Expansion of the (BB) Ru metallacycle with coinage metal cations: formation of B-M-Ru-B (M = Cu, Ag, Au) dimetalacyclodiboryls

In this work, we introduce a novel approach for the selective assembly of heterometallic complexes by unprecedented coordination of coinage metal cations to strained single ruthenium-boron bonds on a surface of icosahedral boron clusters. M(I) cations (M = Cu, Ag, and Au) insert into B-Ru bonds of the (BB)-carboryne complex of ruthenium with the formation of four-membered B-M-Ru-B metalacycles. Results of theoretical calculations suggest that bonding within these metalacycles can be best described as unusual three-center-two-electron B-M ... Ru interactions that are isolobal to B-H ... Ru borane coordination for M = Cu and Ag, or the pairs of two-center-two electron B-Au and Au-Ru interactions for M = Au. These transformations comprise the first synthetic route to exohedral coinage metal boryl complexes of icosahedral closo-{C2B10}clusters, which feature short Cu-B (2.029(2) angstrom) and Ag-B (2.182(3) angstrom) bonds and the shortest Au-B bond (2.027(2) angstrom) reported to date. The reported heterometallic complexes contain Cu(I) and Au(I) centers in uncharacteristic square-planar coordination environments. These findings pave the way to rational construction of a broader class of multimetallic architectures featuring M-B bonds.