Heterobimetallic metallaborane chemistry: Synthesis and characterization of a Lightly Stabilized molybdairidahexaborane, [{Cp*Ir}{(CO)3(THF)Mo}B4H8], and Its Direct Conversion to [{Cp*Ir}{(CO)3(L)Mo}B4H 8] (L = CO, PPh3, NCPh, CNBu, NH3, PPh 3=CHC(O)OMe)

Article abstract of DOI:10.1021/om049308f

The reaction of [Cp*IrB₄H₁₀] (1) with [{η⁶-(C₆H₄)(CH₃) ₂}Mo(CO)₃] in tetrahydrofuran (THF) leads to [Cp*Ir(CO)₃(THF)MoB₄H₈] (2), which was characterized by NMR spectroscopy. Intermediate 2 subsequently decomposes to give the tetracarbonyl analogue [Cp*Ir-(CO)₄MoB ₄H₃] (3). In the presence of free CO, the same reaction constitutes a high-yield synthesis of 3. The treatment of 2 (formed in situ) with different Lewis bases led to the replacement of the THF ligand at the molybdenum center and generation of [Cp*Ir(CO)₃-(L)MoB ₄H₈] (L = PPh₃ (4), NCPh (5), CNBu (6), NH ₃ (7)). Reaction of the benzonitrile derivative 5 with PPh ₃-CHCO₂Me afforded the ylide compound [Cp*Ir(CO)₃(PPh₃=CHCO₂-Me)M ₀B₄H₈] (8). All compounds have been spectroscopically characterized, and 3 and 5-7 have been structurally characterized in the solid state. This work demonstrates that, similarly to metal clusters, metallaboranes with labile metal ligands can serve as versatile synthons.

Full text of DOI:10.1021/om049308f

5994
Organometallics 2004, 23, 5994-6001
Heterobimetallic Metallaborane Chemistry: Synthesis
and Characterization of a “Lightly Stabilized”
Molybdairidahexaborane, [{Cp*Ir}{(CO)3(THF)Mo}B4H8],
and Its Direct Conversion to [{Cp*Ir}{(CO)3(L)Mo}B4H8]
(L ) CO, PPh3, NCPh, CNBu, NH3, PPh3dCHC(O)OMe)
Ramo´n Mac´ıas, Thomas P. Fehlner,* Alicia M. Beatty, and Bruce Noll
Department of Chemistry and Biochemistry, University of Notre Dame,
Notre Dame, Indiana 46556-5670
Received September 6, 2004
The reaction of [Cp*IrB4H10] (1) with [{η6-(C6H4)(CH3)2}Mo(CO)3] in tetrahydrofuran (THF)
leads to [Cp*Ir(CO)3(THF)MoB4H8] (2), which was characterized by NMR spectroscopy.
Intermediate 2 subsequently decomposes to give the tetracarbonyl analogue [Cp*Ir-
(CO)4MoB4H8] (3). In the presence of free CO, the same reaction constitutes a high-yield
synthesis of 3. The treatment of 2 (formed in situ) with different Lewis bases led to the
replacement of the THF ligand at the molybdenum center and generation of [Cp*Ir(CO)3-
(L)MoB4H8] (L ) PPh3 (4), NCPh (5), CNBu (6), NH3 (7)). Reaction of the benzonitrile
derivative 5 with PPh3dCHCO2Me afforded the ylide compound [Cp*Ir(CO)3(PPh3dCHCO2-
Me)MoB4H8] (8). All compounds have been spectroscopically characterized, and 3 and 5-7
have been structurally characterized in the solid state. This work demonstrates that, similarly
to metal clusters, metallaboranes with labile metal ligands can serve as versatile synthons.
Chart 1. “B-Frames” as Molecular Matrices and
Scaffolds: [(Cp*Ir)Co(CO)3B4H7] (I),1
Introduction
Polyhedral boron-containing compounds are uniquely
suited for the construction of polymetallic clusters. The
frame of a borane or heteroborane provides a matrix on
which to bind potentially reactive metal centers. Indeed,
stepwise metal attachment to borane frameworks has
been used successfully as a synthetic route to polyme-
tallic cluster systems (Chart 1, I-III).1-3 Alternatively,
polyhedral borane clusters can be used as molecular
scaffolds on which to construct polymetallic assemblies.
This can be clearly recognized, for example, in the
macropolyhedral species [(PPh3)3(PPh2)2Pd4B20H16],4
which supports a trimetallic string, or in the recent
construction of a {ReIrAu2} butterfly on a rhenacarbo-
rane (Chart 1, IV and V).5
[(Cp*Co)3B4H4] (II),2 [(η5-C5H5)4Ni4B4H4] (III),3
[(PPh3)3(PPh2)2Pd4B20H16] (IV),4 and
[(AuPPh3)2{Ir(CO)3}{Re(CO)2}(PhC)B9H8] (V)5
In polyhedral boron chemistry, the buildup of poly-
metallic clusters has relied mainly on the stepwise
addition of metal centers to a “preassembled” borane
fragment. In the case of carboranes, this has led to the
synthesis of many bimetallic and trimetallic com-
pounds.6-12 In comparison, the parallel development of
polymetallic metallaboranes has been much slower.13-19
This can be attributed in part to the lack of convenient
high-yield synthetic methods to metallaboranes. How-
(7) Grimes, R. N. In Comprehensive Organometallic Chemistry; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
U.K., 1982; Vol. 1.
* To whom correspondence should be addressed. E-mail: fehlner.1@
nd.edu.
(1) Lei, X.; Shang, M.; Fehlner, T. P. Chem. Eur. J. 2000, 6, 2653.
(2) Venable, T. L.; Sinn, E.; Grimes, R. N. Inorg. Chem. 1982, 21,
904.
(8) Grimes, R. N. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,
U.K., 1995; Vol. 1.
(3) Bowser, J. R.; Bonny, A.; Pipal, J. R.; Grimes, R. N. J. Am. Chem.
Soc. 1979, 101, 6229.
(9) Dossett, S. J.; Hart, I. J.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1990, 3481.
(4) Yao, H.-J.; Hu, C.-H.; Sun, J.; Jin, R.-S.; Zheng, P.-J.; Bould, J.;
Greatrex, R.; Kennedy, J. D.; Ormsby, D. L.; Thornton-Pett, M. Collect.
Czech. Chem. Commun. 1999, 64, 927.
(10) Ellis, D. D.; Jelliss, P. A.; Stone, F. G. A. Dalton 2000, 2113.
