680210-53-1Relevant articles and documents
Synthesis, characterization, and alkyne cyclotrimerization chemistry of titanium complexes supported by calixarene-derived bis(aryloxide) ligation
Ladipo, Folami T.,Sarveswaran, Vallipuram,Kingston, Jesudoss V.,Huyck, Rebecca A.,Bylikin,Carr, Shana D.,Watts, Randy,Parkin, Sean
, p. 502 - 514 (2004)
Proximally bridged calix[4]arene compounds (DESC)H2 (3), (DMSHC)H2 (4), (DMSMC)H2 (5), and (DPSC)H2 (6), in which one R2Si group (R=alkyl or aryl) bridges adjacent oxygens, were synthesized via reaction between dialkyl- or diaryldichlorosilane and the corresponding calix[4]arene. Treatment of p- tert -butylcalix[4]arene with Ph2SiCl2 at room temperature or (o-MeC6 H4)2SiCl2 at 80 °C gave (ClPh2SiCl)2Calix-H2 (7) and (o-Tol2SiCl)2Calix-H2 (8), respectively. Titanium dichloride complexes 9-12 (L2 TiCl2, where L2=DESC, DMSHC, DMSMC, or DPSC) were prepared in high yield from reaction of 3-6 with TiCl4. The molecular structures of 7 and 12 were established by single-crystal X-ray diffraction studies. Reduction of 9, 11, and 12 with activated magnesium (Mg*) in the presence of an excess of Me3SiC≡CH produced titananorbornadiene complexes L2Ti{η6-1,2,4-C6H3 (SiMe3)3} (13-15, L2=DESC, DMSMC, or DPSC), which were characterized in solution. Catalytic cyclotrimerization of both terminal and internal alkynes was achieved using catalyst systems derived from L2TiCl2 complexes 9-12 and Mg*. For unsymmetrically substituted internal alkynes, preference for 1,2,4-substitution decreased as the size difference of the substituent groups decreased. The cyclotrimerization of PhC≡CMe was more facile when the calixarene-derived bis(aryloxide) ligand was DPSC versus DMSMC, suggesting that the DPSC ligand may provide a less crowded titanium center and exert greater kinetic control over the course of the cyclotrimerization.
