Synthesis and reactivity of 10-vertex arachno-platinacarboranes

Article abstract of DOI:10.1021/om7012056

Reaction of [Pt₃(CNR)₆] with arachno-4-R′-4- CB₈H₁₃ in THF (tetrahydrofuran) gives the platinamonocarborane species [9,9-(CNR)₂-6-R′-arachno-9,6- PtCB₈H₁₁] (R = Bu_t, R′ = H (1); R - Xyl (C₆H₃Me₂-2,6), R′ = H (2); R = Bu ^t, R′ = Ph (3)). The related compound [9,9-(PMe ₂Ph)₂-arachno-9,6-PtCB₈H₁₂] (5) can be synthesized by treating arachno-4-CB₈H₁₄ with [PtMe₂(PMe₂Ph)₂] in CH₂Cl ₂. Compounds 1-3 and 5 are all formed in high yields (>80%), enabling reactivity studies to be carried out. A single isocyanide ligand in 1 can be easily exchanged for a phosphine, as is the case with [9-CNBu ^t-9-PPh₃-arachno-9,6-PtCB₈H₁₂] (6), or, by using bidentate dppe (Ph₂PCH₂CH₂PPh ₂), both isocyanide groups are replaced, giving [9,9-dppe-arachno-9, 6-PtCB₈H₁₂] (7). Treatment with [NEt₄][CN] allows the isocyanides in 1 to be replaced by cyanide ligands, giving the dianionic complex [NEt₄]₂[9,9-(CN)₂-arachno-9, 6-PtCB₈H₁₂] (8) or the monoanionic species [NEt ₄] [9-CNBu^t-9-CN-arachno-9,6-PtCB₈H ₁₂] (9) depending on the stoichiometry of the reaction. Reaction of 1 or 3 with I₂ yields the platinum(IV) complexes [9,9-(CNBu ^t)₂-9,9-I₂-6-R′-arachno-9,6-PtCB ₈H₁₁] (R′ = H (10), Ph (11)), respectively, by an oxidative addition reaction. Using the same reagent, compound 7 forms solvent-dependent, boronsubstituted products: [9,9-dppe-4,8-I ₂-arachno-9,6-PtCB₈H₁₀] (12) is obtained in CH₂Cl₂, whereas [9,9-dppe-4-{O(CH₂) ₄I}-8-I-arachno-9,6-PtCB₈H₁₀] (13) results when THF is used as solvent.

Full text of DOI:10.1021/om7012056

Organometallics 2008, 27, 2099–2106
2099
Synthesis and Reactivity of 10-Vertex arachno-Platinacarboranes
Michael J. Carr, Thomas D. McGrath, and F. Gordon A. Stone*
Department of Chemistry & Biochemistry, Baylor UniVersity, Waco, Texas 76798-7348
ReceiVed NoVember 30, 2007
Reaction of [Pt3(CNR)6] with arachno-4-R′-4-CB8H13 in THF (tetrahydrofuran) gives the platina-
monocarborane species [9,9-(CNR)2-6-R′-arachno-9,6-PtCB8H11] (R ) But, R′ ) H (1); R ) Xyl
(C6H3Me2-2,6), R′ ) H (2); R ) But, R′ ) Ph (3)). The related compound [9,9-(PMe2Ph)2-arachno-
9,6-PtCB8H12] (5) can be synthesized by treating arachno-4-CB8H14 with [PtMe2(PMe2Ph)2] in CH2Cl2.
Compounds 1–3 and 5 are all formed in high yields (>80%), enabling reactivity studies to be carried
out. A single isocyanide ligand in 1 can be easily exchanged for a phosphine, as is the case with [9-CNBut-
9-PPh3-arachno-9,6-PtCB8H12] (6), or, by using bidentate dppe (Ph2PCH2CH2PPh2), both isocyanide groups
are replaced, giving [9,9-dppe-arachno-9,6-PtCB8H12] (7). Treatment with [NEt4][CN] allows the
isocyanides in 1 to be replaced by cyanide ligands, giving the dianionic complex [NEt4]2[9,9-(CN)2-
arachno-9,6-PtCB8H12] (8) or the monoanionic species [NEt4][9-CNBut-9-CN-arachno-9,6-PtCB8H12]
(9) depending on the stoichiometry of the reaction. Reaction of 1 or 3 with I2 yields the platinum(IV)
complexes [9,9-(CNBut)2-9,9-I2-6-R′-arachno-9,6-PtCB8H11] (R′ ) H (10), Ph (11)), respectively, by an
oxidative addition reaction. Using the same reagent, compound 7 forms solvent-dependent, boron-
substituted products: [9,9-dppe-4,8-I2-arachno-9,6-PtCB8H10] (12) is obtained in CH2Cl2, whereas [9,9-
dppe-4-{O(CH2)4I}-8-I-arachno-9,6-PtCB8H10] (13) results when THF is used as solvent.
(M ) Re,6 Mn,7 Mo,8 n ) 1; M ) Co,9 n ) 2), whereas 9- and
10-vertex {closo-MnCB7} (M ) Fe,10 n ) 1; M ) Fe,10 Co,9
n ) 2) and 10- and 12-vertex {closo-MnCB8} species (M )
Fe,11 Co,9 Re,12 n ) 1; M ) Ru,13 n ) 3) are formed via
Introduction
Our research has concentrated on the synthesis and reactivity
of metallamonocarboranes, still a relatively unexplored area
when compared with that of their dicarborane counterparts.1 The
original work was limited to icosahedral metal-monocarbollide
complexes {MCB10},2,3 but since the discovery of the “Brellochs
reaction”4 and the resulting availability of a range of intermedi-
ate-sized monocarboranes, we have been able to expand our
studies to smaller, subicosahedral metallamonocarborane spe-
cies. This reaction initially provides a facile route from commer-
cially available decaborane (B10H14) to nido- and arachno-
{CB9} species, which can then be further manipulated to form
monocarboranes with fewer then 10 vertices.5 To date the
majority of metallamonocarboranes formed using these mono-
carborane ligands have had a closo configuration. The reaction
of suitable metal carbonyl precursors with 10-vertex monocar-
borane clusters yields 11- and 12-vertex {closo-MnCB9} clusters
oxidative insertion when the anions [closo-CBnHn+1]
- (n ) 7,
8) are treated with appropriate M0 fragments.
