Fluorine N.M.R. Spectra of Sulfur, Phosphorus, and Silicon Fluorides: Hydrolysis and Intra- and Intermolecular Mechanisms of Fluorine Exchange

Gibson, J. A.; Ibbott, David G.; Janzen, A. F.

doi:10.1139/v73-479

Cited by 43 publications

(8 citation statements)

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“…Although this study provides no direct evidence related to the mechanism of axial-equatorial exchange, the postulate that exchange occurs via intermediates 4 or 5 is consistent with our previous suggestion that the lowest energy pathway of axial-equatorial exchange in trigonal bipyramidal molecules involves Lewis acid-base interactions and rapid equilibration of five-and six-coordinate geometries (8). Since SiF,-samples do not exhibit For personal use only.…”

Section: Zntramolecular Axial-equatorial Exchangesupporting

confidence: 82%

“…The relationship between coordination number and intern~olecular fluorine exchange may also be investigated by using a Lewis base, rather than a fluorine ligand, to vary the coordination number of silicon. In such an experiment it was found that addition of a large excess of NH, (10 M) to a sample containing Pr4N+SiF,-(0. inhibited fluorine exchange, presun~ably because SiF,-is converted to SiF,(NH,)- (7,8) and intern~olecular fluorine exchange between sixcoordinate SiF,(base)-and SF6'-is slow on the nmr time scale.…”

Section: Base and Intermolecular Fluorine Exchangementioning

confidence: 99%

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Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Marat¹,

Janzen²

1977

Can. J. Chem.

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. Can. J. Chem. 55,3845 (1977). Intermolecular fluorine exchange in the systems SiF4-SiF,-, MeSiF3-MeSiF4-, PhSiF3-PhSiF4-, SiF,--SiFs2-, SiF4-SiFs2-, and MeSiF,-SiFs2-has been studied by fluorine and proton nmr spectroscopy. Exchange is postulated to involve fluorine-bridged intermediates; alternative pathways of exchange, such as fluoride dissociation or impurity (HF and H20) catalyzed exchange, have been eliminated. Addition of NH3 to SF,--SiFs2-slows down exchange whereas addition of Et2NH to MeSiF, promotes exchange.RONALD KIRK MARAT et ALEXANDER F. JANZEN. Can. J. Chem. 55,3845 (1977). On Btudie par rmn du proton et du fluor 1'Cchange intermolCculaire du fluor dans les systtmes SF4-SiF5-, MeSiF3-MeSiF4-, PhSiF,-PhSiF4-, SiF,--SiFs2-, SiF4-SiF,2-et MeSiF3-SiFs2-. On fait I'hypothese que 1'Cxchange implique des intermediaires a fluor pontC; on Climine la possibilite d'un autre mode d'echange comme la dissociation du fluor ou de 1'6change catalysee par une impurete (HF et H20). L'addition de NH, au systeme SiF5--SiFs2-a pour effet de ralentir I'khange; par contre l'addition de Et2NH a MeSiF, la favorise.[Traduit par le journal]

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Section: Zntramolecular Axial-equatorial Exchangesupporting

confidence: 82%

Section: Base and Intermolecular Fluorine Exchangementioning

confidence: 99%

Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Marat¹,

Janzen²

1977

Can. J. Chem.

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“…In group 14, only a few monosubstituted products of [SiF 6 ] 2- like [SiF 5 (C 6 H 5 )] 2- , [SiF 5 (NH 3 )] - , [SiF 5 (NH(C 2 H 5 ) 2 )] - , cis -[SiF 4 (bipy)], cis -[SiF 4 (ox)] 2- , cis -[SiF 4 (mal)] 2- , and cis -[SiF 2 (ox) 2 ] 2- , , have been identified as octahedral species by 19 F NMR spectroscopy. For Ge only a few single fluoro complexes and the incomplete series, [GeF n X 6 - n ] 2- , n = 3−6, X = NCS - , and n =4−6, X = CN - , N 3 - , including the pairs of stereoisomers for n = 3 and 4, are known …”

Section: Main Group Elementsmentioning

confidence: 99%

Preparation and Spectroscopic Investigations of Mixed Octahedral Complexes and Clusters

1996

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“…Indeed, the low-temperature NMR of SF 4 shows two fluorine signals of equal area. − Like other sulfuranes, SF 4 is a nonrigid molecule which undergoes rapid exchange of ligand positions as revealed by its dynamic NMR spectra at higher temperatures .…”

Section: Introductionmentioning

confidence: 99%

Effective Monkey Saddle Points and Berry and Lever Mechanisms in the Topomerization of SF₄ and Related Tetracoordinated AX₄ Species

Mauksch

Schleyer

2001

Inorg. Chem.

