Modeling the proposed intermediate in alkane carbon-hydrogen bond activation by Cp*(PMe3)Ir(Me)OTf: Synthesis and stability of novel organometallic iridium(V) complexes

Article abstract of DOI:10.1021/om990255p

Addition of HX to CH₂Cl₂ solutions of Cp*IrMe₄ (Cp* = η⁵-C₅Me₅) at low temperature provided Cp*Ir(Me)₃X (X = Cl, 5; X = OSO₂CF₃ = OTf, 6). Both complexes are very thermally sensitive yet proved to be useful precursors for novel cationic iridium(V) complexes. Treatment of 6 with a variety of trisubstituted phosphines, arsines, and stibines (L) afforded compounds 7-12, [Cp*(L)IrMe₃][OTf] (L = PMe₃, 7; L = PEt₃, 8; L = PPh₃, 9; L = AsEt₃, 10; L = AsPh₃, 11; L = SbPh₃, 12). Metathesis of the triflate anion of antimony complex 12 for the tetraphenylborate anion afforded [Cp*(SbPh₃)IrMe₃][BPh₄] (13). The molecular structure of 13 was determined by single-crystal X-ray diffraction analysis. Complex 7 is a potential model for the proposed intermediate on the methane carbon-hydrogen bond activation reaction pathway by Cp*(PMe₃)Ir(Me)OTf, and its relevance to this reaction is discussed. Complex 7 decomposed by reductive elimination of MeCp*. The remaining iridium fragment was trapped by added phosphine to form [cis-{PMe₃}₄IrMe₂][OTf] (14) as an impure mixture. Reaction of 6 with excess dppm (dppm = Ph₂PCH₂PPh₂) afforded [cis-{η²-Ph₂PCH₂-PPh₂} ₂IrMe₂][OTf] (15). The molecular structure of 15 was determined by single-crystal X-ray structure analysis.

Full text of DOI:10.1021/om990255p

Organometallics 1999, 18, 2707-2717
2707
Mod elin g th e P r op osed In ter m ed ia te in Alk a n e
Ca r bon -Hyd r ogen Bon d Activa tion by
Cp *(P Me3)Ir (Me)OTf: Syn th esis a n d Sta bility of Novel
Or ga n om eta llic Ir id iu m (V) Com p lexes
Peter J . Alaimo and Robert G. Bergman*
Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, California 94720
Received April 9, 1999
Addition of HX to CH2Cl2 solutions of Cp*IrMe4 (Cp* ) η5-C5Me5) at low temperature
provided Cp*Ir(Me)3X (X ) Cl, 5; X ) OSO2CF3 ) OTf, 6). Both complexes are very thermally
sensitive yet proved to be useful precursors for novel cationic iridium(V) complexes.
Treatment of 6 with a variety of trisubstituted phosphines, arsines, and stibines (L) afforded
compounds 7-12, [Cp*(L)IrMe3][OTf] (L ) PMe3, 7; L ) PEt3, 8; L ) PPh3, 9; L ) AsEt3,
10; L ) AsPh3, 11; L ) SbPh3, 12). Metathesis of the triflate anion of antimony complex 12
for the tetraphenylborate anion afforded [Cp*(SbPh3)IrMe3][BPh4] (13). The molecular
structure of 13 was determined by single-crystal X-ray diffraction analysis. Complex 7 is a
potential model for the proposed intermediate on the methane carbon-hydrogen bond
activation reaction pathway by Cp*(PMe3)Ir(Me)OTf, and its relevance to this reaction is
discussed. Complex 7 decomposed by reductive elimination of MeCp*. The remaining iridium
fragment was trapped by added phosphine to form [cis-{PMe3}4IrMe2][OTf] (14) as an impure
mixture. Reaction of 6 with excess dppm (dppm ) Ph2PCH2PPh2) afforded [cis-{η2-Ph2PCH2-
PPh2}2IrMe2][OTf] (15). The molecular structure of 15 was determined by single-crystal X-ray
structure analysis.
In tr od u ction
conditions. Although we have explored the reactivity of
1 and 2 extensively, the rapidity with which these
reactions occur, especially with 2, has made the mecha-
nistic details of the C-H bond breaking step difficult
to uncover.
Our research group and others have long been inter-
ested in understanding the mechanistic details of in-
termolecular carbon-hydrogen bond activation by well-
defined homogeneous transition-metal complexes.1-5
More specifically, we have recently been studying the
scope and generality of reactions (eq 1) involving Cp*-
On the basis of previous studies, we have postulated
that the active species in these reactions is the cationic
complex [Cp*(PMe3)Ir(Me)]+. Furthermore, we have
proposed that there are two plausible mechanistic
extremes worthy of serious consideration: the first is a
two-step mechanism consisting of oxidative addition
followed by rapid reductive elimination, and the second,
a concerted σ-bond metathesis. These mechanistic ex-
tremes are illustrated in Scheme 1.
Cp*(L)Ir(Me)X + R-H f Cp*(L)Ir(R)X + CH4
(1)
(PMe3)Ir(Me)X (Cp* ) η5-C5Me5; X ) OTf ) OSO2CF3
(1), X ) BArf ) B(3,5-C6H3(CF3)2)4 (2)).6-11 Our interest
in these compounds stems from their ability to activate
a wide variety of C-H bonds under remarkably mild
The first mechanism is supported by the fact that both
C-H oxidative addition and C-H reductive elimination
reactions are well-precedented with many different
transition metals in a variety of oxidation states.12
However, iridium(V) compounds such as 3 are rare,
calling into question the likelihood of this mechanism.
Although there are a number of reports that invoke the
intermediacy of iridium(V) complexes along reaction
pathways,13-17 only a few organometallic iridium(V)
complexes have been isolated to date.13,18-31
(1) For recent reviews of C-H activation, see refs 2-5.
(2) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154-162 and references therein.
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Ed. Engl. 1998, 37, 2181 and references therein.
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Applied Homogeneous Catalysis with Organometallic Compounds: A
Comprehensive Handbook in Two Volumes; Cornils, B., Herrmann, W.
A., Eds.; Wiley-VCH: New York, 1996; Vol. 2, pp 1081-1092.
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11538-11539.
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Soc. 1997, 119, 5269-5270.
10.1021/om990255p CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/15/1999

2708 Organometallics, Vol. 18, No. 14, 1999
Alaimo and Bergman
Sch em e 1
For the following reasons, we felt that none of the
previously reported Ir(V) complexes provided ample
precedent for 3. First, the complexes (mesityl)3IrO,18
[(mesityl)4Ir][X] (X ) BF4, OTf),19 Tp*IrH4,13,20,21 Cp*
IrH3X (X ) H, SiMe3, SnMe3, SnPh3),22,23 and Cp*Ir-
(H)2(MR3)2 (MR3 ) SiMe3, SnMe3, SnBu3)24-26 have few
they are polyhydrides. First, we consider the fact that
the Pauling electronegativity of iridium (2.20) is more
similar to that of hydrogen (2.20) than to that of carbon
(2.55), suggesting that an iridium-hydride and an
iridium-methide might be electronically very different.
Additionally, the differences between the hydrogen 1s
and the methide sp3 orbitals have been suggested as
explanations for differing H and Me ligand reactivities.12
Because no suitable model for intermediate 3 had been
reported, we felt that it was important to consider the
possibility that a σ-bond metathesis mechanism might
be operative.
It is well-established that C-H activation by high-
valent early-metal systems occurs by σ-bond metathe-
sis.32,33 However, σ-bond metathesis at late-metal cen-
ters is rarely invoked, as these systems tend to undergo
oxidative addition. In fact, we are aware of only one
report of a late-metal system wherein σ-bond metathesis
has been convincingly demonstrated by disproof of an
alternative oxidative addition mechanism. That report
involves B-H bond metathesis with the Ru-CH3 bond
of a coordinatively and electronically saturated ruthe-
nium center.34
Further support for the oxidative addition/reductive
elimination mechanism in our Ir(III) system comes from
recent computational work performed by the research
group of Hall. Density functional calculations (B3LYP)
on the model cation Cp(PH3)IrMe+ have predicted that
the oxidative addition/reductive elimination pathway is
preferred over the σ-bond metathesis pathway. Fur-
thermore, these authors were not able to locate a σ-bond
metathesis transition state, leading them to suggest
that σ-bond metathesis “is doubtful even at higher
energies.”35 Ab initio MO calculations (MP2) on the
same model cation have predicted the same result.36
ligands in common with proposed intermediate 3.
27,28
Second, Cp*IrMe4
is not cationic and does not
contain a phosphine ligand, rendering it electronically
very dissimilar to 3. Third, the only reported cationic
organometallic Ir(V) complexes are the trihydride salts
[Cp(L)IrH3]+ 29,30 and [Cp*(PMe3)IrH3]+,31 prepared from
protonation of Cp′(L)IrH2 (Cp′ ) Cp, Cp*) with HBF4.
Although these cationic iridium(V) complexes may ap-
pear similar to 3, we were uncomfortable considering
them as appropriate models for intermediate 3, since
(15) Go´mez, M.; Robinson, D. J .; Maitlis, P. M. J . Chem. Soc., Chem.
Commun. 1983, 825-826.
(16) Ferrari, A.; Polo, E.; Ru¨egger, H.; Sostero, S.; Venanzi, L. M.
Inorg. Chem. 1996, 35, 1602-1608.
(17) Go´mez, M.; Kisenyi, J . M.; Sunley, G. J .; Maitlis, P. M. J .
Organomet. Chem. 1985, 296, 197-207.
(18) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.;
Hursthouse, M. B. Polyhedron 1993, 12, 2009-2012.
(19) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1992, 3477-3482.
(20) Paneque, M.; Poveda, M. L.; Taboada, S. J . Am. Chem. Soc.
1994, 116, 4519-4520.
(21) Gutie´rrez-Puebla, E.; Monge, AÄ .; Paneque, M.; Poveda, M. L.;
Taboada, S.; Trujillo, M.; Carmona, E. J . Am. Chem. Soc. 1999, 121,
346-354.
(22) Gilbert, T. M.; Hollander, F. J .; Bergman, R. G. J . Am. Chem.
Soc. 1985, 107, 3508-3516.
(23) Gilbert, T. M.; Bergman, R. G. Organometallics 1983, 2, 1458-
1460.
(24) Fernandez, M.-J .; Maitlis, P. M. Organometallics 1983, 2, 164-
165.
