Taming a monomeric [Cu(η6-C6H6)]+ complex with silylene

Realization of a hitherto elusive unsupported η6 binding mode of benzene to a copper(i) cation employing silylene as a ligand. The back-donation from Cu to Si(ii) diminishes the repulsion between d-electrons and the benzene ring and enforces the η6 binding mode.


S1. Experimental Section:
All experiments were carried out under an atmosphere of dry argon or in vaccuo using standard Schlenk technique and in a dinitrogen filled MBRAUN MB 150-G1 glovebox. The solvents used were purified by MBRAUN solvent purification system MB SPS-800. The starting materials 1 and 4 were prepared as reported in the literature. 1 All other chemicals purchased from Aldrich were used without further purification. 1 H, 13 C, 19 F and 29 Si NMR spectra were recorded with Bruker 400 MHz spectrometer, using CDCl 3 and CD 2 Cl 2 as solvent with an external standard (SiMe 4 for 1 H, 13 C and 29 Si and trifluorotoluene for 19 F). Mass spectra were recorded using AB Sciex, 4800 plus MALDI TOF/TOF.

Synthesis of 3:
AgSbF 6 (0.171g, 0.5 mmol) was dissolved in CH 2 Cl 2 (15 mL) and added to the solution of 1 (0.280g, 0.25 mmol) in benzene (15 mL). It was stirred overnight at room temperature. After that, AgBr was separated out from the reaction mixture by filtration and reduced the volume to 15 mL and kept it at 0 o C. Colorless block shaped crystals suitable for X-ray analysis were observed after one day. Yield: 0.260 g (65 %

S3. Deduction of hapticities in 5 and 6
The The effect of the basis sets on the optimized geometries has been also evaluated. We have concluded that the use of a double-basis set (6-31G*) for all atoms does not reproduce the experimental hapticities, which are obtained only by increasing the size of the basis set at the C and H atoms (6-311+G*). The most relevant bond lengths for both cases can be found in the table below. We have also optimized 6 with the 6-311+G* basis set for all atoms including Cu, but it could not be applied for 2, 3 and 5 due to computational limitations. After these prospective calculations, all calculations reported in the article were done at the B3LYP-D3 level of theory. The 6-311+G * basis set was employed for C and H and 6-31G* for all other elements. Compounds 2, 3, 5 and 6 were characterized as true minima of the PES by vibrational analysis.
The NBO analysis was carried out by using the NBO 3.1 program as implemented in Gaussian09. Complex 6 was decomposed into three fragments (Cu + NHC ligand + C 6 H 6 ) for the second order perturbation analysis, while complex 3 were decomposed into five fragments (SiCu + C 6 H 6 + C 3 H 9 Si + C 3 H 9 Si + C 15 H 23 N 2 ).
NCI isosurfaces (s = 0.3 au) were obtained from promolecular densities by means of the NCIPLOT program. 2 "Atoms in Molecules" (AIM) analysis was done with the AIMAll software on the B3LYP electron density. 3 The energy was decomposed by means of the second-generation absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA) 4, 5 implemented in Q-Chem 6 5.0 at the B3LYP-D3 level of theory with CP correction of the BSSE. The ALMO-EDA decomposes the intermolecular interaction energy into further several interactions, namely a frozen term, a polarization effect term and a charge transfer contribution (∆E int = ∆E FRZ + ∆E Pol + ∆E CT ).
Physically, ∆E FRZ contains three contributions that arise without any relaxation of the fragment