Synthesis and characterization of new 19-vertex macropolyhedral boron hydrides

Article abstract of DOI:10.1021/ic990896c

The new boron hydride anions 10-R-B₁₉H₁₉^- (R = H, Thx) were synthesized by the reaction of M₂[B₁₈H₂₀] (M = Na, K) with HBRCl·SMe₂ (R = H, Thx) or HBCl₂·SMe₂ in diethyl ether. The anions are comprised of edge-sharing, nido 10- and 11-vertex cluster fragments, and are characterized by their ¹¹B, ¹¹B{¹H}, and ¹¹B-¹¹B COSY NMR spectra. The salt [(Ph₃P)₂N][B₁₉H₂₀]·0.5THF crystallized in the triclinic space group P1(a = 12.6344-(2) A, b = 13.5978(2) A, c = 14.1401(2) A; α = 77.402(2)°, β = 81.351(2)°, γ = 73.253(2)°). Possible synthetic pathways are discussed. The dianion B₁₉H₁₉^2- is formed by deprotonation of B₁₉H₂₀^- with Proton Sponge (1,8-bis(dimethylamino)naphthalene) in THF, and is identified on the basis of its ¹¹B, ¹¹B{¹H}, and ¹¹B-¹¹B COSY NMR spectra.

Full text of DOI:10.1021/ic990896c

Inorg. Chem. 2000, 39, 463-467
463
Synthesis and Characterization of New 19-Vertex Macropolyhedral Boron Hydrides
Joel A. Dopke, Douglas R. Powell, and Donald F. Gaines*
Department of Chemistry, University of WisconsinsMadison, 1101 University Avenue,
Madison, Wisconsin 53706
ReceiVed July 27, 1999
-
The new boron hydride anions 10-R-B19H19 (R ) H, Thx) were synthesized by the reaction of M2[B18H20]
(M ) Na, K) with HBRCl‚SMe2 (R ) H, Thx) or HBCl2‚SMe2 in diethyl ether. The anions are comprised of
edge-sharing, nido 10- and 11-vertex cluster fragments, and are characterized by their 11B, 11B{1H}, and 11B-11B
COSY NMR spectra. The salt [(Ph3P)2N][B19H20]‚0.5THF crystallized in the triclinic space group P1h (a ) 12.6344-
(2) Å, b ) 13.5978(2) Å, c ) 14.1401(2) Å; R ) 77.402(2)°, â ) 81.351(2)°, γ ) 73.253(2)°). Possible synthetic
2-
-
pathways are discussed. The dianion B19H19 is formed by deprotonation of B19H20 with Proton Sponge (1,8-
bis(dimethylamino)naphthalene) in THF, and is identified on the basis of its 11B, 11B{1H}, and 11B-11B COSY
NMR spectra.
Introduction
Calculational studies by Lipscomb and co-workers have
helped to fuel the pursuit of large boron hydrides by predicting
that spherical closo clusters possessing more than 12 vertexes
should be stable, although none have yet been isolated.1 While
boron hydride clusters have traditionally been thought of as
deltahedral fragments of closo parents possessing 12 or fewer
vertexes, macropolyhedral boranes have been known since the
discovery of B18H22 (Figure 1) by Hawthorne et al.2 Numerous
examples of macropolyhedral clusters exist, with most being
species in which two nominally independent cluster fragments
share a single boron atom,3 one or more B-B edges,3-8 or a
triangular B-B-B face.8 Only two binary boron hydride species
which may be thought of as being derived from a closed parent
possessing more than 12 vertexes have been reported in the
literature: B14H204 and B20H16.8 Recently, a number of macropoly-
hedral heteroborane clusters in which the heteroatom is a
transition metal9 or a main group atom10 have appeared in the
literature.
Figure 1. Stick diagrams representing the structures of syn-B18H22 (top)
and anti-B18H22 (below). Arcs represent bridging hydrogens.
The most widely studied of the macropolyhedral boron
hydrides is anti-B18H22 due largely to its stability and ready
synthesis in high purity.11,12 The structure of anti-B18H22 consists
of two nido 10-vertex clusters fused through a common edge
(1) Bicerano, J.; Marynick, D. S.; Lipscomb, W. N. Inorg. Chem. 1978,
17, 3443. Lipscomb, W. N.; Massa, L. Inorg. Chem. 1994, 33, 5155.
