Dominique Roberto

Modern Surface Organometallic Chemistry

Preface ON THE ORIGINS AND DEVELOPMENT OF ?SURFACE ORGANOMETALLIC CHEMISTRY? The Basic Concept Use of Probe Molecules on Metallic Surfaces as Evidence of Coordination and Organometallic Chemistry at Metal Surfaces Chemical and Structural Analogy between Molecular Clusters and Small Metallic Particles Analogy between Supported Molecular Clusters and Small Supported Catalytic Particles Foundation of Surface Organometallic Chemistry From Organometallic Surface Chemistry to the Elementary Steps Occurring on Surfaces and Stabilization by the Surface of Rather Unstable Molecular Species From Surface Organometallic Chemistry on Oxides to Surface Organometallic Chemistry on Metals From Surface Organometallic Chemistry to Surface-Mediated Organometallic Synthesis Single Metal Site Heterogeneous Catalysts and the Design of New Catalysts PREPARATION OF SINGLE SITE CATALYSTS ON OXIDES AND METALS PREPARED VIA SURFACE ORGANOMETALLIC CHEMISTRY Introduction Surface Organometallic Chemistry on Oxides Reaction of Organometallic Compounds with Supported or Unsupported Group VIII Metals Particles Conclusion CATALYTIC PROPERTIES OF SINGLE SITE CATALYSTS PREPARED VIA SURFACE ORGANOMETALIC CHEMISTRY ON OXIDES AND ON METALS Introduction Stoichiometric Activation of Alkane C-H Bonds Alkane C-C Bond Activation by Tantalum Hydrides. Low Temperature Catalytic Hydrogenolysis of Alkanes Metathesis of Acyclic Alkanes Cross-Metathesis Reactions of Alkanes Homologation of Alkanes Polystyrene Modification and Hydrogenolysis of Linear Alkanes and Polyethylene by a Supported Zirconium Hydride Olefin Metathesis Olefin Epoxidation Deperoxidation of Cyclohexyl Hydroperoxide Some Applications of Supported Nanoparticles Modified by Organometallics Conclusion BUILDING BLOCK APPROACHES TO NANOSTRUCTURED, SINGLE SITE, HETEROGENEOUS CATALYSTS Introduction Current Challenges in Catalysis What is a Nanostructured Catalyst? Benefits of Nanostructuring Catalysts Current Approaches to Nanostructured Catalysts Building Block Approaches to Nanostructured Materials and Catalysis Nanostructured Catalysts via a Non-Aqueous Building Block Methodology A Model for the Growth of Building Block Matrices and a Nanostructuring Strategy A General Procedure for Preparing Nanostructured Catalysts in Silicate Matrices Atomically Dispersed Titanium and Vanadium, Single Site Catalysts Bridge between Nanostructuring and Catalysis Summary TRANSITION METAL SINGLE SITE CATALYSTS ? FROM HOMOGENEOUS TO IMMOBILIZED SYSTEMS Introduction Covalently Anchored Organometallic Complexes on Unmodified Silica Anchoring of Organometallic Complexes via the Metal Center Organometallic Complexes Anchored via a Covalent Linkage to a Ligand Noncovalently Anchored Organometallic Complexes Encapsulated Organometallic Complexes Conclusions CONTROLLED PREPARATION OF HETEROGENEOUS CATALYSTS FOR CHEMO- AND ENANTIOSELECTIVE HYDROGENATION REACTIONS Introduction Catalyst Preparation and Characterization Hydrogenation of Alpha,Beta-Unsaturated Aldehydes Hydrogenation of Aromatic Ketones Enantioselective Hydrogenation Reactions Conclusions WELL-DEFINED SURFACE RHODIUM SILOXIDE COMPLEXES AND THEIR APPLICATION TO CATALYSIS Molecular versus Immobilized Transition Metal Siloxide Complexes in Catalysis Synthesis, Characterization and Catalytic Activity of