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(Ar^F)₄ or TlBF₄, whereas with silver salts only Ag(I)-P-alkene complexes were isolated by transmetallation. Chloride abstraction with NaB(Ar^F)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 V_bur 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(Ar^F)₄, the chlorido bridged dinuclear cation 26 exhibiting short Cu–Cl bonds.