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

A series of new chiral cyclometalated platinum(II) complexes containing car bohydrate 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)-alpha-D-altropyranoside, n=2 or 3) afforded cis-[Pt(ppy)(n-Hmbpa)Cl] (n=2 2a or 3 2b) in high yields. Trea tment of 2a or 2b with an excess of NaOCH3 gave the alkoxoplatinum(II) comp lexes 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 th e ppy ligand and the pyranose ring is in a boat conformation. Moderately in tense 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 c hloride 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 (MLCT)-M-3 emission in both CH3CN and CH2Cl2 at room temperature.