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2001 The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces Jeannine M. Christensen Eastern Illinois University This research is a product of the graduate program in Chemistry at Eastern Illinois University. Find out more about the program.
Recommended Citation Christensen, Jeannine M., "The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces" (2001). Masters Theses. 1569. https://thekeep.eiu.edu/theses/1569
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thesis4_form The Reactivity of Boron and Aluminum Compounds
with Silica Gel Surfaces
(title)
BY
Jeannine M. Christensen
THESIS
SUBMITIED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
Masters of Science in Chemistry
IN THE GRADUATE SCHOOL, EASTERN ILLINOIS UNIVERSITY CHARLESTON, ILLINOIS
2001 YEAR
I HEREBY RECOMMEND THIS THESIS BE ACCEPTED AS FULFILLING THIS PART OF THE GRADUATE DEGREE CITED ABOVE
,:;/~ /01 r I DATE
DATE The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces
Jeannine M. Christensen Eastern Illinois University January 11, 2001 The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces
By: Jeannine M. Christensen
Advisor: Dr. Jonathan P. Blitz
Co-Advisor: Dr. Carol A. Deakyne
Date Submitted: January 11, 2001
Approved by the thesis committee:
Date
I I I I . • I . 11 /()I ·Date
Date ABSTRACT
The unmodified silica gel surface contains isolated silanols, vicinal silanols, and siloxane species. Silica gels can be thermally and/or chemically treated to obtain a desired surface. Hexamethyldisilazane (HMDS) was used to chemically modify the silica gel to obtain a surface that contains vicinal silanol groups and siloxane species. The silica gel was thermally treated at 600°C to create a surface that contains isolated silanols and siloxane species. Four types of silica gels (unmodified, 600°C, HMDS and 600°C/HMDS) were reacted with three boron compounds. The boron compounds used were boron trichloride (BCb), triethyl borane (B(CH2CH3)3) and triethyl borate
(B(OCH2CH3)3). To determine the behavior of the surface species with the boron compound used, infrared spectroscopy and elemental analysis techniques were used.
Infrared spectroscopy studies showed that BCb reacted with isolated silanol groups, vicinal silanols and siloxanes on the silica gel surfaces. The reactions of B(CH2CH3h and B(OCH2CH3)3 with the silica gel surfaces were found to have an effect on isolated silanols and siloxane species, but not on vicinal silanol groups. The spectra of B(CH2CH3)3 modified silca gels were compared to Al(CH2CH3)3 modified silica gels and very little difference was found. With both Al(CH2CH3)3 and B(CH2CH3)3, residual vicinal silanol bands were found in the spectra of the unmodified and HMDS silica gel.
Elemental analysis of the modified silica gels was used to determine the amount of boron chemisorbed on the silica gel surface. The reactivity trend of boron compounds was found to be BCb >B(OCH2CH3)3 >B(CH2CH3)3. The reaction of BCb with the silica gel surfaces was shown to have a reactivity trend of unmodified> 600°C > HMDS > 600°C/HMDS. The reactivity trend for the reaction of B(CH2CH3)3 and B(OCH2CH3) with the silica gel was as follows: unmodified > 600°C > 600°/HMDS > HMDS. The reactivity trend of B(CH2CH3)3 and B(OCH2CH3)3 differed from BCb due to the fact that vicinal silanol species are not reactive with these boron compounds. The elemental analysis of
B(CH2CH3)3 modified silca gel was compared to Al(CH2CH3)3 silica gel and it was found that there was a larger amount of aluminum being adsorbed to the silica gel surface.
Ab initio calculations were performed to understand the difference in reactivity between the aluminum (AICb and Al(CH2CH3)3) and boron (BCb and
B(CH2CH3)3) compounds with an isolated silanol group. Molecular geometries were optimized completely at both the HF/6-31G(d,p) and MP2/6-31(d,p) levels of calculation. The optimum geometries were then used to compute the single point energies that were used to evaluate reaction enthalpies and free energies.
For the overall reactions, the changes in enthalpy and free energy are negative.
Complete reaction pathways were determined for the AICb and BCb reactions with an isolated silanol. Locating the transition states for Al(CH2CH3)3 and
B(CH2CH3)3 reaction pathways has proven difficult.
ii DEDICATIONS
I would like to dedicate this work to my family, especially to my wonderful parents, Wesley and Kathleen Christensen. They have given me the love, support and encouragement I needed to complete this study. To my Dad, thank you for all of your supportive phrases, including "TCB-it". To my Mom, thank you for always knowing how to take my stress away. My sisters, Kristine and
Kathy, for their comedic abilities in making me laugh when I didn't think I could.
And a great big thank you to everyone who helped me in the process. I couldn't have done it without you.
"You were always there to help me You were always there . to guide me You-were always there to laugh with me You were always there to cry with me But most important you were always there to love me and I want to assure you that I am always here to love you"
Susan Polis Schutz
iii ACKNOWLEDGMENTS
I would like to thank both Dr. Jonathan P. Blitz and Dr. Carol A. Deakyne for allowing me to be a part of this research project and for their never-ending patience and guidance throughout. My professional discipline and understanding of chemistry has grown enormously as the result of the enriching time spent with these outstanding educators. My effort spent working on this thesis has provided a quality educational experience and has given me the research capability to continue to grow professionally.
Also, I would like to thank the educators and staff within the Chemistry
Department for their valuable assistance during my time at Eastern Illinois
University. My experience at Eastern Illinois University has been both valuable and rewarding. Thank you, all; for helping me achieve my goals.
iv TABLE OF CONTENTS
Abstract
Dedications iii
Acknowledgments iv
Table of Contents v
List of Tables vii
List of Figures viii
Chapter I: Introduction and Background
A. Introduction 1
B. Silica Gel Surfaces 1
C. Modified Silica Surfaces 3
D. Boron Compounds 4
E. Aluminum Compounds 9
F. Computational Chemistry 12
G. Schrodinger Equation 14
H. Born-Oppenheimer Approximation 14
I. Linear Combination of Atomic Orbitals (LCAO) 15
J. Hartree-Fock Theory 16
K. M011er-Plesset Perturbation Theory 16
L. Basis Sets 17
M. Types of Basis Sets 18
N. Notations Used in Basis Sets 19
0. Reaction Enthalpies and Free Energies 20
v Chapter II: Experimental Section
A. Materials 24
B. Methods 24
C. IR Analysis Preparation 25
D. Liquid IR Preparation 26
E. Quantitative Data Analysis 27
F. Computational Methods 28
Chapter Ill: Results and Discussion
A. Infrared Studies of the Silica Gel Surface 29
B. Infrared Studies of Silica Gels Reacted with Boron Compounds 30
1. Boron Trichloride (BCb) 31 2. Triethyl borane (B(Et)3) 34 3. Triethyl borate ·(B(OEth) 36
C. Elemental Analysis 39
D. B(Eth versus Al(Eth 42
E. Computational Results and Discussion 44
F. Geometrical Parameters 44
G. Reaction Thermochemistry 48
Chapter IV: Conclusion
A. Conclusion 51
References 54
Appendix A 57
vi List of Tables:
Table 1: Elemental Analysis for Statistical Calculations
Table 2: Summary of Band Assignments
Table 3: Isolated Silanol/Siloxane Ratio
Table 4: Elemental Analysis of Boron Compound Reactions
Table 5: Elemental Analysis of B(Eth versus Al(Eth
Table 6: Optimized Bond Lengths and Angles for Reactants
Table 7: Optimized Bond Lengths and Angles for Complex 1
Table 8: Optimized Bond Lengths and Angles for Transition States
Table 9: Optimized Bond Lengths and Angles for Complex 2
Table 10: Optimized Bond Lengths and Angles for Products
Table 11: Single-Point Energies and Enthalpies (in hartrees) Corrected to 298 K for the HF/6-31G(d,p) Geometeries.
Table 12: Single-Point Energies and Free Energies Corrected to 298 K for the HF/6-3.1.G(d,p) Geometeries
Table 13: Single-Point Energies and Enthalpies (in hartrees) Corrected to 898 K for the HF/6-31G(d,p) Geometeries
Table 14: Single-Point Energies and Free Energies Corrected to 898 K for the HF/6-31G(d,p) Geometeries
Table 15: Single-Point Energies and Enthalpies (in hartrees) Corrected to 298 K for the MP2/6-31G(d,p) Geometeries.
Table 16: Single-Point Energies and Free Energies Corrected to 298 K for the MP2/6-31G(d,p) Geometeries
Table 17: Single-Point Energies and Enthalpies (in hartrees) Corrected to 898 K for the MP2/6-31G(d,p) Geometeries
Table 18: Single-Point Energies and Free Energies Corrected to 898 K for the MP2/6-31G(d,p) Geometeries
vii List of Figures:
Figure 1: Silano! and Siloxane Species on the Silica Gel Surface
Figure 2: Thermal Treatment of Silica Gel Surface
Figure 3: Summary of the Silica Gel Surface
Figure 4: Bare Silca Gel
Figure 5: 600°C Silica Gel
Figure 6: HMDS Silica Gel
Figure 7: 600°C/HMDS Silica Gel
Figure 8: BCb Modified Bare Silica Gel
Figure 9: Subtracted Spectrum of Bare Silica Gel Reacted with BC13 - Bare Silica Gel
.Figure 10: Boric Acid
Figure 11 : Liquid Spectrum of BCb
Figure 12: BCb Modified 600°C Silica Gel
Figure 13: Subtracted Spectrum: 600°C Silica Gel Reacted with BCb - 600° Silica Gel
Figure 14: BCb Modified HMDS Silica Gel
Figure 15: Subtracted Spectrum of HMDS Silica Gel Reacted with BCb - HMDS Silica Gel
Figure 16: BCb Modified 600°C/HMDS Silica Gel
Figure 17: Subtracted Spectrum of 600°C/HMDS Silica Gel Reacted with BCl3 - 600°C/HMDS Silica Gel
Figure 18: Summary of BCb Reactions
Figure 19: B(Et)3 Modified Bare Silica Gel
Figure 20: Subtracted Spectrum of Bare Silica Gel Reacted with B(Et)3 - Bare Silica Gel
viii Figure 21: Liquid Spectrum of B(Eth
Figure 22: B(Eth Modified 600°C Silica Gel
Figure 23: Subtracted Spectrum: 600°C Silica Gel Reacted with B(Eth - 600° Silica Gel
Figure 24: B(Et)3 Modified HMDS Silica Gel
Figure 25: Subtracted Spectrum of HMDS Silica Gel Reacted with B(Eth - HMDS Silica Gel
Figure 26: B(Eth Modified 600°C/HMDS Silica Gel
Figure 27: Subtracted Spectrum of 600°C/HMDS Silica Gel Reacted with B(Eth - 600°C/HMDS Silica Gel
Figure 28: Summary of B(Eth Reactions
Figure 29: B(OEth Modified Bare Silica Gel
Figure 30: Subtracted Spectrum of Bare Silica Gel Reacted with B(OEth - Bare Silica Gel
Figure 31: Liquid Spectrum of B(OEt)3
Figure 32: B(OEth Modified 600°C Silica Gel
Figure 33: Subtracted Spectrum: 600°C Silica Gel Reacted with B(OEth- 600° Silica Gel
Figure 34: B(OEth Modified HMDS Silica Gel
Figure 35: Subtracted Spectrum of HMDS Silica Gel Reacted with B(OEth - HMDS Silica Gel
Figure 36: B(OEth Modified 600°C/HMDS Silica Gel
Figure 37: Subtracted Spectrum of 600°C/HMDS Silica Gel Reacted with 8(0Et)3- 600°C/HMDS Silica Gel
Figure 38: Summary of B(OEth Reactions
Figure 39: Computer Generated Model of the Reactants
Figure 40: Computer Generated Models of Complex 1
ix Figure 41: Computer Generated Models of Transition States
Figure 42: Computer Generated Models of Complex 2
Figure 43: Computer Generated Models of the Products
Figure 44: Computer Generated Models of an Isolated Silano! Reacting with Al Ch
Figure 45: Computer Generated Models of an Isolated Silano! Reacting with BCh
Figure 46: Changes in Enthalpy When an Isolated Silano! Reacts with AICh at 298 K
Figure 47: Changes in Free Energy When an Isolated Silano! Reacts with AICh at 298 K
Figure 48: Changes in Enthalpy When an Isolated Silano! Reacts with BCh at 298 K
Figure 49: Changes in Free Energy When an Isolated Silano! Reacts with BCh at 298 K
x Introduction
Silica gels are used as stationary phases in chromatography, as binding agents in pharmaceuticals, as fillers for paints and pigments, and in many other commercial products. The largest uses of silica gels are for absorbents (1) and catalyst supports (2). Boron compounds, especially boron halides, have been used in attempts to manufacture new catalytic material and as molecular probes to better understand the surface groups of silica gels. Aluminum compounds, in particular aluminum alkyls, have been studied mainly for catalytic properties on the silica gel surface. This thesis project used both experimental and theoretical methods to better understand the reactivity of boron and aluminum compounds with silica surfaces.
Silica Gel Surfaces
The empirical formula of sil.ica gel is Si02, however the structure of the silica gel is based on an arrangement of Si04 tetrahedra. At the surface of the silica gel, silanol groups (Si-OH) and siloxanes (Si-0-Si) are formed when the tetrahedral structure is terminated. When hydroxyl groups are bound to silicon atoms on the surface of the gel, the term silanol has been widely used. The structure of silica gels is amorphous, meaning that the structure consists of randomly packed crystals. There has been much discussion of the surface of silica gels. What actually constitutes the surface? lier (3) defines the surface as a boundary that is resistant to nitrogen. In order to study the surface area of the various silica gels,
1 nitrogen is used to perform measurements since it is unable to penetrate beyond the surface, unlike water.
On the surface of unmodified silica gels, one can find siloxane species and three types of silanol groups. The silanol groups consist of isolated silanols, vicinal silanols, and geminal silanols. Each of the different surface species mentioned can be seen in Figure1.
The isolated silanols are also known as free silanols. The structure consists of a hydroxyl group bonded to a silicon atom that is bound to three oxygen atoms.
The name free silanol is used since the silanol group does not take part in hydrogen bonding with other silanol groups. The distance between the silanol · groups prevents hydrogen bonding to adjacent silanols.
The vicinal silanols are also .called bridged silanols. These silanol groups are similar to two free silanol groups closely spaced to each other, which allows for hydrogen bonding to occur. The hydrogen bonding occurs with an adjacent silanol group, which "bridges" the silanol groups.
Geminal silanol groups are species in which one silicon atom bonds with two hydroxyl groups. As with isolated silanols, geminal silanols are prevented from intramolecular hydrogen bonding. Geminal silanols are unable to hydrogen bond due to the large angle strain that would result.
The siloxane species on the silica gel surface consist of two silicon atoms sharing an oxygen atom. This species is the least reactive of the surface species.
However, it is important to note that when the vicinal surface groups are thermally removed, strained siloxane species may be formed creating reactive sites.
2 Modified Silica Surfaces
Silica gels can be modified to alter the chemical and physical properties of the surface. Thermal treatments can be used to modify surface structure. In the temperature range of 150-250° C, any water that has been physically adsorbed on the silica is removed by prolonged heating (2, 3). A treatment of this kind is known as dehydration (Figure 2A). Young (4) studied the effects of temperature on the silica surface. It was found that when silica gel was heated to a temperature of -
400°C, the surface retained more than half of the original vicinal silanol groups.
This type of surface is easily rehydroxylated since the silanol groups of this type are close enough together to allow water to adsorb to the surface. Also, when temperatures above 450°C are used, hydroxyl groups (mainly vicinal species) are further removed, leaving a surface harder to rehydroxylate. When the silica is thermally treated to the temperature of 600°C, the silica surface becomes dehydroxylated. This process condenses the vicinal silanol groups, allowing for an increase in isolated silanols and siloxanes (Figure 28). Therefore, isolated silanol and siloxane species can be found on the 600°C silica gel surface. A complete removal of all surface species is achieved when temperatures greater than 1200°C are used to thermally treat silica.
Chemically modifying the surface with HMDS (hexamethyldisilazane) changes the surface chemistry by methylating silanol groups. The HMDS reacts with the isolated silanol groups, which releases H atoms and produces stable TMS
(trimethylsilyl) groups. In order to better understand the quantity of silanol groups reacted with HMDS, Stark, et. al (5), studied the reaction using radiolabeled
3 hexamethyldisilazane -14C. The samples were then analyzed using a liquid scintillation spectrometer. The results of the study showed a 1: 1 ratio of silanol groups reacted to trimethylsilyl groups formed on the silica surface. Researchers questioned whether or not the ammonia liberated during the reaction would affect the surface of the silica gel. Nawrocki (6) answered this question in 1985. It was found that the production of NH3 during the reaction does not adsorb on the surface. The HMDS silica surface therefore consists of vicinal silanol groups, siloxane groups and TMS groups.
The surface of thermally and chemically treated silica, 600°C/HMDS silica, is comprised of trimethylsilyl groups and siloxanes. This is due to the fact that the thermal treatment removes the vicinal silanol groups and the chemical treatment with HMDS removes the isolated silanol groups by producing the TMS groups. An overview of the silica gel surfaces can be seen in Figure 3.
Boron Compounds
Boron is found as a naturally occurring mineral in nature. It has a variety of uses including preparation of boric acid, glass, enamels, pottery glazes and water softeners. It is the only nonmetal element found in Group 3 of the periodic table.
Boron has been of interest due to its electronic properties. Boron generally has an oxidation state of +3. This indicates that the boron atom is electron deficient and is a Lewis acid because it has an incomplete octet. The electron deficiency of boron has led to interest in its potential catalytic properties. Boron found at the surface
4 of silica gels has been shown to interact with molecules that can transfer protons and electrons (7).
Hambleton and Hockey (8,9) studied the effects of the silica/boron trichloride system on the catalytic cracking ability of cumene. They used a system in which silica treated at 500°C and reacted with BCb was exposed to cumene vapor. They also studied the effects of thermally treated silica reacted with BCb, which was then hydrolyzed and exposed to cumene vapor. The results of this study were disappointing because the catalytic activity of the BCb/silica system for cracking cumene was less than 1% of the usual industrial catalyst. The other complexes studied were silica surfaces modified with aluminum materials (AICb and Al(Me)3), which outperformed the BCb. It was concluded that there were two factors necessary in cumene cracking. First, the surface should be ionic. The aluminum modified surfaces exhibited ionic characteristics, but the boron modified surface demonstrated covalent ptoperties. Second, to be catalytic the surface should have protons available which the systems studied had.
Boron compounds have been used for many years as probe molecules for determining the reactivity of silanol groups and siloxane species on the silica gel surface. It should be noted that the most common boron compounds for this type of research are boron halides, in particular boron trichloride. Many researchers (8-
18) have used this reaction in order to determine the concentration of the surface hydroxyl groups, as well as to make distinctions between isolated, vicinal and geminal silanol groups. The reactions of BCb with the surface species are well
5 documented (10, 12-14, 16, 17, 19,21). It is speculated that BCb reacts with isolated silanols to form monodentate species as in equation (1 ).
H BCl2 / I 0 + BCb 0 + HCI (Eq. 1) I I Si Si
The reaction of BCl3 with vicinal silanol species allows for the formation of a bidentate species and is seen in equation 2.
Cl H H ~ I \\/ 0 0 . + BCb ...... : ...... • 0/ 0 + 2HCI (Eq.2) I I I "" I Si Si Si Si
From previous work preformed by Bermudez (12), it was believed that the geminal species also react with BCb to produce the products seen in equation 3.
HO OH + 2 HCI (Eq. 3)
\Si/+ BCl3······ ...... Si
6 When the surface is totally dehydroxylated, it has been determined that the BCb chemisorbs on the surface. This results in a monodentate species and a Si-Cl species on the surface seen in equation 4.
BC!i I + BCb ...... 0 + Cl (Eq. 4) A I Si Si Si ~i
The reactions of BCb with the silanol groups produce HCI. It was found that the liberation of HCI does not affect the surface groups produced (12,20).
The majority of the researchers have used infrared spectroscopy followed by
Raman spectroscopy, mass spectrometry, and gravimetric techniques to obtain measurements of the silica surface reacted with boron compounds. Bermudez (12) studied this reaction extensively using infrared spectroscopy. The IR bands were assigned to the products of silica reacted with BCb at room temperature and
800°C. He was able to determine the location of the geminal species by observing the hydrolyzed surface compared to the non-hydrolyzed surface. It was found in the IR spectrum that the geminal species produced a ring formation when the boron trichloride was reacted with silica and was further hydrolyzed. Peglar,
Hambleton and Hockey, have also studied the hydrolyzed reaction products of the
BCb/silica system. They concluded that with the formation of the B-OH bond, the isolated silanol species reforms (8, 12). Hambleton and Hockey (9) also found results in which boron trichloride does not react with all the vicinal silanol groups
7 found on the surface. In the study, silica gel was deuterated and then reacted with
BCb. It was found using infrared spectroscopy, that the smaller molecule, 0 20, was able to penetrate the vicinal silanol groups, and that the BCl3 molecule was sterically hindered from reacting. It was found that there were large residual peaks for 0-D and 0-H groups. This type of reaction was performed once again using
450°C treated silica gel, which eliminates most of the vicinal silanol groups. The spectra were viewed and it was determined that there was a decrease in the 0-D and 0-H bands in the spectra. It was concluded that the isolated silanol species were completely reacted, while the vicinal silanols did not react completely with
BCb due to steric hindrance. Morrow and Devi (22) were one of the first research teams to determine whether the less reactive siloxane groups would react with
BCb. They reacted a completely dehydroxylated silica surface with BCl3. It was found that BCl3 chemisorbs strongly on this type of surface producing two new bands in the IR spectrum, proving that the sHoxane groups do react with BCb.
Morrow and McFarlan (15) studied silica gels reacted with a range of small to large hydrogen sequestering agents, including BCb, B(Et)3 and HMDS to determine whether or not steric dimensions affect the amount of silanol groups reacted. They observed the kinetics of the BCb reaction with silica gel by use of fast scanning FT
IR spectrometry. It was found that the reaction was complete after 30 seconds and that initially the vicinal silanol groups were more reactive than the isolated silanols.
