High-activity cobalt catalysts for alkene hydroboration with electronically responsive terpyridine and α-diimine ligands

W. Neil Palmer, Tianning Diao, Iraklis Pappas, Paul J. Chirik

Research output: Contribution to journalArticle

Abstract

Cobalt alkyl complexes bearing readily available and redox-active 2,2′:6′,2″-terpyridine and α-diimine ligands have been synthesized, and their electronic structures have been elucidated. In each case, the supporting chelate is reduced to the monoanionic, radical form that is engaged in antiferromagnetic coupling with the cobalt(II) center. Both classes of cobalt alkyls proved to be effective for the isomerization-hydroboration of sterically hindered alkenes. An α-diimine-substituted cobalt allyl complex proved exceptionally active for the reduction of hindered tri-, tetra-, and geminally substituted alkenes, representing one of the most active homogeneous catalysts known for hydroboration. With limonene, formation of an η3-allyl complex with a C-H agostic interaction was identified and accounts for the sluggish reactivity observed with diene substrates. For the terpyridine derivative, unique Markovnikov selectivity with styrene was also observed with HBPin. (Figure Presented).

Original languageEnglish (US)
Pages (from-to)622-626
Number of pages5
JournalACS Catalysis
Volume5
Issue number2
DOIs
StatePublished - Feb 6 2015

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Alkenes
Cobalt
Olefins
Ligands
Catalysts
Bearings (structural)
Styrene
Isomerization
Electronic structure
Derivatives
Substrates

Keywords

  • Boronates
  • Catalysis
  • Cobalt
  • Hydroboration
  • Redox-active ligands

ASJC Scopus subject areas

  • Catalysis

Cite this

High-activity cobalt catalysts for alkene hydroboration with electronically responsive terpyridine and α-diimine ligands. / Palmer, W. Neil; Diao, Tianning; Pappas, Iraklis; Chirik, Paul J.

In: ACS Catalysis, Vol. 5, No. 2, 06.02.2015, p. 622-626.

Research output: Contribution to journalArticle

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AU - Palmer, W. Neil

AU - Diao, Tianning

AU - Pappas, Iraklis

AU - Chirik, Paul J.

PY - 2015/2/6

Y1 - 2015/2/6

N2 - Cobalt alkyl complexes bearing readily available and redox-active 2,2′:6′,2″-terpyridine and α-diimine ligands have been synthesized, and their electronic structures have been elucidated. In each case, the supporting chelate is reduced to the monoanionic, radical form that is engaged in antiferromagnetic coupling with the cobalt(II) center. Both classes of cobalt alkyls proved to be effective for the isomerization-hydroboration of sterically hindered alkenes. An α-diimine-substituted cobalt allyl complex proved exceptionally active for the reduction of hindered tri-, tetra-, and geminally substituted alkenes, representing one of the most active homogeneous catalysts known for hydroboration. With limonene, formation of an η3-allyl complex with a C-H agostic interaction was identified and accounts for the sluggish reactivity observed with diene substrates. For the terpyridine derivative, unique Markovnikov selectivity with styrene was also observed with HBPin. (Figure Presented).

AB - Cobalt alkyl complexes bearing readily available and redox-active 2,2′:6′,2″-terpyridine and α-diimine ligands have been synthesized, and their electronic structures have been elucidated. In each case, the supporting chelate is reduced to the monoanionic, radical form that is engaged in antiferromagnetic coupling with the cobalt(II) center. Both classes of cobalt alkyls proved to be effective for the isomerization-hydroboration of sterically hindered alkenes. An α-diimine-substituted cobalt allyl complex proved exceptionally active for the reduction of hindered tri-, tetra-, and geminally substituted alkenes, representing one of the most active homogeneous catalysts known for hydroboration. With limonene, formation of an η3-allyl complex with a C-H agostic interaction was identified and accounts for the sluggish reactivity observed with diene substrates. For the terpyridine derivative, unique Markovnikov selectivity with styrene was also observed with HBPin. (Figure Presented).

KW - Boronates

KW - Catalysis

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KW - Hydroboration

KW - Redox-active ligands

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