School of Chemistry, University of KwaZulu-Natal, Scottsville, 3209, South Africa.
Dalton Trans. 2012 Jan 21;41(3):908-20. doi: 10.1039/c1dt11516b. Epub 2011 Nov 17.
Substitution reactions of platinum complexes bearing cyclohexylamine/diamine moieties viz., Pt(H(2)O)(N,N-bis(2-pyridylmethyl)cyclohexylamine)(2), bpcHna; {Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-trans-1,4-cyclohexyldiamine)(4), cHn and {Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-4,4'-dicyclohexylmethanediamine)(4), dcHnm and phenylamine/diamine moieties viz., (Pt(H(2)O)N,N-bis(2-pyridylmethyl)phenylamine)(2), bpPha; {Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-phenyldiamine)(4), mPh; {Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-1,4-phenyldiamine)(4), pPh and {Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-4,4'-diphenylmethanediamine)(4)), dPhm with thiourea nucleophiles were studied in acidified 0.01 M LiCF(3)SO(3) aqueous medium under pseudo-first-order conditions using stopped-flow and UV-visible spectrophotometric techniques. The rate of substitution follows a similar trend in the two sets of complexes and decreases in the order: bpcHna > dcHnm > cHn and bpPha > dPhm ≈ pPh ≈ mPh), respectively. The result of this study has shown that the rigidity and/or the planarity of a diamine bridge linking the two (2-pyridylmethyl)amine-chelated Pt(II) centres, influences the reactivity of the metal centres by protracting similar symmetry elements within the complexes, which determines the amount of steric influences felt on the coordination square-plane. Hence, the order of reactivity is controlled by both the steric hindrance and the magnitude of the trans σ-inductive effect originating from the linker towards the metal centre. These two factors also impact on the acidity of the complexes. The high negative entropies and low positive enthalpies support an associative mode of activation.
在酸化的 0.01 M LiCF3SO3 水介质中，使用停流和紫外可见分光光度技术，研究了带有环己基胺/二胺部分的铂配合物，即[Pt（H2O）（N，N-双（2-吡啶甲基）环己基胺）]（CF3SO3）2，bpcHna；[{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶甲基）-反-1,4-环己基二胺）]（CF3SO3）4，cHn 和 [{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶甲基）-4,4'-二环己基甲二胺）]（CF3SO3）4，dcHnm 和苯甲胺/二胺部分，即[Pt（H2O）N，N-双（2-吡啶甲基）苯甲胺]（CF3SO3）2，bpPha；[{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶甲基）-1,3-苯二胺）]（CF3SO3）4，mPh；[{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶甲基）-1,4-苯二胺）]（CF3SO3）4，pPh 和 [{Pt（H2O）}（2）（N，N，N'，N'-四（2-吡啶甲基）-4,4'-二苯甲撑二胺）]（CF3SO3）4，dPhm 与硫脲亲核试剂反应，在酸化的 0.01 M LiCF3SO3 水介质中，使用停流和紫外可见分光光度技术，在准一级条件下进行了研究。在两组配合物中，取代速率遵循相似的趋势，并按以下顺序降低：bpcHna>dcHnm>cHn 和 bpPha>dPhm≈pPh≈mPh）。这项研究的结果表明，连接两个（2-吡啶甲基）胺螯合 Pt（II）中心的二胺桥的刚性和/或平面性，通过在配合物中延长相似的对称元素，影响金属中心的反应性，从而决定了配位正方形平面感受到的空间位阻的程度。因此，反应性顺序受空间位阻和来自配体到金属中心的顺式σ诱导效应的大小控制。这两个因素也会影响配合物的酸度。高负熵和低正焓支持缔合活化模式。