This was due to the reactivity of BCb and to the fact that BCb reacts bifunctionally with adjacent vicinal groups. Although the vicinal groups reacted more readily, it should be noted that the reaction of the isolated silanols went to completion
8 whereas there were residual vicinal groups left on the surface. When larger molecules, i.e. HMDS and B(Et)3, were reacted with the surface, it was found that these reactants were sterically hindered from reacting with the vicinal silanol groups. It was also found that as the size of the reactant increased, the quantity of silanols reacted decreased. This occurred mainly with vicinal silanol groups.
Aluminum Compounds
Aluminum shares similar properties with boron, since they are both group Ill elements. Aluminum is a highly reactive metal, as well as a strong Lewis acid.
Aluminum compounds are used in industrial applications and are used in common households on a daily basis. In industry, there is a "push" to obtain new or improved catalysts, and many researchers choose to perform studies on aluminum since it has such extensive applications. A commonly known aluminum catalyst is
AICb, which is used in Friede1.:crafts reactions. Friedel-Crafts reactions are used to produce the starting material, ethyl benzene, in the production of polystyrene.
Another catalyst which utilizes aluminum compounds is the Ziegler-Natta catalyst.
The Ziegler-Natta catalyst allows for more rapid polymerization of alkenes, especially ethylene and propylene. This type of catalyst allows for additional polymerization to take place at somewhat lower temperatures and pressures. The
Ziegler-Natta catalyst is commonly prepared from mixing titanium (IV) chloride with an aluminum alkyl, such as Al(Me)3 or Al(Et)3, (23,24) on silica gel support.
As discussed in the boron compounds section, Peglar, Hambleton and
Hockey (9) studied the effects of cumene cracking with silica gels modified with
9 either BC'3, AICb, or Al(Me)3 and found that the aluminum compounds were much more effective. In their studies, they also looked at the infrared spectra of the silica gels modified with these compounds (8). The findings with the BCb have previously been addressed. The reaction of AICl3 with the silica surface was performed in the gas phase. Since AICb is a solid at ambient temperatures, the
AICb was heated to 200°C. At this temperature, AICb is highly dimeric because it is at the solid-gas equilibrium condition (7). It has been seen that AICl3 reacts very similarly to BCb with the possible exception of the following species forming.
Also, when the AICb modified silica gel is hydrolyzed, there are signs of isolated silanol groups reforming, but unlike BCb there is no spectral evidence of aluminum hydroxyls (Al-OH) forming.
A study performed by Diebel (25) examined the modification of silica gels with various aluminum compounds using infrared spectroscopy and elemental analysis. The compounds used were trimethyl aluminum (TMA), triethyl aluminum
(TEAL), diethylaluminum chloride (DEAC), and ethylaluminum dichloride (EADC).
It was found that TMA was more reactive than TEAL with the silica gel surface.
TEAL was less reactive than TMA since it has an alkyl extension of one carbon that showed steric hindrance towards the silica gel surface. The study was also
10 centered on determining how exchanging ethyl groups with chloro groups alters the
reactivity of the reagents mentioned (TEAL, DEAC, EADC). It was thought that the reactivity of these compounds would be affected by the bond energies involved.
The ethyl groups on the compounds should be more labile than the chloro groups since the Al-C bond energy is lower than that of the Al-Cl bond. Therefore, the pattern of reactivity was expected to be: TEAL > DEAC > EADC. It was surprising to find from elemental analysis that the pattern was actually: EADC > TEAL >
DEAC. It was expected that when the various aluminum complexes were reacted with vicinal silanol groups, a bridged aluminum complex would result. In reality, when EADC was reacted with vicinal silanol groups, instead of producing a bridged complex, two dichloroaluminum species were formed. In order for this to be possible, it was assumed that the reaction was sterically allowed. This was especially noticeable with the reaction of EADC with the HMDS modified silica gel, since the majority of suriace contains vicinal silanol groups.
In previous studies, it was found that AICb and BCb react completely with isolated silanol groups and react highly, but not entirely, with vicinal silanol species and siloxane groups found on the surface of the silica gel. Morrow(12) studied the effects of steric hindrance with respect to the various.reagents with the silica gel surface. It was found that B(Eth was limited in reacting with the vicinal silanol groups which directed attention towards the concept that sterically hindered molecules are less reactive. An objective of this thesis is to study the reactivity of boron compounds (BCb, B(Eth and B(OEth) with the silica gel surface by using infrared spectroscopy and elemental analysis. The FT-IR spectroscopy will allow
11 for the determination of which surface species have reacted, and the elemental analysis will establish the amount of boron being absorbed on the surface. This study will look at how the reactivity is affected by the steric hindrance of the molecule, especially between the triethyl borane and triethyl borate compounds.
Diebel (25) found that the reactivity of the aluminum alkyls was affected by steric hindrance. As mentioned above, the TMA was more reactive than the TEAL. It was determined that when the molecule is extended by one carbon group, steric hindrance prohibits the TEAL from reacting with a number of the surface groups, in particular vicinal silanols. One objective of this work is to determine how the reactivities of boron and aluminum compounds differ with an increase in the size of the molecules involved in the reactions with silica gel surfaces. A second goal of this work is to understand how the reactivity of boron and aluminum differs. In order to study the reactivity of boron and aluminum and to better understand the effects of steric hindrance, ab initio calculations will be carried out to probe the energetics of the boron and aluminum reactions.
Computational Chemistry
In the past, when chemists hoped to gain information about chemical systems, they entered their laboratories and performed experiments. With the advent of quantum mechanics, scientists had a new method of solving chemical problems, although they encountered many mathematical hurdles that proved difficult to overcome. Since the 1950s, chemists have used the technology of computers to create a new branch of chemistry called computational chemistry.
Computational chemistry utilizes chemical, mathematical and computer skills to
12 provide information on chemical systems. As computers and computational programs have increased in power, more and more complex molecules have been studied. Using quantum molecular theory, scientists can probe the properties of systems that are undesirable to work with in the laboratory or they can use theoretical data to complement experimental data.
The backbone of computational chemistry is the Schrodinger equation. The
Schrodinger equation uses mathematics to unlock the electronic structure of atoms and molecules. From this powerful equation, a variety of information can be obtained including the following: equilibrium geometries, vibrational frequencies, transition-state structures and thermodynamic properties. The calculations reported in this study were carried out ab initio. The term "ab initio" is Latin for
"from scratch" and indicates that no experimental data are used to simplify solving the Schrodinger equation. Performing ab initio calculations is advantageous since reliable information is obtained for an extensive range of systems. The main disadvantages to this type of calculation are the resources and computational time required.
In this project, computational chemistry has been employed to improve our understanding of the relative reactivities of the aluminum and boron compounds with silica gel, in particular with the isolated silanol species. Through the calculations, the energetics of the reactions from reactants to transition states to products can be followed. To the best of our knowledge, the systems examined in this project have not been studied previously by means of computational chemistry.
13 The Schrodinger Equation
Electronic structure calculations use the time-independent Schrodinger equation to express the particle-wave duality of the electrons present in an atom or molecule. The simplest form of the Schrodinger equation is given in Equation (5), in which His the Hamiltonian operator, which operates on the wave function, \J' and
Eis the total energy of the system.
H\J'=E\J' (5)
The Hamiltonian operator is equal to the sum of the kinetic, T, and potential, V, energy operators (Equation 6).
H=T+V (6)
.Using the definitions of T and V, the simplified Schrodinger equation is expanded into equation 7, in which the kinetic energy is given by the first term and the potential energy is given by the second term.
L1 [-h2/(8n2mi) Vi2]ll' + V(x,y,z)'I'= E 'I' (7)
When the Schrodinger equation is solved, two important quantities are obtained: the energy of the system .and the wave function. The value of the square of the wave function at a given point is proportional to the probability of locating the particle at that point. It should be noted that the Schrodinger equation can be solved exactly only for one-electron atoms. Therefore, a number of approximations are utilized to solve the Schrodinger equation for multiple electron systems.
Born-Oppenheimer Approximation
One simplifying assumption used to solve the many-electron Schrodinger equation is the Born-Oppenheimer Approximation. This approximation allows the
14 electron and nuclear motions to be separated by ignoring the kinetic energy of the
nuclei. Treating the nuclei as stationary is justified for most species since the
nuclei are so immense compared to the electrons found in the system. With the
nuclei fixed in space, the electronic Hamiltonian is used in the Schrodinger
equation and the electronic energy associated with the given set of nuclear
coordinates is obtained. Repeating the calculation with different sets of nuclear
coordinates yields the dependence of the energy of the molecule on the molecular
geometry.
Linear Combination of Atomic Orbitals (LCAO)
Another approximation used to solve the many-electron Schrodinger equation is
the linear combination of•atomic orbitals (LCAO). This method is based on the
. limiting behavior when an electron from one atom approaches, or is close to, the
nucleus of another atom in the system. The electronic wave function then begins
to resemble an atomic orbital of the second atom. The overall wave function is
approximated as a linear combination of the atomic orbitals (Equation 8).
(8)
The 'Pi represents the molecular orbitals, the Cµi represents the molecular orbital
expansion coefficients, and the ~µ represents the fixed set of atomic orbital
functions. The functions~µ are also known as basis functions and, when compiled,
constitute a basis set. Basis sets will be discussed in further detail below.
15 Hartree-Fock Theory
Hartree-Fock theory is a starting point for many computations. This type of calculation is a good level at which to start, since it requires less computational time than higher-level calculations. In the Hartree-Fock method, the Schrodinger equation is solved by considering a single electron moving in a potential where the motions of the other electrons are "averaged out". Initially, a guess is made for the atomic orbital coefficients, one-electron molecular orbitals are set up, and the average field due to the nuclei and the remaining electrons is calculated. The
Schrodinger equation is solved iteratively until the change in the atomic orbital coefficients is below some threshold value. The disadvantage to the Hartree-Fock approach is that it does not take into account the correlated motion of electrons due to their negative charges. In some cases, the energy that is found with the
Hartree-Fock method is less stable·than expected, which can cause errors in following the changes of enthalpy throughout a reaction.
M0ller-Plesset Perturbation Theory
One way electron correlation is taken into account is by using M0ller-Plesset perturbation theory. This higher level of theory generally yields more accurate energies compared to the Hartree-Fock level. M0ller-Plesset perturbation theory treats the Hartree-Fock model as the zero-order problem and the difference in the true Hamiltonian and the Hartree-Fock Hamiltonian as a perturbation. The correlation energy is then expanded as follows:
Ecorrelation = E(2) + E(3) + E(4) + ..... + E(n) (9)
16 The symbol, e
Jensen (29) including just the 2nd order contribution (MP2) accounts for 80 - 90% of the correlation energy. Therefore, in most cases where economical challenges are placed on calculations, the expression for the correlation energy is curtailed after 2nd order. Once the correlation energy is found, the exact energy of the system can now be calculated by adding the Hartree-Fock energy to the correlation energy (Eq. 10).
Eexact =EHartree-Fock + Ecorrelation (1O)
Basis Sets
A basis function is a mathematical description of an atomic orbital. A basis set is the complete set of basis functions used to characterize the molecular orbitals. In the case of ab initio calculations, the basis functions are typically expressed as linearly combined gaussian functions. The use of gaussian functions reduces the time required for the calculations compared to other functions, such as
Slater-type orbitals. Basis sets are chosen to maximize the reliability of the results within the computational time and disk storage available. Whenever possible, large basis sets are used to obtain more accurate approximations to the molecular orbitals by limiting the restrictions on the locations of the electrons. Thus, one of the steps involved in carrying out molecular orbital calculations is selecting an appropriate basis set.
17 Types of Basis Sets
I. Minimal Basis Sets
As the name indicates, minimal basis sets include the minimum number of basis functions required for each atom. This number is determined by the number of occupied atomic orbitals in the isolated atom. The hydrogen and carbon atoms will be used to demonstrate the atomic orbitals in this type of basis set. H: 1s; C:
1S, 2s, 2px, 2py, 2pz.
II. Split Valence Basis Sets
Split-valence basis sets utilize two functions to describe each of the valence atomic orbitals. Expanding the basis set in this way allows the size of the valence orbitals to adjust to the environment. The hydrogen and carbon atoms are used to better illustrate this type of basis set. It should be noted that the primed orbitals differ in size from the unprimed orbitals. H: 1s, 1s'; C: 1s, 2s, 2s', 2px, 2py, 2pz,
2px', 2py', 2pz'.
111. Polarized Basis Sets
When an atom is in a molecule or in the presence of an electric field, its charge density distorts from spherical symmetry. Polarization functions, which are atomic orbitals of higher angular momentum then are occupied in the free atom, are needed to properly describe this distortion. Typically, p- and d- functions are added to hydrogen atoms and d- and f- functions are added to heavy atoms.
18 IV. Diffuse Function Basis Sets
Basis sets with diffuse functions are required to correctly determine the energies of electrons far from nuclear centers. Diffuse functions are valence s-, p and possibly d-functions with large radii and are especially important in studies of anions and excited states.
Notation Used in Basis Sets
Now that the different types of basis sets have been discussed, the notation used to describe the basis set employed in a given calculation will be discussed.
This is best done with an example, namely the 6-311 +G(2d ,2p) basis set. The 6 indicates that six gaussian functions are summed to represent the core atomic orbitals. The core arid valence orbitals are separated by the dash between the 6 and the 311. The 311 denotes the number of gaussian functions summed to represent the s- and p-type valence orbita!s. The 3 specifies that there is one s type valence orbital and one set of p-type valence orbitals (the innermost valence orbitals) that are linear combinations of three gaussian functions. The 11 following the 3 designates that there are two additional sets of s- and p- type valence orbitals comprised of one gaussian function each. Plus signs are used when diffuse functions are incorporated into the basis set. A single "+" sign denotes that one s diffuse function and one set of p-diffuse functions have been added to the basis set for non-hydrogen atoms. The letter "G" indicates that the atomic orbitals are expanded as linear combinations of gaussian functions. The terms in parentheses are used to show the types and number of sets of polarization functions employed
19 for heavy (non-hydrogen) atoms and hydrogen atoms (heavy atoms, hydrogen atoms). For the example cited, the "2d" indicates that there are two d-function sets
(10 d-orbitals) on each heavy atom and the "2p" indicates that there are two p function sets (6 p-orbitals) on each hydrogen atom. Thus, for the 6-311 +G(2d,2p) basis set, a carbon atom has 5 s-orbitals, 4 sets of p-orbitals, and 2 sets of d orbitals, and a hydrogen atom has 3 s-orbitals and 2 sets of p-orbitals. Therefore, each carbon atom has 27 basis functions and each hydrogen atom has 9 basis functions in this basis set.
A complete description of the level of calculation also designates the theory used. Both the Hartree-Fock (HF) and second order M0ller-Plesset (MP2) methods were utilized in this research. Therefore, the complete level of calculation is expressed as, for example, HF/6-31G(d,p) or MP2/6-311+G(d,p).
Reaction Enthalpies and Free. Energies
The goal of this research is to understand the chemical changes that occur on the silica gel surface after modification with boron and aluminum compounds.
Thermodynamics can be used to study the changes in enthalpy and free energy for these reactions. The enthalpy change for a reaction is given in equation 11, in which U is the internal energy, Pis the pressure and Vis the volume.
AH= AU+ A(PV) (11)
Since gas-phase reactions were examined in this computational work, the APV term can be converted to RTAn, where n is the number of moles involved (equation
12).
20 AH = AU + RT An (12)
The internal energy, U, can be expanded in terms of all the energy components in the system, seen in equation 13.
U = Eelectronic + Etranslational + Erotational + Evibrational + Enuclear (13)
The computational chemistry program Gaussian 98, calculates the energy of a molecule at rest at 0 K. Therefore, thermal correction terms are added to obtain the internal energy of the molecule at 298 K (equation 14).
Thermal Correction to Energy= ZPE + Erot + Etrans + AEvib (14)
The rotational and translational energies are treated classically, and are equal to~
RT per degree of freedom. AEvib represents the difference in the vibrational energy at temperature T and the zero-point energy (ZPE). It is calculated using standard statistical formulas (30).
The change in internal energy for a reaction at 298 K is determined using equation 15 (29).
AU29s= AEo + AZPE+ A(AEv)29s + AEr29s + AEt29s (15)
The difference in the molecular energies of the products and reactants at 0 K is denoted AE0. AZPE is the change in the zero point energies of the products and reactants. The vibrational energy difference, A(AEv)298, results from the change in the vibrational energy going from reactants to products at 298 K. AE?98 and AE/98 are the changes in translational and rotational energies, respectively, between products and reactants at 298 K.
21 The reaction enthalpy is then calculated via equations 16 and 17.
~H298 = ~u298 + RT ~n (16)
An example of a reaction enthalpy relevant for this work is given in equation 18. 29s_ H29s H29B H29s ~ H - complex - HCI - BCl2SIOH3 (18)
The enthalpy is then used to determine the Gibb's free energy. The change in free energy indicates whether or not a chemical reaction will occur spontaneously at the given temperature and pressure. The expression for the change in Gibb's free energy is shown in equation 19.
~G=~H-T~S (19)
For an individual molecule at 298 K, the free energy is expressed as:
G29B = H29s _ TS29s (20)
The entropy is computed in the program using statistical thermodynamics (31), and the expressions for the rotational, translational and vibrational entropies are given in equations 21, 22, and 23.
Strans= 5/2R + R ln((V/NA)((2rtMksT)/h 2 )~)) (21)
Srot = !R [3 +In ({"rt/cr)((8n:2ke T)/h2) ~ "(1112'3] (22)
Some of the terms in the previous equations are as follows: M is the total molecular mass, k8 is Boltzmann's constant, cr is the symmetry index, and I is the moment of inertia. The change in free energy is calculated by subtracting the free energies of the reactants from those of the products. The reaction enthalpies and free
22 energies have also been calculated at 898 K, following the same procedures as above.
23 Experimental
Materials
Toluene (Mallinckrodt) was dried using 4 A molecular sieves (Davison
Chemicals) activated at 250°C for 26 hours. Hexanes (Mallinckrodt) were dried with calcium hydride (Aldrich) for 24 hours with stirring in N2 (g). The glove box was.continuously purged with N2 (g). The bare silica gel (unmodified Davision 948,
W.R.Grace Corp.) was heated at 248°C with argon streamed into a fluidized bed to remove adsorbed surface water. The 600°C silica gel was prepared by heating bare silica in air for 6 hours. The HMDS (Lancaster Synthesis Inc.), hexamethyldisilizane, silica was prepared from toluene slurry (5 mmol HMDS/g
Si02). The reaction was allowed to proceed for two hours with frequent swirling.
The product was filtered and washed three times with 10 ml portions of dried toluene. The· silica was then evacuated at 110°C for two hours. The HMDS silica was heated for 24 hours at 248°C prior to use. The 600°C/HMDS silica gel was first treated by heating the silica to 600°C for 6 hours and then treated in the same fashion as the HMDS silica. The boron compounds used were boron trichloride
(1.0 M solution in heptane), triethylborane (1.0 M solution in hexanes), and triethyl borate (99%), all used as received from Aldrich Chemical Company.
Methods
All reactions were performed in a N2 (g) purged glove box. The reactions of various boron compounds with the bare (unmodified) silica gels were completed as follows: One gram of bare silica and 20 ml of hexane were added to a side-arm
24 flask. Then 10 mmol of boron compound per gram of silica was added to the flask and allowed to react for two hours. The supernatant liquid was then removed using a flat head syringe, and the silica was washed with 10 ml of dry hexane. The liquid was removed and this step was repeated twice more. The modified silica gel in a sealed flask was then evacuated for 1-% hours at room temperature to remove residual solvent. The sealed flask was transferred into the glove box for storage.
For the modified silica gels (600°C, HMDS, 600°C/HMDS) the same procedure was followed except 5 mmol of boron compound/g of silica was used rather than 1O mmol/g.
IR Analysis Preparation
For the analysis of the silica gel and products formed, a Nicolet 5PC FT-IR spectrometer was used. The Nicolet has a mercury cadmium telluride (MCT) detector that was cooled with liquid nitrogen prior to use. The computer software involved in the collection of the spectra was Omnic. The technique used for the collection of the spectra was diffuse reflectance spectroscopy. For each spectrum obtained, the following parameters were used: 64 scans, 4 cm-1 resolution, KBr beam splitter, and Happ-Genzel apodization.
Potassium chloride was used as a reference for the background scans and as a diluent for the sample matrix. The KCI (EM Science) was ground to a fine consistency by use of a mortar and pestle. The KCI was further mulled for two minutes by use of a Wig-L-Bug device, which produced a fine KCI powder with a
25 particle size from 5-10µm. The KCI was evenly distributed on a watch glass and heated for 48 hours at 150°C to remove any trapped water.
To obtain a background spectrum, approximately 150 mg of KCI was added to a Harrick controlled atmospheric cell while in the glove box. For the sample preparation, -135 mg of KCI was mixed with 15 mg of sample to create a sample matrix. The samples were all prepared in a N2(g) purged glove box.
Liquid IR Preparation
For the liquid analysis of the boron compounds and filtrate from the HMDS silica gel reacted with BCb, a Nicolet 20 DBX FT-IR spectrometer was used. The computer software involved in the collection of the spectra was Omnic. The spectra were obtained using 64 scans at a resolution of 4 cm·1 using a 0.5 mm IR liquid transmission cell that was seaied using rubber septa. The cell was flushed with dry hexane and then purged with N2 (g) for about two minutes. A syringe was used to transfer the liquid to the cell. For the background spectrum, dry hexane was used. The boron samples were prepared in the N2 (g) purged glove box by adding 20 ml of dry hexane and 4 ml of the boron compound to a round bottom flask. The flask was sealed with a rubber septum in order to take the sample outside the protected atmosphere. For the transfer of the compound to the IR cell, a stream of N2 (g) was bubbled through the flask using a syringe. To allow the gas to exit the flask, an open syringe was used. The stream of N2 (g) was removed and the open syringe was sealed using the plunger portion of the syringe and liquid was
26 removed and immediately transferred to the IR cell. The analysis of the solution was taken without delay to prevent moisture from affecting the results.
The liquid spectrum of the filtrate from the reaction of HMDS silica gel with
BCl3 was prepared by syringing out the solution from the reaction flask while in the glove box. The solution was transferred to a round bottom flask and sealed with a
rubber septum. The flask was transferred outside of the glove box and the solution was transferred to the IR cell in the same procedure as the boron compounds.
