Chemistry of [1-Cp*-arachno-1-IrB4H10] and [1-Cp*arachnoo-1-IrB3H9]: Synthesis and characterization of the new substituted iridaboranes [1-Cp*-arachno-1- IrB3H7-2-l], [1-Cp*-arachno-1-IrB(2)H (6)-2-l], and [1-Cp*-arachno-1-IrB(4)H (8)-2,5-(Br)(2)] (l = PMe(3), PMe(2)Ph, PMePh(2), py, NEt3)

Article abstract of DOI:10.1021/om049960a

The treatment of [Cp*IrB₄H₁₀] (1) and [Cp*IrB₃H₉] (2) with typical Lewis bases afforded the new substituted iridatetra- and iridatriboranes [Cp*IrB ₃H₇L] (L = PMe₃ (3), PMe₂Ph (5), PMePh₂ (7), PPh₃ (10), py (12), NEt₃ (14)) and [Cp*IrB₂H₆L] (L = PMe₃ (4), PMe ₂Ph (6), PMePh₂ (8), PPh₃ (11), py (13), NEt₃ (15)), respectively, plus the adduct BH₃L as coproduct. With PPh₃, py, and NEt₃, the formation of the iridapentaborane [1-Cp*-nido-1-IrB₄H₈] (9) was also observed. The molecular structure of [Cp*IrB₂H₆L] was confirmed by X-ray diffraction analysis on compounds 4, 8, and 13. The substituted iridatetraboranes were found to decompose in solution and in the solid state with decomposition pathways that depend on the nature of the L-B bond and the concentration of the free Lewis bases. Two routes involving the apparent disproportionation of iridaborane-base adducts were found to compete with the loss of a {BH} unit. A reaction cycle driven by the Lewis acid/base chemistry of BH₃ was constructed from these reactions. The P-B bond is labile, leading to ligand exchange with free Lewis bases. For compound 3, the equilibrium constant for the exchange with PMe₂Ph, PMePh ₂, and py was measured. In contrast to reaction with nucleophiles, treatment of 1 with bromine and N-bromosuccinimide led to the formation of the dibromo- and monobromo derivatives [1-Cp*-1-H-2,5-(Br)₂- arachno-1-IrB₄H₇] (16) and[1-Cp*-1-H-2-Br-arachno-1- IrB₄H₈] (17), respectively. The molecular structure of 16 was confirmed by X-ray diffraction analysis.

Full text of DOI:10.1021/om049960a

2124
Organometallics 2004, 23, 2124-2136
Ch em istr y of [1-Cp *-a r a ch n o-1-Ir B4H10] a n d
[1-Cp *-a r a ch n o-1-Ir B3H9]: Syn th esis a n d
Ch a r a cter iza tion of th e New Su bstitu ted Ir id a bor a n es
[1-Cp *-a r a ch n o-1-Ir B3H7-2-L],
[1-Cp *-a r a ch n o-1-Ir B2H6-2-L], a n d
[1-Cp *-a r a ch n o-1-Ir B4H8-2,5-(Br )2] (L ) P Me3, P Me2P h ,
P MeP h 2, p y, NEt3)
Ramo´n Mac´ıas,* Thomas P. Fehlner, and Alicia M. Beatty
Department of Chemistry and Biochemistry, University of Notre Dame,
Notre Dame, Indiana 46556-5670
Received J anuary 14, 2004
The treatment of [Cp*IrB4H10] (1) and [Cp*IrB3H9] (2) with typical Lewis bases afforded
the new substituted iridatetra- and iridatriboranes [Cp*IrB3H7L] (L ) PMe3 (3), PMe2Ph
(5), PMePh2 (7), PPh3 (10), py (12), NEt3 (14)) and [Cp*IrB2H6L] (L ) PMe3 (4), PMe2Ph (6),
PMePh2 (8), PPh3 (11), py (13), NEt3 (15)), respectively, plus the adduct BH3L as coproduct.
With PPh3, py, and NEt3, the formation of the iridapentaborane [1-Cp*-nido-1-IrB4H8] (9)
was also observed. The molecular structure of [Cp*IrB2H6L] was confirmed by X-ray
diffraction analysis on compounds 4, 8, and 13. The substituted iridatetraboranes were found
to decompose in solution and in the solid state with decomposition pathways that depend
on the nature of the L-B bond and the concentration of the free Lewis bases. Two routes
involving the apparent disproportionation of iridaborane-base adducts were found to compete
with the loss of a {BH} unit. A reaction cycle driven by the Lewis acid/base chemistry of
BH3 was constructed from these reactions. The P-B bond is labile, leading to ligand exchange
with free Lewis bases. For compound 3, the equilibrium constant for the exchange with
PMe2Ph, PMePh2, and py was measured. In contrast to reaction with nucleophiles, treatment
of 1 with bromine and N-bromosuccinimide led to the formation of the dibromo- and
monobromo derivatives [1-Cp*-1-H-2,5-(Br)2-arachno-1-IrB4H7] (16) and[1-Cp*-1-H-2-Br-
arachno-1-IrB4H8] (17), respectively. The molecular structure of 16 was confirmed by X-ray
diffraction analysis.
In tr od u ction
unsymmetrical cleavage of boranes to give ionic prod-
ucts. This pathway was observed, for example, in the
reactions of diborane(6) with NH3 and NH2-, which
Reactions of Lewis bases with polyhedral boron-con-
taining compounds have been investigated ever since
the first boron hydrides were prepared.1,2 In the earlier
works, it was found that boranes undergo many reac-
tions with ligands to produce simple Lewis acid-base
adducts. Such reactions are known as symmetrical
cleavage. Some representative examples are the reac-
tion of B2H6 with CO to give BH3CO1b or the formation
of B3H7[(CH3)3N] and BH3[(CH3)3N] from the treat-
ment of B4H10 with trimethylamine.1c In contrast, it was
also recognized that some Lewis bases promote the
afforded [BH2(NH3)2]+[BH4]-,1d,e and H2NBH2 and
- 1f,g
BH4
,
respectively. Similarly, the reaction of B4H10
with NH3 proceeded by unsymmetrical cleavage to yield
the salt [BH2(NH3)2]+[B3H8]-.1h In some cases, saltlike
products were obtained from reactions of Lewis base
substituted borane adducts with nonsubstituted bo-
ranes. Thus, the reaction of B2H4(PMe3)2 with B4H10
afforded the salt B3H6(PMe3)2+B3H8-, which reacts with
a slight excess of NMe3 to give the neutral tetraborane-
(8) adduct B4H8(PMe3), in excellent yields.1i
* To whom correspondence should be addressed. E-mail: rmaza@
nd.edu.
Alternatively, polyhedral boranes can react with
Lewis bases to form borane adducts with displacement
of molecular hydrogen, without cleavage of the cluster
framework. Thus, B4H8(CO) resulted from the reaction
of B4H10 with CO;2a similarly, nido-decaborane(14),
B10H14, reacts with CH3CN to give the bis(adduct)
arachno-decaborane(12), B10H12(CH3CN)2, and H2(g).2b
(1) (a) Shore, S. G. In Boron Hydride Chemistry; Muetterties, E. L.,
Ed.; Academic Press: New York, 1975; p 79. (b) Burg, A. B.; Schels-
inger, H. I. J . Am. Chem. Soc. 1937, 59, 780. (c) Parry, R. W.; Edwards,
L. J . J . Am. Chem. Soc. 1959, 81, 3554. (d) Schultz, D. R.; Parry, R.
W. J . Am. Chem. Soc. 1958, 80, 4-8. (e) Shore, S. G.; Parry, R. W. J .
Am. Chem. Soc. 1958, 80, 8-12. (f) Schaeffer, G. W.; Basile, L. J . J .
Am. Chem. Soc. 1955, 77, 331. (g) Shore, S. G.; Hickam, C. W., J r.;
Cowles. D. J . Am. Chem. Soc. 1965, 87, 2755. (h) Hough, W. V.;
Edwards, L. J . Adv. Chem. Ser. 1961, No. 32, 184. (i) Kameda, M.;
Shimoi, M.; Kodama, G. Inorg. Chem. 1984, 23, 3705.
These and other pioneering works on borane adduct
chemistry played a role in understanding the cluster-
geometry/electron-counting paradigm,3,4 characteriza-
(2) (a) Brennan, G. L.; Schaeffer, R. J . Inorg. Nucl. Chem. 1961,
20, 205. (b) Schaeffer, R. J . Am. Chem. Soc. 1957, 79, 1006.
10.1021/om049960a CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/26/2004

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2125
Sch em e 1
tion of new fluxional processes,5 and development of
synthetic procedures.1 The preparation of important
deltahedral starting materials such as, for example,
carboranes utilizes base adduct chemistry.
chemistry than p-block elements, they may provide
reaction pathways not available to clusters formed
exclusively by main-group elements. Therefore, we
anticipate that reactions of metallaboranes with Lewis
bases will generate new chemistry, involving novel
reaction mechanisms, stoichiometric cycles, and the
formation of new species with potential applications in
synthesis and catalysis. The following describes the
chemistry of the five-vertex arachno-iridapentaborane
[Cp*IrB4H10] (1) and four-vertex arachno-iridatetrabo-
rane [Cp*IrB3H9] (2) with typical phosphorus and
nitrogen bases as well as a typical electrophile.
Reactions of metallaboranes with Lewis bases have
been hindered by the lack of good synthetic routes, and
systematic studies have been limited to a few cases,
including small metal-rich species.6-8 The development
of a general route to metallaboranes via condensation
of monoboranes on a metal template now permits a
systematic study of their reaction chemistry.9 Thus,
borane displacement by Lewis bases, ligand substitution
on boron and metal sites, and ortho metalation of
aromatic bases have been reported recently.10,11 In some
aspects, these reactions parallel the early results found
with boron hydrides but also illustrate how the presence
of transition-metal centers can lead to a different
chemistry. Thus, the metal can compete with the boron
sites for the Lewis bases, leading, for example, to metal
fragment displacement versus borane displacement or
ligand substitution at metal sites rather than at a boron
site. As transition metals exhibit richer coordination
Resu lts a n d Discu ssion
A. Syn th esis a n d Ch a r a cter iza tion of New Ir id -
a b or a n es. 1. St r u ct u r es. [1-Cp *-1-H -a r a ch n o-1-
Ir B3H6-2-(L)] a n d [1-Cp *-1-H-a r a ch n o-1-Ir B2H5-2-
(L)]. The reaction of 1 with PMe3, PMe2Ph, PMePh2,
PPh3, NC5H5(py), and Et3N causes borane displacement
and formation of new phosphine-substituted iridatet-
raboranes of the general formula [1-Cp*-1-H-arachno-
1-IrB3H6-2-(L)] (L ) PMe3 (3), PMe2Ph (5), PMePh2 (7),
PPh3 (10), py (12), NEt3 (14); Scheme 1). These new
species are unstable in solution as well as in the solid
state, affording the corresponding substituted irida-
triboranes of general formula [1-Cp*-1-H-arachno-1-
IrB2H5-2-(L)] (L ) PMe3 (4), PMe2Ph (6), PMePh2 (8),
PPh3 (11), py (13), NEt3 (15)).
(3) Williams, R. E. Adv. Inorg. Chem. Radiochem. 1976, 18, 67-
142.
(4) Wade, K. Adv. Inorg. Chem. Radiochem. 1976, 18, 1-66.
(5) Gaines, D. F. Boron Chemistry-4; Pergamon: Oxford, U.K., 1980.
(6) Housecroft, C. E.; Fehlner, T. P. Inorg. Chem. 1986, 25, 404-
405.
(7) Housecroft, C. E.; Buhl, M. L.; Long, G. J .; Fehlner, T. P. J . Am.
Chem. Soc. 1987, 109, 3323-3329.
(8) Barton, L.; Bould, J .; Fang, H.; Hupp, K.; Rath, N. P.; Gloeckner,
C. J . Am. Chem. Soc. 1997, 119, 631-632.
(9) Fehlner, T. P. Organometallics 2000, 19, 2643-2651.
(10) Lei, X.; Shang, M.; Fehlner, T. P. Organometallics 2000, 19,
5266-5272.
(11) Pangan, L. N.; Kawano, Y.; Shimoi, M. Organometallics 2000,
19, 5575-5581.
We were unable to obtain suitable single crystals of
[Cp*IrB3H7(L)], but the structures are clear from the
spectroscopic data and are in accord with electron-
counting rules.3,4 The molecular ions and fragmentation
patterns are in agreement with their formulations. The

