Dinuclear Cp*Co Amido and Alkoxo Complexes: Synthesis, Structures, and Reactivity

Facile Transformations of a Binuclear Cp*Co(II) Diamidonaphthalene Complex to Mixed-Valent Co(II)Co(III), Co(III)(μ-H)Co(III), and Co(III)(μ-OH)Co(III) Derivatives

A diamido-bridged dicobalt complex supported by a diamidonaphthalene ligand, Cp*₂Co₂(μ-1,8-C₁₀H₈(NH)₂) (1), was synthesized, and the reactivity relevant to redox transformations of the Co₂N₂ core was investigated. It was found that the Co(II)-Co(II) bond allows for protonation by [HPPh₃][BF₄] resulting in a bridging hydride, [1H]⁺, with pK_a ∼ 7.6 in CH₂Cl₂. The diamidonaphthalene ligand can stabilize the binuclear system in the Co(II)Co(III) mixed-valent state (1⁺), which is capable of binding CO to afford [1-CO]⁺. Surprisingly, the mixed-valent complex also activates H₂O to furnish a Co(III)Co(III) hydroxy complex [1-OH]⁺ accompanied by release of H₂. The hydroxy ligand in [1-OH]⁺ is exchangeable, as demonstrated by ¹⁸O-labeling experiments on [1-OH]⁺ with H₂¹⁸O that led to the heavier isotopolog [1-¹⁸OH]⁺.

Recent advances in well-defined, late transition metal complexes that make and/or break C-N, C-O and C-S bonds

Chemical transformations that result in either the formation or cleavage of carbon-heteroatom bonds are among the most important processes in the chemical sciences. Herein, we present a review on the reactivity of well-defined, late-transition metal complexes that result in the making and breaking of C-N, C-O and C-S bonds via fundamental organometallic reactions, i.e. oxidative addition, reductive elimination, insertion and elimination reactions. When appropriate, emphasis is placed on structural and spectroscopic characterization techniques, as well as mechanistic data.

A density functional theory study of paramagnetic cyclopentadienylcobalt(III) derivatives: fluoride versus cyanide

The cobalt(III) complexes Cp₂Co₂F₄ and Cp₂Co₂(CN)₄ have been studied by density functional theory methods as representatives of the experimentally known Cp₂Co₂X₄ species with the weak-field fluoride ligand and the strong-field cyanide ligand. Both complexes were found to have relatively complicated energy surfaces with low-energy triplet and quintet spin state structures as well as the expected singlet-state structures for Co(III) complexes. This existence of singlet-, triplet-, and quintet-state structures of similar energies complicates the study of these complexes by density functional theory. The B3LYP* method of Reiher et al. was chosen in an effort to provide the most reliable estimates of the relative energies of the singlet, triplet, and quintet spin states. The lowest-energy Cp₂Co₂F₄ structure was found to be a doubly bridged quintet spin state structure, with similar triplet and singlet structures lying within ∼4 kcal mol⁻¹ of this quintet structure. The lowest-energy Cp₂Co₂(CN)₄ structure was found to be a triplet spin state structure, with a singlet structure lying within ∼1 kcal mol⁻¹ of this triplet structure. Almost all of the Cp₂Co₂X₄ structures were found to have nonbonding Co···Co distances in excess of 2.9 Å, as expected for Co(III) complexes. In general, structures with trans stereochemistry of the Cp and other terminal ligands were found to be of lower energy than the corresponding structures with cis stereochemistry.