Mono- and Di-nuclear Tris(pyrazolyl)borato-Oxo-Tungsten(V) Complexes with the Phenolate Ligands: Syntheses and Structures, and Magnetic, electrochemical and UV/Vis/NIR sprectroscopic properties

A series of oxo-tungsten() complexes of the type [W(Tp*)(O)Cl(OAr)] (mononuclear) and [{W(Tp*)(O)Cl}2(μ-OO)] (dinuclear, where ‘OO’ denotes a para-substituted bis-phenolate bridging ligand) has been prepared and many members structurally characterised. The complexes have been studied by a variety of physical techniques (electrochemistry; EPR spectroscopy; magnetic susceptibility; UV/Vis/NIR spectroelectrochemistry) in order to evaluate the electronic and magnetic interactions between the redox-active, paramagnetic metal centres and to compare the magnitudes of these interactions with those observed for the Mo() analogues. It was found that both electronic interactions (as measured by the separation between successive metal-centred redox processes) and magnetic exchange interactions (as determined from variable-temperature magnetic susceptibility studies) are reduced in the W() dinuclear complexes compared to their Mo() analogues, which we ascribe to a poorer d(π)–p(π) overlap between metal and bridging ligand orbitals. In addition the complexes have been fully characterised by UV/ Vis/NIR spectroscopy in all accessible oxidation states, as well as by EPR spectroscopy.