- Email: [email protected]
The facile cleavage of methyl groups from tetramethylsilane by antimony(V) chloride
3982
Notes
2"3--
2"1
,.9 I -
I
~
P.7
I
1.5
1"3--
OI - -
~%
I 32
I 3~
I 36
I 38
I ~o
i0 3
"kFig. 2. Log of line broadening against reciprocal temperature for 3,5-dimethyl pyridine exchange in CHCI3. Q Experimental points. Theoretical curve. line broadening versus the inverse of the absolute temperature was linear and gave an apparent activation energy of-2.8_+0.2kcal/mole. In methylene chloride the line broadenings were the same as in carbon tetrachloride within experimental error for equal values of PM for the two solutions. Since this base formed an adduct the exchange rate was too fast to measure by this method. The fast rate of exchange for DMSO as compared to 4-methyl pyridine may reflect the difference in the enthalpies of adduct formation for these two bases. The enthalpy of Reaction (l) is given by AH = AHar-- 1/3 AHp where AH~ is the enthalpy change for adduct formation and AHp is the enthalpy change for forming the trimer and was found[3] to be - 2 . 2 8 kcal/mole adduct for DMSO and -14.06 kcal/mole adduct for 4-methyl pyridine.
Department of Chemistry University of Minnesota Minneapolis, Minnesota 55455 U.S.A. J. inorg, nucl. Chem., 1971, Vol. 33, pp. 3 9 8 2 - 3 9 8 4 .
M A T T H E W J. P E T R I N W A R R E N L. R E Y N O L D S
Pe rgamon Press.
Printed in G r e a t Britain
The facile cleavage of methyl groups from tetramethylsilane by antimony(V) chloride (Received 8 April 1971) SEVERAL anhydrous metal chlorides have been reported to cleave unsubstituted alkyl groups from tetraalkylsilicon compounds according to Equation (1):
Notes R4Si -[- MCI,, "-'->R:~SiCI+ RMCI,, ,
3983 ( 1)
where M = AI(II1)[1], Ga(l l l) [2], Sb(V)[3], Bi(lll)[4], Hg(ll)[5], or Fe(lll)[1,3]. However, the authenticity of some of these reports has been called into question[6]. The observed cleavage of (CzH.~hSi in the presence of AICI:,, for example, is believed to have been caused not by the anhydrous metal halide alone but instead by the presence of moisture and/or HC1 and thus of the strong acid HAICI.,: (C.,HD4Si + HCI(+ AICI3) ~ (CzH.0:3SiCI+ C2H6.
(2)
This conclusion is supported by the fact that under rigorous anhydrous conditions AICI3 does not cleave even phenyl-silicon bonds [7], which are, in general, more reactive toward electrophilic reagents than are alkyl-silicon bonds. The claims that alkyl groups are cleaved from silicon by BiCI3 and FeCI:~ are also questionable based on similar grounds [6]. The reported cleavages of alkyl groups from silicon by GaCI.~, HgClz, and SbCI5 all appear to be genuine, although the reported ability of SbClz to cleave phenyl groups from (C~H5)2SiC1218] has been accepted with some reservation[6]. Nevertheless, among these latter three chlorides only GaC13 is known to give a clean reaction and high yields under mild reaction conditions. Only 15 per cent cleavage of (C2H5)4Si according to Reaction ( 1) occurs with HgCI2 after a reaction time of 2 hr at 140-150 ° [5], and between 50 and 100 per cent cleavage of one alkyl group from (CzHs)(CH3)3Si has been estimated to occur with SbCI~ after 24 hr at 100°C. In the course of conducting NMR studies of some organoantimony(V) complexes, we have found that SbCL very readily cleaves methyl groups from (CH3)4Si at room temperature. The reaction suggests that cleavage of silicon-carbon bonds by SbCI5 is much more facile than had been previously supposed and that SbCI.~ may have considerable synthetic utility in systems where it would be desireable to cleave such bonds under mild reaction conditions. Moreover. it is an example of a facile reaction between a common diamagnetic Lewis acid and a widely used NMR reference compound that is normally regarded as being chemically inert. RESULTS AND DISCUSSION When (CH3hSi and SbCI~ in dry dichloromethane solution are mixed in equimolar amounts under anhydrous conditions at room temperature, Reaction (3) proceeds quantitatively (> 98% yield): (CH3hSi + SbCI.~ ~ (CH3)3SiCI + CH:3C1+ SbCI:~.
