1
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Formation of Strong Boron Lewis Acid Sites on Silica. Inorg Chem 2024; 63:4939-4946. [PMID: 38451151 PMCID: PMC10951953 DOI: 10.1021/acs.inorgchem.3c04121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 02/20/2024] [Accepted: 02/21/2024] [Indexed: 03/08/2024]
Abstract
Bis(1-methyl-ortho-carboranyl)borane (HBMeoCb2) is a very strong Lewis acid that reacts with the isolated silanols present on silica partially dehydroxylated at 700 °C (SiO2-700) to form the well-defined Lewis site MeoCb2B(OSi≡) (1) and H2. 11B{1H} magic-angle spinning (MAS) nuclear magnetic resonance (NMR) data of 1 are consistent with that of a three-coordinate boron site. Contacting 1 with O═PEt3 (triethylphosphine oxide TEPO) and measuring 31P{1H} MAS NMR spectra show that 1 preserves the strong Lewis acidity of HBMeoCb2. Hydride ion affinity and fluoride ion affinity calculations using small molecules analogs of 1 also support the strong Lewis acidity of the boron sites in this material. Reactions of 1 with Cp2Hf(13CH3)2 show that the Lewis sites are capable of abstracting methide groups from Hf to form [Cp2Hf-13CH3][H313C-B(MeoCb2)OSi≡], but with a low overall efficiency.
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2
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Geometry and electronic structure of Yb(III)[CH(SiMe 3) 2] 3 from EPR and solid-state NMR augmented by computations. Phys Chem Chem Phys 2024; 26:8734-8747. [PMID: 38416412 PMCID: PMC10936694 DOI: 10.1039/d4cp00281d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 02/12/2024] [Indexed: 02/29/2024]
Abstract
Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and - still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-the-art magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe3)2]3, a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre-two-electron Yb-γ-Me-β-Si secondary metal-ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb-carbon bond contains some π-character, reminiscent of the so-called α-H agostic interaction.
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3
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A Supported Ziegler-Type Organohafnium Site Metabolizes Polypropylene. J Am Chem Soc 2023; 145. [PMID: 37921588 PMCID: PMC10655186 DOI: 10.1021/jacs.3c05940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 10/26/2023] [Accepted: 10/30/2023] [Indexed: 11/04/2023]
Abstract
Cp2Hf(CH3)2 reacts with silica containing strong aluminum Lewis sites to form Cp2Hf-13CH3+ paired with aluminate anions. Solid-state NMR studies show that this reaction also forms neutral organohafnium and hafnium sites lacking methyl groups. Cp2Hf-13CH3+ reacts with isotatic polypropylene (iPP, Mn = 13.3 kDa; Đ = 2.4; mmmm = 94%; ∼110 C3H6/Hf) and H2 to form oils with moderate molecular weights (Mn = 290-1200 Da) in good yields. The aliphatic oils show characteristic 13C{1H} NMR properties consistent with complete loss of diastereoselectivity and formation of regioirregular errors under 1 atm H2. These results show that a Ziegler-Natta-type active site is compatible in a common reaction used to digest waste plastic into smaller aliphatic fragments.
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4
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Effects of surface acidity on the structure of organometallics supported on oxide surfaces. Chem Commun (Camb) 2023; 59:4115-4127. [PMID: 36912586 DOI: 10.1039/d3cc00047h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
Abstract
Well-defined organometallics supported on high surface area oxides are promising heterogeneous catalysts. An important design factor in these materials is how the metal interacts with the functionalities on an oxide support, commonly anionic X-type ligands derived from the reaction of an organometallic M-R with an -OH site on the oxide. The metal can either form a covalent M-O bond or form an electrostatic M+⋯-O ion-pair, which impacts how well-defined organometallics will interact with substrates in catalytic reactions. A less common reaction pathway involves the reaction of a Lewis site on the oxide with the organometallic, resulting in abstraction to form an ion-pair, which is relevant to industrial olefin polymerization catalysts. This Feature Article views the spectrum of reactivity between an organometallic and an oxide through the prism of Brønsted and/or Lewis acidity of surface sites and draws analogies to the molecular frame where Lewis and Brønsted acids are known to form reactive ion-pairs. Applications of the well-defined sites developed in this article are also discussed.