Quantitative Data Analysis
For quantitative data analysis, samples were sent to Galbraith Laboratories
(Knoxville, Tennessee). The method Galbraith used for analysis of boron and silicon was inductively coupled plasma emission spectroscopy. For the analysis of boron the wavelength used for determination was 249.77 nm and for silicon
251.611 nm. In order to obtain statistical information for the samples, four samples of HMDS silica treated with BCb and one sample of HMDS silica were sent for
boron and silicon analysis. The HMDS silica sample was sent as a blank to determine if boron was present on the silica gel surface before reaction with the
boron compounds. The results from the analysis for boron were converted to mmol
of 8 per gram of silica and the amount of silicon present is reported as a weight
percent (Table 1). It was found that the blank sample carried a negligible amount of boron and therefore it was not considered to be a factor. The relative standard deviation of the boron and silicon were calculated to be 8.14% and 5.40%,
respectively.
27 Computational Methods
The electronic structure calculations were performed using the Gaussian 98
(32) series of computer programs on a SGl-64 workstation. The first step in obtaining information on a chemical system is to optimize the geometry of the molecule of interest. To do this, an appropriate basis set and theoretical method must be chosen. For the purpose of this research, the 6-31 G(d,p) basis set was used with both the HF and MP2 methods. Equilibrium structures were determined at the HF/6-31G(d,p) level and then reoptimized at the MP2/6-31G(d,p) level. The calculated energies are for the molecule at rest at 0 K. In order to obtain energies at 298 K and 898 K, thermal energy corrections were evaluated using the optimum geometry at the appropriate level. The computed vibrational frequencies were scaled by the usual factors of 0.8929 for the HF/6-31G(d,p) calculations and
0.9427 for the MP2/6-31G(d,p) calculations. The next step was obtaining single point energies, i.e.· recalculating the·energy of a HF or MP2 equilibrium structure at a higher level of theory. Single-point energies were evaluated at the MP2/6-
31 G(d,p) (HF geometries only}, MP2/6-31+G(d,p), MP2/6-311+G(d,p) and MP2/6-
311 +G(2d,2p) levels of theory. In this way, the effect of expanding the basis set on the reaction thermodynamics could be assessed.
28 Results and Discussion
Infrared Studies of the Silica Gel Surface
The silica gel surface has been studied using many techniques, including
XPS and 29Si CPMAS NMR, but the most common has been infrared spectroscopy. The unmodified silica has isolated, vicinal and geminal silanol groups and siloxane groups. The spectrum of bare silica can be found in Figure 4.
The absorbance of the non-hydrogen bonded, isolated silanol groups exhibits a sharp characteristic peak at -3742 cm·1.
The broad peak for the hydrogen bonded, vicinal silanols can be found from
-3660 - 3200 cm·1. The vicinal groups with weak hydrogen bonds can be found at a higher wavenumber than that for strongly. hydrogen bonded groups.
For many years it has been a debated issue on whether or not geminal species exist on the surface. Geminal silanol groups are now known to exist on the silica gel surface. It is believed that the geminal peak is separated from the isolated silanol peak by a mere 1-2 cm·1• which makes it extremely difficult to assign bands in the infrared spectrum. There was hesitation to assign the geminal band on the small shoulder of the isolated silanol peak due to speculation it was an artifact. Therefore, there was an incentive to determine whether the shoulder was an artifact or due to the geminal species. The next step was to study the silica surface by 29Si CPMAS NMR. Sindorf and Maciel (26, 27) used this technique and determined that geminal silanols do exist in a distinct band at -92 ppm in the spectrum. Also in the spectrum, the isolated and vicinal silanol groups' bands are
29 identified at -100 ppm. Morrow and other researchers (20) have argued that infrared spectroscopy cannot distinguish between the isolated and geminal silanol groups.
The broad peaks found at 1880 cm·1 and 1620 cm·1 are due to the siloxane
(Si-0-Si) combination and overtone bands. It should be noted, that in all of the spectra featured a peak is present at - 2350 cm·1, which is indicative of C02 found within the spectrometer.
The 600°C silica (Figure 5) has isolated silanol groups and siloxane bands.
Therefore, the bands to be expected are at 3742 cm·1 for the isolated silanol groups and the broad bands at 1880 cm·1 and 1620 cm·1 for the siloxane groups.
The HMDS treated silica (Figure 6) contains vicinal silanols, siloxanes, and trimethylsilyl groups. There are two peaks that arise from the C-H stretching of the
TMS groups. The first. peak is sharp and symmetric and can be found around 2960 cm·1 and the other peak is smaller, less intense and is found at -2906 cm·1. These peaks are associated with the asymmetric and symmetric C-H stretching vibrations, respectively. The other bands located in the spectrum come from the vicinal silanol groups, in the region of 3600-3200 cm·1• and the siloxane bands.
The HMDS/600°C treated silica gel (Figure 7) has trimethylsilyl groups and siloxane bands.
Infrared Studies of Silica Gels Reacted with Boron Compounds
The spectra presented are shown in the range of 4000-1300 cm·1 due to several complications. First, silica gel is a strongly adsorbing material in the region
30 below 1300 cm- 1, which makes it difficult to assign peaks. Second, in some cases, the product formed by the reaction of the silica gels with the boron compounds
became hydrolyzed (due to some moisture entering the glove box) making band
assignments more complicated. Last, when the spectral subtraction is performed,
spectral artifacts may arise which obscure the details of the spectra. In order to
perform a spectral subtraction, a peak is chosen to become the standard. For the
spectra presented, the siloxane peaks were selected since they are present in all of the spectra to be subtracted. It is desired to null the siloxane peaks to reveal
spectral changes, but during that procedure, other peaks may be compromised.
Therefore, caution is taken when viewing and assigning bands to the spectra.
Table 2 shows a summary of the band assignments that will be discussed.
BC/3 Reactions with Unmodified and· Modified Silica Gels
When BCb reacts with unmodified silica gel, it is able to react with isolated
and vicinal silanol species and siloxanes (10, 12-14, 16, 17,19). The spectrum was taken once the reaction was complete and can be seen in Figure 8. In order to
clearly see the spectral changes, the spectrum of the unmodified silica reacted with
BCb (Fig.8) was subtracted from the spectrum of the unmodified, unreacted silica
gel (Fig.4) and can be seen in Fig.9. From the spectrum it can be seen that the
3742 cm-1 peak has diminished, indicating that the reaction of BCb with the isolated
silanol species is complete. The increase in the 3660-3200 cm-1 band shows that
water has physically adsorbed on the surface. However, it is not spectrally clear
the extent to which the vicinal silanols have reacted due to the adsorbed water on
31 the surface. It should be noted that there is a small sharp peak at 3695 cm-1. This peak can. be attributed to either a spectral artifact or it can be associated with hydrolysis of the product. Hambleton and Hockey (17) have studied the effects of the hydrolyzed product and have assigned this peak to a single boron hydroxyl group on the silica gel surface. The peak range from 1470 - 1430 cm-1 is due to the B-0 stretching from the (=Si-O-B-Cl2) surface species, which is in agreement with Morrow (16). The strong band from 1400 - 1350 cm-1 is related to the SiOB species from the vicinal silanol groups reacting with BCb. The peak in the
1400 cm- 1 region is broader than those obtained by other research groups, and brought suspicion that it was caused by the hydrolysis of the product. In order to assign bands to the hydrolyzed products, a spectrum of boric acid was taken that can be seen in Fig.10. It can be seen from this spectrum that the band in the region of 1500 - 1350 cm-1· is caused by the B-0' stretch. The broad band can be attributed to the overlap of the stretching of the B-0 band between the BCb reacted silica and the B-0 band for the hydrolyzed product. The reaction of the siloxane species with BCb is difficult to confirm using infr~red spectroscopy. The reasoning is that when the siloxane species are reacted with BCb it produces a monodentate species (=Si-O-B-Cl2) and a Si-Cl species. The monodentate species can be seen as previously discussed, but the Si-Cl species is much harder to account for. The
Si-Cl stretching peak is found in the 550 - 450 cm-1 region, which was not observable due to the fact that it is not within the range of the instrument used (17).
It should also be noted that the excess BCb does not physically adsorb on the silica surface (12). The liquid spectrum of BCb can be seen in Figure 11. The
32 spectral bands from molecular 8Cb are not observed in the spectra presented, with the exception of a weak band present at 927 cm-1.
The spectrum of 600°C silica modified with 8Cb can be seen in Fig.12. The difference spectrum of the 8Cb reacted with 600° C silica (Fig.12) from 600°C silica gel (Fig.5) can be seen in Fig. 13. The 600°C silica gel surface has isolated silanol groups and siloxanes available for reaction with 8Cb. It is evident that the isolated silanols have reacted from the negative peak at 37 42 cm- 1 found on the spectrum.
A large symmetrical peak is evident at 3215 cm-1• This is attributed to 8-0H stretching from the hydrolysis of the product. The broad peak in the 1452 cm- 1 region is due to the 8-0 stretch from the production of the (=Si-0-8-Cl2) surface species as well as the 8-0 stretch from hydrolyzed product.
The HMDS silica gel reacted with the 8Cb spectrum (Fig.14) was spectrally subtracted from the HMDS silica gel spectrum (Fig.6) to yield the difference spectrum (Fig.15). It is believed that the HME>S silica gel allows 8Cb to react mainly with vicinal silanol groups and some siloxane species. The diminished peak from 3660 - 3490 cm-1 indicates that the vicinal silanol groups have reacted with the 8Cb. The sharp peak at 3215 cm-1 is present from the 8-0H stretch from the product being hydrolyzed. The spectrum shows that the TMS peaks are negative; therefore, it was necessary to test the filtrate from the product to ensure that TMS groups were not being removed by the reaction with 8Cb. A spectrum of the filtrate
(from the reaction of HMDS silica gel with 8Cb) was taken and then subtracted from a spectrum of dry hexane. Loss of TMS groups was not detected from the spectrum. The negative peaks at -2960 and 2906 cm-1 are thus considered a
33 subtraction artifact. The peak at 1417 cm- 1 is due to the formation of a Si08 unit from vicinal silanol groups reacting with 8Cb to form a bidentate species.
The spectrum of the 600°C/HMDS silica gel reacted with 8Cb (Fig.16) was subtracted from the 600°C/HMDS silica gel spectrum (Fig.7) to yield the difference spectrum (Fig.17). On this surface, the vicinal silanol groups have been thermally removed and the isolated silanol groups were "blocked" by chemically modifying the surface with HMDS leaving only siloxane species. The peak at 3215 cm- 1 is the
8-0H stretching of a hydrolyzed product. This indicates that the siloxanes have reacted producing (=Si-0-8-Ch) surface species that have been hydrolyzed. The
8-0 stretching peak from the monodentate species is present in the spectrum at
1450 cm- 1. The production of the Si08 peaks in the spectrum has demonstrated that siloxane species react with 8Cb. The proposed reactions of 8Cb with the silica gel surface species are summarized in Figure 18.
B(Et)3 Reactions with Unmodified and Modified Silica Gels
The unmodified silica gel reacted with 8(Et)3 spectrum (Fig.19) was subtracted from the unmodified silica gel (Fig. 4) to produce the difference spectrum (Fig.20). From the subtracted spectrum, it can clearly be seen that the isolated silanol species have reacted due to the negative peak found at 3742 cm- 1.
In agreement with McFarlan (28), the 8-0 stretch from a monodentate species is found at 1345 cm- 1. The vicinal silanol groups have not reacted due to the large residual band at 3640 - 3200 cm- 1. It should be noted that the production of the 8-
0H stretch resulting from the hydrolyzed product could contribute to the increase in
34 the band. Also, since there is not an additional 8-0 stretch, it eliminates the possibility that a bidentate (=Si0)28Et species exists on the surface. There are three new peaks that have formed, and they are located in the CH stretching region of 3000 - 2800 cm·1. Accompanying the production of these new peaks, CH bending peaks have been observed in the 1500 -1370 cm·1 region. A liquid spectrum of 8(Et)3 was taken and can be found in Figure 21. Similar to 8C'3, spectral bands from molecular 8(Eth did not contribute to the reaction spectra presented, meaning that excess 8(Eth was not adsorbed on the surface.
The spectrum of 600°C silica gel reacted with 8(Eth (Fig.22) was subtracted from the 600°C spectrum (Fig.5) to yield the difference spectrum (Fig.23). In this spectrum, it is evident that the isolated silanol species have reacted with the 8(Et)3 by the presence of the negative peak at 37 42 cm·1. The 8-0 stretch from the monodentate species is present at 1351 cm·1: The CH stretching peaks and CH bending. peaks are also present.
The HMDS silica gel reacted with 8(Eth spectrum (Fig.24) was subtracted from the HMDS silica gel spectrum (Fig.6) producing the difference spectrum
(Fig.25). If Figure 24 were compared to Figure 6, one would find there is very little difference between the spectra. The subtracted spectrum indicates that there are vicinal silanol species still present on the surface and negative peaks for the TMS species due to a subtraction artifact. The only noticeable peaks relating to the reaction of 8(Eth with the HMDS silica gel is the 8-0 stretch from the monodentate species, at 1355 cm·1, and the CH bending. Since the HMDS silica surface consists of vicinal silanol species and siloxane groups, the 8-0 stretch found is
35 speculated to be the result of siloxane groups reacting with B(Et)3. The reaction was very small and this is shown by the intensity of the B-0 stretch (notice the y axis scale compared to the other spectra). This indicates that the size of the molecule may be a factor in the reactivity of the surface.
The 600°C/HMDS silica gel reacted with B(Eth spectrum (Fig. 26) was subtracted from the 600°C/HMDS silica gel (Fig.7) to obtain the difference spectrum (Fig.27). A small broad peak was found at 3215 cm·1 indicating that the product had been hydrolyzed producing a B-OH stretch. The CH stretch, CH bend and B-0 stretch from the monodentate species at 1360 cm·1 are also present in the spectrum. The reactions of the silica gel surface species with B(Eth have been summarized in Figure 28.
B(OEt)a Reactions with Unmodified·and Modified Silica Gels
The spectrum of the reaction of B(OEth with the unmodified silica gel (Fig.
29) was subtracted from the spectrum of the unmodified silica gel (Fig. 4) to generate the difference spectrum (Fig. 30). From this spectrum, it is shown that the isolated silanols have reacted due to the negative peak at 37 42 cm·1. The B-0 band is also present in the spectrum at 1342 cm·1 indicating that a monodentate species has formed. Also, from the presence of the B-OH stretch seen near 3215 cm·1, the product has been hydrolyzed. It is evident from the spectrum that the vicinal silanol species have not reacted. As in the reactions of B(Eth with the silica gels, CH stretching and bending are observed in the 3000 - 2800 cm·1 region and the 1500 - 1370 cm·1 region, respectively. The liquid spectrum of B(OEth can be
36 seen in Figure 31. As with the other boron compounds, there are no contributions to the spectra from adsorbed B(0Et)3.
The spectrum of 600°C silica gel reacted with B(OEth (Fig.32) was subtracted from the 600°C spectrum (Fig.5) to yield the difference spectrum
(Fig.33). It is seen that the isolated silanol groups have been reacted due to the negative peak at 37 42 cm- 1 and to the presence of the B-0 stretching from the formation of the monodentate species at 1346 cm- 1. The spectrum also contains the CH stretching and bending bands. It is evident that the surface has been hydrolyzed due to the B-OH stretch at 3215 cm-1.
The HMDS silica gel reacted with the B(OEth spectrum (Fig.34) was spectrally subtracted from the HMDS silica gel spectrum (Fig.6) to yield the difference spectrum (Fig.35). From the spectra, the 3660 - 3200 cm-1 band is indicative of the presence of residual vicinal silanol species. Within this region, a symmetrical peak emerges at 3215 cm" 1 indicating that the B-OH stretch is present.
This proves that the surface has been reacted with the B(OEth and then hydrolyzed. The spectrum also contains CH stretching and bending. It is speculated that the B-0 stretch at 1350 cm- 1 indicates that the siloxane species have reacted to form a monodentate species.
The spectrum of the 600°C/HMDS silica gel reacted with B(OEth (Fig.36) was subtracted from the 600°C/HMDS silica gel spectrum (Fig.7) to generate the difference spectrum (Fig.37). Since siloxanes are the only species on the surface, it is proposed that the (=Si-B(OEt)z) and the (=Si-OEt) species will form. On the spectrum, there is a small broad peak in the location of the B-OH stretching
37 indicating that the surface has been hydrolyzed. Also seen is the CH stretching and bending peaks and the B-0 stretch from the monodentate SiOB species at
1348 cm- 1. The reactions of B(0Et)3 with the silica gel surface species have been summarized in Figure 38.
From the reactions of the boron compounds with the unmodified and 600°C silica gel surfaces, the isolated silanol peak (3754 - 3723 cm- 1) and the siloxane peak (1942 - 1763 cm- 1) were integrated. The siloxane band was used as an internal standard in order to quantify the reaction of the isolated silanol peak. In order to obtain quantitative information, a ratio of the isolated silanol band was taken with respect to the siloxane band and these values can be found in Table 3.
The amount of isolated silanol groups that remain after the silica gel has reacted can be found by taking the ratio of the boron reacted silica with the unreacted silica. When the silica surface is modified with BCb, the isolated silanols react completely and the vicinal silanol species atso react, but not entirely. The findings from the ratios obtained contradict this. The data show that the reaction of the unmodified silica gel with BCb had the largest amount of unreacted silanol groups on the surface compared to the other boron compounds. This is also true for the
600°C silica gel. As mentioned earlier, various research groups (9, 12) have found that BCl3 reacts completely with the isolated silanol groups. Also, researchers have found that larger molecules are sterically hindered from reacting with all the isolated silanol groups on the surface. It was also surprising to find that the data revealed that the B(Et)3 reacted to a greater extent than B(OEth, which contradicts the previous IR spectra. These discrepancies can be explained by the hydrolysis
38 problem. It was previously mentioned that when the product resulting from the
BCb reaction with isolated silanol species is hydrolyzed, isolated silanol species are reformed (8, 12). Our results indicate that the products were hydrolyzed during the preparation for infrared spectroscopy procedure. Further proof that the products were hydrolyzed can be seen in the IR spectra taken, which were discussed earlier.
Elemental Analysis
The elemental analysis results can be found in Table 4. A trend of the reactivity of boron compounds was found to be: BCb > B(OEth > B(Et)3. The findings indicate that the reactivity of the surface with BCb is ordered: unmodified >
600°C > HMDS > 600°C/HMDS. However, the reactivity trend of B(OEth and
B(Eth with the silica gel surface is as follows: unmodified > 600°C > 600°C/HMDS
> HMDS. The difference of the reactivity trends for the boron compounds reacted with the silica gel surfaces will be addressed below.
The unmodified silica gel was shown to chemisorb the greatest amount of boron on the surface since all silanol species and siloxanes are present for reaction with the boron compounds. The BCb reacted the strongest, which is due to its reactive nature as well as its ability to react bifunctionally with vicinal silanol groups. B(Eth and B(OEth do not react with vicinal silanols. Morrow and
McFarlan (15) found that BCb was initially more reactive with vicinal silanol groups than with isolated silanols. This indicated, or they suspected, that the BCb reacted bifunctionally. When the studies turned to larger molecules, including B(Eth and
39 HMDS, it was found that very little to none of the compounds reacted with the vicinal silanol groups and that the reaction went through the isolated silanol species. This was verified using fast scanning FT-IR with the presence of a large residual band in the 3660 - 3200 cm- 1 region of the spectra. The H(OEth modified silica gel chemisorbed -26% less boron and the B(Eth modified silica gel chemisorbed less than half the boron on the surface compared to the BCb modified silica gel (Table 4). It was surprising to find that B(OEth is more reactive than
B(Et)3. This raises the question of whether or not steric hindrance or steric dimension really plays a dominant role since B(OEth is larger than B(Et)3.
The boron compounds reacted with 600°C silica gel are able to react with isolated silanols and siloxane species. This silica gel reduces the amount of boron on the surface since the vicinal silanol groups have been removed. The BCb reacts to a greater extent with the surface than B(OEth and B(Eth since B(OEth reacts one third less and B(Eth reacts t\vo thirds less than BCb (Table 4). The reactivity of these groups will be studied using computational chemistry.
The HMDS silica gel surface contains vicinal silanol groups and siloxanes.
The HMDS silica gel is much more reactive with BCb than with B(OEth and B(Et)3.
This is evident by the small amount of boron adsorbed on the silica gel surface from B(Eth and B(OEth compared to BCb, which suggests that not all the vicinal groups are reacted. This is in agreement with a study preformed by Hambleton and Hockey (17). It was proven that vicinal silanol groups were able to undergo
0 20 exchange but some vicinal groups were unavailable for reaction with BCb due to the larger size of the boron trichloride. If the vicinal silanol groups are unable to
40 react with BCb due to size constraints, it would be much harder for B(OEth and
B(Et)3 to react since these molecules are much larger than BCb. When B(OEth and B(Eth are reacted with HMDS silica, the quantity of boron adsorbed on the surface is very low. Compared to the BCb, B(OEt)3 contained 84% and B(Eth contained 91 % less boron chemisorbed on the surface after reaction (Table 4).
This indicates that the reagents do not react with vicinal silanol groups, which has been shown through IR studies. Studies by Morrow and McFarlan (15) on silica gel reacted with B(Et)3, have shown using IR spectra that a large residual band of vicinal silanol groups remains on the surface. It was believed that the B(Eth was sterically hindered from reacting with vicinal groups. It has been shown that
B(OEth reacted with the HMDS silica gel has more boron chemisorbed on the surface compared to B(Et)3. The effect of steric hindrance does not explain the phenomenon a!one. The energetics of the. reactions need to be considered to properly explain the reactivity differences of these molecules.
The 600°C/HMDS silica gel has been chemically and thermally treated leaving only siloxane species on the dehyroxlyated surface. The amount of boron chemisorbed on the surface shows that these reagents are reactive with siloxane species. This was not unexpected since many research groups found similar results on totally dehydroxylated silica gels (13, 16). B(OEth reacted around 64% and B(Eth reacted 39% with the silica gel surface relative to BCb (Table 4). The values indicate that B(OEth and B(Et)3 are more reactive with siloxanes than they are with vicinal silanol groups. This might be explained by the reactivity of the siloxanes present on the surface. The siloxanes present on the dehydroxylated
41 surface are of higher energy due to the strained angles that form during thermal treatment.
Overall, the differences in the reactivity between the boron compounds was not surprising since the IR studies have shown that B(Eth and B(OEth do not react with vicinal silanol groups.
