Iridium-iron-monocarborane clusters from oxidative insertion reactions of [IrCl(CO)(PPh3)2] with ferracarborane anions

Article abstract of DOI:10.1021/ja065042n

The nine-vertex ferracarborane salt [N(PPh₃)₂][7,7,7- (CO)₃-closo-7,1-FeCB₇H₈] (1) reacts with an excess of [IrCl(CO)(PPh₃)₂] in the presence of TI[PF ₆] to form, successively, the bimetallic species [7,7,9,9,9-(CO) ₅-7-PPh₃-closo-7,9,1-IrFeCB₆H₇] (3), in which one {BH} vertex has formally been subrogated by an {Ir(CO) ₂(PPh₃)} unit, and the trimetallic complex [6,7,9-{Ir(CO)(PPh₃)₂}-7,9-(μ-H)₂-7,9,9-(CO) ₃-7-PPh₃-closo-7,9,1-IrFeCB₆H₆] (5), which contains an {FeIr₂} triangle. The {FeIrCB₆} core in 5 resembles that in 3 with, in addition, the Fe...Ir connectivity being spanned by an {Ir(CO)(PPh₃)₂} fragment and the consequent Fe-Ir and Ir-Ir bonds bridged by hydrido ligands. In contrast to the above, treatment of the 10-vertex diferracarborane salt [N(PPh₃) ₂][6,6,6,10,10,10-(CO)₆-closo-6,10,1-Fe₂CB ₇H₈] (2) with the same reagents yields two very different, trimetallic complexes, namely [8,10-{Ir(μ-PPh₂)(Ph)(CO)(PPh ₃)}-8-(μ-H)-6,6,6,10,10-(CO)₅-closo-6,10,1-Fe ₂CB₇H₇] (6) and [6,7,10-{Fe(CO) ₃}-6-(μ-H)-6,10,10,10-(CO)₄-6-PPh₃-closo-6, 10,1-IrFeCB₇H₇] (7). In 6, an exo-polyhedral {IrPh(CO)(PPh₃)} moiety is attached to a {closo-6,10,1-Fe ₂CB₇} framework via a PPh₂-bridged Fe-Ir bond and a B-H-Ir agostic-type linkage, the iridium center formally having inserted into one P-Ph bond of a PPh₃ unit. Complex 7 contains an {IrFeCB ₇} cluster core, with an exo-polyhedral {Fe(CO)₃} moiety bridging a {BIrFe} triangular face and with an additional Ir-H-Fe bridge. However, this metal atom arrangement reveals that iridium and iron moieties have exchanged exo- and endo-polyhedral sites with respect to the 10-vertex metallacarborane. X-ray diffraction studies upon 3, 5, 6, and 7 confirmed their novel structural features; some preliminary reactivity studies upon these compounds are also reported.

Full text of DOI:10.1021/ja065042n

Published on Web 12/05/2006
Iridium-Iron-Monocarborane Clusters from Oxidative
Insertion Reactions of [IrCl(CO)(PPh3)2] with Ferracarborane
Anions
Andreas Franken, Thomas D. McGrath,* and F. Gordon A. Stone*
Contribution from the Department of Chemistry & Biochemistry, Baylor UniVersity,
Waco, Texas 76798-7348
Received July 14, 2006; E-mail: tom_mcgrath@baylor.edu; gordon_stone@baylor.edu
Abstract: The nine-vertex ferracarborane salt [N(PPh3)2][7,7,7-(CO)3-closo-7,1-FeCB7H8] (1) reacts with
an excess of [IrCl(CO)(PPh3)2] in the presence of Tl[PF6] to form, successively, the bimetallic species
[7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3), in which one {BH}- vertex has formally been subrogated
by an {Ir(CO)2(PPh3)} unit, and the trimetallic complex [6,7,9-{Ir(CO)(PPh3)2}-7,9-(µ-H)2-7,9,9-(CO)3-7-
PPh3-closo-7,9,1-IrFeCB6H6] (5), which contains an {FeIr2} triangle. The {FeIrCB6} core in 5 resembles
that in 3 with, in addition, the Fe‚‚‚Ir connectivity being spanned by an {Ir(CO)(PPh3)2} fragment and the
consequent Fe-Ir and Ir-Ir bonds bridged by hydrido ligands. In contrast to the above, treatment of the
10-vertex diferracarborane salt [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10, 1-Fe2CB7H8] (2) with the same
reagents yields two very different, trimetallic complexes, namely [8,10-{Ir(µ-PPh2)(Ph)(CO)(PPh3)}-8-
(µ-H)-6,6,6,10,10-( CO)5-closo-6,10,1-Fe2CB7H7] (6) and [6,7,10-{Fe(CO)3}-6-(µ-H)-6,10,10,10-(CO)4-6-
PPh3-closo-6,10,1-IrFeCB7H7] (7). In 6, an exo-polyhedral {IrPh(CO)(PPh3)} moiety is attached to a {closo-
6,10,1-Fe2CB7} framework via a PPh2-bridged Fe-Ir bond and a B-HFIr agostic-type linkage, the iridium
center formally having inserted into one P-Ph bond of a PPh3 unit. Complex 7 contains an {IrFeCB7}
cluster core, with an exo-polyhedral {Fe(CO)3} moiety bridging a {BIrFe} triangular face and with an
additional Ir-H-Fe bridge. However, this metal atom arrangement reveals that iridium and iron moieties
have exchanged exo- and endo-polyhedral sites with respect to the 10-vertex metallacarborane. X-ray
diffraction studies upon 3, 5, 6, and 7 confirmed their novel structural features; some preliminary reactivity
studies upon these compounds are also reported.
Introduction
We have been investigating the possibility of stepwise
addition of metal centers to metallacarborane clusters as a
possible route to polymetallic cluster hybrids. Such an approach
has the additional advantage that it can provide access to
heteropolymetallic products by judicious choice of the added
metal reagents. Specifically, we have employed metallacarbo-
rane complexes containing monocarbon carborane ligands,
because the resulting clusters often retain an overall anionic
charge as a consequence of the high formal charge (typically
3- or more) upon the carborane fragment itself.3 Thus, addition
of an electrophilic transition metal-ligand fragment to a
metallacarborane anion can afford products containing multiple
metal centers. Among the latter class, we have recently
synthesized bi-, tri-, and tetrametallic derivatives of 11-vertex
rhenium-,1k,4,5 manganese-,6 and molybdenum-monocarbo-
The assembly of “hybrid clusters”, that is, species that contain
both metal and (hetero)borane cluster units, is an area that has
intrigued and challenged cluster chemists for some time and
which continues to present significant synthetic obstacles.1 Such
compounds may display structural and electronic properties
typical of both boron- and metal-based clusters and also unique
features at the interface of the two. However, synthetic routes
to these species are often limited as borane derivatives may be
rather reducing, resulting in elimination of the metallic portion.
Activation of the boron reagent to open and accept multiple
metal centers is often also necessary. Conversely, the reducing
tendency of boranes has in some cases been useful in encourag-
ing the growth of very high nuclearity clusters.2
(1) Examples include: (a) Venable, T. L.; Sinn, E.; Grimes, R. N. Inorg. Chem.
1982, 21, 904. (b) Wynd, A. J.; Robbins, S. E.; Welch, D. A.; Welch, A.
J. J. Chem. Soc., Chem. Commun. 1985, 819. (c) Do, Y.; Knobler, C. B.;
Hawthorne, M. F. J. Am. Chem. Soc. 1987, 109, 1853. (d) Bown, M.;
Fontaine, X. L. R.; Greenwood, N. N.; MacKinnon, P.; Kennedy, J. D.;
Thornton-Pett, M. J. Chem. Soc., Dalton Trans. 1987, 2781. (e) Carr, N.;
Gimeno, M. C.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1990, 2247.