2126 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
state structures. The 11B{1H} spectra of 4, 6, 8, and 11
exhibit a broad singlet around -18 ppm and a doublet
close to -24 ppm, the latter arising from 1J (B,P)
coupling between the substituted boron atom and the
phosphorus nucleus of the phosphine ligands. Upon
coupling with the proton nuclei, the broad singlet
becomes a broad triplet for 4 and 6, whereas the doublet
becomes a doublet of triplets (dt) for 4 and a ddd for 6.
This coupling was not resolved for 8 and 11, due to the
broadness of the peaks. The amine derivatives 13 and
15 show a doublet and a triplet in the 11B NMR spectra,
where the doublet corresponds to the N-substituted
boron atom and is shifted by about 25 ppm to lower field
than the corresponding resonances of the phosphine
analogues. The proton NMR shows three B-H terminal
resonances and a Cp* signal in the low-field region and
B-H-B bridging resonances and Ir-H terminal reso-
nances at high field. The BHB resonances for the
phosphine and NEt3 derivatives appear near -6 ppm,
whereas that for pyridine is found at -3.41 ppm. The
two Ir-H hydride resonances are found between -16
and -19 ppm.
F igu r e 1. Molecular structure of [Cp*IrB2H6(py)] (13).
11B NMR spectra of 3 and 5 exhibit a doublet and two
triplets in a 1:1:1 ratio; the resonance at the highest
field becomes a doublet under proton decoupling, indi-
cating that this is the site of the phosphine substitution.
7 and 10 also exhibit three resonances in the 11B NMR,
but the coupling with the hydrogen and the phosphorus
atoms were not resolved, due to the broadness of the
peaks. The 11B NMR spectra of the phosphine series (3,
5, 7, 10) are very similar, whereas those of the nitrogen
bases 12 and 14 exhibit the expected shift of the
resonance of the N-substituted boron to lower field. The
proton NMR spectra show one Cp* signal around 2.00
ppm, four B-H terminal proton resonances between 4
and 2 ppm, two B-H-B bridging hydrogen signals
between -1 and -5 ppm, and one Ir-H hydride
resonance at high field. In addition, the 1H NMR
spectrum of 5 shows two doublets at +1.09 and +0.99
ppm, assigned to the methyl groups of the prochiral
phosphine PMe2Ph. 3 and 7 exhibit only one doublet for
the methyl group of the phosphine ligands. The 31P{1H}
spectra of 3 and 5 show a broad quartet centered at -9.7
and -5.3 ppm, respectively, whereas the spectra of 7
and 10 consist of a broad peak at 1.1 and 4.8 ppm,
respectively. These data are consistent with four-ver-
tex butterfly cluster structures with the iridium atom
on a “hinge” position (Scheme 1). The phosphine coor-
dinates a “wingtip” position; therefore, these new com-
pounds are derivatives of 212 in which phosphine
substitution results in the loss of a B-H terminal
hydrogen atom and one Ir-H hydride: i.e., phosphine-
substituted “borallyl” complexes.13
[1H-1H]-COSY experiments (Tables 3 and 4) and
1H{selective 11B} NMR for 4 and 13 permitted assign-
ment of the resonances. The correlation experiments
showed that there are strong cross-peaks between the
B-H-B bridging hydrogen and the three terminal B-H
hydrogen atoms. This is reflected in the one-dimensional
1H{11B} NMR, in which the resonance of the bridging
hydrogen atom is resolved as an apparent quintet for 4
and an apparent quartet for 13. The two-dimensional
spectra also displayed weak cross-peaks between the
B-H-B hydrogen atoms and the Ir-H hydrides. Fur-
thermore, the Ir-H hydride atoms exhibited weak cross-
peaks with each other and with the Cp* ligands.
However, none of these weak off-diagonal signals is
manifest in the coupling patterns of the 1D 1H{11B}
NMR spectra of 4 and 13, and the hydride resonances
are a singlet and a doublet (2J (H,P)) for 4 and two
singlets for 13.
[1-Cp *-n id o-1-Ir B4H8] (9). The reactions of 1 with
PPh3, pyridine (py), and triethylamine (Et3N) at room
temperature afforded mixtures of the corresponding
substituted arachno-tetraboranes and arachno-irida-
triboranes, together with a new species, which was also
found to be formed in the conversion of 3 to 4 at high
temperature. Of limited stability, this compound could
only be characterized spectroscopically in mixtures
optimized for its concentration maximum. The data
suggest it is the iridapentaborane [1-Cp*-nido-IrB4H8]
(9; Scheme 1).
The mass spectrum of the reaction mixture at high
Products 4, 8, and 13 were characterized by X-ray
diffraction analysis (Figure 1, Table 1), and the molec-
ular structures show them to be iridatriboranes consist-
ing of a triangle formed by the organometallic fragment
{Cp*IrH2} and the boron vertices {BH2} and {BHL} (L
) PMe3 (4), PMePh2 (8), py (13)). Distances and angles
given in Table 2 fall within the ranges of existing
structural data on related iridaboranes.12,14,15
concentrations of the iridapentaborane exhibits
a
broad envelope centered at 376 with a cutoff of m/z
380 consistent with the parent molecular ion of 9,
[C10H23B4Ir]+, and some H fragmentation. The 11B{1H}
NMR spectrum of 9 shows a singlet at -8.9 ppm that
becomes a doublet of triplets in the coupled spectrum.
1
The H{11B} NMR spectrum consists of two triplets of
The NMR data of these iridatriboranes are gathered
in Tables 3-5 and are fully in accord with the solid-
(13) Greenwood, N. N.; Kennedy, J . D.; Reed, D. J . Chem. Soc.,
Dalton Trans. 1980, 196-200.
(14) Boocock, S. K.; Toft, M. A.; Inkrott, K. E.; Hsu, L. Y.; Huffman,
J . C.; Folting, K.; Shore, S. G. Inorg. Chem. 1984, 23, 3084-3091.
(15) Bould, J .; Greenwood, N. N.; Kennedy, J . D.; McDonald, W. S.
J . Chem. Soc., Dalton Trans. 1985, 1843-1847.
(12) Lei, X.; Shang, M.; Fehlner, T. P. Chem. Eur. J . 2000, 6, 2653-
2664.