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5
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Cationic Tantalum Hydrides Catalyze Hydrogenolysis and Alkane Metathesis Reactions of Paraffins and Polyethylene. J Am Chem Soc 2023; 145:4964-4968. [PMID: 36827508 DOI: 10.1021/jacs.2c13610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023]
Abstract
Sulfated aluminum oxide (SAO), a high surface area material containing sulfate anions that behave like weakly coordinating anions, reacts with Ta(═CHtBu)(CH2tBu)3 to form [Ta(CH2tBu)2(O-)2][SAO] (1). Subsequent treatment with H2 forms Ta-H+ sites supported on SAO that are active in hydrogenolysis and alkane metathesis reactions. In both reactions Ta-H+ is more active than related neutral Ta-H sites supported on silica. This reaction chemistry extends to melts of high-density polyethylene (HDPE), where Ta-H+ converts 30% of a low molecular weight HDPE (Mn = 2.5 kg mol-1; Đ = 3.6) to low molecular weight paraffins under hydrogenolysis conditions. Under alkane metathesis conditions Ta-H+ converts this HDPE to a high MW fraction (Mn = 6.2 kDa; Đ = 2.3) and low molecular weight alkane products (C13-C32). These results show that incorporating charge as a design element in supported d0 metal hydrides is a viable strategy to increase the reaction rate in challenging reactions involving reorganization of C-C bonds in alkanes.
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6
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A Tungsten Oxo Alkylidene Supported on Sulfated Zirconium Oxide for Olefin Metathesis. Organometallics 2023. [DOI: 10.1021/acs.organomet.3c00008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
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7
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Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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8
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Ring Contraction of a Tungstacyclopentane Supported on Silica: Direct Conversion of Ethylene to Propylene. J Am Chem Soc 2022; 144:18761-18765. [PMID: 36197795 DOI: 10.1021/jacs.2c07934] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The reaction of W(NAr)(13C4H8)(OSiPh3)2 (1) (NAr = 2,6-diisopropylphenylimido) with silica partially dehydroxylated at 700 °C (SiO2-700) is highly dependent on the reaction conditions. The primary product of this reaction is W(NAr)(13C4H8)(OSiPh3)(OSi(O-)3) (2) when the reaction is carried out in the dark. Grafting 1 onto SiO2-700 in ambient lab light results in the formation of 2, W(NAr)(13CH213CH2)(OSiPh3)(OSi(O-)3) (4), and one isomer of square-pyramidal W(NAr)(13CH213CH(13Me)13CH2)(OSiPh3)(OSi(O-)3) (3). Heating 2 to 85 °C for 6 h results in the formation of 3, 4, W(NAr)(13CH(13Me)13CH213CH2)(OSiPh3)(OSi(O-)3) (5), and W(NAr)((13CH2)213CH(13Me)(13CH2)2)(OSiPh3)(OSi(O-)3) (6). Photolysis of 2 with blue LEDs (λmax = 450 nm) produces 4, both isomers of 3, 5, and free ethylene. In the presence of excess ethylene and blue LED irradiation at 85 °C, 1/SiO2-700 catalyzes the direct conversion of ethylene to propylene.
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9
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Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica. Angew Chem Int Ed Engl 2022; 61:e202205745. [DOI: 10.1002/anie.202205745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Indexed: 11/10/2022]
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10
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Abstract
Sulfated zirconium oxide (SZO) capped with silylium-like ions reacts with (cod)Ir(py)Cl (cod = 1,5-cyclooctadiene; py = pyridine) to form [Ir(cod)py][SZO] (1) and Me3SiCl. 1 can also be formed in reactions of phosphonium functionalized SZO and [Ir(cod)(OSi(OtBu)3]2, which forms [Ir(cod)P(tBu)2Ph][SZO] (2), followed by reaction with pyridine to form 1. FTIR and 15N{1H} MAS NMR spectroscopy are consistent with coordination of pyridine in 1 to an electrophilic iridium. 1 is moderately active in the dearomative hydroboration of pyridine. The primary product of this reaction is 1,2-dihydropyridine, which converts to the 1,4-dihydropyridine product at long reaction times. 1 catalyzes the dearomative hydroboration of a variety of substituted pyridines and is also reactive toward pyrazines and N-methylimidazole.
