Zirconocene-dinitrogen

In 1982, a most remarkable reaction was discovered by Bercaw et al. which involved the reductive coupling of the terminal carbonyl ligands of [CpFe(CO)2]2- When 1 equivalent of the permethylated zirconocene dinitrogen complex [(rj-CsMe Zr k (29) was treated with 2 equivalents of [CpFe(CO)2]2 in toluene above -20°C, 3 equivalents of N2 evolved... 

The effect of such a slight change in ligand environment has been previously noted for Cp vs. Cp e.g. strikingly in zirconocene-dinitrogen... 

Knobloch DJ, Toomey HE, Chirik PJ. Carboxylation of an ansa-zirconocene dinitrogen complex regiospecific hydrazine synthesis from N2 and CO2. J Am Chem Soc. 2008 130 4248-4249. 

Semproni SP, Knobloch DJ, Mikmann C, Chirik PJ. Redox-induced N2 hapticity switching in zirconocene dinitrogen complexes. Angem Chem Int Ed. 2013 52 5372—5376. 

Dimethylselenides, bacterial degradation, 12, 610 Dimethylsilyl bridges, in -titanocenes, 4, 619 Dimethylsilylene-bridged -zirconocenes, synthesis, 4, 949 Dimethyl sulfoxide, for water-solubilization, 1, 827 Dinitrogens... 

Bis(i -cyclopentadienyl)titanium or titanocene, (Tj-C5H5)2Ti (1), and bis(i7-cyclopentadienyl)zirconium or zirconocene, (i7-C5H5)2Zr (2), although frequently referred to in the literature, have never actually been isolated as discrete chemical compounds. However, these molecules have been implicated as highly reactive intermediates in a wide variety of chemical reactions with olefins, hydrogen, carbon monoxide, and dinitrogen. In recent years some discrete, well-characterized bis(7j-cyclopenta-dienyl) and bis(Tj-pentamethylcyclopentadienyl) complexes of low-valent titanium and zirconium have been isolated and studied, and it has become possible to understand some of the reasons for the remarkable reactivity of titanocene- and zirconocene-related organometallics toward small unsaturated molecules. 

Dinitrogen complexes of titanocene and zirconocene are excellent sources for generating metallocene species in situ, which are highly active and are readily trapped by organic and inorganic unsaturated compounds. Eq (13) is an example that involves carbonyl coupling in iron-carbonyl to give the metallacyclic compound [118]. 

Exchanging one cyclopentadienyl ligand by the related indenyl fragment resulted in very different reactivity patterns depending on the reaction conditions. For example, exposure of the isolated zirconocene sandwich complexes [(p -C5Me5)(p -C9H5-l-R -3-R )Zr] (where R =Me, Pr, Bu R = Me) to dinitrogen (1 atm) forms the dimeric species 37 with an... 

Scheme 17 (A) Reversible, redox-induced hapticity switch of the dinitrogen ligand in an ansa-zirconocene complex and (B) reevaluation of the dinitrogen complexes formed on reduction [(ri -CsHsljZrfRICI]. ...

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