(11) Ellis, D. D.; Jeffery, J. C.; Jelliss, P. A.; Kautz, J. A.; Stone, F.
G. A. Inorg. Chem. 2001, 2041.
(5) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Angew.
Chem., Int. Ed. 2003, 42, 5728.
(12) Carr, N.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.;
Went, M. J. Organometallics 1993, 12, 4350.
(6) Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.; Woollam, S.
F. J. Chem. Soc., Dalton Trans. 1993, 3559.
(13) Kennedy, J. D. Prog. Inorg. Chem. 1984, 32, 519.
(14) Kennedy, J. D. Prog. Inorg. Chem. 1986, 34, 211.
10.1021/om049308f CCC: $27.50 © 2004 American Chemical Society
Publication on Web 11/03/2004

Heteobimetallic Metallaborane Chemistry
Organometallics, Vol. 23, No. 25, 2004 5995
Scheme 1
ever, this situation changed with the development of a
general route to a class of metallaboranes derived from
mono(cyclopentadienyl)metal chlorides.20 The majority
of compounds prepared from this route contain two
metal centers ranging from groups 5 to 9. Thus, the
availability of (homo)bimetallic metallaboranes opens
an attractive alternative to earlier methods for the
construction of polymetallic clusters.
In this regard, mixed-metal clusters of the group 6
metallaboranes have been prepared in high yield by
controlled cluster expansion reactions with metal car-
bonyls M2(CO)8 (M ) Fe, Co).1,21 However, reports of
clusters containing early-late metals that differ by
three d-block groups are scarce and little is known of
their reactivity.22 These mixed-metal clusters are of
interest because the presence of a polar metal-metal
bond could lead to interesting chemistry via cooperative
M-M’ interactions. It has been already demonstrated
that the hybrid character of a metallaborane creates
reaction possibilities not seen for transition-metal com-
plexes or boranes individually.23,24 For example, it has
been suggested that heterobimetallic metal hydrides
possessing both hydridic M-H bonds and acidic M-H
bonds are potentially excellent reducing agents.25,26
Thus, metallaboranes in which an early transition metal
is bound to a late transition metal are good candidates
for hydrogenation catalysts. Here we describe the reac-
tion of [Cp*IrB4H9] (1) with the molybdenum complex
[η6-(xylene)Mo(CO)3]. Subsequent substitution reactions
at the molybdenum center of the labile initial product
afford a significant series of molybdairidaborane deriva-
tives. These mixed-metal clusters represent the first
examples of Mo-Ir heterobimetallic metallaboranes.
Compound 3 was sufficiently stable to allow its
purification by column chromatography on silica gel.
1
The orange product was characterized by H and 11B
NMR spectroscopy, X-ray diffraction analysis, and ad-
ditional standard techniques. In contrast, the unstable
tetrahydrofuran derivative 2 could be characterized only
by NMR spectroscopy in solution.
Metal fragment addition to a metallaborane is a
common approach to the buildup of clusters. Similarly,
the formation of compound 2 involves the addition of a
{Mo(CO)3(THF)} group to the five-vertex arachno-
iridapentaborane 1 and elimination of H2. The reaction
can be viewed as a formal substitution of the apical
Ir-H hydride and one BH hydrogen atom of the {B4H9}
fragment by the molybdenum center.
Results and Discussion
Reaction of [Cp*IrB4H10] (1) with [{η6-C6H4-
(CH3)2}Mo(CO)3]. We discovered that in the early
stages of the reaction of the iridapentaborane 1 with
stoichiometric amounts of (η6-xylene)tricarbonylmolyb-
denum the molybdairidahexaborane [1-Cp*-2,2,2-(CO)3-
2-(THF)-nido-1,2-IrMoB4H8] (2) (Scheme 1) is formed.
In solution, this bimetallic metallaborane decomposes,
giving the tetracarbonyl analogue [1-Cp*-2,2,2,2-(CO)4-
nido-1,2-IrMoB4H8] (3) in modest yields.
In tetrahydrofuran, the reaction between 1 and the
(arene)tricarbonylmolybdenum complex to give 2 was
completed in about 30 min, depending on the concentra-
tion of the reactants, and was accompanied by the
generation of gas presumed to be H2. In contrast, in
benzene the iridapentaborane did not react with the
molybdenum complex and both reactants were recov-
ered unchanged. This suggests that arene displacement
by THF is necessary for the reaction to proceed. In fact,
dissolution of (η6-arene)Mo(CO)3 in THF or acetone
leads to rapid loss of the arene (minutes or less) and
solvent addition to generate (L)3Mo(CO)3 (L ) acetone,
THF).27
(15) Barton, L., Strivastava, D. K. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: New York, 1995; Vol. 1.
(16) Bould, J.; Crook, J. E.; Greenwood, N. N.; Kennedy, J. D.;
McDonald, W. S. J. Chem. Soc., Chem. Commun. 1983, 949.
(17) Bould, J.; Crook, J. E.; Kennedy, J. D. Inorg. Chim. Acta 1993,
203, 193.
(18) Kim, Y.-H.; Cooke., P. A.; Greatrex, R.; Kennedy, J. D.;
Thornton-Pett, M. J. Organomet. Chem. 1998, 550, 341.
(19) Kim, Y.-H.; McKinnes, Y. M.; Cooke, P. A.; Greatrex, R.;
Kennedy, J. D.; Thornton-Pett, M. Collect. Czech. Chem. Commun.
1999, 64, 938.
(20) Fehlner, T. P. Organometallics 2000, 19, 2643.
(21) Aldridge, S.; Shang, M.; Fehlner, T. P. Inorg. Chem. 1998, 37,
928.
(22) Lucas, N. T.; Blitz, J. P.; Petrie, S.; Stranger, R.; Humphrey,
M. G.; Heath, G. A.; Otieno-Alego, V. J. Am. Chem. Soc. 2002, 124,
5139.
It is probable that (THF)3Mo(CO)3 is the species that
reacts with 1 (Scheme 1). The complete mechanism is
unclear, but displacement of THF by a hydride of 1 from
(THF)3Mo(CO)3 that generates a metallaborane inter-
(23) Hong, Y.; Beatty, A. M.; Fehlner, T. P. J. Am. Chem. Soc. 2002,
124, 10280.
(24) Hong, Y.; Beatty, A. M.; Fehlner, T. P. J. Am. Chem. Soc. 2003,
125, 16367.
(25) Casey, C. P.; Wang, Y.; Tanke, R. S.; Hazin, P. N.; Rutter, E.
