Freeman Lucas A, Obi Akachukwu D, Machost Haleigh R, Molino Andrew, Nichols Asa W, Dickie Diane A, Wilson David J D, Machan Charles W, Gilliard Robert J
Department of Chemistry, University of Virginia 409 McCormick Road, PO Box 400319 Charlottesville Virginia 22904 USA
Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University Bundoora Victoria 3086 Australia
Chem Sci. 2021 Jan 22;12(10):3544-3550. doi: 10.1039/d0sc06851a.
The mono- and dianions of CO (, CO and CO ) have been studied for decades as both fundamentally important oxycarbanions (anions containing only C and O atoms) and as critical species in CO reduction and fixation chemistry. However, CO anions are highly unstable and difficult to study. As such, examples of stable compounds containing these ions are extremely limited; the unadulterated alkali salts of CO (, MCO, MCO, M = alkali metal) decompose rapidly above 15 K, for example. Herein we report the chemical reduction of a cyclic (alkyl)(amino) carbene (CAAC) adduct of CO at room temperature by alkali metals, which results in the formation of CAAC-stabilized alkali CO and CO clusters. One-electron reduction of CAAC-CO adduct () with lithium, sodium or potassium metal yields stable monoanionic radicals [M(CAAC-CO)] (M = Li, Na, K, ) analogous to the alkali CO radical, and two-electron alkali metal reduction affords dianionic clusters of the general formula [M(CAAC-CO)] () with reduced CO units which are structurally analogous to the carbonite anion CO . It is notable that crystalline clusters of these alkali-CO salts may also be isolated the "one-pot" reaction of free CO with free CAAC followed by the addition of alkali metals - a process which does not occur in the absence of carbene. Each of the products was investigated using a combination of experimental and theoretical methods.
一氧化碳的单阴离子和双阴离子（CO⁻、CO₂⁻和CO₃²⁻）作为具有根本重要性的氧碳阴离子（仅含碳和氧原子的阴离子）以及一氧化碳还原和固定化学中的关键物种，已被研究了数十年。然而，一氧化碳阴离子非常不稳定，难以研究。因此，含有这些离子的稳定化合物的例子极为有限；例如，纯净的一氧化碳碱金属盐（MCO、MCO₂、M = 碱金属）在15 K以上会迅速分解。在此，我们报告了在室温下用碱金属对一氧化碳的环状（烷基）（氨基）卡宾（CAAC）加合物进行化学还原，这导致形成了由CAAC稳定的碱金属一氧化碳和二氧化碳簇。用锂、钠或钾金属对CAAC-CO加合物（）进行单电子还原，会产生稳定的单阴离子自由基[M(CAAC-CO)]⁻（M = Li、Na、K、），类似于碱金属一氧化碳自由基，而双电子碱金属还原则得到通式为[M(CAAC-CO)]²⁻（）的双阴离子簇，其中一氧化碳单元被还原，其结构类似于碳酸根阴离子CO₃²⁻。值得注意的是，这些碱金属一氧化碳盐的晶体簇也可以通过游离一氧化碳与游离CAAC的“一锅法”反应，然后加入碱金属来分离——这一过程在没有卡宾的情况下不会发生。使用实验和理论方法相结合的方式对每种产物进行了研究。
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