The synthesis of 4′-aryl substituted terpyridines by Suzuki cross-coupling reactions: substituent effects on ligand fluorescence
作者：Wendy Goodall、Kerstin Wild、Kathryn J. Arm、J. A. Gareth Williams
DOI：10.1039/b205330f
日期：——
Several 4â²-aryl-substituted 2,2â²:6â²,2â³-terpyridines (tpy-C6H4R) have been prepared by palladium-catalysed cross-coupling of 4â²-bromoterpyridine or 4â²-triflate-terpyridine (triflate = trifluoromethylsulfonyloxy) with aryl boronic acids or esters, RC6H4B(ORâ²)2
(R = H, m-NH2, p-CHO, -NO2, -CN, -NMe2, -NPh2). The new ligand 4â²-mesitylterpyridine (mesityl = 2,4,6-trimethylphenyl) was prepared in the same way. Similarly, 4â²-bromophenylterpyridine (tpy-Ï-Br) has been cross-coupled with aryl halides to generate several new biaryl-substituted terpyridines (tpy-Ï-C6H4R where R = H, p-CN, NMe2, NPh2), together with two related compounds with pendent 3- or 4-pyridyl groups (tpy-Ï-C6H4-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-Ï-C6H4NO2), 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 1â5 ns. The emission spectra of the aminobiphenyl-substituted compounds (tpy-Ï-C6H4NRâ³2, where Râ³ = 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-C6H4NRâ³2). 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.
通过钯催化的交叉偶联反应，制备了几种4′-芳基取代的2,2′:6′,2″-三联吡啶（tpy-C6H4R），涉及4′-溴三联吡啶或4′-三氟甲磺酸酯三联吡啶（triflate = 三氟甲磺酰氧基）与芳基硼酸或硼酸酯的反应，RC6H4B(OR′)2（R = H, m-NH2, p-CHO, -NO2, -CN, -NMe2, -NPh2）。新配体4′-三甲基苯基三联吡啶（mesityl = 2,4,6-三甲基苯基）也通过相同方法制备。类似地，4′-溴苯基三联吡啶（tpy-Φ-Br）已与芳基卤化物交叉偶联，生成了几种新的双芳基取代三联吡啶（tpy-Φ-C6H4R，其中R = H, p-CN, NMe2, NPh2），以及两种含有3-或4-吡啶基侧链的相关化合物（tpy-Φ-C6H4-py）。对于选定的化合物，还研究了替代的偶联策略，即反应一个三联吡啶-4-硼酸酯或三联吡啶-4-苯基硼酸酯与适当的芳基卤化物（例如制备tpy-Φ-C6H4NO2），但通常发现效果较差。所有化合物在紫外区域都有荧光发射，双芳基取代的化合物相比于单芳基系统仅有轻微的红移，但其伴随质子化产生的进一步红移对前者更为显著。溶液中的荧光寿命在1~5纳秒范围内。氨基联苯取代化合物的发射光谱（tpy-Φ-C6H4NR″2，其中R″ = Me或Ph）随着溶剂极性的增加显示出较大的红移，表明存在分子内电荷转移态，这与先前报道的两种省略苯环的类似物（tpy-C6H4NR″2）一致。然而，与后者不同，氨基联苯化合物在质子化或与路易斯酸性金属离子结合时，其发射几乎完全淬灭。
