Addition of methyl triflate to a hafnocene dinitrogen complex: Stepwise N₂ methylation and conversion to a hafnocene hydrazonato compound

Treatment of the hafnocene complex bearing a strongly activated, side-on bound dinitrogen ligand, [(η⁵-C₅Me₄H) ₂Hf]₂(μ₂,η², η²-N₂), with two equivalents of methyl triflate yielded a mixture of products, one of which was identified as the triflato hafnocene methyl diazenide compound, (η⁵-C₅Me ₄H)₂Hf(OTf)(N₂(CH₃)), arising from methylation of one of the nitrogen atoms. This reactivity contrasts with that of the zirconocene congener, [(η⁵-C₅Me ₄H)₂Zr]₂(μ₂,η², η²-N₂), where methyl triflate addition yields a variety of products that lack new nitrogen-carbon bonds. The methylated hafnocene product, (η⁵-C₅Me₄H) ₂Hf(OTf)(N₂(CH₃)) 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.