Unexpected structural preference with metallophilic Ag-Au contacts in silver(i)-N-heterocyclic carbene cluster; experimental and theoretical approach

A novel synthetic donor-atom-selective approach has been adopted for the synthesis of a heterobimetallic cluster of a new NCN-pincer, 1,3-bis-(1-methyl-1H-benzo[d]imidazol-2-yl-methyl)-1H-imidazol-3-ium hexafluorophosphate (1 center dot HPF6). The complex [Ag-3(1)(3)][PF6](3) (2) has been prepared via the Ag2O route; which undergoes transmetallation to yield a cluster that seems to be the first example of the heterobimetallic trinuclear system [Au-Ag-2(1)(2)Cl][PF6](2), 3. Finally, the trinuclear cluster geometries of 2 and 3 were confirmed via SCXRD studies. Interestingly, Au(i) binds preferentially with soft donor C-carbene, which trans-metallated from the cluster of 2. In both the cyclic trinuclear clusters, the M-M interactions were further inspected using gauge independent atomic orbital (GIAO) computations. Both 2 and 3 are luminescent and possess sigma-aromaticity; the NICS values indicate that 3 is more aromatic than 2.