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 R 2 Zn (R = Me, Et, C 6 F 5 ), 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 13 C 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.