Bite angles, diphosphines

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] ... 

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... 

Recently, we [53] and others [54] simultaneously reported an example of a complex in which the transition metal dictates the coordination mode, viz. urea-functionalized phosphine 20, which forms a trans palladium complex, complemented by hydrogen bonding ofthe urea fragments (Figure 10.6). Bear in mind that any monophosphine, and even wide bite angle diphosphines, give trans complexes with a hydrocarbyl palladium halide. More interestingly, the urea moieties can function as a host for another halide ion. 

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. 

Lenero, K.A., Kranenburg, M., Guari, Y., Kamer, P.C.J., van Leeuwen, P.W.N.M., Sabo-Etienne, S. and Chaudret, B. (2003) Ruthenium dihydrogen complexes with wide bite angle diphosphines. Inorg. Chem., 42, 2859. 

Stereoselectivity in hydroformylation reactions, as a result of the supporting ligand set (e.g. large bite angle diphosphines or chiral diphosphines) or by stereocontrol of the substrate has also been discussed by Breit. Rhodium complexes supported by large bite angle diphosphines such as bisbi, biphephos and xantphos, shown in Scheme 10, are now well-established... 

Dudle B, Rajesh K, Blacque O, Berke H (2011) Rhcaiium nitrosyl complexes bearing large-bite-angle diphosphines. Organometallics 30 2986-2992... 

Another approach to large-bite-angle diphosphines was claimed by BASF [57]. First, l,2-bis(ort/zo-chlorophenyl)-substituted cyclic five- or six-membered backbones were constructed, which were eventually decorated with diphenylphosphino groups (Scheme 2.19). 

Scheme 2.19 Large-bite-angle diphosphines with a cydopentane backbone. 2.1.3...

Figure 5.3 Large-bite-angle diphosphines suitable for isomerization-hydroformylation.

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... 

Using bite angle considerations this should be interpreted as a bite angle effect, where rigid wide bite angle diphosphines produce a destabilizing effect on the transition states required for the undesired side reaction to take place. Based on the... 

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... 

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