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Reactions of metallocenes with potassium and potassium amide in liquid ammonia
J. Inorg, Nucl. Chem., 1964, Vol. 26, pp. 2099 to 2102. PergamonPre~ Ltd. Printed in Northern Ireland
REACTIONS OF METALLOCENES WITH POTASSIUM AND POTASSIUM AMIDE IN LIQUID AMMONIA G. W. WATT and L. J. BAYE Department of Chemistry, The University of Texas, Austin, Texas
(Received 22 April 1964) Abstract--Both (CsHs)2Fe and (CsHs)~Ni are soluble in fiquid ammonia at --33-5 ° but show no evidence of formation of stable ammoniates; (CsHs)2Cr however forms 9- and 4-ammoniates. Both (CsHs)2Fe and (CsH~)2Ni are unreactive toward ammonia solutions of potassium amide at -- 33.5 °; (C6H6)~Cr reacts to form CrN. All three metallocenes are reduced to the metals by solutions of potassium in ammonia at - 3 3 . 5 ° without evidence for reduction to species in which the metal is in the formal 1 + oxidation state. The validity of Fischer and Wilkinson's reported synthesis of (CsHs)~Ti is questioned.
DIVERGENTviews with regard to the character of the bonding in ferrocene and certain of its analogues,tl'z) work relating to the effective charge on the central metal atoms in metallocenes,ts'a~ and evidence for the existence of iron in the 1+ oxidation state tS'6J made it of interest to study, by potentiometric titrations, reactions between metallocenes and liquid ammonia solutions of an alkali metal. If an ionic model for bis-cyclopentadienyl compounds of transitional metals is considered t1'~'7~ it is conceivable that they could be reduced to species in which the metal is in the formal 1 q- oxidation state. In order to detect possible complications arising from reactions of amide ion, the corresponding reactions with potassium amide in ammonia were studied. Observations relative to the formation of ammoniates were also recorded. At --33-5, (CsHs)~Fe and (CsHs)2Ni are soluble in liquid ammonia; upon evaporation of the solvent, these two metallocenes are recovered unassociated with solvent molecules. WILKINSONet al. ts~ reported that (CsHs)2Cr forms blue and lavender ammoniates at low temperatures and a salmon-pink ammoniate that is stable up to 75°; none of these solvates was characterized. The present studies show that blue (CsHs)~Cr'9NHa is stable from--50 t o - - 3 6 °, loses ammonia over the interval --36 to --32 ° to form lavender (CsHs)2Cr'4NH3 which is stable up to --20 ° and is completely deammoniated over the range --20 to --15 °. The supposedly room-temperature-stable salmon-pink ammoniate has been shown to consist of finely divided (CsHs)2Cr. ~1~H. M. McCONNELL and R. E. ROBERTSON, J. Phys. Chem. 64, 70 (1960). c2~ R. S. BECKER and D. R. SCOTT, J. Chem. Phys. 35, 516 (1961). ~81E. M. SHUSTOROVlCHand M. E. DYATmNA, Dokl. Akad. Nauk. SSSR 131, 113 (1960); Zh. Neorg. Khim. 6, 1247 (1961). t41 S. S. BATSANOV,lZV. Sibirsk. Otd. Akad. Nauk SSSR 110 (1962). ~5~E. O. FISCHER and F. ROEHRSCHEID, Z. Naturforsch. 17b, 483 (1962). ~6~H. B. GRAY, I. BERNAL and E. BILLIO, J. Amer. Chem. Soc. 84, 3404 (1962). c7) F. A. MATSEN, J. Amer. Chem. Soc. 81, 2023 (1959). ~8) G. WILFaNSON, F. A. COTTON and J. M. BIRM~OHAM, J. lnorg. Nucl. Chem. 2, 95 (1956). 2099
2100
G.W. WATT and L. J. BAYE
