1.3- Butadiene hydroamination

Butadiene and isoprene give rise to mixtures of what are usually called telom-ers, namely 1 1 telomers between the amine and the 1,3-diene (trae hydroamination products), 1 2 telomers and even higher homologs together with oligomers of the diene as exemplified in Eq. (4.41). 

In fact, catalytic systems which effect solely the hydroamination of 1,3-butadiene and isoprene are rare and usually specific to the diene and to the amine. Thus morpholine adds to 1,3-butadiene in the presence of RhCf.lHjO to give a mixture of 1,2-(Markoviiikov) and 1,4-hydroamination products in good overall yield (Eq. 4.42) [171,172). 

The same catalytic system has been tested for the hydroamination of 1,3-butadiene with cyclic amines from the three-membered ring aziridine to the seven-mem-bered ring perhydroazepine. Although arizidine does not lead to a hydroamination reaction, all other cyclic amines give rise to a mixture of 1 1 telomers in fair to excellent yields (e.g., Eq. 4.47) [181]. 

The first examples of hydroamination of 1,3-dienes catalyzed by alkali metals appeared as early as in 1928 for the production of pest destroying agents [197]. For example, reacting NH3 with 1,3-butadiene in the presence of sodium for more than 10 days yields 45% tri(butenyl)amine and 55% of high boiling bases rich in carbon (Eq. 4.52). 

In fact, the stereochemistry of the hydroamination seems to depend strongly on the experimental conditions. For example, for the condensation of Et2NH with 1,3-butadiene, either cis-l-diethylamino-2-butene (n-BuLi, CgHs-EtjO) [204, 205], or trans-l-diethylamino-2-butene (sec-BuLi, THF) [155] can be obtained in ca. 98% yield stereoselectivity. In some cases, telomerization products are also formed [205]. 

Steric effects play a role in determining product distribution since substitution of 1,3-butadiene markedly increases selectivity of hydroamination.308... 

Palladium-catalyzed 1,4-hydroamination of conjugated dienes is usually accompanied by large amounts of 2 1 telomerization product [21,22]. It was shown that the use of an amine hydrochloride as a cocatalyst increased the selectivity for the 1,4-hydroamination product [23]. Thus, 1,3-butadiene and 2-3-dimethylbuta-1,3-diene gave a fair yield in the palladium-catalyzed 1,4-amination shown in [Eq.(5)]. 

Similar catalytic activity for the hydroamination with amines could be realized under low pressures (<10 MPa) by the use of metal amide catalysts preformed before the alkylation step. The metal amide can be prepared in situ by reacting the metal, e. g., sodium, with the amine in the presence of 1,3-butadiene, whereby the sodium amide is produced and the diene hydrogenated to 2-butene. 

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. 

No dimerization of substituted or cyclic dienes occurs by using Pd-PPh3 as a catalyst under usual conditions, instead the 1 1 adducts are formed. For example, dimerization of isoprene using Pd-PPh3 is slow. 1,2-Hydroamination of 1-phenyl-butadiene with aniline proceeded to afford the amine 15, and two products 16 and 17 were obtained from isoprene when an exotic Pd complex 18 was used as a catalyst [6]. 

More recently, the hydroamination of butadiene, isoprene, and cyclohexadiene to form 1 1 adducts with high selectivity catalyzed by nickel and palladium complexes has... 

Reduced nickel salts in the presence of a large amount of phosphine catalyze the hydroamination of 1,3-butadiene with EtjNH (Eq. 4.44) [175, 176]. 

Dzhemilev and Tolstikov et al. have studied the influence of phosphines and additives in the hydroamination of 1,3-butadiene with morpholine catalyzed by the Ni(acac)2/phosphine/AlEt3/ additive (1/3/3/10) system [180]. With CF3CO2H as additive, the reaction is highly selective (>93%) for the formation of l-(N-morpholino)-2-butene (>80% yield) by using P(w-Bu)3 or P(OEt)s as phosphine. With the same system and PCI3 as phosphine, a mixture of 3-(N-morpholino)-l-butene (70%) and l-(N-morpholino)-2-butene (30%) is formed (TOE = 21 h ). 

While the intermolecular hydroamination of butadiene derivatives with group 4 metal catalysts has not yet been reported, an interesting 1,2-addition of diethyl-amine to the Buckminsterfullerene Ceo, which can indeed be seen as a conjugated polyene, was described (26) [177]. 

---