- Email: [email protected]
Arylthallium trifluoroacetates carbon-13 and fluorine-19 nuclear magnetic resonance: The substituent effect of the bis(trifluoroacetato)- thallium(III) group
339
Journal of Organometallic Chemistry, 70 (1974) 0 Elsevier Sequoia .%A., Lausanne -Printed in
ARYLTHALLIUM
339-342
The Netherlands
TRIFLUOROACETATES
CARBON-13 AND FLUORINE-19 NUCLEAR MAGNETIC RESONANCE: THE SUBSTITUENT EFFECT OF THE BIS(TRIFLUOROACETATO)THALLIU.M( HI) GROW
WILLIAM KITCHING*, DAVID PRAEGER Department
of Chemistry,
University
DAVID DODDRELL** of Organic Chemistry,
Department (Australia)
and CHRISTOPHER
of Queensland,
University
Brisbane
J. MOORE
(Australia)
of New England. Armidale.
New South
Wales
WILLIAii ADCOCK School of Physical Sciences, (Received
October
Flinders
University,
South Australia (Australia)
9th. 1973)
Summary I3 C NMR data for a series of arylthallium trifluoroacetates (ArTlX* , X = 0COCF3 ) are reported and assigned. The range of carbon-thallium couplings to be expected, the dependence on the disposition of coupled nuclei, and chemical shift effects are discussed. The Tl(OCOCF, )2 group is shown to be a powerful electron withdrawing group, from both the I3 C data and I9 F substituent chemical shifts of the p-fluorophenyl derivative.
Organothallium chemistry is currently an area of great interest [ 1, 21, but this renaissance has not included any I3 C NMR studies, which are of increasing importance in bonding and general constitutional aspects of organometallic chemistry. We report I3 C NMR studies of a series of arylthallium trifluoroacetates [l, 31, which indicate the range of carbon-thallium coupling constants to be expected, the dependence on disposition of the coupled nuclei, and chemical shift effects. I9 F substituent chemical shifts of p-fluorophenyl derivatives and these l3 C data, explain an important characteristic of aromatic thallation by T1(OCOCF3 )3 in CF, COOH viz. the absence of di- or poly-thallated products [4] _
l
* Address correspondence to this author. (1974: Department Columbus. Ohio. 43210 U.S.A.) * Queen Elizabeth (II) Research Fellow, 1973-1974.
of Chemistry.
Ohio State University.
6
1 T’XZ
4
% 8
TIX;’
3
2
, --Q-
:H,
146.3 140.9 (9329) fJ (G48)
126.9 (793)
d
137.1 (646)
132.0 (-GOO)
12G.6 (820)
123.4 (849)
141,6 (812)
137,Q (766)
137.6 (676)
6
129,3 (966)
127.0 (896)
126.9 (878)
G
21.0 (br)
20.1 (107)
20.4 (110)
7
19.7 (br)
23.9 (402)
23.8 (469)
8
a Spectra were recorded tn the FT mode for undcgassed THF solutiorm at 22.6 MHz. The a-carbon of THF wns tnken as 67.0 ppm from TM3 Quoted values in ppm from TMS. Values in porcntheses are coupiing constnnts in Hz. h Broader pcnks, due in pnrt to partini resolution of coupiing from goaT and 205T1 (7 ratlo -1.0098). Other factors mny also contribute. C Other thnn J1, data here to bc rcgerded us less precise, due to much signal overlapping. d C4 doublet completely obscured but ca. 140 ppm.
