A titanium redox-switch enables reversible C-C bond forming and splitting reactions.

Using an Earth-abundant transition metal to mediate formation and splitting of C-C σ-bonds, in response to electrical stimuli, constitutes a promising strategy to construct complex organic skeletons. Here, we showcase how [ BuN][N] reacts with an isocyanide adduct of a tetrahedral and high-spin Ti complex, [(Tp )TiCl] (1), to enact N-atom transfer, C-N bond formation, and C-C coupling, to form a dinuclear complex, [(Tp )Ti{AdN(N)C-C(N)NAd}Ti(Tp )] (3), with two Ti ions bridged by a disubstituted oxalimidamide ligand ( Bu = -butyl, Tp = hydrotris(3--butyl-5-methylpyrazol-1-yl)borate, Ad = 1-adamantyl). Magnetic and computational studies reveal two magnetically isolated d Ti ions, and electrochemical studies unravel a reversible two-electron oxidation at -0.

Inverse Trans Influence and Uranium-Arene σ-Bonding Drive Molecular Geometry: Ligand Modification from Hard to Soft Flips the Oxide from Axial to Equatorial.

A rare example of an equatorially bound terminal uranium(V) oxo complex in a chelating sulfur-based ligand environment, namely [(mes(ArS))U(O)(THF)] (), is presented. Octahedrally coordinated is obtained by reaction of the mesitylene-anchored tris-thiophenolate-coordinated uranium(III) complex [U((SAr)mes)] () with the oxygen-atom transfer reagent NO. The observed, equatorially bound oxo ligand in is in stark contrast to its known tris-aryloxide analog, [(mes(ArO))U(O)(THF)] (), where the oxo ligand occupies the typically observed axial coordination site.

Utilization of a Chelating Bis[(dialkylamino)cyclopropenimine] to Isolate a Series of Heavier Zero-Valent Group 14 Tetracarbonyl Iron Complexes.

We report on the utilization of the ethylene-bridged bis[(dialkylamino)cyclopropenimine] (bisCPI) ligand, L, to give access to new main-group E(II) halide complexes (E = Ge, Sn, Pb; 1, 2, 3). Subsequent reduction with Collman's reagent (NaFe(CO) • dioxane) enables the isolation of a series of zero-valent tetrylone-tetracarbonyl iron complexes, (L)E(Fe(CO) (E = Ge (4), Sn (5), Pb (6)). Compounds 4 - 6 were reacted further with iron pentacarbonyl to yield the bis-tetracarbonyl iron complexes (L)E[(Fe(CO)] (E = Ge (7), Sn (8), Pb (9)).

Towards Surface-Enhanced Homogeneous Catalysis: Tailoring the Enrichment of Metal Complexes at Ionic Liquid Surfaces.

When talking about homogeneous catalyst systems, it has long been assumed that the system at hand consists of a transition metal complex in solution with the liquid interface representing the composition of the bulk solution. Now, in light of considerable developments in the study of metal complexes dissolved in ionic liquids with their negligible vapor pressures, more detailed studies of the composition at the liquid/gas interface became possible. These investigations revealed pronounced surface enrichment and segregation effects of high relevance for practical applications.

An Icosahedral 55-Atom Iron Hydride Cluster Protected by Tri--butylphosphines.

Nanoclusters are nanometer-sized molecular compounds characterized by significant metal-metal bonding and low average oxidation states, and they exhibit unique properties distinct from those of small metal complexes or nanoparticles. Unlike noble metals stable in metallic forms, the synthesis of nanometer-sized iron clusters has been precluded by the relatively weak iron-iron bonds and the high reactivity of low oxidation state iron, despite the extensive history of molecular iron compounds. Here, we report the synthesis and characterization of a cationic 55-atom iron cluster with a 1.

A Trithia-Bridged N-Heterotriangulene: The Hitherto Missing Electron Donor.

The very first representative of trithia-bridged N-heterotriangulene, a triphenylamine with sulfur atoms bridging the ortho-positions, was synthesized by a sequence of regioselective sulfenylation with phthalimidesulfenyl chloride followed by Lewis acid-catalyzed electrophilic cyclization. X-ray crystallography revealed a saddle-shaped geometry of the polycyclic scaffold. UV/Vis absorption spectroscopy and cyclic voltammetry were used to characterize the optoelectronic properties.

A Surface-Active Pt(II) Bis-N-Heterocyclic Carbene (NHC) Complex for Interface-Enhanced Supported Ionic Liquid Phase (SILP) Catalysis.

