α-Stabilization by Silyl and Phosphino Substitution

Römer, Bettina; Gatev, Geo G.; Zhong, and Meili; Brauman, John I.

doi:10.1021/ja970279s

Cited by 51 publications

(25 citation statements)

References 46 publications

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“…These data might indicate that the carbene lone pair interacts with the σ* orbitals of both the silyl and the phosphino groups (negative hyperconjugation). 90,91 However, the electron localization function (ELF) analysis 82 of both the bent and linear forms of XIi* leads to a rather different conclusion ( Figure 14). For the ground-state bent form (Figure 14a), the lone pair on the carbon atom is directed away from both the phosphorus and silicon, indicating that neither the triple bond (C) nor the cumulene (D) structure is the best formulation for phosphinosilylcarbenes.…”

Section: Iv31 Phosphinosilyl-and Phosphinophosphoniocarbenesmentioning

confidence: 99%

Stable Carbenes

et al. 1999

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Section: Iv31 Phosphinosilyl-and Phosphinophosphoniocarbenesmentioning

confidence: 99%

Stable Carbenes

et al. 1999

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“…Due to the relatively low level of covalency in f-block carbene complexes, stabilizing groups a-to the carbene center have been required to date, particularly phosphorus subsituents. It has been calculated that a PH 2 group is able to stabilize a carbanion charge by up to À89.1 kJmol -1 , [35][36][37] and phosphorus(V) substituents would be expected to provide even better stabilization. However, and like Schrock alkylidenes, in such systems there is a high degree of charge accumulation at the carbene center, and so such species tend to be nucleophilic, which also reflects the relative energies of the uranium and carbene frontier orbitals.…”

Section: Covalent Uranium Carbene Chemistrymentioning

confidence: 99%

Covalent Uranium Carbene Chemistry

Gregson

Wooles

Cooper

et al. 2015

Comments on Inorganic Chemistry

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After seminal reports of covalent uranium carbene U=C complexes in the 1980s by Gilje, the area fell dormant for around 30 years. However, in the past five years, there has been a resurgence of interest in the area. Despite recent advances, the classification of these U=C complexes as either methanediides, carbenes, or alkylidenes has remained a contentious issue. Herein, we review U=C complexes reported to date, along with reactivity and computational studies, and conclude that although U=C complexes sit midway on the continuum between rare-earth methanediides and Schrock-type alkylidenes, they can be justifiably described as carbenes.

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“…As pointed out by Brauman and co‐workers, the carbanion stability can only be deduced from its basicity by means of isodesmic reactions [see Eqs. (1) and (2)] “if we assume that the substituents [X] primarily influence these reactions by their effect on the anions” 4a. This assumption, however, can not be made for the halogen substituents X.…”

Section: Homolytic Cx Bond Energies δEa(x) and δEn(x) Of Ch2x− And Cmentioning

confidence: 99%

α‐Stabilization of Carbanions: Fluorine Is More Effective than the Heavier Halogens

2006

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Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthday "Carbanions", more precisely organometallic compounds, are among the most important reagents in organic synthesis. [1][2][3] Gas-phase experimental [4] and theoretical [5] investigations have contributed much to our knowledge of how the basicity and stability of carbanions CH 2 X À depend intrinsically, that is, in the absence of solvent and counterions, on their structure, in particular, on the nature of the a-substituent X. Thus, it has been established that third-and higher-period substituents X (e.g., Cl, SH) substantially decrease the proton affinity (PA) of CH 2 X À , whereas second-row substituents (e.g., F, OH) are significantly less effective in reducing the basicity of these species. This follows from the trend in the energy change DE isod (X) associated with the isodesmic reaction in Equation (1) of the proton transfer from CH 3 X to CH 3 À .This reaction energy is equal to the difference in the proton affinities of CH 3 À and CH 2 X À [Eq. (2)].It becomes some 10-20 kcal mol À1 more exothermic if one goes from second-to higher-period substituents X, which implies that the basicity of CH 2 X À , as measured by the proton affinity PA(CH 2 X À ), decreases. The common explanation is that, compared to substituents of the second period, thirdand higher-period substituents stabilize the carbanion more effectively, that is, the strength of their CÀX bond leads to more stabilization. This has been ascribed to the fact that

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α-Stabilization by Silyl and Phosphino Substitution

Cited by 51 publications

References 46 publications

Stable Carbenes

Stable Carbenes

Covalent Uranium Carbene Chemistry

α‐Stabilization of Carbanions: Fluorine Is More Effective than the Heavier Halogens

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