The role of 8-quinolinyl moieties in tuning the reactivity of palladium(II) complexes: a kinetic and mechanistic study. Issue 3 (1st February 2019)

• Record Type: Journal Article
• Authors: Onunga, Daniel O.; Jaganyi, Deogratius; Mambanda, Allen
• Is Part Of: Journal of coordination chemistry. Volume 72:Issue 3(2019)
• Page Start: 499
• Page End: 515
• Publication Date: 2019-02-01
• Subjects: π-Conjugation -- electronic effects -- quinoline -- σ-donation; Coordination compounds -- Periodicals; 541.2242
• DOI: 10.1080/00958972.2019.1573994
• Languages: English
• ISSNs: 0095-8972

Abstract

Abstract: The rate and mechanism of chloride substitution from Pd(II) complexes, chlorobis-(2-pyridylmethyl)aminepalladium(II), 1, chloro-8-[(2-pyridylmethyl)amino]quinolinepalladium(II), 2, chloro-N-(2-pyridinylmethylene)-8-quinolinaminepalladium(II), 3, and chlorobis(8-quinolinyl)aminepalladium(II), 4, are reported. The labile chloride was substituted from the complexes by thiourea nucleophiles viz, thiourea (Tu), N, N′-dimethylthiourea (Dmtu) and N, N, N′, N′-tetramethylthiourea (Tmtu). The reactions were monitored under pseudo -first-order conditions in methanol using stopped-flow spectrophotometry as a function of concentration and temperature. All the reactions obeyed the rate law k obs = k 2 [Nu] following the order1 >3 >2 >4 with4 exhibiting the slowest rate of substitution due to the stronger σ-donor effect of 8-quinolyl moiety of the coordinated ligand, which makes the Pd center more electron-rich. This slows the nucleophilic attack by the nucleophiles. The values of the thermodynamic parameters (Δ H # and Δ S # ) support an associative substitution mechanism. The trends in the DFT calculated data support the experimentally observed order of the reactivity of the complexes.