One of the major shortcomings in olefin metathesis is a limited stereocontrol of the alkene product. In our efforts to address this shortcoming, a series of bidentate N-heterocyclic (NHC) ligands containing a pyridyl group were synthesized in a straightforward three-step procedure starting from the respective anilines and inexpensive 2-chloroethylamine hydrochloride. This NHC precursors as hexafluorophosphate salt were used to produce cationic, dimeric silver complexes with two PF<sub>6</sub><sup>-</sup> counteranions. Their dimeric structures could be confirmed via X-ray diffraction. The NHC ligands could be transferred via transmetallation onto ruthenium starting with dichloro(p-cymene)ruthenium(II) as precursor. The monomeric, 18-electron ruthenium complexes were obtained as hexafluorophosphate salts, and their structures were confirmed by NMR spectroscopy as well as single crystal structure analysis. Our hypothesis is, that the simultaneous binding of the pyridyl group and the chloride to the metal center will be the basis for the preference of the Z-product during olefin metathesis. Attempts to introduce an alkylidene into the cymene ruthenium complex or to activate the precursor complex for olefin metathesis in situ with an alkylidene generating group have failed so far but other approaches, including the use of other ruthenium precursor complexes, including alkylidenes, is under current investigation.

Synthesis of bidentate, unsymmetric N-heterocyclic carbene ligands for potential applications in cis-selective olefin metathesis

255th National Meeting (2018)

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