Well-defined N-heterocyclic carbene silver halides of 1-cyclohexyl-3-arylmethylimidazolylidenes: synthesis, structure and catalysis in A3-reaction of aldehydes, amines and alkynes.
Structurally well-defined N-heterocyclic carbene silver chlorides and bromides supported by 1-cyclohexyl-3-benzylimidazolylidene (CyBn-NHC) or 1-cyclohexyl-3-naphthalen-2-ylmethylimidazolylidene (CyNaph-NHC) were synthesized by reaction of the corresponding imidazolium halides with silver(I) oxide while cationic bis(CyBn-NHC) silver nitrate was isolated under similar conditions using imidazolium iodide in the presence of sodium nitrate. Single-crystal X-ray diffraction revealed a dimeric structure through a nonpolar weak-hydrogen-bond supported Ag-Ag bond for 1-cyclohexyl-3-benzylimidazolylidene silver halides [(CyBn-NHC)AgX](2) (X = Cl, 1; Br, 2) but a monomeric structure for N-heterocyclic carbene silver halides with the more sterically demanding 1-cyclohexyl-3-naphthalen-2-ylmethylimidazolylidene ligand (CyNaph-NHC)AgX (X = Cl, 4; Br, 5). Cationic biscarbene silver nitrate [(CyBn-NHC)(2)Ag](+)NO(3)(-)3 assumed a cis orientation with respect to the two carbene ligands. The monomeric complexes (CyNaph-NHC)AgX 4 and 5 showed higher catalytic activity than the dimeric [(CyBn-NHC)AgX](2)1 and 2 as well as the cationic biscarbene silver nitrate 3 in the model three component reaction of 3-phenylpropionaldehyde, phenylacetylene and piperidine with chloride 4 performing best and giving product in almost quantitative yield within 2 h at 100 °C. An explanation for the structure-activity relationship in N-heterocyclic carbene silver halide catalyzed three component reaction is given based on a slightly modified mechanism from the one in literature.
Department of Fine Chemicals, East China University of Science & Technology, Shanghai, China.
Yanbo
Y
Li
Xiaofeng
X
Chen
Yin
Y
Song
Ling
L
Fang
Gang
G
Zou
D000114:Acetylene / Q000031:analogs & derivatives; D000447:Aldehydes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray / Q000379:methods; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D008024:Ligands; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D010880:Piperidines; D018030:Silver Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction / Q000379:methods
D000447:Aldehydes; D000480:Alkynes; D000588:Amines; D001965:Bromides; D006571:Heterocyclic Compounds; D008024:Ligands; D010880:Piperidines; D018030:Silver Compounds; C044736:phenylacetylene; C030011:carbene; C032727:piperidine; C421487:3-phenylpropanal; C037548:silver chloride; C047751:silver bromide; D000114:Acetylene; D008697:Methane