Stoichiometric C-C coupling reactions in the coordination sphere of an iridium(III) alkyl

Article abstract of DOI:10.1021/om049837j

An alkyl hydride α¹-acetone complex of iridium or its α-elimination product undergoes insertion into alkenes to give a carbene dihydride via a proposed pathway that involves C-C bond formation by a rare C(sp³)-C(sp³) reductive elimination followed by a double C-H activation. In MeCN solution, reversible α-elimination equilibrates this carbene dihydride insertion product with its MeCN adduct, an iridium alkyl hydride with diaster-eotopic trans triphenylphosphine ligands ( ²J_PP = 382 Hz). Alkynes also react, but they give a coupled η³-allyl complex via a proposed pathway that involves C-C bond formation by C(sp³)-C(sp²) reductive elimination. Crystal structures of key products are reported.

Full text of DOI:10.1021/om049837j

3378
Organometallics 2004, 23, 3378-3387
Articles
Stoich iom etr ic C-C Cou p lin g Rea ction s in th e
Coor d in a tion Sp h er e of a n Ir id iu m (III) Alk yl
Xingwei Li, Leah N. Appelhans, J ack W. Faller,* and Robert H. Crabtree*
Department of Chemistry, Yale University, 225 Prospect Street,
New Haven, Connecticut 06520-8107
Received March 4, 2004
An alkyl hydride η1-acetone complex of iridium or its R-elimination product undergoes
insertion into alkenes to give a carbene dihydride via a proposed pathway that involves
C-C bond formation by a rare C(sp3)-C(sp3) reductive elimination followed by a double
C-H activation. In MeCN solution, reversible R-elimination equilibrates this carbene
dihydride insertion product with its MeCN adduct, an iridium alkyl hydride with diaster-
eotopic trans triphenylphosphine ligands (2J PP ) 382 Hz). Alkynes also react, but they give
a coupled η3-allyl complex via a proposed pathway that involves C-C bond formation by
C(sp3)-C(sp2) reductive elimination. Crystal structures of key products are reported.
1. In tr od u ction
transition-metal complex is in general thermodynami-
cally more stable than that in a first- or second-row
complex.9 Probably for this reason, a previously pro-
posed mechanism for an iridium-catalyzed reaction of
alkene insertion into an activated aryl-H bond seems
to avoid the C-C reductive elimination step.8 Examples
of iridium-mediated stoichiometric C-C bond forming
reactions are also rather limited.10-13 Previously pro-
posed C-C reductive eliminations from Ir(III) usually
included at least one sp2 carbon, and most reports
involved vinyl-vinyl or vinyl-acyl reductive elimination
to form conjugated systems.6,10,11 C(sp)-C(sp2)10b and
C(sp2)-C(sp3)6a,12 reductive elimination from iridium are
already very rare; only a very few examples can be found
for the C(sp3)-C(sp3) case, and this C-C reductive
elimination is oxidatively promoted by single-electron
oxidation of the Ir(III) center.13
We recently reported the synthesis of trans-[(H)Ir-
(OCMe2)(CH2NMePy)(PPh3)2]BF4 (1) and its equilibra-
tion with trans-[(H)2Ir(dCHNMePy)(PPh3)2]BF4 (2) in
noncoordinating solvents via a reversible R-elimination
(Scheme 1).14 In a weakly coordinating or noncoordi-
nating solvent, both 1 and 2 can be regarded as direct
precursors to coordinatively unsaturated species, due
to the presence of the labile acetone ligand in 1 or the
possibility of the incoming ligand being accommodated
by a retro R-elimination in 2.
Iridium complexes have been widely used as catalysts,
for example, in hydrogenation,1 dehydrogenation,2 trans-
fer hydrogenation,3 and hydrosilation.4 However, progress
in iridium-catalyzed C-C bond-forming reactions lags
far behind, and only limited examples exist in iridium-
catalyzed allylic alkylation,5 cycloaddition,6 acylsilane
derivative formation,7 and alkene insertion into an
activated aryl-H bond.8 This is probably due to the
difficulty of C-C reductive elimination from an iridium-
(III) center, expected to be the last step of the catalytic
cycle, since the metal-carbon bond in a third-row
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10.1021/om049837j CCC: $27.50 © 2004 American Chemical Society
Publication on Web 06/05/2004

C-C Coupling in an Iridium(III) Alkyl
Organometallics, Vol. 23, No. 14, 2004 3379
Sch em e 1
Sch em e 2
Both this feature and the rarity of iridium catalysts
for C-C coupling led us to attempt an iridium-catalyzed
coupling reaction between 2-(dimethylamino)pyridine
(NMe2Py), the ligand precursor for 1 and 2, and the
alkene RCHdCH2, a possible incoming ligand for 1 and
2 (eq 1). This reaction is closely related to the well-
proceeded. Indeed, styrene reacts rapidly with 2 in CH2-
Cl2 at room temperature after 2 h to yield 3a (Scheme
2). The 1H NMR resonances (CD2Cl2) for 3a at δ -10.45
(td) and -17.52 (td) clearly indicated the presence of
two mutually coupled hydrides cis to the PPh3 ligands.
