Catalytic reduction of 1-iodooctane by nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide: Effects of added proton donors and a mechanism involving both metal- and ligand-centered one-electron reduction of nickel(II) salen

Catalytic reduction of 1- and 2-bromooctanes by a dinickel(I) Schiff base complex containing two salen units electrogenerated at carbon cathodes in dimethylformamide

“…1 that the anodic and cathodic peak currents for 0.50 mM Ni 2 (II)L are less than those for 1.0 mM Ni(II) salen but more than those for 0.50 mM Ni(II) salen, suggesting that the diffusion coefficient of Ni 2 (II)L should be smaller than that of Ni(II) salen in DMF. On the basis of recent research [6][7][8], it also needs to be pointed out that the reduction of Ni 2 (II)L could be both metal-and ligand-centered (Scheme 1). Shown in Fig.…”

“…The catalytic electrochemical reaction usually involves the cleavage of carbon-halogen bonds to afford radical intermediates, which can undergo coupling, disproportionation, intramolecular cyclization [3], ring expansion [5], and abstraction of hydrogen atoms from the solvent to give various products. More recently, it has been discovered that the one-electron reduction of nickel(II) salen can be either metal-or ligand-centered [6][7][8] and alkylation can take place at the imino (C@N) bonds of the ligand. Consequently, the overall product yields are often much less than 100%.…”

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

“…In earlier work from our laboratory, it was found that these two states differ in energy by only 2--3 kcal mol − 1 , suggesting that 13 and 14 are both accessible electrochemically [35]. Accordingly, either 13 or 14 can attack 1 nucleophilically to expel a chloride ion to yield a methoxychlor radical intermediate and to regenerate 12 (Reaction 2).…”

“…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).…”