Activation of Molecular Hydrogen by Bis(η5,η1‐pentafulvene)‐titanium Complexes – Efficient Formation of Titanium(III)hydrides

The synthesis and crystal structures of two dinuclear titanocene hydride complexes are reported. Both complexes, namely bis(η⁵‐(di‐para‐tolylmethyl)cyclopentadienyl)titanium hydride dimer, [(η⁵‐C₂₀H₁₉)₂Ti(μ‐H)]₂ ( 2a ), and bis(η⁵‐2‐adamantylcyclopentadienyl)‐titanium hydride dimer, [(η⁵‐C₁₅H₁₉)₂Ti(μ‐H)]₂ ( 2b ), are formed via activation of molecular hydrogen by the corresponding bis(η⁵,η¹‐pentafulvene)titanium complexes 1a and 1b at ambient temperatures and pressures in high yields. The hydride complexes 2a and 2b exhibit planar [Ti₂H₂] cores and, as a result of the heterolytic cleavage of molecular hydrogen, substituted Cp Ligands were formed during the reaction.     

Elusive Silane–Alane Complex [SiH⋅⋅⋅Al]: Isolation,Characterization, and Multifaceted Frustrated Lewis Pair Type Catalysis

The super acidity of the unsolvated Al(C₆F₅)₃ enabled isolation of the elusive silane–alane complex [Si? H???Al], which was structurally characterized by spectroscopic and X‐ray diffraction methods. The Janus‐like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated‐Lewis‐pair‐type catalysis. When compared with the silane–borane system, the silane–alane system offers unique features or clear advantages in the four types of catalytic transformations examined in this study, including: ligand redistribution of tertiary silanes into secondary and quaternary silanes, polymerization of conjugated polar alkenes, hydrosilylation of unactivated alkenes, and hydrodefluorination of fluoroalkanes.     

Formation of Dialkyl 2‐[3‐Alkoxy‐1‐(alkylimino)‐1‐chloro‐3‐oxopropan‐2‐ylidene]hydrazine‐1,1‐dicarboxylates of α‐(Alkoxycarbonyl)imidoyl Chlorides from PhosphineDiazo Ester Zwitterions and Nef‐Isocyanide Adducts

A novel transformation involving phosphine? diazo ester zwitterions (generated from dialkyl azodicarboxylates with Ph₃P) and α‐(alkoxycarbonyl)imidoyl chlorides (prepared from α‐addition of acyl chlorides to alkyl isocyanides) to afford dialkyl 2‐[3‐alkoxy‐1‐(alkylimino)‐1‐chloro‐3‐oxopropan‐2‐ylidene]hydrazine‐1,1‐dicarboxylates in moderate yields, is described.     

Synthesis and Crystal Structures of t‐Butyl‐Pyridine Adducts of ZnR2 (R = Me,i‐Pr,t‐Bu,Cp*)

Lewis acid‐base adducts of the general type R₂Zn(4‐tBuPy)_x (R = Me 1 , iPr 2 , tBu 3 , Cp* 4 ; x = 1, 2) were obtained in high yields from reactions of ZnR₂ with the Lewis base 4‐tBu‐Pyridine. Compounds 1 – 4 were characterized by multinuclear NMR (¹H, ¹³C) and IR spectroscopy and elemental analyses, 1 and 4 also by X‐ray diffraction at single crystals.     

Two‐Dimensional Networks of [AuCl4]– and [AuBr4]– Anions

Several salts of protonated amines and aza‐aromatics with [AuCl₄]^– and [AuBr₄]^– anions contain two‐dimensional (“square”) anionic networks that display short halogen ··· halogen contacts. The Au₄ quadrilaterals formed by neighboring anions of the networks are to a good approximation squares, with sides of around 7.5 Å for tetrachloridoaurates and 8 Å for tetrabromidoaurates.     

Hexakis(2,4,6‐triisopropylphenyl)cyclotristannoxane – a Molecular Diorganotin Oxide with Kinetically Inert Sn–O Bonds

The single‐crystal X‐ray structure analysis of hexakis(2,4,6‐triisopropylphenyl)cyclotristannoxane, cyclo‐[(2,4,6‐i‐Pr₃‐C₆H₂)₂SnO]₃ ( 1 ), is reported and reveals this compound to contain an almost planar six‐membered ring. Redistribution reactions of 1 with cyclo‐(t‐Bu₂SnO)₃ and t‐Bu₂SiCl₂, respectively, failed and indicate an unusual kinetic inertness of the Sn–O bonds in 1 as compared to related molecular diorganotin oxides containing less bulkier substituents. The redistribution reaction of cyclo‐(t‐Bu₂SnO)₃ with cyclo‐(t‐Bu₂SnS)₂ leads to an equilibrium involving the trimeric diorganotin oxysulphides cyclo‐t‐Bu₂Sn(OSnt‐Bu₂)₂S ( 2 a ) and cyclo‐t‐Bu₂Sn(SSnt‐Bu₂)₂O ( 2 b ).     

