Stabilization of Interstellar CSi 2 Species by Donor Base Ligands: L-CSi 2 -L; L = cAAC Me , NHC Me , and PMe 3 .

The donor ligand bonded singlet (L) 2 Si 2 C containing a bent Si 2 C unit in the middle has been studied by theoretical quantum mechanical calculations (NBO, QTAIM, EDA-NOCV analyses) [L = cAAC, NHC, Me 3 P]. EDA-NOCV analysis suggests that this Si 2 C is possible to stabilize by a pair of donor base ligands. The bond dissociation energy of the Si 2 C fragment is endothermic (85-45 kcal/mol) with a sufficiently high intrinsic interaction energy (Δ E int = -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 Si 2 C 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) 2 Si 2 C-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 Si 2 C backbone to empty hybrid orbital of Ni(CO) 3 fragment. A sufficiently strong π-back-donation from (OC) 3 Ni to Si 2 C has also been identified.