i. novel, one-pot reactions towards molecular alkaline earth species, ii. exploring weak...
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I. Novel, One-Pot Reactions towards Molecular Alkaline Earth Species
Yuriko Takahashi
Ruhlandt Group
Syracuse University
II. Exploring Weak Interactions as Structure Determining Factors in MOCVD volatility
1
Education and Research Experience
Dept. of Engineering, Applied Chemistry, Saitam University, Japan (April 2005 - March 2007 )
B.A. Chemistry, Augustana College, SD (May 2009)
Summer Research Program at Lehigh University, PA (2008 Summer)
Summer Research Program at Syracuse University, NY (2009 Summer)
Ph.D. Candidate, Syracuse University, NY (2009 - )
I. Exploration of a benign, efficient synthetic route for alkaline earth metal compounds
II. Evaluation of influence of weak interactions on thermal properties of target compounds
2
What is involved?
Inert gas synthetic techniques
NMR (mechanistic) studies
Structural studies, crystallography
Thermogravimetric analysis (TGA)
Ligand synthesis
3
Inert Gas Synthetic Techniques
◆ All reactions are carried out under inert gas condition
◆ Solvents – dried, and degassed prior to use
◆ Starting materials - dried over CaH2 and distilled under vacuum or inert gas prior to use
Dry box Schlenk lineSolvent system
4
What is involved?
Inert gas synthetic techniques
NMR (mechanistic) studies
Structural studies, crystallography
Thermogravimetric analysis (TGA)
Ligand synthesis
5
Highly attractive reagents
Inexpensive
Earth abundant
Mg and Ca are biocompatible
Sr and Ba are found in electronic materials
Attractive substitutes for selected rare-earth metals
H
AcRaFr
LaBaCs
YSrRb
ScCaK
MgNa
BeLi
H
AcRaFr
LaBaCs
YSrRb
ScCaK
Na
BeLi
Mg
Why Alkaline Earth Metals?
6
Applications
Synthetic Chemistry Catalysis
• Hydroamination, Hydrophosphination, Hydrosilylation
Selective deprotonation agents
Polymer Chemistry Polymerization initiators
• Lactides, Caprolactone , Styrene
Material Chemistry Hydrogen storage
Synthetic bone scaffolds
MOCVD (Metal Organic Chemical Vapor Deposition) precursors
The Chemistry of Organolithium Compounds. Wiley: New York, 2004. Elschenbroich, C., Organometallics. Wiley-VCH Verlag GmbH & Co,: KGaA, Weinheim, 2006. Crimmin, M. R.; Casely, I. J.;Hill, M. S., J. Am. Chem. Soc. 2005, 127, 2042 Westerhausen, M., Coord. Chem. Rev. 1998, 176, 157. Yanagisawa, A.; Habaue, S.; Yamamoto, H., J. Am. Chem. Soc. 1991, 113, 8955. Otway, D. J.; Rees, W . S., Jr., Coord. Chem. Rev. 2000, 210, 279. Harder, S.; Feil, F.; Weeber, A., Organometallics 2001, 20, 1044.
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H
AcRaFr
LaBaCs
YSrRb
ScCaK
MgNa
BeLi
H
AcRaFr
LaBaCs
YSrRb
ScCaK
Na
BeLi
Mg
Ba
Mg
Sr
Ca
size
Ionic Radii (Å)
0.72
1.00
1.18
1.35
CN = 4
CN = 6
CN = 6
CN = 6
High oxo- and hydrophilicity
Tendency towards aggregation and subsequently poor volatility
Challenges
Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.
