Co(III) Complexes with N2S3-Type Ligands as Structural/Functional Models for the Isocyanide Hydrolysis Reaction Catalyzed by Nitrile Hydratase

Coordination of PPh3 with a [Mo2O2(μ-S)2]2+ Phosphinoyldithioformate Complex and Its Influence on Episulfide Sulfur Abstraction

Phosphinoyldithioformate ligands in binuclear molybdenum-sulfur complexes offer a synergistic environment for sulfur transfer (SAT) reactions. Relevant complex, 3, and its SCN- derivative, 4, as two salts 4a and 4b were formed. Reactions of 3, and 4b with cyclohexene sulfide (CS), styrene sulfide (SS), and propylene sulfide (PS) were studied. Different stabilities of 3 and 4b, as 4b > 3, allowed comparisons of reactivity based on the ability of the ligands to accommodate the episulfides. A moderate reactivity of CS, SS, and PS with 3 was arranged as CS > SS > PS, while its reactivity with 4b was negligible. The addition of PPh3 was found to increase the rate of reaction of 3 with CS to form Ph3PS. PPh3 reacted with SS and PS, to form Ph3PS and polythioether as SS < PS. PPh3 reacts with 3 to abstract a sulfur atom. The mechanism of the SAT reaction is proposed to take place in two steps to form a sulfurated complex followed by its sulfur expulsion, while the addition of PPh3 replaces the expulsion step with a faster Ph3PS formation. 3 was ascertained as an efficient catalyst and the nonrigid ligands accommodated the episulfides and PPh3 in their reactions without evident catalyst deactivation.

Formal 1,1-Hydrocyanation Reaction of Alkynyl Halides with Isocyanides Enabled by Dual Nickel/Base Catalysis Relay

We herein describe a formal 1,1-hydrocyanation reaction of alkynyl halides with isocyanides enabled by a dual nickel/base catalysis relay. tert-Butyl isocyanide serves as a "HCN" precursor that is introduced to the α-position of alkynyl halides, and the halogen atom is moved to the β-position. As a result, a series of (Z)-3-bromo/iodo acrylonitrile derivatives could be obtained in moderate yields. Mechanistic experiments were carried out, and the collective data could support our proposal of the mechanism details.

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.