Examples of open cluster nido- and arachno-metallamono-
carboranes are much more limited. Some 10-vertex {nido-
MCB8} (M ) Ru, Os14) and {arachno-MCB8} (M ) Fe,11 Ru,14
Ir,15 Pt16,17) compounds have been identified, along with a single
{nido-PtCB9} species.17 However, the yields of these com-
pounds are generally low, and studies of further reactions have
therefore been restricted to the anion [4,9-{Fe(CO)4}-9,9,9-
(CO)3-arachno-9,6-FeCB8H11]-.11
To add to this relatively small portfolio of open metallam-
onocarboranes and further extend our knowledge of their
chemistry, we herein present the high-yield synthesis of several
(6) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Organometallics
2003, 22, 2842.
(7) (a) Du, S.; Farley, R. D.; Harvey, J. N.; Jeffery, J. C.; Kautz, J. A.;
Maher, J. P.; McGrath, T. D.; Murphy, D. M.; Riis-Johannessen, T.; Stone,
F. G. A. Chem. Commun. 2003, 1846. (b) Du, S.; Jeffery, J. C.; Kautz,
J. A.; Lu, X. L.; McGrath, T. D.; Miller, T. A.; Riis-Johannessen, T.; Stone,
F. G. A. Inorg. Chem. 2005, 44, 2815.
* Corresponding author. E-mail: gordon_stone@baylor.edu.
(1) Grimes, R. N. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon Press: Oxford, U.K.,
1982, Vol. 1, Section 5.5. Grimes, R. N. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, U.K., 1995; Vol. 1, Chapter 9. Hosmane, N. S., Maguire,
J. A. In ComprehensiVe Organometallic Chemistry III; Mingos, D. M. P.;
Crabtree, R. H., Eds.; Pergamon Press: Oxford, U.K., 2007; Vol. 3, Section
3.05. Grimes, R. N. Coord. Chem. ReV. 2000, 200–202, 773.
(2) McGrath, T. D.; Stone, F. G. A. J. Organomet. Chem. 2004, 689,
3891.
(8) Lei, P.; McGrath, T. D.; Stone, F. G. A. Chem. Commun. 2005,
3706.
(9) Lu, X. L.; McGrath, T. D.; Stone, F. G. A. Organometallics 2006,
25, 2590.
(10) Franken, A.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005,
24, 5157.
(11) Franken, A.; McGrath, T. D.; Stone, F. G. A. Inorg. Chem. 2006,
45, 2669.
(3) McGrath, T. D.; Stone, F. G. A. AdV. Organomet. Chem. 2005, 53, 1.
(4) Brellochs, B. In Contemporary Boron Chemistry; Davidson, M. G.,
Hughes, A. K., Marder, T. B., Wade, K., Eds.; Royal Society of Chemistry:
Cambridge, U.K., 2000; p. 212.
(12) Carr, M. J.; McGrath, T. D.; Stone, F. G. A. Inorg. Chem. 2008,
47, 713.
(13) Du, S.; Hodson, B. E.; Lei, P.; McGrath, T. D.; Stone, F. G. A.
Inorg. Chem. 2007, 46, 6613.
(5) (a) Brellochs, B.; Backovsky, J.; Stíbr, B.; Jelínek, T.; Holub, J.;
Bakardjiev, M.; Hnyk, D.; Hofmann, M.; Císarová, I.; Wrackmeyer, B. Eur.
J. Inorg. Chem. 2004, 3605. (b) Stíbr, B. Pure Appl. Chem. 2003, 75, 1295.
(c) Franken, A.; Jelínek, T.; Taylor, R. G.; Ormsby, D. L.; Kilner, C. A.;
Clegg, W.; Kennedy, J. D. Dalton Trans. 2006, 5753.
(14) Alcock, N. W.; Jasztal, M. J.; Wallbridge, M. G. H. J. Chem. Soc.,
Dalton Trans. 1987, 2793.
(15) Fontaine, X. L. R.; Kennedy, J. D.; Thorton-Pett, M.; Nestor, K.;
Stíbr, B.; Jelínek, T.; Base, K. J. Chem. Soc., Dalton Trans. 1990, 2887.
10.1021/om7012056 CCC: $40.75
2008 American Chemical Society
Publication on Web 04/04/2008

2100 Organometallics, Vol. 27, No. 9, 2008
Carr et al.
Scheme 1a
a
Reagents and conditions: (i) [Pt3(CNR)6] in THF (1, 2, and 3), or [PtMe2(PMe2Ph)2] in CH2Cl2 (5); (ii) 1 with PPh3 in CH2Cl2; (iii) 1 with dppe
in CH2Cl2; (iv) 1 with n molar equivalents of [NEt4][CN] in CH2Cl2; (v) 1 or 3 with I2 in CH2Cl2; (vi) 7 with I2 in CH2Cl2 (12) or in THF (12 +
13). Key: b ) C, O ) BH, gray O ) B.
