title: Chiral tetranuclear and dinuclear copper(ii) complexes for TEMPO-mediated aerobic oxidation of alcohols: are four metal centres better than two?
abstract: The one-pot reaction of 3,5-di-tert-butyl-2-hydroxybenzaldehyde, (R)-2-aminoglycinol and Cu(OAc)2·2H2O in a 1 : 1 : 1 ratio in the presence of triethylamine led to the isolation of X-ray quality crystals of the chiral complex (R)- in high yield. The single crystal structure of (R)- reveals a tetranuclear copper(ii) complex that contains a {Cu4(μ-O)2(μ3-O)2N4O4} core. A reaction using (1S,2R)-2-amino-1,2-diphenylethanol as precursor under the same conditions generated the chiral complex (S,R)-; its structure was determined by single crystal X-ray crystallography and was found to contain a {Cu2(μ-O)2N2O2} core. Both (R)- and (S,R)- have been used for catalytic aerobic oxidation of benzylic alcohols in combination with the TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) radical. (R)- selectively catalyses the conversion of various aromatic primary alcohols to the corresponding aldehydes with high yields (99%) and TONs (770) in the air, while (S,R)- exhibits less promising catalytic performance under the same reaction conditions. The role of the cluster structures in (R)- and (S,R)- in controlling the reactivity towards aerobic oxidation reactions is discussed.
authors.affiliation: Department of Sciences, John Jay College, The City University of New York, New York, NY 10019, USA. guzhang@jjay.cuny.edu.
authors.forename: Guoqi
authors.initials: G
authors.lastname: Zhang
authors.forename: Gloria
authors.initials: G
authors.lastname: Proni
authors.forename: Sherry
authors.initials: S
authors.lastname: Zhao
authors.forename: Edwin C
authors.initials: EC
authors.lastname: Constable
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Housecroft
authors.forename: Markus
authors.initials: M
authors.lastname: Neuburger
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Zampese
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003497:Cyclic N-Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D012545:Schiff Bases / Q000737:chemistry
chemical_list: D000438:Alcohols; D056831:Coordination Complexes; D003497:Cyclic N-Oxides; D012545:Schiff Bases; D003300:Copper; C003959:TEMPO