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)

A series of titanium complexes have been prepared using either salt metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H {Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine} (1) with [TiCl(4)(THF)(2)] results in the formation of a nucleophilic ring-opening product of the coordinated tetrahydrofuran (THF) ligand [Ap*TiCl(2)(OC(4)H(8)Cl)] (7). Alkylation with benzylmagnesium chloride gave rise to the corresponding benzyl complex [Ap*TiBn(2)(OC(4)H(8)Cl)] (8). However, THF ring opening was overcome by adopting an amine elimination route instead of salt metathesis. Mono(aminopyridinato)titanium trichloro complexes were prepared in high yields using [(CH(3))(2)NTiCl(3)], together with the corresponding sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO ("dry methylaluminoxane"). The catalysts show moderate activity toward propene polymerization, while ethylene-propylene copolymers in high-productivity with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of 2-ethylidenenorbornene (ENB) with ethylene or ethylene-propylene, together with a very good incorporation of ENB. In all cases, the activity increases with an increase in the steric bulk of the protecting ligand.

Abstract. Triorganoboranes BR 3 , Et-9-BBN, BPh 3 , and B(C 6 F 5 ) 3 , were compared in their reactivity towards various dialkynyl(diorgano)tin. 1,1-Carboboration took place readily in two consecutive steps (inter-and intramolecular), leading either to stannoles or to 1,4-stannabora-cyclohexa-2,5-dienes, or mixtures thereof. The weakest Lewis-acidic triorganoboranes BEt 3 and Et-9-BBN afford selectively stannoles with

Lithiated 4‐methyl‐2‐[(trimethylsilyl)amino]pyridine (ApTMSH) undergoes a salt metathesis reaction with [ScCl3(thf)3] and FeCl3, at low temperature in thf, to yield the homoleptic complexes [Sc(ApTMS)3] (1) and [Fe(ApTMS)3] (2). An analogous reaction with MnCl2, CoCl2 and FeCl2 using two equivalents of 4‐tert‐butylpyridine (tBuPy) as additional donor ligand affords the structurally analogous cis complexes [Mn(ApTMS)2(tBuPy)2] (3), [Co(ApTMS)2(tBuPy)2] (4) and [Fe(ApTMS)2(tBuPy)2] (5). If FeCl2 is used without tBuPy, the highly symmetric trinuclear complex [Fe3(ApTMS)6Li2O] (6) is obtained. Furthermore, the use of ZnCl2 in a reaction with lithiated ApTMSH yields the dimeric complex [Zn2(ApTMS)4] (7) in which two ApTMS ligands bridge the two metals. All complexes have been characterised by X‐ray crystal structure analysis. To the best of our knowledge, complexes 1 and 2 and 5 are the first scandium and iron aminopyridinates, respectively, and complex 3 is the first manganese aminopyridinate complex which contains no additional anionic ligand. Complexes 4 and 7 are rare examples of cobalt and zinc aminopyridinates. This study proves that aminopyridinato ligands are highly universal ligands since they are able to stabilize early and late transition metals. Aminopyridinates of every first row transition metal are now available. The magnetic properties of all paramagnetic complexes were investigated. All complexes are high‐spin complexes and the trinuclear iron complex 6 exhibits a weak antiferromagnetic coupling.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)