Enforced Deformation of Porphyrins by Short-Strap Bridging
Wijesekera, T.P., Paine III, J.B., David Dolphin, Einstein, F.W.B., and Jones, T.
J. Am. Chem. Soc.
The UV of I (n = 9, 10, 11) shows that I (n = 11) is essentially undistorted (UV almost identical to that of etioporphyrin), that I (n = 10) is slightly distorted, and that I (n = 9) is severely distorted. The x-ray crystallography of I (n = 9) shows that despite the large change in planarity the strain due to the 9-membered strap is evenly distributed in the molecule The diamagnetic ring current effects on the 1H NMR of I (n = 9) show that distortion only slightly diminishes the aromaticity. The bond lengths in I (n = 9) and the preparation of I, e.g., via II dehydrogenation, and III [R = CH:C(CN)2, CHO; R1 = EtO2C, CO2H, H] are discussed.