Ligand structural factors in the establishment of intramolecular Pt · · · H hydrogen-bridging interactions in pentafluorophenyl complexes of platinum

Abstract

Anionic complexes with molecular formula [Q][Pt(C ₆ F ₅ ) ₃ L] [Q = NBu ₄ ⁺ , L = diphenyl-2-pyridylmethane 1, 2-benzylpyridine 2, 2-(hydroxymethyl)pyridine 3 or 2-hydroxyaniline 4; Q = PPh ₃ Me ⁺ , L = 2-isopropylaniline 5] were prepared by cleavage of the pentafluorophenyl bridging system in [Q] ₂ [Pt ₂ (µ-C ₆ F ₅ ) ₂ (C ₆ F ₅ ) ₄ ] with L. The analogous complex [NBu ₄ ][Pt(C ₆ F ₅ ) ₃ (2-Ph ₂ PC ₆ H ₄ CHO)] 6 was prepared by substitution of the chloride ion by the ligand L in [NBu ₄ ] ₂ [Pt(C ₆ F ₅ ) ₃ Cl]. The ligands L contain hydrogen atoms which are suitable, from the point of view of both their structure and acidic properties, for establishing hydrogen-bridging interactions with the platinum centre. Proton NMR spectra of some of these complexes show displacement of the signal corresponding to the hydrogen atom towards higher frequencies but no Pt–H coupling. The structure of complex 1 was determined by single crystal X-ray diffraction (Pt · · · H distance 2.65 Å). The decisive factors for the existence of Pt · · · H hydrogen-bridging interactions in solution and in the solid state are discussed.