Ligand exchange ion–molecule reactions of simple silyl and germyl cations

Xavier, Luciano A.; Pliego, Josefredo R.; Riveros, José M.

doi:10.1016/s1387-3806(03)00164-7

Cited by 16 publications

(15 citation statements)

References 39 publications

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“…Several possibilities have been considered: [3,4] Recently, Riveros and co-workers examined the methide (CH 3 À ) exchange between H 3 Si + and MeGeH 3 and concluded that it proceeds through a methyl bridge. [8] + (I D + ) as described above, we now turn to a theoretical study of I + covering static and dynamic aspects in turn.…”

Section: Similar Behavior Is Observed If Si(ch 3 )mentioning

confidence: 99%

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How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺

et al. 2006

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In our Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry [1] studies on the gas-phase reactivity of Group 14 derivatives, we initially examined the behavior of tetramethylsilane, Si(CH 3 ) 4 (TMS). Using mild electron ionization (nominal energies between 10 and 12 eV) and pressures in the range 10 À8 -10 À5 mbar, the main ion observed is the trimethylsilyl cation, Si(CH 3 ) 3 + , formed through the fast decomposition of the radical cation Si(CH 3 ) 4 + C. A striking feature of the spectrum is the presence at low pressures of a weak signal ( % 1 %) at m/z 161 that fades away a few seconds after the ionization process. It corresponds to the most abundant isotopomer of the ion Si 2 (CH 3 ) 7 + (I + ). The stoichiometry of this species suggests a somewhat unusual electronic structure, which prompted us to carry out a more detailed study.Some important databases [2] do not report the existence of I + , although this ion was reported in 1974 by Klevan and Munson [3] as the product of reaction (1), which takes place under high-pressure conditions (0.3 Torr).Using high-pressure mass spectrometry, Stone and coworkers carried out a careful study of this reaction, as well as of similar processes involving Ge and Sn derivatives.[4] They also determined D r H m (1) and D r S m (1) for reaction (1) as (À22.3 AE 0.4) kcal mol À1 and (À35.2 AE 0.9) cal mol À1 K À1 , respectively. These values lead to a value for D r G m (1) of (À11.8 AE 0.7) kcal mol À1 . Herein, we report our observations that under the lowest pressures indicated above, kinetic excitation of Si(CH 3 ) 3 + by means of on-resonance irradiation or slightly off-resonance irradiation (SORI) under multiple-collision conditions [5] increases the yield of I + . In the presence of a cooling gas and without ion excitation, the abundance of this ion increases rather slowly. As expected from the value of D r G m (1), the equilibrium abundance observed under our working conditions is small.[6] Figure 1 shows a spectrum of ion I + .Collision-induced decomposition (CID) experiments on I + using argon as the target gas and energies at the center of mass below 2 eV show that Si(CH 3 ) 3 + is the only ion formed. This observation also indicates a "fragile" bond between Si(CH 3 ) 3 + and TMS, in agreement with the results reported in reference [3].Similar experiments using perdeuterated tetramethylsilane, Si(CD 3 ) 4 (TMSD), yield the ion Si 2 (CD 3 ) 7 + (I D + ), and CID experiments conducted as indicated for I + lead to the formation of Si(CD 3 ) 3 + as the sole ionic product. The study of mixtures of TMS and TMSD was generally conducted using 1:1 mixtures and nominal pressures of the individual reagents of about 1-2 10 À7 mbar, with argon being added up to pressures of 8 10 À7 -1.

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Section: Similar Behavior Is Observed If Si(ch 3 )mentioning

confidence: 99%

“…[7][8] The geometry optimization was carried out using a very flexible basis-set expansion, namely 6-311 + G(3df,2pd). The optimized geometry of I + corresponds to a C 3h -symmetric structure, in which a totally planar CH 3 group is symmetrically bonded to two Si(CH 3 ) 3 moieties.…”

