Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts

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Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts Christian Schöttle, Erjia Guan, Alexander Okrut, Nicolás A. Grosso-Giordano, Andrew Palermo, Andrew Solovyov, Bruce C. Gates, and Alexander Katz J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b13013 • Publication Date (Web): 08 Feb 2019 Downloaded from http://pubs.acs.org on February 9, 2019

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Journal of the American Chemical Society

Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts Christian Schöttle1, Erjia Guan2, Alexander Okrut1, Nicolás A. Grosso-Giordano1, Andrew Palermo2, Andrew Solovyov1, Bruce C. Gates2* and Alexander Katz1* 1Department

of Chemical and Biomolecular Engineering, University of California at Berkeley, Berkeley, California 94720, USA. 2Department of Chemical Engineering, University of California at Davis, One Shields Avenue, Davis, California 95616, USA ABSTRACT: Although essentially molecular, noble metal species provide active sites and highly tunable platforms for design of supported catalysts, the susceptibility of the metals to reduction and aggregation and the consequent loss of catalytic activity and selectivity limit opportunities for their application. Here, we demonstrate a new construct to stabilize supported molecular noble metal catalysts, taking advantage of sterically bulky ligands on the metal that serve as surrogate supports and isolate the active sites under conditions involving steady-state catalytic turnover in a reducing environment. The result is demonstrated with an iridium pair-site catalyst incorporating P-bridging calix[4]arene ligands dispersed on siliceous supports, chosen as prototypes because they offer weakly interacting surfaces on which metal aggregation is prone to occur. This catalyst was used for hydrogenation of ethylene in a flow reactor. Atomic-resolution imaging of the Ir centers and spectra of the catalyst before and after use show that the metals resisted aggregation and deactivation, remaining atomically dispersed and accessible for catalysis. This strategy thus allows stabilization of the catalysts even when they are weakly anchored to supports.

Introduction

Results and Discussion

Supported metal catalysts with molecular structures and atomic dispersions are generating intense interest because they offer unprecedented opportunities for precise design of catalytic sites combined with maximally efficient use of expensive noble metals.1–5 This field has been invigorated by newly developed capabilities for atomic-resolution imaging of the metals on the supports and innovations that extend the class of catalysts beyond those incorporating single, isolated metal atoms to those incorporating pairs of metal atoms in the catalytic sites.3,6–11 Approaches for stabilizing molecular catalysts on supports have advanced our understanding of strong metal–support interactions and how these interactions lead to binding of the metal in a state of high dispersion.2,12–27 But the support can be much more than a platform for anchoring the metal. Here, we demonstrate a general approach for stabilization of an active site in a supported molecular catalyst, relying on sterically bulky ligands that control transport of reactants and products to and from the catalytically active metal centers while hindering deactivation via metal aggregation. Bulky calixarenes have been used previously to stabilize open, coordinatively unsaturated bonding sites in catalysts,28,29 but they have not heretofore been used to stabilize sites under steady-state conditions involving catalytic turnover. Our approach is demonstrated with the P-bridging calix[4]arene diiridium complex [Ir(CO)2PPhL]2 1 (Figure 1a) supported on fumed, dehydroxylated silica, which has been chosen as a prototypical weakly interacting surface, one that we posited should not hinder metal aggregation.30–32 To demonstrate generality of the concept illustrated here, we also supported 1 on a crystalline zeolitic silicate material, which has the SSZ-70 framework topology.33

