Dinuclear iridium complexes containing cp* and carbonyl ligands: synthesis, structure, and reactivity

Article abstract of DOI:10.1021/om900186j

The syntheses of the monomeric cationic complexes [Cp^*(CO) Ir(R)(CH₂Cl₂)] were attempted (Cp^*) η5-C₅Me₅, R) Me, H). The target complexes were not obtained; instead, dimeric products were is

Full text of DOI:10.1021/om900186j

3546
Organometallics 2009, 28, 3546–3551
Dinuclear Iridium Complexes Containing Cp* and Carbonyl
Ligands: Synthesis, Structure, and Reactivity
Joseph M. Meredith, Karen I. Goldberg, Werner Kaminsky, and D. Michael Heinekey*
Department of Chemistry, UniVersity of Washington, Box 351700, Seattle, Washington 98195-1700
ReceiVed March 10, 2009
The syntheses of the monomeric cationic complexes [Cp*(CO)Ir(R)(CH2Cl2)] were attempted (Cp* )
η5-C5Me5, R ) Me, H). The target complexes were not obtained; instead, dimeric products were isolated
in high yields. The reaction between Cp*(CO)Ir(Me)Cl and [Li(Et2O)2.5][BArF ] afforded the cationic
4
complex [{Cp*(CO)Ir(Me)}2(µ-Cl)][BArF ] (4) in high yield. Complex 4 has been characterized by H
1
4
NMR, 13C{1H} NMR, and IR spectroscopies. Reaction of Cp*(CO)Ir(H)2 with [CPh3][BArF ] produced
4
the dicationic complex [Cp*(CO)Ir(µ-H)]2[BArF ] (9) in excellent yield. Complex 9 has been characterized
4 2
by 1H NMR and IR spectroscopies as well as elemental analysis and single-crystal X-ray diffraction. An
X-ray structural determination was also carried out on the related complex [Cp*(Cl)Ir(µ-H)]2 (14). The
solid-state structures of 9 and 14 are compared briefly.
Scheme 1. Reported PMe3 Complexes (1a, b)4 and Target
Introduction
Carbonyl Complexes (2a, b)
The global reserves of natural gas are vast, rivaling those of
petroleum. Unfortunately, the remote location of most gas
reserves, coupled with the low energy density of gaseous
hydrocarbons, hinders the utilization of this resource. Conversion
of methane to methanol affords a readily transportable liquid
that has a wide range of uses. Current processes for the
production of methanol from methane are relatively inefficient.
Ideally, this transformation would be carried out using a
transition metal catalyst and oxygen as the terminal oxidant.
Presently, only a handful of homogeneous catalysts have been
identified that are capable of converting methane to methanol,
usually in highly acidic media.1 The most promising systems
are based on PtII and PdII catalysts.2 The acidic conditions
employed in these reactions mitigate the Lewis basicity of the
oxidized product. Even so, catalyst inhibition by these “deac-
tivated” oxidized products remains problematic.3 Catalytic cycles
based on a less electronegative metal such as Ir may be less
prone to this type of inhibition.
We expected the carbonyl complexes [Cp*(CO)Ir(R)(CH2Cl2)]
(R ) Me (2a), H (2b)) to be more stable under oxidizing
conditions while maintaining the C-H activation chemistry of
1 (Scheme 1).
In this work, we report that replacing PMe3 with CO resulted
in an increased tendency of the fragments [Cp*(CO)Ir(R)]+ to
form dimeric complexes such as [{Cp*(CO)Ir(Me)}2(µ-Cl)]-
[BArF ] and [Cp*(CO)Ir(µ-H)]2[BArF ] (ArF ) C6F5). The
The cationic IrIII complexes [Cp*(PMe3)Ir(R)(CH2Cl2)] (Cp*
) η5-C5Me5; R ) Me (1a), H (1b)) studied by Bergman and
co-workers undergo facile C-H activation reactions.4 However,
the proclivity of phosphine ligands toward oxidation renders
complexes 1a and 1b less attractive for this type of catalysis.
4
4 2
analogous PMe3 complexes have not been reported. In our
preparative reactions, the monomeric complexes 2a and 2b were
not isolable. The increased electrophilicity and smaller steric
demand of the carbonyl complexes appear to work in concert
to promote dimerization. In general, the dimeric products
containing the Cp*(CO)Ir(R) moiety were found to be unreactive
toward C-H bonds.
* Corresponding author. E-mail: heinekey@chem.washington.edu.
(1) (a) Goldshleger, N. F.; Eskova, V. V.; Shilov, A. E.; Shteinman,
A. A. Zh. Fiz. Khim. 1972, 46, 1353. (b) Periana, R. A.; Taube, D. J.; Evitt,
R. R.; Lo¨ffler, D. G.; Wentrcek, P. R.; Voss, G.; Masuda, T. Science 1993,
259, 340. (c) Lin, M.; Hogan, T. E.; Sen, A. J. Am. Chem. Soc. 1996, 118,
4574. (d) Periana, R. A.; Mironov, O.; Taube, D. J.; Gamble, S. Chem.