(25) Fernandez, M.-J .; Maitlis, P. M. J . Chem. Soc., Dalton Trans.
1984, 2063-2066.
(26) Ruiz, J .; Spencer, C. M.; Mann, B. E.; Taylor, B. F.; Maitlis, P.
M. J . Organomet. Chem. 1987, 325, 253-260.
(27) Isobe, K.; Bailey, P. M.; Maitlis, P. M. J . Chem. Soc., Chem.
Commun. 1981, 808-809.
(28) Isobe, K.; Miguel, A. V. d.; Nutton, A.; Maitlis, P. M. J . Chem.
Soc., Dalton Trans. 1984, 929-933.
(32) Watson, P. L. J . Am. Chem. Soc. 1983, 105, 6491-6493.
(33) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203-219.
(34) Hartwig, J . F.; Bhandari, S.; Rablen, P. R. J . Am. Chem. Soc.
1994, 116, 1839-1844. Perhaps this is not surprising, since the
reactivity patterns of Ru(II) (d6) suggest that it behaves like a d0 metal
center.
(29) Heinekey, D. M.; Millar, J . M.; Koetzle, T. F.; Payne, N. G.;
Zilm, K. W. J . Am. Chem. Soc. 1990, 112, 909-919 (L ) PMe3, PPh3,
PCy3, P(i-Pr)3, PMe2Ph, P(OPh)3, MPTB (1-methyl-4-phospha-3,5,8-
trioxabicyclo[2.2.2]octane), AsPh3, SbPh3, P(H)(Ph)(n-decyl)).
(30) Heinekey, D. M.; Payne, N. G.; Schulte, G. K. J . Am. Chem.
Soc. 1988, 110, 2303-2305.
(35) Strout, D. L.; Zaric´, S.; Niu, S.; Hall, M. B. J . Am. Chem. Soc.
1996, 118, 6068-6069.
(36) Su, M.-D.; Chu, S.-Y. J . Am. Chem. Soc. 1997, 119, 5373-5383.
(31) Gilbert, T. M.; Bergman, R. G. J . Am. Chem. Soc. 1985, 107,
3502-3507.

Novel Organometallic Iridium(V) Complexes
Organometallics, Vol. 18, No. 14, 1999 2709
Sch em e 2
To gain evidence for the predicted iridium(V) inter-
mediate on the oxidative addition/reductive elimination
pathway, a number of seemingly straightforward ex-
periments were undertaken; however, all attempts
failed to identify such a species in these reactions. These
efforts included low-temperature NMR spectroscopic
experiments to (a) directly monitor C-H activation in
situ and (b) spectroscopically characterize an iridium-
(V) intermediate generated by protonation (HOTf) or
methylation (MeOTf) of Cp*(L)Ir(Me)2, Cp*(L)Ir(H)2, or
Cp*(L)Ir(Me)(H).37 We reasoned that if the C-H bond
activation reaction by Cp*(PMe3)Ir(Me)OTf (1) were
indeed proceeding by oxidative addition, [Cp*(L)Ir(Me)2-
(H)][OTf] (3) would likely be an extremely short-lived
species, due to the fact that C-H reductive elimination
from such an intermediate should be rapid. Hence, our
lack of direct observation of 3 by no means rules out
the oxidative addition pathway.
We therefore decided to synthesize [Cp*(PMe3)IrMe3]-
[OTf] (7), a potential model compound that should be
less reactive toward reductive elimination than hydride
3, and explore its chemistry. We expected that complex
7 would undergo reductive elimination more sluggishly
than the putative intermediate [Cp*(PMe3)Ir(Me)2(H)]-
[OTf] (3), since C-C reductive elimination is known to
have a higher kinetic barrier than C-H reductive
elimination (eqs 2 and 3).38 This paper describes the
results of our investigation.
δ 2.9 and -0.2 ppm. In this reaction too, neither ethane
1
nor MeCp* was detected by H NMR spectroscopy.
The addition of anhydrous hydrochloric acid by vacuum
transfer to frozen solutions of tetramethyl complex 4
(0.04 M in CD2Cl2, -196 °C) followed by warming to
-78 °C resulted in the rapid formation of a bright yellow
solution. Low-temperature 1H and 13C{1H} NMR spectra
indicated that protonolysis of an Ir-CH3 bond occurred
to form the neutral complex Cp*Ir(Me)3Cl (5) (Scheme
2). Likewise, dropwise addition of triflic acid (0.04 M in
CD2Cl2) to a cold solution of 4 (0.04 M in CD2Cl2, -78
°C) resulted in formation of another bright yellow
compound formulated as Cp*Ir(Me)3OTf (6) on the basis
1
of its low-temperature H, 13C{1H}, and 19F{1H} NMR
spectra (Scheme 2). Addition of excess acid (HX; X )
Cl, OTf) did not provide a route into complexes Cp*Ir-
(Me)2X2, Cp*Ir(Me)X3, and Cp*Ir(X)4 in detectable quan-
tities by 1H NMR spectroscopy; instead, no further
reaction was observed.
kC-H red elim
The 1H NMR spectrum of compound 5 exhibited
resonances for the pentamethylcyclopentadienyl ligand
at δ 1.35 (s, 15H), a single methyl group positioned trans
to the chloride ligand at δ 0.98 (s, 3H), and the two
chemically equivalent methyl groups cis to the chloride
ligand at δ 1.62 (s, 6H). The 1H NMR spectrum of
compound 6 was similar. The 13C{1H} NMR spectra for
complexes 5 and 6 were also similar, with resonances
observed for the two types of carbon atoms of the Cp*
rings as well as two resonances for the two types of
metal-bound methyl groups. Both compounds 5 and 6
proved to be air- and temperature-sensitive. While
solutions (CD2Cl2) of 5 or 6 were stable for weeks at
-80 °C, complete decomposition occurred in minutes at
0 °C. The products resulting from thermal decomposi-
tion of 5 or 6 were not identified, but neither ethane
nor MeCp* was detected by 1H NMR spectroscopy. Due
to the very high thermal instability of complexes 5 and
6, characterization by low-temperature NMR spectros-
copy was required. Weaker acids, including acetic acid,
trifluoroacetic acid, and p-toluenesulfonic acid, did not
react with 4 at room temperature.
[Cp*(L)Ir(Me)2(H)][X]
8
fast
Cp*(L)Ir(Me)X + CH4 (2)
kC-C red elim
[Cp*(L)IrMe3][X]
8
slow?
Cp*(L)Ir(Me)X + C2H6 (3)
Resu lts
Syn t h esis, Th er m olysis, a n d P r ot on olysis of
Cp *Ir Me4 (4). The synthesis of Cp*IrMe4 (4) was
reported by the Maitlis group in 1981.27,28 Thermolysis
of 4 at 75 °C in CD2Cl2 resulted in formation of
hexamethylcyclopentadiene (MeCp*, 1 equiv, vide infra)
and methane (1.3 equiv) as the only identified products
1
(eq 4). Neither ethane nor ethylene was detected by H
NMR spectroscopy.
Cp*IrMe4
f MeCp* + CH4
(4)
4
The addition of either anhydrous HCl or HOTf to
room-temperature solutions of tetramethyl complex 4
resulted in immediate formation of a complicated mix-
At t em p t ed Su b st it u t ion R ea ct ion s of Cp *Ir -
(Me)3OTf (6) w ith An ion ic Nu cleop h iles. A variety
of anionic nucleophiles were introduced to solutions of
triflate 6 at low temperature in order to assess the
utility of 6 as a precursor for neutral iridium(V)
complexes (eq 5). The potential ligands were added as
ture of compounds (1H NMR spectroscopy). A H NMR
1
spectrum of the hydrochloric acid reaction mixture
indicated the formation of methane, but ethane, ethyl-
ene, ethyl chloride, and methyl chloride were not
detected, nor was MeCp* observed. Instead, eight major
unassigned resonances between δ 2.1 and 1.7 ppm were
present. The 1H NMR spectrum of the triflic acid
reaction was more complicated, containing a resonance
for methane and >20 unassigned resonances between
+ Nu- N Cp*Ir(Me)3Nu + TfO- (5)
Cp*Ir(Me) OTf
3
6
methylene chloride or THF solutions to methylene
chloride or THF solutions of 6 at -78 °C, and the
resulting mixtures were monitored by variable-temper-
ature NMR spectroscopy. These reactions were moni-
(37) Burger, P.; Arndtsen, B. A.; Luecke, H. F.; Bergman, R. G.
Unpublished results.
(38) See ref 12, p 330.

2710 Organometallics, Vol. 18, No. 14, 1999
Alaimo and Bergman
Sch em e 3
was very slow at low temperatures (-78 °C), and
decomposition of 6 was rapid near 0 °C. To circumvent
these difficulties, trimethylphosphine was vacuum-
transferred onto a frozen solution (-196 °C) of 6 and
then warmed to an intermediate temperature (-25 °C).
This provided for efficient substitution with very little
decomposition of 6. Since the product (7) was moderately
thermally sensitive in solution (t1/2 = 18 h, room
temperature), removal of the volatile materials in vacuo
at -29 °C was performed to obtain 7 cleanly. Subse-
quent washing with pentane afforded air- and temper-
ature-sensitive 7 in 87% isolated yield. The 1H, 13C{1H},
19F{1H}, and 31P{1H} NMR spectra were consistent with
the given formulation. Additionally, the compound was
characterized by FTIR and high-resolution mass spec-
trometry (FAB). Due to its thermal sensitivity, neither
the melting point nor the elemental composition was
determined for 7.
Treatment of a methylene chloride solution of 6 with
other trisubstituted phosphines, as well as arsine and
antimony ligands (L), at -78 °C resulted in the forma-
tion of the complexes [Cp*(L)IrMe3][OTf] (8-12; L )
PEt3, 8; L ) PPh3, 9; L ) AsEt3, 10; L ) AsPh3, 11; L
) SbPh3, 12), which are analogous to 7 (Scheme 3).
