Synthesis of a linear bis-porphyrin with a Ru(phen)22+-complexed 2,2′-bipyridine spacer

Abstract

A linear bis-porphyrin bridged by a 5,5′-diphenyl-2,2′-bipyridine rod-like spacer complexing a [Ru(phen)₂]²⁺ fragment has been synthesized in 7.4% yield by one-pot condensation of 3,5-di-tert-butylbenzaldehyde, 4,4′-dimethyl-3,3′-dihexyl-2,2′-methylenedipyrrole and the [Ru(phen)₂]²⁺ complex of 5,5′-bis(p-formylphenyl)-2,2′-bipyridine, followed by chloranil oxidation. The protected dialdehyde (5,5′-bis[(5,5-dimethyl-1,3-dioxan-2-yl)phenyl]-2,2′-bipyridine) was obtained in 80% yield by Suzuki coupling of 2-[4-(5,5-dimethyl-1,3-dioxan-2-yl)phenyl]-4,4,5,5-tetramethyl-1,3-dioxaborolane and 5,5′-dibromo-2,2′-bipyridine, using [Pd(PPh₃)₄] as catalyst. A new procedure is reported for the preparation of 5,5′-dibromo-2,2′-bipyridine, which is obtained in 80% yield by Stille homocoupling of 2,5-dibromopyridine in the presence of hexamethylditin.