Bulk Gold-Catalyzed Reactions of Diazoalkanes with Amines and O 2 to Give Enamines
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Bulk Gold-Catalyzed Reactions of Diazoalkanes with Amines and O2 to Give Enamines Yibo Zhou • Robert J. Angelici • L. Keith Woo
Received: 2 February 2010 / Accepted: 19 March 2010 / Published online: 20 April 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Bulk gold powder, consisting of approximately 5–50 lm particles, catalyzes reactions of diazoalkanes E(H)C=N2, where E is CO2Et or PhC(O), with amines R1R2NH and O2 to give enamine products (R1R2N) (E)C=CH(E) in 58–94% yield. The reactions are proposed to occur by initial formation of surface-bound (E)(H)C: carbene groups that are attacked by nucleophilic amines. The enamine products are very different than those obtained in reactions catalyzed by homogeneous transition metal complexes. These reactions of diazoalkanes, amines, and O2 represent a new type of bulk gold-catalyzed reaction. Keywords Oxidation
Gold Catalysis Amines Enamines
hydrocarbon and alcohol oxidation [1–8]. On the other hand, bulk gold metal is well-known for its poor catalytic properties [1]. However, we have shown in previous studies that bulk gold powder with particle sizes of *1,000 nm is capable of catalyzing reactions of isocyanides (C:N–R) with amines and O2 to produce carbodiimides (in the case of primary amines) [9] or ureas (in the case of secondary amines) [10], and reactions of carbon monoxide CO with primary amines and O2 to give ureas [11]. Bulk gold powder also catalyzes the oxidation (O2) of CO to CO2 under alkaline conditions [12]. We have also shown that primary and secondary amines with O2 give imines (Eq. 1) using gold powder [13] and Au/Al2O3 (with C50 nm Au particles) [14] R1
N H
R 2 + ½ O2
Au
R1
N
R 2 + "H2 O"
(1)
1 Introduction Nano-sized gold particles (\5 nm) supported on metal oxides catalyze a variety of reactions including CO,
Electronic supplementary material The online version of this article (doi:10.1007/s10562-010-0339-7) contains supplementary material, which is available to authorized users. Y. Zhou R. J. Angelici (&) L. Keith Woo Ames Laboratory and Department of Chemistry, Iowa State University, Ames, IA 50011-3111, USA e-mail: [email protected] Y. Zhou e-mail: [email protected] L. Keith Woo e-mail: [email protected]
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as catalysts. Recently, others have shown that these oxidative dehydrogenation reactions of amines are catalyzed by the nanogold catalysts Au/TiO2, Au/C and Au/CeO2 [15–17]. Many of our studies of bulk goldcatalyzed reactions were inspired by known reactivities of ligands (e.g., CO and C:N–R) in transition metal complexes [18]. In one recent investigation, we used known reactions of diazoalkanes (R2C=N2) [19–24] with transition metal complexes that give carbene complexes (M = CR2) to generate carbene groups (:CR2) on gold powder surfaces. Chemical evidence for these carbenes was the observation that gold powder catalyzes the coupling of two carbene groups in the reaction: 2 R2C=N2 ? R2C=CR2 ? 2 N2 [25]. For the specific case of ethyl diazoacetate (EDA), the reaction (Eq. 2) gives both cis and trans ole
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