Wiring terpyridine : approaches to alkynylthienyl 2,2 ':6 ',2 ''-terpyridines

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)center dot 1.3MeCN, [Ru(1)(2)][PF6]2 center dot 2MeNO(2), 2{[Ru(2)(2)][PF6](2)}center dot 5MeCN, [Ru(3)(2)][PF6](2) and [Ru(5)(2)][PF6](2)center dot MeCN are presented, and among the homoleptic complexes, pi-stacking interactions between thiophene and pyridine rings leading to pairs of associated cations provide a common structural motif.