Cobalt mediated C–H bond functionalization: emerging tools for organic synthesis

Abstract

International audienceno abstrac

Cobalt(II)‐Catalyzed C−N Bond Formation: Synthesis of Aryl‐Substituted Imidazo[1,2‐a]pyridines

“…On the basis of the above experiments and previous literature reports, [24] we have proposed ap ossible reaction mechanism for2 -aryl imidazo[1,2-a]pyridines (Scheme 3). The in situ generated cobalt(III)s pecies (under O 2 atmosphere)m ay perform as a p-acid and nucleophilic additions of NH 2 and ap yridyl group to Co III ,p roduced cobalt(III) complex A.…”

“…For 3-arylimidazo[1,2-a]pyridines,i nitially imine was formed by the reactiono f2 -aminopyridine with phenylacetaldehyde under the present reaction conditions, which on tautomerization produced enamine D.T he in situ generated cobalt(III) species (under the oxygen atmosphere)u ndergoes nucleophilic addition with pyridyl and NH 2 groups, followed by coordination with enamine to produce Co III complex E. [24] Subsequently, alkene insertiong ave the alkenyl Co III complex F.N ext, reductive elimination can take place to deliver the desired product (3a)w ithc oncurrent formation of Co I species C.F inally,C o I is oxidizedt oC o II by oxygen to complete the catalytic cycle (Scheme 4).…”

Metal Coordination Complexes as Redox Mediators in Regenerative Dye-Sensitized Solar Cells

“…Co-based organometallic complexes tend to form stable compounds with a coordination number of CN = 6, adopting an octahedral geometry. Co is a versatile element that can be used in organic synthesis as a catalyst for a variety of reactions [84,85], for example as a water splitting homogenous catalyst [86,87], and as a potent building block for anticancer activity drugs [88].…”

Recent Developments in Cobalt Catalyzed Carbon–Carbon and Carbon–Heteroatom Bond Formation via C–H Bond Functionalization

“…In comparison with the cobalt-catalyzed direct Csp 2 -H bond functionalization, there are few examples of Csp 3 -H bond functionalization. 68 Reports of low-oxidation-state cobalt congeners that perform the cleavage of strong bonds remain sparse. 69 Brookhart 70 and Bradley 69a succeeded in developing the more challenging Co I -catalyzed Csp 3 -H bond activation with hydrogen transfer to form enamines.…”