(3 )
At initial (CHD,Si and SbC15 concentrations of 0.60M the reaction is complete in less time than is required to record the NMR spectrum of the mixture (ca. 1 rain). The same reaction also occurs in carbon tetrachloide under similar conditions, except that ca. 15 min is required for complete reaction at 38° in this nonpolar solvent. The identities of CH3C1 and (CH:~)3SiCI were verified by comparison of their N M R chemical shifts to those of authentic samples of the compounds in the same solvent. SbCI.~ was isolated by vacuum distillation of the solvent and volatile products and was identified by chlorine analysis and a melting point determination. The cleavage of a methyl group from (CH3)~SiCI can also be accomplished quantitatively with SbCI5 in dichloromethane at room temperature: (CHD.~SiCI + SbCI5 --~ (CH3)2SiC12 + CH.~CI + SbCI:~.
(4)
I. Z. M. Manulkin, Zh. obsch. Khim. 18,299 (1948). 2. H. Schmidbaur and W. Findeiss, Angew. Chem. intern, ed. 3. 696 (1964); idem. Chem. Ber. 99. 2187 (1966). 3. G. A . Russell, J . A m . chem. Soc. 81, 4815 (1959). 4. Z. M. Manulkin, Zh. obsch. Khim. 20, 2004 (1950). 5. Z. M. Manulkin, Zh. obsch. Khim. 16, 235 (1946). 6. C. Eaborn and R. W. Bott, In Organometallic Compounds o f the Group I V Elements (Edited by A. G. MacDiarmid), Vol. 1. pp. 363,429. Marcel Dekker, New York (1968). 7. J. D. Austin, C. Eaborn and J. D. Smith, J. chem. Soc. 4744 (1963). 8. A. Ya. Yakubovich and G. V. Motsarev, Zh. obsch. Khim. 23, 1414 (1953).
3984
Notes
However, the reaction is considerably slower than that observed for (CHa)4Si. A reaction half-life of the order of 1 hr was observed at 38 ° for a 1-3M (CH3hSiCI solution containing a nine-fold excess of SbCIs. No reaction was observed between (CH3)2SiClz and SbCI5 in dichloromethane after 2 days at room temperature. Thus the rate of methyl group replacement decreases markedly in the order (CH3)4Si > (CH3)3SiCI > (CH3)zSiCIz, as expected for electrophilic attack at carbon, and the stepwise cleavage of two methyl groups from (CH3)4Si can be readily achieved. The quantitative yields of CH3C1 and SbCla in Reactions (3) and (4) may result from the formation of (CHa)SbCh, perhaps via the often postulated four-center mechanism for alkyl group-halogen interchange, and subsequent disproportionation of this organoantimony(V) species:
/ R4Si + SbCI5 ~ R3Si
\
R
\ /
SbC4 --~ R3SiC1 + [RSbC14]
(5)
CI [RSbCI4] ~ RCI + SbC13.
