Triazaphospholes versus Triazoles: An Investigation of the Differences between “Click”-Derived Chelating Phosphorus- and Nitrogen-Containing Heterocycles

A new
class of pyridyl-functionalized triazaphospholes bearing
either tBu or SiMe3 substituents
at the 5-position of the N3PC heterocycle have been prepared
via the “click” reaction starting from 2-(azidomethyl)­pyridine
and the corresponding phosphaalkynes. In order to investigate the
electronic structure and donor–acceptor properties of such
novel chelating and low-coordinate phosphorus heterocycles, calculations
at the DFT level have been carried out. Moreover, cyclic voltammetry
measurements were performed and the results were compared with those
for the structurally related triazole-based systems, demonstrating
a significant influence of the phosphorus atom as well as the substitution
pattern on the electronic properties of the novel compounds. The P,N
hybrid ligands form Re­(I) complexes of the type [(N∧mN)­Re­(CO)3Br] via coordination of the nitrogen
atom N2 to the metal center rather than via the phosphorus
atom, as verified crystallographically.