Tuning the electronic effects of aromatic phosphorus heterocycles: an unprecedented phosphinine with significant P(π)-donor properties

Abstract

A hitherto unprecedented electronic situation has been observed for a substituted, pyridyl-functionalized phosphinine. In contrast to previous studies, this compound shows considerable π-donor properties as the result of the rather strong +M effect of the CH3S-substituent, changing the electronic properties of this low-coordinate and aromatic phosphorus heterocycle substantially.

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

“…It was anticipated that the Starting from p-substituted benzaldehydes, the corresponding pyrylium salts and phosphinines 1517 could indeed be prepared (Scheme 5). 38 The molecular structure of the pyrylium salt 14 is shown in Figure 12. For the analysis of the electronic structure of phosphinines 5 and 1517, see Section 2.1.6.…”

“…This particular electronic situation is caused by the special shape and orientation of the LUMO and HOMO of the phosphinine ligand, and is unique in comparison with other π donors. 38 For further investigation of the electronic differences between the P,N-hybrid ligands and their bipyridine analogues, 2-(2¤-pyridyl)-4,6-diphenylphosphinine (5) was treated in a competition experiment with one equivalent of the tungsten complex [W(CO) 4 (6)] in toluene (Scheme 7).…”

ReI Complexes of Pyridylphosphinines and 2,2′‐Bipyridine Derivatives: A Comparison

“…As we have demonstrated before, the pyrylium salt route depicted in Scheme is a modular synthetic procedure and allows the introduction of different substituents in the aryl groups in 4‐ and 6‐position of the heterocycle. In the context of investigating substituent effects on electronic properties of phosphinines, we have recently synthesized a series of derivatives of 1 and 2 via the corresponding substituted, highly fluorescent pyrylium salts , . It turned out, that a fluorine atom in para ‐position of the 4‐aryl ring has only a marginal effect on the energetic position of the frontier orbitals of the pyridyl‐functionalized heterocycles.…”

“…Pyrylium salts pypy‐BF 4 and pypy‐F‐BF 4 were converted into the corresponding pyridylphosphinines and 2,2′‐bipyridine derivatives 1 , 1‐F , 2 and 2‐F , as recently described by us (Scheme ) , . Heating [Re(CO) 5 X] (X = Cl, Br) in a solution of the pyridylphosphinine 1 and 1‐F gives the corresponding Re I complexes of the type [(P ^ N)Re(CO) 3 X], according to Scheme .…”

Developing a new phosphorus-carbon bond synthesis

“…Until today, this method is still used as a straightforward synthesis of 2,4,6triarylphosphinine because of the good yields and a wide variety of triaylpyrylium salts are available. [117][118] Polycyclic annulated phosphole derivatives can be synthesised via intramolecular cascade cyclisation (Scheme 1.27). [119][120] The cyclisation process is initiated by the attack of phosphorus onto the C-C triple bond, and it generally proceeds at ambient conditions and the yields are good.…”