Lipscomb, W. N.; Massa, L. Inorg. Chem. 1992, 31, 2299.
(2) Pitochelli, A. R.; Hawthorne, M. F. J. Am. Chem. Soc. 1962, 84, 3218.
(3) Rathke, J.; Schaeffer, R. J. Am. Chem. Soc. 1973, 95, 3402.
(4) Huffman, J. C.; Moody, D. C.; Schaeffer, R. Inorg. Chem. 1981, 20,
741.
(5) Rathke, J.; Schaeffer, R. Inorg. Chem. 1974, 13, 3008. Huffman, J.
C.; Moody, D. C.; Rathke, J. W.; Schaeffer, R. J. Chem. Soc., Chem.
Commun. 1973, 308. Rathke, J.; Moody, D. C.; Schaeffer, R. Inorg.
Chem. 1974, 13, 3040. Hermanek, S.; Fetter, K.; Plesek, J. Chem.
Ind. 1977, 606. Friedman, L. B.; Cook, R. E.; Glick, M. D. J. Am.
Chem. Soc. 1968, 90, 6862. Friedman, L. B.; Cook, R. E.; Glick, M.
D. Inorg. Chem. 1970, 9, 1452. Hosmane, N. S.; Franken, A.; Zhang,
G.; Rajik, R.; Smith, R. Y.; Spielvogel, B. F. Main Group Met. Chem.
1998, 21, 6.
(9) Sneath, R. L.; Little, J. L.; Burke, A. R.; Todd, L. J. J. Chem. Soc.,
Chem. Commun. 1970, 693. Sneath, R. L.; Todd, L. J. Inorg. Chem.
1973, 12, 44. Cheek, Y. M.; Greenwood, N. N.; Kennedy, J. D.;
McDondald, W. S. J. Chem. Soc., Chem. Commun. 1982, 80.
(10) Bould, J.; Kennedy, J. D.; Thornton-Pett, M. J. Chem. Soc., Dalton
Trans. 1992, 563. Kennedy, J. D.; St´ıbr, B. In Current Topics in the
Chemistry of Boron; Kabalka, G., Ed.; Royal Society of Chemistry:
Cambridge, 1994. Kennedy, J. D.; Drda´kova´, E.; Thornton-Pett, M.
J. Chem. Soc., Dalton Trans. 1994, 229. Casanova, J., Ed. The Borane-
Carborane-Carbocation Continuum; Wiley: New York: 1998. Je-
l´ınek, T.; Cisarova´, I.; St´ıbr, B.; Kennedy, J. D.; Thornton-Pett, M. J.
Chem. Soc., Dalton Trans. 1998, 2965. Jel´ınek, T.; Kilner, C. A.;
Barrett, S. A.; Thornton-Pett, M.; Kennedy, J. D. Chem. Commun.
1999, 18, 1905.
(6) Simpson, P. G.; Folting, K.; Dobrott, R. D.; Lipscomb, W. N. J. Am.
Chem. Soc. 1963, 85, 1879. Simpson, P. G.; Folting, K.; Dobrott, R.
D.; Lipscomb, W. N. J. Chem. Phys. 1963, 39, 2339.
(11) Olsen, F. P.; Vasavada, R. C.; Hawthorne, M. F. J. Am. Chem. Soc.
1968, 90, 3946.
(12) (a) Gaines, D. F.; Nelson, C. K.; Steehler, G. A. J. Am. Chem. Soc.
1984, 106, 7266. (b) Wallbridge, M. G. H.; McAvoy, J. S. J. Chem.
Soc., Chem. Commun. 1969, 1378. (c) Bould, J.; Greenwood, N. N.;
Kennedy, J. D. Polyhedron 1983, 2, 1401. (d) Brewer, C. T.; Grimes,
R. N. J. Am. Chem. Soc. 1985, 107, 3552. (e) Lawrence, S. H.;
Wermer, J. R.; Boocock, S. K.; Banks, M. A.; Keller, P. C.; Shore, S.
G. Inorg. Chem. 1986, 25, 367. (f) Dobson, J.; Keller, P. C.; Schaeffer,
R. Inorg. Chem. 1968, 7, 399. (g) Plesek, J.; Hermanek, S.; St´ıbr, B.;
Hanousek, F. Collect. Czech. Chem. Commun. 1967, 32, 1095.
