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 CaC(2) solubility and protolysis in DMSO and formulate a strategy for CaC(2) 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 CaC(2) protolysis under ambient conditions, taking into account its known heterogeneity and considering three polymorphs of CaC(2). 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 CaC(2) insolubility in DMSO is of thermodynamic nature. We confirm the unique role of water and specific properties of DMSO in CaC(2) activation and explain how the activation is realized. The proposed strategy for the utilization of CaC(2) in sustainable organic synthesis is outlined.