The Electrochemical Behaviour of Organonickel Complexes: Mono‐, Di‐ and Trivalent Nickel

Abstract

The redox properties of organometallic nickel complexes of the type [(α-diimine)

Cationic tris(pyrazolyl)borate bipyrimidine complexes

“…Cyclic voltammograms at lower scan rates reveal that the couple becomes increasingly irreversible, indicating that in both cases, the reduction is chemically irreversible. The lack of sufficient related nickel Tp R complexes makes comparisons difficult, but similar observations have been made for the bipyrimidine complex [(bpym)Ni(Mes)Br] which reduces irreversibly at -1.49 V [3].…”

“…2,2 0 -Bipyrimidine (bpym) is a useful ligand in coordination chemistry able to act as a chelating bidentate [1][2][3] or bridging bis-bidentate ligand [4][5][6][7][8][9][10][11][12][13][14]. [11,12].…”

Electron transfer in organonickel complexes of α-diimines: Versatile redox catalysts for C–C or C–P coupling reactions – A review

“…A reversible wave E 2 (E R2 /E O2 ) was observe after a first irreversible reduction wave (E R1 ) for the more basic ligands tmphen, dmbpy or bpy. The cathodic peak potentials E R1 and E R2 increase (shift positively) along the series tmphen > dmbpy > bpy > bpym > bpz > iPr-DAB > bpm [38]. This series represents decreasing basicity or increasing p-accepting ability, which goes along with low lying p * LUMOs, of the diimine ligand.…”

“…4) [37,38]. Quantum chemical calculations have revealed almost exclusively bpy p * -centred lowest unoccupied molecular orbitals (LUMO) for [Ni(Mes) 2 (bpy)] [35] and spectroelectrochemical investigations (UV-vis-NIR and EPR, see also later) have unequivocally proved the bpy-centred character of the reduced species [Ni(II)(Mes) 2 (bpy)] nÀ (n = 1 and 2) [37,38]. Oxidation of the complex leads to rapid decomposition.…”

“…A number of such complexes have been prepared independently either by electrochemical means [28,32,33] or by chemical methods (see Scheme 4, reaction A) [34][35][36][37]. In this latter case also other a-diimine ligands were introduced and the complexes were submitted to detailed studies of their electrochemical properties using electrochemical and spectroelectrochemical (UV-vis-NIR and EPR) methods [38]. Also their general chemical and physical properties were investigated by optical spectroscopy, XRD and EXAFS spectroscopy in combination with quantum chemical calculations [35][36][37].…”