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2127
Ta ble 1. Exp er im en ta l X-r a y Diffr a ction P a r a m eter s a n d Cr ysta l Da ta for 4, 8, 13, a n d 16
4
8
13
16
empirical formula
fw
cryst dimens (mm)
space group
C
13H30B2IrP
C23H34B2IrP
555.29
0.2 × 0.2 × 0.1
P21/c
C15H26B2IrN
434.19
0.2 × 0.2 × 0.1
P21/n
C10H23B4Br2Ir
538.54
0.4 × 0.4 × 0.2
P21/n
431.16
0.3 × 0.2 × 0.1
P21/c
a, Å
b, Å
c, Å
13.8721(6)
8.3612(3)
15.1509(6)
90
101.035(1)
90
1724.82(12)
4
1.660
13.3097(7)
20.8741(10)
8.5511(4)
90
98.543(1)
90
2349.4(2)
4
1.570
13.4635(8)
9.4005(6)
14.0187(9)
90
114.128(1)
90
1619.25(18)
4
1.781
9.4317(5)
13.4815(6)
12.5332(6)
90
99.538(1)
90
1571.61(13)
4
2.276
R, deg
â, deg
γ, deg
V, Å3
Z
D(calcd), g cm-3
µ(Mo KR), mm-1
temp, K
7.813
100(2)
61
5.756
100(2)
56
8.231
100(2)
56
13.554
100(2)
56
2θmax, deg
transmissn factors
no. of rflns collected
no. of obsd rflns (I > 2θ(I)
no. of params refined
R
1.00(0.43
20 745
5237
1.00(0.73
23 451
5828
1.00(0.68
16 936
4012
1.00(0.47
16 126
3912
184
250
198
154
0.0216
0.0534
1.037
0.0154
0.0373
1.085
0.0137
0.0324
1.025
0.0252
0.0638
1.127
Rw
goodness of fit
largest peak in final diff map, e Å-3
1.704
1.756
0.828
2.676
Ta ble 2. Selected In ter a tom ic Len gth s (Å) a n d
An gles (d eg) for [Cp *Ir B2H6(P Me3)] (4),
[Cp *Ir B2H6(P P h 2Me)] (8), a n d [Cp *Ir B2H6(C5NH5)]
(13)
Ta ble 4. 11B{1H} a n d 1H{11B} NMR Da ta for
[Cp *Ir B2H6(p y)] (13) in C6D6 a t Room Tem p er a tu r e
assignta
δ(11B), ppm δ(1H), ppmb
[1H-1H]-COSY
B(2)-H(3)
B(3)-H(4)
B(3)-H(5)
µ-H(6)
Ir(1)-H(1)
Ir(1)-H(2)
0.3c
3.84d
3.32
3.20
(3,6)s, (3,5)s
(4,6)s, (4,5)s
(5,6)s
(6,5)s
(1,2)w, (1,6)w, (1, Cp*)w
(2,1)w, (1,6)w, (2,Cp*)w
4
8
13
-22.1e
Bond Lengths
-3.41f
-16.70
-18.47
Ir(1)-B(2)
Ir(1)-B(3)
B(2)-B(3)
B(2)-Ea
2.146(3)
2.157(3)
1.815(4)
1.931(3)
2.143(2)
2.154(2)
1.829(3)
1.930(2)
2.132(2)
2.175(2)
1.828(3)
1.593(3)
Assignments were made on the basis of 1H-{11B(selective)}
a
b
experiments and [1H-1H]-COSY spectroscopy. Additional 1H
Bond Angles
NMR data: δ 8.45 (d, 3J (HH) ) 6 Hz, 2H, NC5H5), 6.36 (t, 3J (HH)
) 8 Hz, 1H, NC5H5), 5.95 (m, 2H, NC5H5), 2.20 (s, 15H, Cp*). c Site
B(2)-Ir(1)-B(3)
Ir(1)-B(2)-B(3)
Ir(1)-B(3)-B(2)
B(3)-B(2)-E
49.89(10)
65.38(12)
64.73(12)
119.76(18)
115.22(13)
50.39(8)
65.11(10)
64.50(9)
118.53(14)
113.65(10)
50.22(9)
66.11(10)
63.68(10)
115.05(16)
119.51(14)
d
of C5NH5 substituent, s; 11B, d 1J (BH) ) 111 Hz. Doublet of
doublets, 2J (HH) 11 Hz, 3J (HH) 4 Hz. e Broad triplet, 1J (BH) )
103 Hz. f Quartet, 2J (HH) ) 10 Hz.
Ir(1)-B(2)-E
a
E ) P for 4 and 8, and E ) N for 13.
(Scheme 1). Compound 9 is an analogue of the known
[1-(CO)3-nido-1-FeB4H8] and [1-(Cp)-nido-1-CoB4H8].16,17
[1-Cp *-1-H-2,5-(Br )2-a r a ch n o-1-Ir B4H8] (16). The
reaction of compound 1 with either Br2 or N-bromosuc-
cinimide in dichloromethane afforded the dibromo-
substituted derivative [1-Cp*-1-H-2,5-(Br)2-arachno-1-
IrB4H7] (16), together with small amounts of the
monobromo analogue [1-Cp*-1-H-2-Br-arachno-1-IrB4H8]
(17) (Scheme 1). Both compounds were characterized by
spectroscopic means, and the molecular structure was
confirmed by X-ray diffraction analysis of 16 (Table 1).
As we were unable to obtain the structure of 1 in
our earlier work, that of 16 is worthy of some discus-
sion. The structure is based on an open four-sided
pyramidal arachno arrangement, which can be formally
obtained by removing two adjacent vertices of con-
nectivity 4 and 5 from a pentagonal-bipyramidal cage
(Figure 2). Compound 16 is, therefore, an 8 skeletal
electron pair (sep) arachno-iridaborane derivative of the
parent B5H11, with the apical BH group replaced by the
isolobal {Cp*Ir} fragment (Figure 2). This structure
resembles that found in the isoelectronic group 8 and 9
Ta ble 3. 11B{1H} a n d 1H{11B} NMR Da ta for
[Cp *Ir B2H6(P Me3)] (4) in C6D6 a t Room
Tem p er a tu r e
assignta
δ(11B), ppm
δ(1H), ppmb
[1H-1H]-COSY
B(2)-H(3)
B(3)-H(4)
B(3)-H(5)
µ-H(6)
Ir(1)-H(1)
Ir(1)-H(2)
-24.8c
1.59d
(3,5)s, (3,4)m, (3,6)s
(4,5)s, (4,6)s, (4,1)w
(5,6)s
(6,1)w, (6,2)w
(1,Cp*)w, (1,2)w
(2,Cp*)w
-19.1e
3.05f
2.83
-6.36g
-17.06
-19.04h
Assignments were made on the basis of 1H{11B(selective)}
a
b
experiments and [1H-1H]-COSY spectroscopy. Additional 1H
NMR data: δ 2.13 (s, 15H, Cp*), 0.69 (d, 2J (HP) ) 17 Hz, Me).
c Site of PMe3 substituent: d, 1J (BP) ) 99; 11B, dt, 1J (BH) + 1J (BP)
1
1
) 113 Hz, J (BH) ) 42 Hz. 31P{1H} NMR: d 16.3 (q, J (BP) ) 95
Hz, PMe3). Broad multiplet, nJ (HH) + J (HP) ) 10 Hz. e Broad
d
2
triplet, 1J (BH) ) 103 Hz. f Broad doublet, 2J (HH) ) 20 Hz.
Quintet, 2J (HH) + 2J (HP) ) 9 Hz. Doublet, 3J (HP) ) 17 Hz.
g
h
equal relative intensity at 2.69 and -4.09 ppm, assigned
to the B-H terminal and B-H-B bridging hydrogen
atoms, respectively, together with a singlet at 2.08 ppm
from the Cp* ligand. The relative intensities of the
terminal and bridging resonances, calibrated with the
known resonances of 10 and 11 present in the reaction
mixture, were found to correspond to 4 H each. The
proposed structure of 9 is based on a square-planar
pyramid with the metal center at the apical position
(16) Greenwood, N. N.; Savory, C. G.; Grimes, R. N.; Sneddon, L.
G.; Davison, A.; Wreford, S. S. J . Chem. Soc., Chem. Commun. 1974,
718.
(17) Miller, V. R.; Weiss, R.; Grimes, R. N. J . Am. Chem. Soc. 1977,
99, 5646-5651.

2128 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
Ta ble 5. 11B{1H} a n d 1H{11B} NMR Da ta (p p m ) for
[Cp *Ir B2H6(P Me2P h )] (6), [Cp *Ir B2H6(P MeP h 2)] (8),
a n d [Cp *Ir B2H6(P P h 3)] (11) in C6D6 a t Room
Tem p er a tu r ea
The effect of the bromine atoms is also reflected by a
deshielding of the two adjacent BHB bridging hydrogen
atoms. In contrast, the unique BHB hydrogen atom and
the IrH hydride do not shift significantly upon bromi-
nation. The [1H-1H]-COSY spectra of 1 and 16 show
strong correlations between the two types of bridging
hydrogen atoms. The BH terminal hydrogens also
exhibit cross-peaks with the BHB bridging hydrogen
atoms. The IrH hydride shows weak correlations with
terminal and bridging hydrogen atoms of the borane
fragment, as well as the methyl groups of the Cp* ring;
however, it appears in the 1H one-dimensional spectrum
as a singlet.
2. P r op er ties. Lew is Ba se Ad d u cts. Compound 1
undergoes facile cleavage with Lewis bases, leading to
borane displacement and formation of new boron-
coordinated iridatri- and iridatetraboranes. This reac-
tivity pattern reflects preferred substitution at a boron
site versus the metal site and stands in contrast with
related compounds, e.g. [(η6-C6Me6)RuB4H10]. This arach-
no-ruthenapentaborane also reacts with PMe3 to give
BH3‚PMe3, but in the ruthenatetraborane product, [(η6-
C6Me6)(PMe3)RuB3H7], the phosphine ligand coordi-
nates to the metal center rather than to the “borallyl”
fragment. The nature of the substitution process de-
pends principally on the particular requirements of the
metal fragment versus those of the borane fragment.
In the molecular structures of the iridatriboranes
[1-Cp*-1-(H)2-arachno-1-IrB2H4-2-(L)] (L ) PMe3 (4),
PMePh2 (5), NC5H5 (13)), the substituents at the boron
vertices are trans to the Cp* ligand, indicating that
steric effects may be important in the final conformation
of the molecules. The B-B distance is slightly shorter
for the PMe3 derivative. The average value of the B-B
distances of these iridatriboranes, 1.824(4) Å, is longer
than the 1.773(8) Å B-B single-bond distance in the
ferratriborane analogue, [(Cp)(CO)2FeB2H5],21 as well
as the average distance of the hydrogen-bridged B-B
bond (1.744 Å) found in substituted triborane deriva-
tives, [B3H7(L)] (L ) NCS-, NCSe-, NCBH3-, NH3,
CO).22-25
6b
8c
11d
assignt
δ(11B)
δ(1H)
δ(11B)
δ(1H)
δ(11B)
δ(1H)
B(2)-H(3) -24.3e
B(3)-H(4) -18.3
B(3)-H(5)
1.59f -24.9g
3.06i -18.3
2.83
2.21 -23.1h
3.18 -16.7
3.03
2.58
3.21
3.09
µ-H(6)
-6.01j
-5.71
-5.13
-17.04
-17.83m
Ir(1)-H(1)
Ir(1)-H(2)
-16.99
-16.96
-18.74k
-18.50l
Chemical shifts are given in parts per million. Additional 1H
a
b
NMR data: δ 7.48 (m, 1H, Ph), 7.38 (m, 2H, Ph), 7.01 (m, 2H,
2
Ph), 2.11 (s, 15H, Cp*), 1.17 (d, J (HP) ) 11 Hz, 3H, Me), 1.10 (d,
2J (HP) ) 11 Hz, 3H, Me). c Additional 1H NMR data: δ 7.43 (m,
1H, Ph), 7.03 (m, 1H, Ph), 6.91 (m, 2H, Ph), 2.04 (s, 15H, Cp*),
d
1.52 (d, 2J (HP) ) 12 Hz, 3H, Me). Additional 1H NMR data: δ
7.65 (m, 1H, Ph), 7.63 (m, 2H, Ph), 7.00 (m, 1H, Ph), 2.03 (s, 15H,
Cp*). e Site of PMe2Ph substituent: d, 1J (BP) ) 96 Hz; 11B, br ddd,
1J (BH) ≈ 120 Hz, 1J (BP) ) 96 Hz, 1J (BH) ) 42 Hz. 31P{1H} NMR:
δ 3.4 (q, 1J (BP) ) 53 Hz, PMe2Ph). f Broad m, nJ (HH) ) 9.7 Hz.
g
Site of PMePh2 substituent: d, 1J (BP) ) 96 Hz. 31P{1H} NMR:
1
h
δ +10.1 (q, J (BP) ) 55 Hz, PMePh2). Site of PPh3 substituent:
coupling not resolved due to broadness of the peak. 31P{1H} NMR:
δ +10.0 (br). Doublet, 2J (HH) ) 20 Hz. Quintet, 2J (HH) +
i
j
2J (HP) ) 10 Hz. Doublet, 3J (HP) ) 17 Hz. Doublet, 3J (HP) )
k
l
17 Hz. Doublet, 3J (HP) ) 16 Hz.
m
The primary mode of M-B bonding in the metalla-
triboranes appears to be sharing of electron density
between the boron-boron bond and a suitable metal
orbital, resulting in a MBB three-center-two-electron
bond.21 The average value of the Ir-B distances, 2.151-
(2) Å, is slightly longer than the sum of the covalent
radii (2.08 Å), being consistent with three-center B-Ir-B
bonding. On the other hand, the changes of the B-B
bond length could be, in part, ascribed to differences in
the characteristics of the metal-based vacant orbital (Ir
vs Fe). The Ir-B bond distances of the L-substituted
boron atoms are somewhat shorter than those of the
nonsubstituted boron atoms. This asymmetry suggests
that there is a small, but possibly significant, influence
of the Lewis bases on the adjacent Ir-B bond. The
F igu r e 2. Molecular structure of [Cp*IrB4H8(Br)2] (16).
metallaboranes [Cp*FeB4H11],18 [(η6-C6Me6)RuB4H10],19
[Cp*CoB4H10],20 and [(PMe2Ph)2(CO)IrB4H9].14
The NMR data of compound 16 are gathered in Table
6. For comparison, we have also included the spectro-
scopic data of the parent iridapentaborane 1 and as-
signed the resonances to the corresponding cluster
positions. The 11B NMR spectrum of the bromo deriva-
tive exhibits two doublets of equal intensity, and the
1H NMR spectrum of the boron-bound hydrogen atoms
shows a 2:2:2:1:1 relative intensity pattern. In addition,
the resonance of the apical Ir-H hydrogen atom appears
at the highest field.
(21) Coffy, T. J .; Medford, G.; Plotkin, J . L.; J ., G.; Huffman, J . C.;
The resonances of the bromo-substituted boron atoms
in 16 are shifted 7 ppm to low field with respect to 1.
Shore, S. G. Organometallics 1989, 8, 2404-2409.
(22) Andrews, S. J .; Welch, A. J . Inorg. Chim. Acta 1984, 88, 153-
160.
(23) Andrews, S. J .; Welch, A. J . Inorg. Chim. Acta 1985, 105, 89-
(18) Peldo, M. A.; Beatty, A. M.; Fehlner, T. P. Organometallics
2003, 22, 3698-3702.
97.
(24) Glore, J . D.; Rathke, J . W.; Schaeffer, R. Inorg. Chem. 1973,
(19) Kawano, Y.; Kawakami, H.; Shimoi, M. Chem. Lett. 2001,
1006-1007.
12, 2175-2178.
(25) Nordman, C. E.; Reimann, C. J . Am. Chem. Soc. 1959, 81,
3538-3543.
(20) Venable, T. L.; Grimes, R. N. Inorg. Chem. 1982, 21, 887-895.

