A Convenient and Stable Heterogeneous Nickel Catalyst for Hydrodehalogenation of Aryl Halides Using Molecular Hydrogen.

Invited for this month's cover is the group of Matthias Beller at the Leibniz Institute for Catalysis in Rostock in collaboration with Muhammad Anwar and Sarim Dastgir at the Qatar Environment and Energy Research Institute in Doha. The image illustrates a hydrodehalogenation of polybrominated diphenyl ether (PBDE) using a heterogeneous nickel catalyst supported on titanium oxide and dihydrogen. The Research Article itself is available at 10.1002/cssc.202102315.

A Convenient and Stable Heterogeneous Nickel Catalyst for Hydrodehalogenation of Aryl Halides Using Molecular Hydrogen.

Hydrodehalogenation is an effective strategy for transforming persistent and potentially toxic organohalides into their more benign congeners. Common methods utilize Pd/C or Raney-nickel as catalysts, which are either expensive or have safety concerns. In this study, a nickel-based catalyst supported on titania (Ni-phen@TiO2 -800) is used as a safe alternative to pyrophoric Raney-nickel. The catalyst is prepared in a straightforward fashion by deposition of nickel(II)/1,10-phenanthroline on titania, followed by pyrolysis. The catalytic material, which was characterized by SEM, TEM, XRD, and XPS, consists of nickel nanoparticles covered with N-doped carbon layers. By using design of experiments (DoE), this nanostructured catalyst is found to be proficient for the facile and selective hydrodehalogenation of a diverse range of substrates bearing C-I, C-Br, or C-Cl bonds (>30 examples). The practicality of this catalyst system is demonstrated by the dehalogenation of environmentally hazardous and polyhalogenated substrates atrazine, tetrabromobisphenol A, tetrachlorobenzene, and a polybrominated diphenyl ether (PBDE).

A State-of-the-Art Heterogeneous Catalyst for Efficient and General Nitrile Hydrogenation.

Cobalt-doped hybrid materials consisting of metal oxides and carbon derived from chitin were prepared, characterized and tested for industrially relevant nitrile hydrogenations. The optimal catalyst supported onto MgO showed, after pyrolysis at 700 °C, magnesium oxide nanocubes decorated with carbon-enveloped Co nanoparticles. This special structure allows for the selective hydrogenation of diverse and demanding nitriles to the corresponding primary amines under mild conditions (e.g. 70 °C, 20 bar H2 ). The advantage of this novel catalytic material is showcased for industrially important substrates, including adipodinitrile, picolinonitrile, and fatty acid nitriles. Notably, the developed system outperformed all other tested commercial catalysts, for example, Raney Nickel and even noble-metal-based systems in these transformations.

Titanium(IV) imido complexes of imine imidazol-2-imine ligands.

Free imine imidazol-2-imine ligands with two different substitution patterns have been isolated for the first time and they were found to exist as an equilibrium mixture of geometric and mesomeric isomers. The relative ratios of these isomers are dependent on both the nature of the substituents and of the solvent. The synthesis of the titanium(IV) alkyl and arylimido complexes of these ligands was unexpectedly found to be very selective and was successfully achieved only with the lesser sterically-demanding 2,4,6-trimethylphenyl derivative IMesN^Imine 2a. The solid-state structure of the alkylimido complex further confirms the zwitterionic character of the ligand. The isolated titanium imido complexes were found to be active catalysts for the polymerisation of ethylene.

New stable aryl-substituted acyclic imino-N-heterocyclic carbene: synthesis, characterisation and coordination to early transition metals.

The synthesis of the bulky 1-(1-arylimino-2,2-dimethylpropyl)-3-(aryl)imidazolium salt from the corresponding imidazole and the activated imidoyl chloride is presented. The absence of acidic protons adjacent to the iminic carbon allowed for the first isolation of an imino-N-heterocyclic carbene of this ligand class. The free carbene was isolated, structurally characterised, and coordinated to titanium, zirconium, hafnium and chromium. The resulting metal halide complexes were fully characterised and were tested at room temperature and atmospheric pressure for their activity as ethylene polymerisation catalysts. The Zr(IV) complex was found to be the most active with a productivity of 140 kg PE mol M(-1) h(-1).

