McMahon Research Group - Department of Chemistry · 2/24/2011 · integrated approach involving...
1
Benzothiophene Carbenes Carbonyl Diazide & Diazirinone Group Members Brent Amberger Thomas Draxler Brian Esselman Ben Haenni Funding The McMahon group has an interest in the areas of astrochemistry, reactive intermediates, and combustion chemistry. The inherent complexity of these chemical environments demands an integrated approach involving organic synthesis, matrix isolation spectroscopy, mechanistic studies, rotational spectroscopy, and computational chemistry. Through these combined efforts, it is possible to generate and characterize the prototypical reactive intermediates in organic chemistry and to probe their structure in unprecedented detail. These fundamental structural, spectroscopic, and mechanistic data provide a foundation for understanding the chemistry of organic matter in harsh environments. Introduction Selected Recent Publications Matrix Isolation !# $ % &'% ()% #) Unsaturated Carbon Chains Ethynyl-Cylcobutadienes Tuesday, February 23, 2010 A precursor, or a reactive intermediate, is generated in the gas phase and then frozen in an inert gas (N 2 , Ar, Xe, Ne) at 10 to 25 K on a spectroscopic window. The matrix-isolated compounds can then be studied using IR, UV- vis, or EPR spectroscopy. Often, irradiation of the precursor using either a Hg or Xe lamp yields the reactive species, whose identity is confirmed by comparison to calculated spectra. The matrix can then be further irradiated with varying wavelengths of light to study the photochemical properties and reactivity of these species. Orion Nebula viewed from the Hubble Telescope CCSD/cc-pVDZ (unscaled) hν > 330 nm Ar, 15 K S H S H S H H S H H S H S H H ISC 0.0 3.2 0.8 13.0 12.7 17.4 -0.5 -12.7 56.6 40.8 11.7 0.4 -18.8 Potential Energy Surface, Values in kcal/mol Enthalpy Laura Kopff Terese Kreifels Alex Nolan Joshua Shutter Andrew Wiederhold Menke, J. L.; McMahon, R. J., Photochemistry of Matrix-isolated 5-cyano-2H-pyran-2-one (δ-cyano-α- pryrone) and cyanocyclobuta-1,3-diene. Can. J. Chem. 2011, 89 (2), 186-194. Thomas, P. S.; Bowling, N. P.; Burrmann, N. J.; McMahon, R. J., Dialkynyl Carbene Derivatives: Generation and Characterization of Triplet tert-Butylpentadiynylidene (t-Bu−C≡C−C:−C≡C−H) and Dimethylpentadiynylidene (Me−C≡C−C:−C≡C−Me). J. Org. Chem. 2010, 75 (19), 6372-6381. Menke, J. L.; Patterson, E. V.; McMahon, R. J., Effects of Cyano Substituents on Cyclobutadiene and Its Isomers. J. Phys. Chem. A 2010, 114 (22), 6431–6437. Shaffer, C. J.; Esselman, B. J.; McMahon, R. J.; Stanton, J. F.; Woods, R. C., Attempted Isolation and Characterization of Diazirinone (N 2 CO). J. Org. Chem. 2010, 75 (6), 1815–1821. Synthesis, Matrix Isolation, Spectroscopy, Mechanistic Studies, and Computational Chemistry McMahon Research Group Computational studies have been carried out on both the 2- and 3-substituted benzothiophene carbenes and their possible rearrangement products at the B3LYP/6-31G* level of theory. For the 2-benzothiophene system, the following potential energy surface (PES) was generated connecting the observed bicyclic product with both rotomers of the carbene. Currently studies are underway to finish mapping the PES for the 3-substituted benzothiophene carbene. Thermolysis of a tosyl hydrazone salt leads to 2- diazomethyl benzothiophene, 11, which can be isolated in an Ar or N 2 matrix. Irradiation of the diazo compound at hν ≥ 472 nm leads to disappearance of the peaks associated with the diazo compound and growth of peaks corresponding to the bicyclic allene 12, as characterized by IR spectroscopy. Further irradiation gives no change in the spectrum. ! > 472 nm S N 2 H S H H The exploration of unsaturated carbon chains of varying lengths has been a primary focus of the group. The HC 3 H, HC 5 H, and HC 7 H systems have been synthesized and characterized. They are believed to be important molecules in the Interstellar Medium (ISM). Further studies of the substituted RC 3 R are currently underway. The Bergman cyclization of tetraethynylcyclobutadiene derivative 8 has been proposed as a key step in a pathway leading to fullerene formation. As a model of the complex system, we intend to characterize the family of ethynyl-substituted cyclobutadienes. The ethynylcyclobutadienes that contain