Toward a quantitative evaluation of the strength of Cp2M···η 2–borate interactions

Abstract

Amine-boranes might be a crucial material toward a successful energy transition. A precise description of metal–ligand interactions involved in the homogeneous catalysis of the dehydrogenation of amine-boranes would represent a major step toward a global understanding of the reaction process. η 2 interactions between borates and organometallic compounds were identified as key intermediates in the reaction pathways. Herein are proposed tailored topological descriptors to measure the efficiency of several metallocenes to activate B–H bonds in prototypical Cp2M···η 2–borates complexes. The combined use of QTAIM and ELF partitions were used to ascertain the 3C/2e interactions between borates and metallocenes. The strength of the B–H bond is affected by two different parameters: the nature of the ligands bonded to the borates and the effect of the interaction with the metallocene. The use of tailored descriptors allows to evaluate the activation of the B–H bond due to the sole effect of the interaction between the borates and the metallocenes. Herein, we suggest the concomitant use of the electron density ratios $$\frac{{\rho \left( {{\text{BCP}}\;{\text{B}} - {\text{H}}_{\text{complex}} } \right)}}{{\rho \left( {{\text{BCP}}\;{\text{B}} - {\text{H}}_{{{\text{free}}\;{\text{borate}}}} } \right)}}$$ and distance ratios $$\frac{{d\left( {{\text{B}} - {\text{H}}_{\text{complex}} } \right)}}{{d\left( {{\text{BCP}}\;{\text{B}} - {\text{H}}_{\text{free borate}} } \right)}}$$ of the B–H bonds to classify the {borates + metallocenes} systems as a function of the strength of the B–H interaction with the metallocene. We further suggest to complement this evaluation based on the QTAIM analysis by a quantization of the contribution of the metallic center on the protonated basin defined within the ELF framework.