6
14002 (183)
137.1 (800)
143.7 134,o (9634) ” (B6G)
141,o (196)
4
127.0 (806)
130.7 (183)
4
141.3 (166)
143 137.4 (9766) 8 (7B6)
126.9 (878)
3
129.3 (968)
3
2
-o-
5
2
1BO 137,5 (9902) o (676)
1
41 Hz1 and (=_Fgnt 118.7 ppm [JP--F) 287 Hz1
lG0.3 141.6 (8841) h (512)
&iJ
Compound
at 162.4 ppm [J(C-F)
SHIFTSAND ’ 3C- 203,go5T1 COUPLING CONSTANTS
3
2
Entry
x = CCOCF3.>c=C
‘SC CHEMICAL
TABLE 1
341
The I3 C data are assembled in Table 1. C1 (bearing thallium) was assigned on the basis of its large one-bond coupling (9-10 kHz) and large o-effect (dowufield by = 20 ppm) of the thallium group. With a pulse interval of 1 s, the p-tolyl derivative showed (besides signals for C, , CH3 and OCOCJF, ) two doublets of essentially equal intensity, with another doublet of ca. l/5 the above intensity. This is consistent with the expectation of very similar T1 values for protonated ortho (C, , C6 ) and meta(C3 , Cs ) carbons (both T, much less than pulse spacing) and a longer TX (and much longer than pulse spacing) for C, (bearing the CH3 group) resulting in some saturation and loss of intensity. The mesityl derivative [ArT1(OCOCF3 )* ; Ar = 2,4,6_trimethylphenyl] under the same conditions, showed one strong doublet (in the aryl region) which must be assigned to the protonated C3,5, and two other doublets (with intensity ratio of ca. 2/l) assigned to C2.6 and C, respectively, consistent with these methylated carbons having longer T1 values (and comparable to pulse spacing) than C3,5 _ On these bases, consistent patterns of chemical shifts and coupling constants emerged. In line with the above, examination of Ar, TIOCOCF, (Ar = 2-deutero-4-methyl) confirmed J(Tl-C,,,, ) > J(Tl--C,,,,, ). Regarding coupling constants, the one-bond coupling of 9-10 kHz is noteworthy and probably associated with the high effective nuclear charge on thallium as well as the large gyromagnetic ratio. The sequence J(Tl-C,,,, )> concurs with data for phenyl derivatives of other J(Tl-C,,,, ) > J(Tl-C,,) heavy metals (e.g. Hg, Sn, Pb) [5, 63 * with the meta-carbon and metal defining a strictly trans planar array**. Methyl substitution, particularly ortho or para to thallium, decreases the one-bond coupling significantly. Comparisons of coupling in alkyl and aryl derivatives of other metals (e.g. Sn, Hg) [6, 81 * lead to the suggestion that the J values reported herein will be a guide to couplings in alkylthallium compounds, and where a strong angular dependence of vicinal coupling is anticipated [9, lo] ***_ Compared with the parent hydrocarbon [12], C, and ortho carbons experience substantial downfield shifts ((Yand fl effects) of 18-23 ppm and 5-9 ppm respectively, while meta-carbons in the main, experience upfield (y) effects of 0-Z ppm’ . A significant trend is discerned in the substituent chemical shift (SCS) values’ + of C, @am to Tl) in entries l-3 of Table 1 where values of +2.3, +3.2 and +3.7 ppm are observed, and imply substantial electron-withdrawal by TQOCOCF, )Z _ Examination of the I9 F spectra of p-F& H, T1(OCOCF3 )2 in a number of solvents confirms the above effect (Table 2). The SCS value** of -9.3 ppm for CF3 COOH solvent can be compared with SCS values of ca. -5 and -10 ppm for p-CT3 and p-NO2 respectively. [ 121. This powerful electron-withdrawal
* For I-Q. Sn and Pb tbis sequence is proven by deuteration &cfo.> JpmJ exists c31 as it does in phenylmercury compounds. See ref. 7. coupling has been demonstrated *** A pronounced “Karplus type” dependence of vicinal ’ ggHg-‘3C + ~~~~knds are manifested in phenyl type derivatives of other heavy metal.. e.g.. m . phenyltri. methyllad;cr, 8. f effects [ of the Pb
in
342 TABLE
2
i9F SUBSTITUENT
CHEMICAL
Compound F -0
-Ti(OCOCF,),
F-@aTIOCOCFe
SHIFTS
OF pnra-FLUOROPHENYLTHALLHJM
SYSTEMS
=
J(TI-F)
Solvent
SCS
CF5COOH Pylidine DMSO THF Dioxen CHC13 =
