Schlenk's Early “Free” Carbanions

Harder, Sjoerd

doi:10.1002/1521-3765(20020715)8:14<3229::aid-chem3229>3.0.co;2-3

Cited by 18 publications

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“…In solution 1(Yb) and 1(Ca) both exist as a pair of diastereomers and have close similarity in their 1 H NMR and IR spectra (see Supporting Information). [15] Crystals of the solvent-separated ion-pair 2(Yb) were obtained by a procedure similar to that used for the Ca analogue: [16] the addition of THF to a solution of bis(9-Me 3 Sifluorenyl)ytterbium·(THF) 2 in benzene results in crystallization of 2 (Yb). The structure of 2(Yb) is identical to its Ca analogue and can also be described with the "metal-in-a-box" model: the [Yb 2+ ·(THF) 6 ] ion is encapsulated in a box of fluorenyl ligands and cocrystallized benzene molecules.…”

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confidence: 99%

“…The structure of 2(Yb) is identical to its Ca analogue and can also be described with the "metal-in-a-box" model: the [Yb 2+ ·(THF) 6 ] ion is encapsulated in a box of fluorenyl ligands and cocrystallized benzene molecules. [16] Both (dipp-nacnac) complexes, 3(Yb) and 3(Ca), crystallize as C 2 -symmetric molecules, which are stabilized by CÀ H···p interactions between the dipp-nacnac ligands. [17] Not only their molecular geometries [18] but also their dynamic behavior in solution is strikingly similar: the activation energy for inversion of puckering in the metal-N-C-C-C-N ring, which was shown to be metaldependent, [17] is 17.6(1) kcal/mol for both the Ca as well as the Yb complex.…”

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The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

Harder

2004

Angew Chem Int Ed

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The structures and chemical behavior of heavier alkalineearth metal complexes (Ca, Sr, and Ba) [1] have often been compared to that of early d-and f-block metal complexes. [2][3][4][5][6][7][8][9][10][11] In particular, parallels with "hot" lanthanide(ii) complexes [12] have been observed. Lanthanide complexes are d 0 species with a limited radial extension of their f orbitals. Therefore, orbital factors do not affect their chemistry as much as in transition-metal chemistry. As for complexes of the heavier alkaline-earth metals, their bonding and structures are mainly determined by electrostatic and steric factors.There is ample evidence for the striking similarity in the chemistry of Ca II and Yb II : 1) crystal structures of Ca and Yb analogues are always isomorphous and have exceptionally similar cell constants, [7,8,10] 2) the observation of nearly identical IR spectra of Ca and Yb analogues suggests a striking similarity in bonding, [2] 3) analogous Ca and Yb complexes display similar gas-phase behavior: electron-diffraction studies of [Cp *2 Ca] (Cp* is pentamethyl cyclopentadiene) and [Cp *2 Yb] reveal similar Cp* centroid -M-Cp* centroid angles of 154 (3)8 and 158(4)8, respectively, [13] and 4) analogous reactivities of Ca II and Yb II complexes have been reported. [8,9] These parallels in the chemistry of Ca and Yb complexes prompted us to repeat the calcium chemistry recently reported by us, but with ytterbium. The substitution of Ca for Yb in benzylcalcium-based initiators for stereoselective styrene polymerization [15,20] and an investigation of its polymerization chemistry is here of special importance.The syntheses and crystallization of the Yb II complexes were greatly facilitated by the strong similarity with their calcium analogues: in all cases exactly the same procedures as for their Ca analogues were followed. The Yb II complexes 1(Yb)-5(Yb) were prepared and the structures of 1(Yb)-

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The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

Harder

2004

Angew Chem Int Ed

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“…Metal‐free catalysts were prepared according to the early pioneering routes of Wilhelm Schlenk reported nearly a century ago (Scheme ) 11. Although Schlenk initially believed in the existence of pentavalent N, for example, Ph 3 CNMe 4 , the ion pair character in [Ph 3 C − ][Me 4 N + ] is well‐established 12. As [Ph 3 C − ][Me 4 N + ] shows limited stability,13 we also tested Schlenk′s “naked” amide [Ph 2 N − ][Me 4 N + ] in catalysis.…”

Section: Methodsmentioning

confidence: 99%

“…It is questionable, however, to what extent the amide anion in [Ph 2 N − ][Me 4 N + ] is “naked”. The crystal structure of Schlenk′s early “free” carbanion, [Ph 3 C − ][Me 4 N + ], already revealed a network of nonclassical CH⋅⋅⋅C hydrogen bonds between [Me 4 N + ] (CH donor) and [Ph 3 C − ] (C acceptor) 12. Although [Ph 2 N − ][Me 4 N + ] crystallized in thin needle‐like crystals that are unsuitable for a crystal structure determination, the related [ p ‐tolyl 2 N − ][Me 4 N + ] crystallized as plates of which we determined a crystal structure (Figure 1).…”

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confidence: 99%

Early Main Group Metal Catalysis: How Important is the Metal?

2014

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Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph2N−][Me4N+] and [Ph3C−][Me4N+]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of ArNCO and RNCNR (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated CC bonds in H2CCHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.

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“…Carbanions containing Ph 3 C – have already been prepared a century ago by Schlenk, but they were not recognized as such at that time. Harder has hinted recently to that fact and proved these early results by the X‐ray structure analysis of [Me 4 N][Ph 3 C] . Looking at the body of literature, one can state that free carbanions are stabilized by employing resonance to decrease the charge density on the carbon center and hence reduce its basicity .…”

Section: Introductionmentioning

confidence: 96%

Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl₃)₃]^–

et al. 2016

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Disproportionation reactions of Si 2 Cl 6 in the presence of [nBu 4 N]Cl in halogenated solvents yield the compound [nBu 4 N][C(SiCl 3 ) 3 ](1). X-ray structure analysis of 1 proves the existence of a planar carbanion, which is stabilized by three trichlorosilyl groups. Quantum chemical analysis shows the [a] 5028 presence of highly polar bonds in the anion. Planarization of the anion can be explained by the interaction of the occupied lone pair at the carbon atom with the antibonding σ* orbitals of the Si-Cl bonds (negative hyperconjugation).

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Schlenk's Early “Free” Carbanions

Cited by 18 publications

References 13 publications

The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

Early Main Group Metal Catalysis: How Important is the Metal?

Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl₃)₃]^–

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Schlenk's Early “Free” Carbanions

Cited by 18 publications

References 13 publications

The Chemistry of CaII and YbII: Astoundingly Similar But Not Equal!

The Chemistry of CaII and YbII: Astoundingly Similar But Not Equal!

Early Main Group Metal Catalysis: How Important is the Metal?

Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl3)3]–

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Product

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The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl₃)₃]^–