Proton‐Assisted Hydrogen Activation on Polyhedral Cations

The treatment of [1,1‐(PR₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] (PR₃=PMe₃ ( 2 ) or PPh₃ and PMe₃ ( 3 ); Py=pyridine) with triflic acid (TfOH) affords [1,3‐μ‐(H)‐1,1‐(PR₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ (PR₃=PMe₃ ( 4 ) or PMe₃ and PPh₃ ( 5 )). These products result from the protonation of the 11‐vertex closo‐cages along the Rh(1)? B(3) edge. These unusual cationic rhodathiaboranes are stable in solution and in the solid state and they have been fully characterized by multinuclear NMR spectroscopy. In addition, compound 5 was characterized by single‐crystal X‐ray diffraction. One remarkable feature in these structures is the presence of three {Rh(PPh₃)(PMe₃)}‐to‐{ηⁿ‐SB₉H₈(Py)} (n=4 or 5) conformers in the unit cell, thus giving an uncommon case of conformational isomerism. [1,1‐(PPh₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] ( 1 ), that is, the bis‐PPh₃‐ligated analogue of compounds 2 and 3 , is also protonated by TfOH, but, in marked contrast, the resulting cation, [1,3‐μ‐(H)‐1,1‐(PPh₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ ( 6 ), is attacked by a triflate anion with the release of a PPh₃ ligand and the formation of [8,8‐(OTf)(PPh₃)‐9‐(Py)‐nido‐8,7‐RhSB₉H₉] ( 9 ). The result is an equilibrium that involves cationic species 6 , neutral OTf‐ligated compound 9 , and [HPPh₃]⁺, which is formed upon protonation of the released PPh₃ ligand. The resulting ionic system reacts readily with H₂ to give cationic species [8,8,8‐(H)(PPh₃)₂‐9‐(Py)‐nido‐8,7‐RhSB₉H₉]⁺ ( 7 ). This reactivity is markedly higher than that previously found for compound 1 and it introduces a new example of proton‐assisted H₂ activation that occurs on a polyhedral boron‐containing compound.     

From Nongelating to Gelating: Synthesis and Structural Self‐Assembling Property Relationships of a Homologous Series of Oligo(amide–triazole)s

A homologous series of oligo(amide–triazole)s (OAT) [ OAT‐CO₂H‐2 n and OAT‐COPrg‐(2 n +1) ] with an increasing number of primary amide (CONH) and triazole hydrogen‐bonding functionalities was prepared by an iterative synthetic procedure. It was found that their self‐assembly and thermoreversible gelation strength had a strong correlation to the number of hydrogen‐bonding moieties in the oligomers. There also existed a threshold value of the number of CONH units, above which all the oligomers became organogelators. Hence, oligomers with ≤4 CONH units are devoid of intermolecular hydrogen bonding and also non‐organogelating, whereas those that contain >4 CONH units show intermolecular association and organogelating properties. For the organogelators, the T_gel value increases monotonically with increasing number of CONH units. On the basis of FTIR measurements, both the CONH and triazole C? H groups were involved in the hydrogen‐bonding process. A mixed xerogel that consisted of a 1:1 weight ratio of two oligomers of different lengths ( OAT‐CO₂H‐6 and OAT‐CO₂H‐12 ) was found to show microphase segregation according to differential scanning calorimetry, thus indicating that oligomers that bear a different number of hydrogen‐bonding units exhibited self‐sorting to maximize the extent of intermolecular hydrogen bonding in the xerogel state.     

Well‐Defined Molecular Magnesium Hydride Clusters: Relationship between Size and Hydrogen‐Elimination Temperature

