Structural and Coordination Studies of “Pearl Oysterlike” Porphyrins

We report the coordination studies of porphyrins with pre-organized but yet flexible straps, each bearing over the center of the porphyrin either a 2,2-malonic acid diethyl ester residue or a 2,2-malonic acid residue. The straps are attached to the porphyrin via two adjacent meso positions, 5,10 and 15,20, respectively, and the 2,2-malonic acid diethyl ester groups are connected to the straps on benzylic carbon atoms. These two structural features allow a significant flexibility of the straps, as confirmed by the comparison of the X-ray structures of the zinc, nickel, and lead complexes of porphyrin 1. In the latter, the influence of the lone-electron pair of lead is clearly demonstrated. The coordination of bismuth is also reported.