Synthetic and Structural Studies of Heteroatom-Polyborane Clusters: Simple, High-Yield Syntheses of nido-11-Vertex Thia- And Phosphaboranes, Thia- and Phosphadicarbaboranes, and the First Thiaphosphaborane

Article abstract of DOI:10.1021/ic980445c

A synthetic sequence involving the reaction of a phosphorus or sulfur dihalide with a monoanionic boron cluster followed by an in situ dehydrohalogenation reaction initiated by proton sponge results in the clean insertion of the heteroatom into the cage framework. Using this method, a range of nido-11-vertex thia- and phosphaboranes. thia- and phosphadicarbaboranes, and the first thiaphosphaborane has been produced in high yields. Thus, the reaction of decaborane with SCl₂ or RPCl₂ and excess proton sponge gave the known anions, nido-7-SB₁₀H₁₁^- (1^-) and nido-7-RPB₁₀H₁₁^- [2a^- (R = Me) and 2b^- (R = Ph)], respectively. Acidification of 1^-, 2a^-, and 2b^- resulted in the isolation of nido-7-SB₁₀H₁₂ (1) and nido-7-RPB₁₀H₁₂ (2a and 2b), respectively, in near-quantitative yields. Reaction of nido-5,6-C₂B₈H₁₂ with SCl₂ or RPCl₂ in the presence of proton sponge produced the new compounds, nido-7,10,11-SC₂B₈H₁₀ (3) (77%) and nido-7,10,11-RPC₂B₈H₁₀ [R = Me (97%) 4a, Ph (83%) 4b], respectively. Reaction of arachno-6-SB₉H₁₁ with PhPCl₂ and proton sponge resulted in the formation of the new mixed heteroatom cage, nido-10-Ph-7,10-SPB₉H₉ (5), which is the first example of a thiaphosphaborane cluster. Consistent with their nido skeletal electron counts, all clusters were shown by spectroscopic and DFT/GIAO computational studies to have similar cage frameworks containing a five-membered open face.

Full text of DOI:10.1021/ic980445c

Inorg. Chem. 1998, 37, 5269-5277
5269
Synthetic and Structural Studies of Heteroatom-Polyborane Clusters: Simple, High-Yield
Syntheses of nido-11-Vertex Thia- and Phosphaboranes, Thia- and Phosphadicarbaboranes,
and the First Thiaphosphaborane
Alexandra M. Shedlow and Larry G. Sneddon*
Department of Chemistry, University of Pennsylvania Philadelphia, Pennsylvania 19104-6323
ReceiVed April 20, 1998
A synthetic sequence involving the reaction of a phosphorus or sulfur dihalide with a monoanionic boron cluster
followed by an in situ dehydrohalogenation reaction initiated by proton sponge results in the clean insertion of
the heteroatom into the cage framework. Using this method, a range of nido-11-vertex thia- and phosphaboranes,
thia- and phosphadicarbaboranes, and the first thiaphosphaborane has been produced in high yields. Thus, the
-
reaction of decaborane with SCl2 or RPCl2 and excess proton sponge gave the known anions, nido-7-SB10H11
(1-) and nido-7-RPB10H11- [2a- (R ) Me) and 2b- (R ) Ph)], respectively. Acidification of 1-, 2a-, and 2b-
resulted in the isolation of nido-7-SB10H12 (1) and nido-7-RPB10H12 (2a and 2b), respectively, in near-quantitative
yields. Reaction of nido-5,6-C2B8H12 with SCl2 or RPCl2 in the presence of proton sponge produced the new
compounds, nido-7,10,11-SC2B8H10 (3) (77%) and nido-7,10,11-RPC2B8H10 [R ) Me (97%) 4a, Ph (83%) 4b],
respectively. Reaction of arachno-6-SB9H11 with PhPCl2 and proton sponge resulted in the formation of the new
mixed heteroatom cage, nido-10-Ph-7,10-SPB9H9 (5), which is the first example of a thiaphosphaborane cluster.
Consistent with their nido skeletal electron counts, all clusters were shown by spectroscopic and DFT/GIAO
computational studies to have similar cage frameworks containing a five-membered open face.
proton sponge (PS, 1,8-bis(dimethylamino)naphthalene) were purchased
from Aldrich and used as received. Both S2Cl2 and SCl2 were purchased
from Aldrich, and were purified by passing them through a -45 °C
trap. Sulfuric acid (99.999%) and 1.0 M HCl‚Et2O were purchased
from Aldrich and stored under N2 until used. 1,2-Dimethoxyethane
(glyme) and tetrahydrofuran (THF) were dried over sodium benzophe-
none ketyl and freshly distilled before use. Methylene chloride was
dried over P2O5, transferred onto activated 4 Å molecular sieves, and
stored under vacuum until used. Heptane and hexane were purchased
from Fisher and used as received. All other reagents and solvents were
reagent grade unless otherwise noted.
Introduction
The development of systematic, high yield synthetic routes
for the construction of heteroatom-polyborane clusters, such
as the polyhedral thiaboranes and phosphaboranes, has been a
formidable challenge. Because of the high reactivity of most
polyhedral borane anions, multiple reaction pathways are
possible during the heteroatom insertion reaction which can lead
to low yields of desired materials.1 In this paper, a surprisingly
simple method for heteroatom insertion is presented that is used
to synthesize, in high yields, a range of isoelectronic and
isostructural nido-11-vertex thia- and phospha-boranes, thia- and
phosphadicarbaboranes, and the first thiaphosphaborane cluster.
Physical Measurements. 1H NMR spectra at 500.1 MHz, 11B NMR
spectra at 160.5 MHz, 31P NMR spectra at 81.0 MHz, and 13C NMR
spectra at 125.7 MHz were obtained on a Bruker AM-500 spectrometer.
1H NMR spectra at 200.1 MHz and 11B NMR spectra at 64.2 MHz
were obtained on a Bruker AF-200 spectrometer. Both instruments
were equipped with the appropriate decoupling accessories. All 11B
chemical shifts are referenced to external BF3‚O(C2H5)2 (0.00 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 then referenced to Me4Si (0.00 ppm). All 31P
chemical shifts are referenced to external 85% H3PO4 (0.0 ppm) with
a negative sign indicating an upfield shift. Two-dimensional COSY
11B-11B NMR experiments were performed at 160.5 MHz using the
procedures described previously.5 NMR data are presented in Table
1.
