The surface science of nanoparticles for catalysis: electronic and steric effects of organic ligands
Source abstract
Abstract
Recent studies demonstrate the important roles of surface ligands in creating metal-organic interfaces that can significantly improve both catalytic activity as well as selectivity of chemically synthetized nanoparticle (NP) catalysts. Both steric and electronic effects can be efficiently used to tune catalytic properties of the NPs. Here, we overview the recent advancements in the field of the surface science of NPs for their catalytic applications and discuss the steric and electronic effects of ligands immobilized at the NP surface on the activity and selectivity of catalytically active NPs in different catalytic reactions.
Source: openaire · Quality: candidate unverified · Source record ↗
Research context
OpenAlex topics: Catalytic Processes in Materials Science · Nanomaterials for catalytic reactions · Electrocatalysts for Energy Conversion
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (92)
Show source-provided references
1. Albani D, Vile G, Mitchell S, Witte PT, Almora-Barrios N, Verel R, Lopez N, Perez-Ramirez J (2016) Ligand ordering determines the catalytic response of hybrid palladium nanoparticles in hydrogenation. Catal Sci Technol 6:1621–163110.1039/C5CY01921D ↗
2. Aliaga C, Park JY, Yamada Y, Lee HS, Tsung C-K, Yang P, Somorjai GA (2009) Sum frequency generation and catalytic reaction studies of the removal of organic capping agents from Pt nanoparticles by UV−ozone treatment. J Phys Chem C 113:6150–615510.1021/jp8108946 ↗
3. Altmann L, Kunz S, Bäumer M (2014) Influence of organic amino and thiol ligands on the geometric and electronic surface properties of Colloidally prepared platinum nanoparticles. J Phys Chem C 118:8925–893210.1021/jp4116707 ↗
4. Anderson NC, Hendricks MP, Choi JJ, Owen JS (2013) Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding. J Am Chem Soc 135:18536–1854810.1021/ja4086758 ↗
5. Anderson NC, Owen JS (2013) Soluble, chloride-terminated CdSe nanocrystals: ligand exchange monitored by 1H and 31P NMR spectroscopy. Chem Mater 25:69–7610.1021/cm303219a ↗
6. Ansar SM, Kitchens CL (2016) Impact of gold nanoparticle stabilizing ligands on the colloidal catalytic reduction of 4-Nitrophenol. ACS Catal 6:5553–556010.1021/acscatal.6b00635 ↗
7. Badia A, Cuccia L, Demers L, Morin F, Bruce Lennox R (1997) Structure and dynamics in Alkanethiolate monolayers self-assembled on gold nanoparticles: a DSC, FT-IR, and deuterium NMR study. J Am Chem Soc 119:2682–269210.1021/ja963571t ↗
8. Bonet F, Delmas V, Grugeon S, Herrera Urbina R, Silvert PY, Tekaia-Elhsissen K (1999) Synthesis of monodisperse au, Pt, Pd, Ru and Ir nanoparticles in ethylene glycol. Nanostruct Mater 11:1277–128410.1016/S0965-9773(99)00419-5 ↗
9. Bonifacio CS, Carenco S, Wu CH, House SD, Bluhm H, Yang JC (2015) Thermal stability of Core–Shell nanoparticles: a combined in situ study by XPS and TEM. Chem Mater 27:6960–696810.1021/acs.chemmater.5b01862 ↗
10. Bresó-Femenia E, Godard C, Claver C, Chaudret B, Castillón S (2015) Selective catalytic deuteration of phosphorus ligands using ruthenium nanoparticles: a new approach to gain information on ligand coordination. Chem Commun 51:16342–1634510.1039/C5CC06984J ↗
11. Schoenbaum CA, Schwartz DK, Will Medlin J (2013) Controlling surface crowding on a Pd catalyst with thiolate self-assembled monolayers. J Catal 303:92–9910.1016/j.jcat.2013.03.012 ↗
