Towards Silanone via Bromosilanols and Bromosiloxanes

Stable silanones, R₂Si=O, the silicon analogue of ketones, have not yet been isolated.

Here, we report the synthesis and X-Ray structural analysis of lithium bromosilanolate 3 and the reaction of bromosiloxane 5 with silyllithium in hexane and in THF, which we believe yields a transient silanone.

Reaction of 2 with )Me₃Si(₂NLi yields trimer 3. X-Ray structural analysis of 3 reveals significant Li-Br interactions, i.e. r(Li--Br) = 2.20 Å (shorter than the sum of their ionic radii), a very short r(Si-O) = 1.58 Å and a relatively long r(Si-Br) = 2.29 Å.(see Figure 1) These structural features point to a major contribution of a R₂Si=O···LiBr complex character in 3. The structural features of 3 resemble those of dialkyl substituted dimeric R₂Si=O-LiBr complex recently published by Ishida Iwamoto et al.² Hydrolysis of 3 yields diol 4. Disappointingly, heating 3 to 70°C in hexane or THF does not lead to LiBr elimination, indicating strong intermolecular bonding in 3.¹

To prevent aggregation through strong O-Li-O interactions as in 3, the hydroxyl group in 2 was replaced by a siloxy group, i.e., 5. Interestingly, reaction of 5 with tBu₂MeSiLi is solvent dependent. In hexane this reaction yields tris(silyl)silyllithium 7. However, in THF disilane 8 is produced together with what we believe is the transient silanone 9. As expected, hydrolysis of 9 yields diol 4. We continue our efforts to isolate silanone 9.