Synthesis, Reactivity and Aromatic Characteristics of Porphyrinoids Derived from -Alkylcarbaporphyrin-2-Carbaldehydes: Isolation of Nickel(II) and Palladium(II) Complexes, Weakly Diatropic 21-Oxycarbaporphyrins and Strongly Aromatic Trioxycarbaporphyrins.

Acid catalyzed condensation of -alkyltripyrranes with trialdehydes derived from 1,3-cyclopentadiene or methyl-1,3-cyclopentadiene, followed by oxidation with aqueous ferric chloride solutions, gave 23-alkyl-21-carbaporphyrin-2-carbaldehydes in 22-27% yield together with weakly aromatic oxycarbaporphyrins. The carbaporphyrins reacted with palladium(II) acetate or nickel(II) acetate to give organometallic complexes but in both cases alkyl group migration took place to generate 21-alkyl derivatives. Although this type of reactivity had been observed previously for palladium complexes, this is the first time the phenomenon has been seen in nickel(II) carbaporphyrins.

Synthesis, Protonation and Aromatic Characteristics of a Series of 1,10-Phenanthroline-Fused Porphyrinoids.

A series of porphyrin analogues with fused 1,10-phenanthroline units were synthesized. The proton NMR spectra for phenanthroline-fused heteroporphyrins showed significantly upfield shifted -proton resonances compared to related porphyrinoid systems and the peaks corresponding to alkyl substituents directly attached to these macrocycles were also observed further upfield. These results indicate that the presence of the phenanthroline unit leads to reduced diatropicity, but the internal NH resonance was also further upfield, a result that is inconsistent with this interpretation.

Assessment of Conjugation Pathways in -Methylporphyrins that Are Fused to Acenaphthylene, Phenanthrene, or Pyrene: Evidence for the Presence of Alternative Aromatic Circuits.

Acenaphtho-, phenanthro-, and pyrenopyrrole esters, readily available from Barton-Zard reactions of ethyl isocyanoacetate with nitroarenes, were reacted with methyl iodide and KOH in DMSO to give -methylpyrroles and subsequent cleavage of the ester moieties was accomplished with KOH in ethylene glycol at 200 °C. Condensation with two equiv of an acetoxymethylpyrrole in refluxing acetic acid-2-propanol afforded a series of annulated tripyrranes. Cleavage of the terminal -butyl ester groups with trifluoroacetic acid, followed by condensation with a diformylpyrrole and oxidation with FeCl, gave -methyl acenaphtho-, phenanthro-, and pyrenoporphyrins.

Serendipitous Discovery of Conjugated Dipyrromethene-Linked Nitronaphthoporphyrins.

Acid-catalyzed condensation of a nitronaphthalene-fused dipyrrylmethane with dipyrrylmethane dialdehydes afforded unique dipyrromethene-naphthoporphyrin conjugates together with expected nitronaphthoporphyrins. The unusual conjugated system retained aromatic porphyrin-type characteristics but afforded highly modified UV-vis spectra with multiple absorptions throughout the visible region.

Synthesis, Spectroscopic Properties, and Metalation of 3-Alkoxybenziporphyrins.

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics.

Linear Extension of Carbaporphyrin Chromophores: Synthesis, Protonation, and Metalation of Anthro[2,3-]carbaporphyrins: Evidence for 30π-Electron Aromatic Circuits in a Palladium(II) Complex.

Acid-catalyzed condensation of a naphtho[2,3-]indane dialdehyde with a tripyrrane, followed by an oxidation step, afforded an anthro[2,3-]-21-carbaporphyrin. The presence of a fused anthracene unit induced minor bathochromic shifts and did not significantly affect the aromatic characteristics of the carbaporphyrin core. Protonation led to the formation of a monocation with similar diatropic properties, but the dication generated in the presence of a large excess of trifluoroacetic acid had a weakened Soret band absorption and a broad absorption at 754 nm.

Aromatic Character and Relative Stability of Pyrazoloporphyrin Tautomers and Related Protonated Species: Insights into How Pyrazole Changes the Properties of Carbaporphyrinoid Systems.

Pyrazoloporphyrins (PzPs), which are porphyrin analogues incorporating a pyrazole subunit, are examples of carbaporphyrin-type structures with a carbon atom within the macrocyclic cavity. DFT calculations were used to assess a series of 17 PzP tautomers, nine monoprotonated species and four related diprotonated PzP dications. The geometries of the structures were optimized using M06-2X/6-311++G(d,p), and the relative stabilities computed with the cc-PVTZ functional.

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems.

The unique environment within the core of carbaporphyrinoid systems provides a platform to explore unusual organometallic chemistry. The ability of these structures to form stable organometallic derivatives was first demonstrated for N-confused porphyrins but many other carbaporphyrin-type systems were subsequently shown to exhibit similar or complementary properties. Metalation commonly occurs with catalytically active transition metal cations and the resulting derivatives exhibit widely different physical, chemical and spectroscopic properties and range from strongly aromatic to nonaromatic and antiaromatic species.