-9.3 -2.4 -2.1 4.1 4.5 -6.0
240 230 240 233 226
Pyridine THF
-1.0 -1.8
113 112
*
o spectra wererecorded for ea. lo-12 weight/volume percent solutions at 56.44 MHz
probably accounts for the absence of dithallation*. There is the anticipated reduction in the SCS as the donor action of solvent improves, while the reduced SCS and J(Tl-F) values for (p-F& H4 )2 TlOCOCF, are associated with less electron deficiency at the metal. This, and other chemical and spectroscopic information on thallation and oxythallation, will be discussed in detail at a later date. Acknowledgements The authors are grateful to the Australian Research Grants Committee for funding at their respective institutions_ References EC. Taylor and A. McKiiop. Accounts Chem. Res.. 3 (1970) 338. A-G. Lee, The Chemistry of Thallium. Eisevier Publishing Co.. New York, 1971. A- MeRiiiozi. J-D_ Hunt end EC. Tavlor, .I. Orpanometal. Chem.. 24 (1970) 77. P.M. Henry, J. Org. Chem.. 35 (1970) 3083. F.J. Wtigert and J.D. Roberts, J. Amer. Chem. Sot.. 91 (1969) 494. D. Doddreh. M.L. Bullpitt. C.J. Moore. C.W. Fang, W. Kitching, W. Adcock and B. Gupta. Tetrahe&on Lett. (1973) 665. 7 P.J. Banney. M.Sc. Thesis. University of Queensland. 1969. 8 H.G. KuiviIa, J.L. Considine. R.J. Mynott and R.H. Anne. J. Organometal. Chem., 55 (1973) 11. 9 D. Doddfell. I. Burfitt. W. Kitching, M. Bullpitt. R.J. Mynott. J.L. Considine. H.G. KuivIla and R.H. sarma, J. Amer. C&m_ SOC.; (1973) submitted for publication. 10 D. Praeger. unpublished results. 11 J.B. Stothen. Carbon-13 NMR Spectroscopy. Academic Press. London, 1972, P. 95. 12 R.W. Taft. E;Price. 1-R. Fox, 1-C. Lewis. K-K. Anderson and G-T. Lewis. J. Amer. Chem. Sot.. 85 (1963) 3146. 13 A.J. Smith. w. _4dcock end W. Kitching, J. Amer. Chem. Sot.. 92 (1970) 6140 and related papers.
* For other discussions of the substituent effects of metei~onteining see ref. 13.
groups @Y
19
F resonance)
Journal of Organometallic Chemistry, 70 (1974) 0 Elsevier Sequoia .%A., Lausanne -Printed in
ARYLTHALLIUM
339-342
The Netherlands
TRIFLUOROACETATES
CARBON-13 AND FLUORINE-19 NUCLEAR MAGNETIC RESONANCE: THE SUBSTITUENT EFFECT OF THE BIS(TRIFLUOROACETATO)THALLIU.M( HI) GROW
WILLIAM KITCHING*, DAVID PRAEGER Department
of Chemistry,
University
DAVID DODDRELL** of Organic Chemistry,
Department (Australia)
and CHRISTOPHER
of Queensland,
University
Brisbane
J. MOORE
(Australia)
of New England. Armidale.
New South
Wales
WILLIAii ADCOCK School of Physical Sciences, (Received
October
Flinders
University,
South Australia (Australia)
9th. 1973)
Summary I3 C NMR data for a series of arylthallium trifluoroacetates (ArTlX* , X = 0COCF3 ) are reported and assigned. The range of carbon-thallium couplings to be expected, the dependence on the disposition of coupled nuclei, and chemical shift effects are discussed. The Tl(OCOCF, )2 group is shown to be a powerful electron withdrawing group, from both the I3 C data and I9 F substituent chemical shifts of the p-fluorophenyl derivative.
Organothallium chemistry is currently an area of great interest [ 1, 21, but this renaissance has not included any I3 C NMR studies, which are of increasing importance in bonding and general constitutional aspects of organometallic chemistry. We report I3 C NMR studies of a series of arylthallium trifluoroacetates [l, 31, which indicate the range of carbon-thallium coupling constants to be expected, the dependence on disposition of the coupled nuclei, and chemical shift effects. I9 F substituent chemical shifts of p-fluorophenyl derivatives and these l3 C data, explain an important characteristic of aromatic thallation by T1(OCOCF3 )3 in CF, COOH viz. the absence of di- or poly-thallated products [4] _
l
* Address correspondence to this author. (1974: Department Columbus. Ohio. 43210 U.S.A.) * Queen Elizabeth (II) Research Fellow, 1973-1974.
of Chemistry.