Commun. 2002, 20, 2376. (e) Jones, C. J.; Taube, D.; Ziatdinov, V. R.;
Periana, R. A.; Nielsen, R. J.; Oxgaard, J.; Goddard, W. A., III Angew.
Chem., Int. Ed. 2004, 43, 4626.
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Fujii, H. Science 1998, 280, 560. (b) Muehlhofer, M.; Strassner, T.;
Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1745.
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Tellers, D. M.; Yung, C. M.; Arndtsen, B. A.; Adamson, D. R.; Bergman,
R. G. J. Am. Chem. Soc. 2002, 124, 1400. (c) Golden, J. T.; Andersen,
R. A.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123, 5837.
Results and Discussion
Synthesis of [{Cp*(CO)Ir(Me)}2(µ-Cl)][BArF ] (4). Initial
4
attempts to synthesize [Cp*(CO)Ir(Me)(CH2Cl2)] (2a) began
with chloride abstraction reactions of Cp*(CO)Ir(Me)Cl (3).
Compound 3 reacts with [Li(Et2O)2.5][BArF ] in dichloromethane
4
to form the dimeric complex [{Cp*(CO)Ir(Me)}2(µ-Cl)][BArF ]
4
(4) (Scheme 2). Complex 4 is likely formed by trapping of the
16e- chloride abstraction product [Cp*(CO)Ir(Me)][BArF ] by
4
the chloride ligand of the remaining starting material 3. Similar
homobimetallic complexes of the form [LnM(µ-X)MLn], which
10.1021/om900186j CCC: $40.75
2009 American Chemical Society
Publication on Web 05/04/2009

Iridium Complexes with Cp* and Carbonyl Ligands
Organometallics, Vol. 28, No. 12, 2009 3547
Scheme 2. Chloride Abstraction from Cp*(CO)Ir(Me)Cl (3)
Scheme 3. Reaction of [{Cp*(CO)Ir(Me)}2(µ-Cl)][BArF ] (4)
4
by [Li(Et2O)2.5][BArF ]
with CO Gas
4
frequency of 3 (2010 cm-1, CH2Cl2).9 The Ir center in 4 is less
electron-rich than that of 3, so less back-donation to the π*
antibonding orbital of the CO ligand occurs. The observed CO
stretching band for 4 is also broader and less intense than that
of 3. This change in line shape may be attributed to overlapping
CO stretching bands from the diastereomers of 4. X-ray quality
crystals of 4 were isolated by layering CH2Cl2 solutions of 4
with pentane; however, disorder between the CO, Me, and Cl
ligands prevented us from refining the structure completely.10
Dichloromethane solutions containing 4 and diethyl ether
showed no evidence of C-H bond activation, even after
extended storage at ambient temperature. When these solutions
were warmed above ambient temperature, decomposition of
complex 4 was observed. Dichloromethane solutions of 4 were
unreactive toward oxygen (3 atm, ambient temperature, 1 week).
Reactions of Cp*(CO)Ir(Me)2. The formation of halide-
bridged 4 suggested that Ir complexes containing halide ligands
were poor starting materials for the preparation of 2a. The
known complex Cp*(CO)Ir(Me)2 (6) was chosen as a more
appropriate starting material. The neutral boron reagent B(C6F5)3
was expected to abstract a methyl anion from 6 to afford the
desired complex 2a.4,11 To confirm B(C6F5)3 as a suitable
reagent, a CO trapping experiment was conducted. Dichlo-
romethane solutions of 6 and B(C6F5)3 were prepared at 196
K, then pressurized with CO gas. The only observed product
was the expected cationic dicarbonyl complex [Cp*(CO)2Ir(Me)]
(5) (Scheme 4). These experiments imply formation of the
reactive 16e- complex [Cp*(CO)Ir(Me)][MeB(C6F5)3] (7).
Dichloromethane solutions of 7 examined by 11B{1H} NMR
spectroscopy exhibit a singlet resonance at -15.6 ppm, char-
acteristic of the uncoordinated anion [MeB(C6F5)3].12 When 6
and B(C6F5)3 were dissolved in nonpolar solvents such as
benzene and toluene, the product settled out of solution as an
oil. These observations show that the structure of 7 is not
Cp*(CO)Ir(Me)(µ-MeB(C6F5)3), in which the anion [MeB-
(C6F5)3] acts as a ligand.13
contain a single halide as the only ligand bridging the metal
centers, have been reported.5 These dimers are commonly
formed during halide abstraction reactions that do not go to
completion.6
The reaction of 3 and [Li(Et2O)2.5][BArF ] (0.5 equiv) formed
4
1
compound 4 in quantitative yield (by H NMR spectroscopy).
