Phosphines dinitrogen

IR spectra, 712 magnetic properties, 710 synthesis, 709 quinones, 716 tertiary phosphines dinitrogen, 713 tris bipyridyl)... 

Chromium(I) complexes, 702 alkyl isocyanides, 704-709 aryl isocyanides, 704-709 2,2 -bipyridyl, 709 electrochemistry, 713 electronic spectra, 712 ESR spectra, 712 IR spectra, 712 magnetic properties, 710 synthesis, 709 cyanides, 703 fluorophosphine, 716 isocyanides crystallography, 708 electrochemistry, 709 spectroscopy, 708 synthesis, 707 1,10-phenanthroline, 709 electrochemistry, 713 electronic spectra, 712 ESR spectra, 712 IR spectra, 712 magnetic properties, 710 synthesis, 709 tertiary phosphines dinitrogen, 713 tris(bipyridyl)... 

Electrochemical oxidation of closed - shell, teitiary phosphine dinitrogen complexes of molybdenum and tungsten give successively 17- and 16 - electron species. The stability of the electron - deficient species is determined by the rate of loss of dinitrogen removal of electrons... 

Molybdenum(0) also forms a variety of dinitrogen complexes (41), especially when there are phosphine ligands in the molybdenum coordination sphere (see Fig. 7c). This type of complex has been extensively studied because the coordinated dinitrogen is reduced to ammonia upon acidification. 

Osmium(II) forms no hexaaquo complex and [Os(NH3)g] +, which may possibly be present in potassium/liquid NH3 solutions, is also unstable. [Os(NH3)5N2] and other dinitrogen complexes are known but only ligands with good 7r-acceptor properties, such as CN, bipy, phen, phosphines and arsines, really stabilize Os , and these form complexes similar to their Ru analogues. 

C. By Oxidation.—This year s literature has been notable for attempts to study the details of certain phosphine oxidation reactions. In one such investigation nitric acid was found to oxidize phosphines, or phosphine sulphides, to phosphine oxides with inversion of configuration at phosphorus, whereas dinitrogen tetroxide, in the absence of acid, was found to oxidize the same compounds with predominant retention. The partial racemization observed with the latter reagent was probably due to the racemization of the oxides, since methylphenyl-n-propylphosphine oxide... 

Pure phosphine is rendered pyrophoric by traces of dinitrogen trioxide, nitrous acid, or similar oxidant. 

The conversion of molecular nitrogen to ammonia constitutes a potentially useful energy-storage reaction utilizing abundant raw material. The interaction of molecular dinitrogen with metal centers has been studied in considerable depth. It has been shown that N2 can be bound and reduced to NH3 at Mo, W, V, or Fe centers, particularly where these metals are in a low oxidation state and have a tertiary phosphine environment.312... 

Active catalysts for dinitrogen activation have been prepared by reduction at a mercury pool of M0CI5 in basic methanolic solutions containing MgCl2, phospholipids, and various tertiary phosphines.319 The turnover number reached several hundreds per Mo center. Both ammonia and hydrazine were formed in a ratio of about 1 10. 

IV. Molybdenum Dinitrogen Complexes with Polydentate Phosphine... 

The alternative mechanistic scenario for the protonation and reduction of end-on terminally coordinated N2 through the Schrock cycle is represented by the Chatt cycle which has been developed many years earlier (5). This system is based on Mo(0) and W(0) dinitrogen complexes with phosphine coligands (Fig. 3). As expected, the intermediates of the dinitrogen reduction scheme are very similar to those of the Schrock cycle. Moreover, a cyclic generation of NH3 from N2 has been demonstrated on the basis of this system, however, with very small yields (3,4a). In order to obtain general insight into the mechanism of the Chatt cycle we have studied most of the intermediates of Fig. 3 with... 

DFT calculations were performed on Mo dinitrogen, hydra-zido(2-) and hydrazidium complexes. The calculations are based on available X-ray crystal structures, simplifying the phosphine ligands by PH3 groups. Vibrational spectroscopic data were then evaluated with a quantum chemistry-assisted normal coordinate analysis (QCA-NCA) which involves calculation of the / matrix by DFT and subsequent fitting of important force constants to match selected experimentally observed frequencies, in particular v(NN), v(MN), and 8(MNN) (M = Mo, W). Furthermore time-dependent (TD-) DFT was employed to calculate electronic transitions, which were then compared to experimental UVATs absorption spectra (16). As a result, a close check of the quality of the quantum chemical calculations was obtained. This allowed us to employ these calculations as well as to understand the chemical reactivity of the intermediates of N2 fixation (cf. Section III). 

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