Chelation-assisted, copper(II)-acetate-accelerated azide-alkyne cycloaddition.
We described in a previous communication a variant of the popular Cu(I)-catalyzed azide-alkyne cycloaddition (AAC) process where 5 mol % of Cu(OAc)(2) in the absence of any added reducing agent is sufficient to enable the reaction. 2-Picolylazide (1) and 2-azidomethylquinoline (2) were found to be by far the most reactive carbon azide substrates that convert to 1,2,3-triazoles in as short as a few minutes under the discovered conditions. We hypothesized that the abilities of 1 and 2 to chelate Cu(II) contribute significantly to the observed high reaction rates. The current work examines the effect of auxiliary ligands near the azido group other than pyridyl for Cu(II) on the efficiency of the Cu(OAc)(2)-accelerated AAC reaction. The carbon azides capable of binding to the catalytic copper center at the alkylated azido nitrogen in a chelatable fashion were indeed shown to be superior substrates under the reported conditions. The chelation between carbon azide 11 and Cu(II) was demonstrated in an X-ray single-crystal structure. In a limited set of examples, the ligand tris(benzyltriazolylmethyl)amine (TBTA), developed by Fokin et al. for assisting the original Cu(I)-catalyzed AAC reactions, also dramatically enhances the Cu(OAc)(2)-accelerated AAC reactions involving nonchelating azides. This observation leads to the hypothesis of an additional effect of chelating azides on the efficiencies of Cu(OAc)(2)-accelerated AAC reactions, which is to facilitate the rapid reduction of Cu(II) to highly catalytic Cu(I) species. Mechanistic studies on the AAC reactions with particular emphasis on the role of carbon azide/copper interactions will be conducted based on the observations reported in this work. Finally, the immediate utility of the product 1,2,3-triazole molecules derived from chelating azides as multidentate metal coordination ligands is demonstrated. The resulting triazolyl-containing ligands are expected to bind with transition metal ions via the N(2) nitrogen of the 1,2,3-triazolyl group to form nonplanar coordination rings. The Cu(II) complexes of bidentate T1 and tetradentate T6 and the Zn(II) complex of T6 were characterized by X-ray crystallography. The structure of [Cu(T1)(2)(H(2)O)(2)](ClO(4))(2) reveals the interesting synergistic effect of hydrogen bonding, π-π stacking interactions, and metal coordination in forming a one-dimensional supramolecular construct in the solid state. The tetradentate coordination mode of T6 may be incorporated into designs of new molecule sensors and organometallic catalysts.
Kuang
Gui-Chao
GC
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
Michaels
Heather A
HA
Simmons
J Tyler
JT
Clark
Ronald J
RJ
Zhu
Lei
L
D000085:Acetates / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D001386:Azides / Q000737:chemistry*; D002614:Chelating Agents / Q000138:chemical synthesis* / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D003500:Cyclization; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D000085:Acetates; D000480:Alkynes; D001386:Azides; D002614:Chelating Agents; D009942:Organometallic Compounds; D003300:Copper
Chem Rev. 2008 Aug;108(8):2952-3015
18698735
Inorg Chem. 2000 Aug 21;39(17):3894-901
11196786
Angew Chem Int Ed Engl. 1998 Sep 4;37(16):2262-2265
29711441
Chemistry. 2009;15(12):2755-8
19197920
Acc Chem Res. 2000 Jun;33(6):325-35
10891050
Org Lett. 2009 Nov 5;11(21):4954-7
19810690
Chem Commun (Camb). 2008 Jun 7;(21):2459-61
18491014
Org Lett. 2004 Aug 19;6(17):2853-5
15330631
J Am Chem Soc. 2004 Aug 4;126(30):9152-3
15281783
J Am Chem Soc. 2008 Nov 19;130(46):15304-10
18950175
J Am Chem Soc. 2003 Oct 22;125(42):12692-3
14558801
J Org Chem. 2002 May 3;67(9):3057-64
11975567
J Am Chem Soc. 2007 Sep 5;129(35):10666-7
17676852
Org Lett. 2007 Nov 22;9(24):4999-5002
17956110
Angew Chem Int Ed Engl. 2002 Jul 15;41(14):2596-9
12203546
Chemistry. 2010 Jun 1;16(21):6278-84
20397167
Chem Rev. 1998 Jun 18;98(4):1375-1406
11848937
Inorg Chem. 2010 Jun 7;49(11):4820-9
20441174
J Am Chem Soc. 2007 Oct 24;129(42):12705-12
17914817
Chem Commun (Camb). 2010 Apr 7;46(13):2274-6
20234930
Inorg Chem. 2010 May 3;49(9):4278-87
20369825
J Am Chem Soc. 2003 Mar 19;125(11):3192-3
12630856
Chem Soc Rev. 2010 Apr;39(4):1302-15
20309487
Chembiochem. 2008 Jun 16;9(9):1481-6
18504727
Chem Soc Rev. 2010 Apr;39(4):1231-2
20309482
J Am Chem Soc. 2005 Jan 12;127(1):210-6
15631470
Chembiochem. 2003 Nov 7;4(11):1246-8
14613121