Kirill P. Birin

NMR-based analysis of structure of heteroleptic triple-decker (phthalocyaninato) (porphyrinato) lanthanides in solutions

A novel approach for the structural analysis of heteroleptic triple‐decker (porphyrinato)(phthalocyaninato) lanthanides(III) in solutions is developed. The developed approach consists in molecular mechanics (MM+) optimization of the geometry of the complex taking into account the lanthanide‐induced shift (LIS) datasets. LISs of the resonance peaks in 1H NMR spectra of a series of symmetric complexes [An4P]Ln[(15C5)4Pc]Ln[An4P], where An4P2− is 5,10,15,20‐tetrakis(4‐methoxyphenyl)porphyrinato‐dianion, [(15C5)4Pc]2− is 2,3,9,10,16,17,24,25‐tetrakis(15‐crown‐5)phthalocyaninato‐dianion and Ln = La, Ce, Pr, Nd, Sm, Eu, are analyzed. Analysis of LISs showed two sets of protons in the molecule with opposite signs of shift. Two‐nuclei analysis of LISs testifies isostructurality of the whole series of investigated complexes in solution despite contraction of the lanthanide ions. Model‐free separation of contact and dipolar contributions of LISs was performed with one‐nucleus technique and did not show changes in contact and dipolar terms within the investigated series. MM+ optimization of the molecular structure allowed the interpretation of features of LIS for each particular group of protons. Parameterization of MM + ‐optimized model of molecule with values of structure‐dependent dipolar contributions of LIS allows the development of the precise structural model of the triple‐decker complex in solution. This approach allows the determination of the geometry and structure of the sandwich macrocyclic tetrapyrrolic complexes together with conformational analysis of flexible peripheral substituents in solutions. The developed method can be applied with minor modifications for the determination of structural parameters of other types of lanthanides(III) complexes with tetrapyrrolic ligands and also supramolecular systems based on them. Copyright

Synthesis and Self-Organization of Zinc β-(Dialkoxyphosphoryl)porphyrins in the Solid State and in Solution

The first synthesis and self-organization of zinc β-phosphorylporphyrins in the solid state and in solution are reported. β-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-β-(dialkoxyphosphoryl)porphyrins 1 Zn-3 Zn starting from the β-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 β-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 β-phosphorylporphyrins can be regarded as new model compounds for the weakly coupled chlorophyll pair in the photosynthesis process.

Efficient scrambling-free synthesis of heteroleptic terbium triple-decker (porphyrinato)(crown-phthalocyaninates).

New heteroleptic triple-decker terbium complexes of general structure [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[Br(4)TPP] (Tb-TD) and [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[(15C5)(4)Pc] (Tb-TD*) (Br(4)TPP = tetrakis-meso-(4-bromophenyl)-porphyrin, (15C5)(4)Pc = tetra-(15-crown-5)-phthalocyanine) are synthesized with 48% and 57% yields, respectively. The triple-decker complexes were prepared by interaction of generated in situ terbium monoporphyrinate [Br(4)TPP]Tb(acac) and corresponding double-decker precursors. The heteroleptic double-decker precursor [Br(4)TPP]Tb[(15C5)(4)Pc] was prepared for the first time in a two step one-pot synthesis. No ligand scrambling was observed in the synthesis of Tb-TD, while 4% scrambling was determined in the case of Tb-TD*. High yields of target triple-decker complexes were achieved despite the presence of electron-donating crown-ether fragments with low thermal stability at the phthalocyanine deck. Analysis of lanthanide-induced paramagnetic shifts of protons of Tb-TD together with data of previously reported La, Pr, Nd and Eu analogues allowed precise separation of contributions of contact and dipolar lanthanide terms as well as verification of isostructurality of complexes within the series.

