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  • Title: Addition of methyl triflate to a hafnocene dinitrogen complex: stepwise n(2) methylation and conversion to a hafnocene hydrazonato compound.
    Author: Knobloch DJ, Benito-Garagorri D, Bernskoetter WH, Keresztes I, Lobkovsky E, Toomey H, Chirik PJ.
    Journal: J Am Chem Soc; 2009 Oct 21; 131(41):14903-12. PubMed ID: 19785422.
    Abstract:
    Treatment of the hafnocene complex bearing a strongly activated, side-on bound dinitrogen ligand, [(eta(5)-C(5)Me(4)H)(2)Hf](2)(mu(2),eta(2),eta(2)-N(2)), with two equivalents of methyl triflate yielded a mixture of products, one of which was identified as the triflato hafnocene methyl diazenide compound, (eta(5)-C(5)Me(4)H)(2)Hf(OTf)(N(2)(CH(3))), arising from methylation of one of the nitrogen atoms. This reactivity contrasts with that of the zirconocene congener, [(eta(5)-C(5)Me(4)H)(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)), where methyl triflate addition yields a variety of products that lack new nitrogen-carbon bonds. The methylated hafnocene product, (eta(5)-C(5)Me(4)H)(2)Hf(OTf)(N(2)(CH(3))) provides a platform for additional transformations for the functionalized dinitrogen core. Treatment with additional methyl triflate results in a second nitrogen-carbon bond formation to yield a rare example of a triflato hafnocene hydrazonato complex. Loss of methane and formation of the hafnocene bis(triflate) accompany the transformation. Isotopic labeling studies and other experiments are consistent with a pathway involving initial methylation of the unsubstituted nitrogen in the methyl diazenido ligand followed by deprotonation by a triflate anion.
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