Table 1. Analytical and Physical Data
Anal./%b
compd
ν
max(CN)a/cm-1
yield (%)
C
H
N
1
2
3
4
5
6
7
8
[9,9-(CNBut)2-arachno-9,6-PtCB8H12]
[9,9-(CNXyl)2-arachno-9,6-PtCB8H12]
2201 s, 2179 s
2181 s, 2155 s
2203 s, 2181 s
2216 s, 2186 s, 2162 m
91
85
81
2
92
94
95
98
94
74
72
82
63
28.1 (28.0)
40.4 (40.2)
37.4 (37.3)
42.3 (42.0)
35.3 (35.2)
44.2 (44.3)
45.9 (46.1)
38.6 (38.8)c
33.0 (33.1)
18.4 (18.2)
25.5 (25.5)
33.7 (33.9)
36.3 (36.2)
6.5 (6.4)
5.3 (5.3)
6.3 (6.3)
6.6 (6.6)
6.0 (5.7)
5.7 (5.6)
5.2 (5.2)
8.7 (8.7)
7.4 (7.6)
4.3 (4.2)
4.4 (4.3)
3.6 (3.6)
4.1 (4.1)
5.9 (5.7)
5.1 (4.9)
5.2 (5.1)
6.8 (6.7)
[9,9-(CNBut)2-6-Ph-arachno-9,6-PtCB8H11]
[9,9-(CNBut)2-6-Ph-8-CNBut-arachno-9,6-PtCB8H9]
[9,9-(PMe2Ph)2-arachno-9,6-PtCB8H12]
[9-CNBut-9-PPh3-arachno-9,6-PtCB8H12]
[9,9-dppe-arachno-9,6-PtCB8H12]
2184 s
2.0 (2.2)
[NEt4]2[9,9-(CN)2-arachno-9,6-PtCB8H12]
[NEt4][9-CNBut-9-CN-arachno-9,6-PtCB8H12]
[9,9-(CNBut)2-9,9-I2-arachno-9,6-PtCB8H12]
[9,9-(CNBut)2-9,9-I2-6-Ph-arachno-9,6-PtCB8H11]
[9,9-dppe-4,8-I2-arachno-9,6-PtCB8H10]
[9,9-dppe-4-{O(CH2)4I}-8-I-arachno-9,6-PtCB8H10]
2106 m, 2096 m
2176 s, 2112 m
2260 m, 2225 s
2260 m, 2216 s
9.4 (9.6)
7.5 (7.7)
3.9 (3.9)
3.5 (3.5)
9
10
11
12
13
a Measured in CH2Cl2; a broad, medium-intensity band observed at ca. 2500–2550 cm-1 in the spectra of all compounds is due to B-H absorptions.
b Calculated values are given in parentheses. c Solid contains 0.25 molar equiv of [NEt4][CN].
arachno-platinamonocarboranes and report the results of pre-
liminary reactivity studies carried out on these compounds.
temperature in tetrahydrofuran (THF). Analogous complexes
[9,9-(CNXyl)2-arachno-9,6-PtCB8H12] (2; Xyl ) C6H3Me2-2,6)
and [9,9-(CNBut)2-6-Ph-arachno-9,6-PtCB8H11] (3) were ob-
tained in a similar manner using [Pt3(CNXyl)6] or arachno-4-
Ph-4-CB8H13, respectively (Scheme 1). Compounds 1–3 were
all obtained in high yields. Physical and spectroscopic data for
all reported species (1–13) are detailed in Tables 1 and 2.
The solid-state structure of 1 was unequivocally established
by an X-ray diffraction study, the results of which are illustrated
in Figure 1. The arachno configuration of 1 was confirmed by
Results and Discussion
The arachno 10-vertex platinum complex [9,9-(CNBut)2-
arachno-9,6-PtCB8H12] (1) was readily obtained by the reaction
(18 h) of arachno-4-CB8H14 with [Pt3(CNBut)6],18 at ambient
(16) Base, K.; Stíbr, B.; Zakharova, I. A. Synth. React. Inorg. Met-Org.
Chem. 1980, 509.
(17) Stíbr, B.; Jelínek, T.; Kennedy, J. D.; Fontaine, X. L. R.; Thorton-
Pett, M. J. Chem. Soc., Dalton Trans. 1993, 1261.
(18) Green, M.; Howard, J. A. K.; Murray, M.; Spencer, J. L.; Stone,
F. G. A. J. Chem. Soc., Dalton Trans. 1977, 1509.

Synthesis of 10-Vertex arachno-Platinacarboranes
Organometallics, Vol. 27, No. 9, 2008 2101

2102 Organometallics, Vol. 27, No. 9, 2008
Carr et al.
Chart 1
isolobal {Br:CNBut} moiety. Thus, although there is no
overall change in cluster architecture upon substitution, the
µ-H atom that formerly bridged the B(7)—B(8) connectivity
is no longer present. All three CNBut groups in 4 therefore
behave as two-electron donors with, correspondingly, very
similar geometric parameters within each ligand. Attempts
to synthesize 4 from 3 by direct reaction with CNBut were
unsuccessful, and given the low yield of 4, it is unwise to
speculate upon its precise mechanism of formation. We note,
however, that similar B-CNBut substitution has been
reported in the synthesis of bis(isocyanide) derivatives of
{NiCB10} clusters using {Ni0(CNBut)2} synthons.20
The 11B{1H} NMR spectrum for 4 shows a separate res-
onance for each of the eight boron atoms. Unresolved coupling
to the platinum nucleus allows the peak at δ 13.2 to be assigned
to B(4), and the resonance at δ -24.0 can be assigned to the
isocyanide-substituted boron atom, B(8), as no coupling to a
hydrogen nucleus is apparent for this peak in the proton-coupled
11B NMR spectrum. The 1H NMR spectrum shows a diagnostic
broad peak at δ –2.20 corresponding to the single B-H-B
bridge, and the IR spectrum reveals three strong CN stretching
bands at 2216, 2186, and 2162 cm-1; the latter can be tentatively
assigned to B-CN due to its smaller intensity and broader
nature.
Figure 1. Structure of a whole molecule of compound 1 showing
the crystallographic labeling scheme. Selected distances (Å):
Pt(9)-B(4) 2.157(4), Pt(9)-B(10) 2.219(3), Pt(9)-C(11) 1.984(2),
C(11)-N(12)1.149(3), N(12)-C(13)1.465(3). TheC(11)-Pt(9)-
C(11)a angle is 91.65(13)°. In this and subsequent figures,
thermal ellipsoids are drawn with 40% probability, and for clarity
only chemically significant hydrogen atoms are shown. Sym-
metry code (a): + x, ½ - y, + z.
the presence of two hydrogen atoms bridging the “gunwale”
boron vertices on the open face, analogous to [arachno-
B10H14]2-. The cage carbon atom resides in the three-connected
6-position, and the platinum center is in the 9-position ligated
by three boron atoms. A molecular plane of symmetry bisects
these atoms and the boron atoms in positions 2 and 4 and
coincides with a crystallographic mirror plane. Interatomic
distances involving the platinum center are Pt(9)–B(4) )
2.157(4) Å, Pt(9)–B(10) ) 2.219(3) Å, and Pt(9)–C(11) )
1.984(2) Å.
