Triazaphospholes versus Triazoles: An Investigation
of the Differences between “Click”-Derived Chelating
Phosphorus- and Nitrogen-Containing Heterocycles
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Abstract
A new
class of pyridyl-functionalized triazaphospholes bearing
either <sup><i>t</i></sup>Bu or SiMe<sub>3</sub> substituents
at the 5-position of the N<sub>3</sub>PC 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<sup>∧</sup><sup>m</sup>N)Re(CO)<sub>3</sub>Br] via coordination of the nitrogen
atom N<sup>2</sup> to the metal center rather than via the phosphorus
atom, as verified crystallographically