New trans-[Pd(L-κS,O)2] complexes from N,N-dialkyl-N′-aroylthioureas prepared by photo-induced isomerization of their cis-[Pd(L-κS,O)2] counterparts and their thermal trans-cis isomerization

• Published in: Inorganica Chimica Acta 2018-11, Vol.483, p.440-447
• Main Authors: Nkabyo, Henry A., Koch, Klaus R.
• Format: Article
• Language: English
• Subjects: Acetonitrile; Chemical elements; Chloroform; Crystallization; Isomerization; Ligands; Melting points; NMR spectroscopy; Photo-induced cis-trans isomerization; Reversion; Single crystals; Thermal trans → cis relative reversion rates; trans-bis(N,N-Diethyl-N′-4-methylbenzoylthioureato)-palladium(II); trans-bis(N,N-Dimethyl-N′-benzoylthioureato)-palladium(II); X ray spectra; X-ray diffraction
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2018.08.028

[Display omitted] •Photochemical synthesis of trans-[Pd(L-κS,O)2] from the cis-[Pd(L-κS,O)2]•The cis → trans[Pd(L-κS,O)2] is photochemical, trans → cis is a thermal process.•Relative rates of reversion trans → cis are estimated in acetonitrile and chloroform. Photo-induced isomerization of cis-[Pd(L1,2-κS,O)2] (HL1 = N,N-diethyl-N′-4-methyl-benzoylthiourea, HL2 = N,N-dimethyl-N′-benzoylthiourea) in acetonitrile solution leads to the reproducible and clean isomerization of rare, new trans-[Pd(L1,2-κS,O)2] complexes, isolated by vapour diffusion crystallization and characterized by single-crystal X-ray diffraction. The isolated trans-[Pd(L1,2-κS,O)2] complexes show higher melting points to the corresponding cis-[Pd(L1,2-κS,O)2] precursors. Time resolved 1H NMR spectroscopy of the isolated trans-[Pd(L1,2-κS,O)2] complexes in chloroform, shows these to spontaneously revert to their cis-[Pd(L1,2-κS,O)2] counterparts in the absence of light by a simple first-order process at relative rates of the order k1 = 0.23 × 10−2 min−1 and k2 = 0.18 × 10−2 min−1 respectively. The reversion trans → cis of these complexes is confirmed also in acetonitrile using reversed-phase HPLC following irradiation of dilute solutions with polychromatic light, at higher relative rates of k1 = 2.6 × 10−2 min−1 and k2 = 4.9 × 10−2 min−1 respectively.