Mechanistic studies on the alcoholysis and aminolysis of [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}]

The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic [(MeZn)₂{μ-N(H)tBu}{μ-N(CH₂Py)₂}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the exchange of the μ-N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)₂(μ-OMe){μ-N(CH₂Py)₂}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridylmethyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Extensive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[μ-(MeO?H?NHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates with Zn[μ-(RNH ? H ? NHR)]Zn functionalities, respectively. We were able to detect the latter by ¹H NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition of the complex leading to the hexanuclear amide [{Zn(μ-N(H)Ph)}{MeZn(μ-N(H)Ph)}₂{μ-N(CH₂Py)₂}]₂ (4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)₂{μ-N(CH₂Py)₂}₂Zn{μ-(OMe₂Si)₂O}] (5). The X-ray structures of complexes 1-5 are discussed.     

The Combination of 4‐Hydroxythiazoles with Azaheterocycles: Efficient Bidentate Ligands for Novel Ruthenium Complexes

Herein the syntheses of three novel ligands, in which an azaheterocycle is connected with a thiazole subunit: 4‐methoxy‐5‐methyl‐2‐pyridine‐2‐yl‐1,3‐thiazole ( 1 ), 4‐methoxy‐5‐methyl‐2‐pyrimidine‐2‐yl‐1,3‐thiazole ( 2 ) and 4‐methoxy‐5‐phenyl‐2‐pyridine‐2‐yl‐1,3‐thiazole ( 3 ) are reported. Because these ligands are cyclic versions of 1,4‐diazadienes, they offer good prerequisites for the synthesis of metal complexes and were employed as chelating ligands. Three novel heteroleptic cationic complexes of the type Ru(bpy)₂( L ), with bpy = 2,2′‐bipyridine were successfully synthesised. The Ru^II complexes as well as the ligands were characterised by means of mass spectrometry, NMR, UV/Vis and IR spectroscopy and elemental analysis. Furthermore, an X‐ray structure of Ru(bpy)₂ 2 (PF₆), as far as we know the first example where a thiazole is directly connected to a Ru^II core, is presented in this paper.     

A supramolecular hexameric ring from alumazene and methylsulfonate

A dealkylsilylation reaction of alumazene [2,6-(i-Pr)2C6H3NAlMe]3 (1) with trimethylsilyl methylsulfonate in a 1:2 molar ratio in toluene afforded a supramolecular cyclic hexamer {Me[2,6-(i-Pr)2C6H3NAl]3(O3SMe)2}6 (2) composed of six intact alumazene rings and possessing two types of bridging sulfonate groups. Changing the reagent molar ratio to 1:3 caused the third sulfonate to partially substitute the last alumazene methyl group in an eta2 fashion and introduced a disorder in the crystal lattice.     

Synthesis of mononuclear and dinuclear ruthenium(II) tris(heteroleptic) complexes via photosubstitution in bis(carbonyl) precursors

A novel, and quite general, approach for the preparation of tris(heteroleptic) ruthenium(II) complexes is reported. Using this method, which is based on photosubstitution of carbonyl ligands in precursors such as [Ru(bpy)(CO)(2)Cl(2)] and [Ru(bpy)(Me(2)bpy)(CO)(2)](PF(6))(2), mononuclear and dinuclear Ru(II) tris(heteroleptic) polypyridyl complexes containing the bridging ligands 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) and 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (Hbpzt) have been prepared. The complexes obtained were purified by column chromatography and characterized by HPLC, mass spectrometry, 1H NMR, absorption and emission spectroscopy and by electrochemical methods. The X-ray structures of the compounds [Ru(bpy)(Me(2)bpy)(bpt)](PF(6))x0.5C(4)H(10)O [1x0.5C(4)H(10)O], [Ru(bpy)(Me(2)bpy)(bpzt)](PF(6))xH(2)O (2xH(2)O) and [Ru(bpy)(Me(2)bpy)(CH(3)CN)(2)](PF(6))(2)xC(4)H(10)O (6xC(4)H(10)O) are reported. The synthesis and characterisation of the dinuclear analogues of 1 and 2, [{Ru(bpy)(Me(2)bpy)}(2)bpt](PF(6))(3)x2H(2)O (3) and [{Ru(bpy)(Me(2)bpy)}(2)bpzt](PF(6))(3) (4), are also described.     

Silicon–Heteroaromatic [FeFe] Hydrogenase Model Complexes: Insight into Protonation,Electrochemical Properties,and Molecular Structures

To learn from Nature how to create an efficient hydrogen‐producing catalyst, much attention has been paid to the investigation of structural and functional biomimics of the active site of [FeFe]‐hydrogenase. To understand their catalytic activities, the μ‐S atoms of the dithiolate bridge have been considered as possible basic sites during the catalytic processes. For this reason, a series of [FeFe]‐H₂ase mimics have been synthesized and characterized. Different [FeFe]‐hydrogenase model complexes containing bulky Si–heteroaromatic systems or fluorene directly attached to the dithiolate moiety as well as their mono‐PPh₃‐substituted derivatives have been prepared and investigated in detail by spectroscopic, electrochemical, X‐ray diffraction, and computational methods. The assembly of the herein reported series of complexes shows that the μ‐S atoms can be a favored basic site in the catalytic process. Small changes in the (hetero)‐aromatic system of the dithiolate moiety are responsible for large differences in their structures. This was elucidated in detail by DFT calculations, which were consistent with the experimental results.     

