New synthetic routes to azacarborane clusters: Nitrile insertion reactions of nido-5,6-C2B8H11- and nido-B10H13-

Article abstract of DOI:10.1021/ja960787m

A synthetic sequence involving the initial nucleophilic attack of the isoelectronic nido-5,6-C₂B₈H₁₁^- or nido-B₁₀H₁₃^- anions at a nitrile carbon, followed by nitrile hydroboration and cage-insertion, has been fouud to yield new azacarborane clusters in good yields. Thus, the reaction of nido-5,6-C₂B₈H₁₁^- with refluxing acetonitrile gave the azatricarbaborane anion arachno-7-CH₃-5,7,14,12-C₃NB₈H₁₁^- (1^-) in 65% yield, while nido-B₁₀H₁₃^- reacted with acetonitrile, benzyl cyanide, or CH₃¹³CN to give the azamonocarbaborane anions arachno-7-CH₃-7,12-CNB₁₀H₁₃^- (2a^-), arachno-7-Bn-7,12-CNB₁₀H₁₃^- (2b^-), and arachno-7-CH₃-7,12-¹³CNB₁₀H₁₃^- (2a^--¹³C), respectively. Single-crystal X-ray studies of the isoelectronic clusters, 1^- and 2a^-, showed that hydroboration of the nitrile occurred, with the resulting imino group inserting into the cage framework in a position bridging the B2 and B11 borons. Consistent with their arachno skeletal electron counts, 1^- and 2a^- have cage frameworks containing two six-membered open faces that may be derived from a bicapped hexagonal antiprism by removal of two non-adjacent five-coordinate vertices. Alternatively, 1^- and 2a^- may be considered as having 10-vertex arachno frameworks with exopolyhedral bridging imine substituents. Acidification of 1^- resulted in loss of one boron and the imine nitrogen and formation of the known tricarbaborane nido-6-CH₃-5,6,9-C₃B₇H₁₀. In contrast, acidification of 2^- led to loss of only one boron to yield the new azamonocarbaborane hypho-12-R-12,13-CNB₉H₁₅ (3). A single-crystal X-ray study confirmed that 3 has an 11-vertex hypho structure, containing two six-membered open faces, that is based on a 14-vertex closo polyhedron missing three vertices. In 3, further hydroboration of the CN group occurred, such that the carbon contains an additional hydrogen and the nitrogen is connected to two borons. Deprotonation of 3 with Proton Sponge, 1,8-bis(dimethylamino)naphthalene, initially yielded hypho-12-R-12,13-CNB₉H₁₄^- (3^-), which subsequently underwent a skeletal rearrangement to yield the isomeric anion hypho-12-R-12,11-CNB₉H₁₄^- (4^-). A single-crystal X-ray study of 4^- confirmed that it has an 11-vertex hypho structure with one seven-membered and one five-membered open face. Subsequent acidification of 4^- resulted in loss of one additional boron to give hypho-8-R-8,13-CNB₈H₁₄ (5). Deprotonation with Proton Sponge gave the new anion hypho-8-R-8,13-CNB₈H₁₃^- (5^-). Based upon spectral and computational data, 5 and 5^- are proposed to have the CN unit incorporated into a 10-vertex hypho structure.

Full text of DOI:10.1021/ja960787m

J. Am. Chem. Soc. 1996, 118, 6407-6421
6407
New Synthetic Routes to Azacarborane Clusters: Nitrile
Insertion Reactions of nido-5,6-C2B8H11 and nido-B10H13
-
-
Andrew E. Wille, Kai Su, Patrick J. Carroll, and Larry G. Sneddon*
Contribution from the Department of Chemistry, UniVersity of PennsylVania,
Philadelphia, PennsylVania 19104-6323
ReceiVed March 11, 1996X
-
Abstract: A synthetic sequence involving the initial nucleophilic attack of the isoelectronic nido-5,6-C2B8H11 or
-
nido-B10H13 anions at a nitrile carbon, followed by nitrile hydroboration and cage-insertion, has been found to
yield new azacarborane clusters in good yields. Thus, the reaction of nido-5,6-C2B8H11- with refluxing acetonitrile
gave the azatricarbaborane anion arachno-7-CH3-5,7,14,12-C3NB8H11- (1-) in 65% yield, while nido-B10H13- reacted
-
with acetonitrile, benzyl cyanide, or CH313CN to give the azamonocarbaborane anions arachno-7-CH3-7,12-CNB10H13
(2a-), arachno-7-Bn-7,12-CNB10H13- (2b-), and arachno-7-CH3-7,12-13CNB10H13- (2a--13C), respectively. Single-
crystal X-ray studies of the isoelectronic clusters, 1- and 2a-, showed that hydroboration of the nitrile occurred,
with the resulting imino group inserting into the cage framework in a position bridging the B2 and B11 borons.
Consistent with their arachno skeletal electron counts, 1- and 2a- have cage frameworks containing two six-membered
open faces that may be derived from a bicapped hexagonal antiprism by removal of two non-adjacent five-coordinate
vertices. Alternatively, 1- and 2a- may be considered as having 10-vertex arachno frameworks with exopolyhedral
bridging imine substituents. Acidification of 1- resulted in loss of one boron and the imine nitrogen and formation
of the known tricarbaborane nido-6-CH3-5,6,9-C3B7H10. In contrast, acidification of 2- led to loss of only one
boron to yield the new azamonocarbaborane hypho-12-R-12,13-CNB9H15 (3). A single-crystal X-ray study confirmed
that 3 has an 11-vertex hypho structure, containing two six-membered open faces, that is based on a 14-vertex closo
polyhedron missing three vertices. In 3, further hydroboration of the CN group occurred, such that the carbon
contains an additional hydrogen and the nitrogen is connected to two borons. Deprotonation of 3 with Proton Sponge,
1,8-bis(dimethylamino)naphthalene, initially yielded hypho-12-R-12,13-CNB9H14- (3-), which subsequently underwent
a skeletal rearrangement to yield the isomeric anion hypho-12-R-12,11-CNB9H14- (4-). A single-crystal X-ray study
of 4- confirmed that it has an 11-vertex hypho structure with one seven-membered and one five-membered open
face. Subsequent acidification of 4- resulted in loss of one additional boron to give hypho-8-R-8,13-CNB8H14 (5).
-
Deprotonation with Proton Sponge gave the new anion hypho-8-R-8,13-CNB8H13 (5-). Based upon spectral and
computational data, 5 and 5- are proposed to have the CN unit incorporated into a 10-vertex hypho structure.
arachno-6,8-S2B7H8- + CH3CN (1) reflux8
Introduction
(2) H+
The syntheses, structures, and chemistry of hybrid clusters,
such as the polyhedral azacarboranes, containing both electron-
deficient and electron-rich cage atoms, are of continuing interest
in polyhedral cluster chemistry since these clusters may show
bonding and structural properties intermediate with those of the
classical and nonclassical cluster classes. Although several
azaboranes1 and metallaazaboranes2 have recently been reported,
there remain only a few azacarborane clusters, nido-7,8,10-
C2NB8H11,3 arachno-µ8,9-NH2-5,6-C2B8H11,3 arachno-11-But-
5,10,11-C2NB8H12,4 and arachno-6,9-CNB8H13.5 These aza-
carboranes have been synthesized employing reagents such as
nitrous acid, NH2But or sodium nitrite, giving yields ranging
from 15 to 68%. Thus, general efficient synthetic routes to
azacarboranes have not yet been developed.
hypho-5-CH3-5,11,7,14-CNS2B7H9 (1)
arachno-6,8-C2B7H12- + CH3CN (1) reflux8
(2) H+
nido-6-CH3-5,6,9-C3B7H10 + NH3 (2)
These results suggested that borane-anion/nitrile reactions
might provide general routes to a variety of new azacarborane
and/or carborane clusters. Indeed, in this paper, we report our
synthetic and structural studies of a variety of such clusters that
have resulted from the reactions of nitriles with the isoelectronic
-
-
anions, nido-5,6-C2B8H11 and nido-B10H13
.
Experimental Section
We have previously reported6 that the carbon atoms in nitriles
are susceptible to nucleophilic attack by certain polyhedral
thiaborane and carborane anions and that such reactions lead
to either CN or carbon insertion reactions, producing new
thiaazacarboranes or tricarbaboranes. Thus, the reaction of
All manipulations were carried out by using standard high vacuum
or inert-atmosphere techniques as described by Shriver.7
Materials. Decaborane, B10H14, was obtained from laboratory stock
and sublimed before use. The carborane, nido-5,6-C2B8H12, and its
anion were prepared according to the literature methods.8 Benzyl
cyanide, PPN+Cl- (bis(triphenylphosphoranylidene)ammonium chlo-
ride), and Proton Sponge (PS, 1,8-bis(dimethylamino)naphthalene) were
purchased from Aldrich and used as received. Sulfuric acid (99.999%)
-
acetonitrile with arachno-6,8-S2B7H8 results in CN insertion
to give hypho-5-CH3-5,11,7,14-CNS2B7H9 (eq 1) while the
reaction of the isoelectronic carborane anion arachno-6,8-
-
C2B7H12 with acetonitrile results in carbon insertion to yield
and 1.0 M HCl/Et2O were purchased from Aldrich and stored under
N2 until use. The labeled CH313CN was prepared as reported previ-
ously.9 Acetonitrile and methylene chloride were dried by distillation
over P2O5 and freshly distilled from molecular sieves before use.
nido-6-CH3-5,6,9-C3B7H10 (eq 2).
X Abstract published in AdVance ACS Abstracts, June 15, 1996.
S0002-7863(96)00787-1 CCC: $12.00 © 1996 American Chemical Society

6408 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
Diethyl ether was dried over sodium benzophenone and freshly distilled
before use. Heptane and hexane were purchased from Fisher and used
as received. Oil dispersed NaH was obtained from Aldrich, washed
with dry hexane under a nitrogen atmosphere, and then vacuum dried.
Physical Measurements. 1H NMR spectra at 200.1 MHz and 11B
NMR at 64.2 MHz were obtained on a Bruker AF-200 spectrometer,
equipped with the appropriate decoupling accessories. 1H NMR spectra
at 500.1 MHz, 11B NMR spectra at 160.5 MHz, and 13C NMR spectra
at 125.7 MHz were obtained on a Bruker AM-500 spectrometer. All
11B chemical shifts are referenced to external BF3‚O(C2H5)2 (0.0 ppm)
with a negative sign indicating an upfield shift. All 1H and 13C chemical
shifts were measured relative to internal residual protons or carbons in
the lock solvents and are referenced to Me4Si (0.0 ppm). Two-
dimensional COSY 11B-11B NMR experiments were performed at 64.2
or 160.5 MHz using the procedures described previously.10 Infrared
spectra were obtained on a Perkin-Elmer 7770 Fourier transform
spectrometer or a Perkin-Elmer 1430 spectrophotometer. Microanalysis
was performed at Robertson Microlit, Madison, NJ. Melting points
were obtained on a standard melting point apparatus and are uncor-
rected.
mmol) of NaH. The flask was connected to the vacuum line and 50
mL of acetonitrile vacuum distilled into the flask at -196 °C. The
mixture was then allowed to warm to room temperature. After the
gas evolution ceased (∼40 min), the solution was filtered into another
100-mL flask under a N2 atmosphere. The 11B NMR spectrum taken
after reflux for 10 days under a N2 atmosphere showed complete
disappearance of the nido-5,6-C2B8H11-. At this time, 2.16 g (3.76
mmol) of PPN+Cl- was added to the flask and the mixture stirred at
room temperature for 2 h. The acetonitrile was then vacuum evaporated
and 20 mL of CH2Cl2 added. After filtration of the solution, ∼20 mL
of diethyl ether and ∼5 mL of heptane were added and the solution
filtered again. Slow evaporation of the remaining solvent afforded 1.73
g (2.46 mmol, 65.4% yield) of white, crystalline PPN+-arachno-7-CH3-
5,7,14,12-C3NB8H11- (PPN+1-). Anal. Calcd: C, 68.35%; H, 6.41%;
N, 3.99%. Found: C, 67.68%; H, 6.11%; N, 4.01%. IR (KBr, cm-1
)
3360 (s), 3020 (m), 2935 (m), 2525 (vs), 2480 (vs), 1530 (m), 1480
(s), 1420 (m), 1360 (m), 1215 (m), 1160 (m), 1150 (m), 1090 (m),
1050 (w), 980 (m), 950 (m), 775 (w), 735 (w), 700 (w), 655 (w), 580
(w), 515 (w).
