Examples include the important role of tunneling in the one-or two water-bridged tautomerization of formamidine and azaindole, keto-enol and amino-enol processes. Furthermore, some of these cases validated experimental observations. Using a one-dimensional tunneling approximation, tunneling has also been studied for the intermolecular tautomerization of the simplest phosphinous acid (H2POH) and secondary phosphine oxides. However, whether an accurate multidimensional tunneling method would find a tunneling mechanism to be viable has not been explored for the kinetically favored water-catalyzed tautomerization of phosphinylidenes. Since solvents, which stabilize the phosphinylidenes, usually contain trace amounts of water, and considering the above sets of examples of waterassisted tunneling-driven tautomerism, studies to accurately assess the possibility of tunneling in the water-bridged tautomerization of phosphinylidenes are warranted.