Phosphite hgands

Deerenberg, S., Schrekker, H.S., van Strijdonck, G.P.F., Kamer, P.C.J., van Leeuwen, P.W.N.M., Fraanje, J, and Goubitz, K. (2000) New chiral phosphine-phosphite hgands in the enantioselective palladium-catalyzed allylic alkylation. 

Since the bisphosphine or monophosphine greatly accelerates the copper-catalyzed reaction [58], a survey of the known diphosphines was carried out and revealed that 0.5% of copper(II) triflate and 0.5% of phosphine are sufficient, although enantioselectivity was at the most 44% [59]. The chiral phosphite hgand based on tartrate 22 (Scheme 14) was also observed to exert the same hgand acceleration [60],but the ee was not so satisfactory [61]. 

These [6]-heterohelicene-based phosphite Hgands were also appHed to the asymmetric hydroformylation of terminal alkenes catalyzed by [Rh(acac)(CO)2] (11EJ03849). After optimization, the (+)-(P,S)-35... 

One of the commercial apphcations of bulky phosphites is the production of 3-methylpentane-11,5-diol by hydroformylation of 3-methylbut-3-en-l-01 by Kuraray [17]. Furthermore, they reported the use of bulky phosphite in the hydroformylation of vinyl acetate and 7-octenal, the latter providing an intermediate for the preparation of nonanediol. The high reactivity induced by bulky phosphite hgands has also led to the application of hydroformylation in the functionalization of natural product derivatives that are otherwise hardly reactive. Syntheses of important intermediates to fine-chemicals have been reported by hydroformylation of dihydroluran [18], glucal derivatives [19] and methyl oleate [20] (see also chapter 6 for further details). 

Remarkably, Claver et al showed that in a square planar rhodium carbonyl chloride complex two bulky phosphite hgands lb were able to coordinate in a trans orientation [19b]. This complex was isolated from the reaction mixture after performing hydroformylation in chlorinated solvent. The steric hindrance of the bulky ligands is less in the square planar trans complex than in the trigonal bipyramidal rhodium hydride. In the absence of CO pressure one of the carbonyl ligands can be replaced by a bulky... 

The catalyst discovered by Takaya et al. using (R,S) BINAPHOS, a phosphine-phosphite hgand of Ci symmetry [14] has provided ee s as high as 96% as well as total conversions and high regioselectivities. The origin of the stereodifferentiation in rhodium catalyzed hydroformylation has been discussed in theoretical reports [15, 16]. 

Nozaki, K. Sato, N. Tonomura, Y. Yasutomi, M. Takaya, H. Hiyama, T. Matsnbara, T Koga, N. Mechanistic aspects of the altemating copolymerization of propylene with carbon monoxide catalyzed by Pd(II) complexes of unsymmetiical phosphine-phosphite hgands. J. Am. Chem. Soc. 1997, 119,... 

Similar to water, alcohols can also attack phosphorous acid triesters. The reaction can be used for the synthesis of phosphite hgands by transesterification (see above), but they may also play a role in degradation processes, where alcohols produced from the reduction of product aldehydes interfere with the phosphite ligand. 

Very recently, Schmalz and coworkers [19] demonstrated the successful utilization of mixed Taddol-derived phosphine-phosphite hgands 2. Employing a mixture of trimethylsilyl cyanide (TMSCN) and MeOH for in situ generation of HCN, they obtained for the first time in high yielding conversions excellent enantiomeric excesses for substituted styrenes. The best results were reported for dexibuprofen precursor 6, with an enantiomeric excess of 92% and 100% isolated yield (Scheme 8.3). 

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