Molecular orbital theory of pentacoordinate phosphorus

Hoffmann, Roald; Howell, James M.; Muetterties, E. L.

doi:10.1021/ja00764a028

Cited by 289 publications

(139 citation statements)

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“…The trends www.chemeurj.org in the various energy terms were interpreted in the conceptual framework provided by the quantitative molecular orbital (MO) model contained in Kohn-Sham DFT. [18] Qualitative MO analyses of pentacoordination were carried out in the early seventies by Hoffmann and co-workers, [19] who arrived at a bonding mechanism that naturally incorporates the 3-center-4-electron (3c-4e) bond proposed by Pimentel and Rundle [20] to account for the hypervalency of the central atom in species such as F 3 À and XeF 2 . Originally, the 3c-4e bond was formulated in terms of the valence p s atomic orbitals (AOs) of a linear arrangement of three atoms that yields a well-known pattern of three MOs: y 1 , y 2 , and y 3 , shown in Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Pierrefixe

Guerra

Bickelhaupt

2008

Chemistry A European J

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Why is silicon hypervalent and carbon not? Or why is [Cl-CH(3)-Cl](-) labile with a tendency to localize one of its axial C-Cl bonds and to largely break the other one, while the isostructural and isoelectronic [Cl-SiH(3)-Cl](-) forms a stable pentavalent species with a delocalized structure featuring two equivalent Si-Cl bonds? Various hypotheses have been developed over the years focusing on electronic and steric factors. Here, we present the so-called ball-in-a-box model, which tackles hypervalence from a new perspective. This model reveals the key role of steric factors and provides a simple way of understanding the above phenomena in terms of different atom sizes. Our bonding analyses are supported by computation experiments in which we probe, among other things, the shape of the S(N)2 potential-energy surface of Cl(-) attacking a carbon atom in the series of substrates CH(3)Cl, (.)CH(2)Cl, (..)CHCl, and (...)CCl. Our findings for ClCH(3)Cl(-) and ClSiH(3)Cl(-) are generalized to other Group 14 central atoms (Ge, Sn, and Pb) and axial substituents (F).

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Section: Introductionmentioning

confidence: 99%

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Pierrefixe

Guerra

Bickelhaupt

2008

Chemistry A European J

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“…Here, we find, however, that their contribution is not essential for the hypervalence in Li 3 -. Nowadays, the bonding in hypervalent species is described, instead, in terms of the 3-center-4-electron (3c-4e) bond [20]. This model was proposed simultaneously by Pimentel and Rundle [21] to account for the hypervalency of the central atom in species such as F 3 -and XeF 2 .…”

Section: Introductionmentioning

confidence: 99%

Hypervalence and the delocalizing versus localizing propensities of H–3, Li–3, CH–5 and SiH–5

Pierrefixe

Bickelhaupt

2007

Struct Chem

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Lithium and silicon have the capability to form hypervalent structures, such as Li 3 -and SiH 5 -, which is contrasted by the absence of this capability in hydrogen and carbon, as exemplified by H 3 -and CH 5 -which, although isoelectronic to the former two species, have a distortive, bond-localizing propensity. This well-known fact is nicely confirmed in our DFT study at BP86/TZ2P. We furthermore show that the hypervalence of Li and Si neither originates from the availability of low-energy 2p and 3d AOs, respectively, nor from differences in the bonding pattern of the valence molecular orbitals; there is, in all cases, a 3-center-4-electron bond in the axial X-A-X unit. Instead, we find that the discriminating factor is the smaller effective size of C compared to the larger Si atom, and the resulting lack of space around the former. Interestingly, a similar steric mechanism is responsible for the difference in bonding capabilities between H and the effectively larger Li atom. This is so, despite the fact that the substituents in the corresponding symmetric and linear dicoordinate H 3 -and Li 3 -are on opposite sides of the central atom.

