Distinct Reactivity Differences of Metal Oxo and Its Corresponding Hydroxo Moieties in Oxidations: Implications from a Manganese(IV) Complex Having Dihydroxide Ligand

Abstract

The Mn+OH moiety in a manganese(IV) complex has more powerful electron‐transfer capability than its corresponding Mn+O moiety. An Mn+O moiety can abstract hydrogen from a substrate, then rebind the OH group from its reduced M(n−1)+OH form to the substrate radical. In contrast, the active center with an Mn+OH cannot perform similar rebound from its reduced M(n−1)+OH2 group (see scheme; HAT=hydrogen abstraction).

A merged copper(I/II) cluster isolated from Glaser coupling

“…As a consequence, the [( t BuC≡CCu I 3 )-(μ 2 -OH)-Cu II ]@ Py[8] species shows high SET and HAT reactivity with substrates in a broad scope while the [Cu II -(OH)-Cu II ]@ Py[6] only undergoes a SET reaction pathway with strong reducing agents (e.g., TMPD). Particularly, the [( t BuC≡CCu I 3 )-(μ 2 -OH)-Cu II ]@ Py[8] exhibits HAT reactivity with hydrocarbons with C(sp 3 )–H bond dissociation energy up to 99 kcal mol −1 like other high-valent Mn(IV and V), Fe(IV), and Cu(III) oxygen species 58 . Compared with the common [Cu II -(OH)-Cu II ] species that is often considered as catalytic species in Cu/O 2 -based organic transformations, the remarkable oxidation ability and high reactivity of the bi-cluster intermediate [( t BuC≡CCu I 3 )-(μ 2 -OH)-Cu II ] implies that the in situ formed organometallic/copper–oxygen merged clusters may serve as the true catalytic species in both Glaser coupling reaction and other Cu/O 2 -catalyzed organic transformations.…”

Mechanisms in manganese catalysed oxidation of alkenes with H2O2

“…These complexes have shown activity in the epoxidation of alkenes employing H 2 O 2 [83][84][85][86] (and t BuOOH also) as terminal oxidant, as well as hydrogen abstraction. [87][88][89][90][91] In contrast to the TMTACN family of ligands the methyl groups on the non-bridging nitrogen atoms of the 85 The product distribution in the epoxidation of selected alkenes, catalysed by [Mn II (Me 2 EBC)(Cl) 2 ] in acetone/water with excess H 2 O 2 (17.7 equiv. w.r.t.…”

Synthesis, Structural Studies, and Oxidation Catalysis of the Late-First-Row-Transition-Metal Complexes of a 2-Pyridylmethyl Pendant-Armed Ethylene Cross-Bridged Cyclam

“…[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] The manganese complex of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane [15] (Me2EBC, Scheme 1) in particular, has a diverse and rich oxidation chemistry utilizing oxidation mechanisms ranging from hydrogen atom abstraction, electron transfer, concerted oxygen transfer, to the oxygen rebound mechanism. [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] This compound, which we propose to call "the Busch catalyst", was initially targeted as a potential oxidation catalyst because the rigid cross-bridged ligand could strongly bind the oxygen-reactive manganese ion and prevent it from being deactivated in the form of MnO2. [1] [2] [3] [4] Additional critical ligand properties are thought to be the two available cis labile coordination sites for oxidant and substrate interaction, the methyl groups sterically preventing dimerization which might deactivate the catalyst, and the saturated and all-tertiary nitrogen nature of the ligand, which minimizes the possibility of ligand oxidation and catalyst destruction.…”