Syntheses of Four-Coordinate Nickel(II)-Phosphine Compounds and a Rapid Suzuki–Miyaura Cross-Coupling Reaction for Short Laboratory Sessions

Abstract

[NiBr2(PPh3)2] and [NiBr2(dppe)] are prepared from nickel bromide hydrate and phosphine. These brightly colored coordination compounds are then converted into the related organometallic compounds trans-[NiBr(Mes)(PPh3)2] and [NiBr(Mes)(dppe)] (Mes = 2,4,6-Me3C6H2) by reaction with the Grignard reagent MesMgBr. Characterization of the compounds is accomplished by a combination of UV–vis and multinuclear NMR spectroscopies. [NiBr(Mes)(dppe)] is a highly active precatalyst for the Suzuki–Miyaura cross-coupling of 4′-bromoacetophenone and phenylboronic acid. The catalytic reaction is complete in as little as 15–20 min with only a 1 mol % precatalyst loading, and the reaction can be carried out in air. Results are assessed by 1H NMR spectroscopy, or the solid 4-acetylbiphenyl product can be isolated following aqueous workup and recrystallization. The experiments are flexible and accommodate a variety of laboratory schedules and student skill levels. Each experimental component has been designed to be completed within a 3 h laboratory period.