(7) Simpson, P. G.; Lipscomb, W. N. J. Chem. Phys. 1963, 39, 26.
(8) Miller, N. E.; Muetterties, E. L. J. Am. Chem. Soc. 1963, 85, 3506.
Friedman, L. B.; Dobrott, R. D.; Lipscomb, W. N. J. Am. Chem. Soc.
1963, 85, 3505. Bachmann, H. R.; No¨th, H.; Rinck, R. Chem. Phys.
Lett. 1974, 29, 627. Dobrott, R. D.; Friedman, L. B.; Lipscomb, W.
N. J. Chem. Phys. 1964, 40, 866. Miller, N. E.; Forstner, J. A.;
Muetterties, E. L. Inorg. Chem. 1964, 3, 1690. Enemark, J. H.;
Friedman, L. B.; Lipscomb, W. N. Inorg. Chem. 1966, 5, 2165.
10.1021/ic990896c CCC: $19.00 © 2000 American Chemical Society
Published on Web 01/21/2000

464 Inorganic Chemistry, Vol. 39, No. 3, 2000
Dopke et al.
components were removed under vacuum. Metathesis with [Ph3PMe]-
Br in CH3CN and subsequent reprecipitation from CH2Cl2/Et2O
provided 0.47 g (0.93 mmol, 73% yield) of 11B NMR pure Ph3PMe-
[B19H20] as a free-flowing yellow powder. MALDI-MS, calcd (obsd):
226.3 (228.3) m/z.
Preparation of B19H20- Using H2BCl‚SMe2. A 50 mL Schlenk flask
containing a stir bar was charged with excess KH and B18H22 (0.42 g,
1.94 mmol). Dry THF (25 mL) was added, and the contents were stirred
on the Schlenk line for 2 h to yield a green-yellow solution. The slurry
was filtered into a 100 mL Schlenk flask containing a stir bar, and the
volatile components were removed in vacuo to yield a yellow solid.
Et2O (40 mL) was syringed into the flask to generate a slurry prior to
addition of H2BCl‚SMe2 (1.01 g, 9.18 mmol) by syringe. The yellow
solid dissolved, and the solution slowly turned a lemon-yellow color
with formation of a white precipitate. The flask contents were stirred
overnight. Hexanes (25 mL) were added, and the flask was allowed to
stand until precipitation was complete. The supernatant was removed
by filtration, and the precipitate was extracted with CH3CN until the
filtrate was colorless. The potassium cation was displaced in CH3CN
by addition of [Ph3PMe]Br. After filtration and reprecipitation from
CH2Cl2/Et2O, the product Ph3PMe[B19H20] was recovered as a yellow
powder in 80% yield (0.52 g, 1.02 mmol) based on starting B18H22.
Preparation of 10-Thx-B19H19-. The reaction procedure is identical
to that presented in the preceding paragraph with substitution of
ThxBHCl‚SMe2 for H2BCl‚SMe2. The compounds were used in the
following amounts: B18H22 (0.30 g, 1.39 mmol), 2,3-dimethyl-2-butene
(5 mL), H2BCl‚SMe2 (0.91 g, 8.24 mmol). Yield: Et4N[ThxB19H19]
(54%, 0.329 g, 0.76 mmol). MALDI-MS (negative mode), calcd
(obsd): 310.4 (312.4) m/z.
Reaction of Ph3PMe[B19H20] with Proton Sponge. An excess of
Proton Sponge (0.67 g, 3.13 mmol) was added to a THF solution (40
mL) of Ph3PMe[B19H20] (0.274 g, 1.26 mmol, of B18H22; 0.61 g, 5.52
mmol, of ClBH2‚SMe2; 0.46 g, 1.29 mmol of [Ph3PMe]Br) in a 100
mL three-necked flask. The contents were stirred overnight. The pot
mixture contained a yellow solution with a light-colored precipitate.
The volatile components were removed under vacuum and the solids
washed with 100 mL of Et2O to remove any residual Proton Sponge.
The flask contents were filtered, and the solids were washed with 30
mL portions of dry CH3CN until the washings were colorless. The
filtrate was transferred to a 200 mL Schlenk flask and concentrated
under vacuum. The contents were reprecipitated once from CH3CN/
Et2O, and once from CH2Cl2/Et2O, to give 0.488 g (0.68 mmol, 54%
yield based on B18H22) of PSH[Ph3PMe][B19H19].