Additional [Li(Et2O)2.5][BArF ] (up to 2.5 equiv) had no effect
4
on compound 4. Both of the Ir atoms in 4 are stereocenters,
and 4 was formed as a statistical mixture of diastereomers.
Diastereomeric mixtures of compounds of the form [LnM(µ-
X)MLn] have been reported for Ru, Ni, and Pd.7
1
The H and 13C{1H} NMR spectra of 4 contain two sets of
nearly overlapping signals indicating the presence of two
Cp*Ir(CO)Me moieties in almost identical environments. For
example, the two signals from the methyl protons of the Cp*
ligands differ by only 2 and 37 ppb in the 1H and 13C{1H} NMR
spectra, respectively. Reaction of 4 with CO in dichloromethane
resulted in formation of the starting complex 3 and the
dicarbonyl complex [Cp*(CO)2Ir(Me)][BArF ] (5) (Scheme 3).
4
The identity of 5 was confirmed by comparison to the previously
8
1
reported H NMR spectral data.
In the IR spectra of 4, the CO stretching frequency (2030
cm-1, CH2Cl2) is 20 cm-1 higher than the CO stretching
(5) Some examples of dimers with one halide as the only bridging
ligand: (a) Winter, C. H.; Arif, A. M.; Gladysz, J. A. Organometallics 1989,
8, 219. (b) Butts, M. D.; Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc. 1996,
118, 11831. (c) Huhmann-Vincent, J.; Scott, B. L.; Kubas, G. J. Inorg.
Chem. 1999, 38, 115. (d) Cave, G. W. V.; Alcock, N. W.; Rourke, J. P.
Organometallics 1999, 18, 1801. (e) Bannwart, E.; Jacobsen, H.; Hu¨bener,
R.; Schmalle, H. W.; Berke, H. J. Org. Met. Chem. 2001, 622, 97. (f) Shen,
H.; Jordan, R. F. Organometallics 2003, 22, 1878. (g) Oberbeckmann-
Winter, N.; Braunstein, P.; Welter, R. Organometallics 2004, 23, 6311. (h)
Zhang, J.; Barakat, K. A.; Cundari, T. R.; Gunnoe, T. B.; Boyle, P. D.;
Petersen, J. L.; Day, C. S. Inorg. Chem. 2005, 44, 8379. (i) Wu, F.; Jordan,
R. F. Organometallics 2006, 25, 5631. (j) Yamashita, M.; Takamiya, I.;
Jin, K.; Nozaki, K. Organometallics 2006, 25, 4588. (k) Szuromi, E.; Shen,
H.; Goodall, B. L.; Jordan, R. F. Organometallics 2008, 27, 402. (l) Basu,
S.; Arulsamy, N.; Roddick, D. M. Organometallics 2008, 27, 3659.
(6) (a) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686. (b) Vicente, J.; Abad,
J.-A.; Frankland, A. D.; Lo´pez-Serrano, J.; Ram´ırez de Arellano, M. C.;
Jones, P. G. Organometallics 2002, 21, 272. (c) Hahn, F. E.; Heidrich, B.;
Pape, T.; Hepp, A.; Martin, M.; Sola, E.; Oro, L. A. Inorg. Chim. Acta
2006, 359, 4840. (d) Sangtrirutnugul, P.; Tilley, T. D. Organometallics 2008,
27, 2223.
The reactivity of 7 was explored by attempted reaction with
benzene. Dichloromethane solutions containing 6, 1.1 equiv of
(9) Sridevi, V. S.; Fan, W. Y.; Leong, W. K. Organometallics 2007,
26, 1173.
(10) The interested reader will find more information concerning this
crystallographic study in the Supporting Information.
(11) Peters, J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999,
121, 9871.
(12) (a) Dagorne, S.; Guzei, I. A.; Coles, M. P.; Jordan, R. F. J. Am.
Chem. Soc. 2000, 122, 274. (b) Bibal, C.; Santini, C. C.; Chauvin, Y.; Valle´e,
C.; Olivier-Bourbigou, H. Dalton Trans. 2008, 21, 2866.
(13) (a) Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J. Organometallics
1997, 16, 842. (b) Stephan, D. W.; Stewart, J. C.; Gue´rin, F.; Spence, R. E.
v. H.; Xu, W.; Harrison, D. G. Organometallics 1999, 18, 1116. (c) Beswick,
C. L.; Marks, T. J. Organometallics 1999, 18, 2410.
(7) (a) Jimnez-Tenorio, M.; Palacios, M. D.; Puerta, M. C.; Valerga,
P. Organometallics 2004, 23, 504. (b) Alberti, D.; Goddard, R.; Po¨rshke,
K. Organometallics 2005, 24, 3907. (c) Ding, Y.; Goddard, R.; Po¨rshke,
K. Organometallics 2005, 24, 439. (d) Foley, S. R.; Shen, H.; Qadeer, U. A.;
Jordan, R. F. Organometallics 2004, 23, 600.
