Catalytic Oxidation of Alcohol via Nickel Phosphine Complexes with Pendant Amines

Nickel complexes were prepared with diphosphine ligands that contain pendant amines, and these complexes catalytically oxidize primary and secondary alcohols to their respective aldehydes and ketones. Kinetic and mechanistic studies of these prospective electrocatalysts were performed to understand what influences the catalytic activity. For the oxidation of diphenylmethanol, the catalytic rates were determined to be dependent on the concentration of both the catalyst and the alcohol and independent of the concentration of base and oxidant. The incorporation of pendant amines to the phosphine ligand results in substantial increases in the rate of alcohol oxidation with more electron-donating substituents on the pendant amine exhibiting the fastest rates

Catalytic Oxidation of Alcohol via Nickel Phosphine Complexes with Pendant Amines

Nickel complexes were prepared with diphosphine ligands that contain pendant amines, and these complexes catalytically oxidize primary and secondary alcohols to their respective aldehydes and ketones. Kinetic and mechanistic studies of these prospective electrocatalysts were performed to understand what influences the catalytic activity. For the oxidation of diphenylmethanol, the catalytic rates were determined to be dependent on the concentration of both the catalyst and the alcohol and independent of the concentration of base and oxidant. The incorporation of pendant amines to the phosphine ligand results in substantial increases in the rate of alcohol oxidation with more electron-donating substituents on the pendant amine exhibiting the fastest rates

The Influence of the Second and Outer Coordination Spheres on Rh(diphosphine)₂ CO₂ Hydrogenation Catalysts

A series of [Rh­(PCH₂X^RCH₂P)₂]⁺ complexes was prepared to investigate second and outer coordination sphere effects on CO₂ hydrogenation catalysis, where X is CH₂ (dppp) or X–R is N–CH₃, N–CH₂COOH (glycine), N–CH₂COOCH₃ (Gly-OMe), or N–CH₂C­(O)­N–CH­(CH₃)­COOCH₃ (GlyAla-OMe). All of these complexes were active for CO₂ reduction to formate, with the N–CH₃ derivative offering an 8-fold enhancement over the dppp derivative, which is consistent with increased electron density around the metal. Despite the increase in rate with the addition of the pendant nitrogen, the addition of electron withdrawing amino acids and dipeptides to the amine resulted in complexes with reductions in rate of 1 to 2 orders of magnitude, most consistent with a change in p<i>K</i>_a of the pendant amine, resulting in lower activity. Collectively, the data suggest multiple contributions of the pendant amine in this catalytic system

Redox Pairs of Diiron and Iron–Cobalt Complexes with High-Spin Ground States

A series of iron and iron–cobalt bimetallic complexes were isolated: LFe₂Cl (<b>1</b>), LFe₂ (<b>2</b>), Li­(THF)₃[LFe₂Cl]­(Li­(THF)₃[<b>2-Cl</b>]), LFeCoCl (<b>3</b>), and LFeCo (<b>4</b>), where L is a trianionic tris­(phosphineamido)­amine ligand. As elucidated by single-crystal X-ray diffraction studies and quantum-chemical calculations, the Fe^IIFe^II and Fe^IICo^II complexes, <b>1</b> and <b>3</b>, respectively, have weak metal–metal interactions (the metal–metal distances are 2.63 and 2.59 Å, respectively) with a partial bond order of 0.5. The formally mixed-valent complexes, Fe^IIFe^I (<b>3</b>) and Fe^IICo^I (<b>4</b>), have short metal–metal bonds (2.32 and 2.26 Å, respectively) with a formal bond order of 1.5. On the basis of magnetic susceptibility measurements, complexes <b>1</b>–<b>4</b> are all paramagnetic with high-spin ground states, <i>S</i> = 3–4, which are proposed to arise from ferromagnetic coupling of the two metals’ spins through a direct exchange mechanism. Zero- and applied-field Mössbauer spectra corroborate the presence of distinct oxidation and spin states for the iron sites. The reduction potentials of <b>1</b> and <b>3</b> are −1.48 and −1.60 V (vs Fc⁺/Fc), respectively. Other characterization data are also reported for this series of complexes, electronic absorption spectra and anomalous X-ray scattering data

Redox Pairs of Diiron and Iron–Cobalt Complexes with High-Spin Ground States

A series of iron and iron–cobalt bimetallic complexes were isolated: LFe₂Cl (<b>1</b>), LFe₂ (<b>2</b>), Li­(THF)₃[LFe₂Cl]­(Li­(THF)₃[<b>2-Cl</b>]), LFeCoCl (<b>3</b>), and LFeCo (<b>4</b>), where L is a trianionic tris­(phosphineamido)­amine ligand. As elucidated by single-crystal X-ray diffraction studies and quantum-chemical calculations, the Fe^IIFe^II and Fe^IICo^II complexes, <b>1</b> and <b>3</b>, respectively, have weak metal–metal interactions (the metal–metal distances are 2.63 and 2.59 Å, respectively) with a partial bond order of 0.5. The formally mixed-valent complexes, Fe^IIFe^I (<b>3</b>) and Fe^IICo^I (<b>4</b>), have short metal–metal bonds (2.32 and 2.26 Å, respectively) with a formal bond order of 1.5. On the basis of magnetic susceptibility measurements, complexes <b>1</b>–<b>4</b> are all paramagnetic with high-spin ground states, <i>S</i> = 3–4, which are proposed to arise from ferromagnetic coupling of the two metals’ spins through a direct exchange mechanism. Zero- and applied-field Mössbauer spectra corroborate the presence of distinct oxidation and spin states for the iron sites. The reduction potentials of <b>1</b> and <b>3</b> are −1.48 and −1.60 V (vs Fc⁺/Fc), respectively. Other characterization data are also reported for this series of complexes, electronic absorption spectra and anomalous X-ray scattering data