Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Apr 1;8(4):2931-2941.
doi: 10.1039/c6sc05551f. Epub 2017 Feb 1.

Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts

L M Martínez-Prieto  1 , I Cano  1 , A Márquez  2 , E A Baquero  1 , S Tricard  1 , L Cusinato  1 , I Del Rosal  1 , R Poteau  1 , Y Coppel  3 , K Philippot  3 , B Chaudret  1 , J Cámpora  2 , P W N M van Leeuwen  1
Affiliations

Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts

L M Martínez-Prieto et al. Chem Sci. .

Abstract

Ligand control of metal nanoparticles (MNPs) is rapidly gaining importance as ligands can stabilize the MNPs and regulate their catalytic properties. Herein we report the first example of Pt NPs ligated by imidazolium-amidinate ligands that bind strongly through the amidinate anion to the platinum surface atoms. The binding was established by 15N NMR spectroscopy, a precedent for nitrogen ligands on MNPs, and XPS. Both monodentate and bidentate coordination modes were found. DFT showed a high bonding energy of up to -48 kcal mol-1 for bidentate bonding to two adjacent metal atoms, which decreased to -28 ± 4 kcal mol-1 for monodentate bonding in the absence of impediments by other ligands. While the surface is densely covered with ligands, both IR and 13C MAS NMR spectra proved the adsorption of CO on the surface and thus the availability of sites for catalysis. A particle size dependent Knight shift was observed in the 13C MAS NMR spectra for the atoms that coordinate to the surface, but for small particles, ∼1.2 nm, it almost vanished, as theory for MNPs predicts; this had not been experimentally verified before. The Pt NPs were found to be catalysts for the hydrogenation of ketones and a notable ligand effect was observed in the hydrogenation of electron-poor carbonyl groups. The catalytic activity is influenced by remote electron donor/acceptor groups introduced in the aryl-N-substituents of the amidinates; p-anisyl groups on the ligand gave catalysts several times faster the ligand containing p-chlorophenyl groups.

PubMed Disclaimer

Figures

Scheme 1
Scheme 1. Synthesis of zwitterionic imidazolium-amidinate ligands.
Scheme 2
Scheme 2. Synthesis of platinum nanoparticles using imidazolium-amidinate ligands as stabilizers.
Fig. 1
Fig. 1. TEM images and size histograms of (a) Pt/ICy·(p-tol)NCN0.1, (b) Pt/ICy·(p-tol)NCN0.2 and (c) Pt/ICy·(p-tol)NCN0.5.
Fig. 2
Fig. 2. HRTEM image of Pt/ICy·(p-tol)NCN0.2 (left, right bottom) and fast Fourier transformation analysis (right, top) with the planar reflections.
Fig. 3
Fig. 3. ATR FT-IR spectra of (a) Pt/ICy·(p-tol)NCN0.1, (b) Pt/ICy·(p-tol)NCN0.2 and (c) Pt/ICy·(p-tol)NCN0.5 after CO adsorption.
Fig. 4
Fig. 4. 13C CP-MAS NMR spectrum of Pt/ICy·(p-tol)NCN0.5 NPs.
Fig. 5
Fig. 5. 13C MAS NMR spectrum of (a) Pt/ICy·(p-tol)NCN0.1 (2.3 nm), (b) Pt/ICy·(p-tol)NCN0.2 (2.1 nm), (c) Pt/ICy·(p-tol)NCN0.5 (1.9 nm) and (d) Pt/CO/ICy·(p-tol)NCN0.2 (1.2 nm) after exposure to 13CO (1 bar, 20 h, at r.t.).
Scheme 3
Scheme 3. Synthesis of Pt/CO/ICy·(p-tol)NCN0.2 NPs.
Fig. 6
Fig. 6. 15N CP/Hahn-echo MAS of (a) Pt/CO/ICy·(Ph)NC15N0.2 and (b) [H·ICy·(Ph)NC15N]+·[BPh4]–.
Fig. 7
Fig. 7. X-ray photoelectron spectroscopy (XPS) of (a) the N 1s signals of ICy·(p-tol)NCN (blue) and Pt/ICy·(p-tol)NCN0.2 (red), (b) the Pt 4f5/2 and 4f7/2 signals of Pt/ICy·(p-tol)NCN0.2 and (c) the N 1s signals of Pt/ICy·(p-ClC6H4)NCN0.2 (top), Pt/ICy·(p-tol)NCN0.2 (center) and Pt/ICy·(p-anisyl)NCN0.2 (bottom).
Fig. 8
Fig. 8. 15N CPMG MAS NMR of Ru/ICy·(Ph)NC15N stabilized with (a) 1 equiv., (b) 0.5 equiv., (c) 0.2 equiv. and (d) 0.1 equiv.
Fig. 9
Fig. 9. 15N CPMG MAS NMR of Ru/ICy·(Ph)NC15N0.2 (a) before and (b) after exposure to 13CO (1 bar, 20 h, at r.t.). (c) Calculated 15N NMR displacements of ICy·(Ph)NCN after CO insertion on a [Ru6] cluster model.
Fig. 10
Fig. 10. Coordination modes of ICy·(Ph)NCN at the Ru55H70 surface (a) κ1N monocoordinated Z/E conformer (E ads: –25.0 kcal mol–1); (b) κ1N monocoordinated Z/Z conformer (E ads: –33.3 kcal mol–1); (c) μ2-κ1N, κ1N′ bicoordinated Z/Z conformer (E ads: –47.9 kcal mol–1).
See this image and copyright information in PMC

References

    1. Clusters and Colloids. From Theory to Applications, ed. G. Schmid, Wiley-VCH, Weinheim, 1994.
    2. Nanoparticles. From Theory to Application, ed. G. Schmid, Wiley-VCH, Weinheim, 2004.
    3. Nanocatalysis Series Nanoscience and Technology, ed. H. Ulrich and L. Uzi, Springer, Heidelberg, 2007.
    1. Roucoux A., Schulz J., Patin H. Chem. Rev. 2002;102:3757. - PubMed
    2. Nanoparticles and Catalysis, Wiley-Interscience, New York, 2008.
    3. Nanomaterials in Catalysis, ed. P. Serp and K. Philippot, Wiley-VCH, Weinheim2013.
    4. Roucoux A. and Philippot K., in Handbook of Homogeneous Hydrogenations, ed. J. G. de Vries and C. J. Elsevier, Wiley-VCH, Weinheim, 2007, vol. 9, pp. 217–255.
    5. Bayram E., Linehan J. C., Fulton J. L., Roberts J. A. S., Szymczak N. K., Smurthwaite T. D., Ozkar S., Balasubramanian M., Finke R. G. J. Am. Chem. Soc. 2011;133:18889. - PubMed
    6. Balanta A., Godard C., Claver C. Chem. Soc. Rev. 2011;40:4973. - PubMed
    1. An K., Somorjai G. A. ChemCatChem. 2012;4:1512.
    2. Gonzalez-Galvez D., Nolis P., Philippot K., Chaudret B., van Leeuwen P. W. N. M. ACS Catal. 2012;2:317.
    3. Martinez-Prieto L. M., Carenco S., Wu C. H., Bonnefille E., Axnanda S., Liu Z., Fazzini P. F., Philippot K., Salmeron M., Chaudret B. ACS Catal. 2014;4:3160.
    4. Martínez-Prieto L. M., Ferry A., Rakers L., Richter C., Lecante P., Philippot K., Chaudret B., Glorius F. Chem. Commun. 2016;52:4768. - PubMed
    1. Martinez-Prieto L. M., Urbaneja C., Palma P., Campora J., Philippot K., Chaudret B. Chem. Commun. 2015;51:4647. - PubMed
    1. Marquez A., Avila E., Urbaneja C., Alvarez E., Palma P., Campora J. Inorg. Chem. 2015;54:11007. - PubMed

LinkOut - more resources