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11
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Abstract
Exposure of a solution of the square pyramidal tungstacyclopentane complex W(NAr)(OSiPh3)2(C4H8) (Ar = 2,6-i-Pr2C6H3) to ethylene at 22 °C in ambient (fluorescent) light slowly leads to the formation of propylene and the square pyramidal tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). No reaction takes place in the dark, but the reaction is >90% complete in ∼15 min under blue LED light (∼450 nm λmax). The intermediates are proposed to be (first) an α methyl tungstacyclobutane complex (W(NAr)(OSiPh3)2(αMeC3H5)), and then from it, a β methyl version. The TBP versions of each can lose propylene and form a methylene complex, and in the presence of ethylene, the unsubstituted tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). The W-Cα bond in an unobservable TBP W(NAr)(OSiPh3)2(C4H8) isomer in which the C4H8 ring is equatorial is proposed to be cleaved homolytically by light. A hydrogen atom moves or is moved from C3 to the terminal C4 carbon in the butyl chain as the bond between W and C3 forms to give the TBP α methyl tungstacyclobutane complex. Essentially, the same behavior is observed for W(NCPh3)(OSiPh3)2(C4H8) as for W(NAr)(OSiPh3)2(C4H8), except that the rate of consumption of W(NCPh3)(OSiPh3)2(C4H8) is about half that of W(NAr)(OSiPh3)2(C4H8). In this case, an α methyl-substituted tungstacyclobutane intermediate is observed, and the overall rate of formation of W(NCPh3)(OSiPh3)2(C3H6) and propylene from W(NCPh3)(OSiPh3)2(C4H8) is ∼20 times slower than in the NAr system. These results constitute the first experimentally documented examples of forming a metallacyclobutane ring from a metallacyclopentane ring (ring contraction) and establish how metathesis-active methylene and metallacyclobutane complexes can be formed and reformed in the presence of ethylene. They also raise the possibility that ambient light could play a role in some metathesis reactions that involve ethylene and tungsten-based imido alkylidene olefin metathesis catalysts, if not others.
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12
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Abstract
Understanding how a ligand affects the steric and electronic properties of a metal is the cornerstone of the inorganic chemistry enterprise. What happens when the ligand is an extended surface? This question is central to the design and implementation of state-of-the-art functional materials containing transition metals. This perspective will describe how these two very different sets of extended surfaces can form well-defined coordination complexes with metals. In the Green formalism, functionalities on oxide surfaces react with inorganics to form species that contain X-type or LX-type interactions between the metal and the oxide. Carbon surfaces are neutral L-type ligands; this perspective focuses on carbons that donate six electrons to a metal. The nature of this interaction depends on the curvature, and thereby orbital overlap, between the metal and the extended π-system from the nanocarbon.
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13
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A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R
3
Si
+
Species. Angew Chem Int Ed Engl 2022; 61:e202117279. [DOI: 10.1002/anie.202117279] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Indexed: 11/12/2022]
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14
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Reactions of Triisobutylaluminum with Unbridged or Bridged Group IV Metallocene Dichlorides. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00067] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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15
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A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R
3
Si
+
Species. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202117279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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Solid-state 11B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand. Dalton Trans 2021; 50:14855-14863. [PMID: 34604875 DOI: 10.1039/d1dt02981a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active 11B nucleus. We measured solid-state 11B{1H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B2P2) that contain planar boron centers and weak M → BR3 linkages ([(B2P2)M][BArF4] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling (CQ) values (4.4-4.7 MHz) and large span (Ω) values (93-139 ppm). However, the solid-state 11B{1H} NMR spectrum of K[Au(B2P2)]- (4), which contains tetrahedral borons, is narrow and characterized by small CQ and Ω values. DFT analysis of 1-4 shows that CQ and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR3 linkage relates to the reduction in CQ and 11B NMR shielding properties. Thus solid-state 11B NMR spectroscopy contains valuable information about M → BR3 linkages in complexes containing the B2P2 ligand.