(f) Jeffery, J. C.; Jelliss, P. A.; Stone, F. G. A. J. Chem. Soc., Dalton Trans.
1994, 25. (g) Nishiara, Y.; Deck, K. J.; Shang, M.; Fehlner, T. P.
Organometallics 1994, 13, 4510. (h) Liao, Y.-H.; Mullica, D. F.; Sappen-
field, E. L.; Stone, F. G. A. Organometallics 1996, 15, 5102. (i) Lei, X.;
Shang, M.; Fehlner, T. P. Organometallics 2000, 19, 5226. (j) Ghosh, S.;
Fehlner, T. P.; Noll, B. C. Chem. Commun. 2005, 3080. (k) McGrath, T.
D.; Du, S.; Hodson, B. E.; Stone, F. G. A. Organometallics 2006, 25, 4444.
(2) For example: (a) Schmid, G.; Pfeil, R.; Boese, R.; Brandermann, F.; Meyer,
S.; Calis, G. H. M.; van der Velden, J. W. A. Chem. Ber. 1981, 114, 3634.
(b) Schmid, G.; Huster, W. Z. Naturforsch. B 1986, 41, 1028. See also:
(c) Hall, K. P.; Mingos, D. M. P. Prog. Inorg. Chem. 1984, 32, 237.
(3) (a) McGrath, T. D.; Stone, F. G. A. J. Organomet. Chem. 2004, 689, 3891.
(b) McGrath, T. D.; Stone, F. G. A. AdV. Organomet. Chem. 2005, 53, 1.
(4) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Organometallics
2003, 22, 2842.
(5) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Angew. Chem., Int.
Ed. 2003, 42, 5728.
(6) 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.
9
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J. AM. CHEM. SOC. 2006, 128, 16169-16177
16169

A R T I C L E S
Chart 1
Franken et al.
Chart 3
ranes,7 including a unique pair of tetrametallic “butterfly”
complexes that are supported by a metallacarborane substrate.
As part of these studies, we are also investigating reactions of
the newly available8 ferracarborane salts [N(PPh3)2][7,7,7-(CO)3-
closo-7,1-FeCB7H8] (1) and [N(PPh3)2][6,6,6,10,10,10-(CO)6-
closo-6,10,1-Fe2CB7H8] (2) (see Chart 1) with cationic transition
metal fragments. Whereas reactions of fragments such as {Cu-
(PPh3)}+ or {Ag(PPh3)}+ with 1 and 2 give relatively simple
bi- and trimetallic complexes, respectively,8 we have found that
use of Vaska’s compound, [IrCl(CO)(PPh3)2], ostensibly a
source of the {Ir(CO)(PPh3)2}+ moiety, affords both discrete
and condensed cluster products. These novel and often unex-
pected species are the subject of this report. (Vertex numbering
in the closed 9- and 10-vertex clusters discussed herein is shown
in Chart 2.)
complexes 3 and 5 were obtained in good yields, compound 4
was only a minor product and was often isolated only in very
low and variable amounts. The compounds were separable by
column chromatography on silica gel and were characterized
by the data listed in Tables 1-3. However, the structures of all
three products initially were definitively established by X-ray
diffraction studies, the results of which are depicted in Figures
1-3, respectively, and are appropriately discussed before the
compounds’ spectral data.
Chart 2
As is immediately apparent from Figure 1 and Chart 3,
compound 3 is a single-cluster metallacarborane. It consists of
a nine-vertex polyhedron, with {Ir(CO)2(PPh3)} and {Fe(CO)3}
vertexes in adjacent five-coordinate sites and joined by a metal-
metal bond (Ir(1)-Fe(1) ) 2.7128(11) Å), and with the carbon
atom in a four-coordinate position, all of these sites being
consistent with established preferences.9,10 The metal-metal
distance here is similar to that (2.706(2) Å) in the iridaferrabo-
Results and Discussion
Syntheses and Structural Studies. Three neutral iridium-
iron-carborane compounds, [7,7,9,9,9-(CO)5-7-PPh3-closo-
7,9,1-IrFeCB6H7] (3), [6,8,8,8-(CO)4-6-H-6-PPh3-10-OPPh3-
closo-6,8,1-IrFeCB7H7] (4), and [6,7,9-{Ir(CO)(PPh3)2}-7,9-(µ-
H)2-7,9,9-(CO)3-7-PPh3-closo-7,9,1-IrFeCB6H6] (5) (see Chart
3), were prepared by reaction of the ferracarborane salt 1 with
an excess of the iridium synthon [IrCl(CO)(PPh3)2], with Tl-
[PF6] added to remove chloride as insoluble TlCl. Although
(9) (a) Williams, R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67. (b) Ott,
J. J.; Gimarc, B. M. J. Am. Chem. Soc. 1986, 108, 4303.
(10) (a) Grimes, R. N. In ComprehensiVe Organometallic Chemistry; Wilkinson,
G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon Press: Oxford, U.K.,
1982; Vol. 1, Section 5.5. (b) Grimes, R. N. In ComprehensiVe Organo-
metallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon Press: Oxford, U.K., 1995; Vol. 1, Chapter 9.
(7) Lei, P.; McGrath, T. D.; Stone, F. G. A. Chem. Commun. 2005, 3706.
(8) Franken, A.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005, 24,
5157.
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16170 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Iridium−Iron−Monocarborane Clusters
A R T I C L E S
Table 1. Analytical and Physical Data
analb (%)
1
compd
color
ν
max(CO)a/cm-
C
H
[7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3)
[6,7,9-{Ir(CO)(PPh3)2}-7,9-(µ-H)2-7,9,9-
orange
green
2071 s, 2031 w, 1985 s
2017 s, 1996 s, 1961 s, 1913 s
39.3 (39.3)
49.8 (49.6)
3.2 (3.0)
3.8 (3.8)
(CO)3-7-PPh3-closo-7,9,1-IrFeCB6H6] (5)
[8,10-{Ir(µ-PPh2)(Ph)(CO)(PPh3)}-8-(µ-H)-6,6,6,10,10-
(CO)5-closo-6,10,1-Fe2CB7H7] (6)
[6,7,10-{Fe(CO)3}-6-(µ-H)-6,10,10,10-(CO)4-6-
PPh3-closo-6,10,1-IrFeCB7H7] (7)
orange
2050 s, 2045 s, 1996 s, 1951 w
2067 s, 2036 s, 2020 s, 1999 s, 1928 m
46.9 (47.2)
36.4 (36.1)
3.6 (3.5)
3.0 (2.8)
yellow-green
[9,9,9-(CO)3-7,7-(CNXyl)2-7-PPh3-closo-7,9,1-IrFeCB6H7] (8)
[8,10-{Ir(µ-PPh2)(Ph)(CNXyl)(PPh3)}-8-(µ-H)-6,6,10,10-
(CO)4-6-CNXyl-closo-6,10,1-Fe2CB7H7] (9)
red
orange
2015 s, 1957 s
1998 s, 1970 s, 1935 m
51.2 (51.0)
51.7 (52.0)c
4.1 (4.3)
4.4 (4.2)
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. In
addition, νmax(NC): for 8, 2150 s, 2124 s cm-1; for 9, 2142 s, 2123 s cm-1
for 9, 2.0 (2.0). c Cocrystallized with 1.0 mol equiv of CH2Cl2.