Acidification of arachno-7-CH3-5,7,14,12-C3NB8H11- (PPN+1-):
Synthesis of nido-6-CH3-5,6,9-C3B7H10. In a 100-mL round-bottom
Synthesis of PPN+-arachno-7-CH3-5,7,14,12-C3NB8H11- (PPN+1-).
A 100-mL round-bottom flask fitted with a vacuum stopcock was
charged with 0.46 g (3.76 mmol) of nido-5,6-C2B8H12 and 0.17 g (7.08
-
flask, 1.93 g (2.75 mmol) of PPN+-arachno-7-CH3-5,7,14,12-C3NB8H11
was dissolved in 20 mL of CH2Cl2. The solution was maintained at 0
°C, while 5 mL of H2SO4 was slowly added. The solution was then
stirred for 30 min. The CH2Cl2 layer was removed and the H2SO4
layer extracted twice with CH2Cl2. Vacuum fractionation of the
combined CH2Cl2 solutions through -45 and -196 °C traps afforded
0.11 g (0.80 mmol, 41.5% yield) of nido-6-CH3-5,6,9-C3B7H10 in the
-45 °C trap, which was identified by comparison of its 11B NMR and
mass spectrum with literature values.5
(1) (a) Hertler, W. R.; Klanberg, F.; Muetterties, E. L. Inorg. Chem. 1967,
6, 1696-1706. (b) Basˇe, K.; Plesˇek, J.; Heˇrma´nek, S. J. Chem. Soc., Chem.
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2479-2493. (h) Basˇe, K.; Hanousek, F.; Plesˇek, J.; Sˇt´ıbr, B. J. Chem. Soc.,
Chem. Commun. 1981, 1162-1163. (i) Basˇe, K. Collect. Czech. Chem.
Commun. 1983, 48, 2593-2603. (j) Todd, L. J.; Arafat, A.; Baer, J.;
Huffman, J. C. Mol. Struct. Energ., AdV. Boron Boranes 1986, 5, 287-
295. (k) Arafat, A.; Baer, J.; Huffman, J. C.; Todd, L. J. Inorg. Chem.
1986, 25, 3757-3761. (l) Boese, R.; Kro¨ckert, B.; Paetzold, P. Chem. Ber.
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479-480. (n) Sˇt´ıbr, B.; Kennedy, J. D.; Jel´ınek, T. J. Chem. Soc., Chem.
Commun. 1990, 1309-1310. (o) Mu¨ller, J.; Paetzold, P.; Boese, R. Heteroat.
Chem. 1990, 1, 461-465. (p) Mu¨ller, J.; Runsink, J.; Paetzold, P. Angew.
Chem., Int. Ed. Eng. 1991, 30, 175. (q) Zahradn´ık, R.; Balaji, V.; Michl, J.
J. Comput. Chem. 1991, 12, 1147-1156. (r) Paetzold, P. Pure Appl. Chem.
1991, 63, 345-350. (s) No¨th, H.; Geisberger, G.; Linti, G.; Loderer, D.;
Rattay, W.; Salzbrenner, E. Pure Appl. Chem. 1991, 63, 351-355. (t)
Mu¨ller, J.; Paetzold, P.; Englert, U.; Runsink, J. Chem. Ber. 1992, 125,
97-102. (u) Meyer, F.; Mu¨ller, J.; Paetzold, P.; Boese, R. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1227-1229. (v) Hnyk, D.; Bu¨hl, M.; Schleyer, P.
v. R.; Volden, H. V.; Gundersen, S.; Mu¨ller, J.; Paetzold, P. Inorg. Chem.
1993, 32, 2442-2445. (w) Meyer, F.; Mu¨ller, J.; Schmidt, M. U.; Paetzold,
P. Inorg. Chem. 1993, 32, 5053-5057. (x) Jel´ınek, T.; Kennedy, J. D.;
Sˇt´ıbr, B. J. Chem. Soc., Chem. Commun. 1993, 1628-1629. (y) Paetzold,
P.; Mu¨ller, J.; Meyer, F.; Hansen, H-P.; Schneider, L. Pure Appl. Chem.
1994, 66, 255-262. (z) Jel´ınek, T.; Kennedy, J. D.; Sˇt´ıbr, B. J. Chem. Soc.,
Chem. Commun. 1994, 677-678. (aa) Roth, M.; Paetzold, P. Chem. Ber.
1995, 128, 1221-1224. (bb) Lomme, P.; Meyer, F.; Englert, U.; Paetzold,
P. Chem. Ber. 1995, 128, 1225-1229.
-
Synthesis of PSH+-arachno-7-CH3-7,12-CNB10H13 (PSH+2a-).
A 100-mL round-bottom flask fitted with a vacuum stopcock was
charged with 0.59 g (4.82 mmol) of nido-B10H14 and 1.14 g (5.32 mmol)
of Proton Sponge. The flask was connected to the vacuum line and
20 mL of acetonitrile was added by vacuum distillation. The flask
was warmed to room temperature, which resulted in the formation of
nido-B10H13-, as evidenced by 11B NMR.11 The flask was fitted with
a condenser and the reaction mixture refluxed under a N2 atmosphere
for 4 days. The acetonitrile was removed in vacuo to leave a red oil,
which was then dissolved in CH2Cl2. Hexane was slowly added,
causing separation of a red layer at the bottom with the product forming
a suspension in the yellow CH2Cl2/hexane layer. Separation of the
yellow layer and subsequent extraction of the red oil with additional
CH2Cl2/hexane gave, after removal of the solvent, 0.98 g (2.59 mmol,
53.7% yield) of PSH+-arachno-7-CH3-7,12-CNB10H13- (PSH+2a-), as
a yellow solid. Anal. Calcd: C, 50.90%; H, 9.34%; N, 11.13%; B,
28.63%. Found: C, 50.50%; H, 9.40%; N, 10.84%; B 28.42%. IR
(KBr, cm-1) 3310 (m), 3030 (w), 2950 (w), 2510 (vs), 2470 (vs), 1510
(w), 1460 (m), 1410 (w), 1380 (w), 1230 (w), 1195 (w), 1125 (w),
1040 (m), 1010 (w), 840 (w), 775 (m), 595 (w), 385 (w).
Synthesis of PSH+-arachno-7-CH3-7,12-13CNB10H13- (PSH+2a--
13C). In a similar manner as described above, 0.81 g (6.63 mmol) of
nido-B10H14 and 1.46 g (6.81 mmol) of Proton Sponge were dissolved
in 5 mL of CH313CN. The reaction was refluxed for 2 days and the
subsequent isolation afforded a crude yield of 1.85 g (4.89 mmol, 73.8%
(2) (a) Kester, J. G.; Huffman, J. C.; Todd, L. J. Inorg. Chem. 1988, 27,
4528-4532. (b) Basˇe, K.; Bown, M.; Fontaine, X. L. R.; Greenwood, N.
N.; Kennedy, J. D.; Sˇt´ıbr, B.; Thornton-Pett, M. J. Chem. Soc., Chem.
Commun. 1988, 1240-1241. (c) Nestor, K.; Fontaine, X. L. R.; Kennedy,
J. D.; Sˇt´ıbr, B.; Basˇe, K.; Thornton-Pett, M. Collect. Czech. Chem. Commun.
1991, 56, 1607-1617.
-
crude yield) of PSH+-arachno-7-CH3-7,12-13CNB10H13 (PSH+2a--
13C) as a yellow solid.
Synthesis of PSH+-arachno-7-Bn-7,12-CNB10H13- (PSH+2b-). A
250-mL round-bottom flask fitted with a vacuum stopcock was charged
with 2.00 g (16.37 mmol) of nido-B10H14 and 3.46 g (16.14 mmol) of
Proton Sponge. This mixture was then dissolved in 20 mL of benzyl
cyanide. The flask was fitted with a condenser and the reaction mixture
heated at 80 °C under a N2 atmosphere for 2 days. The remaining
benzyl cyanide was removed in vacuo by heating at 100 °C for 3 h to
leave a red oil, which was then dissolved in CH2Cl2. Fractional
recrystallization by addition of hexane caused precipitation of an orange
oily material. This material was redissolved in CH2Cl2 and isolated as
a solid by addition of the CH2Cl2 solution to a large excess of heptane.
(3) Plesˇek, J.; Sˇt´ıbr, B.; Herˇma´nek, S. Chem. Ind. (London) 1974, 662-
663.
(4) Janousˇek, Z.; Fusek, J.; Sˇt´ıbr, B. J. Chem. Soc., Dalton Trans. 1992,
2649-2650.
(5) Holub, J.; Jelinek, T.; Plesˇek, J.; Sˇt´ıbr, B.; Herˇma´nek, S.; Kennedy,
J. D. J. Chem. Soc., Chem. Commun. 1991, 1389-1390.
(6) Kang, S. O.; Furst, G. T.; Sneddon, L. G. Inorg. Chem. 1989, 28,
2339-2347.
(7) Shriver, D. F.; Drezdzon, M. A. Manipulation of Air SensitiVe
Compounds, 2nd ed., Wiley: New York, 1986.
(8) Plesˇek, J.; Heˇrma´nek, S. Collect. Czech. Chem. Commun. 1974, 39,
821-826.
(9) Plumb, C. A.; Sneddon, L. G. Organometallics 1992, 11, 1681-
(11) Chambers, J. Q.; Norman, A. D.; Bickell, M. R.; Cadle, S. H. J.
Am. Chem. Soc. 1968, 90, 6056-6062.
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7, 772-776.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6409
The solid was removed by filtration and dried under vacuum to yield
(vs), 2430 (s), 2350 (w), 1465 (m), 1430 (m), 1415 (m), 1395 (m),
1360 (m), 1310 (m), 1265 (w), 1230 (w), 1190 (m), 1165 (m), 1150
(m), 1100 (s), 1010 (m), 970 (w), 930 (w), 840 (m), 820 (w), 775 (s),
725 (w), 595 (w), 485 (w). Anal. Calcd: C, 52.25%; H, 9.87%; N,
11.43%; B, 26.45%. Found: C, 51.88%; H, 9.68%; N, 10.89%; B,
26.20%.
3.48 g (7.67 mmol, 46.9% yield) of PSH+-arachno-7-Bn-7,12-
-
CNB10H13 (PSH+2b-) as a yellow solid. Anal. Calcd: C, 58.25%;
H, 8.66%; N, 9.26%. Found: C, 58.20%; H, 7.53%; N, 8.63%. IR
(KBr, cm-1) 3320 (w), 3060 (w), 3025 (w), 2960 (w), 2920 (w), 2510
(vs), 1605 (w), 1490 (m), 1455 (s), 1415 (m), 1385 (m), 1270 (m),
1225 (m), 1185 (m), 1160 (m), 1100 (w), 1080 (w), 1030 (m), 1005
(m), 835 (w), 770 (m), 705 (m), 610 (w), 490 (w), 420 (w).
Synthesis of hypho-12-CH3-12,13-13CNB9H14- (PSH+3a--13C) and
hypho-12-CH3-12,11-13CNB9H14- (PSH+4a--13C). To a sample of 3a-
13C (∼0.05 g, 0.32 mmol) in CH2Cl2 was added an excess of Proton
Sponge in CH2Cl2. After 5 min, an NMR sample was removed and
used to obtain the 11B NMR spectra of PSH+3a--13C. The remainder
of the solution was stirred overnight. The anion was isolated as
described above for the unlabeled compound to give PSH+4a--13C as
a yellow solid (∼0.1 g, 0.27 mmol, 80% yield).
Synthesis of hypho-12-CH3-12,13-CNB9H15 (3a). In a 100-mL
round-bottom flask, 2.41 g (6.38 mmol) of PSH+2a- was dissolved in
50 mL of CH2Cl2. The solution was maintained at 0 °C, while 10 mL
of H2SO4 was slowly added. The solution was then stirred for 6 h.
The CH2Cl2 layer was removed and the H2SO4 layer extracted twice
with CH2Cl2. The combined CH2Cl2 solutions were vacuum evaporated
at -30 °C. Then, 50 mL of hexane was added and the solution was
filtered. The solution was concentrated in vacuo at -30 °C. The
product was recrystallized from CH2Cl2 and hexane to yield 0.06 g
(0.39 mmol, 6.1% yield) of hypho-12-CH3-12,13-CNB9H15 (3a) as a
white solid. Mp 62-63 °C. Anal. Calcd: C, 15.65%; H, 11.82%;
N, 9.13%; B, 63.40%. Found: C, 16.20%; H, 11.29%; N, 8.64%; B,
59.29%. IR (KBr, cm-1) 3290 (s), 2955 (m), 2560 (s, br), 2190 (m),
1455 (m), 1390 (w), 1320 (w), 1265 (w), 1145 (w), 1095 (m), 1080
(m), 1010 (m), 890 (w), 835 (w), 815 (w), 740 (m), 710 (w), 670 (w),
625 (w), 595 (w), 525 (w). Exact mass calcd for 12C211B914N1H18
155.2277, found 155.2272.
