Silver(I) Complexes of 1,3‐Dialkyl‐4,5‐dimethylimidazol‐2‐ylidenes and their Use as Precursors for the Synthesis of Rhenium(V) NHC Complexes

Abstract

Abstract Ag(BF 4 ) reacts with N‐heterocyclic carbenes (NHC) of the type 1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐ylidene (L R , R = Me, Et, i‐Pr) under formation of [Ag(L R ) 2 ] + complexes. [Ag(L Et ) 2 ](BF 4 ) and [Ag(L i‐Pr ) 2 ](BF 4 ) can be isolated from such procedures as air‐stable solids, while the methyl derivative decomposes rapidly in the reaction mixture. The Ag–carbene bond lengths in [Ag(L i‐Pr ) 2 ](BF 4 ) are 2.08(1) Å. This is in accordance with the bonding situation in other Ag NHC complexes and does on its own not allow conclusions to be drawn concerning the bonding order or the reactivity of the compound. Reactions of [Ag(L Et ) 2 ](BF 4 ) with common rhenium(V) starting materials such as [ReOCl 3 (PPh 3 ) 2 ] or (NBu 4 )[ReOCl 4 ] give the known Re V NHC complex [ReO 2 (L Et ) 4 ] + . This transmetallation reaction represents a new approach to rhenium or technetium NHC complexes which possess potential for applications in nuclear medicine.