The IR spectrum of 1 shows two strong CN stretching bands
at 2201 and 2179 cm-1, and its 11B{1H} NMR spectrum shows
a 1:1:2:2:2 set of resonances, consistent with the symmetric
structure determined by X-ray crystallography. Platinum satel-
lites are observed for the resonance at δ 25.6 [J(PtB) ) 314
Hz], allowing this to be assigned to B(4); unresolved coupling
to the platinum nucleus is also apparent for the peak at δ –15.9,
and this peak is therefore tentatively allocated to B(8) and B(10).
The 1H NMR spectrum shows a diagnostic broad resonance at
δ –3.17 corresponding to the B-H-B bridges.19 In the 13C{1H}
NMR spectrum coupling to the platinum nucleus is observed
for the CtN resonance at δ 137.8 [J(PtC) ) 1255 Hz], while
a broad resonance is observed at δ 53.4 that corresponds to the
cage carbon atom. The IR and NMR spectra for compounds 2
and 3 are similar to those of 1 and therefore merit little further
comment.
A second species was obtained during the synthesis of 3. It
was separated in low yield by column chromatography and
initially identified as [9,9-(CNBut)2-6-Ph-8-CNBut-arachno-9,6-
PtCB8H9] (4; see Chart 1) by an X-ray diffraction study (Figure
2). Compound 4 is closely related to 3, except that the {BH2}
unit at position 8 in compound 3 has been replaced by the
Figure 2. Structure of compound 4 showing the crystallographic
labeling scheme. Selected distances (Å): Pt(9)-B(4) 2.233(3),
Pt(9)-B(8) 2.245(3), Pt(9)-B(10) 2.157(3), Pt(9)-C(90) 1.987(3),
C(90)-N(91) 1.151(4), N(91)-C(92) 1.459(4), Pt(9)-C(93) 1.966(3),
C(93)-N(94) 1.148(4), N(94)-C(95) 1.469(4), B(10)-C(11)
1.543(4), C(11)-N(12) 1.144(4), N(12)-C(13) 1.464(4). The
C(90)-Pt(9)-C(93) angle is 95.52(12)°.
(19) Todd, L. J.; Siedle, A. R. Prog. Nucl. Magn. Reson. Spectrosc.
1979, 3, 87.

Synthesis of 10-Vertex arachno-Platinacarboranes
Organometallics, Vol. 27, No. 9, 2008 2103
Phosphine-substituted 10-vertex arachno-platinacarborane
species similar to 1–3 have been identified previously,16,17 and
these are now found to be accessible in good yield from the
reaction of arachno-4-CB8H14 with complexes such as
[PtMe2(PMe2Ph)2]. Addition of [PtMe2(PMe2Ph)2] to a stirred
CH2Cl2 solution of arachno-4-CB8H14 yielded [9,9-(PMe2Ph)2-
arachno-9,6-PtCB8H12] (5), in near quantitative yield (see
Scheme 1). Compound 5 has been previously isolated in low
yields (<3%) as a byproduct in a reaction between [arachno-
6-CB9H14]- and [PtCl2(PMe2Ph)2].17
The open nature of these arachno 10-vertex platinacarbo-
ranes (1–5) suggested that it may be possible to add further
metal centers to these compounds and thus engender larger
mixed-metal clusters. However, all reactions attempted in this
area have thus far proved fruitless. Oxidative addition of
neutral M0 fragments, as well as deprotonation (NaH) and
subsequent addition of cationic metal fragments, resulted in
either recovery of the starting material or simple ligand
exchange between metal centers. The complex [9-CNBut-9-
PPh3-arachno-9,6-PtCB8H12] (6) was first identified from
such a ligand exchange reaction when attempts were made
to add an iridium center to 1 using [IrCl(CO)(PPh3)2].
Compound 6 (see Scheme 1) can more readily be obtained
by simply stirring a CH2Cl2 solution of 1 with PPh3. The
11B{1H} NMR spectrum of 6 shows a 1:1:2:1:1:2 set of
resonances; unresolved coupling to the platinum nucleus is
again observed for the lowest field peak at δ 26.8, which is
assigned to B(4). Two broad resonances in the 1H NMR
spectrum at δ –2.75 and –3.76 are assigned to the two
B-H-B bridges, and a broad unresolved peak in the 13C{1H}
NMR at δ 141.4 is assigned to the cyano carbon atom. The
31P{1H} NMR spectrum shows a single resonance with 195Pt
satellites at δ 28.8 [J(PtP) ) 2687 Hz], and the IR spectrum
Figure 3. Structure of the dianion of compound 8 showing the
crystallographic labeling scheme. Selected distances (Å): Pt(9)-B(4)
2.145(4), Pt(9)-B(8) 2.211(4), Pt(9)-B(10) 2.213(4), Pt(9)-C(91)
2.019(4), C(91)-N(92) 1.143(4), Pt(9)-C(93) 2.004(4), C(93)-N(94)
1.157(5). The C(91)-Pt(9)-C(93) angle is 90.62(15)°.
{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11]-, forming the
monoiron species [2,2,2-(CO)3-closo-2,1-FeCB8H9]-.11 Unfor-
tunately, no such reaction occurs with the arachno-platinacar-
boranes described here, and they are recovered unchanged after
heating toluene or xylene solutions to reflux temperatures for
24 h.
Addition of I2 in the presence of a base such as Et3N has
been used successfully to oxidatively close arachno-monocar-
boranes to their nido or closo counterparts.5 This methodology
was also applied to the present arachno-platinamonocarboranes.