Experimental Section
All manipulations were carried out using standard high vacuum or
inert-atmosphere techniques as described by Shriver.2
Materials. Decaborane, B10H14, was obtained from laboratory stock
3
and sublimed before use. The carborane nido-5,6-C2B8H12 was
prepared according to the literature methods. The arachno-6-SB9H11
was prepared as previously reported.4 KH (35 wt % dispersed in
mineral oil) and oil-dispersed NaH were rinsed with hexane and then
vacuum-dried prior to use. The compounds RPCl2 (R ) Me, Ph) and
High- and low-resolution mass spectra were obtained on a VG-
ZAB-E high-resolution mass spectrometer using negative ionization
techniques. Infrared spectra were obtained on a Perkin-Elmer 7770
Fourier transform spectrometer or a Perkin-Elmer 1430 spectropho-
tometer. Gas chromatography/mass spectrometry (GC/MS) was per-
formed on a Hewlett-Packard 5890A gas chromatograph (equipped with
a cross-linked methylsilicone column) interfaced to a Hewlett-Packard
5970 mass selective detector.
(1) For general reviews of heteroatom-polyboranes, see: (a) Todd, L. J.
In ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon Press: New York, 1982; Vol.
1, pp 543-553. (b) Todd, L. J. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Housecroft,
C. E., Eds.; Pergamon Press: New York, 1995; Vol. 1, 257-273. (c)
Binder, H.; Hein, M. Coord. Chem. ReV. 1997, 158, 171-232.
(2) Shriver, D. F.; Drezdzon, M. A. Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley: New York, 1986.
(3) Plesˇek, J.; Herˇma´nek, S. Collect. Czech. Chem. Commun. 1974, 39,
821-826.
(4) Rudolph, R. W.; Pretzer, W. R. Inorg. Synth. 1983, 22, 226-230.
(5) Kang, S. O.; Carroll, P. J.; Sneddon, L. G. Organometallics 1988, 7,
772-776.
S0020-1669(98)00445-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/12/1998

5270 Inorganic Chemistry, Vol. 37, No. 20, 1998
Table 1. NMR Data for New Compounds
Shedlow and Sneddon
δ (multiplicity,
δ (multiplicity,
compounds
nucleus
11Ba,b
assignment, J (Hz))
compounds
nucleus
assignment, J (Hz))
nido-7,10,11-SC2B8H10 (3)
-0.46 (d, B9, JBH 139, JBB ∼ 38),
nido-7,10,11-PhPC2B8H10 (4b) 11Ba,b
-6.2 (d, B4, JBH 149),
-3.5 (d, B4, JBH 145),
-7.2 (d, B9, JBH 154),
-15.0 (d, B6, JBH 174),
-16.6 (d, B8, JBH 174),
-19.1 (d, B2, JBH 150),
-21.1 (d, B5, JBH 156),
-22.1 (d, B3, JBH 156),
-41.3 (d, B1, JBH 150)
-6.8 (d, B5, JBH 158),
-10.9 (d, B8, JBH 140, JBB ∼ 30),
-12.5 (d, B2, JBH ∼ 200),
-14.0 (d, B6, JBH 190),
-15.4 (d, B3, JBH 215),
-38.0 (d, B1, JBH 153)
11B (calc)c 0.13 (B9), -1.5 (B4),
-6.2 (B5), -8.8 (B8),
-12.9 (B2), -14.5 (B3),
-15.1 (B6), -39.5 (B1)
11B-11Ba,b observed crosspeaks:
B1-B2,3,4,5,6;
11B (calc)c,h -2.1 (B4), -6.0 (B9),
-15.0 (B6), -16.0 (B8),
-16.9 (B2), -20.8 (B5),
-22.7 (B3), -42.4 (B1)
11B-11Ba,b observed crosspeaks:
B1-B2,3g,4,5,6;
B2-B3,6; B3-B4;
B2-B3,6; B3-B4,8g;
B4-B5,8,9; B5-B6,9;
B8-B9;
B4-B5,9; B5-B6;
B8-B9;
missing B3-B8
missing B4-B8; B5-B9
1H{11B}b,d 7.80-7.54 (m, phenyl),
3.14 (s, CH), 2.59 (s, CH),
2.38 (1, BH), 2.31 (1, BH),
2.14 (1, BH), 2.09(1, BH),
1.91 (1, BH), 1.88 (1, BH),
1.61 (1, BH), 1.53 (1, BH)
1H{11B}b,d 3.29 (s, CH), 3.07 (s, CH),
2.81 (BH), 2.76 (BH),
2.34 (BH), 2.20 (BH),
2.15 (BH), 1.92 (BH),
1.79 (BH), 1.68 (BH)
13Cb,f
59.0 (d, JCH 141),
46.5 (d, JCH 189)
13Cb,f
134.50-134.48 (d, i-C6H5,
JPC 2.7), 134.13-134.01
(d, p-C6H5, JPC 15),
130.29-130.19
(d, JPC 12.9), 129.12
(s, o-C6H5), 47.72
(br, CH), 33.68
(d of d, CH,
CH 186, JCP 24)
nido-7,10,11-MePC2B8H10 (4a) 11B{1H}a,b -5.6 (d, B4, JBH 142),
-7.3 (d, B9, JBH 131),
-14.6 (d, B6, JBH 173),
-16.6 (d, B2, JBH 171),
-18.8 (d, B8, JBH 156),
-21.4 (d, B5, JBH 113),
-22.0 (d, B3, JBH 128),
-41.7 (d, B1, JBH 148)
11B (calc)c -2.1 (B4), -6.0 (B9),
-15.0 (B6), -16.0 (B8),
-16.9 (B2), -20.8 (B5),
-22.7 (B3), -42.4 (B1)
11B-11Ba,b observed crosspeaks:
B1-B2,3,4,5,6;
J
31Pb,j
-68.60 (s)
nido-10-Ph-7,10-SPB9H9 (5) 11Ba,b
-5.5 (d, B4, JBH 138),
-6.1 (d, B5, JBH ∼ 118),
-7.4 (d, B8, JBH 189),
-9.5 (d, B2,6, JBH 168),
-14.7 (d, B9,3 JBH broadg),
-19.6 (d, B11, JBH 169,
B2-B3,6;
B3-B4,8;
JBP 64), -38.5 (d, B1,
B4-B5,8,9;
JBH 155)
B5-B6;
11B (calc)c,i -2.9 (B4), -5.0 (B8), -6.2 (B5),
-7.8 (B2), -9.3 (B6),
missing B4,5-B9
1H{11B}b,d 2.93 (s, CH), 2.47 (s, CH),
2.30 (1, BH), 2.22 (d,
-13.4 (B3), -13.5 (B9),
-17.5 (B11), -41.9 (B1)
11B-11Ba,b observed crosspeaks:
B1-B2,3,4,5,6;
CH3, JHP 9), 2.20 (1, BH),
2.03 (1, BH), 1.98 (1, BH),
1.65 (1, BH), 1.62 (1, BH),
1.39 (2, BH)
B2,6g-B3,11; B3-B4;
B4-B5,8,9; B5-B9;
13Cb,f
47.91 (me, CH,
B8-B9; missing B3-B8,
JCH 139, J ∼ 28),
B5-B6
34.29 (d of d, CH,
1H{11B}b,d 7.99-7.12 (m, phenyl),
2.71 (3, BH), 2.52 (2, BH),
2.43 (1, BH), 2.32 (1, BH),
2.18 (1, BH), 1.65 (1, BH)
J
CH 184, JCP 24),
7.91 (q, CH3, JCH 139)
-74.40 (s)
31Pb,j
13Cb,f
31Pb,j
134.03-120.58 (m, phenyl)
-48.95 (s)
a 160.5 MHz. b CD2Cl2. c DFT B3LYP/6-311G*//B3LYP/6-311G*. d 500.1 MHz. e Apparent septet. f 125.7 MHz. g Overlapped. h MePC2B8H10.
i MePSB9H9. j 81.0 MHz.