Determination of organophosphate pesticides in sea and surface water with ultrasound-assisted dispersive liquid–liquid micro-extraction coupled to GC-MS/MS analysis

A sensitive enrichment method for the detection and quantification of 20 organophosphate pesticides in sea water and surface water was improved and validated. The compounds were extracted using ultrasound-assisted dispersive liquid–liquid microextraction and were analysed with an optimised Gas Chromatography - Tandem Quadrupole Mass Spectrometry (GC-MS/MS) method. Calibrations and validations were conducted for spiked local pond and Baltic Sea water. Recoveries of the organophosphate compounds from the different matrices ranged from about 25% to 70% and from 30% to 130% for pond and sea water, respectively. Obtained limit of detection (LoD) for both matrices was about 3 ng L^?1 and the limit of quantification (k = 3) was 12 and 7 ng L^?1 for pond and sea water, respectively. Valid extractability at the LoD level could be proven.     

Facile and Reliable Emission-Based Nanomolar Anion Sensing by Luminescent Iridium Receptors Featuring Chelating Halogen-Bonding Sites

An anion sensor is presented that combines a bidentate hydrogen- (HB) or halogen-bonding (XB) site with a luminescent monocationic Ir fragment for strong binding of common anions (K_a up to 6×10⁴ m ⁻¹) with diagnostic emission changes. A new emission-based protocol for fast and reliable detection was derived on the basis of correction for systematic but unspecific background effects. Such a simple correction routine circumvents the hitherto practical limitations of systematic emission-based analysis of anion binding with validated open-source software (BindFit). The anticipated order of K_a values was obeyed according to size and basicity of the anions (Cl>Br=OAc) as well as the donor atom of the receptor (XB: 6×10⁴ m ⁻¹ > HB: 5×10³ m ⁻¹), and led to submicromolar limits of detection within minutes. The results were further validated by advanced NMR techniques, and corroborated by X-ray crystallographic data and DFT analysis, which reproduced the structural and electronic features in excellent agreement. The results suggest that corrected emission-based sensing may become a complementary, reliable, and fast tool to promote the use of XB in various application fields, due to the simple and fast optical determination at high dilution.     

Crystallographic and computational study of the structure of copper(II) 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl

The reaction of M(OAc)₂ with 2,2′-bis(2-hydroxybenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl (H₂L1) allows the synthesis of 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl complexes of Cu(II) (CuL1), Co(II) (CoL1) and Ni(II) (NiL1) that were characterized by elemental analysis, FTIR spectroscopy and for CuL1 also by X-ray crystallography verifying a tetradentate binding mode of L1 via an (ONNO) motif of the two phenolic oxygen atoms and two azomethine nitrogen atoms. Recrystallization from a solvent mixture of dichloromethane and methanol promotes the formation of methanol adducts. Different binding modes of the methanol–complex were investigated using density functional theory calculations and binding energies, and thermodynamic data of the interaction are reported. The results show that the favored interaction occurs when the methanol molecule acts as a Lewis acid weakly binding via an O–H···O hydrogen bridge to a phenoxide moiety leading to an elongation of the respective M–O bond.

     

Pentanuclear Nickel(II) Complex with two Vertex-Shared Triaminoguanidine Fragments and Symmetric Capping Ligand

The pentanuclear nickel(II) complex [Ni₅(saltag^Br)₂(tptz)₄] ( Ni5 ) with the tritopic triaminoguanidine-derived Schiff-base ligand H₅saltag^Br (1,2,3-tris[(5-bromosalicylidene)amino]guanidine) and tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine) as capping ligands is reported. Ni5 crystallizes in the triclinic space group P1 with the central nickel(II) ion linking two triangular arrangements of nickel(II) ions supported by two tritopic triaminoguanidine ligands. The octahedral coordination of the four peripheral nickel(II) ions is complemented by capping tridentate tptz ligands. By variation of the synthesis also the corresponding trinuclear nickel(II) complex [Ni₃(saltag^Br)(tptz)₃]NO₃ ( Ni3 ) is accessible. Magnetic measurements for Ni3 and Ni5 reveal a singlet ground state with antiferromagnetic coupling between the nickel(II) ions, which in the case of Ni5 can only be simulated assuming a two-J exchange coupled spin topology. For both complexes significant zero-field splitting for the nickel(II) ions is evident from the measured magnetic data, which can be verified by theoretical studies revealing a magnetic anisotropy with strong rhombic distortion due to the presence of the tptz co-ligands in both compounds.