A theoretical survey of unsaturated or multiply bonded and divalent silicon compounds.  Comparison with carbon analogs

Luke, Brian T.; Pople, J. A.; Krogh-Jespersen, M.-B.; Apeloig, Yitzhak; Karni, Miriam; Chandrasekhar, J.; Schleyer, Paul von Ragué

doi:10.1021/ja00262a014

Cited by 289 publications

(163 citation statements)

References 22 publications

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“…Moreover, the results are consistent with the observation of Si-Li scalar coupling at low temperature and with conclusions from a b initio calculations (5 …”

Section: Introductionsupporting

confidence: 89%

Concerning the Si—Li bonding in phenylsilyllithiums as studied by variable temperature Li nuclear magnetic resonance

Buncel¹,

Venkatachalam²,

Edlund³

1986

Can. J. Chem.

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A variable temperature 7Li nrnr study of equimolar mixtures of two structurally related phenylsilyllithiums supports a bimolecular exchange mechanism between monomeric structures as being responsible for the collapse of the 7~i signals of the two species. The different exchange rates indicated in MTHF and THF parallel the observations from a Si-Li coupling study. The experimental data provide support for a mainly ionic Si-Li bond, although some orbital interaction is indicated.ERWIN BUNCEL, T. KRISHNAN VENKATACHALAM et ULF EDLUND. Can. J. Chem. 64, 1674 (1986.Les rCsultats d'une Ctude des spectres rmn du 7~i , effectuk a des tempkratures variables sur des mklanges CquimolCculaires de deux phCnyl silyl lithium relikes par leur structure, sont en accord avec la suggestion qu'un mkanisme d'Cchange bimolCculaire entre les structures monombres est responsable de la coalescence des signaux 7~i des deux espkes. Les diverses vitesses dlCchange dans le MTHF et le THF sont parallbles celles obtenues lors d'une ktude du couplage Si-Li. Les donnCes expkrimentales fournissent un support a llhypoth&se d'une liaison Si-Li qui serait principalement ionique, mCme s'il semble exister quelques interactions entre orbitales.[Traduit par la revue] IntroductionThe precise nature of bonding in organolithium compounds has been a topic of considerable controversy (1). On the basis of recent ab initio calculations it has been argued that the carbon-lithium bond is predominantly ionic, i.e. ca 80% ionic character, and in fact more ionic than the Li-F bond (2).

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“…Moreover, the results are consistent with the observation of Si-Li scalar coupling at low temperature and with conclusions from a b initio calculations (5 …”

Section: Introductionsupporting

confidence: 89%

Concerning the Si—Li bonding in phenylsilyllithiums as studied by variable temperature Li nuclear magnetic resonance

Buncel¹,

Venkatachalam²,

Edlund³

1986

Can. J. Chem.

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“…Fluorine (29) and, to a lesser extent, chlorine both stabilise singlet silylenes by n-donation and consequently dissociation reactions in which SiF2 and SiC12 are products require less energy than reactions producing SiHF and SiHC1, while those producing SiH2 are the least favourable.…”

Section: Iii) Dissociation Reactions In Silyl Radicalsmentioning

confidence: 99%

A theoretical study of silyl anions and radicals. Change of mechanism from vertex inversion to edge inversion with increasing substitution by halogens

Hopkinson¹,

Rodriquez²,

Lien³

1990

Can. J. Chem.

