Rigid multinuclear arrays assembled around platinum centres

Abstract

A series of cis- and trans-platinum(II) acetylide complexes of the type [Pt^II(PBuⁿ₃)₂L₂](L = 2,2′-bipyridin-4-ylethynyl or 2,2′ : 6′,2″-terpyridin-4′-yl-ethynyl or -butadiynyl) has been prepared and fully characterized. These metalloligands represent the first examples of oligopyridine σ-alkynyl derivatives of platinum(II). The crystal structure of the bis(terpyridin-4′-ylethynyl)platinum compound has been determined; it is centrosymmetric and confirms the trans arrangement of the two sets of ligands around a slightly distorted square-planar platinum(II) core. Reaction of the corresponding bis(bipyridin-4-ylethynyl)platinum compound with 1 or 2 equivalent(s) of cis-[Ru(bipy)₂Cl₂]·2H₂O, cis-[Os(bipy)₂Cl₂](bipy = 2,2′-bipyridine) or [Re(CO)₅Cl] afforded, respectively, dinuclear MPt or trinuclear M₂Pt complexes. Homoleptic complexation of the unco-ordinated bipy moiety in the MPt complexes with iron(II) salts allows synthesis of heptanuclear M₃Pt₃Fe complexes (M = Ru^II, Os^II or Re^I). The photophysical properties, measured at 293 and 77 K, and half-wave potentials derived for the various multinuclear complexes remained comparable to those recorded for the corresponding unsubstituted mononuclear parent compounds. It was further shown that the spacer does not quench the excited states of the terminal photoactive subunit, but photons collected by the central platinum(II) complex are transferred quantitatively to the peripheral metal complexes.