Crystallographic Studies of Organosilicon Porphyrins: Stereoelectronic Effects of Axial Groups on the Nonplanarity of the Porphyrin Ring

Organosilicon tetraphenylporphyrins (Si(TPP)R2) with alkyl, alkenyl, alkynyl, and aryl groups at the axial positions (R) were synthesized. X-ray crystallographic studies demonstrated that the porphyrin ligands are virtually “planar” in Si(TPP)(CH2CH2CH3)2 and Si(TPP)(CHCH2)2, nearly planar but slightly “waved” in Si(TPP)(CH2Si(CH3)3)2 and Si(TPP)(C⋮CC6H5)2, and moderately “ruffled” in Si(TPP)(C6H5)2.