AbstractWith N-aromatic substituted diazadienes (DAD) and R3 = R4 = aryl) nickel(O) forms complexes of composition (DAD)2Ni which are prepared preferably by reduction of Ni(II) salts in the presence of DAD. The groups R1, R2 and/or the o-substituents of the aryl system determine the conformation of the DAD and its sterical ligand properties. An X-ray structure analysis of (DAD)2Ni 17 (DAD = glyoxalbis( 2,6-dimethyl-phenylimine)) shows a dihedral angle of 44° between the two chelate planes. With twisted N-aryl substituents nickel seems to prefer planar coordination (formal low spin Ni(II)) of two DADs over tetrahedrally coordinated formal nickel(O) state.

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Belt-Shaped Molecules by a Repetitive Synthetic StrategyBelt-shaped molecules of the general type 2 containing up to five benzene ring units (cf. 37

~ ~~~~ Aus dem Diazadien (DAD) Glyoxalbis(diisopropylmethylimin) (1) und wasserfreiem Nickelbromid wird (DAD)NiBr, (2) erhalten, dessen Reaktion mit Hauptgruppenmetall-alkylen zu wenig stabilen Zwischenprodukten fuhrt. Mit dem sperrigen o-Tolylmagnesiumbromid wird unter formaler HBr-Abspaltung die Metallierung des Diisopropylmethyl-Rests von 2 in y-Stellung zum nachsten aktivierenden Zentrum (N) unter Bildung eines N -C-Chelatrings erreicht. Eigenschaften und Struktur dieses Produkts (3) einer neuartigen Alkanaktivierung werden diskutiert. Metalation of a Non-activated Alkyl Group in Nickel Complexes')The diazadiene (DAD) glyoxalbis(diisopropy1methylimine) (1) reacts with anhydrous nickel bromide to yield (DAD)NiBr, (2). Its reactions with main group metal alkyls lead to rather unstable intermediates. With the bulky o-tolylmagnesium bromideunder formal HBr abstractionmetalation of the diisopropylmethyl substituent occurs in y-position to the next activating center (N) with formation of an N-C chelate. Properties and structure of this product 3 from this novel alkane activation reaction are discussed.

Abstract Reduction of anhydrous nickel(II) compounds in the presence of diazadienes RN=CR'-CR' = NR, |(DAD), yields (DAD)2Ni(0). This complex 1 with R = CH(i-C3H7)2 is especially reactive and comproportionates with DADNiBr2 (2) to yield the bromobridged dimeric nickel(I) species (DADNiBr)2 (3). The crystal and molecular structure of 3 has been determined by single crystal X-ray diffraction: Space group Pbca with a = 1225.8(12), b = 1474.8(14) and c = 2167.4(22) pm; Ra = 0.076, 1034 reflections. Catalytic tetramerisation of substituted alkynes with 1 is discussed in view of the very easy formation of dimers 3.