Manganese-Catalyzed C–H Activation

Abstract

Manganese is found in the active center of numerous enzymes that operate by an outer-sphere homolytic C−H cleavage. Thus, a plethora of bioinspired radical-based C−H functionalizations by manganese catalysis have been devised during the past decades. In contrast, organometallic C−H activation by means of manganese catalysis has emerged only recently as an increasingly viable tool in organic synthesis. These manganese(I)-catalyzed processes enabled a variety of C− H functionalizations with ample scope, which very recently set the stage for substitutive C−H functionalizations. The versatile manganese catalysis largely operates by an isohypsic, thus redox-neutral, mode of action through chelation assistance, and provided step-economical access to structurally divers compounds of relevance to inter alia bioorganic, agrochemical, and medicinal chemistry as well as the material sciences.

Manganese‐Catalyzed C−H Alkynylation: Expedient Peptide Synthesis and Modification

“…[4] While most C À Ht ransformations were thus far accomplished with the aid of precious transition metals,t he use of earth-abundant base metal catalysts has gained recent momentum, [5] with considerable progress accomplished by less toxic manganese catalysts. [6] However,d espite recent advances by the groups of Wang, Kuninobu, Fairlamb,a nd Ackermann, among others, [7][8][9][10][11] the organometallic manganese C À Hactivation regime is severely limited to addition reactions onto multiple CÀHet or CÀC bonds.I ndeed, in stark contrast to other [12] transition metals, [13] manganese-catalyzed substitutive CÀHa ctivation with organic halides have proven to be elusive.W ithin our program on sustainable C À Ha ctivation, [14] we have now established the first manganese-catalyzed C À Hfunctionalization with organic halides,o nw hich we report herein. In addition to the conceptual advance,n otable features of our approach include 1) versatile CÀHa lkynylations by manganese(I) catalysis with silyl, aryl, and alkyl haloalkynes, 2) as ignificant rate acceleration through as ynergistic catalysis manifold, and 3) robust C À Ha lkynylations for the latestage modification of peptides,thereby 4) setting the stage for versatile syntheses and modifications [15] of densely decorated acyclica nd cyclic peptides (Figure 1).…”

Efficient V2O5/TiO2 composite catalysts for dimethoxymethane synthesis from methanol selective oxidation

“…4 The catalytic test showed that the reducibility and oxidizability of catalyst determines its catalytic activity. 52 Compared to VTi catalyst, sample VTiSi showed the highest activity of 51% methanol conversion and DMM selectivity of 99% among all samples at 413 K. Moreover, when the temperature increased to 423 K, the DMM selectivity was still kept at 98% with the methanol conversion of 52%. The sample VTi exhibited a highest methanol conversion of 43% of and a DMM selectivity of 89% at 413 K. The selectivity for MF was 10% and 1% for DME.…”

Manganese‐Catalyzed Redox‐Neutral C−H Olefination of Ketones with Unactivated Alkenes

“…[4] Diverse products were obtained with varied reaction conditions,w hilst the corresponding catalytic versions have remained untouched thus far.G iven our interest in using earth-abundant manganese catalysts for C À Ha ctivation, [5,6] we herein disclose the first manganese-catalyzed redox-neutral C À Ho lefination of ketones with unactivated alkenes (Scheme 1c). [4] Diverse products were obtained with varied reaction conditions,w hilst the corresponding catalytic versions have remained untouched thus far.G iven our interest in using earth-abundant manganese catalysts for C À Ha ctivation, [5,6] we herein disclose the first manganese-catalyzed redox-neutral C À Ho lefination of ketones with unactivated alkenes (Scheme 1c).…”

“…[4] Diverse products were obtained with varied reaction conditions,w hilst the corresponding catalytic versions have remained untouched thus far.G iven our interest in using earth-abundant manganese catalysts for C À Ha ctivation, [5,6] we herein disclose the first manganese-catalyzed redox-neutral C À Ho lefination of ketones with unactivated alkenes (Scheme 1c). Mn 2 (CO) 10 showed lower efficiencyand non-carbonyl manganese,aswell as other transition-metal carbonyls did not promote the reaction at all (entries [3][4][5]. [7] At the outset, acetophenone (1a)a nd styrene (2a)w ere selected as model substrates to screen reaction parameters (Table 1).…”