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17
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Interconversion of Molybdenum or Tungsten d 2 Styrene Complexes with d 0 1-Phenethylidene Analogues. J Am Chem Soc 2021; 143:17209-17218. [PMID: 34633807 DOI: 10.1021/jacs.1c08086] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Upon addition of 5-15% PhNMe2H+X- (X = B(3,5-(CF3)2C6H3)4 or B(C6F5)4) to Mo(NAr)(styrene)(OSiPh3)2 (Ar = N-2,6-i-Pr2C6H3) in C6D6 an equilibrium mixture of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2 is formed over 36 h at 45 °C (Keq = 0.36). A plausible intermediate in the interconversion of the styrene and 1-phenethylidene complexes is the 1-phenethyl cation, [Mo(NAr)(CHMePh)(OSiPh3)2]+, which can be generated using [(Et2O)2H][B(C6F5)4] as the acid. The interconversion can be modeled as two equilibria involving protonation of Mo(NAr)(styrene)(OSiPh3)2 or Mo(NAr)(CMePh)(OSiPh3)2 and deprotonation of the α or β phenethyl carbon atom in [Mo(NAr)(CHMePh)(OSiPh3)2]+. The ratio of the rate of deprotonation of [Mo(NAr)(CHMePh)(OSiPh3)2]+ by PhNMe2 in the α position versus the β position is ∼10, or ∼30 per Hβ. The slow step is protonation of Mo(NAr)(styrene)(OSiPh3)2 (k1 = 0.158(4) L/(mol·min)). Proton sources such as (CF3)3COH or Ph3SiOH do not catalyze the interconversion of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2, while the reaction of Mo(NAr)(styrene)(OSiPh3)2 with pyridinium salts generates only a trace (∼2%) of Mo(NAr)(CMePh)(OSiPh3)2 and forms a monopyridine adduct, [Mo(NAr)(CHMePh)(OSiPh3)2(py)]+ (two diastereomers). The structure of [Mo(NAr)(CHMePh)(OSiPh3)2]+ has been confirmed in an X-ray study; there is no structural indication that a β proton is activated through a CHβ interaction with the metal. W(NAr)(CMePh)(OSiPh3)2 is also converted into a mixture of W(NAr)(CMePh)(OSiPh3)2 and W(NAr)(styrene)(OSiPh3)2 (Keq = 0.47 at 45 °C in favor of the styrene complex) with 10% [PhNMe2H][B(C6F5)4] as the catalyst; the time required to reach equilibrium is approximately the same as in the Mo system.
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18
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Active Sites in a Heterogeneous Organometallic Catalyst for the Polymerization of Ethylene. ACS CENTRAL SCIENCE 2021; 7:1225-1231. [PMID: 34345672 PMCID: PMC8323245 DOI: 10.1021/acscentsci.1c00466] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Indexed: 06/13/2023]
Abstract
Heterogeneous derivatives of catalysts discovered by Ziegler and Natta are important for the industrial production of polyolefin plastics. However, the interaction between precatalysts, alkylaluminum activators, and oxide supports to form catalytically active materials is poorly understood. This is in contrast to homogeneous or model heterogeneous catalysts that contain resolved molecular structures that relate to activity and selectivity in polymerization reactions. This study describes the reactivity of triisobutylaluminum with high surface area aluminum oxide and a zirconocene precatalyst. Triisobutylaluminum reacts with the zirconocene precatalyst to form hydrides and passivates -OH sites on the alumina surface. The combination of passivated alumina and zirconium hydrides formed in this mixture generates ion pairs that polymerize ethylene.
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19
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Ethylene Polymerization Activity of (R 3P)Ni(codH) + (cod = 1,5-cylcooctadiene) Sites Supported on Sulfated Zirconium Oxide. Inorg Chem 2021; 60:6946-6949. [PMID: 33844523 DOI: 10.1021/acs.inorgchem.1c00454] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PAr3 containing o-OMe, o-Me, or o-Et substituents reacts with Brønsted sites on sulfated zirconium oxide (SZO) to form [HPAr3][SZO]. The phosphonium sites on this material react with bis(cyclooctadiene)nickel [Ni(cod)2] to form [Ni(PAr3)(codH)][SZO] that are active in ethylene polymerization reactions. Selective poisoning studies with pyridine show that ∼90% of the Ni(PAr3)(codH)+ sites in this material are active in polymerization reactions.
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20
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21
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Solid-State 45Sc NMR Studies of Cp* 2Sc–OR (R = CMe 2CF 3, CMe(CF 3) 2, C(CF 3) 3, SiPh 3) and Relationship to the Structure of Cp* 2Sc-Sites Supported on Partially Dehydroxylated Silica. Organometallics 2020. [DOI: 10.1021/acs.organomet.9b00840] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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22
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Origin of the 29Si NMR chemical shift in R3Si–X and relationship to the formation of silylium (R3Si+) ions. Dalton Trans 2020; 49:16453-16463. [DOI: 10.1039/d0dt02099k] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The origin in deshielding of 29Si NMR chemical shifts in R3Si–X, where X = H, OMe, Cl, OTf, [CH6B11X6], toluene, and OX (OX = surface oxygen), as well as iPr3Si+ and Mes3Si+ were studied using DFT methods.