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Structures for trivalent silyl anions SiH,F&,,) and SiH,C\j.,,), where n takes values from 0 to 3, have been optimized at the HF/6-3 1 + +G* level and single point calculations made at the MP2/6-3 1 + +G* level (core included). SiH3-and ions containing one halogen invert by the vertex mechanism in which the lone-pair has T-symmetry, and the monosubstituted ions have high barriers (SiH2F-45.2 kcal/mol and SiH2Cl-44.0 kcal/mol). Further substitution by halogens results in a change to the edge inversion mechanism involving a T-shaped transition structure with the lone-pair coplanar with the ligands. Baniers (kcal/mol) at the MP2/6-3 1 + +G* level including ZPE are lower than for the monosubstituted ions and are SiHC1, and SiC1,. In SiLi,-edge inversion is preferred, but the surface is much flatter and the barrier is low (9.8 kcal/mol). Trivalent silyl radicals SiH,F(3.,,), SiH,C1(3.,,) and SiF,,C1(3.n) (with n having values 0 to 3) have also been examined with the 6-31 + +G* basis set, with optimization at the UHF level and single point calculations at the UMP2 level.Radicals SiH,, SiH2F, SiH2C1, and SiHC12 all invert by the vertex mechanism. Increased halogenation results in a change of mechanism and SiF3, SiCl,, SiF2C1, and SiFC12 invert by the edge mechanism. For radical SiHF, the calculated barriers for the two mechanisms are almost identical with the higher level of theory slightly favouring edge inversion.Key words: inversion mechanism, halogenated silyl radicals and anions. Inversion of a pyramidal molecule AX3 (1, X = Y = Z. C3" r-donors or a-acceptors raises the barrier to inversion (2-7) and point group) usually proceeds through a planar trigonal structure halogens, which have both these properties, are particularly 2 which has D3h symmetry. When X = Y = Z = H, the effective (calculated barriers of CH2FP and SiH2F-are 24 and magnitude of the barrier to inversion increases as A becomes 58 kcal/mol, respectively). Increasing the number of halogen more electropositive due to the greater stabilization of the substituents should further increase the banier to inversion by pyramidal structure through HOMO-LUMO interactions (I).this vertex mechanism, but recent studies (8) Previously we reported barriers to inversion for monosubstiThe barriers to inversion of hydrides from the second row, then, tuted silyl anions (9) and the discovery that increasing halogen are larger than those for analogous molecules from the first row substitution in the isolelectronic phosphines results in a change and the silyl anion SiH3-has a much larger barrier than the in the inversion mechanism stimulated us to extend our work to methyl anion CH3-(26 kcal/mol (2) compared with 0.5 polyhalogenated silyl anions. kcal/mol (3)). Replacing the hydrogens with atoms which areThe parent silyl radical, SiH3, is pyramidal (10) and the barrier to inversion in radicals R3Si are sufficiently large that 'Revision received March 7, 1990. optically active silanes react via the radical with retention of Can. J. Chem. Downloaded from www.nrcresear...

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“…[10], wherein K/Na in DME was used, all reductions were carried out with solid potassium in THF and are very sensitive to changes of the reducing agents or solvents. Thus, attempts to reduce 2,2-dichloro-1,3-dineopentylbenzodiazasilole with potassium in ether, in dioxane, in DME, or in benzene in the presence of two equivalents of dibenzo-18-crown [6] as well as use of potassium/sodium alloy, KC 8 , or rubidium in THF did not give the anticipated silylene. In the naphthalene system, additional problems may arise from the lower LUMO and easier formation of radical anions that may cause different secondary reactions.…”

Section: Resultsmentioning

confidence: 99%

“…The persistence of monomers increases with the relative stability of two-compared to four-valent species, with steric protection and stabilizing electronic factors such as intramolecular higher coordination [5] and pp-pp-bonding [6][7][8]. Thus, for silylenes with nucleophilic substituents, a considerable thermodynamic stabilization has been calculated increasing in the order halosilylenes Ͻ alkoxysilylenes Ϸ mercaptosilylenes K aminosilylenes [6] K diaminosilylenes Ͻ cyclic delocalized diaminosilylenes [7,8]. While germanium and tin are known to form isolable acyclic and cyclic dicoordinate diaminocarbene homologues [2][3][4], the less-favored silylenes are sufficiently stabilized only in the case of five-membered diaminosilylenes [9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Higher carbene homologues: Naphtho[2,3-d]-1,3,2?2-diazagermole, -diazastannole, and attempted reduction of 2,2-dichloronaphtho[2,3-d]-1,3,2-diazasilole

Heinicke¹,

Oprea²

1998

Heteroatom Chem.

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N,N′‐Dineopentyl‐2,3‐diaminonaph‐thalene 1, obtained by reaction of 2,3‐diaminonaph‐thalene with pivaloyl chloride and subsequent re‐duction, was dilithiated and cyclodisubstituted with SiCl4 to give dichloro‐dineopentyl‐naphtho[2,3‐d]‐1,3,2‐diazasilole 2. Treatment of 2 with two equivalents of potassium in THF caused cleavage of the Si–N ring. A silylene could not be detected. The corresponding cyclic diaminogermylene 3 and diamino‐stannylene 4 were obtained by direct ring closure of 1–Li2 with GeCl2·dioxane or SnCl2, respectively. The compounds are structurally characterized by NMR and MS. The properties of 3 and 4 are compared with those of related germylenes and stannylenes. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:439–444, 1998

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A theoretical survey of unsaturated or multiply bonded and divalent silicon compounds. Comparison with carbon analogs

Cited by 289 publications

References 22 publications

Concerning the Si—Li bonding in phenylsilyllithiums as studied by variable temperature Li nuclear magnetic resonance

Concerning the Si—Li bonding in phenylsilyllithiums as studied by variable temperature Li nuclear magnetic resonance

A theoretical study of silyl anions and radicals. Change of mechanism from vertex inversion to edge inversion with increasing substitution by halogens

Higher carbene homologues: Naphtho[2,3-d]-1,3,2?2-diazagermole, -diazastannole, and attempted reduction of 2,2-dichloronaphtho[2,3-d]-1,3,2-diazasilole

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