an ene-diyne (see 9) are of particular interest due to their potential to undergo a photochemical Bergman cyclization. We will synthesize and matrix isolate the desired α-pyrone precursors (see 10) and photochemically produce the cyclobutadienes. Upon characterization utilizing predicted IR frequencies, we will then investigate the photochemical and/or thermal transformations. O O O O h! h!' CO 2 S H H 32 - S S N 2 H Cyano-containing molecules are a class of compounds that have been detected in the ISM, but a significant number of them have yet to be isolated and completely characterized. Proposed syntheses of cyanomethylcarbene (4) and l-HC 4 N (5) are shown below. N 2 hν > 470 nm, Ar, 15 K CCSD/cc-pVDZ (unscaled) Shown below are isomers of CH 3 C 3 CH 3 and their relative energies predicted at the CCSD/cc-pVDZ level of theory. O H OTIPS OMe Br Br O OMe O TMS TMS CBr 4 PPh 3 Pd(PPh 3 ) 4 , CuI THF, reflux, diisopropylamine TMS I 2 O O TMS I TMS O O TMS TMS TMS O O Tetrabutylammonium Fluoride H OTIPS Br Br 1. TBAF 2. [O] Pd(PPh 3 ) 4 , CuI THF, reflux, diisopropylamine TMS A diazo precursor for dimethylpropynylidene (1) has been synthesized and matrix isolated. Irradiation of diazo 3 under matrix-isolation conditions leads to triplet dimethylpropynylidene (1) which can undergo a hydrogen shift to methylvinylacetylene (2). The photochemistry of the CH 3 C 3 CH 3 system is still under investigation. CN N N CN CN h! Br N N n-Bu 4 N(CN) 4 h! PhOCN OEt OEt Li OEt OEt C N N H C N N 2 H C N h! H C N 1. n-BuLi 2. " N H Ts 5 1. HCO 2 H 2. TsNHNH 2 Our interest in prospective molecules to be found in the Interstellar Medium lead us to investigate the metastable molecule diazirinone (6), which can be thermolyzed from the explosive carbonyl diazide (7). Under matrix-isolation conditions, carbonyl diazide (7) will photolyze to produce two isomers of CON 4 and N 2 , but diazirinone (6) was not observed (Beckers, H. and coworkers Angew Chem. Int. Ed. 2010). Under thermolysis conditions, diazirinone was made from carbonyl diazide by the loss of two molecules of dinitrogen (Beckers, H. and coworkers Angew Chem. Int. Ed. 2011). Thus far, computational studies of the pathways below have not identified any viable pathway to diazirinone from carbonyl diazide. We are hopeful that further computational studies will solve this puzzle and explain the thermolysis of carbonyl diazide. A proposed synthesis of the precursor of 1,2-diethynylcyclobutadiene (9) is shown below. The key step is Larock electrophilic iodo-lactonization to produce the α-pyrone 10. Rotational spectroscopy is the study of quantum energy levels associated with the rotational motion of molecules. Spectra, typically in the microwave or millimeter wave regions, can give incredibly precise information about the moments of inertia, and thus geometry, of gaseous molecules. Spectra can consist of hundreds or thousands of individual transitions; solving these spectra is difficult, but once solved, they can be used to unambiguously identify molecules, in the lab, or in space using radio telescopes. Hundreds of spectral lines of carbonyl diazide ( 7 ) in the Cs and/or C2v conformations have been observed. Further spectroscopic work is still required in order to fully understand the complex rotational spectrum. After studying the parent isotopomer, 13 C and 15 N isotopomers will also be studied, helping to pin down a very precise molecular geometry for the observed conformations of carbonyl diazide. C C C H 3 C CH 3 C C C H 3 C H 3 C C C C CH 3 H 3 C (1 - T) 14.4 kcal/mol 0.0 kcal/mol 14.5 kcal/mol H 3 C C C C H CH 2 (2) -30.4 kcal/mol 8 9 10 10 11 12 12 11 12 H H H H H H H H H H H H HC 2 H HC 3 H HC 4 H HC 5 H HC 6 H HC 7 H H C C C C C H C C C H H C C C C C C C H H O N N N N N N O N N N N O N N O N N C O N N N N N N N N O N N N N 2 O N N N N 2 O N N N N 2 O N N N N 2 O N N N N 2 N N N N 2 N N Energies are listed in kcal/mol and computed at the CCSD/cc-pVDZ. h! h! O N N N N N N O N N N N N N O N N N N N N O Cl 3 CO OCCl 3 (Bu) 4 N + N 3 - Ether O N N 400 o C (7) 0.0 kcal/mol C 2 (7) 2.0 kcal/mol C s (7) 11.9 kcal/mol C 2v 6 OH 1. BaMnO 4 2. NH 2 NHTrisyl Acetic Acid N N Trisyl H 1. NaH 2. Heat N 2 h! > 472 nm h! > 330 nm 3 1 2
Transcript of McMahon Research Group - Department of Chemistry · 2/24/2011 · integrated approach involving...