Flash column chromatography was performed using silica gel (230-
400 mesh, Merck). Elemental analyses were performed at Robertson
Microlit, Madison, NJ, or at the University of Pennsylvania microanaly-
sis facility. Melting points were obtained on a standard melting point
apparatus and are uncorrected.
nido-7-SB10H12 (1). A 0.244 g (2.0 mmol) sample of B10H14 was
dissolved in 15 mL of glyme under a N2 atmosphere. To this stirred
solution was added 1.28 g (6.0 mmol) of proton sponge. The solution
was then chilled in an ice-water bath, and 0.24 mL (3.0 mmol) of
S2Cl2 was injected slowly by syringe. The contents slowly warmed to
room temperature, and after 16 h, the solution was filtered to remove
PSH+Cl-. The solvent was then vacuum evaporated, and the oily
residue was washed with diethyl ether. The remaining residue was
dissolved in a minimum of methylene chloride (∼2 mL). This solution
was then added dropwise to 125 mL of heptane with stirring. The
precipitated yellow solid was filtered and then dried in vacuo to yield
0.689 g (1.88 mmol, 94.5%) of PSH+[nido-7-SB10H11]- (PSH+1-) as
a yellow solid. The 11B NMR spectrum of the sample was identical to
that of an authentic sample.6
A methylene chloride solution of 0.689 g of PSH+1- was then chilled
with an ice-water bath, and acidified by slow addition of 2 mL of
concentrated H2SO4. The methylene chloride layer was then extracted,
the solvent vacuum evaporated, and the residue sublimed, yielding 0.271
g (1.78 mmol, 91%) of light-yellow nido-7-SB10H12 (1). The 11B NMR
spectrum of the product was identical to that of an authentic sample.6
No other product was detected by GC/MS. HRMS (m/e) calcd for
1H11
B
32S (P - H): 153.1512. Found: 153.1510.
11
10
nido-7-MePB10H12 (2a). A 0.240 g (2.0 mmol) sample of B10H14
was dissolved in 15 mL of glyme under a N2 atmosphere. To this
stirred solution was added 1.28 g (6.0 mmol) of proton sponge. The
flask was chilled in an ice-water bath, and 0.13 mL (3.0 mmol) of
(6) Hertler, W. R.; Klanberg, F.; Muetterties, E. L. Inorg. Chem. 1967,
6, 1696-1706.

Heteroatom-Polyborane Clusters
Inorganic Chemistry, Vol. 37, No. 20, 1998 5271
1
MePCl2 was injected slowly. The contents gradually warmed to room
temperature, and after 16 h the solution was filtered to remove
PSH+Cl-. The solvent was vacuum evaporated, and the oily residue
was copiously washed with diethyl ether. Addition of 1.5 mL of HCl‚
Et2O precipitated any excess proton sponge. The contents were then
filtered, and the solvent vacuum evaporated to give the crude PSH+-
[nido-7-MePB10H11]- as a yellow oil. A chilled methylene chloride
solution of 2a- was then acidified dropwise with 1 mL of concentrated
H2SO4. The methylene chloride layer was extracted and reduced to
dryness, and sublimation from the yellow oil at 90 °C yielded 0.316 g
(1.90 mmol, 95%) of a pale yellow solid that was confirmed to be
nido-7-MePB10H12 (2a) by comparison with previously reported
spectroscopic data.7,8 Mp 85-87 °C (lit. 86.5-88.5 °C). No other
products were detected by GC/MS.
nido-7-PhPB10H12 (2b). A 0.240 g (2.0 mmol) sample of B10H14
was dissolved in 15 mL of glyme under a N2 atmosphere. To this
stirred solution was added 1.28 g (6.0 mmol) of proton sponge. The
flask was chilled in an ice-water bath, and 0.20 mL (1.5 mmol) of
PhPCl2 was injected slowly. The contents gradually warmed to room
temperature, and after 16 h the solution was filtered to remove
PSH+Cl-. The solvent was vacuum evaporated, and the oily residue
was washed with diethyl ether. Excess proton sponge was precipitated
from the diethyl ether washings using 1 mL of 1.0 M HCl‚Et2O. The
solution was then filtered, and the solvent was vacuum evaporated from
the filtrate to give the resultant crude PSH+[nido-7-PhPB10H11]- as a
yellow oil. A chilled methylene chloride solution of 2b- was then
acidified by dropwise addition of 1 mL of concentrated H2SO4. The
methylene chloride layer was extracted, reduced to dryness, and
sublimation at 90 °C from the yellow oil yielded 0.448 g (1.96 mmol,
98%) of a pale yellow solid which was identified as nido-7-PhPB10H12
(2b) by comparison with previously reported spectroscopic data.8 Mp
81-83 °C (lit. 82-84 °C). According to GC/MS, no other products
were produced.
(m). HRMS (m/e) calcd for 12C2 H1011B831P (P - CH3): 153.1564.
Found: 153.1290. Anal. Calcd for C3H13B8P: C, 21.63; H, 7.87.
Found C, 21.21; H, 7.29.
nido-7,10,11-PhPC2B8H10 (4b). The phenyl analogue was prepared
and isolated in an analogous manner as 4a. A 0.245 g (2.0 mmol)
sample of nido-5,6-C2B8H12 was reacted with proton sponge (0.642 g,
3.0 mmol) and PhPCl2 (0.26 mL, 3 mmol) to yield 0.379 g of nido-
7,10,11-PhPC2B8H10 (4b) (1.66 mmol, 83% yield). No other products
were detected by GC/MS. For 4b: pale yellow solid, mp 73-74 °C.
IR (KBr, cm-1): 3044 (s), 2991 (w), 2564 (s), 2198 (w), 1966 (w),
1897 (w), 1814 (w), 1582 (m), 1573 (m), 1480 (m), 1438 (s), 1335
(m), 1276 (w), 1245 (w), 1184 (m), 1162 (w), 1101 (s), 1069 (m),
1026 (m), 1007 (m), 997 (m), 940 (m), 862 (m), 739 (s), 683 (m), 655
(w), 608 (m), 543 (m), 512 (s), 485 (s), 464 (m). HRMS (m/e) calcd
for 12C8 H1511B831P: 230.1656. Found: 230.1654.
