Bonds are at the very heart of chemistry. Although the order of carbon–carbon bonds only extends to triple bonds, metal–metal bond orders of up to five are known for stable compounds, particularly between chromium atoms. Carbometallation and especially carboalumination reactions of carbon–carbon double and triple bonds are a well established synthetic protocol in organometallic chemistry and organic synthesis. We now extend these reactions to compounds containing chromium–chromium quintuple bonds. Analogous reactivity patterns indicate that such quintuple bonds are not as exotic as previously assumed. Yet the particularities of these reactions reflect the specific nature of the high metal–metal bond orders.

The synthesis and structure of a homobimetallic chromium complex is reported. The ligand used to stabilise the quintuply bonded metals is a sterically fine‐tuned guanidinate. A chromium–chromium bond length of 1.7293(12) Å was observed. It is the shortest metal–metal distance reported for a stable compound yet.

A molecular approach to metal-containing ceramics and their application as selective heterogeneous oxidation catalysts is presented. The aminopyridinato copper complex [Cu(2)(Ap(TMS))(2)] (Ap(TMS)H=(4-methylpyridin-2-yl)trimethylsilanylamine) reacts with poly(organosilazanes) via aminopyridine elimination, as shown for the commercially available ceramic precursor HTT 1800. The reaction was studied by (1)H and (13)C NMR spectroscopy. The liberation of the free, protonated ligand Ap(TMS)H is indicative of the copper polycarbosilazane binding. Crosslinking of the copper-modified poly(organosilazane) and subsequent pyrolysis lead to the copper-containing ceramics. The copper is reduced to copper metal during the pyrolysis step up to 1000 degrees C, as observed by solid-state (65)Cu NMR spectroscopy, SEM images, and energy-dispersive spectroscopy (EDS). Powder diffraction experiments verified the presence of crystalline copper. All Cu@SiCN ceramics show catalytic activity towards the oxidation of cycloalkanes using air as oxidant. The selectivity of the reaction increases with increasing copper content. The catalysts are recyclable. This study proves the feasibility of this molecular approach to metal-containing SiCN precursor ceramics by using silylaminopyridinato complexes. Furthermore, the catalytic results confirm the applicability of this new class of metal-containing ceramics as catalysts.

White phosphorus, yellow arsenic, and AsP3 have been successfully activated by a complex with a CrCr quintuple bond in one step leading to the formation of rare terminally bound cyclo‐P42−, cyclo‐As42−, and cyclo‐AsP3 units. The subsequent reaction with an excess of [W(CO)5(thf)] leads to the coordination of one {W(CO)5} fragment in the thermodynamically most stable form according to DFT calculations.

Mono(aminopyridinato) complexes of the type [ApM(CH2C6H5)3] [M = Zr, Hf and Ap = aminopyridinate] were prepared by treating the three different sterically demanding aminopyridines with one equiv. of tetrabenzylzirconium or ‐hafnium. One of the three benzyl groups is η2‐coordinated in the solid state. However all of the three benzyl substituents are equivalent in solution as evidenced by the 1H NMR spectrum. Treatment of these neutral complexes with B(C6F5)3 afforded the corresponding zwitterionic dibenzyl complexes. The η6‐coordination of the phenyl ring of the B‐bound benzyl group to the metal centre was supported by 1H NMR spectroscopy and confirmed by single‐crystal X‐ray diffraction analysis. These zwitterionic complexes show very low activity for ethylene polymerisation at low temperature since the coordination site is blocked by the η6‐coordinated phenyl ring. At elevated temperature, moderate activity with the formation of high molecular weight polyethylene (PE) was observed. An attempted abstraction of the second benzyl group failed when the zwitterionic complexes were treated with an additional equivalent of B(C6F5)3. Using one equiv. of [R2(Me)NH][B(C6F5)4] (R = C16H33–C18H37) instead of B(C6F5)3, moderate activities of ethylene polymerisation were observed. Treatment of the aminopyridinato metal tribenzyls with [R2(Me)NH][B(C6F5)4] (R = C16H33–C18H37) gave active ethylene polymerisation catalysts which produced low molecular weight PE in the case of the zirconium analogues and higher molecular weight PE in the case of the hafnium example. Propylene homopolymerisation under the same conditions failed. Ethylene–propylene copolymers with separated propene units and alternating sequences were observed in the presence of both monomers.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)