W., Jr. New J. Chem. 1994, 18, 43.
(27) Muetterties, E. L.; Bleeke, J. R.; Sievert, A. C. J. Organomet.
Chem. 1979, 178, 197.
(26) Bullock, R. M.; Casey, C. P. Acc. Chem. Res. 1987, 20, 167.

5996 Organometallics, Vol. 23, No. 25, 2004
Mac´ıas et al.
Scheme 2
mediate that can undergo cluster insertion and uni-
molecular elimination of H2 (Scheme 2) is an attractive
pathway.
Since the isolated yield of 3 is less than 50%, it is
likely that the formation of this metallaborane involves
the addition of a CO molecule generated from decom-
position of the THF derivative (eq 1). Consistent with
time as solids. Furthermore, these crystalline com-
pounds can be handled in air. The PPh3 analogue also
decomposed in solution, but at slower rates. In contrast,
the CNBu derivative is stable in solution and in the solid
state and its stability resembles that of the tetracarbon-
yl compound 3.
Like compound 2, the benzonitrile analogue 5 under-
goes substitution at the molybdenum center. In contrast
to the THF derivative, which can only be generated in
situ, 5 can be isolated in crystalline stable form.
Therefore, 5 gives better control of stoichiometry in
reactivity studies. In addition, 5 is less reactive than 2
in an overall sense and more selective, thereby allowing
the synthesis of species that otherwise would not be
accessible from compound 2.
For example, the reaction between 2 and the carbonyl-
stabilized phosphorus ylide Ph3PdCHCO2Me resulted
in a complex mixture from which we could not identify
or isolate any new compounds. In contrast, the treat-
ment of 5 with the same reagent afforded a new
metallaborane that we identified as [1-Cp*Ir-2,2,2-
(CO)3-2-(PPh3CHCO2Me)-nido-1,2-IrMoB4H8] (8) but
were unable to completely separate from 3. Ph3PdCH-
CO2Me behaves as a weak nucleophile capable of
replacing the benzonitrile ligand. Similar reactivity was
previously observed for [PdCl2(NCPh)2] in the formation
of the substitution product [PdCl2(PPh3CHCO2Me)2].28,29
Structures of 5-7. The structures of 3 and 5-7 were
established by X-ray crystallography, and a summary
of the crystallographic data and selected bond distances
and angles for 5-7 are given in Tables 1 and 2,
respectively. The structure solution of compound 3 gave
a residual peak of 21 e Å-3 near Ir that could not be
modeled satisfactorily; therefore, the molecular metrics
are uncertain. However, the X-ray diffraction data are
sufficient to confirm the molecular connectivity of 3 and
show it to be a member of the series.
[Cp*Ir(CO) (THF)MoB H ]
2
f
3
4
8
2
[Cp*Ir(CO) MoB H ]
+ ... (1)
4
8
34
this hypothesis, the addition of CO gas to the reaction
system leads to higher (67%) yields of 3. Hence, 2 can
be viewed as a “lightly stabilized” metallaborane and
suggests that other Lewis bases should efficiently
generate a series of related mixed metal derivatives.
Substitution Reactions at the Molybdenum Cen-
ter. A variety of Lewis bases were found capable of
replacing the THF ligand in compound 2 (Scheme 1).
In a typical reaction, the iridapentaborane 1 was treated
with stoichiometric amounts of [{η6-C6H4(Me)2}Mo-
(CO)3] to give [{Cp*Ir}{(CO)3(THF)Mo}B4H8] (2). When
the formation of 2 was complete, as judged by NMR,
the appropriate Lewis base was added. This synthetic
procedure led to series of molybdairidahexaboranes of
the general formula [{Cp*Ir}{(CO)3(L)Mo}B4H8] (L )
PPh3 (4), NCPh (5), CNBu (6), NH3 (7)).
Substitution of the THF ligand took place at room
temperature in a few minutes. The benzonitrile and
butyl isocyanide derivatives 5 and 6 were purified by
column chromatography on silica gel, whereas the
ammonia counterpart was isolated by crystalization in
CH2Cl2/hexane at -40 °C. The products were character-
ized by NMR spectroscopy, mass spectrometry, and
elemental analysis. We also determined the crystal
structures of compounds 3 and 5-7 (Tables 1 and 2).
Compounds 5 and 7 decomposed in solution under
argon at +4 °C overnight, giving a brown precipitate
and the tetracarbonyl derivative 3. However, both
species were crystallized from CH2Cl2/hexane at -40 °C,
affording products that were stable for long periods of
A typical structure of the series can be seen in Figure
1, which shows the molecular structure of 7. These
(28) Vicente, J.; Chicote, M. T.; Fernandez-Baeza, J. J. Organomet.
Chem. 1989, 364, 407.
(29) Weleski, E. T., Jr.; Silver, J. L.; Jansson, M. D.; Burmeister, J.
