Binuclear Ni Complexes Research Articles

Kinetic isotope effect offers selectivity in CO2 reduction.

A binuclear Ni complex with N,O donors catalyzes CO2 reduction via its Ni(I) state. The product distribution when H2O is used as a proton source shows similar yields for CO, HCOOH and H2. However, when D2O is used, the product distribution shows a ∼65% selectivity for HCOOH. In situ FTIR indicates that the reaction involves a Ni-COO* and a Ni-CO intermediate. Differences in H/D KIEs on different protonation pathways determine the selectivity of CO2 reduction.

Neutral Ni(II) and Cu(II) complexes of tetraazatetraenemacrocyles

A series of electron donors [neutral Ni(II) and Cu(II) complexes of tetraazatetraenemacrocyclic ligands] differing in metal ion, size of the macrocyclic ligand, and the length of the aliphatic bridges linking the macrocyclic units in dimeric species were synthesized and their redox, structural and spectroscopic properties were studied. The x-ray results for the donors under study show a nearly planar geometry of the monomeric tetraazamacrocyclic complexes and interesting ‘organic-zeolite-like’ structures of the dimers. The dimeric Ni complexes have flexible cavities between the two single ligands linked with aliphatic chains suitable for accommodating some small-sized guests. For the dimeric compounds the metal oxidation [M(II)/M(III)] takes place independently on each centre except one binuclear Ni complex, where the cooperativity of the metal centres was observed. Methyl substituents give rise to irreversibility of the oxidation process of the complexes studied. In the absence of these substituents neither reorganization nor ligand addition/elimination kinetics affect the electrode process. A common scale for the donors under study and some important acceptor compounds (p-benzoquinone, chloranil, tetracyanoethylene and tetracyanoquinodimethane, etc.) was proposed on the basis of their cyclic voltammetric behaviour in the same physicochemical conditions. Copyright © 2000 John Wiley & Sons, Ltd.

Reinvestigation of the nickel phosphine catalysed electrochemical synthesis of poly(2,5-pyridine). X-Ray crystal structures of [Ni2Br2(µ-5-BrC5H3N-C2,N)2(PPh3)2] and [PtBr(5-BrC5H3N-C2)(PPh3)2

Poly(2,5-pyridine) films have been deposited on glassy carbon, platinum and gold electrodes by the electroreduction of a novel binuclear nickel complex, trans(P,N)-bis[bromo(µ-5-bromopyridyl-C2,N)(triphenylphosphine) nickel(II)]. The synthesis, characterisation and electropolymerisation of this complex are described. The results from analytical and electrochemical investigations of poly(2,5-pyridine) are presented. The resultant poly(2,5-pyridine)-modified electrodes display electroactivity in their reduced state and co-ordinate nickel ions. The synthesis and electrochemistry of the analogous platinum and palladium complexes are also discussed.The X-ray crystal structures of the Ni and Pt complexes have been determined. The binuclear Ni complex contains Ni—(C5H4N)—Ni bridges, and the Ni atoms are also co-ordinated by one Br and one PPh3. The platinum complex is mononuclear with the Pt bound to the C2 of the pyridyl ring, to Br and to two trans PPh3 groups.