Phospholes dibenzophospholes

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... 

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]. 

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. 

Further reports on the preparation of phospholes, e.g. (113), by the addition of phosphines to diacetylenes have appeared. Braye and coworkers found that the reaction was best catalysed by concentrated potassium hydroxide or by means of cuprous or mercury salts. Contrary to previous reports the free radical reaction, catalysed by AIBN, also gave good yields. A full account has now been produced of the low inversion barrier of phospholes (114). The energy barriers to inversion of phos-phindoles (115) and dibenzophospholes (116) are significantly higher, results interpreted in terms of disruption of stabilization due to phosphole aromaticity in the planar transition state. The site of protonation of... 

A new synthesis giving good yields of highly substituted phosphole oxides (24) is the reaction of aluminium halide complexes of cyclobutadienes (23) with phosphonous dichlorides (Scheme 2). The synthesis of several substituted dibenzophospholes, e.g., (25), has been reported. ... 

A series of papers describes the synthesis (and some reactions) of highly sterically hindered phosphinic acids based on the dibenzophosphole system, e.g., (36) and (37). These papers describe an improved synthesis of 5-phenyldibenzo-phosphole from tetraphenylphosphonium bromide, as well as that of 5-hydroxy-... 

Dibenzophosphole oxides are prepared by the direct oxidation (H2O2) of the phospholes <69JOCl777> a diarylphosphinic acid can also be used for generating the phosphole ring <56JOC238, 59JOC638) (Equation (28)). 

Only one report has appeared on five-co-ordination in palladium(ii) and platinum(ii) complexes. In a preliminary note three compounds of the type [M(phos)3Bra], where M = Pd or Pt and phos is a 5-alkyl-5fl-dibenzophosphole ligand (28), are said to involve square-pyramidal coordination about the metal atoms, with all the co-ordinated phosphorus atoms in basal sites. In each molecule two of the planar phosphole ligands are mutually parallel, as was found in the analogous nickel(ii) complexes. No further details are given. 

Egan W, Tang R, Zon G, Mislow K (1971) Barriers to pyramidal inversion at phosphorus in phospholes, phosphindoles, and dibenzophospholes. J Am Chem Soe 93 6205... 

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