Synthesis and Self-Assembly of ß-Octa[(4-Diethoxyphosphoryl)phenyl]porphyrins.

The ß-substituted porphyrinoids commonly used to form functional assembled systems in nature yet are still scarcely used in material chemistry probably due to the laborious synthesis of these compounds. In this work, ß-octa[(4-diethoxyphosphoryl)phenyl]porphyrin (2HOPPP) and its metal (Zn(II), Cd(II), Cu(II), and Ni(II)) complexes were prepared in good yields. These highly soluble chromophores were characterized in solution using spectroscopic (NMR, UV-vis, fluorescence), electrochemical, and spectroelectrochemical methods. Attachment of the electron-deficient residue (ArP(O)(OEt)2) to the porphyrin macrocycle leads to easier reductions and harder oxidations of the macrocycle for all complexes studied as compared to corresponding meso-tetra[4-(diethoxyphosphoryl)phenyl]porphyrin derivatives reported previously. We demonstrated that the strong electron-deficient character of the MOPPP porphyrins results principally from the increase in the number of electron-withdrawing groups at the periphery of the tetrapyrrolic macrocycle. Electron-deficient porphyrins are highly required in supramolecular and material chemistry in part due to their ability to form supramolecular assemblies via the coordination of axial ligands to the central metal atom. According to single-crystal X-ray data, ZnOPPP forms in the crystalline phase dimers in which each of the two tetrapyrrolic macrocycles is connected through an unusual combination of hydrogen bonding of two phosphoryl groups and the water molecules axially coordinated to the zinc atom of the partner molecule. The involvement of water molecules in porphyrin binding allows for an increase of distance between two porphyrin mean N4 planes, up to 4.478 Å. The offset of phosphoryl groups attached to the macrocycle through a 1,4-phenylene spacer withdraws the whole porphyrin macrocycle of one molecule from spatial overlap with the macrocycle of a partner molecule and increases the Zn-Zn distance up to 10.372 Å. This still unknown type of porphyrin dimers allows one to get deeper insights into the organization of naturally occurring tetrapyrrolic macrocycles. ZnOPPP also forms a labile dimeric complex in 5.3 × 10-7-5.8 × 10-5 M chloroform solutions. In contrast, other complexes prepared in this work exist as monomeric species under these experimental conditions. The self-association constant of ZnOPPP has been determined by electronic absorption spectroscopy.

Electronic and steric effects controlling monomer-dimer self-assembly in 6H-1,4-diazepinoporphyrazines: an experimental and theoretical study.

A series of 5,7-disubstituted 1,4-diazepinoporphyrazinato magnesium(II) and nickel(II) complexes, including two novel compounds, were obtained by metal-templated macrocyclization. A combination of X-ray diffraction, 1H NMR, UV-vis, and electrochemical analyses allowed us to study their tendency towards H-type dimerization and trace the influence of structural and solvation factors on dimer stability. Based on the physicochemical and theoretical DFT calculation data, it was found that the main binding forces between 6H-1,4-diazepinoporphyrazine decks in the dimers were efficient π-π donor-acceptor interactions induced by the interdeck C-H⋯N hydrogen bonds. Furthermore, the metal-ligand (Pz2- â†’ M2+) electronic interactions have a key influence on the π-π stacking of the porphyrazine cores. It was shown that the displacement of the metal ion out of the macrocycle plane induced by coordinating agents can trigger the dissociation of the dimer, since the resulting enhancement of the donor-acceptor electronic interaction between the metal ion and the π-system of the ligand leads to a subsequent weakening of the π-π stacking of the porphyrazine cores. The TD-DFT calculations predicted the non-degeneracy of the HOMO-1 → LUMO and HOMO → LUMO+1 transitions in the 6H-1,4-diazepinoporphyrazine H-dimers, which explains the Q-band splitting in their UV-vis spectra.

