• Solid state photodimerization in an organic salt of 1,2-bis(4-pyridyl)ethylene and trifluoromethane sulphonic acid via pedal-like motion

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    • Keywords


      Organic salts; 1, 2-bis(4-pyridyl)ethylene; photodimerization; pedal motion.

    • Abstract


      A novel organic salt, [bpeH].TFMS (1), of trans-1,2-bis(4-pyridyl)ethylene (bpe) was synthesized using trifluoromethane sulphonic acid (CF₃SO₃H, TFMS) by self-assembly and its crystal structure was determined by X-ray crystallography. Compound 1 forms hydrogen-bonded assembly of [bpeH]⁺ cations and CF₃SO⁻₃ anions which are held together by N–H· · ·N, C–H· · ·O and C–H· · ·F hydrogen-bonding interactions. An attempt has been made to orient the olefinic C=C bonds of bpe in the organic salt via weak hydrogenbonding interaction for photodimerization reaction in the solid state. The [bpeH]⁺ cations are in parallelorientation in the infinite one dimensional (1D) chain through N–H· · ·N hydrogen bonding. The olefinic C=C bonds of bpe are aligned in criss-cross orientation with a center-to-center distance of 4.97 Å. Even though the distance and the orientation of olefinic C=C bonds do not conform with the Schmidt topochemical criteria, compound 1 undergoes photodimerization reaction in solid state to produce stereo-specific rctt-tetrakis(4- pyridyl)cyclobutane (rctt-tpcb) (2) in 100% yield. The photoreactivity is expected to take place through cooperative movement of 1D chains and pedal-like motion of the pyridyl rings over the double bonds. The photodimerized product 2 undergoes acid-catalyzed isomerization to produce other cyclobutane isomers such as rcct-tpcb and rtct-tpcb. This strategy for synthesizing organic salts is a facile step for the synthesis of cyclobutanederivatives.

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