1
Both H and 13C NMR spectroscopy confirmed that only
one styrene unit is incorporated into the iridium system,
although excess styrene was present. Importantly, the
13C NMR spectrum (CD2Cl2) of 3a showed a very low
field signal at δ 273.5, which is characteristic of a
Fischer carbene. The trans orientation of the two PPh3
ligands is confirmed by the presence of a single peak in
the 31P NMR spectrum. The CH2CH2 unit in 3a also
shows a second-order AA′BB′ coupling pattern in the
1H NMR spectrum, as expected for the structure shown
in Scheme 2. 3a was also obtained in comparable yield
when 1 and styrene were heated in acetone under
reflux, albeit with a much lower reaction rate.
known Murai reaction, where a C(sp2)-H bond is acti-
vated with chelation assistance using a ruthenium cata-
lyst, followed by alkene insertion into the resulting Ru
aryl to yield a C-C coupling product.15 Here, we have
studied the insertion of alkenes and alkynes into alkyl
1 or carbene 2 to give stable Ir(III) insertion products.
In both cases, C-H activation and C-C reductive elimi-
nation are proposed as key steps in the formation of
these Ir(III) products. This work casts light on the rea-
sons for the failure of Murai catalysis in the iridium
system.
Unlike 2, 3a ,b failed to react with acetone to form
the analogue of 1, probably due to the lower reactivity
of the more stable Fisher carbenes stabilized by the
alkyl groups at the R-position. For the same reason, ex-
cess styrene failed to further react with 3a ,b, and at-
tempts to isolate other iridium(III) alkyl complexes from
dissolution of 3a ,b in pyridine, 2-(dimethylamino)pyri-
dine, or CH2Cl2 solutions of PPh3 were all unsuccessful.
However, when 3b was dissolved in the more strongly
ligating solvent CD3CN, 4-d3 was slowly formed at room
temperature. Interestingly, the alkyl complex 4-d3 is in
equilibrium with carbene complex 3b under these
conditions (eq 2). The [alkyl]/[carbene] ratio at equilib-
2. Resu lts a n d Discu ssion
2.1. Alk en e In ser tion in to 1 or 2. Attempted cata-
lytic coupling reactions between PyNMe2 and styrene,
1-hexene, allylbenzene, and vinyltriethoxysilane all fail-
ed in various solvents (acetone, CHCl3, THF, MeCN, and
PhCF3) under reflux conditions with 4 mol % loading of
1 or [Rh(COD)(PPh3)2]BF4. Stoichiometric reactions
were then performed to understand how far the reaction
1
rium was measured at 21-50 °C by H NMR spectro-
scopy. When ln Keq was plotted against T-1, the ther-
modynamic data were found to be ∆H° ) -30.8 kJ /mol
and ∆S° ) -112 J /(mol K) for eq 2 (R2 ) 0.9999, see
Experimental Section). Since the large entropy term
causes this equilibrium to shift toward 4 at lower
temperature, isolation of 4 was attempted after stirring
3b and MeCN for 2 days at 0 °C. 1H NMR spectroscopy
showed that the mixture is composed of 3b and 4 in a
ratio of 1:16, where the equilibrium was still not yet
established. Fortunately, this ratio allows readily dis-
cernible and interpretable 1H, 31P, and 13C NMR spectra
(15) (a) In Activation of Unreative Bonds and Organic Synthesis;
Murai, S., Ed.; Springer: Berlin, 1999. (b) Ritleng, V.; Sirlin, C.; Pfeffer,
M. Chem. Rev. 2002, 102, 1731. (c) Labinger, J . A.; Bercaw, J . E. Nature
2002, 417, 507. (d) Kakiuchi, F.; Chatani, N. Adv. Synth. Catal. 2003,
345, 1077. (e) Dyker, G. Angew. Chem., Int. Ed. 1999, 38, 169. (f) Lim,
Y.-G.; Kang, J .-B.; Kim, Y. H. J . Chem. Soc., Chem. Commun. 1996,
585. (g) Lim, Y.-G.; Lee, K.-H.; Koo, B. T.; Kang, J .-B. Tetrahedron
Lett. 2001, 42, 7609. (h) Chatani, N.; Asaumi, T.; Yorimitsu, S.; Ikeda,
T.; Kakiuchi, F.; Murai, S. J . Am. Chem. Soc. 2001, 123, 10935.
