Synthesis of highly ethynylated mono and dinuclear Pt(II) tethers bearing the 4,4′-bis(ethynyl)biphenyl (debp) unit as central core

Abstract

Mono and bisubstituted bis(ethynyl)biphenyl Pt(II) complexes, i.e. trans-[(RCC)Pt(PPh 3) 2(CC p-C 6H 4 p-C 6H 4CCH)], R= p-NO 2C 6H 4 ( 3b), (η 5-C 5H 5)Fe(η 5-C 5H 4) ( 3c), and trans-[(RCC)Pt(PPh 3) 2(CC p-C 6H 4 p-C 6H 4CC)Pt(PPh 3) 2(CCR)], R=C 6H 5 ( 4a) , p-NO 2C 6H 4 ( 4b), (η 5-C 5H 5)Fe(η 5-C 5H 4) ( 4c), have been synthesized by the dehydrohalogenation reaction from the appropriate Pt monochloro acetylides trans-[(RCC)Pt(PPh 3) 2Cl], R=C 6H 5 ( 1a), R= p-NO 2C 6H 4 ( 1b), R=(η 5-C 5H 4)Fe(η 5-C 5H 5) ( 1c) and HCC p-C 6H 5 p-C 6H 5CCH, (4,4′-bis-ethynylbiphenyl), (DEBP) ( 2). In order to make possible a direct evaluation of the role of Pt centers on the properties of these highly ethynylated complexes, the corresponding species without Pt were prepared, i.e. C 6H 5CCCCC 6H 4C 6H 4CCCCC 6H 5, (4,4′-(bis-phenylethynyl)-diethynylbiphenyl) ( 7), and (η 5-C 5H 5)Fe(η 5-C 5H 4)(CCCCC 6H 4C 6H 4CCCC)(η 5-C 5H 4)Fe(η 5-C 5H 5), (4,4′-(bis-ferrocenylethynyl)-diethynylbiphenyl) ( 8). Preparation of the latter compounds was only achieved by the use of the palladium catalyzed Stille coupling reaction, since the dehydrohalogenation route afforded only homocoupled and polymeric products. The electron-donor or electron-withdrawing ligands coordinated to Pt were chosen for the purpose of tuning the optical properties of the complexes through the different charge distribution along the π-electron conjugation. Characteristic spectroscopic features (UV–vis, FT-IR and NMR) of these complexes are discussed.