Both (CsHs)2Fe and (CsHs)2Ni were found to be unreactive toward ammonia solutions of potassium amide. Chromocene, however, reacted as follows, (C5Hs)~Cr + 2 N H z - ~ Cr(NH2)2 + 2CsHsCr(NH2)2 ~ C r N + N H 3 + ½H2 Potentiometric titration curves gave no evidence for the intermediation of (CsHs) Cr(NH2). Potentiometric titration data and supporting evidence given below for reactions of these three metallocenes with solutions of potassium in ammonia show evidence only for two-electron reductions, (CsHs)2M + 2K + + 2e- --+ M + 2KCsH 5 Changes in potential at a 1 : 1 equivalence ratio were not observed in any case, hence there is no evidence for a one-electron reduction step. It was originally intended to include (CsHs)2Ti in the present studies and to prepare it by the method of FISCHER and WILKINSON.(9) However, we have been unable to produce (C~H5)2Ti by their procedure, by any modification thereof, or by other methods that might reasonably be expected to provide this compound. It is not entirely clear whether FISCHER and WILKINSON used pure TIC12 in reaction with N a C s H 5 or a mixture containing 35 ~ TiCIs and 65 ~ TiCI2. In our efforts to reproduce this result we have used pure TiC12, pure TiCI3, a 35-65 ~ mixture of independently prepared TiCI 3 and TiC12, and a mixture of approximately the same composition co-formed by hydrogen reduction of TiCla. The only pure product that could be isolated was (CsHn)2TiC1. It seems significant that (a) to our knowledge, the FISCHER and WILKINSON synthesis of (C5Hs),Ti has not been confirmed, (b) their published analytical data are marginal, and (c) except for a molecular orbital interpretation c1°) of the structure of (CsHs)2Ti, its reported diamagnetism ~9)remains anomalous. We therefore conclude that the titanium analogue of ferrocene remains to be synthesized; several new approaches to the synthesis of this compound are under consideration. EXPERIMENTAL Materials and Methods
With the exceptions that follow, reagent grade chemicals and standard analytical procedures were employed. Reactions in liquid ammonia were carried out using equipment described elsewhere.~n-ls) Cyclopentadienide ion was determined by a method described elsewhere.~1.~ All of the titanium chlorides were generously supplied by the Pigments Dpartment, E. I. du Pont de Nemours & Co. Ferrocene was prepared by the method of ISSLHBand BRACK.~15~ (Found: Fe, 29.9. Cale. for C~0Hx0Fe: Fe, 30.0~.) Chromocene was prepared as described by WILKINSON.~16~(Found: Cr, 28.5. Calc. for C10H~0Cr: Cr, 28"6%.) All operations involving chromocene were carried out in a helium atmosphere in a dry box in which the integrity of the atmosphere was insured by the presence of a large ~'~ A. K. FISCHERand G. WILKINSON,ar. lnorg. Nucl. Chem. 2, 149 (1956). tx0~W. MOrrITT,J. Amer. Chem. Soc. 76, 3386 (1954). ¢m G. W. WATTand R. J. THOMPSON,Or. Inorg. NacL Chem. 9, 311 (1959). t~ G. W. WATTand J. B. OTTO,Jr., J. Electrochem. Soe. 98, 1 (1951). ,~3~G. W. WATTand D. M. SOWARDS,Or. Electrochem. Soc. 102, 545 (1955). c~4~G. W. WATTand L. J. BA'rE,3". lnorg. NucL Chem. 26, 1531 (1964). cls~K. ISSLEIBand A. BRACK,Z. Naturforsch. lib, 420 (1956). u6J G. WILKINSON,J. Amer. Chem. Soc. 76, 209 (1954).
Reactions of metallocenes with potassium and potassium amide in liquid ammonia
2101
exposed surface of liquid Na-K alloy. Nickelocene was prepared by an established method. (8> (Found: Ni, 30.9. Calc. for Cx0H10Ni: Ni, 31"1%.) Biscyclopentadienyltitanium (IV) chloride was prepared using the procedure of WILKINSON and BI~iINOHAM.(~7) (Found: Ti, 19.2; C1, 28-6. Calc. for Cx0H~0TiCl,: Ti, 19.3; C1, 28"6~.) X-ray diffraction data for (C~Hs)~M where M = Cr, Fe, Ni are given in Table 1.
