Modifying Alkylzinc Reactivity with 2,2'-Dipyridylamide: Activation of t Bu?Zn Bonds for para -Alkylation of Benzophenone
Modifying Alkylzinc Reactivity with 2,2'-Dipyridylamide: Activation of t Bu?Zn Bonds for para -Alkylation of Benzophenone
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用 2,2-联吡啶酰胺修饰烷基锌反应性：激活 t Bu?Zn 键以实现二苯甲酮的对位烷基化
DOI：
10.1002/ange.201302426
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发表时间：
2013
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--
通讯作者：
Armstrong D
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文献类型：
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作者：
Armstrong D
近年来锌酸盐金属配合物化学的许多引人注目的进展集中在仲单酰胺2，2，6，6-四甲基哌啶（TMP）上。由Kondo、Uchiyama及其同事开发的原始TMP锌酸盐试剂[LiZn（TMP）tBu 2]是芳香族和杂芳香族底物的有效碱。[1]Knochel和同事们已经编制了一个新的基于TMP的金属化剂库，包括新戊酸锌[（TMP）Zn-（OPiv）· LiCl]（OPiv=新戊酸盐），它像[LiZn（TMP）tBu 2]一样，显示出强大的去质子化能力和特殊的官能团耐受性，但具有额外的优势，即其芳基锌化衍生物具有长期的空气稳定性。[2]锌酸盐金属化化学的最佳结构定义是涉及TMP钠试剂[（TMEDA）Na（TMP）（tBu）Zn（tBu）]（1; TMEDA= N，N，N '，N'-四甲基乙二胺）的化学。该试剂表现出比上述锌酸锂更高的反应性，其许多芳基锌化衍生物采用类似的结构，其被设计在携带末端配体的Na-阴离子-Zn-阴离子环的结构模板上，即分别在Na和Zn上的中性供体和阴离子（图1）。为了打破该模板并开发可以刺激新反应性的新结构基序，我们研究了用多官能2，2 '-二吡啶基酰胺[dpa，（2-NC 5 H4）2N]代替单官能TMP。提供三个潜在的连接N位点，这种N-桥连的双（N杂环）在各种应用中发现了效用，包括医学，[3]催化，[4]光致发光，[5]和超分子化学。[6]在这里，我们报告了一组显着的新结构，将dpa纳入中性锌，锌酸钠，锌酸钾修饰含有叔丁基配体。初步的反应性研究表明，混合钠锌dpa配合物可以叔丁基化酮二苯甲酮的帕拉（1，6-加成）的位置，这是具有挑战性的，并暗示，该反应可以在亚化学计量的钠组分。通过tBu 2 Zn和胺dpa（H）在己烷溶液中1：1的化学计量比直接合成了中性、杂配的锌配合物[{（dpa）Zn（tBu）} 2]（2）。滤液的NMR研究显示绝对产率高于分离的晶体的70%产率。具有吸引力的沙漏形核心，2的中心对称分子结构（方案1）是二聚体，扭曲的四面体锌原子[7]键合到一个酰胺基单元的去质子化N上，占据另一个的联吡啶口袋并完成其与末端tBu配体的配位。在沙漏描述中（参见支持信息），每个球包含一个褶皱的六原子（NCNCNZn）环，Zn位于距离最近的NCNCN平面1.0991（3）和距离第二个NCNCN平面1.7143（3）。该基序与等电子中性锌二聚体[{MeZnC（H）-Py 2} 2]（Py= 2-吡啶基）的基序非常相似。[8]据我们所知，2代表了第一个晶体学表征的Zn/dpa复合物，显示了ZnCl 2（桥头）N键，尽管它已经在烷基化的二聚衍生物中被注意到，其中二聚化的模式与2中的不同。[9]2中的反/反构象[10]（即两个吡啶基N原子均远离桥头N）也与dpa（H）[11]和上述烷基化dpa衍生物的多晶型物中发现的顺/反构象形成鲜明对比。预计TMP/锌酸盐1和dpa（H）在己烷溶液中会发生简单的转胺反应[12]，但相反，分离的结晶产物..