1
nido-10-Ph-7,10-SPB9H9 (5). A 0.421 g (3.0 mmol) sample of
arachno-6-SB9H11 was dissolved in 15 mL of glyme under a N2
atmosphere. To this stirred solution was added 1.93 g (9.0 mmol) of
proton sponge. A 0.60 mL (4.5 mmol) aliquot of PhPCl2 was injected
slowly. After the contents were allowed to react for 16 h, the solution
was filtered to remove PSH+Cl-. The solvent was then vacuum
evaporated from the filtrate. The oily residue was then extracted with
diethyl ether. Excess proton sponge was precipitated upon the addition
of 2 mL of HCl‚Et2O. The solution was filtered, and the solvent was
vacuum evaporated. The pale yellow solid was dried under vacuum,
affording 0.732 g (2.97 mmol, 99%) of 5. No other products were
detected by GC/MS. For 5: pale yellow solid, mp 110 °C (dec). IR
(KBr, cm-1): 3214 (s), 3099 (w), 2562 (m), 2364 (w), 2259 (w), 1457
(s), 1438 (s), 1195 (s), 1128 (w), 1000 (w), 975 (m), 795 (w), 748 (m),
692 (m), 649 (w), 547 (m), 470 (w), 418 (w). HRMS (m/e) calcd for
1
12C6 H1411B931P132S1: 248.1391. Found: 248.1388. Anal. Calcd for
C6H14B9P1S1: C, 29.24; H, 5.72. Found: C, 30.34; H, 5.19.
Computational Methods. The DFT/GIAO/NMR method,9 using
the GAUSSIAN9410 program, was used in a manner similar to that
previously described.11-13 The geometries were fully optimized at the
DFT B3LYP/6-311G* level within the specified symmetry constraints
(using the standard basis sets included) on a (2)-processor Origin 2000
computer running IRIX 6.4. Calculations that would include the phenyl
exopolyhedral substituent were not possible, since such calculations
would be too large for our available computational resources. Thus,
only methyl- or hydrogen-substituted derivatives were employed for
the calculations. Cartesian coordinates for each calculated structure
are listed in Tables 1-10 of the Supporting Information. Selected
calculated intramolecular bond distances are listed and compared when
possible to crystallographically determined distances in Tables 11-20
of the Supporting Information. The electronic energy (kcal/mol) of
each optimized structure is listed in Table 21 of the Supporting
Information. A vibrational frequency analysis was carried out on each
optimized geometry at the DFT B3LYP/6-311G* level with a true
minimum found for each structure (i.e. possessing no imaginary
frequencies). The NMR chemical shifts were calculated using the
GIAO option within GAUSSIAN94. GIAO NMR calculations were
carried out at the B3LYP/6-311G*//B3LYP/6-311G* level. 11B NMR
GIAO chemical shifts are referenced to BF3‚O(C2H5)2 using an absolute
shielding constant of 102.24 ppm.13,14 13C NMR GIAO chemical shifts
nido-7,10,11-SC2B8H10 (3). A 0.245 g (2.0 mmol) sample of nido-
5,6-C2B8H12 was dissolved in 15 mL of glyme under a N2 atmosphere.
To this stirred solution at 0 °C was added 0.047 g (2.0 mmol) of NaH.
After gas evolution ceased, 0.162 mL (3.0 mmol) of S2Cl2 was injected
slowly. At this point, 0.214 g (1.0 mmol) of proton sponge was quickly
added. The contents were allowed to gradually warm to room
temperature, and after 16 h the solution was filtered to remove
PSH+Cl-. The solvent was then vacuum evaporated. The oily residue
was extracted three times with 30 mL of diethyl ether. Excess proton
sponge was precipitated from the diethyl ether washings using 1 mL
of 1.0 M HCl‚Et2O. The solution was filtered, and the solvent was
vacuum evaporated to give 0.236 g (1.55 mmol, 77%) of nido-7,8,9-
SC2B8H10 (3). According to GC/MS no other product was formed.
For 3: yellow solid, mp 135-137 °C. IR (KBr, cm-1), 3221 (s), 3051
(m), 2567 (s), 2361 (w), 2256 (w), 1457 (s), 1251 (m), 1197 (m), 1071
(w), 1007 (m), 938 (m), 883 (m), 832 (w), 744 (m), 649 (w), 545 (w).
1
HRMS (m/e) cald for 12C2 H1011B832S 154.1428. Found: 154.1242.
Anal. Calcd for C2H10B8S: C, 15.74; H, 6.60. Found: C, 15.59; H,
6.43.
nido-7,10,11-MePC2B8H10 (4a). A 0.245 g (2.0 mmol) sample of
nido-5,6-C2B8H12 was dissolved in 15 mL of glyme under a N2
atmosphere. To this stirred solution was added 0.642 g (3.0 mmol) of
proton sponge; 0.26 mL (3.0 mmol) of MePCl2 was then injected into
the flask. After 17 h the solution was filtered to remove PSH+Cl-.
The solvent was vacuum evaporated, and the orange oily residue was
extracted three times with 50 mL aliquots of diethyl ether. Excess
proton sponge was then precipitated from the diethyl ether using 2 mL
of 1.0 M HCl‚Et2O. The solution was filtered, and the diethyl ether
was vacuum evaporated. The resulting solid was dried under vacuum
to give 0.323 g (1.94 mmol, 97%) of 4a. GC/MS detected no other
products. For 4a: pale yellow solid, mp 138 °C(dec). IR (KBr, cm-1):
3214 (s), 3043 (w), 2562 (m), 2359 (m), 2260 (w), 1471 (s), 1452 (s),
1437 (s), 1419 (s), 1395 (s), 1309 (m), 1194 (m), 1100 (w), 1010 (w),
928 (w), 831 (w), 771 (w), 738 (w), 681 (w), 647 (w), 548 (m), 484
(9) Yang, X.; Jiao, H.; Schleyer, P. v. R. Inorg. Chem. 1997, 36, 4897-
4899 and references therein.
(10) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. T.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian
94, Revision C.3; Gaussian, Inc.: Pittsburgh, PA, 1995.
(11) Keller, W.; Barnum, B. A.; Bausch, J. W.; Sneddon, L. G. Inorg. Chem.
1993, 32, 5058-5066.
(12) Bausch, J. W.; Rizzo, R. C.; Sneddon, L. G.; Wille, A. E.; Williams,
R. E. Inorg. Chem. 1996, 35, 131-135.
(13) Tebben, A. J. Masters Thesis, Villanova University, 1997.
(14) Tebben, A. J.; Bausch, J. W., to be submitted.
(7) Getman, T. D.; Deng, H.-B.; Hsu, L.-Y.; Shore, S. G. Inorg. Chem.
1989, 28, 3612-3616.
(8) Little, J. L. Inorg. Chem. 1976, 15, 114-117.

