Cationic complexes of iridium: Diiodobenzene chelation, electrophilic behavior with olefins, and fluxionality of an Ir(I) ethylene complex

Article abstract of DOI:10.1021/ic025506s

The synthesis of a series of dicationic Ir(III) complexes is described. Reaction of Ir(CO)(dppe)I (dppe = 1,2-bis-(diphenylphosphino)ethane)) with RI (R = CH₃ and CF₃) results in formation of the Ir(III) precursors IrR(CO)-(dppe)(I)₂ (R = CH₃ (1a) and CF₃ (1b)). Subsequent treatment with AgOTf (OTf = triflate) generates the bis(triflate) analogues IrR(CO)(dppe)(OTf)₂ (R = CH₃ (2a) and CF₃ (2b)), which undergo clean metathesis with NaBARF (BARF = B(3,5-(CF₃)₂C₆ H₃)₄^-) in the presence of 1,2-diiodobenzene (DIB) forming the dicationic halocarbon adducts [IrR(CO)(dppe)(DIB)][BARF]₂(R = CH₃ (3a) and CF₃ (3b)). Complexes 3a and 3b demonstrate facile exchange chemistry with acetonitrile and carbon monoxide forming complexes 4 and 5, respectively. NMR investigation of the mechanism reveals that the process proceeds through an η¹-diiodobenzene adduct, where labilization at the coordination site trans to the alkyl group occurs first. Complex 3a reacts with ethylene forming the cationic iridium(I) product [Ir(C₂H₄)₂(CO)(dppe)][BARF] (6), which demonstrates fluxional behavior. Variable-temperature NMR studies indicate that the five-coordinate complex 6 undergoes three dynamic processes corresponding to ethylene rotation, Berry pseudorotation, and intermolecular ethylene exchange in order of increasing temperature based on NMR line shape analyses used to determine the thermodynamic parameters for the processes. The DIB adducts 3a and 3b were also found to promote olefin isomerization of 1-pentene, and polymerization/oligomerization of styrene, α-methylstyrene, norbornene, β-pinene, and isobutylene via cationic initiation.

Full text of DOI:10.1021/ic025506s

Inorg. Chem. 2002, 41, 2095−2108
Cationic Complexes of Iridium: Diiodobenzene Chelation, Electrophilic
Behavior with Olefins, and Fluxionality of an Ir(I) Ethylene Complex
Paul J. Albietz, Jr., Brian P. Cleary, Witold Paw, and Richard Eisenberg*
Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627
Received January 11, 2002
The synthesis of a series of dicationic Ir(III) complexes is described. Reaction of Ir(CO)(dppe)I (dppe ) 1,2-bis-
(diphenylphosphino)ethane)) with RI (R ) CH and CF ) results in formation of the Ir(III) precursors IrR(CO)-
3
3
(dppe)(I)2 (R ) CH (1a) and CF (1b)). Subsequent treatment with AgOTf (OTf ) triflate) generates the bis(triflate)
3
3
analogues IrR(CO)(dppe)(OTf)2 (R ) CH (2a) and CF (2b)), which undergo clean metathesis with NaBARF
3
3
(BARF ) B(3,5-(CF ) C H ) -) in the presence of 1,2-diiodobenzene (DIB) forming the dicationic halocarbon adducts
3 2
6 3 4
[IrR(CO)(dppe)(DIB)][BARF]2 (R ) CH (3a) and CF (3b)). Complexes 3a and 3b demonstrate facile exchange
3
3
chemistry with acetonitrile and carbon monoxide forming complexes 4 and 5, respectively. NMR investigation of
the mechanism reveals that the process proceeds through an η1-diiodobenzene adduct, where labilization at the
coordination site trans to the alkyl group occurs first. Complex 3a reacts with ethylene forming the cationic iridium(I)
product [Ir(C H ) (CO)(dppe)][BARF] (6), which demonstrates fluxional behavior. Variable-temperature NMR studies
2
4 2
indicate that the five-coordinate complex 6 undergoes three dynamic processes corresponding to ethylene rotation,
Berry pseudorotation, and intermolecular ethylene exchange in order of increasing temperature based on NMR line
shape analyses used to determine the thermodynamic parameters for the processes. The DIB adducts 3a and 3b
were also found to promote olefin isomerization of 1-pentene, and polymerization/oligomerization of styrene,
R-methylstyrene, norbornene, â-pinene, and isobutylene via cationic initiation.
Introduction
The activation and functionalization of C-H bonds of
organic molecules using cationic late metal centers is also
an area of research that has gained considerable attention.
Due to the natural abundance of hydrocarbons, facile
conversion into more useful materials is a goal that is avidly
being pursued by chemists in both academia and industry.
Some recent examples8-10 of C-H bond activation of
hydrocarbons describe use of [(Cp*)IrMe(PMe3)(CH2Cl2)]+
and [PtMe(sol)(NN)]+ complexes (NN ) Me4en or Ar2DAB,
sol ) weakly coordinating solvent) where bond cleavage is
observed under relatively mild reaction conditions. In these
systems, the common thread is generation of a cationic
metal-alkyl complex where weakly coordinating solvents/
ligands and noncoordinating counterions are used to avoid
deactivation of the metal center.
The design and synthesis of “electrophilic” late transition
metal complexes for conducting bond activation chemistry
is an area of growing interest in organometallic chemistry
and catalysis. One of the earliest examples of a late metal
complex capable of promoting electrophilically driven
transformations is the palladium(II) species [Pd(NCMe)4]-
[BF4]2, which, owing to the lability of its ligands and the
2+ charge for CdC bond polarization and activation, was
found to (1) polymerize styrene,1 ethyl vinyl ether,2 N-
vinylcarbazole,2 and 1,3-cyclohexadiene;3 (2) oligomerize
ethylene into C4, C6, C8, and C10 products;1 (3) isomerize
1-butene1 into trans- and cis-2-butene; and (4) promote other
organic transformations.2,4,5 Sen and co-workers also de-
scribed other electrophilic solvento complexes to promote
related transformations.2,6,7
* Authortowhomcorrespondenceshouldbeaddressed.E-mail: rse7@chem.
rochester.edu.
(6) Sen, A.; Thomas, R. R. Organometallics 1982, 1, 1251-1254.
(7) Thomas, R. R.; Chebolu, V.; Sen, A. J. Am. Chem. Soc. 1986, 108,
4096-4103.
(1) Sen, A.; Lai, T.-W. J. Am. Chem. Soc. 1981, 103, 4627-4629.
(2) Sen, A.; Lai, T.-W.; Thomas, R. R. J. Organomet. Chem. 1988, 358,
567-588.
(3) Sen, A.; Lai, T.-W. Organometallics 1982, 1, 415-417.
(4) Jiang, Z.; Sen, A. J. Am. Chem. Soc. 1990, 112, 9655-9657.
(5) Sen, A. Acc. Chem. Res. 1988, 21, 421-428.
(8) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1973.
(9) Holtcamp, M. W.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
1997, 119, 848-849.
(10) Johansson, L.; Ryan, O. B.; Tilset, M. J. Am. Chem. Soc. 1999, 121,
1974-1975.
10.1021/ic025506s CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/22/2002
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Albietz et al.
Perhaps one of the most impressive examples11-16 employ-
ing an electrophilic late metal system is that using the cationic
diimine complex [Pd(Me)(sol)(Ar2DAB)]+ (Ar2DAB ) dia-
ryldiazabutadiene, sol ) coordinated solvent) for ethylene
and R-olefin polymerizations. The reported palladium(II)
complexes demonstrate catalytic activities comparable to
those of the extensively studied metallocenes,11,17,18 and allow
for alteration of the polymer characteristics by changing the
substituents on the aryl ring of the Ar2DAB. Similar success
has also been achieved for CO/C2H4 copolymerizations using
the related palladium(II) systems19 [PdMe(sol)(L-L)]+ (L-L
) diimine or diphosphine and sol ) coordinated solvent).
As a d6 metal ion, Ir(III) is thought to possess electrophilic
character similar to that of Pd2+ but its configuration in a
coordinatively saturated environment confers inertness on
its cationic complexes. In the study noted above involving
[(Cp*)IrMe(PMe3)(CH2Cl2)]+, Bergman showed that this in-
ertness can be overcome through the use of a halocarbon as
a weakly coordinating ligand.8 Specifically, in the presence
of 13CH4, exchange of the methyl ligand is seen which pro-
ceeds by dichloromethane loss and C-H bond activation.
Similarly, past work by Crabtree20 has shown that reaction
of C6H4I2 with the labile Ir(III) disolvate IrH2(Me2CO)2(P-
Ph3)2+ results in clean coordination of the halocarbon forming
Results and Discussion
Synthesis of IrR(CO)(dppe)I2 Where R ) CH3 and CF3
(1a and 1b). The synthesis of the Ir(III) precursor complexes
may be accomplished by conducting an oxidative addition
reaction in CH2Cl2 between Ir(dppe)(CO)I and either CH3I
at room temperature or CF3I at -78 °C. Complete structural
data (NMR, micro, and X-ray analyses) for complex 1a have
been previously described.23 The geometry of 1a was
assigned on the basis of observation of two 31P resonances
at δ 23.9 and -3.61 (JP-P ) 4.9 Hz) for dppe, the methyl
1H resonance at 0.56 ppm as a doublet of doublets (JH-P
)
4.1 and 6.7 Hz), and the coupling of the carbonyl 13C
resonance (δ ) 169.7) showing that it is trans to one dppe
donor (and cis to the other with JC-P of 146 and 6 Hz).
Synthesis of the corresponding trifluoromethyl complex
1b was undertaken to generate a complex having enhanced
electrophilicity at the Ir(III) center relative to 1a and without
an alkyl ligand capable of migratory insertion, as had been
seen for 1a.21 Reaction of CF3I with the Ir(I) precursor Ir-
(dppe)(CO)I at room temperature produces three geometric
isomers [1b:1c:1d (ratio ) 1:4:1)] of IrCF3(CO)(dppe)I2, in
addition to minor amounts of the triiodide complex fac-Ir-
(CO)(dppe)I3.24 However, when the oxidative addition is
conducted at -78 °C, approximately 90% formation of
isomer 1b (eq 1) results. After chromatographic purification,
this isomer can be obtained as a yellow air-stable solid in
80% yield.
