Modulating the Proton Affinity of Silanol and Siloxane Derivatives by Tetrel Bonds

The proton affinity (PA) on the oxygen atom in silanol and siloxane derivatives is enhanced by the formation of tetrel bonds with small Lewis bases [B···R₃SiOH, B···R₃SiOSiR₃, B···R₃SiOSiR₃···B; B = H₂O, CO, NH₃, HCN, H₂S; R = H, Me], as shown by MP2/jul-cc-pVTZ calculations. The complexed systems become more basic than ether and other carbon-related compounds, and even more basic than pyridine in some specific cases, reaching values up to 959.4 kJ/mol (H₃N···H₃SiOSiH₃···NH₃ complex). Changes on PAs are directly related to very large binding energies for the protonated species. Topological methods and the natural bond orbital scheme are used to rationalize the observed trends. The PA enhancement should be taken into account when dealing with silanols and siloxanes in different environments.