1
of 4, even though it cannot be isolated. In the H NMR
spectrum, the Ir-CH proton appeared as a multiplet

3380 Organometallics, Vol. 23, No. 14, 2004
Li et al.
activation product is of interest. This Ir(III) intermedi-
ate is susceptible to â-hydride elimination, but only the
R-elimination product is ever observed here, owing to
the presence of the R-N atom. A kinetic preference of
R- over â-elimination was reported before.18,19
In pathway b, one of the PPh3 ligands dissociates to
generate a vacant site, and this five-coordinate species
is trapped by an alkene, followed by alkene insertion
into one of the Ir-H bonds to give a linear or branched
Ir(III) alkyl species (only the linear species is shown in
Scheme 3), followed by PPh3 recoordination to give a
carbene alkyl hydride intermediate, with the alkyl cis
to the carbene. A migratory insertion20 of the alkyl into
the carbene generates an alkyl hydride, which may also
undergo R-elimination to lead to product 3. In this
pathway, no Ir(I) intermediate and no reductive elimi-
nation are involved.
We studied phosphine exchange between 3b and tris-
(p-fluorophenyl)phosphine to probe the possibility of
pathway b (eq 3). It is not appropriate to use 2 for this
at δ 3.94 and the hydride as a doublet of doublets at δ
-16.27 (2J PH ) 16.5 Hz, 2J PH ) 13.4 Hz). Upon decoup-
ling of 31P, the Ir-CH signal becomes a doublet of
doublets (3J HH ) 8.6 Hz, 3J HH ) 3.4 Hz) and the hydride
signal becomes a singlet. Diasterotopicity was noted for
all three CH2 groups of the CH2CH2CH2Ph chain. The
31P NMR spectrum of 4 showed an AB quartet pattern
2
1
(δ 17.41 and 9.20, J PP ) 382.1 Hz). H and 31P NMR
spectra show that we have a rare case of a pair of
inequivalent trans-PPh3 ligands that allows measure-
2
ment of the trans J PP; it is the chirality of the alkyl
ligand (Ir-C) that renders them diastereotopic.
Two pathways are possible for the formation of 3a ,b
from 2 and alkenes, as shown in Scheme 3. In path a,
retro R-elimination of 2 generates an alkyl ligand and
a vacant site, which is occupied by the incoming alkene
RCHdCH2, followed by alkene insertion into the hy-
dride to give either a linear or branched Ir(III) alkyl
species.15a,b Alkene or alkyne insertion is expected to
be much more favorable into hydride than into alkyl16
(Ir-CH2NMePy) unless hydride and alkene or alkyne
are trans to each other,17 unlikely in this case. The
disruption of the stable metallacycle during the alkyl
insertion that would be required here may make it even
less likely. The hydride insertion product is then pro-
posed to undergo a C-C reductive elimination to yield
an Ir(I) intermediate, which is expected to be stabilized
by the π-acceptor RCHdCH2. This Ir(I) intermediate
then undergoes a double C-H activation (oxidative
addition) of N(Me)CH2CH2R, as proposed by us14 and
others18 in similar systems. The alternative N-CH3
double C-H activation product was not observed, prob-
ably because it gives a less stable Fischer carbene,
although the (Me)NCH2CH2R group is sterically more
hindered. The fate of the product from the first C-H
study, because retro R-elimination of 2 accommodates
the incoming phosphine ligand to make an iridium(III)
tris(phosphine) species, which was directly observed
from 31P NMR spectroscopy when PPh3 was added to
the CH2Cl2 solution of 2. No such complication exists
for 3b, which is closely related to 2 in structure. We
believe that the rate of PPh3 dissociation in 3b would
be greater than or similar to that in 2 for both steric
(18) Examples of double C-H activation to form Fisher carbenes:
(a) Boutry, O.; Gutierrez, E.; Monge, A.; Nicasio, M. C.; Perez, P. J .;
Carmona, E. J . Am. Chem. Soc. 1992, 114, 7288. (b) Luecke, H. F.;
Arndtsen, B. A.; Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1996,
118, 2517. (c) Ho, V. M.; Watson, L. A.; Huffman, J . C.; Caulton, K. G.