Attempted synthesis of titanocene Titanium (II) chloride and NaCsHs were brought together under the conditions described by FISCHERand WILKINSON;(~) there was no evidence of reaction after 24 hr at 26 °. Following removal of the solvent under reduced pressure, an X-ray diffraction pattern identified unreacted TIC12 and NaCsHs but not NaC1. The residue was leached with tetrahydrofuran; a black residue remained. (Found: Ti, 40.3; C1, 59"8. Calc. for TiCI~: Ti, 40"3 ; C1, 59'7 %.) Evaporation of the tetrahydrofuran left a white solid. (Found: C5H5-, 73"9. Calc. for NaCsHs: C5H5-, 74.0 %.) TABLE 1 . - - X - R A Y DIFFRACTION DATA FOR
(CsHs)2Cr
(CsH6)~Fe
(CsHs)~M* (CsHs)~Ni
d,A
l/t0
d,A
IHo
d,A
I/lo
6.05 5.13 4.78 4.17 3.99 3.63
1.00 0-90 0-70 0.50 0.50 0-40?
5.88 5.16 4.71 4-10 3.69 2.56
0.40 1.00 0.10 0.10 0.10 0.05?
5.95 5.11 4.71 3.96 3.66 1.92
0-70 1.00 0.40 0.40 0.40 0-30?
* Cu K~ radiation, Ni filter, 35 kv tube voltage, 15 ma filament current, 4-12 hr exposure time, relative intensities estimated visually. ? Less intense lines not included here. The foregoing procedure was repeated except that a mixture of 65 % TiCI2 and 35 % TIC18 was used. The tetrahydrofuran assumed a green color over a period of 3 hr; thereupon, the solvent was removed under reduced pressure and the residue was extracted with petroleum ether to give a green solution. An X-ray diffraction pattern for the petroleum ether-insoluble residue showed the presence of TiCI2, NaCsHs, and NaC1, but not TiCI~. Evaporation of the petroleum ether solution yielded dark green microcrystals. (Found: Ti, 22.6; C1, 16.4. Calc. for C10Hx0TiCl: Ti, 22.3; C1, 16.6%.) Attempts to sublime this product under reduced pressure (a) resulted only in decomposition. When a sample of the original reaction mixture (in tetrahydrofuran) was exposed to the atmosphere, red crystals of (CsHs)2TiCI~ separated and were identified by an X-ray diffraction pattern. When the foregoing procedures failed to provide (CsHs)~Ti, the experiment was repeated using a co-formed mixture of TiClz and TiCls of about the same composition indicated above; the results were substantially the same. In similar experiments, use of pure TIC13 also resulted in the formation of (CsHs)2TiCI. (Found : Ti, 22.4; C1, 16-6. Calc. for CtoHx0TiCl: Ti, 22.3; C1, 16.6%.) Other variables in the procedure of FISCHER and WILKINSONwere studied, but without success. In other unsuccessful attempts to produce (CsHs),Ti, the following reactions (in tetrahydrofuran unless otherwise indicated) were investigated: (1) Reduction of (CsHs)2TiC12 with LiA1H,, (18) Na2S,O4, and NaH,POs. (2) Reduction of (CsHs)~TiC1 with LiAIH, and with potassium in liquid ammonia. (3) The interaction of TiCI2 and C~H6 in diethylamine.
Reactions with ammonia A 0"1285 g sample of (CsHs)~Fe was dissolved in excess anhydrous liquid ammonia and stirred for 80 hr. There was no evidence of reation. Evaporation of the solvent left an orange coloured c17) G. WILKINSONand J. M. BIRMINGHAM,J. Amer. Chem. Soc. 76, 4281 (1954). (ls~ j. M. BIRMINGHAM,A. K. FISCHERand G. WILKINSON,Naturwissenschaften 42, 96 (1955).
