Donor‐Functionalized Polydentate Pyrylium Salts and Phosphinines: Synthesis, Structural Characterization, and Photophysical Properties

Abstract

A series of donor‐functionalized pyrylium salts have been prepared by classical condensation reactions which were further converted into the corresponding thienyl‐ and pyridyl‐substituted polydentate λ3‐phosphinines by reaction with P(SiMe3)3. Further chemical modification of these phosphorus heterocycles with Hg(OAc)2 in the presence of methanol resulted in the formation of λ5‐phosphinines. The photophysical properties of a selected series of thienyl‐ and pyridyl‐functionalized pyrylium salts, λ3‐ and λ5‐phosphinines, were investigated and the results compared and supported by theoretical calculations on the DFT level. Significant fluorescence was observed for the pyrylium salts and λ5‐phosphinines. In contrast, the heteroaromatic substituted λ3‐phosphinines show very little emission which is consistent with the low oscillator strength predicted by DFT calculations for this π→π* transition. Furthermore, all three classes of compounds show readily observable phosphorescence in solution, which was determined by time‐gated detection at low temperature.

An unprecedented cyclometallated platinum(ii) complex incorporating a phosphinine co-ligand: synthesis and photoluminescence behaviour

“…The spectrum of the proligand is dominated by an intense band centred at 278 nm (ε = 43700 M -1 cm -1 ), accompanied by a shoulder at 312 nm, and a weak, low-energy tail, around 350 nm. There have been very few studies of the photophysical properties of phosphinines, but we note that the spectrum is similar to that of the related 2,6-thienyl-4-methylphosphinine, 16 albeit somewhat blueshifted. The intense bands can reasonably be attributed to π−π* transitions in the aromatic rings; lower-energy transitions would be expected in the thienyl derivative owing to the more electrondonating nature of thiophene compared to benzene.…”

“…On the basis of TD DFT calculations, Mueller et al assigned a similarly weak lowenergy tail to a symmetry-forbidden S 0 →S 1 transition. 16 The absorption spectrum of the Pt(II) complex 1 shows an intense band at a similar value to L p , presumably due to the superposition of intraligand transitions in the phosphinine with those of the phenylpyridine, but there are clearly now additional, moderately intense bands in the 330-400 nm region (Fig. 3, Table 1).…”

Cyclometalation of Aryl‐Substituted Phosphinines through CH‐Bond Activation: A Mechanistic Investigation

“…The preparation of phosphinine complexes containing transition metals in medium‐to‐higher oxidation states, on the other hand, has been largely neglected13 due to their extreme sensitivity to nucleophilic attack 14. Recently, we could achieve the synthesis and crystallographic characterization of hitherto unknown phosphinine–M II[15–17] and cationic phosphinine–M III[18] complexes containing the chelating P,N hybrid ligand 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine19 (Figure 1, type B ). It turned out that an efficient protection of the PC double bond along with a kinetic stabilization of the corresponding complexes occurred, due to the incorporation of a sterically demanding aryl group in the ortho position of the phosphinine ligand.…”

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

“…16,17 We recently started to investigate the synthesis, reactivity, and coordination chemistry of 2-(2¤-pyridyl)-4,6-diphenylphosphinine (5), which is readily available from the pyridyl-functionalized pyrylium salt and P(SiMe 3 ) 3 . 18 Interestingly, the pyrylium salt route further allows the preparation of (bi)pyridines such as 2-(2¤-pyridyl)-4,6-diphenylpyridine (6). These nitrogen derivatives have an identical substitution pattern to the corresponding phosphinines, making the direct comparison of structurally related heterocycles possible for the first time (Scheme 2).…”