Binding Small Molecules to a cis-Dicarbonyl 99TcI-PNP Complex via Metal-Ligand Cooperativity

Metal-ligandcooperativity is a powerful tool for the activationof various bonds but has rarely, if ever, been studied with the radioactivetransition metal Tc-99. In this work, we explore this bondactivation pathway with the dearomatized PNP complex cis-[Tc-99(I)((PNP tBu)-P-Pyr*)(CO)(2)] (4), which was synthesizedby deprotonation of trans-[Tc-99(I)((PNP tBu)-P-Pyr)(CO)(2)Cl] with (KOBu)-Bu- t . Analogous to its rheniumcongener, the dearomatized compound reacts with CO2 toform the carboxy complex cis-[Tc-99(I)((PNP tBu)-P-Pyr-COO)(CO)(2)] and with H-2 to form the mono-hydride complex cis-[Tc-99(I)((PNP tBu)-P-Pyr)(CO)(2)H] (7). Substrateswith weakly acidic protons are deprotonated by the Bronsted basicpincer backbone of 4, yielding a variety of intriguingcomplexes. Reactions with terminal alkynes enable the isolation ofacetylide complexes. The deprotonation of an imidazolium salt resultsin the in situ formation and coordination of a carbene ligand. Furthermore,a study with heterocyclic substrates allowed for the isolation ofpyrrolide and pyrazolide complexes, which is uncommon for Tc. Thespectroscopic analyses and their solid-state structures are reported. Deprotonation of trans-[Tc-99(I)((PNP tBu)-P-Pyr)(CO)(2)Cl] with (KOBu)-Bu- t in tetrahydrofuranyields the highly reactive, dearomatized cis-[Tc-99(I)((PNP tBu)-P-Pyr*)(CO)(2)], which readily reacts with dihydrogen (H-2) and carbon dioxide (CO2) as its rhenium homologue.The observed reactivities with small molecules via metal-ligandcooperativity are extended to substrates comprising weakly acidicprotons, which are deprotonated by the pincer backbone of the reactivecomplex.

Automated summary

This study investigates the role of metal-ligand cooperativity in the activation of various bonds using a radioactivetransition metal Tc-99 compound. The compound showed reactivity with CO2 and H-2, resulting in the formation of new complexes. Different ligands were isolated through reactions and their spectroscopic analyses were performed. The study demonstrates the application of metal-ligand cooperativity on substrates with weakly acidic protons.