Heterogenised N-heterocyclic carbene complexes: synthesis, characterisation and application for hydroformylation and C-C bond formation reactions.

The imidazolium salts: 1-mesityl-3-(3-trimethoxysilylpropyl)imidazolium iodide and 1-tert-butyl-3-(3-trimethoxysilylpropyl)imidazolium iodide, abbreviated as (tmpMes)HI (3a) and (tmp(t)Bu)HI (3b), respectively, have been synthesised. The palladium(ii) complexes (η(3)-C(3)H(5)) (tmpMes)PdCl (5a) and (η(3)-C(3)H(5))(tmp(t)Bu)PdCl (5b), rhodium(i) and iridium(i) complexes (η(4)-1,5-COD) (tmpMes)MCl, M = Rh (6a), Ir (7a) and (η(4)-1,5-COD)(tmp(t)Bu)MCl, where M = Rh (6b), Ir (7b), were synthesised by silver transmetallation reactions using the silver(i) complexes (tmpMes)AgI (4a) and (tmp(t)Bu)AgI (4b). The iridium complex 7b has been structurally characterised. The Pd(ii) and Rh(i) complexes have been immobilised by attachment to chemically modified MCM-41. The immobilised palladium(ii) materials have been tested as recyclable catalysts for Suzuki type C-C bond formation reactions in water and the immobilised rhodium(i) materials have been examined for their catalytic ability for the hydroformylation of 1-octene.

Coordination study of a new class of imine imidazol-2-imine ligands to titanium(IV) and palladium(II).

A new family of ligand precursors, N-(1-(2,6-dimethylphenylimino)ethyl)-1,3-bis(aryl)imidazol-2-imine hydrochloride, wherein aryl = 2,4,6-trimethylphenyl (3a) and 2,6-diisopropylphenyl (3b), was prepared and structurally characterised. Deprotonation of the salts yields molecules with delocalised pi-electrons, leading to zwitterionic mesomeric structures. Titanium(IV) (4a,b) and palladium(II) (5a,b) complexes were isolated and also structurally characterised. Two different coordination modes were observed where the ligand is either coordinated in a bidentate fashion as expected, or in a monodentate fashion through the more basic aryliminic nitrogen atom.

First aryl-substituted acyclic imino-N-heterocyclic carbene ligand precursor: synthesis, characterisation and coordination with silver(I) and copper(I).

The first aryl-substituted imino-N-heterocyclic ligand precursor was prepared and structurally characterised, along with the corresponding silver(i) and copper(i) chloride complexes. An unusual T-shape coordination mode for the copper centre was observed.

Stable crystalline annulated diaminocarbenes: coordination with rhodium(I), iridium(I) and catalytic hydroformylation studies.

Stable annulated diaminocarbene ligands 7,9-bis(2,4,6-trimethylphenyl)-6b,9a-dihydroace naphtha[1,2-d]imidazolin-2-ylidene and 7,9-bis(2,6-diisopropylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolin-2-ylidene; designated as (BIAN-SIMes, 5a,) and (BIAN-SIPr, 5b), respectively, have been prepared. The base dependent decomposition of imidazolinium salts via ring opening at the backbone was also observed. The corresponding rhodium(I) and iridum(I) complexes (4-1,5-COD)M(BIAN-SIMes)Cl and (4-1,5-COD)M(BIAN-SIPr)Cl; M= Rh (6a, 6b) and Ir (7a, 7b) have been synthesised by the reaction of free carbene with [M(4-1,5-COD)(-Cl)]2; where M= Rh, Ir. The cationic Ir(I) complexes [(4-1,5-COD)Ir(BIAN-SIMes)Py]BF4 8a and [(4-1,5-COD)Ir(BIAN -SIPr)Py]PF6 8b have also been synthesised. Compounds 4b, 5a, 6a, 6b, 7b and 8b have been structurally characterised. The catalytic activities for the rhodium(I) complexes 6a and 6b were evaluated for the hydroformylation of 1-octene.

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition.

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex.