Stabilization of Interstellar CSi<inf>2</inf> Species by Donor Base Ligands: L-CSi<inf>2</inf>-L; L = cAAC^Me, NHC^Me, and PMe<inf>3</inf>

The donor ligand bonded singlet (L)2Si2C containing a bent Si2C unit in the middle has been studied by theoretical quantum mechanical calculations (NBO, QTAIM, EDA-NOCV analyses) [L = cAAC, NHC, Me3P]. EDA-NOCV analysis suggests that this Si2C is possible to stabilize by a pair of donor base ligands. The bond dissociation energy of the Si2C fragment is endothermic (85-45 kcal/mol) with a sufficiently high intrinsic interaction energy (ΔEint = −89 to −48 kcal/mol). Fifty percent of the total stabilization energy arises from electrostatic interactions, and nearly 45% is contributed by covalent orbital interaction between Si2C and (L)2 fragments in their singlet states. 75-80% of the orbital interaction energy is contributed by two sets of σ-donation L → SiCSi ← L. The π-back-donation is only 15-10%. The dispersion energy is not negligible (3-5%). The interaction energy is highest for 1 (L = cAAC) among three compounds. Additionally, (cAAC)2Si2C-Ni(CO)3 (4) has been studied. The interaction energy between 1 and Ni(CO)3 is nearly 61 kcal/mol with the major contribution coming from donation of electron cloud from electron rich Si2C backbone to empty hybrid orbital of Ni(CO)3 fragment. A sufficiently strong π-back-donation from (OC)3Ni to Si2C has also been identified.