Synthesis of hypho-12-Bn-12,13-CNB9H14- (PSH+3b-). Samples
for spectroscopic analysis were synthesized by addition of an excess
of Proton Sponge in CH2Cl2 to a solution of ∼0.05 g of 3b in CH2Cl2.
After the solution was stirred for 5 min, PSH+3b- was isolated as
described above for PSH+3a- to give PSH+-hypho-12-Bn-12,13-
CNB9H14- (PSH+3b-) as a crude, yellow solid in estimated quantitative
yield. Samples could be stored at -78 °C, but decomposed to PSH+4b-
after several hours at room temperature. IR (KBr, cm-1) 3320 (m),
3060 (w), 3030 (w), 2960 (w), 2930 (w), 2860 (w), 2500 (vs), 1605
(w), 1465 (m), 1455 (m), 1415 (w), 1385 (w), 1270 (w), 1225 (m),
1185 (m), 1160 (m), 1080 (s), 1030 (s), 1005 (s), 835 (w), 770 (s),
705 (w), 605 (w).
Synthesis of hypho-12-CH3-12,13-13CNB9H15 (3a-13C). In a 100-
mL round-bottom flask, 2.31 g (6.11 mmol) of PSH+2a--13C was
dissolved in 50 mL of CH2Cl2. The solution was maintained at 0 °C,
while 10 mL of H2SO4 was slowly added. The 3a-13C was then isolated
as described above for the unlabeled compound to give a white solid
in similar yield (∼0.05 g, 0.32 mmol, 5% yield).
Synthesis of hypho-12-Bn-12,11-CNB9H14- (PSH+4b-). In a 100-
mL round-bottom flask, 0.11 g (0.48 mmol) of 3b was dissolved in 10
mL of CH2Cl2. To this was added a solution of 0.13 g (0.61 mmol) of
Proton Sponge dissolved in 10 mL of CH2Cl2. After the solution was
stirred overnight, the resulting anion was isolated as described above
for PSH+4a- to yield 0.13 g (0.29 mmol, 60.4% yield) of PSH+-hypho-
12-Bn-12,11-CNB9H14- (PSH+4b-). IR (KBr, cm-1) 3280 (m), 3060
(w), 3020 (w), 2960 (w), 2920 (w), 2850 (w), 2490 (s), 1605 (w), 1465
(m), 1455 (m), 1415 (s), 1395 (s), 1310 (s), 1225 (m), 1185 (m), 1165
(m), 1115 (m), 1090 (m), 1065 (m), 1020 (m), 930 (m), 835 (m), 770
(s), 705 (m), 625 (w), 485 (w), 420 (w), 385 (w). Anal. Calcd: C,
59.53%; H, 9.08%; N, 9.47%. Found: C, 56.35%; H, 8.66%; N, 8.82%.
Synthesis of hypho-12-Bn-12,13-CNB9H15 (3b). In a 250-mL
round-bottom flask, 50 mL of CH2Cl2 was added to 20 mL of H2SO4.
The solution was maintained at 0 °C, while 9.60 g (21.16 mmol) of
PSH+2b- dissolved in 200 mL of CH2Cl2 was slowly added. The
solution was then stirred for 5 h. The CH2Cl2 layer was removed and
the H2SO4 layer extracted twice with CH2Cl2. The combined CH2Cl2
solutions were vacuum evaporated at -30 °C. Then, 50 mL of hexane
was added and the solution was filtered. The solution was concentrated
by vacuum evaporation at -30 °C. The product was recrystallized
from CH2Cl2 and hexane to yield 0.32 g (1.39 mmol, 6.6% yield) of
hypho-12-Bn-12,13-CNB9H15 (3b) as a white solid. Mp 136-38 °C,
Anal. Calcd: C, 41.86%; H, 9.66%; N, 6.10%. Found: C, 42.01%;
H, 9.56%; N, 5.76%. IR (KBr, cm-1) 3290 (m), 3070 (w), 3040 (w),
2930 (w), 2560 (vs), 1605 (w), 1560 (w), 1495 (w), 1455 (m), 1390
(w), 1265 (w), 1190 (m), 1090 (m), 1030 (w), 1005 (m), 820 (w), 750
(m), 705 (m), 610 (w). Exact mass calcd for 12C811B914N1H22 231.2590,
found 231.2594.
-
Acidification of hypho-12-R-12,13-CNB9H14 (PSH+3a- and
PSH+3b-). To an NMR sample of either PSH+3a- or PSH+3b- in
CH2Cl2 was added an excess of 1.0 M HCl/Et2O. This resulted in the
immediate regeneration of the original neutral molecules, 3a or 3b,
respectively, as observed by 11B NMR.
Synthesis of hypho-8-CH3-8,13-CNB8H14 (5a). In a 100-mL round-
bottom flask, 0.09 g (0.24 mmol) of PSH+4a- was dissolved in 20 mL
of CH2Cl2. The solution was maintained at 0 °C, 2 mL of H2SO4 was
added dropwise, and the solution was stirred for several hours. The
CH2Cl2 layer was removed and the H2SO4 layer extracted twice with
CH2Cl2 and the combined CH2Cl2 solutions then concentrated by
vacuum evaporation at -30 °C. Then, 20 mL of hexane was added
and the solution was dried over MgSO4 and filtered. The resulting
solution was fractionated overnight through -50 and -196 °C traps.
The -50 °C trap contained 0.02 g (0.14 mmol, 58.3% yield) of hypho-
8-CH3-8,13-CNB8H14 (5a) as a colorless liquid. IR (CCl4 sol, NaCl
plates, cm-1) 3330 (s), 2960 (m), 2930 (w), 2900 (w), 2870 (w), 2560
(s, br), 1450 (m), 1380 (w), 1350 (m), 1315 (w), 1260 (w), 1200 (w),
1150 (m), 1105 (m), 1070 (w), 1045 (w), 995 (w), 980 (w), 935 (m),
910 (w), 890 (w). Exact mass calcd for 12C211B814N1H17 143.2105,
found 143.2108.
Synthesis of hypho-8-CH3-8,13-13CNB8H14 (5a-13C). A sample of
PSH+4a--13C (∼0.1 g, 0.27 mmol) was dissolved in CH2Cl2 and reacted
with H2SO4 for 2 h in a similar manner as described above for the
unlabeled compound. The CH2Cl2 layer was removed and concentrated
by vacuum evaporation at -30 °C. Hexane was added, the solution
was filtered, and the solvent was removed at -30 °C. The resulting
oil was dissolved in CD2Cl2 to obtain the 11B NMR spectrum of 5a-
13C.
Synthesis of hypho-12-CH3-12,13-CNB9H14- (PSH+3a-). Samples
for spectroscopic analysis were synthesized by addition of an excess
of Proton Sponge in CH2Cl2 to a solution of ∼0.05 g of 3a in CH2Cl2.
After the solution was stirred for 5 min, the product, PSH+3a-, was
precipitated by addition of hexane to a CH2Cl2 solution and the solvent
was decanted. Washing with additional hexane and drying under
-
vacuum for 1 h afforded PSH+-hypho-12-CH3-12,13-CNB9H14
(PSH+3a-) as a crude, yellow solid in estimated quantitative yield.
Samples could be stored at -78 °C but decomposed to PSH+4a- after
several hours at room temperature. IR (KBr, cm-1) 3290 (m), 3060
(w), 2940 (m), 2865 (m), 2830 (w), 2790 (w), 2500 (vs), 1580 (w),
1465 (m), 1455 (m), 1420 (m), 1390 (m), 1265 (w), 1225 (m), 1190
(m), 1165 (w), 1140 (w), 1100 (s), 1030 (s), 940 (w), 835 (w), 770 (s),
610 (w).
Synthesis of hypho-12-CH3-12,11-CNB9H14- (PSH+4a-). In a 100-
mL round-bottom flask, 0.08 g (0.52 mmol) of 3a was dissolved in 20
mL of CH2Cl2. To this was added a solution of 0.12 g (0.56 mmol) of
Proton Sponge dissolved in 2 mL of CH2Cl2. Then, the solution was
stirred overnight at room temperature. The anion was precipitated by
addition of hexane to the CH2Cl2 solution and the solvent was decanted.
Washing with additional hexane and drying under vacuum afforded
0.17 g (0.46 mmol, 88.5% yield) of PSH+-hypho-12-CH3-12,11-
Synthesis of hypho-8-Bn-8,13-CNB8H14 (5b). In a 100-mL round-
bottom flask, 0.13 g (0.29 mmol) of PSH+4b- was dissolved in 20
mL of CH2Cl2. The solution was maintained at 0 °C, 2 mL of H2SO4
was added dropwise, and the solution was stirred for several hours.
The CH2Cl2 layer was removed, the H2SO4 layer was extracted twice
-
CNB9H14 (PSH+4a-) as a yellow solid. IR (KBr, cm-1) 3290 (s),
2960 (w), 2940 (m), 2910 (w), 2880 (w), 2860 (w), 2530 (s), 2490

6410 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
with CH2Cl2, and the combined CH2Cl2 solutions were concentrated
by vacuum evaporation at -30 °C. Then, 20 mL of hexane was added
and the solution was dried over MgSO4 and filtered. The solvent was
vacuum evaporated at -30 °C and the solid was recrystallized from
hexane at -78 °C and dried in vacuo to yield 0.04 g (0.18 mmol, 62.0%
yield) of hypho-8-Bn-8,13-CNB8H14 (5b) as a white solid. Mp 102-
104 °C. IR (KBr, cm-1) 3300 (s), 3030 (w), 2920 (m), 2880 (w), 2850
(w), 2540 (vs), 2500 (s), 2480 (s), 1490 (m), 1450 (m), 1355 (m), 1280
(m), 1125 (m), 1080 (m), 1065 (m), 1050 (m), 1030 (w), 1000 (w),
930 (m), 885 (w), 830 (w), 750 (m), 705 (m), 625 (w), 605 (w), 545
(w), 500 (w). Exact mass calcd for 12C811B814N1H21 219.2419, found
219.2426.
Computational Methods. The combined ab initio/IGLO/NMR
method, using the GAUSSIAN9013 and GAUSSIAN9214 programs, was
used as described previously.15 The geometries were fully optimized
at the HF/6-31G* level within the specified symmetry constraints (using
the standard basis sets included) on a Silicon Graphics International
IRIS 4D/440VGX computer. Selected calculated intramolecular bond
distances are compared to the crystallographically determined distances
in tables in the supporting information. A vibrational frequency analysis
was carried out on each optimized geometry at the HF/3-21G level
and a true minimum was found for each structure (i.e. possessing no
imaginary frequencies). The NMR chemical shifts were calculated
using the IGLO program employing the following basis sets. Basis
DZ: C, B, N 7s3p contracted to [4111, 21]; H 3s contracted to [21].
-
Synthesis of hypho-8-R-8,13-CNB8H13 (PSH+5a-, PSH+5b-).
Samples for spectroscopic analysis were prepared in good yield by
addition of an excess of Proton Sponge to a solution of 5a or 5b in
CH2Cl2. The resulting anion was precipitated by addition of hexane
and the solvent decanted. Washing with additional hexane and drying
under vacuum yielded a crude sample of either hypho-8-CH3-8,13-
Results and Discussion
-
The isoelectronic, 10-vertex nido-5,6-C2B8H11 and nido-
-
-
-
CNB8H13 (PSH+5a-) or hypho-8-Bn-8,13-CNB8H13 (PSH+5b-),
which were found to be too unstable for complete characteri-
zation.
B10H13 anions were both found to readily react with nitriles
to produce new azacarborane products in good yields (eqs 3
and 4).
-
Synthesis of hypho-8-CH3-8,13-13CNB8H13 (PSH+5a--13C). To
an NMR sample of 5a-13C in CD2Cl2 was added excess Proton Sponge.
The formation of PSH+5a--13C was observed by 11B NMR.
