Ion Pairing Effects on Transition Metal Carbonyl Anions

Darensbourg, Marcetta Y.

doi:10.1002/9780470166345.ch5

Cited by 136 publications

(12 citation statements)

References 129 publications

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“…However, 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy and IR spectroscopy were consistent with its formulation. In addition, the ν CN stretches of 2 -PPN are found at slightly lower energy (1894 and 1858 cm –1 ) than those of 2 -Na, which is similar to the spectroscopic changes associated with disruption of contact-ion pairing in the tetraisocyano metalate [Co(CNAr Mes2 ) 4 ] − ([ 1 ] − ), and carbonyl metalates in general. , …”

Section: Results and Discussionmentioning

confidence: 59%

A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

et al. 2016

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The m-terphenyl isocyanide complex, HCo(CNArMes2)4 (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3), serves as a unique example of a well-defined isocyano analogue to HCo(CO)4. Given the well documented Brønsted acidity of HCo(CO)4 in both protic and nonprotic media, the Brønsted acidity of HCo(CNArMes2)4 was assessed for a quantitative comparison. Acid bracketing experiments in THF solution revealed that HCo(CNArMes2)4 has a Morris relative pK α THF value of 38.5–40.7, which is considerably higher than that of HCo(CO)4 (pK α THF (calc) = 11.4) and thereby indicates insignificant Brønsted acidity. Furthermore, the relative acidity of HCo(CNArMes2)4 rivals that of tetra-phosphine cobalt hydrides (i.e., HCo(PR3)4; pK α THF (calc) ≥ 48), despite the good π-acidity properties of the isocyano unit. To systematically determine the effect of substituting an isocyanide for a CO ligand on the acidity of the Co–H unit in HCoL4 complexes, the full series of HCo(CO) n (CNArMes2)4–n monohydrides and [Co(CO) n (CNArMes2)4–n ]− (n = 1–4) metalates were prepared and characterized. Acid bracketing studies on the [Co(CO) n (CNArMes2)4–n ]− metalates in THF solution revealed a regular progression of increasing pK α THF values as isocyanides are added to the Co center. However, the monoisocyanide tricarbonyl hydride, HCo(CO)3(CNArMes2), possesses a pK α THF value of 28.6–32.5, which is also significantly higher than that of HCo(CO)4 and the monophosphine complex HCo(CO)3(PPh3). Accordingly, the unconventional ability of isocyanide ligands to function as stronger σ-donors than organophosphines is discussed within the context of both the Brønsted acidity and spectroscopic features of the HCo(CO) n (CNArMes2)4–n monohydrides.

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Section: Results and Discussionmentioning

confidence: 59%

A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

et al. 2016

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“…For example, treatment of diiodide 1 with 3.1 equiv of KC 8 provides the red-orange monopotassium salt, K[(μ 2 -CNAr Mes2 ) 2 [CpCo] 2 ] (K[ 2 ]), as determined by X-ray diffraction (Figure ). In the solid state, K[ 2 ] is found as a tight ion pair, , with significant π-arene interactions between the CNAr Mes2 mesityl groups and the potassium cation. − The solution IR spectrum of K[ 2 ] in C 6 D 6 features a prominent ν CN stretch centered at 1666 cm –1 , which reflects significant increase in Co→(CN)π* back-donation relative to 2 . 1 H NMR analysis of K[2] in C 6 D 6 solution revealed broad, shifted resonances consistent with a paramagnetic complex.…”

Section: Results and Disscusionmentioning

confidence: 99%

Geometric and Electronic Structure Analysis of the Three-Membered Electron-Transfer Series [(μ-CNR)₂[CpCo]₂]ⁿ (n = 0, 1–, 2−) and Its Relevance to the Classical Bridging-Carbonyl System

et al. 2017

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The dimeric bridging carbonyl complexes [(μ-CO) 2 [CpCo] 2 ] n (n = 0, 1−) have occupied a central position in the understanding of metal−metal bonding interactions when bridging ligands are present. Based on simple electron-counting formalisms, these dimers have been proposed to possess formal Co−Co bond orders of 2 and 1.5, respectively. However, this simple bonding scheme has been contrasted by molecular orbital theory considerations, as well as spectroscopic data that probes M−M bonding interactions generally. While this system has received considerable attention, there has been a long-standing synthetic limitation in that the doubly reduced dianionic dimer, [(μ-CO) 2 [CpCo] 2 ] 2− , has not been amenable to isolation, thereby precluding an analysis of ostensible full-integer reduction in a homologous series. Accordingly, herein is presented the synthesis of a homologous, three-membered series of bridging-isocyanide [(μ-CNAr) 2 [CpCo] 2 ] n dimers, including the dianionic member. Structural and spectroscopic analyses of these [(μ-CNAr) 2 [CpCo] 2 ] n dimers, which feature the m-terphenyl isocyanide CNAr Mes2 (Ar Mes2 = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ), reveal that this series possesses similar overall properties to the bridging carbonyl counterparts. However, high-resolution X-ray crystallographic studies have revealed important structural differences that were not discernible in older studies of the carbonyl complexes. Also presented is the synthesis of the bridging-isocyanide/η 6arene dimers [Co 2 ((η 6 -Mes)(μ-CNAr Mes )) 2 ] n (n = 0, 1+), which are valence isoelectronic to the mono-and dianionic [(μ-CNAr) 2 [CpCo] 2 ] n derivatives. Structural and spectroscopic studies of these η 6 -arene complexes, as well as the related neutral nickel dimer (μ-CNAr Mes ) 2 [CpNi] 2 provide evidence for an electronic structure environment dominated by M→(CN)π* backbonding interactions, rather than direct M−M bonding. This conclusion is supported by DFT-derived molecular orbital analysis on the bridging-isocyanide [(μ-CNAr Mes2 ) 2 [CpCo] 2 ] n dimers.

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“…Ion pairing can also affect the reaction rate of insertion reactions . It is well known that CO insertion in anionic complexes can be strongly accelerated by Lewis acids − that predispose it to accept the alkyl migration by interacting with the lone pair of the CO oxygen atom . Insertion reactions that occur in cationic complexes has also been found to be affected by ion pairing, although to a lesser extent.…”

Section: 4 Other Reactionsmentioning

confidence: 99%

Ion Pairing in Transition-Metal Organometallic Chemistry

2005

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Ion Pairing Effects on Transition Metal Carbonyl Anions

Cited by 136 publications

References 129 publications

A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

Geometric and Electronic Structure Analysis of the Three-Membered Electron-Transfer Series [(μ-CNR)₂[CpCo]₂]ⁿ (n = 0, 1–, 2−) and Its Relevance to the Classical Bridging-Carbonyl System

Ion Pairing in Transition-Metal Organometallic Chemistry

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Ion Pairing Effects on Transition Metal Carbonyl Anions

Cited by 136 publications

References 129 publications

A Well-Defined Isocyano Analogue of HCo(CO)4. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

A Well-Defined Isocyano Analogue of HCo(CO)4. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

Geometric and Electronic Structure Analysis of the Three-Membered Electron-Transfer Series [(μ-CNR)2[CpCo]2]n (n = 0, 1–, 2−) and Its Relevance to the Classical Bridging-Carbonyl System

Ion Pairing in Transition-Metal Organometallic Chemistry

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A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

A Well-Defined Isocyano Analogue of HCo(CO)₄. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

Geometric and Electronic Structure Analysis of the Three-Membered Electron-Transfer Series [(μ-CNR)₂[CpCo]₂]ⁿ (n = 0, 1–, 2−) and Its Relevance to the Classical Bridging-Carbonyl System