Cooperative N-Heterocyclic Carbene (NHC) and Ruthenium Redox Catalysis: Oxidative Esterification of Aldehydes with Air as the Terminal Oxidant

The paper describes a cooperative NHC (N‐heterocyclic carbene) and ruthenium‐based redox catalysis for the mild aerobic oxidative esterification of various aromatic and heteroaromatic aldehydes. The ruthenium(II) complex Ru(bpz)3(PF6)2 (bpz=2,2′‐bipyrazine) as catalyst is shown to be compatible with...

Full description

Saved in:
Bibliographic Details
Published in:Advanced synthesis & catalysis 2013-04, Vol.355 (6), p.1098-1106
Main Authors: Zhao, Junfeng, Mück-Lichtenfeld, Christian, Studer, Armido
Format: Article
Language:English
Subjects:
Aldehydes
Carbenes
Catalysis
Catalysts
cooperative catalysis
organocatalysis
Oxidants
oxidation
Oxidizing agents
Ruthenium
Terminals
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The paper describes a cooperative NHC (N‐heterocyclic carbene) and ruthenium‐based redox catalysis for the mild aerobic oxidative esterification of various aromatic and heteroaromatic aldehydes. The ruthenium(II) complex Ru(bpz)3(PF6)2 (bpz=2,2′‐bipyrazine) as catalyst is shown to be compatible with free NHCs. The NHC is used in these cascade reactions for the umpolung of the aldehyde to form the corresponding Breslow intermediate which in turn gets oxidized to an acylazolium ion by the ruthenium redox catalyst. Air is used as a terminal oxidant for oxidation (regeneration) of the ruthenium catalyst. In addition, we will show that in the absence of the ruthenium redox catalyst and alcohol, NHC‐catalyzed aerobic oxidation of aldehydes delivers the corresponding acids in good to excellent yields. Mechanistic studies and DFT calculations supporting our suggested mechanisms are provided.
ISSN:1615-4150
1615-4169
DOI:10.1002/adsc.201300034