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

From the reactions between M-2((TPB)-P-i)(4) compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M-2((TPB)-P-i)(2)L-2, where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and (TPB)-P-i = 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((TPB)-P-i)(2)(O2CC6H4-m-CH=CH-C6H5) 2, 3A and trans-Mo-2((TPB)-P-i)(2)(O2CC6H4-p-CH=CH-C6H5)(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 H-1 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 delta to L pi* charge transfer transitions. The lifetimes of the (MLCT)-M-1 state fall in the range of 1-10 ps and for the molybdenum complexes the T-1 states are (3)delta delta* with lifetimes similar to 50 mu s while for the tungsten complexes the T-1 are (MLCT)-M-3 with lifetimes in the range of 3-10 ns.