Well-Defined Cobalt(I) Dihydrogen Catalyst: Experimental Evidence for a Co(I)/Co(III) Redox Process in Olefin Hydrogenation

Among the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3 . Compared to related ruthenium and manganese complexes 7 and 8 , this optimal cobalt complex showed improved performance. DFT computations support an innocent non‐classical bifunctional outer‐sphere mechanism on the triplet state potential energy surface.

Section: Figurementioning

confidence: 99%

Cobalt‐Catalyzed Aqueous Dehydrogenation of Formic Acid

Zhou

Wei

Spannenberg

et al. 2019

“…Recently, the groups of Kempe and Kirchner used PNP pincer cobalt and iron complexes for selective hydrogenations of polar bonds with high tolerance of other unsaturated bonds . Moreover, effective cobalt catalysts based on NNP, PBP, and CCC pincers have been reported …”

Section: Introductionmentioning

confidence: 99%

Alkene Metalates as Hydrogenation Catalysts

Büschelberger

Gärtner

Reyes-Rodriguez

et al. 2017

First‐row transition‐metal complexes hold great potential as catalysts for hydrogenations and related reductive reactions. Homo‐ and heteroleptic arene/alkene metalates(1−) (M=Co, Fe) are a structurally distinct catalyst class with good activities in hydrogenations of alkenes and alkynes. The first syntheses of the heteroleptic cobaltates [K([18]crown‐6)][Co(η4‐cod)(η2‐styrene)2] (5) and [K([18]crown‐6)][Co(η4‐dct)(η4‐cod)] (6), and the homoleptic complex [K(thf)2][Co(η4‐dct)2] (7; dct=dibenzo[a,e]cyclooctatetraene, cod=1,5‐cyclooctadiene), are reported. For comparison, two cyclopentadienylferrates(1−) were synthesized according to literature procedures. The isolated and fully characterized monoanionic complexes were competent precatalysts in alkene hydrogenations under mild conditions (2 bar H2, r.t., THF). Mechanistic studies by NMR spectroscopy, ESI mass spectrometry, and poisoning experiments documented the operation of a homogeneous mechanism, which was initiated by facile redox‐neutral π‐ligand exchange with the substrates followed by H2 activation. The substrate scope of the investigated precatalysts was also extended to polar substrates (ketones and imines).

“…The catalytic activity of ( Mes CCC)CoI(N 2 )(PPh 3 ) 6a was tested in the reduction of styrene at room temperature. [27] At the end of the reaction( 2h), the dihydrogens pecies 6b was detected as ar estings tate of the catalytic cycle. This is probably the first case in which aw ell-definedh omogeneous cobalt-dihydrogen complexh as been used as an effective hydrogenation catalyst.…”

Section: Catalytic Reduction 21 Catalytic Hydrogenationmentioning

confidence: 98%

“…The catalytic activity of ( Mes CCC)CoI(N 2 )(PPh 3 ) 6 a was tested in the reduction of styrene at room temperature . At the end of the reaction (2 h), the dihydrogen species 6 b was detected as a resting state of the catalytic cycle.…”

Section: Catalytic Reductionmentioning

confidence: 99%

Cobalt–Pincer Complexes in Catalysis

Junge

Papa

Beller

2018

167

Non-noble metal catalysts based on pincer type compounds are of special interest for organometallic chemistry and organic synthesis. Next to iron and manganese, currently cobalt-pincer type complexes are successfully applied in various catalytic reactions. In this review the recent progress in (de)hydrogenation, transfer hydrogenation, hydroboration and hydrosilylation as well as dehydrogenative coupling reactions using cobalt-pincer complexes is summarised.