Synthesis and Structure of 1,2-Diphenyl-1,2-disila-closo-dodecaborane(12), Reaction with [Zr(NMe2)4] and [Ta(NMe2)5]

Diphenyl-o-silaborane ( 1 ) can be obtained by sublimation as colourless crystalline material in a yield of 23%. The disilaborane 1 was characterized by NMR spectroscopy, mass spectrometry and X-ray structure analysis. The neutral closo cluster 1 reacts with [Zr(NMe₂)₄] or [Ta(NMe₂)₅] to give the dimethylamide adduct [(Me₂N)(PhSi)₂B₁₀H₁₀]^– of the disilaborane.     

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene: A Redox‐Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene ( 1 ) acts as molecular electrochemical sensor for magnesium, calcium, zinc, and cadmium ions in acetonitrile solution. The new redox peak, anodically shifted by ca. 0.40 V, which appears in the cyclic voltammogram of 1 in the presence of even small amounts (10 mol %) of these ions, is unaffected by an excess of alkali metal ions. Metal complexation is accompanied by a batho‐ and hyper‐chromic shift of the band in the visible region of the UV‐Vis spectrum of 1 . A detailed study of the behaviour of 1 towards zinc chloride in acetonitrile solution has revealed that 1 is able to accommodate a maximum of two zinc ions. Oxidation of zinc‐coordinated 1 leads to partial decomplexation. The N‐methyl and N‐benzyl species 1 Me⁺, 1 Me₂²⁺, 1 Bzl⁺ and 1 Bzl₂²⁺ have been synthesized and the former two structurally investigated by X‐ray diffraction. Alkylation causes an anodic shift of the redox potential of the ferrocene nucleus, which is linearly dependent on the number of alkyl groups introduced. Octamethyl‐1, 1′‐di(2‐thiophenyl)ferrocene ( 2 ) has also been synthesized and structurally characterized by X‐ray diffraction. Cyclic voltammetry has revealed that, in contrast to 1 , 2 does not respond to the divalent metal ions studied.     

A Rational Approach to Tetra-Functional Photo-Switches

α,ω-Bis(1,8-dichloroanthracen-10-yl)alkanes with (CH₂)_n-linker units (n=1–4) were synthesized starting from 1,8-dichloroanthracen-10(9H)-one. This was transformed into anthracenes with allyl, bromomethyl and propargyl substituents in position 10; these were converted in various C−C-bond formation reactions (plus hydrogenation), leading to two anthracene units flexibly linked by α,ω-alkandiyl groups. 1,2-Ethandiyl- and 1,3-propandiyl-linked derivatives were functionalized with ethynyl groups in positions 1, 8, 1’ and 8’, and these terminally functionalized by Me₃Sn groups using Me₂NSnMe₃. All linked bisanthracenes were subjected to UV light induced cyclomerization and a series of 9,10 : 9’,10’-photo-cyclomers were obtained. Their thermal cycloreversion and (repeated) switchability was demonstrated. 1,3-Bis{1,8-bis[(trimethylstannyl)ethynyl]anthracen-10-yl}propane served as model compound for photo-switchable acceptor molecules and its open and closed forms were characterized by NMR and DOSY experiments.     

[2,6‐(Trip)2H3C6 ](Cp*)Si: A Stable Monomeric Arylsilicon(II) Compound

Si takes a rest : A bulky σ‐bound terphenyl substituent and a π‐bound Cp* ligand enable the isolation and full characterization of the first aryl‐substituted, monomeric silicon(II) compound 1 , which can be regarded as the “resting state” of a true silylene containing a σ‐bound Cp* group. The conformation of the aryl group prevents aryl–Si π back‐bonding.

     

Nuclear inelastic scattering and Mössbauer spectroscopy as local probes for ligand binding modes and electronic properties in proteins: vibrational behavior of a ferriheme center inside a β-barrel protein

In this work, we present a study of the influence of the protein matrix on its ability to tune the binding of small ligands such as NO, cyanide (CN(-)), and histamine to the ferric heme iron center in the NO-storage and -transport protein Nitrophorin 2 (NP2) from the salivary glands of the blood-sucking insect Rhodnius prolixus. Conventional M?ssbauer spectroscopy shows a diamagnetic ground state of the NP2-NO complex and Type I and II electronic ground states of the NP2-CN(-) and NP2-histamine complex, respectively. The change in the vibrational signature of the protein upon ligand binding has been monitored by Nuclear Inelastic Scattering (NIS), also called Nuclear Resonant Vibrational Spectroscopy (NRVS). The NIS data thus obtained have also been calculated by quantum mechanical (QM) density functional theory (DFT) coupled with molecular mechanics (MM) methods. The calculations presented here show that the heme ruffling in NP2 is a consequence of the interaction with the protein matrix. Structure optimizations of the heme and its ligands with DFT retain the characteristic saddling and ruffling only if the protein matrix is taken into account. Furthermore, simulations of the NIS data by QM/MM calculations suggest that the pH dependence of the binding of NO, but not of CN(-) and histamine, might be a consequence of the protonation state of the heme carboxyls.