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Determination of the 125Te13C coupling constants in 2-substituted tellurophenes
JOURNAL
OF MAGNETIC
RESONANCE
47, 504-506 (1982)
Determination of the 12?e-13CCoupling Constants in 2-Substituted Tellurophenes M. L. MARTIN AND M. TRIERWEILER Laboratoire de Physico-Chimie Mol&ulaire ERA CNRS 315. Universitt de Nantes, F-44072 Nantes, France
V. GALASSO Istituto di Chimica. Universitci di Trieste, I-34127 Trieste, Italy
AND F. FRINGUELLIAND A. TATICCHI Dipartimento
di Chimica, Universitd di Perugia, I-06100 Perugia, Italy
ReceivedJune 25, 1981; revisedDecember4, 1981
Although extensive work has been performed on ‘H, 13C, and ‘25Te NMR for telluro-organic compounds, there is still little experimental evidence regarding sign and magnitude of the coupling constants involving “‘Te. As a contribution in this field (I) we report here some new experimental data on a series of tellurophenes. Selective population transfer (SPT) experiments involving the inversion of unobservable ‘H transitions pertaining to species which contain both the ‘25Te and the “C isotopes at the natural-abundance level enabled basic information about couplings between “‘Te and 13C to be derived. Tellurophene and substituted derivatives were prepared by literature methods (2). The samples were studied in (CD,),CO solutions. The ‘25Te-‘3C coupling constants of the proton-bearing carbons have been obtained with a Bruker WH-90 spectrometer operating at 22.63 MHz for 13C. (Pulse width 10 psec, flip angle 7r/2, and digital resolution 0.3 Hz). However, because of sensitivity limitations and slow longitudinal relaxation, the 1*sTe-‘3C coupling constants of the substituted carbons were difficult to obtain at 22.63 MHz. Experiments involving longer repetition time (3 to 6 set) were also performed at 62.9 MHz in some cases. Moreover, SPT experiments were necessary to obtain coupled spectra of CT and C2 nuclei in exploitable conditions. The “‘Te spectra were recorded at 28.43 MHz with a pulse width of 9 psec (7r/2) and an acquisition time of 3.4 sec. Attenuation of the double irradiation field B2 of the WH-90 spectrometer was required in order to perform the selective inversion of proton transition. Convenient selectivities were obtained with B2 pulse widths of approximately 80 to 500 msec. 504 0022-2364/82/060504-03$02.00/0 Copyright Q 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.
505
NOTES
In order to determine the signs of the two-bond Te-C coupling constants we have performed SPT experiments on a representative compound, 2-acetyl-tellurophene (1). In such experiments involving both the “C and r25Te isotopes at the natural-abundance level, selective inversions of proton transitions are achieved, which are the ‘*‘Te satellites of transitions which are themselves the 13C satellites of the main proton lines. Localization of such unobservable secondary transitions requires an accurate knowledge of all the Te-H, C-H, and H-H coupling constants (Table 1). In order to improve the selectivity in determining the sign of *J(Te-C3), for example, we have found it more convenient to irradiate the (*25Te, 13C3) secondary satellite transitions of proton H5 while detecting polarization in the ‘*‘Te satellite spectrum of C3. Analysis of the polarization patterns obtained for several frequencies of the selective pulse shows that ‘J(Te-C,) has the same sign as *J(TeH5) and that *J(C3-H.,) has the same sign as 3J(H4-H5). It is therefore concluded (I) that *J(Te-C3) is negative and *J(C3-H4) positive. Similar experiments involving selective perturbations in the (‘25Te, 13C4) secondary satellite spectrum of H5 indicate that ‘J(Te-Cd) is positive since it has a sign opposite to that of *J(TeH5). A change