Aluminum compounds versus Boron compounds
A goal of this research is to determine the reactivity difference between aluminum and boron compounds. Diebel (25) studied the reaction of Al(Eth with silica gel surfaces. A comparison of B(Eth and Al(Eth was made using IR spectra as well as elemental analysis.
There are very few differences between the B(Eth and Al(Eth infrared spectra. One difference is that the Al(Eth reactions with silica gel surfaces were not hydrolyzed, unlike the. B(Et)3 modified silica surfaces, during the IR analysis procedure. The bands found in the Al(Eth reacted silica gels were more defined and intense than the B(Et)3. In all the spectra containing vicinal silanol groups, there were residual bands found. But overall, the spectra were very similar.
The results of the elemental analysis of Al(Eth modified silica gels performed by Diebel and the results of the B(Eth reacted silica gels can be found in
Table 5. The results of the elemental analyses are reported in mmol (of B or Al) per gram of silica. The reactivity trend for the Al(Eth with the silica gel was: unmodified> 600°C > HMDS > 600°C/HMDS, whereas the reactivity trend for the
B(Eth with the surface was: unmodified> 600°C > 600°C/HMDS > HMDS. There
42 is also a significant difference between the amount of boron and aluminum adsorbed on the surface. There is three times more aluminum chemisorbed on the unmodified silica gel compared to boron. As for the 600°C silica gel, there is -6 times more aluminum adsorbed on the surface. The amount of aluminum adsorbed on the surface of HMDS silica gel is 0.57 mmol Al/g Si02. When B(Eth is reacted with the HMDS silica gel, it is found that boron adsorbs ten times less than the aluminum at 0.0575 mmol B/g Si02. It is also found that there is a factor of five difference between the aluminum and boron compounds absorbed on the
600°C/HMDS. It is unusual that boron and aluminum react so differently with the
HMDS silica gel. This indicates that not only does steric hindrance affect the reactions, but also the reactivity of the metal used. The results raise the question:
Why would the aluminum compound be more reactive to the surface than the boron when each contains three ethyl groups? In order to study the reactivity differences of aluminum and boron, computational calculations will be used.
43 Computational Results and Discussion
Geometrical Parameters
The goal of the computational research is to describe the energetics of the reactions of the boron (BCb and B(CH2CH3)3) and aluminum (AICb and
Al(CH2CH3)3) compounds with an isolated silanol species. The reaction pathways examined in this work are given in equations 24 to 27.
AICb + SiOH4~complex 1~transition state~ complex 2~AICl2-SiOH 3 + HCI (24)
BCb + SiOH44 complex 1~ transition state~ complex 2~BCl 2-SiOH 3 + HCI (25)
Al(Eth + SiOH4~complex 1~ transition state~ complex 2~ AIEt2-SiOH3 + Et (26)
B(Eth + SiOH4~complex 1~ transition state~ complex 2~ BEt2-SiOH3 +Et (27)
Figures 39-43 depict the optimum structures of the reactants, complexes, transition states and products obtained computationally. It should be noted that the isolated silanol group has been modeled with three hydrogen atoms attached to the silicon atom, rather than the usual three oxygen atoms. This simplification was made to reduce the computational time required to study the complexes and transition states. The Cartesian coordinates for the optimized geometry of each relevant species can be found in Appendix A. The optimum bond lengths, in angstroms, and bond angles, in degrees, for the reactants, complexes 1 and 2, transition states, and products calculated at the HF/6-31G(d,p) and MP2/6-
31G(d,p) levels are given in Tables 6-10.
The reaction steps for AICb interacting with the isolated silanol have been illustrated using space-filling models in Figure 44. As the AICb-SiOH4 complex 1 is formed from the reactants AICb and SiOH4, the Al-Cl, Si-0, and 0-H bond lengths
44 all increase and the Al-0 bond is formed (Tables 6 and 7). Although the changes are in the same direction for the MP2 calculations, the Si-0, 0-H and Al-0 bond lengths are longer than they are for the HF calculations. Similar results are found for the other complexes as well.
It was believed that the hydrogen atom attached to the oxygen atom of the isolated silanol group would be the most likely atom to be transferred in the formation of the products AICl2-Si0H3 and HCI. Therefore, in order to locate the transition state, AICl2SiOH3-HCI complex 2 was generated and then averaged with complex 1 (Table 9). The geometry of the transition state obtained at the HF level shows that the 0-H bond length has increased by 0.48 A, the Al-Cl bond length has increased by 0.28 A, and the H-CI bond length has decreased to 1.42 A (Table 8).
The Si-0-AI bond angle has increased by 14°, with a corresponding shortening of the Si-0 bond by 0.06 A and the Al-0 bond by 0.25 A. Unfortunately, reoptimizing the transition state structure at the MP2 level led to a structure similar to complex 1 with no imaginary frequencies.
Some of the results for complex 2 were surprising (Table 9). In particular, the Si-0-AI bond angle is nearly linear unlike the bent angle found for complex 1.
The Al-0 and Si-0 bond lengths have decreased further, the 0-H distance has increased by 1.47 A, and the Al-Cl bond length, with respect to the transferred chlorine atom, has increased by 0.31 A. Further evidence that the HCI molecule is forming is that the distance between the hydrogen and chlorine atoms has decreased by 0.15 A. The AICl2-SiOH3 product has a linear Si-0-AI bond angle, similar to complex 2, and the Al-Cl and Si-0 bond lengths are within 0.01 A of
45 those bond lengths in the reactants (Tables 6 and 10). The H-CI bond in the product is 0.004 A shorter than in complex 2.
The reaction scheme for 8C'3 interacting with the isolated silanol is presented in Figure 45. In the formation of the 8C'3-SiOH4 complex 1, the 8-CI, Si-
0, and 0-H bond lengths have increased compared to the reactants and the 8-0 bond has formed. These results are similar to those found for the AIC'3-SiOH4 complex 1 (Tables 6 and 7). In addition, the Si-0-8 bond angle is bent in complex
1 and is -2° smaller than the corresponding Si-0-AI bond angle.
We have searched extensively for a transition state for the 8C'3 system similar to that found for the AICb system; however, thus far, no such transition state has been found. The transition state that has been located for the 8Cl3 system shows movement of a Cl atom rather than the lighter hydroxyl H atom (Table 8). In this transition state, one 8-CI bond length has increased by 0. 72 A, whereas the O
H bond length has increased by only 0.12 A. The distance between the hydrogen and chlorine atoms is 1. 71 A. The other 8-CI bonds and the Si-0 bond have decreased in length, whereas the 8-0 bond length has increased by 0.13 A. The
Si-0-8 bond angle remains bent with a 5° decrease compared to complex 1. The search for the transition state for the 8C'3 system at the MP2 level has thus far been unsuccessful. The only structure located at this level has the chlorine leaving group interacting with the silicon atom, which is not representative of the surface reaction. Time constraints have prevented additional searches.
In the formation of complex 2 from the transition state, two of the 8-CI bonds have lengthened by 0.02 A and the third has lengthened by 1.9 A (Tables 8 and 9).
46 Moreover, the hydrogen atom has moved away from the oxygen atom by 1. 7 A to form HCI. The 8-0 bond length has decreased by 0.13 A and the Si-0 bond length has decreased by merely 0.05 A. The Si-0-8 angle remains bent but increases by
6°. The geometries of the products are very similar to that of complex 2, with changes in the 8-CI, 8-0, Si-0 and H-CI bond lengths in the range of 0.001 to
0.004 A. The Si-0-8 bond angle remains bent in the product, unlike the linear Si-
0-AI bond angle obtained for the AICb system. The MP2 optimum bond lengths generally differ from the HF values by no more than 0.01 - 0.05 A. The only deviations outside of this range were found for complex 2, in which the hydrogen and chlorine atoms are separated from the 8Cl2-SiOH3 complex.
For the reactions of Al(CH2CH3)3 and 8(CH2CH3)3with the isolated silanol, it
proved difficult to obtain optimized geometries for complex 2 and the transition
state. This difficulty was due to the floppy nature of the ethyl groups and to the
possibility that these compounds may not form a stable complex 2. Therefore, only the geometries of the reactants, complex 1 and products will be compared (Tables
6, 7 and 10). Also worth noting is the fact that the C-C and C-H bond lengths of the
methyl or methylene groups are essentially unchanged throughout the reaction
scheme and therefore will not be considered further. The space-filling models of these systems are depicted in Figures 39, 40 and 43.
In the reaction of Al(Eth with the isolated silanol there is a slight increase
(0.02 A) in the Al-C bond length when complex 1 is formed, and the Si-0 bond
length increases by 0.05 A. The 0-H bond length does not change and the Si-0-H
bond angle decreases by 3°. The Al-0 bond in the Al(Eth system is 0.08 A longer
47 than the corresponding bond in the AICb system. Comparing the products and complex 1, the Al-C and the Si-0 bond are shorter by 0.03 A and 0.08 A, respectively, in the products. The Al-0 bond has also shortened similarly to what was found for the AICb system. The HF/6-31G(d,p) optimum Si-0-AI bond angle is again linear in the product. However, when the geometry is optimized at the MP2 level, the Si-0-AI bond angle is bent by 24.5°. The differences in the HF and MP2 bond lengths for these molecules range from 0.003 to 0.03 A.
When complex 1 is formed from 8(Et)3 and the isolated silanol, the 8-C, Si-
0 and 0-H bond lengths increase by a negligible amount. One major difference in the results for 8(Et)3 and 8Cl3 at the HF level is that the 8-0 bond in the 8Cb complex 1 is -1.60 A, whereas it is 2.87 A in the 8(Et)3 complex 1. When the geometry is optimized at the MP2 level, the bond length in the latter complex between the boron and oxygen decreases.dramatically to 1.88 A. Thus it is only at the higher level of calculation that the boron and oxygen interact. The Si-0-8 angle is bent in the 8(Et)3 complex as it is in the 8Cb complex. The differences in the 8-C and Si-0 bond lengths increase slightly when complex 1 and the
8Et2SiOH3 product are compared. The 8-0 bond shortens by 1.5 A at the HF level and by 0.29 A at the MP2 level. The Si-0-8 bond angle remains bent with a 1° increase.
Reaction Thermochemistry
Reaction enthalpies and free energies have been evaluated with single-point energies calculated for both the HF/6-31G(d,p) and MP2/6-31G(d,p) optimized
48 structures. Tables 11 - 18 give the enthalpy changes and free energy changes at room temperature and at 898 K. The reactions were examined at 898 K to determine how the 898 K silica gel reacts with the aluminum and boron compounds. It should be noted that in all cases, each of the four overall reactions examined (equations 24 - 27) have negative enthalpies and free energies of reaction. In addition, only the 298 K thermochemical data based on the HF/6-
31G(d,p) geometries will be discussed, since the trends in the data are essentially independent of temperature and the level at which the geometries were optimized.
The only noticeable exception to this observation is that the reaction free energy for the formation of complex 1 is much more positive, and therefore less favorable, at
898 K than at 298 K.
The relative enthalpy changes that occur along the AICb + SiOH4 reaction pathway at 298 K can be found in Figure 46, a-nd the relative free energy changes can be found in Figure 47. The data are based on the MP2/6-311+G(2d,2p)/HF/6-
31G(d,p) single-point energies (Tables 11 and 12). Although there is some fluctuation in the absolute ~G and ~H values computed at the various calculational levels, the relative changes are more consistent.
The changes in enthalpy and free energy for the formation of complex 1 indicate that this is a spontaneous, exothermic process. The energy released when complex 1 is formed is sufficient to overcome the reaction barrier, i.e.,
~G(transition state - reactants) =0.0 kJ/mol. The transformation from the transition state to complex 2 is an essentially thermoneutral, favorable process.
49 The differences in the enthalpy and free energy changes observed for this reaction pathway reveal the significant role that entropy plays in this reaction.
The relative enthalpy changes for the BCb + SiOH4 reaction pathway at 298
K are presented in Figure 48, and the relative free energy changes are presented in Figure 49. See Tables 11 and 12, also. As complex 1 forms from the reactants, the change in enthalpy is negative and the change in free energy is positive again demonstrating that the decrease in entropy is a definite factor. Comparing Figures
46 - 49, one notes that for each step in the reaction scheme the effect of entropy is similar for both the AICb and BCb reactions. For the transition states located thus far, the transition state associated with the BCl3 reaction is more reactant-like whereas that associated with the AICb reaction is more product-like (Figures 39 -
43). In addition, formation of the BCb-SiOH4 complex 1 does not supply enough energy to overcome the activation barrier.(Figure 49), suggesting that BCb is less reactive than AICb.
The changes in enthalpy and free energy for the reactions with the isolated silanol and Al(CH2CH3)3 and B(CH2CH3)3 are given in Tables 11 - 18. For the reaction at 298 K involving Al(Eth the formation of complex 1 is both exothermic and exoergic. In contrast, for the reaction involving B(Eth the production of complex 1 is exothermic but endoergic. These results suggest that the value of
~G(transition state - reactants) will be smaller for the Al(Eth reaction than for the
B(Eth reaction, which remains to be confirmed.
50 Conclusion
The objective of this study was to understand the reactivity of boron and aluminum compounds with silica gel surfaces utilizing both experimental and theoretical methods. The silica surfaces (unmodified, 600°C, HMDS, and
600°C/HMDS) were reacted with BCb, B(CH2CH3)3 and B(OCH2CH3)3 to examine how the surface species were affected. The surface was studied through the use of infrared spectroscopy and elemental analysis techniques.
Through infrared spectroscopy, it was found that BCb was reactive with the isolated, vicinal and siloxane surface species. However, B(CH2CH3)3 and
B(OCH2CH3h were reactive with isolated silanols and siloxanes, but not with vicinal silanol groups. The spectra of the Al(CH2CH3)3 and B(CH2CH3)3 modified silica gels were compared and both were found to have residual bands in the vicinal silanol species region.
To determine the amount of boron that adsorbed on the silica gel surface elemental analysis was used. The reactivity trend for the boron compounds studied was found to be the following: BCb > B(OCH2CH3)3 > B(CH2CH3)3. The reaction of BCb with the silica gel surfaces was shown to have a reactivity trend of unmodified> 600°C > HMDS > 600°C/HMDS. The reactivity trend for the
B(OCH2CH3)3 and B(CH2CH3)3 differed from the BCb in that the trend was the following: unmodified >600°C > 600°C/HMDS > HMDS. This was not surprising since the vicinal silanol groups are not reacting with these boron compounds.
Al(CH2CH3)3 and B(CH2CH3)3 elemental analysis results were compared and it was found that more aluminum was adsorbed on the various silica gel surfaces. In
51 order to understand the reactivity differences of aluminum and boron compounds, computational chemistry was utilized.
The energetics of the reactions between the aluminum (AICb and
Al(CH2CH3)3) and boron (BCb and B(CH2CH3)3) compounds with an isolated silanol species were evaluated using computational methods. The geometries of the molecules were optimized at two levels: HF/6-31G(d,p) and MP2/6-31G(d,p). The transition state found for the reaction of AICb with an isolated silanol calculated at the HF/6-31G(d,p) level showed the hydrogen atom from the hydroxyl group moving towards the chlorine atom to form the products, Si-O-AICl2 and HCI.
However, it was found that for the reaction of BCb with an isolated silanol, the heavier chlorine atom moves towards the hydrogen to form products. A substantial effort was made to find a pathway for the BCl3 reaction similar to that for the AICb reaction, but it was unsuccessful. Also, thus far calculations at the MP2 level have been unsuccessful at finding transition states for these reactions. The transition state and complex 2 were not located for either the Al(CH2CH3)3 or the B(CH2CH3)3 reaction with the isolated silanol, which may be due to the floppy nature of the ethyl groups and to the fact that complex 2 may not be a stable structure. Therefore, in order to obtain these structures, future studies will replace the ethyl groups with methyl groups to reduce complications and computational time.
The enthalpies and free energies of the reactions were calculated at room temperature and 898 Kat both the HF/6-31G(d,p) and MP2/6-31G(d,p) levels. The overall enthalpies and free energies for the reactions were found to be negative.
The trends in the data obtained were independent of temperature and level at
52 which the geometries were optimized. The data suggest that AICb is more reactive than BCb. The BCb transition state is more reactant-like, whereas the transition state for AICb is more product-like. Also, the formation of complex 1 for the BCl3 reaction does not supply enough energy to overcome the activation barrier. For the reactions of Al(CH2CH3)3 and B(CH2CH3)3 with an isolated silanol, the formation of complex 1 is exothermic and exoergic for aluminum but exothermic and endoergic for boron. Further studies are necessary to determine the reactivity trend for these compounds. Unfortunately, due to time constraints, the reactions of
Al(OCH2CH3)3 and B(OCH2CH3)3 with an isolated silanol were not investigated. In the future, these compounds will be studied using methoxy groups to determine how the reactivity compares with Al(CH3CH2h and B(CH3CH2)3.
53 REFERENCES
1. lier, R.K. The Chemistry of Silica: Solubility, Polymerization, Colloid and
Surface Properties, and Biochemistry; John Wiley & Sons: New York, 1979.
2. Hair, M.L. Infrared Spectroscopy in Surface Chemistry, Marcel Dekker, Inc.:
New York, 1967.
3. lier, R.K. The Colloid Chemistry of Silica and Silicates; Cornell University
Press: New York, 1955.
4. Young, G.Y. J. of Colloid Sci., 1958, 13, 67.
5. Stark, F.O.; Johannsen, O.K.; Vogel, G.E.; Chaffee, R.G.; Lacefield, RM. J.
Phys. Chem. 1968, 72, 2750.
6. Nawrocki, J. Chromatographia, 1985, 20, 308.
7. Vansant, E.F.; Van Der Voort, P.; Vrancken, K.C. Characterization and
Chemical Modification of the Silica Surface; Elsevier Science: Amsterdam,
1995.
8. Peglar, R.J.; Hambleton, F.H.; Hockey, J.A. J. Cata/. 1971, 20, 309.
9. Hambleton, F.H.; Hockey, J.A. J. Cata/. 1971, 20, 321.
10. Hair, M.L.; Hertl, W. J. Phys. Chem. 1973, 77, 2070.
11. Hockey, J.A. J. Phys. Chem. 1970, 74, 2570.
12. Bermudez, V.M. J. Phys. Chem. 1971, 75, 3249.
13. Morrow, B.A.; Cody, I.A. J Phys. Chem. 1975, 79, 761.
14. Hair, M.L. J. Colloid Interface Sci. 1977, 60, 154.
15. Morrow, B.A.; McFarlan, A.J. J. Non-Cryst. Solids 1990, 120, 61.
16. Morrow, B.A.; Devi, A. Chem. Comm. 1971, 1237.
54 17. Hambleton, F.H.; Hockey, J.A. Trans. Faraday Soc. 1966, 62, 1694.
18. Kunawicz, J. Trans. Faraday Soc. 1971, 67, 848.
19. Armistead, C.G.; Tyler, A.J.; Hambleton, F.H.; Mitchell, S.A.; Hockey, J.A. J.
Phys. Chem. 1969, 73, 3974.
20. Morrow, B.A.; Gay, l.D. J. Phys. Chem. 1988, 92, 5569.
21. Hair, M.L.; Hertl, W. J. Phys. Chem. 1969, 73, 2372.
22. Morrow, B.A.; Devi, A. Can. J. Chem. 1970, 48, 2454.
23. Murray, J. Cata/. 1970, 18, 52.
24. Arlman, J. Cata/. 1964, 3, 99.
25. Diebel, RE., M.S. thesis, Eastern Illinois University, 1998.
26. Sindorf, D.W.; Maciel, G.E. J. Phys. Chem. 1982, 86, 5208.
27. Sindrof, D.W.; Maciel, G.E. J. Phys. Chem. 1982, 86, 5516.
28. McFarlan, A.J., PhD thesis, University of Ottawa, 1989.,
29. Jensen, F. Introduction to Computational Chemistry; John Wiley & Sons:
New York, 1999.
30. Pople, J.A., Beveridge, D.L. Approximate Molecular Orbital Theory,
McGraw-Hill: New York, 1970.
31. Adamson, AW. Physical Chemistry; Academic Press College Division:
Orlando, 1986.
32. Gaussian 98, Revision A.7, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, 0. Farkas, J. Tomasi, V. Barone, M. Cassi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari,
55 J. B. Foresman, J. Cioslowski, J. V. Ortiz, A.G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle, and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1998.
56 Appendix A: Cartesian Coordinates for Optimized Structures
Reactants
AICl 3~
HF MP2 Al 0.000000 0.000000 0.000000 Al 0.000000 0.000000 0.000000 Cl 0.000000 0.000000 2.077250 Cl 0.000000 0.000000 2.072240 Cl 1. 798951 0. 000000 -1. 038625 Cl 1.794613 0.000000 -1.036120 Cl -1 .798951 0. 000000 -1. 038625 Cl -1. 794613 0.000000 -1.036120
BCl3~
HF MP2 B 0.000000 0.000000 0.000000 B 0.000000 0.000000 0.000000 Cl 0.000000 0.000000 1.744757 Cl 0.000000 0.000000 1.736756 Cl 1.511004 0.000000 -0.872379 Cl 1.504075 0.000000 -0.868378 Cl -1.511004 0.000000 -0.872379 Cl -1.504075 0.000000 -0.868378
Al(Eth~
HF MP2 Al 0.219149 0.202521 0.171140 Al 0.244994 0.239086 0.190562 c 0.112145 0.089208 2.153682 c 0.105269 0.077281 2.162119 c 2.029551 0.373186 -0.634147 c 2.030263 0.363966 -0.663753 c -1.414271 0.105706 -0.961946 c -1. 388762 0. 156903 -0. 930462 c -1.286835 0.015414 2.786912 c -1.318952 -0.027489 2.723075 H 0.654103 0.941479 2.569764 H 0.620308 0.926499 2.624833 H 0.697750 -0.777713 2.469122 H 0.688607 -0.794646 2.478807 H -1.241735 -0.052586 3.871368 H -1.328643 -0.128031 3.809832 H -1.841499 -0.850175 2.434141 H -1.846942 -0.889708 2.314159 H -1.882560 0.892006 2.545697 H -1.911929 0.853367 2.475193 c 2.116876 0.518807 -2.162136 c 2.031298 0.462446 -2.194876 H 2.616287 -0.493279 -0.319585 H 2.623477 -0.503037 -0.352032 H 2.530935 1.219886 -0.159903 H 2.566003 1.221076 -0.240763 · H 3.145222 0.596319 -2.507392 H 3.041468 0.514578 -2.604857 H 1.594547 1.406093 -2.510535 H 1.497349 1.348825 -2.538665 H 1.670608 -0.330982 -2.672093 H 1.541651 -0.398714 -2.651024 c -1.811138 -1.326413 -1.379465 c -1.739241 -1.294380 -1.312792 H -2.252699 0.560213 -0.434076 H -2.240671 0.598400 -0.406461 H -1.271359 0.704501 -1.861507 H -1.260079 0.740808 -1.845726 H -2.706498 -1.335492 -1.995920 H -2.637246 -1.349954 -1.930341 H -2.014284 -1.956842 -0.516670 H -1.922170 -1.911450 -0.431099 H -1.025722 -1.811637 -1.954629 H -0.935351 -1. 768491 -1.879032
57 Reactants cont.
B(Eth:.
