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.