- Email: [email protected]
Reactions of tellurium(IV) chlorides with boron trihalides
3261
Notes
J. inorg, nucL Chem., 1972, Vol. 34, pp. 3261-3262.
Pergamon Press.
Printed in Great Britain
Reactions of tellurium(IV) chlorides with boron trihalides (Received 6 January 1972) STUDIES of the products of reaction of methylselenium(IV) chlorides [1.2] and methyltellurium(IV) bromides [3] with boron trihalides have shown no evidence of M --->.4(M=Se, Te; A=BCI3 or BBr:~) bond formation. In the reaction of (CH3)2TeBr2 and BBra, however, an adduct of unusual stoichiometry, [(CH3)2TeBr2]2BBr3, was formed; the instability of this species prevented its characterization. In this communication the examination of the comparable dimethyltellurium dichloride-boron trichloride reaction system and the results of certain related experiments are reported. EXPERIMENTAL AND RESULTS Attempted reaction o f a-(CH3)2 TeCI2 and BCI3 White. crystalline c~-(CH3)2TeCI~ (1-20g, 5'25 m-mole), prepared according to Vernon's method [4], was weighed into a vacuum line reaction vessel, and BC13(12"2 m-mole) and benzene (10 ml) condensed therein at -195°C. The system was allowed to warm slowly to room temperature, after which volatile materials were removed. The solid white residue contained 54.5 per cent Te[(CH:0._,TeCI: requires 55.6 percent Te]. Similar experiments carried out using no solvent and allowing the system to remain at - 7 8 °, -- 15° and 0°C for extended periods also led to full recovery of (CH3)2TeCI,_, with no indication of a reaction product stable at room temperature.
Reaction o f a-(CH:~).,TeCl.~ and BBr3 In a vacuum line vessel (CH3)._,TeCI2(1'68 g, 7.38 m-mole) and BBr3 (1"34 g, 5'34 m-mole) were dissolved in CrH~ (10 ml). I.R. spectroscopic examination of the volatile substances subsequently removed indicated only BCla, BBra and CrHr. The colorless solid residue contained 37.8% Te and had a cryoscopically determined molecular weight in benzene of 3 3 1 - 17. [(CH3)2TeBr., requires 40.1% Te; the calculated molecular weight is 318]. The yield of (CH3)2TeBr2 was quantitative. If, in this reaction, a large excess of BBr3 was used an adduct of composition [(CH.0._,TeBr.,]eBBr:~ was recovered [3]. Attempted reaction o f a-(CH3)_,TeBrz and BCl3 Colorless (CH3)2TeBr2 (1-14g, 3-5m-mole) was combined with BCI3 (18.1 m-mole) and CrH~ (5 ml) in a vacuum line trap and allowed to stand for 1.5 hr at room temperature. Removal of the volatiles gave a residue of 1-14 g of unreacted (CH3)2TeBr2. Reaction o f TeCl~ and BBr3 In a manner similar to the procedures described above TeCI4 (0.590 g, 2.20 m-mole) and BBr~ (5.3 g, 21 m-mole) were allowed to react in benzene. A yellow solid melting above 360°C was recovered. (Found: Te, 28.9%. TeBr4 requires 28'5% Ire.) The weight relationships indicated quantitative conversion of the tetrachloride to TeBr4. .4 ttempted reaction o f TeBr4 and BBr3 An amount of TeBr4 was mixed with a ten-fold excess of BBr3 in a glass tube. After sealing the tube and its contents were agitated for 7 days at room temperature. During this period no detectable reaction of TeBr4 and BBr:~ was observed and, after opening the tube, the TeBr4 was recovered quantitatively. 1. 2~ 3. 4.
K.J. Wynne and J. W. George,J. Am. chem. Soc. 87, 4570 (1965). K.J. Wynne and J. W. George, J. A m. chem. Soc. 91, 1649 (1969). M.T. Chen and J. W. George, J. A m. chem. Soc. 90, 4580 (1968). R. H. Vernon, J. chem. Soc. 117, 86 (1920).
