SYNTHESIS OF STABLE N',N',N'',N''-TETRAMETHYLGUANIDINE-SUBSTITUTED SIGMA(4)(P)-ORGANOPHOSPHORUS AND SIGMA(3)(P)-ORGANOPHOSPHORUS COMPOUNDS WITH N-PROTONATED P-N BONDS - THE FIRST SIGMA(3)-PHOSPHORUS-SUBSTITUTED AMMONIUM-SALTS

The dependence of the protolytic decomposition rate of phosphorus amid es on the substituents at phosphorus is decribed. On treatment with HC l, the N',N',N'',N''-tetramethylguanidine(= TMG)-substituted sigma(4)( P) compounds 5 and 9 formed salts that were protonated at the imino ni trogen atoms and were completely stable in the solid state, and surpri singly stable in solution. Even with a large excess of HCl, only the i mino nitrogen atom underwent protonation, with formation of HCl2- as a counter anion, without cleavage of the P-N bond. The basicity of the imino nitrogen atom also protected sigma(3)(P) species from electrophi lic attack, and the ionic compounds 12, 14, and 20c were formed, provi ding examples of the first stable sigma(3)(P) amides with one or two p rotonated P-N bonds. Such unusual stability is associated with steric protection by the Ph3C (= trityl) group and charge delocalization over the TMG-moiety. In contrast, MeP(TMG)(2) was unstable towards HCl, wh ereas treatment with HSbF6 led to the phosphonium salt 24, where proto nation had occurred at phosphorus. The same result was obtained when t riphenylmethylphosphonous dichloride 1 was allowed to react with 3 equ ivalents of HTMG, forming the stable phosphonium salt 19, soluble in w ater, which was converted to the bicationic species 20c upon treatment with HCl. - The basicity of the tritylated phosphorus compounds was f ound to increase in the order 5 < 2 < 19 < 13 < HTMG < 21; the basic c entre is the phosphorus atom in 21 and the imino nitrogen atom in all other compounds. The fluorinating agent Et3N . 3 HF caused rapid conve rsion of compound 6 to 25, the nucleophilic attack of fluoride ion at phosphorus could not be prevented by the stabilizing effects mentioned . - All compounds were investigated by H-1- and P-31-NMR spectroscopy. The crystal structures of compounds 5, Ph3CP(=O)-(H)TMG,and 6, [5 . 2 HCl], were determined; 6 is protonated at the imino nitrogen, leading to a longer P-N bond [5: 161.6(2), 6: 168.7(2) pm], and the counterio n is HCl2-. In the structure of 20c, [Ph3CP(TMG)(2)] . 3 HCl, the cati on is protonated at both imino N atoms and the counterions are Cl- and HCl2- (one of each).