Wiring terpyridine: approaches to alkynylthienyl 2,2′:6′,2″-terpyridines

Abstract

The reaction of triisopropylsilylethyne or trimethylsilylethyne with 4′-(5-bromo-2-thienyl)-2,2′:6′,2″-terpyridine (1) leads to 4′-(5-triisopropylsilylethynyl-2-thienyl)-2,2′:6′,2″-terpyridine (3) or 4′-(5-trimethylsilylethynyl-2-thienyl)-2,2′:6′,2″-terpyridine (4). The latter compound may be deprotected to give 4′-(5-ethynyl-2-thienyl)-2,2′:6′,2″-terpyridine (5). Treatment of the complexes [Ru(1)₂][PF₆]₂, [Ru(tpy)(1)][PF₆]₂ and [Ru(2)₂][PF₆]₂ (2 = 4′-(4-bromo-2-thienyl)-2,2′:6′,2″-terpyridine) with triisopropylsilylethyne yields the corresponding homoleptic and heteroleptic alkynylthienyl-terminated ruthenium(II) complexes, for which spectroscopic and electrochemical data are presented. The reaction of [RuCl₂(DMSO)₄] with 5 leads to [Ru(5)₂][PF₆]₂, in which the tpy ligands bear conjugated thienyl and alkynyl groups; the latter can also be accessed by deprotection of [Ru(3)₂][PF₆]₂. The single-crystal structures of ligands 2 and 4, and of [Ru(1)(tpy)][BPh₄]₂·1.3MeCN, [Ru(1)₂][PF₆]₂·2MeNO₂, 2{[Ru(2)₂][PF₆]₂}·5MeCN, [Ru(3)₂][PF₆]₂ and [Ru(5)₂][PF₆]₂·MeCN are presented, and among the homoleptic complexes, π-stacking interactions between thiophene and pyridine rings leading to pairs of associated cations provide a common structural motif.