Reactivity of imidazolate Au(I) cyclic trinuclear compounds, CTCs, with iodine or MeI: a computational/experimental study

Cyclic trinuclear complexes (CTCs) of d10 metal frames, obtained through the reaction between angular ditopic anionic bridging ligands and 11th group elements M(I) complexes, have aroused considerable attention due to their potential application in optoelectronics and molecular recognition. Experimental evidences show that the reaction of gold(I) CTCs, featuring imidazolate bridging ligands, with different substrates (CH3I and I2) result to the formation of carbene, bis-carbene or square planar complexes depending on the nature of both the reactants depending on and of the substituent at the imidazolyl ring. Herein, we report the results of a detailed computational investigation of the reactivity by considering two different substituents at the ring ligand: methyl or benzyl groups. All the electronic and steric factors ruling the reactivity have been pointed out and, in particular, the not innocent behaviour of the imidazolyl rings in the activation of C-I bonding. Experimentally, the X-ray crystal structure demonstrates that the reaction between the gold(I) CTC - having 1-methyl-imidazolate as bridging ligand- with MeI provides the formation of a square planar gold complex with the formation of new Au-I and Au-CH3 linkages. In Figure 1 is reported the optimized structure obtained by computational calculations within Gaussian 16 package. Such a reactivity, beyond to the classic addition of iodine traditionally classified as "oxidative addition", has been explained accordingly to the newly introduced Inverted Ligand Field concept. A reasonable explanation has been also provided for the role of the different substituents at the imidazolyl ring in the reactivity.