Syntheses of Quadruply Two- And Three-Atom, Aza-Bridged, Cofacial Bis(5,10,15,20-tetraphenylporphyrins)

Article abstract of DOI:10.1021/ja00011a024

Several syntheses for quadruply aza-bridged, cofacial bis(5,10,15,20-tetraphenylporphyrins) were investigated. Reaction of 5,10,15,20-tetrakis(α-bromo-m-tolyl)porphyrin (2) with p-toluenesulfonamide or cyanamide and Cs₂CO₃ at high dilution in dimethylformamide produced the tosyl and cyano dimers 3a and 3b in 8% yield each. The method of choice was the reaction of porphyrin 2 with tosylamido porphyrin 5a under the same conditions to give dimer 3a in 38% yield. Biphenyl radical anion induced desulfonylation of 3a provided the amino dimer 3c (41%). Reaction of porphyrin 2 with tosylamido porphyrin 13 provided the dimer 14 (of reduced bridge length) in 1% yield. Other methods for the synthesis of 3a and 3c are also discussed. UV/vis and ¹H NMR spectroscopic results suggest an eclipsed "screwed-down" preferred conformation for these dimers, and molecular models are used to illustrate this conformational possibility. (1) Several terms have been used to describe the orientation of one porphyrin ring parallel and coplanar on top of another (i.e., strati by Kagen,^5b face to face by Collman,^5a and cofacial by Chang^3b). Whereas the term cofacial is now generally the most commonly used descriptor, we prefer the usage of strati (from stratum, Latin for covering) for the specific naming of compounds, since it allows for more detailed structural information than simple letter-number shorthand abreviations. Moreover, a new shorthand naming system will be presented in the body of this account,¹⁷ which derives naturally from the strati terminology used in the Experimental Section.