Chiral biarylamido/anisole complexes of yttrium in enantioselective aminoalkene hydaroamination/cyclisation

Abstract

A group of chiral, dibasic, biaryl-bridged amido proligands containing peripheral methoxyphenyl (anisole) ligation are developed for the synthesis of new amide complexes of yttrium and lanthanum. A potentially tetradentate bis(amidoanisole) system L¹11 gives, on reaction with [Y{N(SiMe₂H)₂}₃(THF)] a crystallographically-characterised bis complex [YL¹11(HL¹11)] presumably as a result of low steric demand, since a more bulky version L²22 gives the target [L²22Y{N(SiMe₂H)₂}(THF)]. The molecular structure of the latter reveals a similar cis-α structure to our recently reported Schiff-base analogue. Variable-temperature NMR studies are consistent with low rigidity in the molecular structure. A potentially tridentate, amidoanisolyl/amido proligand L³33 gives complexes [L³33M{N(SiMe₂H)₂}(THF)_n] (M = Y, n = 1; M = La, n = 2). Chiral non-racemic versions of the above complexes were tested in the hydroamination/cyclisation of 2,2′-dimethylaminopentane to the corresponding pyrrolidine. Activities were relatively low compared to recently reported examples, and ee values were in the range 20–40% despite the well-expressed chirality of the catalysts.