Spectral data for complexes 8-12 are consistent with
the given formulations. The 1H NMR spectrum of
complex 9 displays broad resonances for the aryl protons
of the triphenylphosphine ligand. The corresponding
aryl carbon resonances for 9 in the 13C{1H} NMR
spectrum are also broad. We presume that this is likely
due to hindered Ir-P bond rotation on the NMR time
scale.
tored by placing the cold (-78 °C), flame-sealed NMR
tube into the precooled NMR probe (-80 to -30 °C,
depending on the reaction), acquiring a low-temperature
1H NMR spectrum, increasing the temperature (usually
in 10 or 15 °C increments), and recording spectra at each
successive temperature (-70, -60, -50 °C, etc.) until
room temperature was attained. None of these reactions
afforded isolable compounds. The anionic nucleophiles
used included hydride sources (hydridoborates, hydri-
doboranes, aluminum hydrides, alkali-metal hydrides,
alkaline-earth hydrides), carbon nucleophiles (alkali-
metal reagents, Grignard reagents, dialkyl cuprate
reagents, dialkyl zinc reagents; all performed in THF-
d8), oxygen anions (hydroxides, alkoxides, aryloxides,
acetates, siloxides, peroxides), thiolates, cyanides, and
sodium azide.
Triflate salt 12 was converted to tetraphenylborate
salt 13 by anion metathesis in CH2Cl2 (eq 6). Single
In some reactions, no shift in the 1H NMR resonances
for the free ligand or 6 was observed (aside from the
temperature dependence of the chemical shift values).
In many cases, though, a shift of the resonances was
observed for both the incoming nucleophile and 6,
indicating some interaction between the two species
(possibly substitution of the nucleophile for the triflate
ligand). In runs where an excess of the nucleophile was
added, resonances for both free and bound nucleophile
were observed. Conversely, when a stoichiometric de-
ficiency of the nucleophile was added, we observed
resonances for both the iridium triflate starting material
6 and the iridium-containing product. However, in all
cases decomposition occurred upon warming to room
temperature, resulting in mixtures of unidentified
[Cp*(SbPh )IrMe ][OTf]
+ NaBPh4 CH Cl 8
3
3
2
2
12
[Cp*(SbPh )IrMe ][BPh ]
+ NaOTfV (6)
3
3
4
13
crystals of [Cp*(SbPh3)IrMe3][BPh4] (13) suitable for
X-ray diffraction study were grown by vapor diffusion
of pentane into a methylene chloride solution at -30
°C over 3 days. The molecular structure of 13 is shown
in Figure 1. The complex crystallizes with two methyl-
ene chloride molecules in the triclinic space group P1h
with two formula units in the unit cell. The iridium
atom has an approximate four-legged piano-stool coor-
dination geometry: coordinated by a Cp* ligand, three
methyl ligands, and a SbPh3 ligand. The Ir-C distances
for the Cp* ligand range from 2.22 to 2.37 Å. The longest
Ir-C distance corresponds to the carbon atom closest
to the antimony ligand. The shortest Ir-C distances
correspond to the carbon atoms furthest from the
antimony ligand. Apparently, the large Sb atom is in
close contact with one side of the Cp* ligand, causing
the carbon atoms to be pushed away from the Sb atom.
Crystal data and structure refinement details are given
in Table 1. Selected bond lengths and angles are listed
in Table 2.
1
products that appeared similar (by H NMR spectros-
copy) to the thermal decomposition products of triflate
6. To determine the source of decomposition in these
reactions, we allowed some of them to stand at -30 °C
for up to 36 h before warming to room temperature.
However, even in these runs, complicated product
mixtures were obtained. Since none of the reactions with
anionic nucleophiles resulted in the formation of a clean
isolable material, they were not pursued further.
Su bstitu tion Rea ction s of Cp *Ir (Me)3OTf (6)
w ith Neu tr a l Liga n d s. Addition of trimethylphos-
phine to a frozen methylene chloride solution of bright
yellow triflate complex 6 resulted in formation of the
colorless phosphine salt [Cp*(PMe3)IrMe3][OTf] (7)
(Scheme 3). Substitution of the phosphine for triflate
To our knowledge, this crystal structure represents
only the third crystallographically characterized com-
plex containing an Ir-Sb bond.39,40 In 1991, Balch and
co-workers reported the complex [Ir2(SbF2)(CO)2Cl2(µ-
+
dpma)2][BF4], in which the SbF2 unit bridges two

Novel Organometallic Iridium(V) Complexes
Organometallics, Vol. 18, No. 14, 1999 2711
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for Com p ou n d s 13 a n d 15
13
15
empirical formula
C
57H63SbIrBCl4
C55H54Cl4IrP4-
SO3F3
fw
1214.72
1310.01
cryst color, habit
cryst dimens, mm
cryst syst
lattice type
lattice params
a, Å
colorless, blades
clear, blades
0.35 × 0.27 × 0.09 0.43 × 0.09 × 0.07
triclinic
monoclinic
primitive
primitive
11.2311(7)
14.5216(10)
17.1433(11)
76.863(1)
87.807(1)
69.632(1)
2550.0
14.4780(3)
20.9230(5)
17.9432(4)
b, Å
c, Å
R, deg
â, deg
93.128(1)
γ, deg
V, Å3
space group
Z
D
P1h (No. 2)
P21/n (No. 14)
4
1.603
2
calcd, g/cm3
1.582
F000
temp, °C
1212.00
-155 ( 1
33.89
2624.00
-147 ( 1
28.74
µ(Mo KR), cm-1
diffractometer
radiation
F igu r e 1. ORTEP diagram of the cationic portion of [Cp*-
(SbPh3)IrMe3][BPh4]‚2CH2Cl2 (13), with partial atom label-
ing scheme. The anion and the methylene chloride mol-
ecules were omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.
SMART CCD
Mo KR (λ ) 0.710 69 Å),
graphite monochromated
detector position, mm
exposure time, s/frame
scan type
2θmax, deg
no. of rflns measd
total
unique
Rint
corrns
structure soln
refinement
60.00
10.0
ω (0.3°/frame)
iridium atoms.39 The Ir-Sb bond distances in this
complex are 2.655(1) Å. In 1996, Werner and co-workers
reported the crystal structure of [IrCl(C2H4)2(Sb(i-
Pr)3)2].40 The Ir-Sb bond distances in this complex are
2.546(1) and 2.655(1) Å. In our complex (13), the Ir-Sb
bond distance is 2.5848(8) Å.
52.2
52.4
13 970
8703
0.047
26 113
9882
0.044
Lorentz-polarization
direct methods (SIR92)
full-matrix least squares
∑w(|Fo| - |Fc|)2
Complexes 7-12 displayed a range of air and tem-
perature sensitivities. Phosphine salts 7-9 were
moderately air-sensitive and moderately temperature-
sensitive. Methylene chloride solutions of 7-9 decom-
posed in a few minutes upon exposure to air to give
unidentified products. Benzene or methylene chloride
solutions of 7-9 stored in the dark eliminated MeCp*
(vide infra) over the course of 2 days. Qualitative results
suggest that the rate of the thermal decomposition of
7-9 is independent of added phosphine. When two
equimolar CD2Cl2 solutions of 7, 8, or 9 were placed in
NMR tubes and free phosphine was added to only one
tube, the rate of disappearance of the iridium starting
material and the rate of appearance of MeCp* were
approximately the same in both tubes (1H NMR).
Additionally, the rate of elimination of MeCp* appears
to be independent of solvent. When three equimolar
solutions of 7 were prepared in C6D6, CD2Cl2, and CD3-
CN, respectively, placed in NMR tubes, and allowed to
react at room temperature in the dark, the rate of
appearance of MeCp* was approximately the same in
all three tubes (1H NMR). Finally, two solutions of 7
(CD2Cl2) at different concentrations (1.1 and 10 mM)
formed MeCp* (room temperature, darkness) at the
same approximate rate (1H NMR), implying that the
reaction proceeds unimolecularly.
function minimized
least-squares weights
w ) (σ2(Fo))-1 ) [σc (Fo) +
2
(p2/4)Fo
]
2
-1
p factor
0.0310
5031
0.0300
all non-hydrogen atoms
6378
anomalous dispersion
no. of observns (I >
3.00σ(I))
no. of variables
rfln/param ratio
287
17.53
645
9.89
residuals: R; Rw; R(all) 0.045; 0.044; 0.097 0.029; 0.031; 0.061
goodness-of-fit indicator 1.28
max shift/error in final 0.00
cycle
0.90
0.02
final diff map
max peak, e/Å3
min peak, e/Å3
1.61
-1.75
0.98
-0.64
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 13
Ir(1)-Sb(1)
Ir(1)-C(1)
Ir(1)-C(2)
Ir(1)-C(3)
Ir(1)-C(4)
Ir(1)-C(5)
Ir(1)-Cp Cent
Ir(1)-C(11)
Ir(1)-C(12)
2.5848(8)
2.29(1)
2.23(1)
2.22(1)
2.27(1)
2.37(1)
1.9254(4)
2.13(1)
2.12(1)
Ir(1)-C(13)
Sb(1)-C(14)
Sb(1)-C(20)
Sb(1)-C(26)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
2.17(1)
2.10(1)
2.13(1)
2.11(1)
1.45(1)
1.42(1)
1.43(1)
1.44(1)
1.41(1)
Sb(1)-Ir(1)-C(11)
Sb(1)-Ir(1)-C(12)
Sb(1)-Ir(1)-C(13)
112.4(3) C(12)-Ir(1)-Cp Cent 115.4(3)
79.0(3) C(12)-Ir(1)-Cp Cent 113.2(3)
77.1(3) Ir(1)-Sb(1)-C(14)
Arsine salts 10 and 11 are mildly air- and tempera-
ture-sensitive. Methylene chloride solutions of 10 or 11
decompose over a few hours upon exposure to air giving
115.4(3)
119.9(3)
117.0(3)
100.8(4)
99.8(4)
Sb(1)-Ir(1)-Cp Cent 127.31(3) Ir(1)-Sb(1)-C(20)
C(11)-Ir(1)-C(12)
C(11)-Ir(1)-C(13)
75.2(4) Ir(1)-Sb(1)-C(26)
75.7(4) C(14)-Sb(1)-C(20)
C(11)-Ir(1)-Cp Cent 120.3(3) C(14)-Sb(1)-C(26)
(39) Balch, A. L.; Catalano, V. J .; Chatfield, M. A.; Nagle, J . K.;
Olmstead, M. M.; Reedy, P. E. J . Am. Chem. Soc. 1991, 113, 1252-
1258 (dpma ) bis((diphenylphosphino)methyl)phenylarsine).
(40) Werner, H.; Ortmann, D. A.; Gevert, O. Chem. Ber. 1996, 129,
411-417.
