Manganese Triazacyclononane Oxidation Catalysts Grafted under Reaction Conditions on Solid Cocatalytic Supports

Schoenfeldt, Nicholas J.; Ni, Zhenjuan; Korinda, Andrew W.; Meyer, Randall J.; Notestein, Justin M.

doi:10.1021/ja204761e

Cited by 44 publications

(32 citation statements)

References 99 publications

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“…Thus, the computed Zr-C(benzene) mean distance is found to be 2.71 Å, somewhat overestimated vs. the EXAFS-derived distance [2.35 (±2) Å] and the average distance for cationic Zr(IV)-η 6 -benzene complexes [2.62(±2) Å] in the Cambridge Crystallographic Database (34). This is not completely unexpected, and in other combined DFT + EXAFS studies, DFT calculations sometimes have overestimated bond distances (41)(42)(43). As a consequence of the benzene coordination, the Zr centers of chemisorbed species C/S A and C/S B are displaced substantially from the anionic surface coordination sites S A and S B , respectively, and the C•C 6 H 6 /AlS structure converges to a unique conformation in which the cationic complex lies between the S A and S B vicinal sulfate groups (Fig.…”

Section: Resultsmentioning

confidence: 73%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13 C-cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η 5 O rganometallic molecule-derived heterogeneous catalysts are of increasing interest owing to their enhanced thermal stability and activity vs. their homogeneous analogs, and their atomically precise tailorable metal-ligand structures vs. other heterogeneous catalysts (1, 2). Furthermore, it is becoming increasingly evident that the inorganic support in many systems is noninnocent and can function as both a ligand and an activator, with the chemically important but poorly understood nature of the catalyst-support interaction strongly modulating catalytic activity and selectivity (3, 4). When adsorbed on Lewis acidic, dehydroxylated alumina surfaces, group 4 complexes such as Cp 2 ZrR 2 (Cp = η 5 -C 5 H 5 ; A, R = H; B, R = CH 3 ) and Cp*Zr (CH 3 ) 3 [C, Cp* = η 5 -C 5 (CH 3 ) 5 ] were argued on the basis of highresolution solid-state NMR spectroscopy to transfer an alkyl anion to unsaturated, Lewis acidic surface sites as in Fig. 1 (complexes B, C → qualitative model D) (5, 6). The resulting catalysts are extremely active for olefin hydrogenation and polymerization, and analogous ion-paired species form the basis for large-scale industrial polymerization processes (7,8). However, kinetic poisoning experiments in which the catalytic sites are titrated in situ with H 2 O or t BuCH 2 OH indicate that ≤5% of D-type sites are catalytically significant, likely reflecting, among other factors, the established heterogeneity of alumina surfaces (5, 6, 9), hence rendering active site structural and chemical descriptions necessarily imprecise. In contrast to these results, chemisorption of such organozirconium precursors on SiO 2 , Al 2 O 3 , and SiO 2 -Al 2 O 3 surfaces having appreciable coverage by weakly acidic OH groups predominantly yields covalently bound, poorly electrophilic Etype species via Zr-CH 3 protonolysis with CH 4 evolution (5, 6, 10, 11). Although the E-type sites may be characterized in some detail by high-resolution solid-state NMR and extended X-ray adsorption fine structure spectroscopy (EXAFS), they display minimal catalytic turnover in the absence of added, complicating activators [e.g., methylalumoxane or B(C 6 F 5 ) 3 ], and the fraction of catalytically significant sites is unknown (12, 13). In such situations, it is experimentally impossible to unambiguously distinguish catalytically significant sites from inactive "spectator" sites, hence to fully understand the catalytic chemistry.-In marked contrast to the above results, chemisorption of these same organozirconium molecules on highly Brønsted "super...

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Section: Resultsmentioning

confidence: 73%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Such chemical transformations are challenging to accomplish selectively in organic synthesis, and, for this reason, activation of C-H groups has attracted considerable attention in recent years (27,28). We suggest that, in the initial step, Fe(IV) = O abstracts the H5′′ atom from the primary substrate, leading to the generation of a substrate radical.…”

Section: Resultsmentioning

confidence: 97%

“…The ORF snoK (804 bp) was deleted from the cosmid pSnogaori with the aid of the λ Red recombinase system (34). The (cm R ) resistance gene was subsequently removed with the aid of pFLP2 (35) expressing the FLP recombinase, followed by conjugation into S. albus (32) from E. coli ET12567/pUZ8002 (28), resulting in the strain S. albus/ pSnoΔK. The ORF for snoN was introduced to the strain S. albus/pSnogaori by the plasmid pIJTLMN (9,770 bp), leading to the final strain S. albus/pSnogaori+N.…”