12. Chandran SP, Chaudhary M, Pasricha R, Ahmad A, Sastry M (2006) Synthesis of gold Nanotriangles and silver nanoparticles using Aloevera plant extract. Biotechnol Prog 22:577–58310.1021/bp0501423 ↗
13. Chen G, Xu C, Huang X, Ye J, Lin G, Li G, Tang Z, Wu B, Yang H, Zhao Z, Zhou Z, Gang F, Zheng N (2016) Interfacial electronic effects control the reaction selectivity of platinum catalysts. Nat Mater 15:564–56910.1038/nmat4555 ↗
14. Chen MS, Goodman DW (2004) The structure of catalytically active gold on Titania. Science 306:252–25510.1126/science.1102420 ↗
15. Chen M, Goodman DW (2008) Catalytically active gold on ordered titania supports. Chem Soc Rev 37:1860–187010.1039/b707318f ↗
16. Crumlin EJ, Mutoro E, Hong WT, Biegalski MD, Christen HM, Liu Z, Bluhm H, Yang S-H (2013) In situ ambient pressure X-ray photoelectron spectroscopy of cobalt perovskite surfaces under cathodic polarization at high temperatures. J Phys Chem C 117:16087–1609410.1021/jp4051963 ↗
17. Cusinato L, del Rosal I, Poteau R (2017) Shape, electronic structure and steric effects of organometallic nanocatalysts: relevant tools to improve the synergy between theory and experiment. Dalton Trans 46:378–39510.1039/C6DT04207D ↗
18. Dablemont C, Lang P, Mangeney C, Piquemal J-Y, Petkov V, Herbst F, Viau G (2008) FTIR and XPS study of Pt nanoparticle functionalization and interaction with alumina. Langmuir 24:5832–584110.1021/la7028643 ↗
19. Dong A, Ye X, Chen J, Kang Y, Gordon T, Kikkawa JM, Murray CB (2011) A generalized ligand-exchange strategy enabling sequential surface functionalization of colloidal nanocrystals. J Am Chem Soc 133:998–100610.1021/ja108948z ↗
20. Dunleavy J (2006) Sulfur as a catalyst poison. Platinum Metals Rev 50:11010.1595/147106706X111456 ↗
21. Ertl G (2008) Reactions at surfaces: from atoms to complexity (Nobel lecture). Angew Chem Int Ed 47:3524–353510.1002/anie.200800480 ↗
22. Fedorov A, Liu H-J, Lo H-K, Copéret C (2016) Silica-supported cu nanoparticle catalysts for alkyne Semihydrogenation: effect of ligands on rates and selectivity. J Am Chem Soc 138:16502–1650710.1021/jacs.6b10817 ↗
23. Feng B, Hou Z, Yang H, Xiangrui Wang YH, Li H, Qiao Y, Zhao X, Huang Q (2010) Functionalized poly (ethylene glycol)-stabilized water-soluble palladium nanoparticles: property/activity relationship for the aerobic alcohol oxidation in water. Langmuir 26:2505–251310.1021/la9027755 ↗
24. Ferri D, Bürgi T (2001) An in situ attenuated Total reflection infrared study of a chiral catalytic solid−liquid Interface: Cinchonidine adsorption on Pt. J Am Chem Soc 123:12074–1208410.1021/ja011769u ↗
25. Fritzinger B, Capek RK, Lambert K, Martins JC, Hens Z (2010) Utilizing self-exchange to address the binding of carboxylic acid ligands to CdSe quantum dots. J Am Chem Soc 132:10195–1020110.1021/ja104351q ↗
26. Fritzinger B, Moreels I, Lommens P, Koole R, Hens Z, Martins JC (2009) In situ observation of rapid ligand exchange in colloidal nanocrystal suspensions using transfer NOE nuclear magnetic resonance spectroscopy. J Am Chem Soc 131:3024–303210.1021/ja809436y ↗
27. Gehl B, Flege JI, Aleksandrovic V, Schmidt T, Kornowski A, Bernstorff S, Falta J, Weller H, Bäumer M (2008a) Plasma modification of CoPt3 nanoparticle arrays: a route to catalytic coatings of surfaces. J Vac Sci Technol A 26:908–91210.1116/1.2936222 ↗