C(12)-Ir(1)-C(13)
131.0(4) C(20)-Sb(1)-C(26)
100.7(4)
unidentified decomposition products. Thermolysis (room
temperature) of methylene chloride solutions of 10 or

2712 Organometallics, Vol. 18, No. 14, 1999
Alaimo and Bergman
Sch em e 4
11 in the dark induces elimination of MeCp* more
slowly than for the phosphine analogues 7-9. These
reactions proceed over the course of 4 days, compared
to 2 days for 7-9.
Although triphenylantimony salt 12 is mildly sensi-
tive to both air and temperature, it is the most stable
of these complexes that we have found. Decomposition
in air required >4 h, and decomposition from room-
temperature thermolysis in the dark required >5 days.
Neither the air- nor the thermal-decomposition products
for complexes 7-12 were isolated.
Complex 7 appeared to form tetrakis(trimethylphos-
phine) complex 14 as the major iridium-containing
product. Triethylphosphine complex 8 appeared to give
a product (“[cis-{PEt3}4IrMe2][OTf]”) analogous to 14,
but triphenylphosphine complex 9 did not.
Room-temperature thermolysis of 8 in the presence
of added triethylphosphine (5 equiv) gave a reaction
mixture whose 31P{1H} NMR spectrum contained two
triplets. However, room-temperature thermolysis of 9
in the presence of added triphenylphosphine (5 equiv)
gave a reaction mixture whose 31P{1H} NMR spectrum
contained only several singlets, not two triplets as would
be predicted for cationic [cis-{PPh3}4IrMe2]+. Moreover,
removal of the volatile materials in vacuo, followed by
washing with ether and pentane to remove excess
triphenylphosphine, showed that only three triphe-
nylphosphine groups had been incorporated into the
iridium-containing product. The major product of the
thermolysis of 9 in the presence of triphenylphosphine
was not isolated; however, it was assigned as a five-
coordinate Ir(III) (“[{PPh3}3IrMe2][OTf]”) complex, based
Although thermolysis of a methylene chloride solution
of 7 at room temperature in the dark resulted in the
formation of MeCp* and unidentified iridium-containing
products, repeating this experiment in the presence of
a 3-fold (or greater) excess of trimethylphosphine gave
a different result. This experiment resulted in the
formation of MeCp* as the major organic product (97%
yield by NMR integration vs Cp2Fe internal standard),
[cis-{PMe3}4IrMe2][OTf] (14) as the major iridium-
containing product, and several minor unidentified
iridium-phosphine-containing products (Scheme 4).
Complex 14, formed in ∼60% yield (vs internal stan-
dard), could not be isolated in pure form, even by
repeated recrystallization. It was therefore character-
ized by 1H, 19F{1H}, and 31P{1H} NMR spectroscopy, as
1
on the H NMR integrations and the precedent42-45 for
five-coordinate d6 complexes bearing three triphenylphos-
phine ligands. This type of structure has been rational-
ized on the basis of the greater steric requirements of
the triphenylphosphine ligand relative to either trim-
ethyl- or triethylphosphine ligands.
1
well as FABMS. The H NMR spectrum of 14 included
all the expected resonances for the cis-disposed complex,
including one resonance for the chemically equivalent
iridium-bound methyl groups and two resonances for
the two inequivalent sets of trimethylphosphine ligands,
as well as resonances for the unidentified iridium-
containing products. The stereochemistry of the complex
was assigned on the basis of the 31P{1H} NMR spec-
trum, which contained two triplets (δ -48.85, -61.02,
2J PP ) 18.0 Hz) for the two coupled sets of two trim-
ethylphosphine ligands, and by analogy to complex 15
(vide infra). The identity of hexamethylcyclopentadiene
was confirmed by comparison of the volatile materials
of the reaction mixture to independently synthesized
material by 1H and 13C{1H} NMR spectroscopy and GC-
MS.41
Although complexes 7 and 8 appeared to undergo
reductive elimination of MeCp* to presumably generate
the remaining iridium fragment “[{PR3}IrMe2]+”, trap-
ping of this fragment by added phosphine ligand was
relatively inefficient, since only intractable product
mixtures were isolated. This prompted us to attempt
to trap the iridium species in the reaction by using a
chelating phosphine. Treatment of a methylene chloride
solution of 6 with 2 equiv of bis(diphenylphosphino)-
methane at -78 °C gave MeCp* and [cis-(η2-Ph2PCH2-
PPh2)2IrMe2][OTf] (15) (Scheme 5). The 31P{1H} NMR
2
signals at δ -61.31 (t, J PP ) 14.5 Hz) and -63.33 (t,
2J PP ) 14.4 Hz) indicated that the stereochemistry at
(42) Cotton, F. A.; Matusz, M. Inorg. Chim. Acta 1987, 131, 213-
216.
In fact, all three phosphine salts 7-9 eliminated
MeCp* thermally in the presence of added phosphine.
(43) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A. Acta Crystallogr.
1985, C41, 698-699.
(44) Hoffman, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 97,
4221-4228.
(41) Courtneidge, J . L.; Davies, A. G.; Shields, C. J .; Yazdi, S. N. J .
Chem. Soc. Perkin Trans. 2 1988, 799-805.
(45) La Placa, S. J .; Ibers, J . A. Inorg. Chem. 1965, 4, 778-783.

Novel Organometallic Iridium(V) Complexes
Organometallics, Vol. 18, No. 14, 1999 2713
Sch em e 5
1
iridium was cis. The H NMR spectrum of this complex
displayed a signal for the iridium-bound methyl groups
(δ 0.74), two signals for the diastereotopic methylene
protons of the diphosphine ligand spacer unit (δ 5.93,
5.24), and the expected number of aryl resonances. The
13C{1H} and the DEPT 135 NMR spectra of compound
15 displayed the expected upfield resonances but some-
what unusual aryl resonances. Three sets of four
resonances appeared between 133 and 128 ppm. One
set of four appeared as singlets, one set of four appeared
as 1:2:1 triplets, and one set of four appeared as 1:1:1
triplets. All of these resonances were positive in the
DEPT 135 spectrum, indicating that they correspond
to the aryl methine carbon atoms. The ipso-carbon
atoms were not observed in either the 13C{1H} or the
DEPT 135 NMR spectrum. Additionally, the observed
“coupling constants” were independent of spectrometer
frequency (400 vs 500 MHz). These rather unusual
patterns may be due to virtual P-C coupling.46-48 In
the interest of clarity, we have deposited a copy of a
partial spectrum in the Supporting Information of this
paper.
F igu r e 2. ORTEP diagram of the cationic portion of [cis-
{η2-Ph2PCH2PPh2}2IrMe2][OTf] (15), with partial atom
labeling scheme. The anion and the methylene chloride
molecules were omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 15
Ir(1)-P(1)
Ir(1)-P(2)
Ir(1)-P(3)
2.331(1)
2.382(1)
2.357(1)
Ir(1)-P(4)
Ir(1)-C(51)
Ir(1)-C(52)
2.339(1)
2.148(5)
2.135(5)
P(1)-Ir(1)-P(2)
P(1)-Ir(1)-P(3)
P(1)-Ir(1)-P(4)
P(2)-Ir(1)-P(3)
P(2)-Ir(1)-P(4)
P(3)-Ir(1)-P(4)
P(1)-Ir(1)-C(51)
P(1)-Ir(1)-C(52)
71.44(5)
P(2)-Ir(1)-C(51)
P(2)-Ir(1)-C(52)
P(3)-Ir(1)-C(51)
P(3)-Ir(1)-C(52)
P(4)-Ir(1)-C(51)
P(4)-Ir(1)-C(52)
C(51)-Ir(1)-C(52)
163.8(1)
88.2(1)
92.7(1)
167.0(1)
90.9(1)
95.3(1)
84.4(2)
102.41(5)
172.71(5)
97.61(5)
104.18(5)
72.06(4)
94.2(1)
90.4(1)
alkynes, amines, anilines, pyridines, amine oxides,
alcohols, ethers, phosphine oxides, dimethyl sulfoxide,
and triphenylbismuth) were added to cold methylene
chloride solutions of 6 in the method described above
for anionic nucleophiles. None of these reactions yielded
isolable iridium(V) salts (eq 7).
Single crystals of [cis-{η2-Ph2PCH2PPh2}2IrMe2][OTf]
(15) suitable for X-ray diffraction analysis were grown
by vapor diffusion of pentane into a concentrated
solution of 15 in methylene chloride at -30 °C. The
molecular structure of 15 is shown in Figure 2. The
compound cocrystallizes with two methylene chloride
molecules in the monoclinic space group P21/n with four
formula units in the unit cell. The iridium atom is
pseudo-octahedrally coordinated by the two bidentate
phosphine ligands and two methyl ligands. The methyl
groups are cis to one another, and there is local,
approximate C2 symmetry in the molecule. Additionally,
the chelation of the phosphorus ligands is not planar.
The carbon atoms of the four-membered chelate rings
are 0.34 (C(25)) and 0.24 Å (C(50)) from the planes
defined by Ir(1)-P(1)-P(2) and Ir(1)-P(3)-P(4), re-
spectively. One of the CH2Cl2 molecules is disordered.
Crystal data and structure refinement details are given
in Table 1. Selected bond lengths and angles are listed
in Table 3.
Cp*Ir(Me) OTf
+ L′ N [Cp*(L′)Ir(Me)3][OTf] (7)
3
6
Discu ssion
Th er m a l Decom p osition of 5 a n d 6. The initial
goal of this work was to synthesize several new iridium-
(V) neutral and cationic complexes and to explore their
stability and reactivity. The protonolysis reactions of 4
provided two new neutral compounds of this type, 5 and
6. Due presumably to the inherent instability of iridium
in the +5 formal oxidation state and the high lability
of chloride and triflate ligands, complexes 5 and 6 are
very thermally sensitive. In fact, 5 and 6 were stable
for weeks at -80 °C in methylene chloride solution but
for only 1-2 min at 0 °C. Aside from methane, the
decomposition products resulting from warming solu-
tions of 5 or 6 to room temperature were not identified.
Attem p ted Syn th esis of Neu tr a l Ir id iu m (V) Sp e-
cies. Since compounds 5 and 6 were so thermally
A variety of additional neutral ligands (L′; carbon
monoxide, nitriles, isonitriles, olefins, dienes, allene,
(46) For leading references, see refs 47 and 48.
(47) Pregosin, P. S.; Kunz, R. Helv. Chim. Acta 1975, 58, 423-431.
(48) Redfield, D. A.; Nelson, J . H.; Cary, L. W. Inorg. Nucl. Chem.
Lett. 1974, 10, 727-733.

