Synthesis, Structure, and Bonding of Weakly Coordinating Anions Based on CN Adducts
Synthesis, Structure, and Bonding of Weakly Coordinating Anions Based on CN Adducts
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DOI：
10.1021/ja902450b
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发表时间：
2009-07-01
影响因子：
15
通讯作者：
Voss, Karsten
中科院分区：
文献类型：
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作者：
Bernsdorf, Arne;Brand, Harald;Voss, Karsten
将二氰酰胺（dca）、三氰甲烷（tcm）和四氰硼酸盐（tcb）的碱盐或银盐加入乙醚中的B(C6F5)(3)溶液中，得到含有大量B(C6F5)(3)加成阴离子[E(CN)(n)(-)]中心点[B(C6F5)(3)](n)的盐：E = n (dca_nb, n = 1,2; B = B(C6F5)(3))；E = C (tcb_nb with n = 1,2,3), E = B （tcb_nb with n = 1,2,3,4）。盐轴承这些阴离子如B [(CN)中心点B (C6F5) (3) (4) (-) (= [B (CN)(4)(-)]中心圆点(B (C6F5) (3)] (4)), C ((CN)中心点B (C6F5) (3) (3) (-) (= [C (CN)(3)(-)]中心圆点(B (C6F5)(3))(3)),和N [(CN)中心点B (C6F5) (3) (2) (= [N (CN)(2)(-)]中心圆点(B (C6F5)(3)](2))可以准备好的收益。它们的热稳定性可达200摄氏度以上，可溶解于极性有机溶剂中。根据化学计量，可以观察到单、二、三或四加合物的形成。dca_2b、tcm_3b和tcb_4b盐的固态结构仅表现为长阳离子中心点中心点阴离子接触，因此相互作用弱，阴离子体积大，包裹在B(C6F5)(3)基团之间的dca、tcm或tcb核只有很小的畸变。这就是为什么这些阴离子可以被认为是弱配位阴离子。在B3LYP/6-31+G(d)计算的基础上，研究了加合物阴离子形成的能量学、结构趋势和电荷转移。由于tcm_3b和tcb_4b容易获得，也可以大量制备，因此这些阴离子可以作为其他广泛使用的弱配位阴离子的真正替代品。此外，由于空间和电子的原因，似乎有理由期望作为阳离子早期过渡金属催化剂的反离子，阴离子可能表现出离子配对减少，从而提高催化活性。
The addition of alkali or silver salts of dicyanoamide (dca), tricyanomethanide (tcm) and tetracyanoborate (tcb) to a solution of B(C6F5)(3) in diethyl ether affords salts containing very voluminous B(C6F5)(3) adduct anions of the type [E(CN)(n)(-)]center dot[B(C6F5)(3)](n):E = N (dca_nb with n = 1, 2; b = B(C6F5)(3)); E = C (tcm_nb with n = 1, 2, 3), and E = B (tcb_nb with n = 1, 2, 3, 4). Salts bearing these anions such as B[(CN)center dot B(C6F5)(3)](4)(-) (= [B(CN)(4)(-)]center dot[B(C6F5)(3)](4)), C[(CN)center dot B(C6F5)(3)](3)(-) (= [C(CN)(3)(-)]center dot[ B(C6F5)(3)](3)), and N[(CN)center dot B(C6F5)(3)](2-) (=[N(CN)(2)(-)]center dot[ B(C6F5)(3)](2)) can be prepared in good yields. They are thermally stable up to over 200 degrees C and dissolve in polar organic solvents. Depending on the stoichiometry mono-, di-, tri-, or tetraadduct formation is observed. The solid state structures of dca_2b, tcm_3b and tcb_4b salts show only long cation center dot center dot center dot anion contacts and thereby weak interactions, large anion volumes and only small distortions of the dca, tcm or tcb core enwrapped between B(C6F5)(3) groups. That is why these anions can be regarded as weakly coordinating anions. On the basis of B3LYP/6-31+G(d) computations the energetics, structural trends and charge transfer of the adduct anion formation were studied. Since tcm_3b and tcb_4b are easily accessible and can also be prepared in large quantities, these anions may be utilized as a true alternative to other widely used weakly coordinating anions. Moreover, for both steric and electronic reasons it seems reasonable to expect that as counterions for cationic early transition metal catalysts such anions may show reduced ion pairing and hence increased catalytic activity.