Lossen rearrangement by Rh(III)-catalyzed C-H activation/annulation of aryl hydroxamates with alkynes: access to quinolone-containing amino acid derivatives.

A convenient and robust method for the preparation of new CF3-containing 2-quinolones has been developed via a Rh(III)-catalyzed C-H activation/Lossen rearrangement/annulation cascade of N-pivaloyloxy-arylamides with internal alkynes bearing an α-CF3-α-amino acid moiety on the triple bond. This work expands the scope of valuable products that are available through C-H activation/annulation reactions of arylamides in organic synthesis.

Selective Metal-Controlled Synthesis of Trifluoromethylated (Indolin-2-ylidene)methyl- and Quinolin-3-ylphosphonates.

Metal-catalyzed (Cu, Ag, Au) reactions of alkynylphosphonates with 1-(2-aminophenyl)-2,2,2-trifluoroethan-1-ones were developed. Terminal alkyne diethyl ethynylphosphonate reacted with ketones to give different products depending on the catalyst used. With a CuI/PPh3 catalytic system, the formation of CF3-containing indoline derivatives was observed with good yields. The use of AgSbF6 as a catalyst led to quinoline derivatives in high yields. The less reactive 2-substituted ethynylphosphonates required gold complexes as catalysts to provide the corresponding 2-aryl(alkyl) substituted 4-(trifluoromethyl)quinolin-3-ylphosphonates with good yields.

Chameleonic Behavior of the α-Methylcyclopropyl Group and Its Through-Space Interactions: A Route to Stabilized Three Redox States in Diarylnitroxides.

The α-methylcyclopropyl (MCP) group with conformationally dependent electronic properties is suggested as an additional structural "instrument" for stabilization of both open-shell and ionic states of diarylnitroxides, to be used as "ambipolar" redox active materials. New MCP-substituted diphenylnitroxides (fully characterized by electrochemical, spectral, and X-ray data) are the most stable nitroxides of the diaryl type known to date [τ1/2 in benzene exceeds three months (2310 h)]. The radicals are capable to reversible oxidation and reduction, yielding stable oxoammonium cations and aminoxyl anions. DFT investigation of the electronic structure and geometry of the compounds confirmed the conformational switching of the cyclopropyl orientation relative to the adjacent aromatic π system is dependent on the nitroxide's redox state. Additional through-space stabilizing interaction between the π-acceptor orbital of the NO+ moiety and the cyclopropyl "banana" bond orbital was also detected, highlighting its good hyperconjugative ability. The estimated σ(para)MCP value (-0.32) confirms its strong electron-donating properties.

Coordination self-assembly through weak interactions in meso-dialkoxyphosphoryl-substituted zinc porphyrinates.

The self-assembly of seven zinc 10-(dialkoxyphosphoryl)-5,15-diarylporphyrinates Zn5-Zn11 containing different substituents at the phosphonate and aryl groups was investigated. Single crystals of Zn5-Zn9 complexes were grown under the same conditions and analyzed by X-ray structural analysis. A supramolecular self-assembly is observed in all crystals through weak coordinative bonding of the phosphoryl group of one porphyrin molecule to the zinc(ii) ion of a second molecule. The geometry of the porphyrin macrocycle is similar in all of the studied crystals and the central zinc atom in each case adopts a distorted tetragonal pyramidal environment. However, the Zn5-Zn7 porphyrins display a 1D polymeric structure while the Zn8 and Zn9 complexes exist as discrete cyclotetramers in the crystals. This data demonstrates that the non-coordinating meso-aryl substituents of meso-(dialkoxyphosphoryl)porphyrins influence their crystalline organization. A self-assembly of the Zn5-Zn11 complexes is also observed in toluene and chloroform solutions over a large temperature range (223-323 K). According to NMR studies, the associates exhibit dynamic behavior. A well-defined supramolecular aggregate of complex Zn10 at 10-3 M in toluene and chloroform solutions was unambiguously characterized as a cyclotetramer [Zn10]4 by 1H NMR spectroscopy at 223 K. The structure of the Zn10 association in toluene and chloroform shows a concentration dependence. When a solution of Zn10 in toluene was diluted from 10-3 M to 10-5 M, the average number of molecules in the associated unit decreased to about two.

