Über die Oxo‐cyclotetraphosphane (PBut)4O1–4

Contributions to the Chemistry of Phosphorus. 243 On the Oxocyclotetraphosphanes (PBu^t)₄O_1–4 Under suitable conditions, the reaction of tetra‐tert‐butylcyclotetraphosphane, (PBu^t)₄, with dry atmospheric oxygen gives rise to the corresponding monoxide (PBu^t)₄O ( 1 ) which has been isolated by column chromatography. The reaction with hydrogen peroxide furnishes a mixture of oxocyclotetraphosphanes (PBu^t)₄O_1–4 consisting of two constitutionally isomeric dioxides (PBu^t)₄O₂ ( 2 a , 2 b ), the trioxide (PBu^t)₄O₃ ( 3 ), and the tetraoxide (PBu^t)₄O₄ ( 4 ), in addition to 1 . According to the ³¹P NMR parameters the oxygen atoms are exclusively exocyclically bonded to the phosphorus four‐membered ring. Which of the P atoms are present as λ⁵‐phosphorus follows from the different low‐field shifts of the individual P nuclei compared with the starting compound. Accordingly, 1 is 1,2,3,4‐Tetra‐tert‐butyl‐1‐oxocyclotetraphosphane, 2 a and 2 b are 1,2,3,4‐Tetra‐tert‐butyl‐1,2‐dioxo‐ and ‐1,3‐dioxocyclotetraphosphane, respectively, 3 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3‐trioxocyclotetraphosphane, and 4 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3,4‐tetraoxocyclotetraphosphane. When the oxidation reaction proceeds a fission of the P₄ ring takes place.     

Rate constants for the gas‐phase reactions of Cl atoms with a series of ethers

The laser photolysis–resonance fluorescence technique has been used to determine the absolute rate coefficient for the Cl atom reaction with a series of ethers, at room temperature (298 ± 2) K and in the pressure range 15–60 Torr. The rate coefficients obtained (in units of cm³ molecule⁻¹ s⁻¹) are dimethyl ether (1.3 ± 0.2) × 10⁻¹⁰, diethyl ether (2.5 ± 0.3) × 10⁻¹⁰, di‐n‐propyl ether (3.6 ± 0.4) × 10⁻¹⁰, di‐n‐butyl ether (4.5 ± 0.5) × 10⁻¹⁰, di‐isopropyl ether (1.6 ± 0.2) × 10⁻¹⁰, methyl tert‐butyl ether (1.4 ± 0.2) × 10⁻¹⁰, and ethyl tert‐butyl ether (1.5 ± 0.2) × 10⁻¹⁰. The results are discussed in terms of structure–reactivity relationship. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 105–110, 2000     

Sterically hindered phenols in negative ion mobility spectrometry–mass spectrometry

Negative corona discharge atmospheric pressure chemical ionization (APCI) was used to investigate phenols with varying numbers of tert‐butyl groups using ion mobility spectrometry–mass spectrometry (IMS‐MS). The main characteristic ion observed for all the phenolic compounds was the deprotonated molecule [M–H]⁻. 2‐tert‐Butylphenol showed one main mobility peak in the mass‐selected mobility spectrum of the [M–H]⁻ ion measured under nitrogen atmosphere. When air was used as a nebulizer gas an oxygen addition ion was seen in the mass spectrum and, interestingly, this new species [M–H+O]⁻ had a shorter drift time than the lighter [M–H]⁻ ion. Other phenolic compounds primarily produced two IMS peaks in the mass‐selected mobility spectra measured using the [M–H]⁻ ion. It was also observed that two isomeric compounds, 2,4‐di‐tert‐butylphenol and 2,6‐di‐tert‐butylphenol, could be separated with IMS. In addition, mobilities of various characteristic ions of 2,4,6‐trinitrotoluene were measured, since this compound was previously used as a mobility standard. The possibility of using phenolic compounds as mobility standards is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A Cyclic Hydroxylaminato‐aminoxide Complex of Gallium

The reaction of HON(tBu)CH₂CH₂N(tBu)OH with tri‐tert‐butyl gallium affords a hydroxylaminato complex of the formula [tBu₂Ga{ON(tBu)CH₂CH₂N(H)(tBu)O}], which contains a monoanionic bishydroxylaminato ligand with one anionic and one neutral, but tautomeric aminoxide end, both linked to gallium by their oxygen atoms leading to a seven‐membered ring. The compound was characterised by elemental analysis, ¹H and ¹³C NMR and determination of its crystal structure.     

