Copper(i) and silver(i) chemistry of vinyltrifluoroborate supported by a bis(pyrazolyl)methane ligand

Abstract

Although unsaturated organotrifluoroborates are common synthons in metal–organic chemistry, their transition metal complexes have received little attention. [CH₂(3,5-(CH₃)₂Pz)₂]Cu(CH₂CHBF₃), (SIPr)Cu(MeCN)(CH₂CHBF₃) and [CH₂(3,5-(CH₃)₂Pz)₂]Ag(CH₂CHBF₃) represent rare, isolable molecules featuring a vinyltrifluoroborate ligand on coinage metals. The X-ray crystal structures show the presence of three-coordinate metal sites in these complexes. The vinyltrifluoroborate group binds asymmetrically to the metal site in [CH₂(3,5-(CH₃)₂Pz)₂]M(CH₂CHBF₃) (M = Cu, Ag) with relatively closer M–C(H)₂ distances. The computed structures of [CH₂(3,5-(CH₃)₂Pz)₂]M(CH₂CHBF₃) and M(CH₂CHBF₃), however, have shorter M–C(H)BF₃ distances than M–C(H)₂. These molecules feature various inter- or intra-molecular contacts involving fluorine of the BF₃ group, possibly affecting these M–C distances. The binding energies of [CH₂CHBF₃]⁻ to Cu⁺, Ag⁺ and Au⁺ have been calculated at the wB97XD/def2-TZVP level of theory, in the presence and absence of the supporting ligand CH₂(3,5-(CH₃)₂Pz)₂. The calculation shows that Au⁺ has the strongest binding to the [CH₂CHBF₃]⁻ ligand, followed by Cu⁺ and Ag⁺, irrespective of the presence of the supporting ligand. However, in all three metals, the supporting ligand weakens the binding of olefin to the metal. The same trends were also found from the analysis of the σ-donation and π-backbonding interactions between the metal fragment and the π and π* orbitals of [CH₂CHBF₃]⁻.