(8) Maitlis, P. M.; Kang, J. W. J. Organomet. Chem. 1971, 26, 393.

3548 Organometallics, Vol. 28, No. 12, 2009
Scheme 4. Reactions of Cp*(CO)Ir(Me)2 (6)
Meredith et al.
Scheme 5. C-H Activation by [Cp*(PMe3)Ir(Me)(CH2Cl2)]+
Scheme 6. Reaction between Cp*(CO)Ir(H)2 (8) and
(1a)
[CPh3][BArF ]
4
B(C6F5)3, and between 20 and 300 equiv of benzene were slowly
warmed from 196 to 298 K and monitored by NMR spectros-
copy. Complex 7 was expected to react stoichiometrically with
benzene, in direct analogy with 1a (Scheme 5). This reaction
would produce 1 equiv each of CH4 and the cationic complex
[Cp*(CO)Ir(Ph)(L)] (L ) solvent or weakly coordinated anion).
These products were not observed. These observations indicate
that 7 does not react cleanly with benzene under mild conditions.
The accepted mechanism for C-H activation by complex 1a
involves oxidative addition of substrate R′-H to form a cationic,
seven-coordinate IrV intermediate.14 The lack of observed C-H
activation by 7 may be attributed to the difficulty of accessing
IrV in the carbonyl-containing species.
The infrared spectrum of 9 exhibits a single CO stretching
band at high frequency (2066 cm-1, KBr). This stretching
frequency indicates a low degree of back-bonding from iridium
to the π* antibonding orbital of the CO ligand, consistent with
formulation of 9 as dicationic and electron-deficient. Attempts
to obtain NMR spectra of 9 after isolation were prevented by
the poor solubility of 9 in most solvents, including dichlo-
romethane and fluorobenzene. Unfortunately, compound 9
decomposes immediately to multiple products upon exposure
to other polar solvents such as tetrahydrofuran, acetone, or
acetonitrile. While monitoring the synthesis of 9 by NMR
spectroscopy, two 1H NMR signals were observed and assigned
to the Cp* and hydride ligands of 9 (δ ) 2.07, s, 30 H, Cp*;
-15.13, s, 2 H, Ir-H). These signals increased in intensity until
they accounted for most of the organometallic species in
Synthesis and Reactivity of [Cp*(CO)Ir(µ-H)]2[BArF ]
4 2
(9). Synthesis of complex 2b by hydride abstraction from
Cp*(CO)Ir(H)2 (8) was attempted in dichloromethane solution,
using [CPh3][BArF ] (Scheme 6). Complex 2b was expected to
4
dimerize readily, based on the reported thermal instability of
1b, which forms the dimeric complex [{Cp*(PMe3)Ir(H)}2(µ-
H)] when warmed above 253 K. Solutions prepared according
to Scheme 6 and kept at low temperatures throughout prepara-
tion and acquisition of 1H NMR spectra contained signals from
many different Cp*Ir-containing products. Among the observed
products were the dimeric complex [{Cp*(CO)Ir(H)}2(µ-
H)][BArF ]15 and an Ir-(HCPh3) complex. (The Ir-(HCPh3)
4
1
complex was identified by an upfield shift in the H NMR
signals for HCPh3.16) These solutions precipitated dark red
crystals upon warming to room temperature. A single-crystal
X-raydiffractionstudyidentifiedthedimericcomplex[Cp*(CO)Ir(µ-
H)]2[BArF ] (9), which contains two terminal CO ligands and
4 2
two bridging hydride ligands (Figure 1).
(14) (a) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc.
2000, 122, 1816. (b) Strout, D. L.; Zari, S.; Niu, S.; Hall, M. B. J. Am.
Chem. Soc. 1996, 118, 6068. (c) Niu, S.; Hall, M. B. J. Am. Chem. Soc.
1998, 120, 6169.
(15) Heinekey, D. M.; Fine, D. A.; Harper, T. G. P.; Michel, S. T. Can.
J. Chem. 1995, 73, 1116.
(16) Sweet, J. R.; Graham, W. A. G. Organometallics 1983, 2, 135.
Figure 1. ORTEP of the cationic portion of [Cp*(CO)Ir(µ-
H)]2[BArF ] (9). Thermal ellipsoids are at the 50% probability level.
4 2
Non-hydride hydrogen atoms and [BArF ] counteranions have been
4
omitted for clarity. Hydride ligands were not located but are
depicted at areas of greatest electron density.

