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A hydrocarbon‐soluble barium anthracene complex was prepared by means of metal vapour synthesis. Reaction of 9,10‐bis(trimethylsilyl)anthracene (Anth′′) with barium vapour gave deep purple Ba(Anth′′) which after extraction with diethyl ether crystallised as the cyclic octamer [Ba(Anth′′)⋅Et2O]8. Dissolution in benzene or toluene led to replacement of the Et2O ligand with a softer arene ligand and isolation of Ba(Anth′′)⋅arene. Diffusion ordered spectroscopy (DOSY NMR) measurements in benzene‐d6 indicate solution species with a molecular weight that equals a trimeric constitution. Natural population analysis (NPA) assigned charges of +1.70 and −1.70 to Ba and Anth′′, respectively, relating to highly ionic Ba2+/Anth′′2− bonding. Preliminary reactivity studies with air, Ph2C=NPh, or H2 show that the complex reacts as a Ba0 synthon by release of neutral Anth′′. This soluble molecular Ba0/BaII redox synthon provides new routes for the syntheses of barium complexes under mild conditions. [ABSTRACT FROM AUTHOR]

The spectral analysis of the 29 valence electron (ve) complexes Cp*Fe(Et2C2B3H2-5-R)CoCp* (1a, R = H; 1b, R = Cl; 1c, R = Br) confirm the association between the unpaired electron and iron, suggesting a formal oxidation state of Fe(III). The paramagnetic 31 ve dianion 1a(super 2-) has the unpaired electron on cobalt. The mixed-ligand 29 ve FeCo complex Cp*Fe(Et2C2B3H3)CoCp and the diamagnetic 30 ve dicobalt complexes are also investigated.

Cyclic voltammetry, 1HNMR and ESR studies of paramagnetic anionic species help examine the redox characteristics of various cobaltacarborane sandwich complexes. Analysis of NMR chemical shift helps assign paramagnetic NMR signals and yields more information about the influence of reductions in various regions of the molecules. NMR and ESR studies reveal that reduction occurs mainly in cobalt, and the effects of reduction is significant for the Cp protons.

Cyclic voltammetry, NMR and ESR spectroscopy were used in the study of the electrochemical behavior of the ferracarborane clusters Cp*FeIIH(Et2C2B4H4) andCp*FeIII(Et2C2B4H4) and the phenylene-linked diiron species (Et2C2B4H4)FeIIH(C5Me4-C6H4-C5Me4)FeIII(Et2C2B4H4), ((Et2C2B4H4)FeH(C5Me4))2C6H4 and ((Et2C2B4H4)FeIII(C5Me4))2C6H4. Results showedthe importance of the R2C2B4H4(super 2-) ligands as organometallic synthetic agents and as mono- and dimetallic complex electronic stabilizers.

Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non‐conjugated) mono‐, di‐ and tri‐substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect. [ABSTRACT FROM AUTHOR]

Tetra-tert-butyl-P5-deltacyclene 5 represents one of only two asymmetric P-C cage compounds, which are available in highly enantiomerically enriched versions. This paper reports about stereoselective substitution reactions of 5 to develop the chemistry of optically active P-C cages further. Electrophilic substitution of the only secondary phosphorus atom P1 of the cage with methyl and benzyl groups was achieved with 92% and _99% de, but the yields of the reactions are limited due to competing processes. The uncatalyzed hydrophosphination reaction of a monosubstituted allene and two α,β-unsaturated carbonyl compounds with 5 proved to be the method of choice. cis- Butanone-P5-deltacyclene 12 is formed in 92% yield and with >99% de and cis-pentanone-P5-deltacyclene 13a is accessible with >99% de for P1 and 92% de for the attached carbon atom at the same time. Besides stereoselectivity, the hydrophosphination reaction of 5 performs with a good regioselectivity. The chiral cage 5 controls the stereoselectivity of its reactions for the cage elements as well as for the α position of a substituent. [ABSTRACT FROM AUTHOR]

Cage-chiral P5-deltacyclene 1 is available as a pair of highly enriched P-C cage enantiomers 1′ and 1″, which exist as pairs of epimers a and b. Deprotonation of cage atom P1 initiates a rearrangement reaction, in which P1 and the neighboring carbon atom C4, together with its substituent, change places to form optically active iso-P5-deltacyclene enantiomers 6″ and 6′, again as pairs of epimers. The CD spectra of related pairs of optically active cages 1 and 6 consist of almost mirror-symmetric curves, an indicator of mirror-symmetric cage structures. This surprising result was verified by an absolute structure determination of the W(CO)5 complex 9a″. With the exception of the two cage nuclei that had changed places in relation to starting material 1′, all other cage nuclei of rearrangement product 6a″ occupy mirror-symmetric positions. To the best of our knowledge, this represents the first cage-inversion reaction of an optically active compound. P1 is the only active donor center of 6 involved in the bonding of M(CO)5 fragments (M = Cr, Mo, W). The chiroptical properties of Cr(CO)5 complex 7a′ and W(CO)5 complex 9a″ are almost mirror-symmetric and resemble those of the free cages 6′ and 6″, respectively. The coordinated transition-metal complex fragments do not contribute significantly to the Cotton effects of the P-C cage. A DFT analysis of the deprotonated cage anions [ 1 - H]- and [ 6 - H]- predicts a driving force of -20.3 kcal mol-1 for the rearrangement reaction. [ABSTRACT FROM AUTHOR]