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2129
Ta ble 6. 11B a n d 1H NMR Da ta (p p m ) for [Cp *Ir B4H10] (1) a n d [Cp *Ir B4H8Br 2] (16) in C6D6 a t Room
Tem p er a tu r ea
1
16
assigntb
δ(11B)
δ(1H)c
[1H-1H]-COSY
assignt
δ(11B)
δ(1H)d
[1H-1H]-COSY
B(2,5)-H(1)
B(2,5)-H(2)
B(3,4)-H(3)
µ-H(4)
-12.6(2)e
+3.47(2)
+2.55(2)h
+2.42(2)j
-4.74(2)
-4.10(1)
-13.82(1)
(1,2)s, (1,3)m, (1,4)s
(2,3)s, (2,4)s, (2,6)m
(3,4)s, (3,5)s
(4,5)s, (4,6)m
(5,1)m
B(2,5)-H(1)
-5.4(2)f
+4.05(2)g
(1,2)m, (1,3)s
-4.2(2)i
B(3,4)-H(2)
µ-H(3)
µ-H(4)
Ir(1)-H(5)
-7.0(2)k
+2.33(2)
-2.75(2)l
-4.16(1)m
-13.48(1)
(2,3)s, (2,4)s
(3,4)s, (3,5)w
µ-H(5)
Ir(1)-H(6)
(6,1)w, (6,Cp*)s
(5,1)w, (5,Cp*)m
a
b
Chemical shifts are given in parts per million. Relative intensities are given in parentheses. The assignments of the hydrogen atoms
H(1) and H(2) are arbitrary; the other assignments were made on the basis of 1H{11B(selective)} experiments and [1H-1H]-COSY
spectroscopy. c Additional 1H NMR data: δ 1.59 (s, 15H, Cp*). Additional 1H NMR data: δ 1.59 (s, 15H, Cp*). e Triplet, 1J (BH) ) 130
d
Hz. f Doublet, 1J (BH) ) 163 Hz. Doublet, 2J (HH) ) 8 Hz. Quartet, 2J (HH) + 3J (HH) ) 5 Hz. Doublet of triplets, 1J (BH) ) 144, 42 Hz.
g
h
i
Quartet, 2J (HH) + 3J (HH) ) 4 Hz. Doublet, 1J (BH) ) 162 Hz. Quartet, 2J (HH) + 3J (HH) ) 8 Hz. Quintet, nJ (HH) ) 6 Hz.
j
k
l
m
rane [(PMe2Ph)2(CO)IrB4H9].14 This crystal structure
Ta ble 7. Selected In ter a tom ic Len gth s (Å) a n d
An gles (d eg) for [Cp *Ir B4H8Br 2] (16)
contrasts with the C1 symmetry found for the isoelec-
tronic ruthenaborane [(η6-C6Me6)RuB4H10],19 in which
Bond Lengths
Ir(1)-B(2)
Ir(1)-B(3)
Ir(1)-B(4)
Ir(1)-B(5)
B(2)-Br(1)
2.178(4)
2.140(4)
2.131(4)
2.183(4)
2.004(4)
B(5)-Br(2)
B(2)-B(3)
B(3)-B(4)
B(4)-B(5)
1.998(4)
1.845(6)
1.838(6)
1.841(6)
the unique apical H atom bridges a Ru-B edge.
Both the 11B and the 1H NMR spectra of 16 agree with
the Cs symmetry found in the solid state. The IrH
hydrogen atom does not exhibit coupling with boron
atoms, even at low temperatures, demonstrating its
metal hydride character. In contrast, the RuH apical
hydrogen atom of [(η6-C6Me6)RuB4H10] displays strong
coupling with the boron atoms, B(2) and B(5), indicating
its RuHB bridging character and fluxional behavior in
solution. These results suggest that the iridium center
has a higher tendency than the ruthenium fragment to
retain the unique apical hydrogen atom. This affinity
is also observed in arachno-[(Cp*Ir)2B2H8], in that it
does not decompose to give nido-[(Cp*Ir)2B2H6], even
though both nido-[(Cp*M)2B2H6] species (M ) Co, Rh)
exist.12,20,28,29 Possibly the strong Ir-H bond ultimately
determines the substitution of Lewis bases to the boron,
whereas the Ru-H-B bond favors the substitution at
the metal site.
Bond Angles
B(2)-Ir(1)-B(3)
B(3)-Ir(1)-B(4)
B(4)-Ir(1)-B(5)
B(2)-Ir(1)-B(5)
B(2)-B(3)-B(4)
B(3)-B(4)-B(5)
B(3)-B(2)-Ir(1)
B(4)-B(5)-Ir(1)
50.57(16) B(2)-B(3)-Ir(1)
50.97(17) B(5)-B(4)-Ir(1)
50.52(17) B(3)-B(4)-Ir(1)
87.14(16) B(4)-B(3)-Ir(1)
65.78(18)
66.20(19)
64.79(19)
64.25(18)
108.9(3)
108.1(3)
Br(2)-B(5)-Ir(1) 119.8(2)
Br(1)-B(2)-Ir(1) 119.0(2)
63.65(18) B(3)-B(2)-Br(1)
112.8(3)
114.5(3)
63.28(18) B(4)-B(5)-Br(2)
pyridine ligand exhibits the largest difference in the
series PMe3, PMePh2, py, as reflected in the degree of
shortening of the adjacent iridium-boron bond.
Th e In ter m ed ia te. Compound 9 is analogous to the
cobaltaborane [1-Cp*-nido-1-CoB4H8]. This species was
obtained as the result of the thermal rearrangement of
its isomer, [2-Cp*-nido-2-CoB4H8], as well as the pyro-
lytic H2 loss of [1-Cp*-arachno-1-CoB4H10].20,26 In con-
trast, we were unable to isolate 9 by chromatographic
methods. This creates a problem, as it is difficult to
account for the difference of stability between the
iridapentaborane and its cobalt counterpart. On the
other hand, the spectroscopic data strongly support our
assignment of 9 as [1-Cp*-nido-IrB4H8]. Compound 9
is possibly unstable only under the conditions of the
reaction with 1, i.e., an excess of PPh3, precluding its
purification by routine chromatographic techniques.
Br om in e Der iva tives. The molecular structure of
the dibromoiridapentaborane 16 indicates Cs symmetry
with the mirror plane passing through the iridium atom,
the hydride ligand, and the five-membered ring of the
η5-Cp* group. The conformation of the pentamethylcy-
clopentadienyl ligand is staggered with respect the
B4H7Br2 fragment, thereby minimizing the repulsion.
The bromine substituents occupy exo-polyhedral posi-
tions in a cis configuration with respect to the B4 plane
of the {B4H7Br2} ligand. The B-Br distances are within
the normal ranges found in other metal-boron clusters
(Table 7),27 and the Ir-B and B-B bond lengths
compare well with those of the analogous iridapentabo-
B. Rea ction s a n d Mech a n ism s. 1. Ch a r a cter is-
tics of th e Rea ction s. Rea ction s of 1 w ith Lew is
Ba ses. The reactions of the five-vertex arachno-irida-
pentaborane 1 with PMe3, PMe2Ph, and PMePh2 (eq 1,
Scheme 1) was complete in a few minutes and quanti-
tatively gave the four-vertex iridatriboranes and the
borane adduct. In contrast, 1 reacted more slowly with
[Cp*IrB4H10] + 2L f [Cp*IrB3H7(L)] + BH3‚L (1)
PPh3, py, and NEt3 with relative rates in the order PMe3
≈ PMe2Ph ≈ PMePh2 > py > PPh3 > NEt3 for compa-
rable concentrations.
For the reaction of 1 with PPh3 changes in the
concentrations of the reactants and products versus time
are shown in Figure 3 with an initial 1 to PPh3 ratio of
1:5. The initial slope of the plot of 10 is nonzero, whereas
those for 9 and 11 appear to be zero. Hence, the data
exhibit the classic time behavior for a consecutive series
of reactions where 10 is intermediate in the formation
of 9 and 11. In contrast to 11, 9 slowly decomposes.
When the ratio 1:PPh3 is reduced to 1:2 (at approxi-
mately the same absolute concentration of 1), the same
qualitative profile is observed (Figure 4). However, the
(26) Nishihara, Y.; Deck, K. J .; Shang, M.; Fehlner, T. P.; Haggerty,
B. S.; Rheingold, A. L. Organometallics 1994, 13, 4510-4522.
(27) Stockman, K. E.; Boring, E. A.; Sabat, M.; Finn, M. G.; Grimes,
R. N. Organometallics 2000, 19, 2200-2207.
(28) Lei, X.; Shang, M.; Fehlner, T. P. J . Am. Chem. Soc. 1999, 121,
1275.
(29) Lei, X.; Bandyopadhyay, A. K.; Sabat, M.; Fehlner, T. P.
Organometallics 1999, 18, 2294.