+
IrH2(C6H4I2)(PPh3)2 . Complete structural characterization
of the adduct was accomplished, including an X-ray diffrac-
tion analysis.
In studies designed to generate Ir(III) complexes having
adjacent labile sites, the syntheses of the bis(triflate) complex
IrCH3(CO)(dppe)(OTf)2 (dppe ) 1,2-bis(diphenylphosphi-
no)ethane, OTf ) triflate) and the dicationic acetyl complex
[Ir(C(O)CH3)(dppe)(MeCN)3]2+ were previously reported.21
The triflate complex was shown to be a weak electrolyte in
dichloromethane, and the acetonitrile complex gave evidence
of moderately facile exchange in the position trans to the
Me ligand. In continuing efforts focused on exploring the
electrophilic behavior of these iridium(III) systems, we re-
cently described the generation of two adducts of 1,2-diio-
dobenzene (DIB) following Crabtree’s approach20 and found
the resultant complexes to exhibit electrophilic behavior lead-
ing to polymerization or oligomerization of several olefins.22
Herein we report in detail the synthesis and characterization
of these DIB complexes along with their observed reaction
chemistry with different olefinic substrates. The study also
describes the synthesis of a bis(ethylene) complex of Ir(I)
obtained in this investigation and its fluxional behavior.
(11) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995,
117, 6414-6415.
(12) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometallics 1997,
16, 2005-2007.
(13) Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M. J. Am.
Chem. Soc. 1996, 118, 11664-11665.
(14) Svejda, S. A.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc. 1999,
121, 10634-10635.
(15) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart,
M. J. Am. Chem. Soc. 2000, 122, 6686-6700.
(16) Ittel, D. F.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169-1203.
(17) Haggin, J. Chem. Eng. News 1996, 74, 6-7.
(18) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Reiger, B.; Waymouth,
R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(19) Drent, E.; Budzelaar, P. H. M. Chem. ReV. 1996, 96, 663-681.
Orientation of the CF3 group relative to dppe may be
unambiguously determined on the basis of the JF-P coupling
2096 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
constants, where JF-P(cis) ≈ 4-10 Hz and JF-P(trans) ≈ 40-
50 Hz. (See Supporting Information Figure S.9.) Moreover,
the asymmetry of complex 1b and the magnitudes25 of the
THF by these complexes also occurs and supports their
presumed electrophilic nature.
J
C-P coupling constants (5.7 and 139.7 Hz) indicate that the
CO ligand has both trans and cis orientations relative to dppe
phosphine donors, thereby substantiating the assignment.
With regard to IR characterization of the compound, the νCO
of 1b is 28 cm-1 higher in energy than the methyl analogue
1a, demonstrating the electron-withdrawing effect of the CF3
group. In all of the complexes described in this paper, the
∼25-30 cm-1 difference in νCO between the CH3 and CF3
analogues is a general trend.
Synthesis of IrR(CO)(dppe)(OTf)2 Where R ) CH3 and
CF3 (2a and 2b). Halide abstraction from the diiodide
complex 1b using AgOTf in CH2Cl2 (eq 2) proceeds cleanly,
forming IrCF3(CO)(dppe)(OTf)2 (2b) in 70% yield, similar
to that reported for 1a.21 Complex 2b is a white solid that
demonstrates limited solubility in CH2Cl2. The product
retains the geometry of the starting complex as indicated by
small JF-P values (≈6 Hz) for phosphorus coupling to the
CF3 group and the JC-P values (130 and 6.1 Hz) for coupling
between the CO ligand and dppe phosphine donors. In the
19F NMR spectrum of the complex, three resonances of equal
intensity are observed, one at δ 55.88 for the Ir-CF3 group
and the other two located further upfield at δ -13.62 and
-14.30 for the inequivalent OTf- ligands.
Complexes 3a and 3b demonstrate clean spectroscopic
1
features in their 31P, 19F, and H NMR spectra. Complete
metathesis of the OTf- ions is evidenced by the absence of
the triflate resonances in the 19F NMR spectrum, and by the
presence of aryl CF3 groups of the BARF anion at 0.24 ppm.
Likewise, 1:1 resonances in the 31P{1H} NMR spectra (δ
27.28 and 3.95 for 3a; δ 25.74 and -1.20 for 3b) indicate
that the complexes each have two inequivalent 31P environ-
ments resulting from different ligands trans to the dppe
phosphine donors. For the 13CO-labeled compounds, the
magnitudes of JP-C (ca. 7 and 120 Hz) in the 13C{1H} NMR
spectra indicate the carbonyl orientation relative to dppe.
While the coordinated diiodobenzene resonances are partially
masked by the dppe phenyl groups, dissolution of the
complexes in CD3CN cleanly results in rapid conversion to
the corresponding bis(acetonitrile) complexes 4a and 4b (vide
infra) with concomitant liberation of 1 equiv of diiodoben-
zene.
Partial assignment of the coordinated diiodobenzene
resonances for the two complexes was accomplished by
conducting H,H-COSY experiments (see Supporting Infor-
mation, Figure S.1). The doublet of doublets observed in
the aromatic region [δ 6.97 and 7.39 for 3a; δ 6.85 and 7.4
(overlapping with a phenyl resonance of dppe) for 3b]
integrate to 1H each and therefore can only belong to the
diiodobenzene ligand. On the basis of this presumption, the
other resonances for this ligand can also be assigned by
correlation of the cross peaks in the respective H,H-correlated
spectra of the two complexes.
The diiodobenzene adducts are stable solids and can be
stored at room temperature for weeks with no apparent
decomposition. In solution, 3a slowly isomerizes without
liberation of free diiodobenzene forming a symmetrical
species (3a′) as evidenced by a single resonance at δ 35.20
(s) in the 31P{1H} NMR spectrum and a triplet (JP-H ) 4.0
Hz) for the Ir-CH3 group at 1.23 ppm. Observation of 3a′
commences within 20 min at room temperature. For 3b in
solution, slow decomposition is noted over several hours
unless the solution is cooled or free diiodobenzene is added.
While the nature of the decomposition was not elucidated,
it may relate to the reactivity of the trifluoromethyl ligand
when bound to a cationic metal center with adjacent labile
coordination sites.26,27
Synthesis of [IrR(CO)(dppe)(o-diiodobenzene)][BARF]2
Where R ) CH3 and CF3 (3a and 3b). Synthesis of
diiodobenzene adducts 3a and 3b (eq 3) can be accomplished
starting from the Ir(III) bis(triflate) complexes IrR(CO)-
(dppe)(OTf)2, 2. When metathesis of the coordinated OTf-
ligands of either 2a or 2b is carried out with 3 equiv of
NaBARF in CH2Cl2 in the presence of 3 equiv of diiodo-
benzene, formation of a single iridium species is observed.
After filtration of the NaOTf precipitate and subsequent
solvent evaporation, thermally stable off-white solids are
obtained in high yields (80-90%). The diiodobenzene
adducts are very soluble in CH2Cl2, slightly less soluble in
Et2O, insoluble in hydrocarbon solvents (benzene, toluene,
hexane, etc.), and reactive with more polar solvents (MeCN,
acetone, alcohols, MeNO2, etc.). As described below, some
of the reactions result in clean displacement of diiodobenzene
to generate the Ir(III) disolvento species. Polymerization of
(20) Crabtree, R. H.; Faller, J. W.; Mellea, M. F.; Quirk, J. M. Organo-
metallics 1982, 1, 1361-1366.
(21) Cleary, B. P.; Eisenberg, R. Inorg. Chim. Acta 1995, 240, 135-143.
(22) Albietz, P. J., Jr.; Cleary, B. P.; Paw, W. Eisenberg, R. J. Am. Chem.
Soc., in press.
(23) Cleary, B. P. Thesis, University of Rochester, 1995.
(24) Can be independently generated by reaction of I2 with Ir(CO)(dppe)I.
(25) Deutsch, P. P.; Eisenberg, R. J. Am. Chem. Soc. 1990, 112, 714-
721.
(26) Huang, D.; Koren, P. R.; Folting, K.; Davidson, E. R.; Caulton, K. G.
J. Am. Chem. Soc. 2000, 122, 8916-8931.
(27) Huang, D.; Caulton, K. G. J. Am. Chem. Soc. 1997, 119, 3185-3186.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2097

Albietz et al.
in a previous report. However, heating a solution of 4a in
MeCN-d3 to 75 °C in the NMR spectrometer yielded no
evidence of acyl formation.
Ligand Exchange Chemistry of Complexes 3a and 3b.
The lability of coordinated diiodobenzene was examined by
conducting various exchange reactions. Since acetonitrile
rapidly displaces diiodobenzene at room temperature, a closer
investigation at low temperatures was carried out. For 3a,
no reaction is observed below -40 °C, while for 3b,
exchange does not occur below -25 °C. The temperature
difference suggests the greater lability of diiodobenzene for
the Ir-CH3 analogue 3a. Interestingly, intermediates are
observed (4aq and 4bq) for both processes, the resonances
of which diminish with appearance of the final bis(acetoni-
trile) adducts 4a and 4b. Furthermore, free diiodobenzene
is not detected in the 1H NMR spectra until the final
complexes grow in, suggesting a stepwise exchange process
where the intermediate is a monodentate diiodobenzene
complex (Scheme 1).
Synthesis of [IrR(CO)(dppe)(NCMe)2][BARF]2 Where
R ) CH3 and CF3 (4a and 4b). The MeCN adducts 4 may
be generated via two pathways (eq 4). The first is similar to
that used for the diiodobenzene complexes, namely, meta-
thesis of the OTf- ligands with BARF- in the presence of
MeCN, while the second is by exchange of diiodobenzene.
The latter pathway is discussed in more detail below.
