A Highly Reactive Mononuclear Non-Heme Manganese(IV)–Oxo Complex That Can Activate the Strong C–H Bonds of Alkanes

Abstract

A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of -4.4 in the oxidation of para-substituted thioanisoles.

Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme RuIVO Complex

“…[49][50][51][52][53] However, in the case of a dissociative oxygen non-rebound reaction, the substrate radical escapes from the cage and then reacts with a second metal-oxo molecule to give hydroxylated products (Scheme 1A, pathways e and f for alkane hydroxylation; Scheme 1B, pathways j and k for allylic C-H bond activation). [54][55][56][57][58][59] We have shown recently that this radical dissociative mechanism prevails in C-H bond activation reactions by Fe IV O, Mn IV O, Cr IV O, and Fe V O catalysts in nonheme systems. [54][55][56][57][58][59] Very recently, we have also shown that an interplay of tunneling and spin inversion probability has to be taken into account in 2+ (1, terpy = 2,2′:6′,2′′-terpyridine, bpm = 2,2′-bipyrimidine; see Figure 1 for DFT-optimized structure), follows a dissociative oxygen non-rebound mechanism (Scheme 1A, reaction pathway e).…”

“…[54][55][56][57][58][59] We have shown recently that this radical dissociative mechanism prevails in C-H bond activation reactions by Fe IV O, Mn IV O, Cr IV O, and Fe V O catalysts in nonheme systems. [54][55][56][57][58][59] Very recently, we have also shown that an interplay of tunneling and spin inversion probability has to be taken into account in 2+ (1, terpy = 2,2′:6′,2′′-terpyridine, bpm = 2,2′-bipyrimidine; see Figure 1 for DFT-optimized structure), follows a dissociative oxygen non-rebound mechanism (Scheme 1A, reaction pathway e). While the oxidation of styrene and thioanisole by 1 occurs via an OAT mechanism, we show that the oxidation of cyclohexene by 1 affords products resulted from a C-H bond activation reaction rather than an epoxidation reaction.…”

“…These results are in line with our earlier results reported in the reactions of nonheme Fe IV O, Mn IV O, Cr IV O, and Fe V O complexes. [54][55][56][57][58][59] To support the dissociation hypothesis, we performed DFT calculations for the reaction of 1 and ethylbenzene (SI, Tables S2, S7, and S12). The DFT calculations resulted in a reaction barrier of 15.3 kcal mol -1 for the S = 1 state ( 3 TS E , Figure 4, the left superscript refers to the multiplicity M = 2S + 1 per convention), relative to the sum of the energies of the separated reactants ( 3 R E+RuO , as opposed to the reactant complex, 3 RC E ).…”

Molecular Iron-Based Oxidants and Their Stoichiometric Reactions

“…Most Fe(IV)-oxo complexes have been prepared using PhIO, or a derivative, as oxidant. This strategy has also commonly been employed for the preparation of the "high-valent" complexes of other first row transition metal ions, e.g., Cr(V)oxo [96], Co(IV)oxo [97], Mn(IV)oxo [98], and Mn(V)oxo [99]. All these species are formed in accordance to the general reaction Scheme 15.…”

Synthesis, characterization, cis-ligand substitution and catalytic alkane hydroxylation by mononuclear nickel(II) complexes stabilized with tetradentate tripodal ligands

“…Several reports on nonheme metal complexes are available, especially of the first-row transition metals such as manganese [2][3][4][5], iron [6][7][8][9][10][11], copper [12][13][14] and cobalt [15] in their high valent metal-oxo, peroxo, superoxo forms and play crucial roles in the organic oxygenation reactions. The nickel metal is not an exception to this list, as a large number of nickel complexes with tripodal ligands such as tris(2-pyridylmethyl)amine (TPA), N-tetramethylated cyclam (n-TMC), N, N-dimethyl-N 0 ,N 0 -bis(pyridin-2-ylmethyl)ethane-1,2-diamine (iso-BPMEN), N,N-dimethyl-N 0 ,N 0 -bis(quinolin-2-ylmethyl)ethane-1,2-diamine (iso-BQMEN) are known (Scheme 1) [16][17][18][19][20].…”