in the sign of *J(Te-C) of tellurophenes may therefore be introduced by a change in the nature of the substituent and in compound 1 the algebraic decrease of 2J(Te-C) is about 20 Hz when going from site C4 to site C3 vicinal to the substituent. We have also shown by means of appropriate selective polarization transfers that all the couplings *J(C3-H4), *J(C,-H3), *J(C,-H,), *J(C2-H3), 3J(C3-H& 3J(Cg-H3), 3J(C2-H 4) , and 3J(C2-H5) have a positive sign (Table 1). The signs of the *J(Te-C) coupling constants measured in other tellurophenes (Table 2) bearing a carbonyl substituent can be safely assigned by analogy with 2-acetyltellurophene. However, sign variations cannot be excluded for the other substituents; such a situation would be congruent with the results of our theoretical calculations (7). TABLE J(HH)(-t0.15
COUPLINGCONSTANTS INVOLVINGC~
J(TeC)
OR&),
Hz),J(CH)(+O.lO Hz),
AND J(TeH)
OR +0.15 (k0.3
Hz)
= = = = = =
+6.8 +5.7 +2.6 +4.5 +8.6 3.8
4J(H3HS) ‘J(CIHs) 2J(C4H3) ‘J(C,H,) 3J(C,H,) 4J(CrH4)
= = = = = =
= +317.7 = (-)33.1
‘J(TeC$)
= +274.3
*J(TeC4)
= -91.7
)J(TeH4)
= -13.0
‘J(TeH,)
= = = = = =
J (TeC)
‘J(TeC5) *J(TeC,*)
J(TeH)
*J(TeHS)
+4.2 +161.5 +163.6 +183.5 +3.6 5.9
Hz FORCOUPLINGS
IN 2-ACETYLTELLUROPHENE(~)
‘J(H,H,) *J(C,H,) ‘J(C,HS) *J(CsH4) 3J(C2H4) 3J(CyHj)
‘J(H,Hs) ‘J(C,H,) ‘J(CIH4) ‘J(C,H,) ‘J(C2H,) *J(CZHT)
J(HH) J(CH)
(k0.5
1
+1.2 +10.8 f4.7 +10.9 +2.8 0.75
‘+J(CsHr)
= 0.65
5J(CsHr) “J(C,H,) 4J(CrHS)
= 0.15 = 1.2 = 0.75
= f14.0
‘J(TeC3)
= -5.4
= -11.2
‘J(TeH2*)
= 2.9
506
NOTES TABLE
tz5Te-t3C COUPLING R COOH COCH3 CHO COOCH9 Br SCH, CH,OH H
2
Hz) AND‘*‘Te CHEMICAL SHE-E (IN ppm (CH9)*Te) IN ~-SUBSTITIJTE~I TELLUROPHENES
CONSTANTS
(IN
‘J(TeC*)
‘J(TeCr)
‘J(TeC,)
‘J(TeCs)
297.6 274.3 290.2 299.6 373.8 335.4 289.2 302.4
-5.4 -5.4 -3.5 -5.3 (q4.7 I<31 I<31 5.6
13.9 14.0 15.1 13.5 7.0 6.7 7.0 5.6
317.6 317.7 321.6 317.8 310.5 304.5 297.5 302.4”
WITH
RESPECT
‘J(TeCx) (-)39.0 (-)33.1 (-)34.0 (-)36.7 (-)31.7
TO
6( rZ5Te) 861.1 824.6 803.8 862.0 959.7 886.0 775.0 793.4
a Values ‘J = 302.40 Hz and *J = 5.84 Hz have been measured independently (6).
The absolute values and signs of the J(Te-C) coupling constants for the series of 2-substituted tellurophenes examined are given in Table 2. It appears that whereas the magnitude of the one-bond couplings is very large, comparatively small values of the couplings involving two intervening bonds are measured. This behavior parallels that of the J(Se-C) coupling constants in related compounds (3). Note also that ‘J(Te-C,) and ‘J(Te-CJ are about 2.7 times larger than ‘J(Se-C,) and ‘J(Se-C5), respectively. This factor is significantly larger than the simple ratio 77Se,which is about 2 (4), and such behavior may be attrib[r~:s(o)ll25T~/[rJ(~)l uted principally to the fact that in addition to the Fermi-contact term, the orbital and spin-dipolar terms also play an important role in such couplings, as shown by our quantum-mechanical calculations. A peculiar aspect is the high sensitivity of the direct and geminal couplings to the electron-releasing or -withdrawing nature of the substituent; e.g., there is a spread as large as 100 Hz for ‘J(Te-C2), which can be compared with only 30 Hz observed for ‘J(Se-C2) in related compounds. Another aspect worth mentioning is the difference in sign and magnitude shown within each molecule by the geminal *J(Te-C3), *J(Te-C,), and *J(Te-Cx), which emphasizes a strong orientational effect of the Te lone pairs on *J(Te-C), in agreement with current thinking about geminal XC couplings and with experimental evidence on pentane-2,4-dione Te(I1) compounds (5). ACKNOWLEDGMENTS The authors greatly acknowledge Dr. H. Martineau for the collaboration experiments. F.F. and A.T. thank the C.N.R. of Italy for financial support.
