The synthesis of 4′-aryl substituted terpyridines by Suzuki cross-coupling reactions: substituent effects on ligand fluorescence

Abstract

Several 4Ј-aryl-substituted 2,2Ј:6Ј,2Љ-terpyridines (tpy-C 6 H 4 R) have been prepared by palladium-catalysed crosscoupling of 4Ј-bromoterpyridine or 4Ј-triflate-terpyridine (triflate = trifluoromethylsulfonyloxy) with aryl boronic acids or esters, RC 6 H 4 B(ORЈ) 2 (R = H, m-NH 2 , p-CHO, -NO 2 , -CN, -NMe 2 , -NPh 2 ). The new ligand 4Ј-mesitylterpyridine (mesityl = 2,4,6-trimethylphenyl) was prepared in the same way. Similarly, 4Ј-bromophenylterpyridine (tpy--Br) has been cross-coupled with aryl halides to generate several new biaryl-substituted terpyridines (tpy--C 6 H 4 R where R = H, p-CN, NMe 2 , NPh 2 ), together with two related compounds with pendent 3-or 4-pyridyl groups (tpy--C 6 H 4 -py). For selected compounds, the alternative coupling strategy of reaction of a terpyridine-4-boronate or terpyridine-4-phenylboronate with the appropriate aryl halide has also been investigated (e.g. to prepare tpy--C 6 H 4 NO 2 ), but was generally found to be less satisfactory. All of the compounds are fluorescent in the UV region of the spectrum, the biaryl-substituted compounds being only slightly red-shifted compared to the monoaryl systems, but with the further red-shift that accompanies protonation being more significant for the former. Fluorescence lifetimes in solution are in the range 1-5 ns. The emission spectra of the aminobiphenyl-substituted compounds (tpy--C 6 H 4 NRЉ 2 , where RЉ = Me or Ph) display a large red-shift with increasing solvent polarity, suggesting the involvement of an intramolecular charge transfer state, as found previously for the two analogues omitting the phenyl ring (tpy-C 6 H 4 NRЉ 2 ). In contrast to the latter, however, protonation or binding of a Lewis acidic metal ion to the aminobiphenyl compounds serves to quench almost completely their emission.

A Modular “Toolbox” Approach to Flexible Branched Multimacrocyclic Hosts as Precursors for Multiply Interlocked Architectures

“…This approach turned out to be much more fruitful compared with the second possible variant, that is, Suzuki cross-coupling of 15 with the corresponding halogenated heterocycles. [23] The products of these coupling reactions (16)(17)(18) all carry heterocycles that can coordinate to transition-metal ions. This set of molecules can thus be connected to each other through the use of metal ions with their wide variety of coordination geometries.…”

“…Hunters diamine 1, [9, 12a] extended diamines 6 and 7, [9, 12a] 4-(2,2';6',2''-terpyridine-4'-yl)phenylboronic acid pinacol ester, [23] and perylene 32 [36] were synthesized according to literature procedures. All acid chlorides were obtained from the corresponding isophthalic acids by reaction with SOCl 2 .…”

Phenanthroline‐ and Terpyridine‐Substituted Tetralactam Macrocycles: A Facile Route to Rigid Di‐ and Trivalent Receptors and Interlocked Molecules

“…[25a] 9, [29] 10, [27] and 11 [13] were synthesized according to literature procedures. The synthesis of 2 and the corresponding analytical characterization has been reported previously; [13] further attempts to optimize the yield by using other conditions for the Suzuki cross-coupling reaction or by using the borylated TLM 7 were not successful.…”

Amphiphilic Dendrimers with Heteroleptic Bis([2,2′: 6′,2″]terpyridine)‐Ruthenium(II) Cores

“…Substitution at C(4') (for conventional numbering, see Scheme 1) is a particularly convenient process [16]. Both Pd-catalyzed Sonogashira [17] and Suzuki crosscouplings [18] [19] have been used to introduce halogenated terpyridine moieties into dendritic structures, without any problems arising from complexation of Pd II to the ligands [20].…”