Hydroamination reviews

Hydroaminomethylahon of alkenes [path (c)j wiU not be considered [12]. This review deals exclusively with the hydroaminahon reaction [path (d)], i.e. the direct addition of the N-H bond of NH3 or amines across unsaturated carbon-carbon bonds. It is devoted to the state of the art for the catalytic hydroamination of alkenes and styrenes but also of alkynes, 1,3-dienes and allenes, with no mention of activated substrates (such as Michael acceptors) for which the hydroamination occurs without catalysts. Similarly, the reachon of the N-H bond of amine derivatives such as carboxamides, tosylamides, ureas, etc. will not be considered. 

Although the hydroamination of Michael systems is beyond the scope of this review, it is interesting to note the high yield (98%, TOE = 2 h ) obtained using the above cationic rhodium complexes for the hydroamination of 2-vinylpyridine with morpholine. Indeed, without catalyst, the hydroamination yield is only 5% [167]. 

K. Tani and Y. Kataoka, begin their discussion with an overview about the synthesis and isolation of such species. Many of them contain Ru, Os, Rh, Ir, Pd, or Pt and complexes with these metals appear also to be the most active catalysts. Their stoichiometric reactions, as well as the progress made in catalytic hydrations, hydroal-coxylations, and hydrocarboxylations of triple bond systems, i.e. nitriles and alkynes, is reviewed. However, as in catalytic hydroaminations the holy grail", the addition of O-H bonds across non-activated C=C double bonds under mild conditions has not been achieved yet. 

Organometallic complexes of the /-elements have been reported that will perform both intra-and intermolecular hydroamination reactions of alkenes and alkynes, although these lie outside of the scope of this review.149-155 Early transition metal catalysts are not very common, although a number of organometallic systems exist.156-158 In these and other cases, the intermediacy of a metal imido complex LnM=NR was proposed.159,160 Such a species has recently been isolated (53) and used as a direct catalyst precursor for N-H addition to alkynes and allenes (Scheme 35).161,162... 

Based on the established mechanism for titanium-catalyzed hydroamination, the authors propose a reversible reaction between a titanium imide complex and the alkyne to form metalloazacyclobutene 86, which in turn undergoes 1,1-insertion of the isonitrile into the Ti-C bond. The generated five-membered ring iminoacyl-amido complex 87 with the new C-C bond is protonated by the primary amine to afford the desired three-component coupling product, with regeneration of the catalytic imidotitanium species. Very recently, titanium-catalyzed carbon-carbon bond-forming reactions have been reviewed.122... 

The use of catalytic SILP materials has been reviewed recently [10] covering Friedel-Crafts reactions [33-37], hydroformylations (Rh-catalyzed) [38], hydrogenation (Rh-catalyzed) [39,40], Heck reactions (Pd-catalyzed) [41], and hydroaminations (Rh-, Pd-, and Zn-catalyzed) [42]. Since then, the SILP concept has been extended to additional catalytic reactions and alternative support materials. In this paper we will present results from continuous, fixed-bed carbonylation and hydroformylation reactions using rhodium-based SILP catalysts as reaction examples demonstrating the advantages of the SILP technology for bulk chemical production. 

For leading reviews on hydroamination, see (a) Brunet, J.J. and Neibecker, D. (2001) Catalytic Heterojunctionalization (eds A. Togni and H. Griitzmacher), Wiley-VCH Verlag GmbH, Weinheim, pp. 91-141 ... 

Summaries of results of hydroamination mediated with Rh(I) amide complexes584 and comprehensive reviews giving detailed information of the field are available.585-587 Therefore, only the more important relatively new findings are presented here. In most of the transformations reported transition metals are applied as catalysts. The feasibility of the use of tcrt-BuOK was demonstrated in the base-catalyzed amination of styrenes with aniline.588... 

The third part of this chapter reviews previously described catalytic asymmetric reactions that can be promoted by chiral lanthanoid complexes. Transformations such as Diels-Alder reactions, Mukaiyama aldol reactions, several types of reductions, Michael addition reactions, hydrosilylations, and hydroaminations proceed under asymmetric catalysis in the presence of chiral lanthanoid complexes. 

Muller, T.E., Hultzsch, K.C., Yus, M., Foubelo, F., and Tada, M. (2008) Hydroamination direct addition of amines to alkenes and alkynes. Chemical Reviews, 108, 3795-3892 and references therein. 

Abstract This review deals with the synthesis and the catalytic application of noncyclopentadienyl complexes of the rare-earth elements. The main topics of the review are amido metal complexes with chelating bidentate ligands, which show the most similarities to cyclopentadienyl ligands. Benzamidinates and guanidinates will be reviewed in a separate contribution within this book. Beside the synthesis of the complexes, the broad potential of these compounds in homogeneous catalysis is demonstrated. Most of the reviewed catalytic transformations are either C-C multiple bond transformation such as the hydroamination and hydrosilylation or polymerization reaction of polar and nonpolar monomers. In this area, butadiene and isoprene, ethylene, as well as lactides and lactones were mostly used as monomers. 

During the last two decades, lanthanide catalysis has been extensively explored [3], considering the unique properties and the absence of toxicity of these "heavy" metals which make them environmentally friendly. Olefin transformations catalysed by organolanthanides such as oligomerisation, hydrogenation, hydrosilylation, hydroamination, polymerisation, have attracted much attention. The two latter reactions can be initiated by hydrides (which act as precatalysts, such as for MMA polymerisation [4]), but do not involve hydrides as intermediates in the catalytic cycle and therefore will not be considered in the present review. 

Intra- and inter-molecular asymmetric hydroamination reactions have been reviewed. ... 