New Phases in the Lithiumnitridovanadate System — The Solid Solution Li7‐2xMgx[VN4] with 0 ≤ x ≤ 1

Solid solution phases Li_7‐2xMg_x[VN₄] (0 < x ≤ 1) with varying Mg‐content are obtained as yellow microcrystalline powders from heat treatment of mixtures of VN, Li₃N and Mg₃N₂ or from mixtures of Li₇[VN₄] and Mg₃N₂ at 1370 K in N₂ atmosphere at ambient pressure. At substitution parameter values of x > 0.5 a subsequent distortion from the ideal cubic unit cell to an orthorhombic unit cell is observed. The crystal structure of Li_7‐2xMg_x[VN₄] with x ≈ 1 was refined from neutron and X‐ray powder diffraction data (space group Pbca, No. 61, a = 963.03(3) pm, b = 958.44(3) pm, c = 951.93(2) pm, neutron pattern 14° — 156° 2θ, step non‐linear ≈ 0.0782° 2θ, No. of measured points 1816, R_p = 0.089, R_wp = 0.115, R_Bragg = 0.155, R_F = 0.114; X‐ray pattern 10° — 98° 2θ, step 0.005° 2θ, No. of measured points 17600, R_p = 0.028, R_wp = 0.045, R_Bragg = 0.113, R_F = 0.133, structure variables: 45). The crystal structure resembles a Li₂O type superstructure with the atomic arrangement of β‐Li₇[VN₄] and with two crystallographic Li‐sites each substituted by Mg with statistical occupation factors of 0.5. Chemical analyses prove the composition and XAS spectroscopy at the V K‐edge support the +5 oxidation state assignment for vanadium. XAS data also support the tetrahedral coordination of vanadium by N as indicated by the structure refinements.     

Superoxide Compounds of the Large Pseudo‐Alkali‐Metal Ions Tetramethylammonium, ‐Phosphonium,and ‐Arsonium

Compounds of the three large cations tetramethylammonium, tetramethylphosphonium, and tetramethylarsonium with the superoxide radical anion were synthesized by either metathesis or ion exchange in liquid ammonia. They were obtained from concentrated solutions as ammoniates in the form of long needle‐shaped single crystals. [N(CH₃)₄]‐(O₂)?3NH₃ crystallizes in the monoclinic crystal system, whereas the two compounds [E(CH₃)₄](O₂)?2NH₃ (E=P, As) are isostructural and belong to the orthorhombic crystal system. The cation–anion packing in all three crystal structures is related to the sodium chloride structure. All structures contain hydrogen bonds between the ammonia molecules and between ammonia and the superoxide. The solvent of crystallization was easily released from the crystals upon complete removal of the solvent from the reaction vessel, leading to polycrystalline samples. The Raman spectra of all three solvent‐free compounds show the symmetric stretching mode of the superoxide ion at about 1123 cm^?1. The desolvated [N(CH₃)₄](O₂) was investigated by powder X‐ray diffraction, and the crystal structure was solved by ab initio simulated annealing methods by using rigid‐body models of the constituent molecular ions. The superoxide ion shows rotational disorder. The magnetic susceptibility of tetramethylammonium superoxide follows the Curie–Weiss law with a high‐temperature effective magnetic moment of 1.66(3) μ_B and a paramagnetic Curie temperature of Θ=?13(6) K. Complementary electron paramagnetic resonance spectroscopy revealed that the average g factor is temperature‐dependent. It decreased from 2.15 at 10 K to 1.66 at 100 K, possibly due to the onset of rotational motion of the superoxide ion and in accordance with the lower‐than‐expected effective magnetic moment.     

Isolation and Structural Characterization of Di‐ and Tetra‐protonated Forms of the Macrocyclic Hexaamine trans‐6,13‐Dimethyl‐1,4,8‐11‐tetraazacyclodecane‐6,13‐diamine

Cations derived by protonation of the ligand title compound (L¹) have been structurally characterized in their di‐ and tetra‐ protonated forms in the salts [H₂L¹][ClO₄]₂·2H₂O and [H₄L¹][ZnCl₄]₂·4H₂O. In both structures, one half of the formula unit comprises the asymmetric unit of the structure, the macrocycle being centrosymmetric, with the two macrocycles adopting similar conformations. In both salts, a pair of diagonally opposed macrocyclic secondary amine groups are protonated; in the [H₄L¹]⁴⁺ salt, the additional pair of protons are accommodated on the exocyclic pendant amine groups. The dispositions of the pendent amines differ between the two structures, being ‘equatorial’ with respect to the macrocyclic ring in the [H₂L¹]²⁺ salt, and ‘axial’ in the [H₄L¹]⁴⁺ salt. In other structurally characterized compounds containing [H₄L¹]⁴⁺ the equatorial disposition was found in the ferricyanide adduct, while in the tetraperchlorate salt the axial disposition was identified. The differences in disposition of the exocyclic groups are ascribed to the extensive H‐bonding in the lattices.     

