Dinitrogen (N 2 ) complexes of technetium ( 99 Tc) are rare, and only two examples have been reported. To complement this important class of complexes also for 99 Tc, two different pincer-type complexes of 99 Tc were studied to assess their abilities for coordinating dinitrogen. The reactions of the 99 Tc III complex [ 99 TcCl 3 (PPh 3 ) 2 (NCCH 3 )] with the pincer ligands PNP tBu and Pyr PNP tBu respectively gave [ 99 Tc(PNP tBu )Cl 2 ] and [ 99 Tc( Pyr PNP tBu )Cl 3 ], the first structurally characterized 99 Tc complexes with mer-coordinated pincer ligands. Reductions with [Co(Cp*) 2 ] under N 2 gave the mononuclear bis-dinitrogen complex [ 99 Tc I (PNP tBu )(N 2 ) 2 ] and the dinuclear complex [ 99 Tc I ( Pyr PNP tBu )(N 2 )Cl] 2 (μ-N 2 ) with both a bridging and a terminal N 2 ligand. Spectroscopy and crystal structures confirm their identities. The complexes are stable under a dinitrogen atmosphere, and the N 2 ligands are tightly bound. The results for the complexes with the PNP tBu pincer allow a comparison to its rhenium homologue, which has recently been shown to split the N 2 ligand with the formation of a nitrido complex.
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 tBu *)(CO) 2 ] (4), which was synthesized by deprotonation of trans-[ 99 Tc I ( Pyr PNP tBu )(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 tBu −COO)(CO) 2 ] and with H 2 to form the mono-hydride complex cis-[ 99 Tc I ( Pyr PNP tBu )(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.
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