A Platinum molecular complex immobilised on the surface of graphene as active catalyst in alkyne hydrosilylation

Abstract A platinum complex bearing a N‐heterocyclic carbene (NHC) ligand functionalised with a pyrene‐tag is immobilised onto the surface of reduced graphene oxide (rGO). The hybrid material composed of an organometallic complex and a graphene derivative is ready available in a single‐step process under mild reaction conditions. This methodology preserves the inherent properties of the active catalytic centre and the support. The platinum hybrid material is an efficient catalyst in hydrosilylation of alkynes and can be recycled and reused for ten runs without significant loss of activity due to its high stability. Interestingly, the catalytic properties of the platinum complex are enhanced after immobilisation onto graphene. The influence of graphene in hydrosilylation of alkynes is discussed

Catalytic conversion of alkynes to α-vinyl sulfides mediated by carbene-linker-carbene (CXC) rhodium and iridium complexes

The catalytic activity of a set of mono- and bimetallic Rh(I) and Ir(I) complexes bearing carbene-linker-carbene (CXC) bis-triazolylidene ligands (with X = O, N) coordinated in a bridging or chelating fashion was evaluated in the hydrothiolation of alkynes. The hydrothiolation of 1-hexyne with thiophenol in the absence of an external base or other additives was selected as a model reaction. All rhodium complexes are highly selective catalysts towards Markovnikov product formation and display superior activity compared to the related iridium derivatives. DFT calculations were carried out to rationalize the reaction mechanism and selectivity of this process. Neutral dinuclear [Rh2Cl2(cod)2(μ-COC)] was found to be the most effective catalyst for this transformation. Its applicability was further studied towards the hydrothiolation of different alkyl and aryl alkynes using predominantly aryl thiols and proved to be one of the most active and selective catalysts towards the α-vinyl sulfide product to date

First homoleptic MIC and heteroleptic NHC-MIC coordination cages from 1,3,5-triphenylbenzene-bridged tris-MIC and tris-NHC ligands

The preparation of a triphenylbenzene-bridged tris-(1,2,3-triazolium) salt allowed us to obtain the first homoleptic tris-MIC cylinder-like cages of Ag and Au. The silver MIC-based cage reacts with the trisNHC-Ag analogue to form the corresponding heteroleptic NHC–MIC silver cage in an unusual reaction involving the simultaneous exchange of the tris-NHC and tris-MIC ligands.MINECO (CTQ2014-51999-P) and UJI (P11B2014-02).Published versio

Dual role of graphene as support of ligand-stabilized palladium nanoparticles and carbocatalyst for (de)hydrogenation of N-heterocycles

The hybrid material composed of palladium nanoparticles (PdNPs) functionalized with N-heterocyclic carbene ligands (NHCs) immobilized onto the surface of reduced graphene oxide (rGO) results in an efficient catalytic material towards hydrogenation and dehydrogenation of N-heterocycles. The rGO plays a dual role by acting as a carbocatalyst in acceptorless dehydrogenation of N-heterocycles and as a support for the palladium nanoparticles facilitating its interaction with molecular hydrogen turning this hybrid material into an effective hydrogenation catalyst. Hot filtration experiments support the heterogeneous nature of the process underlining the strong interaction of palladium nanoparticles with the graphene enabled by π-interactions of the ligand with the support. The mild conditions used in both transformations of this system without requiring any additives facilitates its potential application in hydrogen storage technologies in the form of liquid organic hydrogen carriers (LOHCs). At the same time, the hybrid material is a robust and efficient catalytic platform that can be recovered and reused up to eight runs in both transformations without significant deactivation. The use of a single solid catalysts that is recyclable in hydrogen conversion and reconversion through (de)hydrogenation of N-heterocycles paves the way for the development of efficient hydrogen storage materials

Synthesis of Highly Stable 1,3-Diaryl-1H-1,2,3-triazol-5-ylidenes and Their Applications in Ruthenium-Catalyzed Olefin Metathesis

The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions

A Size‐Flexible Organometallic Box for the Encapsulation of Fullerenes

A palladium‐cornered molecular square with four pyrene‐bis(imidazolylidene) bridging ligands is reported. This metallo‐polygon can encapsulate C60 and C70. The X‐ray diffraction structures of the empty cage as well as the cages complexed with both fullerenes are described. The fullerene encapsulation produces perturbations in the structural parameters of the metallo‐square, showing that it can adjust the shape of its cavity to the size of each fullerene

Isolation of a potassium bis(1,2,3-triazol-5-ylidene) carbazolide: a stabilizing pincer ligand for reactive late transition metal complexes

