Triple-decker complexes comprising heterocyclic middle-deck with coinage metals

Earlier accounts of triple-decker complexes comprising main group elements and transition metals in the middle-deck, motivated us to synthesize triple-decker complexes containing coinage metals in the middle-deck. As a result, we have explored the reactivity of open-cage nido‑ [(Cp*M)2{μ-B2H2E2}], 1–3 (Cp* = η5-C5Me5, 1: M = Co, E = S; 2: M = Co, E = Se; 3: M = Rh, E = Se) with [CuBr(SMe2)]. All the reactions yielded triple-decker complexes, [(Cp*M)2{μ-B2H2E2CuBr}], 4–6 (4: M = Co, E = S; 5: M = Co, E = Se; 6: M = Rh, E = Se) having [CuBr] in the middle-deck. The removal of the SMe2 ligand resulted in the formation of complexes 4–6 as a single product. These complexes are examples of triple-decker species having a planar 5-membered [B2E2Cu] (E = S or Se) middle deck, in which the Cu exists as Cu(I) with an elongated M-Cu bonding interaction. Synthesized complexes have been established by ESI-MS, multinuclear nuclear magnetic resonance (NMR), and IR spectroscopy. The solid-state structures of 5 and 6 were confirmed by single-crystal X-ray diffraction analyses. Density functional theory (DFT) analyses of these complexes have presented a high electron donation from the [B2E2] (E = S or Se) fragment of the middle ring to the axial metals and a weak bonding interaction between group 9 metals and Cu.