Reactions involving Two-co-ordinating Phosphorus

A series of two-co-ordinated, conjugated compounds (139) was prepared by simple condensation as shown. Most of these were stable at O C. Attempts to prepare a similarly conjugated compound (140) gave the dimer (141) instead.  

Phosphenium ions (142) with isocyanides gave the new 1,3-azaphospheten cations (143) with t-butyl isocyanide and larger substituents on the amino groups elimination of isobutene occurred to give cyanophosphines, e.g. (144). The reaction of chlorophosphenium ions (145) with silylated amidines gave the new 1,3,2-diaza-phospheten cations (146). Several new phosphonium salts have been obtained from phosphenium ions and 1,3-dienes or o-quinones, e.g. (147).  

A series of phosphino substituted diphosphenes (148) has been prepared as shown and the structure of three examined by X-ray crystallography. The P-P-P angle was less than 90° in two cases in agreement with expectations from ab initio calculations. The syntheses of the new, stable diphosphenes (149), (150), and (151) have been described. 

The new, thermally stable 1-phosphadiene (134) has been prepared as shown, using a deficiency of DBU with excess DBU a mixture of (134) and (135) is obtained. Phosphonio-phospha-alkenes (136) has been prepared by elimination of an amino group of (137) by treatment with Lewis acids. Iminophosphines (138) and the phospha-alkyne (139) gave diphosphirenes (140) which rearranged at higher temperatures to the azadiphosphetines (141). The same phospha-alkyne (139) and tetrazines (142) gave the 1,2,3-azadi-phospholes (143) a plausible multistep mechanism for this unusual reaction is proposed. 

Amino-iminophosphines have been known for more than a decade and have always been isolated as the trans isomers. The first example of a cis amino-iminophosphine, (144), has now been isolated (144) does not isomerize when heated or exposed to UV irradiation New, thermally stable heteroatom substituted iminophosphines include the aryloxy-iminophosphines e.g. (145), and 

A phosphenium ion with one pentamethylcyclopentadienyl substituent, (151), has been isolated for the first time, and its . 90 

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The organization of this Chapter has been changed somewhat from last year. Phosphonous and phosphinous acids and their derivatives, and cyclic esters of phosphorous acid, are not discussed separately from phosphorous acid and its derivatives, because of the similarity of the reactions involved. Two-co-ordinate phosphorus compounds are treated in a separate section like last year phospha-alkenes without phosphorus-heteroatom bonds are not covered. 

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