28. Gehl B, Frömsdorf A, Aleksandrovic V, Schmidt T, Pretorius A, Flege J-I, Bernstorff S, Rosenauer A, Falta J, Weller H, Bäumer M (2008b) Structural and chemical effects of plasma treatment on close-packed colloidal nanoparticle layers. Adv Funct Mater 18:2398–241010.1002/adfm.200800274 ↗
29. Gomes R, Hassinen A, Szczygiel A, Zhao Q, Vantomme A, Martins JC, Hens Z (2011) Binding of Phosphonic acids to CdSe quantum dots: a solution NMR study. J Phys Chem Lett 2:145–15210.1021/jz1016729 ↗
30. Grunes J, Zhu J, Somorjai GA (2003) Catalysis and nanoscience. Chem Commun:2257–226010.1039/b305719b ↗
31. Hassinen A, Moreels I, de Mello Donegá C, Martins JC, Hens Z (2010) Nuclear magnetic resonance spectroscopy demonstrating dynamic stabilization of CdSe quantum dots by Alkylamines. J Phys Chem Lett 1:2577–258110.1021/jz100781h ↗
32. Hens Z, Martins JC (2013) A solution NMR toolbox for characterizing the surface chemistry of colloidal nanocrystals. Chem Mater 25:1211–122110.1021/cm303361s ↗
33. Hinnemann B, Moses PG, Bonde J, Jørgensen KP, Nielsen JH, Horch S, Chorkendorff I, Nørskov JK (2005) Biomimetic hydrogen evolution: MoS2 nanoparticles as catalyst for hydrogen evolution. J Am Chem Soc 127:5308–530910.1021/ja0504690 ↗
34. Hostetler MJ, Stokes JJ, Murray RW (1996) Infrared spectroscopy of three-dimensional self-assembled monolayers: N-Alkanethiolate monolayers on gold cluster compounds. Langmuir 12:3604–361210.1021/la960249n ↗
35. Hüfner S (1995) Photoelectron spectroscopy: principles and applications. (springer Verlag)10.1007/978-3-662-03150-6 ↗
36. Jeong H, Kim C, Yang S, Lee H (2016) Selective hydrogenation of furanic aldehydes using Ni nanoparticle catalysts capped with organic molecules. J Catal 344:609–61510.1016/j.jcat.2016.11.002 ↗
37. Knittel F, Gravel E, Cassette E, Pons T, Pillon F, Dubertret B, Doris E (2013) On the characterization of the surface chemistry of quantum dots. Nano Lett 13:5075–507810.1021/nl402192d ↗
38. Krishnan P, Liu M, Itty PA, Liu Z, Rheinheimer V, Zhang M-H, Monteiro PJM, Yu LE (2017) Characterization of photocatalytic TiO2 powder under varied environments using near ambient pressure X-ray photoelectron spectroscopy. Sci Rep 7:4329810.1038/srep43298 ↗
39. Kunz S, Iglesia E (2014) Mechanistic evidence for sequential displacement–reduction routes in the synthesis of Pd–au clusters with uniform size and clean surfaces. J Phys Chem C 118:7468–747910.1021/jp500537v ↗
40. Kwon SG, Krylova G, Sumer A, Schwartz MM, Bunel EE, Marshall CL, Chattopadhyay S, Lee B, Jellinek J, Shevchenko EV (2012) Capping ligands as selectivity switchers in hydrogenation reactions. Nano Lett 12:5382–538810.1021/nl3027636 ↗
41. Laibinis PE, Whitesides GM, Allara DL, Tao YT, Parikh AN, Nuzzo RG (1991) Comparison of the structures and wetting properties of self-assembled monolayers of n-alkanethiols on the coinage metal surfaces, copper, silver, and gold. J Am Chem Soc 113:7152–716710.1021/ja00019a011 ↗
42. Lang H, Alan May R, Iversen BL, Chandler BD (2003) Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts. J Am Chem Soc 125:14832–1483610.1021/ja0364120 ↗
43. Lee KY, Lee YW, Lee J-H, Han SW (2010) Effect of ligand structure on the catalytic activity of au nanocrystals. Colloids Surf A Physicochem Eng Asp 372:146–15010.1016/j.colsurfa.2010.10.019 ↗
44. Li D, Wang C, Tripkovic D, Sun S, Markovic NM, Stamenkovic VR (2012) Surfactant removal for colloidal nanoparticles from solution synthesis: the effect on catalytic performance. ACS Catal 2:1358–136210.1021/cs300219j ↗
45. Liu H, Mei Q, Li S, Yang Y, Wang YY, Liu H, Zheng LR, An P, Zhang J, Han B (2018) Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles promoted by the cooperation of steric and electronic effects. Chem Commun 54:908–91110.1039/C7CC08942B ↗
46. Liu P, Qin R, Gang F, Zheng N (2017) Surface coordination chemistry of metal nanomaterials. J Am Chem Soc 139:2122–213110.1021/jacs.6b10978 ↗
47. Lopez N, Janssens TVW, Clausen BS, Xu Y, Mavrikakis M, Bligaard T, Nørskov JK (2004) On the origin of the catalytic activity of gold nanoparticles for low-temperature CO oxidation. J Catal 223:232–23510.1016/j.jcat.2004.01.001 ↗
48. Love JC, Wolfe DB, Haasch R, Chabinyc ML, Paul KE, Whitesides GM, Nuzzo RG (2003) Formation and structure of self-assembled monolayers of Alkanethiolates on palladium. J Am Chem Soc 125:2597–260910.1021/ja028692+ ↗
49. Luksirikul P, Tedsree K, Moloney MG, Green MLH, Tsang SCE (2012) Electron promotion by surface functional groups of Single Wall carbon nanotubes to overlying metal particles in a fuel-cell catalyst. Angew Chem Int Ed 51:6998–700110.1002/anie.201201589 ↗
50. M LG, Begoña P, Masoud S, Núria L, Javier P-R (2017) Hybrid palladium nanoparticles for direct hydrogen peroxide synthesis: the key role of the ligand. Angew Chem Int Ed 56:1775–177910.1002/anie.201610552 ↗
51. Maeda N, Hungerbühler K, Baiker A (2011) Asymmetric hydrogenation on Chirally modified Pt: origin of hydrogen in the N–H–O interaction between Cinchonidine and ketone. J Am Chem Soc 133:19567–1956910.1021/ja2054918 ↗
52. Marit K, Anja H, Paul D, Andreas T, Stephan B, Benjamin R, Erhard K, Unger Wolfgang ES (2017) Detection of suspended nanoparticles with near-ambient pressure x-ray photoelectron spectroscopy. J Phys Condens Matter 29:47400210.1088/1361-648X/aa8b9d ↗
53. "Market Report. Global Catalyst Market." In. 2015
54. Marshall ST, Schwartz DK, William Medlin J (2011) Adsorption of oxygenates on Alkanethiol-functionalized Pd(111) surfaces: mechanistic insights into the role of self-assembled monolayers on catalysis. Langmuir 27:6731–673710.1021/la104921p ↗
55. Martin R, Buchwald SL (2008) Palladium-catalyzed Suzuki−Miyaura cross-coupling reactions employing Dialkylbiaryl phosphine ligands. Acc Chem Res 41:1461–147310.1021/ar800036s ↗
56. McCue AJ, McKenna F-M, Anderson JA (2015) Triphenylphosphine: a ligand for heterogeneous catalysis too? Selectivity enhancement in acetylene hydrogenation over modified Pd/TiO2 catalyst. Catal Sci Technol 5:2449–245910.1039/C5CY00065C ↗
57. McFadden CF, Cremer PS, Gellman AJ (1996) Adsorption of chiral alcohols on “chiral” metal surfaces. Langmuir 12:2483–248710.1021/la950348l ↗
58. Meemken F, Hungerbühler K, Baiker A (2014) Monitoring surface processes during heterogeneous asymmetric hydrogenation of ketones on a Chirally modified platinum catalyst by operando spectroscopy. Angew Chem Int Ed 53:8640–864410.1002/anie.201402981 ↗
59. Mizrahi MD, Krylova G, Giovanetti LJ, Ramallo-López JM, Liu Y, Shevchenko EV, Requejo FG (2018) Unexpected compositional and structural modification of CoPt3 nanoparticles by extensive surface purification. Nanoscale 10:6382–639210.1039/C8NR00060C ↗
