Retention of the Zn−Zn bond in [Ge9Zn−ZnGe9]6− and Formation of [(Ge9Zn)−(Ge9)−(ZnGe9)]8− and Polymeric [−(Ge9Zn)2−−]

Reactions of Zn^I₂L₂ (where L=[HC(PPh₂NPh)]⁻) with solutions of the Zintl phase K₄Ge₉ in liquid ammonia lead to retention of the Zn−Zn bond and formation of the anion [(η⁴‐Ge₉)Zn−Zn(η⁴‐Ge₉)]⁶⁻, representing the first complex with a Zn−Zn unit carrying two cluster entities. The trimeric anion [(η⁴‐Ge₉)Zn{μ₂(η¹:η¹Ge₉)}Zn(η⁴‐Ge₉)]⁸⁻ forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn₂Cp*₂ (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with K₄Ge₉ in ethylenediamine yielded the linear polymeric unit {[Zn[μ₂(η⁴:η¹Ge₉)]}²⁻ with the first head‐to‐tail arrangement of ten‐atom closo ‐clusters. All anions were obtained and structurally characterized as [A (2.2.2‐crypt)]⁺ salts (A =K, Rb). Copious computational analyses at a DFT‐PBE0/def2‐TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo ‐[Ge₉Zn]²⁻ and (paramagnetic) [Ge₉Zn]³⁻.     

Metallocages for Metal Anions: Highly Charged [Co@Ge9]5− and [Ru@Sn9]6− Clusters Featuring Spherically Encapsulated Co1− and Ru2− Anions

Endohedral clusters count as molecular models for intermetallic compounds—a class of compounds in which bonding principles are scarcely understood. Herein we report soluble cluster anions with the highest charges on a single cluster to date. The clusters reflect the close analogy between intermetalloid clusters and corresponding coordination polyhedra in intermetallic compounds. We now establish Raman spectroscopy as a reliable probe to assign for the first time the presence of discrete, endohedrally filled clusters in intermetallic phases. The ternary precursor alloys with nominal compositions “K₅Co_1.2Ge₉” and “K₄Ru₃Sn₇” exhibit characteristic bonding modes originating from metal atoms in the center of polyhedral clusters, thus revealing that filled clusters are present in these alloys. We report also on the structural characterization of [Co@Ge₉]^5? ( 1a ) and [Ru@Sn₉]^6? ( 2a ) obtained from solutions of the respective alloys.     

Convergent Total Syntheses of (−)‐Rubriflordilactone B and (−)‐pseudo‐Rubriflordilactone B

A highly convergent strategy for the synthesis of the natural product (?)‐rubriflordilactone B, and the proposed structure of (?)‐pseudo‐rubriflordilactone B, is described. Late stage coupling of diynes containing the respective natural product FG rings with a common AB ring aldehyde precedes rhodium‐catalyzed [2+2+2] alkyne cyclotrimerization to form the natural product skeleton, with the syntheses completed in just one further operation. This work resolves the uncertainty surrounding the identity of pseudo‐rubriflordilactone B and provides a robust platform for further synthetic and biological investigations.     

The lifetimes of gas phase CO2˙− and N2O˙− calculated from the transition probability of the autodetachment process A− → A + e−

A procedure to calculate the quantum mechanical transition probability of a unimolecular primary chemical process, A^? → A + e^? is investigated for the circumstance where A^? and A have different numbers of vibrational and rotational degrees of freedom (one is linear, the other not). A procedure is introduced to deal with the coupling between the vibrational and rotational motions. The proposed method was applied to calculating the lifetimes of CO₂^˙? and N₂O^˙? in the gas phase. The geometry optimizations and frequency calculations for CO₂, CO₂^˙?, N₂O, and N₂O^˙? are performed at HF, MP2, and QCISD(T) levels with 6-31G* or 6–31+G* basis sets, in order to obtain reliable geometric and spectroscopic information on these systems. Lifetimes are calculated for several of the lower vibrational–rotational states of the anions, as well as for the Boltzmann distribution of states at 298 K. The lifetime of the lowest vibrational–rotational state of CO₂^˙?, is 1.03 × 10^?4 s, and of the lowest vibrational state with rotational levels weighted by Boltzmann distribution at 298 K, 1.50 × 10^?4 s. These values are in good agreement with the experimental number, 9.0 ± 2.0 × 10^?5 s, and support the experimental evidence that CO₂^˙? was formed in its ground vibrational level by the techniques used. The lifetime of CO₂^˙? calculated with Boltzmann distribution over its vibrational and rotational levels at 298 K, is 1.51 × 10^?5 s. There are no direct measurements of the lifetime of N₂O^˙?, but it was estimated to be greater than 10^?4 s from experimental evidence. The predicted lifetimes of N₂O^˙?, at its lowest vibrational–rotational state (0 K) and lowest vibrational state with rotational levels weighted by the Boltzmann distribution at 298 K, are 238 and 19.1 s, respectively. The lifetime of N₂O^˙? at thermal equilibrium at 298 K is 6.66 × 10^?2 s, indicating that electron loss from the excited vibrational states of N₂O^˙? is significant. This study represents the first theoretical investigation of CO₂^˙? and N₂O^˙? lifetimes. © 1994 John Wiley & Sons, Inc.     

