Abstract
The low-coordinate and low-valent quintuply-bonded dichromium complex Cr2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (1) characterized by our group behaves like alkynes, so we further examine reactivity of 1 with small molecules. Treatment of 1 with four equiv of acetonitrile respectively results in a complexation product {Cr2[μ-κ2-HC(NDipp)2][μ-HC(NDipp)2][η2-NC(CH3)C(CH3)N]}2 (2) and (μ-η2,η2-MeCN)2(MeCN)2Cr2[μ-κ2-HC(NDipp)2]2 (3).Complex 2 is formed via C-C coupling of two molecules of MeCN. On the other hand, the C-N triple bond of MeCN is activated via coordination to the Cr2 unit in 3. Treatment of 1 with propiononitrile or isobutyronitrile gives complexes (μ-η2,η2-EtCN)2(EtCN)2Cr2[μ-κ2-HC(NDipp)2]2 (4) and (μ-η2,η2-iPrCN)2(iPrCN)2Cr2[μ-κ2-HC(NDipp)2]2 (5). Both structures of 4 and 5 are similar to that of complex 3. Surprisingly, reaction of complex 1 with trimethylsilyl cyanide (Me3SiCN) is complicated and results in three products: Cr(Me3SiNC)6 (6), {Cr(μ-CN)2[μ-HC(NDipp)2]}2 {[Cr(CN(TMS)2)(μ-HC(NDipp)2)]2(μ-CN)4[Cr(CN)]2} (7) and Cr[μ-HC(NDipp)2][CN(TMS)2](CNTMS)3 (8). The characterization of complexes 6-8 indicates this reaction proceeds through cleavage of Cr-Cr quintuple bond, inversion of C-N functionality of Me3SiCN and Si-N bond cleavage. In all complexes 6, 7 and 8, trimethylsilyl cyanide binds the metal center through its C instead of N atom. Treatment of 1 with 9-borabicyclo[3.3.1]nonane(9-BBN) gives Cr2[HC(NDipp)2] (9-borabicyclo[3.3.1]nonyl)2(μ2-O-9-borabicyclo[3.3.1]nonyl)(μ2-THF) (9).Treatment of the 1 with benzoyl azide results in the formation of the mononuclear complex Cr{[HC(NDipp)2]C(NPh)O}2 (10). We recently succeeded in characterizing boron-containing diamido transition-metal complexes. Therefore, we tried to employ the boron-containing diamido ligand Li2[HB(N-2,6-iPr2C6H3)2] to react with chromium, molybdenum and tungsten species.