Binding of a TlCl Entity by a Tetragold Tetramercaptothiacalixarene Metalloligand via Metallophilic Interactions

The successive auration of p-tert-butyltetramercaptotetrathiacalix[4]arene, H₄ (MTC[4]), with gold(I) phosphine units was investigated. Through deprotonation with NaOMe, followed by salt metathesis reactions with (PR₃ )AuCl (R=Me, Ph) complexes with two and three [(PR₃ )Au]⁺ moieties could be prepared and isolated, namely [(Ph₃ PAu)₂ H₂ (MTC[4])] and [(Me₃ PAu)₃ H(MTC[4])]. In [(Me₃ PAu)₃ H(MTC[4])] two gold atoms already come close enough to undergo aurophilic interactions. To introduce a fourth [(PR₃ )Au]⁺ entity TlOEt had to be used for the deprotonation, which led to the finding that four gold atoms organised by the (MTC[4])^4- coordination platform are able to bind and stabilize a TlCl entity, yielding [(Me₃ PAu)₄ TlCl(MTC[4])]. As evidenced by structural and theoretical investigations the binding occurs through strong metallophilic interactions, which lead to photoluminescence at low temperatures.

Copper(i) complexes based on ligand systems with two different binding sites: synthesis, structures and reaction with O2

The synthesis of the ligand systems L1 and L2 with two different N₃-binding sites linked through a dibenzofuran spacer and their coordination properties towards a variety of Cu^I precursors are reported. The reaction of L1 with copper halides leads to the formation of a bimetallic species [(L1)(Cu^ICl)₂] (1), and metallodimers [((L1)(Cu^IX)₂)₂(μ-(Cu)(μ-X)₂)] (2: X = Br, 3: X = I) in which two dicopper complexes are bridged by a (μ-(Cu)(μ-X)₂)-moiety whereas L2 reacts with copper chloride to afford {[Cu(L2)Cl₂]}_n (8). Furthermore, starting from L1 in combination with copper(i) salts of weakly coordinating anions the dicopper complexes [(L1)(Cu^I(NCCH₃))₂](BF₄)₂ (4), [(L1)(Cu^I(NCCH₃))(Cu(Y))](Y) (5: Y = OTf, 6: Y = ClO₄) and [(L1)(Cu(dppe))](PF₆)₂ (7) were isolated, and employing L2, the complexes [(L2)(Cu^I(NCCH₃))₂](Z)₂ (9: Z = PF₆, 10: Z = OTf) and [(L2)(Cu(dppe))](PF₆)₂ (11) were obtained. Complexes 4-6 as well as 9 and 10 react rapidly with O₂ to form metastable O₂ adducts in acetone at -90 °C, where O₂ is bound between the two copper centers within one dicopper molecule, as evidenced by UV/Vis spectroscopy, kinetic investigations, Raman spectroscopy and studies with ligands containing the isolated donor sites. The reactivity of the O₂ adducts towards selected substrates was also investigated, showing their ability to act as electrophiles as well as nucleophiles.

O2 activation at a trispyrazolylborato nickel(ii) malonato complex

To support mechanistic inferences made for an iron-based dioxygenase model, a nickel analogue, i.e. a TpNi-malonate (1) was prepared. 1 proved to represent a rare case of a nickel complex reacting with O₂ in a controlled manner - mechanistically different from the iron case - and leads to hydroxylation of the malonate.

A Hexanuclear Iron(II) Layer with Two Square-Planar FeO4 Units Spanned by Tetrasiloxide Ligands: Mimicking of Minerals and Catalysts

A hexanuclear iron(II) siloxide complex has been prepared by reacting an incompletely condensed silsesquioxane first with NaOMe and then with Fe(OTf)₂. In the process of product formation, the siloxane framework undergoes a transformation and it was shown that this happens already upon addition of base: Treatment of the ligand precursor with NaOMe leads to a completely condensed silsesquioxane cage with 12 Si atoms that is composed of 2 equiv of the tetrasiloxide ligands found in the product complex. Its iron centers form a two-dimensional array reminiscent of the situations found in minerals and two-dimensional oxide films caused by segregation of FeO_x and silica. As the hexairon(II) assembly contains two high-spin square-planar FeO₄ units-suggested to represent the active sites in Fe-zeolites, which react with N₂O to generate strongly oxidizing sites-it was treated with Me₃NO. This led to the oxidation of two of the iron centers to the oxidation state +III and elimination of one iron ion, so that a pentanuclear, mixed valent iron siloxide was formed. All complexes were fully characterized.

A high-spin square planar iron(ii)-siloxide and its tetrahedral allogon – structural and spectroscopic models of Fe-zeolite sites

The so far closest molecular model for the α-Fe sites in Fe-zeolites faithfully mimics the unique structure and spectroscopic features.

Dioxygenation of cysteamine to hypotaurine at a tris(pyrazolyl)borate iron(ii) unit - cysteamine dioxygenase mimicking?

