 1,4,7‐Triazacyclononane Derivatives and Their Application in Ni‐Catalyzed Csp ³ −Csp ³ Kumada Cross‐Coupling

   https://doi.org/10.1002/hlca.202300170  

   Hu, Chi‐Herng; Byeong Chae, Ju; Mirica, Liviu M. (December 2023, Helvetica Chimica Acta)

   Abstract Herein, we report four new chiral 1,4,7‐triazacyclononane (TACN) derivatives and their corresponding nickel(II) chloride complexes. All TACN ligands are bearing one chiral N‐substituent and two alkyl (methyl ortert‐butyl) N‐substituents, and we have developed a new synthetic method for the dimethyl‐substituted TACN derivative, in order to prevent the rotational isomers that hinder the cyclization reaction. The nickel complexes change their coordination geometry significantly depending on the steric bulk of the N‐alkyl substituents, from a dinuclear tris(μ‐chloro)dinickel complex to mononuclear Ni‐dichloride and Ni‐chloride complexes. These complexes were then employed in the alkyl‐alkyl Kumada cross‐coupling reaction and revealed that the more sterically hindered ligands produced more homocoupled product rather than the cross‐coupled product, while the mononuclear Ni‐dichloride complex exhibited significantly lower catalytic activity. These chiral complexes were also employed in enantioconvergent cross‐coupling reactions as well, to afford significant enantioenrichment. Overall, the least sterically hindered Ni complex yields the best yields in the alkyl‐alkyl Kumada cross‐coupling reaction among the four complexes investigated, as well as the highest enantioselectivity. 

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2. Octahedral iron( iv )–tosylimido complexes exhibiting single electron-oxidation reactivity

   https://doi.org/10.1039/C9SC02526J  

   Sabenya, Gerard; Gamba, Ilaria; Gómez, Laura; Clémancey, Martin; Frisch, Jonathan R.; Klinker, Eric J.; Blondin, Geneviève; Torelli, Stéphane; Que, Lawrence; Martin-Diaconescu, Vlad; et al (October 2019, Chemical Science)

   High valent iron species are very reactive molecules involved in oxidation reactions of relevance to biology and chemical synthesis. Herein we describe iron( iv )–tosylimido complexes [Fe IV (NTs)(MePy 2 tacn)](OTf) 2 ( 1(IV)NTs ) and [Fe IV (NTs)(Me 2 (CHPy 2 )tacn)](OTf) 2 ( 2(IV)NTs ), (MePy 2 tacn = N -methyl- N , N -bis(2-picolyl)-1,4,7-triazacyclononane, and Me 2 (CHPy 2 )tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1(IV)NTs and 2(IV)NTs are rare examples of octahedral iron( iv )–imido complexes and are isoelectronic analogues of the recently described iron( iv )–oxo complexes [Fe IV (O)(L)] 2+ (L = MePy 2 tacn and Me 2 (CHPy 2 )tacn, respectively). 1(IV)NTs and 2(IV)NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, 1 H-NMR, resonance Raman, Mössbauer, and X-ray absorption (XAS) spectroscopy as well as by DFT computational methods. Ferric complexes [Fe III (HNTs)(L)] 2+ , 1(III)–NHTs (L = MePy 2 tacn) and 2(III)–NHTs (L = Me 2 (CHPy 2 )tacn) have been isolated after the decay of 1(IV)NTs and 2(IV)NTs in solution, spectroscopically characterized, and the molecular structure of [Fe III (HNTs)(MePy 2 tacn)](SbF 6 ) 2 determined by single crystal X-ray diffraction. Reaction of 1(IV)NTs and 2(IV)NTs with different p -substituted thioanisoles results in the transfer of the tosylimido moiety to the sulphur atom producing sulfilimine products. In these reactions, 1(IV)NTs and 2(IV)NTs behave as single electron oxidants and Hammett analyses of reaction rates evidence that tosylimido transfer is more sensitive than oxo transfer to charge effects. In addition, reaction of 1(IV)NTs and 2(IV)NTs with hydrocarbons containing weak C–H bonds results in the formation of 1(III)–NHTs and 2(III)–NHTs respectively, along with the oxidized substrate. Kinetic analyses indicate that reactions proceed via a mechanistically unusual HAT reaction, where an association complex precedes hydrogen abstraction. 

