Influence of substituted pyridines in the chemical behavior of dimethyl sulfoxide ruthenium complexes

• [Rucl2(S–DMSO)2(X–py)2 complexes with X = H (1), 4-CONH2 (2), 3-CONH2 (3) are reported.
• DMSO/X–pyridine combination provided complexes with high redox potentials.
• During photolysis at 350 nm, DMSO is photosubstituted by CH3CN.
• In absence of external stimulus, the X–pyridines were released in the order 3 > 2 > 1.
• The complexes undergo ROMP only with external stimulus.

[RuCl2(S–DMSO)2(X–py)2] type complexes, with X = H (1), 4-CONH2 (2), or 3-CONH2 (3), exhibited trans,cis,cis conformational isomer (species A), with additional cis,cis,cis isomer type (species B) for 1. Electronic spectra with bands in the wavelength range of 270–450 nm were unchanged for 120 min at 25 °C in CH3CN. Irradiation at 350 nm provided replacement of DMSO ligands by CH3CN solvent molecules. Cyclic voltammetry studies in CH3CN revealed an electrochemical–chemical process with a Ru–(S–DMSO) to Ru–(O–DMSO) linkage isomerization for species B from 1. The complexes were inactive for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) for 60 min at 25 °C. However, polyNBE was produced by aging the complex solutions for 90–200 min at 25 °C, raising the temperature to 50 °C, irradiating the solutions at 350 nm for 5–10 min or when the complexes were in the presence of NBu4ClO4.

The substituents in pyridine, X = H (isomers A and B), 4-CONH2 (isomer A) and 3-CONH2 (isomer A), provided latency in Ru–DMSO type complexes for ROMP, which could be activated under specific conditions (temperature; aging; irradiation; presence of NBu4ClO4). The behavior of the complexes in solution was studied to characterize this chemical reactivity.Figure optionsDownload as PowerPoint slide