L. J. Organomet. Chem. 1975, 102, 365.

Heteobimetallic Metallaborane Chemistry
Organometallics, Vol. 23, No. 25, 2004 5997
Table 1. Experimental X-ray Diffraction Parameters and Crystal Data for [{Cp*Ir}{(CO)4Mo}B4H8] (3),
[{Cp*Ir}{(CO)3(NCC6H5)Mo}B4H8] (5), [{Cp*Ir}{(CO)3(CNBu)Mo}B4H8] (6), and [{Cp*Ir}{(CO)3(NH3)Mo}B4H8]
(7)
3
5
6
7
empirical formula
C
14H23B4IrMoO4
C
20H28B4IrMoNO3
C
18H32B4IrMoNO3
C
13H26B4IrMoNO3
fw
586.70
0.50 × 0.32 × 0.04
P21/c
661.81
0.69 × 0.43 × 0.03
C2/c
641.83
0.30 × 0.16 × 0.06
Pbca
575.73
0.28 × 0.10 × 0.07
P21/c
cryst dimens (mm)
space group
a, Å
16.8242(8)
11.9429(5)
19.9351(9)
90
103.9170(10)
90
29.2740(6)
10.5875(2)
17.3862(4)
90
119.8180(10)
90
13.7651(3)
13.8575(3)
24.5446(5)
90
90
90
4681.88(17)
8
1.821
6.232
8.7480(3)
26.1356(11)
8.6082(3)
90
108.253(2)
90
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
3888.0(3)
8
4675.24(17)
8
1869.10(12)
4
Z
D(calcd), g cm-3
µ(Mo KR), mm-1
temp, K
2.005
1.880
2.046
7.496
6.244
7.792
100(2)
100(2)
100(2)
63
100(2)
2θmax, deg
56
66
66
transmissn factors
no. of rflns collected
no. of obsd rflns (I > 2θ(I))
no. of params refined
R
1.0000-0.6000
41 601
9670
0.8495-0.0997
60 441
8813
0.6986-0.2590
35 279
6231
0.653-0.468
28 786
6302
433
308
347
246
0.0612
0.1498
1.052
0.0328
0.0854
1.024
0.0227
0.0493
1.033
0.0272
0.0598
1.082
Rw
goodness of fit
largest peak in final diff map, e/Å3
20.787
3.160
1.233
3.797
Table 2. Selected Interatomic Lengths (Å) and
Angles (deg) for [{Cp*Ir}{(CO)3(NCC6H5)Mo}B4H8]
(5), [{Cp*Ir}{(CO)3(CNBu)Mo}B4H8] (6), and
[{Cp*Ir}{(CO)3(NH3)Mo}B4H8] (7)
5
6
7
Lengths
Ir(1)-Mo(2)
Ir(1)-B(3)
Ir(1)-B(6)
Mo(2)-B(3)
Mo(2)-B(6)
Mo(2)-C(1)
Mo(2)-C(2)
Mo(2)-C(3)
Mo(2)-Ea
C(1)-O(1)
C(2)-O(2)
C(3)-O(3)
N-C
2.8521(2)
2.8566(2)
2.140(3)
2.095(3)
2.460(4)
2.293(3)
1.954(3)
1.955(4)
2.001(3)
2.177(3)
1.164(3)
1.159(4)
1.144(4)
1.192(7)
1.836(5)
1.815(5)
1.846(5)
2.8534(3)
2.146(4)
2.099(3)
2.470(4)
2.270(3)
1.927(3)
1.960(3)
2.013(3)
2.297(3)
1.177(4)
1.151(4)
1.140(4)
2.146(3)
2.096(3)
2.476(3)
2.287(3)
1.926(3)
1.980(3)
2.007(3)
2.210(2)
1.180(3)
1.146(3)
1.146(3)
1.145(3)
1.831(5)
1.824(5)
1.847(4)
B(3)-B(4)
B(4)-B(5)
B(5)-B(6)
1.825(5)
1.825(5)
1.855(5)
Angles
Figure 1. Molecular structure of 7, the NH3 derivative.
B(3)-Mo(2)-B(6)
B(4)-B(3)-Mo(2)
C(1)-Mo(2)-Ea
B(3)-Mo(2)-C(2)
Ir(1)-Mo(2)-C(3)
Mo(2)-N-C
81.19(10)
115.23(17)
163.31(10)
146.67(10)
169.96(8)
174.3(2)
81.09(12)
115.5(2)
159.12(12)
145.03(12)
172.34(14)
92.88(14)
116.6(2)
161.58(14)
145.87(14)
173.60(10)
distances are very similar within the series, being
slightly longer for compound 6. The {Mo(CO)3L} frag-
ment (L ) NCPh (5), CNBu (6), NH3 (7)) binds in an
asymmetric fashion within the cluster. Thus, the
Mo(2)-B(3) length is significantly longer than the
Mo(2)-B(6) distance (0.152(4) Å average difference).
This difference is consistent with the presence of a
bridging hydrogen atom at the Mo(2)-B(3) edge, result-
ing in a longer Mo-B interaction. In contrast, the
Ir(1)-B(3) edge is only slightly longer than the Ir(1)-
B(6) edge with an average difference within the series
of 0.047(4) Å.
The Mo(2)-C(1) bond corresponds to the carbonyl that
is trans to the L ligand. In the benzonitrile and
ammonia (5 and 7) derivatives the length of this bond
is slightly shorter (0.027(3) Å) than in the isocyanide
analogue 6; conversely, the C(1)-O(1) distances are
Mo(2)-C-N
160.0(5)
C(1)-Mo(2)-C(2)
C(1)-Mo(2)-C(3)
C(2)-Mo(2)-E
C(3)-Mo(2)-E
B(3)-Mo(2)-E
B(6)-Mo(2)-C(3)
Mo(2)-C(1)-O(1)
Mo(2)-C(2)-O(2)
Mo(2)-C(3)-O(3)
B(6)-Mo(2)-E
90.44(11)
76.05(11)
93.65(10)
87.88(11)
79.87(9)
90.93(13)
78.17(13)
94.93(14)
82.06(12)
81.06(13)(
137.50(13)
171.1(2)
90.71(15)
78.83(14)
96.97(13)
85.06(13)
77.81(12)
136.87(14)
172.3(3)
135.79(11)
172.5(2)
177.4(3)
177.0(3)
177.6(3)
173.3(3)
175.3(3)
174.5(3)
135.26(9)
138.93(11)
136.98(12)
a E ) N for 5 and 7, and E ) C for 6.
molydairidaboranes have a {1-Ir-2-Mo-B4} pentagonal-
pyramidal core geometry (Chart 1, I). The framework
structures correspond exactly to what one expects for
an eight-SEP, six-vertex nido cluster.30 The Ir-Mo bond
(30) Wade, K. Adv. Inorg. Chem. Radiochem. 1976, 18, 1.

5998 Organometallics, Vol. 23, No. 25, 2004
Mac´ıas et al.
Figure 2. 1H{11B} NMR spectra.
Scheme 3. Proposed Fluxional Process in
slightly longer for the former pair of compounds. In
addition, in comparison with NCPh, the CNBu ligand
exhibits a longer C-N distance (0.047(7) Å), which
suggests that the latter displays stronger π-acceptor
character.
[2,2,2-(CO)3-nido-2-FeB5H9]
The angle between the L group and the trans-carbonyl
ligand C(1)O(1) is close to 160° throughout the series;
the carbonyl faces the pentagonal face of the cluster,
and the L ligand is cis to the bridging hydrogen bond,
H(2,3). In all the species, the carbonyl, C(2)O(2), is
almost trans to this bridging hydrogen atom, and the
third carbonyl, C(3)O(3), forms an angle close to 170°
with the iridium center. This stereochemistry can be
rationalized on the basis of 6-coordinate octahedral
molybdenum, in which the metal is a formally saturated
18-electron center. This implies bonding vectors toward
the B(3)H(2,3) bond and the Ir(1)B(6) edge of the
iridapentaborane fragment in addition to the four
terminal ligands.
