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1. Diverse Coordination Geometries Derived from Trisaminocyclohexane Ligands with Appended Outer‐Sphere Hydrogen Bond Donors

   https://doi.org/10.1002/ejic.202300434  

   Ekanayake, Danushka M. ; Sheridan, Patrick E. ; Lindeman, Sergey V. ; Fiedler, Adam T. ( September 2023 , European Journal of Inorganic Chemistry)

   With the aim of constructing hydrogen‐bonding networks in synthetic complexes, two new ligands derived fromcis,cis‐1,3,5‐triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer‐sphere H‐bond donors. The TACH framework offers a facial arrangement of threeN‐donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X‐ray structural characterization of a series of Cu^I‐X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H₃L^R, R=pyrrole or indole) coordinate in the intended facialN₃manner, yielding four‐coordinate complexes with idealizedC₃symmetry. The N−H units of the outer‐sphere heterocycles form a hydrogen‐bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H₃L^pyrroleand H₃L^indolewith divalent transition metal chlorides (M^IICl₂, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer‐sphere H‐bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH‐based ligands with pendant H‐bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H‐bonding interactions.

    

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2. Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

   https://doi.org/10.1002/ange.201913259  

   Le, Trung ; Nguyen, Hao ; Perez, Lisa M. ; Darensbourg, Donald J. ; Darensbourg, Marcetta Y. ( January 2020 , Angewandte Chemie)

   With the goal of generating anionic analogues to MN₂S₂⋅Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂²⁻prepared from the Cys‐X‐Cys biomimetic, ema⁴⁻ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂resulted from loss of M originally residing in the N₂S₂⁴⁻pocket, replaced by protonation at the amido nitrogens, generating H₂ema²⁻. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂⁴⁻cavity holding a single metal, to a binucleating H₂ema²⁻with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂product. By computational studies we compared the conformations of “linear” ema⁴⁻to ema⁴⁻frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema²⁻that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.

    

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3. Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

   https://doi.org/10.1002/anie.201913259  

   Le, Trung ; Nguyen, Hao ; Perez, Lisa M. ; Darensbourg, Donald J. ; Darensbourg, Marcetta Y. ( January 2020 , Angewandte Chemie International Edition)

   With the goal of generating anionic analogues to MN₂S₂⋅Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂²⁻prepared from the Cys‐X‐Cys biomimetic, ema⁴⁻ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂resulted from loss of M originally residing in the N₂S₂⁴⁻pocket, replaced by protonation at the amido nitrogens, generating H₂ema²⁻. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂⁴⁻cavity holding a single metal, to a binucleating H₂ema²⁻with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂product. By computational studies we compared the conformations of “linear” ema⁴⁻to ema⁴⁻frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema²⁻that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.

    

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4. N 3 -Ligated nickel( ii ) diketonate complexes: synthesis, characterization and evaluation of O 2 reactivity

   https://doi.org/10.1039/d0dt01338b  

   Elsberg, Josiah G. ; Peterson, Austin ; Fuller, Amy L. ; Berreau, Lisa M. ( January 2020 , Dalton Transactions)

   Interest in O 2 -dependent aliphatic carbon–carbon (C–C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O 2 -dependent aliphatic C–C bond cleavage at ambient temperature in Ni( ii ) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl ( 7-Cl ; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt 3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni( ii ) diketonate complexes of the general formula [(TERPY)Ni(R 2 -1,3-diketonate)]ClO 4 ( 1 : R = CH 3 ; 2 : R = C(CH 3 ) 3 ; 3 : R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1 H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1 H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY) 2 Ni](ClO 4 ) 2 ( 4 ). Through selective crystallization 1–3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R 2 -1,3-diketonate)]X (X = ClO 4 : 5 : R = CH 3 ; 6 : R = C(CH 3 ) 3 ; 7-ClO4 : R = Ph; X = Cl: 7-Cl : R = Ph) using 1 H NMR and ESI-MS revealed the presence of [(MBBP) 2 Ni](ClO 4 ) 2 ( 8 ). Analysis of aerobic acetonitrile solutions of analytically pure 1–3 , 5 and 6 containing NEt 3 and in some cases H 2 O using 1 H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes ( 4 and 8 ) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3 , 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N 3 -ligated Ni( ii ) complexes of unsubstituted diketonate ligands do not exhibit O 2 -dependent aliphatic C–C bond clevage at room temperature, including in the presence of NEt 3 and/or H 2 O. 

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5. A linear cobalt(II) complex with maximal orbital angular momentum from a non-Aufbau ground state

   https://doi.org/10.1126/science.aat7319  

   Bunting, Philip C. ; Atanasov, Mihail ; Damgaard-Møller, Emil ; Perfetti, Mauro ; Crassee, Iris ; Orlita, Milan ; Overgaard, Jacob ; van Slageren, Joris ; Neese, Frank ; Long, Jeffrey R. ( December 2018 , Science)

   null (Ed.)

   Orbital angular momentum is a prerequisite for magnetic anisotropy, although in transition metal complexes it is typically quenched by the ligand field. By reducing the basicity of the carbon donor atoms in a pair of alkyl ligands, we synthesized a cobalt(II) dialkyl complex, Co(C(SiMe 2 ONaph) 3 ) 2 (where Me is methyl and Naph is a naphthyl group), wherein the ligand field is sufficiently weak that interelectron repulsion and spin-orbit coupling play a dominant role in determining the electronic ground state. Assignment of a non-Aufbau (d x 2 –y 2 , d xy ) 3 (d xz , d yz ) 3 (d z 2 ) 1 electron configuration is supported by dc magnetic susceptibility data, experimental charge density maps, and ab initio calculations. Variable-field far-infrared spectroscopy and ac magnetic susceptibility measurements further reveal slow magnetic relaxation via a 450–wave number magnetic excited state. 

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