Influence of the Ligand's Electronic Effect on iClick Reaction of Ni(II)-Azido Complexes with Alkynes: Synthesis,
Surajit Das1, Jayanta Bag1, Sayan Sarkar1
1Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata, 700009, India.
Abstract:
The synthesis and characterization of two new square planer Ni(II)-azido complexes [Ni(N3)(L)]-1 of 1-N3 and 2-N3 using electronically varied N/S/O donor tridentate ligands (where H2LOMe: (E)-2-(((2-mercaptophenyl)imino)methyl)-6-methoxyphenol), H2Lt Bu: (E)-2,4-di-tert-butyl-6-(((2-mercaptophenyl)imino)methyl)phenol) were reported. Azido moiety in Ni-azido complexes was found as more dipolar than free azide ion. Six number of [3+2] cycloaddition coupling product of 1-N3/2-N3 and three different alkynes were isolated and well characterized as [Ni(triazolate)(L)]-1 (1/ t Bu-T) complexes. In triazolate complexes originated from terminal alkyne, the triazolate ligand was coordinated via the N1-T atom whose (1-T2) crystal structure was presented. The triazolato products of symmetrical and unsymmetrical nonterminal alkynes were isolated as N2-T mode of binding. The conversion of N1-T/N3-T to N2-T as well as the stability in a particular mode of binding was proposed as thermal control of their equilibrium based on the variable temperature 19F NMR studies on 1-T3/2-T3. The detail kinetic studies resulted that the reaction with methyl propiolate follows zero-order rate law, whereas other two alkynes showed first-order rate. Mostly, the electron-poor ethyl-4,4,4-trifluorobut-2-ynoate always react faster than dimethyl but-2-ynedioate, and Ni(II)-azido complex with Lt Bu ligated always react with a particular alkyne in a faster rate than the same of LOMe.
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