p-Substituent effects on the redox chemistry of the diaryltriazenido-bridged dirhodium complexes [Rh2(CO)4−n(PPh3)n(μ-p-XC6H4NNNC6H4X′-p)2] (n = 0–2)
作者:Neil G. Connelly、Paul R. G. Davis、Emma E. Harry、Phimphaka Klangsinsirikul、Monika Venter
DOI:10.1039/b002939o
日期:——
The complexes [Rh2(CO)4(μ-p-XC6H4NNNC6H4Xâ²-p)2] (X = Xâ²Â = H, Me, Et, OMe, CN, F, Cl or Br; X = H, Xâ²Â = OMe or NO2) were prepared in a two-step reaction involving the cleavage of [Rh(μ-Cl)(CO)2}2] with the diaryltriazene p-XC6H4NNNHC6H4Xâ²-p followed by the deprotonation of the resulting mononuclear triazene complex [RhCl(CO)2N(C6H4X-p)NNHC6H4Xâ²-p}] with NEt3. Yields of the dimeric products were maximised by carefully controlling the reaction time for each step. Reaction of the tetracarbonyls with PPh3 gave the mono- and di-substituted species [Rh2(CO)4ân(PPh3)n(μ-p-XC6H4NNNC6H4Xâ²-p)2] (n = 1 or 2), the reaction times again depending on the substituents X and Xâ². Each binuclear complex undergoes at least one reversible one-electron oxidation reaction at a platinum electrode in CH2Cl2. In some cases, e.g. X = Xâ²Â = OMe, as many as three oxidation waves are observed; for X = H, Xâ²Â = NO2, n = 1 or 2, well-defined reduction waves are apparent. The oxidation potential depends on the extent of carbonyl substitution (for each incremental increase in n the potential is decreased by ca. 300 mV) and on the triazenide ligand substituent such that E°Ⲡfor the first oxidation wave can be varied systematically over a range of 800 mV. There is a linear relationship between E°Ⲡfor the first oxidation step and the Hammett parameter Ïp but a poorer correlation for the second oxidation process.
复合物[Rh2(CO)4(δ-p-XC6H4NNNC6H4Xâ²-p)2](X = Xâ²Â = H、Me、Et、OMe、CN、F、Cl 或 Br;XÂ=H,Xâ²Â=OMe 或 NO2)的制备分两步进行,先用二元三氮烯 p-XC6H4NNHC6H4Xâ²-p 裂解[Rh(δ-Cl)(CO)2}2],然后用 NEt3 对生成的单核三氮烯络合物[RhCl(CO)2N(C6H4X-p)NNHC6H4Xâ²-p}]进行去质子化反应。通过仔细控制每个步骤的反应时间,最大限度地提高了二聚产物的产量。四羰基与 PPh3 反应产生了单取代和二取代物种 [Rh2(CO)4ân(PPh3)n(δ-p-XC6H4NNNC6H4Xâ²-p)2](n = 1 或 2),反应时间同样取决于取代基 X 和 Xâ²。每个双核复合物在 CH2Cl2 中的铂电极上至少发生一次可逆的单电子氧化反应。在某些情况下,例如 X = Xâ²Â = OMe,可观察到多达三个氧化波;对于 X = H、Xâ²Â = NO2、n = 1 或 2,可观察到明确的还原波。氧化电位取决于羰基取代的程度(n 每增加一个增量,电位就会降低约 300 mV)和三嗪配体取代基,因此第一个氧化波的 E°Ⲡ可以在 800 mV 的范围内有系统地变化。第一个氧化步骤的 E°Ⲡ与哈米特参数 Ïp 之间呈线性关系,但第二个氧化过程的相关性较差。