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The reaction of pentaborane(9) with sodium cyanide and sodium cyanotrihydroborate
Polyhedron Vol. 4. No. 2, pp. 321-324. Printed in Great Britain.
1985
0277-5387/85 53.00 + .@I @ 1985 Pergamon Press Ltd.
THE REACTION OF PENTABORANE(9) WITH SODIUM CYANIDE AND SODIUM CYANOTRIHYDROBORATE Department
J. G. TAYLOR and M. G. H. WALLBRIDGE* of Chemistry, University of Warwick Coventry CV4 7AL, England (Received 9 April 1984; accepted 14 April 1984)
Abstract-The reaction of pentaborane(9) with NaCN occurs in a 1: 1 molar ratio at temperatures between - 30” and + 10°C to yield the complex Na[B5H&Nl, which can be isolated in the form of a dioxanate. When excess pentaborane(9) is used the reaction is relatively clean and yields predominantly the [B9H,4]- ion. With NaBH,CN no intermediates of the type Na[B,H,CN] are detected, and the major product is the [B,H,,]- ion, but no hydrogen is evolved in the reaction. Structures for the intermediate anions are suggested. No monocarbon carbaboranes were detected in any of the reactions.
The boron hydrides are usually described as being electron deficient, and not unexpectedly therefore they react with a range of nucleophiles. Interactions with the cyanide ion in particular are varied and lead to bridging,’ cleavage,’ and adduct type products, depending on the borane used, as shown in eqns (l)-(3). B2H, + CN- -
[H3BCNBH3]-
(1)
B4H,, + 2CN- + [BH,CN]- + [B3H7C’Nl- (2) B,,H,, + 2CN- + [B,,,H,,CNl’- + HCN
(3)
The adduct type reaction, (3), was of interest to us since the [B,0H,3CN12- anion can be protonated to give B,0H,2CNH3, which is a useful precursor to CB,,, and CB, carbaborane frameworks, where the carbon atom has become incorporated into a cage system.3 We were encouraged to investigate the reaction with pentaborane(9), B5H9, (l), for two reasons. Firstly, a preliminary investigation had reported the formation of a simple 1: 1 salt, Na[B,H&N], but the product had not been further characterised.’ Secondly, we had shown in related studies that (l), on reaction with the hydride ion as a nucleophile, underwent a rearrangement reaction with the evolution of hydrogen to yield the B,H,,- ion.4
*Author to whom correspondence should be addressed.
Here we describe the results of investigations of the action of both NaCN and NaBH,CN on (l), at low and ambient temperatures.
EXPERIMENTAL The reactions were performed using standard vacuum line techniques. In order to facilitate the recording of the “B NMR spectra, the 100cm3 round-bottomed reaction flask was fitted with a side-arm incorporating a 5 mm diameter NMR tube that could be flame-sealed. The “B NMR spectra were recorded at a frequency of 128.4 MHz on a Bruker WH400 spectrometer. No deuterated lock solvents were used, and peaks in the spectra were externally referenced to BF,.etherate (0 ppm). The IR spectra were recorded on a Perkin-Elmer 580 spectrometer by means of KBr disks. Carbon and hydrogen analyses were performed by Elemental Micro-Analysis Ltd., Devon. Reagent grade pentaborane(9) sodium cyanide, sodium cyanotrihydroborate, 1, 2-dimethoxyethane and 1,4-dioxan were used, the solvents being dried over lithium aluminum hydride prior to vacuum-line transfer. Reaction of pentaborane(9) with NaCN and NaBH,CN Dry finely ground sodium cyanide (0.31 g, 6.3 mmol) and degassed 1, 2-dimethoxyethane (10 cm3) were placed in a 100 cm3 round-bottomed flask fitted with a side-arm which contained a small sir&red disc, and a sealed-on 5 mm NMR tube 321
322
J. G. TAYLOR and M. G. H. WALLBRIDGE
