163929-87-1Relevant academic research and scientific papers
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.
Redox-catalyzed binding of dinitrogen by molybdenum N-tert- hydrocarbylanilide complexes: Implications for dinitrogen functionalization and reductive cleavage
Peters, Jonas C.,Cherry, John-Paul F.,Thomas, J. Christopher,Baraldo, Luis,Mindiola, Daniel J.,Davis, William M.,Cummins, Christopher C.
, p. 10053 - 10067 (2007/10/03)
The splitting of dinitrogen (1 atm, THF, 25 °C) by Mo(N[R]Ar)3 (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2) giving 2 equiv of nitride N≡Mo(N[R]Ar)3 is found to be accelerated in the presence of sodium amalgam. Careful control of the Mo(N[R]Ar)3 concentration led to the isolation and characterization of the anionic dinitrogen complex, [(THF)(xNa)][(N2)Mo(N[R]Ar)3], where x is from 0 to 3. Via electrochemical experiments and synthetic studies, [(THF)(x)Na][(N2)Mo(N[R]Ar)3] is found to be a key intermediate in the acceleration of N2 splitting by Mo(N[R]Ar)3 in the presence of sodium amalgam. Accordingly, in the presence of an electron acceptor, [(THF)(x)Na][(N2)Mo(N[R]Ar)3] reacts with Mo(N[R]Ar)3 to give the neutral N2-bridged complex (μ-N2){Mo(N[R]Ar)3}2, which in turn splits to 2 equiv of nitride N≡Mo(N[R]Ar)3. It is seen that the function of sodium amalgam in this system is as a redox catalyst, accelerating the conversion of Mo(N[R]Ar)3 to (μ-N2){Mo(N[R]Ar)3}2, a dinuclear dinitrogen complex that does not lose N2 readily. Electrochemical or chemical outer-sphere oxidation of [(THF)(x)Na] [(N2)Mo(N[R]Ar)3] leads to rapid N2 evolution with regeneration of Mo(N[R]Ar)3, presumably via the neutral mononuclear dinitrogen complex (N2)Mo(N[R]Ar)3. In situ generated [(THF)(x)Na][(N2)Mo(N[R]Ar)3] was efficiently trapped by ClSiMe3 to give (Me3SiNN)Mo(N[R]Ar)3. This complex underwent reaction with methyl triflate to give the dimethyl hydrazido cationic species, [(Me2NN)Mo(N[R]Ar)3][OTf]. The synthesis of the monomethyl complex (MeNN)Mo(N[R]Ar)3 also was achieved. Experiments designed to trap the neutral mononuclear dinitrogen complex (N2)Mo(N[R]Ar)3 gave rise to efficient syntheses of heterodinuclear dinitrogen complexes including (ph[1Bu]N)3Ti(μ-N2)Mo(N[R]Ar)3, which also was synthesized in its 15N2-labeled form. Synthesis and characterization data for the new N-adamantyl-substituted three-coordinate molybdenum(III) complex Mo(N[Ad]Ar)3 (Ad = 1-adamantyl, Ar = 3,5-C6H3Me2) are presented. The complex is found to react with dinitrogen (1 atm, THF, 25 °C) in the presence of sodium amalgam to give the dinitrogen anion complex [(THF)(x)Na] [(N2)Mo(N[Ad]Ar)3]; the synthesis does not require careful regulation of the Mo(N[Ad]Ar)3 concentration. Indeed, under no conditions has Mo(N[Ad]Ar)3 been observed to split dinitrogen or to give rise to a dinuclear μ-N2 complex; this striking contrast with the reactivity of Mo(N[R]Ar)3 (R = C(CD3)2CH3) is attributed to the enhanced steric protection at Mo afforded by the 1-adamantyl substituents.
Dinitrogen cleavage by three-coordinate molybdenum(III) complexes: Mechanistic and structural data
Laplaza, Catalina E.,Johnson, Marc J. A.,Peters, Jonas C.,Odom, Aaron L.,Kim, Esther,Cummins, Christopher C.,George, Graham N.,Pickering, Ingrid J.
, p. 8623 - 8638 (2007/10/03)
The synthesis and characterization of the complexes Mo[N(R)Ar]3 (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2), (μ-N2){Mo[N(R)Ar]3}2, (μ-15N2){Mo[N(R)Ar]3}2, NMo[N(R)Ar]3, 15NMo[N(R)Ar]3, Mo[N(t-Bu)Ph]3, (μ-N2){Mo[N(t-Bu)Ph]3}2, and NMo[N(t-Bu)Ph]3 are described. Temperature-dependent magnetic susceptibility data indicate a quartet ground state for Mo[N(R)Ar]3. Single-crystal X-ray diffraction studies for Mo[N(R)Ar]3 and NMo[N(t-Bu)Ph]3 are described. Extended X-ray absorption fine structure (EXAFS) structural studies for Mo[N(R)AR]3, (μN2){Mo[N(R)Ar]3}2, and NMo[N(R)AR]3 are reported. Temperature-dependent kinetic data are given for the unimolecular fragmentation of (μ-N2){Mo[N(R)Ar]3}2 to 2 equiv of NMo[N(R)Ar]3 and for the fragmentation of (μ-15N2){Mo[N(R)AR]3}2 to 2 equiv of 15NMo[N(R)AR]3. The temperature dependence of the 15N2 isotope effect for the latter N2 cleavage process was fitted to a simple harmonic model, leading to a prediction for the difference in NN stretching frequencies for the two isotopomers. The latter prediction was consistent with the Raman spectroscopic data for (μ-N2){Mo[N(R)Ar]3}2 and (μ-15N2){Mo[N(R)Ar]3}2. The Raman spectroscopic data and EXAFS results are both consistent with an NN bond order of approximately 2 in (μ-N2){Mo[N(R)Ar]3}2. Temperature-dependent magnetic susceptibility data consistent with a triplet ground state are given for (μ-N2){Mo[N(t-Bu)Ph]3}2.