2714 Organometallics, Vol. 18, No. 14, 1999
Alaimo and Bergman
unstable, we sought to derivatize them further and
isolate other neutral high-valent iridium species. For
most of these derivatization reactions we used triflate
6, as we expected substitution to be more facile with
this complex. Since triflate 6 was not isolable, all
reactions utilizing 6 as a starting material required its
in situ generation at -78 °C. Unfortunately, no neutral
iridium(V) complexes were successfully synthesized by
this route. On the basis of NMR spectroscopic evidence,
we believe that some interaction between the anionic
ligand and the metal complex occurred in many of these
reactions. However, it is unclear whether the observed
complex 7 analogous to that which we hypothesize for
3.
However, we detected no ethane in these reaction
1
mixtures by H NMR spectroscopy. Rather than under-
going reductive elimination of ethane, methylene chlo-
ride solutions of 7 reacted to give MeCp* and uniden-
tified iridium-containing products. Complex 7 also lost
MeCp* in the presence of added phosphine (>3 equiv),
and the remaining iridium fragment “[(PMe3)IrMe2]+”
formed in the reaction was trapped, in part, as [cis-
{PMe3}4IrMe2][OTf] (14). We can rationalize the ab-
sence of H3C-CH3 reductive elimination in our system.
Carbon-carbon reductive elimination reactions in other
systems are most commonly observed when at least one
group involved is an sp2-hybridized carbon. The scarcity
of systems which couple two sp3 centers has been
explained by a high kinetic barrier for these types of
reactions, relative to those involving sp2 centers.66,67
The migration of alkyl or hydride groups between a
transition metal and a cyclopentadienyl ligand has been
observed in other laboratories. Examples include (a) the
migration of an alkyl group from a transition metal to
a cyclopentadienyl ligand,68-71 (b) the migration of a
hydride group from a metal to a cyclopentadienyl
ligand,72-77 (c) oxidative C-C bond cleavage of a func-
tionalized cyclopentadienyl ligand (the reverse process
of (a)),78-82 and (d) the reversible migration of an ethyl
group between a metal center and a Cp ligand.83
1
change in the H NMR chemical shift values resulted
from a true substitution of the anionic ligand for the
triflate or from some other weak interaction. Although
it is possible that there is an unusually high barrier for
substitution of the anionic ligand for the iridium-bound
triflate, we believe that the decomposition of the reac-
tion mixtures to intractable products is best explained
by inherent instability of the target complexes.
Sta bility of [Cp *(P Me3)Ir Me3][OTf] a n d Its Rel-
eva n ce to C-H Bon d Activa tion . Careful addition
of trimethylphosphine to triflate complex 6 results in
the formation of the (trimethylphosphine)iridium salt
7. The trimethylphosphine salt 7 is a potential model
for the proposed oxidative addition intermediate 3 in
the methane C-H bond activation reaction.6-11 We
initially hypothesized that complex 7 would be more
stable than presumed intermediate 3, since reductive
elimination of two sp3-hybridized carbon ligands is
relatively rare.49-64 This is especially true for third-row
transition metals. Furthermore, C-H reductive elimi-
nation is much more common, as proposed in eq 2 for
complex 3.65 It was our hope that upon thermolysis 7
would undergo a carbon-carbon reductive elimination
reaction in order to form ethane and Cp*(PMe3)Ir(Me)-
OTf 1 (eq 3); this would render the reactivity of model
Ad d ition of oth er Neu tr a l Liga n d s to Com p lex
6. Other phosphines (PR3, R ) Et, Ph), as well as arsines
(AsR3, R ) Et, Ph) and triphenylantimony, reacted with
complex 6 to displace the triflate ligand and form the
corresponding trimethyliridium salts (8-12). These
(66) Churchill, M. R.; Fettinger, J . C.; J anik, T. S.; Rees, W. M.;
Thompson, J . S.; Tomaszewski, S.; Atwood, J . D. J . Organomet. Chem.
1987, 323, 233-246.
(67) A reveiwer has commented that “all indications...indicate that
such reductive eliminations require prior ligand dissociation to a 16-
electron intermediate”. We agree that, in some systems, prior ligand
dissociation is required to effect reductive elimination, but this does
not seem to be universally true (see, for example: Buchanan, J . M.;
Stryker, J . M.; Bergman, R. G. J . Am. Chem. Soc. 1986, 108, 1537).
We therefore do not see a need to postulate its occurrence here,
although we obviously cannot determine from our data whether Cp
“slippage” occurs prior to the reductive elimination step.
(68) Crowe, W. E.; Vu, A. T. J . Am. Chem. Soc. 1996, 118, 5508-
5509.
(49) For examples of reductive elimination reactions involving two
sp3 carbon centers, see refs 50-64.
(50) There are many more examples of C-C reductive elimination
not involving two sp3 carbon atoms. For leading references, see ref 12.
(51) From Au(III): Tamaki, A.; Magennis, S. A.; Kochi, J . K. J . Am.
Chem. Soc. 1974, 96, 6140-6148.
(52) From Au(III): Komiya, S.; Albright, T. A.; Hoffmann, R.; Kochi,
J . K. J . Am. Chem. Soc. 1976, 98, 7255-7265.
(53) From Ni(II): Yamamoto, T.; Abla, M. J . Organomet. Chem.
1997, 535, 209-211.
(69) Miller, F. D.; Sanner, R. D. Organometallics 1988, 7, 818-825.
(70) Fachinetti, G.; Floriani, C. J . Chem. Soc., Chem. Commun.
1974, 516-517.
(54) From Pd(II): Moravskiy, A.; Stille, J . K. J . Am. Chem. Soc.
1981, 103, 4182-4186.
(55) From Pd(II): Gillie, A.; Stille, J . K. J . Am. Chem. Soc. 1980,
102, 4933-4941.
(71) Werner, H.; Hofmann, W. Angew. Chem., Int. Ed. Engl. 1977,
16, 794-795.
(56) From Pd(II): Ito, T.; Tsuchiya, H.; Yamamoto, A. Bull. Chem.
Soc. J pn. 1977, 50, 1319-1327.
(72) Paneque, M.; Maitlis, P. M. J . Chem. Soc., Chem. Commun.
1989, 105-106.
(57) From Pd(IV): Markies, B. A.; Canty, A. J .; Boersma, J .; van
Koten, G. Organometallics 1994, 13, 2053-2058.
(58) From Pd(IV): Byers, P. K.; Canty, A. J .; Crespo, M.; Pud-
dephatt, R. J .; Scott, J . D. Organometallics 1988, 7, 1363-1367.
(59) From Pt(II): DiCosimo, R.; Whitesides, G. M. J . Am. Chem.
Soc. 1982, 104, 3601-3607.
(73) J ones, W. D.; Kuykendall, V. L.; Selmeczy, A. D. Organome-
tallics 1991, 10, 1577-1586.
(74) Pedersen, A.; Tilset, M. Organometallics 1993, 12, 3064-3068.
(75) Kubas, G. J .; Kiss, G.; Hoff, C. D. Organometallics 1991, 10,
2870-2876.
(76) Ryan, O. B.; Tilset, M.; Parker, V. D. Organometallics 1991,
10, 298-304.
(60) From Pt(II): Foley, P.; DiCosimo, R.; Whitesides, G. M. J . Am.
Chem. Soc. 1980, 102, 6713-6725.
(77) J ones, W. D.; Maguire, J . A. Organometallics 1985, 4, 951-
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(61) From Pt(IV): Goldberg, K. I.; Yan, J .; Winter, E. L. J . Am.
Chem. Soc. 1994, 116, 1573-1574.
(78) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789-
805.
(62) From Pt(IV): Goldberg, K. I.; Yang, J .; Breitung, E. M. J . Am.
Chem. Soc. 1995, 117, 6889-6896.
(79) Barretta, A.; Cloke, F. G. N.; Feigenbaum, A.; Green, M. L. H.;
Gourdon, A.; Prout, K. J . Chem. Soc., Chem. Commun. 1981, 156-
158.
(80) Crabtree, R. H.; Dion, R. P. J . Chem. Soc., Chem. Commun.
1984, 1260-1261.
(81) Crabtree, R. H.; Dion, R. P.; Gibboni, D. J .; McGrath, D. V.;
Holt, E. M. J . Am. Chem. Soc. 1986, 108, 7222-7227.
(82) Eilbracht, P.; Mayser, U. Chem. Ber. 1980, 113, 2211-2220.
(83) Benfield, F. W. S.; Green, M. L. H. J . Chem. Soc., Dalton Trans.
1974, 1324-1331.
(63) (a) From Pt(IV): Hill, G. S.; Puddephatt, R. J . Organometallics
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Organometallics 1999, 18, 1408-1418.
(64) From Pt(IV): Brown, M. P.; Puddephatt, R. J .; Upton, C. E. E.
J . Chem. Soc., Dalton Trans. 1974, 2457-2465.
(65) Theoreticians have rationalized the relative difficulty of C-C
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tion: Low, J . J .; Goddard, W. A. J . Am. Chem. Soc. 1986, 108, 6115-
6128.

Novel Organometallic Iridium(V) Complexes
Organometallics, Vol. 18, No. 14, 1999 2715
condensation of a calculated pressure of gas from a bulb of
known volume into the reaction vessel at -196 °C. Known-
volume bulb vacuum transfers were accomplished with a
digital MKS Baratron gauge attached to a high-vacuum line.
Ma ter ia ls. Unless otherwise noted, reagents were pur-
chased from commercial suppliers and used without further
purification. Potassium bromide (Aldrich), Celite (Aldrich),
silica gel (Merck 60, 230-400) and alumina (Brockman I,
Aldrich) were dried in vacuo at 250 °C for 48 h. Toluene
(Fisher) was either distilled from sodium metal under N2 or
passed through a column of activated alumina (type A2, size
12 × 32, Purifry Co.) under nitrogen pressure and sparged
with N2 prior to use. Pentane, hexanes, and benzene (Fisher)
were either distilled from purple sodium/benzophenone ketyl
under N2 or passed through a column of activated alumina
(type A2, size 12 × 32, Purifry Co.) under nitrogen pressure
and sparged with N2 prior to use. Diethyl ether and tetrahy-
drofuran (Fisher) were distilled from purple sodium/benzophe-
none ketyl under N2 prior to use. Methylene chloride (Fisher)
was either distilled from CaH2 (Aldrich) under N2 or passed
through a column of activated alumina (type A2, size 12 ×
32, Purifry Co.) under nitrogen pressure and sparged with N2
prior to use. Deuterated solvents (Cambridge Isotope Labo-
ratories) were purified by vacuum transfer from the appropri-
ate drying agent (Na/Ph2CO or CaH2) prior to use. Trimeth-
ylphosphine (Aldrich) and triethylphosphine (Aldrich) were
vacuum-transferred from sodium metal prior to use.
reactions proceeded cleanly at -25 °C, and the products
are air- and temperature-sensitive, as is trimethylphos-
phine complex 7. To our knowledge, complexes 7-12
represent the only characterized cationic iridium(V)
organometallic complexes that are not polyhydrides. The
stability of complexes 7-12 lends credence to the
postulate that cationic Ir(V) organometallic complexes
are reasonable intermediates on reaction pathways.
