Stable ion NMR and GIAO-DFT study of novel cations from 8,16-dicyano[2.2]metacyclophanedienes and from strategically substituted/benzannelated dihydropyrenes: charge-induced tropicity modulation and pi-switching.
The dicyanometacyclophanediene 1 is diprotonated at the cyano groups (1H2 2+) in various superacid media. Upon quenching, intact 1 and the ring-closed CPD 2 were obtained in a 3:2 or 3:1 ratio, depending on the superacid system. Compound 2 undergoes ring opening in the superacid to give the ipso-monoprotonated 2H+, which on quenching furnishes 1-cyanopyrene as a major product together with 2 and 1. The dication 3 2+, with strongly deshielded internal methyls, was generated from the epoxyannulene 3. Ketones 4-6 and ester 7 are O/C diprotonated to give paratropic carboxonium-annulenium dications (4H2 2+, 5H2 2+, 6H2 2+, and 7H2 2+, respectively). Ester 8 gives a trication by two-electron oxidation and O-protonation. Conjugated carboxylic acid 9 gives a mixture of two dications by CO and ring protonation. The dibromo derivatives 10 and 11 form carboxonium ions, whereas the monobromo derivative 12 is O/C diprotonated to give an oxonium-annulenium dication. Charge delocalization modes and tropicity in the resulting species are evaluated by NMR and GIAO-DFT. Facile formation of 2 from 1 in quenching experiments indicates that thermal closing can be achieved with the diprotonated dinitrile, without imposing skeletal rearrangement.
D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D005459:Fluorides / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D011522:Protons; D011721:Pyrenes / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism; D013464:Sulfuric Acids / Q000737:chemistry
C527425:8,16-dicyano(2.2)metacyclophane-1,9-diene; D002412:Cations; D007477:Ions; D009570:Nitriles; D011522:Protons; D011721:Pyrenes; D013464:Sulfuric Acids; C046106:fluorosulfonic acid; D005459:Fluorides