Highest possible symmetry! Nine Sn atoms are arranged to give an almost perfect sphere around a Cu atom in the endohedrally filled Zintl ion [Cu@Sn9]3−. The rapid equilibration of the nine Sn atoms on the spectral NMR timescale leads to an exceptionally sharp 63Cu NMR signal. In contrast to the more common endohedrally filled fullerenes, the title complexes can be synthesized in macroscopic quantities as [K([2.2.2]crypt)]+ salts.

The activation and cleavage of C–C single bonds mediated by transition metal complexes is one of the most challenging reactions, both practically and in terms of understanding, in the field of metal organic chemistry. In this review the fundamental reactions – oxidative addition, β‐carbon elimination, retro‐allylation, and radical cleavage – so far successfully applied for this transformation are discussed in terms of their mechanisms, their intrinsic problems, and their published examples, which are still fairly rare. Decarbonylation, as another fundamental reaction, is only touched briefly. This group of reactions is today poised to set aside its shadow existence as an exotic reaction class. Meanwhile the number of catalytic and even enantioselective processes involvingC–C single bond cleavage is slowly increasing, although the substrates used in these reactions are still limited to quite special connection patterns. The basic challenges for the future and the paradigms concerning this reaction are presented.

Experimental and theoretical charge density studies and molecular orbital analyses suggest that the complexes [Cp2Ti(PMe3)SiH2Ph2] (1) and [Cp2Ti(PMe3)SiHCl3] (2) display virtually the same electronic structures. No evidence for a significant interligand hypervalent interaction could be identified for 2. A bonding concept for transition-metal hydrosilane complexes aims to identify the true key parameters for a selective activation of the individual M-Si and Si-H bonds.

We will outline that the sign and magnitude of J(Si,H) coupling constants provide a highly sensitive tool to measure the extent of Si-H bond activation in nonclassical silane complexes. Up to now, this structure-property relationship was obscured by erroneous J(Si,H) sign determinations in the literature. These new findings also help to identify the salient control parameters of the Si-H bond activation process in nonclassical silane complexes.

SUMMARY: As reported recently, our results about the ring distribution in the polybutadiene (resp. cyclobutene) system at the metathesis polymerization/depolymerization equilibrium differ strongly from literature data published earlier. To support our findings with thermodynamic data, the product spectrum in toluene was determined at equilibrium in dependence of the feed concentration (0.1 to 1.8 mol [2C 4 H 6 2]/L) and the temperature (4 8C to 508C). For better understanding of the ring-chain distribution we introduced the turning point. This is the feed concentration at which the differential change of the ring equilibrium concentration equals that of the chains. In contrast to the terminology used until now, as for example "cut off point" or "critical concentration", the turning point describes what exactly happens in the system and has a physical meaning not only for the integral ring concentration but also for the concentration of every individual ring. The integral turning point was determined, it is temperature dependent. A strong preference for the cyclic trimers (especially for the all-trans one) was observed, which is the only ring size to show a temperature influence as a whole. The all-trans cyclic trimer is built the most exothermically in comparison with any other cyclic geometric isomer. The ctt-isomer is built endothermically. Tetramers are disfavoured regarding the pentamers. The amount of trans double bonds in the trimers at 25 8C is 97%. The trans amount decreases with increasing ring size and approaches a trans/cis ratio of about 83/17 at 25 8C. In the whole temperature region the polymeric chains show a most probable distribution. The trans/cis ratio in the polymeric fraction as a function of the temperature follows a clear tendency in accordance with the thermodynamic prediction. The trans respectively cis double bonds are distributed randomly across the chains. For all cases mentioned, quantitative thermodynamic data are presented.