Figure 2. Structure of B19H20- in stick form. Arcs represent bridging
hydrogens.
so as to impart a center of symmetry. The syn-B18H22 isomer,
in which the two cluster fragments are fused in a similar way
to yield overall C2 symmetry, has also been characterized.6 The
boron atoms common to both cluster fragments in each isomer
lack terminal hydrogens. Syn- and anti-B18H22 are diprotic acids
-
2-
forming the anions B18H21 and B18H20 by loss of one and
two of the six bridge hydrogens, respectively.11,13
Recent developments in the area of rational cluster enlarge-
ment14 utilizing the reactive nido decaborane(14) dianion
2-
B10H12 have led us to investigate the octadecaborane(22)
system. Although the decaborane-like dianion B18H202- is less
reactive than B10H122-, it has been shown that transition metal
moieties can be inserted into the 18-vertex framework to
generate 19-vertex metallaboranes in low to moderate yield.9
As a result it seemed that 19-vertex boron hydrides could be
generated by insertion of monoboron moieties into the dianion
2-
B18H20 to yield the first known nonadecaborate clusters.
Herein we report the synthesis and characterization of the anions
10-R-B19H19- (R ) H, Thx), and the dianion B19H192-, by the
extension of decaborane cluster growth strategies to the octa-
decaborane(22) system.
Experimental Section
All experiments were carried out using standard inert atmosphere
techniques unless otherwise stated. NaH (60% in mineral oil; Aldrich
Chemical Co.) and KH (35% in mineral oil; Aldrich) were washed
with dry hexanes prior to use. THF (Na/anthracene), CH3CN (CaH2),
and pentane (CaH2) were distilled from the indicated drying agent prior
to use. Anhydrous Et2O (Mallinckrodt) was used as received. B18H22
was synthesized by the literature method.12a Proton Sponge (1,8-bis-
(dimethylamino)naphthalene), chloroborane-dimethyl sulfide, and
dichloroborane-dimethyl sulfide were purchased from Aldrich Chemi-
cal Co. and used as received. ThxBHCl‚SMe2 (Thx ) tertiary hexyl,
(CH3)2CH-C(CH3)2) was synthesized by reaction of 2,3-dimethyl-2-
butene with neat H2BCl-SMe2 at 0 °C for 2 h. 11B NMR spectra were
acquired on a Varian Unity 500 (160.4 MHz) or Bruker AM-360 (115.5
MHz) spectrometer and referenced externally to BF3‚OEt2 in C6D6 (δ
) 0). Negative mode MALDI-TOF mass spectra were acquired on a
Bruker Reflex II spectrometer equipped with a nitrogen laser in
reflectron mode using dithranol (1,6-dihydroxynaphthalene; Aldrich
Chemical Co.) as a matrix.
Crystallographic Characterization of [(Ph3P)2N][B19H20]‚0.5THF.
Crystals suitable for analysis were grown by layering a CH3CN solution
of the product with a 1:1 (v/v) mixture of Et2O/pentane. A yellow
crystalline plate (dimensions 0.44 × 0.12 × 0.04 mm) was selected.
Intensity data were collected at 133(2) K using a Siemens SMART
CCD area detector15 mounted on a Siemens P4 diffractometer equipped
with graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å). Unit
cell parameters were determined from a nonlinear least-squares fit of
6450 peaks in the range 3.0 < Θ < 25.0°. The first 50 frames were
repeated at the end of data collection and yielded a total of 286 peaks
showing a variation of -0.12% during the data collection. The data
were corrected for absorption by the empirical method,16 giving
minimum and maximum transmission factors of 0.738 and 0.956,
respectively. The data merged to form a set of 10 670 independent data
with R(int) ) 0.0483.
-
One-Pot Synthesis of B19H20 Using HBCl2‚SMe2. A 50 mL
Schlenk flask containing a stir bar was charged with excess NaH. Solid
B18H22 (0.29 g, 1.33 mmol) was added under nitrogen in a glovebag.
Upon addition of dry Et2O (25 mL) by syringe, hydrogen evolution
was observed and the flask contents turned yellow. Na2B18H20
precipitated as the flask contents were stirred vigorously overnight.
