Alkylation of [2,2′-([2,2′-bipyridine]-6,6′-diyl)bis[phenolato]-N,N′,O,O′]nickel(II) during catalytic reduction of 1-iodooctane

Electrochemical and catalytic properties of [2,2′-([2,2′-bipyridine]-6,6′-diyl)bis[phenolato]-N,N′,O,O′]nickel(II), 1, for the reduction of alkyl halides have been investigated in an attempt to find a more stable catalyst than nickel(II) salen-type complexes. Cyclic voltammetry of 1 in the presence of 1-iodooctane reveals that the nickel(II)–nickel(I) couple becomes irreversible, but that minimal catalytic activity is exhibited. This finding combined with a low turnover number, incomplete substrate reduction, and meager product yields from controlled-potential electrolyses indicates that electrogenerated [2,2′-([2,2′-bipyridine]-6,6′-diyl)bis[phenolato]-N,N′,O,O′]nickelate(I) is a poor catalyst. Analysis of post-electrolysis material by means of 1H NMR, HPLC, ESI–MS, and LC–MS techniques reveals that up to four alkyl moieties are incorporated into the structure of the original catalyst, leading to complete deactivation of the catalyst as determined from an examination of post-electrolysis solutions by means of cyclic voltammetry. Modest prevention of the alkylation can be accomplished by addition of a proton donor to the system. Mechanistic details of the modification and ways to prevent this modification are discussed.