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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Tuning the reactivity of chelated dinuclear Pt(II) complexes through a flexible diamine linker. A detailed kinetic and mechanistic study
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Tuning the reactivity of chelated dinuclear Pt(II) complexes through a flexible diamine linker. A detailed kinetic and mechanistic study

机译：通过灵活的二胺接头调节螯合的双核Pt（II）配合物的反应性。详细的动力学和力学研究

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The rate of displacement of the aqua ligands by three neutral nucleophiles (Nu) of different steric demands, namely thiourea (tu), N,N'-dimethylthiourea (dmtu) and N,N,N',N'-tetramethylthiourea (tmtu) and an anionic nucleophile (I-) in complexes of the form [{Pt(H2O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-N(CH2)(n)N](CF3SO3)(4) , n = 2 (En); 3 (Prop); 4 (But); 6 (Hex); 8 (Oct) and 10 (Dec), was studied under pseudo first-order conditions as a function of concentration, temperature and pressure using stopped-flow techniques and UV-visible spectrophotometry. The pseudo first-order rate constants, k(obs)(1(st)/2(nd)), for the simultaneous substitution of the aqua ligands and the proposed subsequent dechelation of the pyridyl units, respectively, agreed well to the rate law: k(obs)(1(st)/2(nd)) = k(2)(1(st)/2(nd))[Nu]. High negative activation entropies, negative volumes of activation and second-order kinetics for the displacement reactions all support an associative mode of activation. Except for Prop, the rate of the simultaneous substitution of the aqua ligands in the complexes was found to increase as the chain length of the linker increases from En to Hex, beyond which any further increase in chain length is not accompanied by a further increase in reactivity. The reactivity trend of the even-bridged complexes with C-2h symmetry is ascribed to a concomitant decrease in axial steric influences imposed on one side of the square-planar picolyl chelates by the other as the chain length increases. Based on the model structures of the complexes, this kind of steric imposition occurs only in complexes with an even number of CH2 groups within the linker. The Prop complex, having a C-2v symmetry showed exceptional high reactivity towards the nucleophiles. A cage effect, evolving from its bowl-shaped molecular structure, is proposed to explain this high reactivity. The order of reactivity of the nucleophiles increased in the order I- tu approximate to dmtu > tmtu, in line with the strong electrostatic interactions between the highly polarizable iodide nucleophile and the Pt centers, steric retardation effects in the case of tmtu and dominating positive inductive effects for the dmtu nucleophile.
机译：三种具有不同空间需求的中性亲核试剂（Nu），即硫脲（tu），N，N'-二甲基硫脲（dmtu）和N，N，N'，N'-四甲基硫脲（tmtu）对水配体的置换速率和[{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶基甲基）-N（CH2）（n）N]形式的配合物中的阴离子亲核试剂（I-） （CF3SO3）（4），n = 2（En）; 3（Prop）; 4（But）; 6（Hex）; 8（Oct）和10（Dec），是在伪一阶条件下作为函数进行研究的使用停止流动技术和紫外可见分光光度法测定浓度，温度和压力。伪一级速率常数k（obs）（1（st）/ 2（nd））用于同时取代水配体和拟议的吡啶单元随后的脱螯反应分别与速率定律非常吻合：k（obs）（1（st）/ 2（nd））= k（2）（1（st）/ 2（nd））[ Nu。高的负活化熵，负的活化体积和置换反应的二级动力学都支持缔合的活化模式。除Prop以外，发现随着连接子链长从En到Hex的增加，络合物中水配体的同时取代率也会增加，超过此长度，链长的任何进一步增加都不会伴随着Pn的进一步增加。反应性。具有C-2h对称性的偶数桥连配合物的反应性趋势归因于随着链长的增加，轴向空间位阻影响施加在方形平面甲基吡啶螯合物的一侧。基于配合物的模型结构，这种空间位阻仅在接头中具有偶数个CH2基团的配合物中发生。具有C-2v对称性的Prop配合物对亲核试剂显示出异常高的反应活性。从其碗形分子结构演变而来的笼效应被提出来解释这种高反应性。亲核试剂的反应顺序以I- tu的顺序增加，近似于dmtu> tmtu，这与高度极化的碘化物亲核试剂与Pt中心之间的强静电相互作用，tmtu时的位阻效应和支配性有关dmtu亲核试剂具有积极的诱导作用。

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