Acetonitrile complexes 4a and 4b retain the geometry of the
bis(triflate) analogues as indicated by the 1:1 resonances in
their 31P{1H} NMR spectra (δ 22.50 and 17.49 for 4a; δ
22.55 and 19.50 for 4b) and the JC-P values (ca. 8 and 120
Hz) for the carbonyl ligands. The coordinated MeCN
Examination of exchange using CO as the incoming ligand
gave similar results. Complex 3b exchanges with CO less
rapidly and less extensively than 3a as a result of weaker
back-bonding between CO and the more electrophilic metal
center. For 3a, an initial unsymmetrical intermediate (5aq)
is observed at δ 33.4 and 18.3, which over the period of 3
h goes away as the tri(carbonyl) complex fac-IrCH3(CO)3-
(dppe)2+ (5a) grows in at 25.3 ppm (Figure 1). Like the
exchange reactions with MeCN, free diiodobenzene is not
observed until conversion to the final product begins.
Exchange of CO for diiodobenzene in 3b occurs more
slowly, with complete conversion to the unsymmetrical
intermediate (5bq) taking ca. 2 h. Again, free diiodobenzene
is not observed during this process, suggesting that it remains
coordinated to the metal, but only ca. 10% (by 31P NMR) of
the final product fac-IrCF3(CO)3(dppe)2+ (5b) is formed after
several hours. The remaining mixture of products consists
of other unidentified species as evidenced by multiple
resonances in the 31P{1H} NMR spectrum and may result
from the reactivity of the cation-coordinated trifluoromethyl
ligand.26,27,29
1
molecules are observed as singlets in the H NMR spectra
at δ 2.63 and 1.80 for 4a and δ 2.78 and 1.75 for 4b.
Due to strong coordination of MeCN, the donors exchange
slowly when dissolved in acetonitrile-d3, where the t1/2 for
the exchange process of 4b at room temperature is ap-
proximately 1 week. Both of the coordinated MeCN mol-
ecules exchange at roughly the same rates for 4b, whereas
the upfield MeCN ligand of 4a exchanges more rapidly than
the other, presumably due to the stronger trans labilizing
effect of the CH3 ligand relative to the dppe phosphines.
Migratory insertion of CO does not occur for either 4a or
4b as indicated by the νCO values (2115 and 2144 cm-1,
respectively) and chemical shifts of CO in the 13C{1H} NMR
spectra (δ 163 and 159, respectively). For comparison, the
corresponding NMR and IR data for the previously re-
ported21,28 acyl complex are quite different (δ ) 202 and
νCO ) 1656 cm-1). While the lack of CO insertion was
expected for the CF3 complex 4b, it was not for the analogous
methyl complex 4a in view of the fact that a geometric
isomer of 4a was found to undergo facile migratory insertion
Reactions using 13CO as the incoming ligand provide
additional information regarding the nature of the intermedi-
ate based on the JP-C coupling constants. Starting from either
3a or 3b, the observed intermediate demonstrates a small
JP-C value (7.0 and 3.8 Hz, respectively) indicating that 13CO
is cis to both 31P nuclei of dppe. It is also clear that the second
exchange forms fac-IrR(CO)(13CO)2(dppe)2+, which dem-
onstrates a large JP-C value (JP-C ≈ 90 Hz) supporting a
trans orientation of the second 13CO ligand relative to one
of the 31P nuclei of dppe. On the basis of these observations,
the most consistent mechanism is that shown in pathway 1
of Scheme 1, where exchange initially occurs at the
(28) The original assignment of the inserted product described in ref 21
was found incorrect as indicated by the JC-P magnitudes (ca. 5-7
Hz) of the 13CO analogue. Therefore, CO is cis to dppe, not trans as
originally assigned.
(29) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Liable-Sands, L. M.
J. Am. Chem. Soc. 1997, 119, 11544-11545.
2098 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
Figure 1. Time-elapsed 31P{1H} NMR spectra (gradual warming from -10 °C to room temperature) for exchange of 1,2-diiodobenzene by CO. Complex
(δ): 3a (27.28 and 3.95); 5aq (33.4 and 18.3); 5a (25.3).
Scheme 1
coordination site trans to the iridium alkyl group due to its
greater trans-directing ability. Further support for the η1-
diiodobenzene complex comes from a H,H-COSY of the
intermediate 5aq obtained at -20 °C (Supporting Informa-
tion, Figure S.2). On the basis of the large downfield shift
of one of the DIB resonances (H1, ca. δ 7.99), the doublet
of doublets coupling pattern, and the corresponding cross
peaks, this resonance can be assigned as the proton adjacent
to the uncoordinated iodine atom. Likewise, the reactions
with MeCN appear to proceed via the same pathway as
evidenced by similar chemical shifts in the 31P{1H} NMR
spectra of the intermediate species. In all of the aforemen-
tioned cases, the second exchange appears to be slower than
the first, indicating that loss of DIB is the rate-determining
step of the reaction.
Reaction Chemistry with Ethylene. Recently reported
work22 has shown extensive reaction chemistry of the
diiodobenzene adducts with different olefinic substrates,
portions of which are further described below. Although 3a
does not show evidence of reaction when the simplest of
the olefins (ethylene) is present in stoichiometric amounts,
chemistry does occur when the latter is present in large
excess (eq 5). Condensation of ethylene into a CD2Cl2
solution of 3a results in formation of a new iridium complex
Inorganic Chemistry, Vol. 41, No. 8, 2002 2099

Albietz et al.
after several days (ca. 5 days when 300 equiv is added). The
major product from the reaction demonstrates a broad
resonance at ca. δ 22 in the 31P{1H} NMR spectrum.
Furthermore, a broad resonance at ca. 2.6 ppm, a second-
order pattern centered at ca. 2.9 ppm [JP-H ) 18 Hz,
PCH2CH2P], and free diiodobenzene are observed in the 1H
NMR spectrum. Interestingly, neither the Ir-CH3 group nor
any hydrides are detected. Additionally, removal of ethylene
does not result in regeneration of 3a, indicating the occur-
rence of further reaction after diiodobenzene exchanges with
ethylene.30
From the broad 31P{1H} NMR resonance and the appear-
ance of the dppe backbone protons as a symmetrical second-
order pattern, it is reasonable to suggest that this product is
a fluxional, five-coordinate Ir(I) species. Strong support for
this notion was obtained from comparison of the NMR data
with spectra obtained for the related analogues IrX(CO)2-
(dppe), where X ) halide or C(O)-2,4,6-C6H2Me3.23,31
Likewise, the broad resonance at 2.6 ppm could tentatively
be assigned as the coordinated olefin. On the basis of these
assumptions, independent generation of the product was
pursued via a different route in an attempt to ascertain the
nature of the product of the reaction of 3a with ethylene.
Halide abstraction from Ir(13CO)(dppe)I using AgPF6 in the
presence of ethylene results in clean formation of the cationic
diolefin complex 6-13CO (eq 5) with appearance and
chemical shifts of the resonances identical to those obtained
from the reaction of 3a-13CO with ethylene. With regard to
To gain further insight into the fluxional behavior of the
diolefin adduct, low-temperature NMR studies were con-
ducted as shown in Figures 2 and 3. In the 31P{1H} NMR
spectra, decreasing the temperature of a CD2Cl2 solution of
6-13CO results in initial broadening of the peak at δ 22 as
the coalescence temperature (Tc ≈ -10 °C) is approached,
followed by decoalescence into two peaks at δ 25.6 and 19.7
(JP-P ) 9.8 Hz) which become increasingly sharper, reveal-
ing JC-P of 7.4 and 131 Hz at ca. -70 °C (Figure 2). The
results are consistent with the static structure of 6-13CO
containing two distinct 31P environments for dppe, with one
of the phosphines trans to 13CO and the other cis, which are
averaged by a dynamic process.
1
The variable-temperature H NMR spectra were equally
informative (Figure 3). The second-order pattern at δ 2.9
representing the rapidly equilibrating dppe backbone H’s (see
Figure 3 inset) broadens as the temperature is decreased and
decoalesces below -40 °C into two separate resonances,
indicating two distinct types of dppe H’s at the slow
exchange limit (ca. -80 °C). 31P decoupling of the 1H NMR
spectrum at -90 °C confirms the assignment of the dppe
backbone resonances at δ 2.95 and 2.67 with JP-H ) 18 and
26 Hz, respectively.
For the coordinated ethylene resonance at ca. 2.5 ppm,
sharpening is observed when the temperature is initially
lowered, indicating a decrease in the rate of intermolecular
exchange between free and coordinated olefin. Further
cooling below 0 °C results in separation of the two
overlapping ethylene resonances. The two peaks decoalesce
(δ 2.54, Tc ) -60 °C; δ 2.34, Tc ) -70 °C) into two
resonances each (δ 3.08 and 1.80; 2.48 and 2.20, respec-
tively) as the slow exchange limit is approached (Figure 4b;
discussed in more detail below). The observation of four
distinct olefinic resonances at the slow exchange limit
indicates equivalence of the two ethylene ligands due to
presence of a mirror plane within 6. At -90 °C, the six
resonances (four for ethylene and two for the dppe backbone
H’s) in the range δ 2.95-1.80 integrate to 2 H’s each relative
to the 20 phenyl protons, supporting the assignment.
Interpretation of Variable-Temperature NMR Experi-
ments. The variable-temperature NMR spectra suggest that
averaging of the ligands coordinated to iridium is taking place
via three dynamic processes. Starting from the slow exchange
limit (ca. -90 °C), coalescence of the four distinct ethylene
peaks (Ha, Hb, Hc, and Hd) into two sets occurs indicating
equivalency of Ha/Hc and Hb/Hd as the temperature is raised.
The energy barrier is ca. 9 kcal/mol based on the rate
constants at the corresponding coalescence temperatures and
indicates that this is the lowest energy process. Ethylene
proton equilibration into two sets most likely results from
“propeller” rotation,32-35 wherein the molecule spins rapidly
about the metal-olefin axis thereby interconverting the trans
H’s.
the reduction of Ir(III) to Ir(I) in the conversion of 3a to 6,
the exact nature of the oxidation product(s) is not clear at
this time. From the reaction, butene isomers have been
1
positively identified as byproducts using GC/MS and H
NMR spectral analyses with comparison to known standards
(trace higher olefinssC6 and C8sare also detected by the
former method). Likewise, reactions conducted with 3a-
13CH3 demonstrate that methane is generated as the primary
13C-labeled product with no evidence of insertion into CO
or ethylene. No evidence of propylene or acetaldehyde as
an oxidation byproduct is seen during the reaction.