5272 Inorganic Chemistry, Vol. 37, No. 20, 1998
Shedlow and Sneddon
followed by acidification of the resulting anion 1-, using a two-
phase methylene chloride/aqueous H2SO4 system, results in the
formation of nido-7-SB10H12 (1) in a typical yield of 91% (eqs
1 and 2). The acidification of the proton sponge salt can only
B10H14 + 3PS + SCl2 f
PSH+[nido-7-SB10H11]-
+ 2PSH+Cl- (1)
1-
2PSH+[nido-7-SB10H11]- + H2SO4 f
12 + (PSH+) SO
(2)
2-
4
2nido-7-SB10H
2
1
be accomplished by a strong acid system such as aqueous H2-
SO4. Thus, prior to acidification with H2SO4, the reaction
mixture containing 1- can be treated with HCl‚Et2O to easily
remove any excess proton sponge as (PSH+)2SO42-, without
producing nido-7-SB10H12.
Compound 1 was sublimed and isolated as an air-sensitive,
yellow solid in 91% yield. Comparison of both its 11B and 1H
NMR spectra with those of literature values5,6 clearly confirm
its identity. As shown in Figure 1a, the proposed structure and
experimentally observed chemical shifts and assignments were
also found to be in excellent agreement with DFT/GIAO/NMR
calculations at the DFT B3LYP/6-311G*//B3LYP/6-311G*
level.9
Isoelectronic with nido-7-SB10H12 (1) are the known 11-vertex
nido-7-RPB10H12 phosphaboranes, where R ) Me, Ph (2a and
2b). A crystallographic determination7 of the methyl compound
has confirmed a cage geometry consistent with that proposed
for the nido-7-SB10H12 cluster. The nido-7-RPB10H12 (R ) Me,
Ph) compounds were first synthesized by the reaction of the
decaborane dianion with a phosphorus dihalide in a 33% yield.8
Shore7 later prepared nido-7-MePB10H12 in a 12% yield by
reaction of K2+[B11H13]2- with MePCl2 over 7 days at room
temperature.
Figure 1. Optimized cage geometries for (a) nido-7-SB10H12, experi-
mental (1) and DFT/GIAO calculated chemical shifts (I) and assign-
ments {exp(assgn) [calc(assgn)]}, 16.3(B5) [19.2(B5)], -1.7(B2,3)
[0.31(B2,3)], -3.9(B8,11) [-4.2(B8,11)], -10.9(B9,10) [-11.3-
(B9,10)], -17.8(B1) [-18.5(B1)], -25.2(B4,6) [-26.8(B4,6)]; (b) nido-
7-CH3PB10H12, experimental (2a) and DFT/GIAO calculated chemical
shifts (IIa) and assignments {exp(assgn) [calc(assgn)]}, 1.9(B5) [5.1-
(B5)], -8.5(B2,3) [-8.0(B2,3)], -13.0(B8,11) [-13.5(B8,11)], -18.4-
(B9,10) [-18.1(B9,10)], -26.0(B1,4,6) [-25.3(B1), -26.4(B4,6)].
are referenced to TMS using an absolute shielding constant of 184.38
ppm and are corrected according to the method described by Schleyer.15
31P NMR GIAO δ values were first referenced to PH3 using an absolute
shielding constant of 557.2396 ppm and then converted to the H3PO4
reference scale using the experimental value of δ(PH3) ) -240 ppm.
Results
When a method similar to that used for the synthesis of nido-
7-SB10H12, was used, it was found that the overnight reaction
of decaborane with RPCl2 (R ) Me, Ph) and excess proton
sponge at room temperature produced the anions nido-7-
Improved Syntheses of the nido-7-SB10H12 Thiaborane and
the nido-7-RPB10H12 Phosphaboranes. Two previous syn-
thetic routes to nido-7-SB10H12 have been reported. One method
-
-
MePB10H11 (2a-) and nido-7-PhPB10H11 (2b-) in almost
quantitative yields. The reaction mixture was treated with HCl‚
Et2O to precipitate any unreacted proton sponge, followed by
acidification of the phosphaborane anions (2a- or 2b-) again
using the two-phase CH2Cl2/aqueous H2SO4 system, to give
nido-7-MePB10H12 (2a) and nido-7-PhPB10H12 (2b) in almost
quantitative yields (eqs 3-4).
-
involves the initial synthesis of arachno-6-SB9H12 from
decaborane and ammonium polysulfide. Pyrolytic dispropor-
-
tionation of the cesium salt of the arachno-6-SB9H12 anion
then gives nido-7-SB10H11-. Protonation produces the neutral
nido-7-SB10H12 in a 37% yield, with an overall 33% yield from
B10H14.6 More recently it was found that when nido-6-SB9H11,
which can be synthesized in 86.5% yield by iodine oxidation
of arachno-6-SB9H12 ,
- 4,16 was refluxed with NaBH4, the nido-
B10H14 + 3PS + RPCl2 f
7-SB10H11- anion is produced.5 This anion can then be acidified
using aqueous HCl in methylene chloride to give nido-7-SB10H12
in ∼60% yield based on consumed nido-6-SB9H11. The overall
yield of nido-7-SB10H12 from B10H14 using this procedure is
46.7%. Unfortunately, both of the above procedures require
the initial cage degradation of B10H14 to form SB9H12-, followed
by a second cage insertion reaction to form SB10H12. Thus, at
the outset of this work there was no efficient synthetic route to
the nido-7-SB10H12 cluster.
PSH+[nido-7-RPB10H11]- + 2PSH+Cl- (3)
2PSH+[nido-7-RPB10H11]- + H2SO4 f
2nido-7-RPB10H12 + (PSH+)2SO4
2-
(4)
2a, R ) Me, 95% yield
2b, R ) Ph, 98% yield
Compounds 2a and 2b were sublimed and isolated as air-
sensitive, yellow solids. Comparisons of the 11B and 1H NMR
spectra of 2a and 2b with those in the literature7,8 confirm their
identity. GC/MS showed the presence of no other compounds.
Density functional theory calculations at the B3LYP/6-311G*
level performed on compound 2a produced the optimized
geometry II (Figure 1b). A comparison (Supporting Informa-
tion) of calculated bond lengths with those determined crystal-
As described in the Experimental Section, it has now been
found that the reaction of decaborane with S2Cl2 (or SCl2) and
proton sponge (PS), at room temperature in DME or THF,
(15) Maerker, C.; Schleyer, P. v. R.; Salahub, D. R.; Malkina, O. L.; Malkin,
V. G., submitted.
(16) Pretzer, W. R.; Rudolph, R. W. J. Am. Chem. Soc. 1976, 98, 1441-
1447.