2102
G . W . WATT and L. J. BAX,~
residue that gave an X-ray diffraction pattern that led to data identical with those listed for ferrocene in Table 1. When 0.0725 g of (CsH~)sNi was stirred with a large excess of liquid ammonia for 36 hr, there was no evidence of reaction; the green residue remaining after volatilization of the solvent gave X-ray diffraction data in excellent agreement with those given for nickelocene in Table 1. Condensation of excess liquid ammonia on 0.8201 g of (CsH6)2Cr at --50 °, resulted in the formation of a pale blue ammoniate. At --50 ° the liquid ammonia was pumped offand the pressure was reduced to ca. 10-3 mm. The blue solid remained unchanged and there was no change in pressure over 2 hr. The temperature was raised to --36 °, whereupon evolution of NH8 began and continued up to --32 °, where the colour of the solid phase changed from pale blue to deep lavender. In three separate experiments employing different weights of (CsHs)2Cr, the NH3 evolved over the range --36 to --32 ° was removed with a Toepler pump and measured; the resulting NHs/(CsH~)2Cr ratios were 9.02, 8.98 and 8.90. When the temperature .was further increased, NHs evolution occurred over the range --20 to --15°; at the latter temperature the colour of the solid changed from deep lavender to salmon pink. The NH~/(CsH~)~Cr ratios over the interval --20 to --15 ° were 3.99, 4.02 and 3.95. Further NHs evolution did not occur when the solid was heated from - 1 5 ° to room temperature; a sample of the salmon-pink solid gave an X-ray diffraction pattern substantially identical with that for chromocene (Table 1). (Found: Cr, 28'4. Calc. for CaoH10Cr: Cr, 28.6%.) When this product was heated to 75 °, its colour changed to ruby red, withoutgas evolution; this solid also was identified as chromocene by its X-ray diffraction pattern.
Reactions with potassium amide There was no evidence of reaction when 0-0859 g of ferrocene in 50 ml of ammonia was titrated potentiometrically with the potassium amide formed catalytically from 0"1146 g of potassium in 30.4 ml of ammonia. Following evaporation of the solvent, ferrocene was recovered unchanged and identified by its X-ray diffraction pattern (Table 1). Similarly, titration of 0.0826 g of nickelocene in 75 ml of ammonia with 0.1025 Mpotassium amide solution resulted in neither change in potential nor visual evidence of reaction; nickelocene was recovered unchanged and identified via its X-ray diffraction pattern (Table 1). When 0.1838 g of chromocene in 75 ml of ammonia was titrated with 0.1220 M potassium amide solution, the potential remained essentially constant until 2 molar equivalents of the amide solution had been added. Thereupon, the potential increased sharply by ca. 800 mV and the lavender ammoniate was replaced completely by a gelatinous brown-black solid. By digestion for 3 hr at --33.5 °, the latter changed to a granular solid, which was separated by filtration and washed three times with 50ml portions of ammonia. (Found: Cr, 78.6; N, 21.4. Calc. for CrN: Cr, 78.7; N, 21"3~o.) This product did not give a useful X-ray diffraction pattern. During the course of the reaction (including the digestion period), 1.02 milliequivalents of hydrogen was collected. The presence of KCsH5 in the residue from the combined supernatant solution and washings was confirmed by an X-ray diffraction pattern, t14~ A total of 128.0 mg of C5H5- was recovered t14~as compared with 131.3 nag used as (CsHs)2Cr. Reactions with potassium In separate experiments, 0"0776 g of (C~H~)2Fe, 0.0812 g of (CsHs)~Ni, and 0-2054 g of (CsHs)2Cr-each in 75 ml of ammonia--were titrated potentiometrically with solutions of potassium in ammonia that were 0.1362, 0.1002 and 0.1350 M, respectively. In all three cases, black precipitates formed progressively and the potentials remained essentially constant until almost exactly 2 molar equivalents of potassium solution was added; thereupon increases in potential of several hundred millivolts were recorded. The black precipitates were washed four times with 50 ml portions of ammonia and shown to consist of the corresponding metals by X-ray diffraction patterns and by analysis (e.g., Found: Fe, 99"5 %.) After evaporation of the solvent from the combined supernatant solution and washings, KCsH~ was identified by X-ray diffraction patterns and CsHs- was recovered (98-99 %) by the method previously described, c14~ Acknowledgment--This work was supported by The Robert A. Welch Foundation and The United States Atomic Energy Commission.
