../  1  2

CATALYSIS AND SUPRAMOLECULAR CHEMISTRY

 

Elaboration of catalytic systems avoiding
cyclodextrin / phosphine association

 

 

 

 

Use of anionic β-CDs

Another possibility was to use anionic β-CDs in the presence of TPPTS. In particular, a sulfobutylated CD derivative with an average molar substitution degree of 7 has been used (the sulfobutylated groups are randomly positioned on the primary and secondary faces – Figure 3). No strong interaction was observed because of electrostatic repulsions between the CD anionic groups and the TPPTS sulfonate groups. However, during the course of the Tsuji-Trost and hydroformylation reactions, the presence of this CD did not allow to reach similar catalytic activity to those obtained with the most effective CD, namely the Rame-β-CD, (CD partially substituted by methyl groups; among the 21 hydroxyles, 12.6 on average are substituted by methyl groups). Actually, we demonstrated that this anionic CD did not adsorb at the aqueous/organic interface.

 

Figure 3 : anionic β-CD	Figure 4 : anionic methylated β-CD

 

Use of an anionic methylated β-CD

We then synthesized the heptakis(2,3-di-O-methyl-6-O-sulfopropyl)β-CD (Figure 4), an anionic CD having surface active properties. Interestingly, the absence of interaction with TPPTS is a consequence of the permethylation on the CD secondary face and does not result from electrostatic repulsions. In terms of activity, this CD is much more efficient than Rame-β-CD. From a selectivity point of view, the intrinsic properties of the catalytic system are fully preserved as the chemo- and regio-selectivities are identical to those observed without mass transfer promoter in the hydroformylation reaction [P2].

 

Use of a rigid diphosphine

Another possibility consists in using a rigid diphosphine with a strong chelating ability such as sulfoxantphos. We demonstrated that the native β-CD and Rame-β-CD are not capable to decoordinate the diphosphine from the metal.

 

 

The Rame-β-CD / sulfoxantphos association has been studied in the hydroformylation reaction of 1-decene. The presence of Rame-β-CD classically implies an increase in the conversion and chemo-selectivity but also an improvement of the regio-selectivity. This increase in the n/i ratio results both from the inability of Rame-β-CD to decoordinate a phosphorus atom from the rhodium and from the steric hindrance generated by the sulfoxantphos ligand around the rhodium [P1].

 

 

Publications :

 

• P 1. Sulfonated Xantphos ligand and methylated cyclodextrin: a winning combination for rhodium catalysed hydroformylation of higher olefins in aqueous medium.

  L. Leclercq, F. Hapiot, S. Tilloy, K. Ramkisoensing, J. N. H. Reek, P. W. N. M. van Leeuwen, E. Monflier,
  Organometallics 24 (2005) 2070-2075.

• P 2. Heptakis(2,3-di-O-methyl-6-O-sulfopropyl)-β-cyclodextrin : a genuine supramolecular carrier for Aqueous Organometallic Catalysis.

  D. Kirschner, T. Green, F. Hapiot, S. Tilloy, L. Leclercq, H. Bricout, E. Monflier,
  Adv. Synth. Catal. 348 (2006) 379-386.

 

../    1   2

Top