New derivatives of [NHMe3][7-Me-μ-(9,10-HMeC)-nido-7-CB 10H10]

Article abstract of DOI:10.1021/om030487v

[NHMe₃][7-Me-μ-(9,10-HMeC)-nido-7-CB₁₀H ₁₀] (1) reacts with [PdCl₂(PPh₃)₂] in refluxing ethanol solutions to afford four compounds which are the result of PPh₃ addition. Three of

Full text of DOI:10.1021/om030487v

Organometallics 2004, 23, 3335-3342
3335
New Der iva tives of
[NHMe3][7-Me-µ-(9,10-HMeC)-n id o-7-CB10H10]
J onathan Bould,† Anna Laromaine,†,‡ Clara Vin˜as,† Francesc Teixidor,*,†
Lawrence Barton,§ Nigam P. Rath,§ Rudolph E. K. Winter,§ Raikko Kiveka¨s,| and
Reijo Sillanpa¨a¨
Institut de Cie`ncia de Materials de Barcelona, 08193 Bellaterra, Spain, Chemistry
Department, University of Missouri, St. Louis, Missouri 63121, Department of Chemistry,
P.O. Box 55, University of Helsinki, Helsinki FIN-00014, Finland, and Department of
Chemistry, University of J yva¨skyla¨, J yva¨skyla¨ FIN 40351, Finland
Received J une 24, 2003
[NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10] (1) reacts with [PdCl2(PPh3)2] in refluxing
ethanol solutions to afford four compounds which are the result of PPh3 addition. Three of
the products are structural isomers, viz. [5-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H9] (2),
[6-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H9] (3), and [2-Me-3-{CHMe(PPh3)}-closo-2-CB10H9]
(4), and the fourth is [7-Me-8-OEt-9-{CHMe(PPh3)}-nido-7-CB10H10] (5). The compounds were
characterized by NMR spectrometry, high-resolution mass spectrometry, and single-crystal
X-ray diffraction studies and are the first derivatives of the “unreactive” [7-R-µ-(9,10-HRC)-
nido-7-CB10H10]- anion (R ) Me) not involving degradation.
In tr od u ction
isomer, which is the most stable, is the thermodynamic
product [7-R-µ-(9,10-HR′C)-nido-7-CB10H11]-, known as
the “unreactive” form since it is inert in the usual
reactions leading to metallacarboranes.4,5 Recent studies
verified this affirmation by theoretical calculations. It
was found that, at the MP2/6-31G*/3-21G+ZPE level,
the “unreactive” isomer is 6.7 kcal/mol more stable than
the reactive one.6 The kinetic isomer undergoes thermal
It is well-known that the isomeric 1,2-closo-C2B10H12
,
1,7- and 1,12- carboranes, and some of their derivatives
undergo a two-electron-reduction reaction with sodium1
to form [C2B10H12]
2- carborane ions. Protonation of this
dianion makes possible the formation of two monoanions
of the formula [C2B10H13]-.2 One of them is the kinetic
compound [7,9-R2-nido-C2B10H11]- (I; R ) R′ ) H), also
rearrangement2b,7 to the second isomer [7-R-µ-(9,10-
-
HR′C)-nido-7-CB10H11
]
(II; R ) R′ ) H). Recently, a
known as the “reactive” form. Its dianionic [7,9-R2-nido-
more convenient, direct, high-yield route8 to alkylated
derivatives of the thermodynamic isomer has been
developed, thus prompting us to attempt to further
investigate its chemistry.
2-
7,9-C2B10H10
]
form features an open six-membered
face,2c and it has proven to be a versatile ligand for
f-block and early-transition-metal elements.3 The second
† Institut de Cie`ncia de Materials de Barcelona.
‡ Enrolled in the UAB Ph.D. program.
(3) (a) Dustin, D. F.; Dunks, G. B.; Hawthorne, M. F. J . Am. Chem.
Soc. 1973, 95, 1109. (b) Alcock, N. W.; Taylor, J . G.; Wallbridge, M. G.
H. J . Chem. Soc., Dalton Trans. 1987, 1805. (c) Salentine, C. G.;
Hawthorne, M. F. Inorg. Chem. 1976, 15, 2872. (d) Xie, Z.; Chui, K.;
Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 3947. (e) Chui, K.;
Yang, Q.; Mak, T. C. W.; Lam, W. H.; Liu, Z.; Xie, Z. J . Am. Chem.
Soc. 2000, 122, 5758. (f) Khattar, R.; Manning, M. J .; Knobler, C. B.;
J ohnson, S. E.; Hawthorne, M. F. Inorg. Chem. 1992, 31, 268. (g) Zi,
G.; Li, H. W.; Xie, Z. Organometallics 2002, 21, 3464. (h) Xie, Z.; Yan,
Q.; Mak, T. C. W. Angew. Chem., Int. Ed. 1999, 38, 1761. (i) Chui, K.;
Li, H.-W.; Xie, Z. Organometallics 2000, 19, 5447. (j) Zi, G.; Li, H.-W.;
Xie, Z. Chem. Commun. 2001, 1110. (k) Wang, Y.; Wang, H.; Li, H.-
W.; Xie, Z. Organometallics 2002, 21, 3311. (l) Zi, G.; Li, H.-W.; Xie, Z.
Organometallics 2002, 21, 3464.
§ University of Missouri.
| University of Helsinki.
University of J yva¨skyla¨.
(1) (a) Grafstein, D.; Dvorak, J . Inorg. Chem. 1963, 2, 1128. (b)
Zakharkin, L.; Kalinin, V.; Podvisotskaya, L. Izv. Akad. Nauk SSSR,
Ser. Khim. 1967, 10, 2310. (c) Zakharkin, L.; Kalinin, V. Izv. Akad.
Nauk SSSR, Ser. Khim. 1969, 164. (d) Stanko, V.; Gol’typin, Y. V.;
Brattsev, V. Zh. Obshch. Khim. 1969, 39, 1175. (e) Dustin, D. F.;
Dunks, G. B.; Hawthorne, M. F. J . Am. Chem. Soc. 1973, 95, 1109.