JincVol. 34 No. 10-J
3262
Notes DISCUSSION
The general utility of BBr~ in preparing anhydrous bromides and oxybromides from metals, metalloids, and non-metal oxides or sulfides has been reported [5]. In addition, several metal and non-metal chlorides have been coverted to the corresponding bromides via direct reaction with BBrn[6]. For both tellurium(IV) chloride compounds studied here rapid and complete halogen exchange with BBr3 in benzene solution takes place. In the case of the TeCI4 reaction an important driving force may be the lower solubility in benzene of TeBr4 as compared to TeCI4, and in both reactions the greater volatility of BCI3 relative to BBr3 may be significant. Speculation concerning the mechanism by which such an exchange reaction may occur should take note of the similarities in tellurium coordination in solid TeCI4 and (CH3)2TeC12. In the former a tetrameric assemblage of chlorine-bridged TeCI3 units [7] results in a six-fold coordination of Te by chlorine atoms. A not totally dissimilar octahedral coordination of four chlorines and two carbons about Te is attained in crystalline a-(CH3)2TeCI2 through a moderately strong interaction between the Te of one molecule and a chlorine atom of each of two adjacent molecules [8]. Ebulloscopic measurement in acetone solution indicates (CH3)2TeC12 to be monomeric [4], and this condition would be expected also in benzene solution. The several reports [9-14] of the benzene solution behavior of TeCI4 suggest, however, a concentration and/or impurity dependent distribution of associated species with h values ranging from 1 to 4. A possible exchange mechanism involving a sequence of mixed halogen-bridged interactions between Te and B is as follows: / X2TeCI2 + BBr3 = XzCITe
CI
\
\ /
BBr2 = X~TeCIBr + BBr2CI(X = CH3 or CI)
(1)
Br / X2BrTeCI + BBr3 = X2BrTe
CI
\
\ /
BBr2 = X2TeBr2 + BBr2C1
(2)
Br 3BBr2CI = 2BBr3 + BCI~
(3)
BBr~CI could also participate as a reactant in step (2). Repetition of step (2) when X = C1 could lead to TeBr4. In view of the reported precipitation of TeCI3+BCI4 - in the reaction of TeCI4 and BCI3 in benzene [15] it might be anticipated that an analogous bromide species would be obtained from the TeBr4BBr3 system. That no reaction occurs, either in benzene solution or in the absence of solvent, may reflect a significantly lower lattice energy for a tetrabromoborate relative to TeBr4. A c k n o w l e d g e m e n t - The authors are grateful to the National Science Foundation for financial support of this work under grant GP-6189. Department o f Chemistry University o f Massachusetts Amherst, Massachusetts, U.S..4. 5. 6, 7. 8. 9. 10. 11. 12. 13. 14. 15.
M I N G T. C H E N J O H N W. G E O R G E
M. F. Lappert and B. Prokai, J. chem. Soc. (A) 129 (I 967). P.M. Druce, M. F. Lappert, and P. N. K. Riley, Chem. Commun. 486 (1967). B. Buss and B. Krebs, lnorg. Chem. 10, 2795 (1971). G. D. Christofferson, R. A. Sparks, and J. D. McCullough, Acta Crystallogr. 11, 782 (1958). I. R. Beattie and H. Chudzynska, J. chem. Soc. (A) 984 (1967). D. A. Couch, P. S. Elmes, J. E. Fergusson, M. L. Greenfield and C. J. Wilkins, J. chem. Soc. (A) 1813 (1967). N. N. Greenwood, B. P. Straughn and A. E. Wilson, J. chem. Soc. (A) 2209 (1968). N. Katsaros and J. W. George, lnorg. Chim..4eta 3, 165 (1969). I. R. Beattie, P. J. Jones and M. Webster, J. chem. Soc. (A) 218 (1969). I. R. Beattie, R. R. Horder and P. J. Jones, J. chem. Soc. (A) 329 (1970). R. C. Paul, K. K. Paul and K. C. Malhotra,.4ustr. J. Chem. 22, 847 (1969).
