Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(μ-oxo)dinickel(III) complex
Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(μ-oxo)dinickel(III) complex
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DOI：
10.1021/ic0514243
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发表时间：
2006-04-03
影响因子：
4.6
通讯作者：
Suzuki, M
中科院分区：
文献类型：
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作者：
Cho, J;Furutachi, H;Suzuki, M
[Ni-2（OH）（2）（Me-2-tpa）（2）]（2+）（1）（Me-2-tpa =双（6-甲基-2-吡啶基甲基）（2-吡啶基甲基）胺）与H2 O2的反应导致Me-2-tpa配体上的亚甲基氧化得到N-脱烷基化配体，甲基氧化得到基于配体的羧酸盐和醇盐作为最终氧化产物。在氧化途径中产生的一系列顺序反应中间体，双（μ-氧代）二镍（III）（[Ni-2（O）（2）（Me-2-tpa）（2）]（2+）（2）），（μ-超氧）二镍（II）（[Ni-2（O-2）（2）（Me-2-tpa）（2）]（2+）（3）），a（μ-羟）（μ-烷基过氧）二镍（II）（[Ni-2（OH）（Me-2-tpa）（Me-tpa-CH 2 OO）]（2+）（4））和双（μ-烷基过氧）二镍（II）（[Ni-2（Me-tpa-CH 2 OO）（2）]（2+）（5）），并通过包括X射线晶体学在内的各种物理化学测量进行了表征，研究了它们的氧化途径。1与H2 O2在甲醇中在-40 ℃下反应生成2，2与H2 O2反应性极强，生成3。配合物2仅在-40 ° C下在不存在H2 O2的情况下从3中的超氧配体的反硝化分离。2在N2下热分解生成N-脱烷基配体Me-dpa（（6-甲基-2-吡啶基甲基）（2-吡啶基甲基）胺）和配体偶联二聚体（Me-tpa-CH 2）（2）。（Me-tpa-CH_2）（2）的形成表明，配体基自由基Me-tpa-CH_2.作为反应中间体产生，可能是由氧代基团夺取H原子产生的。同位素标记实验表明，发生分子内耦合形成的耦合二聚体。结果表明，氧的反弹到Me-tpa-CH 2。比对于各种高价双（μ-氧代）双金属络合物观察到的慢。相比之下，2和3在O2存在下的分解分别得到羧酸根和醇盐配体（Me-tpa-COO-和Me-tpa-CH 2 O-），而不是（Me-tpa-CH 2）（2），表明Me-tpa-CH 2的反应。与O-2的偶联比Me-tpa-CH 2的偶联快。生成基于配体的过氧自由基Me-tpa-CH 2 OO...虽然存在Me-tpa-CH 2 OO. 3在-20 ℃氧气氛下分解，分离出一种可能的反应中间体4。4和5中的烷基过氧配体可以通过O-O键的均裂或异裂转化为基于配体的醛，并且醛的缩合通过Cannizzaro反应得到羧酸酯和醇盐。
The reaction of [Ni-2(OH)(2)(Me-2-tpa)(2)](2+) (1) (Me-2-tpa = bis(6-methyl-2-pyridylmethyl) (2-pyridyl methyl)amine) with H2O2 causes oxidation of a methylene group on the Me-2-tpa ligand to give an N-dealkylated ligand and oxidation of a methyl group to afford a ligand-based carboxylate and an alkoxide as the final oxidation products. A series of sequential reaction intermediates produced in the oxidation pathways, a bis(mu-oxo)dinickel(Ill) ([Ni-2(O)(2)(Me-2-tpa)(2)](2+) (2)), a bis(mu-superoxo)dinickel(II) ([Ni-2(O-2)(2)(Me-2-tpa)(2)](2+) (3)), a (mu-hydroxo)(mu-alkylperoxo)dinickel(II) ([Ni-2(OH)(Me-2-tpa)(Me-tpa-CH2OO)](2+) (4)), and a bis(mu-alkylperoxo)dinickel(II) ([Ni-2(Me-tpa-CH2OO)(2)](2+) (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with H2O2 in methanol at -40 degrees C generates 2, which is extremely reactive with H2O2, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of H2O2 at -40 degrees C. Thermal decomposition of 2 under N-2 generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridyl methyl) (2-pyridyl m ethyl) a mine) and a ligand-coupling dimer (Me-tpa-CH2)(2). The formation of (Me-tpa-CH2)(2) suggests that a ligand-based radical Me-tpa-CH2. is generated as a reaction intermediate, probably produced by H-atom abstraction by the oxo group. An isotope-labeling experiment revealed that intramolecular coupling occurs for the formation of the coupling dimer. The results indicate that the rebound of oxygen to Me-tpa-CH2. is slower than that observed for various high-valence bis(mu-oxo)dimetal complexes. In contrast, the decomposition of 2 and 3 in the presence Of 02 gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO- and Me-tpa-CH2O-), instead of (Me-tpa-CH2)(2), indicating that the reaction of Me-tpa-CH2. with O-2 is faster than the coupling of Me-tpa-CH2. to generate ligand-based peroxyl radical Me-tpa-CH2OO... Although there is a possibility that the Me-tpa-CH2OO. species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O-2 at -20 degrees C. The alkylperoxo ligands in 4 and 5 can be converted to a ligand-based aldehyde by either homolysis or heterolysis of the O-O bond, and disproportionation of the alclehyde gives a carboxylate and an alkoxide via the Cannizzaro reaction.