Synthesis and Characterization of the Germanium Sulfonate Ge(CH3SO3)2 – a 3D Coordination Network Solid

The reaction of germanium(II)‐bis(2‐methoxyphenyl)methoxide with methanesulfonic acid provides the germanium(II) sulfonate Ge(CH₃SO₃)₂ ( 1 ), which was characterized by X‐ray diffraction, elemental analysis, NMR spectroscopy, and IR spectroscopy. The decomposition process of 1 was investigated by thermal gravimetric analysis (TGA) and temperature‐dependent X‐ray powder diffraction (PXRD) and both are consistent with the formation of GeO₂ as major final product. Single crystal X‐ray diffraction at 110 K revealed the chiral tetragonal space group P4₁2₁2 and formation of a three‐dimensional (3D) coordination network solid. The 3D network is composed of interconnected twenty four‐membered rings comprising bridging methanesulfonate groups, which link the germanium atoms.     

Synthesis and X‐ray single‐crystal structure study of 5,5′‐bis(silyl)‐functionalized 3,3′‐dibromo‐2,2′‐dithiophenes

A high‐yield synthesis toward 5,5′‐bis(silyl)‐functionalized 3,3′‐dibromo‐2,2′‐dithiophenes with very efficient work‐up procedure is presented. The molecular structures of two silyl functionalized dibromo‐dithiophenes in the solid state have been determined to investigate the structural influences of different functional groups on the degree of π‐conjugation within the dithiophene moieties, as well as their packing properties. The planar alignment of the tert‐butyldimethylsilyl‐functionalized dibromo‐dithiophene shows a significantly higher degree of conjugation of the π‐system with a more favorable molecular packing than the skewed arrangement of the triisopropylsilyl‐substituted species. Copyright © 2005 John Wiley & Sons, Ltd.     

Structures of X 34‐nylons in chain‐folded lamellae and gel‐spun fibers

Structural studies and morphological features of a new family of linear, aliphatic even–even, X 34‐nylons, with X = 2, 4, 6, 8, 10, and 12, are investigated with X‐ray diffraction and electron microscopy. Solution‐grown crystals were obtained by isothermal crystallization from N,N‐dimethylformamide solutions. The thickness of lamellar‐like crystals was orders of magnitude less than the chain lengths of the polymer samples used, implying that the chains fold to form chain‐folded lamellae. The results bear a close resemblance, with the noticeable exception of 2 34‐nylon, to those reported for nylon 6 6 and other even–even nylon chain‐folded lamellar crystals. The basic structure of the straight‐stem lamellar core is similar to that of the classic nylon 6 6 triclinic α structure, and the chains tilt ≈42° relative to the lamellar normal. In the case of 2 34‐nylon, the structure resembles the 2 Y nylon series, and the chain tilt angle reduces to 36.6°. These combined results suggest that, even with a relatively low frequency of amide units along the backbone of these molecules, hydrogen bonding is still the dominant element in controlling the behavior, structure, and properties of these polymers. In addition, gels were prepared in concentrated sulfuric acid, and gel‐spun fibers were studied using X‐ray diffraction. The data are interpreted in terms of a modified nylon triclinic α structure that bears a resemblance to the structure of even–even nylons at elevated temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2685–2692, 2002     

1,3‐Dihydro‐1‐hydroxy‐3‐morpholin‐4‐yl‐2,1‐benzoxaborole: product of the reaction of o‐formylphenylboronic acid with morpholine

o‐Formylphenylboronic acid reacts with morpholine to form 1,3‐dihydro‐1‐hydroxy‐3‐morpholin‐4‐yl‐2,1‐benzoxaborole. The typical hydrogen‐bonded dimer motif with a planar benzoxaborole fragment has been obtained in the solid state. Copyright © 2005 John Wiley & Sons, Ltd.     