(6)
No N M R evidence for the appearance of CH3SbCI4 was detected in any of the reaction mixtures, but none might be expected under the reaction conditions employed. Coates [9] reports that CHaSbCI4 appears to be formed at low temperatures from CHzSbCI2 and C12 but decomposes very readily to CH3CI and SbCI3. It may be possible to detect and isolate CH3SbCI4 by reaction of (CH3)4Si and SbCI5 in dichloromethane at low temperatures. The selectivity of SbCI5 in cleaving different alkyl groups from silicon at roomtemperature remains to be investigated. It is noteworthy, however, that Russell [3] has reported observing cleavage of both methyl and ethyl groups in a 2 : 1 ratio from (C2Hs)(CH3)3Si with SbCI5 at 100° after 24 hr. If it is assumed that no redistribution of alkyl groups occurs between (C2Hs)(CH3hSiCI and CH3CI in the presence of SbC13 under the reaction conditions employed, then this result suggests that SbCI5 may have limited selectivity in cleaving alkyl groups from mixed organosilanes. Electronic effects would be expected to favor ethyl group rather than methyl group cleavage, but steric factors normally predominate in electrophilic cleavages of alkyl groups from silicon. GaCI3, for example, cleaves mostly methyl groups from (CzHs)(CHa)3Si, although a detectable amount of ethyl group cleavage also occurs [2].
Acknowledgement-Partial support of this work by National Science Foundation Grant GP-9503 is gratefully acknowledged.
Department of Chemistry Michigan State University East Lansing, Mich. 48823
T H O M A S J. P I N N A V A I A LUIS J. M A T I E N Z O
9. C. E. Coates, M. L. H. Green and K. Wade, Organometallic Compounds Vol. 1. p. 525. Methuen, London (1967).
J. inorg,nucl.Chem., 1971.Vol. 33, pp. 3984-3988. PergamonPress. Printedin Great Britain
Dioxouranium(VI) complexes of some acylhydrazines (First received 19 November 1970; in revised form 28 December 1970) INTRODUCTION
DIOXOURANIUM(VI)complexes of acylhydrazines such as acetylhydrazine (AH), benzoylhydrazine (BH), salicyloyl hydrazine (SH), acetylbenzoyl hydrazine (ABH), diacetyl hydrazine (DAH) and diformylhydrazine (DFH) of the types, UO~(NO3)22L'2HzO and UO2(NO3)z'2L (L = BH, DAH, SH, ABH), UO2(NO3)2"3AH, UOzClz.3BH and UO~(DFH-2H) have been prepared and their physical properties studied. Molar conductance and infrared studies indicate the presence of coordinated nitrate in the complexes.
Notes
2"3--
2"1
,.9 I -
I
~
P.7
I
1.5
1"3--
OI - -
~%
I 32
I 3~
I 36
I 38
I ~o
i0 3
"kFig. 2. Log of line broadening against reciprocal temperature for 3,5-dimethyl pyridine exchange in CHCI3. Q Experimental points. Theoretical curve. line broadening versus the inverse of the absolute temperature was linear and gave an apparent activation energy of-2.8_+0.2kcal/mole. In methylene chloride the line broadenings were the same as in carbon tetrachloride within experimental error for equal values of PM for the two solutions. Since this base formed an adduct the exchange rate was too fast to measure by this method. The fast rate of exchange for DMSO as compared to 4-methyl pyridine may reflect the difference in the enthalpies of adduct formation for these two bases. The enthalpy of Reaction (l) is given by AH = AHar-- 1/3 AHp where AH~ is the enthalpy change for adduct formation and AHp is the enthalpy change for forming the trimer and was found[3] to be - 2 . 2 8 kcal/mole adduct for DMSO and -14.06 kcal/mole adduct for 4-methyl pyridine.
Department of Chemistry University of Minnesota Minneapolis, Minnesota 55455 U.S.A. J. inorg, nucl. Chem., 1971, Vol. 33, pp. 3 9 8 2 - 3 9 8 4 .
M A T T H E W J. P E T R I N W A R R E N L. R E Y N O L D S
Pe rgamon Press.