60. Moglianetti M, Ong QK, Reguera J, Harkness KM, Mameli M, Radulescu A, Kohlbrecher J, Jud C, Svergun DI, Stellacci F (2014) Scanning tunneling microscopy and small angle neutron scattering study of mixed monolayer protected gold nanoparticles in organic solvents. Chem Sci 5:1232–124010.1039/c3sc52595c ↗
61. Morris-Cohen AJ, Donakowski MD, Knowles KE, Weiss EA (2010) The effect of a common purification procedure on the chemical composition of the surfaces of CdSe quantum dots synthesized with Trioctylphosphine oxide. J Phys Chem C 114:897–90610.1021/jp909492w ↗
62. Morris-Cohen, Adam J., Michał Malicki, Mark D. Peterson, John W. J. Slavin, and Emily A. Weiss. 2013. 'Chemical, structural, and quantitative analysis of the ligand shells of colloidal quantum dots', Chem Mater, 25: 1155–116510.1021/cm302108j ↗
63. Nasri NS, Jones JM, Dupont VA, Williams A (1998) A comparative study of sulfur poisoning and regeneration of precious-metal catalysts. Energy Fuel 12:1130–113410.1021/ef980104j ↗
64. Ouyang R, Jiang D-e (2015) Understanding Selective Hydrogenation of α,β-Unsaturated Ketones to Unsaturated Alcohols on the Au25(SR)18 Cluster. ACS Catal 5:6624–662910.1021/acscatal.5b01521 ↗
65. Owen J (2015) The coordination chemistry of nanocrystal surfaces. Science 347:615–61610.1126/science.1259924 ↗
66. Ren D, Lin H, Yu L, Ding R-S, Liu Y-M, Cao Y, He H-Y, Fan K-N (2012) An unusual Chemoselective hydrogenation of Quinoline compounds using supported gold catalysts. J Am Chem Soc 134:17592–1759810.1021/ja3066978 ↗
67. Rodriguez JA, Ma S, Liu P, Hrbek J, Evans J, Pérez M (2007) Activity of CeOx and TiOx nanoparticles grown on au(111) in the water-gas shift reaction. Science 318:1757–176010.1126/science.1150038 ↗
68. Rossi LM, Fiorio JL, Garcia MAS, Ferraz CP (2018) Role and fate of capping ligands in colloidally prepared metal nanoparticle catalysts. Transactions, Dalton
69. Saveleva VA, Papaefthimiou V, Daletou MK, Doh WH, Ulhaq-Bouillet C, Diebold M, Zafeiratos S, Savinova ER (2016) Operando near ambient pressure XPS (NAP-XPS) study of the Pt electrochemical oxidation in H2O and H2O/O2 Ambients. J Phys Chem C 120:15930–1594010.1021/acs.jpcc.5b12410 ↗
70. Schnadt J, Knudsen J, Andersen JN, Siegbahn H, Pietzsch A, Hennies F, Johansson N, Mårtensson N, Öhrwall G, Bahr S, Mähl S, Schaff O (2012) The new ambient-pressure X-ray photoelectron spectroscopy instrument at MAX-lab. J Synchrotron Radiat 19:701–70410.1107/S0909049512032700 ↗
71. Schrader I, Neumann S, Šulce A, Schmidt F, Azov V, Kunz S (2017) Asymmetric heterogeneous catalysis: transfer of molecular principles to nanoparticles by ligand functionalization. ACS Catal 7:3979–398710.1021/acscatal.7b00422 ↗
72. Schrader I, Warneke J, Backenköhler J, Kunz S (2015) Functionalization of platinum nanoparticles with l-proline: simultaneous enhancements of catalytic activity and selectivity. J Am Chem Soc 137:905–91210.1021/ja511349p ↗
73. Snelders DJM, Yan N, Gan W, Laurenczy G, Dyson PJ (2012) Tuning the Chemoselectivity of Rh nanoparticle catalysts by site-selective poisoning with phosphine ligands: the hydrogenation of functionalized aromatic compounds. ACS Catal 2:201–20710.1021/cs200575r ↗
74. Son JG, Choi E, Piao Y, Han SW, Lee TG (2016) Probing organic ligands and their binding schemes on nanocrystals by mass spectrometric and FT-IR spectroscopic imaging. Nanoscale 8:4573–457810.1039/C5NR07592K ↗
75. Stamenkovic VR, Mun BS, Mayrhofer KJJ, Ross PN, Markovic NM (2006) Effect of surface composition on electronic structure, stability, and Electrocatalytic properties of Pt-transition metal alloys: Pt-skin versus Pt-skeleton surfaces. J Am Chem Soc 128:8813–881910.1021/ja0600476 ↗