Acidification of hypho-8-CH3-8,13-CNB8H13- (PSH+5a-). To an
NMR sample of PSH+5a- in CH2Cl2 was added an excess of 1.0 M
HCl/Et2O. This resulted in the immediate regeneration of the original
neutral molecule 5a, as observed by 11B NMR.
nido-5,6-C2B8H11- + CH3CN f
-
arachno-7-CH3-5,7,14,12-C3NB8H11
(3)
(1-)
nido-B10H13- + RCN f
Crystallographic Data. Single crystals of PPN+-arachno-7-CH3-
-
5,7,14,12-C3NB8H11 (PPN+1-) were grown by slow evaporation of
-
arachno-7-R-7,12-CNB10H13
CH2Cl2/Et2O/heptane solutions under argon. The crystal of PPN+1-
was mounted inside a capillary tube which was then sealed with glue
and mounted on the diffractometer. Single crystals of PSH+-arachno-
7-CH3-7,12-CNB10H13- (PSH+2a-), hypho-12-Bn-12,13-CNB9H15 (3b),
and PSH+hypho-12-CH3-12,11-CNB9H14- (PSH+4a-) were grown by
slow evaporation of CH2Cl2/hexane solutions. The cell constants for
all compounds were determined from a least-squares fit of the setting
angles for 25 accurately centered reflections.
(R ) CH3, 2a-; 2a--13C)
(4)
(R ) Bn, 2b-)
The products were isolated as air-stable, crystalline PPN+
(1-) or Proton Sponge H+ salts (2a- and 2b-). Single-crystal
structural determinations of PPN+1- and PSH+2a-, shown in
the ORTEP drawings in Figures 1 and 2, confirm insertion of
both the nitrile carbon and nitrogen into the borane cluster
framework to produce isoelectronic azatricarbaborane (1-) and
azamonocarbaborane (2a-) anions. In both anions, the imine
group bridges the B2 and B11 atoms and lies in a molecular
mirror plane. Accordingly, both cages have two puckered six-
membered open faces, containing the CN unit and four other
cage atoms. In 1-, each face contains one of the original cage
carbon atoms, at C5 or C14, whereas in 2-, each face contains
one bridge hydrogen at the B1-B5 and B8-B14 edges. The
C7-N12 bond distances in 1- (1.310(3) Å) and 2a- (1.307(3)
Å) are consistent with reduction of the acetonitrile carbon-
nitrogen triple bond and are similar to that found previously6
in hypho-5-CH3-5,11,7,14-CNS2B7H9, (C5-N11, 1.298(5) Å).
Collection and Refinement of the Data. For PPN+1- and
PSH+2a-, X-ray intensity data were collected on an Enraf-Nonius
CAD4 diffractometer employing graphite-monochromated Cu KR
radiation and using the ω-2θ scan technique. For PSH+4a-, the data
were collected on a MSC/AFC7R diffractometer employing graphite-
monochromated Cu KR radiation and using the ω-2θ scan technique.
For 3b, the data were collected on an MSC/R-AXIS IIc area detector
employing graphite-monochromated Mo KR radiation with 6° oscil-
lations, exposures of 5 min per frame, a crystal to detector distance of
82 mm, and a temperature of 235 K. For PPN+1-, PSH+2a-, and
PSH+4a-, three standard reflections measured every 3500 s of X-ray
exposure, over the course of data collection, showed no intensity decay
for PPN+1-, and 0.7% and 7.83% decay for PSH+2a- and PSH+4a-,
respectively. A linear decay correction was applied to PSH+2a- and
PSH+4a-. The intensity data for all structures were corrected for
Lorentz and polarization effects, but not for absorption.
The observed basket structures of 1- and 2- can be viewed
in at least two ways. If the nitrile-derived carbon and nitrogen
are considered to be part of the cluster framework, then each
cluster would contain 30 skeletal electrons and be a 12-vertex
arachno system (n + 3 skeletal electron pairs). On the basis of
Solution and Refinement of the Structures. The calculations for
PPN+1- and PSH+2a- were performed on a DEC MicroVAX 3100
computer using the Enraf-Nonius Molen structure package. The
calculations for 3b and PSH+4a- were performed on a Silicon Graphics
Indigo R4000 computer using the Molecular Structure Corporation
teXsan12 package. The structures were solved by direct methods
(MULTAN11/82, SIR88 or SIR92). Refinement was by full-matrix
least-squares techniques based on F to minimize the quantity ∑w(|Fo|
- |Fc|)2 with w ) 1/σ2(F). For PPN+1-, PSH+2a-, and 3b, non-
hydrogen atoms were refined anisotropically and hydrogens were
refined isotropically. For PSH+4a-, non-hydrogen atoms were refined
anisotropically and hydrogens were refined isotropically, except for
the cage-methyl hydrogens and the hydrogen on N2 which were
included as constant contributions to the structure factors and were
not refined.
(13) Frisch, M. J.; Head-Gordon, M.; Trucks, G. W.; Foresman, J. B.;
Schlegel, H. B.; Raghavachari, K.; Robb, M.; Binkley, J. S.; Gonzalez, C.;
Defrees, D. J.; Fox, D. J.; Whiteside, R. A.; Seeger, R.; Melius, C. F.;
Baker, J.; Martin, R. L.; Kahn, L. R.; Stewart, J. J. P.; Topiol, S.; Pople, J.
A. Gaussian 90, ReVision H, Gaussian, Inc.: Pittsburgh, PA, 1990.
(14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
Johnson, B. G.; Wong, M. W.; Foresman, J. B.; Robb, M. A.; Head-Gordon,
M.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley,
J. S.; Gonzalez, C.; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.;
Stewart, J. J. P.; Pople, J. A. Gaussian 92/DFT, ReVision F.2; Gaussian,
Inc.: Pittsburgh, PA, 1993.
Crystal and refinement data are given in Table 2. Refined positional
parameters are given in tables in the supporting information. Selected
intramolecular bond distances are presented in Tables 3-6.
(15) Keller, W.; Barnum, B. A.; Bausch, J. W.; Sneddon, L. G. Inorg.
Chem. 1993, 32, 5058-5066.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6411
δ (multiplicity, assignment, J (Hz))
Table 1. NMR Data
compounds
nucleus
11Ba,b
arachno-7-CH3-5,7,14,12-C3NB8H11 (PPN+1-)
5.6 (d, B1,8, JBH 132), 2.3 (d, B10, JBH 154), -8.3 (d, B3, JBH 132),
-20.9 (d, B11, JBH 114), -23.3 (d, B2, JBH ∼160), -23.9
(d, B4,9, JBH 134)
11B (calc)c
11B-11Bb,d
1H{11B}b,e,f
4.6 (B1,8), 4.9 (B10), -5.9 (B3), -24.5 (B11), -27.7 (B2),
-25.8 (B4,9)
observed crosspeaks: B1,8-B2, B1,8-B3, B2-B3, B3-B4,9,
B4,9-B10
6.46 (br, NH), 3.06 (1, BH), 2.50 (2, BH), 2.43 (s, CH3), 1.87
(1, BH), 1.55 (s, 2, CH, 1, BH), 1.40 (1, BH), 1.20 (2, BH)
210.5 (br, C7), 40.8 (d, br, C5,14, JCH 151), 30.6 (q, C7a, JCH 132)
-7.5 (d, B10, JBH 142), -8.4 (d, B11, JBH 161), -9.3 (d, B3,
JBH 130), -11.6 (d, B1,8, JBH 135), -15.9 (d, B5,14, JBH ∼175),
-17.1 (d, B2, JBH 125), -24.0 (d, B4,9, JBH 134)
-3.4 (B10), -12.4 (B11), -4.8 (B3), -13.9 (B1,8), -18.5 (B5,14),
-22.5 (B2), -27.6 (B4,9)
13Cb,f,g
11Ba,b
arachno-7-CH3-7,12-CNB10H13- (PSH+2a-)
11B (calc)c
11B-11Bb,d
1H{11B}f,i,j
observed crosspeaks: B1,8-B2, B1,8-B4,9, B2-B3h, B3-B4,9,
B4,9-B5,14, B4,9-B10h, B5,14-B10h, B5,14-B11h
8.33 (br, NH), 2.91 (1, BH), 2.27 (s, CH3), 2.02 (1, BH), 1.87
(1, BH), 1.27 (5, BH), 0.86 (2, BH), -8.08 (2, BHB)
197.8 (br, C7), 30.6 (q, C7a, JCH 129)
13Cf,g,i
arachno-7-CH3-7,12-13CNB10H13- (PSH+2a--13C)
arachno-7-Bn-7,12-CNB10H13- (PSH+2b-)
11B{1H}a,b
-7.5 (s, B10), -8.5 (s, B3), -9.3 (s, B11), -11.6 (s, B1,8),
11 13
-15.9 (s, B5,14), -17.2 (d, B2, J C 57), -24.0 (s, B4,9)
B
1H{11B}b,f,j,k
2.49 (d, CH3, JH C 5), 2.47 (1, BH), 2.26 (1, BH), 2.11 (1, BH),
13
1.53 (5, BH), 1.12 (2, BH), -7.74 (2, BHB)
13C{1H}b,f,g,l
197.3 (q, 13C7, J B 60)
13 11
C
11Ba,i
-7.0 (d, B10, JBH ∼145), -8.0 (d, B3, JBH obscured), -8.4
(d, B11, JBH ∼120), -10.9 (d, B1,8, JBH 124), -15.2
(d, B5,14, JBH 122), -15.6 (d, B2, JBH ∼100), -23.0
(d, B4,9, JBH 135)
7.27 (m, br, C6H5), 4.24 (s, CH2), 2.60 (1, BH), 2.33 (1, BH),
2.12 (1, BH), 1.56 (2, BH), 1.50 (2, BH), 1.37 (1, BH), 1.14
(2, BH), -7.76 (2, BHB)
15.9 (d, B4, JBH 148), 3.8 (d, B11, JBH 128), -7.1 (d, B2 or B8,
JBH 173), -8.4 (d, B2 or B8, JBH 172), -19.6 (d, B1, B9, JBH 146),
-37.1 (d of d, B5 or B10, JBH 190, JBµH 30), -38.5 (d of d, B5 or
B10, JBH 177, JBµH 35), -52.7 (d, B3, JBH 150)
1H{11B}b,f,j,k
hypho-12-CH3-12,13-CNB9H15 (3a)
11Ba,m
11B (calc)c
11B-11Bd,m
17.8 (B4), 3.5 (B11), -7.6 (B2), -8.0 (B8), -13.9 (B1),
-14.1 (B9), -36.6 (B5), -37.0 (B10), -57.6 (B3)
observed crosspeaks: B1(B9)-B3, B1(B9)-B4, B1(B9)-B5(B10),
B1(B9)-B10(B5), B1(B9)-B2(B8), B1(B9)-B8(B2), B2(B8)-B3,
B8(B2)-B3, B3-B4, B4-B5(B10), B4-B10(B5)
4.39 (1, BH), 2.69 (1, BH), 2.58 (1, BH), 2.47 (1, BH), 2.38 (2, BH),
1.37 (2, BH), 1.01 (1, NH), 0.56 (br, 1, CH), 0.41 (1, BH), 0.15
(d, CH3, JHH 7), -1.04 (1, BHB), -1.53 (1, BHB), -1.61 (1, BHB),
-1.68 (1, BHB)
1H{11B}f,j,m
13Cb,f,g
33.70 (br, C12), 20.4 (q, C12a, JCH 127)
hypho-12-CH3-12,13-13CNB9H15 (3a-13C)
11B{1H}a,m
16.1 (s, B4), 4.1 (d, B11, J C 53), -7.0 (s, B2 or B8), -8.3 (s, B2 or
11 13
B
