MM quadruple bonds supported by cyanoacrylate ligands. Extending photon harvesting into the near infrared and studies of the MLCT states

Abstract

The compounds trans-M2(TiPB)2(L)2 and trans-M2(TiPB)2(L′)2 have been prepared from the reactions between M2(TiPB)4 (TiPB = 2,4,6-triisopropylbenzoate, M = Mo or W) and LH or L′H (∼2 equiv.), respectively, where L = O2CC(CN)CH–C6H4–NPh2 and L′ = O2CC(CN)CH–C4H3S–C6H4–NPh2. These cyanoacrylate ligands promote intense M2δ to L or L′ π*-transitions that span the range 550–1100 nm. The two molybdenum complexes have been characterized by single crystal X-ray studies that reveal the extensive L–M2222–L or L′–M2222–L′ M2δ–ligand π-conjugation. The new compounds have been characterized by electronic structure calculations employing density functional theory (DFT) and time-dependent-DFT, cyclic voltammetry, electronic absorption and steady state emission spectroscopy and femtosecond (fs) and nanosecond (ns) time resolved transient absorption (TA) and fs time-resolved infrared spectroscopy (TRIR). The latter allows the determination of the S1 states as 1MLCT that are delocalized over both L and L′. For molybdenum the T1 states are 3MoMoδδ* whereas for tungsten they are 3MLCT.