Although it was not possible to synthesize nido or closo species,
some of the arachno clusters did react to yield further novel
arachno species. Thus, treatment of 1 with I2 at -78 °C led to
the formation of [9,9-(CNBut)2-9,9-I2-arachno-9,6-PtCB8H12]
(10). Instead of the whole cluster being oxidized and closing,
oxidation is confined to the platinum center: the formal oxidation
state of the now octahedral platinum center in 10 is +4 with
two iodides taking up the extra coordination sites (see Scheme
1). The 11B{1H} NMR spectrum of 10 again shows a 1:1:2:2:2
set of resonances, albeit over a narrower field range. The
resonance corresponding to B(4) at δ 17.2, identified by
unresolved coupling to the platinum nucleus, is shifted upfield
compared to the analogous peak (δ 25.6) for its precursor 1.
Two broad resonances are visible in the 13C{1H} NMR spectrum
at δ 116.7 and 116.2 for the two chemically different (exo and
endo) cyano carbon atoms, as is a broad peak at δ 53.4 that
corresponds to the cage carbon. The 1H NMR spectrum shows
the characteristic broad resonance corresponding to the two
B-H-B bridges at δ -2.01.
It proved difficult to obtain single crystals of 10 suitable for
X-ray diffraction analysis, but good quality single crystals were
obtained for its phenylated counterpart, [9,9-(CNBut)2-9,9-I2-
6-Ph-arachno-9,6-PtCB8H11] (11), obtained from 3 and I2. The
solid-state structure of 11 is illustrated in Figure 4, and its
spectroscopic data are similar to those of 10. Both compounds,
although stable for prolonged periods of time in their solid form,
decompose in solution relatively quickly. Decomposition ap-
parently leads to a mixture of Pt(II) species including the
precursors 1 and 3, species with iodide substitution at boron
vertices, and [PtI2(dppe)]. These were partially characterized
by NMR spectroscopy or preliminary X-ray diffraction studies,
but they could not be isolated in sufficient amounts to permit
full characterization.
shows one strong CN stretching band at 2184 cm-1
.
It is notable that even with an excess of PPh3 only one
CNBut ligand in 1 can be replaced, forming compound 6.
Nevertheless, both isocyanides can be replaced by using the
bidentate ligand, dppe (Ph2PCH2CH2PPh2), giving [9,9-dppe-
arachno-9,6-PtCB8H12] (7) in a similar manner to 6. The
11B{1H} NMR spectrum of 7 shows a 1:1:2:2:2 set of
resonances akin to that of compounds 1–3 and 5, and the
31P{1H} NMR spectrum shows a single resonance at δ 57.2
[J(PtP) ) 2596 Hz].
Treatment of 1 with 2 equiv of [NEt4][CN] yields quantita-
tively the dianionic species [NEt4]2[9,9-(CN)2-arachno-9,6-
PtCB8H12] (8; see Scheme 1). Its 11B{1H} NMR spectrum again
shows a 1:1:2:2:2 set of resonances consistent with molecular
symmetry. The 13C{1H} NMR spectrum shows a CtN reso-
nance at δ 139.3 with 195Pt satellites [J(PtC) ) 1046 Hz] and
the IR spectrum for 8 shows two CN stretching bands at 2106
and 2096 cm-1. The solid-state structure of 8 was confirmed
via an X-ray diffraction study and is illustrated in Figure 3.
Compound 8 can also be formed when the phosphine derivatives
(5–7) are treated with a slight excess of [NEt4][CN]. Careful
treatment of 1 with 1 equiv of [NEt4][CN] gives the monoan-
ionic species [NEt4][9-CNBut-9-CN-arachno-9,6-PtCB8H12] (9;
see Scheme 1). The different ligands coordinated to the platinum
center in 9 account for the 1:1:2:2:1:1 set of resonances seen in
its 11B{1H} NMR spectrum. Two CtN stretching bands at 2176
and 2112 cm-1 in the IR spectrum of 9 can be assigned to the
isocyanide and cyanide ligands, respectively.
Attempts were made to form closo 10-vertex platinacarbo-
ranes from species 1–3 and 5–7. Heating to elevated tempera-
tures had recently been found to facilitate cage closure in [4,9-

2104 Organometallics, Vol. 27, No. 9, 2008
Carr et al.
Figure 4. Structure of compound 11 showing the crystallographic
labeling scheme. Selected distances (Å) and angles (deg):
Pt(9)-I(91) 2.7325(3), Pt(9)-I(92) 2.7481(3), Pt(9)-B(4)
2.275(4), Pt(9)-B(8) 2.294(5), Pt(9)-B(10) 2.324(4), Pt(9)-C(13)
1.956(4),C(13)-N(14)1.149(4),N(14)-C(15)1.469(4),Pt(9)-C(19)
1.973(4), C(19)-N(20) 1.152(4), N(20)-C(21) 1.468(4). Se-
lected angles are: I(91)-Pt(9)-I(92) 93.129(10), I(91)-Pt(9)-
C(13)85.57(11),I(91)-Pt(9)-C(19)84.95(10),I(92)-Pt(9)-C(13)
85.13(11), I(92)-Pt(9)-C(19) 83.52(10), C(13)-Pt(9)-C(19)
164.77(14).
Figure 5. Structure of compound 13 showing the crystallographic
labeling scheme. Selected distances (Å): Pt(9)-B(4) 2.190(4),
Pt(9)-B(8) 2.195(4), Pt(9)-B(10) 2.240(4), Pt(9)-P(91) 2.2932(10),
Pt(9)-P(92) 2.2857(12), B(4)-O(40) 1.408(5), O(40)-C(41)
1.429(4), C(44)-I(45) 2.162(4). The P(91)-Pt(9)-P(92) angle is
84.24(4)°.
1
no additional coupling in a H-coupled 11B NMR spectrum,
indicating that the corresponding boron atom has been substi-
tuted. The 31P{1H} NMR spectrum shows a single, broad
resonance with 195Pt satellites at δ 51.8 [J(PtP) ) 2327 Hz]. In
the 13C{1H} NMR spectrum, notably, the resonance correspond-
ing to the carbon nucleus adjacent to the oxygen (δ 67.8) shows
coupling to the platinum nucleus [3J(PtC) ) 38 Hz]. The solid-
state structure of 13 was unequivocally determined via an X-ray
diffraction study, of which the result is presented in Figure 5:
this is entirely consistent with the spectral data.
