Klaus-Richard Pörschke

tmeda-Nickel-Komplexe: III. (N,N,N′,N′-Tetramethylethylendiamin)-(dimethyl)nickel(II)

Abstract (tmeda)Ni(acac) 2 reacts with the main group metal compounds (tmeda)Mg-(CH 3 ) 2 , (tmeda)&[;Al(CH 3 ) 3 &]; 2 , and (C 2 H 5 O)Al(CH 3 ) 2 at 0°C to give (tmeda)Ni-(CH 3 ) 2 ( 1 ), which can be isolated as fine yellow crystals in 50–80% yield. Complex 1 , which is the simplest dialkyl nickel(II) compound with a “hard” donor ligand, is surprisingly stable and decomposes only at 79°C. 1 is converted by bipy to (bipy)Ni(CH 3 ) 2 and by Me 2 PC 2 H 4 PMe 2 to (Me 2 PC 2 H 4 PMe 2 )Ni(CH 3 ) 2 . Upon reaction of 1 with strong π-acceptor molecules (acrylic acid methylester, methyl vinyl ketone, acrylonitrile, tetracyanoethene, tetrafluoroethene, maleic anhydride) reductive elimination of the methyl groups takes place to give the complexes (tmeda)Ni(π-ligand) n ( n = 1, 2) and ethane.

Synthese, Struktur und Reaktivität von (tmeda)Ni(C2F4)

Abstract The reactions of Ni(cod) 2 (cod  1,5-cyclooctadiene), Ni(cdt) (cdt  trans , trans , trans -1,5,9-cyclododecatriene), and Ni(C 2 H 4 ) 3 with N , N , N ′, N ′-tetramethyl-ethylenediamine (tmeda) and tetrafluoroethene in ether yield almost quantitatively yellow needles of (tmeda)Ni(C 2 F 4 ) ( 1 ). 1 can also be obtained from the reaction of Ni(η 3 -C 3 H 5 ) 2 /tmeda or (tmeda)Ni(CH 3 ) 2 with C 2 F 4 . An X-ray diffraction study of the crystal structure of 1 confirms the trigonal-planar (or pseudo-square-planar) coordination of nickel by the tmeda and C 2 F 4 ligands. 1 reacts slowly with ethyne at 20°C to afford red-brown crystals of the nickelacyclopentene derivative (tmeda)Ni(CHCHC 2 F 4 ) ( 2 ).

Pyridine-based mono(ligand)nickel(0) complexes of 1,6-heptadiene, 1-phenyl-2-trimethylsilyl-acetylene, and 1,4-bis(trimethylsilyl)-1,3-butadiyne

Abstract The reaction of rac/meso-(μ-η2,η2-C7H12){Ni(η2,η2-C7H12)}2 with 2,6-dimethylpyridine (Me2py) affords (Me2py)Ni(η2,η2-C7H12) (1). Complex 1 serves as precursor for the preparation of the Ni(0)-bis(alkyne) complexes (Me2py)Ni(η2-PhCCSiMe3)2 (2) and {(Me2py)Ni}2(μ-η2,η2-Me3SiCCCCSiMe3)2 (3). The latter is the first complex in which two metal centers are bridged by two butadiyne ligands. For 1–3 the molecular structures have been determined by X-ray crystallography.

Cation–Cation Pairing by N-C-H···O Hydrogen Bonds

The pairing of ions of opposite charge is a fundamental principle in chemistry, and is widely applied in synthesis and catalysis. In contrast, cation-cation association remains an elusive concept, lacking in supporting experimental evidence. While studying the structure and properties of 4-oxopiperidinium salts [OC5 H8 NH2 ]X for a series of anions X(-) of decreasing basicity, we observed a gradual self-association of the cations, concluding in the formation of an isolated dicationic pair. In 4-oxopiperidinium bis(trifluoromethylsulfonyl)amide, the cations are linked by NH⋅⋅⋅OC hydrogen bonds to form chains, flanked by hydrogen bonds to the anions. In the tetra(perfluoro-tert-butoxy)aluminate salt, the anions are fully separated from the cations, and the cations associate pairwise by NCH⋅⋅⋅OC hydrogen bonds. The compounds represent the first genuine examples of self-association of simple organic cations based merely on hydrogen bonding as evidenced by X-ray structure analysis, and provide a paradigm for an extension of this class of compounds.

tmeda-Nickel-Komplexe: I. (tmeda)Ni(η2-C4H6)2 und {(tmeda)Ni(η2C4H6)}2(η2,η2-C4H6)

Abstract Tris(ethene)nickel(0) reacts with tmeda and butadiene in ether below −40°C to yield a deep-red solution of (tmeda)Ni(η2-C4H6)2 (3a), from which red crystals of the thermolabile dinuclear complex {(tmeda)Ni(η2-C4H6)}2(η2,η2-C4H6) (3b) can be separated. Results in the formation of mononuclear 3a, which also forms upon dissociation of 3b in solution, was identified from its 1H and 13C NMR spectra. Above −40°C, 3a,b decompose in solution, which coupling of the butadiene ligands to afford Ni(η3,η3,η2-C12H18), which was shown to be an intermediate of the nickel-catalyzed cyclotrimerisation reaction of butadiene. Thus 3a,b are the first butadiene complexes of nickel that are catalytically active despite the presence of stabilizing ligands.