76. Marshall ST, O’Brien M, Oetter B, Corpuz A, Richards RM, Schwartz DK, William Medlin J (2010) Controlled selectivity for palladium catalysts using self-assembled monolayers. Nature Materials 9:853–85810.1038/nmat2849 ↗
77. Stowell CA, Korgel BA (2005) Iridium nanocrystal synthesis and surface coating-dependent catalytic activity. Nano Lett 5:1203–120710.1021/nl050648f ↗
78. Taguchi T, Isozaki K, Miki K (2012) Enhanced catalytic activity of self-assembled-monolayer-capped gold nanoparticles. Adv Mater 24:6462–646710.1002/adma.201202979 ↗
79. Talapin DV, Lee J-S, Kovalenko MV, Shevchenko EV (2010) Prospects of colloidal nanocrystals for electronic and optoelectronic applications. Chem Rev 110:389–45810.1021/cr900137k ↗
80. Tao F, Grass ME, Zhang Y, Butcher DR, Renzas JR, Liu Z, Chung JY, Mun BS, Salmeron M, Somorjai GA (2008) Reaction-driven restructuring of Rh-Pd and Pt-Pd Core-Shell nanoparticles. Science 322:932–93410.1126/science.1164170 ↗
81. Tataurova YN (2014) Proton NMR studies of functionalized nanoparticles in aqueous environments. University of, Iowa
82. Tolman CA (1977) Steric effects of phosphorus ligands in organometallic chemistry and homogeneous catalysis. Chem Rev 77:313–34810.1021/cr60307a002 ↗
83. Tsunoyama H, Ichikuni N, Sakurai H, Tsukuda T (2009) Effect of electronic structures of au clusters stabilized by poly (N-vinyl-2-pyrrolidone) on aerobic oxidation catalysis. J Am Chem Soc 131:7086–709310.1021/ja810045y ↗
84. Villa A, Wang D, Veith GM, Vindigni F, Prati L (2013) Sol immobilization technique: a delicate balance between activity, selectivity and stability of gold catalysts. Catal Sci Technol 3:3036–304110.1039/c3cy00260h ↗
85. Von White G, Mohammed FS, Kitchens CL (2011) Small-angle neutron scattering investigation of gold nanoparticle clustering and ligand structure under Antisolvent conditions. J Phys Chem C 115:18397–1840510.1021/jp112020r ↗
86. Wu B, Huang H, Yang J, Zheng N, Gang F (2012) Selective Hydrogenation of α,β-Unsaturated Aldehydes Catalyzed by Amine-Capped Platinum-Cobalt Nanocrystals. Angew Chem Int Ed 51:3440–344310.1002/anie.201108593 ↗
87. Yamamoto S, Bluhm H, Andersson K, Ketteler G, Ogasawara H, Salmeron M, Nilsson A (2008) In situ x-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions. J Phys Condens Matter 20:18402510.1088/0953-8984/20/18/184025 ↗
88. Zeng B, Palui G, Zhang C, Zhan N, Wang W, Ji X, Chen B, Mattoussi H (2017) Characterization of the ligand capping of hydrophobic CdSe–ZnS quantum dots using NMR spectroscopy. Materials, Chemistry of
89. Zhou K, Li Y (2012) Catalysis based on nanocrystals with well-defined facets. Angew Chem Int Ed 51:602–61310.1002/anie.201102619 ↗
90. Zhou Z-Y, Kang X, Yang S, Chen S (2012) Ligand-mediated Electrocatalytic activity of Pt nanoparticles for oxygen reduction reactions. J Phys Chem C 116:10592–1059810.1021/jp300199x ↗
91. Zhou Z-Y, Tian N, Li J-T, Broadwell I, Sun S-G (2011) Nanomaterials of high surface energy with exceptional properties in catalysis and energy storage. Chem Soc Rev 40:4167–418510.1039/c0cs00176g ↗
92. Zhu Y, Qian H, Drake BA, Jin R (2010) Atomically Precise Au25(SR)18 Nanoparticles as Catalysts for the Selective Hydrogenation of α,β-Unsaturated Ketones and Aldehydes. Angew Chem Int Ed 49:1295–129810.1002/anie.200906249 ↗