Well-Defined Surface Rhodium Siloxide Complexes Solid-State NMR Method in Catalysis by Surface Organometallics Mechanism of Hydrosilylation Catalyzed by Surface versus Soluble Rhodium Siloxide Complexes CARBONYL COMPOUNDS AS METALLIC PRECURSORS OF TAILORED SUPPORTED CATALYSTS Introduction Catalysts Prepared from Metal Carbonyls of Groups 6, 7, 10 and Gold Catalysts Prepared from Metal Carbonyls of Group 8: Iron, Ruthenium and Osmium Catalysts Prepared from Metal Carbonyls of Group 9: Cobalt, Rhodium and Iridium Concluding Remarks EXPLOITING SURFACE CHEMISTRY TO PREPARE METAL-SUPPORTED CATALYSTS BY ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION Introduction Surface Organometallic Chemistry Strategies to Avoid the Contamination of Metal Deposits How to Manage the Nucleation and Growth Steps Concluding Remarks ADVANCED DESIGN OF CATALYST SURFACES WITH METAL COMPLEXES FOR SELECTIVE CATALYSIS Introduction Isolation and Epoxidation Activity of a Coordinatively Unsaturated Ru Complex at a SiO2 Surface Chiral Self-Dimerization of V Complexes on a SiO2 Surface for Asymmetric Catalysis Molecular Imprinting Rh-Dimer and Rh-Monomer Catalysts Re Clusters in HZSM-5 Pores for Direct Phenol Synthesis Conclusion SURFACE ORGANOMETALLIC CHEMSITRY OF D(0) METAL COMPLEXES Introduction Ligands Susceptible to React with Hydroxyl Groups of an Inorganic Oxide Ligands Susceptible to Reaction with Lewis Acid Sites of Inorganic Oxides Reactivity of Hydrocarbyl-Metal Complexes and the Metal Atom Inorganic Oxides as Supports for Organometallic Species Models for Surface Organometallic Species Tuning the Catalytic Activity of Surface Organometallic Species Relevant Aspects of the Full Characterization of Some Selected Species Concluding Remarks SURFACE ORGANOLANTHANIDE AND ?ACTINIDE CHEMISTRY Introduction Surface Organolanthanide Chemistry SOLnC Surface Organoactinide Chemistry, SOAnC Catalytic Applications of SOLnC and SOAnC Conclusions and Perspectives ISOCYANIDE BINDING MODES ON METAL SURFACES AND IN METAL COMPLEXES Introduction Modes of Isocyanide Coordination in Transition Metal Complexes Adsorption of Isocyanides (C=N-R) on Metal Surfaces Conclusions MOLECULAR INSIGHT FOR SILICA-SUPPORTED ORGANOMETALLIC CHEMISTRY THROUGH TRANSITION METAL SILESQUIOXANES Introduction Organometallic POSS Derivatives Conclusions SURFACE-MEDIATED NANOSCALE FABRICATION OF METAL PARTICLES AND WIRES USING MESOPOROUS SILICA TEMPLATES AND THEIR SHAPE/SIZE DEPENDENCY IN CATALYSIS Introduction Surface-Mediated Synthesis of Metal/Alloy Nanowires Using Mesoporous Templates Characterization of Nanowires and Nanoparticles in FSM-16 and HMM-1 Mechanism for Formation of Pt Nanowires in Mesoporous Silica Templates Isolation and Characterization of Metal/Alloy Nanowires Free from the Silica Supports Novel Surface-Mediated Fabrication of Rh and RhPt Nanoparticles Using Mesoporous Templates in Supercritical Carbon Dioxide Other Surface-Mediated Synthesis of Metal Nanowires on Porous Membrane and Graphite Steps Shape/Size Dependency in Catalysis of Metal/Alloy Nanowires and Particles in Mesoporous Silica Templates Synthesis of Pt and Au Nanoparticle Arrays in Mesoporous Silica Films and their Electric/Magnetic Properties in Terms of the Quantum-Size Effect Conclusion SURFACE-MEDIATED ORGANOMETALLIC SYNTHESES Introduction Group 7: Rhenium Group 8 Group 9 Group 10 Conclusion