When they are viewed as metal complexes, these
bimetallic metallahexaboranes can be regarded as fea-
turing either a Mo(0) center bound to a four-electron
neutral η3-Cp*IrB4H8 ligand or a Mo(II) center linked
to an anionic six-electron η3-Cp*IrB4H82- fragment (i.e.
isolectronic with arachno-B5H92-). Since the iridapen-
taborane fragment formally replaces two THF molecules
of the starting (THF)3Mo(CO)3 to give compound 2, and
the (CO)3LMo group formally substitutes two hydrogen
atoms from [Cp*IrB4H10] (1), both descriptions are
notionally valid. The description of the Cp*IrB4H8
fragment as a 4-electron bidentate ligand is consistent
with a 6-coordinate octahedral center, whereas a 6-elec-
tron tridentate Cp*IrB4H8 fragment implies a 7-coor-
dinate Mo center.
the solid-state structures of compounds 3 and 5-7. The
11B{1H} NMR spectra consist of four signals of relative
intensity 1, indicating that the Cs symmetry is main-
tained. Of the four boron resonances, one appears at
around 45 ppm for all compounds and is at significantly
lower field than the other three signals lying between
1
10 and -5 ppm. The H NMR spectra also reflect the
asymmetry of the compounds (Figure 2)
The molybdairidaboranes have the same bridging
hydrogen configuration as the ferrahexaborane [2,2,2-
(CO)3-nido-2- FeB5H9];31 however, the latter exhibits a
dynamic behavior at ambient temperature, in which the
Fe-H-B bridging hydrogen atom moves between the
B(3)-Fe(2) and B(6)-Fe(2) edges of the pentagonal face
(Scheme 3). In contrast, variable-temperature NMR
experiments demonstrated that compound 3 is not
fluxional, even at 100 °C in toluene-d8. Even the
Mo(CO)4 group is static, as the 13C NMR shows four
distinct carbonyl resonances at room temperature.
In the series, eight different proton resonances as-
sociated with boron atoms are observed. One of the BH
terminal 1H resonances appears near the aromatic
region. The other three terminal BH resonances occur
between 4 and 3 ppm. Four signals around 0 ppm and
1
in the negative region of the H spectra correspond to
the bridging hydrogen atoms. The resonance at highest
NMR Characterization. The NMR data of the
molybdairidaboranes in solution are fully in accord with
(31) Shore, S. G.; Ragaini, J. D.; Smith, R. L.; Cottrell, C. E.; Fehlner,
T. P. Inorg. Chem. 1979, 18, 670.

Heteobimetallic Metallaborane Chemistry
Organometallics, Vol. 23, No. 25, 2004 5999
field is reasonably assigned to the MoHB hydrogen
atom. 1H{11B} selective experiments permit correlation
of the lowest field BHt proton resonance with the lowest
field 11B signal and the 11B resonance at around 9 ppm
with the MoHB hydrogen atom. Hence, these two boron
resonances are assigned to cluster positions B(6) and
B(3), respectively (Figure 1).
A comparison of the proton cluster resonances (Figure
2) reveals that the MoHB signal shifts significantly
through the series from the highest field resonance of
the tetracarbonyl derivative to the lowest field signal
of the ylide and THF species. Interestingly, the com-
pounds that are more stable in solution (i.e. 3 and 6)
exhibit the MoHB resonance at the highest field,
whereas for the least stable species (i.e. 2 and 8) the
resonance shifts to low fields. The MoHB resonance
correlates with the stability of the corresponding met-
allahexaborane relative to ligand displacement or loss.
In compound 2, the THF resonances were assigned
to the broad signals at 3.68 and 1.52 ppm. The NH3
ligand of 7 led to a broad peak at 0.09 ppm assigned to
NH protons, which in toluene-d8 shifted from 0.20 ppm
Figure 3. Representation of the IR spectra. The average
frequencies are given in boldface type, which for the PPh3,
NCPh, and NH3 derivatives coincide with one of the
spectral bands. The dotted lines do not imply assignments
and illustrate only frequency shifts.
1
at 29 °C to -0.15 ppm at -60 °C. In the H and 31P
NMR spectra of the Mo-ylide complex 8, the resonances
of the methine proton and the phosphorus atom shift
to lower field on coordination. This change is consistent
with coordination of the ylide ligand to the molybdenum
center. As the NMR data of the coordinated ylide ligand
is similar to that found in the palladium complex
{PdCl2(PPh3HCC(O)Me)2],28,29 we propose that the ylidic
carbon binds the molybdenum atom. However, the ylidic
electron pair is delocalized and therefore either the
carbon or the oxygen can act as donors. Inspection of
leads to charge buildup and correspondingly more facile
ligand loss.
This different degree of Mo-CO “back-bonding” con-
forms with the slight elongation of the C(1)-O(1) bond
that is observed when the CtNBu trans ligand in 6 is
replaced by NtCPh or NH3 in 5 and 7, respectively.
Conclusions
1
the H{11B} NMR spectrum at the bottom of Figure 2
The synthesis of “lightly stabilized” metallaboranes
2 and 3 has allowed the systematic study of substitution
reactions at a molybdenum center incorporated into an
iridaborane framework. The series of derivatives gener-
ated provides the first spectroscopic and structural data
for mixed-metal Mo-Ir metallaboranes. The substitu-
tion chemistry can be extended to other Lewis bases,
affording controlled functionalization of the {MoIrB}
hybrid core and concomitant change of the electronic
contributions of the Mo metal. The molybdenum frag-
ment in 2 and 5 is a reactive center with potential
cooperative effects between the adjacent boron and
iridium atoms. Reactions with organic substrates may
lead to the synthesis of new hybrid clusters and/or to
useful transformations of the organic reagents.
reveals that there are weak signals (indicated as
asterisks) in the negative region of the spectrum that
can be assigned to a second {Mo(CO)3L} derivative. Note
that the shift of the MoHB resonance in this presumed
coordination isomer is close to that of the THF com-
pound 2. This is consistent with coordination of the ylide
via the carbonyl oxygen atom rather than the methine
carbon atom. However, without definitive structural
data, the bonding mode of the ligand remains uncertain.
