Abstract
Although silylene‐carbonyl complexes are known for decades, only recently isolable examples have been accomplished. In this work, the bonding situation is re‐evaluated to explain the origins of their remarkable stability within the Kohn‐Sham molecular orbital theory framework. It is shown that the chemical bond can be understood as CO interaction with the silylene via a donor‐acceptor interaction: a σ‐donation from the σ CO into the empty p‐orbital of silicon, and a π‐back donation from the sp 2 lone pair of silicon into the π*CO antibonding orbitals. Notably, it was established that the driving force behind the surprisingly stable Si−CO compounds, however, is another π‐back donation from a perpendicular bonding R−Si σ‐orbital into the π*CO antibonding orbitals. Consequently, the pyramidalization of the central silicon atom cannot be associated with the strength of the π‐back donation, in sharp contrast to the established chemical bonding model. Considering this additional bonding interaction not only shed light on the bonding situation, but is also an indispensable key for broadening the scope of silylene‐carbonyl chemistry.
Highlights
The chemistry of transition metal-carbonyl complexes has been the focus of attention for more than a century.[1]
We demonstrate that the key effect from the gallium- and silicon-based ligands is to strengthen such orbital interaction
J. 2021, 27, 10601 – 10609 www.chemeurj.org calculated values for the SiÀ C bond length at the BP86-D3(BJ)/ def2-SVP level are between 1.809 to 1.938 Å, which is in good agreement with previous theoretical calculations,[12,16,17] and experimental structures.[16,17]
Summary
The chemistry of transition metal-carbonyl complexes has been the focus of attention for more than a century.[1]. Various types of stable carbon- and siliconcontaining compounds have been synthesized and structurally characterized that demonstrate the ability to encompass similar chemical bonding and reactivity patterns as transition metals.[4] In particular, group 14-carbonyl complexes have been pursued for decades. The CO stretching frequency in the IR spectra show a bathochromic shift (v=1945 cmÀ 1 and 1908 cmÀ 1 for 5 and 6, respectively; vs free CO, v=2143 cmÀ 1), in line with a strong donor-acceptor interaction These novel SiÀ CO are extraordinary stable but the current chemical bond model lead to an ambiguous interpretation of the structure and spectroscopical properties.
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