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“…Attention has focused, especially, upon hypervalent molecules (3), i.e., molecules having Lewis structures with more than eight valence electrons about a central atom (e.g., silicon, phosphorus, sulfur, chlorine) (4)(5)(6)(7)(8)(9)(10)(11)(12).…”

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confidence: 99%

A theoretical study of the CSH₄ and CPH₅ hypersurfaces. Geometries, tautomerization, and dissociation of sulfonium and phosphonium ylides

Mitchell¹,

Wolfe²,

Schlegel³

1981

Can. J. Chem.

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. Can. J. Chem. 59,3280 (1981). Calculations have been performed at four basis set levels (STO-3G, STO-3G*, 4-31Ci, 4-31G*) on the model ylides rnethylenesulfurane (CH,SH,) and methylenephosphorane (CH,PH,), their stable tautomers (CH,SH and CH,PH,), their dissociation products (SH,, PH, and CH,), and the protonated species CH,SH,+ and CH,PH,+. At each basis set level all geometries have been optimized fully, using the FORCE method. The conformational behaviour of the ylides as a function of C-X bond-stretching, C-X torsion. and CH, (or SH,) bending has been examined in some detail. The experimental properties (i.e., geometries, relative stabilities, proton affinities, rotation-inversion behaviour) of sulfonium and phosphonium ylides are reproduced well by the model calculations with the 4-31G* basis set, which contains d-type functions on both carbon and sulfur (or phosphorus). All other basis sets are deficient in different ways and for different reasons, whichare discussed in detail. The principal result of this work is the conclusion that d-type functions are essential for a proper description of the hypervalent species CH,SH, and CH,PH,, but not for the normal-valent species SH,, PH,, CH,SH, and CH,PH,. The conclusion concerning hypervalent species reverses our earlier views. The role of the d-type functions is to concentrate charge into the C-X region of the ylides, and thus to stabilize the system. Evidence for this effect has been obtained from quantitative perturbational molecular orbital (PMO) analyses of interactions associated with the carbon lone pair. as well as comparisons of electron density plots with and without the d AO's. A second conclusion is that the imposition of various geometrical constraints such as assumed C-X, C-H, or X-H bond lengths, and HCH or XH, bond angles, as was necessary for computational reasons in all previous work on such systems, has major and previously unrecognized consequences. For example. the assumption that the CH, moiety is planar in CH,SH, leads to very similar geometries with and without d AO's, although only in the latter case does such a geometry at carbon correspond to the true energy minimum: in the absence of d AO's the C-S bond length is maintained by a symmetry-enforced barrier to dissociation. These and other consequences of geometrical constraints at carbon, sulfur, or phosphorus are analyzed in detail.DAVID JOHN MITCHELL, SAUL WOLFE et H . BERNHARD SCHLEGEL. Can. J. Chem. 59, 3280 (1981). Utilisant quatre ensembles de base (STO-3G, STO-3G*, 4-31G, 4-31G*), on a effectue des calculs sur des modeles d'ylures de methylenesulfurane (CH,SH,) et de methylenephophorane (CH,PH,), sur leurs tautomeres stables (CH,SH et CH,PH,), sur leurs produits de dissociation (SH,, PH, et CH,) et sur leurs especes protonees CH,SH,, CH3PH3+. Faisant appel a la methode de FORCE, on a optimise pleinement toutes les geometries pour tous les ensembles de base. On a examine soigneusement le comportement conformationnel des ylures en fonction de l'elongation de la liaison C-X, de l...

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Molecular orbital theory of pentacoordinate phosphorus

Cited by 289 publications

References 8 publications

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Hypervalence and the delocalizing versus localizing propensities of H–3, Li–3, CH–5 and SiH–5

A theoretical study of the CSH₄ and CPH₅ hypersurfaces. Geometries, tautomerization, and dissociation of sulfonium and phosphonium ylides

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Molecular orbital theory of pentacoordinate phosphorus

Cited by 289 publications

References 8 publications

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

Hypervalence and the delocalizing versus localizing propensities of H–3, Li–3, CH–5 and SiH–5

A theoretical study of the CSH4 and CPH5 hypersurfaces. Geometries, tautomerization, and dissociation of sulfonium and phosphonium ylides

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A theoretical study of the CSH₄ and CPH₅ hypersurfaces. Geometries, tautomerization, and dissociation of sulfonium and phosphonium ylides