I. Novel, one-pot reactions towards molecular alkaline earth species
Safe
Inexpensive
Simple
Available starting materials
Minimize environmental impact
Classic Synthetic Routes
9
Direct metallation via
anhydrous NH3(l) activation
Ae[N(SiMe3)2]2(thf)2 + 2 HL
2 KL + AeI2 Ae + 2 HL
NH3(l)
Ae = Ca, Sr, BaHL = Protonated ligand
Salt Elimination
Transamination
Ae(L)2
•Limited surface area of metal slows reaction•Work with condensed NH3
•Poor for bulky HL•Require highly acidic HL
•Prior synthesis of Ae[N(SiMe3)2]2(thf)2
•Highest quality AeI2
•Preparation of KL
Gillett-Kunnath, M. M. Doctoral Dissertation, Syracuse University, 2007
Redox Transmetallation/
10
pKa (Benzene) = 43 (in DMSO)
Ae + HgPh2 {AePh2(thf)n} + Hg
{AePh2(thf)n} + 2 HL AeL2(thf)n + 2 C6H6
Ae = Ca, Sr, Ba
THF
THF
Redox transmetallation
Ligand exchange
Torvisco, A., et al. Coord. Chem. Rev., 2011, 255, 1268. Hitzbleck, J., et al. Chem. Eur. J. 2004, 10, 3315. Deacon, G. B., et al. Dalton Trans, 2009, 4878. Deacon, G. B., et al. Organometallics, 2008, 27, 4772. Deacon, G. B., et al. Dalton Trans, 2011, 40, 1601. Hauber, S-O., et al. Angew. Chem. Int. Ed., 2005, 44, 5871. Cole, M.L., et al. Dalton Trans, 2006, 3360. Deacon, G. B., et al. N J Chem, 2010, 34, 1731.
Ligand Exchange (RTLE)
Toxicity of mercurial limits the use of this route
L = cyclopentadienide, pyrazolate, formamidinate, aryloxide
HgPh2
LD50 = 50-400 mg kg-1
oral, rat
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HgPh2 BiPh3
LD50 = 50-400 mg kg-1 LD50 = 180 g kg-1
oral, rat oral, dog
Environmental Friendly
Hg2+/Hg Bi3+/Bi
E0(V) 0.852 0.30
Eo (V)M2+
(aq) + 2e- → M(s))
Ca2+ -2.87
Sr2+ -2.89
Ba2+ -2.90
An alternative to HgPh2
Attractive alternative synthetic route
Redox Transmetallation/
12Gillett-Kunnath, M. M.; MacLellan, J. G.; Forsyth, C. M.; Andrews, P. C.; Deacon, G. B.; Ruhlandt-Senge, K. Chem. Commun. 2008, 37, 4490.
Ligand Exchange (RTLE) using BiPh3
3 Ae(xs) + 2 BiPh3 + 6 HL 3 Ae(L)2(thf)n + 2 Bi + 6 C6H6
THF
Sonication
Advantages of RTLE utilizing BiPh3
Commercially available starting materials
One-pot; time and cost effective
Environmentally benign
Easy work-up
Good product yields
BiPh3
LD50 = 180 g kg-1
oral, dog
Ae = Ca, Sr, Ba
N NH
H
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Objectives
SiMe3
NH
SiMe3
NH SiMe3
OH
Explore mechanism of RTLE reaction utilizing BiPh3
Demonstrate feasibility of RTLE utilizing BiPh3 for the synthesis of alkaline earth metal organometallics
Investigate/examine influence of ligands acidity (pKa) on the reaction rate
Experimental Procedure
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NMR tube sealed with a J-Young tap •Ba metal filings (0.50 mmol, excess)• BiPh3 (0.15 mmol)• HL (0.45 mmol)• Cyclohexane (internal standard)• D8-THF (0.6 mL) anhydrous
•All reactions carried out under inert gas conditions •Sonication, T = 60 oC
•Monitored by 1H-NMR spectroscopy
Example of NMR data
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0 h
2 h
10 h
BiPh3
C6H6
Cyclohexane(internal standard)
SiMe3
NH
SiMe3
SiMe3
N
SiMe3
HMDS
3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6
THF
Sonication
0
20
40
60
80
100
0 5 10 15
Co
nce
ntr
atio
n (
%)
Time (h)
Free ligand
Deprotonated ligand
BiPh3
Mechanistic Considerations
16
3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6
THF, N2
Sonication
SiMe3
NH
SiMe3
Kinetic Investigation
17
Heterogeneous nature of the reactions
Active area of the metal surface is unknown and is continuously changing
We get kinetic data from indirect measurements of the chemical composition of the bulk solution
Kinetic results are certainly sufficient for surveying average trends
Rogers, H. R., et al. J. Am. Chem. Soc. 1980, 102, 217. Olson, I. A., et al. J. Phys. Chem. A 2011, 115, 11001.