The order of stability of salts 7-12 [Cp*(L)Ir(Me)3]-
[OTf] toward loss of MeCp* is phosphines < arsines <
antimony. This order seemed counterintuitive to us.84
Assuming that the cationic iridium(V) center is a “hard”
Lewis acid, we expected that the phosphine salts 7-9
would be most stable, and the antimony salt 12 would
be least stable. At the present time, we have no
explanation for the observed stability trend. Calcula-
tions on this series of complexes might offer some
insight into this problem.
Con clu sion s
The synthesis and solution characterization of two
new neutral iridium(V) complexes has been achieved.
These compounds have served as convenient precursors
for a variety of fully characterized cationic iridium(V)
species. These results support the notion that the
paucity of iridium(V) complexes in the literature may
not preclude the intermediacy of such a species along
the reaction pathway for C-H bond activation by Cp*-
(PMe3)Ir(Me)OTf (1). Compound 7, which so far is our
best structural model of the proposed intermediate (3)
on the methane C-H bond activation pathway, decom-
poses by reductive elimination of MeCp*. In the pres-
ence of added phosphine, the iridium fragment is
trapped as [cis-{L}4IrMe2][OTf]. We plan to continue our
search for iridium(V) species (e.g., alkyl hydrides) that
will undergo simple reductive elimination reactions.
Cp *Ir Me4 (4). Synthesis of 4 was performed according to
literature methods,27,28 except that the scale was increased by
a factor of 10.85 1H NMR (C6D6): δ 1.03 (s, 15H, C5(CH3)5);
0.96 (s, 12H, Ir(CH3)4) (lit.28 1H NMR (C6D6): δ 1.03 (s, 15H,
C5(CH3)5); 0.92 (s, 12H, Ir(CH3)4)).
Cp *Ir (Me)3Cl (5). In the glovebox, an NMR tube was
charged with 4 (4.8 mg, 0.012 mmol) and 0.5 mL of CD2Cl2.
The tube was then fitted with a Cajon adapter. On a vacuum
line, the tube was freeze-pump-thaw degassed three times,
and HCl(g) (0.013 mmol) was added to the frozen (-196 °C)
solution by vacuum transfer. The solution was thawed to -78
°C to allow mixing. The solution was then freeze-pump-thaw
degassed three times to remove the methane generated,
carefully warming the solution only to -78 °C in the thaw
cycles. The tube was then flame-sealed under vacuum. In this
way, the complex was obtained in >95% purity by NMR.
Repeating this reaction in the presence of a ferrocene internal
standard provided an NMR yield of 94%. 1H NMR (CD2Cl2,
-21 °C): δ 1.62 (s, 6H, cis-Ir(CH3)2); 1.35 (s, 15H, C5(CH3)5);
0.98 (s, 3H, trans-Ir(CH3)). 13C{1H} NMR (CD2Cl2, -21 °C): δ
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless otherwise noted, reactions
and manipulations were performed at 23 °C in an inert-
atmosphere (N2) glovebox, or using standard Schlenk and high-
vacuum-line techniques. Glassware was dried overnight at 150
°C before use. All NMR spectra were obtained using Bruker
AM-400 or DRX-500 MHz spectrometers. Except where noted,
all NMR spectra were acquired at room temperature. In cases
where assignment of 13C{1H} NMR resonances from the initial
13C{1H} NMR spectrum was ambiguous, resonances were
assigned using standard DEPT 45, 90, and/or 135 pulse
sequences. Infrared (IR) spectra were recorded using samples
prepared as KBr pellets, and spectral data are reported in
wavenumbers (cm-1). Mass spectrometric (MS) analyses were
obtained at the University of California, Berkeley Mass
Spectrometry Facility on VT ProSpec, ZAB2-EQ, and 70-FE
mass spectrometers. Unless otherwise noted, all FAB MS data
were acquired from samples in a methylene chloride/3-ni-
trobenzyl alcohol matrix. Elemental analyses were performed
at the University of California, Berkeley Microanalytical
facility, on a Perkin-Elmer 2400 Series II CHNO/S Analyzer.
Sealed NMR tubes were prepared by attaching the NMR
tube directly to a Kontes high-vacuum stopcock via a Cajon
Ultra-Torr reducing union and then flame-sealing on a vacuum
line. Reactions with gases and low-boiling liquids involved
100.9 (s, C5(CH3) ); 6.81 (s, C5(CH3)5); 4.43 (s, cis-Ir(CH3)2);
5
-1.31 (s, trans-IrCH3). This compound decomposes above 0 °C
in about 1 min. Due to its high thermal sensitivity, compound
5 could not be isolated.
Cp *Ir (Me)3OTf (6). In the glovebox, an NMR tube was
charged with 4 (23.0 mg, 0.0594 mmol) and 0.3 mL of CD2Cl2.
The tube was then fitted with a Cajon adapter. On a vacuum
line, the tube was cooled to -78 °C. Triflic acid (10.7 mg,
0.0713 mmol) in 0.200 mL of CD2Cl2 was added slowly to the
cold solution by gastight syringe, turning the solution bright
yellow. The solution was freeze-pump-thaw degassed three
times to remove the generated methane, carefully allowing the
solution to warm only to -78 °C during the thawing procedure.
The tube was then flame-sealed under vacuum. In this way,
the complex was obtained in >96% purity by NMR. Repeating
this reaction in the presence of a ferrocene internal standard
1
provided an NMR yield of 95%. H NMR (CD2Cl2, -80 °C): δ
1.80 (s, 6H, cis-Ir(CH3)2); 1.42 (s, 15H, C5(CH3)5); 1.13 (s, 3H,
trans-Ir(CH3)). 13C{1H} NMR (CD2Cl2, -80 °C): δ 100.4 (s, C5-
(CH3)5); 13.4 (s, C5(CH3)5); 7.6 (s, cis-Ir(CH3)2); 4.0 (s, trans-
IrCH3). The 13C{1H} NMR resonance of the triflate ligand was
not observed. 19F{1H} NMR (CD2Cl2, -40 °C): δ -77.0. This
(84) Elschenbroich, A. S. Organometallics, A Concise Introduction,
2nd ed.; VCH: New York, 1992; p 154.
(85) For safety concerns, see ref 28.

2716 Organometallics, Vol. 18, No. 14, 1999
Alaimo and Bergman
compound decomposes above 0 °C in about 1 min. Due to its
high thermal sensitivity, compound 6 was not characterized
further.
of CH2Cl2. Compound 9 was obtained as a red powder (401
mg, 0.512 mmol) in 91% yield. H NMR (CD2Cl2): δ 7.51 (br
1
m, 9H, aryl); 7.20 (br m, 6H, aryl); 1.66 (d, J ) 1.8 Hz, 15H,
C5(CH3)5); 0.92 (d, J ) 9.1 Hz, 6H, cis-Ir(CH3)2); 0.34 (s, 3H,
trans-IrCH3). 13C{1H} NMR (CD2Cl2): δ 134.2 (d, J ) 9.3 Hz,
aryl); 133.7 (br s, aryl); 132.0 (br s, aryl); 129.4 (d, J ) 10.6
Hz, aryl); 129.1 (d, J ) 10.5 Hz, aryl); 105.6 (d, J ) 2.8 Hz,
C5(CH3)5); 8.0 (s, C5(CH3)5); 7.6 (d, J ) 5.6 Hz, trans-IrCH3);
1.3 (d, J ) 10.7 Hz, cis-Ir(CH3)2). The 13C{1H} NMR resonance
of the triflate ligand was not observed. 19F{1H} NMR (CD2-
Cl2): δ -77.2 (s). 31P{1H} NMR (CD2Cl2): δ 5.46 (s). IR: 3410
(m), 2920 (m), 2335 (w), 1483 (m), 1436 (s), 1380 (m), 1292 (s),
1260 (s), 1165 (s), 1146 (s), 1093 (s), 1027 (s), 843 (w), 749 (s),
702 (s) cm-1. FABMS (m/z): 635.3 (M+ - OTf).
Gen er a l P r oced u r e for t h e Syn t h esis of Com p lexes
7-12. In the glovebox, a 50 mL Schlenk flask was charged
with 4, CH2Cl2, and a Teflon stirbar. The flask was fitted with
a septum, attached to a vacuum line, and cooled to -78 °C.
To the cold, stirred solution was added a CH2Cl2 solution of
CF3SO3H by gastight syringe over 1 min. The resulting bright
yellow solution of 6 was stirred at -78 °C for 5 min. Trialky-
lphosphine, -arsine, or -antimony was then added as a CH2-
Cl2 solution by gastight syringe over 1 min. The resulting
reaction mixture was allowed to stand in a -25 °C freezer
overnight. The volatile materials were then removed in vacuo
while the reaction mixture was maintained at -29 °C (dry ice/
o-xylene bath). The remaining residue was warmed to room
temperature, quickly brought into the glovebox, and rapidly
triturated at room temperature with pentane (5 × 2 mL) and
Et2O (5 × 2 mL). The remaining residue was dissolved in CH2-
Cl2 (5 mL) and the solution filtered through Celite. The volatile
materials were removed in vacuo to give compounds 7-12 as
powders that were stored as solids in the glovebox freezer at
-30 °C. Since air-sensitive complexes 7-12 are also relatively
thermally sensitive, they were handled at room temperature
only for brief periods of time. Combustion analyses were not
obtained for complexes 7-9 due to their high thermal sensitiv-
ity and their similarity to compounds 10-12. Although many
NMR spectra for complexes 7-12 were acquired at low
temperature, the short-term thermal stability of these com-
plexes allowed for rapid spectrum acquisition at ambient
temperature. The reported NMR data for 7-12 are for spectra
acquired at room temperature.