Allyl ligands are reactive groups in catalytic processes, such as allylic substitution (Chapter 20) and transition-metal-catalyzed additions of allyl groups to carbonyl compounds (Chapter 12). They are also intermediates in a variety of catalytic processes involving dienes, including the hydroamination (Chapter 16) and telomerization of dienes (Chapter 22). They are also formed by cleavage of the allylic C-H bonds of olefins to form intermediates in allylic oxidation chemistry and as stable species that inhibit the polymerization of a-olefins (Chapter 22). The synthesis, structure, and occurrence of -rj -allyl complexes have been reviewed. ... 

This section focuses on hydroamination catalyzed by transition metal complexes, but many studies on hydroamination catalyzed by acid, base, - main group metals such as mercury and copper, and heterogeneous catalysts have been reported. Because the elementary steps of the mechanisms of these reactions lie outside the scope of this text, this chapter does not present details of the hydroaminations conducted with these t5q>es of catalysts. This material has been presented in many reviews. - ... 

The scope of hydroamination now includes many types of compounds containing N-H bonds and many types of alkenes and alkynes. Because the scope of these reactions is rapidly changing and many reviews of these processes have been published elsewhere, this section of the chapter provides a broad overview of the scope of these reactions. It then... 

Hydroaminations of alkenes have proven to be more challenging to develop than other hydroamination reactions, although some of the first hydroaminations were additions to alkenes. In 1971 Coulson reported the addition of secondary amines to ethylene catalyzed by RhClj. Additions of amides to ethylene and propylene have been published more recently by Widenhoefer, as shown in Equation 16.57, and the addition of aniline to norbomene was published by Milstein and Casakiuovo. Although the turnover numbers for the addition of aniline to norbomene were low, several important mechanistic findings resulted from this work were presented in Chapter 9 and are reviewed in Section 16.5.3.3. Additions of amines to ethylene, propylene, and norbomene are less complicated than additions to higher olefins because these alkenes cannot undergo isomerization to a less reactive internal olefin. Nevertheless, Brunet has reported additions of arylamines to ethylene and hexene catalyzed by platinum halides with acid additive in anionic liquid (Equation 16.58). ... 

The mechanisms of hydroaminations of olefins and alkynes are varied. Many reviews divide these mechanisms into reactions that "activate" the N-H bond or "activate" the olefin. Because each mechanism must somehow cleave both the N-H bond and the C-C Tr-bond, and the term "activate does not have a precise meaning, these mechanisms are divided in this discussion into three classes depending on the type... 

Alkyne hydroamination has been extensively reviewed [3, 4, 10] and important contributions using late transition metals have been realized to give the Markovnikov-type products most typically. Interestingly, in 2007, Fukumoto reported a tris(pyrazolyl borate)rhodium(l) complex for the anti-Markovnikov hydroamination of terminal aUcynes with both primary and secondary amine substrates, although yields with primary amines are always reduced compared to those with secondary amines (Scheme 15.26). Desirable functional group tolerance is also noteworthy for this regioselective hydroamination catalyst [187]. 

Most importantly, this reaction demands control of regioselectivity and can also be carried out asymmetrically (Scheme 15.38). Thus, branched imine or linear allylamine products can be selectively prepared. Diastereoselective and enantiose-lective allene hydroamination can also be targeted with advances in enantioselective catalysis using late transition metals being reviewed in Section 15.3.7. 

Key contributions in the development of late transition metal catalysts toward alkene hydroamination, which precede the 2008 comprehensive review [10], focus on contributions using group 9 and 10 metals. Preferred substrates for these transformations include aminoalkenes [230] for intramolecular reactivity or the use of activated alkenes such as styrene [93, 109, 113, 245] or alkenes substituted with electron-withdrawing substituents to generate hydroamination products via aza-Michael-type reactions [246-249]. Au has also been applied to the hydrofunctionalization of alkenes, although these reactions have demanded the use of protected amine substrates such as ureas [250], tosylamides [251], and carbamates [252]. 

Catalytic asymmetric hydroamination is a long-standing challenge for which there are no general solutions to date. However, there have been advances toward realizing this objective that point toward its powerful potential in the synthesis of chiral, substituted heterocycles and amine small molecules. This focused topic has been comprehensively reviewed by Hultzsch [280] and is briefly summarized in the... 

Indole is one of the most important heterocyclic scaffolds for drug discovery. Approaches for indole synthesis using hydroamination as a key step in their syntheses has been an ongoing area of investigation over the past several years [329, 330]. Early examples focused on one-pot intermolecular hydrohydrazination followed by the Lewis-acid-catalyzed Fischer indole synthesis [331, 332] (Scheme 15.102) or one-pot intermolecular hydroamination followed by cross-coupling to either form a C-N bond (via the Buchwald-Hartwig amination) [333] (Scheme 15.103) or a C-C bond (via a Heck reaction) [334, 335] (Scheme 15.104). Alternatively, o-alkynylanilines can be used directly as substrates for intramolecular hydroamination (Scheme 15.105) [198, 200, 336-340]. These approaches have been thoroughly reviewed [10]. 

SILP catalysis was introduced by Mehnert, in 2002, for slurry-phase hydrofornrylation and hydrogenation reactions [61, 62]. Shordy later, Riisager et al. published the first successful example of continuous gas-phase SILP catalysis [63]. Recendy, many technically relevant examples of SILP catalysis have been published, including exanples of hydroforntylation [64, 65], hydrogenation [66, 67], enantioselective hydrogenation [68, 69], water-gas shift reaction [70, 71], alkene metathesis [72, 73], hydroamination [74] and carbonylation of methanol [75]. Additionally, valuable information about SILP catalysis has been collected in reviews by Riisager et al. [76, 77], Gu and Li [78], van Doorslaer et al. [79] and Virtanen et al. [80fi... 

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