(2) (a) Dunks, G. B.; Wiersema, R. J .; Hawthorne, M. F. J . Chem.
Soc., Chem. Commun. 1972, 899. (b) Dunks, G. B.; Wiersema, R. J .;
Hawthorne, M. F. J . Am. Chem. Soc. 1973, 95, 3174. (c) Getman, T.
D.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem. 1990, 29, 158.
10.1021/om030487v CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/20/2004

3336 Organometallics, Vol. 23, No. 13, 2004
Bould et al.
Sch em e 1. P r od u cts fr om th e Rea ction of [NHMe3][7-Me-µ-(9,10-HMeC)-Nid o-7-CB10H10] (1), w ith
[P d Cl2(P P h 3)2] in a 1:1 Mola r Ra tio in Eth a n ol
Resu lts a n d Discu ssion
Reflux of ethanol solutions of the anionic cluster
species [NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10
]
(1) and [PdCl2(PPh3)2] in a 1:1 molar ratio followed by
thin-layer chromatographic separation of the products
affords low yields of two new zwitterionic non-metal-
containing isomeric cluster species, [5-PPh3-7-Me-µ-
(9,10-HMeC)-nido-7-CB10H9] (compound 2, 10%) and
[6-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H9] (compound
3, 16%), in which there has been an effective replace-
ment of an exo-cluster hydrogen vertex by a PPh3 unit.
The reaction is shown in Scheme 1. The compounds
were characterized by a combination of 11B, 1H, and 31P
NMR spectrometry, high-resolution mass spectrometry
(HRMS), and single-crystal X-ray diffraction studies.
The structures of compounds 2 and 3 are shown in
Figures 1 and 2, respectively, and crystallographic data
and selected distances and angles are given in Tables 1
and 2.
F igu r e 1. Molecular structure of [5-PPh3-7-Me-µ-(9,10-
HMeC)-nido-7-CB10H10] (2).
The 11B spectrum of 2 shows a 2:1:1:2:2:2 relative
intensity pattern appropriate for a molecule with Cs
symmetry, and 3 shows 10 resonances of unit intensity
resulting from the breaking of the pseudo-mirror-plane
symmetry by the phosphonium group bonded to B(6).
Both spectra contain a resonance of unit intensity
coupled to phosphorus (1J (31P-11B) ) 140 Hz (2), 153
Hz (3)). A stick diagram illustrating the 11B{1H} NMR
and heteroborane chemistry,9 where the electrons in the
exo cluster B-L σ-bond arise from the Lewis base group.
Thus, the exo cluster substituent brings an “extra”
electron to the cluster, subrogating either a bridging
hydrogen atom or a delocalized electronic charge in
anionic clusters such as in compounds 2 and 3 reported
here.
The detailed interatomic dimensions of 2 show little
difference within experimental error from those of the
unsubstituted anion 1,10 with the largest difference
being that for the bridged B9-B10 edge, which is only
0.030 Å longer (from 1.847(2) Å in 2 to 1.879(3) Å in 1)
and which produces an attendant increase in the B9-
C12-B10 angle from 68.3(1) to 69.78(14)°. The different
positions of phosphine substitution make little differ-
ence in dimensions for compounds 2 and 3. The asym-
metric unit in 3 contains two independent molecules,
spectra of 2 and 3 and relating them to the previously
-
assigned7a spectrum for [µ-(9,10-H2C)-nido-7-CB10H11
]
is given in Figure 3. The data reveal that PPh3 has
replaced a terminal hydrogen on the lower belt of boron
atoms in the nido-11-vertex monocarbaundecaborane
cluster. Substitution of terminal hydrogen atoms by
Lewis base groups is a very common motif in borane
(4) Alcock, N. W.; Taylor, J . G.; Wallbridge, M. G. H. J . Chem. Soc.,
Dalton Trans. 1987, 1805.
(5) Hewes, J . D.; Knobler, C. B.; Hawthorne, M. F. J . Chem. Soc.,
Chem. Commun. 1981, 206.
(6) McKee, M. L.; Bu¨hl, M.; Schleyer, P. v. R. Inorg. Chem. 1993,
32, 1712.
(7) (a) Plesek, J .; Stibr, B.; Fontaine, X. L. R.; Kennedy, J . D.;
Hermanek, S.; J elinek, T. Collect. Czech. Chem. Commun. 1991, 56,
1618. (b) Plesek, J .; J elinek, T.; Stibr, B.; Hermanek, S. J . Chem. Soc.,
Chem. Commun. 1988, 348.
(8) Vin˜as, C.; Barbera`, G.; Teixidor, F. J . Organomet. Chem. 2002,
642, 16.
(9) (a) Barton, L.; Srivastava, D. K. Metallaboranes. In Comprehen-
sive Organometallic Chemistry II; Wilkinson, G., Abel, E. W., Stone,
F. G. A., Eds., Pergamon: Oxford, U.K., 1995; Vol. 1, Chapter 8, p
275. (b) Kennedy, J . D. Prog. Inorg. Chem. 1984, 32, 519. (c) 1986, 34,
211.
(10) Churchill, M. R.; DeBoer, B. G. Inorg. Chem. 1973, 12(11), 2674.

[NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10
]
Organometallics, Vol. 23, No. 13, 2004 3337
F igu r e 4. Molecular structure of [2-Me-3-{CHMe(PPh3)}-
closo-2-CB10H9] (4), with 50% probability ellipsoids.
observation here. A related thermal rearrangement of
the Me2S substituent in [7-(Me2S)-nido-B11H13] from a
position on the upper open face to the lower pentagonal
belt and thence to the B1 position has been noted
previously.12
F igu r e 2. One of the two independent molecules in the
unit cell of [6-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H10
]
These compounds represent the first derivatives of the
“unreactive” [7-R-µ-(9,10-HRC)-nido-7-CB10H10]- anion
(R ) Me) which do not involve degradation of the
cluster. The course of the reaction reported here, which
adds phosphine to the cluster, is unclear. Phosphine
migration from a metal center to a boron atom in
metallacarborane and metallaborane species is well
established.13 For example, a related phosphine transfer
has been previously reported in (phosphino)metalla-
carboranes with Rh,14 Ni,15 Pd,16 and Pt.17 In these
examples a metal-bonded PPh3 unit migrates and forms
a B-PPh3 bond14,15,17 with the former B(10) in the free
(3), shown with 50% probability ellipsoids.
