1-Alkali-metal-2-alkyl-1,2-dihydropyridines: Soluble Hydride Surrogates for Catalytic Dehydrogenative Coupling and Hydroboration Applications

Ross McLellan, Alan R. Kennedy, Robert E. Mulvey, Samantha A. Orr, Stuart D. Robertson

Research output: Contribution to journalArticleResearchpeer-review

27 Citations (Scopus)

Abstract

Equipped with excellent hydrocarbon solubility, the lithium hydride surrogate 1-lithium-2-tert-butyl-1,2-dihydropyridine (1tLi) functions as a precatalyst to convert Me2NH⋅BH3 to [NMe2BH2]2 (89 % conversion) under competitive conditions (2.5 mol %, 60 h, 80 °C, toluene solvent) to that of previously reported LiN(SiMe3)2. Sodium and potassium dihydropyridine congeners produce similar high yields of [NMe2BH2]2 but require longer times. Switching the solvent to pyridine induces a remarkable change in the dehydrocoupling product ratio, with (NMe2)2BH favoured over [NMe2BH2]2 (e.g., 94 %:2 % for 1tLi). Demonstrating its versatility, precatalyst 1tLi was also successful in promoting hydroboration reactions between pinacolborane and a selection of aldehydes and ketones. Most reactions gave near quantitative conversion to the hydroborated products in 15 minutes, though sterically demanding carbonyl substrates require longer times. The mechanisms of these rare examples of Group 1 metal-catalysed processes are discussed.

Original languageEnglish
Pages (from-to)16853-16861
Number of pages9
JournalChemistry - A European Journal
Volume23
Issue number66
DOIs
Publication statusPublished - 27 Nov 2017
Externally publishedYes

Keywords

  • catalysis
  • dehydrocoupling
  • hydroboration
  • lithium
  • main group

Cite this