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 trans-[(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 ab initio methods). These studies demonstrated that trans-[(py)4TiCl2] has a (3)Eg ground state (dxy(1)dxz,yz(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(η(2)-R2E2)Cl2(py)n] E = C, N intermediates. A new Ti(IV) compound, mer-[(py)3(η(2)-Ph2C2)TiCl2], was prepared by reaction with Ph2C2, along with the previously reported complex trans-(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:η(2)-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(η(8)-COT)Cl], which is a rare example of a mononuclear “piano-stool” titanium complex. The complex trans-[(py)4TiCl2] has thus been shown to be synthetically accessible, have an interesting electronic structure, and be reactive toward oxidation chemistry.