Titanaaziridines or η(2)-imine titanium complexes are considered key intermediates of the titanium-catalyzed hydroaminoalkylation of alkenes. Herein, we present an efficient synthetic route to this class of compounds, starting from N-methylanilines and a bis(η(5):η(1)-pentafulvene)titanium complex. Consecutive reactions on the η(2)-methyleneaniline complexes, characterized for the first time, prove a high chemical versatility. In particular, hydroaminoalkylation products were found in reactions of the three-membered titanacycles with alkenes. For the first time, all the intermediates of the hydroaminoalkylation of alkenes were isolated and characterized.

Atlas as a Titan(ium) is holding the earth-abundant chemistry world. Titanium is the second most abundant transition metal, is a key player in important industrial processes (e.g. polyethylene) and shows much promise for diverse applications in the future.

The reactions of bis­(η5:η1-pentafulvene)­titanium complexes (1) with 19 different secondary amines (Aa–s) have been investigated. Depending on the substitution pattern of 1 and nature of the amine used, different reaction products are formed. With use of bis­(η5:η1-di­(p-tolyl)­pentafulvene)titanium (1b) and N-methylanilines (Aa,b), N-methylbenzylamines (Ac,d), N-methylcyclohexylamine (Ae), and dibenzylamine (Af), titanium monoamides of the type (η5-C5H4CH­(p-tolyl)2)­(η5:η1-C5H4C­(p-tolyl)2TiNR2 (2a–f) have been isolated in high yields and characterized, including by single-crystal X-ray diffraction. By the reactions of bis­(η5:η1-adamantylidene)­titanium (1a) and Af, diethylamine (Ag), and 2-methylpiperidine (Ah) similar monoamides 3f–h are formed. The formation of titanium bis-amides employing different types of secondary amines (Aa–s) is not observed. The formation of titanaaziridines is observed exclusively by using 1a and N-methylanilines (Aa,b), N-benzylphenylamine (Ai), and N-benzyltrimethylsilylamines (Aj,k). The titanaaziridine 4i undergoes a regioselective ring enlargement reaction with 1-hexyne. By the reaction of 4i and phenylacetylene a ring opening with formation of (CpAd)2Ti­(NPh­(CH2Ph)­CCPh) (6) is observed. The acetylide 6 undergoes a thermal decomposition to give the zigzag butadiyne complex 7. In addition to the ring enlargement of 4j by ketones a ketone insertion in the titanium–Cp bond is found, as proved for 8 by single-crystal X-ray diffraction.

No abstract

Hydroaminoalkylation describes the atom-economical catalytic synthesis of amines by forming new Csp3 –Csp3 bonds using readily available amine and alkene feedstocks. Herein, we describe an earth-abundant and cost-efficient titanium catalyst generated in situ using commercially available Ti­(NMe2)4 and a simple to synthesize urea proligand. This system demonstrates high TOFs for hydroaminoalkylation with unactivated substrates and features easy to use commercially available titanium amido precursors. Additionally, a high catalytic activity, scope of reactivity, and regioselectivity are all demonstrated in the transformation of unactivated terminal olefins with various alkyl and aryl secondary amines. Finally, syntheses of useful amine-containing monomers suitable for the generation of amine-containing materials, as well as amine-containing building blocks for medicinal chemistry, are disclosed. These preparative methods avoid the necessity of glovebox techniques and are modified to be useful to all synthetic chemists.