Rings and Cages from Phosphaalkynes

The following section describes metal-assisted syntheses of rings and cages from phosphaalkynes. The phosphaalkyne may either become part of a well-defined transition-metal complex, or alternatively react with metal centers in a cocondensation process. Moreover, it is possible for phosphaalkynes to oligomerize or cooligomerize with other molecules in the coordination sphere of a metal complex. Detachment of the newly constructed ligands is not in all cases possible. 

Cocondensation of nickel atoms, generated by metal vapor synthesis techniques with t-BuC=P, affords equal amounts of the isomeric sandwich complexes 94 and 95. The former compound features an T -phosphirenyl ligand in addition to an T -l -triphospholyl ring, whereas in 95 the metal is sandwiched between two i74-l,3-diphosphete units see Eq. (19).5,c 

The nature of the complexes, synthesized from metal vapor and t-BuC=P, is highly dependent upon the nature of the metal. Thus, with iron, chromium, or vanadium atoms, pentaphosphametallocenes are obtained.51 In contrast, the phosphaalkyne and molybdenum or tungsten atoms afford homoleptic tris[i74-l,3-diphosphete] metal(O) complexes [M(tj4-P2C2- -Bu2)3] (M = Mo, W).51 

Reaction of the azaphosphirene complex 8b with i-Pr(Me3Si)NC=P leads to the displacement of benzonitrile with incorporation of the phosphaalkyne to give 96 as a representative of the rare class of diphosphirene complexes, as shown in Eq. (20).52 

Peripheral reactions of organometallic complexes with phosphaalkynes give access to a variety of four-membered organophosphor ring ligands. 

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