Toward the Understanding of Radical Reactions: Experimental and Computational Studies of Titanium(III) Diamine Bis(phenolate) Complexes

Radical reactions of titanium(III) [Ti(tBu2O2NN′)Cl(S)] (S = THF, 1; S = py, 2; tBu2O2NN′ = Me2N(CH2)2N(CH2-2-O-3,5-tBu2C6H2)2) are described. Reactions with neutral electron acceptors led to metal oxidation to Ti(IV), [Ti(tBu2O2NN′)Cl(TEMPO)] (4) being formed with the TEMPO radical and [Ti(tBu2O2NN′)Cl2] (9) with PhN═NPh. [Ti(tBu2O2NN′)Cl2] was also formed when [Ti(tBu2O2NN′)Cl(S)] was oxidized by [Cp2Fe][BPh4], but the [Cp2Fe][PF6] analogue yielded [Ti(tBu2O2NN′)ClF] (8). The reactions of [Ti(tBu2O2NN′)Cl(S)] with O2 gave [Ti(tBu2O2NN′)Cl]2(μ-O) (3). The DFT calculated Gibbs energy for the above reaction showed it to be exergonic (ΔG298 = −123.6 kcal·mol–1). [Ti(tBu2O2NN′)(CH2Ph)(S)] (S = THF, 5; py, 6) are not stable in solution for long periods and in diethyl ether gave 1:1 cocrystals of [Ti(tBu2O2NN′)(CH2Ph)2] (7) and [Ti(tBu2O2NN′)Cl]2(μ-O) (3), most probably resulting from a disproportionation process of titanium(III) followed by oxygen abstraction by the resulting Ti(II) species. The oxidation of ...