Yttrium hydroamination

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

In 2003, Livinghouse et al. also reported that chelating bis(thiophosphonic amidates) complexes of lanthanide metals, such as yttrium or neodymium, were able to catalyse intramolecular alkene hydroaminations. These complexes were prepared by attachment of the appropriate ligands to the metals by direct metalation with Ln[N(TMS)2]3- When applied to the cyclisation of 2-amino-5-hexene, these catalysts led to the formation of the corresponding pyrrolidine as a mixture of two diastereomers in almost quantitative yields and diastereos-electivities of up to 88% de (Scheme 10.81). 

An yttrium(III) complex derived from ligand (100) has been shown to be a superior catalyst for enantioselective intramolecular hydroaminations of alkenes that provide cyclic amines with enantioselectivities ranging from 69 to 89% ee,132... 

Another interesting aspect is the metal size effect. In general, increasing ionic radii correlate with enhanced catalytic activity in hydroamination/cyclization of aminoalkenes [27,103,114], However, a different tiend is observed for phosphinoalkenes. Here, the mid-sized yttrium shows the highest reactivity, followed by lutetium and samarium, while the largest rare-earth metal, lanthanum, is the least active catalyst system [179],... 

To understand the function of the ionic ate complexes in the catalytic hydroamination reactions, the neutral yttrium chloro complex 212 containing diamide ligand L44 was prepared by the reaction of YCI3 with 1 equiv of Li2L44 to compare with the ate complexes. The neutral yttrium amido complex 213 was obtained from reacting 212 with LiNlPr2 in THF (Scheme 78). 

Scheme 11.10 Catalytic hydroamination/cyclization of aminoalkenes using chiral amino thiophenolate yttrium complexes [61].

Cationic organometallic complexes of scandium, yttrium, and the lantha-noids in synthesis of heterocycles using Diels-Alder reactions and intramolecular hydroamination 06CRV2404. 

These intramolecular hydroaminations lead to the formation of chiral products. Thus, several studies have been devoted to developing ligands for enantioselective, intramolecular hydroaminations of olefins catalyzed by lanthanide complexes. ° Selectivities of these reactions with chiral cyclopentadienyl derivatives have been modest. Selectivities have been higher with catalysts containing non-cyclopentadienyl ligands. Some of tlie most selective catalysts are the yttrium complexes of the bis(thiolate) ligands reported by Livinghouse, the scandium and lutetium complexes of 33 -disubstituted binaphtholates reported by Hultzsch, and the BINAM-based bisamidates of Schafer.- A representative cyclization catalyzed by a member of each of these classes of catalyst are shown in Equation 16.64. 

Although this chapter is formally not covering recent achievements in rare earth chemistry, it must be mentioned that the first examples of asymmetric intermolecular alkene hydroamination have been reported by Hultzsch and coworkers (Scheme 15.13) [85]. Using a bulky binaphtholate yttrium complex at high temperatures with excess alkene substrate, the first examples of this challenging and highly sought after reaction have been realized with unactivated alkenes. 

Chiral binaphtholate yttrium aryl complexes were highly active and enantiose-lective catalysts for asymmetric hydroamination of aminoalkenes as well as kinetic... 

Kim JY, Livinghouse T. Enantioselective intramolecular alkene hydroaminations catalyzed by yttrium complexes of axially chiral bis(thiolate) ligands. Org. Lett. 2005 7(9) 1737-1739. 

Yttrium Computational analysis (DFT) of the competing pathways for C=C bond activation in the intramolecular hydroamination of aminoalkenes, catalysed... 

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