[-nido-7,8-C2B9H11]
2- ligand or a B-PPh2 bond with the
former B(11) in the free nido-o-carboranyl monophos-
phines16a,c and nido-o-carboranyl monothioethers.16b In
an attempt to investigate whether the palladium species
might have a catalytic behavior in the phosphine
addition possibly through Pd metal released during the
1
reaction the procedure was repeated using /2 equiv of
the palladium complex and excess triphenylphosphine.
The result was a reduced yield of the compounds 2 and
3. However, two further interesting minor products were
(11) Gimarc, B. M.; Warren, D. S.; Ott, J . J .; Brown, C. Inorg. Chem.
1991, 30(7), 1598.
(12) Keller, D. L.; Kester, J . G.; Huffman, J . C.; Todd, L. J . Inorg.
Chem. 1993, 32, 5067.
F igu r e 3. Stick diagrams of the 11B{1H} NMR spectra for
(bottom) [6-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H10] (3),
(13) (a) Teixidor, F.; Casabo, J .; Romerosa, A. M.; Vin˜as, C.; Rius,
J .; Miravitlles, C. J . Am. Chem. Soc. 1991, 113, 9895 and references
therein. (b) Bould, J .; Brint, P.; Kennedy, J . D.; Thornton-Pett, M. J .
Chem. Soc., Dalton Trans. 1993, 2335. (c) Bould, J .; Crook, J . E.;
Greenwood, N. N.; Kennedy, J . D.; Thornton-Pett, M. J . Chem. Soc.,
Dalton Trans. 1990, 1441. (d) Vin˜as, C.; Nun˜ez, R.; Teixidor, F.;
Kiveka¨s, R.; Sillanpa¨a¨, R. Organometallics 1999, 18, 4712. (e) Bould,
J .; Rath, N. P.; Barton, L. Angew. Chem. 1995, 34, 1641.
(14) Baker, R. T.; Delaney, M. S.; King, R. E., III; Knobler, C. B.;
Long, J . A.; Marder, T. B.; Paxson, T. E.; Teller, R. G.; Hawthorne, M.
F. J . Am. Chem. Soc. 1984, 106, 2965.
(15) Miller, S. B.; Hawthorne, M. F. J . Chem. Soc., Chem. Commun.
1976, 786.
(16) (a) Vin˜as, C.; Cirera, M. R.; Teixidor, F.; Kiveka¨s, R.; Sillan-
pa¨a¨,R.; Llibre, J . Inorg. Chem. 1998, 37, 6746. (b) Teixidor, F.; Casabo´,
J .; Romerosa, A. M.; Vin˜as, C.; Rius, J .; Miravitlles, C. J . Am. Chem.
Soc. 1991, 113, 9895.
(middle) [5-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H10] (2),
-
and (top) [µ-(9,10-H2C)-nido-7-CB10H11
]
(1).3
one of which featured an incompletely resolved disorder
involving the phosphine group. However, the HRMS and
NMR data fully support the structure shown in Figure
2.
The compounds are stable at room temperature,
although in performing 11B NMR measurements of 2
in C6D5CD3 solution at 90 °C we noted that a slow 2 f
3 isomerization process occurs. This implies a vertex
exchange mechanism. Vertex isomerization by a trian-
gular face rotation has been invoked in [1,2-closo-
C2B10H12] clusters,11 and this could also account for the
(17) Barker, G. K.; Green, M.; Stone, F. G. A.; Welch, A. J .; Wolsey,
W. C. J . Chem. Soc., Chem. Commun. 1980, 627.

3338 Organometallics, Vol. 23, No. 13, 2004
Ta ble 1. Cr ysta l a n d Str u ctu r e Refin em en t Da ta
Bould et al.
2
3
4
5
empirical formula
formula wt
temp/K
cryst syst
space group
a/Å
b/Å
c/Å
C
22H31B10
P
C22H31B10
434.54
120(2)
trigonal
R3h
32.3006(3)
32.3006(3)
14.9362(3)
90, 90, 120
13495.6(3)
21
P
C22H31B10
434.54
120(2)
monoclinic
P21/n
10.457(3)
14.955(4)
15.893(4)
90, 91.82(2), 90
2484.1(11)
4
P
C24.25H38.50B10O1.50P
493.12
120(2)
monoclinic
P21/c
13.5326(1)
17.2277(2)
24.9167(3)
90, 91.4360(10), 90
5807.2(1)
434.54
120(2)
monoclinic
P21/c
9.6187(8)
22.952(2)
11.9724(9)
90, 111.677(5), 90
2456.2(3)
4
R, â, γ/deg
V/ Å-3
Z
8
cryst size/mm
0.22 × 0.20 × 0.06
1.77-27.49
21 776
0.22 × 0.20 × 0.20
2.18-24.99
62 698
0.28 × 0.22 × 0.20
1.87-25.68
24 003
0.28 × 0.20 × 0.20
1.51-25.00
73 224
θ range for data collcn/deg
no. of rflns collected
F(000)
912
4788
912
2088
no. of indep rflns
no. of data/restraints/params
goodness of fit
final R indices (I > 2σ(I))
R1
5610 (Rint ) 0.08)
5610/0/362
1.005
5268 (Rint ) 0.11)
5268/21/325
1.075
4724 (Rint ) 0.17)
4724/0/346
0.998
10 210 (Rint ) 0.17)
10 210/6/631
1.010
0.046
0.112
0.37 and -0.25
0.067
0.187
0.56 and -0.52
0.079
0.229
0.59 and -0.54
0.105
0.323
0.98 and -0.90
wR2(F2)
largest diff peak and hole/e Å-3
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for
[5-P P h 3-7-Me-µ-(9,10-HMeC)-n id o-7-CB10H9] (2) a n d
[6-P P h 3-7-Me-µ-(9,10-HMeC)-n id o-7-CB10H9] (3)
2
3
2
3
B-P1
1.950(2) 1.944(4) B5-B9
1.786(3) 1.776(5) B6-B10
1.808(3) 1.785(5) B6-B11
1.768(3) 1.803(5) B6-B2
1.526(3) 1.525(5) B9-B10
1.634(3) 1.645(5) B9-C12
1.623(3) 1.644(5) B10-C12
1.872(3) 1.869(6) C12-C13
1.809(3)
1.741(3)
1.798(3)
1.794(3)
1.879(3)
1.644(3)
1.641(3)
1.527(3)
1.781(6)
1.783(5)
1.740(5)
1.773(5)
1.842(5)
1.640(6)
1.651(5)
1.511(5)
B5-B1
B5-B10
B5-B6
C7-C71
C7-B8
C7-B11
B8-B9
B1-B6-P1
120.6(2) B1-B5-P1 118.42(14)
B9-C12-B10 69.78(14) 68.1(2)
isolated and characterized by NMR spectroscopy, HRMS,
and single-crystal X-ray diffraction studies as [2-Me-3-
{CHMe(PPh3)}-closo-2-CB10H9] (compound 4, Scheme 1,
4%) and [7-Me-8-OEt-9-{CHMe(PPh3)}-nido-7-CB10H10
(compound 5, Scheme 1, <1%).
