Organolanthanide-catalyzed imine hydrogenation. Scope, selectivity, mechanistic observations, and unusual byproducts

Yasushi Obora, Tetsuo Ohta, Charlotte L. Stern, Tobin J Marks

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Abstract

In this paper we report the Cp'2LnMe2SiCp''2Ln-catalyzed (Cp' = η5-Me5C5; Cp'' = η5-Me4C5) hydrogenation of acyclic imines to yield the corresponding amines. At 190 psi of H2, the observed turnover frequencies (h-1) (100:1 substrate:catalyst ratio, Cp'2Ln, temperature (°C)) are (1) (N-benzylidene(methyl)amine, Ln = La, 50) 0.03; (Ln = Sm, 90) 1.0; (Ln = Sm + PhSiH3, 90) 2.2; (Ln = Lu, 90) 0.60; (2) (N-benzylideneaniline, Ln = Sm, 90) 0.10; (3) (N-benzylidene(trimethylsilyl)amine, Ln = Sm, 90) 0.40; (4) (N-(α-methylbenzylidene)(methyl)amine, Ln = Sm, 90) 0.20; (5) (N-(α-methylbenzylidene)(benzyl)amine, Ln = Sm, 90) 0.70. The stoichiometric reaction of N-benzylidene(methyl)amine with Cp'2SmCH(SiMe3)2 or (Cp'2SmH)2 yields an orthometalated Cp'2Sm-substrate complex which undergoes either hydrogenolysis/hydrogenation or competing C=N insertion of a second substrate molecule to yield a Cp'2Sm-imine-amido complex with a seven-membered chelate ring. The stoichiometric reaction of 2-methyl-1-pyrroline with Cp'2SmCH(SiMe3)2 or (Cp'2SmH)2 yields a Cp'2Sm-imine-amido complex in which two substrate molecules have been coupled to form a six-membered chelate ring (characterized by X-ray diffraction). The stoichiometric reaction of N-benzylidene(trimethylsilyl)amine with (Cp'2SmH)2 yields a desilylated Cp'2Sm-imine-amido complex with a four-membered Sm(NSiMe3)(CPh)N=CHPh chelate ring (characterized by X-ray diffraction). Additional heating of this product under H2 yields S6-symmetric (Cp'2SmCN)6, which contains an unusual chairlike 18-membered (SmCN)6 ring (characterized by X-ray diffraction).

Original languageEnglish
Pages (from-to)3745-3755
Number of pages11
JournalJournal of the American Chemical Society
Volume119
Issue number16
DOIs
Publication statusPublished - Apr 23 1997

ASJC Scopus subject areas

  • Chemistry(all)

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