The solid-state structure of 1 was elucidated on the basis of single-crystal X-ray diffraction (XRD) crystallography and high-angle annular dark-field (HAADF) STEM (Figures 1, 2, S3, S26, the latter two in the Supporting Information, SI). The data show that 1 consists of two Ir atoms, which are bridged with two P-calix[4]arene ligands and are separated by a distance of 2.72 Å, consistent with reported Ir–Ir single-bond distances.34,35 The two Ir atoms comprising the dimer cluster in the solid state have different coordination geometries. One of them, labeled Ir(2) in Figure 1d, is present in a square-planar geometry and the other in tetrahedral. This coordination geometry is related to that observed in a valence-shell dirhodium complex incorporating bridging phosphido ligands.36 The square-planar coordination within the phosphidobridged Rh-dimer corresponds to a 16-electron rhodium species, whereas the tetrahedral coordination corresponds to an 18-electron Rh species, in the solid state and at low temperature in deuterated toluene solution.36,37 Extending these results to the solid-state structure of 1 (Figures 1c, d), we surmise that Ir(2) is a 16-electron and Ir(1) an 18-electron species. This configuration enables a single Ir–Ir bond within the P-bridged Ir dimer. 31P- and 13C-NMR spectra of 1 in deuterated dichloromethane solution at room temperature show a single sharp resonance at δ = 273 ppm (Figures S7 in the SI) and a triplet at δ = 181 ppm (2JP-C = 15.3 Hz) for the bridging phosphorus and the carbonyl ligands (Figures S5, S6 in the SI), respectively. Thus, we surmise an all-square-planar coordination for Ir(1) and Ir(2) (Figures 1b; isomer 1-PP) in this solution, which lacks an Ir–Ir bond, in contrast to the mixedvalence cluster (1-TP) observed in the solid state of 1. Upon lowering the temperature to 223 K, no structural changes were

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observable by 13C NMR spectroscopy. However, at 203 K, only a single broad resonance was observed, indicating a transition between the all-square planar (1-PP) and squareplanar/tetrahedral (1-TP) structure (Figures S6 in the SI), consistent with phenomena observed upon decreasing the temperature of the phosphido-bridged Rh-dimer in deuterated toluene solution.36,37

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coordination sphere); isomer 1-PP (all-square planar coordination sphere); (c) and (d) crystal structure of 1; (e) scheme illustrating 1SiO2.

Figure 2. HAADF-STEM image of 1-SiO2. Inset shows an area in higher magnification, which includes intact dimers as well as debris formed by beam damage.

To isolate the catalytic sites in this Ir-dimer for reaction of gas-phase reactants and avoid solvent effects, we supported 1 on the surface of fumed, dehydroxylated silica (further labeled 1-SiO2; Figure 1e), a weakly interacting support (Figures S11 in the SI), using an alkane solvent, from which 1 partitions to the more polar solid phase.27,30,38 The weak nature of the interactions are evident by the fact that 1 can be fully recovered from 1-SiO2, without any decomposition or ligand loss, by a simple wash with toluene (Figures S15, S16), a finding that is unremarkable given purification of 1 via silica chromatography during its synthesis. EXAFS spectroscopy of 1-SiO2 shows identical Ir-C, Ir-P and Ir-Ir coordination numbers and distances (Table S2, Figure S14a) with 1. This similarity fully supports our assertion of the same molecular structure of the Ir complex in 1 and 1-SiO2. Infrared (IR) spectra of 1-SiO2 recorded under catalytic ethylene hydrogenation conditions demonstrate that catalytic activation proceeds via dissociation of one of the four CO ligands during the course of the first 24 h on stream (Table 1). The loss of CO to open an active center on the Irdimer core was also characterized by EXAFS spectroscopy. The latter data for 1-SiO2 before and after catalysis demonstrate a decrease in the Ir-C contribution that is consistent with the IR data above, and no change in the Ir-Ir and Ir-P coordinations. Thus, besides the loss of the single CO, spectroscopy shows no significant changes to the supported cluster following catalysis (Tables S2, S3, Figure S16). Table 1. CO loss of 1-SiO2 resulting from treatments in various gases at 50 °C. Figure 1. (a) Molecular structure of [Ir(CO)2PPhL]2 (1); (b) [Ir(CO)2PPhL]2: Isomer 1-TP (tetrahedral/square planar

Conditions of flowing gas


treatment

in

Number of CO ligands per Ir-dimer

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Journal of the American Chemical Society none (catalyst as-prepared)

