Routes to Heterotrinuclear Metal Siloxide Complexes for Cooperative Activation of O.

The assembly of heterometallic complexes capable of activating dioxygen is synthetically challenging. Here, we report two different approaches for the preparation of heterometallic superoxide complexes [LCr-η-O][MX] (L = OPhSiOSiPhO, MX = [CoCl], [ZnBr], [ZnCl]) starting from the Cr precursor complex [LCr]Li(THF). The first strategy proceeds via the exchange of Li by [MX] through the addition of MX to [LCr]Li(THF) before the reaction with dioxygen, whereas in the second approach a salt metathesis reaction is undertaken after O activation by adding MX to [LCr-η-O]Li(THF).

Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O at an Iron(II)-Cyclam Center.

In soluble methane monooxygenase enzymes (MMO), dioxygen (O) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate that performs the challenging oxidation of methane to methanol. An analogous mechanism of O activation at mono- or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, -, that activates O to form the corresponding iron(IV)-oxo complex, -, via a mechanism reminiscent of the O activation process in MMO.

Mercaptothiacalixarenes Steer 24 Copper(I) Centers to form a Hollow-Sphere Structure Featuring Cu S Motifs with Exceptionally Short Cu⋅⋅⋅Cu Distances.

Tetramercaptotetrathiacalix[4]arene (LH ) can be used as a coordination platform to bind four Cu ions at the thiolate and thioether S atoms. Donor ligands such as phosphanes can stabilize the resulting [LCu ] units, which then remain monomeric ([(Ph PCu) L]). In the absence of donor ligands, they aggregate, providing a hexamer ([LCu ] ) in high yields, with a hollow-sphere structure formed by an unprecedented Cu S cage that is surrounded by the organic framework of the calixarene chalices.

Activation of tetrafluoropropenes by rhodium(i) germyl and silyl complexes.

The reaction of the rhodium(i) complexes [Rh(E)(PEt3)3] (E = GePh3 (1), Si(OEt)3 (5)) with HFO-1234yf (2,3,3,3-tetrafluoropropene) afforded [Rh(F)(PEt3)3] (2) and the functionalized olefins Z-CF3CH[double bond, length as m-dash]CH(E) (E = GePh3 (4a), Si(OEt)3 (7)). Conceivable reaction pathways were assessed using DFT calculations. Reactions of [Rh(E)(PEt3)3] with HFO-1234ze (E-1,3,3,3-tetrafluoropropene) yielded the rhodium fluorido complex 2 and [Rh{(E)-CH[double bond, length as m-dash]CH(CF3)}(PEt3)3] (9) via two different reaction pathways.

Switching from a Chromium(IV) Peroxide to a Chromium(III) Superoxide upon Coordination of a Donor in the trans Position.

O activation at a chromium(II) siloxide complex in propionitrile leads to a chromium(III) complex with an end-on bound superoxide ligand, while the reaction in tetrahydrofuran leads to a side-on peroxo chromium(IV) compound. The superoxide reacts faster with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl hydroxylamine while the peroxide, unlike the superoxide, proved capable of deformylating aldehydes. The system was found to represent a unique case, where even a switching between the two structures can be achieved via the solvent; its ability to coordinate at the position  to the O ligand is decisive, as supported by density functional theory studies.

In situ generation of PhPO in cyanido-bridged heterometallic {FeLn} molecular squares (Ln = Eu, Sm).

Two new examples of cyanido-bridged {FeLn} molecular squares, with pyim and PPhO as capping ligands at the Ln sites, exhibit weak antiferromagnetic interactions [Ln = Eu (1), Sm (2), pyim = 2-(1H-imidazol-2-yl)pyridine, PPhPO = triphenylphosphine oxide].

The Influence of Alkali Metal Ions on the Stability and Reactivity of Chromium(III) Superoxide Moieties Spanned by Siloxide Ligands.

