Electrochemistry of substituted salen complexes of nickel(II): Nickel(I)-catalyzed reduction of alkyl and acetylenic halides

Metal-Salens As Catalysts In Electroreductive Cyclization and Electrohydrocyclization: Computational and Experimental Studies

“…10,11 Further examination of the Ni(II)-salen orbitals in the present work reveals that the LUMO+1 is low-lying (2.84 kcal/mol above the LUMO) and even more ligand-based than the LUMO. The first metal-based orbital is the LUMO+2 at 16.73 kcal/mol above the LUMO; given this large energy gap, it is unlikely for this metal-based orbital to play any role in the reduction of Ni(II)-salen.…”

Catalytic reduction of 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(methoxybenzene) (methoxychlor) with nickel(I) salen electrogenerated at reticulated vitreous carbon cathodes

“…Electrochemical cells, instrumentation, and procedures for cyclic voltammetry are described in previous publications [36,38]. Short lengths of glassy carbon rod (Grade GC-20, Tokai Electrode Manufacturing Company, Tokyo, Japan) were press-fitted into machined Teflon tubes to construct planar, circular working electrodes with geometric areas of 0.071 cm 2 ; electrical connection to each electrode was made through a stainless-steel rod which was inserted into the opposing open end of each Teflon tube.…”

“…Short lengths of glassy carbon rod (Grade GC-20, Tokai Electrode Manufacturing Company, Tokyo, Japan) were press-fitted into machined Teflon tubes to construct planar, circular working electrodes with geometric areas of 0.071 cm 2 ; electrical connection to each electrode was made through a stainless-steel rod which was inserted into the opposing open end of each Teflon tube. These cathodes were polished with an aqueous suspension of 0.05-μm aluminum oxide on a Master-Tex (Buehler) polishing pad, as previously described [36].…”

“…Instead, the catholyte exhibited a dark brownish-orange color, suggestive of the presence of nickel(II) salen or a modified form of nickel(II) salen. These observations led us to believe that modification of the nickel(I) salen catalyst occurs via addition of an intermediate species to an imino (C_N) bond of the salen ligand [22,27,28,31,[34][35][36]. Such a modified form of nickel(II) salen has a diminished capacity to catalyze the reduction of 1.…”

“…However, when one considers the catalytic reduction of methoxychlor, there is a distinct advantage to the use of electrogenerated nickel(I) salen [22]; the latter is not air-sensitive, which makes it more stable and easier to use than cobalt (I) salen. In previous research conducted in our laboratory, electrogenerated nickel(I) salen has been successfully employed for the catalytic dehalogenation of numerous organic species [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Most relevant to the present work is an earlier investigation [22] that utilized nickel(I) salen, electrogenerated at a reticulated vitreous carbon cathode, for the catalytic conversion of DDT to 4,4ʹ-(ethene-1,1-diyl)bis (chlorobenzene).…”