Non-Redox-Assisted Oxygen−Oxygen Bond Homolysis in Titanocene Alkylperoxide Complexes:  [Cp₂Ti^IV(η¹-OO^tBu)L]^+/0, L = Cl^-, OTf^-, Br^-, OEt₂, Et₃P

Abstract

The titanium(IV) alkylperoxide complex Cp 2 Ti(OO t Bu)Cl (1) is formed on treatment of Cp 2 TiCl 2 with NaOO t Bu in THF at −20 °C. Treatment of 1 with AgOTf at −20 °C gives the triflate complex Cp 2 Ti(OO t Bu)OTf (2), which is rapidly converted to the bromide Cp 2 Ti(OO t Bu)Br (3) on addition of n Bu 4 NBr. The X-ray crystal structures of 1 and 3 both show η 1 -OO t Bu ligands. Complex 2 is stable only below −20 °C; 1 H, 13 C, and 19 F NMR spectra suggest that it also contains an η 1 -OO t Bu ligand. Removal of the chloride from 1 with [Ag(Et 2 O) 2 ]BAr' 4 (Ar' = 3,5-(CF 3 ) 2 C 6 H 3 )) yields the etherate complex [Cp 2 Ti(OO t Bu)(OEt 2 )]BAr' 4 (4). Again, coordination of a fourth ligand to the Ti center indicates an η 1 -OO t Bu ligand in 4. These peroxide complexes do not directly oxidize olefins or phosphines. For instance, the cationic etherate complex 4 reacts with excess Et 3 P simply by displacement of the ether to form [Cp 2 Ti(η 1 -OO t Bu)(Et 3 P)]BAr' 4 (5). Compounds 1-5 all decompose by O-O bond homolysis, based on trapping and computational studies. The lack of direct oxygen atom transfer reactivity is likely due to the η 1 coordination of the peroxide and the inability to adopt more reactive η 2 geometry. DFT calculations indicate that the steric bulk of the t Bu group inhibits formation of the hypothetical [Cp 2 Ti(η 2 -OO t Bu)] + species.

Reaction of a monomeric titanium hydride with dioxygen does not produce a stable titanium hydroperoxide

“…It might be expected that if formed, a Ti-OOH species might rapidly undergo decomposition at room temperature. In support of this hypothesis a recently reported tert-butyl peroxide of Ti has been isolated and found to be stable only at temperatures below −20°C [21,22].…”

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

“…Given that Et 3 P has been shown to serve as a probe for tert- butoxide radicals, 53 we examined reactions between 1a to 4a and Et 3 P (10 equiv) under anaerobic conditions. Analysis of the final reaction mixture by GC/MS showed a 24% yield of Et 2 PO t Bu and 31% yield of Et 3 PO.…”

Structural Characterization and Oxidation Activity of a Nickel(II) Alkylperoxo Complex

“…[1] The alkylperoxo complexes of d 0 early transition-metal ions (groups [4][5][6], in particular, have attracted much attention, owing to their potential as oxygenating reagents for organic compounds (for example, olefin epoxidation). [2][3][4][5] Interest in the alkylperoxo complexes of late transition metals is also growing because of their industrial significance and biological relevance. [6][7][8] Nickel is recognized as one of the most useful metals in promoting various organic transformation reactions, owing its intrinsic redox properties.…”