Section: Similar Behavior Is Observed If Si(ch 3 )mentioning

confidence: 99%

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺

et al. 2006

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“…This feature is particularly interesting because it provides a convenient approach for exploring a variety of secondary condensation type ion/molecule reactions that bear strong resemblance to the fundamental reactions of sol-gel processes. 6,8 Theoretical calculations proved to be valuable to characterize the mechanism and energetics of these reactions. For the hydrolysis of gas-phase SiCl 3 + ion, DFT and ab initio calculations yield comparable results although some differences are observed for the energies of the transition states and intermediates of the reaction.…”

Section: Discussionmentioning

confidence: 99%

“…2 The gas-phase ion chemistry of R 3 Si + ions has been studied in some detail 3 and they are known to be powerful electrophiles that can readily promote reactions by addition-elimination type mechanisms. 4 Our group has studied several aspects of the gas-phase ion/molecule reactions of the tetralkoxysilanes [5][6][7][8] because of the role that these substrates play as precursors of both, sol-gel processes relevant to functional materials, and CVD processes relevant to microelectronics. Silicon tetrahalides, and particularly the fluoro and chloro derivatives, are also known to be intimately related to CVD processes and SiCl 4 and the hydrolysis and ammonolysis of the neutral substrates have been characterized both experimentally 9 and theoretically.…”

Section: Introductionmentioning

confidence: 99%

Gas-phase solvolysis type reactions of SiCl3+ cations

Firmino¹,

Menegon²,

Riveros³

2010

Quím. Nova

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Gas-phase SiCl 3 + ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10 -8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl 3 + is calculated to involve a substantial positive energy barrier.

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“…This ion associates with the parent tetramethylsilane molecule to produce the (CH 3 ) 7 Si + ion [2], that was also observed in the chemical ionization studies of pure tetramethylsilane [3][4][5]. Albeit the structure of this ion was proposed to contain a Si-Si bond with one silicon atom being pentacoordinated [3], the analysis of experimental data and the quantum chemical study of the (CH 3 ) 7 Si + ion [6] allowed authors to suggest a structure corresponding to a C 3h point group in which a planar methyl group is symmetrically bonded to two -Si(CH 3 ) 3 moieties. This structure was found to be a minimum at both B3LYP/ 6-311+G(3df,2pd) and QCISD/6-311+G(d,p) levels of theory [6].…”

Section: Introductionmentioning

confidence: 90%

An assessment of DFT methods for predicting the thermochemistry of ion-molecule reactions of group 14 elements (Si, Ge, Sn)

2013

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Experimental mass-spectrometry data on thermochemistry of methide transfer reactions (CH₃)₃M(+) + M'(CH₃)₄ ↔ M(CH₃)₄ + (CH₃)₃M'(+) (M, M' = Si, Ge or Sn) and the formation energy of the [(CH₃)₃Si-CH₃-Si(CH₃)₃](+) complex are used as benchmarks for DFT methods (B3LYP, BMK, M06L, and ωB97XD). G2 and G3 theory methods are also used for the prediction of thermochemical data. BMK, M06L, and ωB97XD methods give the best fit to experimental data (close to chemical accuracy) as well as to G2 and G3 results, while B3LYP demonstrates poor performance. From the first three methods M06L gives the best overall result. Structures and formation energies of intermediate "mixed" [(CH₃)₃M-CH₃- M'(CH₃)₃] complexes not observed in experiment are predicted. Their structures, better described as M(CH₃)₄ [M'(CH₃)₃](+) complexes, explain their fast decompositions.

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Ligand exchange ion–molecule reactions of simple silyl and germyl cations

Cited by 16 publications

References 39 publications

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺

Gas-phase solvolysis type reactions of SiCl3+ cations

An assessment of DFT methods for predicting the thermochemistry of ion-molecule reactions of group 14 elements (Si, Ge, Sn)

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Ligand exchange ion–molecule reactions of simple silyl and germyl cations

Cited by 16 publications

References 39 publications

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si2(CH3)7+

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si2(CH3)7+

Gas-phase solvolysis type reactions of SiCl3+ cations

An assessment of DFT methods for predicting the thermochemistry of ion-molecule reactions of group 14 elements (Si, Ge, Sn)

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How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺

How Can a Carbon Atom Be Covalently Bound to Five Ligands? The Case of Si₂(CH₃)₇⁺