Phosphinines, the phosphorus analogues of pyridines, have long been regarded as “chemical curiosities” as their electronic and steric properties differ substantially from those of classical phosphorus(III) ligands and pyridines. Recent synthetic methodologies allow the specific derivatization and functionalization of phosphinines, including the incorporation of additional donor functionalities. Considerable steric protection of the otherwise reactive P=C bond has been accomplished. This makes phosphinines and their corresponding metal complexes now interesting for more applied research fields such as homogeneous catalysis and materials science.
Christian Müller, Freie Universität Berlin, Germany, and colleagues describe the recent developments in this field.

Hitherto unknown neutral M(0), M(I), M(II) and cationic M(III) phosphinine-based metal complexes are reported. Of special interest are pyridyl-functionalized phosphinines, the phosphorus derivatives of 2,2´-bipyridine. These sterically protected P,N-hybrid ligands allow for the first time access to coordination compounds with metal centers in medium-to-high oxidation states. Moreover, the cyclometallation of 2-phenylphosphinine derivatives by Rh(III) and Ir(III) precursors has so far been unprecedented and turned out to represent a new reactivity pattern of phosphinines. These novel coordination compounds are very promising candidates for the application as catalysts for the oxidation of water and as novel triplet-emitters for OLEDs.

The review nicely demonstrates that phosphinines can still lead to unexpected discoveries and their future investigation remains an exciting, challenging and rewarding research field.

• Developments in the Coordination Chemistry of Phosphinines,
  Christian Müller, Leen E. E. Broeckx, Iris de Krom, Jarno J. M. Weemers,
  Eur. J. Inorg. Chem. 2013.
  DOI: 10.1002/ejic.201200912