HBCl2‚SMe2 (0.93 g, 6.46 mmol) was added to the slurry by syringe,
immediately producing a dark orange-yellow color. The flask was stirred
for 6 h, after which the contents were filtered through a medium glass
frit and the solids washed with THF until the filtrate was colorless.
The filtrate was transferred to a 250 mL Schlenk flask, and the volatile
The triclinic space group P1h was determined by statistical tests and
verified by subsequent refinement. The structure was solved by direct
methods and refined by full-matrix least-squares methods on F2.17
Hydrogen atom positions were initially determined by geometry and
refined using a riding model. Non-hydrogen atoms were refined with
(15) (a) Data collection: SMART Software Reference Manual, Siemens
Analytical X-ray Instruments, 6300 Enterprise Dr., Madison, WI,
53719-1173, 1994. (b) Data reduction: SAINT Software Reference
Manual, Siemens Analytical X-ray Instruments, 6300 Enterprise Dr.,
Madison, WI 53719-1173, 1995.
(16) G. M. Sheldrick, SADABS, Program for Empirical Absorption
Correction of Area Detector Data, University of Go¨ttingen, Germany,
1996.
(13) Fontaine, X. L. R.; Greenwood, N. N.; Kennedy, J. D.; MacKinnon,
P. J. Chem. Soc., Dalton Trans. 1988, 1785.
(14) Bridges, A. N.; Hayashi, R. K.; Gaines, D. F. Inorg. Chem. 1994, 33,
1243. Bridges, A. N.; Gaines, D. F. Inorg. Chem. 1995, 34, 4523.

19-Vertex Macropolyhedral Boron Hydrides
Inorganic Chemistry, Vol. 39, No. 3, 2000 465
Scheme 1
Scheme 2
+
In the first, loss of halide from ClBH2‚SMe2 allows a BH2
unit to add as a bridging moiety and form the unobserved
intermediate B19H22-. Loss of molecular hydrogen leads to
anisotropic displacement parameters. A total of 564 parameters were
refined against 21 restraints and 10 670 data to give Rw(F2) ) 0.1934
and S ) 1.086. The final R(F) was 0.0645 for the 6940 observed [F >
4σ(F)] data. The largest shift/su (standard uncertainty) was 0.141 in
the final refinement cycle. The final difference map had maxima and
minima of 0.889 and -0.450 e/Å3, respectively.
-
formation of the B19H20 product. The isolation of hydrogen
generated by the reaction of K2B18H20 with ClBH2‚SMe2 on a
high-vacuum line consistently showed ca. 0.13 equiv of H2.
Thus, hydrogen elimination is not a primary route toward
product formation.
Results and Discussion
A second pathway requires formation of B19H22- and transfer
of H- to ClBH2‚SMe2 to make BH3‚SMe2, B19H21, and MCl.
The B19H21 is then deprotonated to form the product. This
second pathway would be indistinguishable from a third route
Haloborane-dimethyl sulfide adducts react with M2B18H20
(M ) Na, K) in diethyl ether to generate the new boron hydride
anions 10-R-B19H19- (R ) H, Thx). This insertion process yields
products which are structurally related to the previously reported
19-vertex metallaboranes.9 Interestingly, the product may be
acquired using either ClBH2‚SMe2 or Cl2BH‚SMe2, suggesting
that the product is accessible by two independent routes.
-
in which deprotonation of B19H22 precedes hydride transfer.
In reactions of K2B18H20 with ClBH2‚SMe2, BH3‚SMe2, and
B18H22 are present in the reaction mixture, consistent with the
postulate that hydride transfer may be significant. The hydrogen
measured may be produced by the reaction of the proposed
2-
The reaction of excess Cl2BH‚SMe2 with B18H20 in the
-
presence of MH (M ) Na, K) in diethyl ether generates the
intermediate B19H22 with a proton source such as B18H22,
-
B18H21-, or B19H21. It may be possible that BH3‚SMe2 acts as
product anion B19H20 (Figure 2), in a convenient one-pot
-
a hydride acceptor, generating BH4-. Although no BH4 was
synthesis. Subsequent cation metathesis and recrystallization
produced Ph3PMe[B19H20] in 73% yield. Reactions carried out
observed in the pot mixture, the presence of a moderately strong
-
in the absence of base gave a near 1:1 mixture of the B19H20
-
acid such as B18H22 would be expected to convert any BH4
product and B18H21- as verified by 11B NMR. We propose that
the dependence of the yield of B19H20- on the presence of base
is the result of the formation of the unobserved neutral
intermediate B19H21.
formed to BH3 adducts.