Aluminum/Nitrogen Cycles and an Open Cage with Al–H and N–H Functions

The cyclic tert‐butyl‐amino alane dimer [tBu–N(H)AlH₂]₂ ( 1 ) was obtained from reaction between alane with tert‐butylamine and its boranate derivative [tBu–N(H)–Al(BH₄)₂)]₂ ( 2 ) subsequently from 1 by hydride/chloride exchange using PbCl₂ followed by reaction with LiBH₄. Both compounds form four‐membered Al₂N₂ cycles with typical Al–N bond lengths of 1.940(5) Å ( 1 ) and 1.945(5) Å ( 2 ) as found from X‐ray diffraction analysis. The tert‐butyl substituents at the nitrogen atoms may be situated at the same side of the ring (cis) or at opposite sides (trans). For compound 1 both isomers are present in solution, showing particular temperature dependent NMR shifts. In the solid both compounds 1 and 2 adopt the trans arrangement. When 1 is reacted with PbCl₂ in half of the molarity ratio used for 2 , surprisingly the novel compound 3 , a zwitterion, can be obtained: [(tBu–N)(Al–H)₃(tBu–N(H))₃Cl((H)N–tBu)₃(Al–H)₂(Al–Cl)(N–tBu)]⁺[(tBu–N)(tBu–N(H))(AlCl₂)₂]^–. X‐ray structure analysis reveals that the anion is made of a tert‐butyl amino aluminum dichloride dimer (central Al₂N₂ ring) with one of the two nitrogen atoms being deprotonated. The cationic counterpart consists of three entities: (i) There is a first seco‐norcubane like Al₃N₄ basket with tert‐butyl groups at the nitrogen atoms, two hydride and one chloride ligand at the aluminum atoms and three hydrogen atoms on the open side of the basket, all pointing in the same direction; (ii) There is a second similar Al₃N₄ basket with the same substituent pattern except that all aluminum atoms have exclusively hydrogen ligands; (iii) Both baskets coordinate a central chloride through the six protons at the open nitrogen face of the baskets in such a way that the chloride lies in the center of a H₆ trigonal anti‐prism [mean H–Cl–H = 56.1(9)°]. As each of the open cages has a positive charge the overall charge by combination with the chloride adds to +1. The structure of the cationic part of 3 is unprecedented in AlN polycycles.     

Isolation and structure of an 18‐membered macrocycle containing two diselenide linkages and its precursor

The structures of the 18‐membered diselenide‐linked macrocycle 10,27‐di‐tert‐butyl 11,28‐dioxo‐2,3,19,20‐tetraselena‐10,12,27,29‐tetraazapentacyclo[28.4.0.0^4,9.0^13,18.0^21,26]tetratriaconta‐1(30),4(9),5,7,13,15,17,21,23,25,31,33‐dodecaene‐10,27‐dicarboxylate, C₃₆H₃₄N₄O₆Se₄, and its precursor di‐tert‐butyl 2,2′‐[diselane‐1,2‐diylbis(2,1‐phenylene)]dicarbamate, C₂₂H₂₈N₂O₄Se₂, are reported. The precusor to the macrocycle contains two tert‐butyl phenylcarbamate arms connected to a diselenide group, with Se—C and Se—Se bond lengths of 1.914 (4) and 2.3408 (6) Å, respectively. The macrocycle resides on a crystallographic center of inversion in space group P with one molecule in the unit cell (Z′ = ). It contains an 18‐membered macrocyclic ring with two diselenide linkages. In this macrocycle, there are two free and two protected amino groups.     

