Phosphaalkynes-Syntheses, Reactions, Coordination Behavior [New Synthetic Methods (73)]

Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low‐coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes. Phosphorus compounds with low coordination numbers have been the subject of considerable interest ever since they were first described. One of the show‐piece examples is 1, known as tert‐butylphosphaacetylene or 3,3‐dimethyl‐1‐phospha‐1‐butyne. 1 and its analogs can, for example, be incorporated into heterocycles, used as new complex ligands, or cyclooligomerized by organometallic reagents. As far as their reactivity is concerned, phosphaalkynes have little in common with nitriles, but clearly show themselves to be related to the isoelectronic alkynes.