Mechanistic Insights into the Directed Hydrogenation of Hydroxylated Alkene Catalyzed by Bis(phosphine)cobalt Dialkyl Complexes

Abstract

The mechanism of directed hydrogenation of hydroxylated alkene catalyzed by bis(phosphine)cobalt dialkyl complexes has been studied by DFT calculations. The possible reaction channels of alkene hydrogenation catalyzed by catalytic species (0, 0, and 0) were investigated. The calculated results indicate that the preferred catalytic activation processes undergo a 1,2 alkene insertion. 0 and 0 prefer the β hydrogen elimination mechanism with an energy barrier of 9.5 kcal/mol, and 0 prefers the reductive elimination mechanism with an energy barrier of 11.0 kcal/mol. The second H coordination in the σ bond metathesis mechanism needs to break the agostic H-βC bond of metal-alkyl intermediates (2 and 2), which owns the larger energetic span compared to the reductive elimination. This theoretical study shows that the most favorable reaction pathway of alkene hydrogenation is the β hydrogen elimination pathway catalyzed by the planar (dppe)CoH. The hydrogenation activity of Co(II) compounds with redox-innocent phosphine donors involves the Co(0)-Co(II) catalytic mechanism.

Cobalt-catalysed alkene hydrogenation: a metallacycle can explain the hydroxyl activating effect and the diastereoselectivity

“…2 ). 14 Our redox mechanism differs slightly, as we find that substrate coordination precedes addition of H 2 , and we conclude that the intermediate formed upon H 2 coordination prefers a Co(0)–H 2 structure over a Co( ii )–dihydride configuration (the dihydride is 2.6 kcal mol –1 higher in energy, Fig. S1, ESI † ).…”

“…2 ). 14 The proposed catalytic cycle starts with oxidative addition of H 2 to a Co(0) species generating a Co( ii )–dihydride, followed by substrate insertion to give an alkyl intermediate. The inter-mediate may undergo direct reductive elimination to yield the product alkane and regenerate Co(0) ( Fig.…”

Cobalt-catalyzed asymmetric hydrogenation of enamides enabled by single-electron reduction

“…3B) dichloride 2a and a Co(0) alkene complex, with the latter undergoing reaction with H 2 to enter the catalytic cycle. A notable pressure dependence was observed with 3a, as hydrogenation of 1 at 55 psi (3.7 atm) of H 2 resulted in only 38.5% yield after 72 hours, highlighting that H 2 is key to favor equilibria to generate and trap a Co(II) dihydride from 3a (21,24). Consistent with this hypothesis, the cobalt diene precursor 4a was effective at the lower H 2 pressure of 55 psi (3.7 atm) and produced levetiracetam in 99.1% yield and 97.5% ee (Fig.…”

“…The proposed mechanism of cobalt-catalyzed hydrogenation of dehydro-a-amino acid derivatives involves formation of a Co(II) dihydride as the active species that promotes alkene insertion ( Fig. 1E) (21). We wondered whether this potential intermediate could be accessed instead from H 2 oxidative addition to Co(0), a pathway reminiscent of Rh(I) and Ir(I) catalysis.…”

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

“…[20,21a-c] Fort he directed hydrogenation of terpinenol, [20] computational studies support formation of metallocycles arising from the Co II oxidation state being maintained throughout the catalytic cycle. [22] An alternative pathway involving am ore traditional Co 0 -Co II [23] cycle was also computed and while energetically reasonable,w as higher in energy than the metallocycle pathway and does not explain the observed diastereoselectivity.D espite these advances, cationic bis(phosphine) cobalt(I) complexes have remained elusive and motivated our studies to explore their catalytic performance and compare them to the neutral cobalt examples as well as the well-established rhodium congeners.…”