title: Alkene Metalates as Hydrogenation Catalysts.
abstract: 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 H2activation. The substrate scope of the investigated precatalysts was also extended to polar substrates (ketones and imines).
authors.affiliation: Institute of Inorganic Chemistry, University of Regensburg, Universitätsstr. 31, 93040, Regensburg, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Büschelberger
authors.affiliation: Institute of Organic Chemistry, University of Regensburg, 93040, Regensburg, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Gärtner
authors.affiliation: Institute of Organic Chemistry, University of Regensburg, 93040, Regensburg, Germany.
authors.forename: Efrain
authors.initials: E
authors.lastname: Reyes-Rodriguez
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstr. 2, 37077, Göttingen, Germany.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Kreyenschmidt
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstr. 2, 37077, Göttingen, Germany.
authors.forename: Konrad
authors.initials: K
authors.lastname: Koszinowski
authors.affiliation: Institute of Organic Chemistry, University of Regensburg, 93040, Regensburg, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Jacobi von Wangelin
authors.affiliation: Institute of Inorganic Chemistry, University of Regensburg, Universitätsstr. 31, 93040, Regensburg, Germany.
authors.forename: Robert
authors.identifier: http://orcid.org/0000-0003-4066-6483
authors.initials: R
authors.lastname: Wolf
keywords: cobalt; hydrogenation; iron; reaction mechanisms; transition metals