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

Abstract

Novel conjugated, pyridyl-functionalised triazaphospholes with either tBu or SiMe3 substituents at the 5-position of the N3 PC heterocycle have been prepared by a [3+2] cycloaddition reaction and compared with structurally related, triazole-based systems. Photoexcitation of the 2-pyridyl-substituted triazaphosphole gives rise to a significant fluorescence emission with a quantum yield of up to 12 %. In contrast, the all-nitrogen triazole analogue shows no emission at all. DFT calculations indicate that the 2-pyridyl substituted systems have a more rigid and planar structure than their 3- and 4-pyridyl isomers. Time-dependent (TD) DFT calculations show that only the 2-pyridyl-substituted triazaphosphole exhibits similar planar geometry, with matching conformational arrangements in the lowest energy excited state and the ground state; this helps to explain the enhanced emission intensity. The chelating P,N-hybrid ligand forms a Re(I) complex of the type [(N^N)Re(CO)3 Br] through the coordination of nitrogen atom N(2) to the metal centre rather than through the phosphorus donor. Both structural and spectroscopic data indicate substantial π-accepting character of the triazaphosphole, which is again in contrast to that of the all-nitrogen-containing triazoles. The synthesis and photophysical properties of a new class of phosphorus-containing extended π systems are described.

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

“…Interestingly, the reaction of pyridotetrazole with t Bu-phosphaalkyne P¸C t Bu turned out to proceed smoothly and selectively toward the desired product 40, and was already completed after 2 h at T = 65°C (Scheme 13). 53 Similarly, the SiMe 3 -substituted triazaphosphole 41 was formed within 1 h by reaction of the pyridotetrazole and P¸C SiMe 3 in toluene. The SiMe 3 group was found to have a rather large influence on the chemical shift of the product, as the phosphorus resonance in the 31 P{ 1 H} NMR spectrum of compound 41 was observed at ¤ = 211.6 ppm, while compound 40 shows a resonance at ¤ = 167.5 ppm in the 31 P{ 1 H} NMR spectrum.…”

Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3‐Dipnictabutadienes

“…This decomposition was monitored by at emperature dependent 31 PNMR from À40 8 8Ct o8 0 8 8C( Supporting Information), which showed that two products are formed. Thef irst reaction step is the adduct formation, which leads to the phosphadiazadiene (I2), similar to 2,a fter migration of a[ W(CO) 5 ] group.T his phosphadiazadiene reacts with as econd diazomethane by a[ 2 + +3] cycloaddition and the migration of a[ W(CO) 5 ]g roup to 6a.I ng eneral, triazaphospholes are obtained by the reaction of phosphaalkenes [17] or phosphaalkynes [18] with an azide (RN 3 ). [14] Them olecular structure of 2 is shown in Figure 2.…”

Organophosphorus Compounds in Organic Electronics

“…However replacing the 2‐pyridyl group with a 3‐pyridyl or a phenyl group greatly reduces the quantum yields. In summary, for highly emissive properties position of the nitrogen atom as well as the presence of the phosphorus atom in the triazole ring are critical …”

“…In summary,f or highly emissive properties position of the nitrogen atom as well as the presence of the phosphorus atom in the triazole ring are critical. [87]…”