Structural and Spectroscopic Characterization of a Monomeric Side-On Manganese(IV) Peroxo Complex

Abstract

the H2O2 source. Few examples for the Mn II -mediated reduction of O2 yielding the Mn–O2 adduct were reported. [7–10] Hoffman and co-workers reported that Mn II TPP(py) can act as an oxygen carrier at low temperature to form a Mn(TPP)(O2) complex with a Mn IV (O2) 2� formalism and the binding mode of the peroxo ligand was suggested as symmetric side-on. [7] Another example reported by the Wieghardt group is the binuclear [L2Mn2(m-O)2(m-O2)] 2+ complex, which contains a peroxo bridge between two Mn IV ions. [9] Recently, Borovik and co-workers showed that reaction of [Mn II H2bupa] � and O2 at ambient temperature produces monomeric Mn III -peroxo complexes. [10] In this system, the noncovalent interactions (hydrogen bonding) within the secondary coordination sphere support the activation of O2. [11] In this report, we demonstrate that the complex [Mn I (CO)3(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH))] � , 1b , with the pendant thiol group in the secondary coordination sphere can activate molecular oxygen, leading to the formation of the monomeric, O2-side-on-bound Mn IV complex, [Mn(O2)(P(C6H3-3-SiMe3-2-S)3)] � , 3. Reaction of cis-[Mn(CO)4(SC6H5)2] � with one equivalent of P(C6H3-3-R-2-SH)3 (R = H or SiMe3) in tetrahydrofuran (THF) solution at 508C, respectively, produced the sixcoordinate [Mn(CO)3(P(C6H3-3-R-2-S)2(C6H3-3-R-2-SH))] � (R = H, 1a ; SiMe3, 1b ) isolated as a yellow solid in high yield (95 % for 1a ; 92 % for 1b ). The IR spectra of 1a and 1b show the same CO stretching bands at 1989(vs), 1908(s), and 1886(s) (Figure 1), consistent with a tricarbonyl derivative possessing pseudo C3v symmetry. [12] Complex 1a can be crystallized by vapor diffusion of diethyl ether into a concentrated THF/CH3CN (3:1, v/v) solution at � 208C in nitrogen. [13] Figure 1 displays a thermal ellipsoid plot of 1a .T he manganese center is coordinated by one phosphorus, two thiolate sulfur atoms, and three CO groups in a facial position, in agreement with the infrared data. The structural data also reveal that 1a contains a pendant thiol group in the secondary