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

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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.

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