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

From the reactions between the quadruply bonded complexes M (TPB), where M = Mo or W and TPB = 2,4,6-triisopropylbenzoate, and the carboxylic acids HOOC-CH -4-B(mesityl), LH (2 equivalents) the complexes trans-M(TPB)L have been prepared. The new compounds have been characterized by H 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, M(T PB)(OCPh) (prepared similarly) and with DFT calculations on model compounds where formate substitutes for TPB. The new compounds M(TPB) L are intensely colored in toluene or THF solutions: red (M = Mo) and green (M = W) and the introduction of the p-B(mesityl) group notably shifts these metal to ligand charge transfer transitions to lower energy in comparison to the benzoate complexes M(T PB)(OC-CH) . Upon the addition of fluoride ions these intense absorptions are shifted to much higher energy in a reversible manner for M = Mo. © 2013 The Royal Society of Chemistry.