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The palladium catalysed Miyaura cross-coupling reactions of 4′-(4-bromophenyl)-2,2′:6′,2″-terpyridine (tpy-ϕ-Br) and 4′-bromo-2,2′:6′,2″-terpyridine (tpy-Br) with bis(neopentyl glycolato)diboron (B2neo2) lead to the first reported examples of boronate ester-substituted terpyridine ligands, L1 and L2. Ligand L1, which incorporates a benzene ring between the terpyridine group and the boron, reacts with transition metals such as iron and ruthenium to generate complexes containing the analogous boronic acid-substituted terpyridine L3. The heteroleptic complex Ru(ttpy)L32+ has also been prepared by an analogous cross-coupling reaction of the bromo complex Ru(ttpy)(tpy-ϕ-Br)2+ with B2neo2 (ttpy = 4′-tolyl-2,2′:6′,2″-terpyridine). The structurally related complex Ru(ttpy)L42+ (L4 = terpyridine-4′-boronic acid) could not be prepared, either directly from L2 or from Ru(ttpy)(tpy-Br)2+, apparently due to competitive hydrodeboration and solvolysis. The complex Ru(ttpy)L32+ reacts with aryl halides under standard palladium-catalysed Suzuki–Miyaura cross-coupling conditions to generate more elaborate 4′-aryl-substituted terpyridyl complexes. Cross-coupling has also been achieved by reaction of Ru(ttpy)(tpy-Br)2+ with an arylboronic acid. The photophysical properties of Ru(ttpy)L32+ are shown to be largely typical of ruthenium bis-terpyridyl complexes.
Aspley et al. (Mon,) studied this question.