Silanone

A silanone in chemistry is the silicon analogue of a ketone. The general description for this class of organic compounds is R1R2Si=O, with silicon connected to a terminal oxygen atom via a double bond and also with two organic residues (R).[1] Silanones are extremely reactive[1] and until 2013 were only detected by argon matrix isolation[2][3] or in the gas phase[4] but not isolated. A synthesis of a stable silanone was reported in 2014. Silanones are of some interest to academic research, with their reactivity being of some relevance to the double bond rule.

The general structure of a silanone

Silanones are unstable and favor oligomerisation to siloxanes. The reason for this instability is the weak pi bond with a small HOMO–LUMO energy gap caused by an unfavorable overlap between the p-orbitals of silicon and oxygen. A second reason for the observed instability is the strongly polarized silicon–oxygen bond, Siδ+–Oδ−.[1]

History

The first to postulate a silanone were Kipping & Lloyd in 1901,[5] but their products were in fact siloxanes. It was not until 2014 that a stable silanone was reported.[6] In this compound, silicon is bonded to a SIDipp (1,3-bis(2,6-iPr2-C6H3)imidazolidin-2-ylidene) group and a (Cp*)Cr(CO)3 group. Its stability is owed to the direct coordination of silicon to chromium and to steric shielding. The reported Si=O bond length is 1.526 Å, in line with expectations. It has been described as a cationic metallosilanone.[1]

Other strategies have recently been used to stabilise silanones,[7] for example coordination to Lewis acids or bases[8] and steric shielding.[9]

References
  1. Sen, S. S. (2014). "A Stable Silanone with a Three-Coordinate Silicon Atom: A Century-Long Wait is Over". Angew. Chem. Int. Ed. 53 (34): 8820–8822. doi:10.1002/anie.201404793. PMID 24990653.
  2. On the proposed thermal interconversion of matrix-isolated dimethylsilylene and 1-methylsilene: their reactions with oxygen atom donors Charles A. Arrington, Robert West, Josef Michl J. Am. Chem. Soc., 1983, 105 (19), pp 6176–6177 doi:10.1021/ja00357a048
  3. Infrared spectroscopic evidence for silicon-oxygen double bonds: silanone and the silanoic and silicic acid molecules Robert Withnall, Lester Andrews J. Am. Chem. Soc., 1985, 107 (8), pp 2567–2568 doi:10.1021/ja00294a070
  4. M. Bogey; B. Delcroix; A. Walters; J-C Guillemin (1996). "Experimentally Determined Structure of H2SiO by Rotational Spectroscopy and Isotopic Substitution". J. Mol. Spectrosc. 175 (2): 421–428. Bibcode:1996JMoSp.175..421B. doi:10.1006/jmsp.1996.0048.
  5. XLVII.—Organic derivatives of silicon. Triphenylsilicol and alkyloxysilicon chlorides F. Stanley Kipping, Ph.D., D.Sc., F.R.S. and Lorenzo L. Lloyd J. Chem. Soc., Trans., 1901,79, 449-459 doi:10.1039/CT9017900449
  6. Filippou, A. C., Baars, B., Chernov, O., Lebedev, Y. N. and Schnakenburg, G. (2014), Silicon–Oxygen Double Bonds: A Stable Silanone with a Trigonal-Planar Coordinated Silicon Center. Angew. Chem. Int. Ed., 53: 565–570. doi:10.1002/anie.201308433
  7. Xiong, Y.; Yao, S.; Driess, M. (2013). "Chemical Tricks To Stabilize Silanones and Their Heavier Homologues with EO Bonds (E=Si–Pb): From Elusive Species to Isolable Building Blocks". Angew. Chem. Int. Ed. 52 (16): 4302–4311. doi:10.1002/anie.201209766. PMID 23450830.
  8. Sun, T.; Li, J.; Wang, H. (2022). "Recent Advances in the Chemistry of Heavier Group 14 Analogues of Carbonyls". Chem. Asian J. 17 (18): e202200611. doi:10.1002/asia.202200611. PMID 35883252. S2CID 251104394.
  9. Kobayashi, Ryo; Ishida, Shintaro; Iwamoto, Takeaki (2019). "An Isolable Silicon Analogue of a Ketone that Contains an Unperturbed Si=O Double Bond". Angew. Chem. Int. Ed. 58 (28): 9425–9428. doi:10.1002/anie.201905198. PMID 31095845. S2CID 157056381.
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