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Electronic spectra of dibenzo[a,d]cycloheptatrienylidene at 77°K and room temperature
Temhdrm
VoL26.
pp. 251 to 254.
Perpmm
Rcu
1970.
Rioled
m Gmt
kit&
ELECTRONIC SPECTRA OF DIBENZO(a, d]CYCLOHEPTATRIENYLIDENE AND ROOM TEMPERATURE
AT 77°K
Y. YAMAMOTO, I. MORITANI, Y. MARDA and S. MURAHASHI Department of Chemistry, Faculty of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka, Japan (Received in Japan 1 August 1969; Received in the UK for publication 15 September 1969) AIra&& Electronic absorption spectra of dibenxo[a,&ycloheptatrienylidene (fa) have teen successfully obtained by both matrix isolation technique at 77°K and flash photolysis at room temperature. It has been found that these two spectra are identical, and hence one can discuss the reactivity of carbenes at roan temperature with relation to the information obtained by physical methods at 77°K. Moreover, it wasalso attempted to investigate the spectra of Lain olefins. INTRODUCTION
EXTENSIVE investigations have been devoted to the chemical reactivity and electronic
states of carbenesi Recently, it has become possible to study these reactive intermediates directly in a rigid glass at 77°K by ESR and optical spectroscopy, and the molecular structures of carbenes have been revealed to a considerable extent.2 As the matrix isolation technique is restricted to give information at low temperature, the problem is whether or not one can discuss the chemical reactivity of carbenes produced at room temperature in connection with the information obtained by physical methods at 77°K. In previous communications, we reported the electronic absorption spectra of 10,l ldihydrodibenzo[a, d]cycloheptadienylidene (IIa) recorded by the matrix isolation technique at 77”Kh and by the flash photolysis of 5diazo-10,l ldihydrodibenzo[u, 4)cycloheptadiene (IIb) in liquid partim at room temperature.3 Both spectra are identical,’ and therefore the above question is eliminated in the case of Ha. In order to clarify whether or not Ia gives an identical spectrum at both 77°K and room temperature, the matrix isolation technique and Bash photolysis were employed. In this paper we wish to add a further example that both spectra at 77°K and at room temperature are identical with respect to Ia.* Moreover, we attempted to observe the spectra of Ia in olefms, because Ia adds to olefms stereospecifically in spite of the ground state triplet carbene.‘. s
Q Ib:
l
Q Ilb:
= (=Nx)
l
= (=N,)
Previously, we could not obtain the spectrum of Ia.- Success depends upon a higher vacuum, i.e., complete deoxygenation. l
251
Y. YA~MOT~, I. MORITANI, Y. MAPDAand S. M-m
252
RESULTS
AND
DISCUSSION
1. Absorption spectrum of dibenzo[a, d]cycloheptatrienylideneat 77°K. A solution of 5_diazodibenzo[a,d]cycloheptatriene (Ib) (ca. 10-4-10-3 M) in a mixture of methylcyclohexane and isopentane was photolyxed at 77°K using a 250 W high pressure Hg lamp with a Pyrex filter. As shown in Fig. 1, the absorption spectrum obtained after irradiating Ib for a few minutes exhibits absorption maxima at 3800, 3950, and 4860 A. A similar spectrum was obtained in a mixture of ethanol and methanol, and the absorption intensity increased with irradiation period. The spectrum was stable at 77”K, but disappeared at higher temperature.
Wavelength (A) RG.
1. Absorption spectrum of dibcnzo(a&yclohcptatrienylidene (- . -
at 77°K.
.) beforeirradiation
-) aHa irradiation I.. . . . . .) after warming up to 25°C
It is to be noted that the shape of the spectrum (Fig 1) is similar to that of the spectrumZe of 10.1ldihydrodibenxo[a, djcycloheptadienylidene (IIa) (Fig. 2). 2. Thejlash photolysisof Sdiazodibenzo[a, d]cycloheptatrieneat room temperature. The flash photolysis of about 5 x lo-$ M solution of 5-diazodibenzo[a,d]cycloheptatriene (Ib) in deoxygenated liquid paraffin at room temperature was studied using the apparatus previously described.6 The change in the transient spectra was investigated with various delay times in the range from 10 psec to 500 psec. As apparent from Fig. 3, the absorption spectrum appearing at the delay time of 10 psec was consistent with the curve of Fig. 1 in the rigid glass at 77°K. Therefore, it may be concluded that the same carbene Ia at low temperature is produced in the liquid paraffin at room temperature by the flash photolysis. The spectrum of the intermediate changed with delay time and then disappeared within 500 psec. The lifetime of the carbene Ia is estimated to be about 10 psec. From these results, it is reasonable to conclude that one can discuss the chemical reactivity of carbenes produced at room temperature in connection with the information obtained by physical methods at low temperature such as 77°K.
