Vinyltrifluoroborate Complexes of Silver Supported by N ‐Heterocyclic Carbenes

Silver complexes involving vinyltrifluoroborate, (IPr)Ag(CH 2 =CHBF 3 ) ( 4 ), [(IPr) 2 Ag][CH 2 =CHBF 3 ] ( 5 ), (SIPr)Ag(CH 2 =CHBF 3 ) ( 6 ) and (IPr*)Ag(CH 2 =CHBF 3 ) ( 7 ) have been synthesized by using (NHC)AgNO 3 [NHC = IPr ( 1 ), SIPr ( 2 ) and IPr* ( 3 )] and K(CH 2 =CHBF 3 ) in a metathesis process. NMR spectroscopic details of 1 – 7 and X‐ray crystal structures of compounds 5 – 7 as well as that of a precursor (IPr)AgNO 3 are reported. Compounds 6 and 7 are more stable in solution compared to 4 (which forms 5 ) indicating a supporting ligand effect in the stability of monomeric (NHC)Ag(CH 2 =CHBF 3 ). Calculated metal–ligand binding energies show that [CH 2 =CHBF 3 ] − is a significantly better ligand for Ag I than CH 2 =CH 2 or isoelectronic CH 2 =CHCF 3 . IPr, SIPr and IPr* carbenes coordinate to Ag(CH 2 =CHBF 3 ) moiety forming silver adducts 4 , 6 and 7 , with binding energies of about –72.1, –72.1 and –83.8 kcal/mol, respectively. The C=C bond length of [CH 2 =CHBF 3 ] − (calculated value of 1.341 Å) increases upon coordination to the silver ion. Experimental data show a similar trend for structurally characterized 6 and 7 . Electrostatic attraction dominates the bonding between the alkene ligand [C 2 H 3 BF 3 ] − and the metal fragments [Ag(IPr)] + and [Ag(SIPr)] + in 4 and 6 . The strongest orbital interaction involves σ‐donation from the occupied π‐orbital of the [C 2 H 3 BF 3 ] − ligand to the vacant orbital of the metal fragment, while Ag I →[C 2 H 3 BF 3 ] − π‐backbonding is relatively weak but not insignificant.