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23
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Abstract
Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging. This paper describes the reaction of Al(ORF)3*PhF (RF = C(CF3)3) with silica partially dehydroxylated at 700 °C (SiO2-700) to form the bridging silanol [triple bond, length as m-dash]Si-OH⋯Al(ORF)3 (1). DFT calculations using small clusters to model 1 show that the gas phase acidity (GPA) of the bridging silanol is 43.2 kcal mol-1 lower than the GPA of H2SO4, but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct3 show that 1 forms weaker ion-pairs than classical WCAs, but stronger ion-pairs than carborane or borate anions. Though 1 forms stronger ion-pairs than these state-of-the-art WCAs, 1 reacts with alkylsilanes to form silylium type surface species. To the best of our knowledge, this is the first example of a silylium supported on derivatized silica.
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24
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Characterization of Reactive Organometallic Species via MicroED. ACS CENTRAL SCIENCE 2019; 5:1507-1513. [PMID: 31572777 PMCID: PMC6764211 DOI: 10.1021/acscentsci.9b00403] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Indexed: 06/10/2023]
Abstract
Here we apply microcrystal electron diffraction (MicroED) to the structural determination of transition-metal complexes. We find that the simultaneous use of 300 keV electrons, very low electron doses, and an ultrasensitive camera allows for the collection of data without cryogenic cooling of the stage. This technique reveals the first crystal structures of the classic zirconocene hydride, colloquially known as "Schwartz's reagent", a novel Pd(II) complex not amenable to solution-state NMR or X-ray crystallography, and five other paramagnetic and diamagnetic transition-metal complexes.
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25
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π-Bond Character in Metal-Alkyl Compounds for C-H Activation: How, When, and Why? J Am Chem Soc 2019; 141:648-656. [PMID: 30525557 DOI: 10.1021/jacs.8b11951] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
C-H bond activation via σ-bond metathesis is typically observed with transition-metal alkyl compounds in d0 or d0fn electron configurations, e.g., biscyclopentadienyl metal alkyls. Related C-H activation processes are also observed for transition-metal alkyls with higher d-electron counts, such as W(II), Fe(II), or Ir(III). A σ-bond metathesis mechanism has been proposed in all cases with a preference for an oxidative addition-reductive elimination pathway for Ir(III). Herein we show that, regardless of the exact mechanism, C-H activation with all of these compounds is associated with π-character of the M-C bond, according to a detailed analysis of the 13C NMR chemical shift tensor of the α-carbon. π-Character is also a requirement for olefin insertion, indicating its similarity to σ-bond metathesis. This observation explains the H2 response observed in d0 olefin polymerization catalysts and underlines that σ-bond metathesis, olefin insertion, and olefin metathesis are in fact isolobal reactions.
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26
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Generation of Phosphonium Sites on Sulfated Zirconium Oxide: Relationship to Brønsted Acid Strength of Surface −OH Sites. J Am Chem Soc 2019; 141:1484-1488. [DOI: 10.1021/jacs.8b13204] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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27
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Activation of C−F Bonds by Electrophilic Organosilicon Sites Supported on Sulfated Zirconia. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201809199] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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28
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Activation of C−F Bonds by Electrophilic Organosilicon Sites Supported on Sulfated Zirconia. Angew Chem Int Ed Engl 2018; 57:14902-14905. [PMID: 30265766 DOI: 10.1002/anie.201809199] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Indexed: 11/07/2022]
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29
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The β‐Agostic Structure in (C
5
Me
5
)
2
Sc(CH
2
CH
3
): Solid‐State NMR Studies of (C
5
Me
5
)
2
Sc−R (R=Me, Ph, Et). Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201805738] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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30
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The β‐Agostic Structure in (C
5
Me
5
)
2
Sc(CH
2
CH
3
): Solid‐State NMR Studies of (C
5
Me
5
)
2
Sc−R (R=Me, Ph, Et). Angew Chem Int Ed Engl 2018; 57:9520-9523. [DOI: 10.1002/anie.201805738] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Indexed: 11/05/2022]
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31
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Bridging the Gap between Industrial and Well‐Defined Supported Catalysts. Angew Chem Int Ed Engl 2018; 57:6398-6440. [DOI: 10.1002/anie.201702387] [Citation(s) in RCA: 152] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Indexed: 12/22/2022]
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32
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33
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A Bulky Pd(II) α-Diimine Catalyst Supported on Sulfated Zirconia for the Polymerization of Ethylene and Copolymerization of Ethylene and Methyl Acrylate. Organometallics 2018. [DOI: 10.1021/acs.organomet.8b00016] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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34
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Abstract
A systematic study showing how the Sc–X bond affects solid-state 45Sc NMR quadrupolar coupling constants in Cp*2Sc–X.