Transformation of a Cp*–Iridium(III) Precatalyst for Water Oxidation when Exposed to Oxidative Stress

The reaction of [Cp*Ir(bzpy)NO₃] ( 1 ; bzpy=2‐benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water‐oxidation catalyst, with several oxidants (H₂O₂, NaIO₄, cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI‐MS techniques provided evidence for the formation of many species that all had the intact Ir–bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen–Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η³ interaction with iridium ( 2 a ). Formal addition of H₂O to 2 a or H₂O₂ to 1 leads to 2 b , in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X‐ray single‐crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal ( 2 c ). A η³ interaction between the three non‐oxygenated carbons of “ex‐Cp*” and iridium is also present in both 2 b and 2 c . Isolated 2 b and mixtures of 2 a – c species were tested in water‐oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min^?1).     

Terminal Alkynes in the Coordination Sphere of Titanocene Complexes – Elementary Steps in Catalytic Dimerizations and Oligomerizations of Alkynes

The titanocene acetylene complex [Cp*₂Ti(η²-Me₃SiC≡CSiMe₃)] ( 14 ) reacts with 1-alkynes such as phenylacetylene ( 15 a ), 1-hexyne ( 15 b ), 1-dodecyne ( 15 c ) and trimethylsilylacetylene ( 15 d ) by ligand exchange and proton shift, to yield exclusively the 1-alkenyltitanocene acetylides [Cp*₂Ti(CH=CHR)(C≡CR)] ( 21 ) (R = Ph ( 21 a ), CH₃(CH₂)₃ ( 21 b ), CH₃(CH₂)₉ ( 21 c ), SiMe₃ ( 21 d )). The X-ray structure of 21 a is presented. In reaction of acetylene HC≡CH ( 15 e ) with 14 other products are formed. However, no intermediates, like [Cp*₂Ti(η²-RC≡CH)] ( 17 ), [Cp*₂Ti(H)C≡CR] ( 17 ) or [Cp*₂Ti=C=CHR] ( 22 ) in reactions of 14 with 15 are detectable. On the other hand, a stable titanocenehydride [Cp*₂Ti(H)OCH₃] ( 23 ) is obtained by oxidative addition of CH₃OH with Cp*₂Ti, generated from 14 .     

First Coordination Polymer of 1,4‐Dihydro‐2,3‐Quinoxalinedione in Ketoamine Tautomeric Form

The first coordination compound of 1,4‐dihydro‐2,3‐quinoxalinedione in ketoamine tautomeric form (denoted as H₂qdione) was reported. H₂qdione was obtained by a solid‐state reaction of o‐phenylenediamine and oxalic acid. Reaction of this ligand with CdCl₂ solvothermally yielded a coordination polymer [Cd(H₂qdione)Cl₂]_n, which was structurally characterized by X‐ray diffraction and IR spectroscopy. Continuous Cd₂Cl₂ diamonds form a double‐sided comb with terminal H₂qdione‐κ²O,O′ as the comb teeth. Interaction of these combs through very extensive π–π stacking, C–H ··· Cl, and N–H ··· Cl hydrogen bonds leads to a novel 3D architecture and significant enhancement of solid‐state luminescence of about 10 times compared to the free H₂qdione ligand.     

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

The isotypic nitridosilicates Li₄Ca₃Si₂N₆ and Li₄Sr₃Si₂N₆ were synthesized by reaction of strontium or calcium with Si(NH)₂ and additional excess of Li₃N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li₄Sr₃Si₂N₆: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR₂ = 0.0903) is made up from isolated [Si₂N₆]^10– ions and is isotypic to Li₄Sr₃Ge₂N₆. The bonding angels and distances within the edge‐sharing [Si₂N₆]^10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca₅Si₂N₆ and Ba₅Si₂N₆, which also exhibit isolated [Si₂N₆]^10– ions.     

Dimers of Ag2+ Ions – Synthesis and Characterization of the Quaternary Silver Fluoride Ag2ZnZr2F14 with [Ag2F7]3– Units

Deep blue‐violet colored powder samples of Ag₂ZnZr₂F₁₄ were synthesized by heating Zn(NO₃)₂·4H₂O, Ag and ZrOCl₂·8H₂O at 300 °C under fluorine atmosphere. The crystal structure of Ag₂ZnZr₂F₁₄ was refined from X‐ray powder diffraction data using the Rietveld method (C2/m, a = 9.0206(1) Å, b = 6.6373(1) Å, c = 9.0563(1) Å, β = 90.44(1)°, Z = 2). The structure is derived from the isotypic Ag₃Zr₂F₁₄ by replacing only one of the two crystallographically different Ag²⁺ ions with Zn²⁺ ions, thus leading to discrete Ag₂F₇ dimers. These dimers are connected via nearly linear Ag–F···F–Ag bridges with short F···F distances of 2.33 Å to form two‐legged ladders. Magnetic susceptibility measurements and density functional calculations show that the two Ag²⁺ ions in each Ag₂F₇ dimer are strongly coupled antiferromagnetically.