which had a constriction where it could be sealed- yielded a dry white solid (1.50 g). Found: C, 34.9; off. Pentaborane(9) (0.40 g, 6.3 mmol) was then H, 7.76, B, 21.6. Calc. for NaB,H,CN. 1.5C4H,0,: condensed into the flask under vacuum at C, 34.4; H, 8.61, B, 22.1%. The IR spectrum of the - 196%. In the low-temperature experiments the solid showed bands at 2500(s), 2460(s) and reaction temperature was allowed to rise slowly 2380(s)cm-’ from v(B-H), and 2250(s), 2210(sh) over 30 min, and was then maintained at - 25°C and 22OO(sh)cm-’ from v(C-N), where s = strong by means of a slush-bath (CC&) for 2 hr. The and sh = shoulder. The reactions of (1) with both NaCN and temperature was then allowed to rise to + 10°C over 4 hr. The reaction mixture was stirred mag- Na[BH,CNl at room temperature were performed netically at the different temperatures, and the in a similar manner, except that the mixture was sodium cyanide dissolved slowly over the 6 hr allowed to warm to room temperature immediately period affording a colourless solution. Checks after the transfer of (1). The reactions appeared to be complete after 34 hr as judged by the disapmade at various times confirmed that no hydrogen was evolved during the reaction. An aliquot of the pearance of (1) from the “B NMR spectra, and the clear solution was filtered into the NMR tube dissolution of the sodium cyanide. through a small sintered glass disc, and the tube RESULTS AND DISCUSSION was then sealed-off and stored at - 196°C. The remaining solution was evaporated to give a clear Sodium cyanide and (1) react in dimethoil which turned pale-yellow after 3-4 hr at room oxyethane in a 1: 1 molar ratio over the temtemperature. Addition of dry 1, 4-dioxan (20 cm3) perature range - 30” to + 10°C. The reaction is to the original cold reaction mixture followed by slow in that the solid cyanide dissolves over about removal of the solvent under vacuum yielded a 6 hr, but the initial reaction products definitely slightly oily white solid. Washing with aliquots arise from a 1: 1 molar reaction, since when excess (10 cm3) of 1,4-dioxan followed by pumping cyanide is used only 1 mole dissolves per mole of
-20
-40
- 60
(PPml Fig. 1. (a) “B(IH) NMR spectrum at + 10°C of B&/Nat3 (1: 1 molar ratio) in 1,2dimethoxyethane. (b) A similar mixture allowed to react at + 25°C. (c) A mixture of B,I$JNaCN (2: 1 molar ratio) allowed to react at + 25°C.
The reaction of pentaborane(9)
(1). However, in contrast the 1 : 1 molar mixture will react further with an exess of (1) as described below. A notable feature is that only minute traces of hydrogen were detected over the course of the reaction. This is in contrast to the reaction involving the hydride ion where, in addition to the 1 mole of hydrogen expected, further hydrogen is evolved as the reaction proceeds.4 The reaction may be followed conveniently by changes in the “B(‘H} NMR spectrum recorded at 10°C. A typical spectrum, as shown in Fig. l(a), is obtained from a reaction mixture (1: 1 molar ratio) which had been allowed to warm from -30” to + 10°C over 6 hr, when all the solid sodium cyanide had dissolved. The major part of the reaction products (for a mass balance of the different products see details of the 1: 1 molar reaction run at room temperature given below) consists of three very broad resonances (labelled A in Fig. la) with relative intensities of 3 : 1: 1. The peaks narrow slightly on cooling to - 6O”C, but do not show any *‘B-‘H coupling at either temperature. The broadness of the peaks, and the lack of any **B-‘H coupling, is reminiscent of the spectra of other substituted pentaborane compounds including the unsymmetrical adducts B,Hg .2L (L = NMe, or PMe,).4d These resonances would appear therefore to be best assigned to an open-cage species, aruchno- [ B5HgCN] -, (2), in which the cyanide group is attached to the B(2) or B(3) positions. Such a species is iso-electronic and -structural with aruchno-B,H,,. The resonance of intensity 3 then arises from the three unsubstituted basal boron atoms, which are either equivalent due to a fluxional process, or not resolved within the very broad peak, The high-field resonance is assigned to the apical boron atom B(l), and the remaining resonance to the B-CN group.
(X’=C,q
X’=H
,
X”=‘-,.
