"Umpolung" at Boron by Reduction of [B(CN)4]- and Formation of the Dianion [B(CN)3]2-
"Umpolung" at Boron by Reduction of [B(CN)4]- and Formation of the Dianion [B(CN)3]2-
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DOI：
10.1002/anie.201105848
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Ignatiev, Nikolai
中科院分区：
文献类型：
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作者：
Bernhardt, Eduard;Bernhardt-Pitchougina, Vera;Ignatiev, Nikolai
含有亲核硼的物种，例如，将质子转化为BCH 3 H键中的双氢原子，得到了很好的研究。例如，在金属硼化物（如MgB 2 [1]）和簇合物（如[B11 H13] 2 [2]）中，亲核硼是常见的，但在其余的硼化学中，它们更稀缺。[3，4] 1924年，Krause报道了第一个含有亲核硼原子的化合物。[5，6]在钠与三苯基硼在乙醚中的反应中，假定形成“NaBPh 3”。后来，该反应被阐明，[7]并且“NaBPh 3”被鉴定为二聚体的混合物（例如Na 2 [Ph 3BH 4C 6 H5 = BPh 2]，Na 2 [Ph 3BH 4C 6 H4 BHPh 2]，方案S1）。在钠与三苯基硼的反应中，[BPh 3][8]确实被检测为中间体，并且发现自由基阴离子[BAr 3][8]通常是不稳定的。[8，9]只有在硼上具有mesityl配体的自由基阴离子可以被分离，因为它的二聚是动力学受阻的。[10[Li（[12] crown-4）2][BMes 3]在2308 ℃以下是稳定的，其结构由单晶X射线衍射确定。[10]二价阴离子[B（C10 H7）3] 2 π [12，13]和[BMes 3] 2 π [14]几乎没有表征，它们的存在是值得怀疑的。[7][15][16][17][18][19][1 [3，19-22]然而，在过去的20年中，除了“（C6 H11）3 PBH 2Li”作为中间体之外，[23，24]已经描述了亲核硼物质的一些例子（方案1），其被充分表征并已在有机合成中发现用途。[3，4]在本文中，我们描述了盐M2 [B（CN）3]（M= Li，Na，K）中前所未有的二价阴离子，其含有形式氧化态+1的亲核硼。该三氰基硼酸根阴离子是根据反应式（1）通过在液氨中用碱金属在[B（CN）4]中进行还原性B2C键裂变而获得的。
Species containing nucleophilic boron, which, for example, convert protons into hydridic hydrogen atoms in BÀH bonds, are well-investigated. For instance, nucleophilic boron in metal borides (eg, MgB2[1]) and clusters (eg,[B11H13] 2À [2]) are common, but in the remaining boron chemistry they are more scarce.[3, 4] In 1924, Krause reported the first compound containing a nucleophilic boron atom.[5, 6] In the reaction of sodium with triphenylboron in diethyl ether, formation of “NaBPh3” was postulated. Later this reaction was elucidated,[7] and “NaBPh3” was identified as a mixture of dimers (eg Na2 [Ph3BÀC6H5= BPh2], Na2 [Ph3BÀC6H4ÀBHPh2], Scheme S1). In the reaction of sodium with triphenylboron [BPh3] À [8] was indeed detected as intermediate and it was found that the radical anions [BAr3] À are generally unstable.[8, 9] Only the radical anion with mesityl ligands at boron can be isolated, because its dimerization is kinetically hindered.[10, 11] The blue [Li ([12] crown-4) 2][BMes3] is stable up to 2308C, and its structure was determined by single crystal X-ray diffraction.[10] The dianions [B (C10H7) 3] 2À [12, 13] and [BMes3] 2À [14] are scarcely characterized, and their existence is doubtful.[7] Moreover, the claimed syntheses of [Ph2B] À,[15][Bu2B] À,[16] and [Bu2BNEt3] À [17, 18] turned out to be questionable.[3, 19–22] Nevertheless during the last 20years, besides “(C6H11) 3PBH2Li” as intermediate,[23, 24] some examples for nucleophilic boron species have been described (Scheme 1), which are fully characterized and have found use in organic synthesis.[3, 4]Herein we describe an unprecedented dianion in the salts M2 [B (CN) 3](M= Li, Na, K), which contains nucleophilic boron in the formal oxidation state+ 1. This tricyanoborate anion was obtained by reductive BÀC bond fission in [B (CN) 4] À by alkaline metals in liquid ammonia according to Equation (1).