Impact on increasing the bent angle in nickel dibenzoporphyrin(2.1.2.1) bows. Evaluation of structural and molecular features from computations

Abstract

Non-planar porphyrin motifs enable particular characteristics relevant for a wide range of applications. We explored (through computations) the features of increasing the bend in the more flexible dibenzoporphyrin (2.1.2.1) core. We decreased the bridge length from the recently reported butadiyne-bridged dibenzoporphyrin(2.1.2.1), and its nickel counterpart. Our results highlighted the flexibility of the dibenzoporphyrin(2.1.2.1) core, which could bend from 122.4° to 103.2° involving a strain energy of <3.4 kcal mol⁻¹, and of 9.1 kcal mol⁻¹ from 116.0° to 97.3° upon incorporating the central nickel atom. For further bent angles, destabilization of the dibenzoporphyrin(2.1.2.1) core increased to 23.7 and 38.5 kcal mol⁻¹, respectively. This structural control modified the HOMO–LUMO gap and optical absorption patterns, and highlighted an increase in the Lewis acid capabilities of the resulting π-hole site perpendicular to the N4 molecular plane, in comparison with the parent nickel porphyrin, evaluated via calculated fluoride ion affinity. In addition, the induced magnetic field had a deshielding region ascribed to N4- and NiN4-motifs, which was retained within the bent cavity. These observations indicate that controlled bending of N4 is a useful synthetic strategy to tune the capabilities of porphyrin- and metalloporphyrin-like species.