Jesús R. Berenguer

Synthesis of mesoporous metal complex-silica materials and their use as solvent-free catalysts

Incorporation of various Pd(II) complexes into the framework of MSU-X mesoporous silica has been achieved by co-condensation using a facile solvent-free one-pot synthesis. The use of ligands with triethoxysilyl terminal groups permitted the synthesis of three different metallosilanes precursors (metal complexes with ligands containing trialkoxysilane terminal groups), which allow for the homogeneous in situ incorporation of metal complexes covalently bonded to the porous support. Inorganic precursor tetraethylorthosilicate was used both as silica source and as solvent for the synthesis of the complexes, avoiding the use of other organic co-solvents, making the synthesis environmentally benign. The gentle synthesis conditions used such as neutral pH, room temperature and mild ethanol extraction of the surfactant, allowed a cleaner route for the immobilization of homogeneous Pd(II) catalysts in mesoporous silica, while protecting the structural and chemical integrity of the metal complexes. For comparison purposes, monomer complexes [trans-PdCl2L2] (L = NH2(CH2)3Si(OEt)3, 4-C5H4N–(CH2)2Si(OEt3), PPh2(CH2)2Si(OEt)3) were synthesized using the same aerobic reaction conditions to those use for the co-condensation processes and fully characterized before their incorporation in the mesoporous silica. The catalytic performance of these materials was tested for the Suzuki-Miyaura reaction under solvent-free conditions. Efficient mixing of all the components was accomplished by applying either magnetic stirring or ball milling. The good yields obtained, even at room temperature, confirmed the catalytic activity of the metal complexes once incorporated into the mesoporous silica framework. The possibility to work under solvent-free conditions even with solid starting reactants, is a significant step forward in the Suzuki-Miyaura coupling reaction because its benefits in terms of cost and impact of the environment.

Synthesis, structures and photophysics of novel luminescent platinum–copper complexes

Abstract The novel hexanuclear platinum–copper complex [Pt2Cu4(C6F5)4(CCtBu)4(acetone)2] (1) and the polynuclear derivative [PtCu2(C6F5)2(CCPh)2]x (2), which crystallises in acetone as [Pt2Cu4(C6F5)4(CCPh)4(acetone)4] (2)·(acetone)4, have been prepared using [cis-Pt(C6F5)2(THF)2] and the corresponding copper–acetylide [Cu(CCR)]x (molar ratio 1:2) as starting materials. Treatment of 1 and 2 with 2,2′-bipyridine (molar ratio Cu–bipy 1:1), afforded the new trinuclear derivatives [{cis-Pt(C6F5)2(μ-CCR)2}{Cu(bipy)}2] (R=tBu 3, Ph 4), in which the dianionic 3-platina-1,4-diyne acts as a didentate bridging ligand to two different cationic Cu(bipy) units through η2-side-on coordination of the alkynyl fragments. While similar treatment of 1 with dppe (Cu–dppe 1:1) yielded [{cis-Pt(C6F5)2(μ-CCtBu)2}{Cu(dppe)}2] (5), the analogous reaction of 2 with dppe afforded a mixture of complexes containing [Pt(C6F5)(CCPh)(dppe)] as the main platinum compound. The crystal structures of 1, 2·(acetone)4, 3 and 4 and the luminescent behaviour of all complexes have been determined. A comparison of the photoluminescent spectra of 1 and 2 with those of the related platinum–silver species [PtAg2(C6F5)2(CCR)2]x and the monomeric [cis-Pt(C6F5)2(CCR)2]2− suggests the presence of emitting states bearing a large cluster [PtM2]x-to-ligand (alkynide) charge transfer (CLCT).

Sol–Gel Coordination Chemistry: Building Catalysts from the Bottom‐Up

The development of synthetic routes for the tailoring of efficient silica‐based heterogeneous catalysts functionalized with coordination complexes or metallic nanoparticles has become a important goal in chemistry. Most of these techniques have been based on postsynthetic treatments of preformed silicas. Nevertheless, there is an emerging approach, so‐called sol–gel coordination chemistry, based on co‐condensation during the sol–gel preparation of the hybrid material of the corresponding complex or nanoparticle modified with terminal trialkoxysilane groups with a silica source (such as tetraethoxysilane) and in the presence of an adequate surfactant. This method leads to the production of new mesoporous metal complex‐silica materials, with the metallic functionality incorporated homogeneously into the structure of the hybrid material, improving the stability of the coordination complex (which is protected by the silica network) and reducing the leaching of the active phase. This technique also offers the actual possibility of functionalizing silica or other metal oxides for a wider range of applications, such as photonics, sensing, and biochemical functions.