REACTIONS OF METALLOCENES WITH POTASSIUM AND POTASSIUM AMIDE IN LIQUID AMMONIA G. W. WATT and L. J. BAYE Department of Chemistry, The University of Texas, Austin, Texas
(Received 22 April 1964) Abstract--Both (CsHs)2Fe and (CsHs)~Ni are soluble in fiquid ammonia at --33-5 ° but show no evidence of formation of stable ammoniates; (CsHs)2Cr however forms 9- and 4-ammoniates. Both (CsHs)2Fe and (CsH~)2Ni are unreactive toward ammonia solutions of potassium amide at -- 33.5 °; (C6H6)~Cr reacts to form CrN. All three metallocenes are reduced to the metals by solutions of potassium in ammonia at - 3 3 . 5 ° without evidence for reduction to species in which the metal is in the formal 1 + oxidation state. The validity of Fischer and Wilkinson's reported synthesis of (CsHs)~Ti is questioned.
DIVERGENTviews with regard to the character of the bonding in ferrocene and certain of its analogues,tl'z) work relating to the effective charge on the central metal atoms in metallocenes,ts'a~ and evidence for the existence of iron in the 1+ oxidation state tS'6J made it of interest to study, by potentiometric titrations, reactions between metallocenes and liquid ammonia solutions of an alkali metal. If an ionic model for bis-cyclopentadienyl compounds of transitional metals is considered t1'~'7~ it is conceivable that they could be reduced to species in which the metal is in the formal 1 q- oxidation state. In order to detect possible complications arising from reactions of amide ion, the corresponding reactions with potassium amide in ammonia were studied. Observations relative to the formation of ammoniates were also recorded. At --33-5, (CsHs)~Fe and (CsHs)2Ni are soluble in liquid ammonia; upon evaporation of the solvent, these two metallocenes are recovered unassociated with solvent molecules. WILKINSONet al. ts~ reported that (CsHs)2Cr forms blue and lavender ammoniates at low temperatures and a salmon-pink ammoniate that is stable up to 75°; none of these solvates was characterized. The present studies show that blue (CsHs)~Cr'9NHa is stable from--50 t o - - 3 6 °, loses ammonia over the interval --36 to --32 ° to form lavender (CsHs)2Cr'4NH3 which is stable up to --20 ° and is completely deammoniated over the range --20 to --15 °. The supposedly room-temperature-stable salmon-pink ammoniate has been shown to consist of finely divided (CsHs)2Cr. ~1~H. M. McCONNELL and R. E. ROBERTSON, J. Phys. Chem. 64, 70 (1960). c2~ R. S. BECKER and D. R. SCOTT, J. Chem. Phys. 35, 516 (1961). ~81E. M. SHUSTOROVlCHand M. E. DYATmNA, Dokl. Akad. Nauk. SSSR 131, 113 (1960); Zh. Neorg. Khim. 6, 1247 (1961). t41 S. S. BATSANOV,lZV. Sibirsk. Otd. Akad. Nauk SSSR 110 (1962). ~5~E. O. FISCHER and F. ROEHRSCHEID, Z. Naturforsch. 17b, 483 (1962). ~6~H. B. GRAY, I. BERNAL and E. BILLIO, J. Amer. Chem. Soc. 84, 3404 (1962). c7) F. A. MATSEN, J. Amer. Chem. Soc. 81, 2023 (1959). ~8) G. WILFaNSON, F. A. COTTON and J. M. BIRM~OHAM, J. lnorg. Nucl. Chem. 2, 95 (1956). 2099
2100
G.W. WATT and L. J. BAYE