Heteroatom-Polyborane Clusters
Inorganic Chemistry, Vol. 37, No. 20, 1998 5273
°C gave the new nido-thiadicarbaborane nido-7,10,11-SC2B8H10
(3) in 77% yield as a yellow solid (eq 5).
nido-5,6-C2B8H12 + 2PS + SCl2 f
nido-7,10,11-SC2B8H10 + 2PSH+Cl-
(5)
3
The reported17,18 11B NMR spectrum for nido-7,9,10-
SC2B8H10 shows five resonances in 1:2:2:2:1 ratios in agreement
with its established Cs symmetry.18,19 The 160.5 MHz 11B NMR
spectrum of the new isomer 3 consists of eight resonances,
indicative of C1 symmetry (Figure 2a). Likewise, the 125.7
MHz 13C NMR spectrum for 3 reveals two different cage CH
resonances observed as doublets at 46.5 and 59.0 ppm. A more
detailed investigation of the 11B NMR spectrum using a 2D
11B-11B COSY experiment (Table 1) led to the preliminary
assignment of the structure shown in eq 6 in which the sulfur
(6)
and carbon atoms occupy adjacent positions on the five-
membered open face. Such a structure can be generated from
nido-5,6-C2B8H12 in a straightforward manner, with the initial
insertion of a -SCl unit onto the C5-C6-B9-B10 edge
followed by dehydrohalogenation, to create the new five-
membered open face containing the original S-C5-C6-B9-
B10 atoms.
DFT/GIAO/NMR calculations were employed to confirm the
structure of 3. Two isomeric structures having C1 symmetry,
as well as the symmetric Cs isomer were examined: nido-
7,10,11-SC2B8H10 (III.a), nido-7,9,11-SC2B8H10 (III.b), and
nido-7,9,10-SC2B8H10 (III.c). The optimized geometries for the
three structures are presented in Figure 3.
Figure 2. 160.5 MHz 11B NMR spectra for (a) nido-7,10,11-SC2B8H10
(3) (b) nido-7,10,11-PhPC2B8H10 (4b), and (c) nido-10-Ph-7,10-SPB9H9
(5).
lographically7 shows good agreement. Similarly, a comparison
of the experimentally determined 11B NMR shifts7,8 and
assignments for 2a and 2b with those for the calculated structure
II show good agreement, with the difference in shifts being
only 0.1-3.2 ppm.
Syntheses of the New 7,10,11-SC2B8H10 Thiadicarbabo-
rane and the 7,10,11-MePC2B8H10 and 7,10,11-PhPC2B8H10
Phosphadicarbaboranes. Isoelectronic with the 11-vertex
thiaborane and phosphaborane clusters 1 and 2 are the thia- and
phosphadicarbaboranes of the general formula EC2B8H10 (E )
S, RP). While no previous phosphadicarbaborane has been
reported, one thiadicarbaborane, nido-7,9,10-SC2B8H10, has been
Although best agreement is found for III.a, the 11B and 13C
NMR chemical shifts calculated for both of the two C1 symmetry
isomers (III.a and III.b) fall in the range of the experimental
NMR shifts of 3 (Figure 4). However, only the boron resonance
assignments of III.a are in agreement with the assignments
determined experimentally by 2D 11B-11B NMR for 3 (Table
1). For example, the experimental 2D 11B-11B NMR spectra
of 3 show that the resonances at -3.4 and -6.8 ppm are 5-
and 4-coordinate, respectively. This agrees with the calculations
on the 7,10,11-isomer (III.a), but disagrees with the calculations
on the 7,9,11-isomer (III.b) that predict the two resonances in
this region (i.e., -1.8 and -3.8 ppm) are 4- and 2-coordinate,
respectively. Likewise, the resonances at -0.46 and -10.9 ppm
in the boron NMR spectrum of 3 show evidence of JBB coupling
(∼30-40 Hz), consistent with their assignment in the calcula-
tions on IIIa as the adjacent B8 and B9 borons.
previously synthesized in a 30% yield from the reaction of
- 17
aqueous bisulfate with K+C2B9H12
.
The structure of this
compound has been confirmed by both electron diffraction and
ab initio/NMR calculations.18,19
Structure III.c (nido-7,9,10-SC2B8H10) corresponds to the
structure proposed for the known isomer, and the GIAO
calculated 11B chemical shifts are in agreement both with those
that were experimentally determined17 (Figure 4 caption) and
with earlier ab initio/IGLO calculations.18 The nido-7,9,10-
SC2B8H10 would be expected to be the most stable isomer since
electron-rich heteroatoms, such as carbon, phosphorus, and
sulfur, are known to favor both low-coordinate cage positions
on the open faces of polyhedral frameworks and arrangements
When the proton sponge initiated in situ dehydrohalogenation
method was used, it was found that the reaction of nido-5,6-
C2B8H12 with proton sponge and SCl2 (or S2Cl2) in DME at 0
(17) Brattsev, V. A.; Knyazev, S. P.; Danilova, G. N.; Stanko, V. I. Zh.
Obshch. Khim. 1975, 45, 1393-1394.
(18) Hynk, D.; Hofmann, M.; Schleyer, P. v. R.; Bu¨hl, M.; Rankin, D. W.
H. J. Phys. Chem. 1996, 100, 3435-3440.
(19) Vondrak, T.; Heˇrma´nek, S.; Plesˇek, J. Polyhedron 1993, 12, 1301-
1310.

5274 Inorganic Chemistry, Vol. 37, No. 20, 1998
Shedlow and Sneddon
Figure 4. Comparison of the experimental chemical shifts and
assignments for 3 with those DFT/GIAO calculated values for nido-
7,10,11-SC2B8H10 (III.a), nido-7,9,11-SC2B8H10 (III.b), and nido-
7,9,10-SC2B8H10 (III.c). Experimentally observed 11B NMR shifts for
nido-7,9,10-SC2B8H10: -2.8(B5), -7.4(B2,3), -13.0(B8,11), -13.8-
(B4,6), -41.5(B1).17,18
Figure 3. Optimized geometries and relative energies for nido-7,10,11-
SC2B8H10 (III.a), nido-7,9,11-SC2B8H10 (III.b), and nido-7,9,10-
SC2B8H10 (III.c).
that allow the maximum separation of the heteroatoms.12,20 The
DFT calculations confirm that the symmetrical 7,9,10-isomer
(III.c) should be the most stable. Thus, the 7,9,10-isomer (III.c)
is 34 kcal/mol lower in energy than III.a, and III.b is 20 kcal/
mol lower than III.a (Figure 3). The exclusive synthesis of
the 7,10,11-isomer, (III.a), the least stable of the three possible
isomers, clearly shows that the mild conditions of the dehy-
drohalogenation heteroatom insertion reaction allows the isola-
tion of kinetic rather than thermodynamic products. Attempts
to isomerize 3 to the other isomers were made by heating a
sealed sample for 40 min at 110 °C. There was extensive
decomposition, but two peaks corresponding to two other
SC2B8H10 isomers were detected by GC/MS.
configuration (Figure 2b). DFT/GIAO/NMR calculations at the
B3LYP/6-311G*//B3LYP/6-311G* level were employed to
examine several possible structures: nido-7,10,11-MePC2B8H10
(IV.a), nido-7,9,11-MePC2B8H10 (IV.b), and nido-7,9,10-
MePC2B8H10 (IV.c). The optimized geometries for the three
isomers are presented in Figure 5. Comparison of the 11B NMR
shifts of the three calculated structures with the experimental
11B NMR shifts of 4a (Figure 6) indicate that while the
calculated shifts of both IV.a (7,10,11-isomer) and IV.b (7,9,11-
isomer) fall in the range of the experimentally determined shifts
for 4a and 4b, only the assignments of IV.a (7,10,11-isomer)
are consistent with the experimental data. For example, the
experimental 2D 11B-11B NMR spectra show that the reso-
nances at -5.6 and -14.6 ppm are 5- and 3-coordinate,
respectively. This is correctly predicted by the calculations on
the 7,10,11-isomer (IV.a) but does not agree with the calcula-
tions on the 7,9,11-isomer (IV.b), where it is predicted that the
two resonances in this region (i.e., -5.0 and -8.1 ppm) are 3-
and 4-coordinate, respectively.
