To further evaluate the origin of enantioselectivity, a distortion-interaction analysis was performed on TSMI-Major and TSMI-Minor. Distortion energy describes the energy required to distort reactants and catalysts from their respective ground states into the necessary transition state conformations. Energy decomposition revealed that the major enantiomer suffers a greater degree of distortion energy, 2.4 kcal/mol (∆∆E ‡ ) more than the minor enantiomer (Figure ). The majority (1.8 kcal/mol) of this 2.4 kcal/mol difference in distortion energy arises from the distortion of the diphenyl phosphine and Cu-DuPhos catalyst, while the remaining 0.6 kcal/mol arises from distortion of the cyclopropene substrate. Despite distortion energy favoring the minor enantiomer, advantageous interaction energy favors the major enantiomer by 5.6 kcal/mol. Interaction energy describes how the distorted catalyst and reactant fragments interact with one another within the TS, a portion of this can be accounted for as dispersion energy. The major enantiomer exhibits favorable dispersions in the form of significant CH-𝜋 interactions between the diphenylphosphine and the cyclopropene methyl group as well as moderate dispersions amongst the Cu-DuPhos isopropyl groups and the cyclopropene substrate (Figure ). A visual comparison of the dispersion interactions in the enantioselectivity-determining transition states shows that TSMI-major enjoys more stabilizing dispersion interactions than TSMI-minor (as evidenced by the greater green areas in the NCI plots of the two TSs shown in Figure ). In addition to the favorable dispersions imparted by its isopropyl groups in TSMI- Major, the Cu-DuPhos catalyst also serves to add steric bulk to the catalytic pocket, blocking more than three-fourths of the pocket when coordinated to PPh2, forcing the cyclopropene substrate to bind in the same location for both enantiomers (see SI page S37). From this analysis, steric interactions have been identified to play a key role in controlling stereoselectivity. Using this information, we chose to investigate the buried volume and steric maps for intermediate 5a with L1, L3, L4 and L5 as ligands. The buried volume analysis reveals that ligand L1 (Figure ) has a slightly smaller available free volume compared to the best ligand L5 (Figure ). However, L5 is more fluctional compared to the rigid biphenyl backbone of L1, thereby accommodating the incoming cyclopropene more readily. This leads to an overall reduction in the background reaction of L5, compared to L1, thus enabling better enantioselectivity in L5. Similarly, despite having the same backbone as L5 (R= i Pr), ligands L3 (R=Me, Figure ) and L4 (R=Et) have more available free volume, leading to overall poorer steric control and slightly lower enantioselectivity. In conclusion, we report asymmetric hydrophosphination of cyclopropenes in high enantio-and diastereoselectivities. Mechanistic studies reveal an unusual dimeric resting state and a surprising rate enhancement effect from DBU, which plays an important role in forming the catalytically active monomer. Proof of concept for enrichment of phosphorus stereocenters is demonstrated through a DyKAT of an unsymmetrically substituted secondary phosphine. Both the enantio-and diastereoselectivity of the product is determined during the migratory insertion step. An analysis of the relevant TSs indicate that selectivity is controlled by a combination of dispersion and steric interactions. These insights will guide future studies on developing methods to set phosphorus stereocenters and design both mono-and bidentate phosphine ligands. These studies help advance our understanding of copper catalysis, hydrofunctionalization, and phosphine synthesis.