Dibenzophosphole derivatives

Oxaphosphetanes containing an unsaturated substituent R at Cj are exceptionally short-lived. Only the unusually stable dibenzophosphole derivatives 52c, 53c, and 53b can be detected, but not even this phosphorus environment provides sufficient stabilization to allow detection of 53d, the oxaphosphetane that would be formed from an ester-stabilized ylide (21c). Strongly electron-withdrawing substituents are required in addition to a five-membered ring, as in structure F (Tables 4 and 5), the first known... 

Dibenzophosphole A was in fact the first type of phosphole to be prepared [9], but it has only very recently been used as a building block for the preparation of jr-conjugated systems. In this regard, polymer 70 is obtained with a high polydis-persity (Mn = 5 X 102 Mw = 6.2 X 103) by Ni-catalyzed homo-coupling of derivative 69 (Scheme 4.20) [52]. The presence of o3-P centers, which are potential donor sites for the Ni catalyst, does not prevent C-C bond formation. This macromolecule is photoluminescent in the solid state (2em = 516 nm), a property of potential interest for the development of OLEDs [52]. 

New Diop-type ligands are derived from tartaric acid and were originally developed for asymmetric hydrogenation. Most important is the phosphole analog 2.2-dimethyl-4,5-bis(5//-dibenzophosphol-5-ylmethyl)-l,3-dioxolane (DTPHOL or Diop-DBP)57 l6°, which is successfully applied to asymmetric hydroformylation mainly if used with rhodium catalysts i r 7i. 119, ifio kut ajso platinum complexes47,88,124,138. 

A novel chiral ligand type for asymmetric hydroformylation with rhodium and platinum complexes11 125,1 54,156 is the hydroxyproline derived (2S,4>S)-l-(/err-butoxycarbonyl)-4-(diphenylphosphino)-2-[(diphenylphosphino)methyl]pyrrolidine [(-)-BPPM]2-6. As with other diphosphane systems, modifications of BPPM by exchange of either one or both of the different diphenylphosphane groups with dibenzophosphole (DBP) units [BPPM-2DBP, BPPM-4DBP and BPPM-(DBP)2] have been studied158. 

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. 

Phenyldibenzophosphole can be obtained by allowing phosphorns pentaphenyl to decompose in pyridine. Pentaphosphoranes similar to (6.481) can be obtained from phenyldibenzophosphole by employing scheme (6.921). Treatment with excess lithium in tetrahydrofnran gives a yellow-orange lithium derivative from which either a free radical anion or the parent dibenzophosphole can be obtained. 

Phospholane- and 1,2,3,4,5,6-hexahydrophosphinine derivatives, tetra-hydro- and hexahydrophosphepines, as well as a dibenzophosphole were applied as the P(III)-reactant. The corresponding phosphine oxides formed were reduced by Ph2SiH2 in the course of the reaction. A typical realization using 1-phenyl-dibenzophosphole as the catalyst in the bromination of 2-phenylethanol is shown in Scheme 64. Another group dealing with the catalytic Appel reaction utilized the reagents triphenylphosphine oxide and oxalyl chloride in the chlorination of alcohols (Scheme 65). ... 

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