Hannes Vitze

Redox‐Active p‐Quinone‐Based Bis(pyrazol‐1‐yl)methane Ligands: Synthesis and Coordination Behaviour

The synthesis, structural characterisation and coordination behaviour of mono- and ditopic p-hydroquinone-based bis(pyrazol-1-yl)methane ligands is described (i.e., 2-(pz2CH)C6H3(OH)2 (2a), 2-(pz2CH)-6-(tBu)C6H2(OH)2 (2b), 2-(pz2CH)-6-(tBu)C6H2(OSiiPr3)(OH) (2c), 2,5-(pz2CH)2C6H2(OH)2 (4)). Ligands 2a, 2b and 4 can be oxidised to their p-benzoquinone state on a preparative scale (2a ox, 2b ox, 4 ox). An octahedral Ni II complex [trans-Ni(2c)2] and square-planar Pd II complexes [Pd2bCl2] and [Pd2b ox Cl2] have been prepared. In the two Pd II species, the ligands are coordinated only through their pyrazolyl rings. The fact that [Pd2bC12] and [Pd2b oxC12] are isolable compounds proves that redox transitions involving the p-quinone substituent are fully reversible. In [Pd2b oxCl2], the methine proton is highly acidic and can be abstracted with bases as weak as NEt(3). The resulting anion dimerises to give a dinuclear macrocyclic Pd II complex, which has been structurally characterised. The methylated ligand 2-(pz2CMe)C6H3O2 (11 ox) and its Pd II complex [Pd11 oxCl2] are base-stable. A new class of redox-active ligands is now available with the potential for applications both in catalysis and in materials science.

Copper Complexes of Mono‐ and Ditopic [(Methylthio)methyl]borates: Missing Links and Linked Systems En Route to Copper Enzyme Models

TMEDA-free (TMEDA: tetramethylethylenediamine) LiCH(2)SMe is a suitable reagent for the selective introduction of (methylthio)methyl groups into PhBBr(2) and its p-silylated derivative Me(3)Si--C(6)H(4)--BBr(2). The resulting compounds, R*--C(6)H(4)--B(Br)(CH(2)SMe) (R*=H: 2; R*=SiMe(3): 7) and PhB(CH(2)SMe)(2) (3), form cyclic dimers through B--S adduct bonds in solution and in the solid state. Compounds 2 and 3 have successfully been used for preparing the (N(2)S) scorpionate [PhBpz(2)(CH(2)SMe)](-) ([5](-)) (pz: pyrazol-1-yl) and the (NS(2)) scorpionate [PhBpz(CH(2)SMe)(2)](-), respectively. Compound 7 proved to be an excellent building block for the heteroditopic poly(pyrazol-1-yl)borate p-[pz(3)B--C(6)H(4)--Bpz(2)(CH(2)SMe)](2-) ([10](2-)) that mimics the two ligation sites of the copper enzymes peptidylglycine alpha-hydroxylating monooxygenase and dopamine beta-monooxygenase. Treatment of the monotopic tripod [5](-) with CuCl and CuBr(2) results in the formation of complexes K[Cu(5)(2)] and [Cu(5)(2)]. An X-ray crystallography study of K[Cu(5)(2)] revealed a tetrahedral (N(2)S(2)) coordination environment for the Cu(I) ion, whereas the Cu(II) ion of [Cu(5)(2)] possesses a square-pyramidal (N(4)S) ligand sphere (S-atom in the axial position). The remarkable redox properties of K[Cu(5)(2)] and [Cu(5)(2)] have been assessed by cyclic voltammetry and quantum chemical calculations. The reaction of K[Cu(5)(2)] with dry air leads to the Cu(II) species [Cu(5)(2)] and to a tetranuclear Cu(II) complex featuring [PhB(O)pz(2)](2-) ligands. Addition of CuCl to K(2)[10] gives the complex K(3)[Cu(10)(2)] containing two ligand molecules per Cu(I) center. The Cu(I) ion binds to both heteroscorpionate moieties and thereby establishes a coordination environment similar to that of the Cu(I) ion in K[Cu(5)(2)].

The low-temperature structure of diethyl ether magnesium oxybromide.

The crystal structure of the title compound, hexa-μ2-bromido-μ4-oxido-tetrakis[(diethyl ether)magnesium], [Mg4Br6O(C4H10O)4], determined from data measured at 173 K, differs from the previously known structure of diethyl ether magnesium oxybromide, which was determined from room-temperature data [Stucky & Rundle (1964 ▶). J. Am. Chem. Soc. 86, 4821–4825]. The title compound crystallizes in the tetragonal space group I , whereas the previously known structure crystallizes in a different tetragonal space group, namely P 21 c. Both molecules have crystallographic symmetry and show almost identical geometric parameters for the Mg, Br and O atoms. The crystal of the title compound turned out to be a merohedral twin emulating a structure with apparent Laue symmetry 4/mmm, whereas the correct Laue group is just 4/m. The fractional contribution of the minor twin component converged to 0.462 (1).