Comparison of the IR Spectra. The average CO
stretching frequency decreases by 83 cm-1 on moving
through the series from the tetracarbonyl derivative 3
to the ammonia analogue 7 (Figure 3). The band at the
highest frequency shifts by 9 cm-1 to lower values,
whereas the band with the lowest wavenumber suffers
a significant shift of 46 cm-1 from 3 to 7. However, the
greatest νCO shifts toward low frequencies are observed
when one carbonyl is substituted by CNBu and then by
PPh3. In particular, either the band at 1976 or 1968
Experimental Section
General Considerations. All reactions were carried out
under an argon atmosphere using standard Schlenk-line
techniques.32 Solvents were distilled immediately before use
under a dinitrogen atmosphere: sodium benzophenone ketyl
for hexanes and tetrahydrofuran and calcium hydride for
dichloromethane. All commercial reagents were used as re-
ceived without further purification. The iridapentaborane 1
and the (arene)tricarbonylmolybdenum complex were prepared
by following synthetic procedures previously reported.1,33 NMR
cm-1 in 6 shifts a minimum of 84 and 76 cm-1
,
respectively, to lower values when the isocyanide ligand
is substituted by PPh3.
Significantly, the order of decreasing average fre-
quency for the five compounds is exactly the same as
found for the MoHB chemical shift. Decreasing CO
frequency is an accepted measure of increasing negative
charge buildup on the metal center. Hence, it appears
that replacement of the fourth CO of the Mo(CO)4
fragment with increasingly poorer π-acceptor ligands
(32) Shriver, D. F., Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds; Wiley-Interscience: New York, 1986.
(33) Pidcock, A.; Smith, J. D.; Taylor, B. W. J. Chem. Soc. A 1967,
872.

6000 Organometallics, Vol. 23, No. 25, 2004
Mac´ıas et al.
spectra were recorded on a 400 MHz Bruker instrument. NMR
references: internal (C6D6, δH 7.16 ppm) for 1H; external
([(Me4N)(B3H8)] in acetone-d6, δB -29.7 ppm) for 11B; external
(H3PO4 in D2O, δP 0.0 ppm) for 31P. IR spectra were recorded
on a Nicolet 205 FT-IR spectrometer. Mass spectra were
acquired on a Finnigan MAT Model 8400 mass spectrometer.
M-H-W Laboratories, Phoenix, AZ, performed elemental analy-
sis.
X-ray Structure Determinations. The crystallographic
details of 3 and 5-7 are gathered in the Supporting Informa-
tion. All data were collected on a Bruker Apex CCD diffrac-
tometer at 100(2) Κ with Mo KR radiation (λ ) 0.710 73 Å).
Relevant data for the crystallographically studied compounds
are summarized in Table 1.
orange. After 5 min of stirring, the THF was evaporated to
give a brown residue, which was dissolved in CH2Cl2 and
filtered through silica gel. The resulting bright orange solution
was treated with 19 mg (0.07 mmol) of PPh3 to give a bright
red mixture, which was stirred for 1 h at room temperature.
Then, the solvent was evaporated to dryness and the residue
extracted with hexane. The hexane solution was refrigerated
at 4 °C, and overnight red star-shaped crystals were isolated.
The NMR of the remaining residue (after extraction with
hexane) showed the peaks of 1, BH3‚PPh3, and the iridatribo-
rane and iridatetraborane adducts [Cp*IrB2H6(PPh3)] and
[Cp*IrB3H7(PPh3)].34 The red crystals were characterized as
[1-Cp*-2,2,2-(CO)3-2-PPh3-nido-1,2-IrMoB4H8] (4, 14 mg, 0.02
mmol, 29%). IR (KBr): 2522 (m, νBH), 2504 (m, νBH), 2456 (m,
νBH), 2427 (m, νBH), 1975 (s, νCO), 1892 (vs, νCO), 1865 (vs, νCO),
1837 (sh, νCO). HR-MS (FAB): m/z 823.1536 (M+ - H), calcd
for C31H38O3B4IrPMo; measd m/z 823.1562. Anal. Calcd for
C31H38O3B4IrPMo: C, 45.35; H, 4.67. Found: C, 45.25; H, 4.71.
11B NMR (C6D6): d 51.2 (br, 1B), 11.0 (br, 1B), -4.3 (br, 2B).
1H{11B} NMR (C6D6): δ 7.78-7.76 (6 H, PPh), 7.16-6.94 (9
H, PPh), 6.77 (s, 1H, BHt), 4.20 (s, 1H, BHt), 3.66 (s, 1H, BHt),
3.11 (s, 1H, BHt), 1.75 (s, 15H, Cp*), -0.01 (s, 1H, BHB), -3.08
(s, 1H, BHB), -3.56 (s, 1H, BHB), -8.92 (s, 1H, MoHB). 31P-
{1H} NMR (C6D6): δ 54.7 (s).
Reaction of [Cp*IrB4H10] (1) with [{η6-(C6H4)(CH3)2}-
Mo(CO)3]. Method 1: Without Free CO. A 36 mg portion
of the iridapentaborane 1 was treated with 27 mg (0.094 mmol)
of the molybdenum complex in 4 mL of tetrahydrofuran. The
solution became bright yellow; then, a few minutes later, it
turned to orange, and finally it changed to brown and became
cloudy with a suspension. The reaction mixture was filtered
through silica gel to give a bright brown solution (the silica
gel retained a brown residue). The solvent was evaporated and
the residue examined by NMR in C6D6 and characterized as
compound 2.
Synthesis of [{Cp*Ir}{(CO)3(NCPh)Mo}B4H8] (5). A 38
mg portion (0.1 mmol) of 1 was treated with 29 mg (0.1 mmol)
of [{η6-1,2-(CH3)2-C6H4}Mo(CO)3] in 1.5 mL of THF. A 5-fold
excess of benzonitrile was added, and the reaction mixture was
stirred for 30 min at room temperature under argon. The
solvent was evaporated to dryness, yielding an orange-yellow
residue, which was chromatographed on a silica gel column.
Elution with hexane/CH2Cl2 (1:1) afforded a yellow band that
was crystallized from hexane/CH2Cl2 to give, after drying
under vacuum, 50 mg (0.07 mmol) of [1-Cp*-2,2,2-(CO)3-2-
(NCC6H5)-nido-1,2-IrMoB4H8] (5; 70% yield). IR (KBr): 2958
(w, νCH). 2915 (w, νCH), 2516 (m, νBH), 2464 (m, νBH), 2250 (w,
νNC), 1971 (s, νCO), 1897 (s, νCO), 1889 (s, νCO), 1798 (s, νCO),
1589 (w, νCC), 1442 (w, νCC), 1377 (w, νCC). LR-MS (FAB): m/z
662 (M+), calcd for C20H28O3B4NIrMo; found weak envelope
with cutoff at m/z 666 and maximum at m/z 659 {M+ - 3(H)},
strong envelope with cutoff at m/z 639 and maximum at m/z
634 that corresponds to {M+ - CO}. Anal. Calcd for C20H28O3B4-
NIrMo: C, 36.29; H, 4.26. Found: C, 36.37; H, 4.41. 11B{1H}
NMR (C6D6; peaks are too broad to resolve the nJ(B,H)
coupling): δ 46.3 (s, 1B), 8.9 (s, 1B), -4.8 (s, 1B), -5.2 (s, 1B).