323
peratures. The low-field resonance, B (intensity 4), exhibits a “B-lH coupling of 94 Hz which is intermediate between the values normally associated with B-H (terminal) (cu. 140 Hz) and B-H (bridging) (cu. 40 Hz).’ However, the high-field signal, B’, (intensity 1) does not show any “B-‘H coupling, and presumably arises from a B-CN group. It would appear therefore as though the initial attack of the cyanide ion occurs at the apical boron atom, yielding an ion as in (2), or possibly occupies a bridging position between the apical site and one of the basal atoms causing asymmetry in the field around the apical boron, and a broadening of the resonance. Although nucleophilic substitution in (1) is usually found to occur at the basal borons, it is known that such substitution can also occur at the apical position as in B5Hg - 2L [L = PMe3,* Ph,P(CHz)PPhzs]. Also since the room temperature product appears to be basal substituted, it is relevant that a rapid isomerisation process is known to occur in alkyl- and halopentaboranes, when the group is transferred at ambient temperatures or above from the apical to basal positions.@j Species C (Fig. la) arises from the urachno[B9H14]- ion, as shown by a comparison of ilB NMR chemical shifts and coupling constants,9 and becomes a major product if the reaction is run at room temperature as outlined below. The species D and E were not unambiguously identified, but it is likely that D is an end product of B-H condensation reactions [i.e. (B,H,)2-], in view of the presence of [B9H14]-, and small amounts of the [B3H8]- ion (F) also observed. The chemical shift and “B-*H coupling constant of D do in fact compare well with those of the [B,2H,2]2- ion.” A solid product can be isolated from the reaction mixture by the addition of 1,4-dioxan. After wash-
(X
=
CN)
, X’ ‘=CN)
The two resonances B, B’ in Fig. l(a) arise from a reactive low-temperature intermediate, since they disappear at the same rate over a few hours when the NMR sample is warmed to room temperature, and do not appear at all in reaction mixtures which have been held throughout at ambient tem-
ing and pumping dry the IR spectrum shows evidence for the existence of B-H (cu. 2500 cm-‘), C = N (cu. 2200 cm-‘) and co-ordinated dioxan. The solvated species appears to have a composition best represented by Na[B5H9CN] 1SC,H,O,.
324
J, G. TAYLOR
and M G. H. WALLBRIDGE
When the reaction (1: 1 molar ratio) was carried out at 25°C over 4 hr, the “B NMR spectrum of the clear solution (Fig. lb) was similar to that discussed above, but no signals due to the species B were observed. The overall mass balance (based on the ratios of integrated in~nsities in the irB NMR spectrum) for the different products was approximately [B,H&Nl- (55% PJU- t20%), species D, [Bi2H1J2-? (2073, and [B,H& (5%). The other unknown minor species E in the lowtemperature spectrum also disappears on warming, but does so at a different rate to B, and we assume therefore that these two species are not related. Significant changes did occur in the final spectrum when 2 moles of (1) was allowed to react with 1 mole of cyanide at 25°C for 4 hr. In this case no resonances due to either species A or B were observed, and the spectrum contained essentially only resonances arising from the [B,H,J ion, (Fig. lc) species D again presumably [B,2H,&, and also [BH,CNJ-, (G), which was only formed in any signi~cant quantity when excess of (1) was present. The relative proportions of these three products from the integrated ratios were 80, 10 and 5% respectively, with other minor resonances making up the remaining 5% of the products. The reactions involving an excess of (1) were always the cleanest, giving the minimum number of products, and again a notewo~hy feature of the reaction is the absence of any hydrogen being evolved over the 4 hr reaction time. Only a few reactions between (1) and Na[BH,CN] were investigated. The 1: 1 molar reaction carried out at room temperature showed no broad signals (A or B) assigned to [B,H&N]- as above. Instead the major products were again the [$HJ anion, and the species, [Bi2H,J2-?, together with smaller quantities of F, [B3Hgl- and traces of unreactcd [BH,CNl-, and [BH,CNBH3]-. All of the reactions described were carried out
many times with very little variation in the results. Possibly the most interesting point is the fate of the cyanide ion, in that the only obvious product which incorporates it is the [B5H9wion, but in many of the reactions it would appear to act as an interm~iate in the conversion of (1) to higher borane anions. We have not detected any incorporation of the cyanide ion into the borane fragment, to form a monocarbon carbaborane as found with B,0H,4; instead it acts as a simple su~tituent as in the [B,H&N]- ion, We have not detected any HCN in the reactions, and in view of these results it is tempting to speculate that the conversion of (1) to higher anions may be generally catalysed by anions, and of the three investigated in any detail (H-, BH; and m-) it is not surprising that hydrogen evolution occurs with the hydridic ions. We are currently investigating further whether other non-hydridic anions are also capable of achieving similar tr~sfo~ations. Ack~~w~edge~enr-We
gift of pentaborane(9), this work.
