Effect of Pincer Methylation on the Selectivity and Activity in (PNP)Cobalt-Catalyzed C(sp2)-H Borylation

Boran Lee, Tyler P. Pabst, Paul J. Chirik

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Cobalt complexes supported by a tetramethylated PNP pincer ligand (Me4iPrPNP = 2,6-(iPr2PCMe2)2(C5H3N)) have been synthesized and structurally characterized. Examples include cobalt(I)-choride, -methyl, -aryl, and -benzofuranyl derivatives. The performance of these compounds was evaluated in the catalytic borylation of fluorinated arenes using B2Pin2 as the boron source. While P-C bond cleavage, a known deactivation pathway in [(PNP)Co]-catalyzed borylation, was suppressed, the overall activity and selectivity of the borylation of fluoroarenes was reduced as compared to the previously reported [(PNP)Co] catalyst lacking isopropylene spacers. Stoichiometric reactions support an increased barrier for oxidative addition to cobalt(I), a result of the increased steric profile and decreased conformational flexibility of the pincer resulting from methylation distal to the active site. With a more activated substrate such as benzofuran, catalytic borylation with cobalt(I) precatalysts and HBPin was observed. Monitoring the progress of the reaction by NMR spectroscopy revealed the presence of cobalt(III) intermediates during the course of the borylation, supporting a cobalt(I)-(III) redox cycle.

Original languageEnglish (US)
Pages (from-to)3766-3774
Number of pages9
JournalOrganometallics
Volume40
Issue number22
DOIs
StatePublished - Nov 22 2021

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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