Synthesis, structure, solid-state thermolysis, and catalytic properties of binuclear Ce, Nd, Eu, and Gd cymantrenecarboxylate complexes with DMSO

New rare-earth cymantrenecarboxylate complexes [Ln2(μ,η2-O2CCym)2(μ2-O2CCym)2-(η2-O2CCym)2(DMSO)4] (Cym = (η5-C5H4)Mn(CO)3, Ln = Ce (1), Nd (2), Eu (3), Gd (4)) were synthesized and characterized by X-ray diffraction. In dimeric structures 1–4, two of four bridging carboxylates are chelating-bridging, and Ln atoms have coordination number 9. The catalytic activity of complex 2 in the polymerization of 2,3-dimethyl-1,3-butadiene was investigated. The thermal decomposition of the synthesized compounds was studied by DSC and TGA. According to the X-ray powder diffraction data, the final thermal decomposition product of 1 in air consists of CeO2 and Mn3O4. Under the same conditions, complexes 2–4 afford mixtures of LnMn2O5 and Mn2O3.

A hybrid halobismuthate light-harvesting material with an optical band gap of 1.70 eV

A new organic–inorganic hybrid material (C15H14N4)BiBr5·H2O with an optical band gap of 2.24 eV, having 1-D chains of bromobismuthate anions in its composition, has been obtained from an aqueous solution and characterized. The partial replacement of Br by I resulted in the formation of a thermally stable (<155 °C) black compound (C15H14N4)BiBrI4·H2O with an optical band gap of 1.70 eV, which can be proposed as a promising light-harvesting material for dye-sensitized solid-state solar cells. Further replacement of Br by I results in the formation of red-orange colored (C15H14N4)BiI5 with a band gap of 2.10 eV.

Orientation-induced redox transformations in Langmuir monolayers of double-decker cerium bis[tetra-(15-crown-5)-phthalocyaninate] and multistability of its Langmuir-Blodgett films

The spectral, electrochemical, and optical properties of Langmuir-Blodgett films (LBFs) and cast films from a solution of new double-decker cerium bis[tetra-(15-crown-5)-phthalocyaninate] (Ce(R4Pc)2) are studied. Based on analysis of compression isotherms and quantum-chemical calculations, schemes of the organization of Ce(R4Pc)2 molecules at different states of its monolayers are proposed. Correlation dependences are determined in order to relate the optical and electrochemical characteristics of monolayers and LBFs of sandwich-type lanthanide phthalocyaninates to the ionic radii of their metal centers. The valent state of Ce ions in a monolayer-forming complex is determined, and a sequence of redox transformations occurring in LBF uppon appliance of a potential is proposed, one of the transformations being associated with the Ce3+/Ce4+ redox transition. Orientation-induced intramolecular electron transfer is revealed in the planar supramolecular system. It is shown that, during the formation of a monolayer from a Ce(R4Pc)2 solution, a tetravalent metal center passes to a trivalent state. Monolayer compression to a high surface pressure reverts the complex to the electronic state typical of the solution. The reversible transformations observed upon the monolayer compression result from intramolecular electron transfer from the 4f-orbital of Ce to the phthalocyanine ring and backwards. The high operation rate and the reversibility of switching between the stable states, which are determined by means of the surface plasmon resonance technique, upon a stepwise change in the electrode potential within the range of 200–850 mV may underlie the development of optoelectronic systems. With a large number of molecules in a stacking aggregate, changes in the distance between the decks of the complex that occur with changes in the oxidation level of the metal center can substantially modulate the sizes of molecular ensembles. A supramolecular device capable of performing mechanical work can be developed based on this effect.

Novel one-pot regioselective route towards heteroleptic lanthanide (phthalocyaninato)(porphyrinato) triple-decker complexes

A novel one-pot method for the regioselective preparation of early heteroleptic lanthanide (porphyrinato)(phthalocyaninato) complexes of double- and triple-decker structure [(Por)Ln(Pc) and (Por)Ln(Pc)Ln(Por), respectively] is developed. Sandwich-type complexes are synthesized for La, Ce and Pr following this procedure, with yields up to 30%. Tetrakis(15-crown-5)-phthalocyanine [(15C5)4PcH2] and tetrakis-meso-(4-methoxyphenyl)-porphyrin (An4PH2) are used as macrocyclic tetrapyrrolic ligands. The complexes are widely characterized with various physico-chemical methods (NMR and UV-vis spectroscopy, MALDI-TOF mass spectrometry). Quantum chemistry calculations for intermediates of the process are performed. The results of calculations explain the high regioselectivity of the triple-decker complex formation in the developed method.