]
The structures of compounds 4 and 5 are shown in
Figures 4 and 5, respectively, with selected distances
and angles given in Tables 3 and 4. The 11B{1H} NMR
spectrum of 4 shows a 1:1:3:3:2 pattern rather than the
expected 1:1:1:1:2:2:2 pattern, indicating a coincidental
overlap of four resonances. The low-field singlet in the
11B NMR spectrum at +19.6 ppm indicates the presence
of a substituent on boron. Indeed, the cluster hydrogen
atoms overlapping peaks in the 1H{11B} NMR spectrum
are all contained between +1.45 and +1.61 ppm.
F igu r e 5. Molecular structure of one of the two indepen-
dent molecules in the unit cell of [7-Me-8-OEt-9-{CHMe-
(PPh3)}-nido-7-CB10H10] (5), shown with 50% probability
ellipsoids and with phenyl rings, except for ipso carbon
atoms, and noncage hydrogen atoms omitted to aid clarity.
two-electron donor to the cluster, comparable to the
PPh3 substituent in compounds 2 and 3, so that,
together with the cluster carbon vertex, the cage achieves
an overall 2n + 2 skeletal electron pair count required
for a closo 11-vertex cluster.18 Only one other alkylidene-
triphenylphosphorane-substituted borane cluster, CH2-
(PPh3)B3H7, has been characterized previously, made
directly from -CHR(PPh3) (R ) H, Me, Ph) and
B3H7.thf.19 A structural characterization has been car-
1
Features in the H NMR spectrum due to the -CHMe-
(PPh3) moiety are a doublet of doublets at +1.78 ppm
for the Me group and two overlapping quartets at +3.58
ppm for the H atom, which collapse to a doublet and
quartet, respectively, with 31P decoupling (3J (31P-1H)
) 20.4 Hz). The doublet and quartet are mutually
3
coupled with J (1H-1H) ) 7.4 Hz.
A single-crystal X-ray diffraction study of compound
4 reveals a closo-monocarbaundecaborane cluster in
which the phosphine substituent now resides on an
organic side chain arising, presumably, from addition
to the bridging {µ-HMeC} group in the starting carbo-
rane cluster and resulting in a zwitterionic alkylidene-
triphenylphosphorane derivative. The group acts as a
(18) (a) Wade, K. J . Chem. Soc., Chem. Commun. 1971, 792. (b)
Williams, R. E. Inorg. Chem. 1971, 10, 210. (c) Rudolph, R. W.; Pretzer,
W. R. Inorg. Chem. 1972, 11, 1974. (d) Mingos, D. M. P. Nature (Phys.
Sci.) 1972, 236, 99. (e) Williams, R. E. Adv. Inorg. Chem. Radiochem.
1976, 18, 67. (f) Wade, K. Adv. Inorg. Chem. Radiochem. 1976, 18, 1.
(g) Rudolph, R. W. Acc. Chem. Res. 1976, 9, 446.

[NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10
]
Organometallics, Vol. 23, No. 13, 2004 3339
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for
atomic orbital for a σ-bond. The exo cluster disposition
of the -CHMe(PPh3) group in 4 clearly proves the
classical nature of this carbon. However, the endo
nature of the bridging {µ-HMeC} group in 1 and 2 or 3
may balance the fact that the number of orbitals
invested parallels the number of connectivities. The
endo feature supports a nonclassical carbon, while the
number of orbitals/number of connectivities suggests the
contrary. We feel that the synthesis of 4 indicates that
in 1-3 the bridging carbon in the {µ-HMeC} group has
more nonclassical than classical character. The incom-
ing PPh3 requires an atomic orbital for the C-P
coupling, which is available after disconnecting one C-B
connectivity. Then, the original endo configuration of
the former bridging {µ-HMeC} group is switched to an
exo disposition. Our view is that if the bridging {µ-
HMeC} group had not been an integral part of the
cluster, relocation of the -CHMe(PPh3) moiety to an exo
cluster position would not have been necessary. A
further argument that supports this view is that once
the C-B connectivity is broken and in order to preserve
the cluster integrity new B-B connectivities are gener-
ated that ultimately produce the closo species 4 (see
Scheme 4).