Cyclometallated platinum(II) complexes of 1,3-di(2-pyridyl)benzenes: tuning excimer emission from red to near-infrared for NIR-OLEDs

The Pt(II) complex N^C2^N-1,3-di(2-pyridyl)benzene platinum chloride (PtL1Cl) is known to display efficient triplet luminescence in the green region of the spectrum, and to form an unusually emissive excimer that emits around 690 nm. In this contribution, the introduction of trifluoromethyl groups into either the 4- or 5-position of the pyridyl rings of the ligand is shown to lead to a red-shift in the excimer band, moving it into the near infra-red (NIR) region. The new ligands, synthesised by either Suzuki or Stille cross-coupling methods, are 1,3-bis(4-(trifluoromethyl)pyridin-2-yl)benzene HL27, 1,3-bis(4-(trifluoromethyl)pyridin-2-yl)-4,6-difluorobenzene HL28, and 1,3-bis(5-(trifluoromethyl)pyridin-2-yl)-4,6-difluorobenzene HL29, from which the corresponding Pt(II) complexes PtLnCl have been prepared. The monomer and excimer emission energies in solution are compared with those of PtL1Cl and PtL22Cl {HL22 = 1,3-di(2-pyridyl)-4,6-difluorobenzene}. The order for the monomer can be rationalised in terms of the stabilising effects of the F atoms and the CF3 groups on the HOMO and LUMO respectively. The order of excimer emission proves to be subtly different, but the most red-shifted complex in both cases is PtL27Cl. The electroluminescence of neat films of the complexes as emitting layers in OLEDs displays uniquely excimer-like emission, extending well into the technologically important NIR region.

Coordination and Organometallic Complexes as Second-Order Nonlinear Optical Molecular Materials

Coordination and organometallic complexes with second-order nonlinear optical (NLO) properties have attracted increasing attention as potential molecular building block materials for optical communications, optical data processing and storage, or electrooptical devices. In particular, they can offer additional flexibility, when compared to organic chromophores, due to the presence of metal–ligand charge-transfer transitions, usually at relatively low-energy and of high intensity, tunable by virtue of the nature, oxidation state, and coordination sphere of the metal center. This chapter presents an overview of the main classes of second-order NLO coordination and organometallic complexes with various ligands such as substituted amines, pyridines, stilbazoles, chelating ligands (bipyridines, phenanthrolines, terpyridines, Schiff bases), alkynyl, vinylidene, and cyclometallated ligands, macrocyclic ligands (porphyrins and phthalocyanines), metallocene derivatives, and chromophores with two metal centers. The coverage, mainly from 2000 up to now, is focused on NLO properties measured at molecular level from solution studies, as well as on NLO properties of bulk materials.

Determination of the quadratic hyperpolarizability of trans-4-[4-(dimethylamino)styryl]pyridine and 5-dimethylamino-1,10-phenanthroline from solvatochromism of absorption and fluorescence spectra: a comparison with the electric-field-induced second-harmonic generation technique

For fluorescent compounds, the combined use of absorption and emission solvatochromic data allows to estimate indirectly the cavity radius of the molecule in solution, a very critical parameter in the application of the solvatochromic method for the determination of the quadratic hyperpolarizability beta of dipolar molecules. For two test compounds, trans-4-[4-(dimethylamino)styryl]pyridine (DASP) and 5-dimethylamino-1,10-phenanthroline (DAPHEN), the beta values so obtained are compared with those obtained by the EFISH (Electric Field Induced Second-Harmonic generation) technique. For DAPHEN, the versatility of the method described in this work in the presence of more than one electronic transition contributing to the non-linear optical response is demonstrated.

Cyclometalated IrIII Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores

Cyclometalated cationic Ir(III) complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir(ppy)(2)(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R=NO(2), H, Me, NMe(2); Y(-)=PF(6) (-), C(12)H(25)SO(3) (-), I(-)) and [Ir(ppy)(2)(4-R,7-R-1,10-phen)]Y (R=Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir(III), acting as a donor push system, to pi* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more pi delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the mubeta absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO(2) group. By using a combined experimental (the EFISH technique and (1)H and (19)F PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the mubeta values of these cationic NLO chromophores. In CH(2)Cl(2), concentration-dependent high absolute values of mubeta are obtained for [Ir(ppy)(2)(5-NO(2)-1,10-phen)]Y if Y is a weakly interacting anion, such as PF(6) (-), whereas with a counterion, such as C(12)H(25)SO(3) (-) or I(-), which form tight ion-pairs, the absolute value of mubeta is lower and quite independent of the concentration. This mubeta trend is partially due to the perturbation of the counterion on the LUMO pi* levels of the phenanthroline. The correlation between the mubeta value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.

