Phosphino phosphaalkene

Table 5.7 Dependance of the phosphorus chemical shift on the substituents of the phosphino group in a series of phosphino phosphaalkenes...

Since both amino and bulky substituents are known to stabilize cycloprope-nium salts [20], we chose to investigate the Lewis-acid induced P-N bond cleavage of the phosphaalkene 9, which is readily synthesized from the corresponding bis(phosphino)diazomethane 8 [21]. Indeed, treatment of 9 with two equivalents of BF3.Et2NH complex at room temperature afforded diphosphirenium salt 2 Pa as non-air sensitive pale-yellow crystals (mp 118°C) in 60% yield [22a] (Scheme 6). Subsequently, we found that using BF3.Et20 in the place of... 

Bis(phosphino)diazomethane is obtained as air-stable orange crystals by reaction (6.657). It looses nitrogen to produce a phosphaalkene, presumably by rearrangement of the bis (phosphino) carbene. 

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