New Functional Cyclic Aminomethylphosphine Ligands for the Construction of Catalysts for Electrochemical Hydrogen Transformations

Abstract

Eight-membered cyclic functional bisphosphines, namely 1,5-di-aryl-3,7-di(2-pyridyl)-1,5-diaza-3,7-diphosphacyclooctanes (aryl=2-pyridyl, m-tolyl, p-tolyl, diphenylmethyl, benzyl, (R)-(+)-(α-methyl)benzyl), with 2-pyridyl substituents on the phosphorus atoms have been synthesized by condensation of 2-pyridylphosphine, formaldehyde, and the corresponding primary amine. The structures of some of these bisphosphines have been investigated by X-ray crystallography. The bisphosphines readily form neutral P,P-chelate complexes [(κ(2)-P,P-L)MCl2], cationic bis-P,P-chelate complexes [(κ(2)-P,P-L)2 M](2+), or a five-coordinate complex [(κ(2)-P,P-L)2 NiBr]Br. The electrochemical behavior of two of the nickel complexes, and their catalytic activities in electrochemical hydrogen evolution and hydrogen oxidation, including the fuel-cell test, have been studied.

Nickel Complexes of Pyridine‐Functionalized N‐Heterocyclic Carbenes: Syntheses, Structures, and Activity in Electrocatalytic Hydrogen Production

“…The five‐coordinate geometry of the nickel ion in 1a is not rare; five‐coordinate geometries can be divided into two categories: the trigonal bipyramid and the tetragonal pyramid . The square‐pyramidal geometry is commonly formed with pentadentate chelating ligands, or from a combination of tridentate and bidentate chelating ligands , .…”

“…It appears that the nickel compounds with a benzimidazole‐based carbene ligand are more readily reduced with less negative half‐wave potentials (–1.53 V, –1.55 V) than those with the imidazole‐based carbenes (–1.66 V, –1.71 V), indicating the imidazole‐based ligands to be slightly more electron‐donating. The redox potentials of these nickel compounds with the relatively hard pyridyl ligands occur at rather negative potentials compared to Ni centers that are coordinated with softer phosphane ligands , …”

Organometallic Polymer Electrolyte Membrane Fuel Cell Bis‐Ligand Nickel(Ii) Complex of 1,5‐Di‐P‐Tolyl‐3,7‐Dipyridine‐1,5,3,7‐Diazadiphosphacyclo‐Octane Catalyst

“…A binding event between the two proximal Cu centers and a single O 2 molecule was proposed to form a Cu 2 O 2 intermediate species. It was established that a proper electronic environment of the bound O 2 is important for the substrate directing the proton transport. In particular, a targeted proton transfer is required for the selective O‐O reactivity, while the specific protonation of the O 2 ‐carrying superoxo adduct bypasses the formation of peroxo‐type adducts by facilitation of the multielectron processes.…”

“…[37] Ther eduction of an O 2 speciesl igated by two proximal Cu I (phenC) sites suggested that two Cu I species were necessary for the efficient four-electron reduction of O 2 . [38] Ab inding event between the two proximal Cu centers and as ingle O 2 molecule was proposed to form aC u 2 O 2 intermediates pecies.I tw as established [40] that ap roper electronic environment of the bound O 2 is important for the sub- In the Figure 4aschematic representation of the reactions on the anode and cathode sides of the PEMFC,c atalyzed by the immobilized [Ni(P Py 2 N 3 p-Tol…”

“…Synthesis of the complex [Ni(P Py 2 N p-Tol 2 ) 2 ] 2 + ·2[BF 4 ] À has been described previously. [39][40]…”