0
20
40
60
80
100
0 5 10 15
Co
nce
ntr
atio
n (
%)
Time (h)
Free ligand
Deprotonated ligand
BiPh3
Mechanistic Considerations
18
20% of BiPh3
left over
3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6
THF, N2
Sonication
50 % of product: t50%conv = ca. 5h
SiMe3
NH
SiMe3
Direct Metallation
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3 Ba(xs) + 6 HN(SiMe3)2
THF, N2
Sonication
0
20
40
60
80
100
0 5 10 15 20 25 30
Co
nce
ntr
atio
n (
%)
Time (days)
Free ligand
Deprotonated ligand
Direct metallation and RTLE based BiPh3 occur simultaneously
Direct metallation was not complete
Rate for RTLE (t50%conv = 5h ) is much faster than that for direct metallation
SiMe3
NH
SiMe3
ca. 26 days
After t50%conv
product decomposition
0
20
40
60
80
100
0 50 100 150 200 250 300 350 400 450 500
Co
nce
ntr
atio
n (
%)
Time (h)
DM
RTLE vs. Direct Metallation – HCp*
20
ca. 21 days
0
20
40
60
80
100
0 50 100 150 200 250 300 350 400 450 500
Co
nce
ntr
atio
n (
%)
Time (h)
RTLE + DM
DM
RTLE vs. Direct Metallation – HCp*
21
ca. 22 h
ca. 21 days
RTLE vs. Direct Metallation – Ph2pzH
22
0
20
40
60
80
100
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
Co
nce
ntr
atio
n (
%)
Time (h)
RTLE + DM
DM
N NH
H
1 h
2.5 h
Reactions between Ba metal and the pyrazole ligand are not enhanced by the BiPh3.
RTLE vs. Direct Metallation
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pKa 5.60 ± 0.38[1] 11[2] 13.03[3] 14[4] 22.6[4] 26.1[4]
t50 % conv. 3.5 h 4 h 2.5 h 5 h 6 h 22 h
DM
t50 % conv. 25 h 4 h 1 h26
days19 days
21 days
SiMe3
NH
SiMe3
NH SiMe3
N NH
H
OH
DM
RTLE
[1]Estimated pKa values of silylamides was calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (© 1994-2012 ACD/Labs). [2]Sinha, A., et al. Organometallics, 2006, 25, 1412. [3]Aggarwal, V. K., et al. J. Org. Chem., 2003, 68, 5381. [4]Bordwell, F.A.; Bausch, M.J. Am. Chem. Soc. 1983, 105, 6188.
RTLE vs. Direct Metallation -Pyrazoles
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[Sr(Me2pz)2(Me2pzH)4][Ca(Me2pz)2(Me2pzH)4]
Hitzbleck, J.; O'Brien, A.Y.; Forsyth, C.M.; Deacon, G.B.; Ruhlandt-Senge, K. Chem., Eur. J. 2004, 10, 3315.
Form stable complexes through hydrogen bonding
Conclusions
25
RTLE utilizing environmentally benign BiPh3 provides an excellent alternative for synthesis of organoalkaline earth complexes
Replaces organomercury
One-pot, convenient
Variety of ligands
Dramatically improves reaction rates over direct metallation
II. Exploring Weak Interactions as Structure Determining Factors in MOCVD Volatility
MOCVD process deposits thin films on a substrate Semiconductor
High temperature super conductors
Computer memory
27
H
AcRaFr
LaBaCs
YSrRb
ScCaK
MgNa
BeLi
H
AcRaFr
LaBaCs
YSrRb
ScCaK
Na
BeLi
Mg
Ba
Mg
Sr
Ca
size
Ionic Radii (Å)
0.72
1.00
1.18
1.35
CN = 4
CN = 6
CN = 6
CN = 6
High oxo- and hydrophilicity
Tendency towards aggregation and subsequently poor volatility
Challenges
Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.
