A new ground-state organic electron donor has been prepared that features four strongly π-donating iminophosphorano substituents on a bispyridinylidene skeleton. Cyclic voltammetry reveals a record redox potential of −1.70 V vs. saturated calomel electrode (SCE) for the couple involving the neutral organic donor and its dication. This highly reducing organic compound can be isolated (44 %) or more conveniently generated in situ by a deprotonation reaction involving its readily prepared pyridinium ion precursor. This donor is able to reduce a variety of aryl halides, and, owing to its redox potential, was found to be the first organic donor to be effective in the thermally induced reductive S–N bond cleavage of N,N-dialkylsulfonamides, and reductive hydrodecyanation of malonitriles.

Four members of a new family of powerful bispyridinylidene organic reducing agents have been prepared, which exploit iminophosphorano (-N=PR3; R = Ph, Cy) π-donor substituents. Electrochemical studies show exceptionally high oxidation potentials, ranging from 1.30 to 1.51 V versus SCE. These new reductants were shown to effectively convert 1-bromonaphthalene to naphthalene under mild reaction conditions. From the redox potentials, substituent constants (σp(+)) for the iminophosphorano groups Ph3P=N- (-1.82) and Cy3P=N- (-2.21) were determined, demonstrating their superior π-donating properties compared to traditional amino substituents.

The development of molecular catalysts and materials that can convert carbon dioxide (CO2) into a value-added product is a great chemical challenge. Molecular catalysts set benchmarks in catalyst investigation and design, but their incorporation into solid-state materials, and optimization of the electrochemical operating conditions, is still needed. For example, rhenium­(I) diimine catalysts show almost quantitative selectivity for the conversion of CO2 to carbon monoxide (CO) in acetonitrile (MeCN), but the modification of diimine backbones can be challenging if the goal is to incorporate such molecules into materials. Presented here is a rhenium­(I) complex with a 2-(2′-quinolyl)­benzimidazole (QuBIm-H) ligand, where N-alkylation with a pyrene derivative allows access to a catalyst that can be adsorbed onto electrodes for aqueous CO2 reduction chemistry. The rhenium­(I) catalysts are inactive for homogeneous CO2 reduction in MeCN. However, when adsorbed on edge-plane graphite, the same complexes show good activity for heterogeneous aqueous CO2 reduction, with 90% selectivity for CO. Comparative electrochemical studies between covalent and noncovalent modification of the graphite surfaces were also carried out for related rhenium­(I) tricarbonyl complexes.

A series of ClRe(CO)3-containing complexes with 1-methyl-1H-benzo[d]imidazol-2-yl)quinoline (Me-QuBIm), 1-benzyl-1H-benzo[d]imidazol-2-yl)quinoline (Bn-QuBIm), and 2-(1-(4-methoxybenzyl)-1H-benzo[d]imidazol-2-yl)quinoline (OMeBn-QuBIm) ligands were prepared and characterized. Each complex was characterized using 1H and 13C NMR, infrared, UV–vis, and fluorescence spectroscopies, and cyclic voltammetry. The physical properties of each complex are similar to the parent ClRe(CO)3(2-(1H-benzo[d]imidazol-2-yl)quinoline) complex. However, the electrochemical behavior is distinct from the parent, showing reversible voltammograms and poor CO2 reduction activity. Addition of K+ or Mg2+ as Lewis acids modestly increases catalytic currents, but at large overpotentials. The work presented here is consistent with a mechanism that involves rhenium reduction and deprotonation of imidazole and benzimidazole prior to CO2 reduction electrocatalysis.

Bis(cyclopentadienyl)aluminum and -gallium species of the type (Pytsi)ECp2 [E = Al (2a), Ga (2b); Pytsi = C(SiMe3)2SiMe2(2-C5H4N)] have been prepared from NaCp and respective dichlorides (Pytsi)ECl2 in isolated yields of 65% (2a) and 83% (2b). In addition to applying standard methods of characterization (NMR spectroscopy, CHN analysis, and MS), the molecular structures of both compounds were solved by single-crystal X-ray crystallography. Reactions between 2a or 2b with Zr(NMe2)4 in benzene, followed by addition of an excess of ClSiMe3, gave the first ansa-zirconocene dichlorides with aluminum (4a) or gallium (4b) in bridging position. The gallium compound 4b was isolated in a yield of 40% and characterized by NMR spectroscopy, CHN analysis, and mass spectrometry. The aluminum species 4a could not be obtained in an analytically pure form; it was characterized by NMR spectroscopy, and its molecular structure was determined by single-crystal X-ray analysis. The angle between the two planes of the Cp ligands in 4a was found to be 57.17(11)°, which is larger than in Cp2ZrCl2 (α = 53.5°) and smaller than in silicon-bridged ansa-zirconocene dichlorides (e.g., Me2Si(C5H4)2ZrCl2: α = 60.1°). Crystallization attempts of 4a from DCCl3 solutions gave crystals of the new species (Pytsi)AlCl[(C5H4)ZrCp] (7), which was characterized by NMR spectroscopy and single-crystal X-ray analysis. In comparison to the Pytsi-containing species 2a and 2b, the less sterically protected compound [2-(Me2NCH2)C6H4]AlCp2 (6), which was prepared from NaCp and [2-(Me2NCH2)C6H4]AlCl2 in yields of 94% and characterized by standard methods (NMR, CHN, and MS), reacted with Zr(NMe2)4 to give the known Cp2Zr(NMe2)2. The targeted ansa-species was not formed, as judged by 1H NMR spectroscopy. The gallium-bridged compound 4b and Cp2ZrCl2, respectively, had been tested for polymerizations of ethylene utilizing MAO as an activator (300 equiv of MAO; 5 or 10 μmol of precatalyst; 15 or 70 psi), resulting in activities of 637 to 1080 for 4b and of 640 to 2601 kg PE (mol Zr)−1 h−1 atm−1 for Cp2ZrCl2.