Syntheses, Structures, and Electrochemical Properties of Platinum(II) Complexes Containing Di-tert-butylbipyridine and Crown Ether Annelated Dithiolate Ligands

A series of new platinum(II) complexes containing both 4,4‘-di-tert-butyl-2,2‘-bipyridine (dbbpy) and the extended tetrathiafulvalenedithiolate ligands have been prepared and characterized. These complexes include [Pt(dbbpy)(C₈H₄S₈)] (1; C₈H₄S₈^2- = 2-{(4,5-ethylenedithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(ptdt)] (2; ptdt = 2-{(4,5-cyclopentodithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(mtdt)] (3; mtdt = 2-{(4,5-methylethylenedithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(btdt)] (4; btdt = benzotetrathiafulvalenedithiolate), [Pt(dbbpy)(C₈H₆S₈)] (5; C₈H₆S₈^2- = 2-{4,5-bis(methylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(3O-C₆S₈)] (6; 3O-C₆S₈^2- = 2-{4,5-dithia-(3‘,6‘,9‘-trioxaundecyl)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), and [Pt(dbbpy)(4O-C₆S₈)] (7; 4O-C₆S₈^2- = 2-{4,5-dithia-(3‘,6‘,9‘,12‘-tetraoxatetradecyl)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate). The crystal structures of a new ligand precursor (2-[4,5-dithia-(3‘,6‘,9‘,12‘-tetraoxatetradecyl)-1,3-dithiol-2-ylidene]-4,5-bis(2-cyanoethylsulfanyl)-1,3-dithiole, IIIc) and complexes 5−7 have been determined by X-ray crystallography. Complexes 1−7 show intense electronic absorption bands in the UV−vis region due to the intramolecular mixed metal/ligand-to-ligand charge-transfer transition, and they display significant solvatochromic behavior. Redox properties of these compounds have been investigated by cyclic voltammetry, and complex 7 shows a significant response for Na⁺ ions with a large positive shift of ca. 45 mV.