Binding Small Molecules to a cis -Dicarbonyl 99 Tc I -PNP Complex via Metal-Ligand Cooperativity.

Metal-ligand cooperativity is a powerful tool for the activation of various bonds but has rarely, if ever, been studied with the radioactive transition metal 99 Tc. In this work, we explore this bond activation pathway with the dearomatized PNP complex cis -[ 99 Tc I ( Pyr PNP t Bu *)(CO) 2 ] ( 4 ), which was synthesized by deprotonation of trans -[ 99 Tc I ( Pyr PNP t Bu )(CO) 2 Cl] with KO t Bu. Analogous to its rhenium congener, the dearomatized compound reacts with CO 2 to form the carboxy complex cis -[ 99 Tc I ( Pyr PNP t Bu -COO)(CO) 2 ] and with H 2 to form the mono-hydride complex cis -[ 99 Tc I ( Pyr PNP t Bu )(CO) 2 H] ( 7 ). Substrates with weakly acidic protons are deprotonated by the Brønsted basic pincer backbone of 4 , yielding a variety of intriguing complexes. Reactions with terminal alkynes enable the isolation of acetylide complexes. The deprotonation of an imidazolium salt results in the in situ formation and coordination of a carbene ligand. Furthermore, a study with heterocyclic substrates allowed for the isolation of pyrrolide and pyrazolide complexes, which is uncommon for Tc. The spectroscopic analyses and their solid-state structures are reported.