Dibenzophosphole complexes

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... 

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. 

We have excluded the widely studied dibenzophospholes from this review because they have no free dienic system and, thus, act only as classical 2-electron ligands. But, we have included a section on arsole and stibole complexes, and a brief comparison between azametallocenes and their phosphorus analogs in order to illustrate the influence of the heteroatom upon the properties of these systems. This review is intended to be a complete coverage of the literature up to October 1981. 

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. ... 

The use of asymmetric catalysts in chiral syntheses is taking on increasing importance. Asymmetric ligands or asymmetric metal complexes used in these transformations are quite expensive and need to be efficiently separated from reaction mixtures and recycled. Scheme 16 shows the preparation of a polymer-anchored dibenzophosphole-DIOP platinum-tin catalysts system. The asymmetric ligand places the Pt-SnClj system in a chiral environment. This catalyst has given the highest enantiometric excesses ever observed in catalytic hydroformylation. The initially achieved 70-83% e.e. values were improved to >95% by the use of triethylorthoformate (TEOF) as the solvent. ... 

Oxaphosphetanes from semi-stable ylides have been detected spectroscopically only in the special case of the dibenzophosphole group [43]. Naked betaines, i.e. those that are not complexed with metal ions, have not been found because they cyclize too rapidly for detection by NMR [6]. 

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. 

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