.
b Calculated values are given in parentheses. In addition, % N: for 8, 2.8 (3.0);
Table 2. 1H and 13C NMR Dataa
compd
1H/δb
13C/δc
3
7.67-7.25 (m, 15H, Ph), 2.13 (br s, 1H, cage CH)
213.7 (Fe-CO), 176.3 (d, J(PC) ) 9, Ir-CO),
133.7-128.6 (Ph), 19.1 (br, cage C)
5
6
7.47-6.98 (m, 45H, Ph), 3.67 (br s, 1H, cage CH),
-17.31 (dd, J(PHtransoid) ) 65, J(PHcisoid) )
14, 1H, Ir-H-Ir), -18.85 (dd, J(PHcisoid) )
18 and 10, 1H, Ir-H-Fe)
226.7 (Fe-CO), 169.3 (d, J(PC) ) 26, Irendo-CO),
167.8 (dd, J(PC) ) 27 and 27, Irexo-CO),
133.1-127.9 (Ph), 25.8 (br, cage C)
7.45-6.81 (m, 30H, Ph), 6.91 (br s, 1H, cage CH),
-9.61 (br, 1H, B-H F Ir)
219.2 (d, J(PC) ) 30, Fe(10)-CO), 210.3 (Fe(6)-CO),
178.1 (dd, J(PCtransoid) ) 99, J(PCcisoid) ) 6, Ir-CO),
133.6-127.9 (Ph), 103.3 (br, cage C)
212.0 (Fe-CO), 207.7 (Fe-CO), 178.8 (d, J(PC) )
14, Ir-CO), 134.5-128.4 (Ph), 106.0 (br, cage C)
217.4 (CO), 138.5 (d, J(PC) ) 10, CtN), 135.2-126.7 (Ph and C6H3),
18.6 (Me), 16.2 (br, cage C)
222.6 (br, CO), 218.1 (br, CO), 215.1 (CO), 212.8 (CO), 173.3 (Fe-CtN),
141.2 (d, J(PC) ) 9, Ir-CtN), 135.7-121.7 (Ph and C6H3),
101.7 (br, cage C), 18.6 (Me), 18.5 (Me)
7
8
9
8.39 (br s, 1H, cage CH), 7.45 (m, 15H, Ph),
-17.22 (d, J(PH) ) 7, 1H, Fe-H-Ir)
7.40-7.03 (m, 21H, Ph and C6H3), 2.39 (s, 6H, Me),
2.32 (s, 6H, Me), 1.87 (br s, 1H, cage CH)
7.45-6.82 (m, 36H, Ph and C6H3), 6.70 (br s, 1H, cage CH),
2.19 (s, 6H, Me), 2.09 (s, 6H, Me),
-9.85 (br, 1H, B-H F Ir)
a Chemical shifts (δ) in ppm, coupling constants (J) in hertz, and measurements at ambient temperatures in CD2Cl2. b Resonances for terminal BH protons
c
occur as broad unresolved signals in the range δ ca. -1 to +3. 1H-decoupled chemical shifts are positive to high frequency of SiMe4.
Table 3. 11B and 31P NMR Dataa
compd
11B/δb
31P/δc
3
5
6
40.4 (2B), -11.2 (2B), -12.8 (2B)
108.4 (B(6)), 46.9, -6.7 (2B), -8.1, -14.1
34.2 (B(8)), 13.7 (2B), 11.8, 9.9, -9.5, -13.9
8.6
5.1, 2.7, -20.3 (br)
137.1 (µ-PPh2),
19.9 (PPh3)
18.9
7
8
9
80.6 (B(7)), 45.3, 15.7, 8.2, 4.2, -3.6, -12.6
41.2 (2B), -13.4 (4B)
33.6 (B(8)), 13.9 (2B), 12.2 (2B), -10.4, -13.8 125.5 (µ-PPh2),
8.7
25.0 (PPh3)
a Chemical shifts (δ) in ppm, coupling constants (J) in hertz, and
measurements at ambient temperatures in CD2Cl2. b 1H-decoupled chemical
shifts are positive to high frequency of BF3·Et2O (external); resonances are
of unit integral except where indicated. c 1H-decoupled chemical shifts are
positive to high frequency of 85% H3PO4 (external).
Figure 1. Structure of 3 showing the crystallographic labeling scheme. In
this and subsequent figures, thermal ellipsoids are drawn with 40%
probability, only chemically significant H atoms are shown, and all but the
ipso carbon atoms of phosphorus-bound Ph groups are omitted. Selected
distances (Å) and angles (deg) are as follows: Ir(1)-Fe(1) 2.7128(11),
B(3)-Ir(1) 2.391(8), B(4)-Ir(1) 2.382(8), B(6)-Ir(1) 2.226(8), B(8)-
Ir(1) 2.229(7), B(2)-Fe(1) 2.335(8), B(5)-Fe(1) 2.294(8), B(6)-Fe(1)
2.119(9), B(8)-Fe(1) 2.116(7); P(1)-Ir(1)-Fe(1) 162.45(5).
rane [1,1,1,2,2-(CO)5-2,4-(PPh3)2-closo-1,2-FeIrB5H4].11 Clearly,
in the reaction, one {BH} vertex of the precursor has been lost,
a result that is not uncommon in such reactions,10,12 and its site
formally assumed by the incoming iridium center. The details
of the formation of 3 are not entirely clear, but it is notable that
the insertion of the iridium fragment is an oxidative process,
with the metal oxidation state in the product formally +III
compared to +I in the starting Vaska’s compound. In this
respect, the reaction here may be compared with the earlier
reported formation of the nine-vertex iridacarborane [7-CO-7,7-
(PPh3)2-closo-7,1-IrCB7H8] from [closo-1-CB7H8]- and the
same metal reagent, although in that case no Tl[PF6] was added
and no {BH} unit was lost.13 In the present case, the iridium
center additionally undergoes PPh3 f CO substitution, but as
(11) Bould, J.; Rath, N. P.; Fang, H.; Barton, L. Inorg. Chem. 1996, 35, 2062.
(12) (a) Kennedy, J. D. Prog. Inorg. Chem. 1984, 32, 519. (b) Kennedy, J. D.
Prog. Inorg. Chem. 1986, 34, 211. (c) Barton, L.; Srivastava, D. K. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995; Vol. 1,
Chapter 8.
(13) St´ıbr, B.; Kennedy, J. D.; Thornton-Pett, M.; Drada´kova´, E. Collect. Czech.
Chem. Commun. 1992, 57, 1439.
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A R T I C L E S
Franken et al.
coupling of ca. 9 Hz due to the iridium-bound phosphine. This
ligand itself gives rise to a corresponding singlet at δ 8.6 in the
31P{1H} NMR spectrum.
The extrusion of a {BH} vertex in the formation of 3 is
perhaps surprising given the known14 stability of 10-vertex
systems. However, the identity of compound 4, whose structure
is shown in Figure 2, may provide some suggestions as to the
processes involved. The molecule of 4 is again a single-cluster
species and consists of a closo-10-vertex {6,8,1-IrFeCB7} cluster
to which is appended at B(10) a two-electron donor Ph3PdO
ligand (B(10)-O(10) ) 1.461(7) Å). The latter substituent
lowers the overall charge upon the formal {arachno-CB7H7-
(OPPh3)} carborane moiety to 4- (cf. 5- for the unsubstituted
{arachno-CB6H7} unit in 3), and correspondingly the iridium
center bears an H- ligand, rather than a CO group as in 3, with
the overall complex again being neutral. Traces of adventitious
O2 or H2O in the reaction mixture might have generated
Ph3PO molecules from the PPh3 liberated during formation of
3, or the oxide might be a contaminant in the [IrCl(CO)(PPh3)2]
reagent. In our experience, ligand-borane adducts [L‚BH3] are
often observed (11B NMR) as side products in reactions where
boron vertexes may be eliminated. In the present system,
arguably, loss of the ligand-substituted B(10) vertex in com-
pound 4 (as [Ph3PO·BH3]) could lead directly to a closed
{IrFeCB6} intermediate and thence to compound 3 itself by CO
scavenging.