A new tetranuclear magnesium hydride cluster, [{ NN ‐(MgH)₂}₂], which was based on a N? N‐coupled bis‐β‐diketiminate ligand ( NN ^2?), was obtained from the reaction of [{ NN ‐(MgnBu)₂}₂] with PhSiH₃. Its crystal structure reveals an almost‐tetrahedral arrangement of Mg atoms and two different sets of hydride ions, which give rise to a coupling in the NMR spectrum (J=8.5 Hz). To shed light on the relationship between the cluster size and H₂ release, the thermal decomposition of [{ NN ‐(MgH)₂}₂] and two closely related systems that were based on similar ligands, that is, an octanuclear magnesium hydride cluster and a dimeric magnesium hydride species, have been investigated in detail. A lowering of the H₂‐desorption temperature with decreasing cluster size is observed, in line with previously reported theoretical predictions on (MgH₂)_n model systems. Deuterium‐labeling studies further demonstrate that the released H₂ solely originates from the oxidative coupling of two hydride ligands and not from other hydrogen sources, such as the β‐diketiminate ligands. Analysis of the DFT‐computed electron density in [{ NN ‐(MgH)₂}₂] reveals a counterintuitive interaction between two formally closed‐shell H^? ligands that are separated by 3.106 Å. This weak interaction could play an important role in H₂ desorption. Although the molecular product after H₂ release could not be characterized experimentally, DFT calculations on the proposed decomposition product, that is, the low‐valence tetranuclear Mg(I) cluster [( NN ‐Mg₂)₂], predict a structure with two almost‐parallel, localized Mg? Mg bonds. As in a previously reported β‐diketiminate Mg^I dimer, the Mg? Mg bond is not characterized by a bond critical point, but instead displays a local maximum of electron density midway between the atoms, that is, a non‐nuclear attractor (NNA). Interestingly, both of the NNAs in [( NN ‐Mg₂)₂] are connected through a bond path that suggests that there is bonding between all four Mg^I atoms.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

Arylation with Unsymmetrical Diaryliodonium Salts: A Chemoselectivity Study

Phenols, anilines, and malonates have been arylated under metal‐free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti‐ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal‐free reagents.     

Investigation of Functionalized α‐Chloroalkyllithiums for a Stereospecific Reagent‐Controlled Homologation Approach to the Analgesic Alkaloid (−)‐Epibatidine

Four putative functionalized α‐chloroakyllithiums RCH₂CHLiCl, where R=CHCH₂ ( 18 a ), CCH ( 18 b ), CH₂OBn ( 18 c ), and CH[O(CH₂)₂O] ( 18 d ), were generated in situ by sulfoxide–lithium exchange from α‐chlorosulfoxides, and investigated for the stereospecific reagent‐controlled homologation (StReCH) of phenethyl and 2‐chloropyrid‐5‐yl ( 17 ) pinacol boronic esters. Deuterium labeling experiments revealed that α‐chloroalkyllithiums are quenched by proton transfer from their α‐chlorosulfoxide precursors and it was established that this effect compromises the yield of StReCH reactions. Use of α‐deuterated α‐chlorosulfoxides was discovered to ameliorate the problem by retarding the rate of acid‐base chemistry between the carbenoid and its precursor. Carbenoids 18 a and 18 b showed poor StReCH efficacy, particularly the propargyl group bearing carbenoid 18 b , the instability of which was attributed to a facile 1,2‐hydride shift. By contrast, 18 d , a carbenoid that benefits from a stabilizing interaction between O and Li atoms gave good StReCH yields. Boronate 17 was chain extended by carbenoids 18 a , 18 b , and 18 d in 16, 0, and 68 % yield, respectively; α‐deuterated isotopomers D ‐ 18 a and D ‐ 18 d gave yields of 33 and 79 % for the same reaction. Double StReCH of 17 was pursued to target contiguous stereodiads appropriate for the total synthesis of (?)‐epibatidine ( 15 ). One‐pot double StReCH of boronate 17 by two exposures to (S)‐D ‐ 18 a (≤66 % ee), followed by work‐up with KOOH, gave the expected stereodiad product in 16 % yield (d.r.～67:33). The comparable reaction using two exposures to (S)‐D ‐ 18 d (≤90 % ee) delivered the expected bisacetal containing stereodiad (R,R)‐DD ‐ 48 in 40 % yield (≥98 % ee, d.r.=85:15). Double StReCH of 17 using (S)‐D ‐ 18 d (≤90 % ee) followed by (R)‐D ‐ 18 d (≤90 % ee) likewise gave (R,S)‐DD ‐ 48 in 49 % yield (≥97 % ee, d.r.=79:21). (R,S)‐DD ‐ 48 was converted to a dideuterated isotopomer of a synthetic intermediate in Corey’s synthesis of 15 .     

