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. 2020 Aug 11;11(1):4009.
doi: 10.1038/s41467-020-17815-z.

Silicon-silicon π single bond

Soichiro Kyushin  1 , Yoshikuni Kurosaki  2 , Kyohei Otsuka  2 , Haruna Imai  2 , Shintaro Ishida  3 , Toru Kyomen  4 , Minoru Hanaya  2 , Hideyuki Matsumoto  5
Affiliations

Silicon-silicon π single bond

Soichiro Kyushin et al. Nat Commun. .

Abstract

A carbon-carbon double bond consists of a σ bond and a π bond. Recently, the concept of a π single bond, where a π bond is not accompanied by a σ bond, has been proposed in diradicals containing carbon and heteroatom radical centers. Here we report a closed-shell compound having a silicon-silicon π single bond. 1,2,2,3,4,4-Hexa-tert-butylbicyclo[1.1.0]tetrasilane has a silicon-silicon π single bond between the bridgehead silicon atoms. The X-ray crystallographic analysis shows that the silicon-silicon π single bond (2.853(1) Å) is far longer than the longest silicon-silicon bond so far reported. In spite of this unusually long bond length, the electrons of the 3p orbitals are paired, which is confirmed by measurement of electron paramagnetic resonance, and magnetic susceptibility and natural bond orbital analysis. The properties of the silicon-silicon π single bond are studied by UV/Vis and 29Si NMR spectroscopy, and theoretical calculations.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Synthesis, structure, and magnetic property of 2.
a Concepts of a double bond (top) and a π single bond (bottom). b Synthesis of 2. c Molecular structure of 2. Thermal ellipsoids are drawn at the 30% probability level. Selected bond length (Å) and angle (°): Si1–Si2 2.3090(7), Si1–Si1’ 2.853(1), Si1–C1 1.921(3); Si2–Si1–Si1’ 51.83(2), Si2–Si1–Si2” 103.65(4), Si2–Si1–C1 128.07(2), Si1’–Si1–C1 176.1(1), Si1–Si2–Si1’ 76.35(4). d Temperature-dependent magnetic susceptibility of 2. The data were measured 12 times at each temperature. The black dots denote average values and the error bars show SDs.
Fig. 2
Fig. 2. Electronic properties of 2.
a Frontier orbitals and their energy levels of 2 calculated at the B3LYP/6-31G(d) level. b UV/Vis spectrum of 2 in benzene at room temperature with transitions calculated at the TD-DFT B3LYP/6-31G(d) level.
Fig. 3
Fig. 3. Energy curves of 2 and 5–10 calculated at the B3LYP/6-31G(d) level.
The terms SB and LB denote short-bond and long-bond isomers, respectively.
See this image and copyright information in PMC

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