Benzothiophene Carbenes
Carbonyl Diazide & Diazirinone
Group MembersBrent AmbergerThomas DraxlerBrian Esselman
Ben Haenni
Funding
The McMahon group has an interest in the areas of astrochemistry, reactive intermediates, and combustion chemistry. The inherent complexity of these chemical environments demands an integrated approach involving organic synthesis, matrix isolation spectroscopy, mechanistic s tud ies , r o ta t i ona l spec t roscopy, and computational chemistry. Through these combined efforts, it is possible to generate and charac te r i ze the p ro to typ ica l reac t i ve intermediates in organic chemistry and to probe their structure in unprecedented detail. These fundamental structural, spectroscopic, and mechanistic data provide a foundation for understanding the chemistry of organic matter in harsh environments.
Introduction
Selected Recent Publications
Matrix Isolation
!"#$%"&'%"()%"#)"
Unsaturated Carbon Chains
Ethynyl-Cylcobutadienes
Tuesday, February 23, 2010
A precursor, or a reactive intermediate, is generated in the gas phase and then frozen in an inert gas (N2, Ar, Xe, Ne) at 10 to 25 K on a spectroscopic window. The matrix-isolated compounds can then be studied using IR, UV-vis, or EPR spectroscopy. Often, irradiation of the precursor using either a Hg or Xe lamp yields the reactive species, whose identity is confirmed by comparison to calculated spectra. The matrix can then be further irradiated with varying wavelengths of light to study the photochemical properties and reactivity of these species.Orion Nebula viewed from the Hubble Telescope
CCSD/cc-pVDZ (unscaled)
hν > 330 nmAr, 15 K
S
H
SH
S
H
H
S
H H
SH
S
H
H
ISC
0.0
3.2
0.8
13.012.7
17.4
-0.5
-12.7
56.6
40.8
11.7
0.4
-18.8
Potential Energy Surface, Values in kcal/mol
Enth
alpy
28 29
30
31
32
33
Laura KopffTerese Kreifels
Alex NolanJoshua Shutter
Andrew Wiederhold
Menke, J. L.; McMahon, R. J., Photochemistry of Matrix-isolated 5-cyano-2H-pyran-2-one (δ-cyano-α-pryrone) and cyanocyclobuta-1,3-diene. Can. J. Chem. 2011, 89 (2), 186-194.
Thomas, P. S.; Bowling, N. P.; Burrmann, N. J.; McMahon, R. J., Dialkynyl Carbene Derivatives: Generation and Characterization of Triplet tert-Butylpentadiynylidene (t-Bu−C≡C−C:−C≡C−H) and Dimethylpentadiynylidene (Me−C≡C−C:−C≡C−Me). J. Org. Chem. 2010, 75 (19), 6372-6381.
Menke, J. L.; Patterson, E. V.; McMahon, R. J., Effects of Cyano Substituents on Cyclobutadiene and Its Isomers. J. Phys. Chem. A 2010, 114 (22), 6431–6437.
Shaffer, C. J.; Esselman, B. J.; McMahon, R. J.; Stanton, J. F.; Woods, R. C., Attempted Isolation and Characterization of Diazirinone (N2CO). J. Org. Chem. 2010, 75 (6), 1815–1821.
Synthesis, Matrix Isolation, Spectroscopy, Mechanistic Studies, and Computational ChemistryMcMahon Research Group
Computational studies have been carried out on both the 2- and 3-substituted benzothiophene carbenes and their possible rearrangement products at the B3LYP/6-31G* level of theory. For the 2-benzothiophene system, the following potential energy surface (PES) was generated connecting the observed bicyclic product with both rotomers of the carbene. Currently studies are underway to finish mapping the PES for the 3-substituted benzothiophene carbene.
!
Thermolysis of a tosyl hydrazone salt leads to 2-diazomethyl benzothiophene, 11, which can be isolated in an Ar or N2 matrix. Irradiation of the diazo compound at hν ≥ 472 nm leads to disappearance of the peaks associated with the d iazo compound and growth o f peaks corresponding to the bicyclic allene 12, as characterized by IR spectroscopy. Further irradiation gives no change in the spectrum.
! > 472 nm
S
N2
H S
H
H34 32 - S
The exploration of unsaturated carbon chains of varying lengths has been a primary focus of the group. The HC3H, HC5H, and HC7H systems have been synthesized and characterized. They are believed to be important molecules in the Interstellar Medium (ISM). Further studies of the substituted RC3R are currently underway.
