Synthesis, structure, reactivity and photoluminescence of lanthanide(III) monoporphyrinate complexes

A series of cationic lanthanide(III) monoporphyrinate complexes of the general formula [Ln(Por)(H₂O)₃]Cl (Ln = Yb³⁺ and Er³⁺; Por = porphyrinate dianion) were prepared via the protonolysis of Ln(NR₂)₃ with porphyrin free bases (H₂Por). An unexpected neutral oxalate-bridged Yb porphyrinate dimer [Yb(Por)(DME)]₂(μ-η²:η²-O₂CCO₂) was isolated and structurally characterized by X-ray crystallography when the protonolysis was carried out in an atmosphere of carbon dioxide. The coordinated aqua molecules of the cationic porphyrinate complexes are very labile and can be easily displaced by good donor solvents such as DMF or anionic tripodal ligand L₂X^- (L₂X^- = L_OMe^- and T_p^H-) to form the neutral complex [Ln(Por)(Cl)(DMF)₂] or [Ln(Por)(L₂X)], respectively. [Yb(Por)(H₂O)₃]Cl underwent dimerization to give the dimer [Yb(Por)(μ-OH)(H₂O)]₂ when dissolved in basic solution and [Yb(Por)(μ-Cl)(H₂O)]₂ in dilute HCl solution. Furthermore, [Yb(Por)(H₂O)₃]Cl behaves as a living catalyst for the cyclotrimerization of phenyl isocyanate to l,3,5-triphenyl-s-triazin-2,4,6-trione. Photoluminescence studies showed that the porphyrinate dianion, acting as an antenna, sensitized Ln³⁺ (Ln³⁺ = Nd³⁺, Er³⁺ and Yb³) ion emission in the near-infrared region, and that [Ln(TDPAPP)(L_OMe)] complexes exhibited excellent optical limiting capability. Protonolysis of Ln(NR₂)₃ with N-confused porphyrin free bases (H₂NCP) followed by the addition of the encapsulating tripodal anion, L_OMe, gave lanthanide(III) N-confused porphyrinate complexes of the general formula [Ln(NCP)(L_OMe)] (Ln = Yb³⁺ and Er³⁺; NCP = N-confused porphyrinate dianion), whose X-ray structures revealed an η² agostic interaction between the metal center and the inner C-H bond of the NCP ligand.