A different reaction takes place when compound 7 is similarly
treated with I2. Now, rather than oxidative addition of iodine
to the platinum center, substitution at boron vertices occurs (see
Scheme 1), with [9,9-dppe-4,8-I2-arachno-9,6-PtCB8H10] (12)
being isolated from the reaction of I2 with 7 in CH2Cl2. Here,
two iodine atoms have replaced the terminal hydrogen atoms
at positions 4 and 8. The 11B{1H} NMR spectrum of 12 shows
a 1:1:1:1:1:2:1 set of resonances, with unresolved coupling to
the platinum nucleus observed for the peak at δ 14.4, so that
this resonance can be assigned to B(4); this resonance also
Conclusions
1
remains a singlet in the H-coupled 11B NMR spectrum, con-
firming that an iodine atom is attached to B(4). The 31P{1H}
NMR spectrum shows a single, broad resonance with 195Pt
satellites at δ 50.7 [J(PtP) ) 2488 Hz].
The reaction of arachno-4-CB8H14, and its phenylated cousin
4-Ph-arachno-4-CB8H13, with platinum-isocyanide complexes
provides a facile, high-yielding route to new arachno-platina-
monocarborane species, adding to the relatively sparsely studied
class of open metallamonocarboranes. The synthesis of these
complexes in such high yields has allowed preliminary inves-
tigation of their reaction chemistry. Their {PtCB8} cores,
however, have thus far proven to be unusually stable for such
open metallacarborane clusters, withstanding various attempted
cage-closure reactions and the addition of further metal centers.
Oxidative addition of I2 to the platinum center, as in the
formation of 10 and 11, or iodine-promoted cage substitution,
as occurred in the synthesis of 12 and 13, show an insight into
the type of reaction chemistry that may be possible for these
species. These various products highlight how subtle changes
in the precursors or conditions can have a significant effect upon
reactivity. It is anticipated that the high-yielding synthesis of
all these arachno-platinamonocarboranes can ultimately be
exploited to reveal further interesting reaction chemistry in the
future.
When the reaction that formed 12 is carried out with THF as
solvent, [9,9-dppe-4-{O(CH2)4I}-8-I-arachno-9,6-PtCB8H10]
(13) is instead produced as the major product, with compound
12 formed in lesser yield. The {O(CH2)4I} moiety attached to
the cage in 13 is assumed to result from a boron-bound THF
substituent that initially is introduced via iodine-promoted
oxidative substitution,21 and which subsequently undergoes
nucleophilic attack by I- at its three-coordinate oxygen atom
to give a neutral species. Several examples of cluster-bound
THF substituents being opened by halide ions in this manner
have been reported previously.22
The 11B{1H} NMR spectrum of 13 shows a 1:1:1:2:1:1:1 set
of resonances, with platinum satellites observed for the reso-
nance at δ 39.6 [J(PtB) ) 334 Hz], allowing the latter to be
assigned to B(4). Its chemical shift is considerably downfield
when compared with similar resonances discussed above, due
to its oxygen substituent, while the resonance at δ –26.7 shows
Experimental Section
(20) McGrath, T. D.; Franken, A.; Kautz, J. A.; Stone, F. G. A. Inorg.
Chem. 2005, 44, 8135.
General Considerations. Reactions were carried out under an
atmosphere of dry nitrogen using Schlenk line techniques. Solvents
were distilled from appropriate drying agents under nitrogen prior
to use. Petroleum ether refers to that fraction of boiling point 40-60
°C. Chromatography columns (ca. 20 cm in length and ca. 2 cm in
diameter) were packed with silica gel (Acros, 60–200 mesh).
(21) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 2001, 2791.
(22) (a) Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.; Woollam,
S. F. Organometallics 1994, 13, 157. (b) Gómez-Saso, M.; Mullica, D. F.;
Sappenfield, E. L.; Stone, F. G. A. Polyhedron 1996, 15, 793. (c) Batten,
S. A.; Jeffery, J. C.; Rees, L. H.; Rudd, M. D.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1998, 2839.

Synthesis of 10-Vertex arachno-Platinacarboranes
Organometallics, Vol. 27, No. 9, 2008 2105
Table 3. Data for Crystal Structure Analyses of Compounds 1, 4, 8, 11, and 13
1
4
8
11
13
formula
fw
space group
C11H30B8N2Pt
471.94
Pnma
C22H41B8N3Pt
629.15
P1
C19H52B8N4Pt
618.22
C2/c
C17H34B8I2N2Pt
801.83
P21/c
C31H42B8I2OP2Pt
1027.96
P1
j
j
a, Å
b, Å
c, Å
11.6161 (8)
17.7030 (12)
9.5129 (6)
90
90
90
1956.2 (2)
4
0.7164
47 288
3064
11.4393 (3)
11.5230 (3)
12.9427 (3)
80.784 (1)
81.299 (2)
61.667 (1)
1476.71 (6)
2
0.1415
31 116
8447
0.0347
31.728 (8)
11.472 (3)
17.010 (5)
90
109.609 (13)
90
5833 (2)
8
0.4826
36 026
7221
0.044
0.0667, 0.0393
14.3012 (11)
10.3809 (7)
22.6397 (14)
90
125.297 (4)
90
2743.2 (3)
4
0.7374
42 894
7509
0.0538
0.0529, 0.0511
10.086 (2)
11.493 (2)
17.784 (4)
77.85 (3)
74.33 (3)
71.97 (3)
1869.2 (6)
2
0.5516
35 441
9086
0.0491
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
µ(Mo KR), cm-1
no. of reflns measd
no. of indep reflns
Rint
0.0429
0.0498, 0.0222
wR2, R1 (all data)a
0.0612, 0.0375
0.0688, 0.0335
2
2 2
a wR2 ) [∑{w(Fo - Fc ) }/∑w(Fo2)2]1/2; R1 ) ∑||Fo| - | Fc||/∑|Fo|.
