Kaur Aman, Ribelli Thomas G, Schröder Kristin, Matyjaszewski Krzysztof, Pintauer Tomislav
Department of Chemistry and Biochemistry, Duquesne University , 600 Forbes Avenue, 308 Mellon Hall, Pittsburgh, Pennsylvania 15282, United States.
Inorg Chem. 2015 Feb 16;54(4):1474-86. doi: 10.1021/ic502484s. Epub 2015 Jan 27.
Synthesis, characterization, electrochemical studies, and ATRP activity of a series of novel copper(I and II) complexes with TPMA-based ligands containing 4-methoxy-3,5-dimethyl-substituted pyridine arms were reported. In the solid state, Cu(I)(TPMA*(1))Br, Cu(I)(TPMA*(2))Br, and Cu(I)(TPMA*(3))Br complexes were found to be distorted tetrahedral in geometry and contained coordinated bromide anions. Pseudo-coordination of the aliphatic nitrogen atom to the copper(I) center was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br complexes, whereas pyridine arm dissociation occurred in Cu(I)(TPMA*(1))Br. All copper(I) complexes with substituted TPMA ligands exhibited a high degree of fluxionality in solution. At low temperature, Cu(I)(TPMA*(1))Br was found to be symmetrical and monomeric, while dissociation of either unsubstituted pyridine and/or 4-methoxy-3,5-dimethyl-substituted pyridine arms was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br. On the other hand, the geometry of the copper(II) complexes in the solid state deviated from ideal trigonal bipyramidal, as confirmed by a decrease in τ values ([Cu(II)(TPMA*(1))Br][Br] (τ = 0.92) > [Cu(II)(TPMA*(3))Br][Br] (τ = 0.77) > [Cu(II)(TPMA*(2))Br][Br] (τ = 0.72)). Furthermore, cyclic voltammetry studies indicated a nearly stepwise decrease (ΔE ≈ 60 mV) of E1/2 values relative to SCE (TPMA (-240 mV) > TPMA*(1) (-310 mV) > TPMA*(2) (-360 mV) > TPMA*(3) (-420 mV)) on going from [Cu(II)(TPMA)Br][Br] to [Cu(II)(TPMA*(3))Br][Br], confirming that the presence of electron-donating groups in the 4 (-OMe) and 3,5 (-Me) positions of the pyridine rings in TPMA increases the reducing ability of the corresponding copper(I) complexes. This increase was mostly the result of a stronger influence of substituted TPMA ligands toward stabilization of the copper(II) oxidation state (log β(I) = 13.4 ± 0.2, log β(II) = 19.3 (TPMA*(1)), 20.5 (TPMA*(2)), and 21.5 (TPMA*(3))). Lastly, ARGET ATRP kinetic studies show that with more reducing catalysts an induction period is observed. This was attributed to slow regeneration of Cu(I) species from the corresponding Cu(II).
报道了一系列新型铜（I和II）配合物与含4-甲氧基-3,5-二甲基取代吡啶臂的基于TPMA的配体的合成、表征、电化学研究及原子转移自由基聚合（ATRP）活性。在固态下，发现Cu(I)(TPMA*(1))Br、Cu(I)(TPMA*(2))Br和Cu(I)(TPMA*(3))Br配合物的几何形状为扭曲四面体，且含有配位溴阴离子。在Cu(I)(TPMA*(2))Br和Cu(I)(TPMA*(3))Br配合物中观察到脂肪族氮原子与铜（I）中心的假配位，而在Cu(I)(TPMA*(1))Br中发生了吡啶臂解离。所有含取代TPMA配体的铜（I）配合物在溶液中表现出高度的动态性。在低温下，发现Cu(I)(TPMA*(1))Br是对称且单体的，而在Cu(I)(TPMA*(2))Br和Cu(I)(TPMA*(3))Br中观察到未取代吡啶和/或4-甲氧基-3,5-二甲基取代吡啶臂的解离。另一方面，固态下铜（II）配合物的几何形状偏离理想的三角双锥，这通过τ值的降低得到证实（[Cu(II)(TPMA*(1))Br][Br]（τ = 0.92）>[Cu(II)(TPMA*(3))Br][Br]（τ = 0.77）>[Cu(II)(TPMA*(2))Br][Br]（τ = 0.72））。此外，循环伏安法研究表明，从[Cu(II)(TPMA)Br][Br]到[Cu(II)(TPMA*(3))Br][Br]，相对于饱和甘汞电极（SCE），E1/2值几乎呈逐步下降（ΔE≈60 mV）（TPMA（-240 mV）>TPMA*(1)（-310 mV）>TPMA*(2)（-360 mV）>TPMA*(3)（-420 mV）），证实了TPMA吡啶环4位（-OMe）和3,5位（-Me）中供电子基团的存在增加了相应铜（I）配合物的还原能力。这种增加主要是由于取代TPMA配体对铜（II）氧化态稳定化的更强影响（logβ(I)=13.4±0.2，logβ(II)=19.3（TPMA*(1)），20.5（TPMA*(2)）和21.5（TPMA*(3)））。最后，ARGET ATRP动力学研究表明，使用更多的还原催化剂会观察到一个诱导期。这归因于相应Cu(II)中Cu(I)物种的缓慢再生。
