Structurally Mapping Alkyl and Amide Basicity in Zincate Chemistry: Diversity in the Synthesis of Mixed Sodium-Zinc Complexes and Their Applications in Enolate Formation
Structurally Mapping Alkyl and Amide Basicity in Zincate Chemistry: Diversity in the Synthesis of Mixed Sodium-Zinc Complexes and Their Applications in Enolate Formation
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DOI：
10.1021/acs.organomet.0c00339
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发表时间：
2020-12-14
期刊：
影响因子：
2.8
通讯作者：
Hevia, Eva
中科院分区：
文献类型：
--
作者：
Mastropierro, Pasquale;Livingstone, Zoe;Hevia, Eva
虽然碱金属锌酸盐在有机合成中显示出有希望的用途，但这些化合物通常是原位制备的，并且它们的身份仍然模糊不清。本文合成了以螯合硅基（双）氨基配体{Ph2Si(NAr*)(2)}(2-) （Ar* = 2,6-二异丙基苯基）为配体的新型锌酸钠家族。采用同步双金属方法，混合金属碱NaZn(HMDS)(2)R (2) [R = CH2SiMe3；HMDS = N(SiMe3)(2)]得到溶剂分离的烷基锌酸盐离子对RPh2Si(NAr*)（2) Zn(R)）。{Na(THF)(6)}(+)](3)，表明2更倾向于通过其两个Zn-N键作为其（酰胺）碱反应，而不是使用其烷基。另一种方法是用两种单金属碱基依次使用NaR和Zn(HMDS)(2)得到三（氨基）锌酸盐[{Ph-2 Si(NaR *)(2)Zn(HMDS)) {Na(THF)(6))+](6)。6的形成是通过1的初始单钠化，提供氨基胺[{Ph 2 Si(NHAr*)(NAr*)-Na}(2)](5)，然后与Zn（HMDS）进行共络合和脱原生(2)步骤。以2,4,6-三甲基苯乙酮(7)为例，研究了锌酸钠3和6接触锌烯醇酸盐的能力，分别得到锌酸钠[{(THF)NaZnR[OC(=CH2)Mes](2)}(2)](8)和[{(THF)NaZn(OC(=CH)Mes)(3)}(2)](9)。这些研究表明，螯合硅基（双）酰胺{Ph2Si(NAr*)(2)}（2-）远不是一个无辜的旁观者，是7去质子化的有效碱，当异电位锌酸钠3的一部分时，表现出意想不到的优于CH2SiMe3烷基的动力学碱性。烯醇化物8和9的双金属组成与全钠[{(THF)Na(OC(= CH2)Mes)}(4)]（10）的双金属组成相反，全钠[{(THF)Na(OC(= CH2)Mes)}(4)]（10）是由同感烷基锌酸盐NaZnR3(4)与7反应而得到的，同时消除了ZnR2。揭示了这些双金属体系中Mg对Zn的不同行为，7与镁类似物3 [{Ph2Si(NAr*)(2)Mg(R)}(-){Na(THF)(6)}(+)]（11）反应生成镁酸酯酸酯[{Ph2Si(NAr*)(2)Mg(O(=CH)Mes) (THF)}(-){Na-(THF)(5)}(+)](12)，其中螯合硅基（双）酰胺配体保留，酮的金属化由烷基作用。
While alkali metal zincates have shown promising utility in organic synthesis, frequently these compounds are prepared in situ, and their identities remain blurred. Herein, the synthesis of a new family of sodium zincates featuring the chelating silyl(bis)amido ligand {Ph2Si(NAr*)(2)}(2-) (Ar* = 2,6-diisopropylphenyl) is presented. Using a synchronized bimetallic approach, 2-fold deprotonation of Ph2Si(NHAr*)(2) (1) by mixed-metal base NaZn(HMDS)(2)R (2) [R = CH2SiMe3; HMDS = N(SiMe3)(2)] afforded the solvent-separated ion pair alkyl zincate RPh2Si(NAr*)(2) Zn(R)). {Na(THF)(6)}(+)] (3), showing a dear preference for 2 to react as bis(amide) base via its two Zn-N bonds rather than reacting using its alkyl group. Alternatively, a stepwise approach using two single-metal bases sequentially, NaR and Zn(HMDS)(2) affords the tris(amido) zincate [{Ph-2 Si(NAr*)(2)Zn(HMDS)) {Na(THF)(6))+] (6). Formation of 6 takes place by initial monosodiation of 1, furnishing the amido-amine [{Ph 2 Si(NHAr*)(NAr*)-Na}(2)] (5), which in turn undergoes a co-complexation and deprotozincation step with Zn(HMDS)(2). Using 2,4,6-trimethylacetophenone (7) as a case study, the ability of sodium zincates 3 and 6 to access zinc enolates was investigated, affording sodium zincates [{(THF)NaZnR[OC(=CH2)Mes](2)}(2)] (8) and [{(THF)NaZn(OC(=CH)Mes)(3)}(2)] (9), respectively. These studies revealed that the chelating silyl(bis)amide {Ph2Si(NAr*)(2)}(2-) far from being an innocent spectator is an effective base for the deprotonation of 7, showing an unexpected superior kinetic basicity than the CH2SiMe3 alkyl group when part of sodium heteroleptic zincate 3. The bimetallic constitution of enolates 8 and 9 contrasts with that of all-sodium [{(THF)Na(OC(= CH2)Mes)}(4)] (10) obtained by reacting the homoleptic alkylzincate NaZnR3 (4) with 7, with the concomitant elimination of ZnR2. Revealing the divergent behavior of Mg versus Zn in these bimetallic systems, reaction of 7 with the magnesium analog of 3, [{Ph2Si(NAr*)(2)Mg(R)}(-){Na(THF)(6)}(+)] (11), produces magnesiate enolate [{Ph2Si(NAr*)(2) Mg(O(=CH )Mes) (THF)}(-){Na-(THF)(5)}(+)] (12), where the chelating silyl(bis)amide ligand is retained and metalation of the ketone is actioned by the alkyl group.