Cycloaddition reactions phosphasilenes

The reactivity of phosphasilenes with organic compounds, for example, [2 + 2]-cycloaddition reaction (8) has been intensively investigated. The reactivity of phosphasilenes with transition metal complexes, however, is comparatively unexplored (9,10). The described phosphasilene 1 can imdergo unprecedented EtZ isomerization of the Si=P bond upon coordination to tungsten (11). Another remarkable reactivity study describes the coordination of group 10 transition metals to phosphasilene 1 generating dinuclear platinum and palladium complexes with Si—P bond cleavage and a bissilylene nickel complex from a Ni(0) precursor (12). 

The ability of the Si=P bond to serve as a dienophile for a [2+4]-cycloaddition (hetero-Diels-Alder reaction) has been verified by the reaction of 15a with cyclopentadiene (Eq. 10).14 The components react at 60°C in benzene to give a quantitative yield of 25, which was isolated as a colorless solid. Interestingly, a Br0nsted acid (C—H)/base (Si=P) reaction, as in the case of 15a and phenylacetylene, was not observed. In the mass spectrum of25, the molecular peak but also the free phosphasilene 15a+ have been detected. Similar behavior was observed for related ad-... 

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