8 9 10
The Bergman cyclization of tetraethynylcyclobutadiene derivative 8 has been proposed as a key step in a pathway leading to fullerene formation. As a model of the complex system, we intend to characterize the family of ethynyl-substituted cyclobutadienes. The ethynylcyclobutadienes that contain an ene-diyne (see 9) are of particular interest due to their potential to undergo a photochemical Bergman cyclization.
We will synthesize and matrix isolate the desired α-pyrone precursors (see 10) and photochemically produce the cyclobutadienes. Upon characterization utilizing predicted IR frequencies, we will then investigate the photochemical and/or thermal transformations.
O
O
O
Oh! h!'
CO2
16 1712 18 19
S
H
H32 - S
S
N2
H
Cyano-containing molecules are a class of compounds that have been detected in the ISM, but a significant number of them have yet to be isolated and completely characterized. Proposed syntheses of cyanomethylcarbene (4) and l-HC4N (5) are shown below.
N2
hν > 470 nm, Ar, 15 K
CCSD/cc-pVDZ (unscaled)
Shown below are isomers of CH3C3CH3 and their relative energies predicted at the CCSD/cc-pVDZ level of theory.
O
HOTIPS OMe
BrBr
O
OMe
O
TMS TMS
CBr4
PPh3
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
I2
O
O
TMS I
TMS
O
O
TMS
TMS
TMS
O
O
TetrabutylammoniumFluoride
HOTIPS
BrBr
1. TBAF
2. [O]
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
A diazo precursor for dimethylpropynylidene (1) has been synthesized and matrix isolated. Irradiation of diazo 3 under matrix-isolation conditions leads to triplet dimethylpropynylidene (1) which can undergo a hydrogen shift to methylvinylacetylene (2). The photochemistry of the CH3C3CH3 system is still under investigation.
CN
NN
CN CN
h!
Br
NN n-Bu4N(CN)
4
h!
PhOCNOEt
OEt
Li
OEt
OEt
CN
N
H
CN
N2
H
CN
h!
HCN
1. n-BuLi
2. "
NH
Ts
5
1. HCO2H
2. TsNHNH2
Our interest in prospective molecules to be found in the Interstellar Medium lead us to investigate the metastable molecule diazirinone (6), which can be thermolyzed from the explosive carbonyl diazide (7).
Under matrix-isolation conditions, carbonyl diazide (7) will photolyze to produce two isomers of CON4 and N2, but diazirinone (6) was not observed (Beckers, H. and coworkers Angew Chem. Int. Ed. 2010). Under thermolysis conditions, diazirinone was made from carbonyl diazide by the loss of two molecules of dinitrogen (Beckers, H. and coworkers Angew Chem. Int. Ed. 2011). Thus far, computational studies of the pathways below have not identified any viable pathway to diazirinone from carbonyl diazide. We are hopeful that further computational studies will solve this puzzle and explain the thermolysis of carbonyl diazide.
A proposed synthesis of the precursor of 1,2-diethynylcyclobutadiene (9) is shown below. The key step is Larock electrophilic iodo-lactonization to produce the α-pyrone 10.
Rotational spectroscopy is the study of quantum energy levels associated with the rotational motion of molecules. Spectra, typically in the microwave or millimeter wave regions, can give incredibly precise information about the moments of inertia, and thus geometry, of gaseous molecules. Spectra can consist of hundreds or thousands of individual transitions; solving these spectra is difficult, but once solved, they can be used to unambiguously identify molecules, in the lab, or in space using radio telescopes. Hundreds of spectral lines of carbonyl diazide (7) in the Cs and/or C2v
conformations have been observed. Further spectroscopic work is still required in order to fully understand the complex rotational spectrum. After studying the parent isotopomer, 13C and 15N isotopomers will also be studied, helping to pin down a very precise molecular geometry for the observed conformations of carbonyl diazide.
C C CH3C CH3
C C CH3C
H3C
CC C
CH3H3C
(1 - T) 14.4 kcal/mol 0.0 kcal/mol
14.5 kcal/molH3C
CC
C
H
CH2
(2) -30.4 kcal/mol
8
910
10
11 12
12
11
12
H H
H H
H H
H H
H H
H H
HC2H
HC3H
HC4H
HC5H
HC6H
HC7H
H C C C C C H
C C C HH
C C C CCC CH H
O
NNNN
N NO
NN
NN
O
N N
O
NN
C
O
NN
N
NN N
NN
O
N N
N N2
O
N NN N2O
N NN N2
O
N NN N2
O
N NN N2
N N
N N2
N N
Energies are listed in kcal/mol and computed at the CCSD/cc-pVDZ.
