Carborane acids. New "strong yet gentle'' acids for organic and inorganic chemistry
Carborane acids. New "strong yet gentle'' acids for organic and inorganic chemistry
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DOI：
10.1039/b415425h
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发表时间：
2005-01-01
影响因子：
4.9
通讯作者：
Reed, CA
中科院分区：
文献类型：
--
作者：
Reed, CA
二十面体碳硼烷阴离子（例如 CHB11Cl11-）是已知配位性最低、化学惰性最强的阴离子之一。它们也是碱性最低的化合物之一，因此它们的共轭酸 H（碳硼烷）是超强酸（即强于 100% H2SO4）。酸度测量表明，H(CHB11Cl11) 是目前已知的最强的纯布朗斯台德酸，超过了三氟甲磺酸和氟硫酸。尽管如此，它也是一种极其温和的酸——因为它的共轭碱几乎不参与化学反应。碳硼烷酸将共轭碱中的质子酸性与阴离子亲核性和破坏性氧化能力分开，达到以前未达到的程度。因此，许多长期寻找的高酸性活性阳离子，如质子化苯 (C6H7+)、质子化 C-60 (HC60+)、叔碳阳离子 (R3C+)、乙烯基阳离子 (R2C=C+ - R)、硅离子 (R3Si+) 和离散水合氢离子（H3O+、H5O2+ 等）可以很容易地以碳硼烷形式分离出来盐并在室温下通过 X 射线晶体学进行表征。
Icosahedral carborane anions such as CHB11Cl11- are amongst the least coordinating, most chemically inert anions known. They are also amongst the least basic, so their conjugate acids, H( carborane), are superacids (i.e. stronger than 100% H2SO4). Acidity scale measurements indicate that H(CHB11Cl11) is the strongest pure Bronsted acid presently known, surpassing triflic and fluorosulfuric acid. Nevertheless, it is also an extremely gentle acid - because its conjugate base engages in so little chemistry. Carborane acids separate protic acidity from anion nucleophilicity and destructive oxidative capacity in the conjugate base, to a degree not previously achieved. As a result, many long-sought, highly acidic, reactive cations such as protonated benzene (C6H7+), protonated C-60 (HC60+), tertiary carbocations (R3C+), vinyl cations (R2C=C+ - R), silylium ions (R3Si+) and discrete hydronium ions (H3O+, H5O2+ etc.) can be readily isolated as carborane salts and characterized at room temperature by X-ray crystallography.