均相氧化偶合催化剂:第一种稳定的氧四核固体[(Pip)n CuX] 4 O 2(n = 1或2,Pip =哌啶,X = Cl,Br,I)的化学计量和特征
摘要:
卤化铜(I)与哌啶(Pip)在无氧的二氯甲烷或硝基苯中定量反应,形成四核铜(I)络合物[(Pip)n CuX] 4;n = 1或2,X = Cl,Br或I。这些络合物非常易溶,并且完全将双氧还原为二氧代桥联配体,化学计量为Δ[Cu(I)] /Δ[O 2 ] = 4.0。稳定的含氧固体[(Pip)n CuX] 4 O 2模拟酪氨酸酶铜蛋白。它们充当酚的均相氧化偶合催化剂。具有高分子吸收率的近红外电子跃迁光谱可诊断四核“ Cu 4 X 4核心结构。电子跃迁更可能是由于至少三个卤素配体和铜(II)中心之间的电荷转移所致。[(Pip)n CuX] 4 O 2在二氯甲烷中的室温EPR光谱是各向同性的,具有4条超细线。[PipCuX] 4 O 2的室温固态EPR光谱显示了d x 2 - y 2的轴向光谱基态,表明围绕铜(II)中心的五个配位体的方形锥体排列。循环伏安法测量表明,当X = Br或I时,它
均相氧化偶合催化剂:第一种稳定的氧四核固体[(Pip)n CuX] 4 O 2(n = 1或2,Pip =哌啶,X = Cl,Br,I)的化学计量和特征
摘要:
卤化铜(I)与哌啶(Pip)在无氧的二氯甲烷或硝基苯中定量反应,形成四核铜(I)络合物[(Pip)n CuX] 4;n = 1或2,X = Cl,Br或I。这些络合物非常易溶,并且完全将双氧还原为二氧代桥联配体,化学计量为Δ[Cu(I)] /Δ[O 2 ] = 4.0。稳定的含氧固体[(Pip)n CuX] 4 O 2模拟酪氨酸酶铜蛋白。它们充当酚的均相氧化偶合催化剂。具有高分子吸收率的近红外电子跃迁光谱可诊断四核“ Cu 4 X 4核心结构。电子跃迁更可能是由于至少三个卤素配体和铜(II)中心之间的电荷转移所致。[(Pip)n CuX] 4 O 2在二氯甲烷中的室温EPR光谱是各向同性的,具有4条超细线。[PipCuX] 4 O 2的室温固态EPR光谱显示了d x 2 - y 2的轴向光谱基态,表明围绕铜(II)中心的五个配位体的方形锥体排列。循环伏安法测量表明,当X = Br或I时,它
Homogeneous oxidative coupling catalysts. Mechanism of catalysts formation by oxidation of [(Pip)nCuX]4 (n=1 or 2, Pip=piperidine, X=Cl, Br or I) by dioxygen in aprotic media
作者:Mohamed A. El-Sayed、Taher S. Kassem、Hisham A. Abo-Eldahab、Ali E. El-Kholy
DOI:10.1016/j.ica.2004.08.025
日期:2005.1
This paper reports the mechanism of formation of oxidative coupling catalysts [(PiP)(n)CuX](4)O-2, n = 1 or 2 and X = Cl, Br or I, which represent half of the catalytical cycle, Scheme 1. The mechanism has been described as a pre-equilibrium between [(Pip)(n-)CuX](4) and O-2. K values are very sensitive to how strong the hydrogen-bonding between copper (1) tetranuclear and incoming dioxygen is, such association is also sensitive to the variation of X. The pronounced pre-equilibrium is the reason behind the oxidation of [(Pip)(n)CuI](4), which is not the case for pyridine type of ligands. The pre-equilibrium followed by rate determining step k(2), which is responsible to the formation of the oxidative coupling catalysts [(PiP)(n)CuX](4)O-2. The overall reaction is a second-order process, first order in each [[(PiP)(n)CuX](4)] and [O-2], with rate constant k(on) (k(on) = Kk(2)) and exothermic DeltaH(not equal) varying from -3 to -12 kcal mol(-1) and DeltaS(not equal) varying from -87 to -65 cal deg(-1) mol(-1). k(on) were found to be very sensitive to n value 1 or 2 and to the type of X (Cl, Br or I). (C) 2004 Elsevier B.V. All rights reserved.