HF MP2 B 0.230264 0.224166 0.132943 B 0.222006 0.282791 0.179137 c 0.283305 0.234183 1.729239 c 0.151815 0.315816 1.757153 c 1.639217 0.234183 -0.619270 c 1.647081 0.132844 -0.488638 C-1.143150 0.084262 -0.659998 c -1.084851 0.346181 -0.703647 C-1.023408 0.413090 2.509461 c -1.101546 -0.238812 2.437597 H 1.002760 0.989506 2.047733 H 0.232959 1.390922 1.981660 H 0.749492 -0.711610 2.020918 H 1.048836 -0.126333 2.199228 H -0.852026 0.382939 3.581700 H -1.083128 -0.068627 3.514064 H -1.742775 -0.365453 2.273975 H -1.188943 -1.313914 2.280340 H -1.493633 1.366250 2.283830 H -2.006319 0.224352 2.046294 c 1.661553 0.413090 -2.141028 c 1.796716 0.487358 -1.967473 H 2.124912 -0.711610 -0.361380 H 1.917301 -0.921260 -0.330038 H 2.274768 0.989506 -0.155451 H 2.381284 0.681194 0.110902 H 2.675830 0.382939 -2.528727 H 2.813537 0.320554 -2.323311 H 1.231038 1.366250 -2.435439 H 1.555328 1.535534 -2.145020 H 1.097932 -0.365453 -2.646275 H 1.128733 -0.109149 -2.588003 c -1.488657 -1.409271 -0.859476 c -1.468789 -1.099713 -1.084168 H -1.963211 0.557497 -0.125890 H -1.924218 0.806281 -0.179476 H -1.090629 0.557497 -1.637246 H -0.923863 0.915568 -1.621181 H -2.423343 -1.524076 -1.399117 H -2.369465 -1.119973 -1.697021 H -1.595756 -1.926111 0.090104 . H -1.661185 -1.705975 -0.198886 H -0.719845 -1.926111 -1.427017 H -0.673441 -1.585168 -1.650179
SiOH4:
HF MP2 Si -0.020821 -0.031807 -0.528766 Si -0.016814 -0.024860 -0.536278 0 -0.002474 -0.013571 1.115388 0 -0.011761 -0.029761 1.132766 H 1.349173 -0.041141 -1.084474 H 1.350701 -0.034751 -1.096762 H -0.727785 -1.254652 -0.935223 H -0.724003 -1.247916 -0.937378 H -0.719331 1.151442 -1.074481 H -0.714629 1.156004 -1.086746 H 0.409226 0.698216 1.573794 H 0.417407 0.712790 1.566646
58 Complex 1
SiOH4-AICb:
HF MP2 Al 0.488823 -0.348917 -0.004942 Al 0.504611 -0.351502 0.005373 Cl 0.379258 -2.381762 0.603528 Cl 0.337787 -2.389492 0.542353 Cl 0.622280 0.024659 -2.086507 Cl 0.425503 0.125218 -2.050591 Cl 1.627333 0.945066 1.223564 Cl 1.807931 0.830468 1.159500 Si -2.230271 1.585895 0.047043 Si -2.217319 1.576542 0.033950 0 -1.336391 0.144603 0.386412 0 -1.272739 0.210506 0.569603 H -1.222494 2.571087 -0.325028 H -1.234624 2.632110 -0.184633 H -3.166781 1.271381 -1.033580 H -2.944226 1.196622 -1.177920 H -2.939262 1.914649 1.287106 H -3.135819 1.857544 1.142798 H -1.802041 -0.575924 0.795928 H -1.731649 -0.497687 1.046321
HF MP2 Si -0.875725 -1.177769 -2.007921 Si -0.858924 -1.160864 -1.983494 0 -0.616336 -0.949909 -0.300579 0 -0.714627 -0.932219 -0.245626 H 0.357102 -0.807222 -2.690716 H 0.415579 -0.821376 -2.607268 H -1.156199 -2.616499 -2.080470 H -1.158863 -2.595930 -2.066945 H -2.034977 -0.382174 -2.399104 H -1.978550 -0.343128 -2.439631 H -0.812217 -1.671865 0.284872 H -0.712555 -1.733143 0.302504 B 0.170294 0.223365 0.467046 B 0.166119 0.239218 0.482425 Cl -0.560171 0.210887 2.139447 Cl -0.490102 0.275805 2.162325 Cl -0.194587 1.721528 -0.511971 Cl -0.199463 1.695389 -0.529054 Cl 1.930385 -0.258945 0.435213 Cl 1.886374 -0.323704 0.374562
59 Complex 1 cont.
SiOH4-Al(Eth:
HF MP2 Al 0.607403 -0.232252 0.221938 Al 0.612912 -0.277908 0.254123 c 0.652301 -2.227432 0.353896 c 0.672719 -2.266165 0.326701 c 1.463148 0.736936 1.755991 c 1.466720 0.769579 1.725511 c 0.677095 0.603802 -1.598264 c 0.621290 0.556238 -1.560759 c -0.206051 -3.024082 -0.643303 c -0.230896 -2.969412 -0.695530 c 1.337557 2.270520 1.772949 c 1.213574 2.282452 1.656911 c 2.062671 0.519831 -2.268107 c 2.015684 0.463317 -2.204408 Si -2. 727160 0.585347 -0.203302 Si -2.625838 0.672834 -0.193569 0 -1.356668 0.219734 0.727202 0 -1.337563 0.126716 0.805250 H 0.386077 -2.526259 1.370660 H 0.420489 -2.616990 1.333402 H 1.693837 -2.540592 0.243554 H 1.705972 -2.596454 0.169797 H 2.523366 0.474983 1.768582 H 2.547859 0.595295 1.710693 H 1.083049 0.336227 2.701308 H 1.149902 0.392090 2.706011 H -0.052044 0.136357 -2.264343 H -0.099703 0.077532 -2.232699 H 0.384893 1.654906 -1.540879 H 0.328434 1.611142 -1.518494 H -0.096298 -4.100230 -0.522196 H -0.162516 -4.058524 -0.644216 H 0.055617 -2.790411 -1.672465 H 0.023544 -2. 678973 -1. 716077 H -1.265766 -2.802323 -0.528428 H -1.281341 -2.711284 -0.544463 H 1.831132 2.722873 2.630982 H 1.690028 2.833812 2.470609 H 0.297307 2.594445 1.802785 H 0.146867 2.519574 1.699022 H 1.773409 2.713737 0.881593 H 1.585590 2.700756 0.720949 H 2.077613 0.982431 -3.252919 H 2.054308 0.913567 -3.198717 H 2.382020 -0.511995 -2.396718 H 2.335369 -0.574949 -2.311803 H 2.825149 1.017155 -1.672392 H 2.768375 0.969300 -1.596443 H -3.887564 0.402721 0.682223 H -3.837297 0.627772 0.639908 H -2.651237 1.977433 -0.659296 H -2.370706 2.045819 -0.642377 H -2.743358 -0.353961 -1.323067 H -2.691828 -0.270561 -1.307885 H -1.400194 0.401603 1.655454 H -1.373511 0.384426 1.736581
60 Complex 1 cont.
SiOH4-B(Etb:
HF MP2 B -0.772535 0.306205 -1.346462 B -0.337139 0.218194 -0.691136 c -0.505744 1.826354 -0.956707 c -0.350946 1.807022 -0.444406 c 0.417303 -0.473985 -2.062566 c 0.786998 -0.265364 -1.731533 c -2.174162 -0.400345 -1.052851 c -1.772756 -0.521461 -0.750715 c -1.227584 2.408830 0.264313 c -1.244043 2.362893 0.666864 c 0.099814 -1.737396 -2.869649 c 0.979778 -1.772670 -1.911709 c -2.121779 -1.277638 0.215766 c -2.455209 -0.887387 0.574095 Si 2.393804 0.036918 2.593928 Si 1.962482 -0.192884 1.447463 0 1.068201 -0.457176 1.748517 0 0.362436 -0.433472 0.892364 H -0.811371 2.385707 -1.849581 H -0.678204 2.242484 -1.396666 H 0.563830 2.009733 -0.869033 H 0.668163 2.182773 -0.305366 H 1.104409 -0.724378 -1.248747 H 1.753320 0.199297 -1.494314 H 0.980599 0.224870 -2.681805 H 0.515066 0;173483 -2.699246 H -2.970085 0.330548 -0.931237 H -2.439680 0.149678 -1.304159 H -2.460887 -1.031958 -1.891571 H -1.717703 -1.432896 -1.350366 H -1.005873 3.465331 0.387251 H -1.175610 .3.448973 0.744392 H -0.919948 1.904231 1.175175 . H -0.968137 1.961004 1.645661 H -2.305774 2.312363 0.182589 H -2.291336 2.113840 0.497291 H 1.001068 -2.182586 -3.281970 H 1.798689 -2.001543 -2.595476 H -0.563212 -1.520907 -3.703334 H 0.081357 -2.239350 -2.313558 H -0.385684 -2.494160 -2.260723 H 1.197979 ·-2.262662 -0.962207 H -3.075486 -1.765244 0.393339 H -3.473923 -1.245498 0.422811 H -1.887086 -0.686799 1.095912 H -2.520919 -0.038184 1.256970 H -1.368873 -2.056664 0.129217 H -1.918529 -1.692744 1.080537 H 2.044591 0.368645 3.990912 H 1.922615 -0.438114 2.899302 H 3.431689 -1.014680 2.622445 H 2.817361 -1.171081 0.771413 H 2.912801 1.230800 1.912606 H 2.408201 1.177471 1.173996 H 0.592016 -1.220237 2.027900 H -0.330179 -0.387960 1.565701
61 Transition State
HF Si -2.204460 -1.128732 -1.168642 0 -1.384895 -0.190675 0.030948 Al 0.481910 0.246248 0.259849 Cl 1.380175 -1.629165 0.656272 Cl 0.983599 1.117570 -1.605033 H -1.140119 -1.768599 -1.931611 H -3.047896 -2.075764 -0.434091 H -3.013642 -0.199404 -1.959988 H -1.914804 0.229590 0.699075 Cl 0.271122 1.566925 1.911231
HF Si 2.488843 0.109929 -0.324866 0 0.777435 0.361733 -0.450327. H 2.686221 -1.300238 -0.657407 H 3.054830 1.024756 -1.314049 H 2.895196 0.435646 1.040624 H 0.300590 1.311668 -0.321254 B -0.370779 -0.415967 -0.023302 Cl -1.380209 -1.086277 -1.276461 Cl -1.159194 1.992302 0.262766 Cl -0.292728 -1.131018 1.573657
62 Complex 2
HF MP2 Si 2.942518 -0.204163 0.000613 Si -1.098669 2.013962 0.920514 0 1.314221 -0.119654 -0.000180 0 -0.451743 0.586828 0.307192 Al -0.337196 -0.418928 0.000523 Al 1.005223 -0.051615 -0.314060 Cl -1.298663 -0.921678 -1.794500 Cl 1.037202 -2.032900 -0.908599 Cl -1.298817 -0.917565 1.796558 Cl 2.697671 1.137796 -0.465550 H 3.425938 -0.910447 1.200948 H -0.067343 3.065542 0.923568 H 3.427212 -0.907962 -1.200676 H -2.225507 2.421463 0.068834 H 3 .490405 1. 169020 0. 002160 H -1.563463 1.765811 2.292951 Cl -0.818747 2.269267 -0.002429 Cl -3.043905 -1.384987 0.496433 H 0.406830 2.600557 -0.010064 H -1.962731 -0.710386 0.373882
HF MP2 Si 0.317053 2.292941 -0.014691 · Si 0.158107 2.232768 -0.070705 0 0.177239 0.621876 -0.019596 0 -0.034757 0.531278 -0.097614 B 0.962631 -0.437603 -0.006216 B 0.896250 -0.449130 -0.027774 Cl 0.239022 -2.049845 -0.025179 . Cl 0.375332 -2.113362 -0.101989 Cl 2.726858 -0.298773 0.031032 Cl 2.607364 :.0.080318 0.135764 H 1.074105 2.707119 -1.203413 H 1.019578 2.632940 -1.189670 H -1.049634 2.818040 -0.051431 H -1.198968 2.760853 -0.226571 H 1.009032 2.705576 1.213517 H 0.741546 2.626945 1.217191 Cl-3.517724 -0.154155 0.020689 Cl -3.274894 -0.228686 0.092550 H -2.321961 -0.571751 -0.016368 H -2.011471 -0.103848 -0.038830
63 Products
HF MP2 Si -2.196413 1.541197 -0.853116 Si -2.216459 1.555880 -0.860420 0 -0.922017 0.642957 -0.358579 0 -0.924280 0.648715 -0.358828 Al 0.375764 -0.264062 0.145908 Al 0.388729 -0.272680 0.150917 Cl 0.381505 -2.336031 -0.094001 Cl 0.385580 -2.336676 -0.088576 Cl 2.029924 0.645918 1.030853 Cl 2.037016 0.635924 1.029009 H -1.753984 2.514313 -1.868202 H -1.773944 2.529801 -1.873362 H -3.228218 0.666934 -1.439380 H -3.246141 0.681548 -1.448860 H -2.771117 2.263076 0.296538 H -2.792856 2.274237 0.289422
HF MP2 Si -1.793601 1.338221 -0.684724 Si -1.756521 1.323911 -0.679243 0 -0.878006 -0.029152 -0.413353 0 -0.922317 -0.136632 -0.450795 B 0.286236 -0.387816 0.089398 B 0.279432 -0.410576 0.085384 Cl 0.754265 -2.087030 0.113068 Cl 0.829315 -2.069643 0.157367 Cl 1.414648 0.811346 0.754061 Cl 1.321439 0.863234 0.721264 H -1.056542 2.243806 -1.577107 H -0.970218 2.205785 -1.552711 H -3.036827 0.886033 -1.318127 H -3.023394 0.954298 -1.318462 H -2.074859 1.993997 0.600003. H -1.996547 1.960050 0.623299
HF MP2 Al 0.154543 0.458544 0.033121 Al 0.267711 0.482695 -0.043217 c -1.121926 1.158513 1.368448 c -1.225240 1.077220 1.099522 c 1.529737 1.562467 -0.856593 c 1.715616 1.658666 -0.671208 c -2.138519 0.158081 1.941089 c -2.244831 -0.007319 1.470425 c 1.423274 3.084287 -0.661708 c 1.616269 3.117804 -0.205647 Si 0.023132 -2.762532 -0.760541 . Si -0.222072 -2.728440 -0.602179 0 0.087230 -1.191795 -0.373494 0 0.314720 -1.172752 -0.527884 H -1.649415 2.003421 0.922353 H -1.733239 1.908369 0.598938 H -0.546209 1.601089 2.183759 H -0.808062 1.521083 2.009679 H 2.506053 1.220501 -0.507194 H 2.672017 1.232127 -0.353621 H 1.523011 1.325324 -1.920865 H 1.744995 1.619279 -1.764434 H -2.798774 0.623412 2.668912 H -3.044903 0.381884 2.101882 H -1.644869 -0.672224 2.437381 H -1.775512 -0.828377 2.012793 H -2. 764952 -0.265206 1.161407 H -2.712475 -0.436181 0.583888 H 2.225780 3.615074 -1.167408 H 2.441935 3. 723240 -0.582038 H 1.469115 3.358942 0.388719 H 1.630227 3.193833 0.882008 H 0.486692 3.474591 -1.051326 H 0.691987 3.585579 -0.546026 H 0.171745 -3.605167 0.445595 H 0.693024 -3.542671 -1.425312 H -1.268930 -3.091567 -1.399874 H -0.290225 -3.333176 0.745110 H 1.104611 -3.119530 -1.703924 H -1.569658 -2.798071 -1.206029