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The topomerization mechanisms of the SF(4) and SCl(2)F(2) sulfuranes, as well as their higher (SeF(4), TeF(4)) and isoelectronic analogues PF(4)(-), AsF(4)(-), SbF(4)(-), SbCl(4)(-), ClF(4)(+), BrF(4)(+), BrCl(2)F(2)(+), and IF(4)(+)), have been computed at B3LYP/6-31+G and at B3LYP/6-311+G. All species have trigonal bipyramidal (TBP) C(2)(v)() ground states. In such four-coordinated molecules, Berry rotation exchanges both axial with two equatorial ligands simultaneously while the alternative "lever" mechanism exchanges only one axial ligand with one equatorial ligand. While the barrier for the lever exchange in SF(4) (18.8 kcal mol(-1)) is much higher than that for the Berry process (8.1 kcal mol(-1)), both mechanisms are needed for complete ligand exchange. The F(ax)F(ax) and F(eq)F(eq) isomers of SF(2)Cl(2) have nearly the same energy and readily interconvert by BPR with a barrier of 7.6 kcal mol(-1). The enantiomerization of the F(ax)F(eq) chiral isomer can occur by either the Berry process (transition state barrier 8.3 kcal mol(-1)) or the "lever" mechanism via either of two C(s)() transition states, based on the TBP geometry: Cl(ax) <--> Cl(eq) or F(ax) <--> F(eq) exchanges with barriers of 6.3 and 15.7 kcal mol(-1), respectively. Full scrambling of all ligand sites is possible only by inclusion of the lever mechanism. Planar, "tetrahedral", and triplet forms are much higher in energy. The TBP C(3)(v) structures of AX(4) either have two imaginary frequencies (NIMAG = 2) for the X = F, Cl species or are minima (NIMAG = 0) for the X = Br, I compounds. These "effective monkey saddle points" have degenerate modes with two small frequencies, imaginary or real. Although a strictly defined "monkey saddle" (with degenerate frequencies exactly zero) is not allowed, the flat C(3)(v) symmetry region serves as a "transition state" for trifurcation of the pathways. The BPR mechanism also is preferred over the alternative lever process in the topomerization of the selenurane SeF(4) (barriers 5.9 vs. 12.1 kcal mol(-1)), the tellurane TeF(4) (2.1 vs. 6.4), and the interhalogen cations ClF(4)(+) (2.5 vs 14.8), BrF(4)(+) (4.7 vs. 11.3), BrF(2)Cl(2)(+) (14.6 vs. 17.4), and IF(4)(+) (1.4 vs. 6.0), as well as for the series PF(4)(-) (7.0 vs. 9.0), AsF(4)(-) (9.3 vs. 17.2), and SbF(4)(-) (3.8 vs. 5.3 kcal mol(-1)), all computed at B3LYP/6-311+G with the inclusion of quasirelativistic pseudopotentials for Te, I, and Sb. The heavier halogens increasingly favor the lever process, where the barrier (2.6 kcal mol(-1)) pertaining to the effective monkey saddle point (C(3)(v) minimum for SbCl(4)(-)) is less than that for the Berry process (8.2 kcal mol(-1)).

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Fluorine N.M.R. Spectra of Sulfur, Phosphorus, and Silicon Fluorides: Hydrolysis and Intra- and Intermolecular Mechanisms of Fluorine Exchange

Cited by 43 publications

References 2 publications

Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Preparation and Spectroscopic Investigations of Mixed Octahedral Complexes and Clusters

Effective Monkey Saddle Points and Berry and Lever Mechanisms in the Topomerization of SF₄ and Related Tetracoordinated AX₄ Species

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Fluorine N.M.R. Spectra of Sulfur, Phosphorus, and Silicon Fluorides: Hydrolysis and Intra- and Intermolecular Mechanisms of Fluorine Exchange

Cited by 43 publications

References 2 publications

Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Preparation and Spectroscopic Investigations of Mixed Octahedral Complexes and Clusters

Effective Monkey Saddle Points and Berry and Lever Mechanisms in the Topomerization of SF4 and Related Tetracoordinated AX4 Species

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Effective Monkey Saddle Points and Berry and Lever Mechanisms in the Topomerization of SF₄ and Related Tetracoordinated AX₄ Species