260265-92-7Relevant academic research and scientific papers
Shining light on dinitrogen cleavage: Structural features, redox chemistry, and photochemistry of the key intermediate bridging dinitrogen complex
Curley, John J.,Cook, Timothy R.,Reece, Steven Y.,Mueller, Peter,Cummins, Christopher C.
, p. 9394 - 9405 (2008)
The key intermediate in dinitrogen cleavage by Mo(N[t-Bu]Ar)3, 1 (Ar = 3,5-C6H3Me2), has been characterized by a pair of single crystal X-ray structures. For the first time, the X-ray crystal structure of (μ-N2)[Mo(N[t-Bu]Ar)3]2, 2, and the product of homolytic fragmentation of the N-N bond, N≡Mo(N[t-Bu] Ar)3, are reported. The structural features of 2 are compared with previously reported EXAFS data. Moreover, contrasts are drawn between theoretical predictions concerning the structural and magnetic properties of 2 and those reported herein. In particular, it is shown that 2 exists as a triplet (S = 1) at 20°C. Further insight into the bonding across the MoNNMo core of the molecule is obtained by the synthesis and structural characterization of the one- and two-electron oxidized congeners, (μ-N2)[Mo(N[t-Bu]Ar) 3]2[B(ArF)4], 2[B(Ar F)4] (ArF = 3,5-C6H 3(CF3)2) and (μ-N2)[Mo(N[t-Bu]Ar) 3]2[B(ArF)4]2, 2[B(ArF)4]2, respectively. Bonding in these three molecules is discussed in view of X-ray crystallography, Raman spectroscopy, electronic absorption spectroscopy, and density functional theory. Combining X-ray crystallography data with Raman spectroscopy studies allows the N-N bond polarization energy and N-N internuclear distance to be correlated in three states of charge across the MoNNMo core. For 2[B(ArF) 4], bonding is symmetric about the μ-N2 ligand and the N-N polarization is Raman active; therefore, 2[B(ArF)4] meets the criteria of a Robin-Day class III mixed-valent compound. The redox couples that interrelate 2, 2+, and 22+ are studied by cyclic voltammetry and spectroelectrochemistry. Insights into the electronic structure of 2 led to the discovery of a photochemical reaction that forms N≡Mo(N[t-Bu]Ar)3 and Mo(N[t-Bu]Ar)3 through competing N-N bond cleavage and N2 extrusion reaction pathways. The primary quantum yield was determined to be Φp = 0.05, and transient absorption experiments show that the photochemical reaction is complete in less than 10 ns.
Base-catalyzed dinitrogen cleavage by molybdenum amides
Trai, Yi-Chou,Cummins, Christopher C.
, p. 63 - 69 (2008/10/08)
The amides Mo(NRAr)3 (R=CMe3 or C(CD3)2CH3, Ar=3,5-C6H3Me2) and HMo(η2-Me2CNAr)(NRAr)2 (R=CHMe2 or CH(CD3)2, Ar=3,5-C6H3Me2) are known to effect the six-electron reductive cleavage of dinitrogen in the absence of added reagents to provide terminal nitrido molybdenum complexes of formula NMo(NRAr)3. However, this reaction typically has required a lengthy incubation period at -35°C during which N2 uptake takes place. This work reports on the catalytic effect of addition of stoichiometric amounts of N-heterocyclic bases such as 2,6-dimethylpyrazine, 1-methylimidazole, 4-dimethylaminopyridine (DMAP), and pyridine itself. Certain combinations of molybdenum amide and base lead to complete conversion to NMo(NRAr)3 within minutes at 25°C, 1 atm of N2, in ether or n-pentane solution. Monitoring of reaction progress and probing for possible intermediates has been carried out using 2H NMR spectroscopy, while taking advantage of samples labeled with CD3 groups. In some cases the 2H NMR data are in accord with intermediate base adduct formation, while in other cases adducts are not observed. The effect of potassium hydride in THF as the added base similarly has been investigated. 2002 Elsevier Science B.V. All rights reserved.
