Synthesis and study of chelating diamide complexes of titanium: new alkyne cyclotrimerization catalysts and new electroluminescent oligomers and polymers
Creators: name: Kah, Daniel Alverson Tan Kiang
Publisher: name: University of British Columbia
Year: 2009

description: Titanium complexes containing a propylene bridged diamide ligand [RN(CH2)3NR]2- (1.6a,b) (a, R = 2,6-(CH3)2C6H3 (BAMP); b, R = 2,6-iPr2C6H3 (BAIP)) were synthesized. The dichloride derivatives, [RN(CH2)3NR]TiCl2 (1.10a,b), were prepared by reacting the silylated diamines R(Me3Si)N(CH2)3N(SiMe3)R (1.9a,b) with TiCL4. In the presence of two equivalents of diphenylacetylene, the reduction of complex 1.10a with an excess of 1% Na/Hg amalgam yielded the metallacyclopentadiene complex (BAMP)Ti(C4Ph4) (1.11). At ambient temperature, complex 1.11 catalyzes the cyclotrimerization of 1-hexyne to 1,3,5- and 1,2,4- tributylbenzenes. A proton nuclear magnetic resonance (¹H NMR) spectroscopy study shows that the rate of cyclotrimerization increases with temperature. Analysis of the resulting tributylbenzene by gas chromatography coupled to mass spectroscopy reveals the formation of both isomers in equal amounts. Using this method, phenylacetylene was also converted to the corresponding triphenylbenzene. Reaction with trimethylsilylacetylene and 1-phenyl-1-propyne was also attempted, but only slight amounts of the substituted arenes were formed. No substituted benzene is detected when either 3-hexyne or 4-octyne was used as a substrate. The metallacyclopentadiene complex (BAIP)Ti(C4Et4) (1.12) was synthesized by the reduction of complex 1.10b in the presence of 3-hexyne. Cyclotrimerization of 1-hexyne was also achieved by complex 1.12, but at a higher temperature than for complex 1.11. At 141 °C, complete conversion of 1-hexyne to 1,3,5- and 1,2,4- tributylbenzene by complex 1.12 is observed by ¹H NMR spectroscopy. In this case, the ratio of isomers obtained was 5:4, but the identity of the two isomers could not be determined unambiguously. In addition, complex 1.12 was found to catalyze the cyclotrimerization of diphenylacetylene to hexaphenylbenzene. Similar results as those found for complex 1.11 were obtained when trimethylsilylacetylene, 1-phenyl-lpropyne, 3-hexyne, and 4-octyne were used as substrates for cyclotrimerization by complex 1.12. The preparation of poly(l,4-phenylenevinylene) (PPV) containing either sulfonate or carboxylate polar groups was attempted. The synthesis of the sodium salt of poly[2,5-bis(3-sulfonatopropoxy)-l,4-phenylenevinylene] (BSP-PPV) (2.14) by the sulfonium precursor and the modified Gilch routes was attempted. Using the modified Gilch route, a fluorescent solution was obtained, but the isolation of BSP-PPV was unsuccessful. A ¹H NMR study of the fluorescent solution shows primarily the presence of monomer. Similar results were obtained for the synthesis of the sodium salt of poly(2,5-dicarboxy-l,4-phenylenevinylene) (DC-PPV) (2.24). Both the sulfonium precursor and the modified Gilch routes were attempted but we were unable to isolate pure DC-PPV, although the solution was fluorescent consistent with the presence of conjugated materials. Two compounds (2.27 and 2.28) of carboxy-substituted p-phenylenevinylene were synthesized via the Wittig reaction. Both compounds are highly luminescent with fluorescence quantum yields of 0.57 in cyclohexane and 0.91 in dichloromethane, respectively. Both compounds exhibit a lower quantum yield in THF. Two oligomers (2.32 and 2.34) containing two and six methyl ester groups on p-phenylenevinylene, respectively, were synthesized via the Wittig reaction. These oligomers were found to be insoluble in any organic solvent. However, solid state UV-vis spectra of oligomers 2.32 and 2.34 were obtained and their absorption maxima are blue-shifted in comparison to unsubstituted PPV, due to the electron-withdrawing nature of methyl ester groups. [Scientific formulae used in this abstract could not be reproduced.]