Chiroptical Switching Polyguanidine Synthesized by Helix-Sense-Selective Polymerization Using [(R)-3,3‘-Dibromo-2,2‘-binaphthoxy](di-tert-butoxy)titanium(IV) Catalyst

Citations Over TimeTop 10% of 2005 papers

Abstract

A series of chiral binaphthyl titanium alkoxide complexes were synthesized. Among them, chiral titanium complex [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) (R-3) exists as a crystallographic C2 dimer in the solid state but a monomer in solution at room temperature. Application of R-3 in the helix-sense-selective polymerization of achiral carbodiimide, N-(1-anthryl)-N'-octadecylcarbodiimide (1), yielded a well-defined regioregular, stereoregular poly[N-(1-anthryl)-N'-octadecylguanidine] (poly-1b) with a relatively narrow polymer dispersity index of 2.7. Full racemization of poly-1b at +80 degrees C in toluene requires more than 100 h. Interestingly, poly-1b was found to undergo fast reversible chiroptical switching at +38.5 degrees C in toluene. Furthermore, at room temperature, poly-1b shows a positively signed Cotton effect in toluene, but negative ones in THF and chloroform, respectively. The chiroptical switching takes place around the toluene content of 90% (vol) in the mixed toluene/THF solvents. This is the first example of chiroptical switching phenomenon occurring in a helical polymer possessing no chiral moieties in the polymer chains. We believe this reversible chiroptical switching phenomenon occurs by reorientation of anthracene rings relative to the chain director.

Related Papers

• → A pimpinellin monomer and dimer isolated from the roots ofEsenbeckia grandiflora(2004)10 cited
• → Investigation of the Monomer−Dimer Equilibria of Molybdocenes in Water(2000)50 cited
• → New perthiophosphonic acid anhydrides and the direct indication of the dimer‐monomer equilibrium. NMR and X‐Ray Studies(1994)20 cited
• Density functional studies of the cobaltous acid dimer: Preliminary results(2002)
• → A Pimpinellin Monomer and Dimer Isolated from the Roots of Esenbeckia grandiflora.(2005)