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

Abstract

The axial water ligand substitution reaction on the head-to-head (HH) and head-to-tail (HT) amidato-bridged cis-diammineplatinum(III) binuclear complexes, HH-and HT-[Pt 2 (NH 3 ) 4 (m-amidato) 2 (OH 2 ) 2 ] 4+ (amidato ¼ a-pyridonato, a-pyrrolidonato, or pivalamidato), with halide ions (X À ¼ Cl À , Br À ) in acidic aqueous solution reveals a consecutive 2-step kinetics under the pseudo first-order conditions of a large excess concentration of halide ion relative to that of the complex ðC X À bC Pt Þ, corresponding to formation of the monohalo (step 1) and the dihalo complexes (step 2). The first substitution step of all the HH and HT diaqua dimers consists of two parallel reaction pathways: one is the simple substituion path of one of the coordinated aqua ligands with X À , and the other is the replacement in the aquahydroxo complex which is the conjugate base of the diaqua dimer. In step 2, there are three reaction pathway patterns: the direct substitution path, the path via a coordinatively unsaturated intermediate, and the unusual path of OH À replacement.Step 2 proceeds via either one or two paths of the three depending on the nature of the halide ion as well as the bridging ligand. On the other hand, the substitution reaction of the hydrogenphosphato-bridged lantern-type complex, [Pt 2 (m-HPO 4 ) 4 (OH 2 ) 2 ] 2À proceeds in 1-step at C X À bC Pt , in which the first aqua ligand substitution to form the monohalo species is rate-determining and the monohalo species is in rapid equilibrium with the dihalo complex. The rate-determining step consists of parallel pathways similar to step 1 in the amidato-bridged complex systems. r

Axial ligand effect on the reaction mechanism of head-to-head pivalamidato-bridged Pt(III) binuclear complex containing an equatorial bromide ligand with acetone

“…The formation of complex 1 was confirmed by spectrophotometric titration with sodium bromide solution; similar spectral change to complex 3 was observed [14][15][16][17], and the last spectrum agreed to that of complex 2. Complex 2 was prepared according to the procedure reported in the literature [1,3].…”

“…In step 1, the H 2 O ligated to Pt(Br 2 O 2 ) is substituted with enol acetone to form a p-complex. Subsequently, in step 2, a p-r , Scheme 2 appears to be reasonable, considering the reactivity of the amidato-bridged Pt III binuclear complexes studied so far [6][7][8][9][10][14][15][16][17].…”

“…The axial ligand substitution of complex 3 with X À occurs successively in two steps [14][15][16][17]. The first substitution always occurs on the axial site of Pt(N 2 O 2 ), which is followed by the second substitution on the axial site of Pt(N 4 ) [14].…”

Coordination Isomers of Trinuclear Pt2Hg Complex That Differ in Type of Metal–Metal Bond

“…If that is the case, the rate constant required for the migration to show such a sharp coalesced peak should be more than 10 7 s –1 , since a chemical shift difference between Pt II and Pt III sites is typically more than 1000 ppm. However, the typical rate constant for substitution of Pt III –X is much less. − The spectrum can also be explained if we assume that the complex exists in two-covalent form instead of the “dative-covalent form” without halide migration.…”

Formation mechanism of 2-methyl-2-buten-1,4-diol and 2-methyl-3-buten-1,2-diol from 2-methyl-1,3-butadiene on a head-to-head pivalamidato-bridged cis-diammineplatinum(iii) binuclear complex

“…In contrast, it is known that the second step for the reactions of the amidato-bridged complexes with Cland Brconsists of one (k 2 ) or two steps (k 2 and k 3 , or k 2 and k 2 # ), as shown in Scheme 4. 18,20 In the case of the reaction of 1 with Br -, the second step involves k 2 and k 2 # , whereas that for the reactions of the other dimer complexes with Brinvolves k 2 and k 3 . Moreover, for the reaction of the HT a-pyridonato-bridged Pt(III) binuclear complex with p-styrenesulfonate, the second step consists of all three paths (k 2 , k 2 # , and k 3 ).…”