thank Dr. R. E. Wiliiams.for a and the S.E.R.C. for support of
REFERENCES 1. V. D. Aftandilian, H. C. Miller and E. L. Muetterties, .Z. Am. Chem. Sot. 1961.83,2471. 2. W. H. Knoth and E. L. Muetterties, .Z.Znorg. Nuci, Chern. 1961, 20, 66. 3. W. ti. Knoth, J. Am. CZiem. Sot. 1967,S9, 1274. 4. C. G. Savory and M. G. H. Wallbridge, J.C.S. Dalton Trans. 1973, 179. 5. N. W. Alccck, H. M. Colquhoun, G. Haran, J. F. Sawyer and M. G. H. Wahbridse. J.C.S. Dalton Towns. 1982,2243. 6. D. F. Gaines, Ace. Ch&t: Z&es.1973,6,416, and references therein. 7. H. Noth and B. Wrackmeyer, NMR of Boron Compound% Springer-VerlaK Berlin (1978). 8. A. V. Fratini, G. W. Sullivan, M. L. Denmston, R. K. Hertz and S. G. Shore, J. Am. Chem. Sot. 1974,%, 3013. 9. N. N. Greenwood, H. J., Gysiing, J. A. McGinnety and J. D. Owen, J.C.S. Chem. &mm. 1970,505. 10. V. D. Aftandilian, H. C. Miller, G. W. Parshall and E. L. Muetterties, Znorg. Ckem. 1962, 1, 734.
1985
0277-5387/85 53.00 + .@I @ 1985 Pergamon Press Ltd.
THE REACTION OF PENTABORANE(9) WITH SODIUM CYANIDE AND SODIUM CYANOTRIHYDROBORATE Department
J. G. TAYLOR and M. G. H. WALLBRIDGE* of Chemistry, University of Warwick Coventry CV4 7AL, England (Received 9 April 1984; accepted 14 April 1984)
Abstract-The reaction of pentaborane(9) with NaCN occurs in a 1: 1 molar ratio at temperatures between - 30” and + 10°C to yield the complex Na[B5H&Nl, which can be isolated in the form of a dioxanate. When excess pentaborane(9) is used the reaction is relatively clean and yields predominantly the [B9H,4]- ion. With NaBH,CN no intermediates of the type Na[B,H,CN] are detected, and the major product is the [B,H,,]- ion, but no hydrogen is evolved in the reaction. Structures for the intermediate anions are suggested. No monocarbon carbaboranes were detected in any of the reactions.
The boron hydrides are usually described as being electron deficient, and not unexpectedly therefore they react with a range of nucleophiles. Interactions with the cyanide ion in particular are varied and lead to bridging,’ cleavage,’ and adduct type products, depending on the borane used, as shown in eqns (l)-(3). B2H, + CN- -
[H3BCNBH3]-
(1)
B4H,, + 2CN- + [BH,CN]- + [B3H7C’Nl- (2) B,,H,, + 2CN- + [B,,,H,,CNl’- + HCN
(3)
The adduct type reaction, (3), was of interest to us since the [B,0H,3CN12- anion can be protonated to give B,0H,2CNH3, which is a useful precursor to CB,,, and CB, carbaborane frameworks, where the carbon atom has become incorporated into a cage system.3 We were encouraged to investigate the reaction with pentaborane(9), B5H9, (l), for two reasons. Firstly, a preliminary investigation had reported the formation of a simple 1: 1 salt, Na[B,H&N], but the product had not been further characterised.’ Secondly, we had shown in related studies that (l), on reaction with the hydride ion as a nucleophile, underwent a rearrangement reaction with the evolution of hydrogen to yield the B,H,,- ion.4
*Author to whom correspondence should be addressed.
