Approaches to wired terpyridine : Bithienyl alkynyl derivatives of 2,2′:6′,2″-terpyridine and their ruthenium(II) complexes

Two approaches to the formation of ruthenium(II) complexes containing ligands with conjugated 2,2`:6`,2``-terpyridine (tpy), alkynyl and bithienyl units have been investigated. Bromination of 4`-(2 2`,bithien-5`-yl)-2,2`:6`,2``-terpyridine leads to 4`-(5-bromo-2,2`-bithien-5`-yl)-2,2`:6`,2``-terpyridine (1), the single crystal structure of which has been determined. The complexes [Ru(1)(2)][PF6](2) and [Ru(tpy)(1)][PF6](2) have been prepared and characterized. Sonogashira coupling of the bromo-substituent with (TIPS)C CH did not prove to be an efficient method of preparing the corresponding complexes with pendant alkynyl units. The reaction of 4`-ethynyl-2,2`:6`,2``-terpyridine with 5-bromo-2,2`-bithiophene under Sonoashira conditions yielded ligand 2, and the heteroleptic ruthenium(II) complex [Ru(2)9 (tpy)][PF6](2) has been prepared and characterized.