Cationic group 4 metal hydroamination

Tire first chiral group 4 metal catalyst system for asymmetric hydroamination/ cyclization of aminoalkenes was based on the cationic aminophenolate complex (S) 45 [85[. Secondary aminoalkenes reacted readily to yield hydroamination products with enantioselectivities of up to 82% ee (Scheme 11.14). For catalyst solubility reasons, reactions were commonly performed at 100 °G in bromobenzene using... 

Transition metal-benzyl complexes also react readily with nucleophiles, but the origin of this enhanced reactivity results from effects other than the typical rapid rate of nucleophilic attack at an electrophilic benzyUc carbon. As shown in Equation 11.17, benzyl groups can be bound in an fashion, much like an aUyl group. As presented later in this chapter, cationic iq -allyl complexes react with a variety of nucleophiles. iq -Benzyl groups are common in the chemistry of palladium(II), - and these ti -benzyl and phen-ethyl complexes react with a variety of nucleophiles. For example, these complexes react with malonate anions, and they have been shown to react with amines " during some recently developed hydroamination processes. These reactions occur with predominant inversion of configuration. ... 

Neutral group 4 metal complexes appear to possess a relatively broad scope for catalytic hydroaminations. They have been employed for the intramolecular hydroamination of alkynes [2], allenes [3], and alkenes [4] as well as the inter-molecular hydroaminations of alkynes [5] and allenes [6]. Primary aryl- and alkylamines readily react, but secondary amines have posed a greater challenge for this type of transformation with neutral catalysts [7]. For the reactions of the latter, cationic Zr and Ti complexes have been employed in intramolecular cyclizations of aminoalkenes [8]. Very recent work suggests that substrates that are difficult to hydroaminate may favor hydroaminoalkylations instead (Scheme 13.2) [9]. 

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