In recent years, it has become clear that the presence of redox-inactive Lewis acidic metal ions can decisively influence the reactivity of metal-dioxygen moieties that are formed in the course of O activation, in molecular complexes, and metalloenzymes. Superoxide species are often formed as the primary intermediates but they are mostly too unstable for a thorough investigation. We report here a series of chromium(III) superoxide complexes [L Cr]M O (THF) (L= OSiPh OSiPh O , M =Li , Na , K and y=4, 5), which could be accessed, studied spectroscopically and partly crystallized at low temperatures.

A Silylene-Borane Lewis Pair as a Tool for Trapping a Water Molecule: Silanol Formation and Dehydrogenation.

The Lewis acid B(C F ) and the cyclic silane (Ar Si) (1) (Ar =o-(CH ) NCH C H ) are useful precursors to access the silylene(II)-borane adduct Ar Si-B(C F ) (2). Treatment of 2 with water led to coordination and gave the Lewis pair (Ar H O)Si-B(C F ) (3) that exhibits a hydrogen-bond-stabilized silanol unit. It can be converted into the siloxane [(HAr ) SiOB(C F ) ] O (6) by dehydrogenation in the presence of a base.

Sensitized Photochemical CO Reduction by Hetero-Pacman Compounds Linking a Re Tricarbonyl with a Porphyrin Unit.

The hetero-Pacman architecture places two different metal coordination sites in close proximity, which can support efficient energy and/or electron transfer and allow for cooperative activation of small molecules. Here, the synthesis of dyads consisting of a porphyrin unit as photosensitizer and a rhenium unit as catalytically active site, which are held together by the rigid xanthene backbone, is presented. Mononuclear [(NN)Re(CO) (Cl)] complexes for CO reduction in which NN represents a bidentate diimine ligand (e.

Structure and Reactivity of Al-O(H)-Al Moieties in Siloxide Frameworks: Solution and Gas-Phase Model Studies.

Even though aluminas and aluminosilicates have found widespread application, a consistent molecular understanding of their surface heterogeneity and the behavior of defects resulting from hydroxylation/dehydroxylation remains unclear. Here, we study the well-defined molecular model compound, [Al (μ -OH) (THF) (PhSi(OSiPh O) ) ], 1, to gain insight into the acid-base reactivity of cyclic trinuclear Al (μ -OH) moieties at the atomic level. We find that, like zeolites, they are sufficiently acidic to catalyze the isomerization of olefins.

A Biomimetic Nickel Complex with a Reduced CO Ligand Generated by Formate Deprotonation and Its Behaviour towards CO.

Reduced CO species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni-CO complex that is unique in many ways.

Diverse Reactivity of Platinum SF and SF Complexes towards EtOH and Me SiOEt.

The complex trans-[Pt(F)(SF )(PCy ) ] (1) shows a diverse reactivity pattern at the SF ligand towards ethanol and Me SiOEt. This led by deoxyfluorination or alcoholysis to the generation of platinum complexes bearing a metal-bound S(O)F or S(OEt) group. For the latter reaction trans-[Pt(F){S(F)(OEt) }(PCy ) ] is suggested as an intermediate.

Comparing Isomeric Tridentate Carbazole-Based Click Ligands: Metal Complexes and Redox Chemistry.

Two novel bis(triazolyl)carbazole ligands Hbtc1 (3,6-di(tert-butyl)-1,8-bis[(1-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-4-yl)]-9H-carbazole) and Hbtc2 (3,6-di(tert-butyl)-1,8-bis[(4-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-1-yl)]-9H-carbazole), differing in the regiochemistry of triazole attachment, have been synthesized by Cu-catalyzed azide-alkyne cycloaddition, the so-called "click-reactions". Metalation with Ru, Zn, and Ni precursors led to the formation of M(btc) complexes (M=Ru, Zn, Ni), with two deprotonated ligands coordinating to the metal center in tridentate fashion, forming almost perfectly octahedral coordination spheres. The redox properties of M(btc) complexes have been investigated by cyclic voltammetry, UV/Vis spectroscopy, spectroelectrochemistry, and chemically.

Bismuthanes as Hemilabile Donors in an O -Activating Palladium(0) Complex.

