Electronic and Steric Properties of <i>N</i>‑Heterocyclic Boryl Ligands

N-Heterocyclic boryl (NHB) is emerging as an important type of versatile ligand; however, its electronic and steric properties are far from well-known, which is the bottleneck for its rational design. Herein, theoretical evaluation of the scales in electronic and steric properties for various NHBs is presented with NHB–Ir­(CO)3 as the model complex. The calculated Tolman electronic parameters (TEP) reveal general trends about the influence of substitution, backbone saturation, ring size, and heteroatoms. The percent buried volume (%Vbur) of NHBs generally increases with the volume augmentation. The facilitating roles of the PIO-based Bond Index between NHB and the Ir center and the %Vbur on TEP were also analyzed. The systematic scales should be essential for the design, application, and mechanistic understanding of the NHB-based complexes or molecules.