Tin-Chelated Trisphosphineoxide Scorpionate Rare-Earth Porphyrinate Complexes: Synthesis and Photophysical Properties

Abstract

A series of seven-coordinated monoporphyrinate rare-earth(III) complexes featuring a novel tripodal tin-chelated trisphosphineoxide scorpionate ligand with the general formula [(TPP)Ln(PPh₂O)₃Sn] (Ln = Y, La, Dy, Er, Ho, Yb; TPP = 5,10,15,20-tetraphenylporphyrinate) were synthesized by reactions of the potassium tripodal scorpionate ligand [Sn(PPh₂O)₃K] with porphyrinate rare-earth metal chlorides [(TPP)LnCl(dme)] (Ln = Y, Dy, Er, Ho, Yb) or porphyrinate lanthanum borohydride [(TPP)LaBH₄(thf)₂]. The complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and ion mobility mass spectrometry. All complexes emit weak red TPP-based fluorescence, accompanied by near-infrared emission of Er, Ho (rather weak), and Yb (relatively intense with a quantum yield of 1% in dichloromethane solution) of the corresponding complexes. Despite the low intensity, the red fluorescence is characteristic (as referred to the parent free-base TPP) and can be used together with optical absorption for analytical evaluation. Similar photophysical properties can be expected for monoporphyrinate rare-earth metal complexes of other tripodal ligands with a similar binding to the (TPP)Ln moiety.