[1,1‐Co2(CO)6(CNAr)2]: A Structural Mimic of the Elusive D2d Isomer of [Co2(CO)8]

Carpenter, Alex E.; Wen, Isabel; Moore, Curtis E.; Rheingold, Arnold L.; Figueroa, Joshua S.

doi:10.1002/chem.201301997

Cited by 12 publications

(16 citation statements)

References 43 publications

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“…As shown previously, the reaction between the monocarbonyl hydride, HCo(CO)(CNAr Mes2 ) 3 (2-H) and CO does not lead to simple displacement of a CNAr Mes2 ligand, but rather affords the κ 1 -C iminoformyl complex, Co(κ 1 −C−C(H)NAr M e s 2 ) (CNAr Mes2 ) 2 (CO) 2 . 30 Accordingly, the dicarbonyl monohydride, HCo(CO) 2 (CNAr Mes2 ) 2 (3-H) and the corresponding sodium salt Na[Co(CO) 2 (CNAr Mes2 ) 2 ] − (3-Na) were accessed via routes that did not require the addition of free CO. As shown in Scheme 2, reductive cleavage of the previously reported dimer, 45 The corresponding hydride, HCo(CO) 2 (CNAr Mes2 ) 2 (3-H), was obtained by addition of 3,5-dimethylbenzoic acid to 3-Na (Scheme 2). The solid-state structure of 3-H revealed a nearideal trigonal-bipyramidal coordination geometry (Addison− Reedijk τ 5 = 0.98), 46 with two carbonyls and a single CNAr Mes2 ligand occupying the equatorial plane (Figure 4).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Synthetic access to the monoisocyanide-tricarbonyl salt, Na[Co(CO) 3 (CNAr Mes2 )] (4-Na), was achieved by reduction of the dicobalt dimer Co 2 (CO) 6 (CNAr Mes2 ) 2 . 45 As reported previously, this dimer exists in solution at room temperature as a ∼1:1 mixture of 1,1-Co 2 (CO) 6 (CNAr Mes2 ) 2 and 1,2-Co 2 (CO) 6 (CNAr Mes2 ) 2 isomers. Accordingly, addition of 0.1% Na/Hg to Co 2 (CO) 6 (CNAr Mes2 ) 2 in THF solution produced roughly a 1:1:2 mixture of Na[Co(CO) 4 ], Na[Co-(CO) 2 (CNAr Mes2 ) 2 ] (3-Na), and the targeted metalate Na-[Co(CO) 3 (CNAr Mes2 )] (4-Na), respectively, as assayed by 1 H NMR, 13 C{ 1 H} NMR and IR spectroscopy (Scheme 3).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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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: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

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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“…Such dimers have not been reported for the bridging CO system, but they are synthetically accessible for the bridging isocyanide complexes considered here. Accordingly, as shown in Scheme 4, exhaustive thermal decarbonylation of Co 2 (CO) 8 in the presence of 2.0 equiv 76 of CNAr Mes2 provides the η 6 -arene dimer, Co 2 ((η 6 -Mes)(μ-CNAr Mes )) 2 (5), as determined by Xray diffraction (Figure 5). In dimer 5, the η 6 -arene interactions are supplied by flanking mesityl groups of the CNAr Mes2 ligands.…”

Section: ■ Introductionmentioning

confidence: 90%

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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“…Accordingly, in an effort to critically assess isocyanide for carbonyl substitution and complement our previous efforts to systematically generate isolable isocyano analogues to the classical cobalt carbonyls (e.g. [Co(CO) 4 ] n ( n = −1, 0, +1), [Co(CO) 3 ] − , and Co 2 (CO) 8 ), − we describe here the hydride complex HCo(CNAr Mes2 ) 4 ( 1 ; Ar Mes2 = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ) as a well-defined and isolable isocyano analogue to HCo(CO) 4 .…”

Section: Introductionmentioning

confidence: 99%

A Well-Defined Isocyano Analogue of HCo(CO)₄. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides

2016

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Reported here is the synthesis and characterization of the tetrakis(m-terphenyl isocyanide)cobalt hydride HCo(CNArMes2)4 (1; ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3). Monohydride 1 serves as a well-defined isocyano analogue of the tetracarbonyl hydride HCo(CO)4. While tetrakis-phosphine analogues of HCo(CO)4 have been reported previously, these compounds have failed to exhibit a reactivity profile that can be compared and contrasted with HCo(CO)4 in a systematic fashion. Herein, HCo(CNArMes2)4 (1) is shown to be a readily accessed and reactive complex that allows for this comparison. For example, HCo(CNArMes2)4 (1) is found to decompose smoothly to the κ1 -C-iminoformyl complex Co(η6-(Mes)-κ1 C-C(H)NArMes2)(CNArMes2) (2). Kinetic analysis of this decomposition and that of the d 1-isotopomer DCo(CNArMes2)4 (1-d 1) revealed a unimolecular process characterized by a large primary k H/ k D isotope effect (3.2(6)) and no dependence on the presence of free CNArMes2. These data point to rate-limiting hydride α-migration and formation of the κ1-C-iminoformyl species [Co(κ1-C-C(H)NArMes2)(CNArMes2)3] as a critical intermediate. Indeed, ligand substitution reactions of HCo(CNArMes2)4 (1), as well as 13C-labeling experiments of the decomposition product 2, demonstrate that hydride α-migration is the dominant mechanistic feature of this system. Most notably, this behavior is in contrast with that of HCo(CO)4, for which it has been established that CO ligand dissociation is the initial mechanistic feature. Additional support for the critical role of hydride α-migration in HCo(CNArMes2)4 (1) was obtained by the development of catalytic CNArMes2 1,1-hydrogenation to form a stable and isolable methylenimine.

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[1,1‐Co₂(CO)₆(CNAr)₂]: A Structural Mimic of the Elusive D_2d Isomer of [Co₂(CO)₈]

Cited by 12 publications

References 43 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

A Well-Defined Isocyano Analogue of HCo(CO)₄. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides

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[1,1‐Co2(CO)6(CNAr)2]: A Structural Mimic of the Elusive D2d Isomer of [Co2(CO)8]

Cited by 12 publications

References 43 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

A Well-Defined Isocyano Analogue of HCo(CO)4. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides

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[1,1‐Co₂(CO)₆(CNAr)₂]: A Structural Mimic of the Elusive D_2d Isomer of [Co₂(CO)₈]

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

A Well-Defined Isocyano Analogue of HCo(CO)₄. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides