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Paramagnetic complexes intermediates

The NMR spectra [27] of [Fe(HB(pz)3)2] exhibit shifted resonances as would be expected for a paramagnetic complex, but the shifts are intermediate between those observed for fully diamagnetic complexes and the comparable resonances in the fully high-spin [Fe(HB(3,5-(CH3)2pz)3)2] complex. In contrast to the increasing chemical shifts, either in the positive or negative direction, that follow the Curie law, observed at lower temperatures for [Fe(HB(3,5-(CH3)2pz)3)2] and [Fe(HB(3,4,5-(CH3)3pz)3)2], the chemical shifts of [Fe(HB(pz)3)2] decrease as the temperature is decreased, as would be expected for an increase in the percentage of the low-spin complex. [Pg.132]

Mononuclear paramagnetic complexes of type IV with rhenium in the oxidation VI have been reported for R = Mes and Xyl. They were prepared either from (Me3NH)Re04 or Me3Si0Re03 and RMgBr in THF at —78°C, followed by oxidation of the isolated rhenium(V) intermediates [Re02R2]2Mg(THF)2... [Pg.311]

An electrophilic metal-carbene complex intermediate has been proposed in the cyclopropanation reaction, whereas a paramagnetic copper nitrene species, which behaves as an electrophilic, nitrogen-centered radical, is proposed as the intermediate for the aziridination reaction.45 [Cu(Tp GF3 2)(C2H4)] is a good aziridination catalyst, readily converting a variety of olefins into the corresponding A-tosyl aziridines.46... [Pg.447]

Consequently, it is clear from the above considerations that the polymerization of quasisymmetric dienes on paramagnetic complexes of transition metals should be accompanied by the struggle between two trends. On the one hand, the existence of the electric field and specific quantum-chemical interactions ( quantum-chemical field) should decrease the symmetry of the intermediate and the validity of the spin exclusion principle. On the other hand, as already mentioned, the intrinsic paramagnetism of the transition metal should increase the validity of the spin exclusion principle. Which of the two trends prevails, is... [Pg.174]

The kinetics of the photoeatalytic reduction of NO by CO to CO2, N2O, and N2 over MoOa/Si02 catalysts at ambient temperature has been studied mass-spectroscopically using C labeled carbon monoxide. The kinetic data obtained for CO-NO mixtures of different compositions fit well the proposed redox mechanism, which suggest a paramagnetic complex (Mo ". ..NO ") as reaction intermediate. The formation of this complex is proven by EPR experiments. [Pg.421]

In our previous publication [6], we have reported for the first time on the photocatalytic reduction of NO by carbon monoxide over a Mo03/Si02 catalyst (2.5 wt % of Mo). The reduction proceeds under UV-irradiation (X < 360 nm) at ambient temperature, N2, N2O, and CO2 being the reaction products. A redox reaction mechanism was proposed in [6] consisting of two st es (a) photoinduced reduction of the initial surface Mo to Mo by CO and b) dark oxidation of Mo by NO to yield N2O and N2 and to restore Mo. Both stages can be accomplished separately or combined in one photocatalytic process. A Mo-nitrosyl paramagnetic complex was suggested to be an intermediate in the photocatalytic NO reduction by CO. [Pg.421]

The objective of this work was a kinetic study of the photocatalytic NO reduction by CO over Mo03/Si02 catalysts with different Mo loadings to get some quantitative estimates of the process combined with EPR measurements aimed to detect the intermediate Mo-nytrosyl paramagnetic complex. [Pg.421]

Reaction (5) results in the formation of an intermediate paramagnetic complex (Mo "...NO ) which arises from a two-electron transfer from Mo " ion to a NO molecule. This complex has been detected by EPR (see below). Reaction (6) is the interaction of the... [Pg.425]

The reaction mechanism of the NO photocatalytic reduction by CO discussed above suggests that N2O is formed via intermediate paramagnetic complexes (Mo. ..NO ) by reactions (5) and (6). [Pg.428]

Nitroso compounds as a reaction intermediate for nitro compound reductions were investigated as substrates for mechanism understanding by Cenini and his colleagues [18]. The isolation of a paramagnetic complex suggested that the first step of the interaction between Pd(0) and the nitroso species is an electron transfer reaction. The palladium carbomethoxy complex from the reaction of a palla-dium(O) complex with PhNO under CO pressure in methanol was also isolated, which fits with the published reaction mechanism [19]. [Pg.169]

Planar-octahedral equilibria. Dissolution of planar Ni compounds in coordinating solvents such as water or pyridine frequently leads to the formation of octahedral complexes by the coordination of 2 solvent molecules. This can, on occasions, lead to solutions in which the Ni has an intermediate value of jie indicating the presence of comparable amounts of planar and octahedral molecules varying with temperature and concentration more commonly the conversion is complete and octahedral solvates can be crystallized out. Well-known examples of this behaviour are provided by the complexes [Ni(L-L)2X2] (L-L = substituted ethylenediamine, X = variety of anions) generally known by the name of their discoverer I. Lifschitz. Some of these Lifschitz salts are yellow, diamagnetic and planar, [Ni(L-L)2]X2, others are blue, paramagnetic, and octahedral, [Ni(L-L)2X2] or... [Pg.1160]

Monomer-oligomer equilibria. [Ni(Me-sal)2], mentioned above as a typical planar complex, is a much studied compound. In pyridine it is converted to the octahedral bispyridine adduct (/zsoo = 3.1 BM), while in chloroform or benzene the value of is intermediate but increases with concentration. This is ascribed to an equilibrium between the diamagnetic monomer and a paramagnetic dimer, which must involve a coordination number of the nickel of at least 5 a similar explanation is acceptable also for the paramagnetism of the solid when heated above 180°C. The trimerization of Ni(acac)2 to attain octahedral coordination has already been referred to but it may also be noted that it is reported to be monomeric and planar in dilute chloroform solutions. [Pg.1160]

These catalytic reactions are distinguished from the homolytic reactions in that no evidence exists for paramagnetic intermediates. The epoxidation is stereospecific, trans- and c/.v-alkenes yielding trans- and o.v-epoxides, respectively. Under the same conditions, complexes of Cu, Mn, and Fe give no yields or... [Pg.80]


See other pages where Paramagnetic complexes intermediates is mentioned: [Pg.165]    [Pg.12]    [Pg.6]    [Pg.381]    [Pg.333]    [Pg.146]    [Pg.1006]    [Pg.5049]    [Pg.376]    [Pg.967]    [Pg.970]    [Pg.126]    [Pg.180]    [Pg.376]    [Pg.249]    [Pg.5048]    [Pg.1006]    [Pg.4460]    [Pg.11]    [Pg.213]    [Pg.394]    [Pg.321]    [Pg.239]    [Pg.135]    [Pg.139]    [Pg.679]    [Pg.426]    [Pg.498]    [Pg.52]    [Pg.55]    [Pg.18]    [Pg.107]    [Pg.115]    [Pg.49]    [Pg.207]    [Pg.490]   
See also in sourсe #XX -- [ Pg.291 , Pg.292 , Pg.293 , Pg.294 , Pg.295 , Pg.296 , Pg.297 , Pg.298 , Pg.299 , Pg.300 , Pg.301 , Pg.302 , Pg.303 ]




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Intermediates paramagnetic

Paramagnetic complexes

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