Preparative thin-layer chromatography (TLC) was performed on
20 × 20 cm glass plates (Analtech, silica gel GF254). NMR spectra
were recorded at the following frequencies: 1H 360.13, 13C 90.56,
31P 145.78, and 11B 115.5 MHz. The compounds arachno-4-
CB8H14,5a 4-Ph-arachno-4-CB8H13,5c [Pt(bicyclo[2.2.1]heptene)3],23
and [PtMe2(PMe2Ph)2]24 were prepared according to the literature;
all other materials were used as received.
Synthesis of [9,9-(CNBut)2-arachno-9,6-PtCB8H12] and [9,9-
(CNXyl)2-arachno-9,6-PtCB8H12]. Stoichiometric amounts of
[Pt(bicyclo[2.2.1]heptene)3] (1.270 g, 2.66 mmol) and CNBut (0.65
mL, 5.71 mmol) were mixed in THF (30 mL), affording
[Pt3(CNBut)6] in situ. Solid arachno-4-CB8H14 (0.300 g, 2.66 mmol)
was immediately added to this orange solution, and the resulting
mixture was stirred at ambient temperature for 14 h. Volatiles were
removed in vacuo, and the residue was dissolved in CH2Cl2 (ca. 5
mL) and transferred to the top of a chromatography column. Elution
with CH2Cl2-petroleum ether (4:1) afforded a colorless eluate that
was collected and, after evaporation of solvent in vacuo, gave [9,9-
(CNBut)2-arachno-9,6-PtCB8H12] as a white powder (1; 1.142 g,
91%). [9,9-(CNXyl)2-arachno-9,6-PtCB8H12] (2; 0.860 g, 85%) was
synthesized analogously from arachno-4-CB8H14 (0.200 g, 1.78
mmol) using CNXyl in the place of CNBut.
Synthesis of [9,9-(CNBut)2-6-Ph-arachno-9,6-PtCB8H11] and
[9,9-(CNBut)2-6-Ph-8-CNBut-arachno-9,6-PtCB8H9]. By a similar
procedure to that described above for 1, [Pt3(CNBut)6] was
synthesized by mixing [Pt(bicyclo[2.2.1]heptene)3] (0.506 g, 1.06
mmol) and CNBut (0.30 mL, 2.63 mmol) in THF (20 mL), followed
by addition of 4-Ph-arachno-4-CB8H13 (0.200 g, 1.06 mmol) to
this solution. After stirring at ambient temperature for 14 h the
volatiles were removed in vacuo, and the residue was dissolved in
CH2Cl2 (ca. 3 mL) and added to the top of a chromatography
column. Elution using CH2Cl2-petroleum ether (4:1) afforded two
fractions. The first, colorless fraction, after evaporation of solvent
in vacuo, yielded [9,9-(CNBut)2-6-Ph-arachno-9,6-PtCB8H11] (3;
0.470 g, 81%) as a white powder. The second, slower moving, pale
yellow fraction was collected and further purified by preparative
TLC using CH2Cl2-petroleum ether (3:2) as the liquid phase. A
single band (Rf ) 0.32) was removed, which after evaporation of
solvent in vacuo gave [9,9-(CNBut)2-6-Ph-8-CNBut-arachno-9,6-
PtCB8H9] (4; 0.013 g, 2%) as a pale yellow powder.
stirring at ambient temperature for 10 h the volatiles were removed
in vacuo and the resulting residue was added to a chromatography
column. Using CH2Cl2 as eluent, a colorless solution was collected,
which, after evaporation of solvent in vacuo, gave [9,9-(PMe2Ph)2-
arachno-9,6-PtCB8H12] (5; 0.144 g, 92%) as a white, microcrys-
talline solid.
Synthesis of [9-CNBut-9-PPh3-arachno-9,6-PtCB8H12]. Com-
pound 1 (0.100 g, 0.21 mmol) was dissolved in CH2Cl2 (15 mL),
and PPh3 (0.060 g, 0.23 mmol) was added. After 16 h at ambient
temperature, volatiles were removed in vacuo and the residue was
redissolved in CH2Cl2 (ca. 2 mL) and transferred to the top of a
chromatography column. Elution with CH2Cl2-petroleum ether
(4:1) gave a colorless solution, which was collected and, after
evaporation of solvent in vacuo, gave [9-CNBut-9-PPh3-arachno-
9,6-PtCB8H12] (6; 0.128 g, 94%) as a white, crystalline solid.
Synthesis of [9,9-dppe-arachno-9,6-PtCB8H12]. Compound 1
(0.300 g, 0.64 mmol) was dissolved in CH2Cl2 (25 mL), and dppe
(0.260 g, 0.65 mmol) was added. After 16 h at ambient temperature,
volatiles were removed in vacuo, the sample washed with petroleum
ether (3 × 30 mL), and the residue was redissolved in a minimum
amount of CH2Cl2 (ca. 5 mL). Petroleum ether (ca. 50 mL) was
then layered above this solution, and the sample was kept at -30
°C for 72 h. The clear, colorless crystals of [9,9-dppe-arachno-
9,6-PtCB8H12] (7; 0.428 g, 95%) that resulted were collected by
filtration and dried in vacuo.
Synthesis of [NEt4]2[9,9-(CN)2-arachno-9,6-PtCB8H12] and
[NEt4][9-CNBut-9-CN-arachno-9,6-PtCB8H12]. Compound 1 (0.100
g, 0.21 mmol) was dissolved in CH2Cl2 (15 mL), and [NEt4][CN]
(0.066 g, 0.42 mmol) was added. After 4 h at ambient temperature,
volatiles were removed in vacuo, and the residue was washed with
petroleum ether (3 × 30 mL). The white powder that resulted was
dried in vacuo and identified as [NEt4]2[9,9-(CN)2-arachno-9,6-
PtCB8H12] (8; 0.128 g, 98%). [NEt4][9-CNBut-9-CN-arachno-9,6-
PtCB8H12] (9; 0.108 g, 94%) was synthesized in a similar manner
by using just 1 equiv of [NEt4][CN].