Ohio State University.
6
1 T’XZ
4
% 8
TIX;’
3
2
, --Q-
:H,
146.3 140.9 (9329) fJ (G48)
126.9 (793)
d
137.1 (646)
132.0 (-GOO)
12G.6 (820)
123.4 (849)
141,6 (812)
137,Q (766)
137.6 (676)
6
129,3 (966)
127.0 (896)
126.9 (878)
G
21.0 (br)
20.1 (107)
20.4 (110)
7
19.7 (br)
23.9 (402)
23.8 (469)
8
a Spectra were recorded tn the FT mode for undcgassed THF solutiorm at 22.6 MHz. The a-carbon of THF wns tnken as 67.0 ppm from TM3 Quoted values in ppm from TMS. Values in porcntheses are coupiing constnnts in Hz. h Broader pcnks, due in pnrt to partini resolution of coupiing from goaT and 205T1 (7 ratlo -1.0098). Other factors mny also contribute. C Other thnn J1, data here to bc rcgerded us less precise, due to much signal overlapping. d C4 doublet completely obscured but ca. 140 ppm.
6
14002 (183)
137.1 (800)
143.7 134,o (9634) ” (B6G)
141,o (196)
4
127.0 (806)
130.7 (183)
4
141.3 (166)
143 137.4 (9766) 8 (7B6)
126.9 (878)
3
129.3 (968)
3
2
-o-
5
2
1BO 137,5 (9902) o (676)
1
41 Hz1 and (=_Fgnt 118.7 ppm [JP--F) 287 Hz1
lG0.3 141.6 (8841) h (512)
&iJ
Compound
at 162.4 ppm [J(C-F)
SHIFTSAND ’ 3C- 203,go5T1 COUPLING CONSTANTS
3
2
Entry
x = CCOCF3.>c=C
‘SC CHEMICAL
TABLE 1
341
The I3 C data are assembled in Table 1. C1 (bearing thallium) was assigned on the basis of its large one-bond coupling (9-10 kHz) and large o-effect (dowufield by = 20 ppm) of the thallium group. With a pulse interval of 1 s, the p-tolyl derivative showed (besides signals for C, , CH3 and OCOCJF, ) two doublets of essentially equal intensity, with another doublet of ca. l/5 the above intensity. This is consistent with the expectation of very similar T1 values for protonated ortho (C, , C6 ) and meta(C3 , Cs ) carbons (both T, much less than pulse spacing) and a longer TX (and much longer than pulse spacing) for C, (bearing the CH3 group) resulting in some saturation and loss of intensity. The mesityl derivative [ArT1(OCOCF3 )* ; Ar = 2,4,6_trimethylphenyl] under the same conditions, showed one strong doublet (in the aryl region) which must be assigned to the protonated C3,5, and two other doublets (with intensity ratio of ca. 2/l) assigned to C2.6 and C, respectively, consistent with these methylated carbons having longer T1 values (and comparable to pulse spacing) than C3,5 _ On these bases, consistent patterns of chemical shifts and coupling constants emerged. In line with the above, examination of Ar, TIOCOCF, (Ar = 2-deutero-4-methyl) confirmed J(Tl-C,,,, ) > J(Tl--C,,,,, ). Regarding coupling constants, the one-bond coupling of 9-10 kHz is noteworthy and probably associated with the high effective nuclear charge on thallium as well as the large gyromagnetic ratio. The sequence J(Tl-C,,,, )> concurs with data for phenyl derivatives of other J(Tl-C,,,, ) > J(Tl-C,,) heavy metals (e.g. Hg, Sn, Pb) [5, 63 * with the meta-carbon and metal defining a strictly trans planar array**. Methyl substitution, particularly ortho or para to thallium, decreases the one-bond coupling significantly. Comparisons of coupling in alkyl and aryl derivatives of other metals (e.g. Sn, Hg) [6, 81 * lead to the