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45510-GB3
Development of New Phthalocyanine-Based Catalytic Systems
Overall, the first year was very successful for the project. During the regular academic year, three undergraduate and one graduate (MS) students were involved in the project, while seven undergraduate and one graduate (MS) students worked on the project during summer 2007 research program. As the result, several mono- and binuclear phthalocyanine-based compounds mentioned below were prepared and characterized by the variety of spectroscopic and theoretical methods. As discussed below, few mono- and binuclear transition-metal complexes were tested in the variety of catalytic reactions and shown very promising results. Two papers in the high-rank peer-review journals have already been published, one accepted, and two more are currently in preparation. In addition, the first-year project results were presented at ACS national meeting in Chicago. Below we outline the major results obtained in the first year.
Synthesis, characterization, and evaluation of catalytic properties of multinuclear phthalocyanines.
Our first set of the target molecules is generalized in the TOC picture. In these molecules, two Pc macrocycles are linked by the R or S enantiomers of BINOL [(R)-(+)- or (S)-(-)-1,1'-bi-2-naphthol]. The chiral BINOL linkers were chosen because of their well-documented optical stability and strong as well as clearly understandable chiral field described in the past, which is convenient for circular dichroism (CD) data analysis. Enantiopure metal-free R- and S-BINOL linked complexes were prepared by statistical cross condensation of enantiomerically pure R- and S-BINOL linked tetranitriles with eighteen-fold excess of commercially available 4-tert-butyl-phthalonitrile in the presence of lithium N,N-dimethylaminoethanolate in dry refluxing N,N-dimethylaminoethanol for 24 hours. Target metal-free complexes were purified by using several column chromatography separations on silica followed by a set of size-exclusion filtrations and finally chromatography on alumina. Resulting blue microcrystalline compounds were recrystallized from chloroform-methanol and dried in vacuum producing the analytically and enenthiomerically pure target compounds in 7 - 10 % yield. Although these yields look low, they are in the typical range for the preparation of low-symmetry Pcs and currently are subject for optimization in our laboratory. The treatment of both metal-free R- and S-BINOL linked phthalocyanine dimers with zinc acetate or ruthenium carbonyl lead to the formation of respective zinc or ruthenium (isolated as tetra carbonyl compounds) complexes. We found that the ruthenium complexes can serve as good catalysts in the epoxidation reaction between organic alkenes and PhIO. We currently investigating of the asymmetric epoxidation reactions between alkenes and PhIO in the presence of these chiral ruthenium complexes.
Taking into consideration high cost of ruthenium, our next step will be introduction of the iron in the chiral cavity. Since in this case, the formation of Fe-O-Fe oxo-dimer structure is expected, we have investigated catalytic activity of the simple tertiary-butyl substituted iron phthalocyanine dimer, [(tBu)4PcFe-O-FePc(tBu)4]. We found that unlike porphyrin analogues, this dimer is catalytically active in the oxidation of alcohols and transformation of antracene into antraquinone when iodine(III), iodine(V), and organic peroxides were used as the oxidants. The reaction pathways in these catalytic reactions were investigated using GC-MS, APCI MS, UV-vis, MCD, and Mössbauer spectroscopies. We found that the reaction mechanism involves the formation of unique [O=Fe-O-Fe=O] dication.
Synthesis, characterization, and evaluation of catalytic properties of selected mononuclear phthalocyanines.
Several heterogeneous catalysts consist of peripherally substituted cobalt phthalocyanine complexes covalently linked to the synthetic carbons modified by organic aminogroups have been prepared and tested in the catalytic reaction of the oxidation of dodecane-1-thiol in organic solvents. It has been shown that, in general, the catalytic activity of covalently linked cobalt phthalocyanine sulfonamides is higher as compared to the respective cobalt phthalocyanine sulfonic acids. An influence of the length of the linker and surface concentration of the phthalocyanine complexes on the catalytic activity of given catalyst has also been discussed. These catalysts are very good potential candidates for the application in the oil-industry important Merox process.
We have optimized conditions for the preparation of the sterically crowded mononuclear bibenzbarreleno- and tripticeno-containing tetraazaporphyrins and specifically, their magnesium complexes. These compounds will be transformed into the respective transition-metal complexes and investigated in the variety of catalytic reactions during second grant year.
Theoretical modeling of spectroscopic properties of phthalocyanines and their analogues.
The catalytic reaction mechanism in phthalocyanine-based catalytic reactions can be followed by UV-vis spectroscopy. An accurate interpretation of the reaction mechanism requires confident assignment of the observed absorption bands in transition-metal phthalocyanines. Thus, finding the theoretical method, which will allow confident interpretation of UV-vis spectra of transition-metal phthalocyanines and their multinuclear assemblies is an important task. As a starting point we study the accuracy of time-dependent density functional theory (TDDFT) approach coupled with 16 different exchange-correlation functionals and two solvents in the accurate prediction of UV-vis spectra of neutral transition-metal phthalocyanine. In the next grant period, we will investigate accuracy of TDDFT method in the prediction of UV-vis spectra of catalytically important phthalocyanine cation-radical and multinuclear redox-active phthalocyanines.