Benzothiophene Carbenes
Carbonyl Diazide & Diazirinone
Group MembersBrent AmbergerThomas DraxlerBrian Esselman
Ben Haenni
Funding
The McMahon group has an interest in the areas of astrochemistry, reactive intermediates, and combustion chemistry. The inherent complexity of these chemical environments demands an integrated approach involving organic synthesis, matrix isolation spectroscopy, mechanistic s tud ies , r o ta t i ona l spec t roscopy, and computational chemistry. Through these combined efforts, it is possible to generate and charac te r i ze the p ro to typ ica l reac t i ve intermediates in organic chemistry and to probe their structure in unprecedented detail. These fundamental structural, spectroscopic, and mechanistic data provide a foundation for understanding the chemistry of organic matter in harsh environments.
Introduction
Selected Recent Publications
Matrix Isolation
!"#$%"&'%"()%"#)"
Unsaturated Carbon Chains
Ethynyl-Cylcobutadienes
Tuesday, February 23, 2010
A precursor, or a reactive intermediate, is generated in the gas phase and then frozen in an inert gas (N2, Ar, Xe, Ne) at 10 to 25 K on a spectroscopic window. The matrix-isolated compounds can then be studied using IR, UV-vis, or EPR spectroscopy. Often, irradiation of the precursor using either a Hg or Xe lamp yields the reactive species, whose identity is confirmed by comparison to calculated spectra. The matrix can then be further irradiated with varying wavelengths of light to study the photochemical properties and reactivity of these species.Orion Nebula viewed from the Hubble Telescope
CCSD/cc-pVDZ (unscaled)
hν > 330 nmAr, 15 K
S
H
SH
S
H
H
S
H H
SH
S
H
H
ISC
0.0
3.2
0.8
13.012.7
17.4
-0.5
-12.7
56.6
40.8
11.7
0.4
-18.8
Potential Energy Surface, Values in kcal/mol
Enth
alpy
28 29
30
31
32
33
Laura KopffTerese Kreifels
Alex NolanJoshua Shutter
Andrew Wiederhold
Menke, J. L.; McMahon, R. J., Photochemistry of Matrix-isolated 5-cyano-2H-pyran-2-one (!-cyano-"-pryrone) and cyanocyclobuta-1,3-diene. Can. J. Chem. 2011, 89 (2), 186-194.
Thomas, P. S.; Bowling, N. P.; Burrmann, N. J.; McMahon, R. J., Dialkynyl Carbene Derivatives: Generation and Characterization of Triplet tert-Butylpentadiynylidene (t-Bu#C$C#C:#C$C#H) and Dimethylpentadiynylidene (Me#C$C#C:#C$C#Me). J. Org. Chem. 2010, 75 (19), 6372-6381.
Menke, J. L.; Patterson, E. V.; McMahon, R. J., Effects of Cyano Substituents on Cyclobutadiene and Its Isomers. J. Phys. Chem. A 2010, 114 (22), 6431–6437.
Shaffer, C. J.; Esselman, B. J.; McMahon, R. J.; Stanton, J. F.; Woods, R. C., Attempted Isolation and Characterization of Diazirinone (N2CO). J. Org. Chem. 2010, 75 (6), 1815–1821.
Synthesis, Matrix Isolation, Spectroscopy, Mechanistic Studies, and Computational ChemistryMcMahon Research Group
Computational studies have been carried out on both the 2- and 3-substituted benzothiophene carbenes and their possible rearrangement products at the B3LYP/6-31G* level of theory. For the 2-benzothiophene system, the following potential energy surface (PES) was generated connecting the observed bicyclic product with both rotomers of the carbene. Currently studies are underway to finish mapping the PES for the 3-substituted benzothiophene carbene.
!
Thermolysis of a tosyl hydrazone salt leads to 2-diazomethyl benzothiophene, XX, which can be isolated in an Ar or N2 matrix. Irradiation of the diazo compound at hν ≥ 472 nm leads to disappearance of the peaks associated with the d iazo compound and growth o f peaks corresponding to the bicyclic allene XX, as characterized by IR spectroscopy. Further irradiation gives no change in the spectrum.
! > 472 nm
S
N2
H S
H
H34 32 - S
The exploration of varying lengths of unsaturated carbon chains has been a primary focus of the group. The HC3H, HC5H, and HC7H systems have been synthesized and characterized. They are believed to be important molecules in the Interstellar Medium (ISM). Further studies of the substituted RC3R are currently underway.
