Functionalization of Complexed N2O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium

Methyl triflate reacts with the metastable azoxymetallacyclopentene complex Cp*2Zr­(N­(O)­NCPhCPh), generated in situ from nitrous oxide insertion into the Zr–C bond of Cp*2Zr­(η2-PhCCPh) at −78 °C, to afford the salt [Cp*2Zr­(N­(O)­N­(Me)­CPhCPh)]­[O3SCF3] (1) in 48% isolated yield. A single-crystal X-ray structure of 1 features a planar azoxymetallacycle with methyl alkylation taking place only at the β-nitrogen position of the former Zr­(N­(O)­NCPhCPh) scaffold. In addition to 1, the methoxy-triflato complex Cp*2Zr­(OMe)­(O3SCF3) (2) was also isolated from the reaction mixture in 26% yield and fully characterized, including its independent synthesis from the alkylation of Cp*2ZrO­(NC5H5) with MeO3SCF3. Complex 2 could also be observed, spectroscopically, from the thermolysis of 1 (80 °C, 2 days). In contrast to Cp*2Zr­(N­(O)­NPhCCPh), the more stable titanium N2O-inserted analogue, Cp*2Ti­(N­(O)­NCPhCPh), reacts with MeO3SCF3 to afford a 1:1 mixture of regioisomeric salts, [Cp*2Ti­(N­(O)­N­(Me)­CPhCPh)]­[O3SCF3] (3) and [Cp*2Ti­(N­(OMe)­NCPhCPh)]­[O3SCF3] (4), in a combined 65% isolated yield. Single-crystal X-ray diffraction studies of a cocrystal of 3 and 4 show a 1:1 mixture of azoxymetallacyle salts resulting from methyl alkylation at both the β-nitrogen and the β-oxygen of the former Ti­(N­(O)­NCPhCPh ring. As opposed to alkylation reactions, the one-electron reduction of Cp*2Ti­(N­(O)­NCPhCPh) with KC8, followed by encapsulation with the cryptand 2,2,2-Kryptofix, resulted in the isolation of the discrete radical anion [K­(2,2,2-Kryptofix)]­[Cp*2Ti­(N­(O)­NCPhCPh)] (5) in 68% yield. Complex 5 was studied by single-crystal X-ray diffraction, and its solution X-band EPR spectrum suggested a nonbonding σ-type wedge hybrid orbital on titanium, d­(z2)/d­(x2–y2), houses the unpaired electron, without perturbing the azoxymetallacycle core in Cp*2Ti­(N­(O)­NCPhCPh). Theoretical studies of Ti and the Zr analogue are also presented and discussed.