4

24 h in helium, 50 °C

3.9

24 h in ethylene, 50 °C

3.9

24 h in H2, 50 °C

3.1

24 h in ethylene + H2 during catalytic hydrogenation, 50 °C

3.0

Tracking the sample with IR spectroscopy, we replicated the loss of a single CO ligand from 1-SiO2 in a stream of H2 gas at 323 K (Table 1, Figure S18 in the SI). During this reaction, we observed the appearance and growth of a new IR band at 2130 cm-1 (Figures S19, S25 in the SI), assigned to Ir–H.32,39 Because time scales corresponding to both loss of CO ligands and formation of the iridium hydride match the timescale observed for increase in catalytic activity during time on stream under ethylene hydrogenation conditions (Figure S21 in the SI), we conclude that the activation of 1-SiO2 for catalysis was accompanied by the replacement of a single CO ligand with a bound hydride, which subsequently reacted rapidly with ethylene. A subsequent CO treatment after reaction of 1-SiO2 with flowing H2 led to a fast recarbonylation, to give a species again incorporating four CO ligands per Ir2 moiety (Figure S18 in the SI). In contrast, exposure of 1-SiO2 to either pure flowing helium or ethylene gas at temperatures up to 353 K did not lead to desorption of any CO ligands (Tables 1, S4). This result is contrasted with that characterizing the silica-supported molecular catalyst consisting of phosphine-substituted tetrairidium clusters Ir4L13/SiO2 (L1 = calixarene-phosphine), which lost approximately 3 of its 9 CO ligands at 311 K in flowing helium.28 Moreover, the initial rate of CO dissociation from Ir4L13/SiO2 was independent of whether H2 was present,32 demonstrating that the CO dissociation was not hydrogen assisted,28,39 contrary to what was observed for 1-SiO2. We measured a steady-state turnover frequency (TOF) of 540 h-1 for ethylene hydrogenation catalysis at 323 K using 1SiO2 (Figure 3a) as the catalyst, which—significantly— remained stable after more than 90 h on stream, with no observable decrease in activity. This steady-state activity is two orders of magnitude higher than that reported for the calixarenephosphine-bound Ir4L13/SiO2 cluster.39 We attribute the higher activity, at least in part, to the higher Ir oxidation state (+1 on average in 1, vs. 0 in Ir4L13). Bolstering this inference, recent reports demonstrate that the activity of supported iridium carbonyl clusters for ethylene hydrogenation scales with the electron deficiency of the cluster core, correlated with the frequency of the carbonyl band.40

Figure 3. Catalytic activities: (a) TOF of 1-SiO2 showing activation of the catalyst. Inset shows long-term stability. (b) TOFs of 2-SiO2, 3-SiO2 and 4-SiO2. The steady-state activity of 1-SiO2 is represented as a black line for visual clarity. 2-SiO2 is silicasupported Crabtree catalyst; 3-SiO2 is silica-supported Wilkinson catalyst; 4-SiO2 is silica-supported Schrock-Osborn catalyst.

HAADF-STEM images recorded before and after catalysis by 1-SiO2 (Figures 2, 4, S26, S28, the latter two in the SI) show the molecular integrity of the silica-supported sites even after catalysis (the heavy Ir atoms on the light SiO2 support were imaged with atomic resolution), and the dimeric structure of the molecular site is evidenced by the 2.43 ± 0.4 Å distance between the Ir atoms. The similarity of this distance with that found for 1 by single-crystal XRD is consistent with the same Ir dimer structure and Ir–P coordination sphere in the supported samples. EXAFS data recorded before and after catalysis agree with the HAADF-STEM data, further supporting the demonstration of integrity of the Ir–Ir and Ir–P coordination spheres before and after catalysis (Tables S2, S3 in the SI). This conclusion is further corroborated by XANES data (Figure S31



in the SI), which demonstrate a lack of change in the iridium oxidation state as a result of catalysis.

Figure 4. (a) and (b) HAADF-STEM images of 1-SiO2 after catalysis.

Figure 5. HAADF-STEM images of 2-SiO2 (a) before and (b) after catalysis; 4-SiO2 (c) before and (d) after catalysis.


