Organolanthanide complexes amination

The efficiency of the more readily accessible Cp 2Sm and Cp 2Sm(thf)2 complexes was also recognized [128, 129[. Further studies indicate that active catalyst precursors include organolanthanide complexes of the general formula Cp 2Ln-R (Ln = La, Nd, Sm, Yh, Lu) with R = H, T),- C5H5, CH(TMS)2, N(TMS)2 [131[. Generation of the catalytically active species is believed to occur via protonolysis of the Ln-R bond by the amine (Eq. 4.19). 

Intramolecular hydroamination/cyclization, the addition of an N-H bond across an intramolecular carbon-carbon unsaturated bond, offers an efficient, atom economical route to nitrogen-containing heterocyclic molecules (Equation 8.37). Numerous organolanthanide complexes were found to be efficient catalysts for this transformation [124, 125]. The real active intermediates are organolanthanide amides, which are formed by the rapid protonolysis reactions of precatalysts with amine substrates. The proposed catalytic cycle of hydroamination/cyclization of aminoalkenes is presented in Figure 8.37 [124]. 

The organolanthanide-catalyzed alkene hydroamination has been reported. With this approach, amino alkenes (not enamines) can be cyclized to form cyclic amines, and amino alkynes lead to cyclic imine. The use of synthesized C-1 and C-2 symmetric chiral organolanthanide complexes give the amino alcohol with good enantioselectivity. 

Organolanthanide complexes are known to be highly active catalysts for a variety of organic transformations, which can be either intramolecular or intermolecular in character. Successful intramolecular transformations include hydroelementation processes, which is the addition of a H-E (E = N, O, P, Si, S, H) bond across unsaturated C-C bonds, such as hydroamination, hydroalkoxylation, and hydrophosphination. Intermolecular transformations include a series of asymmetric syntheses, the amidation of aldehydes with amines, Tishchenko reaction, addition of amines to nitriles, aUcyne dimerization, and guanylation of terminal aUcynes, amines, and phosphines with carbodiimides. 

The aminoaUene hydroamination/cyclization reactions are highly diastereoselective and can provide concise routes to synthesize some natural products (Scheme 3). Using chiral organolanthanide complexes as catalysts, enantioselec-tive hydroamination/cychzation reactions are achieved, which provide a convenient route for the synthesis of chiral amines from simple, readily available prochiral substrates in a single step. 

A number of (R)- and (,S )-organolanthanide alkyl and amide complexes 1, bearing a homochi-ral substituent R on one cyclopentadienyl ring, were prepared and their catalytic activity in the enantioselective hydroamination-cyclization of 4-pentenylamines 3 was examined 11 113 These complexes are converted to the catalytically active species 2 in the presence of a large excess of the amine. Furthermore, catalyst epimerization (S)-2 to (/ )-2 or vice versa occurs and is complete in the early stages of preparative-scale reactions however, equilibrium homochiralities are frequently high, in some cases >95%. 

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