Group-4 Dipyrrolylmethane Complexes in Intramolecular Olefin Hydroamination

Abstract

Titanium and zirconium complexes bearing the 5,5-dimethyldipyrrolylmethane (dpm) ancillary ligand were tested for their activity in intramolecular hydroamination of olefins. The titanium precatalyst Ti(NMe2)2(dpm), despite being an excellent catalyst for intermolecular alkyne hydroamination, was a relatively poor catalyst for intramolecular olefin hydroamination. The zirconium derivative was significantly more active. With a secondary amine, [Zr(NMe2)2(dpm)]2 did catalyze the hydroamination reaction, albeit slowly. Consequently, the mechanism of the reaction with zirconium may use a 1,2-insertion into a Zr−N amido bond as the key mechanistic step, or the complex may be able to access both the [2 + 2]-cycloaddition and 1,2-insertion mechanisms. The zirconium precatalyst was structurally characterized by X-ray diffraction and is a dimer in the solid state, but solution molecular weight determination gave results closer to the monomer in benzene.

Iridium-Catalyzed, Intermolecular Hydroetherification of Unactivated Aliphatic Alkenes with Phenols

“…In addition, Majumder and Odom reported the intramolecular hydroamination of primary aminoalkenes catalyzed by titanium and zirconium dipyrrolylmethane complexes. [65] Based on the competitive formation of products from hydroamination and oxidative amination, these reactions likely occur by insertion of an alkene into an M À N bond.…”

Transition‐Metal‐Catalyzed Hydroamination Reactions

“…Many group 4 complexes, including simple and commercially available Ti(NMe 2 ) 4 [44] and Zr(NMe 2 ) 4 [45], can mediate intramolecular alkene hydroamination of preferred substrates, such as the one shown in Scheme 15.6. The benchmark reaction temperatures and reaction times of 110 • C and 24 h, respectively, are preferred reaction conditions with a broad range of catalysts, as previously reviewed [10].…”

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

“…36 Furthermore, an interesting dipyrrolylmethane zirconium compound cyclizes both primary and secondary aminoalkenes. 37 Likewise, isolation of the organometallic metal−alkylamine product from olefin insertion has not yet been described for a d 0 or f n d 0 metal amido compound. However, the zirconium vinylamine product of alkyne insertion into a zirconium− nitrogen bond was recently isolated and characterized.…”