B8), -19.5 (s, B1,9), -36.9 (s, B5 or B10), -38.4 (s, B5 or B10),
-52.6 (s, B3)
1H{11B}f,j,k,m,n
4.38 (1, BH), 2.69 (1, BH), 2.56 (1, BH), 2.47 (1, BH), 2.38 (2, BH),
13
1.36 (2, BH), 0.80 (br, 1, CH), 0.15 (d of d, CH3, JHH 7, JH C 3),
-1.05 (1, BHB), -1.55 (1, BHB), -1.62 (1, BHB), -1.70 (1, BHB)
13C{1H}f,g,l,m
32.45 (d, 13C12, J B 60)
13 11
C
hypho-12-Bn-12,13-CNB9H15 (3b)
11Ba,b
15.5 (d, B4, JBH 142), 3.9 (d, B11, JBH 119), -6.6 (d, B2 or B8, JBH 169),
-8.1 (d, B2 or B8, JBH 151), -19.5 (d, B1,9, JBH 141), -37.6 (d of d,
B5 or B10, JBH ∼145, JBµH ∼40), -38.3 (d of d, B5 or B10, JBH ∼125,
JBµH ∼40), -52.9 (d, B3, JBH 149)
1H{11B}b,f,j
7.23 (m, br, C6H5), 3.9 (br, NH), 3.71 (1, BH), 3.03 (1, BH), 2.93 (d, CH,
JHH 13), 2.69 (2, BH), 2.39 (t, CH, JCH 12), 2.08 (s, CH), 1.97 (2, BH),
0.92 (2, BH), -0.28 (1, BH), -0.64 (1, BHB), -1.22 (2, BHB),
-1.33 (1, BHB)
hypho-12-CH3-12,13-CNB9H14- (PSH+3a-)
11Ba,b
-2.5 (d, 1, JBH 126), -16.9 (d, 1, JBH 132), -19.2 (d, B11, JBH 134),
-21.0 (br, 1), -31.7 (d, 1, JBH ∼135), -32.5 (d, 2, JBH ∼137),
-47.3 (br, 2)
from structure in Figure 13a: 0.8 (B4), -10.4 (B5), -16.1 (B8),
-19.9 (B2), -20.7 (B11), -27.5 (B3), -43.6 (B9), -48.9 (B1),
-49.5 (B10)
11B (calc)c
from structure in Figure 13b: 16.3 (B4), -11.5 (B11), -12.3 (B2),
-18.4 (B8), -26.9 (B9), -28.7 (B5), -29.4 (B1), -36.9 (B10),
-56.3 (B3)
1H{11B}b,f,j,n
11B{1H}a,b
2.71 (1, BH), 2.16 (1, NH), 1.97 (1, BH), 1.79 (1, BH), 1.45 (1, CH),
0.91 (d, CH3, JHH 7), 0.67 (2, BH), 0.62 (1, BH), -0.21 (1, BH),
-0.37 (1, BH), -0.57 (1, BHB), -1.87 (1, BHB), -2.12 (1, BHB)
hypho-12-CH3-12,13-CNB9H14- (PSH+3a-13C)
-2.3 (s, 1), -16.9 (s, 1), -19.0 (d, B11, J C 106), -20.8 (s, 1),
11 13
B
-32.3 (s, 3), -47.1 (br, 2)

6412 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
Table 1 (Continued)
compounds
nucleus
δ (multiplicity, assignment, J (Hz))
hypho-12-Bn-12,13-CNB9H14- (PSH+3b-)
11Ba,b
-2.0 (d, 1, JBH 138), -16.9 (d, 1, JBH 130), -19.0 (d, 1, JBH 134),
-21.5 (br, 1), -30.1 (d, 1, JBH 119), -33.1 (d, 1, JBH 138), -33.9
(d, 1, JBH 131), -46.4 (br, 1), -46.8 (br, 1)
7.63 (m, br, C6H5), 2.74 (1, BH), 2.71 (d, CH, JHH 14), 2.24 (t, CH,
JHH 14), 2.04 (1, NH), 1.79 (1, BH), 1.52 (2, CH, BH), 0.80 (1, BH),
0.61 (1, BH), 0.55 (1, BH), -0.29 (2, BH), -0.40 (1, BHB), -1.97
(2, BHB)
13.0 (d, B3, JBH 131), 7.9 (d, B5, JBH 143), 2.4 (d, B7, JBH 121), -10.3
(d, B10, JBH 144), -18.9 (t, B8, JBH 108), -21.6 (d, B2, JBH 116),
-32.8 (d, B9, JBH 130), -35.8 (d, B4, JBH 129), -43.5 (d, B1, JBH 128)
16.2 (B3), 6.5 (B5), 3.5 (B7), -11.5 (B10), -12.0 (B8), -18.9 (B2),
-31.2 (B9), -36.4 (B4), -47.7 (B1)
observed crosspeaks: B1-B2, B1-B3, B1-B4, B1-B5, B1-B7,
B2-B3, B2-B8, B3-B4, B3-B8, B3-B9, B4-B5, B4-B9,
B4-B10, B8-B9
1H{11B}b,f,j,n
hypho-12-CH3-12,11-CNB9H14- (PSH+4a-)
11Ba,i
11B (calc)c
11B-11Bd,i
1H{11B}b,f,j
3.76 (1, BH), 3.44 (1, BH), 2.57 (1, BH), 2.49 (1, NH), 2.19 (1, BH),
1.38 (1, BH), 1.34 (1, CH), 1.10 (1, BH), 1.09 (d, CH3, JHH 7),
0.72 (1, BH), 0.17 (2, BH), -1.12 (1, BH), -2.51 (1, BHB),
-2.59 (1, BHB)
13C{1H}f,g,i
11B{1H}a,i
46.7 (s, C12), 24.8 (s, CH3)
hypho-12-CH3-12,11-13CNB9H14- (PSH+4a-13C)
13.0 (s, B3), 7.9 (s, B5), 2.4 (br, B7, J C obscured), -10.3 (s, B10),
11 13
B
-18.9 (s, B8), -21.6 (d, B2), -32.8 (s, B9), -35.8 (s, B4),
-43.5 (s, B1)
1H{11B}b,f,j
3.75 (1, BH), 3.43 (1, BH), 2.57 (1, BH), 2.47 (1, NH), 2.19 (1, BH),
1.38 (1, BH), 1.26 (br, CH), 1.14 (1, BH), 1.09 (d of d, CH3, JHH 7,
13
JH C 3), 0.72 (1, BH), 0.17 (2, BH), -1.11 (1, BH), -2.51 (1, BHB),
-2.60 (1, BHB)
13C{1H}f,g,i,l
45.5 (d, 13C12, J B 59)
13 11
C
hypho-12-Bn-12,11-CNB9H14- (PSH+4b-)
11Ba,i
12.9 (d, B3, JBH 121), 8.0 (d, B5, JBH 139), 1.3 (d, B7, JBH 123), -10.3
(d, B10, JBH 126), -19.0 (t, B8, JBH 94), -21.8 (d, B2, JBH 131),
-32.9 (d, B9, JBH 102), -35.9 (d, B4, JBH 131), -43.7 (d, B1, JBH 115)
7.2 (m, br, C6H5), 3.79 (1, BH), 3.44 (1, BH), 2.76 (m, 2, CH2), 2.66
(1, BH), 2.40 (1, NH), 2.13 (1, BH), 1.53 (1, CH), 1.41 (1, BH), 1.14
(1, BH), 0.70 (1, BH), 0.17 (2, BH), -1.08 (1, BH), -2.53 (1, BHB),
-2.66 (1, BHB)
25.9 (d, B2, JBH 160), -0.6 (d, B10, JBH 157), -5.0 (d, B3, JBH 130),
-10.2 (d, B12, JBH 149), -33.3 (d of t, B1, JBH 153, JBµH ∼65), -39.5
(d of t, B9, JBH 150, JBµH ∼40), -45.5 (d, B6, JBH 146), -48.5
(d, B4, JBH 144)
1H{11B}f,i,j
hypho-8-CH3-8,13-CNB8H14 (5a)
11Ba,m
11B (calc)c
from structure in Figure 20a: 40.7 (B2), 12.4 (B10), 2.1 (B3),
-9.0 (B1), -23.8 (B12), -24.8 (B6), -30.2 (B9), -55.1 (B4)
from structure in Figure 20b: 40.9 (B2), 13.1 (B10), -8.6 (B12),
-14.4 (B3), -14.7 (B9), -29.5 (B1), -33.4 (B4), -53.2 (B6)
observed crosspeaks: B1-B3, B1-B4, B2-B4, B2-B6, B2-B9,
B3-B4, B4-B6, B4-B10, B6-B9, B6-B10, B6-B12, B9-B12
4.83 (1, BH), 3.63 (1, BH), 2.96 (1, NH), 2.79 (1, BH), 2.65 (1, BH),
1.31 (d, 4, CH3, BH, JCH 7), 1.17 (1, BH), 0.52 (1, CH), 0.36
(1, BH), 0.07 (2, BH), -0.65 (1, BH), -1.98 (1, BHB),
-2.41 (1, BHB)
11B-11Ba,b
1H{11B}b,f,j
hypho-8-CH3-8,13-13CNB8H14 (5a-13C)
hypho-8-Bn-8,13-CNB8H14 (5b)
11B{1H}a,b
25.6 (s, B2), -0.9 (s, B10), -4.7 (d, B3, J C 45), -9.7 (s, B12),
11 13
B
-33.8 (s, B1), -39.4 (d, B9), -46.3 (s, B6), -48.8 (s, B4)
27.9 (d, B2, JBH 169), 1.9 (d, B10, JBH 166), -3.2 (d, B3, JBH 124),
-7.3 (d, B12, JBH 145), -31.6 (d, B1, JBH 134), -36.9 (d,
B9, JBH 108), -43.9 (d, B6, JBH 157), -46.6 (d, B4, JBH 157)
7.22 (m, C6H5), 7.10 (m, C6H5), 7.05 (m, C6H5), 5.06 (1, BH),
∼3.9 (1, BH), 3.06 (1, BH), ∼2.4 (1, BH), 2.31 (d, CH2, JHH 7),
2.05 (1, NH), 1.61 (1, BH), 0.10 (1, BH), 0.02 (3, 2BH, CH),
-0.31 (1, BH), -2.25 (1, BHB), -2.92 (1, BHB)
11Ba,b
1H{11B}f,j,m,n
hypho-8-CH3-8,13-CNB8H13- (PSH+5a-)
11Ba,i
4.6 (d, B2, JBH 133), 2.9 (d, B3, JBH 102), -2.8 (d, B12, JBH 125),
-11.9 (d, B6, JBH 127), -14.2 (d, B1, JBH 133), -16.8 (d, B10,
JBH 142), -49.2 (d, B9, JBH 100), -51.7 (d, B4, JBH 114)
8.8 (B2), 2.0 (B3), -7.4 (B12), -5.7 (B6), -10.6 (B1), -14.6
(B10), -48.4 (B9), -57.9 (B4)
observed crosspeaks: B1-B4, B2-B6, B2-B9, B3-B4, B4-B6,
B4-B10, B6-B9, B6-B10, B6-B12, B9-B12
11B (calc)c
11B-11Ba,b
1H{11B}f,i,j
2.74 (1, BH), 2.46 (1, BH), 2.30 (1, BH), 2.25 (1, BH), 1.94 (1, BH),
1.29 (1, BH), 1.24 (1, CH), 1.05 (d, CH3, JCH 7), -1.02 (1, BH),
-1.72 (1, BH, 2, BHB), -2.32 (1, BHB)
hypho-8-CH3-8,13-13CNB8H13- (PSH+5a-13C)
hypho-8-Bn-8,13-CNB8H13- (PSH+5b-)
11B{1H}a,b
2.5 (s, B2), 1.2 (br, B3, J C obscured), -5.0 (s, B12), -13.9 (s, B6),
11 13
B
-15.5 (s, B1), -18.7 (s, B10), -51.4 (s, B9), -53.8 (s, B4)
3.7 (d, B2, JBH 104), 0.8 (d, B3, JBH 122), -3.8 (d, B12, JBH 134),
-13.0 (d, B6, JBH 124), -15.5 (d, B1, JBH 132), -17.7
11Ba,i
(d, B10, JBH 149), -50.4 (t, B9, JBH 114), -53.0 (d, B4, JBH 134)
f
i
j
a 160.5 MHz. b CD2Cl2. c DZ/6-31G*. d 64.2 MHz. e 200.1 MHz. PPN+ or PSH+ peaks not included. g 125.7 MHz. h Overlapped. CD3CN. 500.1
MHz. k NH not observed. l Labeled carbon only. m C6D6. n Not all terminal BH observed.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6413
Table 2. Crystallographic Data Collection and Structure Refinement Information
compd
PPN+1-
C40H45P2B8N2
702.25
P1h
2
PSH+2a-
B10C16H35N3
377.59
P21/c
3b
PSH+4a-
C16H36B9N3
367.77
P21/c
formula
formula wt
space group
Z
C8B9H22N
229.56
P21/c
4
4
4
cell constants
a, Å
b, Å
10.952(2)
11.741(1)
15.947(2)
106.23(1)
82.74(1)
94.39(1)
1951.3(8)
12.28
12.100(3)
14.306(1)
14.579(3)
6.9727(4)
16.2462(8)
13.0365(7)
11.293(2)
11.986(2)
16.856(3)
c, Å
R, deg
â, deg
114.26(2)
104.513(3)
92.63(2)
γ, deg
V, Å3
2301(2)
3.91
1429.6(1)
0.52
2279.2(7)
3.97
µ, cm-1
crystal size, mm
0.15 × 0.25 × 0.38
0.08 × 0.15 × 0.35
0.45 × 0.22 × 0.20
0.45 × 0.27 × 0.050
d
calc, g/cm3
1.195
1.090
1.066
1.072
radiation
θ range, deg
scan mode
Cu KR (λ ) 1.54184 Å) Cu KR(λ ) 1.54184 Å) Mo KR(λ ) 0.7107 Å) Cu KR(λ ) 1.54184 Å)
2.0-72.0
ω-2θ
2.0-65.0
ω-2θ
+14, -16, (17
4291
2.0-25.0
2.0-60.0
ω-2θ
+12, +13, (17
3374
h, k, l collected
no. of reflcns measured
no. of unique reflcns
(13, +14, (19
+8, (19, (15
10317
2387
8057
7661
3904
3205
no. of reflcns used in refinement (F2 > 3.0σ) 6624
2728
403
1725
252
1928
382
no. of parameters
646
data/parameter ratio
R1
R2
10.3
0.049
0.074
6.8
0.047
0.060
6.85
0.049
0.056
5.05
0.072
0.084
Table 3. Selected Bond Distances (Å) for
Table 5. Selected Bond Distances (Å) for
hypho-12-Bn-12,13-CNB9H15 (3b)
-
arachno-7-CH3-5,7,14,12-C3NB8H11 (1-)
B1-B2
B1-B5
B2-B3
B2-H2
B3-B9
B4-B9
B5-B10
B5-H5,11
B8-H8
B9-H9
1.805(4) B1-B3
1.924(4) B1-H1
1.793(3) B2-B8
1.107(20) B3-B4
1.786(4) B3-H3
1.730(4) B4-B10
1.775(4) B5-B11
