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45510-GB3
Development of New Phthalocyanine-Based Catalytic Systems

Viktor N. Nemykin, University of Minnesota Duluth

Overall, the second year of the project was very successful. During regular academic year, three undergraduate and two graduate (MS) students were involved in the project, while three undergraduate, two graduate (MS) students as well as visiting professor worked on the project during summer 2008 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 been published, one review accepted, one paper submitted and three more are currently in preparation. In addition, the second-year project results were presented at ACS national meeting in New Orleans as well as 5^th International Conference on Poprhyrins and Phthalocyanines in Moscow. Overall, during two years of the project, four research papers were published, one accepted, one submitted, and three are currently in preparation. Below we outline the major results obtained in the second year.
Synthesis, characterization, and evaluation of catalytic properties of multinuclear phthalocyanines.
During second year of the project, we continue exploration of the chiral transition-metal complexes 1 (see PowerPoint slide). In addition, R or S enantiomers of BINOL [(R)-(+)- or (S)-(-)-1,1’-bi-2-naphthol] linked complexes 2, which have smaller chiral cavity as compared to that in complexes 1 were prepared and characterized using NMR, UV-vis, CD, MCD, and MS methods. As expected, smaller chiral cavity in complexes 2 significantly alter spectroscopic (and we believe catalytic) properties of these compounds. Enantiopure metal-free R- and S-BINOL linked complexes 2 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 10 - 15 % yield. We have continued investigation of catalytic activity of the simple tertiary-butyl substituted iron phthalocyanine dimer, [(tBu)4PcFe-O-FePc(tBu)4] (3). We found that unlike porphyrin analogues, this dimer is catalytically active in the oxidation of alcohols, transformation of antracene into antraquinone, carbon-carbon triple bond cleavage, and epoxidation of carbon-carbon double bond when iodine(III), iodine(V), and organic peroxides were used as the oxidants. The reaction mechanism in these catalytic reactions were investigated using GC-MS, APCI MS, UV-vis, MCD, EPR, and Mössbauer spectroscopies as well as computational approach. We found that the reaction mechanism depends on the type of oxidant. When iodine(III) and iodine(V) compounds used as an oxidants, reaction mechanism involves the formation of unique mixed-valence O=Fe^IV(Pc^1-)-O-Fe^III(Pc^2-) core, which can either directly oxidize a substrate molecule or undergo dissociation into two mononuclear O=Fe^IV(Pc^2-) complexes, which also can be involved into catalytic oxidation of organic substrates. In the case of organic peroxides, however, both single- and two-electron oxidation reactions take place with the formation of not only O=Fe^IV(Pc^1-)-O-Fe^III(Pc^2-) core, but also new mixed-valence catalytically less active HO-Fe^IV(Pc^2-)-O-Fe^III(Pc^2-) dimer.
Synthesis, characterization, and evaluation of catalytic properties of selected mononuclear phthalocyanines.
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. We found that in the case of open-shell phthalocyanine-based cation-radicals, a good agreement between theory and experiment can only be reached when LDA and GGA exchange-correlation functionals are used on molecular geometries optimized using hybrid  exchange-correlation functionals.

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