Dibenzophosphole

P-chiral dibenzophosphole oxide (52a) (Scheme 14) shows liquid crystalline behaviour [52], a property that is of interest in the area of electro-optical displays [53]. Chiral resolution of (52a) was achieved by column chromatographic separation of the diastereoisomers obtained following coordination of the o -benzophosphole (52b) to chiral cyclometallated palladium(II) complexes [52]. Notably, the presence of a stereogenic P-centre is sufficient to generate a chiral cholesteric phase. 

In a thorough work with an extensive literature survey, crystal structures, vibrational and 31P NMR spectra of several phosphine complexes of mercury(II) halides HgX2 are presented.235 In the dibenzophosphole complex (dbp)2HgBr2, Hg adopts a distorted tetrahedral coordination (rav(Hg—P) 250.2, rav(Hg—Br) 261.1pm) (cf. the related Cd complex in the previous paragraph), with slightly shorter Hg—P and Hg—Br bonds, respectively, than in the comparable... 

Hydrogenation of 1,3-dienes to terminal olefins is catalyzed by HRh(PPh3)4 and [Rh(CO)2(PPh3)2]2 in the presence of excess phosphine diene insertion into a metal- hydride bond to give a-alkenyl rather than 7r-allyl intermediates was postulated for the initial step (141). Mechanistic studies of the HRh(PPh3)4 catalyst (142) and a more reactive phosphole analog (143) HRh(DBP)4 [5-phenyl-5//-dibenzophosphole (DBP), 7] for... 

Phenyl-dibenzophosphole (164) results from the reaction of tetraphenyl-phosphonium chloride with certain lithium dialkylamides a free-radical mechanism... 

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. 

D. DISODIUM SALT OF 5//-l-(3 -SULFOPHEN YL)-DIBENZOPHOSPHOL-4-SULFONIC ACID... 

Insoluble styrene-divinylbenzene copolymer containing (4R, 5R)-2-[p-phenyl-4,5-bis(5-H-dibenzophosphol-5-ylmethyl)]-l,3-dioxolane groups (J. K. Stille, personal communication) ... 

Changing the ligand structure by substituting two dibenzophosphole groups for two diphenylphosphinyl groups results in a variation of the prevailing chirality in butenes but not in styrene 48). 

It is interesting that when DIOP-DBP is used as the chiral ligand, due to the rigidity of the dibenzophosphole group, attractive interactions between this ligand and the phenyl groups seem less probable, and the model fits both for vinylic and aliphatic internal olefins, as well as for styrene, no data being available for 2-phenyl-1-propene. 

Mixed Oligomers and Polymers Based on Dibenzophosphole or Dithienophosphole... 

Dibenzophospholes A and dithienophospholes B and C (Fig. 4.7) do not display the typical electronic properties and reactivity patterns of phospholes, since the dienic system is engaged in the delocalized benzene or thiophene sextet [7, 10a, 51]. In fact, these building blocks have to be regarded as nonflexible diaryl-phosphines or as P-bridged diphenyl or dithienyl moieties. 

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]. 

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