Structural, spectroscopic, and kinetic investigation of the molybdenum dialkylhydrazido complexes [MoBr(NNC5H10)(dppe)2]Br and [Mo(NNC5H10)(dppe)2]: activation parameters and revised mechanism for N-N cleavage.
The reaction of [Mo(NNC(5)H(10))(dppe)(2)] (B(Mo)) with an excess of acid, HNEt(3)BPh(4), is investigated applying temperature-dependent stopped-flow measurements. The kinetic data indicate a biphasic process with rate constants k(obs(1)) and k(obs(2)) which are both slower than the single rate constant reported by Henderson et al. (Henderson, R. A.; Leigh, G. J.; Pickett, C. J., J. Chem. Soc., Dalton Trans. 1989, 425-430). Moreover, both rate constants exhibit a linear dependence on the acid concentration with a large intercept which is attributed to acid-dependent and acid-independent components of each reaction phase, respectively. All four reaction channels exhibit temperature-dependent reaction rates. Furthermore, B(Mo) and its Mo(IV) analogue [MoBr(NNC(5)H(10))(dppe)(2)]Br (A(Mo)) are characterized structurally and spectroscopically. Density-functional theory calculations are performed to locate possible barriers in the overall reaction scheme and determine their energies, providing additional information for the formulation of a mechanism. The temperature-dependent rate of N-N cleavage is explained by a revised mechanism which involves an alpha-protonated intermediate that is inert with respect to N-N cleavage and is generated from its beta-protonated counterpart by a rapid 1,2-proton shift. The implications of these results with respect to N(2) reduction in the Chatt cycle and the enzyme nitrogenase are discussed.
Dreher
Ameli
A
Institut fur Anorganische Chemie, Christian-Albrechts-Universitat Kiel, Max-Eyth-Strasse 2, 24098 Kiel, Germany.
Mersmann
Klaus
K
Näther
Christian
C
Ivanovic-Burmazovic
Ivana
I
van Eldik
Rudi
R
Tuczek
Felix
F
D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature; D014732:Vibration
D009942:Organometallic Compounds; D008982:Molybdenum; D009584:Nitrogen