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Journal of the American Chemical Society To demonstrate the uniqueness of the structural integrity of 1-SiO2, we compared its performance and structure with those of well-known, highly active silica-supported hydrogenation catalysts (Figure S2 in the SI), consisting of Wilkinson’s ([(PPh3)3RhCl], 3),41 Schrock-Osborn’s ([(PPh3)2Rh(COD)], COD = cyclooctadiene, 4),42 and Crabtree’s catalysts ([(COD)Ir(py)(Pcy3)], py = pyridine, cy = cyclohexyl, 2), 43 all of which have properties tuned by the choice of the phosphine ligands. These three supported catalysts were benchmarked under our standard catalytic reaction conditions used for 1-SiO2 (323 K, 1 bar). Although Wilkinson’s catalyst (3-SiO2) exhibits low activity (TOF < 20 h-1), consistent with its known lack of proficiency for ethylene hydrogenation,41 the Crabtree (2-SiO2) and Schrock-Osborn catalysts (4-SiO2) show high initial activities, with TOF values > 1000 h-1. However, within the first 6–12 h onstream, the activities of these two catalysts plummeted to values below the stable steady-state TOF observed for 1-SiO2 (Figure 3b). HAADF-STEM images of the used catalysts show changes that lead to this deactivation (Figure 5): The metals in 2-SiO2, 4-SiO2, and 3-SiO2 all aggregated into poorly defined clusters (2-SiO2, 4-SiO2; Figure 5) or nanoparticles (3-SiO2; Figure S30, Supporting Information),43 whereas the metal in our ligand-protected dimer catalyst (1-SiO2) retained its initial dispersion. The aggregation of metal in the Wilkinson catalyst 3-SiO2, led to an increased catalytic activity (Figure 3b), because the rhodium metal nanoparticles formed initially are small enough to be more active than the original molecular species (Figure S30 in the SI). The observed aggregation was expected,27,38 and it extends beyond supported catalysts to soluble ones as well.43 The loss of molecular structure in these catalysts corresponds to a loss of ability to tune their properties, such as by the choice of ligands. To demonstrate the generality of this concept, we also supported 1 on the surface of a zeolitic silicate having the SSZ70 framework topology, making 1-SSZ-70. We did this because we expected this crystalline surface topology comprising 12MR hemispherical pockets on the surface to be significantly different from the varied ring sizes comprising our fumed, dehydroxylated silica surface used in the other catalysts. Data characterizing ethylene hydrogenation in the flow reactor (Figure S32 in the SI) demonstrate that 1-SSZ-70 is also a stable catalyst, exhibiting steady-state turnover at about the same times on stream as observed for 1-SiO2, with approximately twice the turnover frequency.

ASSOCIATED CONTENT Supporting Information. Experimental Methods, additional NMR, XRD, (in-situ) FTIR, mass, EXAFS, HAADF-STEM characterization. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] *Email: [email protected]

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENTS C. S. acknowledges the Deutsche Forschungsgemeinschaft (DFG) for a research fellowship, and A.K., A.S., A.O., and C.S. gratefully acknowledge funding from the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Grant DEFG02-05ER15696 and the Management and Transfer of Hydrogen via Catalysis Program funded by Chevron Corporation. The authors are grateful to P. Ercius and C. Song at the Molecular Foundry for their assistance in HAADF-STEM imaging. Work at the Molecular Foundry was supported by the DOE BES, under Contract No. DEAC02-05CH11231. Work in the NMR facility was supported by NIH grant S10OD024998. Work at the University of California, Davis (AP, EG), was supported by the DOE BES Grant DE-FG0204ER15513. X-ray absorption spectroscopy experiments were done at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, beam line 4-1, supported by DOE SC BES under Contract No. DE-AC02-76SF00515.

REFERENCES (1)

(2)

(3)

(4)

Conclusions In summary, catalysts 1-SiO2 and 1-SSZ-70 are robust supported molecular catalysts that exhibit stable turnover and do not show any evidence of metal aggregation during hydrogenation catalysis. These results demonstrate multiple benefits of the bulky calixarene phosphine ligands: they maintain the iridium dimer centers isolated in the ligation sphere – keeping the catalysts as essentially molecular species, and they prevent aggregation of the metal on the supports. Thus, the data demonstrate a new paradigm for stabilizing supported molecular catalysts by isolating the metals, a function that is typically provided by the support. We see opportunities for stabilization of new families of supported molecular metal catalysts, whereby the choice of support can now be unconstrained by requirements of metal–support interactions for catalyst stability.