1.154(21) B8-B9
1.107(19) B9-B10
1.067(21) B10-B11
1.793(4) B1-B4
1.731(4)
1.090(21) B1-H1,2 1.220(20)
1.967(4) B2-H1,2 1.313(20)
B1-B2
B1-C5
B2-B8
B3-B4
B3-H3
B4-C5
1.854(3) B1-B3
1.590(4) B1-H1
1.842(3) B2-C7
1.768(4) B3-B8
1.117(20) B4-B9
1.673(3) B4-H4
1.774(3) B1-B4
1.057(19) B2-B3
1.519(3) B2-H2
1.776(3) B3-B9
1.774(4)
1.782(3)
1.119(23)
1.768(4)
1.764(4) B3-B8
1.030(20) B4-B5
1.753(4) B4-H4
1.851(4) B5-H5
1.818(3) B8-H8,9 1.315(19)
1.908(4) B9-H8,9 1.243(20)
1.853(4) B10-H10 1.120(20)
1.783(4)
1.750(4)
1.075(20)
1.103(22)
1.765(3) B4-B10 1.737(4)
1.101(22) B8-B9
1.115(18) B9-B10 1.742(4)
1.089(20) B10-B11 1.872(4)
1.775(4)
B8-C14 1.588(3) B8-H8
B9-C14 1.676(3) B9-H9
B10-C5 1.658(3) B10-C14 1.642(3) B10-H10 1.084(28)
B11-C5 1.726(3) B11-C14 1.711(3) B11-N12 1.495(3)
B10-H10,11 1.180(20) B11-H5,11 1.358(22) B11-H11 1.107(20)
B11-H11 1.139(22) C5-H5
1.005(21) C7-C7a 1.514(3)
B11-H10,11 1.352(20) C12-C14
C12-H12
N13-B8
1.537(3) C12-B11 1.616(3)
C7-N12 1.310(3) C14-H14 0.897(27) N12-H12 1.033(25)
0.975(20) N13-C12 1.510(3) N13-B2 1.551(3)
1.553(3) N13-H13 0.916(24)
Table 4. Selected Bond Distances (Å) for
-
arachno-7-CH3-7,12-CNB10H13 (2a-)
Table 6. Selected Bond Distances (Å) for
-
hypho-12-CH3-12,11-CNB9H14 (4a-)
B1-B2
B1-B5
B2-B3
B2-H2
B3-B9
B4-B9
B5-B10
B5-H1,5
B8-H8
B9-B14
1.927(4) B1-B3
1.820(4) B1-H1
1.751(3) B2-B8
1.141(22) B3-B4
1.756(4) B3-H3
1.742(3) B1-B4
1.016(25) B1-H1,5 1.283(20)
1.913(3) B2-C7
1.770(4) B3-B8
1.119(20) B4-B5
1.756(4)
B1-B2
B1-B5
B2-B3
B2-H2
B3-B8
B4-B5
B4-H4
B7-H7
B8-H8a
B9-H9
1.803(11) B1-B3
1.770(9) B1-B7
1.727(10) B2-B7
1.800(9) B1-B4
1.798(12) B1-H1
1.817(11) B2-B8
1.804(9)
1.002(56)
1.869(10)
1.752(9)
1.001(60)
1.539(3)
1.716(4)
1.728(4)
1.087(22)
1.173(20)
1.044(54) B2-H2,7 1.288(43) B3-B4
1.780(4) B4-B10 1.770(4) B4-H4
1.717(4) B5-B11 1.945(5) B5-H5
1.683(10) B3-B9
1.758(8) B4-B9
1.176(47) B5-B10
1.706(10) B3-H3
1.754(10) B4-B10 1.743(9)
1.224(21) B8-B9
1.753(4) B8-B14 1.822(4)
1.912(9) B5-H5
1.161(47)
1.865(10)
1.111(17) B8-H8,14 1.243(21) B9-B10 1.763(3)
1.733(4) B9-H9 1.069(17) B10-B11 1.756(4)
1.116(50) B7-H2,7 1.455(41) B8-B9
1.137(47) B8-H8b 1.164(59) B9-B10 1.821(9)
1.052(54) B9-H9,10 1.384(48) B10-H10 1.233(50)
B10-B14 1.708(4) B10-H10 1.106(24) B11-B14 1.942(3)
B11-N12 1.509(3) B11-H11 1.151(22) B14-H14 1.075(23)
B14-H8,14 1.263(20) C7-C7a 1.510(3) C7-N12 1.307(3)
N12-H12 1.012(22)
B10-H9,10 1.479(48) N11-C12 1.463(7) N11-B5 1.547(9)
N11-B10 1.544(7) C12-C12a 1.527(8) C12-B7 1.612(11)
C12-H12 1.185(77)
simple skeletal electron counting rules,16 the compounds should
then adopt cage structures based on a 14-vertex bicapped
hexagonal antiprism missing two vertices. Indeed, the observed
structures can be derived in this manner, as shown in Figure 3,
by removal of the number 6 and 13 vertices. Alternatively,
the -MeCdNH- groups may be viewed as exopolyhedral
substituents bridging the B2 and B11 atoms on open 10-vertex
arachno frameworks, i.e. arachno-µ2,11-(MeCdNH)-5,14-
-
-
C2B8H10 and arachno-µ2,11-(MeCdNH)-B10H12
.
The
-MeCdNH- fragment could then be considered to be con-
nected to the boron cage by a 2-electron covalent bond between
B2 and C7 and a 2-electron coordinate-covalent bond from N12
to B11. In this view, the compounds would be considered
imine-bridged analogs of arachno-6-NMe3-5,7-C2B8H12,17 arach-
2- 19
no-6,9-L2B10H12,18 or arachno-B10H14
.
This interpretation
is supported by the C7-N12 bond distances, which are within
(16) (a) Williams, R. E. Inorg. Chem. 1971, 10, 210-214. (b) Wade, K.
AdV. Inorg. Chem. Radiochem. 1976, 18, 1-66. (c) Williams, R. E. AdV.
Inorg. Chem. Radiochem. 1976, 18, 67-142. (d) Rudolph, R. W. Acc. Chem.
Res. 1976, 9, 446-452.
(17) Garrett, P. M.; Ditta, G. S.; Hawthorne, M. F. J. Am. Chem. Soc.
1971, 93, 1265-1266.

6414 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
Figure 1. ORTEP drawing of the molecular structure of arachno-7-
-
CH3-5,7,14,12-C3NB8H11 (1-).
Figure 3. Derivation of the observed 12-vertex arachno structures of
1- and 2- from a 14-vertex bicapped hexagonal antiprism.
Figure 2. ORTEP drawing of the molecular structure of arachno-7-
-
CH3-7,12-CNB10H13 (2a-).
the normal range for carbon-nitrogen double bonds, and the
bond angles around the C7 center (e.g. for 1-, B2-C7-C7a,
120.0(2)°; B2-C7-N12, 123.9(2)°; C7a-C7-N12, 116.0(2)°)
which suggest C7 sp2 hybridization.
The structures of anions 1- and 2a- are also confirmed by
ab initio/IGLO/NMR calculations.15 In these calculations, the
geometry of the proposed structure is first optimized using ab
initio theory. The bond distances and angles of the optimized
structure can then be compared to the values determined by
X-ray crystallography, and, as shown in Tables S2a and S5a in
the supporting information, the calculated bond lengths for 1-
and 2a- are in agreement with those determined by X-ray
crystallography (Tables 3 and 4). Additionally, the optimized
structure can then be used as input for an IGLO NMR chemical
shift calculation. This then yields 11B NMR chemical shifts
and assignments that can be compared to the experimentally
determined chemical shifts and assignments. The experimental
11B NMR spectrum of 1- consists of six doublets in a 2:1:1:
1:1:2 ratio, indicating Cs symmetry. The doublet at -20.9 ppm
Figure 4. The 11B{1H} NMR spectra of arachno-7-CH3-7,12-
-
-
13CNB10H13 (2a--13C) and arachno-7-CH3-7,12-CNB10H13 (2a-).
is unusually sharp and shows no crosspeaks with other
resonances in the 2-D 11B-11B NMR spectrum, suggesting that
it is a boron located between two carbons. The 11B NMR
spectrum of 2a- (Figure 4) at 160.5 MHz exhibits seven
doublets in a 1:1:1:2:2:1:2 ratio, consistent with a Cs symmetry
(18) (a) Reddy, J. van der Mass; Lipscomb, W. N. J. Chem. Phys. 1959,
31, 610-616. (b) Reddy, J. van der Mass; Lipscomb, W. N. J. Am. Chem.
Soc. 1959, 81, 754. (c) Sands, D. E.; Zalkin, A. Acta Crystallogr. 1962,
15, 410-417.
(19) Kendall, D. S.; Lipscomb, W. N. Inorg. Chem. 1973, 12, 546-
551.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6415
for the cage. As shown in Table 1, the calculated 11B NMR
shifts and assignments for 1- and 2a- are in good agreement
with both the experimental 11B NMR shifts and the crosspeaks
found in the 2-D 11B-11B NMR spectra of these anions.
Further confirmation of the chemical shift assignments for
2a- was obtained in the 11B NMR spectrum of arachno-7-CH3-
7,12-13CNB10H13- (2a--13C), which was readily synthesized by
-
the reaction of nido-B10H13 with 13C-labeled acetonitrile (eq
5).
nido-B10H13- + CH313CN f
-
arachno-7-R-7,12-13CNB10H13
(5)
(2a--13C)
The IGLO NMR calculation and the 2-D 11B-11B NMR
spectrum predict that the resonance at -17.1 ppm should be
due to the boron (B2) that is directly attached to the nitrile
carbon. A comparison of the 11B{1H} NMR spectra of 2a--
13C with that of the unlabeled 2a-, Figure 4, shows that this
resonance in the spectrum of 2a--13C does, indeed, have 11B13C
coupling consistent with this assignment. The magnitude of
this coupling constant, 57 Hz, is in the range of those reported
Figure 5. Possible reaction sequence leading to the formation of
-
arachno-7-CH3-7,12-CNB10H13- (2a-) in the reaction of nido-B10H13
with acetonitrile.
11B13
C
in other polyhedral boranes and carboranes, including, J
) ∼41 Hz for nido-6-CH3-6-13C-5,6,9-C3B7H10,9 J
) 74
11B13
C
Hz for nido-1-13CH3-B5H8, and J
) 64 Hz for nido-2-
11B13
C
13CH3-B5H8.20 Likewise, the proton-coupled 13C NMR spectrum
of 2a- exhibits a quartet assigned to the Me and a broad singlet
assigned to the C7 carbon, while the spectrum of 2a--13C
13C11
B
exhibits a quartet for the C7 carbon, with J
) 60 Hz.
The other spectral data obtained for 1- and 2a- also support
1
their formulations. The H NMR spectrum for 1- shows a
singlet for the methyl at 2.43 ppm and two broad resonances at
6.46 and 1.55 ppm, which are assigned to the NH and terminal
C5,14 protons, respectively. Its proton-coupled 13C NMR
spectrum exhibits a quartet, doublet, and broad singlet arising
from the Me, C5,14, and C7 carbons, respectively. The 1H{11B}
NMR spectrum of 2a- shows, in addition to the terminal BH
resonances, a broad resonance at 8.33 ppm and singlets at 2.27
and -8.08 ppm, which are assigned to the NH, Me, and bridge
hydrogens, respectively. The presence of an NH group in both
compounds is likewise supported by IR stretches at 3360 cm-1
for PPN+1- and 3310 cm-1 for PSH+2a-.