Here we describe the results of investigations of the action of both NaCN and NaBH,CN on (l), at low and ambient temperatures.
EXPERIMENTAL The reactions were performed using standard vacuum line techniques. In order to facilitate the recording of the “B NMR spectra, the 100cm3 round-bottomed reaction flask was fitted with a side-arm incorporating a 5 mm diameter NMR tube that could be flame-sealed. The “B NMR spectra were recorded at a frequency of 128.4 MHz on a Bruker WH400 spectrometer. No deuterated lock solvents were used, and peaks in the spectra were externally referenced to BF,.etherate (0 ppm). The IR spectra were recorded on a Perkin-Elmer 580 spectrometer by means of KBr disks. Carbon and hydrogen analyses were performed by Elemental Micro-Analysis Ltd., Devon. Reagent grade pentaborane(9) sodium cyanide, sodium cyanotrihydroborate, 1, 2-dimethoxyethane and 1,4-dioxan were used, the solvents being dried over lithium aluminum hydride prior to vacuum-line transfer. Reaction of pentaborane(9) with NaCN and NaBH,CN Dry finely ground sodium cyanide (0.31 g, 6.3 mmol) and degassed 1, 2-dimethoxyethane (10 cm3) were placed in a 100 cm3 round-bottomed flask fitted with a side-arm which contained a small sir&red disc, and a sealed-on 5 mm NMR tube 321
322
J. G. TAYLOR and M. G. H. WALLBRIDGE
which had a constriction where it could be sealed- yielded a dry white solid (1.50 g). Found: C, 34.9; off. Pentaborane(9) (0.40 g, 6.3 mmol) was then H, 7.76, B, 21.6. Calc. for NaB,H,CN. 1.5C4H,0,: condensed into the flask under vacuum at C, 34.4; H, 8.61, B, 22.1%. The IR spectrum of the - 196%. In the low-temperature experiments the solid showed bands at 2500(s), 2460(s) and reaction temperature was allowed to rise slowly 2380(s)cm-’ from v(B-H), and 2250(s), 2210(sh) over 30 min, and was then maintained at - 25°C and 22OO(sh)cm-’ from v(C-N), where s = strong by means of a slush-bath (CC&) for 2 hr. The and sh = shoulder. The reactions of (1) with both NaCN and temperature was then allowed to rise to + 10°C over 4 hr. The reaction mixture was stirred mag- Na[BH,CNl at room temperature were performed netically at the different temperatures, and the in a similar manner, except that the mixture was sodium cyanide dissolved slowly over the 6 hr allowed to warm to room temperature immediately period affording a colourless solution. Checks after the transfer of (1). The reactions appeared to be complete after 34 hr as judged by the disapmade at various times confirmed that no hydrogen was evolved during the reaction. An aliquot of the pearance of (1) from the “B NMR spectra, and the clear solution was filtered into the NMR tube dissolution of the sodium cyanide. through a small sintered glass disc, and the tube RESULTS AND DISCUSSION was then sealed-off and stored at - 196°C. The remaining solution was evaporated to give a clear Sodium cyanide and (1) react in dimethoil which turned pale-yellow after 3-4 hr at room oxyethane in a 1: 1 molar ratio over the temtemperature. Addition of dry 1, 4-dioxan (20 cm3) perature range - 30” to + 10°C. The reaction is to the original cold reaction mixture followed by slow in that the solid cyanide dissolves over about removal of the solvent under vacuum yielded a 6 hr, but the initial reaction products definitely slightly oily white solid. Washing with aliquots arise from a 1: 1 molar reaction, since when excess (10 cm3) of 1,4-dioxan followed by pumping cyanide is used only 1 mole dissolves per mole of
-20
-40
- 60
(PPml Fig. 1. (a) “B(IH) NMR spectrum at + 10°C of B&/Nat3 (1: 1 molar ratio) in 1,2dimethoxyethane. (b) A similar mixture allowed to react at + 25°C. (c) A mixture of B,I$JNaCN (2: 1 molar ratio) allowed to react at + 25°C.