Supersilyliertes Ethen trans-(tBu3Si)HC=CH(SitBu3) und Ethin (tBu3Si)C≡C(SitBu3) / Supersilylated Ethene trans-(tBu3Si)HC=CH(SitBu3) and Ethyne (tBu3Si)C≡C(SitBu3)

The supersilylated ethene trans-(tBu3Si)HC=CH(SitBu3) (triclinic, P ī) is accessible from the reaction of tBu3SiCHBr2 with nBuLi at −78 °C in THF or Et2 O. The reaction of Li(H2NCH2CH2NH2)C≡CH with tBu3SiBr leads to the formation of (tBu3Si)C≡CH and (tBu3Si)C≡C(SitBu3). X-Ray quality crystals of (tBu3Si)C≡C(SitBu3) (triclinic, P ī) were obtained by recrystallization from hexane. In contrast to the structures of the disilane tBu3Si-SitBu3 and the disiloxane tBu3Si-O-SitBu3, the sterically crowded ethene trans-(tBu3Si)HC=CH(SitBu3) and ethyne (tBu3Si)C≡C(SitBu3) feature dihedral angles of 60° in the solid-state structures Graphical Abstract Supersilyliertes Ethen trans-(tBu3Si)HC=CH(SitBu3) und Ethin (tBu3Si)C≡C(SitBu3) / Supersilylated Ethene trans-(tBu3Si)HC=CH(SitBu3) and Ethyne (tBu3Si)C≡C(SitBu3)

Sodium penta-fluoro-phenyl-borate.

The crystal structure of the title compound, Na[(C6F5)BH3], is composed of discrete anions and cations. The sodium cations are surrounded by four anions with three short Na⋯B [2.848 (8), 2.842 (7) and 2.868 (8) Å] and two short Na⋯F contacts [2.348 (5) and 2.392 (5) Å], forming a three-dimensional network. The anion is the first structural example of a pentafluorophenyl ring carrying a BH3 group.

An approach to creating novel anions: silylated triel compounds with –CH2– and –O– linkers, [InCl2{O(HO)Si(t-Bu)2}]2 and Li[B(CH2SiMe3)4]

Bis[μ-di-tert-butyl(hydroxy)silanolato]bis[chloridoindium(III)], [In2(C8H19O2Si)2Cl4], (I), is a centrosymmetric two-centre indium complex featuring a system of three annulated four-membered rings; the structure is the first example of an In2O2 ring which is annulated with two Si-O units to form a ring system composed of three rings. The coordination environment of the In centres is a distorted trigonal bipyramid. The crystal packing of (I) is characterized by chains of molecules connected by O-H···Cl hydrogen bonds. The crystal of (I) was a nonmerohedral twin. There is no known example of an In2O2 ring in which the In atoms carry any two halogen ligands. The structure of tetrakis(tetrahydrofuran)lithium tetrakis[(trimethylsilyl)methyl]borate, [Li(C4H8O)4](C16H44BSi4), (II), is composed of discrete cations and anions. The coordination geometries of the Li and B centres is tetrahedral. The cations and anions lie in planes parallel to the ab plane. There are no short contacts between the cations and anions. Compound (II) is the first example of a B centre bonded to four -CH2Si units.

μ2-Acetone-diacetone[μ3-tris­(trifluoro­meth­yl)methano­lato]bis­[μ2-tris­(trifluoro­meth­yl)methano­lato]trilithium

The title compound, [Li3(C4F9O)3(C3H6O)3], features an open Li/O cube with an Li ion missing at one corner. Three of the four bridging O atoms of the cube carry a fluorinated tert-butyl residue, whereas the fourth is part of an acetone molecule. Two of the Li atoms are further bonded to a non-bridging acetone molecule. Two of the lithium ion coordination geometries are very distorted LiO4 tetrahedra; the third could be described as a very distorted LiO3 T-shape with two distant F-atom neighbours. The Li⋯Li contact distances for the three-coordinate Li+ ion [2.608 (14) and 2.631 (12) Å] are much shorter that the contact distance [2.940 (13) Å] between the tetrahedrally coordinated species.

Dibromidotris(dimethyl­amine)magnesium(II)

The Mg centre in the title compound, [MgBr2(C2H7N)3], is pentacoordinated in a trigonal-bipyramidal mode with the two Br atoms in axial positions and the N atoms of the dimethylamine ligands in equatorial positions. The MgII centre is located on a crystallographic twofold rotation axis. The crystal structure is stabilized by N—H⋯Br hydrogen bonds. The N atom and H atoms of one dimethylamine ligand are disordered over two equally occupied positions.

Dimethyl­ammonium nitrate

The title compound, C2H8N+·NO3−, is composed of discrete cations and anions which are connected by classical N—H⋯O hydrogen bonds. Geometric parameters are in the usual ranges.

Dimethylammonium 3,5-bis(trifluoromethyl)pyrazolide

The title compound, C2H8N+·C5HF6N2−, crystallizes with discrete anions and cations, which are linked by N—H⋯N hydrogen bonds to form centrosymmetric dimers. Geometric parameters are in the usual ranges.