Silanone Explained

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 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.

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, Si^δ+–O^δ−.

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.

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

Notes and References

1. A Stable Silanone with a Three-Coordinate Silicon Atom: A Century-Long Wait is Over . S. S. . Sen . . 2014 . 53 . 34 . 8820–8822 . 10.1002/anie.201404793 . 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
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
4. J. Mol. Spectrosc.. 175. 2. 1996. 421–428. Experimentally Determined Structure of H₂SiO by Rotational Spectroscopy and Isotopic Substitution. M. Bogey . B. Delcroix . A. Walters . J-C Guillemin . 10.1006/jmsp.1996.0048. 1996JMoSp.175..421B .
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
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.
7. Chemical Tricks To Stabilize Silanones and Their Heavier Homologues with EO Bonds (E=Si–Pb): From Elusive Species to Isolable Building Blocks . Y. . Xiong . S. . Yao . M. . Driess . . 2013 . 52 . 16 . 4302–4311 . 10.1002/anie.201209766 . 23450830 .
8. T. . Sun . J. . Li . H. . Wang . Recent Advances in the Chemistry of Heavier Group 14 Analogues of Carbonyls . . 2022 . 17 . 18 . e202200611 . 10.1002/asia.202200611 . 35883252 . 251104394 .
9. An Isolable Silicon Analogue of a Ketone that Contains an Unperturbed Si=O Double Bond . Ryo . Kobayashi . Shintaro . Ishida . Takeaki . Iwamoto . . 58 . 28 . 2019 . 9425–9428 . 10.1002/anie.201905198 . 31095845 . 157056381 . free .