Understanding the electronic and pi-conjugation roles of quinoline on ligand substitution reactions of platinum(II) complexes

作者：Kinunda Grace; Jaganyi Deogratius^*

来源：Transition Metal Chemistry, 2014, 39(4): 451-459.

DOI：10.1007/s11243-014-9819-8

A kinetic and mechanistic study of chloride substitution by thiourea nucleophiles, namely thiourea, N-methylthiourea, N,N-dimethylthiourea and N,N,N',N'-tetramethylthiourea in the complexes chlorobis-(2-pyridylmethyl)amineplatinum(II) (Pt1), chloro N-(2-pyridinylmethyl)-8-quinolinamineplatinum(II) (Pt2), chloro N-(2-pyridinylmethylene)-8-quinolinamineplatinum(II) (Pt3) and chlorobis(8-quinolinyl)amineplatinum(II) (Pt4) was undertaken under pseudo-first-order conditions using UV-visible spectrophotometry. The study showed that lability of the chloro leaving group is dependent on the strength of pi-interactions between the filled d pi-orbitals of the metal and the empty pi*-orbitals of the chelating ligand in the following manner: Pt1 > Pt3 > Pt2 > Pt4. Introduction of the quinoline moiety within the non-labile chelated framework of the Pt(II) complexes results in a more electron-rich metal centre which retards the approach of the nucleophile through repulsion. Moreover, the net sigma-effect of the ligand moiety plays a significant role in controlling the reactivity of the complexes. The experimental results are interpreted with the aid of computational data obtained by density functional theory (B3LYP(CPCM)/LANL2DZp//B3LYP/-LANL2DZp) calculations. The mode of substitution remains associative as supported by negative entropies and the dependence of the second-order rate constants on the concentration of entering nucleophiles.

• 出版日期2014-5