suggestion that the J values reported herein will be a guide to couplings in alkylthallium compounds, and where a strong angular dependence of vicinal coupling is anticipated [9, lo] ***_ Compared with the parent hydrocarbon [12], C, and ortho carbons experience substantial downfield shifts ((Yand fl effects) of 18-23 ppm and 5-9 ppm respectively, while meta-carbons in the main, experience upfield (y) effects of 0-Z ppm’ . A significant trend is discerned in the substituent chemical shift (SCS) values’ + of C, @am to Tl) in entries l-3 of Table 1 where values of +2.3, +3.2 and +3.7 ppm are observed, and imply substantial electron-withdrawal by TQOCOCF, )Z _ Examination of the I9 F spectra of p-F& H, T1(OCOCF3 )2 in a number of solvents confirms the above effect (Table 2). The SCS value** of -9.3 ppm for CF3 COOH solvent can be compared with SCS values of ca. -5 and -10 ppm for p-CT3 and p-NO2 respectively. [ 121. This powerful electron-withdrawal
* For I-Q. Sn and Pb tbis sequence is proven by deuteration
in
342 TABLE
2
i9F SUBSTITUENT
CHEMICAL
Compound F -0
-Ti(OCOCF,),
F-@aTIOCOCFe
SHIFTS
OF pnra-FLUOROPHENYLTHALLHJM
SYSTEMS
=
J(TI-F)
Solvent
SCS
CF5COOH Pylidine DMSO THF Dioxen CHC13 =
-9.3 -2.4 -2.1 4.1 4.5 -6.0
240 230 240 233 226
Pyridine THF
-1.0 -1.8
113 112
*
o spectra wererecorded for ea. lo-12 weight/volume percent solutions at 56.44 MHz
probably accounts for the absence of dithallation*. There is the anticipated reduction in the SCS as the donor action of solvent improves, while the reduced SCS and J(Tl-F) values for (p-F& H4 )2 TlOCOCF, are associated with less electron deficiency at the metal. This, and other chemical and spectroscopic information on thallation and oxythallation, will be discussed in detail at a later date. Acknowledgements The authors are grateful to the Australian Research Grants Committee for funding at their respective institutions_ References EC. Taylor and A. McKiiop. Accounts Chem. Res.. 3 (1970) 338. A-G. Lee, The Chemistry of Thallium. Eisevier Publishing Co.. New York, 1971. A- MeRiiiozi. J-D_ Hunt end EC. Tavlor, .I. Orpanometal. Chem.. 24 (1970) 77. P.M. Henry, J. Org. Chem.. 35 (1970) 3083. F.J. Wtigert and J.D. Roberts, J. Amer. Chem. Sot.. 91 (1969) 494. D. Doddreh. M.L. Bullpitt. C.J. Moore. C.W. Fang, W. Kitching, W. Adcock and B. Gupta. Tetrahe&on Lett. (1973) 665. 7 P.J. Banney. M.Sc. Thesis. University of Queensland. 1969. 8 H.G. KuiviIa, J.L. Considine. R.J. Mynott and R.H. Anne. J. Organometal. Chem., 55 (1973) 11. 9 D. Doddfell. I. Burfitt. W. Kitching, M. Bullpitt. R.J. Mynott. J.L. Considine. H.G. KuivIla and R.H. sarma, J. Amer. C&m_ SOC.; (1973) submitted for publication. 10 D. Praeger. unpublished results. 11 J.B. Stothen. Carbon-13 NMR Spectroscopy. Academic Press. London, 1972, P. 95. 12 R.W. Taft. E;Price. 1-R. Fox, 1-C. Lewis. K-K. Anderson and G-T. Lewis. J. Amer. Chem. Sot.. 85 (1963) 3146. 13 A.J. Smith. w. _4dcock end W. Kitching, J. Amer. Chem. Sot.. 92 (1970) 6140 and related papers.
* For other discussions of the substituent effects of metei~onteining see ref. 13.
groups @Y
19
F resonance)