Controlling the spin state of diphenylcarbene via halogen bonding: A theoretical study

Abstract

Halogen bonding has recently become an effective tool to control the spin state of reactive carbenes. In this work, a series of the complexes of diphenylcarbene (DPC) that has a triplet ground state with several halogen bond donors RX were theoretically studied, and in particular, the influence of the formation of halogen bonding on the spin state of DPC was extensively explored. The spin flip depends on the difference of halogen bond energies between triplet and singlet, that is, when the difference is large enough a spin flip may occur. Furthermore, the variations of the geometries on complexation may induce the potential energy surfaces of different spin states to intersect, thus leading to intersystem crossing. Based on the energy analysis of the minimum energy crossing points (MECPs), the systems with a smaller MECP‐triplet energy barrier go through intersystem crossing more easily. Halogen bonds in the complexes, where a spin flip takes place, exhibit a partially covalent character, while other complexes show conventional behaviors of halogen bonding. According to charge decomposition analysis, the charge transfer from HOMO (DPC) to LUMO (RX) is identified as a prominent stabilizing interaction in the whole complexes.

Physical Nature of Differential Spin-State Stabilization of Carbenes by Hydrogen and Halogen Bonding: A Domain-Based Pair Natural Orbital Coupled Cluster Study

“…Although a wide range of computational studies have previously investigated the differential stabilization of the spin states of carbenes by means of implicit solvation models, − only a few took into account the role that direct intermolecular interactions play in this context. ,, In particular, Standard recently applied correlated wavefunction-based methods to calculate E S–T values of several carbenes as well as of their hydrogen-bonded complexes with water and methanol. It was found that in all cases hydrogen bonding selectively stabilizes the singlet state.…”

“…The magnitude of charge transfer is significantly reduced in the triplet state, which qualitatively explains the observed differential spin-state stabilization. Halogen-bonding interactions with singlet carbenes have also been studied computationally in a number of studies, ,− but, to the best of our knowledge, a comparative study of the effect of such intermolecular interactions on the stabilization of singlet and triplet halogen-bonded complexes of carbenes has not been reported.…”

Theoretical study on the noncovalent interactions involving triplet diphenylcarbene

“…Lu et al [39] further discussed the in uence of the formation of halogen bond on the spin state of DPC and the decisive factors in spin slip via density functional theory (DFT) calculations.…”