A kinetic and mechanistic study of dinuclear Pt(II) 2,2 ':6 ',2 ''-terpyridine compounds bridged with polyethyleneglycol ether flexible linkers

作者：Shaira A; Jaganyi D^*

来源：Journal of Coordination Chemistry, 2015, 68(17-18): 3013-3031.

DOI：10.1080/00958972.2015.1064114

• Substitution kinetics
• Mechanistic study
• Dinuclear platinum
• Polyethyleneglycol ether
• Terpyridine

Introduction of ethyleneglycol ether linker decreases the electrophilicity of the platinum center and the whole complex. The rate of substitution reactions is controlled by both electronic and steric hindrance which increases with the length of the linker
A series of dinuclear Pt(II) complexes bridged with polyethyleneglycol ether of the type [ClPt(tpy)O (CH2CH2O)(n)(tpy)PtCl]Cl-2 where n = 1 (Ptdteg), 2 (Ptdtdeg), 3 (Ptdtteg), 4 (Ptdttteg), and linker-free complex, (Ptdt) (where tpy = 2,2':6',2 ''-terpyridine), were synthesized and characterized to investigate the role of bridging polyethyleneglycol ether linker on the substitution reactivity of dinuclear Pt(II) complexes. Substitution reactions were studied using thiourea nucleophiles, viz. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU) under pseudo-first-order conditions as a function of concentration and temperature by conventional stopped-flow reaction analyzer. The reactions gave single exponential fits following the rate law k(obs) = k(2)[Nu]. Introduction of polyethyleneglycol ether linker decreases the electrophilicity of the platinum center and the whole complex. The results obtained indicate that the rate of substitution is controlled by both electronic and steric hindrance which increases with the length of the linker. Experimental results are supported by density functional theory calculations and structures obtained at B3LYP/LANL2DZ level. The order of the reactivity of the nucleophiles is TU > DMTU > TMTU. The magnitude and the size of the enthalpy of activation and entropy of activation support an associative mode of mechanism, where bond formation in the transition state is favored.

• 出版日期2015