8 9 10
The Bergman cyclization of tetraethynylcyclobutadiene derivative 9 has been proposed as the first step in a pathway leading to fullerene formation. As a of model the complex system, we intend to characterize the family of ethynyl-substituted cyclobutadienes. The ethynylcyclobutadienes that contain an ene-diyne (12) are of particular interest due to their potential to undergo a photochemical Bergman cyclization.
We will synthesize and matrix isolate the desired !-pyrone precursors (see 16) and photochemically produce the cyclobutadienes. Upon characterization utilizing predicted IR frequencies, we will then characterize the photochemical and/or thermal transformations.
O
O
O
Oh! h!'
CO2
16 1712 18 19
H H
H H
H H
H H
H H
H H
HC2H
HC3H
HC4H
HC5H
HC6H
HC7H
H C C C C C H
C C C HH
C C C CCC CH H
S
H
H32 - S
S
N2
H
Cyano-containing molecules are a class of compounds that have been detected in the ISM, but a significant number of them have yet to be isolated and completely characterized. Proposed syntheses of cyanomethylcarbene (3) and l-HC4N (4) are shown below.
C C CH3C CH3
CC C
CH3H3C
(1 - T) 14.4 kcal/mol (2 - S) 0.0 kcal/mol
C C CH3C
H3C(3 - S) 14.5 kcal/mol
H3CC
CC
H
CH2
(4) -30.4 kcal/mol
N2
hν > 470 nm, Ar, 15 K
CCSD/cc-pVDZ (unscaled)
I need something here to tie it together.
O
HOTIPS OMe
BrBr
O
OMe
O
TMS TMS
CBr4
PPh3
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
I2
O
O
TMS I
TMS
O
O
TMS
TMS
TMS
O
O
TetrabutylammoniumFluoride
HOTIPS
BrBr
1. TBAF
2. [O]
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
Figure 9. Infrared spectrum (Ar, 10 K) of carbonyl azide (62) (black line) and the B3LYP/6-31G* predicted spectra (red line).
Unpublished reports claim that carbonyl azide does not photolyze through the dinitrene 63 to diazirinone; however, this same report claims diazirinone has been matrix isolated using a gas phase thermolysis.34
Scheme 14. Diazirinone (59) arriving from carbonyl azide (62).
B. AzirinoneAlthough it is not as high as the calculated diazirinone barrier of 27 kcal/mol, a 12 kcal/mol barrier to decomposition may be enough for azirinone to be characterized in matrix
14
N N
OO
NN
h!O
N N NN NN
gas phase thermolysis
596362
A diazo precursor for dimethylpropynylidene has been synthesized and matrix isolated. Irradiation of diazo 3 under matrix-isolation conditions leads to triplet dimethylpropynylidene (1) which can undergo a hydrogen shift to methylvinylacetylene (2). Further studies on the photochemistry of the CH3C3CH3 system is being investigated.
CN
NN
CN CN
h!
Br
NN n-Bu4N(CN)
4
h!
PhOCNOEt
OEt
Li
OEt
OEt
CN
N
H
CN
N2
H
CN
h!
HCN
1. n-BuLi
2. "
NH
Ts
5
1. HCO2H
2. TsNHNH2
OH1. BaMnO4
2. NH2NHTrisylAcetic Acid
NN
Trisyl
H1. NaH
2. Heat
N2 h! > 470 nm h! > 330 nm
3 1 2
Our interest in prospective molecules to be found in the Interstellar Medium lead us to become interested in the metastable molecule diazirinone, which can be thermolyzed from the explosive carbonyl diazide.
Although diazirinone can be produced from the loss of two molecules of dinitrogen from carbonyl diazide, it is unclear the mechanism in which this occurs. Five computational pathways have been explored, I need more here. Brian?
A proposed synthesis of the precursor of 1,2-diethynylcyclobutadiene (12) is shown below. The key step is Larock electrophilic iodo-lactonization to produce the !-pyrone.
O
NNNN
N NO
NNN
N
N
N
O
NN
N
N
N
N
O
Cl3CO OCCl3
(Bu)4N+ N3-
Ether
O
N N
400 oC
0.0 kcal/mol
2.0 kcal/mol11.9 kcal/mol
O
CNN
NNN N
O
C NNN N
N N
O
C NNN N
NN
O
C NN
N N
O
C NNN N
NN
O
CN N
NN
C
O
NN
N
N
O
C NN
N N
N N
NN
O
O
C NN
N N
NN
Wednesday, February 23, 2011
Benzothiophene Carbenes
Carbonyl Diazide & Diazirinone
Group MembersBrent AmbergerThomas DraxlerBrian Esselman
Ben Haenni
Funding
The McMahon group has an interest in the areas of astrochemistry, reactive intermediates, and combustion chemistry. The inherent complexity of these chemical environments demands an integrated approach involving organic synthesis, matrix isolation spectroscopy, mechanistic s tud ies , r o ta t i ona l spec t roscopy, and computational chemistry. Through these combined efforts, it is possible to generate and charac te r i ze the p ro to typ ica l reac t i ve intermediates in organic chemistry and to probe their structure in unprecedented detail. These fundamental structural, spectroscopic, and mechanistic data provide a foundation for understanding the chemistry of organic matter in harsh environments.