In the second dynamic process, the two P donors are
interchanged, as are the dppe backbone protons and in-
equivalent ortho phenyl protons of the dppe ligand. The
(30) No intermediate species are observed during the reaction.
(31) Fisher, B. J. Thesis, University of Rochester, 1983.
2100 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
Figure 2. Low-temperature NMR spectra of complex 6-13CO in CD2Cl2 with 10 equiv of free ethylene in solution: (a) 13C{1H} NMR spectra of Ir-CO
region at 24 and -90 °C and (b) 31P{1H} NMR spectra from 24 to -80 °C.
coalescence temperature is ca. -40 °C for the dppe backbone
resonances in the 1H NMR spectra, -40 °C for the
inequivalent ortho phenyl protons, and -10 °C for the
phosphine resonances in the 31P{1H} NMR spectra. On the
basis of the individual coalescence temperatures and chemical
shift differences from the three sources at their slow exchange
limits, ∆G( was calculated to be ca. 11 kcal/mol for this
second process. The most logical mechanism of fluxionality
to achieve the averaging of resonances required in the second
process is Berry pseudorotation (BPR) wherein axial and
equatorial positions in a trigonal bipyramid are interchanged
around one equatorial site serving as a pivot. However, to
interconvert axial and equatorial dppe phosphines via BPR
in 6 and retain the same structure, three pseudorotations are
required in which the other three ligands (ethylene-1, CO,
ethylene-2) are each used once as the pivot (Figure 4a). It is
interesting to note that while BPR averages equatorial and
axial sites in a trigonal bipyramid, it does not serve to
equilibrate all of the ethylene protons which remain in two
distinct sets.
Finally, the highest energy process appears to be inter-
molecular exchange with free ethylene as indicated by
sharpening of the coordinated ethylene resonance at 2.6 ppm
when the sample is initially cooled (Figure 3, traces from
24 to 0 °C). Since the high-temperature limit was not
investigated, ∆Gq and Tc for the process were not determined.
Simulation of NMR Spectra. In order to obtain accurate
rate constants as a function of temperature for the two lower
energy processes of complex 6, NMR line shape analyses
and simulations were conducted on the 31P{1H} and 1H NMR
spectra using the program Win DNMR (v 7.1.3). The
simulations yielded rate constants as a function of temper-
ature which are presented in Table 2. From these data were
calculated activation parameters, and the results are presented
in Table 1. Spectral simulations and Eyring and Arrhenius
plots are given in the Supporting Information. The ∆Gq and
∆Hq values for the lowest energy process of ethylene
propeller rotation (∼9 kcal/mol and 9.5(6) kcal/mol, respec-
tively) are slightly lower (2-4 kcal/mol) than those reported
for other Ir(I) and Ir(III) olefin complexes,32-35 suggesting
reduced metal-olefin back-bonding in 6 which is a cationic
carbonyl species.
(32) Szajek, L. P.; Lawson, R. J.; Shapley, J. R. Organometallics 1991,
10, 357-361.
The activation parameters calculated from the 31P{1H}
spectra agree with those based on the ortho phenyl proton
resonances since both equilibrations occur in the same
process of Berry pseudorotation. Simulation of the dppe
backbone protons, which are also equilibrated in this process,
was not possible with the program due to their complexity.
(33) Yan, X.; Einstein, F. W. B.; Sutton, D. Can. J. Chem. 1995, 73, 939-
955.
(34) Batchelor, R. J.; Einstein, F. W. B.; Lowe, N. D.; Palm, B. A.;
Xiaoqian, Y.; Sutton, D. Organometallics 1994, 13, 2041-2052.
(35) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. ComprehensiVe Orga-
nometallic Chemistry: The Synthesis, Reactions and Structures of
Organometallic Compounds; Pergamon Press: Elmsford, NY, 1982;
Vol. 3.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2101

Albietz et al.
Figure 3. Low-temperature 1H NMR spectra of complex 6-13CO in CD2Cl2 with 10 equiv of ethylene (not shown) in solution. Peaks at δ 2.9 are the dppe
backbone H’s (shown expanded at left), and the broad peak at δ 2.5 is coordinated ethylene. The inset shows the second-order pattern at ca. 2.9 ppm for
6-13CO more clearly [JP-H ) 18 Hz, PCH2CH2P].
Figure 4. Proposed dynamic processes of complex 6 based on the low-temperature NMR spectra: (a) three Berry pseudorotations to equilibrate the
ethylene and dppe ligands using ethylene-1, CO, and ethylene-2 as pivots, and (b) ethylene equilibration via M-olefin rotation. Intermolecular ethylene
exchange is not illustrated.
The Eyring and Arrhenius plots for the BPR process are
presented in the Supporting Information and yield ∆Hq ≈
10 kcal/mol, ∆Sq ≈ -5 eu, and Ea ≈ 10 kcal/mol. These
values are consistent with those reported in the litera-
ture,23,35,36 and the calculated free energy barriers ∆Gq (ca.
11 kcal/mol) at the corresponding Tc’s for phosphine donors
and phenyl protons compare well with values calculated
directly from the NMR spectra based on ∆ν for the respective
resonances.
For the highest energy process of intermolecular ethylene
exchange, the high-temperature limit was not achieved and
the data are therefore limited. However, on the basis of the
temperature range 0-24 °C, the rate constants calculated
(36) Miller, J. S.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 1067-1073.
2102 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
Table 1. Activation Parametersa for Fluxionality of Complex 6 Starting from the Slow Exchange Limit
g
g
∆Hq
(kcal/mol)
∆Sq
(eu)
Ea
kobsf (s-1
at Tc
)
∆Gq
∆Gq
calc
obs
source
(kcal/mol)
(kcal/mol)
(kcal/mol)
inner ethylene H’sb
(ethylene rotation)
outer ethylene H’sc
(ethylene rotation)
dppe backbone H’sd
(pseudorotation)
9.5(6)
9.5(6)
1(3)
1(3)
9.9(6)
9.9(6)
247 at
9.5
9.2(5)
-70 °C
1.1 × 103
at -60 °C
255 at
-40 °C
200 at
9.3
11.0
11.1
11.3
9.2(6)
ortho phenylene H’s
(pseudorotation)
9.5(6)
10.0(6)
17(3)
-7(2)
-4(2)
9(9)
10.0(6)
10.5(6)
18(3)
11.1(5)
11.2(6)
-40 °C
resonances from 31P NMR
(pseudorotation)
2.1 × 103
at -10 °C
2.5 × 103
>24 °C
overlapping ethylene H’se
(intermolecular exchange)
a Errors are to 90% confidence limit. b δ 2.48 and 2.20. c δ 3.08 and 1.80. d Could not determine ∆Hq, ∆Sq, and Ea from simulation due to the complexity
of the spin system. e Rough estimate from intermolecular exchange between free and coordinated ethylene. f Based on Tc from experimental NMR spectra.
g Values at corresponding Tc.
therefore a mechanism similar to that proposed by Sen39 for
Table 2. Temperature Dependent Rate Constants Determined from
Simulation of the Dynamic Behavior of Complex 6
Pd(NCMe)42+-induced isomerizations is assumed to be
ethylene rotation
31P resonances
operative.
k (s-1
)
T (°C)
k (s-1
)
T (°C)
To probe further the electrophilic activities of the diiodo-
benzene complexes 3, reactions with a variety of olefins were
also conducted. For substrates such as styrene, â-pinene,
isobutylene, R-methylstyrene, and norbornene, polymeriza-
tion or oligomerization (Scheme 2) is found to occur in the
presence of both 3a and 3b. With the exception of nor-
bornene, addition of the respective olefin to dichloromethane
solutions of the diiodobenzene complexes results in exo-
thermic reaction in which the monomer is rapidly consumed
and the solvent begins to boil. In all cases, analysis of the
reaction mixtures demonstrates conversion of the monomer
to polymerized or oligomerized olefin, the results of which
are summarized in Table 3. Polymerizations of styrene and
â-pinene lead to products that are isolated as solids, whereas
isobutylene polymerizations yield viscous oils. The poly-
isobutylene and poly-styrene products demonstrate bimodal
molecular weight distributions, explanations for which have
been described in the literature.40 For R-methylstyrene, a 1:1
ratio of the cyclized dimer and trimer (indane derivatives)
45
110
480
1300
6000
13000
31000
59000
-90
-80
-70
-60
-50
-40
-30
-20
5
25
100
270
610
1240
2800
5000
9900
25000
-70
-60
-50
-40
-30
-20
-10
0
10
24
ortho phenyl resonances
intermolecular exchange
k (s-1
)
T (°C)
k (s-1
)
T (°C)
7
25
80
180
360
890
2500
-70
-60
-50
-40
-30
-20
-10
16
43
215
0
10
24
from the simulations lead to a rough estimate of ∆Hq, ∆Sq,
and Ea of 17(3) kcal/mol, 9(9) eu, and 18(3) kcal/mol,
respectively, consistent with a higher energy intermolecular
exchange process.
1
is observed by H NMR and found consistent with the
reported reactivity2,41 of R-methylstyrene with cationic initia-
tors at or above room temperature. For norbornene, the
reaction is found to be slow and gives an oily product that
is soluble in low-polarity solvents, such as CH2Cl2 or CHCl3.
Reaction Chemistry with Substituted Olefins. Interac-
tion of 3 with other olefins does occur and gives rise to
notable and distinct chemistry, some results of which have
been previously described.22 Reaction of 3 with 1-pentene37
results in double-bond isomerization (Scheme 2) that takes
place at room temperature over several days to yield cis-
and trans-2-pentene. After 5 days at room temperature, the
reaction mixture corresponds to a nearly thermodynamic
distribution38 of 2% 1-pentene, 14% cis-2-pentene, and 84%
trans-2-pentene under these conditions, being slightly en-
riched in the trans isomer. It is thought that no change in
oxidation state of the metal happens during this process and
1
The extremely weak olefinic resonances in the H NMR
spectrum indicate that ring-opening processes42,43 are not
occurring. Furthermore, the complexity of a H,H-COSY of
the isolated oligomer suggests that both 2,3- and 2,7-additions
are occurring due to norbornyl cation formation (vide infra).