Iridium Complexes with Cp* and Carbonyl Ligands
Organometallics, Vol. 28, No. 12, 2009 3549
Scheme 7. Reactions of [Cp*(CO)Ir(µ-H)]2[BArF ]2 (9)
4
Figure 2. ORTEP of [Cp*Ir(Cl)(µ-H)]2 (14). Thermal ellipsoids
are at the 50% probability level. Non-hydride hydrogen atoms have
been omitted for clarity.
N-heterocyclic carbene ligand 1,3,4,5-tetramethylimidazol-2-
ylidene in place of the CO ligands in 9.20
To provide further comparison, an X-ray diffraction analysis
of the reported dimeric complex [Cp*Ir(Cl)(µ-H)]2 (14) was
carried out. Complex 14, like complex 9, contains a formal
double bond between Ir atoms as well as bridging hydride
ligands.21 The ORTEP of 14 is shown in Figure 2. The pertinent
structural parameters of compounds 9 and 14 are shown in
Table 1.
The Ir-Ir distances in 9 (2.7069(3) Å) and 14 (2.7265(7) Å)
are both consistent with structures containing Ir-Ir double
bonds. The hydride ligands of 9 were not located, but areas of
higher electron density were located on either side of the plane
defined by the iridium atom, CO carbon, and Cp* centroid, as
depicted in Figure 1. The hydride ligands of 14 were located,
and as indicated by the structure of 9, the hydride ligands are
situated on either side of the Ir-Cl-Cp*(centroid) plane.
1
solution. As 9 precipitated from solution, the H NMR signals
assigned to 9 decreased in intensity until no organometallic
species remained in solution. Similar 1H NMR spectra that likely
represent [Cp*(CO)Ir(µ-H)]2[BR4]2 have been previously re-
ported from reactions between excess acid and [Cp*Ir(µ-CO)]2
(10) in dichloromethane (R ) 3,5-C6H3(CF3)2, Ph, F).17
Complex 9 was treated with various bases and neutral donor
ligands to explore its reactivity (Scheme 7). The products of
these reactions were identified by comparison with their reported
1H NMR spectra.8,18 Complex 9 reacted cleanly with excess
triethylamine to form 10 in high yield (90% by 1H NMR
spectroscopy). Homogenous solutions resulted when dichlo-
romethane suspensions of 9 were treated with either excess PPh3
1
or CO. Analysis of these samples by H NMR spectroscopy
showed that the expected monomeric complexes [Cp*(CO)Ir(H)-
(PPh3)][BArF ] (11) and [Cp*(CO)2Ir(H)][BArF ] (12) were the
4
4
Experimental Section
major products. The reaction of 9 with CO also produced
[{Cp*(CO)Ir}2(µ-CO)(µ-H)][BArF ] (13) as a minor product,
General Procedures. Unless otherwise noted, all reactions and
manipulations were carried out under an argon atmosphere, using
standard Schlenk or glovebox techniques. Oxygen and water were
removed from gases prior to use by passage through columns of
copper(II) oxide catalyst R3-11 (Chemical Dynamics Corporation)
and calcium sulfate (W.A. Hammond Drierite Company). MBraun
Labmaster 130 and Vacuum Atmospheres Company gloveboxes
equipped with dri-train inert atmosphere purification systems were
employed in the manipulation of air-sensitive compounds.
4
presumably by deprotonation of 9, followed by reaction with
CO.
Solid-State Structure of 9. Complex 9 contains a formal
Ir-Ir double bond bridged by two hydride ligands. There are a
limited set of related molecules available for comparison with
9. The analogous dicationic PMe3 complex, [Cp*(PMe3)Ir(µ-
H)]22+, has not been reported, perhaps because the larger steric
demand of the PMe3 ligands prevents dimerization of
[Cp*(PMe3)Ir(H)]+ fragments. Analogous neutral complexes of
the form [Cp*(CO)M(µ-H)]2 have been previously reported for
osmium and ruthenium;19 however, the reactivity of these
species has not been reported. Yamaguchi and co-workers
reported a similar dicationic dimer of iridium that contains the
1H, 13C{1H}, and 11B{1H} NMR spectra were acquired using
Bruker Avance AV and Avance DRX series 500 MHz spectrom-
1
eters. H NMR chemical shifts were referenced to residual proteo
solvent and reported relative to tetramethylsilane as 0 ppm.
Chemical shifts for 13C{1H} NMR spectra were referenced to the
solvent and reported relative to tetramethylsilane as 0 ppm.
Chemical shifts in 11B{1H} NMR spectra were referenced externally
to neat BF3 · Et2O as 0 ppm. Deuterated solvents were obtained from
Cambridge Isotope Laboratories and vacuum transferred from
calcium hydride (acetonitrile-d3, benzene-d6, fluorobenzene-d5,
dichloromethane-d2), or from deep purple solutions of benzophe-
none ketyl over sodium/potassium alloy (tetrahydrofuran-d8), or
from activated 4 Å molecular sieves (acetone-d6) prior to use.