Introduction
Selected Recent Publications
Matrix Isolation
!"#$%"&'%"()%"#)"
Unsaturated Carbon Chains
Ethynyl-Cylcobutadienes
Tuesday, February 23, 2010
A precursor, or a reactive intermediate, is generated in the gas phase and then frozen in an inert gas (N2, Ar, Xe, Ne) at 10 to 25 K on a spectroscopic window. The matrix-isolated compounds can then be studied using IR, UV-vis, or EPR spectroscopy. Often, irradiation of the precursor using either a Hg or Xe lamp yields the reactive species, whose identity is confirmed by comparison to calculated spectra. The matrix can then be further irradiated with varying wavelengths of light to study the photochemical properties and reactivity of these species.Orion Nebula viewed from the Hubble Telescope
CCSD/cc-pVDZ (unscaled)
hν > 330 nmAr, 15 K
S
H
SH
S
H
H
S
H H
SH
S
H
H
ISC
0.0
3.2
0.8
13.012.7
17.4
-0.5
-12.7
56.6
40.8
11.7
0.4
-18.8
Potential Energy Surface, Values in kcal/mol
Enth
alpy
28 29
30
31
32
33
Laura KopffTerese Kreifels
Alex NolanJoshua Shutter
Andrew Wiederhold
Menke, J. L.; McMahon, R. J., Photochemistry of Matrix-isolated 5-cyano-2H-pyran-2-one (!-cyano-"-pryrone) and cyanocyclobuta-1,3-diene. Can. J. Chem. 2011, 89 (2), 186-194.
Thomas, P. S.; Bowling, N. P.; Burrmann, N. J.; McMahon, R. J., Dialkynyl Carbene Derivatives: Generation and Characterization of Triplet tert-Butylpentadiynylidene (t-Bu#C$C#C:#C$C#H) and Dimethylpentadiynylidene (Me#C$C#C:#C$C#Me). J. Org. Chem. 2010, 75 (19), 6372-6381.
Menke, J. L.; Patterson, E. V.; McMahon, R. J., Effects of Cyano Substituents on Cyclobutadiene and Its Isomers. J. Phys. Chem. A 2010, 114 (22), 6431–6437.
Shaffer, C. J.; Esselman, B. J.; McMahon, R. J.; Stanton, J. F.; Woods, R. C., Attempted Isolation and Characterization of Diazirinone (N2CO). J. Org. Chem. 2010, 75 (6), 1815–1821.
Synthesis, Matrix Isolation, Spectroscopy, Mechanistic Studies, and Computational ChemistryMcMahon Research Group
Computational studies have been carried out on both the 2- and 3-substituted benzothiophene carbenes and their possible rearrangement products at the B3LYP/6-31G* level of theory. For the 2-benzothiophene system, the following potential energy surface (PES) was generated connecting the observed bicyclic product with both rotomers of the carbene. Currently studies are underway to finish mapping the PES for the 3-substituted benzothiophene carbene.
!
Thermolysis of a tosyl hydrazone salt leads to 2-diazomethyl benzothiophene, XX, which can be isolated in an Ar or N2 matrix. Irradiation of the diazo compound at hν ≥ 472 nm leads to disappearance of the peaks associated with the d iazo compound and growth o f peaks corresponding to the bicyclic allene XX, as characterized by IR spectroscopy. Further irradiation gives no change in the spectrum.
! > 472 nm
S
N2
H S
H
H34 32 - S
The exploration of varying lengths of unsaturated carbon chains has been a primary focus of the group. The HC3H, HC5H, and HC7H systems have been synthesized and characterized. They are believed to be important molecules in the Interstellar Medium (ISM). Further studies of the substituted RC3R are currently underway.
8 9 10
The Bergman cyclization of tetraethynylcyclobutadiene derivative 9 has been proposed as the first step in a pathway leading to fullerene formation. As a of model the complex system, we intend to characterize the family of ethynyl-substituted cyclobutadienes. The ethynylcyclobutadienes that contain an ene-diyne (12) are of particular interest due to their potential to undergo a photochemical Bergman cyclization.