The fact that 3a does not polymerize ethylene whereas
both 3a and 3b actiVely promote polymerization/oligomer-
ization of isobutylene, styrene, and â-pinene suggests that
polymerization is occurring via cationic initiation rather than
(39) Sen, A.; Lai, T.-W. Inorg. Chem. 1981, 20, 4036-4038.
(40) Li, T.; Padias, A. B.; Hall, H. K. Macromolecules 1992, 25, 1387-
1390.
(37) Reactions of 3a with 1-hexene also produced internal double bond
isomers. The product distributions were not determined, however, due
to the difficulty in resolving all of the different isomers for accurate
quantification.
(41) Baird, M. C. Chem. ReV. 2000, 100, 1471-1478.
(42) Jeremic, D.; Wang, Q.; Quyoum, R.; Baird, M. C. J. Organomet. Chem.
1995, 497, 43-147.
(38) Bond, G. C.; Hellier, M. J. Catal. 1965, 4, 1-5.
(43) Gilliom, L. R. J. Am. Chem. Soc. 1986, 108, 733-742.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2103

Albietz et al.
Scheme 2
Table 3. Products Obtained from Reaction of Various Olefins with 3a
and 3b in CH2Cl2
of the metal-bound polymer, thereby explaining the lack of
initiator consumption. Further reaction (reductive elimination
or â-hydride elimination) at the metal center may also result
in removal of the metal end group from the polymer.
Additionally, a kinetics argument helps to explain the absence
of metal-containing end groups under normal polymerization
conditions. It has been reported45 that the rate of initiation
of styrene polymerization using HOTf in 1,2-dichloroethane
at 20 °C is 5-6 orders of magnitude less than the rate of
chain propagation. The substantial difference in these rates
results in consumption of only minor amounts of initiator,
such as 3a and 3b in the present study.
a
a
olefin
styrene
complex
Mw
Mw/Mn
3a
3b
3a
3b
3a
3b
3a
3b
3a
3b
22200b
23800b
21900
12900
1940b
3430b
234
262
c
c
5.9
4.9
2.5
2.9
2.6
3.8
1.2
1.2
â-pinene
isobutylene
norbornene
R-methylstyrene
a Determined by SEC and referenced to polystyrene standards. b Bimodal
molecular weight distribution. c 1:1 dimer:trimer.
As postulated for other sufficiently electrophilic rea-
gents,45-47 there are two possible mechanisms for cationic
polymerization. The initiator may react either directly with
the olefin to generate a carbocation or with trace H2O
resulting in generation of H+. In view of the electrophilicities
of the diiodobenzene complexes 3a and 3b, reaction with
adventitious water cannot be completely ruled out, and indeed
might be expected. If this pathway were operative, it would
also explain the lack of an iridium end group on the polymer
since the complexes are not directly reacting with the olefin.
In order to test this notion, reactions were conducted in the
presence of base46,47 (2,6-di-tert-butylpyridine or Na2CO3)
using rigorously dried reagents, but formation of polymer
was still observed. While monomer consumption is slower
when excess base is present,48 complete consumption of the
metal complex does occur, indicating that direct initiation
happens. Moreover, evidence for an iridium end group is
detected in both poly-â-pinene and poly-styrene by 31P{1H}
by a coordination/insertion mechanism. The wide range of
observed polydispersities supports this notion. For reactions
of 3 with R-methylstyrene, formation of the indan derivatives
cannot be rationalized if coordination/insertion catalysis is
operative. For this substrate, reaction with a cationic initiator
at room temperature generates a 3° carbocation that typically
undergoes more rapid intramolecular cyclization than propa-
gation. Furthermore, quenching of styrene polymerization
with tert-butyl alcohol 5 s after styrene addition to a solution
of 3a results in incorporation of a tert-butyl ether end group44
into the polymer chain, as evidenced by a large singlet at δ
1
1.26 in the H NMR spectrum.
Due to the reactivities of the DIB complexes, only minor
amounts are necessary for initiation resulting in unobservable
metal incorporation into the polymer product under normal
reaction conditions, although under other circumstances, it
may be detected (vide infra). Since H+ is liberated during
chain transfer of the polymerization, the starting Ir(III)
complex may be regenerated via protolysis of the Ir-C bond
(45) Odian, G. Principles of Polymerization, 3rd ed.; Wiley-Interscience:
New York, Chichester, Brisbane, Toronto, Singapore, 1991.
(46) Moulis, J. M.; Collomb, J.; Gandini, A.; Cheradame, H. Polym. Bull.
1980, 3, 197-202.
(47) Shaffer, T. D.; Ashbaugh, J. R. J. Polym. Sci. Part A 1997, 35, 329-
344.
(44) Barsan, F.; Baird, M. C. J. Chem. Soc., Chem. Commun. 1995, No.
10, 1065-1066.
2104 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
activated alumina before use. Molecular sieves and alumina were
thoroughly washed with CH2Cl2 and then activated by heating with
a Bunsen burner under vacuum. IrCH3(CO)(dppe)I2,23 IrCH3(CO)-
(dppe)(OTf)2,21 and NaBARF49 were synthesized according to
published procedures. All 13CO-labeled complexes were prepared
according to the same procedures described below for the unlabeled
analogues starting from Ir(13CO)(dppe)I.50
NMR spectroscopy for reactions carried out in the presence
of an excess (4-6 equiv) of 2,6-di-tert-butylpyridine. For
example, a 31P{1H} NMR spectrum of chromatographed
polystyrene demonstrates the presence of a set of broad
resonances centered at 11 ppm corresponding to the dppe
phosphines after a 12 h acquisition. While definitiVe evidence
supporting direct cationic initiation in the absence of base
cannot be offered at this time, its occurrence is highly
plausible on the basis of experiments in the presence of base.
Further support for this view is offered by the fact that
cationic initiation and polymerization by metal complexes
has been seen previously for a few late metal complexes.41
Unless otherwise stated, all reactions and manipulations were
performed in dry glassware under a nitrogen atmosphere using either
standard Schlenk techniques or an inert-atmosphere glovebox. THF,
CH2Cl2, hexanes, pentane, and acetonitrile were purified as
described by Grubbs.51 All NMR spectra were recorded on a Bruker
AMX or Avance 400 MHz spectrometer. 1H and 13C chemical shifts
(δ in ppm) are relative to tetramethylsilane and referenced using
chemical shifts of residual solvent resonances. 31P chemical shifts
(δ in ppm) are relative to an external 85% solution of phosphoric
acid in the appropriate solvent. 19F chemical shifts (δ in ppm) are
referenced externally to CF3C6H5 in the appropriate solvent. Column
chromatography on IrCF3(CO)(dppe)I2 was done using a Biotage
Flash 40 system under 20 psi of nitrogen pressure. GC analyses on
the pentene isomers were conducted using a Shimadzu model 17C
system (oven ) 8 °C, injector ) 26 °C, detector ) 49 °C, helium
flow rate ) 0.3 mL/min) fitted with a 15 m Restek Rtx-5 column
(Crossbond 5% diphenyl-95% dimethyl polysiloxane, 0.25 mm
i.d., 0.25 µm df). Assignments of the pentene double-bond isomers
were established using standards purchased from Aldrich Chemical
Co. The polymers were analyzed by size-exclusion chromatograph
(SEC) in uninhibited THF using three Polymer Laboratories 7.5
mm × 300 mm Plgel mixed-C columns at room temperature and
referenced to polystyrene standards. Elemental analyses were
obtained from Quantitative Technologies, Inc., Whitehouse, NJ.
Mass spectrometry data were obtained on an Hewlett-Packard series
1100 MSD fitted with an atmospheric pressure ionization chamber.
The NMR simulations were conducted using the program Win
DNMR version 7.1.3, which was written by Hans J. Reich from
the Department of Chemistry of the University of Wisconsin,
Madison. The additional program Win NUTS version 5.093 was
also used to process the NMR spectra before importing them into
Win DNMR. For conducting the simulations, the spectra obtained
at the slow exchange limit were initially used to determine the peak
positions, peak widths, coupling constants, and relative peak
percentages where applicable. These values were used as the default
values in the absence of any exchange. The following are the
parameters at the slow exchange limits used for each of the 4
simulations: intermolecular exchange for a 2-spin system [free
ethylene, width ) 3.0 Hz, intensity ) 90%] and [coordinated
ethylene peak, width ) 8.8 Hz, intensity ) 10%]; ortho phenyl
Conclusions
In conclusion, the synthesis, characterization, and reaction
chemistry of dicationic iridium(III) complexes stabilized by
1,2-diiodobenzene have been described. The complexes
readily undergo exchange with acetonitrile and CO. Inves-
tigation of the exchange process demonstrates that the
coordination site trans to the Ir-alkyl group is more labile,
as indicated by the JP-C magnitudes of the η1-DIB intermedi-
ates when 13CO is employed. Although the νCO stretch of
the Ir-CF3 analogue is consistent with a more electrophilic
metal center, the stronger trans labilizing effect of the methyl
group results in more facile dissociation of diiodobenzene.
Finally, the diiodobenzene adducts demonstrate fairly ex-
tensive reaction chemistry with a variety of olefins. For
reactions of 3a with ethylene, reduction to a fluxional five-
coordinate Ir(I) diolefin complex 6 occurs. The fluxional
behavior of 6 was studied by variable-temperature NMR
spectroscopy and line-shape analysis leading to rate constants
and activation parameters for three processes including
ethylene propeller rotation, Berry pseudorotation, and inter-
molecular ethylene exchange. Additional reaction chemistry
with other olefins is also observed in which the diiodoben-
zene complexes demonstrate the ability to initiate cationic
polymerization of different olefins and catalyze double-bond
isomerizations of simple alkenes. The polymerization activi-
ties demonstrated by 3a and 3b indicate that the iridium-
(III) complexes behave as excellent electrophiles.