The new phosphadicarbaboranes, nido-7,10,11-RPC2B8H10 [R
) Me (4a), Ph (4b)], were synthesized as pale yellow,
air-sensitive solids in 83% (4a) and 97% (4b) yields in a manner
similar to 3 by reaction of nido-5,6-C2B8H12 with proton sponge
and methyl- or phenyl-substituted RPCl2 (eq 7).
nido-5,6-C2B8H12 + 2PS + RPCl2 f
Consistent with the proposed structure, the 125.7 MHz 13C-
{1H} NMR spectra of 4a and 4b each show two cage-CH
resonances. The CH resonance near 48 ppm is broad, while
the CH resonance near 34 ppm for both compounds 4a and 4b
is a sharp doublet, clearly showing phosphorus coupling (1JCP
) 24 Hz), thereby allowing the assignment of the two
resonances to the C10 and C11 carbons, respectively. These
assignments are consistent with the relative 13C NMR shifts
nido-7,10,11-RPC2B8H10 + 2PSH+Cl- (7)
R ) Me (4a), Ph (4b)
The 160.5 MHz 11B NMR spectra for 4a and b are somewhat
similar to that of the isoelectronic cluster 3, consisting of eight
resonances, again suggesting C1 symmetry and a 7,10,11-
(20) Williams, R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67-142.

Heteroatom-Polyborane Clusters
Inorganic Chemistry, Vol. 37, No. 20, 1998 5275
The experimental 160.5 MHz 11B{1H} NMR spectrum for 5
reveals seven resonances, in ratios of 1:1:1:2:2:1:1, in the same
ranges found for the other 11-vertex heteroboranes, nido-
7,10,11-RPC2B8H10 (4a,b) and nido-7,10,11-SC2B8H10 (3)
(Figure 2c).
If the formation of 5 was achieved by a heteroatom insertion
process similar to that discussed earlier for 3 and 4, involving
an initial addition of a -P(R)Cl unit to the S6-B7-B8-B9 edge
of nido-6-SB9H11, then the 7,8-structure shown below should
be produced. This would have the phosphorus and sulfur atoms
in adjacent positions.
The spectral and computational characterizations of 5 re-
vealed, however, that it has the 7,10-configuration shown in eq
9. DFT/GIAO/NMR calculations were employed to examine
(9)
Figure 5. Optimized geometries and relative energies for nido-7,10,11-
MePC2B8H10 (IV.a), nido-7,9,11-MePC2B8H10 (IV.b), and nido-7,9,10-
MePC2B8H10 (IV.c).
both cage geometries: nido-8-Me-7,8-SPB9H9 (V.a) and nido-
10-Me-7,10-SPB9H9 (V.b). The optimized geometries and
relative energies of these two structures are shown in Figure 7.
As can be seen in Figure 8, a comparison of the experimental
NMR shifts and 2D 11B-11B determined assignments of 5 with
those calculated for nido-8-Me-7,8-SPB9H9 (V.a) and nido-10-
Me-7,10-SPB9H9 (V.b) clearly favors the nido-10-Me-7,10-
SPB9H9 (V.b) structure for 5. For example, only the calcula-
tions on V.b correctly predict that the resonance at -19.6 ppm
of 5, which exhibits doublet JBP coupling (J ) 64 Hz) in the
11B{1H} NMR spectrum, should be due to the boron (B11) that
is adjacent to the phosphorus atom. The 31P NMR spectrum of
5 consists of one resonance at -48.95 ppm which is in excellent
agreement with the calculated shift of -55.37 ppm for V.b.
Calculations on the relative energies of the two methyl
substituted isomers (V.a and V.b) reveal that the 7,10-isomer
(V.b) is 40 kcal/mol more stable than the 7,8-isomer (Figure
7). Thus, unlike in 3 and 4, in compound 5 maximum separation
of the heteroatoms on the open face is achieved.
calculated for IV.a (7,10,11-isomer) (Figure 6). Likewise, the
observed chemical shift of the phosphorus resonance in the 81.0
MHz 31P NMR spectrum of 4a (-74.4 ppm) is in good
agreement with that calculated for structure IV.a (-82.0 ppm).
As was the case for the SC2B8H10 cage, energy calculations
on the phosphadicarbaboranes reveal that the symmetrical
7,9,10-RPC2B8H10 cluster (IV.c) is the most stable. IV.c is
approximately 26 kcal/mol more stable than IV.a, and IV.b is
more stable than IV.a by ∼19 kcal/mol (Figure 5). Preliminary
investigations by GC/MS reveal that, although significant
decomposition is observed upon heating 4a for 20 min at 110
°C, a mixture containing two new isomers is produced.
Synthesis of the nido-10-Ph-7,10-SPB9H9 Thiaphosphabo-
rane. Isoelectronic with the thiadicarbaboranes and phosphadi-
carbaboranes discussed above are mixed phosphathiaborane
[(R)PSB9H9] clusters. However, no previous examples of this
class of mixed heteroborane have been reported.
Discussion
Again using the proton sponge initiated in situ dehydroha-
logenation method, the new phosphathiaborane, nido-10-Ph-
7,10-SPB9H9, (5) was synthesized in a 98% yield, and isolated
as a pale yellow, air-sensitive solid (eq 8).
A seemingly straightforward route to a phospha- or thiaborane
or carborane could involve the reaction of SCl2 or RPCl2 with
a polyhedral borane nido-dianion. However, there are problems
with this approach.21 One method of forming dianions requires
nido-6-SB9H11 + 2PS + PhPCl2 f
(21) For general methods used for the formation of polyborane dianions,
see: Grimes, R. N. In ComprehensiVe Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
New York, 1982; Vol. 1, pp 459-542 and references therein.
nido-10-Ph-7,10-PSB9H9 + 2PSH+Cl-
(8)
5

5276 Inorganic Chemistry, Vol. 37, No. 20, 1998
Shedlow and Sneddon
Figure 7. Optimized geometries and relative energies for nido-8-Me-
7,8-SPB9H9 (V.a) and nido-10-Me-7,10-SPB9H9 (V.b).
