Cr/Ni‐Catalyzed Vinylation of Aldehydes: A Mechanistic Study on the Catalytic Roles of Nickel and Chromium

Abstract

The roles of nickel and chromium catalysts in the coupling reaction of vinyl halides and aldehydes, the so-called Nozaki-Hiyama-Kishi (NHK) reaction, have been studied by UV/Vis spectroscopy, electrochemical, and spectroelectrochemical methods. Electrochemical studies revealed that nickel plays the central role in activating the vinyl halide by reductive cleavage, to form a rapidly decomposing vinyl-Ni species. The latter can, however, be stabilized in the presence of the Cr complex. The redox behavior of the Ni complexes in the presence of vinyl halide demonstrated that the vinyl halide activation results from interaction with a one-electron reduced nickel species [formally Ni(I) ], not necessarily with a Ni(0) species. It was furthermore shown by UV/Vis spectroscopy and spectroelectrochemical methods that low-valent nickel [Ni(0) ] results from the interaction of the Ni(II) catalyst with CrCl(2) .

Bimetallic Catalysis using Transition and Group 11 Metals: An Emerging Tool for CC Coupling and Other Reactions

“…[124] Recently the reaction mechanism of the Cr/Ni-catalyzed vinylation of aldehydes has been studied using electrochemical and spectroscopic (UV/Vis) methods. [125] These studies have confirmed that Ni II is reduced by Cr II , and have shown that the C À X activation takes place at the nickel center. It has not been established, however, whether the active nickel www.chemeurj.org species is Ni I or Ni 0 .…”

The cyclometalated nickel complex [(Phbpy)NiBr] (Phbpy− = 2,2′-bipyridine-6-phen-2-yl) – Synthesis, spectroscopic and electrochemical studies

“…Upon mixing of PhbpyBr and [Ni(COD) 2 ] in solution a deep purple colour was observed, which is due to the intermediate nickel (0) complex [(PhbpyBr)Ni(COD)] [10] (Scheme 1). During the next few minutes the colour of the mixture turn to bright red, which represents the cyclometalated product [(Phbpy)NiBr], formed through an oxidative addition (Scheme 1).…”

“…Mechanistic studies on these systems, but also on the Cr/Ni catalysed vinylation of aldehydes (NozakieHiyamaeKishi reaction) [9] showed that the Ni(II) pre-catalysts were reduced by one-electron steps to reactive Ni(II) species containing a reduced diimine ligand rather than having the character of a monovalent Ni(I) species [8,10]. Related diimine nickel complexes have also been applied in i) homogeneous electromediated reduction (HEMR) of olefins, ketons or alkyl halides [11]; ii) electrochemical carboxylation of bromostyrenes [12] or aziridines [13]; iii) electroreductive carbonylation of organic halides [14]; or iv) electroreductive coupling of olefins and polyhalo compounds [15].…”

Catalytic Asymmetric Synthesis of Allylic Alcohols and Derivatives and their Applications in Organic Synthesis

“…Recently, Klein, Berkessel, and co-workers used UV/Vis spectroscopy as well as electrochemical and spectroelectrochemical methods to study in detail the catalytic roles of nickel and chromium in the vinylation reaction (Scheme 72). [168] Since the seminal report of Fürstner et al, enantioselective Cr/Ni-mediated vinylation processes have been developed by the research groups of Kishi and Berkessel, who used chiral sulfonamide and salentype ligands, respectively (Figure 4). [163b] The main advantage of this Cr/Ni-mediated reaction compared to the methods discussed previously in this section is the high chemoselectivity of the organochromium reagents for aldehydes; however, the enantioselectivity of the process is often lower (see below).…”