Figure 2. Structure of 4 showing the crystallographic labeling scheme.
Selected distances (Å) and angles (deg) are as follows: B(2)-Ir(1)
2.259(6), B(3)-Ir(1) 2.272(6), B(7)-Ir(1) 2.321(6), B(9)-Ir(1) 2.328(6),
B(10)-Ir(1) 2.087(6), B(4)-Fe(1) 2.203(6), B(5)-Fe(1) 2.195(7), B(7)-
Fe(1) 2.252(6), B(9)-Fe(1) 2.254(6), B(10)-Fe(1) 2.051(5), B(10)-O(10)
1.461(7), O(10)-P(2) 1.546(3), Ir(1)-H(6) 1.689(19); O(10)-B(10)-
Fe(1) 112.0(4), O(10)-B(10)-Ir(1) 125.3(3), B(10)-O(10)-P(2)
135.4(3).
Spectroscopic data for compound 4 (see the Experimental
Section) are fully consistent with the solid-state structure. In
particular, the 11B{1H} NMR spectrum shows four signals in
the ratio 1:2:2:2, with the highest frequency signal (δ 94.6)
remaining a singlet upon retention of proton coupling. This is
assigned to the unique vertex bearing the OdPPh3 substituent:
the high chemical shift is typical of a four-connected boron atom
in such clusters13,15 and the attached oxygen donor would be
expected also to cause further deshielding. Correspondingly, the
phosphine oxide group gives rise to a singlet (δ 46.2) in the
31P{1H} NMR spectrum, with the iridium-bound PPh3 found
to higher field (δ 12.0) and similar to that in compound 3.
Notably, there is also tentative evidence of a 10-PPh3 analogue
of compound 4 in 11B{1H} NMR spectra of the reaction mixture,
with a low-field doublet (δ 76.1, J(PB) ) 120 Hz) that again
has the high chemical shift typical of a four-connected boron
in 10-vertex metallacarborane clusters. Such a complex could
also be an intermediate that leads (via Ph3P‚BH3 loss) to
compound 3 in a manner similar to that described above for 4.
Attempts to isolate this proposed B-PPh3 species, however, were
unsuccessful, perhaps suggestive that it is indeed transitory en
route to compound 3.
The structure of compound 5 was rather more unexpected
than that of either 3 or 4. It is seen (Figure 3) to consist of the
same nine-vertex {closo-7,9,1-IrFeCB6} core as in 3, but with
an additional iridium moiety appended exo-polyhedrally. Indeed,
we have been able to confirm experimentally that reaction of
bimetallic 3 with an excess of [IrCl(CO)(PPh3)2]/Tl[PF6] does
afford the trimetallic product 5. In the latter, the intracluster
Fe-Ir distance Ir(1)-Fe(1) is 2.6525(5) Å, significantly shorter
than that in 3, while the B(3)‚‚‚B(4) (2.038(5) Å) and B(2)-
Figure 3. Structure of 5 showing the crystallographic labeling scheme.
Selected distances (Å) and angles (deg) are as follows: Ir(1)-Fe(1)
2.6525(5), Ir(1)-Ir(2) 2.9517(3), Ir(1)-H(21) 1.84(3), Ir(1)-B(3)
2.389(3), Ir(1)-B(4) 2.328(4), Ir(1)-B(6) 2.147(3), Ir(1)-B(8) 2.187(4),
Fe(1)-B(2) 2.306(4), Fe(1)-B(5) 2.230(4), Fe(1)-B(6) 2.058(3), Fe(1)-
B(8) 2.070(4), Fe(1)-H(31) 1.63(3), Fe(1)-Ir(2) 2.8222(5), Ir(2)-B(6)
2.083(4), Ir(2)-H(21) 1.71(3), Ir(2)-H(31) 1.73(3); Fe(1)-Ir(1)-
Ir(2) 60.194(12), Ir(1)-Fe(1)-Ir(2) 65.167(12), Fe(1)-Ir(2)-Ir(1)
54.639(10).
the overall reaction forming 3 is clearly complex it would be
unwise to speculate further on this one detail of the whole
process. An additional feature revealed by the X-ray diffraction
study of 3 is elongation of the B(3)‚‚‚B(4) (2.056(12) Å) and
B(2)-B(5) (1.986(12) Å) connectivities compared to typical
B-B distances, a feature common in such systems.8
The NMR data for compound 3 are consistent with the solid-
state structure. Thus, the 11B{1H} NMR spectrum reveals a 2:2:2
pattern of resonances, in agreement with molecular Cs symmetry
and with loss of one boron vertex of the starting carborane
1
during the reaction. In addition, the H and 13C{1H} NMR
spectra show resonances at δ 2.13 and 19.1, respectively, typical
positions for the cage {CH} unit in a nine-vertex cluster.8 The
latter spectrum also shows two resonances for metal-bound CO
ligands, at δ 213.7 and 176.3, that are assigned to the Fe-CO
and Ir-CO units, respectively, with the latter showing J(PC)
(14) Schleyer, P. v. R.; Najafian, K. Inorg. Chem. 1998, 37, 3454.
(15) See also, for example: (a) Evans, W. E.; Dunks, G. B.; Hawthorne, M. F.
J. Am. Chem. Soc. 1973, 95, 4565. (b) Briguglio, J. J.; Sneddon, L. G.
Organometallics 1986, 5, 327.
9
16172 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Iridium−Iron−Monocarborane Clusters
A R T I C L E S
Chart 4
B(5) (1.991(5) Å) separations are similarly elongated as those
in 3. The exo-polyhedral iridium center in 5 is an {Ir(CO)-
(PPh3)2} fragment that has displaced one CO group from each
of the cluster metal vertexes and which is attached via two
metal-metal bonds to form an {FeIr2} triangle, with distances
Ir(1)-Ir(2) ) 2.9517(3) and Fe(1)-Ir(2) ) 2.8222(5) Å. Both
of the latter two connectivities are bridged by hydrido ligands,
which were located in the X-ray diffraction experiment (Ir(1)-
H(21) ) 1.84(3), Ir(2)-H(21) ) 1.71(3), Ir(2)-H(31) )
1.73(3), Fe(1)-H(31) ) 1.63(3) Å). The coordination sphere
around Ir(2) is completed by a direct Ir-B σ bond (Ir(2)-B(6)
) 2.083(4) Å). This last feature is shorter than the η-bonded
Ir(1)-B distances in 5 (range 2.147(3)-2.389(3) Å) but similar
in length to exo-IrIII-B σ bonds in related species (range
2.071(14)-2.163(7) Å).16
A further notable aspect of the structure of 5 is that B(6) is
also bonded to the other two metal atoms (Ir(1)-B(6) )
2.147(3), Fe(1)-B(6) ) 2.058(3) Å). Thus, the tetrahedral {BIr2-
Fe} moiety that includes B(6) may be viewed as being fused to
the parent {IrFeCB6} cluster via the {B(6)Fe(1)Ir(1)} face, so
that overall this species has a condensed “double cluster”
architecture. This “capped” closo-9-vertex structure in principle
would formally be converted to a conventional closo-10-vertex
one by a diamond-square-diamond operation17 upon the
B(8)Ir(1)Ir(2)Fe(1) “diamond”. In cluster electron counting
terms,9a,18 the fused-cage architecture of 5 has 10 skeletal
electron pairs (SEPs), as is to be expected for a capped closo-
9-vertex species. By way of comparison, the cluster skeletons
of the precursor 1 (a closo-9-vertex species) and of compounds
3 and 4 (closo-9- and -10-vertex species, respectively), possess
10, 10, and 11 SEPs, respectively, and thus also conform to the
accepted electron counting rules.
