Well‐Defined and Robust Rhodium Catalysts for the Hydroacylation of Terminal and Internal Alkenes

Abstract

A Rh-catalyst system based on the asymmetric ligand tBu2PCH2P(o-C6H4OMe)2 is reported that allows for the hydroacylation of challenging internal alkenes with β-substituted aldehydes. Mechanistic studies point to the stabilizing role of both excess alkene and the OMe-group.

Comparison of Magnesium and Zinc in Cationic π-Arene and Halobenzene Complexes

“…Similar observations have been made in crystal structures of benzyl alkali-metal complexes, in which the hard Li + prefers a σ-bond to the benzylic CH 2 group whereas the softer K + prefers π-bonding with the aryl ring . All reported examples of metal···(π)­PhF complexes generally involve softer metals such as Rh, Ir, Co, and Ga . The Zn···(π)­PhF bond in 4 mainly concerns the p -C atom, and this strong preference was also confirmed by DFT calculations ( vide infra ).…”

“…Similar observations have been made in crystal structures of benzyl alkali-metal complexes, in which the hard Li + prefers a σ-bond to the benzylic CH 2 group whereas the softer K + prefers π-bonding with the aryl ring. 54 All reported examples of metal•••(π)PhF complexes generally involve softer metals such as Rh, 55 Ir, 56 Co, 57 and Ga. 58 The Zn•••(π)PhF bond in 4 mainly concerns the p-C atom, and this strong preference was also confirmed by DFT calculations Although it seems counterintuitive that arene complexes can be prepared in arene/chlorobenzene mixtures but bromobenzene cleaves the Zn•••arene bond, it should be realized that these weak Zn−ligand interactions are highly dynamic. A large excess of a weak Lewis base can replace slightly stronger bases.…”

Synthesis of Highly Fluorinated Arene Complexes of [Rh(Chelating Phosphine)]+ Cations, and their use in Synthesis and Catalysis

“…We and others have shown cationic rhodium(I) complexes ligated by small bite‐angle diphosphine and η‐FC 6 H 5 to be effective pre‐catalysts for intermolecular hydroacylation . However, the substrate scope is limited to aldehydes or alkenes containing a β‐coordinating group . When on the aldehyde, this motif drives the pre‐equilibrium of aldehyde binding by chelation effect and also blocks a vacant site on the corresponding acyl hydride complex that comes from C−H activation.…”

α-Amino Aldehydes as Readily Available Chiral Aldehydes for Rh-Catalyzed Alkyne Hydroacylation

“…To target these important structures, we were attracted to the use of naturally occurring α-amino acids as a readily available feedstock for chiral amino aldehydes to use in HA reactions (eq 1, Scheme ). Although enantioselective HA reactions have been reported, examples of enantioenriched aldehydes being employed as substrates in intermolecular reactions are scarce. , Given the mild reaction conditions employed with our recently reported, highly active small-bite-angle catalysts, we were confident that we should be able to maintain the enantiomeric purity of such aldehydes in HA reactions. In this paper we show that it is possible to utilize α-amino-substituted alkyl aldehydes in HA reactions and describe the application of chiral α-amino aldehydes as effective substrates for the synthesis of synthetically appealing chiral α-amino enones.…”