Modulating the M2δ-to-ligand charge transfer transition by the use of diarylboron substituents

Abstract

From the reactions between the quadruply bonded complexes M₂(TⁱPB)₄, where M = Mo or W and TⁱPB = 2,4,6-triisopropylbenzoate, and the carboxylic acids HOOC–C₆H₄–4-B(mesityl)₂, LH (2 equivalents) the complexes trans-M₂(TⁱPB)₂L₂ have been prepared. The new compounds have been characterized by ¹H NMR, MALDI-TOF MS, UV-Vis-NIR and steady-state emission spectroscopy, time-resolved transient absorption spectroscopy and cyclic voltammetry. These results are compared with the related properties of the benzoates, M₂(TⁱPB)₂(O₂CPh)₂ (prepared similarly) and with DFT calculations on model compounds where formate substitutes for TⁱPB. The new compounds M₂(TⁱPB)₂L₂ are intensely colored in toluene or THF solutions: red (M = Mo) and green (M = W) and the introduction of the p-B(mesityl)₂ group notably shifts these metal to ligand charge transfer transitions to lower energy in comparison to the benzoate complexes M₂(TⁱPB)₂(O₂C–C₆H₅)₂. Upon the addition of fluoride ions these intense absorptions are shifted to much higher energy in a reversible manner for M = Mo.