The Double Bond Between Organosilicon and Phosphorus

6-Tri-t-butylphenylphosphene dimesitylsilene [426] was the first compound known with a double bond between the organosilicon and phosphorus. It was reported in 1984. The compound has been prepared in solution, but due to its high reactivity, it has so far not been isolated in pure form. 

The reaction of equimolar quantities of 2,4,6-tri-r-butylphenylphosphine (1) and dichlorobis(2,4,6-trimethylphenyl)silane (2) with one equivalent of n-butyllithium at 

Although (4) was relatively long-lived in the reaction mixture (ti/2 ca. 1 day at 25 °C, 

The Si NMR spectrum provides the strongest evidence, with a signal at the very low field shift of = + 76.7 ppm (THF). Such low field chemical shifts are typically observed for tricoordinate, pjr-hybridized silicon (41.4 to 94 ppm) [30]. 

Silicon ( f = 1.8) is more electropositive than phosphorus (x = 2.1), and therefore the P = Si bond is expected to be highly polarised with silicon as the positive pole to which the nucleophilic component of a polar reactant molecule will add. 

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