MM quadruply bonded complexes supported by vinylbenzoate ligands: synthesis, characterization, photophysical properties and application as synthons

From the reactions between M(2)(T(i)PB)(4) compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M(2)(T(i)PB)(2)L(2), where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and T(i)PB = 2,4,6-triisopropylbenzoate, and where L = p-vinylbenzoate 2A (M = Mo) and 2B (M = W) have been isolated. Compounds 1A and 2A have been shown to undergo Heck carbon–carbon coupling reactions with phenyliodide to produce trans-Mo(2)(T(i)PB)(2)(O(2)CC(6)H(4)-m-CH[double bond, length as m-dash]CH–C(6)H(5))(2), 3A and trans-Mo(2)(T(i)PB)(2)(O(2)CC(6)H(4)-p-CH[double bond, length as m-dash]CH–C(6)H(5))(2), 4A. The molybdenum compounds 1A and 2A have been structurally characterized by single crystal X-ray crystallography. All the new compounds have been characterized by (1)H NMR, IR, UV-visible absorption and emission spectroscopy, high resolution MALDI-TOF MS, fs- and ns-transient absorption spectroscopy and fs-time-resolved IR spectroscopy. Electronic structure calculations employing density functional theory, DFT, and time-dependent DFT have been employed to aid in the interpretation of spectral data. All compounds show intense absorptions in the visible region corresponding to M(2)δ to Lπ* charge transfer transitions. The lifetimes of the (1)MLCT state fall in the range of 1–10 ps and for the molybdenum complexes the T(1) states are (3)δδ* with lifetimes ∼50 μs while for the tungsten complexes the T(1) are (3)MLCT with lifetimes in the range of 3–10 ns.