Realistic modelling of hydrogen bonding of 2-cyclohexenone with H2O and H3BO3 in the outer coordination sphere of a chiral diene/Rh(i) complex by ab initio molecular dynamics

A full-DFT Born-Openheimer MD (BOMD) study of the potential hydrogen bonding of 2-cyclohexenone pi-complexed to Rh(i) in explicit 1,4-dioxane is presented. The complex is a key intermediate in the academically and industrially important asymmetric Rh-catalysed 1,4-addition of arylboronic acids to alpha,beta-unsaturated ketones with the directing ligand phbod, a chiral bicyclic 1,4-diene. The ketone O atom (O-k) behaves as a single H-bond acceptor persistently throughout most of the simulation time while the donor is mobile and liable to exchange. Well-tempered metadynamics show that H-bonding with a (H2O)(3) cluster is favorable by free energy but kinetically labile while with just H3BO3 is unfavorable but kinetically much more persistent. When both (H2O)(3) cluster and H3BO3 are within H-bond distance from O-k, the non-H-bonded and the various H-bonded species are close in energy, implying the free energy surface is complex and quite flat. The most stable species features a H-bond with a water acceptor but not with H3BO3. The non-H-bonded state is 0.7 kcal mol(-1) higher in free energy. Model static DFT studies reveal that H-bonding with both (H2O)(3) cluster and H3BO3 is favorable by enthalpy, but unfavorable by free energy when the entropy term is added.

Automated summary

A full-DFT Born-Openheimer MD study was conducted to investigate the hydrogen bonding between 2-cyclohexenone and Rh(i) in explicit 1,4-dioxane. The results showed that the ketone O atom persistently acted as a hydrogen bond acceptor, while the donor was mobile and exchangeable. Model static DFT studies revealed that the hydrogen bonding with (H2O)3 cluster and H3BO3 was favorable in enthalpy but unfavorable in free energy when the entropy term was considered.