Understanding the solubilization of Ca acetylide with a new computational model for ionic pairs

The unique reactivity of the acetylenic unit in DMSO gives rise to ubiquitous synthetic methods. We theoretically consider CaC₂ solubility and protolysis in DMSO and formulate a strategy for CaC₂ activation in solution-phase chemical transformations. For this, we use a new strategy for the modeling of ionic compounds in strongly coordinating solvents combining Born-Oppenheimer molecular dynamics with the DFTB3-D3(BJ) Hamiltonian and static DFT computations at the PBE0-D3(BJ)/pob-TZVP-gCP level. We modeled the thermodynamics of CaC₂ protolysis under ambient conditions, taking into account its known heterogeneity and considering three polymorphs of CaC₂. We give a theoretical basis for the existence of the elusive intermediate HC[triple bond, length as m-dash]C-Ca-OH and show that CaC₂ insolubility in DMSO is of thermodynamic nature. We confirm the unique role of water and specific properties of DMSO in CaC₂ activation and explain how the activation is realized. The proposed strategy for the utilization of CaC₂ in sustainable organic synthesis is outlined.