New J . Chem. 2003, 27, 1446. (d) Carmona, E.; Paneque, M.; Poveda,
M. Dalton 2003, 21, 4022.
(19) (a) Schrock, R. R.; Shih, K.-Y.; Dobbs, D. A.; Davis, W. M. J .
Am. Chem. Soc. 1995, 117, 6609. (b) Seidel, S. W.; Schrock, R. R.; Davis,
W. M. Organometallics 1998, 17, 1058. (c) Schrock, R. R.; Seidel, S.
W.; Mo¨sch-Zanetti, N. C.; Shih, K.-Y.; O’Donoghue, M. B.; Davis, W.
M.; Reiff, W. M. J . Am. Chem. Soc. 1997, 119, 11876. (d) Puddephatt,
R. J .; Rendle, M. C.; Tipper, C. F. H. J . Organomet. Chem. 1984, 269,
305.
(20) Carbene migratory insertion into a metal-alkyl bond: (a)
Danopoulos, A. A.; Tsoureas, N.; Green, J . C.; Hursthouse, M. B. Chem.
Commun. 2003, 756. (b) Hoover, J . F.; Stryker, J . M. J . Am. Chem.
Soc. 1990, 112, 464. (c) Casty, G. L.; Stryker, J . M. Organometallics
1997, 16, 3083. (d) Zora, M.; Li, Y.; Herndon, J . W. Organometallics
1999, 18, 4429. (e) Albe´niz, A. C.; Espinet, P.; Manrique, R.; Pe´rez-
Mateo, A. Angew. Chem., Int. Ed. 2002, 41, 2363.
(16) (a) Ghosh, C. K.; Graham, W. A. G. J . Am. Chem. Soc. 1989,
111, 375. (b) Foo, T.; Bergman, R. G. Organometallics 1992, 11, 1811.
(c) Brookhart, M.; Lincoln, D. M. J . Am. Chem. Soc. 1988, 110, 8719.
(d) Brookhart, M.; Volpe, A. F.; Lincoln, D. M.; Horvath, I. T.; Millar,
J . M. J . Am. Chem. Soc. 1990, 112, 5634. (e) Brookhart, M.; Hauptman,
E.; Lincoln, D. M. J . Am. Chem. Soc. 1992, 114, 10394. (f) Matsubara,
T.; Koga, N.; Musaev, D. G.; Morokuma, K. Organometallics 2000, 19,
2318. (g) Matsubara, T.; Koga, N.; Musaev, D. G.; Morokuma, K. J .
Am. Chem. Soc. 1998, 120, 12692.
(17) Selnau, H. E.; Merola, J . E. Organometallics 1993, 12, 3800.

C-C Coupling in an Iridium(III) Alkyl
Organometallics, Vol. 23, No. 14, 2004 3381
Sch em e 3
and electronic reasons. The CH2CH2CH2Ph substituent
should promote PPh3 dissociation sterically, as expected
in a dissociative mechanism for d6 octahedral systems.
Electronically, the -CH2CH2CH2Ph group makes the
iridium center slightly more electron rich, a factor that
should also kinetically favor PPh3 dissociation. A 31P
NMR spectroscopic study (161.91 MHz) of 3b and 10
equiv of tris(p-fluorophenyl)phosphine in CH2Cl2 showed
that only 4% of 3b underwent ligand exchange at 21 °C
then be expected, instead of a mixed bis(phosphine)
species. We therefore prefer path a.
