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

Methyl triflate reacts with the metastable azoxymetallacyclopentene complex Cp* 2 Zr(N(O)NCPhCPh), generated in situ from nitrous oxide insertion into the Zr-C bond of Cp* 2 Zr(η 2 -PhCCPh) at -78 °C, to afford the salt [Cp* 2 Zr(N(O)N(Me)CPhCPh)][O 3 SCF 3 ] ( 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* 2 Zr(OMe)(O 3 SCF 3 ) ( 2 ) was also isolated from the reaction mixture in 26% yield and fully characterized, including its independent synthesis from the alkylation of Cp* 2 Zr=O(NC 5 H 5 ) with MeO 3 SCF 3 . Complex 2 could also be observed, spectroscopically, from the thermolysis of 1 (80 °C, 2 days). In contrast to Cp* 2 Zr(N(O)NPhCCPh), the more stable titanium N 2 O-inserted analogue, Cp* 2 Ti(N(O)NCPhCPh), reacts with MeO 3 SCF 3 to afford a 1:1 mixture of regioisomeric salts, [Cp* 2 Ti(N(O)N(Me)CPhCPh)][O 3 SCF 3 ] ( 3 ) and [Cp* 2 Ti(N(OMe)NCPhCPh)][O 3 SCF 3 ] ( 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* 2 Ti(N(O)NCPhCPh) with KC 8 , 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* 2 Ti(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( z 2 )/d( x 2 - y 2 ), houses the unpaired electron, without perturbing the azoxymetallacycle core in Cp* 2 Ti(N(O)NCPhCPh). Theoretical studies of Ti and the Zr analogue are also presented and discussed.