Cs[H2NB2(C6F5)6] Featuring an Unequivocal 16-Coordinate Cation

Cesium bis(perfluoro-triphenylborane)amide, Cs[H2NB2(C6F5)6] (1), has been prepared by the reaction of sodium salt and CsF in dichloromethane and water. The compound is exceptional for a [H2NB2(C6F5)6](-) salt in that it contains a monatomic solute-free cation. Determination of the molecular structure revealed a novel C2 symmetrical conformation of the weakly coordinating [H2NB2(C6F5)6](-) anion, which gives rise to an unprecedented 16-coordinate (CN 16) Cs(+) cation in a likewise unprecedented tetracosahedral arrangement of F atoms. The poor solubility of 1 allows nearly quantitative separation of Cs(+) from water, which suggests potential applications as an effective (134/137)Cs remover from nuclear waste solutions, administration as an antidote for (134/137)Cs poisoning, and use for (131/137)Cs radiotherapy (brachytherapy). Rb[H2NB2(C6F5)6]·CH2Cl2 (2) has also been characterized, featuring two inequivalent Rb(+) cations having CN 10, one of which involves Rb(+)(η(2)-Cl2CH2)2 coordination.

Reaktion von (1,4-diazabutadien)bis(alken)nickel(0)-Komplexen mit Ethin

Abstract The (1,4-diazabutadiene)bis(alkene)nickel(0) complexes ( i Pr 2 Ph) 2 -dadNi(C 2 H 4 ) 2 [( i Pr 2 Ph) 2 -dad = 2,6- i Pr 2 C 6 H 3 −NCHCHN−C 6 H 3 -2,6- i Pr 2 ] ( 1 ) and ( i Pr 2 Ph) 2 -dadNi(η 2 ,η 2 -C 6 H 10 ) ( 2 ) react with ethyne above −100°C ( 1 ) or −30°C ( 2 ) with coupling of two ethyne molecules to afford the dinuclear complex [( i Pr 2 Ph) 2 - dadNi] 2 (C 4 H 4 ) ( 3 ) which contains a ferrol-type nickelacyclopentadiene-nickel(0) bonding element. A single-crystal X-ray structure study of 3 revealed strongly distorted coordination geometries of the nickel centers, which are also present in solution at low temperature ( 1 H, 13 C-NMR). At higher temperatures dynamic processes take place by which the coordinative distortions at the nickel centers are reversed and the bonding situations of the nickel atoms are exchanged. However, a rotation of the phenyl groups around the NC bonds can be excluded. Similarly, [(Me 2 Ph) 2 -dadNi] 2 (C 4 H 4 ) ( 4 ) has been obtained and characterized.

Organonickel(IV) Chemistry: A New Catalyst?

With scorpionate ligands finding their way into organonickel chemistry, the state of the art of present-day nickel(IV) chemistry is highlighted. Will rapid CX coupling reactions emerge as a domain of higher-oxidation-state nickel chemistry?

Struktur und Dynamik von [(2,6-Me2Ph-dad)Ni]2{σ2(1,4),η4(1-4)-C4H4}

Zusammenfassung Reaction of the (1,4-diazabutadiene)bis(alkene)nickel(0) complexes (2,6-Me 2 Ph-dad)Ni(C 2 H 4 ) 2 and (2,6-Me 2 Ph-dad)Ni(η 2 ,η 2 -C 6 H 10 ) with ethyne gives the dinuclear nickelole complex [(2,6-Me 2 Ph-dad)Ni] 2 {σ 2 (1,4),η 4 (1–4)-C 4 H 4 } ( 2 ). A single-crystal X-ray structure study of 2 ·0.5 toluene ( 2a ) reveals strongly distorted coordination geometries of the formally nickel(II) and nickel(O) centres. From the 1 H and 13 C NMR spectra of dissolved 2 it can be concluded that a rapid dynamic process proceeds in solution even at −80°C (!), presumably a rotation of the (2,6-Me 2 Ph-dad)Ni 0 fragment around the bonding axis to the nickelacyclopentadiene component. At higher temperatures a further dynamic process takes place, leading to an exchange of the bonding environments of the nickel atoms.

Synthese und Reactivität von (2,6-iPr2Ph-dad)Ni(C2F4)☆

Abstract Upon warming the reaction mixture of Ni(cdt), C 2 F 4 , and 2,6- i Pr 2 Ph-dad in THF from −78°C to room temperature the red-violet complex (2,6- i Pr 2 Ph-dad)Ni(C 2 F 4 ) ( 1 ) is obtained. 1 reacts with ethene already at −78°C by coupling of the olefinic ligands with the nickel atom to form the blue nickelatetrafluoro-cyclopentane compound (2,6- i Pr 2 Ph-dad)Ni(C 2 H 4 C 2 F 4 ) ( 2 ).