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Investigation of the 6d and 5f Orbital Contributions in Actinide Complexes Containing Amide, Ketimide, Aryl, and Alkyl Metal-Ligand Bonds

Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2009. / Title from PDF t.p. (viewed Feb. 4, 2010). Source: Dissertation Abstracts International, Volume: 70-04, Section: B, page: 2297. Adviser: Daniel J. Mindiola.

¹H NMR and EPR techniques were used to investigate the electron spin distribution and electronic ground state in several iron tetrapyrrolic macrocycles. The first macrocycle studied is corrole, including [(Me₈C)FeCl] (Me₈C = 2,3,7,8,12,13,17,18-octamethylcorrole) and [(7,13-Me₂Et₆C)FeCl] (7,13-Me₂Et₆C = 7,13-dimethyl-2,3,8,12,17,18-hexaethylcorrole) and four meso-substituted corrolates--[(TPCorr)FeCl], [(4-NO2TPCorr)FeCl], [(4-MeOTPCorr)FeCl] and [(TPCorr)FeClO₄] (TPCorr = 5,10,15-triphenylcorrole). These chloroiron corrolates were all found to be S = 3/2 intermediate-spin iron(III) π cation radical complexes, with the corrole radical strongly antiferromagnetically coupled to the spins of the iron, leading to an overall spin of 1 and large negative π spin densities on the meso positions. Upon addition of imidazole ligands, [(Me₈C)FeCl] and [(7,13-Me₂Et₆C)FeCl2] change to bis imidazole low-spin iron(III) π cation radical species at low temperature. There is little or no ferromagnetic coupling between the radical and the iron center, resulting in large position pi spin densities on the meso positions. The binding of cyanide to [(7,13-Me₂Et₆C)FeCl] causes autoreduction of the complex. An excess of cyanide in the solution can reduce the bis-cyanide complex, a low-spin iron(III) π cation radical which is produced first upon addition of cyanide, to the mono-cyanide complex, which is a normal low-spin iron(III) five-coordinate complex. The redox reaction occurs on the corrole ring instead of at the iron center. Proton relaxation times (T₁ and T₂) of a pyrrole-CH₃ peak from the heme domain of the chicken liver sulfite oxidase were measured by NMR methods. From the relaxation times, it is found that the sulfite oxidase enzyme tumbles as the whole protein rather than the larger Mo domain and the smaller heme domain tumbling somewhat independently. The last macrocycles investigated are chlorins and mono-oxochlorin. Both high-spin tetraphenylchlorinatoiron(III) chloride (TPCFeCl) and octaethylchlorinatoiron(III) chloride (OECFeCl) and their low-spin complexes with different imidazole and pyridine ligands were studied by NMR and EPR. The full peak assignments were made for all high-spin and low-spin species from COSY, NOESY, NOE difference and saturation transfer experiments. The NMR results show that, like TPPFe(III) and TMPFe(III) complexes, the low-spin TPCFe(III) complexes change their ground state from (dxy)²(dxzdyz)³ to (dxzdyz)⁴(dxy)¹ with decrease in the donor strength of the axial ligands, while OECFe(III) complexes keep their ground state unchanged (always (dxy)²(dxydyz)³) with different axial ligands in the temperature range of NMR experiments (+30°C to -90°C)). However, EPR data show that both TPCFe(III) and OECFe(III) complexes have the trend of change to (dxzdyz)⁴(dxy)¹ ground state with weak donor ligands (such 4-cyanopyridine). The electronic structure of [OECFe(t-BuNC)₂]⁺ is the (dxzdyz)⁴(dxy)¹ ground state with a low-lying (dxy)²(d xzdyz)³ excited state. The chlorin ring of [OECFe(tBuNC)₂]⁺ is probably ruffled, as in [OEPFe(t-BuNC)₂]⁺. The NMR spectrum of [OECFe(t-BuNC)₂]⁺ is characterized by the large downfield shift of the pyrrolene protons, indicating the involvement of the A-1 orbital in the spin distribution mechanism. [mono-oxo-OECFe(Im-d₄)₂]Cl (mono-oxo-OEC = 2-oxo-3,3',7,8,12,13,17,18-octaethyl-chlorin) is a low-spin Fe(III) complex with (dxy)²(dxzdyz)³ ground state. The pattern of the chemical shifts of the pyrrole-CH2 and meso protons is similar to that of [OECFe(Im-d₄)₂]Cl, except that more peaks were observed due to its lower symmetry. Finally, DFT calculation on high-spin iron (III) chlorin was carried out to predict the Fermi contact shifts and spin distribution mechanism.