B(C6F5)3 was recrystallized from hexanes at 253 K prior to use,
(17) Heinekey, D. M.; Fine, D. A.; Barnhart, D. Organometallics 1997,
16, 2530.
(18) (a) Ball, R. G.; Graham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.;
McMaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem. 1990, 29,
2023. (b) Wang, D.; Angelici, R. J. Inorg. Chem. 1996, 35, 1321. (c)
Heinekey, D. M.; Michel, S. T.; Schulte, G. K. Organometallics 1989, 8,
1241. (d) Sowa, J. R., Jr.; Zanotti, V.; Facchin, G.; Angelici, R. J. J. Am.
Chem. Soc. 1991, 113, 9185.
(19) (a) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982,
104, 3722. (b) Forrow, N. J.; Knox, S. A. R. J. Chem. Soc., Chem. Commun.
1984, 11, 679. (c) Kang, B.-S.; Koelle, U.; Thewalt, U. Organometallics
1991, 10, 2569.
(20) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2005,
24, 3422.
(21) Gill, D. S.; Maitlis, P. M. J. Organomet. Chem. 1975, 87, 359.

3550 Organometallics, Vol. 28, No. 12, 2009
Meredith et al.
Table 1. Selected Bond Distances and Bond Angles for Complexes 9 and 14
bond distances (Å)
bond angles (deg)
9
14
9
14
Ir(1)-Ir(1′)
Ir(1)-C(1)
Ir(1)-Cl(1)
2.7069(3)
1.895(5)
2.7265(7)
Ir(1′)-Ir(1)-C(1)
Ir(1′)-Ir(1)-Cl(1)
Cl(1)-Ir(1)-H(1)
94.29(14)
91.34(6)
93(2)
2.389(2)
and purity was checked by 1H, 11B{1H}, and 19F NMR spectroscopy.
Elemental analysis was performed by Atlantic Microlab, Inc.,
Norcross, GA.
1.68 (s, 15H, C5Me5), 1.06 (s, 6H, Ir-(Me)2), 0.38 (s, 3H, Ir-Me);
(298 K): δ 2.25-1.75 (many signals, C5Me5).
Synthesis of [Cp*(CO)Ir(µ-H)]2[BArF ]2 (9). A Schlenk flask
4
Compounds 815 and 1421 were prepared according to the reported
procedures.Compounds 39 and 622 were prepared with slight
modification of the reported procedures in order to obtain material
of high purity. These compounds were purified by column chro-
matography (silica gel, 400 mesh, 15 cm × 0.5 cm, eluent )
dichloromethane, Rf ) 0.25 (3); benzene, Rf ) 0.7 (6)). Compound
6 was further purified by sublimation (5 × 10-3 mm Hg, 308 K)
and isolated as a colorless solid.
was charged with 8 (22.7 mg, 63 µmol) and [CPh3][BArF ] (100.0
4
mg, 108 µmol, 1.7 equiv). Dichloromethane (5 mL) was added by
vacuum transfer, affording a homogeneous dark green-brown
solution, which was left unstirred to encourage slow crystal growth.
Product formation was complete within 24 h. The green-brown
dichloromethane solution containing unreacted [CPh3][BArF ] and
4
HCPh3 was removed by filter cannula, leaving behind crystalline
9, which was dried briefly under vacuum and collected as
analytically pure, dark red crystals (64.6 mg, 98%). 1H NMR (500
MHz, CD2Cl2, 298 K): δ 2.07 (s, 30H, C5Me5), -15.13 (s, 2H,
Ir-H). Anal. Calcd for C70H32B2O2F40Ir2: C, 40.60; H, 1.56. Found:
Synthesis of [{Cp*(CO)Ir(Me)}2(µ-Cl)][BArF ] (4). A Schlenk
4
flask was charged with 3 (161 mg, 397 µmol) and [Li(Et2O)2.5]-
[BArF ] (176 mg, 202 µmol, 0.5 equiv). Addition of dichloromethane
4
C, 40.44; H, 1.67. IR (KBr pellet): νCO ) 2066 cm-1
.
(40 mL, vacuum transfer from CaH2) furnished a pale yellow solution,
which was stirred for 16 h. The solution was filtered through a pad of
Celite to remove LiCl, and the filtrate was concentrated to 10 mL.
Pentane was added by cannula, and stirring caused precipitation of 4,
which was isolated after filtration as a yellow powder (231 mg, 80%
yield). Complex 4 was recrystallized from unstirred solutions of
dichloromethane, which were layered with pentane. Compound 4 was
formed as a statistical mixture of diastereomers, observed as two sets
of nearly overlapping resonances in the 1H and 13C{1H} NMR spectra.