64 Products cont.
SiH308Et~:
HF MP2 B -0.124714 0.370751 0.032780 B -0.285427 0.192814 0.222569 c -1.462506 1.165765 -0.283000 c -1.704735 0.875136 0.140191 c 1.178771 1.058493 0.647024 c 1.087997 0.988815 0.182862 c -2.614175 0.345668 -0.870060 c -2.078443 1.076542 -1.340640 c 1.124292 2.561169 0.941789 c 1.004635 2.507275 0.341486 Si 0.942992 -2.235939 -0.128569 Si 1.005992 -2.271741 0.215514 0 -0.091452 -0.964952 .:.o.235192 0 -0.274529 -1.188702 0.233890 H -1.214074 1.991498 -0.952609 H -1.722201 1.840918 0.647836 H -1.786747 1.658650 0.635648 H -2.453778 0.238436 0.613397 H 1.434375 0.520008 1.562544 H 1.756601 0.575086 0.946208 H 2.009797 0.853598 -0.031847 H 1.573747 0.744555 -0.770084 H -3.488289 0.963322 -1.055713 H -3.061181 1.535326 -1.444813 H -2.909874 -0.453870 -0.198339 H -2.100102 0.122323 -1.866903 H -2.328918 -0.116081 -1.809913 H -1.360113 1.719943 -1.850180 H 2.063009 2.917537 1.355063 H 1.987840 2.972934 0.278529. H 0.343198 2.798799 1.657719 H 0.573196 2.777429 1.304843 H 0.925902 3.136818 0.042672··· H 0.378952 2.950295 -0.432482 H 0.247768 -3.431679 -0.629475 H 0.425581 -3.621888 0.192787 H 2.148892 -1.995960 -0.944910 H 1.841797 -2.075569 -0.983902 H 1.349977 -2.460215 1.272245 H 1.842405 -2.116478 1.420202
HCI:
HF MP2 H 0.000000 0.000000 -1.195253 H 0.000000 0.000000 -1.198759 Cl 0.000000 0.000000 0.070309 Cl 0.000000 0.000000 0.070515
~Hs:
HF MP2 c 0.000002 -0.000003 -0.763386 c 0.000003 -0.000004 -0.761709 c 0.000002 -0.000004 0.763383 c 0.000003 -0.000004 0.761706 H 1.012204 0.000021 -1.156298 H 1.015337 0.000026 -1.155209 H -1.012185 0.000021 1.156292 H -1.015316 0.000026 1.155204 H -0.506120 -0.876583 -1.156298 H -0.507691 -0.879294 -1.155209 H -0.506096 0.876583 -1.156280 H -0.507661 0.879294 -1.155190 H 0.506099 -0.876589 1.156310 H 0.507666 -0.879303 1.155223 H 0.506074 0.876588 1.156292 H 0.507635 0.879303 1.155204
65
Table 1: Elemental Analysis for Statistical Calculations
V aI ues Repo rte d f rom Ga lbra1 "th L a b ora t or1es . Samele B (0/o weiaht) Si (% weiaht) 1 0.89 44.60 2 0.95 41.33 3 0.90 41.05 4 0.95 39.20 "blank" <0.019 33.53
VIa ues conve rte d t ommo1 etrg s·oI 2 Samele . mmol B/g Si02 1 0.8627 2 0.9938 3 0.9481 4 1.048 "blank" 2.451E-03 Table 2: Summary of Band Assignments
S~ecies Band Assignment Isolated Silanols -3742 cm- 1 Vicinal Silanols 3660 - 3200 cm_,
Siloxanes 1880 cm- 1 , 1620 cm- 1 CH Stretching 3000 - 2800 cm- 1
CH Bending 1500 - 1370 cm- 1
8-0 stretch from (=SiOBCl2) 1470 - 1430 cm- 1
Si OB species from ( (-Si02)BCI) 1400 - 1350 cm- 1 8-0 stretch from (=SiOBX2), X .Et, OEt -1345 cm- 1
8-0 stretch from hydrolyzed product 1500 - 1350 cm- 1 8-0H stretch from hydrolyzed product -3215 cm_, Table 3: Isolated Silanol/Siloxane Ratio
Isolated Siloxane Isolated Silanol Isolated Silanol Silica Gels and region Region Silanol Remaining Reactions 1942 -1763 cm·1 3754 -3723 cm·1 Ratio Total (o/o} Bare silica gel 3.56 1.623 0.4559 100
600°C silica gel 12.32 7.629 0.6192 100
Reactions with BCl3
Bare silica gel 5.745 0.756 0.1316 28.8
600°C silica gel 2.406 1.401 0.5823 94.0
Reactions with B(Et)a
Bare silica gel 0.637 0.0158 0.02480 5.41
600°C silica gel 19.148 2.085 0.1088 17.5
Reactions with B(OEt)a
Bare silca gel 2.033 0.077 0.03788 8.31
600°C silica gel 4.273 0.5805 0.1359 21.9 Table 4: Elemental Analysis of the Boron Reactions -BCl3 Silica Tvoe Surface Soecies mmol B/ a SiQ, Unmodified Isolated silanols, 1.47 vicinal silanols, and siloxanes 600°C Isolated silanols and 0.922 siloxanes HMDS Vicinal silanols and 0.619 siloxanes 600°C/HMDS Siloxanes 0.211
B(Eth
Silica Tvoe Surface Soecies mmol 8/ a SiO, Unmodified Isolated silancls, 0.610 vicinal silanols, and siloxanes· 600°C Isolated silanols and 0.258 siloxanes HMDS Vicinal silanols and 0.0575 siloxanes 600°C/HMDS Siloxanes 0.0814
8(0Eth -- Silica Tvoe Surface Soecies mmol B/ a Si02 Unmodified Isolated silanols, 1.09 vicinal silanols, and siloxanes 600°C Isolated silanols and 0.610 siloxanes HMDS Vicinal silanols and 0.099 siloxanes 600°C/HMDS Siloxanes 0.134 Table 5: Elemental Analysis of the B(Eth versus Al(Eth
B(Eth
Silica Tvoe Surface Soecies mmol B/ a SiO? Unmodified Isolated silanols, 0.610 vicinal silanols, and siloxanes 600°C Isolated silanols and 0.258 siloxanes HMDS Vicinal silanols and 0.0575 siloxanes 600°C/HMDS Siloxanes 0.0814
Silica Tvoe Surface Soe.cies mmol Al/ a SiO? Unmodified Isolated silanols, 1.80 vicinal silanols, and. · · siloxanes 600°C Isolated silanols and 1.20 siloxanes HMDS Vicinal silanols and 0.57 siloxanes 600°C/HMDS Siloxanes 0.41 Table 6: Optimized Bond Lengths and Angles for Reactants
Bond Length HF MP2 Difference in Bond Angle HF MP2 Difference in Reactant In Angstroms 6-31G{d,~} 6-31G(d,~} HF and MP2 In degrees 6-31G{d,~} 6-31G{d,~} HF and MP2 AICl3 Al-Cl 2.0773 2.0722 0.0051 Cl-Al-Cl 120 120 0 BCl3 B-CI 1.7448 1.7368 0.008 Cl-B-CI 120 120 0 SiOH4 Si-0 1.6444 1.6691 -0.0247 Si-0-H 120.0085 116.7754 3.2331 0-H 0.9414 0.9612 -0.0198 Al(Et)a Al-C 1.9887 1.9831 0.0056 C-Al-C 117.2288 119.7923 -2.5635 C-C 1.5374 1.5343 0.0031 C-H· 1.0923 1.0957 -0.0034 C-H** 1.0875 1.0914 -0.0039 B(Et)a B-C 1.5972 1.5799 0.0173 C-B-C 116.1902 117.6405 -1.4503 C-C 1.5324 1.5302 0.0022 C-H· 1.0907 1.1013 -0.0106 C-H** 1.0863 1.09. -0.0037 * indicates CH2
** indicates CH 3 Table 7: Optimized Bond Lengths and Angles for Complex 1
Bond Length HF MP2 Difference in Bond Angle HF MP2 Difference in Com~lex In Angstroms 6-31G{d,~} 6-31G{d,~} HF and MP2 In degrees 6-31G(d,~} 6-31G{d,~} HF and MP2 AICl3-SiOH4 Al-Cl 2.1248 2.1141 0.0107 Si-0-H 117.5795 117.8182 -0.2387 Al-0 1.9308 1.9476 -0.0168 Si-0-AI 131.4347 129.119 2.3157 Si-0 1.7296 1.7451 -0.0155 Al-0-H 110.8929 111.3297 -0.4368 0-H 0.9506 0.9692 -0.0186 Cl-Al-0 97.9178 97.6185 0.2993 Cl-Al-Cl 116.9505 117.5092 -0.5587 BCl3-SiOH4 B-CI 1.8265 1.8103 0.0162 Si-0-H 118.292 116.8047 1.4873 B-0 1.6077 1.6365 -0.0288 Si-0-B 129.5188 125.2271 4.2917 Si-0 1.7419 1.7588 -0.0169 B-0-H 111.1788 109.7748 1.404 0-H 0.9499 0.9705 -0.0206 Cl-B-0 103.6929 103.4763 0.2166 Cl-B-CI 114.6349 115.5026 -0.8677 Al(Eth-SiOH4 Al-C 2.0062 1.9978 0.0084 Si-0-H 117.3345 116.5542 0.7803 Al-0 2.0778 2.0668 0.011 Si-0-AI 132.623 127.9111 4.7119 Si-0 1.6964 1.7192 -0.0228 Al-0-H 108.8819 110.1252 -1.2433 0-H 0.9469 0.967 -0.0201 C-Al-0 102.8371 102.3676 0.4695 C-Al-C 118.5603 116.6439 1.9164 B(Eth-SiOH4 B-C 1.5997 1.6055 -0.0058 Si-0-H 119.3724 116.7229 2.6495 B-0 2.8745 1.8879 0.9866 Si-0-B 138.3533 130.2474 8.1059 Si-0 1.6515 1.706 -0.0545 B-0-H 100.6884 107.2852 -6.5968 0-H 0.9423 0.9662 -0.0239 C-B-0 94.0981 100.1004 -6.0023 C-B-C 116.2406 115.0281 1.2125 Table 8: Optimized Bond Lengths and Angles for Transition States
Transition Bond Length HF Bond Angle HF State In Angstroms 6-31G{d,~} In degrees 6-31G{d,~} AICb-SiOH4 Al-Cl (s) 2.0954 Si-0-H 131.8664 Al-Cl (I) 2.4016 Si-0-AI 145.488 Al-0 1.7672 Al-0-H 82.6459 Si-0 1.6677 Cl-Al-Cl 118.9757 0-H 1.3967 0-Al-CI (s) 116.1203 H-CI 1.4242 0-Al-CI (I} 77.1719
BCl3-SiOH4 B-CI (s) 1.7515 Si-0-H 124.0243 B-CI (I) 2.5501 Si-0-B 132.9779 B-0 1.4511 B-0-H 95.0265 Si-0 1.7344 Cl-B-CI 121.6204 0-H 1.0707 0-B-CI (s) 116.9204 H-CI 1.7133 0-B-CI (I) 76.7921 s indicates stable atom I indicates leaving atom -- indicates distance Table 9: Optimized Bond Lengths and Angles for Complex 2
Bond Length HF MP2 Difference in Bond Angle HF MP2 Difference in Com~lex In Angstroms 6-31G(d,~} 6-31G{d,~} HF and MP2 In degrees 6-31G(d,~} 6-31G(d,~} HF and MP2 AICl3-SiOH4 Al-Cl 2.0974 2.0688 0.0286 Si-0-AI 117.7551 121.0366 -3.2815 Al-0 1.6783 1.7077 -0.0294 0-Al--H 65.885 35.5477 30.3373 Si-0 1.6305 1.6827 -0.0522 Al--H-CI 61.0307 159.4878 -98.4571 0-H 2.8676 1.9926 0.875 0-Al-CI 119.5963 120.5537 -0.9574 Al-Cl (I) 2.731 4.3394 -1.6084 0-Al--H-CI -179.6531 -179.992 0.3389 H-CI 1.2696 1.2803 -0.0107 Al-Cl-H (I) 61.0307 159.4878 -98.4571 Al--H 3.1098 3.117 -0.0072 BC'3-SiOH4 B-CI 1.7673 1.7458 0.0215 Si-0-B 138.6616 129.9505 8.7111 B-0 1.3189 1.3532 -0.0343 Si-0--H 120.3116 114.6555 5.6561 Si-0 1.6769 1.7124 -0.0355 Cl-B-CI 118.677 119.6393 -0.9623 0--H 2.7696 2.084 0.6856 0--H-CI 135.198 165.7783 -30.5803 B-CI (I) 4.4894 4.1929 0.2965 H-CI 1.2671 1.2763 -0.0092 B--H 3.2873 2.9314 0.3559
I indicates leaving atom -- indicates distance Table 10: Optimized Bond Lengths and Angles for Products
Difference Bond Length HF MP2 in Bond Angle HF MP2 Difference in Product In Angstroms 6-31G{d,~} 6-31G{d,~} HF and MP2 In degrees 6-31G{d,~} 6-31G{d,~} HF and MP2 AIC'2-SiOH3 Al-Cl 2.0858 2.0778 0.008 Si-0-AI 179.7703 179.9882 -0.2179 Al-0 1.6618 1.6831 -0.0213 Cl-Al-Cl 118.6962 118.9798 -0.2836 Si-0 1.6357 1.6566 -0.0209 Cl-Al-0 120.6257 120.5109 0.1148 BC'2-SiOH3 B-CI 1.7627 1.7493 0.0134 Si-0-B 140.368 131.9464 8.4216 B-0 1.3179 1.3441 -0.0262 Cl-B-CI 120.1353 119.3898 0.7455 Si-0 1.6678 1.6974 -0.0296 Cl-B-0 121.3585 121.6457 -0.2872 Al(Et)2-SiOH3 Al-C 1.9755 1.9719 0.0036 Si-0-AI 179.9981 155.4717 24.5264 Al-0 1.701 1.7256 -0.0246 C-Al-C 123.8021 124.1771 -0.375 Si-0 1.619 1.6474 -0.0284 C-Al-0 117.5238 117.6164 -0.0926 B(Et)2-SiOH3 B-C 1.5967 1.5879 0.0088 Si-0-B 139.5711 130.6645 8.9066 B-0 1.3627 1.3816 -0.0189 C-B-C 118.5494 119.6457 -1.0963 Si-0 1.6422 1.6772 -0.035 C-B-0 118.5494 119.6457 -1.0963 HCI H-CI 1.2656 1.2693 -0.0037 Ethane C-C 1.5268 1.5234 0.0034 C-C-H 111.215 111.1842 0.0308 C-H 1.0858 1.0889 -0.0031 Table 11: Single-Point Energies and Enthalpies(in hartrees) Corrected to 298 K for the HF/6-31G(d,p) Geometries
Molecule MP2/6-31G(d,l!I MP2/6-31+G(d,el MP2/6-311+G(d,el MP2/6-311+Gl2d,2pl ZPE Enthaley SPE1+ SPE2+ SPE3+ SPE4+ SPE1 SPE2 SPE3 SPE4 correction correction 298K H correction Hcorrectlon Hcorrectlon Hcorrectlon Reactants AICl3 -1621.0079820 -1621.0150347 -1621.1300294 . -1621.2034278 0.004498 0.010876 -1620.9971060 -1621.0041587 -1621.1191534 -1621.1925518 BCl3 -1403. 7239880 -1403.7301164 -1403.8404601 -1403.8981209 0.007239 0.012653 -1403.7113350 -1403.7174634 -1403.8278071 -1403.8854679 Al(EI), -478.8040355 -478.8152162 -478.9130684 -478.9855814 0.183208 0.19675 -478.6072855 -478.6184662 -478.7163184 -478.7888314 B(Elh -261.6182244 -261.6281205 -261.7103588 -261.7807956 0.189857 0.201638 -261.4165864 -261.4264825 -261.5087208 -261.5791576 SIOH4 -366.4259757 -366.4364174 -366.5027739 -366.5395613 0.036874 0.041758 -366.3842177 -366.3946594 -366.4610159 -366.4978033 Complex 1 AICl,-SiOH4 -1987.4865456 -1987.5044376 -1987.6870621 -1987.7916316 0.043921 0.055299 -1987.4312466 -1987.4491386 -1987.6317631 -1987. 7363326 BCl3-SiOH4 -1770.1659945 -1770.1843398 -1770.3623983 -1770.4525339 0.046936 0.057047 -1770.1089475 -1770.1272928 -1770.3053513 -1770.3954869 Al(Et),-SiOH4 -845.2634141 -845.2837485 -845.4490935 -845.5547948 0.22208 0.240669 -845.0227451 -845.0430795 -845.2084245 -845.3141258 B(Et),-SiOH4 -628.0527590 -628.0734183 -628.2220827 -628.3281061 0.227415 0.245446 -627.8073130 -627.8279723 -627.9766367 -628.0826601 TS AICl3·SiOHc -1987 .4456421 -1987.4641613 -1987.6489398 -1987. 7550036 0.038227 0.049101 -1987.3965411 -1987.4150603 -1987 .5998388 -1987. 7059026 BCl3-SiOH4 -1770.1231159 -1770.1425571 -1770.3212000 -1770.4164310 0.042487 0.052319 -1770.0707969 -1770.0902381 -1770.2688810 -1770.3641120 Complex2 AIC13-SiOH4 -1987.4462569 -1987 .4668960 -1987.6502237 -1987.7561854 0.039573 0.052202 -1987.3940549 -1987.4146940 -1987.5980217 -1987. 7039834 BC13-SiOH4 -1770.177343 -1770.193728 -1770.36976 -1770.465515 0.042477 0.054455 -1770.1228876 -1770. 1392728 -1770.3153047 -1770.4110600 Products SiH30AICl2 -1527.230359 -1527 .246297 -1527 .392403 -1527.477134 0.031637 0.039911 -1527.1904475 -1527.2063864 -1527.3524923 -1527.4372232 SiH.OBCl2 -1309.966921 -1309.980129 -1310.119185 -1310.193265 0.03519 0.043193 -1309.9237278 -1309.9369364 -1310.0759920 -1310.1500719 SiH30Al(Elh -765. 7644266 -765.7826617 -765.9159837 -766.0014424 0.150812 0.164789 -765.5996376 -765.6178727 -765.7511947 -765.8366534 SiH30B(Elh -548.5631682 -548.577908 -548.6973384 -548. 7807083 0.156634 0.16894 -548.3942282 -548.4089680 -548.5283984 -548.6117683 HCI -460.2054379 -460.2076043 -460.2446671 -460.2666148 0.006468 0.009772 -460.1956659 -460.1978323 -460.2348951 -460.2568428 Ethane -79.5433554 -79.5457304 -79.5712497 -79.5950217 0.070728 0.075217 -79.4681384 -79.4705134 -79.4960327 -79.5198047
AH=Complex 1 - Reactants SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 -131.0705770 -132.1144599 -135.4574581 -120.7120871 SCl3 -35.1675116 -39.8282282 -43.3943905 -32.0718317 Al( Et), -82.0243588 -78.6427663 -81.6260765 -72. 1767834 S(Et), -17.0888566 -17.9329420 -18.1156740 -14.9630216
AH= Transition §tale -Complex1 SPE 1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 91.1179020 89.4712135 83.8159727 79.8927478 SCl3 100.1628743 97.2856327 95.7513138 82.3735450
AH=Complex 2 • Iransltlon State SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 6.5274187 0.9617060 4.7707234 5.0387828 SCl3 • 136. 7620492 ·128.7386435 -121.8835674 -123.2600961
AH=Products ..Comelex 2 SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 20.8500906 27.5024811 27.9199293 26.0377370 SCI, 9.1730947 11.8253344 11.5982321 10.8833193
AH=Products- Reactants SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 -12.5751658 -14.1790593 -18.9508328 ·9.7428195 SCl3 ·62.5935919 -59.4559046 -57.9284120 -62.0750635 Al(Et), -200.2511855 -197.5934323 -183.5015383 -183.3185438 S(Et), -161.6298813 -153.1680237 -143.5979594 ·143.3818841 Table 12: Single-Point Energies and Free Energies Corrected to 298 K for the HF/6-31G(d,p) Geometries
Molecule MP2/6-31G(d,pl MP2/6-31+G!d.pl MP2/6-311+Gld.pl MP2/6-311+Gl2d.2pl Entropy Free Enemir: SPE1 + SPE2+ SPE3+ SPE4+ SPE1 SPE2 SPE3 SPE4 J/mol*K correction 298K G correction G correction G correction G correction Reactants AICl 3 -1621.0079820 -1621.0150347 -1621.1300294 -1621.2034278 315.456864 -0.024947 -1621.0329290 -1621.0399817 -1621.1549764 -1621.2283748 BCl3 -1403. 7239880 -1403.7301164 -1403.8404601 -1403.8981209 290.612272 -0.020348 -1403. 7443360 -1403.7504644 -1403.8608081 -1403.9184689 Al( Et), -478.8040355 -478.8152162 -478.9130684 -478.9855814 484.728952 0.141704 -478.6623315 -478.6735122 -478.7713644 -478.8438774 B(Et), -261.6182244 -261.6281205 -261.7103588 -261. 7807956 427.023224 0.153145 -261.4650794 -261.4749755 -261.5572138 -261.6276506 SIOH4 -366.4259757 -366.4364174 -366.5027739 -366.5395613 258.730192 0.012377 -366.4135987 -366.4240404 -366.4903969 -366.5271843 Complex 1 AICl,-SiOH, -1987.4865456 -1987.5044376 -1987.6870621 -1987.7916316 443.989344 0.00488 -1987.4816656 -1987.4995576 -1987.6821821 -1987.7867516 BCl 3-SiOH4 -1770.1659945 -1770.1843398 -1770.3623983 -1770.4525339 402.002904 0.011396 -1770.1545985 -1770 .1729438 -1770.3510023 -1770.4411379 Al(Et),-SiOH4 -845.2634141 -845.2837 485 -845.4490935 -845.5547948 582.446272 0.174526 -845.0888881 -845.1092225 -845.27 45675 -845.3802688 B(Et),-SiOH4 -628.0527590 -628.0734183 -628.2220827 -628.3281061 598.512832 0.177432 -627.8753270 -627.8959863 -628.0446507 -628.1506741 TS AICl,-SiOH4 -1987.4456421 -1987.4641613 -1987.6489398 -1987.7550036 406.249664 -0.000373 -1987.4460151 -1987.4645343 -1987.6493128 -1987.7553766 BCl3-SiOH, -1770.1231159 -1770.1425571 •1770.3212000 -1770.4164310 413.596768 0.006185 -1770.1169309 -1770.1363721 -1770.3150150 -1770.4102460 Complex 2 AICl3-SiOH4 -1987 .4462569 -1987.4668960 -1987.6502237 -1987.7561854 485.820976 -0.002968 -1987.4492249 -1987.4698640 -1987.6531917 -1987.7591534 BCl3-SiOH4 -1770.177343 -1770.193728 -1770.36976 -1770.465515 488.515472 -0.00102 -1770.1783626 -1770.1947478 -1770.3707797 -1770.4665350 Products SiH30AICl2 -1527.230359 -1527.246297 -1527.392403 -1527.477134 377.840304 -0.002996 -1527.2333545 -1527.2492934 -1527.3953993 -1527.4801302
SiH30BCl2 -1309.966921 -1309.980129 -1310.119185 -1310.193265 363.761144 0.001884 -1309.9650368 -1309.9782454 -1310.1173010 -1310.1913809 SiH30Al(Et), -765. 7644266 -765.7826617 -765.9159837 -766.0014424 512.360088 0.106606 -765.6578206 -765.6760557 -765.8093777 -765.8948364 SiH30B(Et), -548.5631682 -548.577908 -548.6973384 -548. 7807083 448.491328 0.11801 -548.4451582 -548.4598980 -548.5793284 -548.6626983 HCI -460.2054379 -460.2076043 -460.2446671 -460.2666148 186.351176 -0.01139 -460.2168279 -460.2189943 -460.2560571 -460.2780048 Ethane -79.5433554 -79.5457304 -79.5712497 -79 .5950217 243.270312 0.047592 -79.4957634 -79.4981384 -79 .5236577 -79.5474297
L\.G-Complex 1 - Reactants SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -92.2531509 -93.2970338 -96.6400320 -81.8946610 SCl3 8.7590597 4.0983431 0.5321807 11.8547395 Al(Et), -34.0204481 -30.6388557 -33.6221659 -24.1728728 S(Et), 8.7981790 7.9540936 7.7713616 10.9240140
L\.G= Transition State -Complex1 SPE1 +G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 93.5989617 91.9522732 86.2970324 82.3738075
SCl3 98.8947771 96.0175355 94.4832167 81.1054478
L\.G=Comolex 2 • Transition State SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr.