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3. Organometallic Ni( ii ), Ni( iii ), and Ni( iv ) complexes relevant to carbon–carbon and carbon–oxygen bond formation reactions

   https://doi.org/10.1039/D1QI01486B  

   Magallón, C.; Griego, L.; Hu, C. H.; Company, A.; Ribas, X.; Mirica, L. M. (March 2022, Inorganic Chemistry Frontiers)

   Herein, the pyridinophanetetradentate ligand 3,6,9-trimethyl-3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene, PyNMe 3 , is used to isolate and structurally characterize well-defined organometallic Ni( ii ) and Ni( iii ) complexes bearing the cycloneophyl fragment, an alkyl/aryl C-donor ligand. Furthermore, spectroscopic and cryo-mass spectrometry studies suggest the formation of a transient Ni( iv ) organometallic complex, and its relevance to C–C and C–O bond formation reactivity studies is discussed. 

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4. Bimetallic nickel-lutetium complexes: tuning the properties and catalytic hydrogenation activity of the Ni site by varying the Lu coordination environment

   https://doi.org/10.1039/C8SC04712J  

   Ramirez, Bianca L.; Sharma, Prachi; Eisenhart, Reed J.; Gagliardi, Laura; Lu, Connie C. (March 2019, Chemical Science)

   We present three heterobimetallic complexes containing an isostructural nickel center and a lutetium ion in varying coordination environments. The bidentate iPr2PCH2NHPh and nonadentate (iPr2PCH2NHAr)3tacn ligands were used to prepare the Lu metalloligands, Lu( i Pr 2 PCH 2 NPh) 3 ( 1 ) and Lu{( i Pr 2 PCH 2 NAr) 3 tacn} ( 2 ), respectively. Reaction of Ni(COD) 2 (where COD is 1,5-cyclooctadiene) and 1 afforded NiLu( i Pr 2 PCH 2 NPh) 3 ( 3 ), with a Lu coordination number (CN) of 4 and a Ni–Lu distance, d (Ni–Lu), of 2.4644(2) Å. Complex 3 can further bind THF to form 3-THF , increasing both the Lu CN to 5 and d (Ni–Lu) to 2.5989(4) Å. On the other hand, incorporation of Ni(0) into 2 provides NiLu{( i Pr 2 PCH 2 NAr) 3 tacn} ( 4 ), in which the Lu coordination environment is more saturated (CN = 6), and the d (Ni–Lu) is substantially elongated at 2.9771(5) Å. Cyclic voltammetry of the three Ni–Lu complexes shows an overall ∼410 mV shift in the Ni(0/I) redox couple, suggesting tunability of the Ni electronics across the series. Computational studies reveal polarized bonding interactions between the Ni 3d z2 (major) and the Lu 5d z2 (minor) orbitals, where the percentage of Lu character increases in the order: 4 (6.0% Lu 5d z2 ) < 3-THF (8.5%) < 3 (9.3%). All three Ni–Lu complexes bind H 2 at low temperatures (−30 to −80 °C) and are competent catalysts for styrene hydrogenation. Complex 3 outperforms 4 with a four-fold faster rate. Additionally, adding increasing THF equivalents to 3 , which would favor build-up of 3-THF , decreases the rate. We propose that altering the coordination sphere of the Lu support can influence the resulting properties and catalytic activity of the active Ni(0) metal center. 

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5. Synthesis, characterization, and electrocatalytic activity of bis(pyridylimino)isoindoline Cu( ii ) and Ni( ii ) complexes

   https://doi.org/10.1039/D0DT03030A  

   Saha, Soumen; Sahil, Sha Tamanna; Mazumder, Md. Motiur; Stephens, Alexander M.; Cronin, Bryan; Duin, Evert C.; Jurss, Jonah W.; Farnum, Byron H. (January 2021, Dalton Transactions)

   null (Ed.)

   Two NNN pincer complexes of Cu( ii ) and Ni( ii ) with BPI Me − [BPI Me − = 1,3-bis((6-methylpyridin-2-yl)imino)isoindolin-2-ide] have been prepared and characterized structurally, spectroscopically, and electrochemically. The single crystal structures of the two complexes confirmed their distorted trigonal bipyramidal geometry attained by three equatorial N-atoms from the ligand and two axially positioned water molecules to give [Cu(BPI Me )(H 2 O) 2 ]ClO 4 and [Ni(BPI Me )(H 2 O) 2 ]ClO 4 . Electrochemical studies of Cu( ii ) and Ni( ii ) complexes have been performed in acetonitrile to identify metal-based and ligand-based redox activity. When subjected to a saturated CO 2 atmosphere, both complexes displayed catalytic activity for the reduction of CO 2 with the Cu( ii ) complex displaying higher activity than the Ni( ii ) analogue. However, both complexes were shown to decompose into catalytically active heterogeneous materials on the electrode surface over extended reductive electrolysis periods. Surface analysis of these materials using energy dispersive spectroscopy as well as their physical appearance suggests the reductive deposition of copper and nickel metal on the electrode surface. Electrocatalysis and decomposition are proposed to be triggered by ligand reduction, where complex stability is believed to be tied to fluxional ligand coordination in the reduced state. 

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