Strain-Releasing Ring-Opening Diphosphinations for the Synthesis of Diphosphine Ligands with Cyclic Backbones

Diphosphine ligands based on cyclobutane, bicyclo[3.1.1]heptane, and bicyclo[4.1.1]octane were synthesized from the corresponding highly strained, small, cyclic organic molecules, i.e., bicyclo[1.1.0]butane, [3.1.1]propellane, and [4.1.1]propellane, employing a ring-opening diphosphination. Under photocatalytic conditions, the three-component reaction of a diarylphosphine oxide, one of the aforementioned strained molecules, and a diarylchlorophosphine results in the smooth formation of the corresponding diphosphines in high yield. The obtained diphosphines can be expected to find applications in functional molecules due to their unique structural characteristics, which likely impart specific properties on their associated metal complexes and coordination polymers (e.g., a zigzag-type structure). The feasibility of the initial radical addition can be estimated using density-functional-theory calculations using the artificial force induced reaction (AFIR) method. This study focuses on the importance of integrating experimental and computational methods for the design and synthesis of new diphosphination reactions that involve strained, small, cyclic organic molecules.