These syntheses appear to require diethyl ether as the solvent.
While the salts M2B18H20 (M ) Na, K) are not highly soluble
in diethyl ether, reactions in toluene, in which M2B18H20 salts
are virtually insoluble, yield no product and effectively preclude
the possility that the reaction occurs heterogeneously. Reactions
in THF, in which the M2B18H20 salts are quite soluble, yield no
B19H20- despite the fact that the reactions will proceed in high
yield when up to 10% THF (v/v) is introduced into the diethyl
ether pot mixture.
Insertion of a BH2+ moiety into B18H20 to make B19H21
2-
followed by deprotonation would lead to the formation of
-
2-
B19H20 (Scheme 1). While B18H20 may act as a proton
acceptor due to its much greater solubility in diethyl ether over
MH, the resulting B18H21- is deprotonated by MH and recycled
into the reaction process as B18H202-. It has been postulated
that B10H122- and B10H13- act as deprotonating agents in cluster
enlargement reactions in the presence of MH for the decaborane-
Layering of pentane/ether (1:1) onto a THF solution of
[(Ph3P)2N][B19H20] produced yellow crystalline prisms of
[(Ph3P)2N][B19H20]‚0.5THF, for which an X-ray diffraction
study confirmed the 19-vertex framework (Figure 3). A sum-
mary of crystallographic information may be found in Table 1.
The anion exists as edge-sharing 10- and 11-vertex nido
fragments whose open faces are anti to one another. Bridge
hydrogens span the B9-B10 edge of the 11-vertex subunit, and
the B12-B13 and B13-B14 edges of the 10-vertex subunit in
a fashion similar to that of B10H14. As a result, none of these
bridging hydrogens are adjacent to the boron atoms common
to both cluster fragments in the solid state. The B-B distances
range from 1.626 Å (B4-B8) to 2.032 Å (B11-B12), with an
average B-B distance of 1.79 Å. In general, the interatomic
distances and angles within the cluster are unexceptional. By
inspection, the B10 vertex, located on the open face of the 11-
(14) system.14
Reactions of ClBH2‚SMe2 with B18H20
2-
also generate
B19H20-, which may be isolated after cation metathesis with
[Ph3PMe]Br in 80% yield. No base is required to achieve high
yields of the product by this method. Attempts to synthesize
B19H20- over NaH in one pot using ClBH2‚SMe2 in analogous
fashion to chemistry utilizing Cl2BH‚SMe2 were unsuccessful,
-
producing B18H21 as the primary boron-containing species in
solution.
Three pathways may be reasonably proposed for the formation
of B19H20- from monochloroborane and B18H202- (Scheme 2).
(17) (a) G. M. Sheldrick, SHELXTL Version 5 Reference Manual, Siemens
Analytical X-ray Instruments, 6300 Enterprise Dr., Madison, WI
53719-1173, 1994. (b) International Tables for Crystallography;
Kluwer: Boston, 1995; Vol. C, Tables 6.1.1.4, 4.2.6.8, and 4.2.4.2.

466 Inorganic Chemistry, Vol. 39, No. 3, 2000
Dopke et al.
Figure 3. Crystallographically determined structure of [(Ph3P)2N]-
[B19H20] with thermal ellipsoids drawn at the 50% probability level.
Table 1. Summary of Crystallographic Information for
[(Ph3P)2N][B19H20]‚0.5THFa
empirical
formula
fw
cryst syst
space group P1h (no. 2)
a, Å
b, Å
c, Å
R, deg
â, deg
C36B19N4P2H50
0.5(C4H8O)
800.15
+
γ
73.253(2)
2260.25(6)
2
V, Å3
Z
Figure 5. 11B-11B COSY NMR (160.4 MHz) spectrum of B19H20- in
CH3CN. The 160.4 MHz 11B{1H} NMR spectrum is plotted on the
vertical and horizontal axes.
triclinic
F (calcd), Mg/m3 1.176
µ, mm-1
T, K
λ, Å
R
0.128
133
0.71073
0.064
0.193
12.6344(2)
13.5978(2)
14.1401(2)
77.402(2)
81.351(2)
Rw
a R ) Σ||Fo| - |Fc||/Σ|Fo|, Rw ) {Σ[w(Fo - Fc2)2]/Σ[w(Fo )2]}1/2
.