for the Fe-CO groups, and at δ 169.3 (d, J(PC) ) 26 Hz) and
167.8 (dd, J(PC) ) 27 and 27 Hz) for the carbonyls on the
endo- and exo-polyhedral iridium centers, respectively. As
would be expected, the 31P{1H} NMR spectrum shows three
singlet resonances, but with no mutual J(PP) coupling discern-
ible. The first resonance (δ 5.1) becomes a broad doublet-of-
doublets in a 1H-coupled 31P NMR spectrum (J(HP) ca. 65 and
10 Hz) and is assigned to P(2) of the PPh3 group on Ir(2)
(crystallographic numbering), which is transoid with respect to
the Ir-H-Ir hydride. The second 31P signal (δ 2.7) shows a
small doublet splitting (J(HP) ca. 10 Hz) upon retention of
proton coupling and is attributed to the phosphine bound to
Ir(1). No J(HP) coupling could be discerned for the third peak
(δ -20.3), as it is broadened by unresolved 11B-31P coupling
and hence is assigned to P(3) of the PPh3 group that is transoid
to the Ir-B σ bond.
In contrast to the formation of 3-5 from the monoiron
precursor 1, the compounds [8,10-{Ir(µ-PPh2)(Ph)(CO)(PPh3)}-
8-(µ-H)-6,6,6,10,10-(CO)5-closo-6,10,1-Fe2CB7H7] (6) and [6,7,-
10-{Fe(CO)3}-6-(µ-H)-6,10,10,10-(CO)4-6-PPh3-closo-6,10,1-
IrFeCB7H7] (7) (Chart 4) are formed when the diiron compound
2 was stirred with [IrCl(CO)(PPh3)2] and Tl[PF6] in CH2Cl2 at
ambient temperature. These two compounds can conveniently
be separated by column chromatography on silica and were
characterized by the data in Tables 1-3. As before, their precise
constitutions were determined by single-crystal X-ray diffraction
studies. These experiments revealed the structures shown in
Figures 4 and 5, respectively.
All NMR data for compound 5 are in accord with the results
of the X-ray study. In its 11B{1H} NMR spectrum, four separate
resonances with relative intensities 1:1:2:1:1 are seen, of which
one very deshielded signal (δ 108.4) remains a singlet in the
fully coupled 11B spectrum and may be assigned to the boron
1
atom involved in the direct B(6)-Ir linkage.19 The H NMR
spectrum shows diagnostic multiplet resonances for the two
metal-bridging hydrides, at δ -17.31 (dd, J(PHtransoid) ) 65 Hz
and J(PHcisoid) ) 14 Hz) and -18.85 (dd, J(PHcisoid) ) 18 and
10 Hz); no mutual coupling between the two hydrides could be
resolved, and both signals become singlets in a 1H{31P} NMR
spectrum. Of these data, the former resonance is assigned to
the Ir-H-Ir bridge on the basis of the large coupling expected
for a transoid arrangement, so that the resonance showing the
smaller coupling must be due to the Ir-H-Fe bridge. A broad
peak at δ 3.67 in the same spectrum, corresponding in intensity
to one proton, may be assigned to the cage CH group, with the
corresponding carbon resonance at δ 25.8 in the 13C{1H} NMR
spectrum. Therein are also seen three CO resonances: at δ 226.7
(16) (a) Churchill, M. R.; Hackbarth, J. J. Inorg. Chem. 1975, 14, 2047. (b)
Fernandez, J. R.; Helm, G. F.; Howard, J. A. K.; Pilotti, M. U.; Stone, F.
G. A. J. Chem. Soc., Dalton Trans. 1990, 1747. (c) Bae, J.-Y.; Lee, Y.-J.;
Kim, S.-J.; Ko, J.; Cho, S.; Kang, S. O. Organometallics 2000, 19, 1514.
(d) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. J. Organomet.
Chem. 2000, 604, 170. (e) Herberhold, M.; Yan, H.; Milius, W.; Wrack-
meyer, B. J. Chem. Soc., Dalton Trans. 2001, 1782. (f) Herberhold, M.;
Yan, H.; Milius, W.; Wrackmeyer, B. Chem.-Eur. J. 2002, 8, 388.
(17) Lipscomb, W. N. Science 1966, 153, 373.
Compound 6 (Figure 4) is seen to be a single-cluster species
and retains the {closo-Fe2CB7} core of the precursor 2, with
the appendage of an iridium unit in an exo-polyhedral site. Thus,
compound 6, like the anion of 2, is a closo-10-vertex cluster
(18) (a) Wade, K. AdV. Inorg. Chem. Radiochem. 1976, 18, 1. (b) Mingos, D.
M. P. Acc. Chem. Res. 1984, 17, 311.
(19) Brew, S. A.; Stone, F. G. A. AdV. Organomet. Chem. 1993, 35, 135.
9
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A R T I C L E S
Franken et al.
transition metal centers have been known for several decades20
and are well-documented as being of considerable importance
in some catalytic processes.21 The present reaction system,
forming 6, also has a close parallel in the reactions of the related
iridium reagent [IrMe(CO)(PR3)2] with [MH(CO)3(η-C5H5)] (M
) Mo, W; R ) p-tolyl,22 Ph23). In these, the reactions are
proposed to occur between an {Ir(CO)(PR3)2}+ cation and an
{M(CO)3(η-C5H5)}- anion, of which the latter may be thought
of as quasi-isolobal24 with the [Fe(CO)3{η-cage}]- anion of
compound 2.
The NMR data for compound 6 (Tables 2 and 3) are in
complete agreement with the structure established by the X-ray
diffraction study. In the 11B{1H} NMR spectrum, six signals
are seen, in the ratio 1:2:1:1:1:1, showing an absence of
molecular symmetry (the integral-2 peak being a 1 + 1
coincidence), consistent with the solid-state structure. The peak
to highest frequency (δ 34.2) shows only a very small
broadening (J(HB) not resolved) upon retention of proton
Figure 4. Structure of 6 showing the crystallographic labeling scheme.
Selected distances (Å) and angles (deg) are as follows: Fe(6)-Fe(10)
2.5626(9), B(2)-Fe(6) 2.182(6), B(3)-Fe(6) 2.178(5), B(7)-Fe(6)
2.203(5), B(9)-Fe(6) 2.212(5), Ir(1)-Fe(10) 2.7321(6), Fe(10)-P(1)
2.2379(12), B(7)-Fe(10) 2.185(5), B(8)-Fe(10) 2.025(5), B(9)-Fe(10)
2.224(5), Ir(1)-C(11) 2.122(4), Ir(1)-P(1) 2.2982(11), Ir(1)‚‚‚B(8)
2.348(4), Ir(1)-H(8) 1.65(4); P(1)-Fe(10)-Fe(6) 146.76(4), Fe(6)-
Fe(10)-Ir(1) 136.28(3), Fe(10)-P(1)-Ir(1) 74.06(3).
