π-Rich σ²P-Heterocycles: Syntheses, Reactivity, and Application Potential of 1,3-Benzazaphospholes

GRAPHICAL ABSTRACT

Abstract

1H-1,3-Azaphospholes and their benzo-fused derivatives are a particular class of aromatically stabilized σ²P heterocycles^1,2 that differ from the well-known phosphabenzenes^1a,3 and other types of azaphospholes^1c by their increased π-density at phosphorus. This is caused by delocalization of the σ³N lone pair in the five-membered ring, the position of N in conjugation to phosphorus, the lack of P-N bonds, and the absence of electron-withdrawing σ²N atoms, and leads to a specific reactivity pattern, in many aspects different from that of other P = C compounds (Figure 1). We present a short overview on new routes to mono- and bidentate benzazaphospholes, substitution reactions at P, C2, and N and also on solvent/additive-dependent addition reactions of tBuLi, which provide access to sterically demanding and P-basic phosphine ligands. In addition, the application potential of bap-W(CO)₅/Ag⁽⁺⁾ initiators for ring-opening-polymerization of 3-5 membered cyclic ethers and of dihydro-benzazaphosphol-2-carboxylate Ni catalysts for the oligomerization of ethylene is shown.

Keywords:

• P-heterocycles
• low-coordinated phosphorus
• reactivity
• complexes
• catalysis