Complexes of zinc(II) tetra-(15-crown-5)-phthalocyaninate with axially coordinates N-donor ligands as potential components of photosensitive materials of telecommunication range

The methods of electron absorption spectroscopy and 1H NMR were used to study the processes of interactions between zinc tetra-(15-crown-5)-phthalocyaninate and a number of N-donor ligands, including 1,4-diazabicyclo[2.2.2]octane, 4-dimethylaminopyridine, 3-aminopyridine, imidazole, 2-amino-5-methylpyridine, 2-methyla-4-aminopyridine, 2,3-diaminopyridine, pyrazine. A new effective method for synthesizing zinc tetra-15-crown-5-phthalocyaninate was developed that allowed one to obtain the complex at a yield of greater than 80% under simple conditions in 2 h. The structure of associates was studied in detail using the example of interactions between zinc tetra-15-crown-5-phthalocyaninate and 1,4-diazabicyclo[2.2.2]octane. 1H NMR studies in a wide temperature range of 213–323 K (−60 to +50°C), as well as quantum-chemical calculations, allowed us to establish the formation of two types of associates of phthalocyanine and 1,4-diazabicyclo[2.2.2]octane with the composition of 1: 1 and 2: 1. Up to a temperature of 253 K, the 1: 1 and 2: 1 associates are in equilibrium with a high rate of interconversion.

On the synthesis of functionalized porphyrins and porphyrin conjugates via β-aminoporphyrins

The synthesis of functionalized porphyrins and their conjugates from meso-tetraarylporphyrins through the acylation and the oxidation of β-aminoporphyrins was investigated. 2,3-Dioxochlorins were prepared by the oxidation of a variety of β-aminoporphyrins and subsequently used in a condensation reaction with functionalized aromatic aldehydes and ammonium acetate to form β-functionalized porphyrins bearing a fused imidazole ring. Under optimized experimental conditions both reactions tolerate various functional groups and afford the products in an appropriate overall yield. The mildness and usefulness of this methodology are illustrated by several examples including the synthesis of porphyrins bearing receptor groups and water-solubilizing moieties.

Electrochemically controlled multistability of ultrathin films of double-decker cerium phthalocyaninates

The spectral and electrochemical properties of Langmuir-Blodgett (LB) films of homoleptic double-decker cerium bis-[tetra-15-crown-5]-phthalocyaninate Ce[R4Pc]2 and its heteroleptic analog [Pc]Ce[R4Pc] were studied. It was shown that during formation of Langmuir monolayers upon contact of both complexes solutions with water subphase the metal center with valent state IV in the solution transforms into one with the valent state III in the monolayer. Upon cyclic compression-expansion of these monolayers, orientation-induced reversible intramolecular transfers of electron from 4f orbital of cerium ion to the phthalocyanine macrocycle (compression) and in reverse direction (expansion) occur in a planar supramolecular system. Scheme of reversible electrochemical transformations occurring in ultrathin films of double-decker cerium crown-phthalocyaninates, one of which is associated with the Ce+3/Ce+4 redox-transition of metal center of the complex, was proposed and substantiated using the results of spectro-electrochemical investigations. It was shown that one of these transformations is associated with the Ce+3/Ce+4 redox transition of metal center of the complex and upon change of metal center oxidation state its size changes, and, consequently, the distance between the decks of the complex also changes. This change in the distance can lead to a substantial (13–15%) modulation of the linear size of molecular assemblies with a large number of molecules in stack. On the basis of this effect the supramolecular device that can perform mechanical work can be developed. Using surface plasmon resonance technique we have demonstrated that a step change in electrode potential in region of 200–1000 mV induces a corresponding optical response reflected in a step change of the resonance angle. High operation speed and reversibility of switching between stable states can serve as a basis for development of optoelectronic switching systems.