Stereospecific carbene polymerisation with oxygenated Rh(diene) species

Breath-taking activation: Stereoregular carbene polymerization proceeds via cationic [(allyl)RhIII–polymeryl]+ species. These are most efficiently generated by oxygenation of the [(diene)RhI] precatalysts, which involves an unusual rearrangement of 2-rhodaoxetane intermediates. This discovery gives detailed insight in the reaction mechanism.Financial support from the European Research Council (ERC, grant agreement 202886-CatCIR), the Netherlands Organization for Scientific Research (NWO-CW), the Dutch Polymer Institute (DPI projects no. 646/647), the University of Amsterdam, the DFG (SFB-583 and Major Research Instrumentation Program) and MICINN/FEDER (Projects CTQ2008-03860 and CTQ2011-22516) is gratefully acknowledged.Peer Reviewe

Stepwise coordination of PtII-180°and PdII-90° metal fragments to the purine nucleobase 9-methylhypoxanthine affords a closed octadecanuclear Pt6Pd12 cluster

Crossing the line: A pH-induced >crossover> in 3D shapes of supramolecular constructs derived from trans(NH3)2Pt II, [PdII(en)], and the purine model nucleobase 9-methylhypoxanthine (see figure) is reported in which [Pd(en)(H 2O)]2+ and [Pd(en)(OH)]+ are the decisive players (en=ethylenediamine). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Financial support from Deutsche Forschungsgemeinschaft, the TU Dortmund, and the Fonds der Chemischen Industrie are gratefully acknowledged. P.J.S.M. thanks the Spanish Ministerio de Economía y Competitividad for funding through the “Ramón y Cajal” program.Peer Reviewe

Dramatically Accelerated Selective Oxygen-Atom Transfer by a Nonheme Iron(IV)-Oxo Complex: Tuning of the First and Second Coordination Spheres

The new ligand N3Py^amideSR and its Fe^II complex [Fe^II(N3Py^amideSR)]­(BF₄)₂ (<b>1</b>) are described. Reaction of <b>1</b> with PhIO at −40 °C gives metastable [Fe^IV(O)­(N3Py^amideSR)]²⁺ (<b>2</b>), containing a sulfide ligand and a single amide H-bond donor in proximity to the terminal oxo group. Direct evidence for H-bonding is seen in a structural analogue, [Fe^II(Cl)­(N3Py^amideSR)]­(BF₄)₂ (<b>3</b>). Complex <b>2</b> exhibits rapid O-atom transfer (OAT) toward external sulfide substrates, but no intramolecular OAT. However, direct <i>S</i>-oxygenation does occur in the reaction of <b>1</b> with mCPBA, yielding sulfoxide-ligated [Fe^II(N3Py^amideS­(O)­R)]­(BF₄)₂ (<b>4</b>). Catalytic OAT with <b>1</b> was also observed

Characterization of Porphyrin-Co(III)-'Nitrene Radical' Species Relevant in Catalytic Nitrene Transfer Reactions

To fully characterize the Co-III-'nitrene radical' species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV-vis, IR, VCD, UHR-ESI-MS, and XANES/XAFS measurements. Reactions of cobalt(II) porphyrins 1(P1) (P1 = meso-tetraphenylporphyrin (TPP)) and 1(P2) (P2 = 3,5-Di(t)Bu-ChenPhyrin) with organic azides 2(Ns) (NsN(3)), 2(Ts) (TsN3), and 2(Troc) (TrocN(3)) led to the formation of mono-nitrene species 3(Ns)(P1), 3(Ts)(P2), and 3(Troc)(P2), respectively, which are best described as [Co-III(por)(NR ''(center dot-))] nitrene radicals (imidyl radicals) resulting from single electron transfer from the cobalt(II) porphyrin to the 'nitrene' moiety (Ns: R '' = -SO2-p-C6H5NO2; Ts: R '' = -SO2C6H6; Troc: R '' = -C(O)OCH2CCl3). Remarkably, the reaction of 1(P1) with N-nosyl iminoiodane (PhI=NNs) 4(Ns) led to the formation of a bis-nitrene species 5(Ns)(P1). This species is best described as a triple-radical complex [(por ''(center dot-))Co-III(NR ''(center dot-))(2)] containing three ligand-centered unpaired electrons: two nitrene radicals (NR?(-)) and one oxidized porphyrin radical (por(center dot-)). Thus, the formation of the second nitrene radical involves another intramolecular one-electron transfer to the "nitrene" moiety, but now from the porphyrin ring instead of the metal center. Interestingly, this bis-nitrene species is observed only on reacting 4(Ns) with 1(P1). Reaction of the more bulky 1(P2) with 4(Ns) results again in formation of mainly mono-nitrene species 3(Ns)(P2) according to EPR and ESI-MS spectroscopic studies. The mono- and bis-nitrene species were initially expected to be five- and six-coordinate species, respectively, but XANES data revealed that both mono- and bis-nitrene species are six-coordinate Oh species. The nature of the sixth ligand bound to cobalt(III) in the mono-nitrene case remains elusive, but some plausible candidates are NH3, NH2-, NsNH(-), and OH-; NsNH(-) being the most plausible. Conversion of mono-nitrene species 3(Ns)(P1) into bis-nitrene species 5(Ns)(P1) upon reaction with 4(Ns) was demonstrated. Solutions containing 3(Ns)(P1) and 5(Ns)(P1) proved to be still active in catalytic aziridination of styrene, consistent with their proposed key involvement in nitrene transfer reactions mediated by cobalt(II) porphyrins