Aluminiumhydrazide. Bildung eines dimeren Di(tert‐butyl)aluminiumhydrazids mit viergliedrigem Al2N2‐Heterozyklus und Umsetzung eines Dialkylaluminiumchlorids mit Dilithium‐bis(trimethylsilyl)hydrazid

Aluminium Hydrazides – Formation of a Dimeric Di( tert ‐butyl)aluminium Hydrazide Containing a Four‐Membered Al₂N₂ Heterocycle and Reaction of Dialkylaluminium Chloride with Dilithium Bis(trimethylsilyl)hydrazide The reaction of di(tert‐butyl)aluminium chloride with tert‐butylhydrazine yielded an adduct ( 1 ) which was isolated in a pure form and characterized by crystal structure determination. 1 reacted with n‐butyllithium by deprotonation and salt elimination to give the corresponding di(tert‐butyl)aluminium hydrazide ( 2 ), which is a dimer in solution and in the solid state and possesses a four‐membered Al₂N₂ heterocycle with two exocyclic N–N bonds. The structure of 2 differs from that of other di(tert‐butyl)aluminium hydrazides which have four‐ or five‐membered heterocycles. Treatment of impure samples of 1 with n‐butyllithium yielded by the cleavage of the N–N bonds a mixture of several unknown products, from which the dimeric, centrosymmetric aluminium amide [(Me₃C)₂AlN(H)CMe₃]₂ ( 3 ) was isolated. A similar product ( 4 ) was obtained in a low yield by the reaction of (Me₃SiCH₂)₂AlCl with the dilithium hydrazide Li₂N₂(SiMe₃)₂. An intact N–N bond was neither found in the second product isolated from this reaction. Instead a tricyclic compound was formed by C–H activation which has two five‐membered AlNSiC₂ heterocycles bridged by Al–N bonds.     

Study of carbonaceous clusters in irradiated polycarbonate with UV–vis spectroscopy

The formation of carbonaceous clusters in ion‐irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultraviolet–visible (UV–vis) spectroscopy. The optical band gap (E_g), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to E_g; for example, a six‐membered‐benzene‐ring‐type structure has an E_g of ≈5.3 eV, whereas a buckminsterfullerene‐type structure has an E_g of ≈4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 μm thick) were irradiated with 45‐MeV Li ions at fluences of 1 × 10¹² to 1 × 10¹³ cm⁻² and were characterized with UV–vis spectroscopy and impedance measurements. The E_g values, calculated from the absorption edge in the 280–315‐nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60–62 carbon atoms per cluster. The sheet conductivity (σ_dc) and loss (tan δ) values of 10⁻¹⁶ Ω⁻¹cm⁻¹ and 10⁻³ for the pristine sample changed to 10⁻¹⁵ Ω⁻¹cm⁻¹ and 10⁻², respectively, for the irradiated samples. This increase in the values of σ_dc and tan δ may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1589–1594, 2000     

Radical Localization in a Series of Symmetric NiII Complexes with Oxidized Salen Ligands

Square‐planar nickel(II) complexes of salen ligands, N,N′‐bis(3‐tert‐butyl‐(5R)‐salicylidene)‐1,2‐cyclohexanediamine), in which R=tert‐butyl ( 1 ), OMe ( 2 ), and NMe₂ ( 3 ), were prepared and the electronic structure of the one‐electron‐oxidized species [ 1 – 3 ]^+. was investigated in solution. Cyclic voltammograms of [ 1 – 3 ] showed two quasi‐reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1 ^+.> 2 ^+.> 3 ^+. was obtained. The cations [ 1 – 3 ]^+. exhibited isotropic g tensors of 2.045, 2.023, and 2.005, respectively, reflecting a lower metal character of the singly occupied molecular orbital (SOMO) for systems that involve strongly electron‐donating substituents. Pulsed‐EPR spectroscopy showed a single population of equivalent imino nitrogen atoms for 1 ^+., whereas two distinct populations were observed for 2 ^+.. The resonance Raman spectra of 2 ^+. and 3 ^+. displayed the ν_8a band of the phenoxyl radicals at 1612 cm^?1, as well as the ν_8a bands of the phenolates. In contrast, the Raman spectrum of 1 ^+. exhibited the ν_8a band at 1602 cm^?1, without any evidence of the phenolate peak. Previous work showed an intense near‐infrared (NIR) electronic transition for 1 ^+. (Δν_1/2=660 cm^?1, ε=21 700 M ^?1 cm^?1), indicating that the electron hole is fully delocalized over the ligand. The broader and moderately intense NIR transition of 2 ^+. (Δν_1/2=1250 cm^?1, ε=12 800 M ^?1 cm^?1) suggests a certain degree of ligand‐radical localization, whereas the very broad NIR transition of 3 ^+. (Δν_1/2=8630 cm^?1, ε=2550 M ^?1 cm^?1) indicates significant localization of the ligand radical on a single ring. Therefore, 1 ^+. is a Class III mixed‐valence complex, 2 ^+. is Class II/III borderline complex, and 3 ^+. is a Class II complex according to the Robin–Day classification method. By employing the Coulomb‐attenuated method (CAM‐B3LYP) we were able to predict the electron‐hole localization and NIR transitions in the series, and show that the energy match between the redox‐active ligand and the metal d orbitals is crucial for delocalization of the radical SOMO.     