Experimental Section
General Procedures and Materials. Trifluoromethyl iodide,
silver(I) triflate (AgOTf, 99.95%), silver(I) hexafluorophosphate
(AgPF6), 1,2-diiodobenzene, styrene, (1S)-(-)-â-pinene, R-meth-
ylstyrene, norbornene, pentene isomers, and 2,6-di-tert-butylpyridine
were purchased from Aldrich Chemical Co. Styrene was distilled
over CaH2 and then filtered through activated Al2O3 before use.
1-Pentene, R-methylstyrene, â-pinene, 1,2-diiodobenzene, and 2,6-
di-tert-butylpyridine were degassed, filtered through activated
Al2O3, and then stored in an N2-filled glovebox over activated
molecular sieves. Acetonitrile-d3 and dichloromethane-d2 were
purchased from Cambridge Isotope in ampules and filtered through
H’s [spin system simplified to ABX2 where JAB ) 0 and JX ≈ JPH
2
≈ JHH ≈ 8.2 Hz, peak widths ) 7.1 Hz]; 31P{1H} NMR
equilibration [spin system used is ABX where JAB ) 9.9 Hz, JAX
) 6.7 Hz, and JBX ) 130.7 Hz, peak widths ) 5.8 Hz]; ethylene
rotation [used a 4-spin system with 1:1:1:1 ratio for the 4 peaks,
peak widths ) 10.8 Hz].
Synthesis of the Iridium Complexes. A. Synthesis of IrCF3-
(CO)(dppe)I2 (1b, 1c, and 1d). A 25 mL Schlenk flask equipped
with a stir-bar was charged with IrI(CO)(dppe) (749 mg, 1 mmol)
and 14 mL of CH2Cl2. The solution was cooled to -78 °C, and
trifluoromethyl iodide was bubbled through the solution. After the
(48) Slower polymerization should be expected in the presence of base
due to its interference with the chain termination/transfer events since
these entail H+ evolution. Reactions conducted between 3a and styrene
in the presence of 2 equiv of 2,6-di-tert-butylpyridine were still
exothermic. Slow monomer consumption was observed only when a
large excess of base was used.
(49) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920-3922.
(50) Deutsch, P. P. Thesis, University of Rochester, 1989.
(51) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2105

Albietz et al.
reaction mixture turned red, the solution was purged with trifluo-
romethyl iodide for an additional 40 s. The reaction mixture was
stirred at -78 °C for 10 min before removal of the low-temperature
bath. After 45 min, the yellow solution was concentrated to
approximately 5 mL in vacuo, and hexanes were added, resulting
in precipitation of a cream-colored solid. The solid was isolated in
air on a frit washing with hexanes yielding 883 mg of a mixture of
isomers (ca. 90% 1b). The material was dissolved in 5 mL of CH2-
Cl2 and injected onto a Biotage 40M cartridge (KP-Sil, 32-63 µm,
60 Å) eluting with 1:1 hexanes/CH2Cl2. The kinetic isomer 1b was
the first yellow fraction off the column. After confirmation of the
purity of the collected fractions, they were combined and concen-
trated until precipitation occurred. A yield of 730 mg (77%) of
pure 1b was obtained as a yellow solid. Concentration of the second
yellow fraction from the column afforded 76 mg of primarily the
thermodynamic isomer 1c, in addition to minor amounts of 1d and
fac-Ir(CO)(dppe)I3. Spectral information for 1b: 1H NMR (CD2-
Cl2) δ 7.20-8.20 (20H, phenyl), 3.10-3.40 (overlapping m, 4H,
PCH2CH2P); 31P{1H} NMR (CD2Cl2) δ 13.28 (qd, JP-P ) 3.9 Hz,
the rapidly stirred solution followed by an additional 5 mL of CH2-
Cl2. After 5 min, the solid NaOTf was removed by filtration and
the solution was concentrated in vacuo to 5 mL, at which point 15
mL of hexanes was added. The solvent was concentrated to 10 mL
and decanted from the oil. After the oil was dried in vacuo, the
resulting solid was thoroughly washed with hexanes and dried,
leaving an off-white solid. Additional washings with hexanes may
be necessary to completely remove any residual 1,2-diiodobenzene.
Crude yield: 582 mg (84%). The material may be purified if
necessary by successive recrystallizations from CH2Cl2/hexanes and
filtrations to remove any remaining sodium salts. Purified yield:
510 mg (73%). 1H NMR (CD2Cl2): δ 7.42-7.85 (overlapping, 39H,
phenyl, BARF), 7.39 (dd, Jmeta ) 1.3 Hz, Jortho ) 8.2 Hz, 1H, DIB),
7.25 (overlapping, 3H, phenyl), 7.11 (td, Jmeta ) 1.3 Hz, Jortho
)
8.0 Hz, 1H, DIB), 7.03 (overlapping, 3H, phenyl), 6.97 (dd, Jmeta
) 1.3 Hz, Jortho ) 8.2 Hz, 1H, DIB), 3.60 (overlapping m, 2H,
PCH2CH2P), 2.97 (overlapping m, 2H, PCH2CH2P), 1.05 (dd, JP-H
) 5.3 and 3.1 Hz, 3H, for 13CH3 complex, JC-H ) 140.6 Hz, Ir-
CH3). 31P{1H} NMR (CD2Cl2): δ 27.28 (d, JP-P ) 3.6 Hz, 1P, cis
to CO), 3.95 (d, JP-P ) 3.6 Hz, 1P, trans to CO). 19F NMR (CD2-
Cl2): δ 0.24 (s, BARF). 13C{1H} NMR (CD2Cl2): δ 161.7 (dd,
JP-C ) 122 and 7.1 Hz, CO), -10.4 (t, JP-C ) 4.2 Hz, for 13CO
and 13CH3 complex, JC-C ) 1.8 Hz, Ir-CH3). IR (thin film): 2106
cm-1 (CO). Anal. Calcd for C98H55B2F48I2P2OIr‚hexanes: C, 44.99;
H, 2.51. Found C, 44.82; H, 2.57. Slow isomerization from 3a to
3a′ in CH2Cl2 begins after ca. 10 min at room temperature. Spectral
information for 3a′: 1H NMR (CD2Cl2) δ 1.23 (t, JP-H ) 4.0 Hz,
3H, for 13CH3 complex, JC-H ) 133.1 Hz, Ir-CH3); 31P{1H} NMR
(CD2Cl2) δ 35.20 (s, 2P); 13C{1H} NMR (CD2Cl2) δ 164.6 (t, JP-C
) 4.5 Hz; for 13CO and 13CH3 complex, JC-C ) 25.1 Hz, CO),
JF-P ) 8.7 Hz, 1P, cis to CO), -10.52 (qd, JP-P ) 3.9 Hz, JF-P
)
)
5.3 Hz, 1P, trans to CO); 19F NMR (CD2Cl2) δ 62.95 (dd, JP-F
8.7 and 5.3 Hz, Ir-CF3); 13C{1H} NMR (CD2Cl2) δ 164 (virtual
dqn, JP-C ) 139.7 and 5.7 Hz, JF-C ) 5.7 Hz, CO); IR (CH2Cl2)
2088 cm-1 (CO). Anal. Calcd for C28H24F3I2P2OIr: C, 35.72; H,
2.57. Found C, 35.78; H, 2.45. Spectral information for 1c: 1H
NMR (CD2Cl2) δ 7.20-8.10 (20H, phenyl), 2.65-3.40 (overlapping
m, 4H, PCH2CH2P); 31P{1H} NMR (CD2Cl2) δ 4.17 (qd, JP-P ) 7
Hz, JF-P ) 8.7 Hz, 1P, cis to CF3), -16.23 (qd, JP-P ) 7 Hz, JF-P
) 48 Hz, 1P, trans to CF3); 19F NMR (CD2Cl2) δ 61.51 (dd, JP-F
) 48 and 8.7 Hz, Ir-CF3); 13C{1H} NMR (CD2Cl2) δ 154.5 (qdd,
JP-C ) 3.8 and 6.0 Hz, JF-C ) 4.0 Hz, CO); IR (CH2Cl2) 2068
cm-1 (CO). Spectral information for 1d: 31P{1H} NMR (CD2Cl2)
δ 8.15 (q, JF-P ) 6.7 Hz, 2P, cis to CF3); 19F NMR (CD2Cl2) δ
54.35 (t, JP-F ) 6.7 Hz, Ir-CF3); 13C{1H} NMR (CD2Cl2) δ 165.4
(qt, JP-C ) 4.6 Hz, JF-C ) 16.5 Hz, CO).
-4.98 (t, JP-C ) 5.4 Hz; for 13CO and 13CH3 complex, JC-C
25.1 Hz, Ir-CH3).
)
D. Synthesis of [IrCF3(CO)(dppe)(DIB)][BARF]2 (3b) Where
DIB ) 1,2-Diiodobenzene. The same procedure was followed as
described above for the synthesis of 3a. IrCF3(CO)(dppe)(OTf)2
(357 mg, 0.362 mmol), 1,2-diiodobenzene (145 µL, 1.11 mmol),
NaBARF (965 mg, 1.09 mmol), and 25 mL of CH2Cl2 were used.
B. Synthesis of IrCF3(CO)(dppe)(OTf)2 (2b). A similar pro-
cedure was followed as described for the synthesis of 2a.21 A 100
mL round-bottom flask containing a stir-bar was charged with
AgOTf (131 mg, 0.51 mmol) and 32 mL of CH2Cl2 in the dark.