The reaction of pentaborane(9)
(1). However, in contrast the 1 : 1 molar mixture will react further with an exess of (1) as described below. A notable feature is that only minute traces of hydrogen were detected over the course of the reaction. This is in contrast to the reaction involving the hydride ion where, in addition to the 1 mole of hydrogen expected, further hydrogen is evolved as the reaction proceeds.4 The reaction may be followed conveniently by changes in the “B(‘H} NMR spectrum recorded at 10°C. A typical spectrum, as shown in Fig. l(a), is obtained from a reaction mixture (1: 1 molar ratio) which had been allowed to warm from -30” to + 10°C over 6 hr, when all the solid sodium cyanide had dissolved. The major part of the reaction products (for a mass balance of the different products see details of the 1: 1 molar reaction run at room temperature given below) consists of three very broad resonances (labelled A in Fig. la) with relative intensities of 3 : 1: 1. The peaks narrow slightly on cooling to - 6O”C, but do not show any *‘B-‘H coupling at either temperature. The broadness of the peaks, and the lack of any **B-‘H coupling, is reminiscent of the spectra of other substituted pentaborane compounds including the unsymmetrical adducts B,Hg .2L (L = NMe, or PMe,).4d These resonances would appear therefore to be best assigned to an open-cage species, aruchno- [ B5HgCN] -, (2), in which the cyanide group is attached to the B(2) or B(3) positions. Such a species is iso-electronic and -structural with aruchno-B,H,,. The resonance of intensity 3 then arises from the three unsubstituted basal boron atoms, which are either equivalent due to a fluxional process, or not resolved within the very broad peak, The high-field resonance is assigned to the apical boron atom B(l), and the remaining resonance to the B-CN group.
(X’=C,q
X’=H
,
X”=‘-,.
323
peratures. The low-field resonance, B (intensity 4), exhibits a “B-lH coupling of 94 Hz which is intermediate between the values normally associated with B-H (terminal) (cu. 140 Hz) and B-H (bridging) (cu. 40 Hz).’ However, the high-field signal, B’, (intensity 1) does not show any “B-‘H coupling, and presumably arises from a B-CN group. It would appear therefore as though the initial attack of the cyanide ion occurs at the apical boron atom, yielding an ion as in (2), or possibly occupies a bridging position between the apical site and one of the basal atoms causing asymmetry in the field around the apical boron, and a broadening of the resonance. Although nucleophilic substitution in (1) is usually found to occur at the basal borons, it is known that such substitution can also occur at the apical position as in B5Hg - 2L [L = PMe3,* Ph,P(CHz)PPhzs]. Also since the room temperature product appears to be basal substituted, it is relevant that a rapid isomerisation process is known to occur in alkyl- and halopentaboranes, when the group is transferred at ambient temperatures or above from the apical to basal positions.@j Species C (Fig. la) arises from the urachno[B9H14]- ion, as shown by a comparison of ilB NMR chemical shifts and coupling constants,9 and becomes a major product if the reaction is run at room temperature as outlined below. The species D and E were not unambiguously identified, but it is likely that D is an end product of B-H condensation reactions [i.e. (B,H,)2-], in view of the presence of [B9H14]-, and small amounts of the [B3H8]- ion (F) also observed. The chemical shift and “B-*H coupling constant of D do in fact compare well with those of the [B,2H,2]2- ion.” A solid product can be isolated from the reaction mixture by the addition of 1,4-dioxan. After wash-
(X
=
CN)
, X’ ‘=CN)
The two resonances B, B’ in Fig. l(a) arise from a reactive low-temperature intermediate, since they disappear at the same rate over a few hours when the NMR sample is warmed to room temperature, and do not appear at all in reaction mixtures which have been held throughout at ambient tem-
ing and pumping dry the IR spectrum shows evidence for the existence of B-H (cu. 2500 cm-‘), C = N (cu. 2200 cm-‘) and co-ordinated dioxan. The solvated species appears to have a composition best represented by Na[B5H9CN] 1SC,H,O,.
