First silver complexes of tetrahydropyrimid-2-ylidenes

The syntheses and characterizations of homoleptic silver(I) carbene complexes of the type LAgCl (3) and [L₂Ag]⁺ ₂[Pd₂Cl₆]^2- (4) (L=dimesityltetrahydropyrimid-2-ylidene) are described. 3 was obtained by reaction of the corresponding tetrahydropyrimidinium salt with silver(I) oxide. Subsequent reaction of 3 with Pd(CH₃CN) ₂Cl₂ afforded complex 4. The crystal structure of 3 has been determined to be a monomer in the solid state. The ¹³C NMR spectra of both 3 and 4 exhibit ¹³ C-^107,109Ag coupling in solution. Furthermore, both compounds show a downfield shift of the carbene carbon of about 20 ppm to about 205 ppm in the ¹³C NMR compared to five-membered ring silver(I) carbene complexes. Unlike other silver-carbene complexes, 3 does not undergo ligand exchange and can thus not be used for carbene transfer to other metals.