Copper(I)-Arene Complexes with a Sterically Hindered Tris(pyrazolyl)borate Ligand

A series of arene copper(I) complexes bearing the hydrotris(3-mesitylpyrazolyl)borate ligand (Tp(Ms)) of general formula Tp(Ms)Cu(arene) (arene = toluene, 1; nitrobenzene, 2; chlorobenzene, 3; and iodobenzene, 4) has been structurally characterized. Complexes 1-3 show a (2)-arene coordination mode to the copper center, whereas the iodobenzene ligand in 4 is coordinated to Cu by the iodine atom. In the absence of excess arene, these compounds undergo arene loss and formation of the dinuclear complex [Tp(Ms)Cu](2) (5), which has also been structurally characterized. Given the number of catalytic systems described in which the Tp(x)Cu core plays the main role, the observation of these adducts assesses their presence in those catalytic systems, a feature not described to date.