Chiral copper-bipyridine complexes: Synthesis, characterization and mechanistic studies on asymmetric cyclopropanation

Wing Sze Lee, Chi Tung Yeung, Kiu Chor Sham, Wing Tak Wong, Hoi Lun Kwong

Research output: Journal article publicationJournal articleAcademic researchpeer-review

14 Citations (Scopus)

Abstract

Chiral bipyridine ligands of different steric properties when reacted with CuCl2formed orange, yellow or green solids of new copper(II) complexes, [Cu(L)Cl2] (L = L2-6), in good yield. Together with [Cu(L1)Cl2], these complexes were characterized in solution by UV-Vis spectroscopy and cyclic voltammetry. The complexes give d-d transitions between 860 and 970 nm, and exhibit one quasi-reversible Cu(II)/Cu(I) couple between +0.405 V and +0.516 V versus NHE. Two of the copper(II) complexes, [Cu(L5)Cl2] and [Cu(L6)Cl2], and a copper(I) complex of L1, [Cu(L1)Cl], were characterized by X-ray crystallography. The triflate derivatives of both the Cu(I) and Cu(II) complexes are active catalysts towards the cyclopropanation of ethyl diazoacetate with styrene. The asymmetric induction suffers when the size difference between the alkyl and alkoxyl groups was minimized. The mechanism of the cyclopropanation was studied with kinetic and competition experiments. The rate is first order in catalyst and ethyl diazoacetate, inverse order with styrene and is strongly affected by the counterion.
Original languageEnglish
Pages (from-to)178-186
Number of pages9
JournalPolyhedron
Volume30
Issue number1
DOIs
Publication statusPublished - 12 Jan 2011
Externally publishedYes

Keywords

  • Asymmetric catalysis
  • Chiral bipyridines
  • Copper-bipyridine complexes
  • Cyclopropanation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Cite this