Printed in G r e a t Britain
The facile cleavage of methyl groups from tetramethylsilane by antimony(V) chloride (Received 8 April 1971) SEVERAL anhydrous metal chlorides have been reported to cleave unsubstituted alkyl groups from tetraalkylsilicon compounds according to Equation (1):
Notes R4Si -[- MCI,, "-'->R:~SiCI+ RMCI,, ,
3983 ( 1)
where M = AI(II1)[1], Ga(l l l) [2], Sb(V)[3], Bi(lll)[4], Hg(ll)[5], or Fe(lll)[1,3]. However, the authenticity of some of these reports has been called into question[6]. The observed cleavage of (CzH.~hSi in the presence of AICI:,, for example, is believed to have been caused not by the anhydrous metal halide alone but instead by the presence of moisture and/or HC1 and thus of the strong acid HAICI.,: (C.,HD4Si + HCI(+ AICI3) ~ (CzH.0:3SiCI+ C2H6.
(2)
This conclusion is supported by the fact that under rigorous anhydrous conditions AICI3 does not cleave even phenyl-silicon bonds [7], which are, in general, more reactive toward electrophilic reagents than are alkyl-silicon bonds. The claims that alkyl groups are cleaved from silicon by BiCI3 and FeCI:~ are also questionable based on similar grounds [6]. The reported cleavages of alkyl groups from silicon by GaCI.~, HgClz, and SbCI5 all appear to be genuine, although the reported ability of SbClz to cleave phenyl groups from (C~H5)2SiC1218] has been accepted with some reservation[6]. Nevertheless, among these latter three chlorides only GaC13 is known to give a clean reaction and high yields under mild reaction conditions. Only 15 per cent cleavage of (C2H5)4Si according to Reaction ( 1) occurs with HgCI2 after a reaction time of 2 hr at 140-150 ° [5], and between 50 and 100 per cent cleavage of one alkyl group from (CzHs)(CH3)3Si has been estimated to occur with SbCI~ after 24 hr at 100°C. In the course of conducting NMR studies of some organoantimony(V) complexes, we have found that SbCL very readily cleaves methyl groups from (CH3)4Si at room temperature. The reaction suggests that cleavage of silicon-carbon bonds by SbCI5 is much more facile than had been previously supposed and that SbCI.~ may have considerable synthetic utility in systems where it would be desireable to cleave such bonds under mild reaction conditions. Moreover. it is an example of a facile reaction between a common diamagnetic Lewis acid and a widely used NMR reference compound that is normally regarded as being chemically inert. RESULTS AND DISCUSSION When (CH3hSi and SbCI~ in dry dichloromethane solution are mixed in equimolar amounts under anhydrous conditions at room temperature, Reaction (3) proceeds quantitatively (> 98% yield): (CH3hSi + SbCI.~ ~ (CH3)3SiCI + CH:3C1+ SbCI:~.
(3 )
At initial (CHD,Si and SbC15 concentrations of 0.60M the reaction is complete in less time than is required to record the NMR spectrum of the mixture (ca. 1 rain). The same reaction also occurs in carbon tetrachloide under similar conditions, except that ca. 15 min is required for complete reaction at 38° in this nonpolar solvent. The identities of CH3C1 and (CH:~)3SiCI were verified by comparison of their N M R chemical shifts to those of authentic samples of the compounds in the same solvent. SbCI.~ was isolated by vacuum distillation of the solvent and volatile products and was identified by chlorine analysis and a melting point determination. The cleavage of a methyl group from (CH3)~SiCI can also be accomplished quantitatively with SbCI5 in dichloromethane at room temperature: (CHD.~SiCI + SbCI5 --~ (CH3)2SiC12 + CH.~CI + SbCI:~.
(4)
I. Z. M. Manulkin, Zh. obsch. Khim. 18,299 (1948). 2. H. Schmidbaur and W. Findeiss, Angew. Chem. intern, ed. 3. 696 (1964); idem. Chem. Ber. 99. 2187 (1966). 3. G. A . Russell, J . A m . chem. Soc. 81, 4815 (1959). 4. Z. M. Manulkin, Zh. obsch. Khim. 20, 2004 (1950). 5. Z. M. Manulkin, Zh. obsch. Khim. 16, 235 (1946). 6. C. Eaborn and R. W. Bott, In Organometallic Compounds o f the Group I V Elements (Edited by A. G. MacDiarmid), Vol. 1. pp. 363,429. Marcel Dekker, New York (1968). 7. J. D. Austin, C. Eaborn and J. D. Smith, J. chem. Soc. 4744 (1963). 8. A. Ya. Yakubovich and G. V. Motsarev, Zh. obsch. Khim. 23, 1414 (1953).
