Difluoroboron complexes

The general interligand C—C coupling reaction shown in Eq. (8) for (metalla-/3-diketonato)BF2 compounds also occurs directly with metalla-/3-diketonate anions, thereby precluding the need to prepare the neutral difluoroboron complexes (53). As a one-pot synthesis, metal carbonyl acetyl compounds can be converted to neutral 77-allyl complexes [Eq. (12)]. 

Difluoroboron complexes are used to protect enolisable carbonyl functions against electrophilic bromination, thus allowing regiospecific radical bromination of other (e.g. benzylic) sites. This is demonstrated in the benzylic bromination of condensed tetralones948. 

Finally, the coupling reaction of vinyl and alkylidene (see Alkylidene) ligands in complexes of the type (166) results in the formation of (jj -allyl)FeCp(CO) complexes (equation 38). The vinyl substituent in these reactions is most often an enolate, whereas the alkyhdene unit is formally of the Fischer carbene type. The ultimate product depends upon the starting material and additional reagents. In the case of (ferra-/3-diketonato)difluoroboron complexes (167), the resulting anion is isolated as tetramethylammonium salt (168). In the case of Fp(acyl) complexes as starting materials, benzoylation of the resultant anions gives complexes (163 ... 

In most cases, the present of CDs will enhance the luminescence. However, CDs can also selectively quench the luminescence of some compoimds. A study of the effect of /3-CD on the fluorescence of xanthene dyes, coumarins and pyromethene-difluoroboron complexes in aqueous solution shows that fi-CD enhances the fluorescence of 7-hydroxycoumarin and coumarins, but quenches the fluorescence of the 7-hydroxy-4-methylcoumarins [73]. This behavior of CDs provides a new approach to multicomponent fluorometric analysis and indicates that CDs can be used for differentiating the structures of similar compounds such as the positional isomers by the selective incorporation of the analyte. 

H. Maeda, Y. Kusunose, Dipyrrolyldiketone difluoroboron complexes novel anion sensors with C-H—X interactions. Chem. Eur. J. 11, 5661-5666 (2005)... 

Difluoroboron(III) complexes of pyrromethene systems have been proposed as PDT agents. Thus, preliminary studies on difluoroboron(III) 1,3,5,7,9- pentamethylpyrromethene 2,8-disulfo-nic acid disodium salt (53), developed as a laser dye, show PDT activity in vitro against ovarian adenocarcinoma cells.288 This compound had Amax 500nm (c 100,000M em ) in ethanol, and shows some photoinstability in water. 

The difluoroboronate chelate complexes of the derivatives of tellur-achromones 104 (X = O) and tellurathiochromone 104 (X = S), which may be viewed as the corresponding tellurachromylium zwitterions 105, were prepared through the demethylation reaction of the 5-methoxy derivatives 104 under the action of the complex BF3-Et20 (88MI4). 

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