Total Syntheses of (−)‐Conidiogenone B, (−)‐Conidiogenone,and (−)‐Conidiogenol

Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6–8 consecutive stereocenters. The concise total syntheses of (?)‐conidiogenone B, (?)‐conidiogenone, and (?)‐conidiogenol have been accomplished in 14–17 steps. The present work features a HAT‐mediated alkene–nitrile cyclization to access the cis‐biquinane, a Nicholas/Pauson–Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton.     

Divergent Total Syntheses of (−)‐Daphnilongeranin B and (−)‐Daphenylline

(?)‐Daphnilongeranin B and (?)‐daphenylline are two hexacyclic Daphniphyllum alkaloids, each containing a complex cagelike backbone. Described herein are the first asymmetric total synthesis of (?)‐daphnilongeranin B and a bioinspired synthesis of (?)‐daphenylline with an unusual E ring embedded in a cagelike framework. The key features include an intermolecular [3+2] cycloaddition, a late‐stage aldol cyclization to install the F ring of daphnilongeranin B, and a bioinspired cationic rearrangement leading to the tetrasubstituted benzene ring of daphenylline.     

Darstellung und Charakterisierung von Thiocyanatderivaten der Hydroboratanionen B10H102− und B12H122−

Preparation and Characterization of Thiocyanate Derivatives of the Hydroborate Anions B₁₀H₁₀^2? and B₁₂H₁₂^2? The reaction of B₁₀H₁₀^2? or B₁₂H₁₂^2? with (SCN)₂ in dichloromethane yields mixtures of thiocyanatohydroborates from which the pure isomers 1-and 2-(SCN)B₁₀H₉^2?, 1, 10-(SCN)₂B₁₀H₈^2?, and 1-(SCN)B₁₂H₁₁^2? are isolated by ion exchange chromatography on diethylaminoethyl cellulose. The structures are determined by ¹¹B and ¹¹B{¹H}NMR spectroscopy. There are characteristic chemical shifts due to apical and equatorial substituents, respectively. In B₁₀H₁₀^2? the substitution at apical positions is prefered. The IR and Raman spectra are similar to those of isosteric halogeno derivatives in the region of ν(BH) and of the borate cages. Because of the high frequencies of ν(CN): 2120–2140 cm^?1 S coordination of SCN^? is supposed.     

Short communication: Thermal stability of the diazohydroborate [1‐N2B10H9]−: degradation to [B20H18]2− anion

The thermal stability of the monodiazohydroborate NMe₄[1‐N₂B₁₀H₉] was studied by thermogravimetric analysis. Under two different atmospheres (air and argon), the thermal decomposition starts at a temperature between 140 and 160 °C. The decomposition residue obtained was separated on a silica gel column. ¹¹B NMR, IR and electrospray mass spectroscopy analyses of the different fractions separated showed that the above decomposition produces (NMe₄)₂[B₂₀H₁₈] as major product (90%), along with smaller amounts of residual NMe₄[1‐N₂B₁₀H₉] (5%), (NMe₄)₂[B₁₂H₁₂] and boric acid. Copyright © 2003 John Wiley & Sons, Ltd.     

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one‐step synthesis. The intermetallic compound K_5?xCo_1?xSn₉ was obtained by the reaction of a preformed Co? Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn₉]^5? clusters that are separated by K⁺ ions. The intermetallic compound K_5?xCo_1?xSn₉ readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (2.2.2‐crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]₅[Co₂Sn₁₇]. The novel polyanion [Co₂Sn₁₇]^5? contains two Co‐filled Sn₉ clusters that share one vertex. Both compounds were characterized by single‐crystal X‐ray structure analysis. The diamagnetism of K_5?xCo_1?xSn₉ and the paramagnetism of [K([2.2.2]crypt)]₅[Co₂Sn₁₇] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co^1? atom in an [Sn₉]^4? nido cluster for [Co@Sn₉]^5? and confirm the stability of the paramagnetic [Co₂Sn₁₇]^5? unit.     

Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl₂^˙? radicals with 2-propen-1-o1 and 2-buten-1-o1 as a function of temperature and with 2, 3-dimethyl-2-butene at room temperature. The rate constants were in the range of 10⁶–10⁹ L mol^?1 s^?1, the activation energies were relatively low (1–10 kJ mol^?1), and the pre-exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, E_T(30), and the hydrogen-bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO₄^˙? with 2-propen-1-o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.     

Concise Syntheses of bis‐Strychnos Alkaloids (−)‐Sungucine, (−)‐Isosungucine,and (−)‐Strychnogucine B from (−)‐Strychnine

The first chemical syntheses of complex, bis‐Strychnos alkaloids (?)‐sungucine ( 1 ), (?)‐isosungucine ( 2 ), and (?)‐strychnogucine B ( 3 ) from (?)‐strychnine ( 4 ) is reported. Key steps included (1) the Polonovski–Potier activation of strychnine N‐oxide; (2) a biomimetic Mannich coupling to forge the signature C23?C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH₃CN‐mediated reduction to fashion the ethylidene moieties in 1 – 3 . DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners.     

Total Synthesis of (−)‐Ophiodilactone A and (−)‐Ophiodilactone B

The first asymmetric total synthesis of (?)‐ophiodilactone A and (?)‐ophiodilactone B, isolated from the ophiuroid (Ophiocoma scolopendrina), is reported. The key features of the synthesis include the highly stereocontrolled construction of the structurally congested γ‐lactone/δ‐lactone skeleton through an asymmetric epoxidation, diastereoselective iodolactonization, and intramolecular epoxide‐opening with a carboxylic acid, and biomimetic radical cyclization of ophiodilactone A to ophiodilactone B.     

Binary alkali metal compounds with the zintl anions [Ge9]4− and [Sn9]4−

The binary germanides M₁₂Ge₁₇ and M₄Ge₉ (M ? Na, K, Rb, Cs) and the stannides M₁₂Sn₁₇ and M₄Sn₉ (M ? K, Rb, Cs) were identified by a combination of direct synthesis, thermogravimetric analysis, vibrational spectroscopy, X-ray powder data and single crystal structure analysis. The M₁₂E₁₇ phases contain the cluster anions [E₉]^4? and [E₄]^4? in the ratio 1:2, forming a hierarchical structure with the cluster anions at the atomic positions of the hexagonal Laves phase MgZn₂. Like the M₄E₄ phases, the M₄Ge₉ compounds are hierarchical derivatives of the cubic Cr₃Si structure but with [Ge₉]^4? anions. The thermogravimetric analyses give strong evidence for the existence of at least one more phase with [E₉]^4? and [E₄]^4? clusters and of the clathrate phases M₆E₁₃₆ in addition to the well-known M₈E₄₄□₂ chlathrates.     

Endohedrally Filled [Ni@Sn9]4− and [Co@Sn9]5− Clusters in the Neat Solids Na12Ni1−xSn17 and K13−xCo1−xSn17: Crystal Structure and 119Sn Solid‐State NMR Spectroscopy

A systematic approach to the formation of endohedrally filled atom clusters by a high‐temperature route instead of the more frequent multistep syntheses in solution is presented. Zintl phases Na₁₂Ni_1?xSn₁₇ and K_13?xCo_1?xSn₁₇, containing endohedrally filled intermetalloid clusters [Ni@Sn₉]^4? or [Co@Sn₉]^5? beside [Sn₄]^4?, are obtained from high‐temperature reactions. The arrangement of [Ni@Sn₉]^4? or [Co@Sn₉]^5? and [Sn₄]^4? clusters, which are present in the ratio 1:2, can be regarded as a hierarchical replacement variant of the hexagonal Laves phase MgZn₂ on the Mg and Zn positions, respectively. The alkali‐metal positions are considered for the first time in the hierarchical relationship, which leads to a comprehensive topological parallel and a better understanding of the composition of these compounds. The positions of the alkali‐metal atoms in the title compounds are related to the known inclusion of hydrogen atoms in the voids of Laves phases. The inclusion of Co atoms in the {Sn₉} cages correlates strongly with the number of K vacancies in K_13?xCo_1?xSn₁₇ and K_5?xCo_1?xSn₉, and consequently, all compounds correspond to diamagnetic valence compounds. Owing to their diamagnetism, K_13?xCo_1?xSn₁₇, and K_5?xCo_1?xSn₉, as well as the d‐block metal free binary compounds K₁₂Sn₁₇ and K₄Sn₉, were characterized for the first time by ¹¹⁹Sn solid‐state NMR spectroscopy.