Binuclear nickel(II) complexes with oxalamidinates as bridging ligands: Synthesis and struktures of compounds with planar, tetrahedral, tetragonal-pyramidal, and octahedral coordination [German]

摘要

Oxalamidines R-1-NH-C(=NR2-C(=NR2)-NH-R-1 react selectively with Ni(acac)(2) under formation of the planar complexes [(acac)Ni(oxalamidinate)Ni(acac)]. Two crystal structures of the binuclear complexes with R = R' = Ph (1) or p-tolyl (2) show that the bridging oxalamidinates bind as bidendate Ligands at each Nickel(II) atom. In contrast, the more sterically demanding fragment (Ph3P)NiBr can only coordinate at sterically less demanding oxalamidinates to form complexes of the type [(Ph3P)NiBr](2)(oxalamidinate) with tetrahedral coordination of Ni-II found by X-ray analyses. Oxalamidines containing additional donor atoms in the side arms react very different, but in each case under formation of binuclear complexes, such as [(acac)(2)Ni](2)(H2E) (8) (with R-1: -(CH2)(3)PPh2, R-2: p-tolyl) in which the oxalamidine acts as bidentate neutral P,N-ligand and the Ni-II atom has an octahedral environment. H2F (with R-1: -(CH2)(3)PPh2; R-2: Mesityl), however, yields the planar complex [(acac)Ni](2)(F) (9) with dianionic oxalamidinate under elimination of acetylacetone. There is no coordination of the donor groups of the side arms in the solid state of complex 9, in contrast to the analogous binuclear complex [(acac)Ni](2)(H) 10 (R-1: -CH2-CH2-2-pyridyl, R-2: Mesityl). In this complex a distorted tetragonal-pyramidal coordination of Ni-II is achieved. 2 reacts with an excess of LiCH3 under elimination of the oxalamidinate to form the cluster compound Li-4(THF)(4)-Ni2Me8 in very good yields, while 9 yields the THF poorer cluster Li-2(THF)(2)Li2Ni2Me8 under similar conditions. [References: 17]