Phosphoranes

from Wikipedia, the free encyclopedia

Phosphorane is a group name for chemical compounds with the sum formula PR 5 , i.e. a pentavalent phosphorus with 5 covalently bound organic residues. The parent compound is the unstable phosphorane PH 5 , now called λ 5 -phosphane . A compound named pentaphenylphosphorane Ph 5 P (Ph = phenyl radical ) according to the old rules would have to be referred to as pentaphenyl-λ 5 -phosphine according to the current recommendations of the IUPAC , which is unusual in practice.

Also ylides are referred to as phosphoranes: This is the name the simplest member of this class, the (Me) 3 P = CH 2 (Me = methyl ), Trimethylmethylen-phosphorane , ie, the name of phosphorane is a neutral, pentavalent phosphorus atom.

Pentaorganylphosphorane PR 5 only exist if there is no acidic proton on the α- carbon atom. For this reason, the first phosphorane to be discovered is Ph 5 P, synthesized by Wittig. If an attempt is made to replace a phenyl group with a methyl group, ylides are formed. In the course of this work, the Wittig reaction named after him was found, which represents a key step in many industrial processes (e.g. synthesis of vitamins ).

If one uses an artifice, but you can still Pentaalkylphosphorane manufacture: Phosphoranes are generally four times (tetrahedral) coordinated phosphonium - salts ( Tetrahedron : manufactured angle 109 °). If the phosphorus atom is squeezed into a ring system that builds up a high tension, a five-fold coordination at the phosphorus center can achieve substantial relaxation, since an equatorial - axial coordination enables the angle to be reduced from 109 ° to 90 °. This concept was first successfully proven in 1971 by Turnblom and Katz in the synthesis of homocubyl-trimethyl-phosphorane . The simplest pentaalkylphosphorane was produced only a little later by Schmidbaur and Holl . Monkowius , Mitzel , Schier and Schmidbaur succeeded in determining the first solid-state structure of a pentaalkyl phosphorane in 2002.

literature

On the subject of pentaalkylphosphoranes, see also:

  • U. Monkowius: Synthesis, structure and coordination chemistry of selected organophosphorus compounds and their nitrogen and arsenic analogues . Dissertation TU Munich, 2003 (PDF; 7.7 MB)

Individual evidence

  1. ↑ EW Turnblom, TK Katz: J. Am. Chem. Soc. 93 (1971), p. 4065.
  2. ↑ H. Schmidbaur, P. Holl, FH Köhler: Angew. Chem. 89: 748 (1977).
  3. ^ H. Schmidbaur, P. Holl: Z. Anorg. General Chem. 458 (1979), p. 249.
  4. ↑ U. Monkowius, NW Mitzel, A. Schier, H. Schmidbaur: J. Am. Chem. Soc. 124 (2002), p. 6126.