Synthesis, structure and spectroscopic properties of lanthanide complexes of N-confused porphyrins

A series of meso-substituted N-confused porphyrins (NCP) is synthesized using the modified Rothemund-Lindsey procedure. Lanthanide N-confused porphyrinate complexes of the general formula [(NCP)Ln(L_OMe)] [Ln³⁺ = Yb³⁺ and Er³⁺; L_OMe- = (η₅-C₅H₅)Co{P(=O)(OMe)₂} ₃^-] are obtained in moderate yields upon interaction of N-confused porphyrin free bases (H₂NCP) with Ln[N(SiMe ₂)₃]·x[LiCl(THF)₃], followed by the addition of the tripodal anion L_OMe- as an effective encapsulating agent for the lanthanide ions. The structural and spectroscopic data for these complexes provide evidence for an η²-agostic interaction between the Ln³⁺ ion and the inner C-H bond of the NCP ligand. Methylation of [(NCTCPP)Yb(L_OMe)] (H₂NCTCPP = 2-azo-5,10,15,20- tetracyanophenyl-21-carbaporphyrin) with methyl iodide yields the novel stable lanthanide complex of the N-methylated derivative of N-confused porphyrins, whose X-ray structure also exhibits an η²-agostic interaction between the metal center and the inner C-H bond of the NCTCPP ligand. The photophysical properties of the N-confused porphyrins and their lanthanide complexes are investigated.