Synthesis and Characterization of P-Si and P-Sn Protected Phosphasilenes and their Anion-Radicals

Compounds with a multiple bond between silicon and heavier main-group elements have recently attracted much attention because of their unique reactivity and electronic properties. In spite of extensive research functionalized unsaturated compounds are still rare. Among them (Cp*)(CO)₂Fe-P=SiR_2,¹ HP=SiR₂² and RZn-P=SiR₂² were reported. Silyl and tin substituents are functional/protecting groups and are in wide use in organic and inorganic chemistry. For example, Si and Sn- metal exchange reactions are used for P-Li bond formation, i.e., (R₃Sn/Si)₃P + MeLi→(R₃Sn/Si)₂PLi + Me-Sn/SiR₃.³

We report the synthesis and multinuclear NMR characterization of P-Si and the first P-Sn -protected phosphasilenes R₂Si=P-R’ (1a-c), where R=tBu₂MeSi and R’=tBuMe₂Si(a), Me₃Sn(b), Bu₃Sn(c), by LiF elimination from corresponding lithium phosphides 2a-c. Reduction of phosphasilenes 1a-c with Li metal or R₃SiLi in hexane or THF yields persistent anion-radicals 3a-c. In contrast, the reaction of 1b,c (R’=R₃Sn) with (Me₃Si)₃SiK in hexane produces quantitatively (Me₃Si)₃Si-SnR₃ accompanied by an NMR-silent elusive species which we believe to be R₂Si=P-K (5); the corresponding anion-radicals 3b and 3c were not detected.

We are currently studying the properties and reactions of the novel 1, 3 and 5.

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