Nucleophilic Reactivity of 4,4′-Disubstituted Diphenyl Sulfides Towards trans-Dichlorobis(pyridine)platinum(II)

Abstract

The kinetics of the reaction of trans-[PtC12py2] with a series of 4,4'-disubstituted diphenyl sulfides, XC6H4SC6H4Y, have been studied at 30° in methanol. A linear free energy correlation has been obtained between the logarithm of the second order rate constant and the sum of the Hamrnett substituent parameters for X and Y. This result is consistent with the notion that bond making is the driving force when divalent sulfur functions as a nucleophile towards platinum(I1) substrates and is consistent with the inability of 4,4'-dinitrodiphenyl sulfide to coordinate to platinum(I1).Les cinttiques des rtactions entre le [PtC12py2]-trans et une strie de diphtnylsulfures disubstituks en -4,4', XC6H4SC6H4Y, ont kt6 etudites i 30 "C dans le mtthanol. Une corrklation lineaire de l'tnergie libre a ttk obtenue entre le logarithme de la constante de vitesse du second ordre et la sornme des parametres de Harnrnett pour les substituants X et Y. Ce rtsultat est consistant avec la notion d'apres laquelle I'ttablissement d'une liaison est la force directive lorsqu'un soufre divalent fonctionne en tant que nucltophile envers le platine(I1); ce rtsultat est Bgalement cohtrent avec le fait que le dinitro-4,4' diphknylsulfure ne se coordonne pas avec le platine(I1).Canadian Journal of Chemistry, 49, 2390Chemistry, 49, (1971 Substitution reactions of square planar dB metal complexes, especially those of platinum(I1) have been well documented (1-3). Previous investigations have utilized trans-[PtCl,py,] as a representative substrate in order to investigate the reactivity of a variety of nucleophiles towards platinum(I1) complexes (4, 5). As part of a general interest in the donor properties of ligands containing a sulfur donor atom, we have undertaken a kinetic study of reaction 1 where Ar,S = a 4,4'-disubstituted diphenyl sulfide and py = pyridine. It was also anticipated that this study [ I ] would provide a quantitative indication of the ability of divalent sulfur in a diary1 sulfide to transmit the electronic effect of a para-substituent. The results of this study are reported at this time. Results and DiscussionThe rates of reaction between trans- [PtCl,py,] and XC6H4SC6H4Y ( = Ar,S) follow the usual two term rate law which is common to substitution reactions of square planar platinum(I1) complexes, viz. eq. 2, where k, is a first order rate The experimental pseudo first order rate constants, k,,,, are related to k , and k, by 151.Typical plots of k,,, us. [XC,H4SC6H4Y] are shown in Fig. 1. The slopes of these linear plots correspond to the various k,'s and the common intercept to k,. The kinetic data are tabulated in Table 1 together with the calculated values of the nucleophilic reactivity constant, nPt0, and the sum of the Hammett substituent parameters for each nucleophile. The nucleophilic reactivity constant has been defined by eq. 6. In order to For personal use only.

Structure−Reactivity Correlations for Complex Formation Reactions between Square-Planar Metal Centers and Thioethers

“…On the contrary, the close similarities between Pd(dien)H 2 O 2+ , Pt(dien)Br + , and Pd(H 2 O) 4 2+ with respect to their reactions with thioethers, indicate that the activation processes for the reactions of these complexes are very similar. Thus, activation processes for the Pd(dien)H 2 O 2+ and Pt(dien)Br + reactions resemble those for the reactions of the neutral complexes, − with bond-making as the important driving force.…”

“…Reactions of Pd(dien)H 2 O 2+ and Pt(dien)Br + with thioethers cannot be regarded as one limiting case, and those of the neutral complexes as another, as has been done in previous investigations . The different reaction trends reported and the so-called “duality behavior” are due to insufficient variations of both electronic and steric properties in previous work. −

4 Correlation between log k 1 and log k f for reactions 1 and 8, respectively. Ligand numbers refer to those listed in Tables and .

5 Steric profiles for reactions of Pd(dien)H 2 O 2+ (a) and Pt(dien)Br + (b) with thioethers according to eqs 10 and 11.

…”

“…Reactivity toward Neutral Platinum(II) and Palladium(II) Complexes. Second-order rate constants for reaction 7 have been measured for several dialkyl sulfides 7 and for a number of 4,4‘-substituted diphenyl sulfides . In the case of dialkyl sulfides, the very narrow regions of electronic and steric factors and the few ligands used do not allow a quantitative analysis.…”

“…In the case of dialkyl sulfides, the very narrow regions of electronic and steric factors and the few ligands used do not allow a quantitative analysis. Since the steric factors were held constant for the diphenyl sulfides, a marked electronic effect was noticed, as evidenced by a linear plot of log k 2 vs the sum of the Hammett substituent parameters …”

“…Thioethers are efficient nucleophiles, forming strong complexes with soft metal centers. A number of reactions between thioethers and square-planar complexes of palladium(II) and platinum(II) have been studied. − So far, there seems to be no general agreement as to how the electronic and steric properties of the thioethers affect their nucleophilicity. From studies of some neutral substrate complexes, it has been concluded that the σ-donor properties of the sulfur atoms are important, whereas the steric requirements of the thioethers are negligible. − On the other hand, steric effects are reported to dominate the reactivity of thioethers toward Pd(dien)OH 2 2+ and Pt(dien)Br + (dien = diethylenetriamine). , Substitution of chloride for thioethers at trans -Pt(py) 2 Cl 2 and PtCl 4 2- is reported to depend on electronic as well as steric factors. , These discrepancies seem to be due to a lack of systematic experimental data based on simultaneous and sufficient variation of electronic as well as steric properties.…”