5,15-Diaryl Substituted Benzochlorins - Synthesis and Structure

Article abstract of DOI:10.1016/S0040-4020(01)81941-4

Nickel 5,15-bis(p-substituted aryl)porphyrins having p-substituents CH3, NO2, N(CH3)2, OTosyl, were treated with 3-(dimethylamino)acrolein to produce the nickel meso-(2''-formylvinyl)porphyrins (1)-(4).These undergo cyclisation to the corresponding nickel diaryl benzochlorins (5) to (8) and thence to the corresponding free bases.All these derivatives show unusual electronic spectra with strong absorptions in the visible region around 700 nm.A crystal structure of the p-dimethylamino benzochlorin (7) reveals a structure highly distorted from planarity, with the macrocycle having a distinct saddle shape.The p-dimethylamino benzochlorin (7a) readily protonates in solution to a dimethylaminoquinomethene moiety.An alternative route to the benzochlorins via decarboxylation of meso-acrylate derivatives and formylation of the formed vinyl compounds, produced dimeric species (15) and (16) which have been characterised by spectroscopic methods; the dimers are composed of a meso-vinyl porphyrin linked to a porphodimethene unit via an ethylenic bridge. (1) - (4) under basic conditions cyclise to the corresponding 5,15-diaryl formyl purpurins.