This dissertation is concerned with the chemistry of the hexarhenium selenide cluster and its use as a synthetic building block. Two themes underlay the research presented here: (1) to create of novel supramolecular arrays and (2) to provide possible solutions to problems associated with the synthesis of inorganic-organic hybrid materials. Star-shaped scaffolding was used to develop a molecular Tinkertoy kit containing pieces which incorporate a variety of angles. Further functionalization of a molecular Tinkertoy based upon TPyP by incorporation of metal ions was discussed and examined along with the new electrochemical and photophysical properties observed. A new metallodendrimer motif containing clusters a the core, within the branches, and on the periphery was developed and discussed. Also addressed is the hitherto unseen electrochemical communication between [Re6(μ3-Se)8]2+ clusters bridged by an organic moiety. Possible solutions to problems involved with the synthesis of inorganic-organic hybrid materials were provided, as well as a demonstration-of-feasibility synthesis demonstrating the successful copolymerization of [Re6(μ3-Se)8]2+ vinylpyridine derivative with styrene.

Models of the heme b centers in the cytochrome bc₁ complex based on octaalkyltetraphenyliron(III) porphyrins (OETPP, OMTPP, and TC₆TPP) with various axial ligands (4-Me₂NPy, 4-CNPy, 1-MeIm, 2-McImH, CN- and t-BuNC) have been synthesized and explored via NMR and EPR spectroscopy and X-ray crystallography. The electron spin distributions and the electronic ground states of the complexes were determined based on the NMR and EPR results. The type of ground state of Fe(III) is defined by the number and nature of the axial ligands and peripheral substituents. Five-coordinate complexes with Cl- are high-spin (HS, S = 5/2) with ∼10% of intermediate spin (IS, S = 3/2) mixed in. Bis-(4-CNPy) porphyrins at relatively high temperatures, as well as five-coordinate perchlorates, have the IS state. Finally, six-coordinate complexes with pyridines, imidazoles, cyanides and isocyanides are all low-spin (LS, S = 1/2), with the (dxy)²(d xz,dyz)³ ground state in the case of strongly and moderately basic axial ligands, and the (dxz,dyz)⁴(dxy)¹ ground state when bound to weak sigma-donors and/or strong pi-acceptors like t-BuNC or 4-CNPy (at low temperatures only). Crystal structures of more than 15 complexes have been obtained in order to establish structure-property relationships in the systems studied. All of them adopt a saddled conformation with different degrees of ruffling and non-planarity and a wide range of dihedral angles between the axial ligands. Non-planar distortion of the macrocycle induced by the steric interaction between the peripheral substituents increases in the order TC₆TPP < OMTPP < OETPP. The rate of ring inversion of the porphyrin cores decreases in the same order, as shown by NMR spectroscopy. While all bis-ligated iron(III) porphyrinate of this study with pyridine or hindered imidazole ligands have close to perpendicular axial ligand orientations, bis-(1-MeIm) complexes have perpendicular as well as close to parallel ligand arrangements both in crystals and in solutions as observed by EPR and Mössbauer spectroscopy and X-ray crystallography. Preliminary Mössbauer studies of four of the complexes of this study have been carried out in the laboratory of Professor A. X. Trautwein, Institute of Physics, University of Lubeck, Germany. The results of the work presented in this dissertation suggest that octaalkyltetraphenylporphyrinatoiron(III) complexes are promising models for the heme b centers in the cytochrome bc₁ complex.