ELECTROCHEMISTRY AS A DIAGNOSTIC-TOOL TO DISCRIMINATE BETWEEN CLASSICAL M-(H)2 AND NONCLASSICAL M-(H2) STRUCTURES WITHIN A FAMILY OF DIHYDRIDE AND DIHYDROGEN METAL-COMPLEXES
ELECTROCHEMISTRY AS A DIAGNOSTIC-TOOL TO DISCRIMINATE BETWEEN CLASSICAL M-(H)2 AND NONCLASSICAL M-(H2) STRUCTURES WITHIN A FAMILY OF DIHYDRIDE AND DIHYDROGEN METAL-COMPLEXES
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DOI：
10.1021/ic00343a025
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发表时间：
1990-09-05
影响因子：
4.6
通讯作者：
ZANELLO, P
中科院分区：
文献类型：
--
作者：
BIANCHINI, C;LASCHI, F;ZANELLO, P
本文详细研究了铁、钴、铑和铱的二氢和二氢配合物的氧化还原性质，并与相应的单氢衍生物的氧化还原性质进行了比较。所有的配合物都含有P（CH 2CH 2 PPh 2）3（PP 3）或N（CH 2CH 2 PPh 2）3（NP 3）作为稳定的共配体。用IR和3，P NMR技术对新的二氢化物[（PP 3）Fe（H）2]及其同位素异构体[（PP 3）Fe（H）（D）]和[（PP 3）Fe（D）2]进行了全面的表征。配合物[（PP 3）Co（H2）] PF 6和[（PP 3）Rh（H2）] BF 4在四氢呋喃中发生不可逆的单电子氧化反应。结果，发生H2配体的去质子化，并且起始jj 1 2-H2化合物转化为相应的单双[（PP 3）MH]+（M= Co，Rh）。与此相反，经典的双金属配合物[（L）Ir（H）2] BPh 4（L= PP 3，NP 3）和[（NP 3）Rh（H）2] BPh 4在四氢呋喃的电位窗口内不显示氧化还原活性。二氢化物[（PP 3）Fe（H）2）]可被氧化生成不稳定的[（PP 3）Fe（H）2]+和[（PP 3）Fe（H）2] 2+，但不发生去质子化反应。顺式（氢化物）（二氢）配合物[（PP 3）Fe（H）（H2）] BPh 4在四氢呋喃中进行单电子还原，得到中性二氢化物。用化学或电化学方法合成了罕见的钴（II）、铑（II）、铁（I）和铁（II）的顺磁性单金属化合物，并用X-带ESR谱进行了表征。2-H_2配位是通过协同给电子/反给电子效应发生的，与金属-烯烃键有一定的相似性。然而，只有对于H2，合适的填充金属轨道和 *（-）之间的相互作用才能足够强以促进分子的裂解。当这种情况发生时，在大多数情况下，金属的形式氧化态增加2个单位，形成金属二氢化物。因此，如果金属的氧化态发生从M-（H2）到M-（H）2的变化，则对络合物的氧化还原性质的研究在阐明结构方面可能是非常有用的。为了探索这种可能性，我们开始详细研究了几种已知的和新的VIII族金属配合物的氧化还原性质，它们的经典或非经典结构已经确定。研究了下列化合物：[（PP 3）Co（H 2）] PF 6（1），23 [（PP 3）Rh（H）2] BF 4（2），4 [（PP 3）Ir（H）2] BPh 4（13），5 [（NP 3）Rh（H）2] BPh 4（14），6 [（NP 3）Ir（H）2] BPh 4（15），6 [（PP 3）Fe（H）2]（3），和[（PP 3）Fe-（H）（H 2）] BPh 4（4）21 [PP 3 = P（CH 2CH 2PPh 2）3; NP 3 = P（CH 2CH 2PPh 2）3]。
The redox properties of a family of dihydride and dihydrogen complexes of iron, cobalt, rhodium, and iridium havebeen studied in detail and comparedwith those of the corresponding monohydrido derivatives. All of the complexes contain as stabilizing coligands either P (CH2CH2PPh2) 3 (PP3) or N (CH2CH2PPh2) 3 (NP3). The novel dihydride [(PP3) Fe (H) 2] and its isotopomers [(PP3) Fe (H)(D)] and [(PP3) Fe (D) 2] have been fully characterized by IR and and 3, P NMR techniques. The complexes [(PP3) Co (H2)] PF6 and [(PP3) Rh (H2)] BF4, which exhibit the nonclassical dihydrogen structure, undergo in tetrahydrofuran irreversible one-electron oxidation. As a result, the deprotonation of the H2 ligand occurs and the starting jj1 2-H2 compounds are converted to the corresponding monohydrides [(PP3) MH]+(M= Co, Rh). In contrast, the classical dihydrides [(L) Ir (H) 2] BPh4 (L= PP3, NP3) and [(NP3) Rh (H) 2] BPh4 show no redox activity within the potential window of tetrahydrofuran. The dihydride [(PP3) Fe (H) 2)] can be oxidized to give the unstable species [(PP3) Fe (H) 2]+ and [(PP3) Fe (H) 2] 2+, but no deprotonation reaction occurs. The c/s-(hydride)(dihydrogen) complex [(PP3) Fe (H)(H2)] BPh4 undergoes one-electron reduction in tetrahydrofuran to give the neutraldihydride. Rare examples of paramagnetic monohydrides of cobalt (II), rhodium (II), iron (I), and iron (II) have been synthesized chemically or electrochemically and characterized by X-band ESR spectroscopy.The bonding model for t? 2-H2 coordination, occurring through cooperative-donation/ir-back-donation effects, bears some re-semblance to metal-olefin-bonding. 1" 3 However, only for H2 can the interaction between a suitable Filled metal orbital and*(-) be strong enough to promote the cleavage of the molecule. When this occurs, and in most instances it does, the formal oxidationstate of the metal is increased by 2 units and a metal dihydride forms. Accordingly, provided a change in the oxidation state of the metal occurs on going from M-(H2) to M-(H) 2, a study of the redox properties of the complexes could be extremely useful in elucidating the structure. To explore such a possiblity, we began a detailed study on the redox properties of several known and novel complexes of group VIII metals for which eitherthe classical or the nonclassical structure havebeen determined. The following compoundshave been investigated:[(PP3) Co (H2)] PF6 (l), 23 [(PP3) Rh (H) 2] BF4 (2), 4 [(PP3) Ir (H) 2] BPh4 (13), 5 [(NP3) Rh (H) 2] BPh4 (14), 6 [(NP3) Ir (H) 2] BPh4 (IS), 6 [(PP3) Fe (H) 2](3), and [(PP3) Fe-(H)(H2)] BPh4 (4) 2i [PP3= P (CH2CH2PPh2) 3; NP3=