Synthese,Struktur, Elektrochemie und optische Eigenschaften von alkinylfunktionalisierten 1,3,2‐Diazaborolen und 1,3,2‐Diazaborolidinen

Syntheses, Structures, Electrochemistry and Optical Properties of Alkyne‐Functionalized 1,3,2‐Diazaboroles and 1,3,2‐Diazaborolidenes The reaction of 2‐bromo‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 3 ) with lithiated tert‐butyl‐acetylene and lithiated phenylacetylene affords the 2‐alkynyl‐functionalized 1,3,2‐diazaboroles 4 and 5 as a thermolabile colorless oil ( 4 ) or a solid ( 5 ). Similarly 2‐bromo‐1,3‐diethyl‐2,3‐dihydro‐1H‐1,3,2‐benzodiazaborole ( 6 ) was converted into the crystalline 2‐alkynyl‐benzo‐1,3,2‐diazaboroles 7 and 8 by treatment with LiC≡C–tBu or LiC≡CPh, respectively. 2‐Ethynyl‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 2 ) was metalated with tert‐butyl‐lithium and subsequently coupled with 2‐bromo‐1,3,‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 3 ) to afford bis(1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborol‐2‐yl)acetylene ( 9 ) as thermolabile colorless crystals. Analogously coupling of the lithiated species with 6 or with 2‐bromo‐1,3‐ditert‐butyl‐1,3,2‐diazaborolidine ( 11 ) gave the unsymmetrically substituted acetylenes 10 or 12 , respectively, as colorless solids. Compounds 4 , 5 , 7 – 10 and 12 are characterized by elemental analyses and spectroscopy (IR, ¹H‐, ¹¹B{¹H}, ¹³C{¹H}‐NMR, MS). The molecular structures of 5 , 8 and 9 were elucidated by X‐ray diffraction analyses.     

A new synthetic route to cyclophosphadithiatriazenes: synthesis and X‐ray structural characterization of the first spirocycle containing thiadiazaphosphetidine and phosphadithiatriazene heterocycles

The phosphetidine 2,4‐Di‐tert‐butyl‐3‐chloro‐1λ⁶‐thia‐2,4‐diaza‐3‐phosphetidine‐1,1‐dioxide, O₂S (^tBuN)₂PCl, reacts with tetrasulfur tetranitride, S₄N₄, in benzene under reflux to afford the novel 4,6‐spirocycle in moderate yield. The deep‐blue crystals of the spirocycle are airstable and high melting in nature. The spiro phosphorus atom subtends a four‐membered P^VS^VIN₂ ring which is saturated, and a six‐membered P^VS N₃ ring which is unsaturated. The single‐crystal X‐ray structure of this first example of the spirocycle reveals a planar PSN₂ ring and a puckered PS₂N₃ ring and the molecule is symmetric in nature. Copyright © 2006 John Wiley & Sons, Ltd.     

1,1‐Diethyl‐1‐germa‐2,3,4,5‐tetra‐tert‐butyl‐2,3,4,5‐tetraphospholan (C2H5)2Ge(tBuP)4, Molekül‐ und Kristallstruktur

1,1‐Diethyl‐1‐germa‐2,3,4,5‐tetra‐ tert ‐butyl‐2,3,4,5‐tetraphospholane (C₂H₅)₂Ge( t BuP)₄, Molecular and Crystal Structure The reaction of the diphosphide K₂[(tBuP)₄] · THF ( 1 ) with the germanium(IV) compound (C₂H₅)₂GeCl₂ leads via a [4 + 1]‐cyclo‐condensation reaction to 1,1‐diethyl‐1‐germa‐2,3,4,5‐tetra‐tert‐butyl‐2,3,4,5‐tetraphospholane (C₂H₅)₂Ge(tBuP)₄ ( 2 ) with the 5‐membered GeP₄ ring system. 2 could be characterized ³¹P NMR spectroscopically, mass spectrometrically and by a single crystal structure analysis.     

