Synthesis of Three Asymmetric N-Confused Tetraarylporphyrins

Abstract

Two monosubstituted and one tetrasubstituted N-confused porphyrins (1-3) were prepared in ca. 3-5% yields using a [2 + 2] synthesis. The monosubstituted porphyrins have carbomethoxy (1) or nitro (2) substituents on one of the meso-phenyl groups, while the meso-phenyl groups of the third NCP (3) are substituted with nitro, bromo, and methyl groups in an AB(2)C pattern. The specific regiochemistry of the aryl rings around the macrocycle in each porphyrin was definitively determined using a combination of 1D ((1)H and (13)C) and 2D (gHMBC, gHSQC and ROESY) NMR spectroscopy. The absorption spectra of 1-3 in CH(2)Cl(2) are similar to those of N-confused tetraphenylporphyrin (NCTPP) but have Soret and Q bands that are shifted to lower energies with smaller extinction coefficients in comparison to those for NCTPP.

Effect of Solvent and Protonation/Deprotonation on Electrochemistry, Spectroelectrochemistry and Electron‐Transfer Mechanisms of N‐Confused Tetraarylporphyrins in Nonaqueous Media

“…[12][13][14][15][16][17][18] The inner-2H form of the porphyrin is mainly observed in strongly proton-accepting nonaqueous solvents, such as N,N'-dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl-sulfoxide (DMSO), while the inner-3H form is exclusively observed in aprotic solvents such as dichloromethane (CH 2 Cl 2 ), chloroform (CHCl 3 ), and toluene. [1] N-Confused porphyrins have unique spectral and coordination properties as compared to porphyrins [1][2][3][4][5][6][7][8][9][19][20][21][22] and have possible applications in the fields of catalysts, functional materials, molecular switches, and ion transducers as well as in the areas of coordination and supramolecular chemistry. [23][24][25][26][27][28][29][30][31][32] The electrochemistry of "normal" free-base porphyrins has been well documented in the literature, [33] but this is not the case for N-confused porphyrins for which the solution electrochemistry is characterized by multiple irreversible processes and only a few free-base derivatives have been electrochemically examined in DMF or CH 2 Cl 2 .…”

Electrochemistry of Methylated N‐Confused Free‐Base Tetraarylporphyrins in Nonaqueous Media

“…N‐confused porphyrins are structurally similar to “normal” porphyrins, but have an inverted pyrrole with a carbon inside the cavity and a nitrogen on the periphery of the π‐system (see structures in Figure ). These compounds have attracted much attention because of their unique spectral and electrochemical properties as compared to “normal” porphyrins …”

Electrochemistry of Nitrated N‐Confused Free‐Base Tetraaryl‐Porphyrins in Nonaqueous Media

“…Twot automeric forms of N-confused free-base porphyrins have been characterized under different solution conditions. [1][2][3][4][5][6][7] One form possesses as ingle protonatedn itrogen in the core of the macrocycle anda nother protono nt he inverted nitrogen while the second form was characterizeda sh aving an unprotonated inverted nitrogen andt wo protonated core nitrogen atoms. The first tautomer is observedi nD MF and labeled as the inner-2H form,w hile the second is observed in CH 2 Cl 2 and labeled as being in an inner-3H form.…”

“…[1] N-Confused porphyrins are structurally similar to "regular" tetrapyrrolic porphyrins but they exhibit unique spectral, electrochemical and coordinationp roperties which result from the N-confused arrangement of one pyrrole group. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] One such difference in redox propertiest he rapid loss of ap roton and formation of am onoanionicm onodeprotonated N-confused porphyrin after the addition of one electron as shown by the mechanism in Scheme1.A nother difference is the existence of ar apid chemical reaction which follows the one-electrono xidationof the neutralc ompound to give ap rotonatedp orphyrin as also illustrated in Scheme1.…”