Mechanism for Forming B,C,N,O Rings from NH₃BH₃ and CO₂ via Reaction Discovery Computations

Abstract

This study employs computational reaction finding tools to probe the unique biphilic reactivity between ammonia-borane (AB) and CO2. The results show that sequential reactions involving multiple equivalents of AB and CO2 can lead to the formation of stable nonplanar B,C,N,O-heterocycles (Cy-BCN). Cy-BCN is shown to emerge through boron-oxygen bond formation, hydroboration, dative bond formation, and single- or double-hydrogen transfers. The most kinetically facile reactions (computed at the coupled cluster singles and doubles with perturbative triples (CCSD(T)) level of theory) result from polarized nitrogen-boron double bonds whereas thermodynamic stability results from formation of covalent boron-oxygen bonds. An important structure, HCOOBHNH2 (DHFAB), contains both of these features and is the key intermediate involved in generation of Cy-BCN. Crucially, it is shown that favorable boron-oxygen bond formation results in production of Cy-BCN species that are more stable than polyaminoboranes. These types of reaction intermediates could serve as building blocks in the formation of B,N-codoped graphene oxide (BCN).

Stepwise basis set selection

“…) are related to carbon dioxide reduction by ammonia borane, a system of interest to carbon‐neutral chemistry and materials development . The polarized BN and BN bonds have been noted as leading to a wide variety of reactivity, which becomes even more complex as CO bonds are introduced as reactive partners . Compared to the previous SBB examples, significant polarizations during reaction means more basis functions will be needed to capture this reactivity.…”

“…Having demonstrated convergence of the SBB algorithm for reaction intermediates, it is now of interest to examine whether these basis function distributions are transferable to different geometries. The transition states for the AB/CO 2 reactions, shown in Figure , will serve as test cases. Transferability of SBB basis sets was tested by taking the ɛ = 1 mHa SBB bases and using these to calculate the corresponding activation energies.…”

Methods for exploring reaction space in molecular systems

“…For instance, this strategy uncovered an unexpected, off‐cycle trap that was preventing a Ni‐based C‐H functionalization catalyst from turning over, which lead to the design of a new catalyst that avoided this trap . A handful of (mostly catalytic) reactions have also been investigated using the original ZStruct, showing it to be a competent tool for reaction exploration …”

Exploration of Reaction Pathways and Chemical Transformation Networks

“…123 Furthermore, several other (catalytic) reactions have been studied with ZStruct. [124][125][126] Recently, Dewyer and Zimmerman addressed the limitations of ZStruct and developed ZStruct2. 127 In ZStruct2, reactants are prealigned to sample so-called driving coordinates that describe the expected elementary reactions.…”