Rate constants for the reactions of OH radicals and Cl atoms with Di‐n‐Propyl ether and Di‐n‐Butyl ether and their deuterated analogs

Using relative rate methods, rate constants for the gas‐phase reactions of OH radicals and Cl atoms with di‐n‐propyl ether, di‐n‐propyl ether‐d₁₄, di‐n‐butyl ether and di‐n‐butyl ether‐d₁₈ have been measured at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in cm³ molecule⁻¹ s⁻¹ units) were: OH radical reactions, di‐n‐propyl ether, (2.18 ± 0.17) × 10⁻¹¹; di‐n‐propyl ether‐d₁₄, (1.13 ± 0.06) × 10⁻¹¹; di‐n‐butyl ether, (3.30 ± 0.25) × 10⁻¹¹; and di‐n‐butyl ether‐d₁₈, (1.49 ± 0.12) × 10⁻¹¹; Cl atom reactions, di‐n‐propyl ether, (3.83 ± 0.05) × 10⁻¹⁰; di‐n‐propyl ether‐d₁₄, (2.84 ± 0.31) × 10⁻¹⁰; di‐n‐butyl ether, (5.15 ± 0.05) × 10⁻¹⁰; and di‐n‐butyl ether‐d₁₈, (4.03 ± 0.06) × 10⁻¹⁰. The rate constants for the di‐n‐propyl ether and di‐n‐butyl ether reactions are in agreement with literature data, and the deuterium isotope effects are consistent with H‐atom abstraction being the rate‐determining steps for both the OH radical and Cl atom reactions. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 425–431, 1999     

catena‐Poly[[diisothio­cyanato­cad­mium(II)]‐bis­[μ‐1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene‐κ2N4:N4′]]: a double‐chain coordination polymer

The coordination geometry of the Cd^II atom in the title complex, [Cd(NCS)₂(C₁₂H₁₂N₆)₂]_n or [Cd(NCS)₂(mbtz)₂]_n, where mbtz is 1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene, is a distorted compressed octa­hedron in which the Cd^II atom lies on an inversion centre, coordinated by four N atoms from the triazole rings of four mbtz ligands and two N atoms from two monodentate NCS⁻ ligands. The structure is polymeric, with 24‐membered spiro‐fused rings extending along [100] and with the 24‐membered ring containing two inversion‐related mbtz mol­ecules.     

Poly[(μ4‐biphenyl‐3,3′,4,4′‐tetracarboxylato)bis[μ2‐1,4‐bis(imidazol‐1‐ylmethyl)benzene]dicobalt(II)]

The asymmetric unit of the title two‐dimensional coordination polymer, [Co₂(C₁₆H₆O₈)(C₁₄H₁₄N₄)₂]_n, contains one Co²⁺ ion, half of a biphenyl‐3,3′,4,4′‐tetracarboxylate (bptc) anion lying about an inversion centre and one 1,4‐bis(imidazol‐1‐ylmethyl)benzene (bix) ligand. The Co^II atom is coordinated by three carboxylate O atoms from two different bptc ligands and two N atoms from two bix ligands constructing a distorted square pyramid. Each Co²⁺ ion is interlinked by two bptc anions, while each bptc anion coordinates to four Co atoms as a hexadentate ligand so that four Co^II atoms and four bptc anions afford a larger 38‐membered ring. These inorganic rings are further extended into a two‐dimensional undulated network in the (10) plane. Two Co^II atoms in adjacent 38‐membered rings are joined together by pairs of bix ligands forming a 26‐membered [Co₂(bix)₂] ring that is penetrated by a bptc anion; these components share a common inversion centre.     