We will synthesize and matrix isolate the desired !-pyrone precursors (see 16) and photochemically produce the cyclobutadienes. Upon characterization utilizing predicted IR frequencies, we will then characterize the photochemical and/or thermal transformations.
O
O
O
Oh! h!'
CO2
16 1712 18 19
H H
H H
H H
H H
H H
H H
HC2H
HC3H
HC4H
HC5H
HC6H
HC7H
H C C C C C H
C C C HH
C C C CCC CH H
S
H
H32 - S
S
N2
H
Cyano-containing molecules are a class of compounds that have been detected in the ISM, but a significant number of them have yet to be isolated and completely characterized. Proposed syntheses of cyanomethylcarbene (3) and l-HC4N (4) are shown below.
C C CH3C CH3
CC C
CH3H3C
(1 - T) 14.4 kcal/mol (2 - S) 0.0 kcal/mol
C C CH3C
H3C(3 - S) 14.5 kcal/mol
H3CC
CC
H
CH2
(4) -30.4 kcal/mol
N2
hν > 470 nm, Ar, 15 K
CCSD/cc-pVDZ (unscaled)
I need something here to tie it together.
O
HOTIPS OMe
BrBr
O
OMe
O
TMS TMS
CBr4
PPh3
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
I2
O
O
TMS I
TMS
O
O
TMS
TMS
TMS
O
O
TetrabutylammoniumFluoride
HOTIPS
BrBr
1. TBAF
2. [O]
Pd(PPh3)4, CuI
THF, reflux,diisopropylamine
TMS
Figure 9. Infrared spectrum (Ar, 10 K) of carbonyl azide (62) (black line) and the B3LYP/6-31G* predicted spectra (red line).
Unpublished reports claim that carbonyl azide does not photolyze through the dinitrene 63 to diazirinone; however, this same report claims diazirinone has been matrix isolated using a gas phase thermolysis.34
Scheme 14. Diazirinone (59) arriving from carbonyl azide (62).
B. AzirinoneAlthough it is not as high as the calculated diazirinone barrier of 27 kcal/mol, a 12 kcal/mol barrier to decomposition may be enough for azirinone to be characterized in matrix
14
N N
OO
NN
h!O
N N NN NN
gas phase thermolysis
596362
A diazo precursor for dimethylpropynylidene has been synthesized and matrix isolated. Irradiation of diazo 3 under matrix-isolation conditions leads to triplet dimethylpropynylidene (1) which can undergo a hydrogen shift to methylvinylacetylene (2). Further studies on the photochemistry of the CH3C3CH3 system is being investigated.
CN
NN
CN CN
h!
Br
NN n-Bu4N(CN)
4
h!
PhOCNOEt
OEt
Li
OEt
OEt
CN
N
H
CN
N2
H
CN
h!
HCN
1. n-BuLi
2. "
NH
Ts
5
1. HCO2H
2. TsNHNH2
OH1. BaMnO4
2. NH2NHTrisylAcetic Acid
NN
Trisyl
H1. NaH
2. Heat
N2 h! > 470 nm h! > 330 nm
3 1 2
Our interest in prospective molecules to be found in the Interstellar Medium lead us to become interested in the metastable molecule diazirinone, which can be thermolyzed from the explosive carbonyl diazide.
Although diazirinone can be produced from the loss of two molecules of dinitrogen from carbonyl diazide, it is unclear the mechanism in which this occurs. Five computational pathways have been explored, I need more here. Brian?
A proposed synthesis of the precursor of 1,2-diethynylcyclobutadiene (12) is shown below. The key step is Larock electrophilic iodo-lactonization to produce the !-pyrone.
O
NNNN
N NO
NNN
N
N
N
O
NN
N
N
N
N
O
Cl3CO OCCl3
(Bu)4N+ N3-
Ether
O
N N
400 oC
0.0 kcal/mol
2.0 kcal/mol11.9 kcal/mol
O
CNN
NNN N
O
C NNN N
N N
O
C NNN N
NN
O
C NN
N N
O
C NNN N
NN
O
CN N
NN
C
O
NN
N
N
O
C NN
N N
N N
NN
O
O
C NN
N N
NN
Wednesday, February 23, 2011
O
NNNN
N NO
NNN
N
N
N
O
NN
N
N
N
N
O
Cl3CO OCCl3
(Bu)4N+ N3-
Ether
O
N N
400 oC
(7) 0.0 kcal/molC2
(7) 2.0 kcal/molCs
(7) 11.9 kcal/molC2v
6
OH1. BaMnO4
2. NH2NHTrisylAcetic Acid
NN
Trisyl
H1. NaH
2. Heat
N2 h! > 472 nm h! > 330 nm
3 1 2