1H NMR (500 MHz, CD2Cl2, 298 K): δ 1.85 (s, 30H, C5Me5), 1.85
(s, 30H, C5Me5), 1.11 (s, 6H, Ir-Me), 1.03 (s, 6H, Ir-Me). 13C{1H}
NMR (125 MHz, CD2Cl2, 298 K): δ 173.69 (s, CO), 172.18 (s, CO),
101.54 (s, C5Me5), 101.51 (s, C5Me5), 9.27 (s, C5Me5), 9.23 (s, C5Me5),
-12.11 (s, Ir-Me), -13.51 (s, Ir-Me). IR (CH2Cl2): νCO ) 2030 cm-1,
m, br.
Reaction of 9 with Triethylamine. A J. Young-style NMR tube
was charged with 9 (11.5 mg, 5.6 µmol) and Et3N (30 µL, 200
µmol, 40 equiv). Upon addition of CD2Cl2 (0.75 mL), the solution
1
quickly became homogeneous and dark orange in color. The H
NMR spectra (CD2Cl2 and C6D6) confirmed that 10 was formed in
90% yield.18
Reaction of 9 with PPh3 to Form [Cp*(CO)Ir(PPh3)(H)]-
[BArF ] (11). A J. Young-style NMR tube was charged with 9 (6.5
4
mg, 3.1 µmol) and PPh3 (10.1 mg, 38.5 µmol, 12 equiv). CD2Cl2
was added and the tube was agitated briefly to afford a pale yellow
solution. The major product of the reaction (54% by NMR) was
the monophosphine 11.18b
Reaction of 9 with CO to Form [Cp*(CO)2Ir(H)][BArF ]
4
(12). A J. Young-style NMR tube was charged with 9 (13.0 mg,
6.3 µmol) and CD2Cl2 (0.75 mL) and pressurized with 1 atm of
CO. After thawing, the tube was sonicated for 24 h. The resulting
solution was pale orange and contained the dicarbonyl cation 12
and the dimeric tricarbonyl monohydride complex [{Cp*(CO)Ir}2(µ-
Treatment of 4 with CO. A J. Young-style NMR tube
containing 4 and CD2Cl2 (0.75 mL) was subjected to three
freeze-pump-thaw degas cycles and pressurized with CO (2 atm).
After 24 h the reaction was complete and the tube contained 3 and
1
5 in approximately equal proportions, as observed by H NMR
CO)(µ-H)][BArF ] (13) as the major products, accounting for 50%
4
spectroscopy.
and 25% of the observed organometallic species, respectively.18c
Preparation of [Cp*(CO)2Ir(Me)][MeB(C6F5)3] (5) from
[Cp*(CO)Ir(Me)][MeB(C6F5)3] (7). A solution of 7 was generated
in situ by the following procedure: a J. Young-style NMR tube
was charged with 6 (7.9 mg, 21 µmol) and B(C6F5)3 (12.3 mg, 23
µmol, 1.1 equiv), CD2Cl2 (0.75 mL) was added by vacuum transfer,
and the tube was thawed to 196 K. The reaction mixture was
agitated to encourage dissolution of the reactants and became pale
yellow and clear. After 5 min the solution was pressurized with
CO (2 atm) and agitated. The yellow color disappeared immediately,
and the solution remained colorless upon thawing to ambient
X-ray Structure Analyses: Sample Preparation and Data
Acquisition for 9. A red crystal prism (0.29 × 0.24 × 0.12 mm)
was mounted on a glass capillary with oil. Data were collected at
130 K on a Nonius FR590 Kappa CCD X-ray spectrometer. The
crystal-to-detector distance was 30 mm and exposure time was 20 s
per degree for all sets. The scan width was 2°. Data collection was
88.4% complete to 31.98° and 99.9% complete to 25° in ϑ. A total
of 44 279 partial and complete reflections were collected covering
the indices h ) -16 to 15, k ) -18 to 16, l ) -19 to 14. A total
1
of 10 236 reflections were symmetry independent, and the Rint
0.0689 indicated that the data were of average quality. Indexing
)
temperature. The H NMR spectrum confirmed formation of 5.
Reaction between [Cp*(CO)Ir(Me)][MeB(C6F5)3] (7) and
Benzene. A CD2Cl2/benzene solution of 7 was generated in situ
by the following procedure: a J. Young-style NMR tube was loaded
with 6 (11.5 mg, 29.8 µmol) and B(C6F5)3 (18.7 mg, 35.4 µmol,
1.2 equiv). Benzene (0.5 mL, 6 mmol, 240 equiv) and CD2Cl2 (0.5
mL) were added by vacuum transfer using liquid nitrogen. Upon
thawing to 196 K, the solids dissolved, affording a pale yellow
solution.The tube was transferred to a precooled NMR probe and
and unit cell refinement indicated a triclinic P lattice. The space
j
group was found to be P1 (No. 2).