Notes
J. inorg, nucL Chem., 1972, Vol. 34, pp. 3261-3262.
Pergamon Press.
Printed in Great Britain
Reactions of tellurium(IV) chlorides with boron trihalides (Received 6 January 1972) STUDIES of the products of reaction of methylselenium(IV) chlorides [1.2] and methyltellurium(IV) bromides [3] with boron trihalides have shown no evidence of M --->.4(M=Se, Te; A=BCI3 or BBr:~) bond formation. In the reaction of (CH3)2TeBr2 and BBra, however, an adduct of unusual stoichiometry, [(CH3)2TeBr2]2BBr3, was formed; the instability of this species prevented its characterization. In this communication the examination of the comparable dimethyltellurium dichloride-boron trichloride reaction system and the results of certain related experiments are reported. EXPERIMENTAL AND RESULTS Attempted reaction o f a-(CH3)2 TeCI2 and BCI3 White. crystalline c~-(CH3)2TeCI~ (1-20g, 5'25 m-mole), prepared according to Vernon's method [4], was weighed into a vacuum line reaction vessel, and BC13(12"2 m-mole) and benzene (10 ml) condensed therein at -195°C. The system was allowed to warm slowly to room temperature, after which volatile materials were removed. The solid white residue contained 54.5 per cent Te[(CH:0._,TeCI: requires 55.6 percent Te]. Similar experiments carried out using no solvent and allowing the system to remain at - 7 8 °, -- 15° and 0°C for extended periods also led to full recovery of (CH3)2TeCI,_, with no indication of a reaction product stable at room temperature.
Reaction o f a-(CH:~).,TeCl.~ and BBr3 In a vacuum line vessel (CH3)._,TeCI2(1'68 g, 7.38 m-mole) and BBr3 (1"34 g, 5'34 m-mole) were dissolved in CrH~ (10 ml). I.R. spectroscopic examination of the volatile substances subsequently removed indicated only BCla, BBra and CrHr. The colorless solid residue contained 37.8% Te and had a cryoscopically determined molecular weight in benzene of 3 3 1 - 17. [(CH3)2TeBr., requires 40.1% Te; the calculated molecular weight is 318]. The yield of (CH3)2TeBr2 was quantitative. If, in this reaction, a large excess of BBr3 was used an adduct of composition [(CH.0._,TeBr.,]eBBr:~ was recovered [3]. Attempted reaction o f a-(CH3)_,TeBrz and BCl3 Colorless (CH3)2TeBr2 (1-14g, 3-5m-mole) was combined with BCI3 (18.1 m-mole) and CrH~ (5 ml) in a vacuum line trap and allowed to stand for 1.5 hr at room temperature. Removal of the volatiles gave a residue of 1-14 g of unreacted (CH3)2TeBr2. Reaction o f TeCl~ and BBr3 In a manner similar to the procedures described above TeCI4 (0.590 g, 2.20 m-mole) and BBr~ (5.3 g, 21 m-mole) were allowed to react in benzene. A yellow solid melting above 360°C was recovered. (Found: Te, 28.9%. TeBr4 requires 28'5% Ire.) The weight relationships indicated quantitative conversion of the tetrachloride to TeBr4. .4 ttempted reaction o f TeBr4 and BBr3 An amount of TeBr4 was mixed with a ten-fold excess of BBr3 in a glass tube. After sealing the tube and its contents were agitated for 7 days at room temperature. During this period no detectable reaction of TeBr4 and BBr:~ was observed and, after opening the tube, the TeBr4 was recovered quantitatively. 1. 2~ 3. 4.
K.J. Wynne and J. W. George,J. Am. chem. Soc. 87, 4570 (1965). K.J. Wynne and J. W. George, J. A m. chem. Soc. 91, 1649 (1969). M.T. Chen and J. W. George, J. A m. chem. Soc. 90, 4580 (1968). R. H. Vernon, J. chem. Soc. 117, 86 (1920).
