π-Rich σ²P-Heterocycles: d¹⁰-Transition Metal Complexes of 1H-1,3-Benzazaphospholes with Unusual Coordination

GRAPHICAL ABSTRACT

Abstract

1H-1,3-Benzazaphospholes are aromatically stabilized σ²P heterocycles^1,2 with increased π-density at phosphorus. This is caused by delocalization of the σ³N lone pair in the five-membered ring and disfavors π-back bonding from d¹⁰ transition metal cations to the ligand within the ring plane. The crystal structures of benzazaphosphole AgCl^2c and CuX complexes^2f display unusual bent or μ-bridging coordination although σ²P-phosphabenzene (phosphinine) ligands typically coordinate CuX groups in the σ-mode within the ring plane.³ Exceptions are complexes with pyridyl-phosphinine pincer ligands^4a or 2-hydroxyphosphinines that acquire increased π-density by the +M-effect of the hydroxy group in o-position.^4b

Keywords:

• Low coordination
• phosphorus heterocycles
• P ligands