Developing bulky P-alkene ligands: stabilization of copper complexes with 14 valence electrons†
Abstract
The new mono dibenzo[b,f]-azepinyl substituted P-alkene ligands 7–9, 20, and 21 were used to synthesize monomeric and dimeric Cu(I) complexes by using metal to ligand ratios of 2 : 1 and 1 : 1, respectively. With the super-bulky tris dibenzo[b,f]-azepinyl substituted P-alkenes 21, only monomers form with a 1 : 1 stoichiometry. Cationic complexes were obtained either by employing [Cu(OTf)]2·C6H6 as the starting material, or by chloride abstractions from the monomeric chlorido complexes with NaB(ArF)4 or TlBF4, whereas with silver salts only Ag(I)-P-alkene complexes were isolated by transmetallation. Chloride abstraction with NaB(ArF)4 gave the 14 ve cationic complex 18, which shows no alkene coordination and a bent coordination geometry due to the steric pressure exerted by the ligand. The buried volumes of the ligands (calculated from X-ray diffraction data) increase in the order 8 < 7 < 9 < 20 < 21 with the last displaying a staggering Vbur of 60.6% (the crystallographic Tolman angle in copper complex 23 amounts to 229°). The bulkiest ligand (21) allowed us to isolate and structurally characterize rare examples of 14 ve Cu(I) complexes, namely the neutral chloride 23 and, after salt metathesis with NaB(ArF)4, the chlorido bridged dinuclear cation 26 exhibiting short Cu–Cl bonds.
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