in performing
the NMR
A. TATICCHI,
J. Magn.
REFERENCES L. MARTIN, M. TRIERWEILER, Reson. 45 155 (1981).
V. GALASSO,
I.
M.
2.
F. FRINGUELLI AND A. TATICCHI, J. Chem. Sot. Perkin I, 199 (1972); F. FRINGUELLI, S. GRONOWITZ, A.-B. H~RNFELDT, I. JOHNSON, AND A. TATICCHI, Acta Chem. Sand. B 30,605 (1976). M. GARREAU, G. J. MARTIN, M. L. MARTIN, J. MOREL, AND C. PAULMIER, Org. Magn. Reson. 6, 648 (1974). J. R. MORTON AND K. F. PRESTON, J. Magn. Reson. 30, 577 (1978). J. C. DEWAN, W. B. JENNINGS, J. SILVER, AND M. S. TOLLEY, Org. Magn. Reson. 11,449 ( 1978). H. J. JAKOBSEN, B. VILLADSEN, AND T. BUNDGAARD, private communication. V. GALASSO, M. L. MARTIN, M. TRIERWEILER, F. FRINGIJELLI, AND A. TATICCHI, J. Mol. Sfrucr.,
3.
4. 5. 6. 7.
in press.
F. FRINGUELLI,
AND
OF MAGNETIC
RESONANCE
47, 504-506 (1982)
Determination of the 12?e-13CCoupling Constants in 2-Substituted Tellurophenes M. L. MARTIN AND M. TRIERWEILER Laboratoire de Physico-Chimie Mol&ulaire ERA CNRS 315. Universitt de Nantes, F-44072 Nantes, France
V. GALASSO Istituto di Chimica. Universitci di Trieste, I-34127 Trieste, Italy
AND F. FRINGUELLIAND A. TATICCHI Dipartimento
di Chimica, Universitd di Perugia, I-06100 Perugia, Italy
ReceivedJune 25, 1981; revisedDecember4, 1981
Although extensive work has been performed on ‘H, 13C, and ‘25Te NMR for telluro-organic compounds, there is still little experimental evidence regarding sign and magnitude of the coupling constants involving “‘Te. As a contribution in this field (I) we report here some new experimental data on a series of tellurophenes. Selective population transfer (SPT) experiments involving the inversion of unobservable ‘H transitions pertaining to species which contain both the ‘25Te and the “C isotopes at the natural-abundance level enabled basic information about couplings between “‘Te and 13C to be derived. Tellurophene and substituted derivatives were prepared by literature methods (2). The samples were studied in (CD,),CO solutions. The ‘25Te-‘3C coupling constants of the proton-bearing carbons have been obtained with a Bruker WH-90 spectrometer operating at 22.63 MHz for 13C. (Pulse width 10 psec, flip angle 7r/2, and digital resolution 0.3 Hz). However, because of sensitivity limitations and slow longitudinal relaxation, the 1*sTe-‘3C coupling constants of the substituted carbons were difficult to obtain at 22.63 MHz. Experiments involving longer repetition time (3 to 6 set) were also performed at 62.9 MHz in some cases. Moreover, SPT experiments were necessary to obtain coupled spectra of CT and C2 nuclei in exploitable conditions. The “‘Te spectra were recorded at 28.43 MHz with a pulse width of 9 psec (7r/2) and an acquisition time of 3.4 sec. Attenuation of the double irradiation field B2 of the WH-90 spectrometer was required in order to perform the selective inversion of proton transition. Convenient selectivities were obtained with B2 pulse widths of approximately 80 to 500 msec. 504 0022-2364/82/060504-03$02.00/0 Copyright Q 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.