[2-Me-3-{CHMe(P P h 3)}-closo-2-CB10H9] (4)
B1-C2
1.646(7)
2.026(7)
2.020(7)
1.520(7)
1.577(7)
1.617(6)
1.802(4)
1.804(4)
B1-B3
1.768(7)
2.005(7)
2.074(7)
1.575(7)
1.673(7)
1.547(6)
1.798(4)
1.806(4)
B1-B4
B1-B5
B1-B6
C(2)-C(3)
C2-B5
B3-C119
P1-C101
P1-C107
B1-B7
C2-B4
C2-B8
C119-C120
P1-C113
P1-C119
C120-C119-B3
B3-C119-P1
C101-P1-C119
C3-C2-B1
112.4(4)
113.8(3)
110.99(19)
124.0(4)
126.2(4)
C120-C119-P1
C113-P1-C119
C107-P1-C119
C119-B3-B9
111.2(3)
109.8(2)
112.2(2)
135.5(4)
C3-C2-B8
Ta ble 4. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for
[7-Me-8-OEt-9-{CHMe(P P h 3)}-n id o-7-CB10H10] (5)
B9′-C1′
C1′-P1′
B8′-B9′
B8′-C7′
C7′-B11′
1.607(9)
1.810(6)
1.917(10)
1.661(11)
1.665(10)
B9′-B10′
C1′-C2′
C7′-C21′
B11′-O1′
B10′-B11′
1.917(10)
1.588(9)
1.472(12)
1.463(9)
1.851(12)
C2′-C1′-P1′
P1-C1-B9
C1′-B9′-B4′
C21′-C7′-B2′
C21′-C7′-B3′
C21′-C7′-B11′
107.7(4)
C2′-C1′-B9′
C1′-B9′-B5′
C1′-B9′-B8′
C1′-B9′-B10′
C21′-C7′-B8′
113.2(5)
121.6(6)
125.1(5)
130.0(5)
124.1(7)
113.0(4)
117.2(5)
112.6(8)
120.1(7)
115.1(7)
Compound 5 is related to 4, but with an additional
two bridging hydrogen atoms, giving it a nido 11-vertex
structure. 11B NMR spectrometry shows a 1:1:2:1:1:2:
1:1 pattern with two singlet resonances of unit intensity,
corresponding to the presence of two substituents on
ried out for R ) H.20 The P-B distances are essentially
equal at 1.632(8) Å in the triborane adduct and 1.607-
(9) Å in compound 4. The geometry of 4 is comparable
to that of the neutral closo-monocarbaundecaborane
cluster with a Lewis base ligand [2-(Me3Si)2-6-Me2S-2-
1
boron. The H{11B} NMR spectrum showed two sets of
the doublet of doublets, which are characteristic for the
methyl group in the methyltriphenylphosphorane sub-
stituent, and the 31P{1H} spectrum showed two singlet
resonances at +34.8 and +35.3 ppm, indicating the
presence of two closely related species in solution. We
were unable to chromatographically separate them, but
slow evaporation of a CH2Cl2/hexane solution gave
crystals of a single species suitable for a single-crystal
X-ray study. The data reveal two unique molecules in
the unit cell with -CHMe(PPh3) and ethoxy substitu-
ents on two boron vertexes in a nido-monocarbaunde-
caborane cluster (Figure 4). The B-OEt and C-Me
positions were disordered, as was one phenyl group on
the triphenylphosphine moiety. The B11′-O1′ distance
of 1.463(9) Å is similar to the C7′- C21′ distance, 1.472-
(12) Å, and is somewhat longer than a range of cage
B-OR separations (1.371-1.409 Å),24 although this is
probably an artifact of the disorder. The bridging
hydrogen atoms evident in the proton spectrum were
also located in the X-ray structure determination. The
molecular formulation shown is supported by the HRMS
data, which exhibits a signal group pattern centered at
m/z 478.3421 (478.3429 calculated) for P+ - H2 on
C24H37B10PO. The ethoxy substituent clearly comes from
the ethanol solvent, and it may also supply the two extra
hydrogen atoms required to achieve the observed nido
cluster.
CB10H9] (6), and related compounds,21 and also to the
-
closo-[PhCB10H10
]
anion (7).22 The most notable fea-
tures for all these compounds are the distances for the
apical six-connected B1 vertex to the lower belt B4-B7
vertexes. These range from 2.005(7) to 2.074(7) Å in 4,
and although they are somewhat long for interboron
distances, they are comparable to those in 6 (1.747(3)-
2.040(7) Å) and 7 (2.015(4)-2.057(4) Å) and are some-
what shorter than in [B11H11
]
2- itself, where they range
from 1.959(7) to 2.159(7) Å.23
The syntheses of compounds 2 or 3 and 4 highlight
the process of converting a nonclassical into a classical
carbon atom. The sequence is shown in Scheme 2.
Initially, in 1,2-R2-closo-1,2-C2B10H10 both carbon atoms
are nonclassical (see Scheme 3) and contribute three
atomic orbitals to the cluster molecular orbitals. The
connectivity of these carbon atoms is 5. The species at
the left in Scheme 2 corresponds to the “kinetic” isomer,
[7,9-R2-nido-7,9-C2B10H11]-. One of the two carbon
atoms invests three atomic orbitals to generate a 3-fold
connectivity. In the “thermodynamic” isomer [7-R-µ-
(9,10-HRC)-nido-7-CB10H11]- (1), the endo carbon atom
invests two atomic orbitals to produce a 2-fold con-
nectivity. Finally, in 4, the carbon atom invests one
The EtO- substitution is not rare in boron chemistry
clusters. Upon reaction of [MCl2(PPh3)2] (M ) Pd, Pt)
with borate anions in refluxing alcohols as solvent,
(19) Chung Choi, P.; Morris, J . H. J . Chem. Soc., Dalton Trans. 1984,
2119.
(20) Andrews, S. J .; Welch, A. J . Acta Crystallogr. 1985, C41, 1496.
(21) Ernest, R. L.; Quintana, W.; Rosen, R.; Carroll, P. J .; Sneddon,
L. G. Organometallics 1987, 6, 80.
(22) Franken, A.; Kilner, C. A.; Thornton-Pett, M.; Kennedy, J . D.
J . Organomet. Chem. 2002, 657, 180.
(23) Volkov, O.; Englebert, U.; Paetzold, P. Z. Anorg. Allg. Chem.
1999, 625, 1193.
(24) (a) Hu, C. H.; Yong, W.; Dou, J . M.; Sun, J .; Hu, K. J .; J in, R.