JincVol. 34 No. 10-J
3262
Notes DISCUSSION
The general utility of BBr~ in preparing anhydrous bromides and oxybromides from metals, metalloids, and non-metal oxides or sulfides has been reported [5]. In addition, several metal and non-metal chlorides have been coverted to the corresponding bromides via direct reaction with BBrn[6]. For both tellurium(IV) chloride compounds studied here rapid and complete halogen exchange with BBr3 in benzene solution takes place. In the case of the TeCI4 reaction an important driving force may be the lower solubility in benzene of TeBr4 as compared to TeCI4, and in both reactions the greater volatility of BCI3 relative to BBr3 may be significant. Speculation concerning the mechanism by which such an exchange reaction may occur should take note of the similarities in tellurium coordination in solid TeCI4 and (CH3)2TeC12. In the former a tetrameric assemblage of chlorine-bridged TeCI3 units [7] results in a six-fold coordination of Te by chlorine atoms. A not totally dissimilar octahedral coordination of four chlorines and two carbons about Te is attained in crystalline a-(CH3)2TeCI2 through a moderately strong interaction between the Te of one molecule and a chlorine atom of each of two adjacent molecules [8]. Ebulloscopic measurement in acetone solution indicates (CH3)2TeC12 to be monomeric [4], and this condition would be expected also in benzene solution. The several reports [9-14] of the benzene solution behavior of TeCI4 suggest, however, a concentration and/or impurity dependent distribution of associated species with h values ranging from 1 to 4. A possible exchange mechanism involving a sequence of mixed halogen-bridged interactions between Te and B is as follows: / X2TeCI2 + BBr3 = XzCITe
CI
\
\ /
BBr2 = X~TeCIBr + BBr2CI(X = CH3 or CI)
(1)
Br / X2BrTeCI + BBr3 = X2BrTe
CI
\
\ /
BBr2 = X2TeBr2 + BBr2C1
(2)
Br 3BBr2CI = 2BBr3 + BCI~
(3)
BBr~CI could also participate as a reactant in step (2). Repetition of step (2) when X = C1 could lead to TeBr4. In view of the reported precipitation of TeCI3+BCI4 - in the reaction of TeCI4 and BCI3 in benzene [15] it might be anticipated that an analogous bromide species would be obtained from the TeBr4BBr3 system. That no reaction occurs, either in benzene solution or in the absence of solvent, may reflect a significantly lower lattice energy for a tetrabromoborate relative to TeBr4. A c k n o w l e d g e m e n t - The authors are grateful to the National Science Foundation for financial support of this work under grant GP-6189. Department o f Chemistry University o f Massachusetts Amherst, Massachusetts, U.S..4. 5. 6, 7. 8. 9. 10. 11. 12. 13. 14. 15.
M I N G T. C H E N J O H N W. G E O R G E
M. F. Lappert and B. Prokai, J. chem. Soc. (A) 129 (I 967). P.M. Druce, M. F. Lappert, and P. N. K. Riley, Chem. Commun. 486 (1967). B. Buss and B. Krebs, lnorg. Chem. 10, 2795 (1971). G. D. Christofferson, R. A. Sparks, and J. D. McCullough, Acta Crystallogr. 11, 782 (1958). I. R. Beattie and H. Chudzynska, J. chem. Soc. (A) 984 (1967). D. A. Couch, P. S. Elmes, J. E. Fergusson, M. L. Greenfield and C. J. Wilkins, J. chem. Soc. (A) 1813 (1967). N. N. Greenwood, B. P. Straughn and A. E. Wilson, J. chem. Soc. (A) 2209 (1968). N. Katsaros and J. W. George, lnorg. Chim..4eta 3, 165 (1969). I. R. Beattie, P. J. Jones and M. Webster, J. chem. Soc. (A) 218 (1969). I. R. Beattie, R. R. Horder and P. J. Jones, J. chem. Soc. (A) 329 (1970). R. C. Paul, K. K. Paul and K. C. Malhotra,.4ustr. J. Chem. 22, 847 (1969).