Figure 6. Comparisons of the experimental chemical shifts and
assignments for 4 with those DFT/GIAO calculated values for nido-
7,10,11-MePC2B8H10 (IV.a), nido-7,9,11-MePC2B8H10 (IV.b), and nido-
7,9,10-MePC2B8H10 (IV.c).
the removal of two protons from a nido-cage structure containing
two bridge-hydrogens. The removal of the second proton is
often difficult and typically requires either strong bases, such
as MeLi, or extended reaction times. Such conditions can cause
cage degradation, leading to the generation of side products and
lower yields. Alternatively, dianions can be generated from
closo-clusters by reduction with agents such as sodium naph-
thalide. Because sodium naphthalide is a strong reducing agent,
cage degradation leading to the generation of numerous side
products is also usually an important drawback of this method.
Thus, regardless of which procedure is used, the conditions
required to generate dianions are generally harsh and can result
in low yields and selectivities due to cage fragmentation.
The synthetic method presented in this paper avoids the
formation of the reactive polyborane dianions. Instead, the
pathway involves the reaction of a phosphorus or sulfur dihalide
with a monoanionic boron cluster, followed by a proton sponge
initiated in situ dehydrohalogenation reaction. Although the
reaction is a one-pot method, the actual reaction sequence must
proceed via a multistep process. A reasonable series of steps
is illustrated in Figure 9 for the reaction of B10H14 with SCl2 or
RPCl2. Initial deprotonation by proton sponge would generate
Figure 8. Comparisons of the experimental chemical shifts and
assignments for 5 with those DFT/GIAO calculated values for nido-
8-Me-7,8-SPB9H9 (V.a) and nido-10-Me-7,10-SPB9H9 (V.b).
charge, the second bridge hydrogen has decreased acidity and
is not removed by proton sponge. However, following the
metathesis reaction in which the -X(R)Cl unit is inserted into
the vacant bridge site, the negative charge is balanced and the
acidity of the bridge hydrogen is restored. Another equivalent
of proton sponge can then abstract this hydrogen to generate a
species such as PSH+[B10H12‚X(R)Cl]-. Such a species was
-
the B10H13 monoanion. Because of the cluster’s negative

Heteroatom-Polyborane Clusters
Inorganic Chemistry, Vol. 37, No. 20, 1998 5277
regenerated by acidification using a two-phase aqueous H2SO4/
methylene chloride system (step 6, Figure 9).
The routes to nido-7-SB10H12 (1) and nido-7-RPB10H12, (2a
and 2b) along with their respective anions are a significant
improvement over the previous literature methods outlined
earlier,5-8 in terms of both convenience and yields. The
syntheses of the new phospha- and thiacarbaboranes, nido-
7,10,11-SC2B8H10 (3), nido-7,10,11-RPC2B8H10 (4a,b), and the
mixed phosphathiaborane, nido-10-Ph-7,10-SPB9H9 (5), il-
lustrate the potential importance of this method for generating
new types of heteroatom-polyboranes derived from other cage
systems. These methods should also be applicable to the
incorporation of a wide range of heteroatoms. Studies of these
possibilities are presently ongoing and will be reported in future
publications.22
Finally, it should also be noted that since each of the 11-
vertex nido-clusters (1-5) has a five-membered open face that
is similar to both the cyclopentadienyl (C5H5-) and dicarbollide
(C2B9H112-) anions, these heteroatom-polyboranes are of
special interest because of their potential metal coordination
Figure 9. Multistep schematic of dehydrohalogenation heteroatom
insertion reaction.
not observed by 11B NMR, but would be expected to be unstable
and readily undergo dehydrohalogenation with elimination of
the remaining chloride on the -X(R)Cl group as PSH+Cl-. This
last step then allows the incorporation of the -X(R) group into
the cage. A similar sequence for the insertion reactions with
nido-5,6-C2B8H12 correctly predicts the formation of the ob-
served 7,10,11-isomers, i.e., nido-7,10,11-SC2B8H10 (3) and
nido-7,10,11-RPC2B8H10 (4a and 4b), rather than the 7,9,11-
or 7,9,10-isomers of these cage systems, even though DFT
calculations clearly show the 7,10,11-isomers are higher in
energy.
The key feature in this synthetic sequence is that proton
sponge acts as both a deprotonating agent and a halogen
scavenger. Other less expensive reagents such as NaH or KH
can be used as the initial deprotonating agent; however, the use
of only proton sponge allows the sequence to be carried out as
a one-pot reaction.
2-
2-
chemistry. Thus, the nido-SB10H10 and nido-RPB10H10
dianions are analogues of dicarbollide anion, while the neutral
compounds, nido-7,10,11-SC2B8H10 (3), nido-7,10,11-RPC2B8H10
(4a and 4b), and nido-10-Ph-7,10-SPB9H9 (5) could be con-
sidered η5- 6-π electron-donor analogues of π-arenes and are
expected to form similar types of sandwich complexes. Thus,
by controlling the elemental composition of these 11-vertex
nido-heteroatom-polyboranes, it is possible to both control their
formal charges and further tune the bonding properties of these
cage systems. This should then allow the production of
extensive series of sandwich complexes derived from these
ligands, that, although isoelectronic and isostructural, will each
exhibit unique properties which are a function of the individual
bonding abilities of the particular metal-coordinated cage. The
fact that compounds 1-5 can now be readily synthesized in
large scales should enable extensive explorations of such
coordination complexes.
In cases where the products have acidic hydrogens, such as
nido-7-SB10H12 (1) and nido-7-RPB10H12, (2a and 2b), they are
also deprotonated by proton sponge to produce their corre-
sponding monoanions, PSH+[nido-7-SB10H12] (PSH+1-) and
PSH+[nido-7-RPB10H12], (PSH+2a- and PSH+2b-). Thus, to
avoid making a mixture of neutral and anionic products, it is
convenient in these reactions to employ an excess of proton
sponge to convert all of the product to its anion (step 5, Figure
9). The excess proton sponge can be easily removed from the
reaction mixture by addition of HCl‚Et2O, followed by filtration
of the insoluble PSH+Cl-. The neutral cluster products are then
Acknowledgment. We thank the National Science Founda-
tion for support of this work. We also thank Dr. Joe Barendt at
Callery Chemical Company and Dr. Tom Baker for gifts of
decaborane. We also thank Dr. George Furst for his assistance
with the NMR experiments and Dr. Joe Bausch for his advice
on the DFT/GIAO calculations.
Supporting Information Available: Tables containing the Carte-
sian coordinates for each optimized geometry, selected calculated
intramolecular bond distances, and a listing of the electronic energy
(kcal/mol) of each structure (22 pages). Ordering information is given
on any current masthead.
(22) Shedlow, A. M.; Sneddon, L. G., manuscripts in preparation.
IC980445C