Synthesis of Chrysoporphyrins and a Related Benzopyrene-Fused System.

Reaction of 6-nitrochrysene with ethyl isocyanoacetate in the presence of a non-nucleophilic base gave a -annulated pyrrole ethyl ester that was used to prepare chrysene-fused tripyrranes and a chrysopyrrole dialdehyde. Chrysene-fused tripyrranes were reacted with a pyrrole dialdehyde, but poor yields of chrysoporphyrins were obtained. However, condensation of the chrysopyrrole dialdehyde with a series of tripyrranes afforded excellent yields of chrysoporphyrins and an acenaphtho-chrysoporphyrin.

Oxyquinoliziniporphyrins: Introduction of a Heterocyclic Dimension to Carbaporphyrinoid Systems.

Oxyquinoliziniporphyrins, novel carbaporphyrinoids that incorporate quinolizone units, were synthesized. These structures exhibit moderate diamagnetic ring currents that are greatly enhanced upon protonation. Addition of trifluoroacetic acid initially gave a monocation, but this was readily converted into a dicationic species.

Synthesis of a Series of Tropone-Fused Porphyrinoids.

A series of tropone-fused porphyrinoids with unique spectroscopic features has been prepared. A dimethyl tropone-fused pyrrole was reacted with lead tetraacetate to give a bis(acetoxymethyl) derivative that condensed with an α-unsubstituted pyrrole -butyl ester to form a tripyrrane intermediate. Cleavage of the -butyl ester protective groups, followed by condensation with a series of aromatic dialdehydes and oxidation with DDQ, afforded the tropone-fused porphyrinoid systems.

Telluracarbaporphyrins and a Related Palladium(II) Complex: Evidence for Hypervalent Interactions.

The reaction of a carbatripyrrin with a tellurophene dicarbinol in the presence of BF·EtO, followed by oxidation with DDQ, afforded the first example of a telluracarbaporphyrin. Although this system exhibits strongly aromatic characteristics, it is prone to air oxidation, giving rise to a hydroxy derivative that was characterized by X-ray crystallography. The initial telluracarbaporphyrin reacted with palladium(II) acetate to give a stable organometallic complex, and X-ray crystallography showed that the palladium cation was coordinated to all four atoms in the CNTeN core.

Synthesis and Characterization of -Methylporphyrins, Heteroporphyrins, Carbaporphyrins, and Related Systems.

MacDonald-type "3 + 1" condensations of an -methyltripyrrane with a series of dialdehydes afforded a matched set of -methylporphyrins, -methylheteroporphyrins, -methyloxybenziporphyrin, -methyloxypyriporphyrin, -methyltropiporphyrin, and a -methylcarbaporphyrin aldehyde. -Unsubstituted heteroporphyrins have been little explored previously, and this strategy was also used to prepare -unsubstituted 21-oxa-, 21-thia-, and 21-selenaporphyrins. In every case, the -methylporphyrinoids exhibited weaker, bathochromically shifted UV-Vis absorptions compared to their core unsubstituted congeners.

Synthesis of 2-bromo- and 2-phenyl-neo-confused porphyrins.

Neo-confused porphyrins (neo-CPs), porphyrin isomers with a 1,3-connected pyrrolic subunit, are aromatic structures with a CNNN coordination core. Previously, examples of neo-CPs with fused benzo units or electron-withdrawing ester substituents have been described. In this paper, two new examples of neo-CPs are reported that lack a fused aromatic unit or an ester moiety, but instead have a bromo or phenyl substituent on the neo-confused ring.

Synthesis of Azulitriphyrins(1.2.1) and Related Benzocarbatriphyrins.

Bis(pyrrolylmethyl)azulene dialdehydes underwent intramolecular McMurry coupling, and following oxidation with DDQ and addition of trifluoroacetic acid, gave aromatic azulitriphyrin cations. The proton NMR spectra for these contracted carbaporphyrinoids showed the internal CH upfield at ca. 2 ppm, while the bridging methine units appeared downfield between 8 and 10 ppm, demonstrating that the macrocycles possess significant 14π electron diamagnetic ring currents.

Azulichlorins and Benzocarbachlorins Derived Therefrom.

Acid-catalyzed condensation of azulidipyrrane aldehydes with a dihydrodipyrrin carbaldehyde afforded the first examples of azulichlorins. These macrocyclic products were isolated in a monoprotonated form, and the free bases proved to be somewhat unstable. The monocations were strongly diatropic, and proton NMR spectroscopy showed the internal C-H at ca.

-Dicarbaporphyrinoid Systems: Synthesis, Spectroscopic Characterization, and Reactivity of 23-Carbabenziporphyrins.

