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− = LOMe− and TpH−) 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)(LOMe)] 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, LOMe, gave lanthanide(III) N-confused porphyrinate complexes of the general formula [Ln(NCP)(LOMe)] (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.