Developments in the Coordination Chemistry of Phosphinines

Abstract

This microreview describes progress in the development and coordination chemistry of donor‐functionalized phosphinines – the phosphorus analogues of pyridines – that has been made during the last five years. The stepwise assembly of 2,4,6‐triarylphosphinines starting from functionalized benzaldehyde and acetophenone derivatives allows the incorporation of additional substituents into specific positions of the aromatic phosphorus heterocycle. This strategy can be used to synthesize chelating phosphinines, which is an essential aspect especially for the preparation of phosphinine‐based transition metal complexes containing metal centres in medium‐to‐high oxidation states. Access to such coordination compounds used to be very difficult because monodentate phosphinines cannot be used for this purpose, due to their weak σ‐donor properties but strong π‐accepting capacities. Moreover, metal complexes of less highly substituted phosphinines turned out to be extremely sensitive to nucleophilic attack, making their straightforward synthesis, characterization and application rather unattractive. The recent strategies in this area facilitate synthetic access to a completely new set of phosphinine‐metal complexes for the first time, leading to a much broader scope for potential applications. New developments in the areas of homogeneous catalysis and materials sciences can consequently be foreseen in the near future.

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

“…The only example of a P-protonated phosphinine reported in the literature so far is a phosphininium salt, which is generated by the reaction of 2,4,6-tri-tert-butyl-1-phosphinine with Et 3 Si(CHB 11 Me 5 Cl 6 ) followed by the addition of triflic acid, as reported by Reed and Nixon. 27 Thus, the reaction of 5 with triflic acid will lead exclusively to protonation of the nitrogen atom of the pyridine moiety, even with an excess of CF 3 SO 3 H. This was confirmed crystallographically for the salt 5¢HOSO 2 CF 3 (7) (Figure 7).…”

A Guide for the Design of Functional Polyaromatic Organophosphorus Materials

“…Notwithstanding, phosphabenzenes possess appealing properties that clearly distinguish them from both phospholes and their nitrogen analogues: pyridines . They are highly aromatic, and present a particular orbital level distribution with a low‐lying LUMO that converts them into electron acceptors . Thus, six‐membered phosphorus heterocycles intuitively open up new possibilities in materials science.…”

Reactions of Pyridyl‐Functionalized, Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

“…[8][9][10][11][12] In contrast to (bi)pyridines, phosphinine-based ligands are especially suitable for the stabilization of electron-rich metal centers due to the pronounced p-acceptor properties of the aromatic phosphorus heterocycle. [8][9][10][11][12][13] On the other hand, the aromaticity of the phosphinine heterocycle is significantly disrupted upon coordination to metal centers in especially higher oxidation states and with reduced p-back-donation capability. Accordingly, the phosphinine core behaves like a cyclophosphahexatriene containing a highly reactive P=C double bond.…”