Synthesis of Novel Heterotetrametallic (d6-d10-d8) Polyalkynyl Complexes Starting from Heterobimetallic Chloride-Bridged (d6-d8) Compounds

The reaction between the half-sandwich cyclopentadienyl complexes [M(η5-C5Me5)Cl2(PEt3)] (M = Rh, Ir) and [cis-M′(C6F5)2(thf)2] (M′ = Pt, Pd; thf = tetrahydrofuran) affords the corresponding chloride-bridged heterobinuclear Rh,Ir/Pt,Pd complexes [(PEt3)(η5-C5Me5)M(μ-Cl)2M′(C6F5)2] (1−4). In contrast, similar reactions with the chloro-bridged binuclear compounds [{M(η5-C5Me5)Cl(μ-Cl)}2] (M = Rh, Ir) lead instead to the unexpected mixed salt complexes {Cp*M(μ-Cl)3MCp*}2[{(C6F5)2M′(μ-Cl)}2] (M = Rh, Ir; M′ = Pt, Pd) (5−8) as a result of chloride transfer. The structures of [(PEt3)(η5-C5Me5)Rh(μ-Cl)2Pt(C6F5)2] (1) and {Cp*Rh(μ-Cl)3RhCp*}2[{(C6F5)2Pd(μ-Cl)}2] (6) have been determined by X-ray diffraction analyses. The reactivity of the new chloride-bridged heterobinuclear compounds 1−4 towards the alkynylating agents [M′′(C≡CR)]n (M′′ = Cu, Ag) has also been investigated: a new type of tetranuclear product, [(PEt3)Cp*M(μ-1κCα:η2-C≡CPh)2M′′2(μ-4κCα:η2-C≡CPh)2Pt(C6F5)2] (M = Rh, Ir; M′′ = Cu, Ag) (9−12), was obtained, and fully characterized in the case of complex [(PEt3)Cp*Rh(μ-1κCα:η2-C≡CPh)2Cu2(μ-4κCα:η2-C≡CPh)2Pt(C6F5)2] (9).

SYNTHESIS AND CHARACTERIZATION OF CATIONIC HETERONUCLEAR COMPLEXES OF PLATINUM(II) AND SILVER(I) BRIDGED BY ALKYNYL LIGANDS

Abstract The dialkynyl complexes cis -[Pt(C  CR) 2 L 2 ] [R  Ph, L 2  2PPh 3 , 2PEt 3 , dppe (dppe  1,2-bis(diphenylphosphino)ethane]; R  t Bu, L 2  2PPh 3 , dppe) react with silver perchlorate in a molar ratio 1:0.5 to give platinum-silver perchlorate salts of the type [Pt 2 Ag(C  CR) 4 L 4 ](ClO 4 ) in excellent yield. The X-ray crystal structure of [Pt 2 Ag(C  CPh) 4 (PPh 3 ) 4 ](ClO 4 ) 1 shows that the cation is formed by two nearly orthogonal cis -[Pt(C  CPh) 2 (PPh 3 ) 2 ] units connected through a silver cation which is unsymmetrically π-bonded to all four acetylene fragments. Similar reactions of cis -[Pt(C  CR) 2 L 2 ] with one equivalent of AgClO 4 afford cationic complexes of general formula [PtAg(C  CR) 2 L 2 ](ClO 4 ), which are believed to be salts, [Pt 2 Ag 2 (C  CR) 4 L 4 ](ClO 4 ) 2 .

Solvent-induced lone pair activity tuning and vapoluminescence in a Pt2Pb cluster

We report a novel cluster, [{Pt(C6F5)(bzq)}2Pb(Spy)2] 1, that displays reversible vapoluminescence to specific organic vapours; this behaviour can be related to the stereochemical activity of the lone pair around the Pb(II) in the ground state and to the distinct distortion of the coordination environment (1 and 1-solvent) upon photoexcitation.

Synthesis, characterization and luminescence properties of homoleptic platinum(II) acetylide complexes

A family of homoleptic tetraalkynylplatinate(II) complexes (NBu4)2[Pt(CCR)4] containing various arylsubstituted (R = C6H4X), where X is an electron-donating, -withdrawing or -delocalizing substituent, and ethynylpyridine (C5H4N-2, C5H4N-4) ligands have been prepared. The structures of complexes with R = (4-CF3)C6H4 (4·2HCCl3), (4-CN)C6H4 (6·H2O) and C5H4N-4 (9b·HCCC5H4N-4·2H2O) have been determined by single-crystal X-ray diffraction. While in the case of 4 two molecules of CHCl3 are incorporated to the anion by short CH⋯π interactions, for the para-pyridylethynyl derivative one H2O molecule connect different anions through moderate N⋯H–O–H⋯N intermolecular interactions, giving an extended one-dimensional chain. The photophysical and electrochemical properties of the complexes have been examined. All of them display emissions at 77 and 298 K in the fluid and solid state, with lifetimes in the microsecond regime. In some cases the emission profile is clearly the envelope of several closely bands, whose relative intensity depends on the excitation energy. On the basis of TD-DFT theoretical calculations on the anion [Pt{CC(4-CN)C6H4}4]2− of complex 6, it is proposed that the emissions are due to triplet intraligand excited states, with both an aryl (or pyridyl) and acetylenic character, which arise from an admixture of π → π*(CCR) IL and dπ(Pt) → π*(CCR) MLCT transitions.

