All-aza
smaragdyrin, a historic but elusive pentapyrrolic macrocycle,
was successfully synthesized and characterized for the first time.
[22]Smaragdyrin BF2-complex 3 was smoothly
synthesized by 2-fold SNAr reaction of 1,9-dibromo-5-mesityldipyrrin
with 5,10-dimesityltripyrrane. Treatment of 3 with methanesulfonic
acid gave [20]smaragdyrin 5 as a stable antiaromatic
compound. Reduction of 5 with NaBH4 under
inert conditions gave [22]smaragdyrin 6 as an aromatic
congener, which was easily oxidized back to 5 in the
air. Complex 3 was interconvertible with its 20π-congener 4 via oxidation with MnO2 and reduction with NaBH4. Treatment of 3 or 4 with CuCl2 in the presence of NaOAc gave hetero bimetal complex 8.
β,β-tripyrrin-bridged earring porphyrins were synthesized through Suzuki-Miyaura cross coupling reactions. These porphyrinoids have multiple cavities and can accommodate two or three metal ions per molecule. The structures of the porphyrins have been elucidated by x-ray diffraction analysis, and feature curved π planes. The electronic spectra of the porphyrins exhibit near-infrared (NIR) absorptions and metal insertion leads to red-shifted and intensified absorption features. Electrochemical analysis and transient absorption measurements indicated that the porphyrins exhibit effective electronic communication between their central and peripheral moieties.
Ar eaction sequence of regioselective peripheral bromination, Suzuki-Miyaura coupling with 2-borylated thiophene or pyrrole,and oxidative ring-closure with FeCl 3 allowed the synthesis of heterole-fused earring porphyrins 4Pd and 9Pd from the parent earring porphyrin 1.Differently pyrrole-fused porphyrins 5H and 6H and their Pd II complexes 5Pd and 6Pd were also synthesized.T he structures of 4Pd, 5H, 6Pd,a nd 8Pd have been revealed by X-rayanalysis to be slightly twisted owingtoconstraints imposed by heterole-fused structures. 5Pd exhibits an intensified band at 1505 nm, while 4Pd and 9Pd displays mall but remarkably red-shifted absorption bands reaching around 2200 nm.
Smaragdyrin had been an important but elusive expanded
porphyrin
until our recent first synthesis (Xie et al., J. Am. Chem.
Soc. 2018, 140, 16553). In this paper, we report
the synthesis of singly and doubly neo-confused [22]smaragdyrin BF2-complexes 13 and 15 both as stable
smaragdyrin mutants by nucleophilic substitution reactions of 1,9-dibromo-5-mesityldipyrrin 1 with singly and doubly N-confused tripyrranes, 10 and 11, respectively. Demetalation of 13 and 15 with methanesulfonic acid furnished singly and
doubly neo-confused [22]smaragdyrin free bases 16 and 18, respectively, both as air-sensitive porphyrinoids. These
neo-confused [22]smaragdyrin free bases display characteristic properties
such as decreased diatropic ring current, regioselective diprotonation
at the inner α-carbon of the neo-confused pyrrole to give 16H
2
2+
and 18H
2
2+
, and
smooth oxygenation at the inner α-position of the neo-confused
pyrroles, giving neo-confused [22]oxosmaragdyrin 17 and
doubly neo-confused [24]dioxosmaragdyrin Cu(II) complex 19Cu via metalation of 18 with CuCl2 in the presence
of NaOAc. Finally, demetalation of 19Cu with methanesulfonic
acid gave the corresponding doubly neo-confused [24]dioxosmaragdyrin 19.
Direct β-to-β linked branched and cyclic porphyrin trimers and pentamers have been synthesized by the Suzuki-Miyaura coupling of β-borylporphyrins and β-bromoporphyrins. The cyclic porphyrin trimer, the smallest directly linked cyclic porphyrin wheel to date, and its twined pentamer, exhibit small electrochemical HOMO-LUMO gaps, broad nonsplit Soret bands, and red-shifted Q-bands, thus indicating large electronic interactions between the constituent porphyrin units.
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