Both (CsHs)2Fe and (CsHs)2Ni were found to be unreactive toward ammonia solutions of potassium amide. Chromocene, however, reacted as follows, (C5Hs)~Cr + 2 N H z - ~ Cr(NH2)2 + 2CsHsCr(NH2)2 ~ C r N + N H 3 + ½H2 Potentiometric titration curves gave no evidence for the intermediation of (CsHs) Cr(NH2). Potentiometric titration data and supporting evidence given below for reactions of these three metallocenes with solutions of potassium in ammonia show evidence only for two-electron reductions, (CsHs)2M + 2K + + 2e- --+ M + 2KCsH 5 Changes in potential at a 1 : 1 equivalence ratio were not observed in any case, hence there is no evidence for a one-electron reduction step. It was originally intended to include (CsHs)2Ti in the present studies and to prepare it by the method of FISCHER and WILKINSON.(9) However, we have been unable to produce (C~H5)2Ti by their procedure, by any modification thereof, or by other methods that might reasonably be expected to provide this compound. It is not entirely clear whether FISCHER and WILKINSON used pure TIC12 in reaction with N a C s H 5 or a mixture containing 35 ~ TiCIs and 65 ~ TiCI2. In our efforts to reproduce this result we have used pure TiC12, pure TiCI3, a 35-65 ~ mixture of independently prepared TiCI 3 and TiC12, and a mixture of approximately the same composition co-formed by hydrogen reduction of TiCla. The only pure product that could be isolated was (CsHn)2TiC1. It seems significant that (a) to our knowledge, the FISCHER and WILKINSON synthesis of (C5Hs),Ti has not been confirmed, (b) their published analytical data are marginal, and (c) except for a molecular orbital interpretation c1°) of the structure of (CsHs)2Ti, its reported diamagnetism ~9)remains anomalous. We therefore conclude that the titanium analogue of ferrocene remains to be synthesized; several new approaches to the synthesis of this compound are under consideration. EXPERIMENTAL Materials and Methods
With the exceptions that follow, reagent grade chemicals and standard analytical procedures were employed. Reactions in liquid ammonia were carried out using equipment described elsewhere.~n-ls) Cyclopentadienide ion was determined by a method described elsewhere.~1.~ All of the titanium chlorides were generously supplied by the Pigments Dpartment, E. I. du Pont de Nemours & Co. Ferrocene was prepared by the method of ISSLHBand BRACK.~15~ (Found: Fe, 29.9. Cale. for C~0Hx0Fe: Fe, 30.0~.) Chromocene was prepared as described by WILKINSON.~16~(Found: Cr, 28.5. Calc. for C10H~0Cr: Cr, 28"6%.) All operations involving chromocene were carried out in a helium atmosphere in a dry box in which the integrity of the atmosphere was insured by the presence of a large ~'~ A. K. FISCHERand G. WILKINSON,ar. lnorg. Nucl. Chem. 2, 149 (1956). tx0~W. MOrrITT,J. Amer. Chem. Soc. 76, 3386 (1954). ¢m G. W. WATTand R. J. THOMPSON,Or. Inorg. NacL Chem. 9, 311 (1959). t~ G. W. WATTand J. B. OTTO,Jr., J. Electrochem. Soe. 98, 1 (1951). ,~3~G. W. WATTand D. M. SOWARDS,Or. Electrochem. Soc. 102, 545 (1955). c~4~G. W. WATTand L. J. BA'rE,3". lnorg. NucL Chem. 26, 1531 (1964). cls~K. ISSLEIBand A. BRACK,Z. Naturforsch. lib, 420 (1956). u6J G. WILKINSON,J. Amer. Chem. Soc. 76, 209 (1954).
Reactions of metallocenes with potassium and potassium amide in liquid ammonia
2101
exposed surface of liquid Na-K alloy. Nickelocene was prepared by an established method. (8> (Found: Ni, 30.9. Calc. for Cx0H10Ni: Ni, 31"1%.) Biscyclopentadienyltitanium (IV) chloride was prepared using the procedure of WILKINSON and BI~iINOHAM.(~7) (Found: Ti, 19.2; C1, 28-6. Calc. for Cx0H~0TiCl,: Ti, 19.3; C1, 28"6~.) X-ray diffraction data for (C~Hs)~M where M = Cr, Fe, Ni are given in Table 1.
