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.