0000000000205212
AUTHOR
Nicolai Lehnert
The Iron Hydrido Complex [FeH(dppe)2]+: Solution and Solid-State Reactivity with Dinitrogen
The blue compound [FeH(dppe)2]BPh4 (1) (dppe = 1,2-bis(diphenylphosphino)ethane) is investigated by optical absorption, vibrational, NMR and Mossbauer spectroscopy as well as magnetic susceptibility measurements. In the solid state, 1 is found to be paramagnetic (S=1) whereas in tetrahydrofuran (thf) solution it is diamagnetic. Importantly, 1 reacts with dinitrogen in thf solution and in the solid state to give the yellow and green dinitrogen complexes 2a and 2b, respectively, both of which have the formula [FeH(N2)(dppe)2]BPh4. Apart from their colour and optical spectroscopic properties, the dinitrogen compounds 2a and 2b also differ in their magnetic, Mossbauer and vibrational properties…
Five-Coordinate Complexes [FeX(depe)2]BPh4, X = Cl, Br: Electronic Structure and Spin-Forbidden Reaction with N2
The bonding of N(2) to the five-coordinate complexes [FeX(depe)(2)](+), X = Cl (1a) and Br (1b), has been investigated with the help of X-ray crystallography, spectroscopy, and quantum-chemical calculations. Complexes 1a and 1b are found to have an XP(4) coordination that is intermediate between square-pyramidal and trigonal-bipyramidal. Mössbauer and optical absorption spectroscopy coupled with angular overlap model (AOM) calculations reveal that 1a and 1b have (3)B(1) ground states deriving from a (xz)(1)(z(2))(1) configuration. The zero-field splitting for this state is found to be 30-35 cm(-1). In contrast, the analogous dinitrogen complexes [FeX(N(2))(depe)(2)](+), X = Cl (2a) and Br (…
ChemInform Abstract: New Developments in Nitrogen Fixation.
The production of ammonia from atmospheric dinitrogen at room temperature and ambient pressure in analogy to nature is a long-term goal for coordination chemists. Novel reactions of N2 -containing transition metal complexes with H2 , the first side-on N2 -bridged structure of an actinide complex, and an interesting variation of synthetic N2 fixation are the key points addressed in this contribution. The results are related to the known chemistry of N2 complexes, and their significance is discussed with respect to enzymatic N2 fixation.
The Reduction Pathway of End-on Coordinated Dinitrogen. II. Electronic Structure and Reactivity of Mo/W−N2, −NNH, and −NNH2 Complexes
DFT calculations (B3LYP/LanL2DZ) of simplified models of [Mo(N(2))(2)(dppe)(2)] and the two protonated derivatives [MoF(NNH)(dppe)(2)] and [MoF(NNH(2))(dppe)(2)](+) (dppe = 1,2-bis(diphenylphosphino)ethane) provide quantitative insight into the reduction and protonation of dinitrogen bound end-on terminally to transition metals. This "asymmetric" reduction pathway is characterized by a stepwise increase of covalency and a concomitant charge donation from the metal center during each protonation reaction. The major part of metal-to-ligand charge transfer occurs after the first protonation leading to coordinated diazenido(-). In contrast, addition of the second proton is accompanied by a mino…
The Reduction Pathway of End-on Coordinated Dinitrogen. I. Vibrational Spectra of Mo/W−N2, −NNH, and −NNH2 Complexes and Quantum Chemistry Assisted Normal Coordinate Analysis
Infrared and Raman spectra of [M(N(2))(2)(dppe)(2)] (M = W, Mo) and the two protonated derivatives [WF(NNH)(dppe)(2)] and [WF(NNH(2))(dppe)(2)](+) (dppe = 1,2-bis(diphenylphosphino)ethane) are presented. Using isotope substituted compounds ((15)N and D) the vibrations of the Y-M-N(2)H(x)() (x = 0, 1, 2; Y = N(2), F) central unit are identified, in particular the M-N and N-N stretching modes. In case of the monoprotonated systems, an equilibrium between metal- and nitrogen-protonated species exists that is clearly detectable in the IR spectra. Making use of theoretical force fields, a quantum chemistry assisted normal coordinate analysis (QCA-NCA) is performed for all three tungsten systems …