Many of the recent eye-catching advances in zincate executed metallation chemistry have centered on the secondary monoamide 2, 2, 6, 6-tetramethylpiperidide (TMP). Developed by Kondo, Uchiyama, and co-workers, the original TMP zincate reagent [LiZn (TMP) tBu2] is an effective base for both aromatic and heteroaromatic substrates.[1] Knochel and coworkers have since compiled a library of new TMP-based metalating agents, including the zinc pivalate [(TMP) Zn-(OPiv)· LiCl](OPiv= pivalate), which like [LiZn (TMP) tBu2], displays strong deprotonating power and exceptional functional-group tolerance but has the added advantage that its arylzincated derivatives boast prolonged air stability.[2] The area of zincate metalation chemistry that is best structurally defined is that involving the sodium TMP reagent [(TMEDA) Na (TMP)(tBu) Zn (tBu)](1; TMEDA= N, N, N’, N’-tetramethylethylenediamine). This reagent, which exhibits enhanced reactivity over the aforementioned lithium zincates, and many of its arylzincated derivatives adopt similar structures, which are designed on an architectural template of a Na–anion–Zn–anion ring carrying terminal ligands, namely a neutral donor and an anion on Na and Zn, respectively (Figure 1). To break this template and develop new structural motifs that could stimulate new reactivity we have investigated replacing monofunctional TMP with multifunctional 2, 2’-dipyridylamide [dpa,(2-NC5H4) 2N]. Offering three potential ligating N sites, this N-bridged bis (N heterocycle) finds utility in a diverse range of applications including medicine,[3] catalysis,[4] photoluminescence,[5] and supramolecular chemistry.[6] Herein we report a remarkable set of novel structures incorporating dpa into neutral zinc, sodium zincate, and potassium zincate modifications containing tert-butyl ligands. Preliminary reactivity studies reveal that the mixed sodium-zinc dpa complexes can tert-butylate the ketone benzophenone at the para (1, 6-addition) position, which is challenging, and hint that the reaction can be made substoichiometric in the sodium component. The neutral, heteroleptic zinc complex [{(dpa) Zn (tBu)} 2](2) was synthesized straightforwardly through the 1: 1 stoichiometric combination of tBu2Zn and the amine dpa (H) in a hexane solution. NMR studies of the filtrate revealed the absolute yield was higher than the 70% yield of the isolated crystals. Possessing an attractive hour-glass-shaped core, the centrosymmetric molecular structure of 2 (Scheme 1) is dimeric with the distorted tetrahedral zinc atom [7] bonded to the deprotonated N of one amido unit, which occupies the dipyridyl pocket of the other and completes its coordination with a terminal tBu ligand. In the hour-glass description (see the Supporting Information), each bulb comprises a puckered, six-atom (NCNCNZn) ring with Zn situated 1.0991 (3) from the nearest NCNCN plane and 1.7143 (3) from the second NCNCN plane. This motif bears a strong resemblance to that of the isoelectronic neutral zinc dimer [{MeZnC (H)-Py2} 2](Py= 2-pyridyl).[8] To our knowledge, 2 represents the first crystallographically characterized Zn/dpa complex showing a ZnÀ (bridgehead) N bond, although it has been noted in alkylated dimeric derivatives wherein the mode of dimerization is distinct from that in 2.[9] The anti/anti conformation [10](ie, both pyridyl N atoms directed away from the bridgehead N) within 2 also contrasts with the syn/anti conformations found in polymorphs of dpa (H)[11] and the aforementioned alkylated dpa derivatives.A simple transamination reaction [12] between TMP/zincate 1 and dpa (H) in a hexane solution was anticipated, but instead the isolated crystalline product …