2130 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
F igu r e 5. Relative concentration changes for the trans-
formation of 3 ([) to 4 (9), BH3‚PMe3 (2), and total boron
concentration (b), after the reaction of 1 equiv of 1 with 2
equiv of PMe3.
F igu r e 3. Relative concentration change of reactants and
products in the reaction of 1 with 5-fold excess of PPh3:
([) 1; (b) 9; (9) 10; (2) 11.
Sch em e 2. Rea ction Cycle
F igu r e 4. Plot of concentration vs time for the reaction of
1 with PPh3 in a 1:2 ratio: ([) 1; (b) 9; (9) 10; (2) 11.
decay of 1 is much slower and the maximum in 10 is
much lower. Both are consistent with 1 being consumed
in a process that depends strongly on phosphine con-
centration, whereas the loss of the initial product 10 is
converted into 9 and 11 in a process that does not
depend strongly on phosphine concentration.
Rea ction s of 2 w ith Lew is Ba ses. The reactivity
of [1-Cp*-1-H-arachno-1-IrB3H8] (2) with the same
Lewis bases (Scheme 1) was examined. The reactions
of 2 with PMe3, PMe2Ph, PMePh2, and py were also
completed in minutes, giving quantitatively the corre-
sponding iridatriboranes and the borane adduct (eq 2,
Scheme 1).
considerable precedent in both borane and metalla-
borane chemistry.30,31 However, there is little informa-
tion in the literature on the chemical fate of the {BH}
unit. Therefore, the overall transformation of 3 into 4
was looked at more closely by NMR.
After the reaction of 1 with 2 equiv of PMe3 to form 3
and BH3PMe3 quantitatively, the transformation of 3
into 4 was followed by NMR. Figure 5 shows a plot of
the concentrations of 3, 4, BH3‚PMe3 and total boron
against time. In about 9 h the initial concentration of 3
decreased by half and an equivalent concentration of 4
is produced. In nearly 30 h, 3 has been converted
quantitatively to 4. The total boron loss corresponds to
the initial concentration of 3; therefore, a {BH} frag-
ment is “literally” lost in the process. Close examination
of the NMR tube showed formation of a white precipi-
tate that was insoluble in C6D6, CH2Cl2, and THF.
In contrast, the same study for a 1:7 ratio of 1 to PMe3
gave the results plotted in Figure 6. Note the time scale
is now days, not hours. After 40 days the conversion
still did not reach completion, showing that excess
phosphine inhibits the conversion of 3 to 4. In addition,
there was a parallel increase in the concentrations of 4
[Cp*IrB3H9] + 2L f [Cp*IrB2H6(L)] + BH3‚L (2)
Consequently, the substituted iridatriboranes
[Cp*IrB2H6(L)] can be prepared directly from 2 via bor-
ane displacement and base substitution at a boron site.
In contrast, with PPh3 the reaction was completed in
4 h, whereas with NEt3 we observed reaction completion
after 16 h. The relative rates follow the trend PMe3 ≈
PMe2Ph ≈ PMePh2 ≈ py > PPh3 > NEt3. PPh3 and py
react faster with compound 2 than with compound 1.
Con ver sion of 3 to 4. The substituted iridatetrabo-
ranes 3, 5, 7, 10, 12, and 14 are unstable in solution as
well as in the solid state, affording the corresponding
substituted iridatriboranes (eq 3, Scheme 2). This
(30) Bould, J .; Greenwood, N. N.; Kennedy, J . D. J . Organomet.
Chem. 1983, 249, 11-21.
(31) Morrey, J . R.; J ohnson, A. B.; Fu, Y. C.; Hill, G. R. Adv. Chem.
Ser. 1961, No. 32, 157-67.
[Cp*IrB3H7(L)] f [Cp*IrB2H6(L)] + {BH} (3)
conversion involves formally a {BH} loss, which has

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2131
other heteroboranes.1,32 This is illustrated, for example,
in the preparation of 1 from 2, in which a {BH} unit
has been formally added to the iridatetraborane to give
the iridapentaborane.12
We have found that the treatment of the iridatribo-
ranes 4, 6, 8, 13, and 15 with BH3‚THF at room
temperature gives 2 and BH3L (eq 5).
[Cp*IrB H ]
[Cp*IrB2H6(L)] + 2BH3 f
+ BH3‚L (5)
3
9
2
Likewise, the reaction of the iridatetraboranes 3, 5,
and 7 with BH3‚THF at room temperature afforded 1
and BH3L (eq 6).
F igu r e 6. Plot of concentration vs time for the transfor-
mation of 3 ([) to 4 (9) and BH3‚PMe3 (2) after the reaction
of 1 equiv of 1 with 7 equiv of PMe3.
[Cp*IrB H ]
[Cp*IrB3H7(L)] + 2BH3 f
+ BH3‚L
4
10
1
Ta ble 8. Su m m a r y of F r ee Rea ction En er gies (k J
m ol-1) a n d Equ ilibr iu m Con sta n ts for th e Liga n d
Exch a n ge Rea ction s of 3 a n d 4 a t 298 K
(6)
BH3 cluster expansion and Lewis base displacement
regenerates the iridapenta- and iridatetra-boranes, 1
and 2.
4 + L′ S 6, 8, 13 + PMe3
3 + L′ S 5 + PMe3
Rea ction Cycle. As summarized in Scheme 2, the
reactions of 1 and 2 and the new substituted iridabo-
ranes permit a reaction cycle to be constructed. For both
the iridapentaborane 1 and iridatetraborane 2, base
displacement of borane and addition of borane to the
L-boron-substituted iridaboranes constitute reversible
reaction sets. These two reversible reactions are con-
nected by {BH} fragment loss and {BH} fragment
addition, thereby generating a four-step reaction cycle.
If we consider the whole cycle with species “in” balanced
against species “out”, the net reaction is
L′
∆G°
Keq
∆G°
Keq
PMe2Ph
PMePh2
py
12
23
30
8.0 × 10-3
9.0 × 10-5
6.0 × 10-6
12
8.0 × 10-3
1
and BH3‚PMe3. The H NMR spectra showed formation
of [Cp*IrH4], and the increase in the concentration of
the iridium hydride parallels the formation of compound
4, suggesting that both species are formed simulta-
neously. Not only does phosphine inhibit the conversion
of 3 to 4, but a large excess permits a second, less
efficient reaction channel to be utilized. Thus, ligand
exchange properties of 3 were examined.
3BH3 + 2L f 2BH3‚L + {BH} + H2
(7)
Liga n d Exch a n ge Rea ction s. The iridatetraborane
3 undergoes a ligand exchange reaction with PMe2Ph
(eq 4, Scheme 2).
In the ligand exchange reactions of 4 with PMe2Ph
and py at high temperature, we observed formation of
[Cp*IrH4], which is also formed in the conversion of 3
to 4 in the presence of free phosphine. [Cp*IrH4] reacts
with an excess of BH3‚THF to give compound 1, pre-
sumably through the formation of 2 (Scheme 2).
[Cp*Ir3H7(PMe3)] + PMe2Ph S
[Cp*Ir3H7(PMe2Ph)] + PMe3 (4)
2. Mech a n istic Con sid er a tion s. The observations
described above permit a rudimentary reaction pathway
to be described. The reaction rate of 1 with PPh3 de-
pends on the concentration of the phosphine. A possible
first step for this reaction is the formation of an irida-
pentaborane adduct, [Cp*IrB4H10(L)], in fast equilibri-
um with free ligand, L, and compound 1. In a subse-
quent rate-determining step, the activated iridaborane
adduct reacts with another molecule of L to give BH3‚L
and the iridatetraborane [Cp*IrB3H7(L)] (Scheme 3).
The substituted iridatetraboranes undergo decompo-
sition through at least two parallel pathways, with
contributions to iridatriborane formation that depend
on the Lewis base, its concentration, and the condi-
tions of the reaction. Thus, the PPh3 derivative 10
decomposes, leading to the formation of 9 and 11. A
likely route is the dissociation of the PPh3-B bond to
give a putative 6 skeletal electron pair (sep) species,
[Cp*IrB3H7], that disproportionates to yield the irida-
pentaborane 9 and the iridatriborane 11, both of which
are observed as products (Scheme 3, path i).
Similarly, we found that iridatriborane 4 undergoes
exchange of PMe3 with an excess of PMe2Ph at low
temperatures. At high temperature, the exchange of
PMe3 in compound 4 with an excess of PMe2Ph and py
is accompanied by decomposition of the iridatriborane
with formation of [Cp*IrH4] and BH3‚L. With PPh3, in
contrast, we did not observe either ligand exchange or
decomposition of the iridatriborane, even at high tem-
peratures.
The relative intensities of the 1H NMR signals for the
L-substituted iridaboranes as a function of tempera-
ture allowed the estimation of the equilibrium constants
(Table 8). The values of the corresponding free ener-
gies reflect the binding energy differences of the Lewis
bases. As expected, the more basic PMe3 ligand forms
more stable boron-substituted iridatri- and iridatetrabo-
ranes, but the differences are not large and are consis-
tent with facile ligand substitution relative to conversion
of 3 to 4.
Clu ster Exp a n sion Rea ction s. {BH} addition via
BH3‚THF is a known method for increasing the size of
the borane fragment in metallaboranes, carboranes, and
(32) Kang, S. O.; Sneddon, L. G. Inorg. Chem. 1988, 27, 3298-3300.

2132 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
Sch em e 3a
a
L ) PMe3, PPh3. Legend: (i) dissociation equilibrium and disproportionation; (ii) {BH} loss via polymer formation.
For PMe3 decomposition of 3 without free phosphine
at room temperature proceeds more rapidly than with
PPh3, and no 9 accompanies the formation of 4. Loss of
{BH} to give an insoluble “polymer” and the substituted
iridatriborane 4 (Scheme 3, path ii) is suggested as a
parallel path for the formation of the iridatriborane.
Since PMe3 forms stronger P-B bonds than PPh3, the
pathway involving dissociation equilibrium is less fa-
vored. This is supported by the measured ligand-
exchange equilibrium parameters. However, when the
temperature is increased, P-B dissociation becomes
more important for PMe3, and evidence for 9 is found.
As the ligand dissociation equilibrium is shifted toward
the formation of the intermediate [Cp*IrB3H7], path i
now contributes to the formation of 9.
In the reaction of 1 with PPh3, the yield of 11 is close
to 50% when the concentration of 9 is at its maximum
value of 15%. These data suggest that at that point at
least 30% of 11 arises through the dissociation/dispro-
portionation pathway, whereas almost 70% arises via
the polymeric {BH} loss. Thus, in the PPh3 system both
decomposition routes operate simultaneously indepen-
dently of the conditions, while for PMe3 at room tem-
perature under stoichiometric conditions the decompo-
sition of 3 follows exclusively the {BH} loss pathway
(Scheme 3, path ii).
the L-B bond determines ultimately the course of the
reaction, whereas changes in the conditions vary the
relative rates of the different processes, leading to fine-
tuning of the reactivity.
We have demonstrated that the reaction of Lewis
bases with metallaboranes can generate interesting
chemistry which produces new compounds, stoichiomet-
ric cycles, and reaction pathways from which insights
of fundamental processes such as the decomposition of
metallaborane adducts can be gained.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were carried out
under an argon atmosphere using standard Schlenk-line tech-
niques.33 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. 1 was prepared by the
procedure described below, which is a modification of the
synthesis reported earlier.12 NMR spectra were recorded on
400 MHz Bruker and 500 MHz Varian spectrometers. NMR
references: internal (C6D6, δH 7.06 ppm) for 1H; external
([(Me4N)(B3H8)] in acetone-d6, δB -29.7 ppm) for 11B; exter-
nal (H3PO4 in D2O, δP 0.0 ppm) for 31P. All J values are given
in Hz. IR spectra were recorded on a Nicolet 205 FT-IR
spectrometer; all values are given in cm-1. Mass spectra were
acquired on a Finnigan MAT Model 8400 mass spectrom-
eter. M-H-W Laboratories, Phoenix, AZ, performed elemental
analyses.
The mechanism suggested in Scheme 3 is clearly not
complete. For example, at room temperature with excess
PMe3, 3 decomposes extremely slowly, giving rise to the
simultaneous formation of [Cp*IrH4], BH3PMe3, and 4.
However, the essential aspects of the more facile
conversion of 1 to iridatetra- and iridatriboranes are
expressed by Scheme 3 and are consistent with our
expectations based on known borane and metal cluster
chemistry.
X-r a y Str u ctu r e Deter m in a tion s. The structure data for
4 have been deposited in conjunction with the preliminary
communication (Cambridge Crystallographic Data Center No.
CCDC-187182).34 In addition, the crystallographic details of
8, 13, and 16 are gathered in the Supporting Information. All
data were collected on a Bruker Apex CCD diffractometer at
100(2) Κ with Mo KR radiation (λ ) 0.710 73 Å).
Relevant data for the crystallographically studied com-
pounds are summarized in Table 1.
Con clu sion s
The reactivity of a metallaborane is strongly con-
trolled by the metal center. This effect on reactivity is
illustrated by the isoelectronic metallapentaboranes
[Cp*IrB4H10] (1) and [(η6-C6Me6)RuB4H10], in which,
after BH3 displacement, the metal centers drive the final
attack of the Lewis base, PMe3, toward the borane
fragment and the metal site, respectively.
Metallaborane adducts undergo decomposition fol-
lowing different reaction pathways, depending on the
Lewis bases and the conditions of the reaction. The PPh3
ligand promotes decomposition throughout ligand dis-
sociation and disproportionation, as well as direct {BH}
loss. In contrast, an excess of PMe3 leads directly to
disproportionation of the metallaborane adduct and
inhibition of {BH} loss. At high temperatures, PMe3
shares the ligand-dissociation pathway. The nature of
Efficien t P r ep a r a tion of [1 Cp *-1-H-a r a ch n o-1-Ir B4H9]
(1). The original synthetic procedure afforded moderate net
yields of [Cp*IrB4H10] (1), starting from [Cp*IrCl2]2 and
monoborane reagents.12 The main drawback of this prepara-
tion was the fact that the reaction of [Cp*IrCl2]2 with LiBH4
gave a 1:1 mixture of [1-Cp*-1-(H)2-arachno-1-IrB3H7] (2) and
[Cp*IrH4]. This iridium hydride was consequently separated
to give pure iridatriborane 2, which is the final precursor to
1. In addition, we have found that the ratio of 2 and [Cp*IrH4]
depends on the warming rate of the reaction mixture from low
temperatures to room temperature; thus, we have obtained
2:[Cp*IrH4] proportions of, for example, 1:7. However, we have
recently demonstrated that some metal hydrides are good
(33) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(34) Macias, R.; Fehlner, T. P.; Beatty, A. M. Angew. Chem., Int.
Ed. 2002, 41, 3860-3862.