Attempted synthesis of titanocene Titanium (II) chloride and NaCsHs were brought together under the conditions described by FISCHERand WILKINSON;(~) there was no evidence of reaction after 24 hr at 26 °. Following removal of the solvent under reduced pressure, an X-ray diffraction pattern identified unreacted TIC12 and NaCsHs but not NaC1. The residue was leached with tetrahydrofuran; a black residue remained. (Found: Ti, 40.3; C1, 59"8. Calc. for TiCI~: Ti, 40"3 ; C1, 59'7 %.) Evaporation of the tetrahydrofuran left a white solid. (Found: C5H5-, 73"9. Calc. for NaCsHs: C5H5-, 74.0 %.) TABLE 1 . - - X - R A Y DIFFRACTION DATA FOR
(CsHs)2Cr
(CsH6)~Fe
(CsHs)~M* (CsHs)~Ni
d,A
l/t0
d,A
IHo
d,A
I/lo
6.05 5.13 4.78 4.17 3.99 3.63
1.00 0-90 0-70 0.50 0.50 0-40?
5.88 5.16 4.71 4-10 3.69 2.56
0.40 1.00 0.10 0.10 0.10 0.05?
5.95 5.11 4.71 3.96 3.66 1.92
0-70 1.00 0.40 0.40 0.40 0-30?
* Cu K~ radiation, Ni filter, 35 kv tube voltage, 15 ma filament current, 4-12 hr exposure time, relative intensities estimated visually. ? Less intense lines not included here. The foregoing procedure was repeated except that a mixture of 65 % TiCI2 and 35 % TIC18 was used. The tetrahydrofuran assumed a green color over a period of 3 hr; thereupon, the solvent was removed under reduced pressure and the residue was extracted with petroleum ether to give a green solution. An X-ray diffraction pattern for the petroleum ether-insoluble residue showed the presence of TiCI2, NaCsHs, and NaC1, but not TiCI~. Evaporation of the petroleum ether solution yielded dark green microcrystals. (Found: Ti, 22.6; C1, 16.4. Calc. for C10Hx0TiCl: Ti, 22.3; C1, 16.6%.) Attempts to sublime this product under reduced pressure (a) resulted only in decomposition. When a sample of the original reaction mixture (in tetrahydrofuran) was exposed to the atmosphere, red crystals of (CsHs)2TiCI~ separated and were identified by an X-ray diffraction pattern. When the foregoing procedures failed to provide (CsHs)~Ti, the experiment was repeated using a co-formed mixture of TiClz and TiCls of about the same composition indicated above; the results were substantially the same. In similar experiments, use of pure TIC13 also resulted in the formation of (CsHs)2TiCI. (Found : Ti, 22.4; C1, 16-6. Calc. for CtoHx0TiCl: Ti, 22.3; C1, 16.6%.) Other variables in the procedure of FISCHER and WILKINSONwere studied, but without success. In other unsuccessful attempts to produce (CsHs),Ti, the following reactions (in tetrahydrofuran unless otherwise indicated) were investigated: (1) Reduction of (CsHs)2TiC12 with LiA1H,, (18) Na2S,O4, and NaH,POs. (2) Reduction of (CsHs)~TiC1 with LiAIH, and with potassium in liquid ammonia. (3) The interaction of TiCI2 and C~H6 in diethylamine.
Reactions with ammonia A 0"1285 g sample of (CsHs)~Fe was dissolved in excess anhydrous liquid ammonia and stirred for 80 hr. There was no evidence of reation. Evaporation of the solvent left an orange coloured c17) G. WILKINSONand J. M. BIRMINGHAM,J. Amer. Chem. Soc. 76, 4281 (1954). (ls~ j. M. BIRMINGHAM,A. K. FISCHERand G. WILKINSON,Naturwissenschaften 42, 96 (1955).
