Preparation, Structure, and Metallophilic Interactions of Dinuclear Silver(I) and Copper(I) Complexes of Selenium Diimides

The complexes [M2{μ-N,N′-Se(NR)2}2](CF3SO3)2 (1, M = Ag, R = tBu; 2, M = Ag, R = Ad; 3, M = Cu, R = tBu; 4, M = Cu, R = Ad; Ad = 1-adamantyl) were prepared in good yields from the reaction of the corresponding selenium diimide with silver or copper triflate in toluene and were characterized in solution using multinuclear NMR spectroscopy. Recrystallization of 1−4 from a variety of solvents produced 1·2CH2Cl2, 2(AdNH3)(CF3SO3) (a few crystals), 3·2thf, and 4·1/2C7H8, which were characterized by X-ray crystallography. All of these salts contain a metallacyclic [M2{μ-N,N′-Se(NR)2}2]2+ [M = Ag, Cu; R = tBu, Ad] cation, the frameworks of which exhibit M···M close contacts of 2.7384(9), 2.751(2), 2.556(2)−2.569(2), and 2.531(1) Å, respectively. The M···M interaction was further explored by PBE/def-TZVP calculations of the dications [M2{μ-N,N′-Se(NR)2}2]2+ (M = Ag, Cu; R = H, Me, tBu, Ad). The geometry optimizations yielded metric parameters that were in good agreement with experimental values, where available. For both metals, it was observed that the M···M distance became shorter, as the organic substituent on nitrogen became bulkier. At the same time, the metallacyclic framework deviated more significantly from planarity. A survey of related dinuclear silver(I) and copper(I) complexes showed that, while there is some correlation between the bite size and the M···M distance, the latter is more dependent on the deviation from planarity of the D2M···MD2 fragment. Atoms in molecules calculations clearly showed the presence of a bond critical point between the two silver or copper centers, as well as two ring critical points. Our computational results are consistent with other recent molecular orbital studies at different levels of theory and indicate the existence of d10−d10 closed-shell metallophilic interactions in 1−4.