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2133
precursors for the synthesis of metallaboranes.16 Thus, we
considered that the reaction of the byproduct, [Cp*IrH4], with
BH3THF could also lead to the arachno-iridapentaborane 1.
This supposition was found to be true, and now we can prepare
1 in a high-yield one-pot reaction.
[Cp *Ir B2H6(P Me2P h )] (6). IR (KBr): 2403 (s, νB-H), 2368
(s, νB-H), 2299 (m, νB-H), 2151 (s, νIr-H). LRMS (EI): m/z 494
(M+); calcd for C18H32B2PIr, found envelope with cutoff at 495
and maximum at 490, which suggests that the ions M+ and
M+ - H2 are overlapped. Anal. Calcd: C, 43.83; H, 6.54.
Found: C, 44.00; H, 6.70.
In a typical synthesis, 91 mg (0.12 mmol) of [Cp*IrCl2]2 in
THF under argon at -40 °C was treated with 5-fold excess of
LiBH4 (2 M in THF). The resulting suspension was allowed to
reach room temperature to give a yellow solution. At this point
the reaction mixture contained mainly 2, [Cp*IrH4], and
LiBH4. To this mixture was added a 10-fold excess of BH3‚
THF (1 M in THF), and the resulting yellow solution was
heated at 60 °C for 2 days. The solvent was evaporated to
dryness and the residue extracted with hexane and filtered
through Celite to give a pale yellow solution. Crystallization
from hexane gave 84 mg (0.22 mmol, 95%) of [Cp*IrB4H10] (1).
Rea ction of [Cp *Ir B4H10] (1) w ith P Me3. A 15 mg portion
(0.04 mmol) of 1 was dissolved in 0.7 mL of C6D6 and placed
in a 5 mm NMR tube, together with a capillary containing an
acetone-d6 solution of [Et4N][B3H8] as external reference. To
this starting solution was added 0.09 mmol of PMe3 (1 M
solution in THF) under an argon atmosphere at room tem-
perature. 11B NMR of the reaction mixture showed the
formation of two new species, plus BH3‚PMe3. The major
component of the mixture was characterized as [1-(Cp*)-1-(H)-
arachno-1-IrB3H6-2-(PMe3)] (3). The reaction mixture was
transferred from the NMR tube to a Schlenk flask and
evaporated to dryness under vacuum. This procedure removed
the excess of PMe3 and the borane adduct BH3‚PMe3. The
resulting yellow residue was subsequently kept in the refrig-
erator under argon for 2 days. After this time, compound 3
was converted quantitatively to the second metallaborane, a
minor component in the first steps of the reaction. Crystal-
lization from hexane at low temperatures gave 12 mg (0.03
mmol, 69% yield) of 4.
[1-(Cp *)-1-(H)-a r a ch n o-1-Ir B3H6-2-(P Me2P h )] (5). 11B
1
NMR (C6D6): δ -5.7 (br d, J (BH) ) 106; {1H}, s, 1B), -12.7
(t, 1J (BH) ) 101, 1B), -19.3 (t, 1J (BH) + 1J (BP) ) 98; {1H}, d,
1J (BP) ) 97, 1B). 1H{11B} NMR (C6D6): δ 7.48 (m, 1H, Ph),
7.30 (m, 2H, Ph), 7.02 (m, 2H, Ph), 3.98 (br. s, 1H, BHt), 3.15
(s, 1H, BHt), 2.85 (dd, 2J (BP) ) 17, 1J (BH) ) 7, 1 H, BHt),
2
2.17 (s, 1H, BHt), 2.08 (s, 15 H, Cp*), 1.09 (d, J (HP) ) 11.3,
3H, Me), 0.99 (d, 2J (HP) ) 11.3, 3H, Me), -4.24 (s, 1H, BHB),
2
2
-4.44 (dq, J (BP) ) 18.9, J (BH) ) 6.5, 1H, BHB), -18.19 (d,
3J (HP) ) 21, 1H, IrH). 31P{1H} NMR (C6D6): δ -5.3 (v br q,
1J (BP) ) 14.0, PMe2Ph). HRMS (EI): m/z 506 (M+); calcd for
C
18H33B3IrP 506.2228 (M+), measd 506.2223.
Rea ction of [Cp *Ir B4H10] (1) w ith P MeP h 2. Following
the same procedure as above, 0.047 mL (0.25 mmol) of PMe2-
Ph was added to 18 mg (0.05 mmol) of 1. A few minutes after
addition of the phosphine, the 1H and 11B NMR spectra showed
that the starting material reacted quantitatively to give BH3‚
PMePh2 and [1-(Cp*)-1-(H)-arachno-1-IrB3H6-2-(PMePh2)] (7).
The reaction mixture was evaporated to dryness under vacuum
and the residue kept under argon for 2 days. After this time,
NMR data demonstrated that compound 7 was transformed
into [1-(Cp*)-1,1-(H)2-arachno-1-IrB2H4-2-(PMePh2)] (8). The
reaction mixture at this point contained mainly compound 8
and BH3‚PMePh2, which were separated by thin-layer chro-
matography (TLC) on silica gel in air, using CH2Cl2-hexane
(1:1) as eluent. A colorless UV-active band was removed at
the bottom of the plate, yielding 5 mg (0.007 mmol, 14%) of 8
as a pale yellow solid.
[Cp *Ir B2H6(P MeP h 2)] (8). IR (hexane): 2445 (s, νB-H),
2389 (s, νB-H), 2305 (w, νB-H), 2135 (m, νIr-H). HRMS (FAB):
m/z 556 (M+); calcd for C23H34B2IrP 556.2214, (M+), measd
556.2187. Anal. Calcd: C, 49.74; H, 6.17. Found: C, 49.92; H,
6.26.
[1-(Cp *)-1,1-(H )2-a r a ch n o-1-Ir B2H 4-2-(P Me3)] (4). IR
(KBr): 2407 (s, νB-H), 2390 (s, νB-H), 2373 (s, νB-H), 2295 (m,
ν
B-H), 2153 (s, νIr-H). HRMS (EI): m/z 430 (M+ - H2); calcd
for C13H28B2PIr 430.174 78 (M+ - H2), measd 430.173 17. Anal.
Calcd for C13H30B2PIr: C, 36.21; H, 7.01. Found: C, 36.40; H,
6.99.
[1-(Cp *)-1-(H)-a r a ch n o-1-Ir B3H7-2-(P MeP h 2)] (7). 11B
NMR (C6D6): δ -5.9 (br), -12.3 (br), -19.1 (br). 1H{11B} NMR
(C6D6): δ 7.40-7.06 (m, 10 H, C6H5), 3.96 (br, 1H, BH), 3.20
(br, 1H, BH), 3.11 (br, 1H, BH), 2.19 (br, 1H, BH), 1.97 (s, 15H,
Cp*), 1.44 (d, 3H, Me), -4.11 (br, 1H, BHB), -4.20 (br, 1H,
[1-(Cp *)-1-(H)-a r a ch n o-1-Ir B3H6-2-(P Me3)] (3). 11B NMR
(C6D6): δ -5.3 (d, 1J (BH) ) 134; {1H}, s, 1B), -12.9 (t, 1J (BH)
) 109, 1B), -20.1 (t, J (BH) + J (BP) ) 112; {1H}, d, J (BP)
1
1
1
3
BHB), -17.95 (d, J (HP) ) 21 Hz, 1H, IrH). 31P NMR (C6D6):
) 103 Hz, 1B). H{11B} NMR (C6D6): δ 3.96 (br. s, 1H, BHt),
1
δ 1.1 (br). HRMS (EI): m/z 568 (M+); calcd for C23H35B3IrP
568.2385 (M+), measd 568.2377.
3.07 (s, 1H, BHt), 2.45 (dd, 2J (HH) ) 7, 2J (HP) ) 19, BHt),
2
2.11 (s, 15 H, Cp*), 1.99 (s, 1H, B-Ht), 0.63 (d, J (HP) ) 11,
9H, Me), -4.32 (quint, 2J (HH) ) 6.9, 1H, BHB), -4.78 (dq,
Rea ction of [Cp *Ir B4H10] w ith P P h 3. To a C6D6 solution
of 1 (11 mg, 0.03 mmol), we added 38 mg (0.14 mmol) of PPh3
in a NMR tube under an argon atmosphere. After addition of
the phosphine, there was no reaction during the first few
minutes. Four hours later, there were small amounts of 1, but
the NMR data showed the formation of new species, which
were characterized as [1-Cp*-nido-1-IrB4H8] (9) and the iri-
datetraborane [1-Cp*-1-H-arachno-1-IrB3H6-2-(PPh3)] (10). Both
species underwent decomposition, giving rise to the formation
of a mixture of [1-Cp*-1,1-(H)2-arachno-1-IrB2H4-(PPh3)] (11),
BH3‚PPh3, and an excess of PPh3. TLC was performed on this
mixture using hexane as eluent. PPh3 was at the front of the
chromatogram, but BH3‚PPh3 and 11 were collected together
almost at the bottom of the plate. NMR spectroscopy demon-
strated significant decomposition of 11 after chromatography,
and therefore, this compound could not be purified further.
[Cp *Ir B2H6(P P h 3)] (11). HRMS (FAB): m/z 618 (M+); calcd
for C28H36B2IrP 615.2135 (M+ - 3H), measd 615.2116.
[1-Cp *-n id o-Ir B4H8] (9). 11B NMR (C6D6): δ -8.9 (dt,
1J (BH) ) 158, 34 Hz; {1H}, s, 4B). 1H{11B} NMR (C6D6): δ
2.08 (s, 15H, Cp*), 2.69 (t, 2J (HH) ) 7, 4H, BHt), -4.09 (t,
2J (HH) ) 7, 4H, BHB). LRMS (EI): m/z 380 (M+), calcd for
2
2
3
1H, J (HH) ) 6.6, J (HP) ) 19.2, BHB), -18.50 (d, J (HP) )
21, 1H, IrH). 31P{1H} NMR (C6D6): δ -9.7 (br q, 1J (BP) )
10.0, PMe3). IR (hexane): 2518 (w, νB-H), 2472 (m, νB-H),
2425 (s, νB-H); 2145 (s, νIr-H). LR-MS(EI): m/z 444 (M+); calcd
for
C13H31B3IrP, found envelope with cutoff at 445 and
maximum at 442; the isotopic pattern suggests that the ions
M+ and M+ - H2 are overlapped with a major contribution of
the latter.
Rea ction of [Cp *Ir B4H10] (1) w ith P Me2P h . A 12 mg
(0.03 mmol) portion of 1 was treated with a 10-fold excess of
PMe2Ph under the same conditions as for the PMe3 reaction
above. Integration versus the external reference showed
quantitative reaction to give BH3‚PMe2Ph and [1-(Cp*)-1-(H)-
arachno-1-IrB3H6-2-(PMe2Ph)] (5). The reaction mixture was
evaporated to dryness under vacuum, giving a pale yellow
precipitate that was kept under argon at low temperatures
for 18 h. After this time, compound 5 converted to [1-(Cp*)-
1,1-(H)2-arachno-1-IrB2H4-2-(PMe2Ph)] (6). At this point, the
reaction gave mainly 6 and the borane adduct, which were
separated by thin-layer chromatography (TLC) on silica gel
in air, using CH2Cl2-hexane (1:5) as eluent. A colorless UV-
active band (Rf ) 0.3) was removed from the TLC plate, giving
1 mg (0.002 mmol, 7%) of 6 as a pale-yellow solid.
C
10H23B4Ir; found envelope with cutoff at 380 and maximum
at 376, which indicates overlap of ions, M+ - n(H2) (n ) 1, 2).