(5)

(6)

(7)

(8)

Cui, X.; Li, W.; Ryabchuk, P.; Junge, K.; Beller, M. Bridging Homogeneous and Heterogeneous Catalysis by Heterogeneous Single-Metal-Site Catalysts. Nat. Catal. 2018, 1 (6), 385–397. https://doi.org/10.1038/s41929-018-0090-9. Gates, B. C.; Flytzani-Stephanopoulos, M.; Dixon, D. A.; Katz, A. Atomically Dispersed Supported Metal Catalysts: Perspectives and Suggestions for Future Research. Catal. Sci. Technol. 2017, 7, 4259–4275. https://doi.org/10.1039/C7CY00881C. Shan, J.; Li, M.; Allard, L. F.; Lee, S.; Flytzani-Stephanopoulos, M. Mild Oxidation of Methane to Methanol or Acetic Acid on Supported Isolated Rhodium Catalysts. Nature 2017, 551 (7682), 605–608. https://doi.org/10.1038/nature24640. Qian, L.; Wang, Z.; Beletskiy, E. V.; Liu, J.; Dos Santos, H. J.; Li, T.; Rangel, M. D. C.; Kung, M. C.; Kung, H. H. Stable and Solubilized Active Au Atom Clusters for Selective Epoxidation of Cis-Cyclooctene with Molecular Oxygen. Nat. Commun. 2017, 8, 1–8. https://doi.org/10.1038/ncomms14881. Oliver-meseguer, J.; Cabrero-antonino, J. R.; Domínguez, I.; Leyva-pérez, A.; Corma, A. Small Gold Clusters Formed in Numbers of 10 7 at Room Temperature. Science 2012, 338 (6113), 3–7. https://doi.org/10.1126/science.1227813. Ortalan, V.; Uzun, A.; Gates, B. C.; Browning, N. D. Direct Imaging of Single Metal Atoms and Clusters in the Pores of Dealuminated HY Zeolite. Nat. Nanotechnol. 2010, 5 (7), 506– 510. https://doi.org/10.1038/nnano.2010.92. Asakura, K.; Kitamura-Bando, K.; Iwasawa, Y.; Arakawa, H.; Isobe, K. Metal-Assisted Hydroformylation on a SiO2-Attached Rh Dimer. In Situ EXAFS and FT-IR Observations of the Dynamic Behaviors of the Dimer Site. J. Am. Chem. Soc. 1990, 112 (25), 9096–9104. https://doi.org/10.1021/ja00181a010. Guan, E.; Gates, B. C. Stable Rhodium Pair Sites on MgO: Influence of Ligands and Rhodium Nuclearity on Catalysis of Ethylene Hydrogenation and H-D Exchange in the Reaction of H2with D2. ACS Catal. 2018, 8 (1), 482–487.



