Phosphine and Thiophene Cyclopalladated Complexes: Hydrolysis Reactions in Strong Acidic Media

Abstract

The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF(4) (R=P(OPh)(3), PPh(3), and SC(4)H(8)) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3-11.7 M range. In all cases, a biphasic behavior was observed with rate constants k(1obs), which corresponds to the initial step of the hydrolysis reaction, and k(2obs), where k(1obs)>k(2obs). The plots of k(1obs) and k(2obs) versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k(1obs) value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh(3), P(OPh)(3), and SC(4)H(8), respectively. Regarding k(2obs), the change occurred in all cases at about 6.5 M H(2)SO(4) and matched up with the results reported for the hydrolysis of the 2-acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of k(i),(obs) (i=1,2) versus cH+. The rate-determining constants, k(0,A-1), k(0,A-2), and k(0,A-SE2) were evaluated in all cases. The R=P(OPh)(3) complex was most reactive due to its π-acid character, which favors the rupture of the trans nitrogen-palladium bond in the A-2 mechanism and also that of the pyridine nitrogen-palladium bond in the A-1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent.

Synthesis and structural characterization of Pd(II) complexes derived from perimidine ligand and their in vitro antimicrobial studies

“…In most cases, the intramolecualr activation of the C-H bond comes about with N-containing ligands, the metal quite often being palladium. The cyclopallaldated compounds formed thus way quite often display a characteristic ability as starting material in organic synthesis and have given way to wide slate of reaction which proceed with notable regio-and stereoselectivity, leading to extensive possibilities for synthetic applications [20][21][22][23]. The synthesized ligand, L and its Pd(II) complexes were tested in vito against a number of microbes and results showed complexes to be more effective as compared to their corresponding ligand, L. DNA interactive studies have also been carried out with CT-DNA and results suggest that Pd(II) complexes have significant DNA binding as compared to their corresponding ligand, L.…”

“…Literature has also revealed that organic moiety may undergo metallation with formation of carbon-metal bond by using transition metal complexes with two electron donor atoms. Cyclometallated complexes constitute an important tool to activate the C-H r bond stabilized by the additional coordination of metal to a heteroatom forming transition metal complexes [20][21][22][23]. C-H functionalization has the potential to become a paradigm shifting for organic synthesis and over the last decade, a large variety of new C-H functionalization methodologies have been developed [20][21][22][23].…”