Mechanisms of the Axial Ligand Substitution Reactions of Dinuclear, Head‐to‐Head α‐Pyrrolidonato‐ and Pivalamidato‐Bridged cis‐Diammineplatinum(III) Complexes with Halide Ions

Abstract

The acid dissociation constant of the axial aqua ligand in the Head-to-Head (HH) dinuclear pivalamidato-bridged cis-di-) and the formation constants of the successive substitution reactions on the axial sites of the HH α-pyrrolidonato-bridged cis-diammineplatinum(III) dinuclear complex and the HH pivalamidato-bridged cis-diammineplatinum(III) dinuclear complex with halide ions X − (X − = Cl − and Br − ) to give monohalo and dihalo complexes were determined spectrophotometrically at 25°C and I = 2.0 M. A kinetic study was also performed for the monohalo and dihalo complex formations. The effect of the bridging ligand upon the axial site reactivity was compared and discussed. The ligand substitution behavior of the monohalo complex was af-

Kinetics and mechanisms of the axial ligand substitution reactions of platinum(III) binuclear complexes with halide ions

“…(10) is reasonable under the experimental conditions ([H + ]40.1 M) [29]. In Scheme 5, the k 2 # path must be included in case (C), which is unusual, though, considering the usual inertness of OH À in M(H 2 O) 5 (OH) (nÀ1)+ .…”

“…Most of the complexes of group (1) and (2) are considerably stable in solid and/or in solution, and have been widely studied. However, no detailed analysis in the reactivity and the reaction mechanism has been reported for platinum(III) dimers except one before our recent studies [27][28][29][30][31][32].…”

“…Table 2 Stepwise formation constants of the monohalo and dihalo complexes for the reaction of platinum(III) binuclear complexes with halide ions determined spectrophotometrically at 25 1C [29]. e The unconditional value was re-calculated [32].…”

“…Furthermore, the kinetic analyses in both reports are insufficient to clarify the detailed reaction mechanism. Thus, re-investigation was carried out on the axial water substitution reaction of the HPO 4 -bridged lantern-type complex with halide and pseudo-halide ions (X À ¼ Cl À , Br À , SCN À ) in acidic aqueous solution (Scheme 7) [32], and the detailed mechanisms were determined based on the mechanistic information obtained from the amidato-bridged platinum(III) binuclear complexes [27][28][29][30][31].…”

“…In this paper, we review our recent kinetic and mechanistic studies on the axial water ligand substitution reactions of the two types of platinum(III) binuclear complexes, the platinumblues derived bis(amidato)-bridged complexes, head-to-head (HH) and head-to-tail (HT) [Pt 2 (NH 3 ) 4 (m-amidato) 2 (OH 2 ) 2 ] 4+ (amidato ¼ a-pyridonato, a-pyrrolidonato, or pivalamidato) [27][28][29], and the tetrakis(hydrogenphosphato)-bridged lantern-type complex, [Pt 2 (m-HPO 4 ) 4 (OH 2 ) 2 ] 2À [32], with halide ions in acidic aqueous solution. These mechanistic studies provide the first detailed information concerning the reactivity of Pt(III) binuclear complexes.…”