Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group) |
| |
| Authors: | Andreas Reisinger Dr Nils Trapp Dr Carsten Knapp Dr Daniel Himmel Dr Frank Breher Prof Heinz Rüegger Dr Ingo Krossing Prof |
| |
| Institution: | 1. Albert‐Ludwigs‐Universit?t Freiburg, Institut für Anorganische und Allgemeine Chemie and Freiburger Materialforschungszentrum (FMF), Albertstr. 21, 79104 Freiburg (Germany);2. Universit?t Karlsruhe (TH), Institut für Anorganische Chemie, Engesserstr. 15, 76131 Karlsruhe (Germany);3. ETH Zürich, Laboratorium für Anorganische Chemie, Wolfgang‐Pauli‐Str. 10, 8093 Zürich (Switzerland) |
| |
| Abstract: | Compounds including the free or coordinated gas‐phase cations Ag(η2‐C2H4)n]+ (n=1–3) were stabilized with very weakly coordinating anions A]? (A=Al{OC(CH3)(CF3)2}4, n=1 ( 1 ); Al{OC(H)(CF3)2}4, n=2 ( 3 ); Al{OC(CF3)3}4, n=3 ( 5 ); {(F3C)3CO}3Al‐F‐Al{OC(CF3)3}3, n=3 ( 6 )). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH2Cl2 solution. As a reference we also prepared the isobutene complex (Me2C?CH2)Ag(Al{OC(CH3)(CF3)2}4)] ( 2 ). The compounds were characterized by multinuclear solution‐NMR, solid‐state MAS‐NMR, IR and Raman spectroscopy as well as by their single crystal X‐ray structures. MAS‐NMR spectroscopy shows that the Ag(η2‐C2H4)3]+ cation in its Al{OC(CF3)3}4]? salt exhibits time‐averaged D3h‐symmetry and freely rotates around its principal z‐axis in the solid state. All routine X‐ray structures (2θmax.<55°) converged within the 3σ limit at C?C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C?C stretching modes indicated red‐shifts of 38 to 45 cm?1, suggesting a slight C?C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C?C distance in M(C2H4)] complexes from experimental Raman data was developed and meaningful C?C distances were obtained. These spectroscopic C?C distances compare well to newly collected X‐ray data obtained at high resolution (2θmax.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG‐cc‐pVTZ methods. In most cases several isomers were considered. Additionally, M(C2H4)3] (M=Cu+, Ag+, Au+, Ni0, Pd0, Pt0, Na+) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation. |
| |
| Keywords: | olefins quantum chemistry Raman spectroscopy silver weakly coordinating anions X‐ray diffraction |
|
|