AICl3 -8.4272015 -13.9929142 -10.1838968 -9.9158373
SCl3 -161.2864711 -153.2630653 -146.4079893 -147.7845179
L\.G=Products -Complex 2 SPE 1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -2.5138779 4.1385126 4.5559607 2.6737685
SCl3 -9.1946235 -6.5423838 -6.7694861 -7.4843988
L\.G=Products- Reactants SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -9.5952687 -11.1991622 -15.9709357 -6.7629224 SCl3 -62.8272578 -59.6895706 -58.1620779 -62.3087294 Al(Et), -203.8769457 -201.2191926 -187.1272986 -186.9443040 S(Et), -163.4178195 -154.9559619 -145.3858977 -145.1698223 Table 13: Single-Point Energies and Enthalpies(in hartrees) Corrected to 898 K for the HF/6-31G(d,p) Geometries
Molecule MP2/6-31G(d,p) MP2/6-31+G(d.pl MP2/6-311+G(d.pl MP2/6-311+G!2d.2pl ZPE Enthalpy SPE1+ SPE2 + SPE3+ SPE4+ SPE1 SPE2 SPE3 SPE4 correction correction 898K H correction H correction H correction H correction Reactants AICl 3 -1621.0079820 -1621.0150347 -1621.1300294 -1621.2034278 0.004498 0.02896 -1620.9790220 -1620.9860747 -1621.1010694 -1621.1744678 BCl3 -1403.7239880 -1403.7301164 -1403.8404601 -1403.8981209 0.007239 0.02971 -1403.6942780 -1403.7004064 -1403.8107501 -1403.8684109 Al{EI), -478.8040355 -478.8152162 -478.9130684 -478.9855814 0.183208 0.263152 -478.5408835 -478.5520642 -478.6499164 -478.7224294 B(Et), -261.6182244 -261.6281205 -261.7103588 -261.7807956 0.189857 0.265669 -261.3525554 -261.3624515 -261.4446898 -261.5151266 SIOH4 -366.4259757 -366.4364174 -366.5027739 -366 .5395613 0.036874 0.061222 -366.3647537 -366.3751954 -366.4415519 -366.4783393 Complex 1 AICl3-SiOH4 -1987.4865456 -1987.5044376 -1987.6870621 -1987.7916316 0.043921 0.096248 -1987.3902976 -1987.4081896 -1987.5908141 -1987.6953836 BCl3-SiOH, -1770. 1659945 -1770.1843398 -1770 .3623983 -1770.4525339 0.046936 0.097001 -1770.0689935 -1770.0873388 -1770.2653973 -1770.3555329
Al(Et),-SiOH4 -845.2634141 -845.2837485 -845.4490935 -845.5547948 0.22208 0.330008 -844.9334061 -844.9537405 -845.1190855 -845.2247868 B(Et),-SiOH4 -628.0527590 -628.0734183 -628.2220827 -628.3281061 0.227415 0.33263 -627.7201290 -627.7407883 -627.8894527 -627.9954761 TS AICl 3-SiOH4 -1987.4865456 -1987.5044376 -1987.6489398 -1987.7550036 0.038227 0.088827 -1987.3977186 -1987.4156106 -1987.5601128 -1987.6661766 BCl,-SiOH, -1770.1231159 -1770.1425571 -1770.3212000 -1770.4164310 0.042487 0.090594 -1770.0325219 -1770.0519631 -1770.2306060 -1770.3258370 Complex 2 AIC13-SiOH4 -1987.4462569 -1987.4668960 -1987.6502237 -1987.7561854 0.039573 0.093751 -1987.3525059 -1987.3731450 -1987.5564727 -1987.6624344 BC1 3-SiOH4 -1770.177343 -1770.193728 -1770.36976 -1770.465515 0.042477 0.094931 -1770.0824116 -1770.0987968 -1770.2748287 -1770.3705840 Products SiH30AIC12 -1527.230359 -1527.246297 -1527.392403 -1527.477134 0.031637 0.070096 -1527.1602625 -1527.1762014 -1527.3223073 -1527.4070382 SiH,OBCl2 -1309.966921 -1309.980129 -1310.119185 -1310.193265 0.03519 0.074081 -1309.8928398 -1309.9060484 -1310.0451040 -1310.1191839 SiH30Al(Et), -765.7644266 -765.7826617 -765.9159837 -766.0014424 0.150812 0.229069 -765.5353576 -765.5535927 -765.6869147 -765.7723734 SiH 30B(Et), -548.5631682 -548.577908 -548.6973384 -548.7807083 0.156634 0.231167 -548.3320012 -548.3467410 -548.4661714 -548.5495413 HCI -460.2054379 -460.2076043 -460.2446671 -460.2666148 0.006468 0.016561 -460.1888769 -460.1910433 -460.2281061 -460.2500538 Ethane -79.5433554 -79.5457304 -79.5712497 -79.5950217 0.070728 0.095468 -79.4478874 -79.4502624 -79.4757817 -79.4995537
&H=Complex 1 . Reactants SPE 1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 -122.1413876 -123.1852705 -126.5282687 -111.7828977 BCI, -26.1543074 -30.8150240 -34.3811863 -23.0586275 Al(Et), -72.9061362 -69.5245437 -72.5078539 -63.0585608 B(Et), -7.4035347 -8.2476200 -8.4303521 -5.2776997
&H= Transition State -Complex1 SPE1 +H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICI, -19.4835387 -19.4835387 80.6050351 76.6818102 BCI, 95.7547269 92.8774853 91.3431665 77.9653976
&H=Complex 2 - Transition State SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 118.7041353 111.4917342 9.5569369 9.8249964 BCI, -130.9834118 -122.9600060 -116.1049299 -117.4814586
&il=Products -Complex 2 SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 8.8386111 15.4910016 15.9084498 14.0262575 BCI, 1.8244322 4.4766718 4.2495696 3.5346568
&H=Products- Reactants SPE1+H corr. SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 -14.0821798 -15.6860733 -20.4578469 -11.2498336 BCI, -59.5585601 -56.4208729 -54.8933802 -59.0400317 Al(Et), -203.7561746 -201.0984214 -187.0065274 -186.8235329 B(Et), -164.2999741 -155.8381165 -146.2680522 -146.0519769 Table 14: Single-Point Energies and Free Energies Corrected to 898 K for the HF/6-31G(d,p) Geometries
Molecule MP2/6-31G!d.pl MP2/6-31+G!d.pl MP2/6-311+Gld.pl MP2/6-311+Gl2d.2pl Entropy Free Enemy SPE1 + SPE2 + SPE3 + SPE4+ SPE1 SPE2 SPE3 SPE4 J/mol*K correction 898K G correction G correction G correction G correction Reactants AICI, -1621.0079820 -1621.0150347 -1621.1300294 -1621.2034278 401.877384 -0.108517 -1621.1164990 -1621.1235517 -1621.2385464 -1621.3119448 BCI, -1403.7239880 -1403.7301164 -1403.8404601 -1403.8981209 371.37184 -0.097332 -1403.8213200 -1403.8274484 -1403.9377921 -1403.9954529 Al( Et), -478.8040355 -478.8152162 -478.9130684 -478.9855814 785.926744 -0.005704 -478.8097395 -478.8209202 -478.9187724 -478.9912854 B(Et), -261.6182244 -261.6281205 -261.7103588 -261 .7807956 715.597888 0.020872 -261.5973524 -261.6072485 -261.6894868 -261.7599236 SIOH4 -366.4259757 -366.4364174 -366.5027739 -366.5395613 348.246872 -0.057908 -366.4838837 -366.4943254 -366.5606819 -366.5974693 Complex 1 AICl3-SiOH4 -1987 .4865456 -1987.5044376 -1987.6870621 -1987.7916316 636.126992 -0.121363 -1987.6079086 -1987.6258006 -1987.8084251 -1987.9129946 BCl3-SiOH4 -1770.1659945 -1770.1843398 -1770.3623983 -1770.4525339 588.64696 -0.104367 -1770.2703615 -1770.2887068 -1770.4667653 -1770.5569009 Al(Et),-SiOH4 -845.2634141 -845.2837485 -845.4490935 -845.5547948 989.674992 -0.008546 -845.2719601 -845.2922945 -845.4576395 -845.5633408 B(Et),-SiOH, -628.0527590 -628.0734183 -628.2220827 -628.3281061 994.587008 -0.007605 -628.0603640 -628.0810233 -628.2296877 -628.3357111 TS AIC13-SiOH4 -1987.4456421 -1987.4641613 -1987.6489398 -1987.7550036 584.345808 -0.123741 -1987.5693831 -1987.5879023 -1987.7726808 -1987.8787446 BCl3-SiOH4 -1770.1231159 -1770.1425571 -1770.3212000 -1770.4164310 596.55472 -0.109302 -1770.2324179 -1770.2518591 -1770.4305020 -1770.5257330 Complex 2 AICl3-SiOH4 -1987 .4462569 -1987.4668960 -1987.6502237 -1987.7561854 681.07152 -0.139234 -1987.5854909 -1987.6061300 -1987.7894577 -1987.8954194 BCl3-SiOH4 -1770.177343 -1770.193728 -1770.36976 -1770.465515 . 678.063224 -0.137026 -1770.3143686 -1770.3307538 -1770.5067857 -1770.6025410 Products SiH30AICl2 -1527.230359 -1527.246297 -1527.392403 -1527.477134 518.636088 -0.107323 -1527.3376815 -1527.3536204 -1527.4997263 -1527.5844572 SiH30BCl2 -1309.966921 -1309.980129 -1310.119185 -1310.193265 507.276528 -0.099452 -1310.0663728 -1310.0795814 -1310.2186370 -1310.2927169 SiH30Al(Et), •765. 7644266 -765.7826617 -765.9159837 -766.0014424 805.390712 -0.046445 -765.8108716 -765.8291067 -765.9624287 -766.0478874 SiH30B(Et), -548.5631682 -548.577908 -548.6973384 -548.7807083 730.605896 -0.018764 -548.5819322 -548.5966720 -548.7161024 -548.7994723 HCI -460.2054379 -460.2076043 -460.2446671 -460.2666148 218.936168 -0.058334 -460.2637719 -460.2659383 -460.3030011 -460.3249488 Ethane -79.5433554 -79.5457304 •79.5712497 -79.5950217 334.11332 -0.018827 -79.5621824 -79.5645574 -79.5900767 -79.6138487
11.G=Complex 1 • Reactants SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -19.7589494 -20.8028323 -24.1458305 -9.4004595 BCI, 91.4768024 86.8160858 83.2499235 94.5724823 Al(Et), 56.8756025 60.2571950 57.2738848 66.7231779 B(Et), 54.7988637 53.9547783 53.7720463 56.9246986
dG= Transition State ..Complex1 SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICI, 101.1471592 99.5004707 93.8452299 89.9220050 BCI, 99.6194041 96.7421624 95.2078436 81.8300747
11.G=Comolex 2 - Transition State SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl 3 -42.2903846 -47.8560972 -44.0470799 -43.7790204 BCI, -215.1582848 -207.1348791 -200.2798030 -201.6563317
11.G=Products -Complex 2 SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl 3 -41.9089052 -35.2565147 -34.8390666 -36.7212588 BCI, -41.4195195 -38.7672798 -38.9943821 -39. 7092949
11.G=Products- Reactants SPE1+G corr. SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -2.8110800 -4.4149735 -9.1867471 0.0212662 BCI, -65.4815979 -62.3439106 -60.8164180 -64.9630695 Al(Et), -208.5423882 -205.8846350 -191.7927410 -191.6097464 B(Et), -165.0849866 -156.6231290 -147.0530648 -146.8369894 Table 15: Single-Point Energies and Enthalpies(in hartrees) Corrected to 298 K for theMP2/6-31G(d,p) Geometries
Compound MP2/6-31+G(d,l!I MP2/6-311+Gld,DI MP2/6-311+Gl2d.2DI ~ Enthalev SPE2+ SPE3+ ~ SPE2 SPE3 SPE4 correction correction 298K Hcorrectlon Hcorrectlon Hcorrectlon Reactants AICl3 -1621.0150661 -1621.1301159 -1621.2033844 0.004736 0.01103 -1621.0040361 -1621.1190859 -1621.1923544 BCl3 -1403.7302039 -1403.8404922 -1403.8980042 0.007604 0.012935 -1403.7172689 -1403.8275572 -1403.8850692 Al(Elh -478.8156428 -478.9137627 -478.9859584 0.178573 0.192373 -478.6232698 -478.7213897 -478. 7935854 B(Elh -261.6289486 -261.7115267 -261.7817112 0.184609 0.196653 -261.4322956 -261.5148737 -261.5850582 SIOH4 -366.4373256 -366.5032045 -366.5399024 0.037723 0.042541 -366.3947846 -366.4606635 -366.4973614 Complex 1 AICl3-SiOH4 -1987.5053362 -1987.6874941 -1987.7918506 0.044859 0.056072 -1987 .4492642 -1987.6314221 -1987.7357786 BCl3-SiOH4 -1770.1855654 -1770.3629161 -1770.4529190 0.048093 0.057929 -1770.1276364 -1770.3049871 -1770.3949900
Al(Elh-SiOH4 -845.2854130 -845.4507515 -845.5560049 0.228394 0.24669 -845.0387230 -845.2040615 -845.3093149 B(Elh-SiOH4 -628.0793649 -628.2299308 -628.3328334 0.235319 0.251656 -627 .8277089 -627.9782748 -628.0811774 Complex2 AICl3-Si0H4 -1987.4608903 -1987.6435769 -1987.7514157 0.041383 0.053427 -1987 .4074633 -1987.5901499 -1987.6979887 BCl3-SiOH4 -1770.1968180 -1770.3723883 -1770.4678497 0.044671 0.055728 -1770.1410900 -1770.3166603 -1770.4121217 Products SiH30AICl2 -1527.2471223 -1527.3927755 -1527.4770077 0.032519 0.041745 -1527.2053773 -1527.3510305 -1527.4352627 SiH30BCl2 -1309.9813008 -1310.1199636 -1310.1938293 0.036282 0.044096 -1309.9372048 -1310.0758676 -1310.1497333 SiH30Al(EI), -765.7831591 -765.916545 -766.0022396 0.155437 0.169143 -765.6140161 -765.7474020 -765.8330966 SiH30B(Et), -548.5777525 -548.6973681 -548. 7800782 0.161552 0.173528 -548.4042245 -548.5238401 -548.6065502 HCI -460.2076168 -460.2446940 -460.2666760 0.006703 0.010008 -460.1976088 -460.2346860 -460.2566680 Ethane -79.5457886 -79.5713826 -79.5950033 0.073077 0.097469 -79.4483196 -79.4739136 -79.4975343 t\H=Complex 1 - Reactants SPE2+H corr. SPE3+H corr. SPE4+H corr. AICI, -132.4373915 -135.6646069 -120.9360389 BCl3 -40.9122806 -44.0195125 -32.9742023 Al(Et). -54.2645826 -57.7819113 -48.2247118 B(Et). -1.6506267 -7.1874593 3.2613464 t\H=Products -Comelex 2 SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 11.7547095 11.6397144 15.9050367 BCl3 16.4784371 16.0328966 15.0186814
t\H=Products- Reactants SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl3 -10.9360911 -15.6663824 -5.8151314 BCl3 -59.7557321 -58.6341356 -62.9341140 Al(Et). -116.2587819 -103.0818607 -104.1890172 B(Et). -66.8544509 -58.3285321 -56.8803284 Table 16: Single-Point Energies and Free Energies Corrected to 298 K for the MP2/6-31G(d,p) Geometries
Compound MP2/6-31+G!d.pl MP2/6-311+G!d.pl MP2/6-311+!;i(2d,21!) Entropy Free Enemy SPE2+ SPE3+ SPE4+ SPE2 SPE3 SPE4 J/mol*K correction 298K G correction G correction G correction Reactants AICl3 -1621.0150661 -1621.1301159 -1621.2033844 313.82092 -0.024607 -1621.0396731 -1621.1547229 -1621.2279914 BCl3 -1403.7302039 -1403.8404922 -1403.8980042 289.1726024 -0.0199 -1403.7501039 -1403.8603922 -1403.9179042 Al( Et), -478.8156428 -478.9137627 -478.9859584 489.017552 0.136841 -478.6788018 -478.7769217 -478.8491174 B(EI), -261.6289486 -261.7115267 -261.7817112 427.291 0.14813 -261.4808186 -261.5633967 -261.6335812 SIOH4 -366.4373256 -366.5032045 -366.5399024 257.592144 0.013289 -366.4240366 -366.4899155 -366.5266134 Complex 1 AICl,-SiOH4 -1987.5053362 -1987.6874941 -1987.7918506 433.725992 0.006818 -1987.4985182 -1987.6806761 -1987. 7850326 BCl3-SiOH4 -1770.1855654 -1770.3629161 -1770.4529190 394.438232 0.013137 -1770.1724284 -1770.3497791 -1770.4397820 Al(Et),-SiOH4 -845.2854130 -845.4507515 -845.5560049 578.781088 0.180964 -845.1044490 -845.2697875 -845.3750409 B(Et),-SiOH4 -628.0793649 -628.2299308 -628.3328334 512.661336 0.193438 -627 .8859269 -628.0364928 -628.1393954 Complex2 AICl3-SiOH4 -1987.4608903 -1987.6435769 -1987.7514157 482.720632 -0.00139 -1987 .4622803 -1987.6449669 -1987.7528057 BCl3-SiOH4 -1770.1968180 -1770.3723883 -1770.4678497 447.127344 0.004952 -1770.1918660 -1770.3674363 -1770.4628977 Products SiH30AICl2 -1527.2471223 -1527 .3927755 -1527.4770077 425.441672 -0.006568 -1527.2536903 -1527.3993435 -1527.4835757 SiH30BCl2 -1309.9813008 -1310.1199636 -1310.1938293 356.342912 0.00363 -1309.9776708 -1310.1163336 -1310.1901993 SiH30Al(Et), -765.7831591 -765.916545 -766.0022396 491.758072 0.113299 -765.6698601 -765.8032460 -765.8889406 SiH30B(Et), -548.5777525 -548.6973681 -548.7800782 434.186232 0.124222 -548.4535305 -548.5731461 -548.6558562 HCI -460.2076168 -460.2446940 -460.2666760 186.401384 -0.0116 -460.2192168 -460.2562940 -460.2782760 Ethane -79.5457886 -79.5713826 -79.5950033 332.033872 -0.016116 -79.5619046 -79.5874986 -79.6111193
AG=Complex 1 - Reactants SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl 3 -91.3883244 -94.6155398 -79.8869718 BCl3 4.4950501 1.3878182 12.4331284 Al( Et), -4.2285659 -7.7458946 1.8113049 B(Et), 49.6954945 44.1586619 54.6074676
AG=Products -Complex 2 SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl 3 -27.9002383 -28.0152335 -23.7499112 BCl3 -13.1840099 -13.6295505 -14.6437657
AG=Products- Reactants SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl 3 -24.1474058 -28.8776971 -19.0264461 BCl3 -59.7216012 -58.6000047 -62.8999830 Al( Et), -338.4908436 -325.3139224 -326.4210789 B(Et), -290.3231043 -281 . 7971854 -280.3489817 Table 17: Single-Point Energies and Enthalpies(in hartrees) Corrected to 898 K for the MP2/6-31G(d,p) Geometries
Compound MP2/6-31+G(d,el MP2/6-311+G(d,l!l MP2/6-311+G(2d,2!!l ZPE Enthaley SPE2+ SPE3+ SPE4+ SPE2 SPE3 SPE4 correction correction 89BK Hcorrectlon Hcorrectlon Hcorrectlon Reactants AICl 3 -1621.0150661 -1621.1301159 -1621.2033844 0.004736 0.029022 -1620.9860441 -1621.1010939 -1621.1743624
BCl 3 -1403. 7302039 -1403.8404922 -1403.8980042 0.007604 0.02984 -1403.7003639 -1403.8106522 -1403.8681642 Al( Et), -478.8156428 -478.9137627 -478.9859584 0.178573 0.260268 -478.5553748 -478.6534947 -478. 7256904 B(EI), -261.6289486 -261.7115267 -261.7817112 0.184609 0.262371 -261.3665776 -261.4491557 -261.5193402 SIOH4 -366.4373256 -366.5032045 -366.5399024 0.037723 0.061786 -366.3755396 -366.4414185 -366.4781164 Complex 1 AIC1 3-SiOH4 -1987.5053362 -1987.6874941 -1987.7918506 0.044859 0.096803 -1987.4085332 -1987.5906911 -1987.6950476
BCl 3-SiOH4 -1770.1855654 -1770.3629161 -1770.4529190 0.048093 0.097557 -1770.0880084 -1770.2653591 -1770.3553620
Al(Et),-SiOH4 -845.2854130 -845.4507515 -845.5560049 0.228394 0.335149 -844.9502640 -845.1156025 -845.2208559 B(Et),-SiOH4 -628.0793649 -628.2299308 -628.3328334 0.235319 0.337637 -627. 7417279 -627.8922938 -627.9951964 Complex 2 AIC1 3-SiOH, -1987.4608903 -1987.6435769 -1987.7514157 0.041383 0.094542 -1987 .3663483 -1987.5490349 -1987.6568737 BCl3-SiOH, -1770.1968180 -1770.3723883 -1770.4678497 0.044671 0.095746 -1770.1010720 -1770.2766423 -1770.3721037 Products SiH 30AICl2 -1527.2471223 -1527 .3927755 -1527.4770077 0.032519 0.073596 -1527. 1735263 -1527.3191795 -1527.4034117
SiH30BCl2 -1309.9813008 -1310.1199636 -1310.1938293 0.036282 0.074733 -1309.9065678 -1310.0452306 -1310.1190963
SiH30Al(Et), -765.7831591 -765.916545 -766.0022396 0.155437 0.232773 -765.5503861 -765.6837720 -765. 7694666
SiH 30B(Et), -548.5777525 -548.6973681 -548. 7800782 0.161552 0.235021 -548.3427315 -548.4623471 -548.5450572 HCI -460.2076168 -460.2446940 -460.2666760 0.006703 0.01678 -460.1908368 -460.2279140 -460.2498960 Ethane -79.5457886 -79.5713826 -79.5950033 0.073077 0.077519 -79.4682696 -79.4938636 -79.5174843
AH=Complex 1 - Reactants SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 -123.2640343 -126.4912497 -111.7626816
BCl3 -31 . 7809308 -34.8881627 -23.8428524 Al(Eth -50.8016008 -54.3189296 -44. 7617301 B(Eth 1.0220916 -4.5147410 5.9340647
AH=Products -Comelex 2 SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 5.2120632 5.0970680 9.3623904
BCl 3 9.6286120 9.1830714 8.1688562
AH=Products- Reactants SPE2+H corr. SPE3+H corr. SPE4+H corr. AICl 3 -7.2972035 -12.0274948 -2.1762438
BCl3 -56.4502780 -55.3286815 -59.6286599 Al( Eth -230.3612735 -217.1843523 -218.2915088 B(Eth -180.8519241 -172.3260053 -170.8778016 Table 18: Single-Point Energies and Free Energies Corrected to 898 K for the MP2/6-31G(d,p) Geometries
Compound MP2/6-31+G(d.pl MP216·311+Gld.p! MP2/6-311+Gl2d.2pl Entropy Free Ene!llv lli!..:!:.. SPE3+ SPE4+ SPE2 SPE3 SPE4 J/mol*K correction 898K G correction G correction G correction Reactants AICI, -1621.0150661 -1621.1301159 -1621.2033844 399.726808 -0.107719 -1621.1227851 -1621.2378349 -1621.3111034 BCI, -1403.7302039 -1403.8404922 -1403.8980042 369.095744 -0.096423 -1403.8266269 -1403.9369152 -1403.9944272 Al( Et), -4 78.8156428 -478.9137627 -478.9859584 797.457848 -0.012532 -478.8281748 -478.9262947 -478 .9984904 B(EI), -261.6289486 ·261.7115267 -261.7817112 724.070488 0.014676 -261.6142726 -261.6968507 -261. 7670352 SIOH4 -366.4373256 -366.5032045 -366.5399024 346.075376 -0.056602 -366.4939276 -366.5598065 -366.5965044 Complex 1 AICl3-SiOH4 -1987.5053362 -1987.6874941 -1987.7918506 624.800904 -0.116933 ·1987.6222692 -1987.8044271 -1987.9087836 BC13-Si0H4 -1770.1855654 -1770.3629161 -1770.4529190 579.396136 -0.100648 ·1770.2862134 -1770.4635641 -1770.5535670 Al(El),-SiOH4 -845.2854130 -845.4507515 -845.5560049 234.705 -0.000782 -845.2861950 -845.4515335 -845.5567869 B(El),·SiOH4 -628.0793649 -628.2299308 -628.3328334 902.685448 0.028839 -628.0505259 -628.2010918 -628.3039944 Complex 2 AICl3-Si0H4 ·1987.4608903 -1987.6435769 -1987.7514157 675.682528 -0.1366 -1987.5974903 -1987.7801769 -1987.8880157 BCl3-Si0H4 -1770.1968180 -1770.3723883 -1770.4678497 634.248376 -0.121222 ·1770.3180400 -1770.4936103 -1770.5890717 Products SiH30AIC12 -1527.2471223 -1527 .3927755 -1527 .4 770077 574.300024 -0.122865 -1527.3699873 -1527.5156405 -1527 .5998727 SiH30BCl2 -1309.9813008 -1310.1199636 -1310.1938293 498.640752 -0.095845 ·1310.0771458 -1310.2158086 -1310.2896743 SiH30Al(Et}., -765.7831591 -765.916545 -766.0022396 781 .855712 -0.034689 -765.8178481 -765.9512340 -766.0369286 SiH30B(EI), -548.5777525 -548.6973681 -548. 7800782 712.920128 -0.00886 -548.5866125 -548.7062281 -548. 7889382 HCI -460.2076168 -460.2446940 -460.2666760 218.919432 -0.05811 -460.2657268 -460.3028040 -460.3247860 Ethane -79.5457886 -79.5713826 -79.5950033 242.52556 -O.D16116 -79.5619046 -79.5874986 -79.6111193
AG=Complex 1 - Reactants SPE2+G corr. SPE3+G corr. SPE4+G corr. AIC13 -14 .5883685 -17.8155839 -3.0870159 BCl3 90.1611844 87.0539525 98.0992627 Al(Eth 94.2734424 90.7561136 100.3133131 B(Et), 151.4215677 145.8847351 156.3335408
AG=Products -Comelex 2 SPE2+G corr. SPE3+G corr. SPE4+G corr. AIC13 -100.3550579 -100.4700531 -96.2047308 BCl3 -65.1969980 -65.6425386 -66.6567538
AG=Products- Reactants SPE2+G corr. SPE3+G corr. SPE4+G corr. AICl3 -49.8874156 -54.6177069 -44. 7664559 BCl3 -58.5952788 -57.4736823 -61.7736607 Al( Eth -151.3585566 -138.1816354 -139.2887919 B(Eth -105.8504083 -97.3244895 -95.8762857 Figures Figure 1: Silanol and Siloxane Species on the Silica Gel Surface
,...... H /H ,...... H 0 0 ? I I Si Si Si
Isolated Silanol Species
/H.-...... _,..H /H ...... /H o ···o" o ··o I I I I Si Si Si Si
Vicinal Silanol Species
Geminal Silanol Species
0 s( 'si
Siloxane Species Figure 2: Thermal Treatment of Silica Gel Surface
(A) Dehydration Process on Silica Gel Surface
H I 0 ...... ""' H H H H H H H I ...... \ / / j .... ;(
0 0 0 0 0 0 + H20 I 1so -2so c .... I / \ ..... I lo\ '( '1 Si Si Si s1i Ji Si Si Si Si Si Unmodified Silica Gel
(B) Dehydroxylation Process on Silica Gel Surface
/H o/"M...... o/H H 0/ 0 0 600°C • I \ + H20 f /0\ I I I I\ Si Si Si Si Si Si Si Si Si Si
Unmodified Silica Gel Figure 3: Silica Gel Surfaces
/H o,...... 1-1 .. ······· .. o,,,./H /H f /0\ I I 600°C .. r lo\ lo\ Si Si Si Si Si Si Si Si Si Si
Unmodified Silica Gel 600°C Silica Gel
Si(CH3)3 ..H...... H HMDS b 0 o/·· '·······a I I ~i s{·')i Si Si HMDS Silica Gel
Si(CH3) /H I 0 f /0\ /0\ HMDS .. I lo\ lo\ Si Si Si Si Si Si Si Si Si Si
600°C Silica Gel 600°C/HMDS Silica Gel Figure 4: Bare Silica Gel
--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--.-0.40
0.35
0.30
0.25 ~ c ::I :!: I 0.20 .= "i .c ::I 0.15 ~
0.10
0.05
'--~~--~~~~~~~--~~~~~~~--.~~~~~~~.K.;;...... ~~~~~~~~~~~~~~~-+0.00 3800 3300 2800 2300 1800 1300
Wavenumbers (cm-1) >1unw-e>11aqn)4 0 0 0 0 0 0 0 N ~ 00 co '<:t N 0 ..- ..- 0 0 0 0 0 0 0 (") ..-
0 0 ..-00
-Q) (!) 0 0 ca (") (.) N "';'- rn E 0 t,) 0 0 -e? 0 Cl) (0 .c E It) :::J 0 c: 0 Cl) ~ 00 > :::J N C'a C) ~ ·-u.
