In this doctoral thesis, we investigated mesoionic N-heterocyclic olefins (mNHOs). mNHOs are a recent class of ligands, derived from structurally similar (mesoionic) N-heterocyclic carbenes, which are widely used as ligands. We described preparation of mNHOs from 1,3,4,5-substituted-1,2,3-triazolium salts and tested their reactivity towards different organometallic precursors. Our focus was on mNHOs’ coordination abilities and properties of their organometallic compounds. We therefore synthesised mNHOs that could enable monodentate and bidentate coordination to the metal center and introduce a stereogenic centre into the organometallic complex. We successfully prepared the first known palladium and gold complexes with mNHOs. Their structures were confirmed using spectroscopic and computational methods. We also described a rare instance of a conformationally stable C(sp$^2$)–C(sp$^3$) stereogenic axis in one of the palladium complexes. Additionally, we prepared a stable Lewis adduct of mNHO with BH$_3$. We tested its reactivity for aldehyde and ketone reductions. Our findings indicate that, compared to related NHC-boranes and MIC-boranes, mNHO-BH$_3$ exhibits higher activity, as no additives were required for the successful reduction of aldehydes.
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