2
2
Figure 6. 11B (bottom) and 11B{1H} (top) NMR (160.4 MHz) spectra
-
of 10-Thx-B19H19 in CH3CN (* ) impurity).
ppm, consistent with alkylation at that site and further supporting
the assertion that B10 is the inserted vertex. A bridge hydrogen
coupling of 41 Hz is also observed for the B8 resonance of
10-Thx-B19H19-, supporting the assertion that the parent and
derivative are structurally analogous.
Figure 4. 11B{1H} (bottom) and 11B (top) NMR (160.4 MHz) spectra
of B19H20 in CH3CN (* ) impurity).
-
The MALDI mass spectra of the 19-vertex anions support
their structures. B19H20- (obsd 228.3 m/z, calcd 226.3 m/z) and
ThxB19H19- (obsd 312.4 m/z, calcd 310.4 m/z) both exhibit mass
envelopes of (M + 2)- in their negative mode mass spectra,
indicating addition of 2H (calcd 228.4 m/z B19H22-; 312.4 m/z
vertex subunit, is expected to be the inserted boron atom as
notional removal of that vertex regenerates the anti-B18H22
framework.
The 11B NMR spectrum of B19H20- indicates an asymmetric
species with chemical shifts ranging from +14 to -42 ppm as
illustrated in Figure 4. The common vertexes which lack
terminal hydrogens appear as singlets in the proton-coupled
spectrum, while all other resonances appear as doublets. The
resonances due to the B10 (55 Hz) and B8 (49 Hz) vertexes
exhibit bridge hydrogen coupling. Although accidental equiva-
lences prevent the measurement of JB-H for some cluster atoms,
an assignment of the 11B NMR spectrum consistent with the
structure was obtained from the 11B-11B COSY NMR spectrum
(Figure 5).
-
ThxB19H21-). The formulation B19H22 is not consistent with
the observed structure as the addition of two electrons would
force one of the cluster fragments to adopt an arachno
configuration. The addition of hydrogen has been observed in
-
the MALDI mass spectrum of B10H13 under identical condi-
tions.18 As a result, we conclude that the addition of hydrogen
is a function of the mass spectral experiment and occurs due to
the presence of the 10-vertex cluster subunit of the analyte.
The nonadecaborate anions are unstable over extended periods
in protic media, decomposing over several weeks to mixtures
of B18H21- and B(OH)3. However, the 19-vertex species neither
protonate nor significantly decompose with brief exposure to 1
M HCl/Et2O. This observation has led to a convenient meth-
-
The alkylated 19-vertex derivative 10-Thx-B19H19 was
isolated as the Et4N+ salt in 54% yield from the reaction of
ThxBHCl‚SMe2 with B18H202- in diethyl ether. The 11B NMR
-
spectrum is similar to that for the B19H20 parent (Figure 6).
Assignments consistent with the 11B-11B COSY NMR spectrum
indicate that the B10 resonance is shifted downfield by ca. 14
(18) Dopke, N. C.; Dopke, J. A. Manuscript in preparation.

19-Vertex Macropolyhedral Boron Hydrides
Inorganic Chemistry, Vol. 39, No. 3, 2000 467
Table 2. 11B NMR Chemical Shifts (ppm) for B19H20
,
-
odology for the removal of B18H21- from samples of the product
by protonation of the impurity to yield B18H22. Extraction of
the octadecaborane with nonpolar solvents and recrystallization
ThxB19H19-, and B19H19 in CH3CN Referenced Externally to
2-
BF3‚OEt2 in C6D6, and Recorded at 160.4 MHza
-
-
2-
-
from CH3CN/Et2O afford pure B19H20-. Solutions of B19H20
B19H20
ThxB19H19
B19H19
are stable to moderate periods of exposure to air or moisture,
while solid samples appear indefinitely stable.
B1
B2
B3
B4
B5
B6
B7
B8
-5.0 (135)
-25.2 (154)
-7.4
-26.4 (160)
-24.2 (142)
-7.9 (124)
5.6
-8.3
-5.8 (132)
-21.8 (148)
-12.1 (149)
-22.4 (129)
-29.7 (136)
-7.5 (136)
13.6
-25.3 (143)
-9.4 (144)
-26.7 (147)
-23.3 (125)
-10.4 (157)
4.2
-
Deprotonation of B19H20 with Proton Sponge (1,8-bis-
2-
(dimethylamino)naphthalene) generates the dianion B19H19
.