We present the preparation and investigation of a fluorine-free surface-active bis-N-heterocyclic carbene (NHC) platinum(II) complex - trans-[Pt(mPEGCIm)Cl] - for interface-enhanced supported ionic liquid phase (SILP) catalysis within a group of (mPEG)-substituted ionic liquids (ILs) ([(mPEG)Im][A] ILs). The complex was characterized by means of single-crystal X-ray diffraction (scXRD) analysis and multinuclear (H, C, Pt) NMR spectroscopy, indicating the presence of two almost equimolar syn-anti-rotamers of the square-planar complex in solution. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) revealed pronounced interface-accumulation of trans-[Pt(mPEGCIm)Cl] in IL solutions of [(mPEG)Im][A] (A=I and PF ).

C-H/F bond activation and borylation with iron.

Reduction of [K{(pyrrpyr)Fe}(μ-N)] (1) with two equiv. of KC in the presence of crown-ether 18-C-6 yields the N adduct [{K(18-C-6)}(pyrrpyr)Fe(N)] (2). Complex 2 heterolytically splits the C-H bond of benzene to form [{K(18-C-6)}(pyrrpyr)Fe(CH)] (3), whereby usage of a diboron Bpin promotes hydride elimination to form the salt [K(18-C-6)HBPin] (4).

A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [Fe(μ-O)Fe] Diamond Core Derived from Dioxygen Activation.

The diiron(II) complex, [(OCO)Fe(MeCN)] (, MeCN = acetonitrile), supported by the bis-phenolate carbene pincer ligand, 1,3-bis(3,5-di--butyl-2-hydroxyphenyl)benzimidazolin-2-ylidene (OCO), was synthesized and characterized by single-crystal X-ray diffraction, H nuclear magnetic resonance, infrared (IR) vibrational, ultraviolet/visible/near-infrared (UV/vis/NIR) electronic absorption, Fe Mössbauer, X-band electron paramagnetic resonance (EPR) and SQUID magnetization measurements. Complex activates dioxygen to yield the diferric, μ-oxo-bridged complex [(OCO)Fe(py)(μ-O)Fe(O(C═O)O)(py)] () that was isolated and fully characterized. In , one of the iron-carbene bonds was oxidized to give a urea motif, resulting in an O(C═O)O binding site, while the other Fe(OCO) unit remained unchanged.

A Caged Neutral 17-Valence-Electron Iron(I) Radical [Fe(CO)(Cl)(P((CH))P)]: Synthetic, Structural, Spectroscopic, Redox, and Computational Studies.

UV irradiation of yellow CHCl solutions of -Fe(CO)(P((CH))P) () and PMe (10 equiv) gives, in addition to the previously reported dibridgehead diphosphine P((CH))P (46%), a green paramagnetic complex that crystallography shows to be the trigonal-bipyramidal iron(I) radical -[Fe(CO)(Cl)(P((CH))P)] (; 31% after workup). This is a rare example of an isolable species of the formula [Fe(CO)(L)(X)] ( = 0-3, L = two-electron-donor ligand; X = one-electron-donor ligand). Analogous precursors with longer P(CH)P segments ( = 12, 14, 16, 18) give only the demetalated diphosphines, and a rationale is proposed.

From d to d: Iron(0) and Iron(I) Complexes Complete the Series of Eight Fe Oxidation States within the TIMMN Ligand Framework.

Reduction of the ferrous precursor [(TIMMN)Fe(Cl)] () (TIMMN = ris-[(3-mesitylidazol-2-ylidene)ethyl]amie) to the low-valent iron(0) complex [(TIMMN)Fe(CO)] () is presented, where the tris(N-heterocyclic carbene) (NHC) ligand framework remains intact, yet the coordination mode changed from 3-fold to 2-fold coordination of the carbene arms. Further, the corresponding iron(I) complexes [(TIMMN)Fe(L)] (L = free site, η-N, CO, py) () are synthesized and fully characterized. Complexes - demonstrate the notable steric and electronic flexibility of the TIMMN ligand framework by variation of the Fe-N anchor and Fe-carbene distances and the variable size of the axial cavity occupation.

A Vanadium Methylidene.

Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH)] (PNP = N[2-PPr-4-methylphenyl], Ar = 2,6-PrCH), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH)] or [(PNP)V(=NAr)(CH)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, HCPPh.

An electrically conducting 3D coronene-based metal-organic framework.

A novel cubic mesoporous metal-organic framework (MOF), consisting of hexahydroxy--hexabenzocoronene (-HBC) and Fe ions is presented. The highly crystalline and porous MOF features broad optical absorption over the whole visible and near infrared spectral regions. An electrical conductivity of 10 S cm was measured on a pressed pellet.

Evolution of Surface Tension and Hansen Parameters of a Homologous Series of Imidazolium-Based Ionic Liquids.

In this study, we systematically analyze the surface tension and Hansen solubility parameters (HSPs) of imidazolium-based ionic liquids (ILs) with different anions ([NTf], [PF], [I], and [Br]). These anions are combined with the classical 1-alkyl-3-methyl-substituted imidazolium cations ([CCIm]) and a group of oligoether-functionalized imidazolium cations ([(mPEG)Im]) based on methylated polyethylene glycol (mPEG). In detail, the influences of the length of the alkyl- and the mPEG-chain, the anion size, and the water content are investigated experimentally.

