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

Abstract

From the reactions between M2(TiPB)4 compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M2(TiPB)2L2, where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and TiPB = 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-Mo2(TiPB)2(O2CC6H4-m-CHCH-C6H5)2, 3A and trans-Mo2(TiPB)2(O2CC6H4-p-CHCH-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 1H 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 M2δ to Lπ∗ charge transfer transitions. The lifetimes of the 1MLCT state fall in the range of 1-10 ps and for the molybdenum complexes the T1 states are 3δδ∗ with lifetimes ∼50 μs while for the tungsten complexes the T1 are 3MLCT with lifetimes in the range of 3-10 ns.