Properties of Phosphinocarbenes

Direct complexation of a free phosphinocarbene has not yet been reported. However, a few complexes featuring a phosphinocarbene ligand in a number of different coordination modes (A, B, and C) have been described. 

In the reaction of the cationic carbyne complex [(OC)5WCNEt2] BF4 with potassium methylphenylphosphide, the two phosphinocarbene complexes 93 and 94 have been isolated as by-products in 4 and 3.5% yield, respectively.85 Here, the phosphinocarbenes simply act as 2-electron donors via the carbenic center. It is also interesting to note that this strategy can be used to prepare the analogous arsinocarbene complexes.8513 

Interestingly, on warming a solution of 94 the phosphine ligand dissociates to afford the new complex 95. An X-ray diffraction study of the latter complex indicates that the phosphinocarbene behaves as a 4-electron ligand (coordination mode B).86 

Kreissl et al. have developed two different strategies for the conversion of neutral carbyne complexes into cationic phosphinocarbene complexes 97 of type B. The first approach relied on the decarbonylation of tungsta-phosphabicyclo[1.1.0]butanone complexes 96.87 

The second synthetic method is much shorter. The carbene complexes 97 are prepared in one step by treatment of the corresponding carbyne derivatives with a chlorophosphine in the presence of a Lewis acid.88 This strategy can also be used to prepare the analogous arsinocarbene complexes.89 

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In this review, we present successively the theoretical aspect, the synthesis, the structural features, the reactivity, and lastly, the ligand properties of phosphinocarbenes. 

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