Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II)

A facile and high-yielding protocol to the known Ti­(II) complex <i>trans</i>-[(py)₄­TiCl₂] (py = pyridine) has been developed. Its electronic structure has been probed experimentally using magnetic susceptibility, magnetic circular dichroism, and high-frequency and high-field electron paramagnetic resonance spectroscopies in conjunction with ligand-field theory and computational methods (density functional theory and <i>ab initio</i> methods). These studies demonstrated that <i>trans</i>-[(py)₄­TiCl₂] has a ³E_g ground state (d_<i>xy</i>¹d_{<i>xz</i>,<i>yz</i>}¹ orbital occupancy), which, as a result of spin–orbit coupling, yields a ground-state spinor doublet that is EPR active, a first excited-state doublet at ∼60 cm^–1, and two next excited states at ∼120 cm^–1. Reactivity studies with various unsaturated substrates are also presented in this study, which show that the Ti­(II) center allows oxidative addition likely via formation of [Ti­(η²-R₂E₂)­Cl₂(py)_<i>n</i>] E = C, N intermediates. A new Ti­(IV) compound, <i>mer</i>-[(py)₃(η²-Ph₂C₂)­TiCl₂], was prepared by reaction with Ph₂C₂, along with the previously reported complex <i>trans</i>-(py)₃TiNPh­(Cl)₂, from reaction with Ph₂N₂. Reaction with Ph₂CN₂ also yielded a new dinuclear Ti­(IV) complex, [(py)₂(Cl)₂­Ti­(μ₂:η²-N₂CPh₂)₂­Ti­(Cl)₂], in which the two Ti­(IV) ions are inequivalently coordinated. Reaction with cyclooctatetraene (COT) yielded a new Ti­(III) complex, [(py)₂­Ti­(η⁸-COT)­Cl], which is a rare example of a mononuclear “piano-stool” titanium complex. The complex <i>trans</i>-[(py)₄­TiCl₂] has thus been shown to be synthetically accessible, have an interesting electronic structure, and be reactive toward oxidation chemistry