Neutral Group‐IV Metal Catalysts for the Intramolecular Hydroamination of Alkenes

Abstract

A detailed comparison of the group-IV metal catalysts Ti(NMe 2 ) 4 , Ind 2 TiMe 2 , Ind 2 ZrMe 2 and Ind 2 HfMe 2 in the intramolecular hydroamination of amino alkenes is presented. Among these catalysts, the benchmark catalyst Ti(NMe 2 ) 4 is the most active in the formation of pyrrolidines. A comparison between Ind 2 TiMe 2 , Ind 2 ZrMe 2 and Ind 2 HfMe 2 suggests that in the synthesis of pyrrolidines, Zr complexes show the highest catalytic activity of the group-IV metal catalysts. Although Ind 2 TiMe 2 -and the Ind 2 ZrMe 2 -catalyzed formation of a pyrrolidine is first-order in the concentration of the substrate, the corresponding Ti(NMe 2 ) 4 -catalyzed cyclization is second-order in the concentration of the substrate. The results obtained for the formation of piperidines catalyzed by Ti(NMe 2 ) 4 , Ind 2 TiMe 2 , Ind 2 ZrMe 2 and Ind 2 HfMe 2 suggest that for these reactions, Ti catalysts show increased catalytic activity compared with the corresponding Zr catalysts. Unfor-

Der Mechanismus der titankatalysierten Hydroaminoalkylierung von Alkenen

“…Als Katalysatoren für Hydroaminoalkylierungen von Alkenen kamen bislang Ta-, [4][5][6][7] Ti- [8] und Zr-Katalysatoren [6b, 9] zum Einsatz, wobei zum Mechanismus der Reaktion bislang nur Vorschläge [4b, 5, 6, 8, 9] und keine genauen Informationen verfügbar sind. Da es für weitere Optimierungen der bisher entwickelten Verfahren unserer Meinung nach jedoch unerlässlich ist, den Reaktionsmechanismus im Detail zu verstehen, haben wir uns entschlossen, die in Schema 2 gezeigte intramolekulare Hydroaminoalkylierung der Aminoalkene 1-H und 1-D kinetisch genau zu studieren, um so erstmals wichtige mechanistische Details der neuen Reaktion offenzulegen.…”

[Ind2TiMe2]: ein Katalysator für die Hydroaminomethylierung von Alkenen und Styrolen

“…[8] Eine mögliche Erklärung hierfür könnten die bislang für Hydroaminoalkylierungen normalerweise erforderlichen drastischen Reaktionsbedingungen mit Temperaturen von meist 130-165 8C [9] sein, bei denen Styrole zur Polymerisation neigen. [10] In ersten Versuchen führten wir intermolekulare Hydroaminoalkylierungen von 1-Octen (2) > 99:1 …”

Highly flexible synthesis of indenylethylamines as ligand precursors for titanium complexes

“…Alkene 9 (17.10 g, 120.3 mmol) was added dropwise and the resulting mixture was stirred at 25 °C for two hours to give a clear solution which was then treated with 3 N NaOH (125 mL) and a solution of sodium borohydride (2.28 g, 60.1 mmol) in 3 N NaOH (125 mL). After this mixture had been stirred for an additional hour, the resulting aqueous solution was decanted from precipitated mercury, saturated with sodium chloride and extracted with 2 Cl 2 (80 mL) was added in portions over a period of five minutes via syringe to form a white suspension which was stirred for 15 minutes. Then triethylamine (40.35 g, 398.7 mmol) was added and the mixture was stirred for additional five minutes at −78 °C.…”