The formation of CuI-vinyl π-complexes relies on a cooperative interplay between ligand polarization and donor softness. To investigate this concept experimentally, a series of vinylic tris(thioether) ligands CH2═CH-E(CH2SPh)3 (E = C, Si, Ge) was synthesized and characterized in solution by multinuclear NMR spectroscopy, with L1-Si additionally studied in the solid state by X-ray crystallography. While the purely carbon-based ligand does not form a CuI complex under comparable conditions, the silicon- and germanium-substituted derivatives yield the one-dimensional coordination polymers Cu(μ2-I)2Cu(μ-L1-E)2n, featuring Cu(μ2-I)2Cu rhomboids bridged by thioether donors and a side-on π-bound vinyl group occupying the fourth coordination site. High-resolution X-ray diffraction data for L1-Si and CP-Si enabled multipole refinement and topological analysis of the experimental electron density. This approach directly confirms the vinyl-Cu(I) π-interaction and reveals subtle, polarization-dependent changes in bond topology induced by main-group substitution. Comparative studies on the isostructural germanium polymer indicate weaker π-bonding but uncover an unprecedented, reversible temperature-dependent site exchange of the Ge atom accompanied by thioether inversion. Overall, the electron-density analysis establishes main-group element polarization as a decisive factor in enabling vinyl-Cu(I) π-bonding and provides a robust experimental framework for the rational design of multifunctional Cu(I) coordination materials.
Wattenberg et al. (Wed,) studied this question.