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A Kinetic and Mechanistic Investigation of Polyethyleneglycol Ether Bridged Dinuclear Platinum(II) 2,2’:6’,2’’-Tpyridine Complexes Aishath Shaira* a,b and Deogratius Jaganyi c,d a. School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa. b. Department of Environment and Natural Science, The Maldives National University, Male’, Maldives. c. School of Pure and Applied Sciences, Mount Kenya University, P.O. Box 342-01000, Thika, Kenya. d. Department of Chemistry, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa. A series of dinuclear Pt(II) complexes bridged with polyethyleneglycol ether of the type [ClPt(tpy)- O(CH 2 CH 2 O)n(tpy)PtCl]Cl 2 where n = 1 (Ptdteg), 2 (Ptdtdeg), 3 (Ptdtteg), 4 (Ptdttteg) and linker free complex, ClPt(tpy)-(tpy)PtCl]Cl 2 , (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 the 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 analyser. The reactions gave single exponential fits following the rate law kobs = k2[Nu]. Introduction of polyethyleneglycol ether linker decreases the electrophilicity of the platinum centre and the whole complex. The results obtained indicate that the rate of substitution reactions is controlled by both electronic and steric hindrance which increases with the length of the linker. Experimental results are supported by the density functional theory (DFT) calculations and structures obtained at LanL2DZ/ B3LYP 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 favoured.
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© The Author(s), 2023
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