1
coupling and is assigned to the B-H F Ir group.19 In the H
NMR spectrum, the same unit gives rise to a broad resonance
at δ -9.61. There is a further signal in this spectrum at δ 6.91
that is in the region characteristic for a cage CH unit in such
10-vertex cages,8 with a corresponding and also characteristic
broad resonance at δ 103.3 in the 13C{1H} NMR spectrum.
Three signals for CO ligands are also seen therein, with those
bound to Fe(6) appearing as one singlet (δ 210.3) and the signal
for those bound to Fe(10) showing doublet structure (δ 219.2;
J(PC) ) 30 Hz) due to coupling with the phosphorus of the
µ-PPh2 unit. The third CO resonance, for the Ir-bound ligand,
is a doublet-of-doublets at δ 178.1 and shows a large coupling
(J(PC) ) 99 Hz) due to the transoid phosphide, with an
additional smaller coupling (J(PC) ) 6 Hz) to the cisoid PPh3
ligand. As expected, the 31P{1H} NMR spectrum shows two
resonances, at δ 137.1 and 19.9, which may be assigned on the
basis of their chemical shifts to the µ-PPh2 and Ir-PPh3 groups,
respectively, with no mutual coupling discernible between the
two types of phosphorus nuclei.
The structure determined for compound 7 is shown in Figure
5. The data were of sufficient quality that the site of the metal-
metal bridging hydride that is evident in NMR data (see below)
could reasonably be confirmed and, crucially, the heavy atom
arrangement was definitively established. Specifically, complex
7 contains a central {closo-6,10,1-IrFeCB7} cluster and an exo-
polyhedral iron unit, so that an iridium fragment has replaced
the formerly five-connected iron vertex at the 6-position in the
precursor and this {Fe(CO)3} moiety now caps a {BIrFe}
triangular face. Like compound 5, the overall structure of 7 may
be viewed as a condensed double cluster: here the 10-vertex
{closo-6,10,1-IrFeCB7} iridaferracarborane is face-fused with
a capping {IrFe2B} tetrahedron (Fe(1)-Ir(6) ) 2.7806(6),
Fe(1)-Fe(10) ) 2.6486(9), Ir(6)-Fe(10) 2.6036(7), B(7)-
Ir(6) ) 2.216(5), B(7)-Fe(10) ) 2.074(5), B(7)-Fe(1) )
2.004(4) Å). The exo-polyhedral Fe(1)-B(7) connectivity is a
Figure 5. Structure of 7 showing the crystallographic labeling scheme.
Selected distances (Å) and angles (deg) are as follows: Ir(6)-Fe(1)
2.7806(6), Ir(6)-Fe(10) 2.6036(7), Ir(6)-H(610) 1.79(4), B(2)-Ir(6)
2.225(5), B(3)-Ir(6) 2.246(5), B(7)-Ir(6) 2.216(5), B(9)-Ir(6) 2.247(5),
B(7)-Fe(10) 2.074(5), B(8)-Fe(10) 2.140(5), B(9)-Fe(10) 2.269(5),
Fe(1)-Fe(10) 2.6486(9), Fe(1)-H(610) 1.68(5), Fe(1)-B(7) 2.004(4);
Fe(10)-Ir(6)-Fe(1) 58.825(19), Ir(6)-Fe(10)-Fe(1) 63.92(2), Fe(10)-
Fe(1)-Ir(6) 57.25(2).
with the anticipated skeletal electron count of 11 SEPs. An
alternative view of 6 is as a fused-cage species: a closo-10-
vertex cluster edge-fused to a triangle; this arrangement (i.e.,
including the triangle) possesses 12 SEPs but this is also
consistent with accepted electron counting rules.
The exo-iridium fragment in 6 is attached via a B-H F Ir
agostic-type interaction, with Ir(1)‚‚‚B(8) ) 2.348(4) Å and
Ir(1)-H(8) ) 1.65(4) Å, and by an Fe-Ir bond (Ir(1)-Fe(10)
) 2.7321(6) Å) that involves the iron vertex that is in the four-
connected cluster site. This latter connectivity is bridged by a
PPh2 moiety (Fe(10)-P(1) ) 2.2379(12), Ir(1)-P(1) )
2.2982(11) Å). The origin of the phosphide is clearly a PPh3
ligand of the precursor iridium reagent, as the iridium center
bears a σ-bonded Ph group (Ir(1)-C(11) ) 2.122(4) Å). Thus,
the iridium center may be considered formally to have oxida-
tively inserted into a P-Ph bond of one phosphine, rather than
into the ferracarborane as in the formation of 3-5. Such
cleavage reactions for PPh3 and other ligands bonded to
(20) For example: Bradford, C. W.; Nyholm, R. S. J. Chem. Soc., Chem.
Commun. 1972, 87.
(21) Leading reviews include: (a) Garrou, P. E. Chem. ReV. 1985, 85, 171. (b)
van Leeuwen, P. W. N. M. Appl. Catal., A 2001, 212, 61. (c) Parkins, A.
W. Coord. Chem. ReV. 2006, 250, 449.
(22) McFarland, J. M.; Churchill, M. R.; See, R. F.; Lake, C. H.; Attwood, J.
D. Organometallics 1991, 10, 3530.
(23) Dahlenburg, L.; Halsch, E.; Wolski, A.; Moll, M. J. Organomet. Chem.
1993, 463, 227.
(24) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
9
16174 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Iridium−Iron−Monocarborane Clusters
A R T I C L E S
direct σ bond, and a bridging hydride is located along the Ir-
(6)-Fe(1) edge (Ir(6)-H(610) ) 1.79(4), Fe(1)-H(610) )
1.68(5) Å). This hydride, located crystallographically, may be
viewed as having migrated from a terminal site upon B(7) to
the metal-metal bridging position, with the exo-{Fe(CO)3}
moiety perhaps being involved via formation of a B(7)-H(7)
F Fe(1) agostic-type interaction. Such hydride migration has
been observed previously where, for example, polymetallic
compounds containing B-H F Ru moieties have transformed
to species containing a direct B-Ru σ bond and an Ru-(µ-H)-
Ru bridging hydride.1h,25
species that might not be expected to be stable and hence its
reversion to a capped 10-vertex geometry.
These comments notwithstanding, it may also be of relevance
to note that we have recently observed formation of a 13-vertex
cupradicarborane from addition of {Cu(PPh3)}+ to a 13-vertex
rhenadicarborane, a process that arguably might also involve a
vertex-expanded bimetallic intermediate.27 Indeed, it is becoming
increasingly clear that established patterns of cluster stability
may not hold so rigidly when multiple metal centers are present.
Clearly, further work is required in this and related systems to
understand fully the processes involved and to isolate and
identify perhaps other side products and intermediates.
Preliminary Reactivity Studies. We have performed some
preliminary investigations upon the reactivity of compounds 3,
5, 6, and 7. In particular, we have attempted to substitute metal-
bound CO groups by other donor ligands and also have
examined some possible reactions of the Ir-Ph unit and the
stability of the bridging phosphide moiety in 6. Most of these
reactions were unsuccessful. Perhaps not surprisingly, com-
pounds 5 and 7 appear rather unstable upon reaction with donor
ligands, and to date we have been unable to isolate any
identifiable products from treatment of these complexes with
isocyanides or phosphines in the presence of Me3NO. Likewise,
both 3 and 6 undergo considerable decomposition upon treat-
ment with a range of donor groups. However, both 3 and 6 do
readily give substitution products upon reaction with CNXyl
(Xyl ) C6H3Me2-2,6) in the presence of Me3NO, affording
the products [9,9,9-(CO)3-7,7-(CNXyl)2-7-PPh3-closo-7,9,1-
IrFeCB6H7] (8) and [8,10-{Ir(µ-PPh2)(Ph)(CNXyl)(PPh3)}-8-
(µ-H)-6,6,10,10-(CO)4-6-CNXyl-closo-6,10,1-Fe2CB7H7] (9),
respectively (Charts 3 and 4).