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35
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A Well-Defined Ni(II) α-Diimine Catalyst Supported on Sulfated Zirconia for Polymerization Catalysis. Organometallics 2017. [DOI: 10.1021/acs.organomet.7b00402] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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36
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Abstract
The spatial arrangement of atoms is directly linked to chemical function. A fundamental challenge in surface chemistry and catalysis relates to the determination of three-dimensional structures with atomic-level precision. Here we determine the three-dimensional structure of an organometallic complex on an amorphous silica surface using solid-state NMR measurements, enabled through a dynamic nuclear polarization surface enhanced NMR spectroscopy approach that induces a 200-fold increase in the NMR sensitivity for the surface species. The result, in combination with EXAFS, is a detailed structure for the surface complex determined with a precision of 0.7 Å. We observe a single well-defined conformation that is folded toward the surface in such a way as to include an interaction between the platinum metal center and the surface oxygen atoms.
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37
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Role of Tricoordinate Al Sites in CH3ReO3/Al2O3 Olefin Metathesis Catalysts. J Am Chem Soc 2016; 138:6774-85. [DOI: 10.1021/jacs.6b00447] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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38
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ChemInform Abstract: Surface Organometallic and Coordination Chemistry Toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities. ACTA ACUST UNITED AC 2016. [DOI: 10.1002/chin.201615211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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39
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The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy. J Am Chem Soc 2016; 138:3831-43. [PMID: 26887899 DOI: 10.1021/jacs.6b00071] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc = 148 K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.
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40
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Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities. Chem Rev 2016; 116:323-421. [PMID: 26741024 DOI: 10.1021/acs.chemrev.5b00373] [Citation(s) in RCA: 480] [Impact Index Per Article: 60.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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41
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Berichtigung: Polymerization of Ethylene by Silica-Supported Dinuclear Cr IIISites through an Initiation Step Involving CH Bond Activation. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201503694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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42
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Corrigendum: Polymerization of Ethylene by Silica-Supported Dinuclear CrIIISites through an Initiation Step Involving CH Bond Activation. Angew Chem Int Ed Engl 2015; 54:6670. [DOI: 10.1002/anie.201503694] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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43
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Heterolytic Activation of C–H Bonds on CrIII–O Surface Sites Is a Key Step in Catalytic Polymerization of Ethylene and Dehydrogenation of Propane. Inorg Chem 2015; 54:5065-78. [DOI: 10.1021/ic502696n] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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44
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MeReO3/Al2O3 and Me4Sn-activated Re2O7/Al2O3 alkene metathesis catalysts have similar active sites. Catal Sci Technol 2015. [DOI: 10.1039/c4cy01710b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
MeReO3/Al2O3 and Re2O7/Al2O3 activated with Me4Sn, which have the same reactivity toward functionalized alkenes and ethylene, share similar surface sites.
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45
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Synthesis and Characterization of Rare Earth Siloxide Complexes, M[OSi(OtBu)3]3(L)x where L is HOSi(OtBu)3 and x = 0 or 1. Organometallics 2014. [DOI: 10.1021/om501047g] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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46
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Bulky Aryloxide Ligand Stabilizes a Heterogeneous Metathesis Catalyst. Angew Chem Int Ed Engl 2014; 53:14221-4. [DOI: 10.1002/anie.201408880] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Indexed: 11/11/2022]
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47
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Differentiation between Chelate Ring Inversion and Aryl Rotation in a CF3-Substituted Phosphine-Sulfonate Palladium Methyl Complex. Organometallics 2014. [DOI: 10.1021/om500699t] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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48
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Lutidine-Derived Ru-CNC Hydrogenation Pincer Catalysts with Versatile Coordination Properties. ACS Catal 2014. [DOI: 10.1021/cs500720y] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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49
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Chlorodiethylaluminum supported on silica: A dinuclear aluminum surface species with bridging μ2-Cl-ligand as a highly efficient co-catalyst for the Ni-catalyzed dimerization of ethene. J Catal 2014. [DOI: 10.1016/j.jcat.2014.02.006] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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50
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Mesostructured Hybrid Organic–Silica Materials: Ideal Supports for Well-Defined Heterogeneous Organometallic Catalysts. ACS Catal 2014. [DOI: 10.1021/cs500262t] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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