An asymmetrically substituted borazine

The B₃N₃ ring in the title compound, 1,3,5‐tri‐tert‐butyl‐2,4‐difluoro‐6‐phenyl­cyclo­triborazane, [PhF₂B₃N₃^tBu₃] or C₁₈H₃₂B₃F₂N₃, an asymmetrically substituted borazine, is distorted from planarity. The molecule resides on a twofold axis. The N atoms of the N—B(Ph)—N group lie on opposite sides of the least‐squares plane formed by the four remaining ring atoms, due to steric accommodation of the tert‐butyl groups, a conformation not previously observed for a borazine. The B—N bond lengths are in the range 1.4283 (14)–1.4493 (12) Å, due to the F substituents residing on two of the B atoms, which also produce a large deviation from 120° in one of the B—N—B angles [ca 113.6 (1)°]. The phenyl group is twisted with respect to the B₃N₃ ring, the interplanar angle being 62.87 (5)°.     

Kinetic Determination of the Gas‐Phase Decarbonylation of Butyraldehyde in the Presence of HCl Catalyst

The gas‐phase kinetics and mechanism of the homogeneous elimination of CO from butyraldehyde in the presence of HCl has been experimentally studied. The reaction is homogeneous and follows the second‐order kinetics with the following rate expression: log k ₁ (s⁻¹ L mol⁻¹) = (13.27 ± 0.36) – (173.2 ± 4.4) kJ mol⁻¹(2.303RT )⁻¹. Experimental data suggested a concerted four‐membered cyclic transition state type of mechanism. The first and rate‐determining step occurs through a four‐membered cyclic transition state to produce propane and formyl chloride. The formyl chloride intermediate rapidly decomposes to CO and HCl gases.     

Ring opening polymerization of lactide promoted by alcoholyzed heteroscorpionate aluminum complexes

The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe₂ ( 1 ) (bpzmp = 2,4‐di‐tert‐butyl‐6‐(bis‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo), promoted both by phenol and isopropanol, has been investigated. The reaction of 1 with phenol afforded the dimeric mono(phenoxo) derivative 2 , whereas the alcoholysis of 1 with the less acidic isopropanol involved the coordinated heteroscorpionate ligand and led to the tetrahedral complex 3 in which the aluminum atom is surrounded by one κ²‐N,O^? coordinated bpzmp ligand and one η¹‐O^? coordinated ppzmp ligand (ppzmp = 2,4‐di‐tert‐butyl‐6‐(i‐propoxy‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo). Complexes 1 – 3 have been tested in the ring opening polymerization (ROP) of L ‐lactide. The dimeric mono(phenoxo) derivative 2 was inactive in the ROP of L ‐lactide. Quite surprisingly, complex 3 was found to be active in ROP of L ‐ and rac‐lactide, showing a good molar‐mass control. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3632–3639, 2010     

Structural verification of a tetrahydrotetrazole compound

Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C₂₅H₃₀N₄O₄, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl₃). A tentative reaction pathway for its dissociation based on ¹H NMR spectral evidence is provided.     

A highly efficient antioxidant based on boron and a Schiff base bridged phenolic diphenylamine: synthesis,crystal structure and thermal and antioxidant properties

Antioxidants can effectively protect vegetable‐oil‐based lubricants against oxidative degradation and prolong their service life. A novel compound, (E)‐4‐({3,5‐di‐tert‐butyl‐2‐[(diphenylboranyl)oxy]benzylidene}amino)‐N‐phenylaniline (BSPD) or {2‐[(4‐anilinophenyl)iminomethyl‐κN]‐4,6‐di‐tert‐butylphenolato‐κO}diphenylboron, C₃₉H₄₁BN₂O, was synthesized by a one‐pot reaction of the Schiff base bridged phenolic diphenylamine 2,4‐di‐tert‐butyl‐6‐{N‐[4‐(phenylamino)phenyl]carboximidoyl}phenol (SPD) with phenylboronic acid. The corresponding single‐crystal X‐ray study revealed that the B atom in BSPD has a typical tetrahedral geometry, and the N,O‐chelated six‐membered ring adopts a chair conformation. According to thermogravimetric analysis, the 5% weight‐loss temperature of BSPD increases to 328 °C and the 95% weight‐loss temperature is up to 414 °C. More importantly, the antioxidant capability of BSPD in vegetable oil is much better than that of commercial antioxidants [diphenylamine (DPA) and 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT)] and unmodified SPD.