Organotitanias: a versatile approach for band gap reduction in titania based materials

The reduction of the band gap of titania is critically important to fully utilize its photocatalytic properties. Two main strategies, i.e. doping and partial reduction of Ti(IV), are the main alternatives available to date. Herein, we report a new synthesis strategy based on one-pot co-condensation of in situ prepared polymetallic titanium-alkoxide complexes with titanium tetrabutoxide. Using this direct reaction, it is possible to introduce organic compounds in the anatase phase, causing site distortions in the crystalline structure of the network. By using this strategy, a yellow and a black titania have been produced, with the latter showing a remarkable photocatalytic activity under visible-light.

Reversible Binding of Solvent to Naked PbII Centers in Unusual Homoleptic Alkynyl‐Based Pt2Pb2 Clusters

We report a series of luminescent sandwich-type clusters [Pt2 Pb2 (C≡CR)8] (R=Tol, 1; C6 H4 OMe-3, 2; C6 H4 OMe-4, 3) with a dynamic Pt2 Pb2 metallic core, which is key to their intriguing stimuli-responsive photophysical properties. The solvent-free solids 1-3 display an orange emission ascribed to charge transfer from Pt-alkynyl fragments to a delocalized orbital with mixed Pt2 Pb2 /C≡CR nature, with a predominant lead contribution and Pb⋅⋅⋅Pb bonding character ((3) MLCCT/(3) IL). They exhibit mechanical, color, and luminescence changes that are reversible and perceivable with the naked eye, which are attributed to small inter- and intramolecular structural modifications induced by gentle grinding. Interestingly, 1 and 2 also exhibit remarkable and fast reversible vapochromic responses to donor solvent vapors (acetone, THFMe-2: yellow; NCMe: green, vs. dry solids: orange). The structures of 1(acetone)2 ⋅2(Me2 CO), 2(acetone)3 , and 2(THFMe-2)2 allow the vapochromic responses to be ascribed to the fast creation/disruption of solvate clusters [Pt2 Pb2 (C≡CR)8 Sx] (x≥2), with concomitant electronic and geometrical modifications within the Pt2 Pb2 core, which are easily accessible through a slight change in the stereochemical activity of the lone pair. The binding of one (or two) solvent molecules to Pb(2+) increases the Pb⋅⋅⋅Pb separation in the metallic core, causing a destabilization of the target orbital and larger energy gaps of the transitions. All the solvates exhibit remarkable rigidochromism upon a decrease in temperature, which is also associated with the gradual increase in the transannular Pb⋅⋅⋅Pb separation, as revealed by X-ray crystallography of 1(acetone)2 at different temperatures. Investigation of the crystal lattice of 1⋅CH2 Cl2 and 3⋅2 CH2 Cl2 further suggests that the lack of vapor stimuli response of complex 3 could be attributed to the presence of competitive additional secondary intermolecular Pb⋅⋅⋅O(OMe) contacts, which give rise to a more compact network built up from extended chains of clusters.

Synthesis and characterization of bis(η2-alkyne)dihalogeno-mercury(II) compounds: crystal structure of [NBu4]2-[{cis-Pt(C6F5)2(CCSiMe3)2}HgBr2]·CH2Cl2

The reactions of [NBu4]2[cis-Pt(C6F5)2(CCR)2](R = But or SiMe3) with HgX2(X = Cl, Br or I) in a 1:1 molar ratio afforded the simple monomeric bis(η2-alkyne)mercury(II) compounds [NBu4]2[{cis-Pt(C6F5)2(CCR)2}HgX2](R = But or SiMe3; X = Cl, Br or I) in which both alkyne units are co-ordinated η2 side-on to the precursor mercury(II) halides. Similar treatment of [NBu4]2[Pt(CCR)4]·2H2O (R = But or SiMe3) with HgX2 in a 1:2 molar ratio gave the corresponding trinuclear 1:2 adducts. All the complexes have been characterized by analytical and spectroscopic data and, in addition, the molecular structure of [NBu4]2[{cis-Pt(C6F5)2(CCSiMe3)2}HgBr2]·CH2Cl2 has been determined by X-ray diffraction methods. The structure of the anion shows that the HgBr2 unit is attached to the dianionic fragment [Pt(C6F5)2(CCSiMe3)2]2– only through η2 side-on co-ordination of the two (trimethylsilyl)ethynyl ligands. The platinum–mercury distance is 3.627(1.5)A.