Comproportionation of cationic and anionic tungsten complexes having an N-heterocyclic carbene ligand to give the isolable 17-electron tungsten radical CpW(CO)2(IMes)(•).
Comproportionation of cationic and anionic tungsten complexes having an N-heterocyclic carbene ligand to give the isolable 17-electron tungsten radical CpW(CO)2(IMes)(•).
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具有N-杂环卡宾配体的阳离子和阴离子钨配合物的比例化得到可分离的17电子钨基CpW(CO)2(IMes)(·)。
DOI：
10.1021/ja202754e
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发表时间：
2011
影响因子：
15
通讯作者：
R. M. Bullock
中科院分区：
文献类型：
--
作者：
John A. S. Roberts;James A. Franz;Edwin F van der Eide;Eric D. Walter;Jeffrey L. Petersen;D. Dubois;R. M. Bullock
本文合成、分离并表征了一系列由钨阴离子、自由基和阳离子组成的化合物，由n -杂环羰基1,3-二（2,4,6-三甲基苯基）咪唑-2-酰基（IMes）支撑，并跨越形式氧化态W(0)、W(I)和W（II）。氢化物CpW(CO)(2)(itimes)H与KH和18-crown-6反应得到钨阴离子[CpW(CO)(2)(itimes)](-)[K(18-crown-6)]（+）。在MeCN (0.2 M (n)Bu(4) n (+)PF（6)(-)）中，[CpW(CO)(2)(IMes)]（-）的电化学氧化在所有扫描速率下都是完全可逆的(E(1/2) = -1.65 V vs Cp(2)Fe(+•/0))，表明CpW(CO)(2)(IMes)（•）是一个持久性自由基。氢化物转移数据(CO) (2) (ime) H Ph值(3)C (+) PF(6)(-)在MeCN提供[cis-CpW (CO) (2) (ime) (MeCN)] (+) PF(6)(-)。[CpW(CO)(2)(IMes)]（-）与[CpW(CO)(2)(IMes)(MeCN)]（+）相比较得到17电子钨自由基CpW(CO)(2)(IMes)（•）。该配合物在(1)H NMR谱中表现出顺磁位移共振，并通过红外光谱、低温EPR光谱和x射线衍射进行了表征。CpW(CO)(2)(IMes)（•）在歧化和二聚化方面是稳定的。报道了CpW(CO)(2)(IMes)（•）和[CpW(CO)(2)(IMes)]（-）之间简并电子转移的核磁共振研究。对CpW(CO)(2)(IH)H进行了DFT计算，并对带有N，N'取代基的NHC配体的相关配合物Me (CpW(CO)（2)(IMe)H）或H (CpW(CO)（2)(IH)H）进行了DFT计算，以与实验研究的带有甲酰基取代基的IH配合物进行比较。计算结果表明，随着NHC配体空间体积的增加，W-H均解键能（BDEs）降低，CpW(CO)(2)(IH)H、CpW(CO)(2)(IMe)H和CpW(CO)(2)(IMe)H分别从67 ~ 64 ~ 63 kcal mol（-1）。计算得到CpW(CO)(2)(itimes)（•）在W处的自旋密度为0.63。计算出W自由基CpW(CO)(2)(IMe)（•）和CpW(CO)(2)(IH)（•）形成弱W-W键。弱键配合物[CpW(CO)(2)(IMe)](2)和[CpW(CO)(2)(IH)](2)的W-W bde分别为6和18 kcal mol(-1)，并且易于解离为w中心自由基CpW(CO)(2)(IMe)（•）和CpW(CO)(2)(IH)（•）。
A series consisting of a tungsten anion, radical, and cation, supported by the N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and spanning formal oxidation states W(0), W(I), and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)(2)(IMes)H with KH and 18-crown-6 gives the tungsten anion [CpW(CO)(2)(IMes)](-)[K(18-crown-6)](+). Electrochemical oxidation of [CpW(CO)(2)(IMes)](-) in MeCN (0.2 M (n)Bu(4)N(+)PF(6)(-)) is fully reversible (E(1/2) = -1.65 V vs Cp(2)Fe(+•/0)) at all scan rates, indicating that CpW(CO)(2)(IMes)(•) is a persistent radical. Hydride transfer from CpW(CO)(2)(IMes)H to Ph(3)C(+)PF(6)(-) in MeCN affords [cis-CpW(CO)(2)(IMes)(MeCN)](+)PF(6)(-). Comproportionation of [CpW(CO)(2)(IMes)](-) with [CpW(CO)(2)(IMes)(MeCN)](+) gives the 17-electron tungsten radical CpW(CO)(2)(IMes)(•). This complex shows paramagnetically shifted resonances in the (1)H NMR spectrum and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)(2)(IMes)(•) is stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)(2)(IMes)(•) and [CpW(CO)(2)(IMes)](-) are reported. DFT calculations were carried out on CpW(CO)(2)(IMes)H, as well as on related complexes bearing NHC ligands with N,N' substituents Me (CpW(CO)(2)(IMe)H) or H (CpW(CO)(2)(IH)H) to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal that W-H homolytic bond dissociation energies (BDEs) decrease with increasing steric bulk of the NHC ligand, from 67 to 64 to 63 kcal mol(-1) for CpW(CO)(2)(IH)H, CpW(CO)(2)(IMe)H, and CpW(CO)(2)(IMes)H, respectively. The calculated spin density at W for CpW(CO)(2)(IMes)(•) is 0.63. The W radicals CpW(CO)(2)(IMe)(•) and CpW(CO)(2)(IH)(•) are calculated to form weak W-W bonds. The weakly bonded complexes [CpW(CO)(2)(IMe)](2) and [CpW(CO)(2)(IH)](2) are predicted to have W-W BDEs of 6 and 18 kcal mol(-1), respectively, and to dissociate readily to the W-centered radicals CpW(CO)(2)(IMe)(•) and CpW(CO)(2)(IH)(•).
H.从 (eta5-C5R5)Cr(CO)3H (R = Ph, Me, H) 转移到甲基丙烯酸甲酯和苯乙烯的动力学和热力学。
DOI：
10.1021/ja034927l
发表时间：
2003
期刊：
Journal of the American Chemical Society.
影响因子：
--
作者：
Tang,Lihao;Papish,ElizabethT;Abramo,GrahamP;Norton,JackR;Baik,Mu-Hyun;Friesner,RichardA;Rappe,Anthony
通讯作者：
Rappe,Anthony