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

• Published in: Journal of chemical sciences (Bangalore, India) India), 2017-06, Vol.129 (6), p.733-739
• Main Author: Peedikakkal, Abdul Malik P
• Format: Article
• Language: English
• Subjects: Acids; Alignment; Bonding strength; Cations; Chain mobility; Chains; Chemical bonds; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Criteria; Crystal structure; Crystallography; Cyclobutane; Derivatives; Ethylene; Hydrogen; Hydrogen bonding; Isomerization; Isomers; Movement; Organic salts; Orientation; Regular Article; Self-assembly; Solid state; Trifluoromethane
• ISSN: 0974-3626; 0973-7103
• DOI: 10.1007/s12039-017-1300-8

A novel organic salt, [bpeH].TFMS ( 1 ), of trans -1,2-bis(4-pyridyl)ethylene (bpe) was synthesized using trifluoromethane sulphonic acid ( CF 3 SO 3 H , TFMS) by self-assembly and its crystal structure was determined by X-ray crystallography. Compound 1 forms hydrogen-bonded assembly of [bpeH] + cations and CF 3 SO 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 hydrogen-bonding interaction for photodimerization reaction in the solid state. The [ bpeH ] + cations are in parallel orientation 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 cyclobutane derivatives. Graphical Abstract SYNOPSIS A novel organic salt of trans -1,2-bis(4-pyridyl)ethylene and trifluoromethane sulphonic acid was characerized by X-ray crystallography. The salt shows unusual photoreactivity via pedal-like motion of C=C double bonds which change from criss-cross to parallel orientation. The photodimerized product undergoes acid-catalyzed isomerization in solution and produces all the isomers of tetrakis(4-pyridyl)cyclobutane.