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Coordinative Saturation
Ligand bulk
Neutral co-ligands
Non-covalent interactions (secondary interactions)
Metal∙∙∙π (arene)
Agostic (M∙∙∙H-C)
Metal∙∙∙F
providing a major factor in the reactivity and physical properties of the alkaline earth organometallics
29
Metal∙∙∙F Metal∙∙∙π Agostic H-Bond
Free energies of rotation (kcal/mol)
18.7 - 19.1 19.0 13.6 - 14.6 15.0 – 40.0
Metal-ligand bonding Secondary interactions
Transition metals Strong Much smaller role
Alkaline earth metals Weak Significant role
Importance of Secondary Interactions
As alkaline earth metal compounds frequently displayweak, highly polar metal-ligand bonding, secondary interactions are an important means to provide steric saturation to the metal center
Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Ruhlandt-Senge, K. in prep.Szatylowicz, H. J. Phys. Org. Chem. 2008, 21, 897-914. Gillett-Kunnath, M.; Teng, W.; Vargas, W.; Ruhlandt-Senge, K., Inorg. Chem. 2005, 44, 4862.
30
Weak interaction of a coordinately unsaturated metal with a C—H bond
Ca[N(SiMe3)(Mes)]2(thf)2
CN = 4 + 1
Ba2(Odpp)4
Deacon, G. B., et al. Chem. Eur. J. 2009, 15, 5503. Gillett-Kunnath, M. et al., Inorg. Chem., 2005, 44, 4862
Secondary Interactions
Agostic (M∙∙∙H—C) Metal―π (arene)
Ba2: CN = 4 +4Ba1: CN = 3 + 9
31
Secondary Interactions
Metal∙∙∙F
KBa(PFTB)3(thf)4
C CF3F3C
OH
CF3
Perfluoro-t-butanolH(PFTB)
Stabilized via M-F interaction
Excellent thermal properties
Previous work with
Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55.
Ba1
C CF3F3C
OH
32
C CF3F3C
OH
CF3
1,1,1,3,3,3-Hexafluoro-2-phenyl-2-propanol
Detailed analysis of strategies to achieve steric saturation
Studies of its effect on:
Coordination pattern
Thermal properties
Possible interactions
Metal∙∙∙F Metal∙∙∙F, Metal―π, M∙∙∙H—C
H(PFTB) H(HFPP)
Evaluation of Secondary Interactions
Direct metallation via ammonia activation
Moderate to good yields with high purity
33
C CF3F3C
OH
Ae + 2THF
-78 oC, NH3 (l)
Monometallic Complexes -Synthesis
Ae = Ca, Sr, Ba
[Ae(HFPP)2(thf)4] + H2
Partial loss of THF co-ligands induced dimerization and extensive M∙∙∙F interactions to achieve coordinative saturation
34
Crystallization from THF Crystallization from toluene
CN = 6 Sr1: CN = 6 Sr2: CN = 4 + 6
Monometallic Complexes -Structures
[Sr(HFPP)2(thf)4] [Sr2(HFPP)4(thf)3]
35
Heterobimetallic Complexes -Synthesis
KH + H(HFPP) [K(HFPP)(thf)]4THF
[BaK(HFPP)3(thf)]24 [Ba(HFPP)2(thf)4] + [K(HFPP)(thf)]4THF
Combination of the two solutions of homometallic complex leads to heterobimetallic formation
36
Heterobimetallic Complexes -Structure
Ba1
36
C CF3F3C
OH
CF3
C CF3F3C
OH
KBa(HFPP)3(thf)4 KBa(PFTB)3(thf)4
1 Ba∙∙∙F 3 K∙∙∙F 0 Ba∙∙∙F 6 K∙∙∙FBuchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55.
37
Magnitude of metal∙∙∙F interactions may potentially effect volatility of alkaline earth metal compounds
Comparison of Thermal Properties by TGA
C CF3F3C
OH
CF3
C CF3F3C
OH
1 Ba∙∙∙F3 K∙∙∙F
6 K∙∙∙F
PFTB HFPP
38
Conclusion/Future work
Secondary non-covalent interactions are an important stabilizing factors
Metal∙∙∙F
Agostic
→ Isolated heterobimetallic alkaline earth metal HFPP complexes
Secondary non-covalent interactions are likely to be a key factor in volatility
Synthesis of another alkali/alkaline earth metal combination complexes is in process for direct comparison of structural features and thermal properties of two groups of compounds based on HFTB and HFPP
Extend the work to divalent lanthanide metals