3984
Notes
However, the reaction is considerably slower than that observed for (CHa)4Si. A reaction half-life of the order of 1 hr was observed at 38 ° for a 1-3M (CH3hSiCI solution containing a nine-fold excess of SbCIs. No reaction was observed between (CH3)2SiClz and SbCI5 in dichloromethane after 2 days at room temperature. Thus the rate of methyl group replacement decreases markedly in the order (CH3)4Si > (CH3)3SiCI > (CH3)zSiCIz, as expected for electrophilic attack at carbon, and the stepwise cleavage of two methyl groups from (CH3)4Si can be readily achieved. The quantitative yields of CH3C1 and SbCla in Reactions (3) and (4) may result from the formation of (CHa)SbCh, perhaps via the often postulated four-center mechanism for alkyl group-halogen interchange, and subsequent disproportionation of this organoantimony(V) species:
/ R4Si + SbCI5 ~ R3Si
\
R
\ /
SbC4 --~ R3SiC1 + [RSbC14]
(5)
CI [RSbCI4] ~ RCI + SbC13.
(6)
No N M R evidence for the appearance of CH3SbCI4 was detected in any of the reaction mixtures, but none might be expected under the reaction conditions employed. Coates [9] reports that CHaSbCI4 appears to be formed at low temperatures from CHzSbCI2 and C12 but decomposes very readily to CH3CI and SbCI3. It may be possible to detect and isolate CH3SbCI4 by reaction of (CH3)4Si and SbCI5 in dichloromethane at low temperatures. The selectivity of SbCI5 in cleaving different alkyl groups from silicon at roomtemperature remains to be investigated. It is noteworthy, however, that Russell [3] has reported observing cleavage of both methyl and ethyl groups in a 2 : 1 ratio from (C2Hs)(CH3)3Si with SbCI5 at 100° after 24 hr. If it is assumed that no redistribution of alkyl groups occurs between (C2Hs)(CH3hSiCI and CH3CI in the presence of SbC13 under the reaction conditions employed, then this result suggests that SbCI5 may have limited selectivity in cleaving alkyl groups from mixed organosilanes. Electronic effects would be expected to favor ethyl group rather than methyl group cleavage, but steric factors normally predominate in electrophilic cleavages of alkyl groups from silicon. GaCI3, for example, cleaves mostly methyl groups from (CzHs)(CHa)3Si, although a detectable amount of ethyl group cleavage also occurs [2].
Acknowledgement-Partial support of this work by National Science Foundation Grant GP-9503 is gratefully acknowledged.
Department of Chemistry Michigan State University East Lansing, Mich. 48823
T H O M A S J. P I N N A V A I A LUIS J. M A T I E N Z O
9. C. E. Coates, M. L. H. Green and K. Wade, Organometallic Compounds Vol. 1. p. 525. Methuen, London (1967).
J. inorg,nucl.Chem., 1971.Vol. 33, pp. 3984-3988. PergamonPress. Printedin Great Britain
Dioxouranium(VI) complexes of some acylhydrazines (First received 19 November 1970; in revised form 28 December 1970) INTRODUCTION
DIOXOURANIUM(VI)complexes of acylhydrazines such as acetylhydrazine (AH), benzoylhydrazine (BH), salicyloyl hydrazine (SH), acetylbenzoyl hydrazine (ABH), diacetyl hydrazine (DAH) and diformylhydrazine (DFH) of the types, UO~(NO3)22L'2HzO and UO2(NO3)z'2L (L = BH, DAH, SH, ABH), UO2(NO3)2"3AH, UOzClz.3BH and UO~(DFH-2H) have been prepared and their physical properties studied. Molar conductance and infrared studies indicate the presence of coordinated nitrate in the complexes.