Low-Coordinate Phosphorus Ligands

The chemistry of low-coordinate trivalent phosphorus compounds intriguingly resembles that of corresponding native carbon relatives,  awarding phosphorus the designation: ‘Phosphorus – the Carbon Copy’. This analogy is based upon the fact that phosphorus and carbon exhibit almost similar electron acceptor and electron donor abilities allowing such phosphorus compounds to be utilized instead of genuine carbon species.

Only recently, have sp2-hybridized phosphorus compounds been utilized as ligands for transition metals in catalysis. The increasing popularity of this class of compound is due to the fact that phosphorus as part of a multiple bond exhibits relatively poor sigma-donor character but displays a strong pi-accepting capacity. Therefore, their electronic properties are significantly different from those of classical lambda3-sigma3-phosphanes and nitrogen relatives. Phosphinine 1 - the P-analogue of pyridine – is already well established in this context. Rhodium complexes displaying phosphinine ligands e.g. show and efficient catalytic activity with high turn over frequencies for the hydroformylation of alkenes. Even polysubstituted alkenes can be converted which is not possible using classical lambda3-sigma3-phosphane ligands.

PLig

Another example for a successful ligand system based upon sp2-hybridized phosphorus centers are the diphosphinidenecyclobutenes 2 that are investigated by Ozawa, Yoshifuji and coworkers. These chelating ligands form catalytically active complexes with Pd and Pt and can efficiently be utilized in the hydroamination of 1,3-dienes, the dehydrosilation of ketones, and the allylation of aniline or C-activated methylene compounds.

Our research is aimed at the synthesis on development of novel chelating ligands that exhibit low-coordinate trivalent phosphorus moieties. Corresponding transition metal complexes are also targeted.

Further reading:

[1]   K. B. Dillon, F. Mathey, J. F. Nixon, Phosphorus: The Carbon Copy, Wiley: Chichester, 1998.

[2]   F. Mathey, Angew. Chem. Int. Ed. 200342, 1578.

[3]   P. Le Floch, Coord. Chem. Rev. 2006250, 627.


© T. Baumgartner, last updated in 08/2017  |  Department of Chemistry  |  Faculty of Science  |  York University