Divalent Titanium via Reductive N-C Coupling of a Ti Nitrido with π-Acids.

The nitrido-ate complex [(PN)Ti(N){μ-K(OEt)}] (1) (PN=(N-(2-PPr-4-methylphenyl)-2,4,6-MeCH) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate Ti complexes having a linear cumulene motif, [K(L)][(PN)Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural Ti center containing a neutral cumulene, [(PN)Ti(NCE)] (E=O, (6); E=NAd (7), NBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy.

Unlocking the Metalation Applications of TMP-powered Fe and Co(II) bis(amides): Synthesis, Structure and Mechanistic Insights.

Typified by LiTMP and TMPMgCl.LiCl, (TMP=2,2,6,6-tetramethylpiperidide), s-block metal amides have found widespread applications in arene deprotonative metalation. On the contrary, transition metal amides lack sufficient basicity to activate these substrates.

Enhanced Photostability of Lead Halide Perovskite Nanocrystals with Mn Incorporation.

Recently, lead halide perovskite nanocrystals (NCs) have shown great potential and have been widely studied in lighting and optoelectronic fields. However, the long-term stability of perovskite NCs under irradiation is an important challenge for their application in practice. Mn dopants are mostly proposed as substitutes for the Pb site in perovskite NCs synthesized through the hot-injection method, with the aim of improving both photo- and thermal stability.

The synthesis and characterization of an iron(VII) nitrido complex.

Complexes of iron in high oxidation states are captivating research subjects due to their pivotal role as active intermediates in numerous catalytic processes. Structural and spectroscopic studies of well-defined model complexes often provide evidence of these intermediates. In addition to the fundamental molecular and electronic structure insights gained by these complexes, their reactivity also affects our understanding of catalytic reaction mechanisms for small molecule and bond-activation chemistry.

Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene.

We introduce the arsenido ligand onto the Ti ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete Ti salt [K(cryptand)][(PN)TiCl] () (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane) in thf/toluene to produce the mixed alkali ate-complex [(PN)Ti(As)](μ-KNa(thf)) () and the discrete salt [K(cryptand)][(PN)Ti≡As] () featuring a terminal Ti≡As ligand. Protonation of or with various weak acids cleanly forms the parent arsinidene [(PN)Ti═AsH] (), which upon deprotonation with KCHPh in thf generates the more symmetric anionic arsenido [(PN)Ti(As){μ-K(thf)}] ().

Benzene-1,4-Di(dithiocarboxylate) Linker-Based Coordination Polymers of Mn, Zn, and Mixed-Valence Fe.

Three new coordination polymers (CPs) constructed from the linker 1,4-di(dithiocarboxylate) (BDDTC)─the sulfur-analog of 1,4-benzenedicarboxylate (BDC)─together with Mn-, Zn-, and Fe-based inorganic SBUs are reported with description of their structural and electronic properties. Single-crystal X-ray diffraction revealed structural diversity ranging from one-dimensional chains in [Mn(BDDTC)(DMF)] () to two-dimensional (2D) honeycomb sheets observed for [Zn(BDDTC)][Zn(DMF)(HO)] (). Gas adsorption experiments confirmed a 3D porous structure for the mixed-valent material [Fe(BDDTC)(OH)] ().

Self-Assembled Supported Ionic Liquids.

Separation and reuse of the catalytically active metal complexes are persistent issues in homogeneous catalysis. Supported Ionic Liquid Phase (SILP) catalysts, where the catalytic center is dissolved in a thin film of a stable ionic liquid, deposited on a solid support, present a promising alternative. However, the dissolution of the metal center in the film leaves little control over its position and its activity.

Deciphering Iron-Catalyzed C-H Amination with Organic Azides: N Cleavage from a Stable Organoazide Complex.

Catalytic C-N bond formation by direct activation of C-H bonds offers wide synthetic potential. En route to C-H amination, complexes with organic azides are critical precursors towards the reactive nitrene intermediate. Despite their relevance, α-N coordinated organoazide complexes are scarce in general, and elusive with iron, although iron complexes are by far the most active catalysts for C-H amination with organoazides.

Iron-Catalyzed Intermolecular C-H Amination Assisted by an Isolated Iron-Imido Radical Intermediate.

Here we report the use of a base metal complex [( pyrpyrr )Fe(OEt )] (1-OEt ) ( pyrpyrr =3,5-tBu -bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of C -H bonds of 9,10-dihydroanthracene (2 a) using 2,4,6-trimethyl phenyl azide (3 a) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1-OEt with control in selectivity for single C-H amination versus double C-H amination. Catalytic C-H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions.