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The effect of an alkyl chain tether on the kinetics and mechanistic behaviour on bifunctional dinuclear platinum(II) complexes bearing N,N’-dipyridylamine ligands

Abstract

Abstract In the current paper, we report the kinetics of bifunctional dinuclear platinum(II) complexes viz., 1,2-N,N’-di-(2,2-dipyridylamine)ethanetetraquaplatinum(II), PtL2, 1,3-N,N’-di-(2,2-dipyridylamine)propanetetraquaplatinum(II), PtL3, 1,4-N,N’-di-(2,2-dipyridylamine)butanetetraquaplatinum(II), PtL4, 1,5-N,N’-di-(2,2-dipyridylamine)pentanetetraquaplatinum(II), PtL5 and 1,6-N,N’-di-(2,2-dipyridylamine)hexanetetraquaplatinum(II), PtL6. The substitution reactions were carried out on tetraqua complexes with thiourea nucleophiles under pseudo-first-order conditions as a function of nucleophile concentration and temperature by stopped-flow and UV-Vis spectrophotometric techniques. An experimental study was conducted with the aim of determining the influence of alkyl chain on the steric and electronic structure of dinuclear platinum(II) complexes. The reactivity of these complexes was dependent on the length of the alkyl spacer. The results obtained herein, demonstrate intriguing effects of the odd-even effects induced by the alkyl chain on the complexes. Artificial constraints imposed by the alkyl chain significantly affect their conformational structure as either to synperiplanar (syn-) or antiperiplanar (anti-) characterized by the odd and even effect. The kinetic, mechanistic and conformational behaviour was influenced by the size of alkyl chain in accordance to odd-even alterations of the spacer. Computational modeling using density functional theory (DFT) calculations supplemented experimental findings that structural features and the reactivity pattern of these organometallic complexes are governed by both steric and electronic effects arising from the flexibility and inductive nature of alkyl spacer. The strong σ-donicity of longer alkyl chain favours sufficient accumulation of electron density at the metal centre and stabilize 14-electron intermediate. The study shows the HOMO-LUMO energy (∆E) is affected by the length of the spacer. Kinetic and DFT data indicate electron donation by the alkyl spacer. The low positive values of enthalpy of activation and significantly large negative values of entropy of activation parameters indicate an associative mechanism of substitution. Key words: Alkyl spacer, thiourea, platinum(II), odd-even effect, associative

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Publication details

The article was received on 14 Aug 2017, accepted on 10 Nov 2017 and first published on 13 Nov 2017


Article type: Paper
DOI: 10.1039/C7NJ03021E
Citation: New J. Chem., 2017, Accepted Manuscript
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    The effect of an alkyl chain tether on the kinetics and mechanistic behaviour on bifunctional dinuclear platinum(II) complexes bearing N,N’-dipyridylamine ligands

    P. A. Wangoli and G. B. Kinunda, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ03021E

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