Tunable π-Interactions in Monomeric Organozinc Complexes: Solution and Solid-State Studies

A series of the calix[4]arene ligands, partially oxygen-depleted at the 1 and 3 positions via the
Sonogashira cross-coupling reaction with several arylacetylenes, were prepared. Upon reaction with R2Zn (R = Me, Et, C6F5), the corresponding organozinc complexes were obtained. X-ray analysis showed
weak π-interactions between the organozinc fragment and the triple bonds. In addition, the solution 13C
NMR studies showed good correlation between the strength of these interactions and electron density at
the acetylene group, with more electron-rich alkynes binding stronger to the Zn center. The latter was
also supported by DFT calculations on a model compound. These results show that, albeit weak,
π-interactions of organozinc compounds can be observed and fine-tuned in both solution and the solid
state.