IrCF3(CO)(dppe)I2 (231 mg, 0.25 mmol) was added as a solid to
the suspension followed by 4 mL of CH2Cl2. After 5 min, AgI
began to precipitate out of solution. The reaction mixture was stirred
for 3.5 h. An aliquot was removed, and a 31P{1H} NMR spectrum
was obtained indicating that the reaction was complete. The AgI
solid was removed by gravity filtration through a medium-porosity
frit revealing a near colorless solution. The filtrate was concentrated
in vacuo, leaving a white solid. If necessary, any yellow impurities
may be removed by washing the product with the minimum amount
of cold CH2Cl2 at -40 °C. Isolated: 203 mg (84%). 1H NMR (CD2-
Cl2): δ 7.47-7.90 (20H, phenyl), 3.10-3.40 (overlapping m, 4H,
1
Purified yield: 775 mg (78%). H NMR (CD2Cl2): δ 7.5-7.98
(overlapping, 39H, phenyl, BARF), 7.36 (overlapping, 3H, phenyl),
7.28 (td, Jmeta ) 1.4 Hz, Jortho ) 8.2 Hz, 1H, DIB), 7.13 (td, Jmeta
) 1.4 Hz, Jortho ) 7.4 Hz, 1H, DIB), 7.00 (overlapping, 3H, phenyl),
6.85 (dd, Jmeta ) 1.4 Hz, Jortho ) 8.2 Hz, 1H, DIB), 3.75
(overlapping m, 2H, PCH2CH2P), 3.38 (m, 1H, PCH2CH2P), 3.13
(m, 1H, PCH2CH2P). 31P{1H} NMR (CD2Cl2): δ 25.74 (qd, JP-P
) 1.5 Hz, JF-P ) 4.8 Hz, 1P, cis to CO), -1.20 (qd, JP-P ) 1.5
Hz, JF-P ) 4.1 Hz, 1P, trans to CO). 19F NMR (CD2Cl2): δ 70.45
(dd, JP-F ) 4.8 and 4.1 Hz, 3F, Ir-CF3), 0.24 (s, 48F, BARF).
13C{1H} NMR (CD2Cl2): δ 156.8 (virtual dqn, JP-C ) 117.4 and
6.7 Hz, JF-C ) 6.7 Hz, CO). IR (thin film): 2133 cm-1 (CO). Anal.
Calcd for C98H52B2F51I2P2OIr; C, 42.90; H, 1.91. Found C, 43.06;
H, 1.79.
PCH2CH2P). 31P{1H} NMR (CD2Cl2): δ 20.39 (virtual qn, JP-P
)
JF-P ) 6.1 Hz, 1P, trans to CO), 11.21 (m, difficult to resolve, 1P,
cis to CO). 19F NMR (CD2Cl2): δ 55.88 (m, difficult to resolve,
3F, Ir-CF3), -13.62 (m, difficult to resolve, 3F, OTf), -14.30 (q,
JF-F ) 2.2 Hz, 3F, OTf). 13C{1H} NMR (CD2Cl2): δ 165.2 (virtual
dqn, JP-C ) 130 and 6.1 Hz, JF-C ) 6.1 Hz, CO). IR (CH2Cl2):
2132 cm-1 (CO). Anal. Calcd for C30H24 F9O7 P2S2Ir‚CH2Cl2: C,
34.77; H, 2.45. Found C, 34.82; H, 2.21.
E. Generation of [IrR(CO)(dppe)(NCCH3)2][BARF]2 Where
R ) CH3 and CF3 (4a and 4b). Complexes 4a and 4b were
generated in NMR tubes following the two representative proce-
dures described below. Procedure 1. A resealable NMR tube was
charged with [IrCH3(CO)(dppe)(DIB][BARF]2 (10 mg, 3.7 µmol)
and 0.5 mL of CD2Cl2. To the colorless solution was added CH3-
1
CN (1 µL, 19.1 µmol). H NMR spectral analysis of the solution
C. Synthesis of [IrCH3(CO)(dppe)(DIB)][BARF]2 (3a) Where
DIB ) 1,2-Diiodobenzene. A 50 mL round-bottom flask equipped
with a stir-bar was charged with IrCH3(CO)(dppe)(OTf)2 (240 mg,
258 µmol), 10 mL of CH2Cl2, and 1,2-diiodobenzene (100 µL, 765
µmol). NaBARF (683 mg, 771 µmol) was then added as a solid to
demonstrated 1 equiv of free 1,2-diiodobenzene, the presence of
two coordinated acetonitrile resonances, and free acetonitrile at δ
1.95. Procedure 2. A resealable NMR tube was charged with IrCH3-
(CO)(dppe)(OTf)2 (11 mg, 11.8 µmol) and 0.25 mL of CD2Cl2. To
the suspension were added ca. 2.5 µL of CH3CN and NaBARF
2106 Inorganic Chemistry, Vol. 41, No. 8, 2002

Cationic Complexes of Iridium
(31.4 mg, 35.4 µmol). CD2Cl2 (0.25 mL) was added, and the NMR
tube was sealed and shaken vigorously. Analysis of the solution
demonstrated conversion to the same product as observed above.
A 19F NMR spectrum also confirmed that complete metathesis had
occurred as evidenced by the absence of any OTf- resonances
(NaOTf precipitate observed) and the presence of the CF3 groups
for the BARF counterion. (JP-C values were determined using 13CO-
enriched samples of 4a/b.) Spectral information for 4a: 1H NMR
(CD2Cl2) δ 7.43-7.72 (overlapping, 44H, phenyl, BARF), 3.00-
3.50 (overlapping m, 4H, PCH2CH2P), 2.63 (s, 3H, NCCH3), 1.80
(s, 3H, NCCH3), 0.30 (dd, JP-H ) 6.3 and 3.2 Hz, 3H, Ir-CH3);
31P{1H} NMR (CD2Cl2) δ 22.50 (d, JP-P ) 4.9 Hz, 1P, trans to
CO), 17.49 (d, JP-P ) 4.9 Hz, 1P, cis to CO); 19F NMR (CD2Cl2)
δ 0.24 (s, BARF); 13C{1H} NMR (CD2Cl2) δ 163 (dd, JP-C ) 123
and 8.1 Hz, CO); IR (thin film) 2115 cm-1 (CO). Spectral
information for 4b: 1H NMR (CD2Cl2) δ 7.46-7.76 (overlapping,
44H, phenyl, BARF), 3.09-3.70 (overlapping m, 4H, PCH2CH2P),
2.78 (s, 3H, NCCH3), 1.75 (s, 3H, NCCH3); 31P{1H} NMR (CD2-
Cl2) δ 22.55 (qd, JP-P ) 1.9 Hz, JF-P ) 5.9 Hz, JC-P ) 115 Hz,
1P, trans to CO), 19.50 (m, JP-P ) 1.9 Hz, JF-P ) 5.6 Hz, 1P, cis
to CO); 19F NMR (CD2Cl2) δ 54.8 (dd, JP-F ) 5.9 and 5.6 Hz, 3F,
Ir-CF3), 0.24 (s, 48F, BARF); 13C{1H} NMR (CD2Cl2) δ 159 (dqn,
JP-C ) 115 and 5.6 Hz, CO); IR (thin film) 2144 cm-1 (CO).
F. General Procedure for Low-Temperature Studies of
MeCN Exchange Reaction with 3a and 3b. Observation of
Intermediate Species 4aq and 4bq. A resealable NMR tube
containing either complex 3a or 3b (5 µmol) and CD2Cl2 was
freeze-pump-thawed three times. A large excess (>20×) of
MeCN was then vacuum transferred into the NMR tube, and the
sample was kept frozen at 77 K. The probe in the NMR
spectrometer was cooled to -85 °C. After slightly thawing the
NMR tube, it was inserted into the probe. The reaction was then
monitored while the temperature was gradually increased. Spectral
information for intermediate species 4aq (-40 °C): 1H NMR (CD2-
Cl2): δ 0.26 (unresolved coupling, 3H, Ir-CH3). 31P{1H} NMR
(CD2Cl2): δ 31.9 (1P, unresolved coupling), 17.9 (1P, unresolved
coupling). Spectral information for intermediate species 4bq (-25
°C): 31P{1H} NMR (CD2Cl2): δ 31.3 (1P, unresolved coupling),
12.7 (1P, unresolved coupling). 19F NMR (CD2Cl2): δ 61.8 (3F,
unresolved coupling, Ir-CF3), 0.24 (s, 48F, BARF).
Spectral information for complex 5b:52 31P{1H} NMR (CD2Cl2) δ
27 (s, 2P, JP-C trans for 13CO reaction ) 88.6 Hz); 19F NMR (CD2-
Cl2) δ 60.5 (t, JP-F ) 4.6 Hz, 3F, Ir-CF3), 0.24 (s, 48F, BARF).
Spectral information for intermediate species 5bq: 1H NMR (CD2-
Cl2): δ 8.03 (dd, Jmeta ) 1.5 Hz, Jortho ) 7.9 Hz, 1H, DIB), 7.43-
7.95 (overlapping, 39H, phenyl, BARF), 7.31 (td, Jmeta ) 1.4 Hz,
Jortho ) 7.8 Hz, 1H, DIB), 7.23 (dd, Jmeta ) 1.4 Hz, Jortho ) 8.2 Hz,
1H, DIB), 7.13 (td, Jmeta ) 1.6 Hz, Jortho ) 7.4 Hz, 1H, DIB), 3.71
(overlapping m, 2H, PCH2CH2P), 3.41 (m, 1H, PCH2CH2P), 3.21
(m, 1H, PCH2CH2P); 31P{1H} NMR (CD2Cl2) δ 32.7 (virtual qn,
JP-P ) JC-P ) 3.8 Hz, 1P), 15.7 (virtual qn, JP-P ) JC-P ) 3.8
Hz, 1P); 19F NMR (CD2Cl2) δ 58.1 (virtual t, JP-F ) 3.8 Hz, 3F,
Ir-CF3), 0.24 (s, 48F, BARF).
Reactions with Olefinic Substrates. A. Reaction of 3a with
Ethylene. A resealable NMR tube was charged with 3a (10 mg,
3.7 µmol) and 0.5 mL of CD2Cl2. The solution was freeze-pump-
thawed 3×, and then ethylene was condensed into the NMR tube
at 77 K. The valve was closed, and the solution was carefully
thawed. The reaction was then monitored periodically over a period
of several days. The reaction time was found to depend on the
amount of ethylene added. For reactions where 200 equiv was
added, complete conversion took 5 days at room temperature. See
below for NMR spectral information of the product.
