Third-Generation W(CNAr)6 Photoreductants (CNAr = Fused-Ring and Alkynyl-Bridged Arylisocyanides).

Homoleptic tungsten(0) arylisocyanides possess photophysical and photochemical properties that rival those of archetypal ruthenium(II) and iridium(III) polypyridine complexes. Previous studies established that extending the π-system of 2,6-diisopropylphenylisocyanide (CNDipp) by coupling aryl substituents para to the isocyanide functionality results in W(CNDippAr)6 oligoarylisocyanide complexes with greatly enhanced metal-to-ligand charge transfer (MLCT) excited-state properties relative to those of W(CNDipp)6. Extending electronic modifications to delineate additional design principles for this class of photosensitizers, herein we report a series of W(CNAr)6 compounds with naphthalene-based fused-ring (CN-1-(2-iPr)-Naph) and CNDipp-based alkynyl-bridged (CNDippCCAr) arylisocyanide ligands. Systematic variation of the secondary aromatic system in the CNDippCCAr platform provides a straightforward method to modulate the photophysical properties of W(CNDippCCAr)6 complexes, allowing access to an extended range of absorption/luminescence profiles and highly reducing excited states, while maintaining the high molar absorptivity MLCT absorption bands, high photoluminescence quantum yields, and long excited-state lifetimes of previous W(CNAr)6 complexes. Notably, W(CN-1-(2-iPr)-Naph)6 exhibits the longest excited-state lifetime of all W(CNAr)6 complexes explored thus far, highlighting the potential benefits of utilizing fused-ring arylisocyanide ligands in the construction of tungsten(0) photoreductants.

Structure, Spectroscopy, and Electrochemistry of Manganese(I) and Rhenium(I) Quinoline Oximes.

Reactions of α- and ß-diimine quinoline aldoximes with Mn(I) and Re(I) tricarbonyl halides afford quinoline oxime complexes. Both Mn(I) and Re(I) complexes experience severe geometric strain due to ligand steric interactions: 6-membered metallocycles exhibit more pronounced distortions than 5-membered ones, consistent with density functional theory structural analyses. Such distortions likely also affect reactivity patterns, as evidenced by Re(I)-induced deoximation of a quinoline variant containing a CF3-ketoxime.

Electrocatalysis of CO2 Reduction in Brush Polymer Ion Gels.

The electrochemical characterization of brush polymer ion gels containing embedded small-molecule redox-active species is reported. Gels comprising PS-PEO-PS triblock brush polymer, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm-TFSI), and some combination of ferrocene (Fc), cobaltocenium (CoCp2(+)), and Re(bpy)(CO)3Cl (1) exhibit diffusion-controlled redox processes with diffusion coefficients approximately one-fifth of those observed in neat BMIm-TFSI. Notably, 1 dissolves homogeneously in the interpenetrating matrix domain of the ion gel and displays electrocatalytic CO2 reduction to CO in the gel. The catalytic wave exhibits a positive shift versus Fc(+/0) compared with analogous nonaqueous solvents with a reduction potential 450 mV positive of onset and 90% Faradaic efficiency for CO production. These materials provide a promising and alternative approach to immobilized electrocatalysis, creating numerous opportunities for application in solid-state devices.

Donor-acceptor ligand-to-ligand charge-transfer coordination complexes of nickel(II).

A family of charge-transfer chromophores comprising square-planar nickel(II) complexes with one catecholate donor ligand and one α-diimine acceptor ligand is reported. The nine new chromophores were prepared using three different catecholate ligands and three different α-diimine ligands. Single-crystal X-ray diffraction studies on all members of the series confirm a catecholate donor-nickel(II)-α-diimine acceptor electronic structure. The coplanar arrangement of donor and acceptor ligands manifests an intense ligand-to-ligand charge-transfer (LL'CT) absorption band that can be tuned incrementally from 650 nm (1.9 eV) to 1370 nm (0.9 eV). Electrochemical studies of all nine complexes reveal rich redox chemistry with two one-electron reduction processes and two one-electron oxidation processes. For one dye, both the singly reduced anion and the singly oxidized cation were prepared, isolated, and characterized by EPR spectroscopy to confirm ligand-localization of the redox processes. The optical and electrochemical properties of these new complexes identify them as attractive candidates for charge-transfer photochemistry and solar-energy conversion applications.

Bench-Stable 2-Halopyridinium Ketene Hemiaminals as Reagents for the Synthesis of 2-Aminopyridine Derivatives.

2-Chloro-1-(1-ethoxyvinyl)pyridinium triflate and several other bench-stable N-(1-alkoxyvinyl) 2-halopyridinium triflates have been developed as reagents for the synthesis of valuable 2-aminopyridine scaffolds via unusually mild SNAr substitutions with amine nucleophiles. Advantages of this approach include an operationally simple mix-and-stir procedure at room temperature or mild heat and ambient atmosphere and without the need for transition metal catalysts, coupling reagents, or high-boiling solvents. The stable N-(1-ethoxyvinyl) moiety serves as a dual SNAr-activating group and pyridine N-protecting group that can be cleaved under thermal, acidic, or oxidative conditions. Preliminary results of other nucleophilic substitutions using oxygen-, sulfur-, and carbon-based nucleophiles are also demonstrated.