Synthesis of [9,9-(CNBut)2-9,9-I2-arachno-9,6-PtCB8H12] and
[9,9-(CNBut)2-9,9-I2-6-Ph-arachno-9,6-PtCB8H11]. Compound 1
(0.100 g, 0.21 mmol) was dissolved in CH2Cl2 (10 mL), and the
solution was cooled to -78 °C. A CH2Cl2 solution (10 mL) of I2
(0.110 g, 0.43 mmol) was slowly added over a period of 1 h. Solid
Na2S2O3 (0.100 g, 0.63 mmol) and water (20 mL) were added, and
the mixture was shaken before separating the yellow CH2Cl2 layer.
The aqueous phase was extracted with further CH2Cl2 (20 mL),
and the combined extracts were dried with MgSO4 before removal
of volatiles in vacuo. The residue was redissolved in the minimum
amount of CH2Cl2 (ca. 2 mL), layered with petroleum ether, and
kept at -30 °C for 72 h. This afforded orange crystals of [9,9-
(CNBut)2-9,9-I2-arachno-9,6-PtCB8H12] (10; 0.113 g, 74%), which
Synthesis of [9,9-(PMe2Ph)2-arachno-9,6-PtCB8H12]. Solid
[PtMe2(PMe2Ph)2] (0.135 g, 0.27 mmol) was added to a CH2Cl2
(10 mL) solution of arachno-4-CB8H14 (0.030 g, 0.27 mmol). After
(23) Crasnell, L. E.; Spencer, J. L. Inorg. Synth. 1990, 28, 127.
(24) Kaur, P.; Brownless, A.; Perera, S. D.; Cooke, P. A.; Jelínek, T.;
Kennedy, J. D.; Stíbr, B.; Thorton-Pett, M. J. Organomet. Chem. 1998,
557, 181.

2106 Organometallics, Vol. 27, No. 9, 2008
Carr et al.
were collected and dried in vacuo. In a similar manner [9,9-
(CNBut)2-9,9-I2-6-Ph-arachno-9,6-PtCB8H11] was synthesized from
compound 3 (0.100 g, 0.18 mmol) and isolated as an orange,
crystalline solid (11; 0.104 g, 72%).
were integrated using SAINT;25 the substantial redundancy in data
allowed an empirical absorption correction (SADABS)25 to be
applied, based on multiple measurements of equivalent reflections.
Structures were solved by direct methods using SHELXS-9726
and refined with full-matrix least-squares on F2 using SHELXL-
97.27 All non-hydrogen atoms were assigned anisotropic displace-
ment parameters. The locations of cage carbon atoms were verified
by examination of their isotropic thermal parameters, in conjunction
with comparisons of B-B and C-B internuclear distances. All
hydrogen atoms in organic functions plus terminal B-H hydrogen
atoms were set riding on their parent atoms in calculated positions;
all other hydrogen atoms were located in difference maps and
allowed positional refinement. All hydrogen atoms were assigned
calculated isotropic thermal parameters defined as Uiso(H) ) 1.2
× Uiso(parent) or Uiso(H) ) 1.5 × Uiso(parent) for methyl groups.
Synthesis of [9,9-dppe-4,8-I2-arachno-9,6-PtCB8H10] and [9,9-
dppe-4-{O(CH2)4I}-8-I-arachno-9,6-PtCB8H10]. Compound 7 (0.100
g, 0.14 mmol) was dissolved in CH2Cl2 (10 mL) and cooled to
-78 °C. A CH2Cl2 (10 mL) solution of I2 (0.100 g, 0.28 mmol)
was slowly added over a period of 1 h. When addition was
complete, the solution was allowed to warm to ambient temperature
and then water (20 mL) and Na2S2O3 (0.100 g, 0.63 mmol) were
added. The mixture was shaken and the CH2Cl2 layer separated.
Two further extractions with CH2Cl2 (2 × 20 mL) were performed,
and the combined extracts were dried over MgSO4 and then
evaporated to dryness in vacuo. The resulting residue was redis-
solved in CH2Cl2 (ca. 5 mL) and added to a chromatography
column, eluting with CH2Cl2-petroleum ether (3:2). A colorless
solution was collected and evaporated in vacuo to give [9,9-dppe-
4,8-I2-arachno-9,6-PtCB8H10] as a white powder (12; 0.110 g, 82%).
In an analogous reaction using THF as the solvent, the major
product of the reaction was [9,9-dppe-4{O(CH2)4I}-8-I-arachno-
9,6-PtCB8H10] (13; 0.091 g, 63%), along with compound 12 (0.032
g, 24%), which eluted from the column before compound 13.
Structure Determinations. Experimental data for compounds
1, 4, 8, 11, and 13 are listed in Table 3. The solid-state structures
of compounds 5–7, 9, and 12 were also determined by X-ray
diffraction studies; experimental data for these compounds can be
found in the crystallographic information file (CIF) in the Sup-
porting Information. Data were collected at 110(2) K on a Bruker-
Nonius X8 APEX CCD area-detector diffractometer using Mo KR
X-radiation (λ ) 0.71073 Å). Several sets of narrow data “frames”
were collected at different values of θ, for various initial values of
ꢁ and ω, and using 0.5° increments of ꢁ or ω. The data frames
Acknowledgment. We acknowledge the Robert A. Welch
Foundation (Grant AA-0006) and Baylor University for
support. The Bruker-Nonius X8 APEX diffractometer was
purchased with funds received from the National Science
Foundation Major Instrumentation Program (Grant CHE-
0321214).
Supporting Information Available: Full details of the crystal
structure analyses in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM7012056
(25) APEX 2, version 2.1-0; Bruker AXS: Madison, WI, 2003.
(26) Sheldrick, G. M. SHELXS-97; University of Göttingen: Germany,
1997.
(27) Sheldrick, G. M. SHELXL-97; University of Göttingen: Germany,
1997.