Abstract
The low-valent and low-coordinate digermanium complex, K2Ge2[N2Ndipp]2 (2), was synthesize by the sterically hindered three-nitrogen donor ligand, Li2[N2Ndipp] (N2Ndipp = 4-methyl-2,6-(N-2,6-iPr2C6H3)2 pyridine). The bond length of Ge(I)-Ge(I) in 2 is 2.5168(6) Å. Treatment of 2 with GeCl2‧dioxane and SnCl2 gives two linear tetranuclear mixed-valence complexes, [MCl]2Ge2[N2Ndipp]2 (3: M = Ge; 4: M = Sn), respectively. These complexes 2, 3, and 4 are starting materials to synthesize the following low-coordinate multinuclear complexes. Treatment of 2 with ZnI2 also produces a tetranuclear mixed-valence Zn(II)-Ge(I)-Ge(I)-Zn(II) complex, [ZnI]2Ge2[N2Ndipp]2(THF) (5), where the internal Ge(I)-Ge(I) bond length is significantly shortened to 2.4060(6)Å. Reaction of 2 with 1M stock solution of GeCl4 in hexane results in the formation of a inverted V-shape pyramidal trinuclear mixed-valence Ge(III)-Ge(II)-Ge(III) complex, [GeCl2][GeCl]2[N2Ndipp]2 (8), where GeCl4 is reduced to GeCl2 and bridges between two Ge(III) atoms. Similar to molecular wire, reaction of 3 or 4 with KNCS undergoes SN2 reaction, giving tetranuclear complexes, [MNCS]2Ge2[N2Ndipp]2 (6: M = Ge; 7: M = Sn). Interestingly, due to the solvent effect, reaction of 3 and 1 equivalent of GeCl4 in n-hexane gave rise to the formation of cyclic pentanuclear germane, [(GeCl2)(GeCl)4][N2Ndipp]2 (9) as the major product. On the contrary, if this reaction is carried out in THF, cyclic tetranuclear germane, [GeCl]4[N2Ndipp]2 (10) is the major product instead. Besides, treatment of Li2[N2Ndipp] with CrCl2 gives the complex Cr2[N2Ndipp]2(THF)2 (12). Upon reduction of 12 with KC8 leads to a quintuply-bonded complex, [(Et2O)KCr(N2Ndipp)]2 (11), which was already reported by our lab. Unfortunately, reaction of 11 with CaI2 failed to give a tetranuclear complex; instead it formed an amazing quintuply-bonded complex, Cr2Ca [N2Ndipp]2(THF)2 (15), where the Cr(I)-Cr(I) bond length is 1.7356(7) Å, shorter than 11, in which the Cr(I)-Cr(I) bond length is 1.7443(10) Å. Moreover, reaction of 11 with AlMe3 produces an asymmetric trichromium complex, [μ-CH3]2Cr3 [N2Ndipp]2(THF) (16). The Cr-Cr bond lengths are 1.8989(6) Å and 2.6283(6) Å, respectively. In addition, the reaction of amidinate ligand, Li[HC(NDipp)2] (NDipp = N-2,6-iPr2C6H3) and CrCl2 produces the Cr[HC(NDipp)2]2. Treatment of the mixture of Cr[HC(NDipp)2]2 and GeCl2‧dioxane gives [(GeCl)(μ-Cl)Cr][HC(NDipp)2]2 (17). There is one chloride that bridges between germanium and chromium atoms. The addition of LiAlH4 to 17 leads to the isolation of heterodinuclear complex, [(GeCl)(CrH)][HC(NDipp)2]2 (18). The distance of Ge-Cr is 2.5610(16) Å and is assigned a single bond. All the synthesized products have been characterized by NMR spectroscopy and elemental analysis, and their molecular structures have been determined by single crystal X-ray crystallography.