Dibenzophosphole selective

Improved variations were described in a later patent [39], Instead of diphenylphosphino groups dibenzophosphole groups were used, which often leads to an increase in rate and selectivity. The rate of reaction was accelerated by high propene pressures, hinting at the common rate equation for hydroformylation under standard conditions. Under optimised conditions (i.e. low CO pressure) l b ratios as high as 288 were obtained for propene. 

Internal alkenes. Dibenzophosphole- and phenoxaphosphino substituted xantphos ligands 31 and 32 [62] (Figure 8.14) show a high activity and selectivity in the rhodium catalysed linear hydroformylation of 1-octene (l b = > 60). More importantly, ligands 31 and 32 exhibit an unprecedented high activity and selectivity in the hydroformylation of trans 2- and 4-octene to linear nonanal. 

Warren has also studied dibenzophosphole oxides. The ketophosphine oxide (230) substrate can be formed and selective reduction to either the erythro (233) or the threo (231) adducts carried out. The normal NaBH4 conditions were used for reduction to the threo isomer and CeCb was added to obtain the erythro adduct. This methodology was applied to the synthesis of ( )- and (Z)-isosafroles (232) and... 

While sodium borohydride is the best-established reagent for this conversion, there are indications that it may not be the most selective. Using a dibenzophosphole oxide derivative as substrate, it was shown that L-Selectride and lithium trielhylborohydride were both capable of giving significantly better stereoselectivity without any drop in overall yield841. 

The complex, [RhH(dbp)4] (selective catalyst for the homogeneous hydrogenation of terminal alkenes at 20 C and less than 1 atm of hydrogen pressure. In its activity and selectivity the complex resembles [RuClH(PPh3)3] but has the advantage of being more stable in the solid state. The kinetic studies of hydrogenation of hex-l-ene are consistent with the mechanism in Scheme 19. ... 

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