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-C5Me4H)2Hf(OTf)(N2(CH3)), arising from methylation of one of the nitrogen atoms. This reactivity contrasts with that of the zirconocene congener, [(η5-C5Me4H)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.