Study of the effects of alkali metal salts on styrene hydroformylation reactions catalyzed by rhodium(I) complexes of bis(phosphite) ligands

Academic Article

Abstract

  • A functionalized α,ω-bis(phosphite-donor) ligand containing two amido groups, 8, has been prepared from tartaric acid. An in situ formed rhodium(I) metallacrown ether complex of 8 has been compared to an in situ formed rhodium(I) complex of (R,R)-Chiraphite for the hydroformylation of styrene. Both Rh(I) complexes are active catalysts, but the complex of (R,R)-Chiraphite exhibits a higher regioselectivity than does the metallacrown ether catalyst (iso/n of 10.1 versus 3.9) as expected. The additions of alkali metal salts to the hydroformylation reactions cause increases in the regioselectivities (approximately 2-fold for both LiBPh4·3dme and NaBPh4 for ligand 8; 3-fold for both LiBPh4· 3dme and NaBPh4 for (R,R)-Chiraphite) with virtually no effect on the activity. The facts that (1) no change in the iso/n ratio is observed upon addition of the noncoordinating salt, TBA·;BPh4, (2) LiBPh4·3dme has little effect on the regioselectivity of an in situ formed rhodium(I) complex of diphos, and (3) the increase in regioselectivity levels out at high salt:Rh ratios suggest the increase in regioselectivity is due to coordination of the alkali metal salt to the oxygen of a carbonyl ligand and to the phosphite oxygens during the regioselectivity-determining step. This proposal is consistent with the observation of only weak 1:1 coordination of LiBPh4·;3dme with a model metallacrown ether, Cw-Mo(CO)4(8) in acetonitrile-d 3. © 2008 American Chemical Society.
  • Authors

    Published In

  • Organometallics  Journal
  • Digital Object Identifier (doi)

    Pubmed Id

  • 10691802
  • Author List

  • Owens SB; Gray GM
  • Start Page

  • 4282
  • End Page

  • 4287
  • Volume

  • 27
  • Issue

  • 17