Structure and spectroscopic properties of luminescent cyclometalated platinum(II) complexes with chiral phosphine substituted carbohydrate ligands

Abstract

A series of new chiral cyclometalated platinum(II) complexes containing carbohydrate phosphine ligands have been prepared. The reaction of [Pt(ppy)Cl]₂ (Hppy = 2-phenylpyridine) with the chiral phosphines n-Hmbpa (methyl 4,6-O-benzylidene-n-deoxy-n-(diphenylphosphino)-α-D-altropyranoside, n = 2 or 3) afforded cis-[Pt(ppy)(n-Hmbpa)Cl] (n = 2 2a or 3 2b) in high yields. Treatment of 2a or 2b with an excess of NaOCH₃ gave the alkoxoplatinum(II) complexes trans-[Pt(ppy)(n-mbpa)] (n = 2 3a or 3 3b). The crystal structure of 3b shows that the phosphorus atom is located trans to the nitrogen atom of the ppy ligand and the pyranose ring is in a boat conformation. Moderately intense UV-vis absorption bands assigned to metal-to-ligand charge-transfer (MLCT) transitions are shifted from ca. 376–382 to ca. 414–416 nm when the chloride ligand is substituted by the pendant alkoxide group. In solid state and 77 K MeOH–EtOH (4∶1) glass solution, complexes 2 and 3 show a vibronic structured emission in the range 450–650 nm. Complex 2 is non-emissive in fluid solution at room temperature whereas 3 shows a long-lived ³MLCT emission in both CH₃CN and CH₂Cl₂ at room temperature.