Divalent dinitrogen activation

The non-classical divalent lanthanide complexes have stronger reducing power than divalent samarium complexes because of their higher reduction potentials. Dinitrogen is not an inert atmosphere for these non-classical divalent lanthanide complexes. Therefore, attempts to prepare non-classical divalent organolanthanide complexes by metathesis reactions in dinitrogen atmosphere have been unsuccessful, and the dinitrogen-activated products were isolated. A typical example is shown in Equation 8.36 [112]. 

So far, studies on the reactivity of the divalent complexes mentioned above in Section 2.3 have been very limited. Dinitrogen activation has been observed not only for isolated divalent complexes but also for systems containing divalent species or trivalent rare earths in the presence of reducing agents, thus displaying divalent-like behaviour this important topic will be developed later in Section 2.3.4. 

It appears that dinitrogen activation is also possible with systems involving divalent ions and non-cyclopentadienyl ligands. Thus, the reaction of Tml2 or with KN(SiMe3)2 in TFIE at low temperature afforded... 

This review covers all organometallic complexes of Sc, Y and the lanthanides reported in the year 2000 and their reactions. Endohedral fullerene complexes of the lanthanides have, as usual, been excluded. Highlights this year include striking reports of lanthanides in non-classical oxidation states (Sections 3.2 and 5), a remarkable reversible dinitrogen activation described in Section 3.9.2 and evidence for the existence of the divalent hydrides LnH2(THF)2 (Ln = Sm, Yb) (Section 3.10). In addition Evans has assessed the utility of electrospray mass spectrometry for the characterization of organolathanides. The results are promising and the spectra and dissociation patterns show sensitivity to the metal and its oxidation state. ... 

New important information about the structure of the intermediate complex was obtained from the X-ray studies of V complex with di-ferf-butylcatecholate [18]. The complex, the structure of which is presented in Figure 4, contains four vanadium ions two are divalent and two trivalent, but they are indistinguishable, thus their oxidation state is 2.5 and the complex can be regarded as existing in a semi-reduced state, similar to the s-r state of FeMoco in the presence of dithionite, which is not sufficiently reduced to activate dinitrogen. 

The low-valent molecular chemistry of rare earths was once thought to be restricted to divalent samarium, europium and ytterbium. This chemistry has now been extended to many of the rare earths in the zero-valent state, to mono- and divalent scandium, to divalent lanthanum, cerium, neodymium, dysprosium and thulium, and to systems in which dinitrogen is activated and that may contain yet other highly reactive divalent rare earths. It is the opinion of the author that this research area is likely to find fascinating developments in the near future. 

Jaroschik F, Momin A, Nief P, Le GofFX-P, Deacon GB, Junk PC. Dinitrogen reduction and C-H activation by the divalent organoneodymium complex [(C5H2tBu3)2Nd (p-I)K([18]crown-6)]. Angew Chem Int Ed. 2009 48 1117-1121. 

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