505
NOTES
In order to determine the signs of the two-bond Te-C coupling constants we have performed SPT experiments on a representative compound, 2-acetyl-tellurophene (1). In such experiments involving both the “C and r25Te isotopes at the natural-abundance level, selective inversions of proton transitions are achieved, which are the ‘*‘Te satellites of transitions which are themselves the 13C satellites of the main proton lines. Localization of such unobservable secondary transitions requires an accurate knowledge of all the Te-H, C-H, and H-H coupling constants (Table 1). In order to improve the selectivity in determining the sign of *J(Te-C3), for example, we have found it more convenient to irradiate the (*25Te, 13C3) secondary satellite transitions of proton H5 while detecting polarization in the ‘*‘Te satellite spectrum of C3. Analysis of the polarization patterns obtained for several frequencies of the selective pulse shows that ‘J(Te-C,) has the same sign as *J(TeH5) and that *J(C3-H.,) has the same sign as 3J(H4-H5). It is therefore concluded (I) that *J(Te-C3) is negative and *J(C3-H4) positive. Similar experiments involving selective perturbations in the (‘25Te, 13C4) secondary satellite spectrum of H5 indicate that ‘J(Te-Cd) is positive since it has a sign opposite to that of *J(TeH5). A change in the sign of *J(Te-C) of tellurophenes may therefore be introduced by a change in the nature of the substituent and in compound 1 the algebraic decrease of 2J(Te-C) is about 20 Hz when going from site C4 to site C3 vicinal to the substituent. We have also shown by means of appropriate selective polarization transfers that all the couplings *J(C3-H4), *J(C,-H3), *J(C,-H,), *J(C2-H3), 3J(C3-H& 3J(Cg-H3), 3J(C2-H 4) , and 3J(C2-H5) have a positive sign (Table 1). The signs of the *J(Te-C) coupling constants measured in other tellurophenes (Table 2) bearing a carbonyl substituent can be safely assigned by analogy with 2-acetyltellurophene. However, sign variations cannot be excluded for the other substituents; such a situation would be congruent with the results of our theoretical calculations (7). TABLE J(HH)(-t0.15
COUPLINGCONSTANTS INVOLVINGC~
J(TeC)
OR&),
Hz),J(CH)(+O.lO Hz),
AND J(TeH)
OR +0.15 (k0.3
Hz)
= = = = = =
+6.8 +5.7 +2.6 +4.5 +8.6 3.8
4J(H3HS) ‘J(CIHs) 2J(C4H3) ‘J(C,H,) 3J(C,H,) 4J(CrH4)
= = = = = =
= +317.7 = (-)33.1
‘J(TeC$)
= +274.3
*J(TeC4)
= -91.7
)J(TeH4)
= -13.0
‘J(TeH,)
= = = = = =
J (TeC)
‘J(TeC5) *J(TeC,*)
J(TeH)
*J(TeHS)
+4.2 +161.5 +163.6 +183.5 +3.6 5.9
Hz FORCOUPLINGS
IN 2-ACETYLTELLUROPHENE(~)
‘J(H,H,) *J(C,H,) ‘J(C,HS) *J(CsH4) 3J(C2H4) 3J(CyHj)
‘J(H,Hs) ‘J(C,H,) ‘J(CIH4) ‘J(C,H,) ‘J(C2H,) *J(CZHT)
J(HH) J(CH)
(k0.5
1
+1.2 +10.8 f4.7 +10.9 +2.8 0.75
‘+J(CsHr)
= 0.65
5J(CsHr) “J(C,H,) 4J(CrHS)
= 0.15 = 1.2 = 0.75
= f14.0
‘J(TeC3)
= -5.4
= -11.2
‘J(TeH2*)
= 2.9
506
NOTES TABLE
tz5Te-t3C COUPLING R COOH COCH3 CHO COOCH9 Br SCH, CH,OH H
2
Hz) AND‘*‘Te CHEMICAL SHE-E (IN ppm (CH9)*Te) IN ~-SUBSTITIJTE~I TELLUROPHENES
CONSTANTS
(IN
‘J(TeC*)
‘J(TeCr)
‘J(TeC,)
‘J(TeCs)
297.6 274.3 290.2 299.6 373.8 335.4 289.2 302.4
-5.4 -5.4 -3.5 -5.3 (q4.7 I<31 I<31 5.6
13.9 14.0 15.1 13.5 7.0 6.7 7.0 5.6
317.6 317.7 321.6 317.8 310.5 304.5 297.5 302.4”
WITH
RESPECT
‘J(TeCx) (-)39.0 (-)33.1 (-)34.0 (-)36.7 (-)31.7
TO
6( rZ5Te) 861.1 824.6 803.8 862.0 959.7 886.0 775.0 793.4
a Values ‘J = 302.40 Hz and *J = 5.84 Hz have been measured independently (6).