(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

https://doi.org/10.1021/acscatal.7b03549. Yang, D.; Xu, P.; Guan, E.; Browning, N. D.; Gates, B. C. Rhodium Pair-Sites on Magnesium Oxide: Synthesis, Characterization, and Catalysis of Ethylene Hydrogenation. J. Catal. 2016, 338, 12–20. https://doi.org/10.1016/j.jcat.2016.02.023. Zhao, Y.; Yang, K. R.; Wang, Z.; Yan, X.; Cao, S.; Ye, Y.; Dong, Q.; Zhang, X.; Thorne, J. E.; Jin, L.; Materna, K. L.; Trimpalis, A.; Bai, H.; Fakra, S. C.; Zhong, X.; Wang, P.; Pan, X.; Guo, J.; Flytzani-Stephanopoulos, M.; Brudvig, G. W.; Batista, V. S.; Wang, D. Stable Iridium Dinuclear Heterogeneous Catalysts Supported on Metal-Oxide Substrate for Solar Water Oxidation. Proc. Natl. Acad. Sci. 2018, 115 (12), 2902–2907. https://doi.org/10.1073/pnas.1722137115. Liu, L.; Corma, A. Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles. Chem. Rev. 2018, 118 (10), 4981–5079. https://doi.org/10.1021/acs.chemrev.7b00776. Grigoropoulos, A.; McKay, A. I.; Katsoulidis, A. P.; Davies, R. P.; Haynes, A.; Brammer, L.; Xiao, J.; Weller, A. S.; Rosseinsky, M. J. Encapsulation of Crabtree’s Catalyst in Sulfonated MIL101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment. Angew. Chem. Int. Ed. 2018, 57 (17), 4532– 4537. https://doi.org/10.1002/anie.201710091. Rimoldi, M.; Fodor, D.; van Bokhoven, J. A.; Mezzetti, A. A Stable 16-Electron Iridium(Iii) Hydride Complex Grafted on SBA-15: A Single-Site Catalyst for Alkene Hydrogenation. Chem. Commun. 2013, 49 (96), 11314. https://doi.org/10.1039/c3cc47296e. Rimoldi, M.; Mezzetti, A. Batch and Continuous Flow Hydrogenation of Liquid and Gaseous Alkenes Catalyzed by a Silica-Grafted Iridium(III) Hydride. Helv. Chim. Acta 2016, 99 (12), 908–915. https://doi.org/10.1002/hlca.201600184. Sheludko, B.; Cunningham, M. T.; Goldman, A. S.; Celik, F. E. Continuous Flow Alkane Dehydrogenation by Supported PincerLigated Iridium Catalysts at Elevated Temperatures. ACS Catal. 2018, 8, 7828–7841. https://doi.org/10.1021/acscatal.8b01497. Huang, Z.; Brookhart, M.; Goldman, A. S.; Kundu, S.; Ray, A.; Scott, S. L.; Vicente, B. C. Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of Alkanes. Adv. Synth. Catal. 2009, 351 (1–2), 188–206. https://doi.org/10.1002/adsc.200800615. Huang, Z.; Rolfe, E.; Carson, E. C.; Brookhart, M.; Goldman, A. S.; El-Khalafy, S. H.; Roy MacArthur, A. H. Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis. Adv. Synth. Catal. 2010, 352 (1), 125–135. https://doi.org/10.1002/adsc.200900539. Saavedra, J.; Doan, H. A.; Pursell, C. J.; Grabow, L. C.; Chandler, B. D. The Critical Role of Water at the Gold-Titania Interface in Catalytic CO Oxidation. Science 2014, 345 (6204), 1599–1602. https://doi.org/10.1126/science.1256018. Marcinkowski, M. D.; Darby, M. T.; Liu, J.; Wimble, J. M.; Lucci, F. R.; Lee, S.; Michaelides, A.; Flytzani-Stephanopoulos, M.; Stamatakis, M.; Sykes, E. C. H. Pt/Cu Single-Atom Alloys as Coke-Resistant Catalysts for Efficient C–H Activation. Nat. Chem. 2018, 10 (3), 325–332. https://doi.org/10.1038/nchem.2915. Bayram, E.; Lu, J.; Aydin, C.; Uzun, A.; Browning, N. D.; Gates, B. C.; Finke, R. G. Mononuclear Zeolite-Supported Iridium: Kinetic, Spectroscopic, Electron Microscopic, and Size-Selective Poisoning Evidence for an Atomically Dispersed True Catalyst at 22 °c. ACS Catal. 2012, 2 (9), 1947–1957. https://doi.org/10.1021/cs300366w. Nicholas, C. P.; Ahn, H.; Marks, T. J. Synthesis, Spectroscopy, and Catalytic Properties of Cationic Organozirconium Adsorbates on “Super Acidic” Sulfated Alumina. “Single-Site” Heterogeneous Catalysts with Virtually 100% Active Sites. J. Am. Chem. Soc. 2003, 125 (14), 4325–4331. https://doi.org/10.1021/ja0212213. Moliner, M.; Gabay, J. E.; Kliewer, C. E.; Carr, R. T.; Guzman, J.; Casty, G. L.; Serna, P.; Corma, A. Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite. J. Am. Chem. Soc. 2016, 138 (48), 15743– 15750. https://doi.org/10.1021/jacs.6b10169.

