The chemistry of some heterocyclic derivatives of phosphorus

The synthesis of 2,2'-biphenylylenebisdiethylphosphine and its use to form heterocyclic diquaternary dibromides by union with alkylene a,w-dibromides and o-xylylene dibromide are described. The thermal decomposition reactions of the cyclic salts, and the dimethiodide of the diphosphine, have been studied and found to proceed in a novel manner to give 9-alkyl-9-phospha­fluorenes. Similar ring-contraction reactions have been observed in the thermal decomposition of analogous salts derived from 2,2 1 -biphenylylenebisdiethylarsine. It is suggested that the ring­contraction reactions shown by the above salts on heating, are examples of a general internal nucleophilic displacement mechanism. The alkaline hydrolysis of quaternary salts of the 9-substituted-9-phosphafluorenes has been studied and found to proceed with opening of the heterocyclic ring. A related reaction leading to ring-expansion is also described. The proton magnetic resonance spectra of certain of the above salts have been examined and the results related to theories concerning the magnitude of coupling constants in organophosphorus compounds. The 9-alkyl-9-phosphafluorenes have unusual properties as ligands in that they form a series of five-co-ordinate tris(phosphine) complexes with cobalt(II), nickel(II), palladium(II) and platinum(II) halides. The properties and probable structures of these complexes are discussed. Some aspects of the co-ordination chemistry of the diphosphine with palladium(II) and nickel(II) compounds are also described