A Highly Active Palladium Catalyst for Intermolecular Hydroamination. Factors that Control Reactivity and Additions of Functionalized Anilines to Dienes and Vinylarenes

Abstract

We report a catalyst for intermolecular hydroamination of vinylarenes that is substantially more active for this process than catalysts published previously. With this more reactive catalyst, we demonstrate that additions of amines to vinylarenes and dienes occur in the presence of potentially reactive functional groups, such as ketones with enolizable hydrogens, free alcohols, free carboxylic acids, free amides, nitriles, and esters. The catalyst for these reactions is generated from [Pd(eta(3)-allyl)Cl](2) (with or without added AgOTf) or [Pd(CH(3)CN)(4)](BF(4))(2) and Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene), which generates complexes with large P-Pd-P bite angles. Studies on the rate of the C-N bond-forming step that occurs by attack of amine on an eta(3)-phenethyl and an eta(3)-allyl complex were conducted to determine the effect of the bite angle on the rate of this nucleophilic attack. Studies on model eta(3)-benzyl complexes containing various bisphosphines showed that the nucleophilic attack was faster for complexes containing larger P-Pd-P bite angles. Studies of substituted unsymmetrical and unsubstituted symmetrical model eta(3)-allyl complexes showed that nucleophilic attack on complexes ligated by Xantphos was faster than on complexes bearing ligands with smaller bite angles and that nucleophilic attack on unsymmetrical allyl complexes with larger bite angle ligands was faster than on unsymmetrical allyl complexes with smaller bite angle ligands. However, monitoring of catalytic reactions of dienes by (31)P NMR spectroscopy showed that the concentration of active catalyst was the major factor that controlled rates for reactions of symmetrical dienes catalyzed by complexes of phosphines with smaller bite angles. The identity of the counterion also affected the rate of attack: reactions of allylpalladium complexes with chloride counterion occurred faster than reactions of allylpalladium complexes with triflate or tetrafluoroborate counterion. As is often observed, the dynamics of the allyl and benzyl complexes also depended on the identity of the counterion.

Primary tert‐ and sec‐Allylamines via Palladium‐Catalyzed Hydroamination and Allylic Substitution with Hydrazine and Hydroxylamine Derivatives

“…This regioselectivity contrasts that obtained from reactions of arylamines, even with the same catalyst. [5] Consistent with the high activity of palladium-xantphos complexes as catalyst for the hydroamination of 1,3-dienes with arylamines, [5] the reaction of benzophenone hydrazone with isoprene occurred in the highest yields when catalyzed by the combination of [{Pd(allyl) Cl} 2 ] and xantphos. Nevertheless, this reaction catalyzed by palladium complexes of several other bisphosphines or generated from alternative precursors formed the hydroamination product in substantial yields.…”

“…[3,4] During studies to develop the scope of the hydroamination of dienes, [5][6][7] we found that the reactions of hydrazine and hydroxylamine derivatives occur irreversibly at the more substituted position of both prenyl and crotyl palladium intermediates. We explored this transformation further because, unlike the products from additions of aziridines, [3,4] the products from addition of hydrazine and hydroxylamine derivatives could be readily transformed into primary tert-alkylamines or sec-alkylamines.…”

“…While studying the reactions of hydrazine derivatives with isoprene as an avenue to expand the scope of the hydroamination of dienes, [5][6][7] we found that these reactions formed the product in which the C-N bond is formed between the hydrazone group and the most substituted carbon atom of the diene. Table 1 shows these reactions catalyzed by palladium complexes containing a series of bidentate phosphine ligands.…”

Ruthenium diphosphine complexes as an efficient hydroamination catalyst

“…Proposed mechanism [29] suggests that a ligand leaves the ruthenium center at the first stage. Subsequently, oxidative addition of an amine to coordinatively unsaturated ruthenium center takes place (Scheme 2).…”

Elektrophile Aktivierung von Alkenen mit Platin(II): sehr viel mehr als eine langsame Variante von Palladium(II)

“…(13)]. [71] Die Autoren gehen nicht von einem nucleophilen Angriff des Amins am Pt-koordinierten Olefin aus, sondern von einem Inner-Sphere-Mechanismus mit intramolekularer Insertion der C-C-Bindung in eine Pt-Amido-Bin- Vinylarene, deren Palladium-katalysierte Hydroaminierung ausführlich untersucht wurde, [65,72,73] Der Einsatz von ionischen Lösungsmitteln für chemische Reaktionen hat in den letzten Jahren bedeutend zugenommen. [78,79] Ionische Lösungsmittel zeichnen sich durch niedrige Flüchtigkeit aus, was umweltbezogene Vorteile mit sich bringen kann.…”