S.; Zheng, P. J . Chin. J . Chem. 2002, 20, 536. (b) Nie, Y.; Hu, C, H.;
Li, X.; Yong, W.; Dou, J . M.; Sun, J .; J in, R. S.; Zheng, P. J . Acta
Crystallogr. 2001, C57, 897.

3340 Organometallics, Vol. 23, No. 13, 2004
Bould et al.
Sch em e 2. F a te of a Non cla ssica l Ca r bon in th e “Kin etic” Isom er [7,9-R2-n id o-7,9-C2B10H11]- to a Cla ssica l
On e in [2-Me-3-{CHMe(P P h 3)}-closo-2-CB10H9] (4) th r ou gh th e “Th er m od yn a m ic”
[7-R-µ-(9,10-HRC)-n id o-7-CB10H10]- Isom er (1)
Sch em e 3. Syn th esis of th e “Th er m od yn a m ic”
Isom er [7-R-µ-(9,10-HRC)-n id o-7-CB10H10]- (1),
P r od u ced Dir ectly fr om th e Rea ction of
pounds and the low yields are indicative of the difficulty
-
of the [7-R-µ-(9,10-HRC)-nido-7-CB10H11
]
(1) to react,
but it fulfills the objective of this work, which potentially
demonstrates that routes to monocarbaundecaboranes
through the readily available [NHMe3][7-Me-µ-(9,10-
HMeC)-nido-7-CB10H10] (1) may be attainable.
1,2-R2-closo-1,2-C2B10H10 w ith Ma gn esiu m Meta l
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Experiments were carried out
under a dry nitrogen atmosphere, with subsequent isolation
and characterizations being carried out in air. Solvents were
dried by conventional methods. [NHMe3][7-Me-µ-(9,10-HMeC)-
nido-7-CB10H10] and [PdCl2(PPh3)2] were prepared by the
literature methods.8,26 1H and 1H{11B} NMR (300.13 MHz), 13C-
{1H} NMR (75.47 MHz), and 11B NMR (96.29 MHz) spectra
were recorded with a Bruker ARX 300 instrument equipped
with the appropriate decoupling accessories. All NMR spectra
were recorded from CDCl3 solutions at 298 K. Chemical shift
values for 11B NMR spectra were referenced to external BF3‚
OEt2, 31P{1H} NMR spectra were referenced to external 85%
Sch em e 4. Su ggested P a th w a y to Con ver t On e
Non cla ssica l Ca r bon Atom fr om
[7-R-µ-(9,10-HRC)-n id o-7-CB10H10]- (1) in to a
Cla ssica l On e in
[2-Me-3-{CHMe(P P h 3)}-closo-2-CB10H9] (4)
1
H3PO4 (minus values upfield), and those for 1H, H{11B}, and
13C{1H} NMR spectra were referenced to Si(CH3)4. Chemical
shifts are reported in units of parts per million downfield from
the reference, and all coupling constants are reported in hertz.
The mass spectra were measured in the FAB mode on a J EOL
MStation J MS-70 spectrometer using 3-nitrobenzyl alcohol (3-
NBA, or 3-NBA/CsI).27 Thin-layer chromatography (TLC)
plates were individually crafted from aqueous slurries of
Aldrich standard grade TLC silica gel with a fluorescent
indicator and dried at ambient temperature.
[5-P P h 3-7-Me-µ-(9,10-H MeC)-n id o-7-CB10H 9] (2) a n d
[6-P P h 3-7-Me-µ-(9,10-HMeC)-n id o-7-CB10H9] (3). [NHMe3]-
[7-Me-µ-(9,10-HMeC)-nido-7-CB10H10] (57 mg, 0.244 mmol) and
[PdCl2(PPh3)2] (175 mg, 0.25 mmol) were stirred at reflux
overnight in ethanol. After it was cooled, the dark solution
was filtered through a plug of silica gel and the filtrate was
reduced in volume (rotary evaporator, ca. 40 °C) and subjected
to preparative TLC (75/25 CH2Cl2/hexane). A colorless band
observed under UV irradiation, A (Rf ) 0.8), and B, a rusty
brown band (Rf ) 0.2), were obtained. Band B did not contain
boron and was not further investigated. Band A was redevel-
oped (20/80 CH2Cl2/hexane), giving two further UV-active
bands at Rf ) 0.3 (C), 0.2 (D). Crystals suitable for single-
crystal X-ray diffraction studies were grown for each compound
by slow evaporation of layered hexane/CDCl3 solutions of the
compound. The bands were identified by NMR spectrometry,
high-resolution mass spectrometry, and single-crystal X-ray
diffraction analyses.
alkoxy group substitution to occupy terminal positions
has been observed.25
The synthesis of compounds 2-5, although obtained
in low yield, opens a way to explore the derivative
chemistry of the “thermodynamic” isomer, [7-R-µ-(9,10-
-
HRC)-nido-7-CB10H11
]
(1), considered up to now a
Band C: [5-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H9] (com-
1
nonreactive species. The diversity of generated com-
pound 2, 10.3 mg, 24 µmol, 10%). H NMR: δ 7.75-7.52 (m,
(25) (a) Hu, C. H.; Yong, W.; Dou, J . M.; Sun, J .; Hu, K. J .; J in, R.
S.; Zheng, P. J . Chin. J . Chem. 2002, 20, 536-538. (b) Nie, Y.; Hu, C,
H.; Li, X.; Yong, W.; Dou, J . M.; Sun, J .; J in, R. S.; Zheng, P. J . Acta
Crystallogr. 2001, C57, 897-899.
(26) Blackburn, J . R.; Nordberg, R.; Stevie, F.; Albridge, R. G.; J ones,
M. M. Inorg. Chem. 1970, 9, 2374.
(27) Siuzdak, G.; Wendeborn, S. V.; Nicolaou, K. C. Int. J . Mass
Spectrom. Ion Processes 1992, 112(1), 79.

[NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10
]
Organometallics, Vol. 23, No. 13, 2004 3341
15H, Haryl), 3.64 (quartet, 3J (1H-1H) ) 6.3, 1H, C12-H), 3.69-
1.33 (br m, 9H, B-H), 1.81 (s, 3H, C7-Me), 1.42 (d, 3J (1H-
atoms show overlapping peaks for the two species at δ +2.38,
+2.27, +1.91, +1.73, +1.22, +0.88, +0.75, -0.38, -0.30 (µ-
H(9′-10′)), -2.34 (µ-H(10′-11′)), -3.42, -3.70. Mass spectrom-
etry shows a peak envelope centered at m/z 478.3421 within
-1.6 ppm of that calculated for the peak profile of P+-H2 in
1
1H) ) 6.3, 3H, C12-Me). H{11B} NMR: δ 7.75-7.52 (m, 15H,
H
aryl), 3.64 (quartet, 3J (1H-1H) ) 6.3, 1H, C12-H), 3.69 (br s,
2H, B8-H and B11-H), 2.92 (br s, 1H, B1-H), 1.96 (br s, 2H,
B2-H and B3-H), 1.49 (br s, 2H, B9-H and B10-H), 1.33
(br s, 2H, B4-H and B6-H), 1.81 (s, 3H, C7-Me), 1.42 (d,
3J (1H-1H) ) 6.3, 3H, C12-Me). 11B{1H} NMR: δ +19.3 (s,
C
24H37B10PO (478.3412).
X-r a y Cr ysta llogr a p h y. Crystals of appropriate dimen-
sions were mounted on glass fibers in a random orientation.
Preliminary examination and data collection was performed
using a Bru¨ker SMART charge coupled device (CCD) detector
system single-crystal X-ray diffractometer using graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å) equipped
with a sealed-tube X-ray source at 120 K. Preliminary unit
cell constants were determined with a set of 45 narrow frames
(0.4° in $) scans. A typical data set consisted of 3636 frames
with a frame width of 0.3° in $ and typical counting time of
15-30 s/frame at a crystal to detector distance of 4.900 cm.
The double-pass method of scanning was used to exclude any
noise. The collected frames were integrated using an orienta-
tion matrix determined from the narrow frame scans. SMART
and SAINT software packages28 were used for data collection
and data integration. Analysis of the integrated data did not
show any decay. Final cell constants were determined by a
global refinement of xyz centroids. Collected data were cor-
rected for systematic errors using SADABS29 based on the
Laue symmetry using equivalent reflections.
1
2B, B8 and B11), 0.0 (d, J (11B-31P) ) 140, 1B, B5), -0.6 (s,
1B, B1), -5.3 (s, 2B, B2 and B3), -12.8 (s, 2B, B9 and B10),
-21.6 (s, 2B, B4 and B6). 31P{1H} NMR: δ +5.7 (quartet,
1J (31P-11B) ) 140). Mass spectrometry shows two envelopes
centered at m/z 433.3121 and 419.2982, within 7.6 and 12 ppm
of the calculated peak profile for (P+ + H) - H2 and (P+ + H)
- CH4 in C22H31B10P.
Band D: [6-PPh3-7-Me-µ-(9,10-HMeC)-nido-7-CB10H9] (com-
pound 3, 16.6 mg, 40.2 µmol, 16%). 1H NMR: δ 7.75-7.52 (m,
3
15H, Haryl), 4.06 (quartet, J (1H-1H) ) 6.0, 1H, C12-H), 1.74
3
(s, 3H, C7-Me), 1.48 (d, J (1H-1H) ) 6.0, 3H, C12-Me). 11B-
{1H} NMR: δ +21.0 (s, 1B, B8 or B11), +14.7 (s, 1B, B11 or
B8), +3.9 (s, 1B, B1 or B5), -1.6 (s, 1B, B5 or B1), -5.5 (s,
1B, B2 or B3), -6.6 (s, 1B, B3 or B2), -12.4 (s, 1B, B9 or B10),
1
-15.2 (s, 1B, B10 or B9), -20.4 (s, 1B, B4), -23.2 (d, J (31P-
1
11B) ) 153, 1B, B6). 31P{1H} NMR: δ +6.2 (quartet, J (31P-
11B) ) 153). Mass spectrometry showed two envelopes centered
at m/z 433.3057 (433.3099 calcd) and 419.2936 (419.2942 calcd)
within 9.6 and 1.4 ppm, respectively, of that calculated for (P+
+ H) - H2 and (P+ + H) - CH4 in C22H31B10P.
Crystal data and intensity data collection parameters are
listed in Table 1.
[2-Me-3-{CHMe(P P h 3)}-closo-2-CB10H9] (4) a n d [7-Me-
8-OEt-9-{CHMe(P P h 3)}-n id o-7-CB10H10] (5). In a similar
experiment [NHMe3][7-Me-µ-(9,10-HMeC)-nido-7-CB10H10] (72
mg, 0.31 mmol) and [PdCl2(PPh3)2] (111 mg, 0.16 mmol) with
added PPh3 (161 mg, 0.61 mmol) were refluxed in ethanol for
24 h, and after cooling the solution was filtered, giving a sandy
colored, non-boron-containing solid (yield 61 mg). The filtrate
was reduced in volume and subjected to preparative TLC as
described above (80/20 CH2Cl2/hexane), giving colorless bands
observed under UV illumination at Rf ) 0.8, 0.7, and 0.2. The
first band contained a mixture of compounds 2 and 3 (5 mg).
The second band was characterized as [2-Me-3-{CHMe(PPh3)}-
Structure solution and refinement for compounds 2, 4, and
5 were carried out using the SHELXTL-PLUS software pack-
age.30 The structures were solved by direct methods and
refined successfully in the monoclinic space groups P21/c, P21/
n, and P21/c, respectively. Full-matrix least-squares refinement
was carried out by minimizing ∑w(Fo - Fc2)2. The non-
2
hydrogen atoms were refined anisotropically to convergence.
The cage hydrogen atoms for all three compounds were located
from difference Fourier syntheses and refined freely for
compounds 2 and 4. The cage H’s for compound 5 were located
but not refined. All other hydrogen atoms were treated using
the appropriate riding model (AFFIX m3).
