In Situ Construction of Three Anion-Dependent Cu(I) Coordination Networks as Promising Heterogeneous Catalysts for Azide–Alkyne “Click” Reactions

Three Cu­(I) coordination networks,
namely, {[Cu2(bpz)2­(CN)­X]·CH3CN}n, (X = Cl, 1;
I, 3), {[Cu6(bpz)6­(CH3CN)3­(CN)3Br]·2OH·14CH3CN}n, (2, bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole),
were prepared by using solvothermal method. The cyanide ligands in
these networks were generated in situ by cleavage of C–C bond
of MeCN under solvothermal condition. The structures of these networks
are dependent on halogen anions. Complex 1 is a ladderlike
structure with μ2-CN– as rung and
μ2-bpz as armrest. The Cl– in 1 is at terminal position but does not extend the one-dimensional
(1D) ladder to higher dimensionalities. Complex 2 is
a three-dimensional (3D) framework comprised of novel planar [Cu3Br] triangle and single Cu nodes, which are extended by μ2-bpz and μ2-CN– to form
a novel (3,9)-connected gfy network. Density functional
theory calculations showed that single-electron delocalization of
Br atom induces the plane structure of [Cu3Br]. Complex 3 also possesses a similar ladderlike subunit as in 1, but the I– acts as bidentate bridge to
extend the ladder to 3D framework with a four-connected sra topology. The three networks show notable catalytic activity on
the click reaction. The compared catalytic results demonstrate that
complex 2 possesses the best catalysis performance among
three complexes, which is ascribed to the largest solvent-accessible
void (porosity: 2 (29.4%) > 1 (25.7%)
> 3 (17.6%)) and the more Cu­(I) active sites in 2. The present combined structure–property studies
provide not only a new synthetic route to obtain a new kind of catalyst
for click reaction but also the new insights on catalyst structure–function
relationships.