Addition of Methyl Triflate to a Hafnocene Dinitrogen Complex: Stepwise N₂ Methylation and Conversion to a Hafnocene Hydrazonato Compound

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.

Recent developments in the homogeneous reduction of dinitrogen by molybdenum and iron

“…In early transition metal chemistry, stoichiometric N 2 functionalisation now includes a range of N-C bond formation reactions, particularly through discoveries by Fryzuk 49 and Chirik. 50,51,52,53,54,55,56 Thus, a current challenge is to make these N-C bond forming reactions catalytic, possibly by using middle (Mo) and late (Fe) transition metals like those described above. Because these reactions can construct value-added chemical compounds, there is significantly more promise for commercialization for fine chemicals than for ammonia synthesis.…”

1,2,3,4‐Tetrasubstituted Cyclopentadienes and Their Applications for Metallocenes: Efficient Synthesis through Zirconocene‐ and CuCl‐Mediated Intermolecular Coupling of Two Alkynes and One Diiodomethane

“…The structure was determined by single‐crystal X‐ray structural analysis (Figure 2). The Me‐Zr‐Me angle is 93.2(2)° and the MeZr bond length is 2.243(2) Å, values that are similar to those of dimethylzirconocenes 18…”

“…[17] Substituted dimethylzirconocene complexes [Cp' 2 ZrMe 2 ] have been proved to be useful as catalysts for olefin polymerization. [18,19] The zirconocene dichlorides 9 were further applied for the synthesis of the corresponding dimethylzirconocenes. As illustrated in Scheme 7, treatment of the zirconocene dichloride 9 b with two equivalents of MeLi generated the dimethylzirconocene complex 10 as a white solid in 91 % yield after isolation.…”

“…The Me-Zr-Me angle is 93.2(2)8 and the Me À Zr bond length is 2.243 (2) , values that are similar to those of dimethylzirconocenes. [18] It is known that dialkyl zirconocene complexes with b-hydrogen atoms, such as [Cp 2 ZrBu 2 ] and [Cp 2 ZrEt 2 ], are not stable. b-Hydride abstraction and reductive elimination readily take place to generate low-valent Cp 2 Zr II species, [20] which have been demonstrated to undergo an oxidative cyclization process with alkynes to afford zirconacyclopentadienes, such as the above-mentioned zirconacyclopentadienes 1, 4, and 6.…”

“…Substituted dimethylzirconocene complexes [Cp′ 2 ZrMe 2 ] have been proved to be useful as catalysts for olefin polymerization 18. 19 The zirconocene dichlorides 9 were further applied for the synthesis of the corresponding dimethylzirconocenes.…”