A new family of -dicarbaporphyrinoids has been prepared using the "2 + 2" MacDonald methodology. Dibutylboron triflate catalyzed condensation of 3-iodo-4-methoxybenzaldehyde with an indene enamine afforded an iodofulvene aldehyde, and a related dimethoxyfulvene was similarly prepared in two steps from 2,4-dimethoxybenzaldehyde. Following protection as the corresponding dimethyl acetals, the iodofulvenes were metalated with BuMgLi at -100 °C and reacted with dimethylformamide to give the required fulvene dialdehyde intermediates.

Rhodium Complexes of Carbaporphyrins, Carbachlorins, adj-Dicarbaporphyrins, and an adj-Dicarbachlorin.

The macrocyclic cavities in carbaporphyrins are well suited for the formation of metalated derivatives. A carbaporphyrin diester and a naphthocarbaporphyrin reacted with [Rh(CO)Cl] to give good-to-excellent yields of rhodium(I) complexes, and these were fully characterized by X-ray crystallography. Both rhodium(I) derivatives were converted into rhodium(III) complexes in refluxing pyridine, albeit in moderate yields.

Tropylium and Porphyrinoid Character in Carbaporphyrinoid Systems. Relative Stability and Aromatic Characteristics of Azuliporphyrin and Tropiporphyrin Tautomers, Protonated Species, and Related Structures.

DFT studies have been carried out on 46 azuliporphyrin (AzP) and tropiporphyrin (TrP) tautomers, cations, and dications. The structures were minimized using DFT-B3LYP/6-311++G(d,p), and the relative stabilities of the tautomers for each series were computed with M06-2X and B3LYP-D3 functionals. Nucleus independent chemical shifts, both NICS(0) and NICS(1) , were calculated for both the center of the macrocycles and the individual pyrrolic and carbocyclic subunits.

Synthesis of Expanded Porphyrinoids with Azulene and Indene Subunits and an opp-Dioxadicarbaporphyrin from Fulvene Carbinols and a Dioxacarbatripyrrin.

In an attempt to prepare quatyrin derivatives, which are hydrocarbon analogues of the porphyrins, azulene-appended fulvene carbinols were self-condensed in the presence of BF·EtO. Although these investigations failed to give structures related to quatyrin, expanded porphyrin analogues were obtained instead. In dichloromethane, the major macrocyclic product consisted of three fulvene units, but when chloroform was used as the reaction solvent, a tetrafulvene macrocycle was isolated.

Naphtho[2,3- b]carbaporphyrins.

Acid-catalyzed condensation of a benzo[ f]indane dialdehyde with a tripyrrane, followed by an oxidation step, afforded the first example of a naphtho[2,3- b]-21-carbaporphyrin. This π-extended porphyrinoid system is strongly aromatic and gave a porphyrin-like UV-vis spectrum with a Soret band at 432 nm. Protonation with TFA gave a monocation, but under highly acidic conditions a C-protonated dication was generated.

Alphabet soup within a porphyrinoid cavity: synthesis of heterocarbaporphyrins with CNNO, CNOO, CNSO and CNSeO Cores from an oxacarbatripyrrin.

The first examples of porphyrin analogues with four different core atoms have been synthesized from an oxacarbatripyrrin intermediate. Acid-catalyzed condensation of the tripyrrin analogue with pyrrole or furan dialdehydes gave 22-oxa- and 22,23-dioxacarbaporphyrins, while reactions with furan, thiophene or selenophene dicarbinols afforded diphenyl dioxa-, oxathia- and oxaselenacarbaporphyrins.

Metalation and Selective Oxidation of Diphenyl-23-oxa-, -thia-, and -selena-21-carbaporphyrins.

The availability of diphenyl-23-oxa-, -thia-, and -selena-21-carbaporphyrins has enabled the reactivity of these systems to be investigated and contrasted. All three heterocarbaporphyrins reacted with palladium(II) acetate in refluxing chloroform-acetonitrile to give organometallic palladium(II) derivatives in good yields. These structures are stable and give UV-vis spectra that show increasing broadening and bathochromic shifts as the size of the heteroatom increases.

Synthesis and Properties of Carbaporphyrin and Carbachlorin Dimethyl Esters Derived from Cyclopentanedialdehydes.

Norbornenes with two ester substituents were prepared by Diels-Alder cycloadditions of cyclopentadiene with dimethyl fumarate and dimethyl 1,1-ethylenedicarboxylate. Oxidation with potassium permanganate gave good yields of related diols that were oxidatively ring-opened to afford cyclopentane dialdehydes. MacDonald-type "3 + 1" condensations with a tripyrrane, followed by oxidation with DDQ in refluxing toluene, gave carbaporphyrin or carbachlorin products in good yields.