Stereostructural effects of the asymmetric chelating ligand (phenyl)(2-pyridyl) ketoxime in Ru(II)-dmso complexes: Syntheses, crystal structures, isomerization, and substitution reactions

(Phenyl)(2-pyridyl) ketoxime (Hppko) is a 2-pyridyl oxime derivative whose metal complexes have been studied as models for catalytic N–O and N=C bond cleavage of coordinated ketoximes. In this study, we report the synthesis, characterization, and reactions-in-solution of trans (Cl), cis (S)-[RuCl 2 (dmso- S ) 2 (Hppko)]·0.5H 2 O ( 1 ·0.5H 2 O; dmso = dimethyl sulfoxide), in which Hppko coordinates to Ru 2+ via pyridyl N (N py ) and ketoxime N (N ox ) as a neutral, asymmetric bidentate ligand. In DMSO, 1 ·0.5H 2 O undergoes selective thermal isomerization to the cis (Cl), cis (S), cis (N ox , S ) isomer ( 2 ), with no detectable formation of the cis (Cl), cis (S), cis (N py ,S) isomer. In water or MeCN, the dmso- S ligand trans to N ox and cis to N py group in 1 is substituted by H 2 O or MeCN to form trans (Cl), cis (N ox ,S)-[RuCl 2 (dmso- S )(solv)(Hppko)] (solv = OH 2 , 3 ; MeCN, 4 ), respectively. Single-crystal X-ray structures of 1 ·0.5H 2 O, 2, 3 , and 4 ·MeCN show elongated N=C bonds relative to free Hppko, indicating π-electron delocalization into the chelate ring. In all structures, an intramolecular hydrogen bond between the Hppko OH group and the O atom of the dmso- S ligand cis to N ox is observed; this interaction is also retained in solution, as evidenced by the selective isomerization of 1 to 2 and the regioselective substitution of dmso- S in 1 to form 3 or 4 . These results indicate that the OH Hppko ···O dmso hydrogen-bonding interaction can control asymmetric ligand orientation and govern isomerization and substitution processes in Ru(II)–Hppko complexes. Computational investigations further validated the structural findings, with DFT-optimized geometries aligning well with experimental data. Absorption spectra calculated using time-dependent density functional theory closely matched the measured DMSO spectra.