The catalytic hydrosilylation of CO₂ is a method for the fixation of the greenhouse gas that provides value-added chemicals. Examples of catalyst-free methods for the hydrosilylation of CO₂ under mild conditions, however, are rare.

Shintaro Ishida, Takeaki Iwamoto, Tohoku University, Sensai, Japan, Soichiro Kyushin, Gunma University, Kiryu, Japan, and colleagues have synthesized 5,10,15,20-tetraphenylporphyrinato(dihydrido)silicon(IV), a six-coordinate silicon dihydride (pictured above). The compound was synthesized via the reaction of a dichloro precursor with LiAlH₄ in tetrahydrofuran (THF), followed by a brief exposure of the resulting solution to dry O₂. The team found that the simple, previously unknown silicon dihydride undergoes a catalyst-free hydrosilylation with CO₂ at ambient temperature and pressure. Combining this hydrosilylation with a subsequent hydrolysis (pictured below) gives formic acid from CO₂.

 

The team performed density functional theory (DFT) calculations, which indicate that the hydride-donor ability of the six-coordinate silicon dihydride is exceptionally high for a neutral silicon hydride, and that the hydride transfer from silicon to CO₂ is a key step for the non-catalytic hydrosilylation.

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• A Six‐Coordinate Silicon Dihydride Embedded in a Porphyrin: Enhanced Hydride‐Donor Properties and the Catalyst‐Free Hydrosilylation of CO₂,
  Shintaro Ishida, Takuroh Hatakeyama, Takuya Nomura, Maiko Matsumoto, Kimio Yoshimura, Soichiro Kyushin, Takeaki Iwamoto,
  Chem. Eur. J. 2020.
  https://doi.org/10.1002/chem.202002587