Dinitrogen fixation chemistry of a molybdenum trisanilide system
Author(s)Curley, John Joseph
Massachusetts Institute of Technology. Dept. of Chemistry.
Christopher C. Cummins.
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Dinitrogen cleavage by Mo(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2) proceeds through the intermediate ([mu]-N2)[Mo(N[t-Bu]Ar)3]2 before forming N=Mo(N[t-Bu]Ar)3 as the product. Both the intermediate bridging N2 complex and the nitride product have been structurally characterized by single-crystal X-ray diffraction. The spectroscopic and structural features of this bridging N2 complex are discussed in comparison to its one- and two-electron oxidized congeners, [([mu]-N2)[Mo(N[t-Bu]Ar)3]2]n+, n = 1, 2. This series of three complexes share a common chromophore, the nature of which was identified with the aid of time-dependent density functional theory. A photochemical reaction of ([mu]-N2)[Mo(N[t-Bu]Ar)3]2 that forms both Mo(N[t-Bu]Ar)3 and N=Mo(N[t-Bu]Ar)3 is described. The dynamics of this photochemical reaction are explored by ultrafast transient absorbance spectroscopy. A synthetic scheme for nitrogen fixation in the form of organic nitriles is initiated from the product of dinitrogen cleavage, N=Mo(N[t-Bu]Ar)3. This synthetic scheme is a closed cycle that returns the molybdenum nitride starting material at the conclusion of the cycle. To achieve this synthetic goal, new methods were developed to form C-N bonds between organic electrophiles and the weakly nucleophilic terminal nitride. In a key reaction, Mo(IV) ketimide complexes, R'O(R)CNMo (N[t-Bu]Ar)3, were shown to react with either SnCl2 or ZnCl2 to afford the corresponding nitrile, RCN, and a ClMo(N[t-Bu]Ar)3 in essentially quantitative yields.(cont.) The chloromolybdenum complex may be reductively recycled to yield Mo(N[t-Bu]Ar)3 for subsequent dinitrogen cleavage. A series of cationic diazoalkane complexes [4-RC6H4C(H)NNMo(N[t-Bu]Ar)3][AlCl4], R = NMe2, Me, H, Br, CN, have been prepared by treatment of the N2-derived diazenido complex Me3SiNNMo(N[t-Bu]Ar)3 with 4-RC6H4CHO and 2 equiv AlCl3. The physical properties of these complexes were determined by the use of X-ray crystallography, cyclic voltammetry, infrared, Raman, UV-vis, and 15N NMR spectroscopies. Electrochemical reduction of these cationic diazoalkane complexes forms the C-C bonded dimer, [mu]-(4-RC6H4C(H)NN)2[Mo(N[t-Bu]Ar)3]2, in a reaction that is proposed to proceed through the neutral, odd-electron complex 4-RC6H4C(H)NNMo(N[t-Bu]Ar)3. The structure of this odd-electron compound is described with the aid of density functional theory. The central C-C bond in [mu]-(4-RC6H4C(H)NN)2[Mo(N[t-Bu]Ar)3]2 is redox non-innocent, and oxidation of these compounds returns the cationic diazoalkane complex from which they were prepared.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Vita.Includes bibliographical references.
DepartmentMassachusetts Institute of Technology. Dept. of Chemistry.
Massachusetts Institute of Technology