1H{11B} NMR (C6D6): δ 7.05-6.95 (m, 1H, C6H5CN), 6.80-
6.75 (m, 2H, C6H5CN), 6.65-6.58 (m, 2H, C6H5CN), 6.91 (s,
1H, BHt), 3.69 (s, 1H, BHt), 3.45 (s, 1H, BHt), 3.12 (s, 1H, BHt),
1.77 (s, 15H, Cp*), -0.07 (q, nJ(H,H) ) 7 Hz, 1H, BHB), -3.27
[{Cp*Ir}{(THF)(CO)3Mo}B4H8] (2): 11B NMR (C6D6) δ 44.7
(br. d, 1J(B,H) ) 137 Hz, 1B), 9.5 (br, 1B), -5.0 (br d, 2B);
1H{11B} NMR (C6D6) δ 6.95 (s, 1H, BHt), 3.68 (br, THF), 3.63
(s, 1H, BHt), 3.45 (s, 1H, BHt), 3.12 (s, 1H, BHt), 1.80 (s, 15H,
Cp*), 1.52 (br, THF), 0.28 (s, 1H, BHB), -3.17 (s, 1H, BHB),
-3.54 (s, 1H, BHB), -6.90 (s, 1H, MoHB).
After the characterization of 2 by NMR spectroscopy, the
solvent was removed under vacuum, the red-brown residue
dissolved in hexane, and this solution applied to a chroma-
tography column. Using hexane as eluent, we isolated an
orange band that we characterized as [1-Cp*-2,2,2,2-(CO)4-
nido-1,2-IrMoB4H8] (3; 14 mg, 0.027 mmol, 29%). IR (cyclo-
hexane): 2523 (w br, νBH), 2488 (w br, νBH), 2465 (w br, νBH),
2042 (s, νCO), 1976 (s, νCO), 1922 (s, νCO), 1906 (s, νCO). LR-MS
(FAB): m/z 587 (M+), calcd for C14H23O4B4IrMo; found envelope
with cutoff at m/z 563 and maximum at 558 {M+ - (CO +
H)}, and the loss of three consecutive CO molecules. Anal.
Calcd for C14H23O4B4IrMo: C, 28.66; H, 3.95. Found: C, 28.86;
1
H, 4.12. 11B NMR (C6D6): δ 51.7 (d, J(B,H) ) 137 Hz, 1B),
n
1
9.7 (t, J(B,H) ) 76 Hz, 1B), -3.2 (d, J(B,H) ) 155 Hz, 1B),
-5.4 (d, J(B,H) ) 151 Hz, 1B). H{11B} NMR (C6D6): δ 6.81
(s, BHt), 3.85 (t, nJ(H,H) ) 7 Hz, BHt), 3.42 (t, nJ(H,H) ) 6
Hz, BHt), 2.97 (m, BHt), 1.66 (s, 15H, Cp*), 0.14 (q, nJ(H,H) )
6 Hz, 1H, BHB), -3.38 (quit, nJ(H,H) ) 8 Hz, 1H, BHB), -3.62
1
1
n
n
n
(quit, J(H,H) ) 7 Hz, 1H, BHB), -3.45 (s, 1H, BHB), -8.10
(quit, J(H,H) ) 8 Hz, 1H, BHB), -10.08 (t, J(H,H) ) 7 Hz,
1H, MoHB). 13C{1H} NMR (C6D5CD3): δ 217.6 (CO), 217.3
(CO), 212.3 (CO), 208.1 (CO), 99.4 (C5Me5), 8.9 (C5(CH3)5).
Method 2: With Free CO. A 48 mg portion (0.17 mmol)
of [η6-(xylene)Mo(CO)3] was added to a solution of 65 mg (0.17
mmol) of 1 in THF under an argon atmosphere. The reaction
mixture was stirred at room temperature for 30 min. Following
this, CO was bubbled through the solution at room tempera-
ture for 1 h. The resulting bright orange solution was
evaporated to dryness, affording an orange residue. The latter
was dissolved in hexane and transferred to the top of a
chromatography column packed with silica gel. Elution with
neat hexane gave an orange fraction. Removal of solvent in
vacuo yielded 3 as an orange powder (65 mg, 0.11 mmol, 67%).
Synthesis of [{Cp*Ir}{(CO)3(PPh3)Mo}B4H8] (4). To 28
mg (0.07 mmol) of 1 dissolved in 5 mL of THF, we added the
molybdenum complex at room temperature under an atmo-
sphere of argon. The initial pale yellow solution of the
iridapentaborane turned to bright orange and then to brown-
n
(t, J(H,H) ) 7 Hz, 1H, MoHB).
Synthesis of [{Cp*Ir}{(CO)3(CNBu)Mo}B4H8] (6). We
treated 0.1064 g (0.279 mmol) of 1 with 0.08 g (0.279 mmol)
of the molybdenum complex in 4 mL of THF at room temper-
ature under argon. After 30 min of stirring, we added 0.14
mL (1.395 mmol) of butyl isocyanide. The brown solution was
stirred for another 30 min. The solvent was evaporated to
dryness, and the brown residue was dissolved in CH2Cl2 to
give a bright yellow solution, which was filtered off through
silica gel under an argon atmosphere. The silica gel retained
a brown residue, and the filtrate gave a yellow solution.
Evaporation of the dichloromethane under vacuum afforded
a yellow residue that was crystallized in hexane to give 81
mg (45% yield) of the yellow iridamolybdahexaborane [1-Cp*-
2,2,2-(CO)3-2-(CNBu)-nido-1,2-IrMoB4H8] (6). IR (KBr): 2959
(w, νCH), 2913 (w, νCH), 2873 (w, νCH), 2515 (m, νBH), 2460 (m,
νBH), 2189 (s, νCN), 1976 (vs, νCO), 1968 (vs, νCO), 1882 (vs, νCO),
1836 (vs, νCO). HR-MS (FAB): m/z 644.1360 (M+ - H), calcd
for C18H31O3NB4IrMo; measd m/z 644.1338. Anal. Calcd for
C18H32O3B4NIrMo: C, 33.68; H, 5.03. Found: C, 33.61; H, 4.99.