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

(37)

(38)

Corma, A.; Garcia, H. Silica-Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis. Adv. Synth. Catal. 2006, 348 (12–13), 1391–1412. https://doi.org/10.1002/adsc.200606192. Hübner, S.; De Vries, J. G.; Farina, V. Why Does Industry Not Use Immobilized Transition Metal Complexes as Catalysts? Adv. Synth. Catal. 2016, 358 (1), 3–25. https://doi.org/10.1002/adsc.201500846. Corma, A.; Garcia, H. Crossing the Borders between Homogeneous and Heterogeneous Catalysis: Developing Recoverable and Reusable Catalytic Systems. Top. Catal. 2008, 48 (1–4), 8–31. https://doi.org/10.1007/s11244-008-9056-5. Pugin, B.; Landert, H.; Spindler, F.; Blaser, H.-U. More than 100,000 Turnovers with Immobilized Ir-Diphosphine Catalysts in an Enantioselective Imine Hydrogenation. Adv. Synth. Catal. 2002, 344 (9), 974–979. https://doi.org/10.1002/16154169(200210)344:93.0.CO;2-Z. Bayram, E.; Linehan, J. C.; Fulton, J. L.; Szymczak, N. K.; Finke, R. G. Determination of the Dominant Catalyst Derived from the Classic [RhCp*Cl 2 ] 2 Precatalyst System: Is It Single-Metal Rh 1 Cp*-Based, Subnanometer Rh 4 Cluster-Based, or Rh(0) n Nanoparticle-. ACS Catal. 2015, 5 (6), 3876–3886. https://doi.org/10.1021/acscatal.5b00315. Okrut, A.; Runnebaum, R. C.; Ouyang, X.; Lu, J.; Aydin, C.; Hwang, S. J.; Zhang, S.; Olatunji-Ojo, O. A.; Durkin, K. A.; Dixon, D. A.; Gates, B. C.; Katz, A. Selective Molecular Recognition by Nanoscale Environments in a Supported Iridium Cluster Catalyst. Nat. Nanotechnol. 2014, 9 (6), 459–465. https://doi.org/10.1038/nnano.2014.72. de Silva, N.; Ha, J.-M.; Solovyov, A.; Nigra, M. M.; Ogino, I.; Yeh, S. W.; Durkin, K. A.; Katz, A. A Bioinspired Approach for Controlling Accessibility in Calix[4]Arene-Bound Metal Cluster Catalysts. Nat. Chem. 2010, 2 (12), 1062–1068. https://doi.org/10.1038/nchem.860. Psaro, R.; Dossi, C.; Fusi, A.; Pergola, R. Della; Garlaschelli, L.; Roberto, D.; Sordelli, L.; Ugo, R.; Zanoni, R. Surface Organometallic Chemistry: Physisorption and Thermal Decomposition of Ir4(CO)12 on Silica. J. Chem. Soc. Faraday Trans. 1992, 88 (3), 369. https://doi.org/10.1039/ft9928800369. Lang, H.; Maldonado, S.; Stevenson, K. J.; Chandler, B. D. Synthesis and Characterization of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles. J. Am. Chem. Soc. 2004, 126 (40), 12949–12956. https://doi.org/10.1021/ja046542o. Palermo, A. P.; Zhang, S.; Hwang, S.; Dixon, D. A.; Gates, B. C.; Katz, A. Weakly Interacting Solvation Spheres Surrounding a Calixarene-Protected Tetrairidium Carbonyl Cluster: Contrasting Effects on Reactivity of Alkane Solvent and Silica Support. Dalt. Trans. 2018, 47 (38), 13550–13558. https://doi.org/10.1039/C8DT01371C. Smeets, S.; Berkson, Z. J.; Xie, D.; Zones, S. I.; Wan, W.; Zou, X.; Hsieh, M.-F.; Chmelka, B. F.; McCusker, L. B.; Baerlocher, C. Well-Defined Silanols in the Structure of the Calcined HighSilica Zeolite SSZ-70: New Understanding of a Successful Catalytic Material. J. Am. Chem. Soc. 2017, 139 (46), 16803– 16812. https://doi.org/10.1021/jacs.7b08810. Mena, I.; Casado, M. a; Polo, V.; García-Orduña, P.; Lahoz, F. J.; Oro, L. a. P-H Activation of Secondary Phosphanes on a Parent Amido Diiridium Complex. Dalton Trans. 2014, 43 (4), 1609– 1619. https://doi.org/10.1039/c3dt52911h. Tejel, C.; Ciriano, M. A.; Villarroya, B. E.; López, J. A.; Lahoz, F. J.; Oro, L. A. A Hexanuclear Iridium Chain. Angew. Chem. Int. Ed. 2003, 42 (5), 529–532. https://doi.org/10.1002/anie.200390152. Kang, S. K.; Albright, T. A.; Wright, T. C.; Jones, R. A. The Bonding and Interconversion in a Series of Rh2(CO)4(PR2)2 Isomers. Organometallics 1985, 4 (4), 666–675. https://doi.org/10.1021/om00123a009. Jones, R. A.; Wright, T. C.; Atwood, J. L.; Hunter, W. E. Reversible Metal-Metal Bond Cleavage Accompanied by a Geometrical Isomerism. Synthesis and Crystal Structures of Isomers of [Rh(μ-(Me3C)2P)(CO)2]2. Catalysis of Alkene Hydroformylation. Organometallics 1983, 2 (3), 470–472. https://doi.org/10.1021/om00075a026. Kent, P. D.; Mondloch, J. E.; Finke, R. G. A Four-Step


