JACS: the synthesis of Ni (II) - 10-phosphine heterocarbrole

Porphyrins are macrocyclic conjugated compounds with tetrapyrrole skeleton, which have special physiological activities in vivo At the same time, they have unique optical and electrochemical properties and are good electronic donors Their photoelectric properties can be controlled by structural modification Due to the existence of lone pair electrons, the phosphorus atoms show electron donating properties in π system The structure and electronic properties can be effectively changed by modifying the phosphorus atoms Considering the characteristics of π system containing phosphorus, the introduction of phosphorus atom into porphyrin framework will open a new chapter in the application of porphyrins Recently, the research group Hiroshi shinokubo of Nagoya University in Japan and Heike fliegl of Karlsruhe Institute of technology in Germany reported the synthesis of Ni (II) 10-phosphors (Ni (II) - 10-phosphacoroles) The results were published in J am Chem SOC (DOI: 10.1021 / JACS 8b3169) By the nucleophilic substitution reaction of bis (α, α '- dibromodipyrrolidone) Ni (II) complex 1 with phosphine anion, the formation of one C-C bond and two C-P bonds at the same time was induced, thus the synthesis of Ni (II) - 10-phosphine heterocarbrole (2) was realized, but the reaction yield was only 13% Through the selection of reaction conditions, the author finally determined that in the presence of PdCl2 (dppf) · CH2Cl2 and potassium TERT butanol, when treating 1 with mesph2, 2 (scheme 1) could be obtained in 52% yield (photo source: J am Chem SOC.) next, the structure of compound 2 was characterized by NMR and hr-ms The peak at - 42.0 ppm in 31 P NMR confirmed the existence of phosphorus atom The 1H NMR spectra show that the four double peaks of pyrrole protons in the aromatic region appear in the range of 7.35-7.69 ppm, indicating that 2 has obvious aromaticity Then, the solid structure of 2 was determined by X-ray diffraction analysis (Figure 1a and 1b) The inner C-P bond of 2 is slightly shorter than that of the outer C-P bond (Figure S13), which indicates that the inner C-P bond of 2 has double bond property, so that π - conjugation between pyrrole α - carbon and phosphorus induces 2 to produce aromaticity (photo source: J am Chem SOC.) (photo source: J am Chem SOC.) later, the author tried to chemically modify the phosphorus in compound 2 (scheme 2) 2 reacts with m-chloroperoxybenzoic acid (m-CPBA) and [Au (SME 2) Cl] to obtain oxide 2-O and complex 2-aucl, respectively The 1H NMR spectrum of 2-O shows that the signal peak of pyrrole proton shifts to high field The structure of 2-O (Figure 1D and 1E) was determined by X-ray diffraction analysis Compared with compound 2, the inner C-P bond is longer, but still shorter than the outer C-P bond The 1H NMR spectra of 2-aucl show that it is weakly aromatic X-ray diffraction analysis showed that the reaction formed a 1:1 complex (Figure 1E, 1F) Compared with compound 2, compound 2-O and 2-aucl showed obvious bond length alternation around the middle carbon atom, indicating that compound 2 lost its aromaticity (photo source: J am Chem SOC.) Figure 2 shows the UV / Vis / NIR absorption spectra of 2, 2-O and 2-aucl in Ch 2Cl2 Compared with porphyrin and 10 azacrown ether, the lowest energy absorption band of 2 has a red shift, and this absorption band has a red shift compared with the core modified porphyrin (701nm) The results show that the electron properties of porphyrins are greatly affected by the modification of the meso position, and the electronic properties of Ni (II) - 10-phosphine heterocarbrole can be controlled by the modification of phosphorus atom (photo source: J am Chem SOC.) then, the electrochemical properties of 2, 2-O and 2-aucl were studied by cyclic voltammetry (Table 1) Compared with compound 2, the oxidation and reduction potentials of 2-O and 2-aucl were increased, which indicated that the oxidation and coordination with gold changed their electronic properties Then, using DFT, the molecular structure of the compound was calculated at B3LYP / 6-31G (d) + SDD level In LUMO of 2-O, π * orbital extends to phosphorus atom and adjacent carbon atom (Figure 3) The results show that there is an interaction between the σ * orbitals of C-P and o-P bonds and the π * orbitals of large rings, which significantly reduces the LUMO energy level of 2-o (photo source: J am Chem SOC.) finally, the author analyzed the ring current effect in 2, 2-O and 2-aucl by gimic method (Figure 4) In accordance with 1H NMR analysis results, there is obvious diamagnetic current around 2 (Figure 4a) At the same time, the results show that 2-O has weak anti aromaticity (Figure 4b), and 2-aucl has weak aromaticity (Figure 4C) (photo source: J am Chem SOC.) Summary: Ni (II) - 10-phosphine was synthesized by palladium catalyzed nucleophilic substitution of bis (α, α '- dibromodipyrrolidone) Ni (II) complex with phosphine anion In this study, phosphorus was introduced into the porphyrin π system, which effectively changed the electronic properties of porphyrin π, but not the molecular size Because of its strong coordination ability, 2-P can be applied to the construction of transition metal catalysts and supramolecular metal complexes based on porphyrins, which greatly expands the application of porphyrins.