Diphosphine ligands, wide bite angle

With the aim of rationalizing the effect of (wide) bite angle diphosphines in catalytic reactions a distinction can be made between two different effects, both related to the bite angle of diphosphine ligands [42] ... 

As bidentates seemed to give more stable complexes, and because trans configurations seemed to be favoured by some of the monodentates, Thomas and Suss-Fink investigated the use of ligands that are bidentate and can coordinate in a trans fashion [11,16], This has led to the development of new diphosphines based on condensation reactions of 2-diphenylphos-phinobenzoic acid with aminoalcohols or diols, reminiscent of the wide bite angle ligands used by Trost for the asymmetric allylic alkylation (Chapter 13.2). The best... 

A family of wide bite angle diphosphine ligands based upon xantphos (8) has been developed and tested in rhodium catalysed hydroformylation. van Leeuwen and co-workers conducted HP IR measurements on a range of Rh/thixantphos... 

Escudero-Adan, E.C., Freixa, Z. and van Leeuwen. P.W.N.M. (2007) Catalysis by design Wide-bite-angle diphosphines by assembly of ditopic ligands for selective rhodium-catalyzed hydroformylation. Angeiv. Chem., Int. Ed., 46. 7247—4750. 

In situ IR and NMR spectra showed that, indeed, the assembled diphosphine coordinates preferentially in the bis-equatorial, wide-bite-angle fashion to the penta-coordinated rhodium carbonyl hydride. Both homo- and heterocombinations of monophosphine ligands can be formed in situ by mixing the components several heterocombinations perform better as catalysts than the respective homocombinations. However, in contrast to the catalysts prepared by Takacs, the present complexes do not equilibrate to afford solely the heterocombination. 

The steric bulk of the diphosphine ligand hardly affects the barriers for methanolysis via the stepwise and concerted reductive elimination pathways. Based on these observations, it was postulated that the high activity and chemoselectivity in the methoxycarbonylation of ethene observed for t-butyl substituted wide bite angle diphosphine ligands are determined by a combination of electronic and steric effects induced by the diphosphine ligand. The high electron density at the metal center... 

Gompared to other wide-bite-angle diphosphine ligands, xantphos-type ligands can be modified easily while retaining their favorable properties, especially in hydroformylation, and as a result many derivatives have been synthesized by several groups and used in fluorous-phase hydroformylation catalysis, aqueous phase catalysis, one-phase hydroformylation and catalyst extraction, catalysis in ionic liquids, hydroformylation with immobilized catalysts, and catalysis in supercritical G02. ... 

Kamer PCJ, van Leeuwen PWNM, Reek JNH (2001) Wide bite angle diphosphines Xantphos ligands in transition metal complexes and catalysis. Acc Chem Res 34 895—904... 

Phosphacyclic diphosphines (73a) and (73b) with wide natural bite angles were synthesized and the effect of the phosphacyclic moieties on the coordination chemistry in the [(diphosphine) Rh(CO)2H] complexes was studied. Both NMR and IR spectroscopy showed that the phosphacyclic xantphos ligands exhibit an enhanced preference for diequatorial chelation compared to the diphenylphosphino-substituted parent compound. In the hydroformylation of 1-octene the introduction of the phosphacyclic moieties leads to higher reaction rates. The dibenzophospholyl- and phenoxaphosphino-substituted xantphos ligands exhibit a high activity and selectivity in the hydroformylation of trans-2- and 4-octene to linear nonanal. CO dissociation rates from the... 

The development of supported aqueous-phase catalysis (SAPC) [275, 276] is a new and efficient way to facilitate the hydroformylation of longer olefins. Most of the SAP catalysts described in the literature use TPPTS as ligand. Only a few sulfonated diphosphine ligands were examined [277]. A water-soluble chelating diphosphine ligand with a wide natural bite angle, based on a xanthene backbone, was studied as a SAP aqueous catalyst. This ligand showed a much better selectivity than the SAP catalysts known so far [278]. 

A water-soluble chelating diphosphine ligand (12) with a wide natural bite angle has been prepared [19a]. These hgands are known to form very selective catalysts for the hydroformylation of 1 -aUcenes, 5delding mainly linear aldehyde as the product. These ligands were also studied as supported aqueous phase catalysts and it was shown that these ligands performed well... 

---