X-ray Structure Analyses: Sample Preparation and Data
Acquisition for 14. A dark red prism (cut down to 0.14 × 0.13 ×
0.12 mm) was mounted on a glass capillary with oil. Data were
collected at 130 K on a Nonius FR590 Kappa CCD X-ray
spectrometer. The crystal-to-detector distance was 30 mm and
exposure time was 10 s per degree for all sets. The scan width was
1
analyzed at 200, 268, and 298 K. H NMR (500 MHz, CD2Cl2,
j
200 K): δ 1.81 (s, 15H, C5Me5), 1.62 (s, 15H, C5Me5), 0.98 (s,
6H, Ir-(Me)2), 0.31 (s, 3H, Ir-Me); (268 K): δ 1.86 (s, 15H, C5Me5),
2°. Data collection was 97.3% complete to 25°in ϑ P1. A total of
19 465 partial and complete reflections were collected covering the
indices h ) -9 to 9, k ) -18 to 18, l ) -13 to 13; 2072 reflections
were symmetry independent and the Rint ) 0.0661 indicated that
the data were of slightly better than average quality (0.07). Indexing
(22) Gomez, M.; Kisenyi, J. M.; Sunley, G. J.; Maitlis, P. M. J.
Organomet. Chem. 1985, 296, 197.

Iridium Complexes with Cp* and Carbonyl Ligands
Organometallics, Vol. 28, No. 12, 2009 3551
Table 2. Crystal Data and Structure Refinement for 9 and 14
(Icorr). Solution by direct methods (SIR97) produced a complete
heavy atom phasing model consistent with the proposed structure.
Details of the structural refinement are shown in Table 2. All
hydrogen atoms were located using a riding model. All non-
hydrogen atoms were refined anisotropically by full-matrix least-
squares. Electron densities of the appropriate sizes for the hydrogen
ligands were located close to Ir; however, refining them completely
freely was unstable for 9. H1a was thus placed at the largest density
peak and its thermal parameter refined to a reasonable value.
9
14
chemical formula
fw
C70H32B2F40Ir2O2
2070.99
C20H32Cl2Ir2
727.81
color/shape
T (K)
red/prism
130(2)
red/cut block
130(2)
λ (Å)
0.71073
0.71073
monoclinic
P21/c
7.2699(7)
14.969(2)
10.4680(13)
90
114.200(7)
90
1039.1(2)
2
13.052
multiscan
680
2.326
0.0383, 0.0726
0.0675, 0.0808
cryst syst
space group
a (Å)
triclinic
j
P1
11.2595(2)
12.5616(3)
13.0354(2)
84.3822(10)
65.2489(11)
87.8949(8)
1666.26(6)
1
4.151
multiscan
992
2.064
0.0464, 0.1129
0.0569, 0.1167
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Conclusions
Syntheses of the cationic mononuclear complexes [Cp*-
(CO)Ir(R)(CH2Cl2)] were attempted in dichloromethane solution
(R ) Me (2a), H (2b)). The dimeric products 4 and 9 were
formed in high yields. Our results indicate that compounds of
the general form Cp*(CO)Ir(R) are ill-suited for C-H bond
activation. Future studies will focus on the synthesis of more
electron-rich complexes of the form [Cp*(L)Ir(R)(S)] and their
utility in C-H activation/functionalization reactions (where L
represents an oxidation-resistant ligand with electronics and
sterics that are similar to those of PMe3 and S represents a labile
solvent molecule). We anticipate that these complexes will be
less susceptible to dimerization than the carbonyl complexes.
Z
abs coeff (mm-1
abs corr
)
F(000)
-1
Fcalc (g cm
)
R1, wR2 (I > 2σ)
R1, wR2 (all data)
and unit cell refinement indicated a monoclinic P lattice. The space
group was found to be P21/c (No. 14).
X-ray Structure Analyses: Data Processing and Structure
Determination. The data were integrated and scaled using hkl-
SCALEPACK.23 This program applies a multiplicative correction
factor (S) to the observed intensities (I) and has the following form:
Acknowledgment. This work was supported by the NSF
as part of the Center for Enabling New Technologies through
Catalysis (CENTC), CHE-0650456. We thank Maurice
Brookhart, William D. Jones, and Melanie S. Sanford for
helpful discussions.
2
2
S ) (e-2B(sin θ)/λ )/scale
(1)
S is calculated from the scale and the B factor determined for
each frame and is then applied to I to give the corrected intensity
Supporting Information Available: CIF files containing crys-
tallographic information for 4, 9, and 14. This material is available
free of charge via the Internet at http://pubs.acs.org.
(23) (a) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(b) Mackay, S.; Edwards, C.; Henderson, A.; Gilmore, C.; Stewart, N.;
Shankland, K.; Donald, A. MaXus; University of Glasgow: Scotland, 1997.
OM900186J