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Int J of Chemical Kinetics

Munisamy

Reddy

2006

A series of dinuclear platinum II complexes of the type [{trans-Pt(H 2 O)(NH 3 ) 2 } 2 -NH 2 (CH 2 ) n H 2 N] 4+ (where n = 2, 3, 4, and 6) were synthesized to investigate the influence of the bridging diamine linker on the reactivity of the platinum centers. The pK a values were determined, and the rates of substitution of the aqua moieties by a series of neutral nucleophiles viz. thiourea, 1,3-dimethyl-2-thiourea, and 1,1,3,3-tetramethyl-2-thiourea were studied as a function of concentration and temperature. All reactions studied gave excellent fits to a single exponential and obeyed the simple rate law, k obs = k 2 [Nu]. Negative activation entropies support an associative mode of substitution. The results obtained suggest that the rate of substitution is definitely influenced by the length of the diamine chain, with the rate of substitution decreasing as the length of the diamine chain increases.

Section: Discussionsupporting

confidence: 85%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Role of bridging diamine linkers on the rate of ligand substitution in a series of dinuclear Pt^II complexes

Int J of Chemical Kinetics

Munisamy

Reddy

2006

“…Substitutions involving TMTU gave the lowest rates, whereas those with TU reacted significantly faster. This trend is in line with the size of TMTU nucleophile relative to TU and DMTU [39,46,47]. The activation parameters in Table 4 show that the entropies of activation are large and negative.…”

Section: Complexsupporting

confidence: 62%

A kinetic study of aqua ligand substitution in dinuclear Pt(II) complexes containing four non-coplanar pyridine ligands

Kinunda

2014

Transition Met Chem

Self Cite

Substitution reactions of the aqua ligands from azine-bridged dinuclear platinum(II) complexes of the type [{cis-Pt(py) 2 (OH 2 )} 2 (l-pzn)](ClO 4 ) 4 [pzn = pyrazine (Pt-PZN), 2,3-dimethylpyrazine (Pt-2,3PZN), 2,5-dimethylpyrazine (Pt-2,5PZN) or 2,6-dimethylpyrazine (Pt-2,6PZN)] by thiourea nucleophiles were investigated under pseudo firstorder conditions as a function of concentration and temperature using the stopped-flow technique. The experimental results are discussed in reference to structures obtained by DFT calculations. The results are in good agreement with the pKa values of the complexes as well as DFT calculations. Compared to [{cis/trans-Pt(NH 3 ) 2 (OH 2 )} 2 (l-pzn)](ClO 4 ) 4 , the complexes in this series react faster by a factor of 10 or 23 respectively due to the presence of pyridine rings, which forces the geometry to allow p-back bonding to take place such that the electrons from the metal centres are accepted to the empty p*-orbitals of the pyridine subunits. The reactivity of the nucleophile is sterically dependent, with N,N,N 0 ,N 0 -tetramethylthiourea reacting three times slower than thiourea. In all complexes and for both substitution steps, the mode of activation remains associative in nature.

“…The steric strain on [Pt(terpy)X] (2− n )+ type complexes is also another reason for the high reactivity 17. Therefore, a vast number of studies have been done on the kinetics of substitution of [Pt(terpy)X] n + ‐type complexes with various nucleophiles 8,13,14,17–33. In terms of their biological properties, these Pt(II) terpy complexes themselves have also been shown to bind to double‐stranded DNA through intercalation 34 and have been found to be cytotoxic against Trypanosoma and Leishmania parasites in addition to human ovarian carcinoma 35,36.…”

Section: Introductionmentioning

confidence: 99%

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

Int J of Chemical Kinetics

Boer

Gertenbach

et al. 2008

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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