Steric control in the oligomerisation of phosphazane dimers; towards new phosphorus-nitrogen macrocycles

The reaction of ClP(mu-NtBu)]2 (1) with H2O (1 : 2 equivalents) in the presence of excess Et3N gives the new chain compound (mu-O)P(mu-NtBu)2P(H)=O]2] (3), consisting of two P2N2 rings linked by a mu-O atom and terminating in P(V)(H)=O groups. A similar chain species is obtained from the reaction of the lithiate of (tBuNH)P(mu-NtBu)2P(H)=O] (5) with ClP(mu-NtBu)2P(NHtBu)] (2), the product being (mu-O)P(mu-NtBu)2P(NHtBu)]2] (6). Compounds 3 and 6 are the first examples of O-bridged chain phosphazanes and potential precursors to new phosphorus-nitrogen macrocycles. The syntheses and X-ray structures of 3, 5 and 6 are reported.