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

Abstract

A new class of pyridyl-functionalized triazaphospholes bearing either t Bu or SiMe 3 substituents at the 5-position of the N 3 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 ∧m N)Re(CO) 3 Br] via coordination of the nitrogen atom N 2 to the metal center rather than via the phosphorus atom, as verified crystallographically.

Recent Developments in the Chemistry of Pyridyl-functionalized, Low-coordinate Phosphorus Heterocycles

“…Interestingly, the reaction of trimethylsilylphosphaethyne with 2-(azidomethyl)pyridine also proceeded straightforwardly, leading for the first time to a TMS-substituted triazaphosphole derivative via this synthetic pathway. 52 As the phosphinine-based P,N ligand 5 undergoes a facile reaction with [Re(CO) 5 Br] under formation of the complex 20, the coordination chemistry of 37 and 38 toward Re(I) was investigated accordingly, and complex [Re(CO) 3 Br(37)] (39) could be characterized crystallographically. The molecular structure of 39 in the crystal is shown in Figure 28, revealing that the chelating ligand 37 coordinates to the Re(I) center via the nitrogen atom N(2) of the triazaphosphole moiety, rather than via the phosphorus atom.…”

Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis, Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds

“…We recently demonstrated that methylene-bridged triazaphospholes of type B (Figure 1) and the corresponding phosphorus-lacking triazoles underwent af acile reaction with Re(CO) 5 Br to form complexes[ (N^N)Re(CO) 3 Br]. [5] We therefore also decided to explore the coordination chemistry of 1a and 6a towards Re I because those bidentate ligands were expected to coordinate in ac helating manner to at ransition-metal centre, in contrastt oc ompounds 2-4.A tthe same time, the [Re(CO) 3 Br] metal fragment offers the possibility of investigating the electronic properties of the ligands by meanso fI R spectroscopy of the resulting coordination compounds.…”

“…[5] We therefore also decided to explore the coordination chemistry of 1a and 6a towards Re I because those bidentate ligands were expected to coordinate in ac helating manner to at ransition-metal centre, in contrastt oc ompounds 2-4.A tthe same time, the [Re(CO) 3 Br] metal fragment offers the possibility of investigating the electronic properties of the ligands by meanso fI R spectroscopy of the resulting coordination compounds. We first paid attention to the coordination chemistry of the triazaphosphole, which could coordinate in either aPN (J)o ra n N^N (K)f ashion ( Figure 10).…”

“…We first paid attention to the coordination chemistry of the triazaphosphole, which could coordinate in either aPN (J)o ra n N^N (K)f ashion ( Figure 10). Compound 1a was thus reacted with an equimolar amount of [Re(CO) 5 Br] in dichloromethane at T = 80 8Ci nasealed NMR tube and the reaction was monitored by meansof 31 …”

“…[3,4] We have recently demonstrated that methylene-bridged, pyridyl-functionalised triazaphospholes of type B (Figure 1) can be used to develop transition-metal complexes with different properties from the analogous triazolebased systems. [5] However, it should be noted that the pyridine and five-membered ring are not in direct conjugationi nc ompound B.…”