A novel complex Tp(Me,Ph)Fe(SCH2CH2NH2) has been synthesized as a speculative model for ADO. Indeed its reaction with O2 led to the dioxygenation of the S atom and thus to hypotaurine. This finding may allow us to draw conclusions on the constitution of the ADO active site, whose structure is still unknown.

Reaction of a polydentate cysteine-based ligand and its nickel(ii) complex with electrophilic and nucleophilic methyl-transfer reagents - from S-methylation to acetyl coenzyme A synthase reactivity

The L-cysteine derived N2S2 ligand precursor H2L and its nickel(ii) complex L2Ni2 were investigated with respect to their behaviour in contact with electrophilic and nucleophilic methylation reagents (H2L = (N,N'-dimethyl-(2R,5R)-bis-(sulfanylmethyl)-piperazine). Treatment of deprotonated L(2-) with MeI led to the selective methylation of the thiolate groups thus generating a novel potential ligand, Me2L, which is neutral and contains two thioether donors. The coordinating properties of Me2L were demonstrated by the synthesis of a first nickel(ii) complex: reaction with NiBr2 led to a mononuclear complex 2 where all donor atoms coordinate to the nickel ion, which completes its octahedral coordination sphere by the two bromide ligands. If, however, the complex [LNi]2 (1) is treated with MeI only one thiolate function per ligand moiety is methylated, while the other one remains a thiolate. This leads to [MeLNi](+) complex metal fragments, which trimerize including a μ3-bridging iodide ion to give the compound 3 that was tested with regards to ACS reactivity. While it behaved inert towards CO, attempts to replace the bridging iodide ligand by methyl units in reactions with nucleophilic methylation reagents led to a product, which could not be identified but reacted with CO. Work-up showed that this protocol had converted the thiolate function of MeL(-) into a thioester function, which corresponds to an ACS-like reactivity.

The reaction of permanganyl chloride with olefins: intermediates and mechanism as derived from matrix-isolation studies and density functional theory calculations

Density functional theory (DFT) calculations predict that the [2+3] addition of tetramethylethylene (TME) to the MnO2 moiety of MnO3Cl is thermodynamically favoured over [2+1] addition (epoxidation), while the kinetic barriers for both reactions are of comparable height. However, in an experimental investigation of the TME/MnO3Cl system by means of matrix-isolation techniques, selective formation of the epoxidation product [ClO2Mn[O[C(CH3)2]2]] (1) was observed. Compound 1 was characterised by IR spectroscopy with the aid of isotopic-enrich-ment experiments in combination with DFT frequency calculations. This result, at first sight surprising, is supported by studies in solution, and, even with the numerically equal energy barriers suggested by the calculations, it can be rationalised in terms of the much broader reaction channel leading to epoxidation as opposed to the much more narrow approach path for formation of the glycolate.

On the trail of CrO2Cl2 in its reactions with organic compounds

The simple metal oxo compound chromyl chloride, CrO2Cl2, displays a very complex reactivity with respect to alkanes, olefins, alcohols, and epoxides. Synergetic investigations applying various techniques and methods have only recently led to an understanding of the key steps in the corresponding mechanisms, which are representative for more complex systems. Product formation seems to be largely determined by radical reactions initiated by this d0-metal compound.

Trapping of an Organic Radical by an O=Cr(VI) Function

Not only capable of generating organic radicals by H abstraction, chromyl chloride can also trap them again (see scheme). This is confirmed by the crystal structure of a Cr(V) oxo alkoxide, which was formed in three successive steps when bisadamantylidene oxide was allowed to react with CrO(2)Cl(2).

[Accident-induced lesions of the facial nerve in relation to the extent of pyramidal pneumatization]

Perilabyrinthine pneumatisation of the petrous pyramid constitutes a risk factor for the facial nerve in its labyrinthine part in a fracture of the temporal bone because serious splintering of bone is possible. Splinters dislocated into the Fallopian canal may damage the nerve seriously. On the other hand a perineural haematoma can flow out of the canal into the neighbouring cells through dehiscences or through the fractured canal walls and a compression of the nerve may be avoided. The decision to undertake early surgical intervention must take into account the degree of pneumatisation of the pyramid in posttraumatic lesions of the facial nerve. The timing and extent of recovery cannot be predicted.

[Electromyography of the larynx]

This paper reports on our experience with electromyography of the larynx in pareses of the recurrent nerve of different causes. Clinical case histories are used to demonstrate the differentiated evaluation of the condition of the damaged recurrent nerve which is possible with the use of electromyography, including reflex electromyography, of the larynx. Knowledge of the type and extent of the lesion of the recurrent nerve only allows limited conclusions to be made about the prognosis of the paresis. For the assessment of the prognosis it is necessary to consider not only the basic disease, but also the actual time at which the electromyography was performed.

[Lingual nerve paresis following tonsillectomy: objective assessment by means of trigemino-facial reflexes (author's transl)]

A case of lingual nerve paresis following tonsillectomy is reported. As in all sensory disorders, assessment can be limited by the lack of objective procedures available. However, with lingual nerve involvement, electromyographic recording of trigemino-facial reflexes can be useful in determining causes of injury.