Metalloradical Reactivity of RuI and Ru0 Stabilized by an Indole-Based Tripodal Tetraphosphine Ligand

Ruthenium-Catalyzed Regioselective Hydrohalogenation of Alkynes Mediated by Trimethylsilyl Triflate

Here we describe a ruthenium-catalyzed regioselective hydrohalogenation reaction of alkynes under mild conditions. Commercially simple halogen sources such as KI, ZnBr₂, and ZnCl₂ were employed to achieve this transformation. Alkynes derived from bioactive molecules such as l-(-)-borneol, l-menthol, and estrone were also suitable for the transformation, demonstrating the potential synthetic value of this new reaction in organic synthesis.

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

Two or more indole molecules tailored to a single non-metal central atom, through any of their C2–7 positions are not only structurally engaging but also constitute a class of important pharmacophores. Although the body of such multi-indolyl non-metallide molecules are largely shared to the anticancer agent bis(indolyl)methane, other heteroatomic analogs also possess similar medicinal properties. This concise review will discuss various catalytic and uncatalytic synthetic strategies adopted for the synthesis of the non-ionic (non-metallic) versions of these important molecules till date.

Metalloradical intermediates in electrocatalytic reduction of CO2 to CO: Mn versus Re bis-N-heterocyclic carbene pincers

This work examines the relative reactivities of Re^I and Mn^I tricarbonyl pyridine-2,6-bis-N-heterocyclic carbene pincers M(CO)₃CNC^BnX (M = Re, Mn and X = Cl and Br) towards catalysis for the electrochemical conversion of CO₂ to CO. Unlike prior well-studied group VII catalysts, Mn(CO)₃CNC^BnX is extraordinarily active, while the new Re(CO)₃CNC^BnX complex surprisingly does not exhibit catalytic response. DFT calculations shed light on this puzzling behavior and show that the redox-active pyridine-2,6-bis-N-heterocyclic carbene ligand facilitates the reduction of the ground-state complexes; however, the extent of electronic delocalization in the reduced intermediates differs in the degree of metalloradical character. The highly-active Mn(CO)₃CNC^BnX complex proceeds through an intermediate with nucleophilic metalloradical character in which 66% of the unpaired electron spin resides on Mn. In contrast, Re(CO)₃CNC^BnX reduction proceeds through an intermediate with less metalloradical character in which only 38% of the unpaired spin is localized on Re with the remainder delocalized over the ligand. The energetic penalty of the electron delocalization of an electron on the ligand affects the M-CO bond strengths and related kinetic barriers. We discuss these observations in the context of turnover-enabling effects in CO₂ reductions mediated by group VII NHC pincer molecular electrocatalysts.

Coordination of 3-Methylindole-Based Tripodal Tetraphosphine Ligands to Iron(+II), Cobalt(+II), and Nickel(+II) and Investigations of their Subsequent Two-Electron Reduction

We report the coordination chemistry of indole based tripodal tetraphosphine ligands to iron(II), cobalt(II) and nickel(II). These complexes are formed by simple synthetic protocols and were characterized by a combination of spectroscopic techniques and single-crystal X-ray analysis. The molecular structures as determined by X-ray diffraction show that the geometry of the nickel and cobalt complexes are distorted trigonal bipyramidal. The monocationic iron(II) complexes also have distorted trigonal bipyramidal geometries, but the dicationic analogue has an octahedral geometry. Two-electron reduction of the cobalt(+II) and the nickel(+II) complexes in the presence of N2 did not lead to the coordination of N2. In contrast, two-electron reduction of the iron(+II) complexes did lead to coordination of dinitrogen to the iron center. The Fe0N2L1H complex has a trigonal bipyramidal geometry, and the N-N bond length of the coordinated dinitrogen ligand is longer than that of free dinitrogen, indicating that coordination to this iron(0) complex results in activation of the N≡N bond.

Metalloradical Reactivity of RuI and Ru0 Stabilized by an Indole-Based Tripodal Tetraphosphine Ligand

The tripodal, tetradentate tris(1-(diphenylphosphanyl)-3-methyl-1H-indol-2-yl)phosphane PP3 -ligand 1 stabilizes Ru in the RuII , RuI , and Ru0 oxidation states. The octahedral [(PP3 )RuII (Cl)2 ] (2), distorted trigonal bipyramidal [(PP3 )RuI (Cl)] (3), and trigonal bipyramidal [(PP3 )Ru0 (N2 )] (4) complexes were isolated and characterized by single-crystal X-ray diffraction, NMR, EPR, IR, and ESI-MS. Both open-shell metalloradical RuI complex 3 and the closed-shell Ru0 complex 4 undergo facile (net) abstraction of a Cl atom from dichloromethane, resulting in formation of the corresponding RuII and RuI complexes 2 and 3, respectively.