Abstract
The reaction of dichloroarylazopyridinepalladium(II) [Pd(aap)Cl2, aap=4-R′C6H4N-N-2-C5H4N; R′= H (1), Me (2), Cl (3)] with pyridine bases [RPy: R-H (a), 2-Me(b), 4-Me(c), 4-Cl(d), 2-Ph(e), 2-PhCH2(f)] has been studied spectrophotometrically in MeCN at 400nm. The products (4) have been isolated and characterized as trans-Pd(RPy)2Cl2. The kinetics of the nucleophilic substitution have been examined under pseudo-first-order conditions with respect to base at 298K and follow the rate law, Rate=k[RPy]2 [Pd(aap)Cl2]. The rate data supports a nucleophilic association path. External addition of Cl− (LiCl) suppresses the rate, which follows the order: k(3)> k(1)>k(2), where k values are linearly related to Hammet σ constants. 2-Substitution in the pyridine base remarkably reduces the rate compared with 4-substitution and is attributed to a steric effect that destabilizes the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (e)>(f)>(b). The 4-substituted pyridines control the rate via the inductive effect and follow the order: (d)>(a)>(c).
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Roy, R., Misra, T.K., Sinha, C. et al. Kinetics and mechanism of nucleophilic substitution of dichloroarylazopyridinepalladium(II) by pyridine bases. Transition Metal Chemistry 22, 453–458 (1997). https://doi.org/10.1023/A:1018550927193
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DOI: https://doi.org/10.1023/A:1018550927193