Influence of Ligand Substitution Pattern on Structure in Cobalt(II) Complexes of Bulky N , N′ ‐Diarylformamidinate N ‐Oxides

Ligand-Based Reactivity of Oxygenation and Alkylation in Cobalt Complexes Binding with (Thiolato)phosphine Derivatives

In our efforts to understand the nature of metal thiolates, we have explored the chemistry of cobalt ion supported by (thiolato)phosphine ligand derivatives. Herein, we synthesized and characterized a square-planar Co^II complex binding with a bidentate (thiolato)phosphine ligand, Co(PS1″)₂ (1) ([PS1″]^- = [P(Ph)₂(C₆H₃-3-SiMe₃-2-S)]^-). The complex activates O₂ to form a ligand-based oxygenation product, Co(OPS1″)₂ (2) ([OPS1″]^- = [PO(Ph)₂(C₆H₃-3-SiMe₃-2-S)]^-). In addition, an octahedral Co^III complex with a tridentate bis(thiolato)phosphine ligand, [NEt₄][Co(PS2*)₂] (3) ([PS2*]^2- = [P(Ph)(C₆H₃-3-Ph-2-S)₂]^2-), was obtained. Compound 3 cleaves the C-Cl bond in dichloromethane via an S-based nucleophilic attack to generate a chloromethyl thioether group. Two isomeric products, [Co(PS2*)(PSS^CH₂Cl*)] (4 and 4') ([PSS^CH₂Cl*]^- = [P(Ph)(C₆H₃-3-Ph-2-S)(C₆H₃-3-Ph-2-SCH₂Cl)]^-), were isolated and fully characterized. Both transformations, oxygenation of a Co^II-bound phosphine donor in 1 and alkylation of a Co^III-bound thiolate in 3, were monitored by spectroscopic methods. These reaction products were isolated and fully characterized. Density functional theory (DFT, the B3LYP functional) calculations were performed to understand the electronic structure of 1 as well as the pathway of its transformation to 2.

Coverage-Dependent Structural Transformation of Cyano-Functionalized Porphyrin Networks on Au(111) via Addition of Cobalt Atoms

The self-assembly process of a cobalt-porphyrin derivative (Co-TCNPP) containing cyanophenyl substituents at all four meso positions on Au(111) was studied by means of scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) under ultrahigh vacuum conditions. Deposition of Co-TCNPP onto Au(111) gave rise to the formation of a close-packed H-bonded network, which was independent of coverage as revealed by STM and LEED. However, a coverage-dependent structural transformation took place upon the deposition of Co atoms. At monolayer coverage, a reticulated long-range ordered network exhibiting a distinct fourfold Co coordination was observed. By reduction of the molecular coverage, a second metal-organic coordination network (MOCN) was formed in coexistence with the fourfold Co-coordinated network, that is, a chevron structure stabilized by a simultaneous expression of H-bonding and threefold Co coordination. We attribute the coverage-dependent structural transformation to the in-plane compression pressure exerted by the molecules deposited on the surface. Our study shows that a subtle interplay between the chemical nature of the building blocks (molecules and metallic atoms) and molecular coverage can steer the formation of structurally different porphyrin-based MOCNs.

Electro- and Photocatalytic Generation of H2 Using a Distinctive CoII "PN3 P" Pincer Supported Complex with Water or Saturated Saline as a Hydrogen Source

Efficient electrocatalytic production of H₂ from mixed water/acetonitrile solutions was achieved using three new Co^II complexes supported by the neutral pincer ligand bis(diphenylphosphino)-2,6-di(methylamino)pyridine ("PN₃ P"). At -1.9 V vs. Fc/Fc⁺ , these catalysts showed 96 % Faradaic efficiency with added water or saturated aqueous saline at rates of up to 316 L(mol cat)^-1 (cm² )^-1  h^-1 using a glassy carbon working electrode. The complex [Co(κ³ -2,6-{Ph₂ PNMe}₂ (NC₅ H₃ )Br₂ ] (1) was also able to photocatalytically reduce water to hydrogen in the presence of a Ru(bpy)₃²⁺ photosensitizer and a reductant.

Synthesis and characterization of metallo-supramolecular polymers from thiophene-based unimers bearing pybox ligands

A series of novel metallo-supramolecular polymers was prepared, based on 2,6-bis(2-oxazolinyl)pyridine chelating groups bridged with thiophene, bithiophene and thienothiophene as a linker, beginning from commercially available (chelidamic) acid.

Spin-state diversity in a series of Co(ii) PNP pincer bromide complexes

We describe the structural and electronic impacts of modifying the bridging atom in a family of Co(ii) pincer complexes with the formula Co(t-Bu)₂P^EPy^EP(t-Bu)₂Br₂ (Py = pyridine, E = CH₂, NH, and O for compounds 1–3, respectively).