Ekctronic spectra of dibcnzo(o. &yclohcptatrknylidenc
3ooo
Wav%$h
at 77°K and room temperature
(A)
253
5oQO
FIG. 2. Absorption spectrum of 10.1ldihydrodibcnzo(~~clohcptadienylidcne
at 77°K.
(-.-.) before irradiation -) after irradiation . . . . . . .) after warming up at 25°C
3. Attempts to observe the absorption spectrum ofdibenzo[a,d]cycloheptatrienyhiene in olejhs. The correlation of chemical reactivity of carbenes with their electronic configurations is a subject of current interest’ It is now generally recognized” that the stereochemistry of the addition of a carbene to an olefin depends upon its spin state, with the triplet carbene addition to an oletin nonstereospecifically and the singlet stereospecitkally. We have previously reported that dibenzo[u,@ycloheptatrienylidene (la) adds to olefms stereospecifically and has triplet ground state.s This results can not be explained by the conventional concept. Therefore the absorption spectrum of Ia in the presence of olefins was investigated. A solution of 5-diazodibenzo[a, @ycloheptatriene (Ib) (10-4-10-3 M) in pent-Z ene was photolyzed at 77°K under the conditions mentioned. Though the absorption intensity of the diaxo Ib decreased after irradiation, no new spectra could be obtained.
I 3ooo
1
4ooo Wavelength (A)
Ro. 3. Flash photolysis of 5diazodibcnz44d)cyclohcptatrkne
5ooo
at room temperature.
254
Y. YAMAMOTO,I. MORITAM, Y. MAEDA and S. Mururussn
The flash photolysis of Ib in deoxygenated diethyl maleate was also carried out, but a decrease of the absorption intensity of Ib was only observed. As no spectra were obtained in the presence of olefms contrary to the results in the absence of olefins, the carbene Ia formed probably reacts with olefms instantaneously even at 77°K. This result is in marked contrast with diphenyl methylene which has ground state triplet and adds to oletins nonstereospeciflcally, but is unreactive at 77”K.Zb These facts are now under investigation. EXPERIMENTAL The diaxo compounds la, and Ib were prepared according to the method described.9 The absorption spectra were recorded on a Gary 15 spectrometer fitted with a low temp attachment Quartz ceils and dewars were obtained from the Eikosha The photolysis experiments were carried out by using a 250 W high pressure Hg lamp through a Pyrex litter. Photolyses were run in the following solvents: methylcyclohexane and isopentane, EtOH and MeOH, pent-2-ene. The flash photolysis was performed following the method given in the literature.6 ~~~~~~nt~-~e flash photolysis.
authors wish to thank Prof. and Dr. H. Tsubomura for the technical advice of the
REFERENCES i W. Kirrnse, Curbene ClwmLrtry. Academic Press, New York (1964). z ’ 1. Moritani, S. Murahashi, M. Nishino, K. Kimuta and H. Tsubomura, T.etr&dron i&rers 373 (1966); ’ A. M. Trorzolo, Accounts o~C!arm. Research 1,329 (1968); ’ A. M. Troaolo and W. A. Gibbons, J. Am. Chem. Sue. 89,239 (1967). 3 1. Moritani, S. Murahashi, H. Ashitaka, K. Kimura and H Tsubomum, J. Am Chem Sm. 90,591(1968). ‘ S. Murahashi, I. Moritani and M. Nishino, Ibid. 89,1257 (1967). 5 I. Moritani, S. Murahaahii M. Nishino, Y. Yamamoto, K. Itoh and N. Mataga, Ibid. 89,1259 (1967). 6 N. Yamamoto, Y. Nakato and H. Tsubomura, Buff. C&m. Sot. Japan 3P,2603 (1966). ’ W. Kirmse, Carbetw Chemistry. Chap. 12 Academic Press, New York (1964). s P. S. Skell and R. C. Woodworth, J. Am C&m. Sot. 784496 (1956). 9 I. Moritani, S. Murahashii K. Yoshinaga and H. Ashitaka, ButZ. Ckm. SC. Jopan 40,1506 (1967).
