Diphosphine trans-chelating

At an early stage, only for diphosphine ligands capable of trans-coordination were detected hydride solvate intermediates [71], but a catalytic pathway based on diphosphine trans-chelation has not been developed to date (see [80b]). 

Excellent ee-values (up to 94%) have been obtained for the hydrogenation of various 2-substituted N-acetyl indoles with an in-situ prepared rhodium catalyst modified with the trans-chelating diphosphine (S,S)-(R,R)-2,2"-bis[l-(diphenyl-phosphino)ethyl]-1,1"-biferrocene (Scheme 16.23) [88]. A strong base was required as co-reagent to observe both high conversion (TOFs of 50-100) and en-... 

Scheme 8 Rhodium complexes of trans-chelating diphosphine ligands...

In this fashion the metal complex should resemble the trans chelating diphosphine 1. (31)... 

The complete inhibition of CH3I oxidative addition observed in the case of trans chelating diphosphines complexes has been attributed to the fact that one of the axial sites of the rhodium center is blocked by the ligand backbone, avoiding the CH3I addition to proceed (Figure 1.3). 

The proposed catalytic cycle is analogous to that for the Monsanto process, but it involves neutral species with a trans-chelating diphosphine. Presumably, the isolated dinuclear compounds 62 a and 62 b act as resting states for the ace-... 

Hong FE, Chang YL et al (2004) Preparation and NMR studies of cobalt-containing diphosphine ligand chelated W, Ru, Au and Pd complexes Suzuki cross-coupling reactions and carbonylation catalyzed by the Pd complex. Dalton Trans 157-165... 

Kuwano R, Uemura T, Saitoh M, Ito Y (1999) Synthesis of a trans-chelating chiral diphosphine ligand with only planar chirality and its application to asymmetric hydrosilylation of ketones. Tetrahedron Lett 40 1327-1330... 

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 diphosphine disulfides of formula R2P(S)P(S)R2 take up a trans conformation in the solid state (see Section 5.2.3), upon coordination to a metal centre they can rearrange to adopt a cis conformation, hence facilitating bidentate chelation of the metal (e.g., Equation 78).117 In addition, a cis-bridging mode has also been proposed for these ligands in bi-metallic complexes.117... 

Jimenez-Rodriguez, C., Roca, F.X., Bo, C, Benet-Buchholz, )., Escudero-Adan, E.C., Ereixa, Z. and van Leeuwen, P.W.N.M. (2006) SPANphos trans-sparming diphosphines as cis chelating ligands . Dalton Trans., 268-278. 

The complexes ci -[PtCl(SnCl3)P2] may be obtained starting from either a cis-bis-phosphine complex of a tertiary aryl phosphine or a chelating diphosphine, e.g. PPh3 or DIOP complexes (20), (although careful examination of the P-31 spectra of the monodentate systems suggests that the trans isomer is also present). 

---