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Alkene Metalates as Hydrogenation Catalysts
Author(s) -
Büschelberger Philipp,
Gärtner Dominik,
ReyesRodriguez Efrain,
Kreyenschmidt Friedrich,
Koszinowski Konrad,
Jacobi von Wangelin Axel,
Wolf Robert
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201605222
Subject(s) - alkene , chemistry , catalysis , homoleptic , styrene , homogeneous catalysis , ligand (biochemistry) , medicinal chemistry , cyclooctadiene , photochemistry , polymer chemistry , organic chemistry , metal , biochemistry , polymer , receptor , copolymer
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(η 4 ‐cod)(η 2 ‐styrene) 2 ] ( 5 ) and [K([18]crown‐6)][Co(η 4 ‐dct)(η 4 ‐cod)] ( 6 ), and the homoleptic complex [K(thf) 2 ][Co(η 4 ‐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 H 2 , 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 H 2 activation. The substrate scope of the investigated precatalysts was also extended to polar substrates (ketones and imines).