2102
G . W . WATT and L. J. BAX,~
residue that gave an X-ray diffraction pattern that led to data identical with those listed for ferrocene in Table 1. When 0.0725 g of (CsH~)sNi was stirred with a large excess of liquid ammonia for 36 hr, there was no evidence of reaction; the green residue remaining after volatilization of the solvent gave X-ray diffraction data in excellent agreement with those given for nickelocene in Table 1. Condensation of excess liquid ammonia on 0.8201 g of (CsH6)2Cr at --50 °, resulted in the formation of a pale blue ammoniate. At --50 ° the liquid ammonia was pumped offand the pressure was reduced to ca. 10-3 mm. The blue solid remained unchanged and there was no change in pressure over 2 hr. The temperature was raised to --36 °, whereupon evolution of NH8 began and continued up to --32 °, where the colour of the solid phase changed from pale blue to deep lavender. In three separate experiments employing different weights of (CsHs)2Cr, the NH3 evolved over the range --36 to --32 ° was removed with a Toepler pump and measured; the resulting NHs/(CsH~)2Cr ratios were 9.02, 8.98 and 8.90. When the temperature .was further increased, NHs evolution occurred over the range --20 to --15°; at the latter temperature the colour of the solid changed from deep lavender to salmon pink. The NH~/(CsH~)~Cr ratios over the interval --20 to --15 ° were 3.99, 4.02 and 3.95. Further NHs evolution did not occur when the solid was heated from - 1 5 ° to room temperature; a sample of the salmon-pink solid gave an X-ray diffraction pattern substantially identical with that for chromocene (Table 1). (Found: Cr, 28'4. Calc. for CaoH10Cr: Cr, 28.6%.) When this product was heated to 75 °, its colour changed to ruby red, withoutgas evolution; this solid also was identified as chromocene by its X-ray diffraction pattern.
Reactions with potassium amide There was no evidence of reaction when 0-0859 g of ferrocene in 50 ml of ammonia was titrated potentiometrically with the potassium amide formed catalytically from 0"1146 g of potassium in 30.4 ml of ammonia. Following evaporation of the solvent, ferrocene was recovered unchanged and identified by its X-ray diffraction pattern (Table 1). Similarly, titration of 0.0826 g of nickelocene in 75 ml of ammonia with 0.1025 Mpotassium amide solution resulted in neither change in potential nor visual evidence of reaction; nickelocene was recovered unchanged and identified via its X-ray diffraction pattern (Table 1). When 0.1838 g of chromocene in 75 ml of ammonia was titrated with 0.1220 M potassium amide solution, the potential remained essentially constant until 2 molar equivalents of the amide solution had been added. Thereupon, the potential increased sharply by ca. 800 mV and the lavender ammoniate was replaced completely by a gelatinous brown-black solid. By digestion for 3 hr at --33.5 °, the latter changed to a granular solid, which was separated by filtration and washed three times with 50ml portions of ammonia. (Found: Cr, 78.6; N, 21.4. Calc. for CrN: Cr, 78.7; N, 21"3~o.) This product did not give a useful X-ray diffraction pattern. During the course of the reaction (including the digestion period), 1.02 milliequivalents of hydrogen was collected. The presence of KCsH5 in the residue from the combined supernatant solution and washings was confirmed by an X-ray diffraction pattern, t14~ A total of 128.0 mg of C5H5- was recovered t14~as compared with 131.3 nag used as (CsHs)2Cr. Reactions with potassium In separate experiments, 0"0776 g of (C~H~)2Fe, 0.0812 g of (CsHs)~Ni, and 0-2054 g of (CsHs)2Cr-each in 75 ml of ammonia--were titrated potentiometrically with solutions of potassium in ammonia that were 0.1362, 0.1002 and 0.1350 M, respectively. In all three cases, black precipitates formed progressively and the potentials remained essentially constant until almost exactly 2 molar equivalents of potassium solution was added; thereupon increases in potential of several hundred millivolts were recorded. The black precipitates were washed four times with 50 ml portions of ammonia and shown to consist of the corresponding metals by X-ray diffraction patterns and by analysis (e.g., Found: Fe, 99"5 %.) After evaporation of the solvent from the combined supernatant solution and washings, KCsH~ was identified by X-ray diffraction patterns and CsHs- was recovered (98-99 %) by the method previously described, c14~ Acknowledgment--This work was supported by The Robert A. Welch Foundation and The United States Atomic Energy Commission.