The synthesis and X-ray crystal structure of a potassium adduct of a monoanionic CNC-pincer ligand featuring two mesoionic carbenes is reported. Owing to the peculiar electronic and steric properties of this ligand, the first neutral stable Ni(II)-hydride, and an unusual Cu(II) complex displaying a seesaw geometry, have been isolated

Ruthenium(II) pincer complexes featuring an anionic CNC bis(1,2,3-triazol-5-ylidene)carbazolide ligand coordinated in a meridional fashion

Please read abstract in the article.GGB thanks the MINECO for a postdoctoral grant (IJCI-2015-23407); EP gratefully acknowledges financial support from MINECO of Spain (CTQ2014-51999-P) and the Universitat Jaume I (P11B2014-02); DIB and GK gratefully acknowledge the National Research Foundation, South Africa (NRF 10552, 105740 and 92521), and Sasol Technology R&D Pty. Ltd., South Africa.http://www.elsevier.com/locate/poly2019-03-15hj2017Chemistr

Ruthenium complexes with an N-heterocyclic carbene NNC-pincer ligand: preparation and catalytic properties

1-Methyl-3-(2-((pyridin-2-ylmethylene)amino)ethyl)-1H-imidazol-3-ium bromide was prepared and used as an N-heterocyclic carbene NNC-pincer ligand precursor. Depending on the coordination strategy, a monometallic [Ru(NNC)(CO3)(PPh3)] complex, or the [Ru(μ-Cl)(NNC)]2(2Cl−) dimer, was obtained. A di-silver complex in which two ligands are monocoordinated to the metal center through the NHC groups was also obtained and characterised. The dimetallic ruthenium complex reacts with alcohols yielding a monohydride species. The preliminary studies on the catalytic activity of the ruthenium dimer indicate that the complex is active in the reduction of ketones and aldehydes under transfer hydrogenation conditions

Towards the development of selective hydrocarbon oxygenation catalysts

The synthesis of pure tris(6-hydroxymethyl-2-pyridylmethyl)amine (H₃L₁₁) is reported for the first time. New complexes of H₃L₁₁ with copper(II), manganese(II) and iron(III) have been characterised by X-ray crystallography. Linear [Fe₃(L₁₁)₂](ClO₄)₃ reveals the tightest Fe-O-Fe angle (87.6°) and shortest Fe...Fe distance (2.834 Å) presently found for a weakly antiferromagnetically-coupled high spin alkoxide-bridged polyiron(III) system. H₃L₁₁ provides a route to various hydrophobic peralkylated TPA ligand derivatives for creating a hydrophobic pocket for the assembly of iron catalysts for the novel 1-hydroxylation of n-alkanes. New 6-py substituted TPA ligands containing methyl (L₁₅) and n-octyl (L₁₆) ether linkages were synthesised via alkylation. Two further novel 6-py substituted ligands were synthesized incorporating n-hexyl substituents on one (L₂₁) and two (L₂₂) of the py moieties. Here a urea spacer group was used to promote hydrogen–bond assisted heterolytic O-O cleavage (generation of the potent FeV=O oxidant) within the hydroxoperoxoiron(III) precursor. High spin [FeII(L)(CH₃CN)[subscript(x)]](CF₃SO₃)₂ complexes (x = 0–2, L = L₁₅,₁₆,₂₁,₂₂) were characterised in solution by ¹H NMR. The structure of [Fe(L₂₂)](CF₃SO₃)₂ reveals a distorted iron(II) centre bound to four N atoms and two urea carbonyls. Iron(II) complexes of H₃L₁₁, L₁₅,₁₆,₂₁,₂₂ and tris(6-Br)-TPA (L₂₄), were investigated for catalysis of the oxygenation of cyclohexane by H₂O₂. Reaction of the iron(II) complexes with H₂O₂ and [superscript(t)]BuOOH was followed by time-resolved EPR and UV-VIS spectrophotometry. A correlation between the observed catalytic activity and the nature of the FeIII(L)-OOR intermediates generated is apparent. A convenient ‘one-pot’ synthesis of benzene-1,3,5-triamido-tris(l-histidine methyl ester) is reported along with attempts at preparing N,N’-bis(pyridylmethyl)-1,3- diaminopropane-2-carboxylic acid (L₂₅), a new water soluble pyridine-amine ligand. The final demetallation step resulted in ligand hydrolysis to the novel amino acid; 1,3-diaminopropane- 2-carboxylic acid which was characterised as its HCl salt by X-ray crystallography