Functionalization of Complexed NO in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium.

Methyl triflate reacts with the metastable azoxymetallacyclopentene complex CpZr(N(O)NCPhCPh), generated from nitrous oxide insertion into the Zr-C bond of CpZr(η-PhCCPh) at -78 °C, to afford the salt [CpZr(N(O)N(Me)CPhCPh)][OSCF] () in 48% isolated yield. A single-crystal X-ray structure of 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 , the methoxy-triflato complex CpZr(OMe)(OSCF) () was also isolated from the reaction mixture in 26% yield and fully characterized, including its independent synthesis from the alkylation of CpZr=O(NCH) with MeOSCF. Complex could also be observed, spectroscopically, from the thermolysis of (80 °C, 2 days). In contrast to CpZr(N(O)NPhCCPh), the more stable titanium NO-inserted analogue, CpTi(N(O)NCPhCPh), reacts with MeOSCF to afford a 1:1 mixture of regioisomeric salts, [CpTi(N(O)N(Me)CPhCPh)][OSCF] () and [CpTi(N(OMe)NCPhCPh)][OSCF] (), in a combined 65% isolated yield. Single-crystal X-ray diffraction studies of a cocrystal of and 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 CpTi(N(O)NCPhCPh) with KC, followed by encapsulation with the cryptand 2,2,2-Kryptofix, resulted in the isolation of the discrete radical anion [K(2,2,2-Kryptofix)][CpTi(N(O)NCPhCPh)] () in 68% yield. Complex 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()/d(-), houses the unpaired electron, without perturbing the azoxymetallacycle core in CpTi(N(O)NCPhCPh). Theoretical studies of Ti and the Zr analogue are also presented and discussed.