Some Aspects of the Chemistry of Nitrogen-Bridged Diphosphorus Compounds

The aminolysis of a number of acyclic and cyclic compounds containing P-NR-P or P-CH2-P skeletons have been studied. The reaction of [Cl(S)P]2NMe with excess dimethylamine gives the tetrakisdimethylamino-derivative [(Me2N)2(S)P]2NMe. By contrast, the unusual ring compounds Me2N(S)P. NR. P(S)(NMe2)S (R=Me or Et) have been isolated from the reactions of [Cl2(S)P]2NR with six mol equiv. of dimethylamine. The reaction of Cl2(O)P. NMe. P(S)Cl2 with dimethylamine initially occurs at the phosphinothioyl centre in non-donor solvents, but in diethyl ether solution, dimethylaminolysis preferentially occurs at the phosphinoyl centre. It is argued that this solvent dependent reactivity may be due to aminolysis being anchiomorically assisted by the phosphinoyl oxygen in non-donor solvents. By contrast, dimethylaminolysis of the cyclodiphosphazane Cl(O)P. NMe. P(S)Cl. NBut occurs exclusively at the phosphinoyl centre in donor and non-donor solvents. Nongeminal bis- and tetrakisdimethylamino-derivatives of Cl2(O)P. NMe. P(S)Cl2 have been isolated. Attempts to synthesise dimethylamino-derivatives of [Cl2(S)P]2NMe and Cl2(O)P. NMe. P(S)Cl2 by a number of other methods were unsuccessful. The compounds, [Cl(X)P)2NR (X=lone pair, R=Me, Et or But; X=O, R=Me or Et; X=S, R=Me) undergo reactions with three mol equiv. of t-butylamine to give cyclodiphosphazanes Cl(X)P. NR. P(X)Cl. NBut. Products of the more complex reactions of (Cl2P)2NMe with methylamine and (Cl2P)2NEt with ethylamine have been identified. The reaction of Cl2P. NMe. P(O)Cl2 with three mol equiv. t-butylamine gives the cyclodiphosphazane ClP. NMe. P(O)Cl. NBut, whereas ButNHP. NMe. P(S)Cl. NBut was the only product isolated from the analogous reaction with Cl2P. NMeP(S)Cl2. No cyclic products were identified from the reactions of Cl2(O)P. NMe. P(S)Cl2 or Cl3P=N-P(O)Cl2 with t-butylamine, the latter compound giving mono- and nongeminal- bis-t-butylamino derivatives. Possible reasons for the ease of cyclodiphosphazane formation in many of these reactions and the dependence of the reaction on the primary amine involved are discussed. Similar reactions of [Cl2(O)P]2CH2 with t-butylamine and i-propylamine gave a new class of ring compound, Cl(O)P. CH2,P(O)Cl. NR (R = But or Pri) (1,2,4-azadiphosphetanes), but no cyclic products were obtained from analogous reactions with Cl2(O)P. CH2CH2. P(O)Cl2. Attempts to prepare pure samples of (Cl2P)2CH2 as a substrate for cyclisation reactions from the reaction of phosphorus trichloride with (Ph2P)2CH2 were unsuccessful, and some of the products of this reaction are described. Both mono- and nongeminalbisdimethylamino derivatives of [Cl2(O)P]2CH2 are obtained on reaction with dimethylamine, although the former derivative was not isolated. Attempted cyclisation of the bisdimethylamino derivative [Me2N(Cl)(O)P]2CH2 by t-butylamine gave the acyclic product, [ButNH(Me2N)(O)P]2CH2, rather than Me2N(O)P. CH2P(O)(NMe2). NBut. The latter cyclic derivative, obtained by heating (Me2N)2(O)P. CH2. P(o)(NMe2)NHBut, was resistant to ring opening by dimethylamine, whereas ring opening occurred in the attempted dimethylaminolysis of Cl(O)P. CH2. P(O)Cl. NBut. Cyclodiphosphazanes ClP-NMe-P(X)Cl-NBut Cl(X)P. NMe. P(X)Cl. NBut (X = O or S) and Cl(o)P. NMe. P(S)Cl. NBut can be formed from reactions of ClP. NMe. PCl. NBut with dimethyl sulphoxide and sulphur. Aminolysis of cyclodiphospha(lIl)zanes ClP. NR. PCl. NBut (R= Me, Et or But) results in the formation of mono- and diamino derivatives, while cyclisation of [Me2N(Cl)P]2NMe with three mol equiv. t-butylamine provides a second route to the 2,4-hisdimethylamino-derivative, Me2NP. NMe. P(NMe2)NBut. Dimethylaminolysis of the mixed oxidation state cyclodiphosphazanes ClP. NMe. P(X)Cl. NBut (X = O or S) is found to occur initially at the phosphorus(Ill) atom. Slow rotation about the phosphorus(III)-nitrogen bonds of dimethylamino-substituted cyclodiphosphazanes has been detected by 1H n. m. r. spectroscopy and the barriers to rotation about these bonds have been measured and discussed