The formation of 1- and 2- can be envisioned to occur by a
reaction sequence similar to that originally proposed for the
-
reactions of acetonitrile with the arachno-6,8-C2B7H12 and
-
arachno-6,8-S2B7H8 anions. Thus, as shown in Figure 5 for
the reaction with nido-B10H13-, a sequence involving the initial
nucleophilic attack at the positive nitrile carbon followed by
nitrile hydroboration would produce an imino intermediate. Such
a species would be highly nucleophilic and the insertion of this
unit in the manner shown is consistent with the electrophilic
nature of the 6,9-borons in the decaborane framework.21
The formation of 1- also involves other cage rearrangements
during insertion of the nitrile group. As shown in Figure 1,
the cage carbon atoms, C5 and C14, in 1- are non-adjacent, in
contrast to their adjacent positions in the starting nido-5,6-
C2B8H11-. If, as shown in Figure 6, insertion of the nitrile were
to occur without skeletal rearrangement, then the adjacent-carbon
arachno-7-CH3-5,7,11,12-C3NB8H11- would be produced. How-
Figure 6. Cage carbon rearrangement in the reaction of nido-5,6-
-
C2B8H11- with acetonitrile to form arachno-7-CH3-5,7,14,12-C3NB8H11
(1-).
The mechanism of carbon rearrangement is unclear, but similar
rearrangements of cage carbons in 10-vertex dicarbaborane
structures have also been observed during thermolytic dehy-
drogenation (at 200 °C) of arachno-5,6-C2B8H122-, which
2- 22
produced nido-5,7-C2B8H10
.
ever, ab initio calculations show that this structure is 57 kcal/
A comparison of the reactions in eqs 1, 3, and 4 with that of
eq 2 demonstrates that nitriles react with polyhedral borane
anions in two distinct ways. The reactions of the arachno-6,8-
-
mol higher in energy than arachno-7-CH3-5,7,14,12-C3NB8H11
.
(20) Onak, T.; Wan, E. J. Magn. Reson. 1974, 14, 66-71.
(21) (a) Su, K.; Barnum, B.; Carroll, P. J.; Sneddon, L. G. J. Am. Chem.
Soc. 1992, 114, 2730-2731. (b) Su, K.; Carroll, P. J.; Sneddon, L. G. J.
Am. Chem. Soc. 1993, 115, 10004-10017.
(22) Sˇt´ıbr, B.; Plesˇek, J.; Herˇma´nek, S. Collect. Czech., Chem. Commun.
1973, 38, 338-342.

6416 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
-
-
-
S2B7H8 (eq 1), nido-5,6-C2B8H11 (eq 3), and nido-B10H13
(eq 4) anions with nitriles result in carbon and nitrogen insertion
to yield azacarborane products. In contrast, the reaction of
-
acetonitrile with arachno-6,8-C2B7H12 (eq 2) results in de-
ammination and monocarbon insertion to produce the tricar-
baborane nido-6-CH3-5,6,9-C3B7H9-. The differences in reac-
tivity may be related to either the relative basicities of the imine
nitrogens or the number of hydrogens in the borane or carborane
cages that are available for further reduction of the imine bond.
-
In arachno-6,8-C2B7H12 there are two additional acidic
hydrogens, and the observed product is consistent with the
complete reduction of the imine and loss of NH3, with the carbon
from the acetonitrile then inserting into the cage to yield the
tricarbaborane. In arachno-6,8-S2B7H8-, 1-, and 2- there are
not sufficient hydrogens present to allow for both deammination
and the generation of a stable cage fragment without extensive
framework rearrangement. These observations suggested that
deammination could perhaps be induced in these anions under
acidic conditions.
Figure 7. ORTEP drawing of the molecular structure of hypho-12-
Bn-12,13-CNB9H15 (3b).
Although attempts to acidify both PPN+1- and PSH+2- with
HCl/Et2O gave no reaction, the two phase reaction23 of PPN+-
-
arachno-7-CH3-5,7,14,12-C3NB8H11 (PPN+1-) with H2SO4
and CH2Cl2 resulted in loss of a “H2BN” unit from the cage
and further insertion of the nitrile carbon to form the known
tricarbaborane, nido-6-CH3-5,6,9-C3B7H10, in 41.5% yield, as
shown in eq 6. The product was identified by its spectral data
as the tricarbaborane previously generated by acidification of
-
the anion obtained from the reaction of arachno-6,8-C2B7H12
and acetonitrile.6 Thus, the reaction of 1- with H2SO4 provides
another synthetic route to this tricarbaborane.
In contrast to the reaction above, the acidification of PSH+-
arachno-7-R-7,12-CNB10H13- (PSH+2a-, PSH+2b-, PSH+2a--
13C) with H2SO4 was found to result in loss of only one cage
boron, producing the hypho-12-R-12,13-CNB9H15 (3a, 3b, 3a-
13C) (eq 7) azamonocarbaboranes.
Figure 8. Comparison of the structures of 2a- and 3a.
The products were isolated in low yields as air-sensitive white
solids. A single-crystal X-ray study of hypho-12-Bn-12,13-
CNB9H15 (3b) confirmed the open cage structure shown in
Figure 7. As shown in Figure 8, the boron framework in this
structure may be generated in a straightforward manner by
removal of the B8 (or B1) boron of 2a-. However, in contrast
to the structures observed for 1- and 2a-, the -CH(Bn)NHd
unit in 3b is bridging between three borons with the carbon
attached to B11 and the nitrogen bridging the B2-B8 edge.
Furthermore, an additional hydrogen is present at C12 and the
C12-N13 distance of 1.510(3) Å, along with the bond angles
around the tetracoordinate C12 carbon (B11-C12-N13,
117.1(2)°; B11-C12-C14, 111.0(2)°; C14-C12-N13,
108.4(2)°), are consistent with a carbon-nitrogen single bond
(Table 5). The molecule contains two six-membered open faces,
H2SO4
-
PSH+arachno-7-R-7,12-CNB10H13
8
CH2Cl2
(R ) CH3, 2a-; 2a--13C)
(R ) Bn, 2b-)
hypho-12-R-12,13-CNB9H15
(7)
(R ) CH3, 3a; 3a-13C)
(R ) Bn, 3b)
(23) (a) Sˇt´ıbr, B. Private communication. (b) Holub, J.; Wille, A. E.;
Sˇt´ıbr, B.; Carroll, P. J.; Sneddon, L. G. Inorg. Chem. 1994, 33, 4920-
4926.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6417
Figure 10. Comparison of the structures of 3a and n-B9H15.
Figure 9. Derivation of the observed and proposed 11-vertex hypho
structures of 3 and 4- from a bicapped hexagonal antiprism.
one on either side of the bridging -CH(Bn)NHd unit. There
are four bridge hydrogens, two located on the B5-B11 and
B10-B11 edges and two others on the B1-B2 and B8-B9
edges.
The structure observed for 3 is consistent with that expected
for an 11-vertex hypho cluster (n+4 skeletal electron pairs),
and may be derived from a 14-vertex bicapped hexagonal
antiprism by removing the number 6, 7, and 14 vertices, as
shown in Figure 9. One other 11-vertex hypho cage, the hypho-
5-CH3-5,11,7,14-CNS2B7H9, has been previously isolated, but
it has a different 11-vertex hypho structure, which is derived
from the bicapped hexagonal antiprism by removing the number
6, 10, and 13 vertices.6 Alternatively, as described above for
1- and 2-, if the -CH(R)NH) group is considered as only an
exopolyhedral unit, then 3 can be considered to be a 9-vertex
arachno framework with the -CH(R)NH) unit bridging the
cage. As shown in Figure 10, 3 has the same boron skeletal
framework as observed for n-B9H15.24 Comparison of the X-ray
determined structures of n-B9H15 and 3b shows that they have
similar distances and angles. The one major difference is that
in 3b the B2-B11 and B8-B11 distances (∼3.30 Å) are
significantly shorter than the corresponding distances in n-B9H15
(∼3.92 Å) and the B9-B10-B11 and B8-B9-B10 angles are
smaller in 3b (109.8(2)° and 114.7(2)°) than in n-B9H15
(∼119.3° and ∼125.1°). These differences are undoubtedly due
to the bridging CN unit in 3b, which requires shortening of the
B2-B11 and B8-B11 bond distances.
Figure 11. The 11B{1H} NMR spectra of hypho-12-CH3-12,13-
13CNB9H15 (3a-13C) and hypho-12-CH3-12,13-CNB9H15 (3a).
good agreement with those crystallographically determined for
3b, as shown in Table S8a in the supporting information. In
the 11B{1H} NMR spectrum of 3a, shown in Figure 11, there
are eight boron resonances, one of intensity two, and two other
pairs of resonances which are closely space together. This is
expected, as it is only the two different substituents on the C12
carbon that disrupt the mirror symmetry of the cage. The
calculated 11B NMR chemical shifts are in good agreement with
the experimental spectrum, as shown in Table 1. The 11B{1H}
The structure of 3 is also supported by ab initio/IGLO/NMR
calculations on 3a. The calculated bond lengths of 3a are in
NMR spectrum of (3a-13C) (Figure 11) shows a J
of 53
C
11B13
Hz, on the resonance at 4.1 ppm, confirming the assignment of
the B11 resonance. Likewise, the ab initio/IGLO/NMR pre-
dicted chemical shifts and assignments agree with those
determined from the 2-D 11B-11B NMR spectrum.
(24) (a) Dickerson, R. E.; Wheatley, P. J.; Howell, P. A.; Lipscomb, W.
N. J. Chem. Phys. 1957, 27, 200-209. (b) Simpson, P. G.; Lipscomb, W.
N. J. Chem. Phys. 1961, 35, 1340-1343. (c) Beaudet, R. A. In AdVances
in Boron and the Boranes; Liebman, J. F., Greenberg, A., Williams, R. E.,
Eds.; VCH Publishers: New York, 1988; pp 417-490.

6418 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
Wille et al.
Figure 12. The 64.2-MHz 11B proton coupled NMR spectra of 3a-
and 4a-.
The deprotonation of 3a, 3b, and 3a-13C with Proton Sponge
initially yields PSH+-hypho-12-R-12,13-CNB9H14- (PSH+3a-,
PSH+3b-, PSH+3a--13C) (eq 8). This anion is unstable at room
temperature and completely isomerizes to a second borane anion,
-
PSH+-hypho-12-R-12,11-CNB9H14 (PSH+4a-, PSH+4b-,
PSH+4a--13C) after the solution is stirred for 24 h (eq 9).
CH2Cl2
hypho-12-R-12,13-CNB9H15 + PS
8
(R ) CH3, 3a; 3a-13C)
(R ) Bn, 3b)
Figure 13. Comparison of the two calculated structures of 3a-.
-
PSH+-hypho-12-R-12,13-CNB9H14
(R ) CH3, 3a-; 3a--13C)
(R ) Bn, 3b-)
(8)
CH2Cl2
-
PSH+-hypho-12-R-12,13-CNB9H14
8
24 h
(R ) CH3, 3a-; 3a--13C)
(R ) Bn, 3b-)
-
PSH+-hypho-12-R-12,11-CNB9H14
(R ) CH3, 4a-; 4a--13C)
(R ) Bn, 4b-)
(9)
The significant differences observed in the 11B NMR spectra
of these two anions (Figure 12) suggest that they have very
different skeletal arrangements. If the anion (PSH+3a-,
PSH+3b-, PSH+3a--13C) is reprotonated with HCl/Et2O before
rearrangement, the initial neutral product (3a, 3b, 3a-13C) is
regenerated (eq 10).
Figure 14. ORTEP drawing of the molecular structure of hypho-12-
-
CH3-12,11-CNB9H14 (4a-).
The structure of 3a- was investigated using the ab initio/
IGLO/NMR calculations. Consistent with the structural deter-
minations of 3b (Figure 7), in 3a there are two sets of bridge
hydrogens, with one set bridging the B5-B11 and B10-B11
edges, and the other set at the B1-B2 and B8-B9 edges.
Optimization of an initial anion structure formed by removal
of a proton from the B8-B9 edge in 3a yielded the structure
for 3a- shown in Figure 13a, in which the boron framework is
unchanged, but the bridge hydrogen initially on the B10-B11
edge has optimized at a bridging position on the B9-B10 edge.
