Pyrrole <sup>β</sup>C−B−N Fused Porphyrins: Molecular Structures and Opto‐Electrochemical Studies
Rajendra Prasad Nandi, Brijesh Chandra, Subhajit Ghosh, Siddhartha P. Sarma, Silvano Geremia, Neal Hickey, Pakkirisamy Thilagar
Abstract
Abstract Herein, we report the design, synthesis, structure, and electrochemical study of doubly β C−B−N fused Ni(II) porphyrins ( 1‐trans , 1‐cis , 2‐trans , and 2‐cis ). These compounds have been synthesized from A 2 B 2 type dipyridyl Ni(II) porphyrins (Ar=Ph for 1 a ; Ar=C 6 F 5 for 2 a ) via Lewis base‐directed electrophilic aromatic borylation reactions. The solution state structures of these compounds have been established using 1 H NMR, 11 B NMR, 1 H‐ 1 H COSY, 1 H‐ 13 C HSQC, and 19 F‐ 13 C HSQC NMR techniques. Single crystal X‐ray analysis have revealed that 1‐trans , 1‐cis , and 2‐trans adopt ruffled conformations, with alternate meso‐carbons on the opposite sides of the mean porphyrin plane. The Soret bands in the absorption spectra of the B−N fused molecules are ~40 nm redshifted compared to unfused Ni(II) porphyrin precursors. The B−N fusion have diminished the redox potential of fused porphyrins. Although 1‐trans and 1‐cis , show four oxidation processes, 2‐trans and 2‐cis show only three oxidation processes. DFT studies have revealed that the tetrahedral geometry of the boron has induced a twist in the π‐conjugation, which destabilizes the HOMO and stabilizes the LUMO in 1‐trans , 1‐cis , 2‐trans , and 2‐cis .