B. Reaction of Ir(13CO)(dppe)I with AgPF6 in the Presence
of Ethylene. A resealable NMR tube was charged with AgPF6 (5.6
mg, 22 µmol) and Ir(13CO)(dppe)I (15 mg, 20 µmol) in the dark.
The NMR tube was connected to the vacuum line and evacuated.
After 0.5 mL of CD2Cl2 was vacuum transferred into the NMR
tube, ethylene was condensed into it at 77 K. The valve was closed,
and the solution was carefully thawed. The NMR tube was then
shaken vigorously. NMR spectral analysis after 30 min demon-
strated clean conversion to 6-13CO. Spectral information at room
temperature for complex 6-13CO: 1H NMR (CD2Cl2) δ 7.53-7.60
(overlapping, 12H, meta and para phenyl H’s), 7.50-7.45 (m, 8H,
ortho phenyl H’s), 2.93 (d with outer coupling, JP-H ) 16 Hz, 4H,
PCH2CH2P), 2.56 (b, 8H, ethylene); 31P{1H} NMR (CD2Cl2) δ 22.0
(b, 2P); 13C{1H} NMR (CD2Cl2) δ 166 (t, JP-C ) 62 Hz, CO).
Spectral information at -90 °C for complex 6-13CO: 1H NMR
(CD2Cl2) δ 7.44-7.57 (overlapping, 12H, meta and para phenyl
H’s), 7.43 (t, 4H, ortho phenyl H’s), 7.20 (t, 4H, ortho phenyl H’s),
3.08 (b, 2H, ethylene), 2.95 (d, JP-H ) 18 Hz, 2H, PCH2CH2P),
2.67 (d, JP-H ) 26 Hz, 2H, PCH2CH2P), 2.48 (b, 2H, ethylene),
2.20 (b, 2H, ethylene), 1.80 (b, 2H, ethylene); 31P{1H} NMR (CD2-
Cl2) δ 25.6 (dd, JP-P ) 9.8 Hz, JC-P ) 7.4 Hz, 1P, cis to CO),
19.7 (dd, JP-P ) 9.8 Hz, JC-P ) 131 Hz, 1P, trans to CO); 13C-
{1H} NMR (CD2Cl2) δ 166 (dd, JP-C ) 131 and 7.4 Hz, CO).
C. Isomerization of 1-Pentene Using 3a. A resealable NMR
tube was charged with 3a (10 mg, 3.7 µmol) and 0.6 mL of CD2-
Cl2. 1-Pentene (20 µL, 183 µmol, 50 equiv) was then added via
microliter syringe, and the NMR tube was sealed and shaken. The
NMR tube was then put into an agitator at room temperature and
monitored periodically for 1 week. After 5 days, the ratios of the
pentene isomers remained constant. After 1 week, the solvent and
pentene isomers were vacuum transferred into a round-bottom flask
and then analyzed by GC. The assignments of the isomers were
made by comparison to known standards. A 1H NMR spectrum of
the nonvolatile residue remaining in the original NMR tube
demonstrated the presence of an organic product consistent with
oligomerized 1-pentene.53
G. General Procedure for CO (or 13CO) Exchange with 3a
and 3b. Generation of [fac-IrR(CO)3(dppe)][BARF]2 Where R
) CH3 and CF3 (5a and 5b). Observation of Intermediates 5aq
and 5bq. A resealable NMR tube containing either complex 3a or
3b (5 µmol) and CD2Cl2 was freeze-pump-thawed three times.
The NMR tube was back-filled with CO at 77 K and then thawed
to room temperature. The reaction was periodically monitored over
the next day. Spectral information for complex 5a (100% conversion
by NMR): 1H NMR (CD2Cl2) δ 7.45-7.77 (overlapping, 44H,
phenyl, BARF), 3.54 (overlapping m, 2H, PCH2CH2P), 3.33
(overlapping m, 2H, PCH2CH2P), 0.34 (t, JP-H ) 6 Hz, 3H, Ir-
CH3); 31P{1H} NMR (CD2Cl2) δ 25.3 (s, 2P, JP-C trans for 13CO
reaction ) 93.8 Hz); IR (thin film) 2179 cm-1 (CO), overlapping
at 2142 cm-1 (CO). Spectral information for intermediate species
5aq (0 °C): 1H NMR (CD2Cl2) δ 8.02 (dd, Jmeta ) 1.5 Hz, Jortho
)
7.9 Hz, 1H, DIB), 7.43-7.90 (overlapping, 39H, phenyl, BARF),
7.36 (dd, Jmeta ) 1.2 Hz, Jortho ) 8.0 Hz, 1H, DIB), 7.31 (td, Jmeta
) 1.3 Hz, Jortho ) 7.5 Hz, 1H, DIB), 7.17 (td, Jmeta ) 1.6 Hz, Jortho
) 7.7 Hz, 1H, DIB), 3.45 (overlapping m, 2H, PCH2CH2P), 3.13
(overlapping m, 2H, PCH2CH2P), 0.61 (dd, JP-H ) 6.7 and 3.5
Hz, 3H, Ir-CH3); 31P{1H} NMR (CD2Cl2) δ 33.4 (unresolved P-P
coupling, 1P), 18.3 (unresolved P-P coupling, JC-P ) 7 Hz, 1P).
(52) For 5b, only approximately 10% of the product is formed by NMR.
The remainder of the material decomposes over time into numerous
unidentified species.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2107

Albietz et al.
D. General Procedure for Polymerization of Styrene and
(1S)-(-)-â-Pinene Using 3a or 3b. A 25 mL round-bottom flask
containing a stir-bar was charged with 4 mL of CH2Cl2 and (1S)-
(-)-â-pinene or styrene (1.27 mmol, 230 equiv). Either 3a or 3b
(5.5 µmol) was then added to the solution as a solid, resulting in
an exothermic reaction and eventually an orange-colored solution.
The solution was stirred for 10 min, and 1H NMR spectral analysis
confirmed consumption of the monomer (an NMR tube scale
reaction demonstrated complete consumption of the same number
of equivalents of the monomer in <3 min; reactions conducted using
more concentrated solutions were extremely exothermic). The
reaction mixture was then quenched with MeOH, resulting in
precipitation of a white solid. The solid was isolated on a frit
washing with MeOH. Typical yields were approximately 85% of a
white solid whose 1H NMR spectrum matched that reported in the
literature (poly-styrene54 and poly-â-pinene55). Reactions were also
conducted in a similar manner in the presence of 2,6-di-tert-
butylpyridine. When a large excess of base was employed,
polymerizations were expectedly slower and therefore necessitated
longer reaction times. After several hours, the reaction mixtures
were quenched with methanol and the polymer was isolated on a
frit washing well with methanol. The products were then purified
by passage through a silica gel column (1 in. diameter × 3 in.
length) eluting with CHCl3. Concentration of the appropriate
fractions yielded a white solid.
°C in an ice bath for 10 min. The ice bath was removed, and the
reaction mixture was stirred for an additional 1 h at room
temperature. The reaction mixture was then quenched with MeOH,
and the volatiles were removed in vacuo on a rotary evaporator
leaving an oil. The oil was dissolved in hexanes and filtered to
remove the iridium-containing species. Removal of the hexanes in
vacuo yielded approximately 1.5 g of a colorless, viscous oil whose
1H NMR spectrum matched that reported in the literature.44
F. General Procedure for Oligomerization of Norbornene
Using Complexes 3a and 3b. A 25 mL round-bottom flask
containing a stir-bar was charged with 6 mL of CH2Cl2 and
norbornene (120 mg, 1.3 mmol, 118 equiv). Either 3a or 3b (11
µmol) was then added to the solution as a solid. The reaction
mixture was stirred at room temperature for 2 days before quenching
with MeOH. After solvent evaporation, the resulting oil was
dissolved in CHCl3 and passed through a silica gel column (1 in.
diameter × 3 in. length). Concentration of the first yellow fraction
off the column yielded approximately 110 mg of a yellow oil whose
1H NMR spectrum matched that reported in the literature.42
G. General Procedure for Oligomerization of r-Methylsty-
rene Using 3a or 3b. The reaction was conducted in an NMR tube,
and the products were characterized spectroscopically. No material
was isolated from the reaction. A resealable NMR tube was charged
with 3a or 3b (5.7 µmol) and 0.5 mL of CD2Cl2. R-Methylstyrene
(285 µmol, 50 equiv) was then added via syringe resulting in an
exothermic reaction. After 5 min, a 1H NMR spectrum was obtained
and confirmed complete conversion of the monomer into a 1:1
(dimer:trimer) mixture whose 1H NMR spectrum matched that
reported in the literature.2
E. General Procedure for Polymerization of Isobutylene
Using Complexes 3a and 3b. A Schlenk flask containing a stir-
bar was cooled to -78 °C under a nitrogen atmosphere. Isobutylene
(1.5-2 mL) was condensed into the flask followed by slow addition
of 3 mL of CH2Cl2 via syringe. A second Schlenk flask containing
a solution of either 3a or 3b (5.5 µmol) in 1 mL of CH2Cl2 was
cannula transferred into the flask containing the isobutylene and
followed by washing with an additional 0.5 mL of CH2Cl2. The
reaction mixture was stirred at -78 °C for 15 min and then at 0
Acknowledgment. We thank the National Science Foun-
dation (Grant CHE-0092446) for support of this work and
Professors Robert Bergman, William Jones, and Frank Feher
for invaluable discussions regarding this chemistry.
(53) Peng, Y. X.; Cun, L. F.; Dai, H. S.; Liu, J. L. J. Polym. Sci. Part A:
Polym. Chem. 1996, 34, 903-906.
Supporting Information Available: Additional figures. This
material is available free of charge via the Internet at http://pubs.
acs.org..
(54) Hasebe, T.; Kamigaito, M.; Sawamato, M. Macromolecules 1996, 29,
6100-6103.
(55) Lu, J.; Kamigaito, M.; Sawamoto, M.; Higashimura, T.; Deng, Y.
Macromolecules 1997, 30, 22-26.
IC025506S
2108 Inorganic Chemistry, Vol. 41, No. 8, 2002