1
closo-2-CB10H9] (compound 4, 5.0 mg, 12 µmol, 4%). H NMR:
Refinement for compound 3 was carried out using SHELX-
97.28 The asymmetric unit of compound 3 contains one ordered
molecule and one-sixth of a disordered molecule. There are
two neighboring equivalent positions for the disordered mol-
ecule, although only one can be present in either position. The
phosphorus atom and the boron atom connected to the
phosphorus atom of the disordered molecule lie on a 3-fold axis,
and the rest of the non-hydrogen atoms are in the vicinity of
the 3-fold axis. Each phenyl group of the disordered molecule
assumes two orientations. Owing to the disorder and low
occupancy of the disordered molecule, the Me and µ-HMeC
groups could not be accurately located or the cage carbon atom
reliably identified. Therefore, all non-hydrogen atoms of the
disordered cage were treated as boron atoms in the final
calculations. The H atoms of the disordered cage were not
located. EADP constraints and DFIX restraints were utilized
in order to keep bond parameters reasonable for the disordered
cage. All non-hydrogen atoms of the ordered molecule and the
phosphorus atom of the disordered molecule were refined
anisotropically, but the atoms of the disordered cage were
refined with isotropic thermal displacement parameters. Hy-
drogen atoms were placed at calculated distances from their
host atoms and treated as riding atoms using the SHELX97
default parameters.31 Refinements of the structure in the lower
symmetry space groups also resulted in a partially disordered
structure.
δ 7.75-7.52 (m, 15H, Haryl), 3.58 (overlapping doublet of
quartets, 3J (1H-1H) ) 7.4, 3J (31P-1H) ) 20.4, 1H, C(119)-
3
3
H), 1.78 (doublet of doublets, J (1H-1H) ) 7.3, J (31P-1H) )
20.4, 3H, C119-Me), 1.61-1.45 (br m, 9H, B-H), 1.28 (s, 3H,
C2-Me). 1H{11B} NMR: δ 7.75-7.52 (m, 15H, Haryl), 3.58
(overlapping doublet of quartets, 3J (1H-1H) ) 7.4, 3J (31P-1H)
3
) 20.4, 1H, C(119)-H), 1.78 (doublet of doublets, J (1H-1H)
) 7.3, 3J (31P-1H) ) 20.4, 3H, C119-Me), 1.61 (br s, 3H, B-H),
1.51 (br s, 3H, B-H), 1.45 (br s, 3H, B-H), 1.28 (s, 3H, C2-
Me). 11B{1H} NMR: δ +19.6 (s, 1B), -6.4 (s, 1B), -12.1 (s,
3B), -14.3 (s, 3B), -20.2 (s, 2B). 31P{1H} NMR: δ +32.2 (s).
Mass spectrometry ((NBA/CsI)) shows an peak envelope
centered at m/z 567.2216 within -2.8 ppm of that calculated
for the peak profile of P+ in C22H31PB10Cs (567.2232). Colorless
cubic single crystals were obtained by slow evaporation of a
CH2Cl2/hexane solution of the compound.
The third band (ca. 1 mg) contained two very closely related
species. The mixture was crystallized by slow evaporation of
a CH2Cl2/hexane solution. The compound was characterized
by a single-crystal X-ray diffraction study, together with NMR
and HRMS, as [7-Me-8-OEt-9-{CHMe(PPh3)}-nido-7-CB10H10
]
(compound 5). 11B{1H} NMR: δ +7.9 (s, 1B, B9′), -6.3 (s, 1B),
-8.6 (s, 2B), -11.6 (s, 1B), -16.5 (s, 1B, B11′), -26.9 (s, 2B),
-32.6 (s, 1B), -35.1 (s, 1B). 31P{1H} NMR: δ +34.8, +35.3 in
ca. 2:1 ratio, respectively. 1H{11B} NMR: overlapping peaks
for both species A and species B in a ca. 2:1 ratio at δ 7.80-
8.00 (m, 15H, Haryl), 3.5 (1H, C9-H), two sets of doublets of
doublets for isomers A and B at δ +1.62 (3J (1H-1H) ) 7.3,
3J (31P-1H) ) 20.5, CHPPh3-CH3), 1.49 (3J (1H-1H) ) 7.6,
3J (31P-1H) ) 20.5, CHPPh3-CH3), 1.38 (s, 3H, C7′-CH3); B-H
(28) Bru¨ker Analytical X-ray, Madison, WI, 2002.
(29) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(30) Sheldrick, G. M. Bru¨ker Analytical X-ray Division, Madison,
WI, 2002.

3342 Organometallics, Vol. 23, No. 13, 2004
Bould et al.
The asymmetric unit of compound 5 contains two unique
molecules, and both exhibit disorder. A phenyl group was
disordered in one of the two molecules and shows large thermal
motion. Rigid-body refinement (AFFIX 66) and thermal el-
lipsoid constraints (EADP) were used to model this disorder.
In the second molecule, the C-Me and B-Et positions are
disordered. These two positions were modeled with partial
occupancy of all the involved atoms, and positional and
thermal parameter restraints (EXYZ and EADP) were used
to model the disorder.
Ack n ow led gm en t. We thank the MCyT (Grant No.
MAT01-1575) for partial support of this research and
the Generalitat de Catalunya (Grant No. 2001/SGR/
00337). J .B. thanks the Ministerio de Educacio´n, Cul-
tura y Deporte, for a stay of foreign researchers in Spain
(Grant No. SAB2000-0293).
Su p p or tin g In for m a tion Ava ila ble: Tables giving com-
plete X-ray data for compounds 2-5. This material is available
free of charge via the Internet at http://pubs.acs.org.
Structure refinement parameters are listed in Table 1.
Drawings of the molecules were made with ORTEP32 with non-
hydrogen atoms represented by 50% probability ellipsoids.
OM030487V
(31) Sheldrick, G. M. SHELX97; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
(32) Farrugia, L. J . J . Appl. Crystallogr. 1997, 30, 565.