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

Radical reactions of titanium­(III) [Ti­(^<i>t</i>Bu2O₂NN′)­Cl­(S)] (S = THF, <b>1</b>; S = py, <b>2</b>; ^<i>t</i>Bu2O₂NN′ = Me₂N­(CH₂)₂N­(CH₂-2-O-3,5-^<i>t</i>Bu₂C₆H₂)₂) are described. Reactions with neutral electron acceptors led to metal oxidation to Ti­(IV), [Ti­(^<i>t</i>Bu2O₂NN′)­Cl­(TEMPO)] (<b>4</b>) being formed with the TEMPO radical and [Ti­(^<i>t</i>Bu2O₂NN′)­Cl₂] (<b>9</b>) with PhNNPh. [Ti­(^<i>t</i>Bu2O₂NN′)­Cl₂] was also formed when [Ti­(^<i>t</i>Bu2O₂NN′)­Cl­(S)] was oxidized by [Cp₂Fe]­[BPh₄], but the [Cp₂Fe]­[PF₆] analogue yielded [Ti­(^<i>t</i>Bu2O₂NN′)­ClF] (<b>8</b>). The reactions of [Ti­(^<i>t</i>Bu2O₂NN′)­Cl­(S)] with O₂ gave [Ti­(^<i>t</i>Bu2O₂NN′)­Cl]₂(μ-O) (<b>3</b>). The DFT calculated Gibbs energy for the above reaction showed it to be exergonic (Δ<i>G</i>₂₉₈ = −123.6 kcal·mol^–1). [Ti­(^<i>t</i>Bu2O₂NN′)­(CH₂Ph)­(S)] (S = THF, <b>5</b>; py, <b>6</b>) are not stable in solution for long periods and in diethyl ether gave 1:1 cocrystals of [Ti­(^<i>t</i>Bu2O₂NN′)­(CH₂Ph)₂] (<b>7</b>) and [Ti­(^<i>t</i>Bu2O₂NN′)­Cl]₂(μ-O) (<b>3</b>), most probably resulting from a disproportionation process of titanium­(III) followed by oxygen abstraction by the resulting Ti­(II) species. The oxidation of [Ti­(^<i>t</i>Bu2O₂NN′)­(κ²-{CH₂-2-(NMe₂)-C₆H₄})] (<b>10</b>), which is a Ti­(III) benzyl stabilized by the intramolecular coordination of the NMe₂ moiety, led to a complex mixture. Recrystallization of this mixture under air led to a 1:1 cocrystal of two coordination isomers of the titanium oxo dimer (<b>3</b>). In one of these isomers, one metal is pentacoordinate and the dimethylamine moiety of the diamine bis­(phenolate) ligand is not bonded to the metal, displaying a coordination mode of the ligand never observed before. The other titanium center is distorted octahedral with two <i>cis</i>-phenolate moieties. In the second unit, the coordination of the two ancillary ligands to the titanium centers reveals mutually <i>cis</i>-phenolate groups in one-half of the molecule and <i>trans</i>-coordinated in the other titanium center, keeping a distorted octahedral environment around each titanium