324
J, G. TAYLOR
and M G. H. WALLBRIDGE
When the reaction (1: 1 molar ratio) was carried out at 25°C over 4 hr, the “B NMR spectrum of the clear solution (Fig. lb) was similar to that discussed above, but no signals due to the species B were observed. The overall mass balance (based on the ratios of integrated in~nsities in the irB NMR spectrum) for the different products was approximately [B,H&Nl- (55% PJU- t20%), species D, [Bi2H1J2-? (2073, and [B,H& (5%). The other unknown minor species E in the lowtemperature spectrum also disappears on warming, but does so at a different rate to B, and we assume therefore that these two species are not related. Significant changes did occur in the final spectrum when 2 moles of (1) was allowed to react with 1 mole of cyanide at 25°C for 4 hr. In this case no resonances due to either species A or B were observed, and the spectrum contained essentially only resonances arising from the [B,H,J ion, (Fig. lc) species D again presumably [B,2H,&, and also [BH,CNJ-, (G), which was only formed in any signi~cant quantity when excess of (1) was present. The relative proportions of these three products from the integrated ratios were 80, 10 and 5% respectively, with other minor resonances making up the remaining 5% of the products. The reactions involving an excess of (1) were always the cleanest, giving the minimum number of products, and again a notewo~hy feature of the reaction is the absence of any hydrogen being evolved over the 4 hr reaction time. Only a few reactions between (1) and Na[BH,CN] were investigated. The 1: 1 molar reaction carried out at room temperature showed no broad signals (A or B) assigned to [B,H&N]- as above. Instead the major products were again the [$HJ anion, and the species, [Bi2H,J2-?, together with smaller quantities of F, [B3Hgl- and traces of unreactcd [BH,CNl-, and [BH,CNBH3]-. All of the reactions described were carried out
many times with very little variation in the results. Possibly the most interesting point is the fate of the cyanide ion, in that the only obvious product which incorporates it is the [B5H9wion, but in many of the reactions it would appear to act as an interm~iate in the conversion of (1) to higher borane anions. We have not detected any incorporation of the cyanide ion into the borane fragment, to form a monocarbon carbaborane as found with B,0H,4; instead it acts as a simple su~tituent as in the [B,H&N]- ion, We have not detected any HCN in the reactions, and in view of these results it is tempting to speculate that the conversion of (1) to higher anions may be generally catalysed by anions, and of the three investigated in any detail (H-, BH; and m-) it is not surprising that hydrogen evolution occurs with the hydridic ions. We are currently investigating further whether other non-hydridic anions are also capable of achieving similar tr~sfo~ations. Ack~~w~edge~enr-We
gift of pentaborane(9), this work.
thank Dr. R. E. Wiliiams.for a and the S.E.R.C. for support of
REFERENCES 1. V. D. Aftandilian, H. C. Miller and E. L. Muetterties, .Z. Am. Chem. Sot. 1961.83,2471. 2. W. H. Knoth and E. L. Muetterties, .Z.Znorg. Nuci, Chern. 1961, 20, 66. 3. W. ti. Knoth, J. Am. CZiem. Sot. 1967,S9, 1274. 4. C. G. Savory and M. G. H. Wallbridge, J.C.S. Dalton Trans. 1973, 179. 5. N. W. Alccck, H. M. Colquhoun, G. Haran, J. F. Sawyer and M. G. H. Wahbridse. J.C.S. Dalton Towns. 1982,2243. 6. D. F. Gaines, Ace. Ch&t: Z&es.1973,6,416, and references therein. 7. H. Noth and B. Wrackmeyer, NMR of Boron Compound% Springer-VerlaK Berlin (1978). 8. A. V. Fratini, G. W. Sullivan, M. L. Denmston, R. K. Hertz and S. G. Shore, J. Am. Chem. Sot. 1974,%, 3013. 9. N. N. Greenwood, H. J., Gysiing, J. A. McGinnety and J. D. Owen, J.C.S. Chem. &mm. 1970,505. 10. V. D. Aftandilian, H. C. Miller, G. W. Parshall and E. L. Muetterties, Znorg. Ckem. 1962, 1, 734.