Page 6 of 8

Page 7 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society

(39)

(40)

Mechanism for the Formation of Supported-Nanoparticle Heterogenous Catalysts in Contact with Solution: The Conversion of Ir(1,5-COD)Cl/γ-Al 2 O 3 to Ir(0) ∼170 /γ-Al 2 O 3. J. Am. Chem. Soc. 2014, 136 (5), 1930–1941. https://doi.org/10.1021/ja410194r. Palermo, A.; Solovyov, A.; Ertler, D.; Okrut, A.; Gates, B. C.; Katz, A. Dialing in Single-Site Reactivity of a Supported Calixarene-Protected Tetrairidium Cluster Catalyst. Chem. Sci. 2017, 8 (7), 4951–4960. https://doi.org/10.1039/C7SC00686A. Yang, D.; Odoh, S. O.; Borycz, J.; Wang, T. C.; Farha, O. K.; Hupp, J. T.; Cramer, C. J.; Gagliardi, L.; Gates, B. C. Tuning Zr6Metal-Organic Framework (MOF) Nodes as Catalyst Supports: Site Densities and Electron-Donor Properties Influence Molecular Iridium Complexes as Ethylene Conversion Catalysts. ACS Catal. 2016, 6 (1), 235–247.

(41)

(42)

(43)

https://doi.org/10.1021/acscatal.5b02243. Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. The Preparation and Properties of Tris(Triphenylphosphine)Halogenorhodium(I) and Some Reactions Thereof Including Catalytic Homogeneous Hydrogenation of Olefins and Acetylenes and Their Derivatives. J. Chem. Soc. A Inorganic, Phys. Theor. 1966, No. 1, 1711. https://doi.org/10.1039/j19660001711. Schrock, R. R.; Osborn, J. A. Catalytic Hydrogenation Using Cationic Rhodium Complexes. I. Evolution of the Catalytic System and the Hydrogenation of Olefins. J. Am. Chem. Soc. 1976, 98 (8), 2134–2143. https://doi.org/10.1021/ja00424a020. Crabtree, R. Iridium Compounds in Catalysis. Acc. Chem. Res. 1979, 12 (9), 331–337. https://doi.org/10.1021/ar50141a005.




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Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts

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