Substitution of strongly nucleophilic bases (alkyllithiums,
[HBEt3]-) for Proton Sponge results in unresolvable contamina-
tion of the product with sizable quantities of B18H202-. Solutions
of B19H192- treated with 1 M HCl/Et2O regenerate B19H20- with
-18.4 (142, 49)
-20.3 (135, 41)
-5.3 (153)
-8.1
-4.2
-8.4
-4.1 (128)
-8.4
-28.2 (153)
-22.4 (148)
12.8 (138)
-42.4 (153)
11.7 (148)
-18.2 (130, 64)
-3.2 (136)
-19.5
B9
-7.4
only trace decomposition to B18H21 (by 11B NMR analysis),
-
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
-21.8 (135, 55)
-5.1
-9.3
supporting the asserted deprotonation of the nonadecaborate.
The dianion B19H192- is identified by its 11B NMR spectrum,
similar to that of the other 19-vertex boron hydrides. The
spectrum consists of 19 resonances over a range of +14 to -36
-7.4
-3.0 (152)
-7.4
-20.1
-8.3
-10.9 (155)
-20.7
-27.6 (136)
-21.1 (148)
13.2 (138)
-42.1 (148)
12.8 (141)
ppm. Presuming a skeletal structure similar to B19H20-, the 11
B
-22.7
11.8 (152)
-35.2 (133)
-1.2 (132)
NMR spectrum may be assigned on the basis of 11B-11B COSY
NMR spectroscopy. 11B NMR chemical shifts for B19H20-, 10-
2-
Thx-B19H19-, and B19H19 are provided in Table 2. The
a Coupling constants (Hz), where measurable, appear next to the
appropriate shift. Boldface atoms represent vertexes common to both
cluster fragments.
resonance assigned to the B8 vertex of the undecaborate cluster
subunit exhibits a large (64 Hz) bridge hydrogen coupling,
indicating that deprotonation occurs on the decaborane subunit.
The resonances most greatly effected by deprotonation of the
evidence implies that deprotonation occurs on the 10-vertex
subunit of B19H20-. While the mono- and dianions have thus
far been resistant to further cluster growth, they provide the
opportunity for further enlargement to new macropolyhedral
species.
nonadecaborate anion are those assigned to the 10-vertex
-
fragment, when compared to B19H20
.
2-
While reactive toward proton sources, the dianion B19H19
has yet to show greater affinity toward cluster growth than the
-
19-vertex monoanion. Attempts to enlarge the 19-vertex B19H20
2-
Acknowledgment. We thank Drs. Nancy C. Dopke (Uni-
versity of Wisconsin) and William C. Boggess (University of
Notre Dame) for the acquisition of mass spectral data. We also
thank the WARF (J.A.D.) and the National Science Foundation
(Grants DMR-9121074, CHE-9629688, and CHE-9310428) for
partial funding and major departmental instrumentation grants.
or B19H19 anions to generate 20-vertex clusters have proven
to be ineffective. No reaction, except decomposition of the
borane anion, has been observed. Further investigations into the
-
2-
reactivity of B19H20 and B19H19 are currently underway.
Conclusion
Both Cl2BH‚SMe2 and ClBH2‚SMe2 effectively convert
Supporting Information Available: Tables giving atomic coor-
dinates, isotropic and anisotropic displacement parameters, bond lengths
and angles, hydrogen coordinates, and torsion angles for [(Ph3P)2N]-
[B19H20‚0.5THF, an X-ray crystallographic file (CIF format) of the
structure of [(Ph3P)2N][B19H20]‚0.5THF, and the 11B NMR spectrum
of B19H192-. This material is available free of charge via the Internet
at http://pubs.acs.org.
-
M2B18H20 to the macropolyhedral boron hydride anion B19H20
in diethyl ether. The analogous reaction utilizing RBHCl‚SMe2
generates the nonadecaborate 10-R-B19H19-. Structurally, these
new binary boron hydride anions consist of edge-sharing 10-
and 11-vertex nido fragments. Treatment of B19H20- with Proton
Sponge generates the dianion B19H192- which converts back to
B19H20- upon treatment with dilute, anhydrous acid. 11B NMR
IC990896C