2134 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
[1-Cp *-1-H-a r a ch n o-1-Ir B3H6-2-(P P h 3)] (10). 11B NMR
(C6D6): δ -7.1 (br, 1B), -11.5 (br, 1B), -17.9 (br, 1B).
1H{11B} NMR (C6D6): δ 7.67 (m, C6H5), 6.99 (m, C6H5), 2.05
(s, 15H, Cp*), 3.80 (br. s, BHt), 3.20 (br. s, BHt), 3.09 (br. s,
BHt), 2.27 (br s, BHt), -3.69 (d, 2J (HP) ) 21, 1H, BHB), -4.39
(br s, 1H, BHB), -17.39 (d, 3J (HP) ) 20, 1H, IrH). 31P{1H}
NMR (C6D6): δ 4.8 (br, BPPh3). LRMS (FAB): m/z 630 (M+),
calcd for C28H37B3IrP; found envelope with cutoff at 631 and
maximum at 628 (M+ - H2).
Rea ction of [Cp *Ir B4H10] (1) w ith P yr id in e. To 32 mg
(0.08 mmol) of 1 dissolved in C6D6 was added 0.03 mL (0.42
mmol) of pyridine. The pale yellow initial solution turned
bright orange. A few minutes after the addition, 1H and 11B
NMR spectra showed formation of new species together with
the starting material, which was present in residual amounts
34 min after the first 11B NMR spectrum. At this point, 9,
[1-Cp*-1-H-arachno-1-IrB3H6-2-(C5NH5)] (12), [1-Cp*-1,1-(H)2-
arachno-1-IrB2H4(C5NH5)] (13), and BH3‚(C5NH5) were the
major species of the reaction mixture. Two days later, com-
pounds 9 and 12 decomposed to give a mixture containing the
borane adduct BH3‚(C5NH5) and the tiriridaborane 13. The
solvent was evaporated to dryness, and the yellow residue was
dried for several hours under vacuum. The resulting yellow
solid was extracted with hexane to give a bright yellow
solution. Crystallization from hexane at low temperatures gave
29 mg (0.067 mmol, 79%) of 13.
(br s, 1H, BHt), 1.12 (t, 3J (H,H) ) 7, 3H, Et), -2.93 (q, 2J (H,H)
) 7, 1H, BHB), -4.53 (br s, 1H, BHB), -18.99 (s, 1H, IrH).
MS experiments were unsatisfactory, due probably to the
instability of 14.
[Cp *Ir B2H6(NEt3)] (15). 11B NMR (C6D6): δ 2.3 (d, 1J (B,H)
) 122, 1B), -23.4 (br t, 1J (B,H) ) 123, 1B). 1H{11B} NMR
(C6D6): δ 2,79 (br. s, 1H, BHt), 1.99 (s, 15H, Cp*), 0.65 (t,
3J (H,H) ) 8, 3H, Et), -4.87 (q, 2J (H,H) ) 8, 1H, BHB), -17.46
(s, 1H, IrH), -19.23 (s, 1H, IrH). MS experiments were
unsatisfactory, due probably to the instability of 15.
Rea ction of [Cp *Ir B3H9] w ith P Me3. A 33 mg portion
(0.04 mmol) of [Cp*IrCl2]2 was treated in THF with a 5-fold
excess of LiBH4 at -40 °C, while allowing the reaction mixture
to reach the room temperature slowly over a period of 2 h.
The solvent was evaporated to dryness and the residue
extracted with hexane to give a yellow solution. 11B NMR
spectroscopy showed that [Cp*IrB3H9] was the only boron-
containing compound in the final reaction mixture; however,
the 1H NMR spectrum demonstrated the presence of [Cp*IrH4]
as the major component.
Monitoring the 11B NMR spectrum of the above mixture
versus the external reference, we added an excess of PMe3,
resulting in the quantitative formation of 4 in just a few
minutes.
Rea ction of [Cp *Ir B3H9] (2) w ith P Me2P h . A 3 mg
portion (0.01 mmol) of 2 was dissolved in C6D6 and placed in
an NMR tube with an external reference. To this solution, we
added 0.007 mL (0.05 mmol) of PMe2Ph under argon. 11B and
1H NMR spectra of the reaction mixture a few minutes after
the addition showed quantitative formation of 6.
[Cp *Ir B2H6(C5NH5)] (13). IR (KBr): 2411 (s, νB-H), 2395
(s, νB-H), 2309 (w, νB-H), 2178 (m), 2144 (m, νIr-H). HRMS
(FAB): m/z 435 (M+); calcd for C15H26B2NIr 432.1646, [M+
3H], measd 432.1650.
-
[Cp *Ir B3H7(C5NH5)] (12). 11B NMR (C6D6): δ 8.6 (d,
1J (HB) ) 128, 1B), -12.3 (br), -11.7 (accidental overlapping
with BH3‚(C5NH5)), -13.9 (d, 1J (HB) ) 142, 1B). 1H{11B} NMR
(C6D6): δ 8.15 (m, 2H, C5NH5), 6.40 (m, 1H, C5NH5), 6.02 (m,
2H, C5NH5), 5.02 (d, nJ (HH) ) 7, 1H, BHt), 4.20 (s, 1H, BH),
3.56 (s, 1H, BHt), 2.17 (s, 15H, Cp*), 2.14 (s, 1H, BHt), -1.54
(q, 2J (H,H) ) 7, 1H, BHB), -4.18 (quint, 1H, BHB), -18.24
(s, 1H, IrH). MS experiments were unsatisfactory, due prob-
ably to the instability of 12.
Rea ction of [Cp *Ir B3H9] (2) w ith P MeP h 2. Under the
same conditions as above, 3 mg (0.01 mmol) of 2 was treated
with a 5-fold excess of PMePh2 to give compound 8. The
reaction is quantitative by NMR.
Rea ction of [Cp *Ir B3H9] (2) w ith P P h 3. A 6 mg portion
(0.016 mmol) of 2 was dissolved in C6D6 and treated with 21
mg (0.081 mmol) of PPh3 at room temperature under argon.
One hour after the addition of the phosphine, the concentration
of 2 was half of its initial value; 4 h later, the reaction was
complete with quantitative formation of 11.
Rea ction of [Cp *Ir B4H10] (1) w ith Et 3N. Under an argon
atmosphere, 0.007 mL (0.052 mmol) of Et3N was added to 10
mg (0.026 mmol) of 1, dissolved in 0.7 mL of C6D6 in a 5 mm
NMR tube. Six hours after addition of the amine, the 11B and
1H NMR spectra of the reaction mixture exhibited new peaks,
but the major species was the starting iridapentaborane.
Therefore, the resulting pale yellow solution was left over-
night in the NMR tube at room temperature. The intensity
of 1 decreased, and the new peaks were more intense. By
comparison with the compounds above, the new species were
identified as [Cp*IrB4H8] (9), [Cp*IrB3H7(NEt3)] (14), and
[Cp*IrB2H6(NEt3)] (15), together with the borane adduct
BH3‚NEt3. Two days later, there was still some compound 1
in the reaction mixture; on the other hand, integration of the
11B NMR spectrum versus the external reference (capillary
containing a solution of [NMe4][B3H8] in acetone-d6) demon-
strated that the concentration of compound 14 decreased and,
in contrast, compound 15 increased in concentration. After 6
days, the initial 1 reacted fully and compounds 9 and 14
decomposed to give a mixture of 15 and borane adduct. The
final total boron concentration of the reaction mixture was half
of the initial concentration. The reaction mixture was trans-
ferred from the NMR tube to a Schlenk tube, the solvent
evaporated, and the residue extracted with hexane. 11B NMR
Rea ction of [Cp *Ir B3H9] (2) w ith p y. An 8 mg portion
(0.02 mmol) of 2 was treated with a 5-fold excess of pyridine
(0.1 mmol) at room temperature under an argon atmosphere
to give [Cp*IrB2H6(py)] (13). The reaction was quantitative by
NMR and took place in a few minutes.
Rea ction of [Cp *Ir B3H9] (2) w ith NEt3. An 8 mg portion
(0.02 mmol) of 2 was treated with 0.02 mL (0.14 mmol) of NEt3
in C6D6. The reaction was complete in about 16 h to give 15
quantitatively.
Rea ction of [Cp *Ir B2H6(P Me3)] (3) w ith BH3‚THF . A 10
mg portion (0.023 mmol) of 3 was dissolved in 0.7 mL of
C6D6 and the solution placed in a 5 mm NMR tube with an
external reference (capillary containing a (CD3)2CO solution
of [Et4N][B3H8]). This starting solution was monitored by 11B
NMR, and then 0.5 mL of BH3‚THF (1 M) was added under
an atmosphere of nitrogen at room temperature. After a few
minutes, the 11B NMR spectrum of the reaction mixture
showed quantitative conversion of 3 to give the starting
iridaborane 1.
Rea ction of [Cp *Ir B3H7(P Me3)] (4) w ith BH3‚THF . A 15
mg portion (0.04 mmol) of 1 was treated with an excess of PMe3
under the same conditions as above. At this point, the reaction
mixture had compounds 4 and 3 in a 18:1 ratio. To this mixture
was added an excess of BH3‚THF under a nitrogen atmosphere
at room temperature to give a mixture of 1 and 2 in a 15:1
ratio. The total boron intensity before and after the addition
of BH3‚THF versus the external reference is maintained,
indicating a quantitative reversible reaction.
spectroscopy on
a sample of the hexane-soluble fraction
exhibited very weak signals, indicating decomposition of the
iridatriborane 15.
[Cp *Ir B3H7(NEt3)] (14). 11B NMR (C6D6): δ 10.9 (d,
1J (B,H) ) 122, 1B), -12.7 (accidental overlap with BH3‚NEt3),
-13.2 (accidental overlap with BH3‚NEt3). 1H{11B} NMR
Rea ction of [Cp *Ir B3H7(P Me2P h )] (5) w ith BH3‚THF .
Using the same conditions and procedure as for the PMe3
derivatives above, 3 mg (0.01 mmol) of 1 was treated with a
2
(C6D6): δ 2.57 (q, J (H,H) ) 7 Hz, 3H, Et), 2.06 (s, 15H, Cp*),
2
3.95 (d, J (H,H) ) 7 Hz, 1H, BHt), 3.25 (br s, 1H, BHt), 3.49