VoL26.
pp. 251 to 254.
Perpmm
Rcu
1970.
Rioled
m Gmt
kit&
ELECTRONIC SPECTRA OF DIBENZO(a, d]CYCLOHEPTATRIENYLIDENE AND ROOM TEMPERATURE
AT 77°K
Y. YAMAMOTO, I. MORITANI, Y. MARDA and S. MURAHASHI Department of Chemistry, Faculty of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka, Japan (Received in Japan 1 August 1969; Received in the UK for publication 15 September 1969) AIra&& Electronic absorption spectra of dibenxo[a,&ycloheptatrienylidene (fa) have teen successfully obtained by both matrix isolation technique at 77°K and flash photolysis at room temperature. It has been found that these two spectra are identical, and hence one can discuss the reactivity of carbenes at roan temperature with relation to the information obtained by physical methods at 77°K. Moreover, it wasalso attempted to investigate the spectra of Lain olefins. INTRODUCTION
EXTENSIVE investigations have been devoted to the chemical reactivity and electronic
states of carbenesi Recently, it has become possible to study these reactive intermediates directly in a rigid glass at 77°K by ESR and optical spectroscopy, and the molecular structures of carbenes have been revealed to a considerable extent.2 As the matrix isolation technique is restricted to give information at low temperature, the problem is whether or not one can discuss the chemical reactivity of carbenes produced at room temperature in connection with the information obtained by physical methods at 77°K. In previous communications, we reported the electronic absorption spectra of 10,l ldihydrodibenzo[a, d]cycloheptadienylidene (IIa) recorded by the matrix isolation technique at 77”Kh and by the flash photolysis of 5diazo-10,l ldihydrodibenzo[u, 4)cycloheptadiene (IIb) in liquid partim at room temperature.3 Both spectra are identical,’ and therefore the above question is eliminated in the case of Ha. In order to clarify whether or not Ia gives an identical spectrum at both 77°K and room temperature, the matrix isolation technique and Bash photolysis were employed. In this paper we wish to add a further example that both spectra at 77°K and at room temperature are identical with respect to Ia.* Moreover, we attempted to observe the spectra of Ia in olefms, because Ia adds to olefms stereospecifically in spite of the ground state triplet carbene.‘. s
Q Ib:
l
Q Ilb:
= (=Nx)
l
= (=N,)
Previously, we could not obtain the spectrum of Ia.- Success depends upon a higher vacuum, i.e., complete deoxygenation. l
251
Y. YA~MOT~, I. MORITANI, Y. MAPDAand S. M-m
252
RESULTS
AND
DISCUSSION
1. Absorption spectrum of dibenzo[a, d]cycloheptatrienylideneat 77°K. A solution of 5_diazodibenzo[a,d]cycloheptatriene (Ib) (ca. 10-4-10-3 M) in a mixture of methylcyclohexane and isopentane was photolyxed at 77°K using a 250 W high pressure Hg lamp with a Pyrex filter. As shown in Fig. 1, the absorption spectrum obtained after irradiating Ib for a few minutes exhibits absorption maxima at 3800, 3950, and 4860 A. A similar spectrum was obtained in a mixture of ethanol and methanol, and the absorption intensity increased with irradiation period. The spectrum was stable at 77”K, but disappeared at higher temperature.
Wavelength (A) RG.
1. Absorption spectrum of dibcnzo(a&yclohcptatrienylidene (- . -
at 77°K.
.) beforeirradiation
-) aHa irradiation I.. . . . . .) after warming up to 25°C
It is to be noted that the shape of the spectrum (Fig 1) is similar to that of the spectrumZe of 10.1ldihydrodibenxo[a, djcycloheptadienylidene (IIa) (Fig. 2). 2. Thejlash photolysisof Sdiazodibenzo[a, d]cycloheptatrieneat room temperature. The flash photolysis of about 5 x lo-$ M solution of 5-diazodibenzo[a,d]cycloheptatriene (Ib) in deoxygenated liquid paraffin at room temperature was studied using the apparatus previously described.6 The change in the transient spectra was investigated with various delay times in the range from 10 psec to 500 psec. As apparent from Fig. 3, the absorption spectrum appearing at the delay time of 10 psec was consistent with the curve of Fig. 1 in the rigid glass at 77°K. Therefore, it may be concluded that the same carbene Ia at low temperature is produced in the liquid paraffin at room temperature by the flash photolysis. The spectrum of the intermediate changed with delay time and then disappeared within 500 psec. The lifetime of the carbene Ia is estimated to be about 10 psec. From these results, it is reasonable to conclude that one can discuss the chemical reactivity of carbenes produced at room temperature in connection with the information obtained by physical methods at low temperature such as 77°K.
