A series of five [Rh­(P2N2)2]+ complexes (P2N2 = 1,5-diaza-3,7-diphosphacyclooctane) have been synthesized and characterized: [Rh­(PPh 2NPh 2)2]+ (1), [Rh­(PPh 2NBn 2)2]+ (2), [Rh­(PPh 2NPhOMe 2)2]+ (3), [Rh­(PCy 2NPh 2)2]+ (4), and [Rh­(PCy 2NPhOMe 2)2]+ (5). Complexes 1–5 have been structurally characterized as square planar rhodium bis-diphosphine complexes with slight tetrahedral distortions. The corresponding hydride complexes 6–10 have also been synthesized and characterized, and X-ray diffraction studies of HRh­(PPh 2NBn 2)2 (7), HRh­(PPh 2NPhOMe 2)2 (8) and HRh­(PCy 2NPh 2)2 (9) show that the hydrides have distorted trigonal bipyramidal geometries. Equilibration of complexes 2–5 with H2 in the presence of 2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo­[3,3,3]­undecane (Verkade’s base) enabled the determination of the hydricities and estimated pK a’s of the Rh­(I) hydride complexes using the appropriate thermodynamic cycles. Complexes 1–5 were active for CO2 hydrogenation under mild conditions, and their relative rates were compared to that of [Rh­(depe)2]+, a nonpendant-amine-containing complex with a similar hydricity to the [Rh­(P2N2)2]+ complexes. It was determined that the added steric bulk of the amine groups on the P2N2 ligands hinders catalysis and that [Rh­(depe)2]+ was the most active catalyst for hydrogenation of CO2 to formate.

We report the synthesis, characterization, and catalytic CO2 reduction activity of two LMn­(CO)3Br complexes with carbene-pyridine-carbene pincer ligands, [MnCNCMe]Br 1 and [MnCNCBn]Br (Bn = benzyl) 2. X-ray crystallography reveals an octahedral coordination environment with an outer sphere Br anion for 1. Catalyst 2 performs the reduction of CO2 to CO at 100 mV more positive potential with similar current densities as 1. We hypothesize the bulkier benzyl arms on the pincer hinder formation of a dimer. They also alter the wingtip electronics, enabling operation at a lower overpotential. We use normal pulse voltammetry and diffusion ordered spectroscopy to quantify a 1e– reduction per manganese center at the catalytic onset. We now show turnover even in the absence of added protons..

Two 1,5-diaza-3,7-diphosphacyclooctane (P 2 N 2 ) ligands with alkyl-substituted phosphines have been synthesized via a versatile method that allows for improved control of the phosphine substituent. The methyl-and benzylsubstituted phosphine P 2 N 2 ligands (P Me 2 N Ph 2 and P Bn 2 N Ph 2 ) were synthesized and characterized by 31 P{ 1 H} NMR, 1 H NMR, and elemental analysis, and their corresponding [Ni(P R 2 N Ph 2 ) 2 ](BF 4 ) 2 complexes were synthesized and characterized by 31 P{ 1 H} NMR, 1 H NMR, and electrochemistry. The structure of the complex [Ni(P Me 2 N Ph 2 ) 2 ](CF 3 SO 3 ) 2 was characterized by X-ray crystallography.

Electroanalytical methods have become central tools for the development of molecular redox chemistry in the context of energy sciences and synthetic methods. Cyclic voltammetry (CV) is a routine diagnostic method for the measurement of the equilibrium potential of a redox couple. When electrochemical processes are reversible, CV may be used to determine the number of electrons involved in the redox transition. However, on the timescale of the measurement, redox couples can appear distorted due to short lifetimes of ion radicals or coupled chemical processes. In these cases, the number of electrons involved in a redox process is unclear when following the most commonly available methods. With the advent of a renaissance in electrochemistry‐based synthetic methods, we report a method based on combination of techniques: Normal Pulse Voltammetry (NPV) and a routine NMR experiment: Diffusion Ordered Spectroscopy (DOSY) to enable the determination of the number of electrons, n for a redox transition of such a couple. These two measurements provide an expeditious way to determine n using commonly available equipment.

The phosphanylbipyridine ligands 6‐(diphenylphosphanyl)‐4,4′‐dimethyl‐2,2′‐bipyridine (PPh2‐Me2‐bipy, a), 4,4′‐di‐tert‐butyl‐6‐(diphenylphosphanyl)‐2,2′‐bipyridine (PPh2‐tBu2‐bipy, b), and 6‐(diisopropylphosphanyl)‐2,2′‐bipyridine (PiPr2bipy, c) and the corresponding dinuclear copper complexes [Cu2(μ‐PPh2‐Me2‐bipy)2(NCCH3)2](PF6)2 (1), [Cu2(μ‐PPh2‐tBu2‐bipy)2(NCCH3)2](PF6)2 (2), [Cu2(μ‐PiPr2bipy)2(μ‐NCCH3)](PF6)2 (3), and [Cu2(μ‐PiPr2bipy)2{μ‐CNCH(CH3)2}](PF6)2 (4) were synthesized. The X‐ray structures of 1–4 show that the complexes are dinuclear with the bidentate bipyridine coordinating to one copper atom and the phosphane moiety coordinating the other copper center. Complexes 3 and 4 possess short Cu–Cu distances with bridging acetonitrile and isocyanide ligands. The cyclic voltammograms of 1–4 were examined under N2 and CO2. Under N2, 1–3 show four quasi‐reversible 1e– reductions, and under CO2, they show current enhancement at the second reduction. In comparison, complex 4 shows four irreversible reductions under N2 and no current enhancement under CO2.