meso‐Functionalization of Boron(III) Subporphyrin with Boron(III) meso‐Lithiosubporphyrin

Abstract

Boron(III) meso-lithiosubporphyrin was prepared by bromine-lithium exchange of B-tolyl B meso-bromosubporphyrin with n-butyllithium at -98 °C. The resulting subporphyrinyllithium was treated with various electrophiles such as benzophenone, N,N-dimethylformamide, CO , chlorotrimethylsilane, N-fluorobenzenesulfonimide, and dimesitylboryl fluoride to give the corresponding meso-functionalized B subporphyrins. The nucleophile was also used to construct B subporphyrin dimers such as bis(B subporphyrinyl)ketone, bis(B subporphyrinyl)carbinol, and disilane-bridged B subporphyrin dimer. The structural, optical, and electrochemical properties of these meso-functionalized B subporphyrins were examined by UV/Vis absorption and fluorescence spectroscopy, electrochemical studies, and DFT calculations.

Nucleophilic Aromatic Substitution (SNAr) and Related Reactions of Porphyrinoids: Mechanistic and Regiochemical Aspects

“…meso‐Diarylsubporphyrins were treated with n BuLi at –98 °C and quenched with a variety of electrophiles (Scheme 27). [ 199 ] Through this method, a variety of useful functional groups were successfully introduced, e.g., formyl, carboxylic acid, TMS, and fluoro ( 137a – f) . Other electrophiles also yielded interesting results; treatment of lithio‐subporphyrin with 1,2‐dichlorotetramethyldisilane yielded a disilyl‐bridged subporphyrin dimer 138 in 18 % and treatment with dimethyl carbonate gave the carbonyl dimer 139 in 59 %.…”

Acetylene and trans‐Ethylene Bridged BIII‐Subporphyrin Dimers

“…Since the first report in 2006, B III subporphyrins have emerged as a promising class of ring‐contracted porphyrinoids with attractive attributes such as 14π‐electronic aromatic characters, bowl‐shaped structures, and variable electronic properties depending on meso ‐substituents . While the chemistry of B III subporphyrins still remains at the infant stage as compared with that of porphyrins, several B III subporphyrin dimers showing notable electronic interactions have been explored in the last decade, which include meso ‐ meso“ linked dimer 1 , meso ‐ meso′ , β ‐ β′ doubly linked dimer 2 , meso ‐ meso′ , β ‐ β′ , β ‐ β′ triply linked dimer 3 , 1,3‐butadiyne bridged dimer 4 , and ketone bridged dimer 5 . These dimers exhibit characteristic optical and electrical properties arising from the porphyrin‐porphyrin electronic interaction.…”

“…The electrochemical properties of 6 and 7 were examined by cyclic voltammetry and differential pulse voltammetry in CH 2 Cl 2 , and are summarized in Table . The reference molecule 8 showed the first oxidation and reduction waves at +0.52 and −2.12 V [vs. ferrocene/ferrocenium ion (Fc/Fc + )] . The electrochemical HOMO–LUMO gap is 2.64 eV.…”

“…[2,3] While the chemistry of B III subporphyrins still remains at the infant stage as compared with that of porphyrins, several B III subporphyrin dimers [4] showingn otable electronic interactions have been explored in the last decade, which include meso-meso" linked dimer 1, [5] meso-meso', b-b' doubly linked dimer 2, [6] mesomeso', b-b', b-b' triply linked dimer 3, [7] 1,3-butadiyne bridged dimer 4, [8] and ketone bridged dimer 5. [9] These dimers exhibit characteristic opticala nd electrical properties arising from the porphyrin-porphyrin electronic interaction. In particular,1 ,3-butadiyne bridged dimer 4 shows multiply split Soret-like bands as well as quite red-shifted and intensified Q-like bands up to 600 nm and ar ed-shifted fluorescences pectrum with ah igh quantum yield (F F = 0.42), indicating the effective electronic interaction betweent he two subporphyrin units through the 1,3-butadiyne bridge.…”

“…The reference molecule 8 showed the first oxidation and reduction wavesa t+ 0.52 and À2.12 V[ vs. ferrocene/ferrocenium ion (Fc/Fc + )]. [9] The electrochemical HOMO-LUMO gap is 2.64 eV.D imer 6 displayed the oxidationp otentials at + 0.19 and + 0.44 Vand the reduction potentiala tÀ1.58 V, indicating its HOMO-LUMO gap to be 1.77 eV,a nd dimer 7 displayed the oxidation potentials at + 0.34 and + 0.67 Va nd the reduction potential at À1.67 V, indicating its HOMO-LUMO gap to be 2.01 eV.T herefore, the HOMO-LUMO gaps of 6 and 7 are considerably smaller as compared with that of 8.T he observed large separations between the first and second oxidationp otentials for both 6 and 7 indicatet he effective conjugation between the two subporphyrin units through trans-ethyleneo ra cetylene group.…”