[Pd(Fmes)2(tmeda)]: A Case of Intermittent C?H⋅⋅⋅F?C Hydrogen‐Bond Interaction in Solution

The X‐ray structure of the title compound [Pd(Fmes)₂(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF₃ groups of the Fmes ligand. The ¹⁹F NMR spectra in CD₂Cl₂ at very low temperature (157 K) detect restricted rotation for the two ortho‐CF₃ groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol^?1) to account for the rotational barrier observed (ΔH^≠=26.8 kJ mol^?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.     

Unzipping Nucleoside Channels by Means of Alcohol Disassembly

Gold nanoparticles capped with simple adenosine derivatives can form colloidal aggregates in nonpolar solvents. Theoretical calculations indicate the formation of organic channels by the supramolecular assembly of the nanoparticles by means of hydrogen bonds between the adenine moieties. The aggregates were only negligibly sensitive to nPrOH, iPrOH, and tBuOH, whereas some showed a similar response to MeOH and EtOH, and others showed high selectivity toward MeOH. DNA nucleoside derivatives (1‐(2‐deoxy‐β‐D ‐ribofuranosyl)‐5‐methyluracil and 2′,3′‐O‐isopropylideneadenosine) as well as thymine and other aromatic compounds such as pyrene derivatives (pyrene, 1‐chloropyrene, 1‐hydroxypyrene, (1‐pyrenyl)methanol, and 2‐hydroxynapthalene) did not induce disassembly of the nanoparticle aggregates. Data suggest that the nucleoside channels allow access to alcohols according to their size, and an efficient interaction between the alcohol and the adenine units destabilizes the hydrogen bonds, which eventually leads to nanoparticle disassembly.     

基于自交联杂萘联苯聚芳醚阴离子交换膜制备及其物理化学性质

以氯甲基杂环聚醚酮(CMPPEK)为原料,加入三乙胺进行铵化,并分别加入二乙烯三胺(DETA)和二乙胺(DEA),生成的仲胺基(或叔胺基)与邻近分子链氯甲基团进行自交联.经过制膜和离子交换反应,制备了DETA自交联杂萘联苯聚芳醚阴离子交换膜(DETA-QPPEK-OH)和DEA自交联杂萘联苯聚芳醚阴离子交换膜(DEA-QPPEK-OH).采用傅里叶变换红外(FTIR)光谱对制备自交联膜的化学结构进行表征.研究了DETA-QPPEK-OH和DEA-QPPEK-OH膜的理化性质,结果表明前者具有较低吸水率和更低溶胀度.通过研究DETAQPPEK-OH和DEA-QPPEK-OH膜的离子传导率随温度的变化规律,结果表明在80°C时其离子传导率分别达到0.060和0.028 S cm-1,表明本文制备的自交联膜具有较高离子传导率.此外还通过热重分析(TGA)对两类自交联膜的热稳定性进行了研究.     

钪元素对AB2型合金Zr1-xScxMn0.6V0.2Ni1.2Co0.1（x=0～1）储氢和电化学性能的影响

用真空电弧熔炼方法制备了Zr1-xScxMn0.6V0.2Ni1.2Co0.1(x=0～1)AB2型储氢合金,研究了Sc元素替代Zr对合金的微观组织结构、气态储氢及电化学性能的影响。研究结果表明,Zr1-xScxMn0.6V0.2Ni1.2Co0.1合金主要是由FCC型C15相、CsCl型结构的(ScZr)Ni相和少量的Ni10Zr7相组成,随Sc含量的增加,C15相丰度逐渐减小,(ScZr)Ni相丰度逐渐增加,当x=0.2时Ni10Zr7相基本消失;Sc元素对合金的首次气态吸氢动力学行为影响较大,随Sc含量的增加,合金吸氢动力学性能逐渐变缓,但吸氢容量逐渐提高,直至达x=1.0时的最大吸氢量1.87%;Sc元素对合金吸氢PCT曲线平衡氢压的影响规律不明显,随Sc含量增加,合金氢化物的形成焓ΔH从-26.66 kJ.mol-1逐渐减小到-8.14 kJ.mol-1。Sc元素的加入可明显改善合金电极的活化性能,提高放电容量,随Sc含量的增加,合金电极最大放电容量从x=0时的350.3 mAh.g-1增加到x=1时的429.8 mAh.g-1,呈先减小后增大的趋势,但电极容量的保持率S100随Sc含量增加而快速下降。