Spectroscopic data characterizing compound 7 are given in
Tables 1-3. The 1H NMR spectrum was informative, displaying
a diagnostic doublet resonance (J(PH) ) 7 Hz) at δ -17.22.
This is in the region typical of metal-metal bridging hydrides,
and the observation of coupling to the iridium-bound phosphine
confirms that this hydride is located on an Ir-Fe edge. Its site
upon the Ir(6)-Fe(1), rather than Ir(6)-Fe(10), connectivity is
intuitively more reasonable given the coordination environments
at each metal atom and is supported by the X-ray diffraction
1
results discussed above. A further H NMR signal, at δ 8.39
and also of relative intensity one, is in the region characteristic
for a cage CH in 10-vertex closo-metalla-monocarborane cages.8
In the 11B{1H} NMR spectrum, there are seven separate
resonances, consistent with the absence of molecular symmetry,
of which one (δ 80.6) remains a singlet in the fully proton-
coupled spectrum and hence may be assigned to B(7), which is
directly σ-bonded to iron.19 Three signals for CO ligands are
evident in the 13C{1H} NMR spectrum of 7, of which the two
for the two {Fe(CO)3} groups are singlets (δ 212.0 and 207.7),
while the Ir-CO resonance (δ 178.8) is a doublet (J(PC) ) 14
Hz), as expected.
X-ray diffraction studies were necessary initially to establish
with certainty which CO groups had been replaced. These
experiments were straightforward; their results have been
included as Supporting Information, and the structures are
summarized in Charts 3 and 4. From these it is seen that, in
compound 8, both of the iridium-bound CO groups in the
precursor 3 have been replaced by CNXyl ligands, while in
compound 9, the sole Ir-CO in 6 has been converted to Ir-
CNXyl and one of the carbonyls bound to five-connected
Fe(6) has also been substituted by CNXyl. Other structural
features of 3 and 6 are retained upon formation of 8 and 9, and
the skeletal electron counts are unchanged upon CO substitution.
Data characterizing compounds 8 and 9 are given in Tables
1-3, and they are fully in accord with the X-ray diffraction
results. The presence of two equivalent CNXyl ligands in 8 gives
rise to a single set of resonances in typical positions and with
The observation that the iridium center in 7 now occupies a
cluster vertex, apparently having exchanged sites with one of
the iron vertexes, is highly unusual in metallacarborane chem-
istry. However, we have recently observed similar behavior
where the addition of cationic {M(CO)2}+ fragments (M ) Rh,
Ir) to 11-vertex rhenium- and manganese-monocarborane
dianions resulted in ejection of {M′(CO)3} vertexes (M′ ) Re,
Mn) and the {M(CO)2} unit assuming the endo-polyhedral
cluster site.26 In the present case, parallels can certainly be
drawn, as both the {M′(CO)3} and {Fe(CO)3} fragments are
conical, d6 groups. However, in the 11-vertex system a 12-vertex
intermediate for the process was proposed, with both metal
centers part of a closed {MM′CB9} cluster prior to extrusion
of the {M′(CO)3} moieties; supporting evidence for this came
from a closely related platinum-manganacarborane system.6
In the case of compound 7, an analogous mechanism would
require expansion of the 10-vertex {Fe2CB7} core of the
precursor 2 to an 11-vertex {IrFe2CB7} species, a suggestion
that would be at odds with the known stability of 10-vertex
systems.14 Moreover, although the face-capped, closo-10-vertex
configuration of 7 has 11 SEPs and so conforms to conventional
electron counting rules, the {IrFe2CB7} intermediate proposed
above would be a nonconventional 11-SEP, closo-11-vertex
1
the expected intensities in the H and 13C{1H} NMR spectra,
while the same spectra for 9 reveal as anticipated two sets of
signals for the two different isocyanide ligands. These spectra
also indicate little change in the chemical shifts of the atoms in
the cage {CH} units of both 8 and 9 compared to their
precursors, while the 1H NMR resonance (δ -9.85) for the B-H
F Ir linkage in 9 is slightly shielded compared with that for 6.
Likewise, the 11B{1H} and 31P{1H} NMR spectra for 8 and 9
are similar to those of the precursors 3 and 6 and confirm no
major structural or electronic changes upon substitution of CO
groups by CNXyl.
(25) (a) Ellis, D. D.; Franken, A.; Stone, F. G. A. Organometallics 1999, 18,
2362. (b) McGrath, T. D.; Stone, F. G. A.; Sukcharoenphon, K. Dalton
Trans. 2005, 2500.
(26) McGrath, T. D.; Du, S.; Hodson, B. E.; Lu, X. L.; Stone, F. G. A.
Organometallics 2006, 25, 4452.
(27) Hodson, B. E.; McGrath, T. D.; Stone, F. G. A. Organometallics 2005,
24, 3386.
9
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A R T I C L E S
Franken et al.
petroleum ether (4:1) from which removal of solvent in vacuo yielded
green microcrystals of [6,7,9-{Ir(CO)(PPh3)2}-7,9-(µ-H)2-7,9,9-(CO)3-
7-PPh3-closo-7,9,1-IrFeCB6H6] (5; 0.09 g; 12%). Data for compound
4: IR (CH2Cl2): νmax(CO) ) 2028 s, 1997 s, 1960 s cm-1. NMR (CD2-
Cl2, 298 K): δH 8.00-6.98 (m, 30H, Ph), 3.31 (br s, 1H, cage CH),
-9.62 (d, J(PH) ) 30, 1H, Ir-H); δB 94.6 (1B, B(10)), 2.9 (2B), -11.3
(2B), -17.4 (2B); δP 46.2 (s, OPPh3), 12.0 (br s, IrPPh3).
Synthesis of [8,10-{Ir(µ-PPh2)(Ph)(CO)(PPh3)}-8-(µ-H)-6,6,6,10,-
10-(CO)5-closo-6,10,1-Fe2CB7H7] and [6,7,10-{Fe(CO)3}-6-(µ-H)-6,-
10,10,10-(CO)4-6-PPh3-closo-6,10,1-IrFeCB7H7]. Compound 2 (0.23
g, 0.25 mmol), [IrCl(CO)(PPh3)2] (0.20 g, 0.25 mmol), and Tl[PF6]
(0.090 g, 0.25 mmol) were stirred in CH2Cl2 (20 mL) for 18 h. The
solvent was removed in vacuo, the residue was extracted with CH2Cl2
(2 mL), and the extract was filtered (Celite) and applied to a
chromatography column. Elution with CH2Cl2/petroleum ether (2:3)
gave successively a yellow-green fraction and an orange fraction that
yielded green microcrystals of [6,7,10-{Fe(CO)3}-6-(µ-H)-6,10,10,10-
(CO)4-6-PPh3-closo-6,10,1-IrFeCB7H7] (7; 0.077 g; 37%) and orange
microcrystals of [8,10-{Ir(µ-PPh2)(Ph)(CO)(PPh3)}-8-(µ-H)-6,6,6,10,-
10-(CO)5-closo-6,10,1-Fe2CB7H7] (6; 0.140 g; 52%), respectively, after
removal of solvent in vacuo.
