Bite angle natural

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... 

Figure 10. Xantphos diphosphine family. Natural bite angles indicated.

We therefore evaluated how the bite angle affected regioselectivity, and studied the counterbalance of non-bonding and orbital effects. We choose two diphosphine ligands (benzoxantphos and homoxantphos) which among the series of xantphos ligands represent the extreme cases of natural bite angle, and used propene as a model for terminal aliphatic alkenes and styrene. 

Yamamoto and Casey separately reported that 2,5-dppm-nor 12 (Figure 8.9) while having a wide natural bite angle (126°) [59], gave an unexpectedly low l b ratio of only 2.6. This result was attributed to its inability to form stable... 

Figure 8 Xantphos derivatives and their natural bite angles.

Natural bite angle, isomeric ratio of LRh(CO)2H, normal ove iso ratio, normaZ-aldehyde product, isomerized product 2-octene, and turnover frequency were determined at 20% alkene conversion. 

Table 10 Natural bite angles, NMR chennical shifts, and Hammett parameter of Y in HRh(ligand)(CO)2 ...

The influence of the dihedral angle on the natural bite angle of Ru complexes bearing biaryl units such as Ci-TunePhos 7, as chiral ligands, has been studied by MM2 <2000JOC6223, 2003TL823> and density functional theory (DFT) methods <2005CCL1555>. 

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.,... 

MetaPLigand Natural bite angle, A C) TOP Lmear branched ratio... 

C. P. Casey, G. T. Whiteker, C. F. Campana, and D. R. Powell, Inorg. Chem., 29, 3376 (1990). Pentacoordinate Fe(CO), Complexes of Diphosphine Ligands with Natural Bite Angles Greater than 120°. 

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