Cyclometallated platinum(II) complexes of 1,3-di(2-pyridyl)benzenes for solution-processable WOLEDs exploiting monomer and excimer phosphorescence

Two cyclometallated platinum(II) complexes, N^C^N-5-fluoro-1,3-di(2-pyridyl)benzene platinum(II) chloride, FPtCl, and N^C^N-5-methyl-1,3-di(2-pyridyl)benzene platinum(II) isothiocyanate, MePtNCS, have been synthesized and characterized. Both complexes are highly efficient phosphorescent green emitters which can also display excimer emission in the red region. They have been studied as triplet emitters in solution-processed, multilayer organic light-emitting diodes (OLEDs), together with the known complex of 5-methyl-1,3-di(2-pyridyl)benzene, MePtCl, for comparison. The trend in efficiencies of the OLEDs prepared correlates with the charge-trapping properties of the complexes. The most efficiently emitting complex, FPtCl, was used as the dopant in a solution-processed white OLED, employing monomer and excimer emission.

Novel N^C^N-cyclometallated platinum complexes with acetylide co-ligands as efficient phosphors for OLEDs

Two new cyclometallated platinum(II) complexes have been prepared that incorporate a terdentate N^C^N-coordinating ligand and a monodentate acetylide co-ligand. The complexes, namely [PtL3–CC–C6H3F2] and [PtL6–CC–C6H3F2] (where HL3 = 5-methyl-1,3-di(2-pyridyl)benzene; HL6 = 5-mesityl-1,3-di(2-pyridyl)benzene; H–CC–C6H3F2 = 3,5-difluorophenylacetylene), were prepared by ligand metathesis from the corresponding chloro complex PtLnCl. Both of the new complexes are intensely luminescent in solution, displaying quantum yields superior to PtLnCl. OLEDs have been prepared using the new compounds as phosphorescent emitters. Although both lead to efficient devices, the best electroluminescence quantum efficiencies are obtained with the derivative of HL6, having the mesityl group on the cyclometallated phenyl ring. The superior performance with this complex can be rationalised in terms of the greater steric hindrance that serves to reduce aggregate-induced quenching.

Fluorinated β-Diketonate Diglyme Lanthanide Complexes as New Second-Order Nonlinear Optical Chromophores: The Role of f Electrons in the Dipolar and Octupolar Contribution to Quadratic Hyperpolarizability

The second-order nonlinear optical (NLO) properties of [Ln(hfac)(3)(diglyme)] (hfac = hexafluoroacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of f electrons in tuning the second-order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, beta(EFISH), initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the beta(EFISH) value of the Lu complex being only 1.2 times that of the Gd complex. The increase of beta(HLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good beta(HLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

Thiocyanate-Free Ruthenium(II) Sensitizer with a Pyrid-2-yltetrazolate Ligand for Dye-Sensitized Solar Cells

The synthesis of the new complex [Ru(Tetrazpy)(dcbpy)2]Cl is reported, along with its spectroscopical, electrochemical, and theoretical characterization. The first dye-sensitized solar cell device with this complex has been prepared, leading to a 3% of conversion efficiency, promising data considering the simplicity of the Tetrazpy ligand.

Linear and nonlinear optical properties of tris-cyclometalated phenylpyridine Ir(III) complexes incorporating π-conjugated substituents.

The synthesis, luminescence, and nonlinear optical properties of a new series of Ir(ppy)3 (ppy = 2-phenylpyridine) complexes incorporating π-extended vinyl-aryl substituents at the para positions of their pyridine rings are reported. Appropriate substitution of the pyridyl rings allows the tuning of the luminescence properties and the second-order nonlinear optical response of this unusual family of three-dimensional chromophores. Theoretical calculations were performed to evaluate the dipole moments, to gain insight into the electronic structure, and to rationalize the observed optical properties of the investigated complexes.