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)(4)TiCl2] (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)(4)TiCl2] has a E-3(g) ground state (d(xy)(1)d(xz,yz)(1) orbital occupancy), which, as a result of spinorbit coupling, yields a ground-state spinor doublet that is EPR active, a first excited-state doublet at similar to 60 cm1, and two next excited states at similar to 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(eta(2)-R2E2)Cl-2(py)(n)] E = C, N intermediates. A new Ti(IV) compound, mer-[(py)(3)(eta(2)-Ph2C2)TiCl2], was prepared by reaction with Ph2C2, along with the previously reported complex trans-(py)(3)Ti=NPh(Cl)(2), from reaction with Ph2N2. Reaction with Ph2CN2 also yielded a new dinuclear Ti(IV) complex, [(py)(2)(Cl)(2)Ti(mu(2):eta(2)-N2CPh2)(2)Ti(Cl)(2)], in which the two Ti(IV) ions are inequivalently coordinated. Reaction with cyclooctatetraene (COT) yielded a new Ti(III) complex, [(py)(2)Ti(eta(8)-COT)Cl], which is a rare example of a mononuclear piano-stool titanium complex. The complex trans-[(py)(4)TiCl2] has thus been shown to be synthetically accessible, have an interesting electronic structure, and be reactive toward oxidation chemistry.