11B{1H} NMR (C6D6; peaks are too broad to resolve the nJ(B,H)
(34) Macias, R.; Fehlner, T. P.; Beatty, A. M. Organometallics 2004,
23, 2124.

Heteobimetallic Metallaborane Chemistry
Organometallics, Vol. 23, No. 25, 2004 6001
coupling): δ 46.6 (s, 1B), 8.6 (s, 1B), -4.3 (s, 1B), -5.7 (s, 1B).
1H{11B} NMR (C6D6): δ 6.74 (s, 1H, BHt), 3.81 (s, 1H, BHt),
3.51 (s, 1H, BHt), 3.03 (s, 1H, BHt), 1.78 (s, 15H, Cp*), -0.21
(q, nJ(H,H) ) 7 Hz, 1H, BHB), -3.33 (quit, nJ(H,H) ) 7 Hz,
1H, BHB), -3.61 (s, 1H, BHB), -9.39 (t, nJ(H,H) ) 7, 1H,
MoHB).
treated with 84 mg (0.25 mmol) of Ph3PdCHC(O)2Me. The
reaction mixture was stirred for 1 h at room temperature. After
this time, the solvent was evaporated to dryness and the
residue extracted with hexane to give a yellow solution and
an orange precipitate. The hexane-soluble fraction contained
[Cp*IrB4H10], [Cp*IrB3H8], and 3, whereas the insoluble
residue was comprised mainly of 5 and a new species which
exhibits the same NMR pattern as the molybdairidahexa-
borane series [1-Cp*-2,2,2-(CO)3-2-(L)-nido-1,2-IrMoB4H8] (L
) CO, THF, PPh3, NtCC6H5, CtNBu, NH3). We propose that
the new species is the ylide derivative [Cp*Ir(CO)3(Ph3-
PCHCO2Me)MoB4H8] (8). HR-MS (FAB): m/z 896.1826 M+,
calcd for C34H42O5PB4IrMo; measd m/z 896.1845. 11B{1H} NMR
(C6D6; peaks are too broad to resolve the nJ(B,H) coupling): δ
44.4 (1B), 8.4 (s, 1B), -5.0 (2B). 1H{11B} NMR (C6D6): δ 7.60-
7.55 (m, C6H5), 7.00-6.94 (m, C6H5), 4.00 (d, 1J(H,P) ) 19 Hz,
1H, PPh3CHCO2CH3), 3.76 (s, 3H, BHt), 3.17 (s, 3H, PPh3-
CHCO2(CH3)), 1.92 (s, 15H, Cp*), -0.05 (s, 1H, B-H-B),
-3.12 (s, 1H, BHB), -3.39 (s, 1H, BHB), -6.14 (s, 1H, MoHB).
31P{1H} NMR (C6D6): 18.4 (br s).
Synthesis of [{Cp*Ir}{(CO)3(NH3)Mo}B4H8] (7). A 46 mg
portion (0.121 mmol) of [Cp*IrB4H10] (1) was treated with 35
mg (0.121 mmol) of [{η6-o-(C6H4)(CH3)2}Mo(CO)3] in 2 mL of
THF. After 30 min of stirring at room temperature under
argon, 2 mL of NH3 was condensed in the reaction flask at
-70 °C. The initial orange solution turned yellow. The reaction
mixture was stirred until it reached room temperature. The
solvent was evaporated to dryness, the residue dissolved in
CH2Cl2, and this mixture filtered through silica gel, giving a
bright yellow solution. The solvent was evaporated to dryness
and the yellow residue examined by NMR. Crystallization in
hexane afforded 25 mg (0.043 mmol, 36%) of yellow [1-Cp*-
2,2,2-(CO)3-2-(NH3)-nido-1,2-IrMoB4H8] (7). IR (KBr): 2524 (m,
νBH), 2465 (m, νBH), 2427 (s, νBH), 1967 (vs, νCO), 1879 (vs, νCO),
1790 (vs, νCO), 1209 (m), 1027 (m), 910 (m). HR-MS (FAB): m/z
579.0968 (M+ - H), calcd for C13H26O3NB4IrMo; measd m/z
579.0958. 11B NMR (C6D6): δ 44.7 (d, 141 Hz, 1B), 7.5 (t, 95
Separation of the reaction mixture was not possible by
chromatographic means; therefore, we subjected the system
to crystallization in CH2Cl2/hexane at -40 °C. However, after
several days the intensity of the concentration of the ylide
derivative decreased and that of the tetracarbonyl analogue
increased, indicating that the former decomposes under the
conditions of crystallization.
1
Hz, 1B), -4.4 (d, 1B), -5.5 (d, 1B). H{11B} NMR (C6D6): δ
6.65 (s, 1H, BHt), 3.28 (t, 6 Hz, 1H, BHt), 2.97 (t, 6 Hz,1H,
BHt), 2.87 (t, 6 Hz, 1H, BHt), 1.54 (s, 15H, Cp*), 0.09 (br. s,
n
3H, NH3), -0.38 (q, J(H,H) ) 6 Hz, 1H, BHB), -3.41 (quit,
nJ(H,H) ) 7, 1H, BHB), -3.60 (s, 1H, BHB), -7.98 (t, nJ(H,H)
) 7, 1H, MoHB).
Acknowledgment. This work was supported by the
National Science Foundation (Grant Nos. CHE 9986880
and CHE 0304008).
Compound 7 decomposed overnight in a CH2Cl2/hexane
solution at 4 °C under an argon atmosphere, giving a brown
precipitate and the tetracarbonyl derivative 2.
Reaction of [1-Cp*-2,2,2-(CO)3-2-(NCC6H5)-nido-1,2-
IrMoB4H8] (5) with PPh3dCHC(O)2Me. A 95 mg portion
(0.25 mmol) of [Cp*IrB4H10] was treated with 71 mg (0.25
mmol) of [{η6-o-(C6H4)(CH3)2}Mo(CO)3] in THF. After 30 min,
0.3 mL of benzonitrile was added and the reaction mixture
stirred for 1 h. The solvent was evaporated to dryness, the
residue dissolved in CH2Cl2, and this solution filtered through
silica gel to give a bright yellow solution of the bezonitrile
derivative 5. The solvent was reduced in volume, and 5 was
Supporting Information Available: Text and tables
giving X-ray diffraction details, atomic coordinates, bond
lengths and angles, isotropic and anisotropic displacement
parameters; crystal data are also available as CIF files. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM049308F