Conclusion
Reactions of the ferracarborane anions of compounds 1 and
2 with a source of the cationic {Ir(CO)(PPh3)2}+ fragment,
derived from Vaska’s compound, result in a variety of product
types that arise from different oxidative insertion processes
involving the iridium moiety. With 1, the iridium center
oxidatively inserts into the ferracarborane cluster, ultimately
giving 3 following elimination of a {BH} vertex: the nature of
the side product 4, obtained in very low yield, implies a possible
mechanism for the boron vertex loss. Further iridium reagent
apparently inserts into a B-H bond of the iridaferracarborane
3 itself, with the final trimetallic, fused cluster product 5
exhibiting several novel structural features. In contrast, reaction
of 2 with the iridium reagent can follow two different oxidative
insertion paths: A formal insertion into a P-Ph bond affords
6, of which the starting diferracarborane cluster is essentially
unchanged; whereas formation of 7 appears to require insertion
of the iridium moiety into the metallacarborane, transiently
giving a proposed 11-vertex trimetallacarborane intermediate
that extrudes an iron center into an exo-polyhedral site. Both
of the complexes 5 and 7 can be considered to be fused, “double
cluster” species of a class that is highly unusual in metallcar-
borane chemistry.
Reactions with CNXyl. (i) Compound 3 (0.092 g, 0.125 mmol)
was dissolved in CH2Cl2 (10 mL), CNXyl (0.033 g, 0.25 mmol) and
Me3NO (0.019 g, 0.25 mmol) were added, and the mixture was stirred
for 1 h. The solvent was removed in vacuo, and the residue was
dissolved in CH2Cl2 (1 mL) and transferred to the top of a chroma-
tography column. Elution with CH2Cl2/petroleum ether (1:1) gave a
red fraction from which removal of solvent in vacuo yielded red
microcrystals of [9,9,9-(CO)3-7,7-(CNXyl)2-7-PPh3-closo-7,9,1-IrFeCB6H7]
(8; 0.084 g; 72%).
Experimental Section
Syntheses. All reactions were carried out under an atmosphere of
dry, oxygen-free nitrogen using Schlenk line techniques. Solvents were
stored over and distilled from appropriate drying agents under nitrogen
prior to use. Petroleum ether refers to that fraction of boiling point
40-60 °C. Chromatography columns (typically ca. 18 cm in length
and ca. 2 cm in diameter) were packed with silica gel (Acros, 60-200
mesh). Filtration through Celite typically employed a plug ca. 5 cm in
length and ca. 2 cm in diameter. Elemental analyses were performed
by Atlantic Microlab, Inc., Norcross, GA, upon crystalline or micro-
crystalline samples that had been dried overnight in vacuo. Where
residual solvent remained after drying, its presence and approximate
(ii) Compound 6 (0.140 g, 0.125 mmol) and CNXyl (0.033 g, 0.25
mmol) were dissolved in CH2Cl2 (10 mL), and Me3NO (19 mg, 0.25
mmol) was added. After being stirred for 18 h, the mixture was treated
as above to give orange microcrystals of [8,10-{Ir(µ-PPh2)(Ph)(CNXyl)-
(PPh3)}-8-(µ-H)-6,6,10,10-(CO)4-6-CNXyl-closo-6,10,1-Fe2CB7H7] (9;
0.130 g; 79%).
X-ray Diffraction Experiments. Experimental data for compounds
3-7 are given in the Supporting Information. X-ray intensity 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 φ and ω, using 0.5° increments of φ or ω. The
data frames were integrated using SAINT;29 the substantial redundancy
in data allowed an empirical absorption correction (SADABS29) to be
applied, based on multiple measurements of equivalent reflections.
All structures were solved using conventional direct methods29,30 and
refined by full-matrix least squares on all F2 data using SHELXTL
version 6.12,30 with anisotropic thermal parameters assigned to all non-
hydrogen atoms. The locations of the cage carbon atoms were verified
by examination of the appropriate internuclear distances and the
magnitudes of their isotropic thermal displacement parameters. All
hydrogen atoms in organic groups, as well as cluster BH and CH
hydrogens for 3, 4, and 7, were set riding in calculated positions; other
cage BH and CH hydrogens, and metal-bound hydrogens, were allowed
positional refinement. All hydrogens had fixed isotropic thermal
parameters defined as Uiso(H) ) 1.2 × Uiso(parent), or Uiso(H) ) 1.5
× Uiso(parent) for methyl groups, apart from the metal-bound hydrides
whose thermal parameters were refined.
1
proportion were confirmed by integrated H NMR spectroscopy, and
this was factored into the calculated microanalysis data. NMR spectra
were recorded at the following frequencies (MHz): 1H, 360.1; 13C,
90.6; 11B, 115.5; 31P, 145.8. The compounds 1,8 2,8 and [IrCl(CO)-
(PPh3)2]28 were prepared according to the literature; all other materials
were used as received. Note that quoted yields for compounds 3-7
are the highest obtained and that these yields are very sensitive to
reaction time and conditions.
Synthesis of [7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7],
[6,8,8,8-(CO)4-6-H-6-PPh3-10-OPPh3-closo-6,8,1-IrFeCB7H7], and
[6,7,9-{Ir(CO)(PPh3)2}-7,9-(µ-H)2-7,9,9-(CO)3-7-PPh3-closo-7,9,1-
IrFeCB6H6]. The compounds 1 (0.19 g, 0.25 mmol), [IrCl(CO)(PPh3)2]
(0.40 g, 0.5 mmol), and Tl[PF6] (0.18 g, 0.5 mmol) were stirred in
CH2Cl2 (20 mL) for 48 h. The solvent was removed in vacuo, the
residue was extracted with CH2Cl2 (2 mL), and the extract was filtered
(Celite) and transferred to the top of a chromatography column. Elution
with CH2Cl2/petroleum ether (1:1) gave an orange fraction from which
removal of solvent in vacuo yielded orange microcrystals of [7,7,9,9,9-
(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3; 0.081 g; 44%). Further elu-
tion, using CH2Cl2/petroleum ether (3:2), gave a small, yellow fraction
from which removal of solvent in vacuo afforded yellow microcrystals
of [6,8,8,8-(CO)4-6-H-6-PPh3-10-OPPh3-closo-6,8,1-IrFeCB7H7] (4;
0.013 g; 5%). Finally, a green fraction was eluted with CH2Cl2/
Each molecule of compound 4 cocrystallized with one-half of a
molecule of CH2Cl2 as solvate in the asymmetric fraction of the unit
cell; some restraining of the C-Cl distance (1.76(2) Å; DFIX card in
SHELXL30) was necessary. In addition, each molecule of compound 6
cocrystallized with one molecule of C5H12 solvate, of which a â-CH2
(28) Vrieze, K.; Collman, J. P.; Sears, C. T.; Kubota, M. Inorg. Synth. 1968,
11, 101.
(29) APEX 2, version 1.0; Bruker AXS: Madison, WI, 2003-2004.
(30) SHELXTL, version 6.12; Bruker AXS: Madison, WI, 2001.
9
16176 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Iridium−Iron−Monocarborane Clusters
A R T I C L E S
unit was disordered over two sites that were assigned refining
complementary occupancies, in the ratio 56:44 at convergence; the C-C
distances in this solvate were restrained toward sensible distances
(1.54(3) Å; DFIX card in SHELXL30).
National Science Foundation Major Instrumentation Program
(Grant CHE-0321214).
Supporting Information Available: Full details of the crystal
structure analyses in CIF format, including data for compounds
8 and 9. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. We thank the Robert A. Welch Foundation
for support (Grant AA-0006). The Bruker-Nonius X8 APEX
diffractometer was purchased with funds received from the
JA065042N
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