Section: Methodsmentioning

confidence: 99%

Divergent non-heme iron enzymes in the nogalamycin biosynthetic pathway

Siitonen

Selvaraj

Niiranen

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Nogalamycin, an aromatic polyketide displaying high cytotoxicity, has a unique structure, with one of the carbohydrate units covalently attached to the aglycone via an additional carbon-carbon bond. The underlying chemistry, which implies a particularly challenging reaction requiring activation of an aliphatic carbon atom, has remained enigmatic. Here, we show that the unusual C5′′-C2 carbocyclization is catalyzed by the non-heme iron α-ketoglutarate (α-KG)-dependent SnoK in the biosynthesis of the anthracycline nogalamycin. The data are consistent with a mechanistic proposal whereby the Fe(IV) = O center abstracts the H5′′ atom from the amino sugar of the substrate, with subsequent attack of the aromatic C2 carbon on the radical center. We further show that, in the same metabolic pathway, the homologous SnoN (38% sequence identity) catalyzes an epimerization step at the adjacent C4′′ carbon, most likely via a radical mechanism involving the Fe(IV) = O center. SnoK and SnoN have surprisingly similar active site architectures considering the markedly different chemistries catalyzed by the enzymes. Structural studies reveal that the differences are achieved by minor changes in the alignment of the substrates in front of the reactive ferryl-oxo species. Our findings significantly expand the repertoire of reactions reported for this important protein family and provide an illustrative example of enzyme evolution.natural product biosynthesis | Streptomyces | crystal structure | α-ketoglutarate-dependent oxygenase | iron-dependent oxygenase

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“…Notestein et al [43,44] prepared heterogeneous Mn(tmtacn) catalyst (O) systems grafted on oxide surfaces under oxidation reaction conditions (Figure 7.4) and investigated the performance of the grafted catalysts in epoxidation using H 2 O 2 . The features of their immobilization method are as follows: (i) no modification of the metal-coordinating tmtacn ligand for attachment to an oxide surface (the synthesis of ligands with silane-coupling reagents is often complicated); (ii) a welldefined structure similar to the homogeneous Mn(tmtacn) dimer (L), resulting in a similar product selectivity; and (iii) unpredictable productivity resulting from interactions between the metal, ligand, surface, and neighboring species.…”

Section: Manganese Triazacyclononane Catalysts Grafted Under Reactionmentioning

confidence: 99%

“…The features of their immobilization method are as follows: (i) no modification of the metal-coordinating tmtacn ligand for attachment to an oxide surface (the synthesis of ligands with silane-coupling reagents is often complicated); (ii) a welldefined structure similar to the homogeneous Mn(tmtacn) dimer (L), resulting in a similar product selectivity; and (iii) unpredictable productivity resulting from interactions between the metal, ligand, surface, and neighboring species. They reported the preparation of the heterogeneous Mn(tmtacn) complex (O) under oxidation conditions, and investigated the structure and performance of the grafted Mn(tmtacn) catalyst (O) [43,44].…”

Section: Manganese Triazacyclononane Catalysts Grafted Under Reactionmentioning

confidence: 99%

Site‐Isolated Heterogeneous Catalysts

Tada

Muratsugu

2013

Heterogeneous Catalysts for Clean Technology

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IntroductionNumerous supported metal catalysts have been utilized for a variety of chemical processes, and their crucial advantages are (i) easy separation of the catalyst and reaction medium, (ii) high durability of the catalyst, and (iii) unique catalytic performance from that of homogeneous analogs. The structures of homogeneous catalysts have been thoroughly studied in organometallic and coordination chemistry, wherein catalytic behavior can be regulated by tuning the ligands of homogeneous metal complexes. In contrast, the heterogeneity and complexity of support surfaces often hinder full understanding of relationships between catalytically active structures and reactivity for heterogeneous catalysts. Regulating catalytic performance at the molecular level therefore remains more difficult for heterogeneous supported metal catalysts compared with their homogenous analogs.To construct well-controlled metal coordination structures for selective catalysis, attachment techniques for metal complexes have been developed, and various homogeneous precursors have been chemically attached to support surfaces in a controllable manner [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. There are several types of attachment techniques: coordination of metal-complex precursors to immobilized ligands on organic polymers [17][18][19][20][21], coordination of metal-complex precursors to functional ligands bound to oxide surfaces [2,4,[22][23][24][25], intercalation into clay materials [26], ion exchange into porous materials such as zeolites and mesoporous silicas [27], and direct attachment of metal-complex precursors onto oxide surfaces [3,6,11,28,29]. The selective immobilization of a homogeneous metal complex can isolate each metal site on a support surface, resulting in the formation of a well-defined single-site catalyst. The interaction between a supported metal complex and support surface often produces a unique metal coordination structure, different from that of a homogeneous counterpart. Consequently, unique catalytic performance can be obtained on the surface.In this chapter, several recent examples of site-isolated heterogeneous catalysts on solid support surfaces are highlighted. The coordination structures of siteisolated supported metal complexes, their unique catalytic performance, and their Heterogeneous Catalysts for Clean Technology: Spectroscopy, Design, and Monitoring, First Edition. Edited

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Manganese Triazacyclononane Oxidation Catalysts Grafted under Reaction Conditions on Solid Cocatalytic Supports

Cited by 44 publications

References 99 publications

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Divergent non-heme iron enzymes in the nogalamycin biosynthetic pathway

Site‐Isolated Heterogeneous Catalysts

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Manganese Triazacyclononane Oxidation Catalysts Grafted under Reaction Conditions on Solid Cocatalytic Supports

Cited by 44 publications

References 99 publications

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Divergent non-heme iron enzymes in the nogalamycin biosynthetic pathway

Site‐Isolated Heterogeneous Catalysts

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Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites