© 2014 American Chemical Society. Dichloromethane solutions of complex 1 catalyze both the aza-Diels-Alder (ADA) reaction of aldimines with cyclopentadiene and the aza-Friedel-Crafts (AFC) reaction between aldimines and indoles. Racemic adducts were obtained in both cases. NMR measurements of mixtures of the aldimine N-(4-methylbenzylidene)aniline (I) and 1, in a 20/1 molar ratio, reveal the formation of the deprotonated compound 2 and the corresponding iminium cation HI+ (H-N+). This cation is responsible for the achiral catalysis. Below 273 K, in 1/1 molar ratio mixtures of 1 and I, the chiral species 1·I (O-H···N) and 2·HI+ (O-···H-N+) were formed by intermolecular hydrogen bonding and proton transfer, respectively. The latter solutions catalyze stoichiometrically the ADA reaction between aldimine I and HCp with 16% ee. With 5 mol % of catalyst loading, a 6% ee can be obtained if the aldimine is slowly added to the solution (20 equiv in 60 h). Above 273 K, solutions containing 1 and aldimine I irreversibly evolve to the aniline complex 3, which was isolated as a racemic mixture. The molecular structure of 3 has been determined by X-ray diffractometric methods. Hydride 5, an intermediate in this reaction, has been isolated and spectroscopically characterized. On the basis of synthetic and spectroscopic studies, a plausible pathway for the formation of 3 from 1 is proposed.

We thank the Ministerio de Economía y Competitividad of Spain (CTQ2012-32095) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. This work was supported by the CONSOLIDER INGENIO 2010 program under the project “Factoría de Crystalización” (CSD2006-0015). R.R. and P.P. acknowledge the CSIC and European Social Fund for JAE grants. The authors acknowledge financial support from the Scientific Policy Vice Chancellor of Zaragoza University for X-ray measurements.

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