[Cp *(AsEt3)Ir Me3][OTf] (10). Compound 10 was synthe-
sized as described above using 99.6 mg (0.257 mmol) of 4 in
30 mL of CH2Cl2, 42.5 mg (0.283 mmol) of CF3SO3H in 10 mL
of CH2Cl2, and 208 mg (1.29 mmol) of triethylarsine in 10 mL
of CH2Cl2. Compound 10 was obtained as a red powder (144
1
mg, 0.211 mmol) in 82% yield. H NMR (CD2Cl2): δ 1.94 (q, J
) 7.8 Hz, 6H, As(CH2CH3)3); 1.56 (s, 15H, C5(CH3)5); 1.47 (t,
J ) 7.7 Hz, 9H, As(CH2CH3)3); 0.97 (s, 6H, cis-Ir(CH3)2); 0.56
(s, 3H, trans-IrCH3). 13C{1H} NMR (CD2Cl2): δ 103.3 (s, C5-
(CH3) ); 12.66 (s, As(CH2CH3)3); 9.6 (s, As(CH2CH3)3); 7.6 (s,
5
C5(CH3)5); 1.8 (s, trans-IrCH3); -8.9 (s, cis-Ir(CH3)2). The 13C-
{1H} NMR resonance of the triflate ligand was not observed.
19F{1H} NMR (CD2Cl2): δ -77.3. IR: 2978 (s), 2934 (s), 2924
(s), 2878 (s), 2850 (m), 2292 (w), 1730 (w), 1632 (w), 1460 (m),
1383 (m), 1271 (s), 1223 (s), 1142 (s), 1072 (w), 1030 (s), 837
(w), 803 (w), 749 (m), 708 (m), 636 (s), 570 (m), 552 (w), 515
(m) cm-1. FABMS (m/z): 535 (M+ - OTf). Anal. Calcd for
C
20H39AsF3IrO3S: C, 35.13; H, 5.75. Found: C, 34.87; H, 5.90.
[Cp *(P Me3)Ir Me3][OTf] (7). Compound 7 was synthesized
as described above using 19.1 mg (0.049 mmol) of 4 in 25 mL
of CH2Cl2, 8.1 mg (0.054 mmol) of CF3SO3H in 5 mL of CH2-
Cl2, and 4.9 mg (0.064 mmol) of trimethylphosphine in 10 mL
of CH2Cl2. Compound 7 was obtained as a colorless powder
[Cp *(AsP h 3)Ir Me3][OTf] (11). Compound 11 was synthe-
sized as described above using 73.1 mg (0.189 mmol) of 4 in
30 mL of CH2Cl2, 31.2 mg (0.208 mmol) of CF3SO3H in 10 mL
of CH2Cl2, and 289 mg (0.944 mmol) of triphenylarsine in 10
mL of CH2Cl2. Compound 11 was obtained as a red powder
1
(25 mg, 0.043 mmol) in 87% yield. H NMR (CD2Cl2): δ 1.60
1
(152 mg, 0.183 mmol) in 97% yield. H NMR (CD2Cl2): δ 7.51
(d, J ) 1.4 Hz, 15H, C5(CH3)5); 1.51 (d, J ) 10.3 Hz, 9H,
P(CH3)3); 0.92 (d, J ) 8.7 Hz, 6H, cis-Ir(CH3)2); 0.48 (s, 3H,
trans-IrCH3). 13C{1H} NMR (CD2Cl2): δ 104.1 (s, C5(CH3)5);
11.4 (d, J ) 44 Hz, P(CH3)3); 7.6 (s, C5(CH3)5); 3.3 (d, J ) 6
Hz, cis-Ir(CH3)2); 2.7 (d, J ) 13 Hz, trans-IrCH3). The 13C{1H}
NMR resonance of the triflate ligand was not observed. 19F-
{1H} NMR (CD2Cl2): δ -77.2 (s). 31P{1H} NMR (CD2Cl2): δ
-27.6 (s). IR: 2998 (s), 2983 (s), 2968 (s), 2938 (s), 2917 (s),
2907 (s), 2292 (w), 1493 (m), 1481 (m), 1460 (m), 1436 (m),
1420 (m), 1375 (m), 1317 (m), 1297 (s), 1262 (s), 1222 (s), 1146
(s), 1076 (w), 1030 (s), 953 (s), 887 (w), 843 (m), 751 (m), 733
(m), 678 (m), 637 (s), 571 (m), 516 (m) cm-1. FABMS (m/z):
calcd for C16H33IrP 449.1949 (M+ - OTf); found 449.1949.
[Cp *(P Et3)Ir Me3][OTf] (8). Compound 8 was synthesized
as described above using 101.3 mg (0.262 mmol) of 4 in 30
mL of CH2Cl2, 43.2 mg (0.288 mmol) of CF3SO3H in 10 mL of
CH2Cl2, and 155 mg (1.31 mmol) of triethylphosphine in 10
mL of CH2Cl2. Compound 8 was isolated as a colorless powder
(m, 9H, aryl); 7.25 (m, 6H, aryl); 1.62 (s, 15H, C5(CH3)5); 1.13
(s, 6H, cis-Ir(CH3)2); 0.65 (s, 3H, trans-IrCH3). 13C{1H} NMR
(CD2Cl2): δ 133.3 (s, aryl); 131.8 (s, aryl); 129.7 (s, aryl); 127.7
(s, aryl); 104.6 (s, C5(CH3) ); 7.7 (s, C5(CH3)5); 4.8 (s, trans-
5
IrCH3); -3.6 (s, cis-Ir(CH3)2). The 13C{1H} NMR resonance of
the triflate ligand was not observed. 19F{1H} NMR (CD2Cl2):
δ -77.0 (s). IR: 3053 (m), 2987 (s), 2922 (s), 2294 (w), 1977
(w), 1895 (w), 1824 (w), 1580 (m), 1481 (s), 1437 (s), 1380 (s),
1264 (br s), 1224 (s), 1186 (m), 1180 (s), 1075 (s), 1028 (s), 1000
(s), 841 (m), 803 (w), 740 (s), 696 (s), 635 (s), 571 (m), 516 (m),
479 (s) cm-1. Anal. Calcd for C32H39AsF3IrO3S: C, 46.37; H,
4.75. Found: C, 46.12; H, 4.79.
[Cp *(SbP h 3)Ir Me3][OTf] (12). Compound 12 was synthe-
sized as described above using 52.8 mg (0.136 mmol) of 4 in
10 mL of CH2Cl2, 22.5 mg (0.150 mmol) of CF3SO3H in 10 mL
of CH2Cl2, and 57.8 mg (0.164 mmol) of triphenylantimony in
5 mL of CH2Cl2. Compound 12 was obtained as a colorless
powder (108 mg, 0.124 mmol) in 91% yield. 1H NMR (CD2-
Cl2): δ 7.60 (m, 3H, aryl); 7.51 (m, 6H, aryl); 7.34 (m, 6H, aryl);
1.60 (s, 15H, C5(CH3)5); 1.17 (s, 6H, cis-Ir(CH3)2); 0.81 (s, 3H,
trans-IrCH3). 13C{1H} NMR (CD2Cl2): δ 135.9 (s, aryl); 132.1
(s, aryl); 130.5 (s, aryl); 124.2 (aryl); 104.1 (s, C5(CH3)5); 7.6
(s, C5(CH3)5); 2.2 (s, trans-IrCH3); -13.6 (s, cis-Ir(CH3)2). The
13C{1H} NMR resonance of the triflate ligand was not observed.
19F{1H} NMR (CD2Cl2): δ -77.3 (s). IR: 3065 (m), 2982 (s),
2916 (s), 2836 (m), 2294 (w), 1973 (w), 1892 (w), 1820 (w), 1725
(w), 1630 (w), 1576 (m), 1480 (s), 1453 (sh), 1433 (s), 1379 (m),
1333 (w), 1262 (s), 1222 (s), 1183 (m), 1148 (s), 1066 (m), 1030
(s), 997 (m), 919 (w), 843 (w), 800 (w), 737 (s), 696 (s), 637 (s),
571 (m), 517 (m), 460 (m) cm-1. FABMS (m/z): 725 (M+ - OTf).
Anal. Calcd for C32H39F3IrO3SSb: C, 43.94; H, 4.49. Found:
C, 44.14; H, 4.75.
1
(136 mg, 0.212 mmol) in 81% yield. H NMR (CD2Cl2): δ 1.88
(m, 6H, P(CH2CH3)3); 1.55 (d, J ) 1.8 Hz, 15H, C5(CH3)5); 1.07
(m, 9H, P(CH2CH3)3); 0.91 (d, J ) 10.8 Hz, 6H, cis-Ir(CH3)2);
0.52 (s, 3H, trans-IrCH3).13C{1H} NMR (CD2Cl2): δ 104.8 (d,
J ) 3.8 Hz, C5(CH3)5); 15.0 (d, J ) 36.3 Hz, P(CH2CH3)3); 9.8
(s, P(CH2CH3)3); 8.9 (d, J ) 4.5 Hz, trans-IrCH3); 7.9 (s, C5-
(CH3)5); -4.7 (d, J ) 11.6 Hz, cis-Ir(CH3)2). The 13C{1H} NMR
resonance of the triflate ligand was not observed. 19F{1H} NMR
(CD2Cl2): δ -77.4. 31P{1H} NMR (CD2Cl2): δ -13.0. Due to
the thermal sensitivity of this compound, 8 was not character-
ized further.