The absolute values and signs of the J(Te-C) coupling constants for the series of 2-substituted tellurophenes examined are given in Table 2. It appears that whereas the magnitude of the one-bond couplings is very large, comparatively small values of the couplings involving two intervening bonds are measured. This behavior parallels that of the J(Se-C) coupling constants in related compounds (3). Note also that ‘J(Te-C,) and ‘J(Te-CJ are about 2.7 times larger than ‘J(Se-C,) and ‘J(Se-C5), respectively. This factor is significantly larger than the simple ratio 77Se,which is about 2 (4), and such behavior may be attrib[r~:s(o)ll25T~/[rJ(~)l uted principally to the fact that in addition to the Fermi-contact term, the orbital and spin-dipolar terms also play an important role in such couplings, as shown by our quantum-mechanical calculations. A peculiar aspect is the high sensitivity of the direct and geminal couplings to the electron-releasing or -withdrawing nature of the substituent; e.g., there is a spread as large as 100 Hz for ‘J(Te-C2), which can be compared with only 30 Hz observed for ‘J(Se-C2) in related compounds. Another aspect worth mentioning is the difference in sign and magnitude shown within each molecule by the geminal *J(Te-C3), *J(Te-C,), and *J(Te-Cx), which emphasizes a strong orientational effect of the Te lone pairs on *J(Te-C), in agreement with current thinking about geminal XC couplings and with experimental evidence on pentane-2,4-dione Te(I1) compounds (5). ACKNOWLEDGMENTS The authors greatly acknowledge Dr. H. Martineau for the collaboration experiments. F.F. and A.T. thank the C.N.R. of Italy for financial support.
in performing
the NMR
A. TATICCHI,
J. Magn.
REFERENCES L. MARTIN, M. TRIERWEILER, Reson. 45 155 (1981).
V. GALASSO,
I.
M.
2.
F. FRINGUELLI AND A. TATICCHI, J. Chem. Sot. Perkin I, 199 (1972); F. FRINGUELLI, S. GRONOWITZ, A.-B. H~RNFELDT, I. JOHNSON, AND A. TATICCHI, Acta Chem. Sand. B 30,605 (1976). M. GARREAU, G. J. MARTIN, M. L. MARTIN, J. MOREL, AND C. PAULMIER, Org. Magn. Reson. 6, 648 (1974). J. R. MORTON AND K. F. PRESTON, J. Magn. Reson. 30, 577 (1978). J. C. DEWAN, W. B. JENNINGS, J. SILVER, AND M. S. TOLLEY, Org. Magn. Reson. 11,449 ( 1978). H. J. JAKOBSEN, B. VILLADSEN, AND T. BUNDGAARD, private communication. V. GALASSO, M. L. MARTIN, M. TRIERWEILER, F. FRINGIJELLI, AND A. TATICCHI, J. Mol. Sfrucr.,
3.
4. 5. 6. 7.
in press.
F. FRINGUELLI,
AND