Bisphenolate ligands

Eilerts, N. W. Heppert, J. A. Bisphenol ligands in the stereocontrol of transformations catalyzed by titanium and tungsten. Polyhedron 1995,14, 3255-3271. 

Amgoune A, Thomas CM, Roisnel T, Carpentier JF. 2006. Ring-Opening Polymerization of Lactide with Group 3 Metal Complexes Supported by Dianionic Alkoxy-Amino-Bisphenolate Ligands Combining High Activity, Productivity, and Selectivity. Chem Eur J 12 169-179. 

Bismuth ligands, 2,989-1061 bonding, 2,1030-1041 7i bonding, 2, 1033-1039 trigonal bipyramidal complexes, 2,1036 Bismuth line, 3,294 Bismuthotungstates, 3, 1042 Bismuth pentafluoride, 3, 292 Bismuth tribromide, 3, 291 Bismuth trichloride, 3, 290 Bismuth trifiuoride, 3, 290 Bismuth triiodide, 3,292 Bismuth trioxide, 3,284 2,2 -Bisphenol metal complexes color photography, 6,109 Bis(trimethylene)triamine metal complexes, 2, 49 4,4 -Bi-l, 2,4-triazolyl metal complexes, 2, 89 polymers... 

The benzopyran ring is not essential for activity. The pyran oxygen can be substituted by nitrogen or can be eliminated in open-ring mono- or bisphenolic compounds. The recently developed CB2-selective ligand HU-308 (5) is an example of such a bicyclic cannabinoid (Hanus et al., 1999). 

The selectivity was found to be dependent on the exact ligand structure. Structures of rhodium hydridodicarbonyls were shown to contain a bis-equatorial coordination mode for bisphenol backbones, 1,3- and 1,4 diol backbones, but apical-equatorial for 1,2-diol based backbones. The latter always lead to low selectivities.217-220 Dimer formation was observed.221... 

Implementation of the C5, C5 -hydroxy lation protocol as described in Scheme 7.19 above (71/72 to 73/74) provided further efficiencies. The C5,C5 -chlorination proceeded uneventfully, but the chloro to alkoxy interchange was difficult and required optimization of the reaction conditions. The catalyst system derived from Pd2dba3 and the X-phos(t-Bu) ligand proved to be effective in the coupling with KOH to provide the desired bisphenol. The resulting product was highly unstable and decomposed under a one-pot alkylation protocol. Isolation of the bisphenol under carefully controlled conditions followed by immediate benzylation (BnBr, NaH, DMF) furnished key intermediate 79 in 70 % yield. 

Besides the phosphite ligands based on BINOL, phosphite ligands based on bisphenol are also used in rhodium-catalyzed hydrogenation. These ligands are shown in Scheme 28.7 and consist of a bisphenol with different substituents on the 3,3, 5,5, and 6,6 -positions. The ligands without substituents on the 6,6 -positions are only fluxionally chiral. The use of readily available chiral alcohols (21 aa-21 aj) such as menthol in combination with bisphenol was thought to induce one of the bisphenol conformations in preponderant amounts [49]. The... 

Scheme 28.7 Monodentate phosphite ligands derived from bisphenol.

However, it is possible that the heterocatalyst becomes the dominant one, either if it is more stable and thus formed in large excess, or if it is a more active, kinetically dominant catalyst. Recently, both Reetz et al. and Feringa/Min-naard/de Vries et al. have shown that this approach can be beneficial. Earlier attempts by Chen and Xiao using mixtures of monodentate phosphites based on bisphenol and a chiral alcohol were not successful [39]. In our experience, the majority of catalysts based on mixtures of monodentate ligands show a poorer performance than the individual homo-catalysts. However, in a few instances there is a positive effect. 

The results obtained for ligands 48 and 50, which contain only one fixed stereocentre, are interesting and very informative about the system. Ligand 48-(R,—), in which only the binaphthyl bridge has a predetermined absolute configuration R, leads to an e.e. of 83% (R-aldehyde), which is quite close to the value of 94% for (R,S)-BINAPHOS. This suggests that in the formation of the complex the binaphthyl bridge controls the conformation of the bisphenol... 

The dicopper(I) complex with dinucleating bisamino-bispyridine ligand 37 as well as the dicopper complex 38 were shown to couple 2,4-di-ferf-butylphenol to the corresponding bisphenol derivative (Eq. 22), while with 2,6-substituted phenols, oxidative coupling at the para-position was observed to yield the diphenoquinone derivatives (Eq. 23) [256,257]. Similar reactivity is observed for various other dicopper systems. 

But not only palladium(O) complexes can activate CO or O2, also palla-dium(II) complexes have been reported to be active in the presence of carbon monoxide or dioxygen as it was shown in the direct synthesis of polycarbonate from CO and phenol or bisphenol A [79,80]. The authors could confirm the positive influence of the NHC ligand comparing the activity and reactivity of the palladium-carbene complex with the corresponding PdBr2 catalyst. The molecular weights and yields of the polycarbonates improved with increasing steric hindrance of the substituents in the l,T-position of the car-bene complex. 

Asymmetric Olefin Hydrogenation Using Monodentate BINOL- and Bisphenol-Based Ligands Phosphonites, Phosphites, and Phosphoramidites... 

FIGURE 14.4 Monodentate phosphite ligands based on bisphenol. 

Tp = tris(pyrazolyl)borate derivative, L = bispyridine (X = NO) or bisphenolate (X = O) bridging ligands [68]. Because of the presence of only 25.5 % as hyperfine coupling-active nuclei Mo ( Mo with 15.9 % and Mo with 9.6 %, both with I = 5/2), the delocalization is evident from the approximately halved hyperfine coupling constants (as compared with mononuclear Mo species) and from the relative ESR intensities of lines corresponding to molecules with Mo- Mo, Mo-Mo and Mo-Mo isotope combinations [67, 68]. 

Bimetallic molybdenum nitrosyl complexes, (containing Mo(I), i.e. a 17e species) with conjugated bridging ligands of the bispyridine family, or the bisphenolate family, present widely separated reduction waves, as shown by McCleverty, Ward, and others [86], The separation can be observed with spacers containing up to four double bonds, or four phenylene units. 

Both diphosphite and diphosphine based catalysts have been reported that will even hydroformylate internal aUcenes to mainly linear products [26,27]. The ligands are based on bisphenol and Xantphos backbones shown in Fig. 6.3. 

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