Matthias Vogt

Amino olefin nickel(I) and nickel(0) complexes as dehydrogenation catalysts for amine boranes

A rare paramagnetic organometallic nickel(I) olefin complex can be isolated using the ligand bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine. This complex and related nickel(0) hydride complexes show very high catalytic activity in the dehydrogenation of dimethylamino borane with release of one equivalent of dihydrogen.

OO Bond Activation in Heterobimetallic Peroxides: Synthesis of the Peroxide [LNi(μ,η2:η2‐O2)K] and its Conversion into a Bis(μ‐Hydroxo) Nickel Zinc Complex

The activation of dioxygen for the subsequent oxygenation or oxidation of hydrocarbons is of importance not only in academia and industrial laboratories but also in nature. Some natural systems employ metalloenzymes containing two redox-active metal centers (e.g., tyrosinase or soluble methane monooxygenase), which cooperate in the activation process. On contact with O2, in a first step the oxidation state of each metal atom is increased by + I and a peroxide unit is formed, which may represent the active species or just an intermediate. In a second step, the O O bond can undergo cleavage with concomitant increase of the metal oxidation states by another unit so that M(m-O)2M cores result, which then perform the oxidation chemistry. Attempts to mimic this kind of reactivity by low-molecular-weight analogues have revealed that whether or not step two occurs can depend on subtle changes of properties of the ligands, counterions, and solvents. 2] Complexes with M(m-O)2M moieties (M = Cu, Fe, Ni, Co) usually exhibit electrophilic character and can abstract hydrogen atoms from ligand substituents or exogenous sources such as solvents or added sacrificial substrates. Heterobimetallic species have attracted great interest because the combination of metals with different individual characteristics may lead to synergistic effects arising from asymmetry. The cyctochrome c oxidase, in which a Cu center cooperates with a (heme)Fe unit for the activation of O2, serves as a natural example. The synthesis of mixed metal complexes LM(m-O)2M’L’, however, is far more difficult than the preparation of homobimetallic analogues. In the past, two strategies were pursued: 1) reaction of heterobimetallic M–M’ precursors with O2, and 2) a two-step process in which a well-defined metal dioxygen complex is treated with a reducing metal compound. These routes have allowed for the preparation of desired heterobimetallic oxo complexes with the metal combinations Cu–Ni, Cu–Pd, Cu–Pt, Cu–Ge, Pt–Mo, Pd–Ge, and Pt–Ge. It is well known that NiO2 complexes can serve as efficient oxidants in organic synthesis. Furthermore, NiO2 intermediates have been inferred as highly active species in several C H bond transformations. The consequences arising from the presence of a heterometal ion for O O bond activation could not be explored owing to the lack of suitable precursors. Recently, some of us reported on the synthesis of the first isolable nickel(II) superoxo complex [LNi(O2)] (1) (L = CH(CMeNR)2, R = 2,6-iPr2C6H3; Scheme 1), [8] which could serve as a suitable precursor for the synthesis of heterobimetallic Ni–M peroxo complexes in accordance with the synthetic strategy (2) mentioned above. Herein, we report the formation of the first heterobimetallic nickel(II) peroxo complex [LNi(m,h:h-O2)K] (2) and a metal-exchange reaction that leads to a heterobimetallic bis(m-hydroxo) complex [LNi(m-

Zero-Valent Amino-Olefin Cobalt Complexes as Catalysts for Oxygen Atom Transfer Reactions from Nitrous Oxide

The synthesis and characterization of several zero-valent cobalt complexes with a bis(olefin)-amino ligand is presented. Some of these complexes proved to be efficient catalysts for the selective oxidation of secondary and allylic phosphanes, as well as diphosphanes, even with a direct P-P bond. With 5 mol % catalyst loadings the oxidations proceed under mild conditions (25-70 °C, 7-22 h, 2 bar N2 O) and afford good to excellent yields (65-98 %). In this process, the greenhouse gas N2 O is catalytically converted into benign N2 and added-value organophosphorus compounds, some of which are difficult to obtain otherwise.

CO2-based hydrogen storage – hydrogen liberation from methanol/water mixtures and from anhydrous methanol

Abstract New strategies for the reforming of methanol under mild conditions on the basis of heterogeneous and molecular catalysts have raised the hopes and expectations on this fuel. This contribution will focus on the progress achieved in the production of hydrogen from aqueous and anhydrous methanol with molecular and heterogeneous catalysts. The report entails thermal approaches, as well as light-triggered dehydrogenation reactions. A comparison of the efficiency and mechanistic aspects will be made and principles of catalytic pathways operating in biological systems will be also addressed.