Optimization of the initial structure generated by the removal
of a bridge hydrogen from the B10-B11 edge in 3a yielded a
different structure, shown in Figure 13b, that is only ∼0.5 kcal/
mol lower in energy. The calculated 11B NMR chemical shifts
of both structures roughly agree with the experimental data, as
shown in Table 1, but the structure in Figure 13a gives better
agreement since it predicts that the resonance calculated at
-20.7 ppm is the B11 boron. Thus, although overlapping
HCl/Et O8
2
-
PSH+-hypho-12-R-12,13-CNB9H14
(R ) CH3, 3a-; 3a--13C)
(R ) Bn, 3b-)
hypho-12-R-12,13-CNB9H15
(10)
(R ) CH3, 3a; 3a-13C)
(R ) Bn, 3b)
The reversibility of the initial deprotonation suggests that the
anion (3a-, 3b-, 3a--13C) retains the same boron framework
as in 3a, 3b, and 3a-13C. In contrast, after the cage rearrange-
ment the new anion (PSH+4a-, PSH+4b-, PSH+4a--13C) is
unreactive to HCl/Et2O, and reaction with H2SO4 results in cage
degradation as described later.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6419
Figure 17. Proposed structure for hypho-8-CH3-8,13-CNB8H13- (5a-).
spectrum of 3a--13C confirms the resonance at -19.0 ppm as
due to B11, since it is the only resonance exhibiting 11B-13C
coupling. Possible fluxional behavior of 3a- in solution is
suggested by the closeness in energy of the two optimized
structures and its 11B NMR spectrum, which has several broad
resonances. Because of this, the exact location of the bridge
and/or endo hydrogens in 3a- cannot be determined with
confidence based upon the experimental and calculated data.
As discussed above, upon standing at room temperature in
solution, 3- quantitatively isomerizes to 4- (eq 9). The structure
of 4a- was determined by a single-crystal X-ray study, as shown
in the ORTEP drawing in Figure 14. As found for 3b, 4a-
also has a structure based on an 11-vertex hypho geometry, but
it has a different arrangement of the cage borons than found in
3b. The structure of 4a- can be derived from the bicapped
hexagonal antiprism by removing the number 6, 13, and 14
vertices, as shown in Figure 8. The -CH(CH3)NH) unit in
4a-, as in 3b, is still bridging three boron atoms, with the carbon
attached to B7 and the nitrogen attached to B5 and B10. In
contrast to 3b, which has two six-membered open faces, in 4a-
there is one five-membered (B1-B7-C12-N11-B5) and one
seven-membered (B8-B2-B7-C12-N11-B10-B9) open
faces. Two bridge hydrogens are located on the seven-
membered face, bridging B2-B7 and B9-B10, and there is
also an endo-BH at B8. The observed structure is also supported
by ab initio/IGLO/NMR calculations, which are in good
agreement (Table S11a, supporting information) with both the
observed bond lengths (Table 6) and the experimental 11B NMR
chemical shifts and assignments (Table 1) of 4a-. The 11B{1H}
NMR spectrum of (4a--13C) shows broadening of the B7
resonance, consistent with11B-13C coupling. This assignment
agrees with both the 2-D 11B-11B NMR spectrum and the ab
initio/IGLO/NMR calculations.
-
Figure 15. Comparison of the structures of 4a- and iso-B9H14
.
Again, as discussed above for 3, if the CN atoms are
considered as only an exopolyhedral unit, then 4- can be
considered to be a 9-vertex arachno borane cluster with a
bridging -CH(R)NH) unit. However, in contrast to 3, 4- has
a boron framework based on the iso-9-vertex arachno geometry.
The “iso” type of 9-vertex arachno framework is much more
common than the “normal”-9-vertex framework observed for
n-B9H15.24 The boron cage framework of 4a- is similar to that
determined crystallographically for arachno-B9H13•CH3CN25
Figure 16. Comparison of the structures of 3a and 4a-.
(25) (a) Wang, F. E.; Simpson, P. G.; Lipscomb, W. N. J. Am. Chem.
Soc. 1961, 83, 491-492. (b) Wang, F. E.; Simpson, P. G.; Lipscomb, W.
N. J. Chem. Phys. 1961, 35, 1335-1339.
resonances in the 2-D 11B-11B NMR spectrum do not allow
complete assignment of the boron resonances, the 11B{1H} NMR

6420 J. Am. Chem. Soc., Vol. 118, No. 27, 1996
and iso-B9H14
- 26 as shown in Figure 15. The major difference
Wille et al.
,
in the structures is that 4a- has a more open cage as a result of
the bridging unit, which forces the B5-B7 bond in 4a- to
lengthen to ∼2.30 Å, compared to the analogous B6-B7 bond
(∼1.79 Å) of iso-B9H14-. The boron skeletal rearrangement
in converting 3 to 4- can be accomplished, as shown in Figure
16, by movement of B11 in 3 from a position on the B5-B10
edge to a position on the B9-B10 edge. The boron skeletal
rearrangement that occurs during the isomerization of 3- to 4-
is consistent with a similar rearrangement that is observed when
n-B9H15 is deprotonated by NH3 to yield n-B9H14-, which then
-
rapidly rearranges to iso-B9H14 at room temperature.27
Protonation of 4- should yield an isomer of 3 with an iso-
B9H15 boron framework, but it was found that the reaction of
(PSH+4a-, PSH+4b-, PSH+4a--13C) with H2SO4 results in
further cage degradation involving loss of a boron to yield
hypho-8-R-8,13-CNB8H14 (5a, 5b, 5a-13C) (eq 11). Subsequent
deprotonation of this product (eq 12) yielded the 10-vertex anion
-
PSH+-hypho-8-R-8,13-CNB8H13
PSH+5a--13C).
(PSH+5a-, PSH+5b-,
H2SO4
-
PSH+-hypho-12-R-12,11-CNB9H14
(R ) CH3, 4a-; 4a--13C)
(R ) Bn, 4b-)
8
CH2Cl2
hypho-8-R-8,13-CNB8H14
(11)
(12)
(R ) CH3, 5a; 5a-13C)
(R ) Bn, 5b)
Figure 18. Derivation of the proposed 10-vertex hypho structures of
5 and 5- from a 13-vertex closo polyhedron.
hypho-8-R-8,13-CNB8H14 + PS f
(R ) CH3, 5a; 5a-13C)
(R ) Bn, 5b)
-
PSH+-hypho-8-R-8,13-CNB8H13
(R ) CH3, 5a-; 5a--13C)
(R ) Bn, 5b-)
The 11B NMR spectra of the anions (5a-, 5b-, 5a--13C) show
1
eight boron resonances. Their H NMR spectra show reso-
nances attributable to three bridge or endo hydrogens and the
bridging -CH(R)NH) group. Based on their skeletal electron
counts (n + 4 skeletal electron pairs), the 5- anions would be
the first 10-vertex hypho boron cages. The ab initio/IGLO/
NMR calculations for 5a- give good agreement with the
experimental 11B NMR chemical shifts (Table 1) for the hypho
structure in Figure 17, which is derived from a 13-vertex closo
polyhedron by removing the number 5, 7, and 11 vertices, as
shown in Figure 18. Also, the calculated chemical shift
assignments agree with the assignments determined by both the
2-D 11B-11B NMR spectrum of 5a- and the 11B{1H} NMR
spectrum of 5a--13C, which shows the expected 11B-13C
coupling on the B3 resonance. The proposed structure of 5a-
can be generated from that of 4a- by a cage degradation
involving the loss of the B8 boron from 4a- and addition of a
bridge hydrogen on the B1-B2 edge.
Figure 19. The 64.2-MHz 11B NMR spectra of 5a: (bottom) proton
coupled and (top) proton decoupled.
H2SO4
-
PSH+-hypho-8-R-8,13-CNB8H13
8
CH2Cl2
(R ) CH3, 5a-; 5a--13C)
(R ) Bn, 5b-)
hypho-8-R-8,13-CNB8H14
(R ) CH3, 5a; 5a-13C)
(13)
The 5- anion was reprotonated by HCl/Et2O to regenerate 5
(eq 13), suggesting that they have the same 10-vertex hypho
cage atom framework.
(R ) Bn, 5b)
Likewise, the assignments determined from the 2-D 11B-11B
NMR spectrum of 5a are consistent with the boron connectivities
predicted for a boron framework similar to that proposed for
5a-. The 1H{11B} NMR spectrum shows, in addition to eight
terminal BH resonances, four hydrogens at upfield chemical
shifts, indicating bridge or endo hydrogens. The 11B NMR
spectrum of 5a (Figure 19) shows eight boron resonances with
(26) (a) Greenwood, N. N.; Gysling, H. J.; McGinnety, J. A.; Owen, J.
D. J. Chem. Soc., Chem. Commun. 1970, 505-506. (b) Greenwood, N. N.;
McGinnety, J. A.; Owen, J. D. J. Chem. Soc., Dalton Trans. 1972, 986-
989. (c) Huffman, J. C. Report No. 82210, Indiana University of Chemistry
Molecular Structure Center.
(27) Schaeffer, R.; Sneddon, L. G. Inorg. Chem. 1972, 11, 3102-3104.
(28) Williams, R. E. Chem. ReV. 1992, 92, 177-207 and references
therein.

New Synthetic Routes to Azacarborane Clusters
J. Am. Chem. Soc., Vol. 118, No. 27, 1996 6421
position, whereas in structure (b), the hydrogens are located at
the B2-B9 edge and at the endo-B1 position. The two
structures are close in energy with structure (a) being only ∼0.6
kcal/mol lower in energy than structure (b). The similar energies
of these structures suggest that hydrogen migration about the
B1-B2-B9 borons could readily occur in solution at room
temperature. Indeed, interconversion between the two optimized
structures can be envisioned to occur easily by moving the endo-
B9 hydrogen on structure (a) to a bridging position on the B2-
B9 edge, while moving the bridge hydrogen on the B1-B2 edge
to the endo-B1 position. However, a more complex dynamic
behavior is suggested by the fact that the IGLO calculated shifts
of neither structure (a) or (b) gave good agreement with either
the experimentally observed 11B NMR chemical shifts or the
assignments determined by the 2-D 11B-11B NMR experiments.
Likewise, the resonance arising from the B3 boron directly
attached to the carbon was experimentally determined (by the
presence of 45 Hz 11B-13C coupling) in the NMR spectrum of
5a-13C to occur at -4.7 ppm, but this value falls between the
IGLO calculated shifts for the two optimized structures:
structure (a), B3, 2.1 ppm; structure (b), B3, -14.4 ppm. Thus,
-
while the structure of the hypho-8-R-8,13-CNB8H13 anion
would seem to be well established by the computational and
experimental data, the exact structure of the neutral hypho-8-
R-8,13-CNB8H14 azamonocarbaborane must be considered
unproven at this point.
In summary, the results discussed above have further
demonstrated that a synthetic strategy involving nucleophilic
attack of a polyhedral borane anion at a polar multiple bond
provides a new route for the synthesis of hybrid cluster
compounds unattainable by more conventional routes. Work
is now in progress aimed at both expanding the scope of these
reactions and exploring the chemical properties of these unique
clusters.
Figure 20. Comparison of the two calculated structures of 5a.
triplet fine coupling observed on the resonances at -33.3 and
-39.5 ppm, consistent with the coupling of each of these borons
to two endo or bridge hydrogens.
The addition of a proton to the 5- anion could, in principle,
occur at a number of places (Figure 17), including bridging
positions at B2-B9, B9-B12, B3-B4, or B4-B10 or the endo
positions at B1, B2, B12, or B4. In ab initio calculations,
structures where the hydrogen was initially placed at the B2-
B9 or B9-B12 edges or in the endo positions on the B1, B2,
or B12 borons yielded the optimized structures shown in Figure
20. Addition of a proton at the B3-B4 or B4-B10 edges or
at the endo-B4 position would result in an unfavorable28 seven-
coordinate boron and therefore, as expected, gave optimized
structures that were much higher in energy. The two structures
in Figure 20 have the same gross skeletal arrangement, and differ
only in the location of two hydrogens. In structure (a), the two
hydrogens are found at the B1-B2 edge and at the endo-B9
Acknowledgment. We thank the National Science Founda-
tion for the support of this research. We also thank Dr. Joe
Barendt of Callery Chemical Co. for a gift of decaborane.
Supporting Information Available: Tables listing refined
positional and thermal parameters, bond distances, bond angles,
calculated atom positions, Cartesian coordinates, and calculated
bond distances for the optimized geometries at the HF/6-31G*
level for all of the systems calculated (56 pages). See any
current masthead page for ordering and Internet access
instructions.
JA960787M