A Boron Activating Effect Enables Cobalt-Catalyzed Asymmetric Hydrogenation of Sterically Hindered Alkenes

Peter Viereck, Simon Krautwald, Tyler P. Pabst, Paul J. Chirik

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

Unsymmetric 1,1-diboryl alkenes bearing one -[BPin] (BPin = pinacolatoboryl) and one -[BDan] (BDan = 1,8-diaminonaphthalatoboryl) substituent each were hydrogenated in high yield and enantioselectivity using C1-symmetric pyridine(diimine) (PDI) cobalt complexes. High activities and stereoselectivities were observed with an array of 2-alkyl-, 2-aryl-, and 2-boryl-substituted 1,1-diboryl alkenes, giving rise to enantioenriched diborylalkane building blocks. Systematic study of substrate substituent effects identified competing steric and electronic demands in the key activating role of the boron substituents, whereby sterically unencumbered boronates such as -[BDan], -[BCat] (BCat = catecholatoboryl), and -[Beg] (Beg = ethylene glycolatoboryl) promote the hydrogenation of trisubstituted alkenes by enabling irreversible α-boron-directed insertion pathways to achieve otherwise challenging hydrogenations of trisubstituted alkenes. Deuterium-labeling studies with 1,1-diboryl alkenes support an insertion pathway generating a chiral intermediate with two different boron substituents and cobalt bound to the same carbon.

Original languageEnglish (US)
Pages (from-to)3923-3930
Number of pages8
JournalJournal of the American Chemical Society
Volume142
Issue number8
DOIs
StatePublished - Feb 26 2020

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Biochemistry
  • Catalysis
  • Colloid and Surface Chemistry

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