New Substituted Iridaboranes
Organometallics, Vol. 23, No. 9, 2004 2135
5-fold excess of PMe2Ph to give compound 5 quantitatively and
also BH3‚PMe2Ph. To this mixture was added an excess of BH3‚
THF to afford the starting iridaborane 1. The conversion is
quantitative.
an orange solution. The hexane solution was concentrated
under vacuum and placed at -40 °C to give 5 mg (0.009 mmol,
31%) of 16.
NMR-Mon itor ed Rea ction s. To investigate the relative
reaction rate of 1 with different Lewis bases, to determine the
reaction rate of the transformation of 3 to give the iridatribo-
rane 4, and to investigate possible mechanistic pathways, we
carried out a series of experiments in which the reaction
mixture was monitored periodically by NMR.
1. Rela tive Rea ction Ra te of [Cp *Ir B4H10] (1) w ith
P Me3, p y, a n d NEt3. 1.1. Rea ction of [Cp *Ir B4H10] (1) w ith
P Me3 in a 5:1 Ra tio. To 4 mg (0.01 mmol) of 1 dissolved in
C6D6 in an NMR tube with the external reference as above,
we added 0.05 mmol of PMe3 under an argon atmosphere to
give 3. The reaction is quantitatively complete a few minutes
after the addition of the phosphine.
1.2. Rea ction of [Cp *Ir B4H10] (1) w ith p y in a 5:1 Ra tio.
A 6 mg portion (0.016 mmol) of 1 was treated with 0.08 mL (6
mg, 0.078 mmol) of pyridine in C6D6. Fourteen minutes after
the addition of the base, the concentration of the starting
iridapentaborane was half of the initial value; 20 min later,
the concentration of 1 was residual, giving a mixture of 12
and 13.
1.3. Rea ction of [Cp *Ir B4H10] (1) w ith NEt3 in a 5:1
R a t io. We added 0.05 mL (0.05 mmol) of NEt3 to 4 mg
(0.01 mmol) of [Cp*IrB4H10] dissolved in C6D6. Six hours
after the addition of the base, the concentration of the irida-
pentaborane was seven-ninths of its initial value; 2 days
after the treatment, the concentration was one-third of the
starting concentration, and after 5 days 1 reacted completely,
affording 15.
2. Rea ction of [Cp *Ir B4H10] (1) w ith P Me3 in a 1:2 Ra tio
a n d th e Con ver sion of 3 to 4. A 7 mg portion (0.018 mmol)
of 1 was treated with 0.036 mmol of PMe3 (1 M in THF) in a
5 mm NMR tube with an external reference at room temper-
ature. The formation of 3 took place a few minutes after
addition of the phosphine; 8 h later, the concentration of the
iridatetraborane decreased by half, and 46 h after the initiation
of the reaction, the conversion of to give the iridatriborane was
complete. The decrease in the total boron intensity cor-
responded to the loss of a {BH} unit. A white solid was formed
on the walls of the NMR tube. This product was insoluble in
C6D6 and CDCl3, but it was soluble in acetone-d6. The 11B NMR
spectrum of this product exhibited a singlet, indicating that
it is not a borane. In addition, the intensity of this peak versus
the external reference was smaller than the total boron loss
of the reaction: i.e., it did not account for the {BH} loss. First-
order kinetic treatment gave a t1/2 value of 6 h for the
transformation of 3 into 4 at room temperature.
Rea ction of [Cp *Ir B2H6(P Me2P h )] (6) w ith BH3‚THF .
The reaction mixture above was treated again with an excess
of PMe2Ph and then evaporated under vacuum, resulting in a
yellow residue that was kept under an argon atmosphere at
room temperature for 2 days. This residue was dissolved in
C6D6 and examined by 11B and 1H NMR. The sample was,
therefore, a combination of compound 6 and a large excess of
BH3‚PMe2Ph. To this mixture, we added an excess of BH3‚
THF, leading to the formation of 2. The integrals versus the
external reference demonstrated quantitative conversion be-
tween the iridaboranes.
Rea ction of [Cp *Ir B3H7(P MeP h 2)] (7) w ith BH3‚THF .
Following the general procedures described above for the PMe3
and PMe2Ph derivatives, we added a 5-fold excess of PMePh2
to a solution of 1 (4 mg, 0.01 mmol) in C6D6 to give 7 and BH3‚
PMePh2; then we added an excess of BH3‚THF to recover the
starting iridaborane quantitatively.
Rea ction of [Cp *Ir B2H6(P MeP h 2)] (8) w ith BH3‚THF .
The reaction mixture above was treated with an excess of
PMePh2, evaporated under vacuum, and kept under argon for
2 days. This residue contained 8 and a large excess of BH3‚
PMePh2. We added an excess of BH3THF, regenerating 2. The
boron intensities of the final iridaborane matched those of the
starting phosphine derivative.
Rea ction of [Cp *Ir B2H6(p y)] (13) w ith BH3‚THF . A
sample of 13, which was not weighed, was treated with an
excess of BH3‚THF, yielding 2. The concentration of the final
iridatetraborane was the same as that of the initial pyridine
derivative, demonstrated by integration versus the external
reference.
Rea ction of [Cp *Ir B2H6(NEt3)] (15) w ith BH3‚THF . We
added an excess of BH3‚THF to a unweighed sample of 15.
The conversion to 2 was quantitative.
Rea ction of [Cp *Ir B4H10] (1) w ith Br 2. A 64 mg portion
of 1 (0.17 mmol) was placed in a Schlenk tube under an argon
atmosphere and then treated with 0.01 mL of Br2 (0.34 mmol)
at room temperature. Gas was released immediately, and the
resulting orange solution was stirred at room temperature for
2 h. The solvent was evaporated to dryness under vacuum to
give an orange residue, which was extracted with hexane to
afford a yellow solution and an orange residue. The hexane
fraction was concentrated under vacuum and placed in the
freezer at -40 °C to give colorless crystals of the dibromo
derivative [Cp*IrB4H8Br2] (16; 42 mg, 0.08 mmol, 46%). IR
(KBr): 2517 (s, νB-H; sh, at 2544 and 2496), 2185 (m, νIr-H),
1008 (s; sh, at 1040), 955 (m, νB-Br), 867 (m, νB-Br). HRMS
(FAB): m/z calcd for C10H22B4Br2Ir, 537.0090, [M - 1]+; found,
537.0123. Anal. Calcd for C10H23B4Br2Ir: C, 22.30; H, 4.30.
Found: C, 22.44; H, 4.35.
3. Rea ction of [Cp *Ir B4H10] (1) w ith P Me3 in a 1:7 Ra tio
a n d th e Con ver sion of 3 to 4. A 12 mg portion (0.03 mmol)
of 1 was treated with 0.2 mL (0.2 mmol) of PMe3 in C6D6 at
room temperature. In contrast with the reaction above, 40 days
after the addition of phosphine 3 was still present in the
reaction mixture. The decrease of the concentration of 3 was
parallel to the increase of 4, [Cp*IrH4], and the borane adduct
BH3‚PMe3.
In the reaction mixture, we detected a second iridaborane
as a minor component, which was characterized by NMR as
the monobromo derivative 17.
[Cp *Ir B4H9Br ] (17). 11B{1H} NMR (C6D6): δ -5.8 (s, 1B),
4. Tim e-Depen den t Beh avior of th e system [Cp*Ir B4H10]
1
-7.5 (s, 2B), -12.0 (br s, 1B). H{11B} NMR (C6D6): δ 4.16 (s,
(1) w ith P P h 3. We followed the reaction between 1 and PPh3
at room temperature. This allowed the time-dependent be-
havior of the system to be investigated and, through this, the
spectroscopic identification of 9 as an intermediate in the
reaction pathway.
4.1. Rea ction of [Cp *Ir B4H10] (1) w ith P P h 3 in a 1:5
Ra tio. To 11 mg (0.03 mmol) of 1 dissolved in 1 mL of C6D6,
we added 38 mg (0.14 mmol) of PPh3 under an argon atmos-
phere at room temperature. The reaction was monitored by
1H and 11B NMR spectroscopy at different intervals of time.
1H, BHt), 3.14 (s, 1H, BHt), 2.76 (s, 1H, BHt), 2.40 (s, 1H, BHt),
1.58 (s, 15H, Cp*), -2.28 (s, 1H, BHB), -4.36 (s, 1H, BHB),
-5.14 (br s, 1H, BHB), -13.34 (s, 1H, IrH).
Rea ction of [Cp *Ir B4H10] (1) w ith N-Br om osu ccin im -
id e. A 3 mL portion of CH2Cl2 was added under an argon
atmosphere to a Schlenk tube containing 10 mg (0.03 mmol)
of 1 and 8.4 mg (0.05 mmol) of N-bromosuccinimide. A yellow
solution and a pale yellow precipitate were formed im-
mediately. The reaction mixture was stirred for 2 h at room
temperature, the solvent evaporated, and the orange residue
extracted with hexane to give an orange insoluble residue and
4.2. Rea ction of [Cp *Ir B4H10] (1) w ith P P h 3 in a 1:2
Ra tio. A 5 mg portion (0.013 mmol) of 1 was treated with 6.9

2136 Organometallics, Vol. 23, No. 9, 2004
Mac´ıas et al.
mg (0.026 mmol) of PPh3 in C6D6 at room temperature. The
reaction was then studied by NMR.
Ack n ow led gm en t. This work was supported by the
National Science Foundation (Grant Nos. CHE 9986880
and CHE 0304008).
5. Liga n d Exch a n ge Rea ction s. 5.1. Rea ction of Com -
p ou n d 3 w ith P Me2P h . A 6 mg portion (0.016 mmol) of 1
was treated with 2 equiv of PMe3 in toluene-d8. To this reac-
tion mixture was added a 20-fold excess of PMe2Ph, and
the reaction exchange was followed by NMR at low tempera-
tures.
5.2. Rea ction of Com p ou n d 4 w ith Lew is Ba ses. A 4
mg portion (0.009 mmol) of compound 4 was treated in toluene-
d8 with a 20-fold excess of PMe2Ph, PMePh2, PPh3, and py,
respectively. The respective reaction mixtures were studied
by NMR at different temperatures.
Su p p or tin g In for m a tion Ava ila ble: Tables and figures
giving NMR integrals for the monitoring of the reactions and
the exchange experiments and tables giving X-ray diffraction
details, atomic coordinates, bond lengths and angles, and
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.
OM049960A