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The mechanism of the experimentally observed formation of the five-membered nickela−carboxylate complex in the nickel(0)-assisted oxidative coupling of CO2 and C2H4 is revealed by means of density functional calculations. The reliability of the applied DFT methodology has been first assessed by comparison to high-level coupled-cluster calculations on a relevant model reaction. The most important stationary points on the potential energy surface associated with the title reaction have been located, and low-energy reaction pathways have been identified. We show that the C−C bond formation occurs in a single step by the reaction of a nickel−ethylene complex with an incoming CO2 molecule. The solvent effect and the influence of the ancillary ligands on the reaction energetics are examined, and both are shown to be important in these reactions.

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The influence of the steric properties of chelating diamines on the self‐assembly of [Pd(N∩N)](NO3)2 complexes with 4,4′‐bpy as bridging ligand has been studied by 1H NMR spectroscopy and X‐ray diffraction (N∩N = N,N,N′,N′‐tetramethylethylenediamine, N,N,N′,N′‐tetraethylethylenediamine, 1,3‐diaminopropane, N,N′‐dimethylpiperazine, homopiperazine and ethylenediamine). Based on crystallographic data, the steric bulk of the chelating amines in the [Pd(N∩N)]2+ cations has been characterised in two different ways. A temperature‐ and concentration‐sensitive trimer/tetramer equilibrium was observed by NMR spectroscopy with every diamine, in which the trimeric species dominated when the chelating amine was the bulky tetraethylethylenediamine. Although the formation of tetramers was preferred with diamines of decreasing steric demands, trimeric aggregates could be observed even with the least congested homopiperazine and ethylenediamine complexes. The distribution of the tectons between the two constituents follows the trend predicted by the steric features of the coordinated diamine ligands. Diffusion NMR spectroscopy has proved to be an efficient tool in the identification of self‐assembled species. The trimer/tetramer equilibrium established with tetramethylethylenediamine as chelating ligand has been observed in solution by using wide‐angle X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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