Herein we show the design and synthesis of an electron-rich, sulfoxide-chelated, ruthenium benzylidene. In contrast to previously reported sulfoxide-chelated ruthenium benzylidenes, this complex is more stable in a cis-dichloro conformation and is thus latent in typical olefin metathesis reactions. The complex was characterized by NMR, UV−vis, and X-ray spectroscopy, alongside density functional theory computations. The latent precatalyst could be activated thermally and, depending on the solvent, by UV−C or visible light. In addition, an original "thermo-chromatic" orthogonal sequence was developed, further improved by the use of a thioether chelated complex, where a divergent two-step synthesis can lead to a dihydrofuran or a dihydropyran depending only on the order by which the different stimuli, heat or light, are applied.
Ruthenium
sulfur-chelated benzylidenes possessing five-membered
chelating architectures exhibiting latency and excellent thermal and
photochemical activation behavior in various metathesis reactions
are well known. On the other hand, six-membered sulfur-Ru-chelates
(Ru–S) are much rarer. Herein, we describe a study of the synthesis,
characterization, and catalytic properties of four new cis-dichlorido ruthenium dithioacetal-chelated complexes. As expected
for sulfur-chelated benzylidenes, the X-ray structures of the complexes
disclosed cis-dichloro configurations for all the
complexes. The catalytic profiles of these complexes were systematically
studied for benchmark RCM and ROMP reactions and provided findings
on latency and activation based on chelating dithioacetal groups.
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