Elif Okutan

Competitive formation of cis and trans derivatives in the nucleophilic substitution reactions of cyclophosphazenes having a mono-spiro P–NHR group

Nucleophilic substitution reactions of N(3)P(3)Cl(4)[NH(CH(2))(3)NMe] (1) and N(3)P(3)Cl(4)[NH(CH(2))(3)O] (2) with mono-functional alcohols (methanol, 2,2,2-trifluoroethanol, phenol) and a secondary amine (pyrrolidine) were used to investigate the relationship between the incoming nucleophile and the proportions of products with substituents that are cis or trans to the spiro NH moiety. The reaction products were characterized by elemental analysis, mass spectrometry, (1)H and (31)P NMR spectroscopy and the configurational isomers by X-ray crystallography. Six products have been characterised with the substituent cis to the spiro NH group for the alcohol (methanol, phenol) and pyrrolidine derivatives of both compounds 1 and 2, compared to just one derivative with the substituent trans to the spiro NH group, that for the pyrrolidine derivative of compound 2. For each reaction the relative proportions of cis and trans isomers were determined by (31)P NMR measurements of the reaction mixtures. It was found that the reactions of compound 1 with all three alcohols and of compound 2 with methanol lead to exclusive formation of isomers with the substituent cis to the NH moiety, whereas all other reactions lead to mixtures of cis and trans isomers in different ratios under standard reaction conditions. However, when crown ether is included in the reaction medium for the reactions of compound 2 with both 2,2,2-trifluoroethanol and phenol, it is found that only cis isomers are formed. All these results are rationalised in terms of the competition between at least two effects; the cis-directing effect by hydrogen bonding of the incoming nucleophile to the spiro N-H group already present on the cyclophophazene ring and the cis-directing effect of the sodium cation coordinating to the oxygen lone pairs of the P-O moiety of the spiro ring.

Novel distyryl BODIPY–fullerene dyads: preparation, characterization and photosensitized singlet oxygen generation efficiency

Novel types of mono- and bis-distyryl-BODIPY–fullerene dyads, 6 and 7, were prepared by Bingel cyclopropanation. Distyryl-BODIPY derivative (3) was reacted with methyl malonyl chloride and malonyl dichloride respectively for the synthesis of compounds 4 and 5 as light-harvesting antennae that contain one and two BODIPY units. Through the Bingel cyclopropanation of these BODIPYs (4 and 5) with fullerene-C60 in the presence of CBr4 and DBU, distyryl-BODIPY–fullerene dyads 6 and 7 were obtained. All newly synthesized compounds were characterized by MALDI-MS, 1H and 13C NMR and elemental analysis. Moreover, the photophysical and photochemical properties of these heavy atom free dyads were investigated for the determination of their photosensitizer and fluorescence abilities in the near IR region to generate singlet oxygen.