Kinetic and mechanistic investigation into the influence of chelate substituents on the substitution reactions of platinum(II) terpyridine complexes

Abstract

The substitution kinetics of the complexes [Pt{4 -(o -CH 3 -Ph)-terpy} Cl]SbF 6 (CH 3 PhPtCl(Sb)), (ClPhPtCl), and [Pt{4 -(o -CF 3 -Ph)-terpy}Cl]SbF 6 (CF 3 PhPtCl), where terpy is 2,2 :6 ,2 -terpyridine, with the nucleophiles thiourea (TU), N,N -dimethylthiourea (DMTU), and N,N,N ,Ntetramethylthiourea (TMTU) were investigated in methanol as a solvent. The substitution reactions of the chloride displacement from the metal complexes by the nucleophiles were investigated as a function of nucleophile concentration and temperature under pseudo-first-order conditions using the stopped-flow technique. The reactions followed the simple rate law k obs = k 2 [Nu]. The results indicate that the introduction of substituents in the ortho position of the phenyl group on the ancillary ring of the terpy unit does influence the extent of π -backbonding in the terpy ring. This controls the electrophilicity of the platinum center, which in turn controls the lability of the chloro-leaving group. The strength of the electron-donating or -withdrawing ability of the substituents correlates with the reactivity of the complexes. Electron-donating

A kinetic investigation into the rate of chloride substitution from chloro terpyridine platinum(II) and analogous complexes by a series of azole nucleophiles

“…Thus, it can be concluded that the differences in the rate of substitution of all the complexes investigated are purely electronic in origin. This is similar to what has been reported in the literature [47].…”

“…It is known that changing its electronic properties influences the Scheme 2 Proposed mechanism of chloride substitution from the investigated complexes by a series of azole nucleophiles [48,49] and r-effects [34,47,50] have been shown to influence the reactivity depending on the moiety attached to the ancillary position on the terpy or on modification of the ligand attachment in the cis position of the metal centre. In the case of p-back-bonding, the terpy ligand accepts electron density from the platinum metal d-orbitals into its vacant p-orbitals rendering the metal centre more electrophilic.…”

From humble beginnings to a modern-day academic institution: 100 years of Chemistry at the University of Natal in Pietermaritzburg

“…This topic fitted in well with the coordination Chemistry studies under Field, and progress was rapid. Typical of his current research is a paper dealing with the kinetics and mechanism of platinum (II) terpyridine complexes (Jaganyi et al, 2008). The research has made great strides and the Research Group is now a very viable one, with input from local students as well as others from Kenya and Tanzania.…”

(1H-Pyrazole-κN2)(2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)platinum(II) bis(perchlorate) nitromethane monosolvate

“…Platinum(II) chelates have been extensively studied since their application as antitumour agents was discovered in the 1960s (Jaganyi et al, 2008). Although cis-diamminedichloroplatinum(II) (cisplatin) has been effective in the treatment of particular tumour cell lines, cisplatin resistance in certain cancer cell lines has sparked much research into developing new-generation platinum-based drugs (Thurston, 2007).…”

“…The substitution kinetics of the title metal chelate have been studied to further develop the understanding of the interactions between the Pt II ion and various nucleophiles. This research is critical to the development of new drugs (Jaganyi et al, 2008). The structure of the title pyrazole-substituted terpyridine-platinum(II) compound, [Pt(pyz)(terpy)](ClO 4 ) 2 Á-CH 3 NO 2 (where terpy is 2,2 0 :6 0 ,2 00 -terpyridine and pyz is pyrazole), (I), was elucidated to further develop the under-standing of the binding mode of the ancillary ligand, i.e.…”