A xanthene-based bismuthane/phosphane chelating ligand has been accessed that has enabled the synthesis of a palladium(0) bismuthane complex. The bismuthane donor proved to be hemilabile as it switched to a dangling position upon addition of O that gave a palladium(II) peroxide complex. Unlike the corresponding 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) palladium peroxide, the bismuth analogue could be employed for catalytic phosphane oxidation and oxidative phenol coupling.

Taming the High Reactivity of Gold(III) Fluoride: Fluorido Gold(III) Complexes with N-Based Ligands.

The synthesis of [NMe ][AuF ] and [NEt ][AuF ], as well as an improved one-pot synthesis of Cs[AuF ], is reported. The new [AuF ] salts were structurally characterized by single crystal X-ray diffraction, NMR spectroscopy, vibrational spectroscopy, and mass spectrometry. These salts are the first gold(III) fluoride salts that can be isolated in pure form and are convenient to be used in usual organic solvents for subsequent synthesis.

The Versatile Behavior of Platinum Alkyne Complexes towards XeF : Formation of Fluorovinyl and Fluorido Complexes.

Reactions of platinum(0) tolane complexes, bearing a chelating ligand with P and N donor atoms, with the electrophilic fluorinating agent XeF give facile access to platinum(II) β-fluorovinyl fluorido complexes. A series of new platinum(II) β-fluorovinyl complexes have been synthesized and were structurally characterized. Further oxidation with XeF led to ortho-metalated platinum(IV) fluorido compounds.

Activation of Dioxygen at a Lewis Acidic Nickel(II) Complex: Characterization of a Metastable Organoperoxide Complex.

In metal-mediated O activation, nickel(II) compounds hardly play a role, but recently it has been shown that enzymes can use nickel(II) for O activation. Now a low-coordinate Lewis acidic nickel(II) complex has been synthesized that reacts with O to give a nickel(II) organoperoxide, as proposed for the enzymatic system. Its formation was studied further by UV/Vis absorption spectroscopy, leading to the observation of a short-lived intermediate that proved to be reactive in both oxygen atom transfer and hydrogen abstraction reactions, while the peroxide efficiently transfers O atoms.

Photochemical Degradation of Various Bridge-Substituted Fluorene-Based Materials.

Photochemical degradation is an important issue to be overcome in advancing the lifetime of fluorene-containing conjugated polymers. In order to optimize the inertness of the materials, a quantitative measure for the efficiency of degradation is needed. Here, we introduce a method to measure a relative quantum yield of the photochemical degradation by monitoring the kinetics of the process by means of UV/vis spectroscopy and liquid chromatography (LC) techniques.

Trapping Aluminum Hydroxide Clusters with Trisilanols during Speciation in Aluminum(III)-Water Systems: Reproducible, Large Scale Access to Molecular Aluminate Models.

To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of Al(i) Bu2 H in dependence on the amount of water used allowed for the isolation of tri- and octanuclear aluminum hydroxide cluster complexes [Al3 (μ2 -OH)3 (THF)3 (PhSi(OSiPh2 O)3 )2 ] (1) and [Al8 (μ3 -OH)2 (μ2 -OH)10 (THF)3 (p-anisylSi(OSiPh2 O)3 )4 ] (2).

Completing the Heterocubane Family [Cp*AlE]4 (E = O, S, Se, and Te) by Selective Oxygenation and Sulfuration of [Cp*Al]4: Density Functional Theory Calculations of [Cp*AlE]4 and Reactivity of [Cp*AlO]4 toward Hydrolysis.

The subvalent aluminum compound [Cp*Al]4 (1) reacts with dioxygen, N2O, or sulfur to yield the heterocubane complexes [Cp*AlX]4 [X = O (2) and S (3)]. Treatment of [Cp*AlO]4 (2) with (tBuO)3SiOH gave [(tBuO)3SiOAlO]4 (6) and Cp*H. The structures and spectroscopic data of the Al clusters are supported by density functional theory (DFT) calculations, which also demonstrate the importance of noncovalent interactions (NCI) in oligomeric Al(I) complexes as well as in [Cp*AlS]4 and the heavier homologues of Se and Te.