Electrochemical, Spectroelectrochemical, and Structural Studies of Mono- and Diphosphorylated Zinc Porphyrins and Their Self-Assemblies.

Three series of porphyrins containing a Zn(II) central metal ion and zero, one, or two phosphoryl groups at the meso-positions of the macrocycle were characterized as to their electrochemical, spectroscopic, and structural properties in nonaqueous media. The investigated compounds are represented as 5,15-bis(4'-R-phenyl)porphyrinatozinc, 10-(diethoxyphosphoryl)-5,15-bis(4'-R-phenyl)porphyrinatozinc, and 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-R-phenyl)porphyrinatozinc, where R = OMe, Me, H, or CN. Linear-free energy relationships are observed between the measured redox potentials at room temperature and the electronic nature of the substituents at the 5 and 15 meso-phenyl groups of the macrocycle. The mono- and bis-phosphoryl derivatives with two p-cyanophenyl substituents provide electrochemical evidence for aggregation at low temperature, a greater degree of aggregation being observed in the case of 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-cyanophenyl)porphyrinatozinc(II). This compound was characterized in further detail by variable-temperature 1H and 31P{1H} NMR spectroscopy in solution combined with single crystal X-ray analysis in the solid state. The data obtained from these measurements indicate that this porphyrin has a dimeric structure in CDCl3 at 223-323 K but forms a 2D polymeric network when it is crystallized from a CHCl3/MeOH mixture.

Fluorinated Unsymmetrical N,N'-Diaryl Imidazolium Salts-New Functionalized NHC-Ligand Precursors.

An efficient and scaled-up synthesis of the imidazol-2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF3 )2 (OR)C-] at the ortho position of the N-aryl substituent was developed. The key step of the method involved the transformation of a Mes-substituted oxazolinium tetrafluoroborate salt through the reaction with the corresponding binucleophilic fluoroalkyl-substituted aniline. The subsequent post-modification of the resulting hydroxyl-containing salt through a simple one-step O-alkylation protocol provided access to a new family of unsymmetrical fluorinated NHC precursors. These compounds were successfully utilized for the preparation of several novel metal complexes. The molecular structures of some NHC precursors and their metal complexes have been unambiguously characterized by single-crystal X-ray diffraction analysis. A preliminary evaluation of the catalytic activity of the palladium complexes was performed on a Buchwald-Hartwig amination reaction. As a result, two PEPPSI-type (PEPPSI=pyridine-enhanced pre-catalyst preparation stabilization and initiation) Pd complexes have demonstrated promising activity in alkane solvents.

Gallium(III) and Indium(III) Complexes with meso-Monophosphorylated Porphyrins: Synthesis and Structure. A First Example of Dimers Formed by the Self-Assembly of meso-Porphyrinylphosphonic Acid Monoester.

The synthesis and structural characterization, both in solution by means of 1H and 31P NMR and UV-vis spectroscopies and in the solid state by X-ray diffraction on single crystal, of a series of gallium(III) and indium(III) meso-mono(diethoxyphosphoryl)porphyrins bearing different peripheral substituents as well as the corresponding monoesters and phosphonic acids are reported. This work describes the first example of the X-ray structure of a self-assembled dimer formed via strong binding between the oxygen atom of the phosphonate substituent and the gallium(III) cations of adjacent porphyrin molecules [Ga-O = 1.9708(13) Å].

Determination of the Structural Parameters of Heteronuclear (Phthalocyaninato)bis(crownphthalocyaninato)lanthanide(III) Triple-Deckers in Solution by Simultaneous Analysis of NMR and Single-Crystal X-ray Data.

Application of a general and convenient approach to the synthesis of heteronuclear crown-substituted triple-decker phthalocyaninates afforded two series of complexes containing one dia- and one paramagnetic Ln(III) ion (for Y and almost the whole lanthanide family), [(15C5)4Pc]M*[(15C5)4Pc]M(Pc) (or [M*,M] for brevity sake), where (15C5) is 15-crown-5; (Pc(2-)) is phthalocyaninato dianion; and M ≠ M* = Y, Nd, Eu, Tb, Dy, Ho, Er, Tm, Yb. This approach consists of using LaPc2 as an efficient Pc(2-) source. The solid-state structures of two complexes ([Tm*,Y] and [Yb*,Y]) were studied by single-crystal X-ray diffraction analysis, providing therefore a structural model for the assignment and analysis of (1)H NMR spectra of the complexes, which is strongly affected by the presence of paramagnetic lanthanide ions. Model validation was performed on complexes containing two different paramagnetic ions-[Dy*,Gd] and [Gd*,Dy] as well as [Tb*,Tm] and [Tm*,Tb]-synthesized by the above-mentioned method.

A Molecular Chameleon: Reversible pH- and Cation-Induced Control of the Optical Properties of Phthalocyanine-Based Complexes in the Visible and Near-Infrared Spectral Ranges.

A series of novel nonperipherally substituted tetra-15-crown-5-dibutoxyoxanthrenocyanines (H2, Mg, Zn), acting as chameleons with the unique properties of switchable absorption and emission in the near-infrared (NIR) spectral range have been synthesized and characterized by X-ray diffraction. The attachment of 15-crown-5-α-dibutoxyoxanthreno moieties to phthalocyanine is responsible for the high solubility of the resulting molecules and the red shift of the Q band to the NIR region and offers a unique possibility for postsynthetic modification of the optical properties of the molecules. Both aggregation of phthalocyanine and its participation in an acid-base equilibrium strongly alter their optical properties. For example, the absorption of complexes can be reversibly tuned from 686 up to 1028 nm because of the cation-induced formation of supramolecular dimers or subsequent protonation of meso-N atoms orf macrocycle, in contrast to peripherally substituted tetra-15-crown-5-phthalocyanines without oxanthrene moieties. The reversibility of these processes can be controlled by the addition of [2.2.2]cryptand or amines. All investigated compounds exhibit fluorescence with moderate quantum yield, which can also be switched between the ON and OFF states by the action of similar agents.

Design of UV-Vis-NIR panchromatic crown-phthalocyanines with controllable aggregation.

Novel magnesium and zinc phthalocyaninates, bearing four lateral electron-rich 15-crown-5-oxanthrene fragments, were synthesized starting from benzo-15-crown-5. Being almost insoluble in common organic solvents, these complexes could be solubilised by interaction with potassium acetate due to the formation of well-defined cofacial supramolecular dimers. A characteristic feature of these dimers is the presence of additional bands in their UV-Vis spectra, which affords the expansion of light absorption region up to ∼750 nm. This new band corresponds to the charge transfer from the peripheral groups to the Pc core, as evidenced by TDDFT calculations. Potassium cations can be reversibly removed from these dimers by [2.2.2]cryptand, resulting in the formation of monodisperse nanoparticles exhibiting absorbances up to 900 nm. This approach can be further used for the fabrication of nanostructured optoelectronic materials based on the synthesized donor-acceptor panchromatic crown-phthalocyanines.

Unusual formation of a stable 2D copper porphyrin network.

Copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin was obtained and characterized by means of cyclic voltammetry, electron paramagnetic resonance, Fourier transform infrared, and UV-visible spectroscopy. Three crystalline forms were grown and studied by means of X-ray diffraction methods (single crystal and powder). The highly electron-withdrawing effect of phosphoryl groups attached directly to the porphyrin macrocycle results in a self-assembling process, with formation of a stable 2D coordination network, which is unusual for copper(II) porphyrins. The resulting 2D structure is a rare example of an assembly based on copper(II) porphyrins where the copper(II) central metal ion is six-coordinated because of a weak interaction with two phosphoryl groups of adjacent porphyrins. The other polymorph of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin contains individual (isolated) porphyrin molecules with four-coordinated copper(II) in a distorted porphyrin core. This polymorph can be obtained only by slow diffusion of a copper acetate/methanol solution into solutions of free base 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in chloroform. It converts to the 2D structure after dissolution in chloroform followed by consecutive crystallizations, using slow diffusion of hexane. A six-coordinated copper(II) porphyrin containing two axially coordinated dioxane molecules was also obtained and characterized by X-ray diffraction crystallography. The association of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in solution was also studied.

An N-bridged high-valent diiron-oxo species on a porphyrin platform that can oxidize methane.

High-valent oxo-metal complexes are involved in key biochemical processes of selective oxidation and removal of xenobiotics. The catalytic properties of cytochrome P-450 and soluble methane monooxygenase enzymes are associated with oxo species on mononuclear iron haem and diiron non-haem platforms, respectively. Bio-inspired chemical systems that can reproduce the fascinating ability of these enzymes to oxidize the strongest C-H bonds are the focus of intense scrutiny. In this context, the development of highly oxidizing diiron macrocyclic catalysts requires a structural determination of the elusive active species and elucidation of the reaction mechanism. Here we report the preparation of an Fe(IV)(µ-nitrido)Fe(IV) = O tetraphenylporphyrin cation radical species at -90 °C, characterized by ultraviolet-visible, electron paramagnetic resonance and Mössbauer spectroscopies and by electrospray ionization mass spectrometry. This species exhibits a very high activity for oxygen-atom transfer towards alkanes, including methane. These findings provide a foundation on which to develop efficient and clean oxidation processes, in particular transformations of the strongest C-H bonds.

Synthesis and self-organization of zinc ß-(dialkoxyphosphoryl)porphyrins in the solid state and in solution.

The first synthesis and self-organization of zinc ß-phosphorylporphyrins in the solid state and in solution are reported. ß-Dialkoxyphosphoryl-5,10,15,20-tetraphenylporphyrins and their Zn(II) complexes have been synthesized in good yields by using Pd- and Cu-mediated carbon-phosphorous bond-forming reactions. The Cu-mediated reaction allowed to prepare the mono-ß-(dialkoxyphosphoryl)porphyrins 1 Zn-3 Zn starting from the ß-bromo-substituted zinc porphyrinate ZnTPPBr (TPP = tetraphenylporphyrin) and dialkyl phosphites HP(O)(OR)(2) (R = Et, iPr, nBu). The derivatives 1 Zn-3 Zn were obtained in good yields by using one to three equivalents of CuI. When the reaction was carried out in the presence of catalytic amounts of palladium complexes in toluene, the desired zinc derivative 1 Zn was obtained in up to 72% yield. The use of a Pd-catalyzed C-P bond-forming reaction was further extended to the synthesis of ß-poly(dialkoxyphosphoryl)porphyrins. An unprecedented one-pot sequence involving consecutive reduction and phosphorylation of H(2)TPPBr(4) led to the formation of a mixture of the 2,12- and 2,13-bis(dialkoxy)phosphorylporphyrins 5 H(2) and 6 H(2) in 81% total yield. According to the X-ray diffraction studies, 1 Zn and 3 Zn are partially overlapped cofacial dimers formed through the coordination of two Zn centers by two phosphoryl groups belonging to the adjacent molecules. The equilibrium between the monomeric and the dimeric species exists in solutions of 1 Zn and 3 Zn in weakly polar solvents according to spectroscopic data (UV/Vis absorption and NMR spectroscopy). The ratio of each form is dependent on the concentration, temperature, and traces of water or methanol. These features demonstrated that zinc ß-phosphorylporphyrins can be regarded as new model compounds for the weakly coupled chlorophyll pair in the photosynthesis process.