Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]⁻ ( 1 ⁻; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ⁻ acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄⁻, ClO₄⁻, ReO₄⁻). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au S and Au P bonds, which is essential for metallaring expansion and contraction.     

Search for solar axions with mass around 1 eV using coherent conversion of axions into photons

A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3-m long 4 T superconducting magnet, a gas container to hold dispersion-matching gas, PIN-photodiode X-ray detectors, and a telescope mount mechanism to track the sun. A mass region around ma=1 eV$m_a=1\text{eV}$ was newly explored. From the absence of any evidence, analysis sets a limit on axion–photon coupling constant to be g_aγγ<5.6–13.4×¹⁰⁻¹⁰ GeV⁻¹$g_{a\gamma \gamma }<5.6\text{–}13.4\times {10}^{\mathrm{-10}}{\text{GeV}}^{\mathrm{-1}}$ for the axion mass of 0.84<ma<1.00 eV$0.84<m_a<1.00\text{eV}$ at 95% confidence level. It is the first result to search for the axion in the g_aγγ–ma$g_{a\gamma \gamma }\text{–}{m}_a$ parameter region of the preferred axion models with a magnetic helioscope.     

A 116-Nuclear Metallosupramolecular Cage-of-Cage Showing Multistep Single-Crystal-to-Single-Crystal Transformation

Here a unique single-crystal-to-single-crystal (SCSC) transformation of a 116-nuclear Au^I₇₂Cd^II₄₀Na^I₄ cage-of-cage ( 2 _CdNa) is reported, which was created from a trigold(I) metalloligand with d -penicillamine by way of a 9-nuclear Au^I₆Cd^II₃ cage ( 1 ). Cage-of-cage 2 _CdNa is composed of 12 cages of 1 that are linked by 4 Cd²⁺ and 4 Na⁺ ions, with its surface being covered by 12 NO₃⁻ ions to form a discrete, spherical molecule with a diameter ca. 4.7 nm. In crystal 2 _CdNa, the cage-of-cage molecules are packed in a cubic lattice with a huge cell volume of ca. 4.5×10⁵ ų_, so as to have large interstices with diameters of more than 3 nm. Upon soaking crystals 2 _CdNa in aqueous Cu(NO₃)₂, all Cd²⁺ and Na⁺ were quickly exchanged by Cu²⁺ to produce an analogous Au^I₇₂Cu^II₄₄ cage-of-cage ( 2 _Cu) in a SCSC manner. Prolonged soaking led to the SCSC transformation to another supramolecular structure ( 2′ _Cu) consisting of 152-nuclear Au^I₇₂Cu^II₈₀ cage-of-cages that are alternately H-bonded with the Au^I₇₂Cu^II₄₄ cage-of-cages. 2′ _Cu showed the accommodation of MoO₄²⁻ and the conversion of MoO₄²⁻ to β-Mo₈O₂₆⁴⁻ in the crystal, with retention of single-crystallinity.     

A new interpretation of the reaction pathway of deprotonative metalation with TMP-Zn-ate/TMEDA Complex [TMEDA.Na(micro-tBu)(micro-TMP)Zn(tBu)

Density functional theory (DFT) calculations of possible reaction pathways and mechanisms for the deprotonation of benzene with Mulvey's reagent, TMEDA.Na(micro-R)(micro-TMP)Zn(R) (TMEDA=N,N,N',N'-tetramethylethylenediamine, R = alkyl, TMP = 2,2,6,6-tetramethylpiperidide) indicate that the deprotonation of benzene with Mulvey's reagent proceeds through a stepwise mechanism, not a one-step mechanism. In the first step, deprotonation involving the TMP ligand on the reagent is kinetically more favorable than that involving the alkyl ligand.     

Metallosupramolecular Structures Derived from a Series of Diphosphine‐bridged Digold(I) Metalloligands with Terminal d‐Penicillamine

In this report, we describe our recent work on the development of a new family of chiral heteroleptic digold(I) metalloligands with mixed diphosphine and d ‐penicillaminate (d ‐pen), [Au₂(dppx)(d ‐pen‐S)₂]^2– (dppx = PPh₂(CH₂)_nPPh₂, n = 1–5) and their application for the construction of chiral multinuclear and metallosupramolecular structures. The reactions of the metalloligands with 3d metal ions produce a variety of chiral heterobimetallic structures retaining the digold(I) metalloligand structure, ranging from discrete trinuclear to infinite helix structures that depend on the type of dppx. In addition, monophosphine and triphosphine analogues of the metalloligands were designed, and their coordination behavior is discussed to show the essential properties and potential extensibility of this class of metalloligands.     

On the kinetic and thermodynamic reactivity of lithium di(alkyl)amidozincate bases in directed ortho metalation

Sequential reaction of HTMP (= 2,2,6,6-tetramethylpiperidine) with nBuLi and Et2Zn affords unsolvated polymer chains of EtZn(micro-Et)(micro-TMP)Li 6. The scope of this reagent in directed ortho metalation (DoM) chemistry has been tested by its reaction with N,N-diisopropylnaphthamide in THF to give EtZn(micro-C10H6C(O)NiPr2-2)2Li.2THF 7. Data reveal that 6 has undergone reaction with 2 equiv of aromatic tertiary amide and imply that it exhibits dual alkyl/amido basicity. DFT calculations reveal that direct alkyl basicity is kinetically disfavored and instead point to a stepwise mechanism whereby 6 acts as an amido base, liberating HTMP during the first DoM event. Re-coordination of the amine at lithium then incurs the elimination of EtH. Reaction of the resulting alkyl(amido)(arylamido)zincate with a second equivalent of N,N-diisopropylnaphthamide eliminates HTMP and affords 7. Both DoM steps involve the exhibition of amido basicity and each reveals a low kinetic barrier to reaction. Understanding of this reaction sequence is tested by treating 6 with N,N-diisopropylbenzamide in THF. On the basis of theory and experiment, the presence of THF solvent (in place of stronger Lewis bases) combined with the use of a sterically less congested aromatic amide is expected to encourage threefold, stepwise reaction. Isolation and characterization of the resulting tripodal zincate Zn(micro-C6H4C(O)NiPr2-2)3Li.THF 8 bears this out and suggests a significant new level of control in zincate-induced DoM chemistry through the combination of experiment and DFT studies.     

Ligand-activated lithium-mediated zincation of N-phenylpyrrole

Metalation of N-phenylpyrrole by using an in situ mixture of ZnCl(2)TMEDA (0.5 equiv; TMEDA=N,N,N',N'-tetramethylethylenediamine) and LiTMP (1.5 equiv; TMP=2,2,6,6-tetramethylpiperidino) was optimized. The reaction carried out at room temperature in THF resulted in incomplete metalation (56 % conversion) and selectivity (mixture of 2-iodo and 2,2'-diiodo derivatives in an 86:14 ratio after trapping with iodine). By using diethyl ether (DEE), toluene, or hexane instead of THF, low conversions of 17, 38, or 23 % were observed, respectively, but the formation of the diiodide was avoided. When hexane was used as solvent, strong lithium-complexing ligands such as [12]crown-4 and N,N'-dimethylpropylideneurea (DMPU) inhibited the reaction whereas more (hemi)labile ligands (TMEDA>THF approximately DME) favored it. This result shows that a temporary accessibility of lithium to interact with the rest of the base and/or the substrate is a prerequisite for an efficient metalation. A 75 % yield of 2-iodo-N-phenylpyrrole was obtained after reaction with the base in the presence of five equivalents of TMEDA for two hours at room temperature, and subsequent trapping with iodine. We were able to successfully replace the spare TMP with a less expensive butyl group.