Ekctronic spectra of dibcnzo(o. &yclohcptatrknylidenc
3ooo
Wav%$h
at 77°K and room temperature
(A)
253
5oQO
FIG. 2. Absorption spectrum of 10.1ldihydrodibcnzo(~~clohcptadienylidcne
at 77°K.
(-.-.) before irradiation -) after irradiation . . . . . . .) after warming up at 25°C
3. Attempts to observe the absorption spectrum ofdibenzo[a,d]cycloheptatrienyhiene in olejhs. The correlation of chemical reactivity of carbenes with their electronic configurations is a subject of current interest’ It is now generally recognized” that the stereochemistry of the addition of a carbene to an olefin depends upon its spin state, with the triplet carbene addition to an oletin nonstereospecifically and the singlet stereospecitkally. We have previously reported that dibenzo[u,@ycloheptatrienylidene (la) adds to olefms stereospecifically and has triplet ground state.s This results can not be explained by the conventional concept. Therefore the absorption spectrum of Ia in the presence of olefins was investigated. A solution of 5-diazodibenzo[a, @ycloheptatriene (Ib) (10-4-10-3 M) in pent-Z ene was photolyzed at 77°K under the conditions mentioned. Though the absorption intensity of the diaxo Ib decreased after irradiation, no new spectra could be obtained.
I 3ooo
1
4ooo Wavelength (A)
Ro. 3. Flash photolysis of 5diazodibcnz44d)cyclohcptatrkne
5ooo
at room temperature.
254
Y. YAMAMOTO,I. MORITAM, Y. MAEDA and S. Mururussn
The flash photolysis of Ib in deoxygenated diethyl maleate was also carried out, but a decrease of the absorption intensity of Ib was only observed. As no spectra were obtained in the presence of olefms contrary to the results in the absence of olefins, the carbene Ia formed probably reacts with olefms instantaneously even at 77°K. This result is in marked contrast with diphenyl methylene which has ground state triplet and adds to oletins nonstereospeciflcally, but is unreactive at 77”K.Zb These facts are now under investigation. EXPERIMENTAL The diaxo compounds la, and Ib were prepared according to the method described.9 The absorption spectra were recorded on a Gary 15 spectrometer fitted with a low temp attachment Quartz ceils and dewars were obtained from the Eikosha The photolysis experiments were carried out by using a 250 W high pressure Hg lamp through a Pyrex litter. Photolyses were run in the following solvents: methylcyclohexane and isopentane, EtOH and MeOH, pent-2-ene. The flash photolysis was performed following the method given in the literature.6 ~~~~~~nt~-~e flash photolysis.
authors wish to thank Prof. and Dr. H. Tsubomura for the technical advice of the
REFERENCES i W. Kirrnse, Curbene ClwmLrtry. Academic Press, New York (1964). z ’ 1. Moritani, S. Murahashi, M. Nishino, K. Kimuta and H. Tsubomura, T.etr&dron i&rers 373 (1966); ’ A. M. Trorzolo, Accounts o~C!arm. Research 1,329 (1968); ’ A. M. Troaolo and W. A. Gibbons, J. Am. Chem. Sue. 89,239 (1967). 3 1. Moritani, S. Murahashi, H. Ashitaka, K. Kimura and H Tsubomum, J. Am Chem Sm. 90,591(1968). ‘ S. Murahashi, I. Moritani and M. Nishino, Ibid. 89,1257 (1967). 5 I. Moritani, S. Murahaahii M. Nishino, Y. Yamamoto, K. Itoh and N. Mataga, Ibid. 89,1259 (1967). 6 N. Yamamoto, Y. Nakato and H. Tsubomura, Buff. C&m. Sot. Japan 3P,2603 (1966). ’ W. Kirmse, Carbetw Chemistry. Chap. 12 Academic Press, New York (1964). s P. S. Skell and R. C. Woodworth, J. Am C&m. Sot. 784496 (1956). 9 I. Moritani, S. Murahashii K. Yoshinaga and H. Ashitaka, ButZ. Ckm. SC. Jopan 40,1506 (1967).