0 0 (") (")
0 0 00 (") >1unw-e>11aqn}t ..- co 0 0 ..-co -CD (!) 0 0 ("') ca N .~ en ";" -E en u c -l!! ::!: Q) :c .Q E :::s c.o c 0 Q) e co0 > ::::s N cu .2> ~ LL 0 0 ("') ("') 0 co0 ("') >tUnll\l-e>11aqn}I .....- 0 0 0 0 0 0 0 c.o I.{) '<:1" (") N .....- c:i c:i c:i c:i ci ci ci I 0 0 (") .....- 0 0 co .....- -Q) (!) ca (.) 0 0 ·-- (") en N en ... 0 ' :?:: E :c CJ -~ u Q) 0- .c 0 E 0 ::J (0 0 c: 0 Q) co > ...... N cu ....Q) :: ~ O') ·-LL 0 0 (") (") 0 0 co (") Figure 8: BCl3 Modified Bare Silica Gel ..--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1.40 1.20 1.00 .ll:: c 0.80 ::::s :E I .ll:: Cii"' 0.60 .c ::::s ~ 0.40 0.20 ,__~~...... ~~~~~~~...... ~~~~~~~~..-~~~~~~~--~~~~~~~--~~~~~~~---4-0.00 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 9: Subtracted Spectrum of Bare Silica Gel reacted with BCl3 - Bare Silica Gel .--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---.-1.20 1.00 0.80 ..:.:: c 0.60 :s ::!: caI ..:.:: a; 0.40 .c :s ::.::: 0.20 0.00 "'-~~.....-~~~~~~~...... -~~~~~~~-...~~~~~~~~,.-~~~~~~~...,-~~~~~~~-t-0.20 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) >1unw-e>11aqn)t ~ 0 ~ 0 ~ 0 N N ..- ..- 0 0 c:i c:i c:i c:i c:i c:i 0 0 ..-('I) 0 0 co..- "C 0 0 ·-CJ ('I) 0 0 ('I) ('I) 0 co0 ('I) Figure 11: Liquid Spectrum of BCl3 r--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-.-1.10 0.90 0.70 .¥c 0.50 ::s :IE I ftS .¥ "i 0.30 .g ~ 0.10 -0.10 1--~~~--,.~~~~...... ~~~~-.-~~~~...... -~~~~...-~~~----.,....-~~~--,.~~~~ ...... ~~~~-+-0.30 1300 1250 1200 1150 1100 1050 1000 950 900 850 Wavenumbers (cm"1) Figure 12: BCl3 Modified 600°C Silica Gel 1.79 1.59 1.39 1.19 ~c ::I 0.99 ::::?: caI ~ 0.79 ~ ::I ~ 0.59 0.39 0.19 -0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 13: Subtracted Spectrum of 600°C Silica Gel reacted with BCl3 - 600°C Silica Gel 1.65 1.45 1.25 1.05 .lil:: c: ::J 0.85 ~ caI .lil:: G> 0.65 .c ::J ~ 0.45 0.25 0.05 -0.15 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 14: BCl3 Modified HMDS Silica Gel --~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--1.19 0.99 0.79 ~c :J :i I 0.59 ~ "i .a :J ~ 0.39 0.19 L.::====;::::::::::!....~~~~~--~~~~~-=:::;:======::;::::::====:::::::=--~~--~~~~~~---l--0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 15: Subtracted Spectrum of HMDS Silica Gel Reacted with BCl3 - HMDS Silica Gel ..------~..-..-..-..-..-..-..-..-..-..-..-..-..---.-1.10 0.90 0.70 ~c: ::::s ~ I 0.50 ~ "i .a ::::s ~ 0.30 0.10 ,__..-..-.__..-..-..-..-..-..-..-...-..-..-..-..-..-..-..-...-..-..-..-..-..-..-..-...----..-..-..-..-..-..-..-..-..-..-..-..-..---f--0.10 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 16: BCl3 Modified 600°C/HMDS Silica Gel 0.44 0.39 0.34 0.29 .:.i::: c: ::s 0.24 ::? cuI .:.i::: 0.19 .8 ::s ~ 0.14 0.09 0.04 -0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 17: Subtracted Spectrum of 600°C/HMDS Silica Gel Reacted with BCl3 - 600°C/HMDS Silica Gel 0.37 0.32 0.27 0.22 ~c ::::s ~ I 0.17 ns a;~ .c ::::s 0.12 !:ii:: 0.07 0.02 -0.03 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 18: BCla Reactions Isolated Silanol Species Cl~CI _...... H I 0 BCb .._ 0 + HCI I I Si Si Vicinal Silanol Species Cl I H H / ······ ... / /B\ o '·········a +2 HCI I I Si Si ISi ISi Siloxanes · Cl~CI I BCb .._ 0 Cl I I Si _fil_ Figure 19: B(Eth Modified Bare Silica Gel --~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--0.28 0.23 0.18 ~c: :::I :E I 0.13 ~ Qi .c :::I ~ 0.08 0.03 ...... ~--...... ------...... ------..------....------..-..-0.02 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 20: Subtraction Spectrum of Bare Silica Gel Reacted with B(Eth - Bare Silica Gel --~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---0.21 0.16 .:.::: 0.11 § :il I ~ -(I) .c 0.06 ~ 0.01 .._~~---~~~~~~~..-~~~~~~~...-~~~~~~~...-~~~~~~~...-~~~~~~--+-0.04 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 21: Liquid Spectrum of B(Eth 1.10 0.90 0.70 ~c: ;:, :E I 0.50 cu ~ "i .c ;:, ~ 0.30 0.10 ....._~r--~~~~~~~~~~~~~r--~~~~~~~~-.--~~~~r--~~~-...~~~~-,--~~~--+-0.10 1284 1236 1188 1140 1092 1043 995 947 899 850 Wavenumbers (cm-1) Figure 22: B(Eth Modified 600°C Silica Gel 2.00 1.80 1.60 1.40 ~ 1.20 c ::::s :l!: I 1.00 ~ -a; .c 0.80 i 0.60 0.40 0.20 0.00 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 23: Subtraction Spectrum of 600°C Silica Gel reacted with B(Eth - 600°C Silica Gel r------.-1.50 1.00 0.50 ~c ::s ::!!: I 0.00 ~ "i,g ::s ~ -0.50 -1.00 ------1.50 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 24: B(Eth Modified HMDS Silica Gel ..--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--.-0.16 0.14 0.12 0.10 ~ c :::s ::!: I 0.08 ]! "i .c :::s 0.06 ~ 0.04 0.02 '--~~.,.-~~~~~~~.,.-~~~~~~~..-~~~~~~~..--~~~~~~~..--~~~~~~---1--0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 25: Subtraction Spectrum of HMDS Silica Gel Reacted with B(Eth - HMDS Silica Gel 0.30 0.25 0.20 0.15 ~ c: :::s ~ I 0.10 ca ~ Qi .c :::s 0.05 ~ 0.00 -0.05 -0.10 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 26: B(Eth Modified 600°C/HMDS Silica Gel .--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0.60 0.50 0.40 ~c ::I :::!: I 0.30 ~ a; .a ::I ~ 0.20 0.10 6===:::::!::::;::::C...~--=~::=:==::::....~~..:::==::..~-=----:::;:::::::======::::::;:=====~:::..~~~~--~~~~~~~~o.oo 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 27: Subtraction Spectrum of 600°C/HMDS Silica Gel Reacted with B(Eth - 600°C/HMDS Silica Gel ------· 0.15 0.10 0.05 ~c :J =F 0.00 ~ 'ii .a :J ~ -0.05 -0.10 '--~~...---~~~~~~~....-~~~~~~~....-~-~~~~~~....-~~~~~~~....-~~~~~~~+-0.15 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 28: B(Et)a Reactions Isolated Silanol Species Et"'s~t _....-/H I 0 B(Eth llli 0 + I I Si Si Vicinal Silanol Species B(Eth· ... No Reaction Siloxanes Et~t I B(Eth llli 0 Et I I Si _fil_ Figure 29: B(OEth Modified Bare Silica Gel 1.15 0.95 0.75 .¥: r:: ::s :! cuI 0.55 .¥: "i .Q::s ~ 0.35 0.15 '--~~-,--~~~~~~~-.--~~~~~~~~~~~~~~~-.--~~~~~~~.....-~~~~~~~+-0.05 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 30: Subtraction Spectrum of Bare Silica Gel Reacted with B(OEth - Bare Silica Gel ------T- 1.00 0.80 0.60 ~c :I :Ii I 0.40 ~ "i"' .a :I ~ 0.20 0.00 '----...------..,...------..,..------...------..,..------~-0.20 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 31: Liquid Spectrum of B(OEth --·--·~-·· 6.00 5.00 4.00 ~c ::s ::& I 3.00 .= ! ~ 2.00 1.00 L-__,,__~~~....--~~~-.-~~~~...-~~~-.-~~~__,.~-.-~~...=:::::::::~==:::;:::====:=::=--..--~~====1-o.oo 1284 1236 1188 1140 1092 1043 995 947 899 850 Wavenumbers (cm"1) Figure 32: B(OEth Modified 600°C Silica Gel ····-·"'"-·--·-"""'-··•••'"•'"''''""' ,, ... , ,. ,.. , , , . .. , . ______---·---- 0.88 0.78 0.68 0.58 .:.:: c ::s 0.48 :E I .:.::tU "i 0.38 .a ::s ~ 0.28 0.18 0.08 -0.02 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 33: Subtraction Spectrum of 600°C Silica Gel Reacted with B(OEth - 600°C Silica Gel ·---·-·-···-·-··------···--···- 0.90 0.70 0.50 ~c :J :ii! I ftS 0.30 ~ "i .a :J ~ 0.10 -0.10 '------.------...------~-o.3o 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 34: B(OEth Modified HMDS Silica Gel ------··-··------·---··----·------·------....- 0.24 0.19 0.14 ~c ::s ::& I ~ "i .a 0.09 ~ 0.04 ,__--...------~------.------+-0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm"1) Figure 35: Subtraction Spectrum of HMDS Silica Gel Reacted with B(OEth - HMDS Silica Gel ....------1.10 0.90 0.70 ~c :I ::&: asI 0.50 ~ 'ii .a :I ~ 0.30 0.10 ~~~....-~~~~~~~..,...... ~~~~~~~...-~~~~~~~....-~~~~~~~..,...-~~~~~~~~-0.10 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 36: B(OEth Modified 600°C/HMDS Silica Gel .------·--·- 0.30 0.25 0.20 ~c ::s =f 0.15 ~ "i .a ::s ~ 0.10 0.05 j n ·~ J#'I' I - I o.oo -- - - - I "'"" 1300 3800 3300 2800 2300 1800 Wavenumbers (cm"1) Figure 37: Subtraction Spectrum of 600°C/HMDS Silica Gel Reacted with B(OEth - 600°C/HMDS Silica Gel 0.15 0.13 0.11 0.09 ~ ::::s :i I 0.07 ~ "i .a ::::s 0.05 ~ 0.03 0.01 -0.01 3800 3300 2800 2300 1800 1300 Wavenumbers (cm-1) Figure 38: B(OEt)a Reactions Isolated Silanol Species Et~OEt .--/'H I 0 0 + EtOH I I Si Si Vicinal Silanol Species H H /·················· ... / B(OEth ... No Reaction ISi ISi Siloxanes Et~OEt I B(OEth... 0 OEt I I Si _fil_ Figure 39: Computer Generated Models of the Reactants ' . ";·. .. /.::--r·;:·:: / ... ·H· ·.· :•: •': : I : :. "', . . . . :·. : : ·. ·... : . ·:: ...... ' ·· ...... · .. .. , .. -.. ·.·. ·" . :. ·. ·. · :.: .,.~. .- ...... ·, ~· . .. , ._: ,· :_:.. .·-~ ...... :. . - . .. ·~ :. 0 •t ' •, ' ' I ' . /:~:<: ..'. .. : ::·.' :. · . ·.:.~?."~.\.. . .•. ... .-.· .. ... - :·· :.'· . '· . ... •...... !.·~ .• •.. '. . . .'...... -... :.:.._.. _. ... . ·: . ..- .. ~ · ..·· ~ r: :1:( =:".:·::;· ...... ·. •' . ti .··: -~: . ..~ . . · ;:, .. '-·:' : . . ··.· -.... '. ~. . . . :-· -:. .. ·.. • ·. . ~ Figure 39 cont': Computer Generated Models of the Reactants ..... ·.;. · ... : .: .H: ;·'· ·.: .'i·k-Jjj ··.·•· . . . \(.~· ~ :;, ·~ ~-'..:. :~·)· .": : .. : , . .... ·. -~ -: · '; ·. : .... ' .: . J :~ • • : 'I. .. •· .. • ·, Figure 40: Computer Generated Models of Complex 1 ·. : .. ·'i: ·,., ' :·; ,,·.• .:7 : ;~ · . ., , ~· :·: ..," ': :" t :: :I · ..• } i-1.. . : .·' . ."·. . ~ H. .· ·.... ~.'.· ~) ' r : ~. ~ .H-.' •~·. ~ :·, H .· ·;'.,·, :.: ..< ti. ... ..·. ·- . H :~ :~;f :· :· ~• . -;·,H . ;'° Figure 41: Computer Generated Models of the Transiti9n States SiOIL-AICI~ ...... ,; ·. : ...... -.: ... ; .. ~ ·... SiOIL-BCI~ . ·...... : ...... ··. .., . ...· :· ...... '\ . ' . ... . . Ct . . .-.. ~/ . Jt . :\~:::-=·~ ~ ~ ...~: ;:,::-: \r:; l:: : :·: ;: ..:./ · '·: ~: .· ;·:' ~ '. : :. . .: :· ::.·.·:··. .·. :.· . .. "' .·· . . . . ".' ·... :... -:- ~- · :,. ·. :· .. ~ :· · ·~H 'S1· · : : ...... _ ...... H •' ~~ :- : f.t ;: :· ',1::: : ' • ', :, Figure 42: Computer Generated Models of Complex 2 : '. .... ·.. ·: ·-: :· : ·:-:· ·.· .·.·.·. ' .. .·:. ... :. : .. ·. : .· : :. .. ·: . ::. -~ .. ·...... ·:· ·. _:: .. .·· _.. _ ~· ·.·. ".. = : ·. . =, : : . ·. ·::. ' ·. :: .. · ...... · ~:- .: . . ·. . "{.- .. .. ·~ ·. =. • ·• ·~ . :':'._~· ·: .. .· :. : ...... " ; :. ; •:a SiOH4-8Cla .·. ·.. ·.. ·. . ·. ~- ·, .-:. · ·.· .· .·.. ·· .. . . •, ·: .....·~: ... -~ : .. . : . . . : ~- ·: ...... : ... -·. ·:.·. •. ··.· : ..• : _.. _.: :.__ :_·· ,. : , .. t~ ··..· :~: . : : ...... '· . .... -~ ·. · ·er ··=·:/{ .· .. :·.: ...... ·: . :. -...._;·· •!·." ··•• : . • • .. . . " ·.· .- ·. •. ··.. : ··:·1" ·': .. : . ·:_; _. . . . . ·.. ' ', '••I . ..· ·...... ::·. .· · •••• "l:: :-:·= ···" ~ . : ... . :.: ~...... ~ ··,_ ;: • , 1 : .. : ::. ::· :;fS:/m ·. : . . ·.. : .. ·. · :' ··.. ·.·...... • ,:y' • ' 1'' ' ·- ' : : .. ·.' ).( ...... l H Figure 43: Computer Generated Models of the Products : : : ·::: ..~ .. Figure 43 cont': Computer Generated Models of the Products .:·:, ·-:.'., '' ... ;.· ·.:~.;,.. ...'·. ·. ·. ..._ .. ., . :· .. Figure 44: Computer Generated Model of an Isolated Silanol Reacting with AIC'3 Reactants Complex 1 Transition State + 7 7 7 H ~ zcr . : [YH SiOH4 AICla SiOH4-AICl3 SiOH4- AICla Complex2 Products ,t.t:~; .~\ ~- ~ ~-r~ ~ ~~·~.'·~. tiJrl:'! '';, ~J iaJ 7 + %' ,;;;? SiOH4- AICla HCI SiH30AICl2 Figu,re 45: Computer Generated Model of an Isolated Silanol Reacting with BCl3 Transition .Reactants Complex 1 State ~tJr'1! M;;~, + -7 7 7 H ·"'' i~ H SiOH4 BC'3 SiQH4- BCla SiQH4· BCla Complex 2 Produc;g t'fum'lli ~ + ''..·\ff :(H:"";.j .'. ,. H "H:i?- SiOH4" BCla SiH3QBCl2 HCI Figure 46: Changes in Enthalpy When an Isolated Silanol Reacts with AICl3 at 298 K 5..-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-. ~,..,.. \ Reactants \ ...... -15 \ / ~~ \ AH= 26 kJ/mol ...... \ / \ / -35 \ AH= 5 kJ/mo.1...... UUUUIUUU,.// \ tHIHIUIUIUU ...... Complex 2 \ i Transition ! State -55 >- AH= -120 kJ/mol ei QI I c w -75 \ AH= 82 kJ/mol / -95 \ I -115 \ 11111111111111 I Complex 1 -135.L.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~----' Figure 47: Changes in Free Energy When an Isolated Silano! Reacts with AICl 3 at 298 K 10~------. 't················ Transition .... ·········· ... AG= -10 kJ/ mol Reactants AG=3 kJ/mol State ...... -10 Products Complex2 -20 -30 >- AG= 82.5 kJ/mol 21 Ill -40 AG= -82 kJ/mol c: w -50 -60 -70 -80 ltllllllllllllli Complex 1 -90 ....______~ Figure 48: Changes in Enthalpy When an Isolated Silanol Reacts with BCl3 at 298 K 60.--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-. !••••••••••••••••• · .. r~~~~iti~-~---\ 40 f State \ 20 I \ AH• 82 kJ/mol / \ o 1muumuuu...... / \ >. E' Reactants ······... / dH= -123 kJ/mol ; CD wc: -20 AH= -32 kJ/m~> ', I \ ·················...... ! Complex 1 -40 -60 dH= 11 kJ/mo1 ...... ~~~~·~~t:...... •••••• ••• •••••• •••••••••••••••••••••••• -80 Complex 2 Figure 49: Changes in Free Energy When an Isolated Silanol Reacts with BCl3 at 298 K 120 100 ir~fun;tl~\ 80 I srate \ 60 r ~ AG= 81 kJ/mol 40 >- e> Q) 20 c w AG= 12 kJ/mol_ ... ······················ ...c~·;.~i;~·;· .. AG= -148 kJ/mol 0 •••••••••••••••••••••••••• Reactants -20 \ \ -40 \ \euuuumu ...... AG= -7 kJ/mol -60 Complex2 ·····•···········•••··•····•· ...... Products -80