Hydroformylation Bite angle

The catalytic hydroformylation of alkenes has been extensively studied. The selective formation of linear versus branched aldehydes is of capital relevance, and this selectivity is influenced by many factors such as the configuration of the ligands in the metallic catalysts, i.e., its bite angle, flexibility, and electronic properties [152,153]. A series of phosphinous amide ligands have been developed for influencing the direction of approach of the substrate to the active catalyst and, therefore, on the selectivity of the reaction. The use of Rh(I) catalysts bearing the ligands in Scheme 34, that is the phosphinous amides 37 (R ... 

Much progress has been made on regioselective hydroformylation of terminal alkenes in favor of the linear product. In particular bidentate phosphine or phosphite ligands, which have a natural bite angle 9 of about 110°, will favor the linear product. The most successful ligand types are BISBI [49, 50], BIPHEPHOS [51,52], and XANTPHOS systems (Scheme 8) [53]. 

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... 

Although early catalysts were based on cobalt, nowadays, rhodium catalysts are preferred because they require lower pressure and afford higher chemo- and regioselectivity [1,2]. In recent years, extensive research into the production of only linear aldehydes has provided impressive results. The application of phosphines with a wide bite angle in the rhodium catalyzed hydroformylation of terminal alkenes enable the regioselectivity to be almost totally controlled [3]. Branched selective hydroformylation, al-... 

Hydroformylation. The hydroformylation results for the series 15-24 are shown in Table 8.2 [60], From the table one can see that the selectivity for linear aldehyde increases with wider bite angles. For ligands 15-19 the l b ratio increases, but at higher bite angles the effect levels off. 

They constitute the first rhodium phosphine modified catalysts for such a selective linear hydroformylation of internal alkenes. The extraordinary high activity of 32 even places it among the most active diphosphines known. Since large steric differences in the catalyst complexes of these two ligands are not anticipated, the higher activity of 32 compared to 31 might be ascribed to very subtle bite angle effects or electronic characteristics of the phosphorus heterocycles. 

A water-soluble diphosphine ligand with large bite angle was prepared by controlled sulfonation of XANTHPHOS. The rhodium complex of the resulting (2,7-bis(S03Na)-XANTHPHOS (51) showed a catalytic activity in propene hydroformylation comparable to Rh/TPPTS (TOF 310 vs 500 h" at 120 °C, 9 bar propene and 10 bar CO/H2 = 1/1) [70]. The regioselectivity... 

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. 

Kamer. P.C.J.. van Leeuwen, P.W.N.M., Goubitz, K. and Fraanje, J. (1995) New diphosphine ligands based on heterocychc aromatics inducing very high regioselectivity in rhodium-catalyzed hydroformylation - Effect of the bite angle. Organometallics, 14, 3081-3089. 

A. L. (2000) Origin of the bite angle effect on rhodium diphosphine catalyzed hydroformylation. Organometallics, 19, 872-883. 

Casey, C.P., Whiteker, G.T., Melville, M.G., Petrovich, L.M., Gavney, J.A., Jr. and Powell, D.R. (1992) Diphosphines with natural bite angles near 120 Deg increase selectivity for n-aldehyde formation in rhodium-catalyzed hydroformylation. J. Am. Chem. Soc.,... 

To control the reaction, different precursors and ligands have been employed to gain selectively for only one aldehyde. The terminal aldehyde was obtained with ligands with bite angles near 120° and a stiff backbone, e.g., xantphos. The aldehydes with an internal double bond were obtained with a monodentate ligand, e.g., triphenylphosphine, with a selectivity of 83%. Double hydroformylation was observed with higher pressures and temperatures. 

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