[Cp *(P P h 3)Ir Me3][OTf] (9). Compound 9 was synthesized
as described above using 218 mg (0.563 mmol) of 4 in 20 mL
of CH2Cl2, 88.7 mg (0.591 mmol) of CF3SO3H in 10 mL of CH2-
Cl2, and 155 mg (0.591 mmol) of triphenylphosphine in 10 mL

Novel Organometallic Iridium(V) Complexes
Organometallics, Vol. 18, No. 14, 1999 2717
[Cp *(SbP h 3)Ir Me3][BP h 4] (13). In the glovebox, a 20 mL
scintillation vial was charged with 12 (100 mg, 0.114 mmol),
NaBPh4 (59 mg, 0.173 mmol), CH2Cl2 (10 mL), and a Teflon
stirbar and sealed with a cap. The reaction mixture was stirred
for 10 min at room temperature and stored in the glovebox
freezer (-30 °C) overnight. The mixture was then filtered
through Celite (1 cm) on a medium-porosity fritted glass filter,
and the volatile materials were removed from the filtrate in
vacuo. The remaining residue was crystallized from CH2Cl2/
pentane at -30 °C. Compound 13 was obtained as colorless
crystals (116 mg, 0.111 mmol) in 97% yield. 1H NMR (CD2-
Cl2): δ 7.63 (t, J ) 7.4 Hz, 3H, aryl); 7.56 (t, J ) 7.7 Hz, 6H,
aryl); 7.37 (m, 14H, aryl); 7.06 (t, J ) 7.3 Hz, 8H, aryl); 6.91
(t, J ) 7.7 Hz, 5H, aryl); 1.53 (s, 15H, C5(CH3)5); 1.20 (s, 6H,
cis-Ir(CH3)2); 0.85 (s, 3H, trans-IrCH3). 13C{1H} NMR (CD2-
Cl2): δ 164.4 (1:1:1:1 q, J CB ) 49 Hz, ipso-aryl); 136.3 (t, J CB
) 2 Hz, aryl); 136.0 (s, aryl); 132.3 (s, aryl); 130.6 (s, aryl);
126.0 (1:1:1:1 q, J CB ) 3 Hz, aryl); 124.1 (s, ipso-aryl); 122.0
(s, aryl); 104.0 (s, C5(CH3)5); 7.7 (s, C5(CH3)5); 2.5 (s, trans-
IrCH3); -13.4 (s, cis-Ir(CH3)2). IR: 3053 (s), 3033 (s), 2982 (s),
2917 (m), 2834 (w), 1960 (w), 1883 (w), 1818 (w), 1725 (w),
1652 (w), 1578 (m), 1478 (s), 1478 (s), 1432 (s), 1377 (m), 1332
(w), 1304 (w), 1261 (m), 1233 (w), 1183 (w), 1135 (w), 1065
(m), 1019 (m), 997 (m), 843 (w), 732 (s), 704 (s), 612 (m), 457
(m) cm-1. Elemental analysis was not obtained for this complex
due to its similarity to complex 12.
s, aryl); 129.8 (virtual 1:2:1 t, J ) 5.2 Hz, aryl); 129.4 (virtual
1:2:1 t, J ) 5.2 Hz, aryl); 129.0 (virtual 1:1:1 t, J ) 5.0 Hz,
aryl); 128.4 (virtual 1:1:1 t, J ) 4.9 Hz, aryl); 45.8 (m, (P-
CH2-P)2); -13.8 (m, Ir-(CH3)2). The 13C{1H} NMR resonances
for the triflate ligand and the ipso-carbon atoms of the phenyl
groups were not observed. 19F{1H} NMR (CD2Cl2): δ -77.3
(s). 31P{1H} NMR (CD2Cl2): δ -61.31 (t, J ) 14.5 Hz); -63.33
(t, J ) 14.4 Hz). IR: 3053 (m), 2952 (m), 2902 (m), 2829 (m),
2355 (w), 1971 (w), 1888 (w), 1810 (w), 1573 (m), 1484 (s), 1435
(s), 1362 (w), 1276 (s), 1257 (s), 1223 (s), 1149 (s), 1136 (s),
1099 (s), 1030 (s), 999 (m), 918 (w), 845 (w), 723 (s), 696 (s)
cm-1. FABMS (m/z): 991.2 (M+ - OTf). Anal. Calcd for
C
53H50F3IrO3P4S: C, 55.83; H, 4.42. Found: C, 55.48; H, 4.64.
Cr ysta l Str u ctu r e Deter m in a tion s of 13 a n d 15. Single
crystals of 13 and 15 were grown by vapor diffusion of pentane
into methylene chloride solutions of each complex at -30 °C
over 3 days. Crystals were mounted on a quartz fiber using
Paratone N hydrocarbon oil. Data were analyzed for agreement
and possible absorption using XPREP.86 An empirical absorp-
tion correction based on comparison of redundant and equiva-
lent reflections was applied using SADABS87 (13, Tmax ) 0.75,
Tmin ) 0.51; 15, Tmax ) 0.87, Tmin ) 0.67). The structures were
solved by direct methods and expanded using Fourier tech-
niques. Hydrogen atoms were included in calculated idealized
positions but not refined. Plots of ∑w(|Fo| - |Fc|)2 versus |Fo|,
reflection order in data collection, (sin θ)/λ, and various classes
of indices showed no unusual trends. All calculations were
performed using the teXsan88 crystallographic software pack-
age of Molecular Structure Corp.
For complex 13, the Ir, Sb, and Cl atoms were refined
anisotropically, while the remaining atoms were refined iso-
tropically. Attempts to refine the carbon atoms anisotropically
led to nonpositive values for some components of the aniso-
tropic displacement parameters. The large residual peaks near
the Ir and Sb atoms can be attributed to Fourier ripple near
these heavy atoms. It is not unusual to see residual peaks of
this magnitude in structures containing heavy atoms such as
Ir and Sb.
[cis-{P Me3}4Ir Me2][OTf] (14). In the glovebox, a 50 mL
Schlenk flask was charged with 7 (60.2 mg, 0.100 mmol), CH2-
Cl2 (20 mL), and a Teflon stirbar and then fitted with a glass
stopper. The flask was placed on a vacuum line, where it was
degassed by three freeze-pump-thaw cycles. To the frozen
solution (-196 °C) of 7 was added trimethylphosphine (0.35
mmol) by vacuum transfer. The resulting mixture was thawed
and stirred at room temperature overnight. (In a separate
NMR experiment, the yield of 14 was calculated to be ∼60%,
based on 1,3,5-trimethoxybenzene internal standard.) The
volatile materials were removed from the reaction mixture in
vacuo, giving a pale yellow residue. In the glovebox, the mildly
air-sensitive solids were triturated with pentane (5 × 2 mL)
and Et2O (5 × 2 mL). The remaining residue was dissolved in
CH2Cl2 (5 mL) and the solution filtered through Celite.
Removal of the volatile materials in vacuo afforded complex
14 as a slightly yellow powder as an impure mixture with other
unidentified compounds. A yield was not determined for this
reaction, since the product could not be isolated cleanly. Major
component: 1H NMR (CD2Cl2) δ 1.53 (d, J ) 9.7 Hz, 18H,
(P(CH3)3)2), 1.46 (t, J ) 4.6 Hz, 18H, (P(CH3)3)2), -0.12 (m,
6H, Ir(CH3)2); 19F{1H} NMR (CD2Cl2) δ -76.9 (s); 31P{1H} NMR
For complex 15, the non-hydrogen atoms were refined
anisotropically, except for Cl(5), which was refined isotropi-
cally. This Cl atom is the minor component of a disordered
molecule of CH2Cl2. Its occupancy was constrained so that the
sum of the occupancies of Cl(5) and Cl(3) was equal to 1.0.
The occupancy of Cl(3) was refined to 0.941(5). Cl(4) had full
occupancy because this site was common to both components
of the disordered CH2Cl2.
Ack n ow led gm en t. We thank Dr. Dana Caulder and
Dr. Fred Hollander of the UC Berkeley X-ray Diffraction
Facility (CHEXRAY), for determination of the crystal
structures of 13 and 15, and Dr. Zhongrui Zhou of the
UC Berkeley Mass Spectrometry Facility for her exper-
tise in analyzing our most sensitive complexes. We
thank Prof. Richard A. Andersen, Prof. Karen I. Gold-
berg, Dr. Daniel A. Dobbs, and Dr. Kristopher P.
McNeill for many helpful discussions. We are grateful
for support of this work by the Director, Office of Energy
Research, Office of Basic Energy Sciences, Chemical
Sciences Division, U.S. Department of Energy, under
Contract No. DE-AC03-76SF00098.
2
2
(CD2Cl2) δ -48.85 (t, J PP ) 18 Hz), -61.02 (t, J PP ) 18 Hz);
FABMS (m/z) 527 (M+ - OTf).
[cis-{P h 2P CH2P P h 2}2Ir Me2][OTf] (15). In the glovebox,
a 50 mL Schlenk flask was charged with 4 (85.6 mg, 0.221
mmol), CH2Cl2 (20 mL), and a Teflon stirbar and fitted with a
rubber septum. The flask was placed on a vacuum line. The
solution was cooled to -78 °C, and HOTf (36.5 mg, 0.243 mmol)
was added as a CH2Cl2 solution (10 mL). The resulting bright
yellow solution of 7 was stirred for 15 min at -78 °C. To the
stirred solution of 7 was added a CH2Cl2 (10 mL) solution of
bis(diphenylphosphino)methane (424 mg, 1.10 mmol) by gastight
syringe. The resulting reaction mixture was stirred at room
temperature overnight. The volatile materials were removed
from the reaction mixture in vacuo, giving a pale yellow
residue. In the glovebox, the mildly air-sensitive solids were
triturated with pentane (10 × 2 mL) and Et2O (10 × 2 mL).
The remaining residue was dissolved in CH2Cl2 (10 mL) and
the solution filtered through Celite. Removal of the volatile
materials in vacuo afforded complex 15 (104 mg, 0.154 mmol)
Su p p or tin g In for m a tion Ava ila ble: Listings of X-ray
structural data for complexes 13 and 15 and a partial 13C-
{1H} NMR spectrum of complex 15. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
as a yellow powder in 93% yield. H NMR (CD2Cl2): δ 7.62-
OM990255P
7.13 (m, 28H, aryl); 6.96 (t, J ) 6.3 Hz, 4H, aryl); 6.87 (t, J )
10.2 Hz, 4H, aryl); 6.77 (t, J ) 8.6 Hz, 4H, aryl); 5.93 (m, 2H,
P-CH2-P); 5.24 (m, 2H, P-CH2-P); 0.74 (m, 6H, Ir(CH3)2).
13C{1H} NMR (CD2Cl2): δ 132.6 (virtual 1:1:1 t, J ) 4.9 Hz,
aryl); 132.0 (virtual 1:2:1 t, J ) 5.3 Hz, aryl); 131.8 (br s, aryl);
131.4 (br s, aryl); 131.3 (virtual 1:1:1 t, J ) 6.0 Hz, aryl); 131.2
(virtual 1:2:1 t, J ) 6.0 Hz, aryl); 131.0 (br s, aryl); 130.4 (br
(86) XPREP, v. 5.03 (part of the SHELXTL Crystal Structure
Determination Package); Siemens Industrial Automation, Inc., 1995.
(87) Sheldrick, G. SADABS: Siemens Area Detector Absorption
correction program; Siemens Industrial Automation, Inc., 1996.
(88) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corp., 1985 and 1992.