Protonolysis approach to the catalytic amination of olefins with bis(phosphine)palladium(II) dialkyls

Evidence That Protons Can Be the Active Catalysts in Lewis Acid Mediated Hetero‐Michael Addition Reactions

“…This step is known to be accelerated by phosphine ligands on palladium, the presence of excess halide ions or weak acids. [19] However, the aza-Michael reaction of the carbamate 3 with the enone 2 b, which can be catalysed by [Pd(CH 3 CN) 2 Cl 2 ], was completely shut down when [Pd(PPh 3 ) 2 Cl 2 ] was used or LiCl was added, and no increase in reaction rate was observed in the presence of trifluoroacetic acid (TFA) ( Table 2). [14,18] Careful analyses of the [Pd(CH 3 CN) 4 ](BF 4 ) 2 -catalysed aza-Michael addition reactions to the cyclohexenones 2 b,c in CH 3 CN [20] revealed that small quantities of the anilines 8 a,b and the tetracyclic compound 9 were formed as side [21] The structure of the tetracyclic compound 9 was confirmed by X-ray crystallography.…”

“…However, Tf 2 NH and hydrolysable [14,15] Examples and extensions of this methodology are listed in Table 7. In addition to benzyl carbamate (3) (runs 1± 3), other nitrogen nucleophiles such as oxazolidin-2-one (18), benzaldehyde oxime (19) (15) could also be catalysed by Br˘nsted acids (runs 7 and 8) and did not require Pd II catalysts. The same method could be applied to the thiols 21 and 22, which reacted rapidly in the presence of Tf 2 NH (entries 9±10).…”

Transition‐Metal‐Catalyzed Hydroamination Reactions

“…Indeed, steady advancement in the application of such late transition metals for these transformations has been realized and extensive examples of hydroamination with alkynes, allenes, dienes, vinyl arenes, and alkenes have been achieved in intra-and intermolecular transformations with variability in observed selectivities (both regio-and stereoselectivities) and proposed mechanistic profiles for these transformations. With late transition metals, the most common mechanistic proposals can be summarized into three broad categories: (i) nucleophilic attack on neutral π-complexes [87][88][89], (ii) nucleophilic attack on allylic complexes (including those derived from dienes and vinyl arenes) [69,[90][91][92][93][94][95][96], and (iii) insertion of C-C multiple bonds into metal-amide or metal-hydride bonds [97,98]. Common to late transition metal catalysts used for this transformation is the use of metal precursors with weakly coordinating counterions, such as TfO − or TsO − , presumably to accommodate the alkene/alkyne coordination that is required during the catalytic cycle.…”

Catalytic Reactivities of Indenyl–nickel, Indenyl–palladium, and PCsp3P–nickel Complexes

“…Noteworthy examples include Pd-PC sp3 P complexes that promote the hydroamination of acrylonitrile [24] and the Heck vinylation of aryl halides [25,26]; for the latter reaction, the PC sp3 P complexes are believed to be more active than their PC sp2 P counterparts. We have begun exploring the catalytic reactivities of Ni-PC sp3 P systems in hydrosilylation of styrene and hydroamination of acrylonitrile and present herein some of our recent results.…”

“…The catalyzed addition of amines to double bonds is thus of great importance since it constitutes an atom-efficient route to amines (i.e., no by-products such as salts or water are formed). Since a number of sterically hindered group 10 metals bearing tridentate PCP, PPP or PNP ligands have proven to be active catalysts for this reaction [24,29], we decided to evaluate the catalytic potential of the cationic derivative [PC sp3 P-Ni(acrylonitrile)] + [27] for the hydroamination of acrylonitrile. We chose aniline as the amine substrate because the weak nucleophilicity of this amine should prevent its possible competition with the olefin for coordination to the metal centre, which is an important step in the proposed mechanism for the hydroamination reaction [30].…”