Allylbenzene (PhCH2CHdCH2) also undergoes the
same type of insertion into 2 to give 3b (91%) in CH2-
Cl2 with an excess (8 equiv) of allylbenzene. In the
course of the reaction, trans-PhCHdCHMe, the isomer-
1
ization product from allylbenzene, was detected by H
NMR spectroscopy. Control experiments showed that
the product 3b failed to catalyze the isomerization of
allylbenzene (10 mol % 3b , 21 °C, CH2Cl2, 4 h). The
trans-PhCHdCHMe product is proposed to arise from
the â-hydride elimination of the branched IrIII-CH-
(CH3)CH2Ph intermediate. The C-C reductive elimina-
tion pathway of this branched intermediate must be
very slow compared with that of the linear Ir(III) alkyl,
since no final corresponding Fisher carbene derived from
the branched Ir(III) alkyl intermediate was detected in
1H NMR spectroscopy. This result is in good agreement
with mechanistic studies on the ruthenium-catalyzed
Murai reaction, where an alkene inserts into a hydride
to reversibly lead to both branched and linear Ru(II)
after 2 h to give free PPh3 and the mono(phosphine)
2
exchange product (AB quartet, δ 16.94, 19.52, J PP
)
286 Hz). After 12 h, 32% of 3b underwent ligand
exchange and the double phosphine exchange product
(δ 16.57) started to be observable. The rate of phosphine
exchange between 3b and tris(p-fluorophenyl)phosphine
is much lower than that of the reaction between 2 and
styrene (75 min, 21 °C, >97% conversion of 2, see
Experimental Section), thus ruling out path b. The
phosphine exchange experiment also suggests that
dissociation of the chelating pyridine ligand of 3b is not
likely either, because a tris(phosphine) complex would

3382 Organometallics, Vol. 23, No. 14, 2004
Li et al.
Sch em e 4
Sch em e 5
1
The hydride region of 6a or 6b in the H NMR spectra
showed one hydride signal as a doublet of doublets, due
to the coupling to two phosphorus atoms in different
environments, while the 31P{1H} NMR spectrum showed
two peaks with essentially equal intensity. These ob-
servations indicate that the two PPh3 ligands are not
intermediates, but only the linear alkyl ligand is further
coupled to the aryl to yield the corresponding product.15a
Previous reports of C-C reductive elimination from
iridium usually involved Ir-C(sp2) or Ir-C(sp),6,10-12
and the surprisingly low barrier for the C-C reductive
elimination here is probably due to the formation of an
Ir(I) intermediate greatly stabilized by excess alkene
and possibly by the subsequent formation of stable cyclic
Fischer carbenes.
2.2. Rea ction betw een a n En on e a n d 1. Methyl
vinyl ketone, significantly different from a terminal
alkene electronically, also reacts with 1 or 2 in acetone
under reflux conditions. Unlike 3, product 5 does not
come from a formal insertion but from the â-C-H
activation of CH2dCHC(O)Me with loss of H2 (Scheme
4). In 5, the newly formed iridacycle is essentially an
iridafuran, owing to the resonance stabilization shown
in Scheme 4. For 5, a very low field doublet signal at δ
10.76 (IrdCHCH) in the 1H NMR spectrum and a triplet
at δ 197.3 (2J PC ) 9.0 Hz, IrdCH) in the 13C NMR
spectrum are both characteristic of the presence of
carbene character in the iridafuran. The Ir-CH2 signal
appears as a triplet (3J PH ) 12.4 Hz), due to the coupling
to two equivalent phosphorus atoms, and the trans
orientation of the two PPh3 ligands also follows from
the single peak in the 31P NMR spectrum. The 1H NMR
spectrum does not show any hydride resonances. The
X-ray crystal analysis confirmed the structure of 5
(Figure 2). Iridafurans are known to be formed through
direct C-H activation.21
1
equivalent. In the H NMR spectrum (CD2Cl2) of 6b, a
3
3
signal at δ 6.24 (dd, J HH ) 12.2 Hz, J HH ) 4.5 Hz,
H-8) is coupled to two different protons: one resonance
3
3
at δ 5.48 (dd, J PH ) 9.6 Hz, J HH ) 4.5 Hz, H-7) and
the other at δ 3.84 (dd, 3J HH ) 12.2, 3J PH ) 7.2 Hz, H-9).
These H-H coupling patterns are consistent with the
presence of an η3-allyl ligand: the 4.5 Hz coupling
constant between H-7 and H-8 is typical for a syn
coupling on an η3-allyl ligand, while the 12.2 Hz one
between H-8 and H-9 is typical for a anti coupling.
3
These J HH coupling constants between H-7, H-8, and
H-9 were determined from 31P-decoupled 1H NMR
spectra, where the H-7 and H-9 signals became doublets
and Ir-H became a singlet. Confirmation of the assign-
ments of H-7 and H-9 for 6b was made by comparison
1
with the H NMR spectrum of 6a , where H-9 (δ 2.84,
m) is further coupled to the two proximal diastereotopic
1
protons in CH2CH2CH2CH3. 13C and H NMR spectra
of 6a ,b are too complicated to allow secure assignment,
and structure elucidation was carried out by an X-ray
crystal analysis of 6b (Figure 3). The internal alkyne
diphenylacetylene also reacts with 1 or 2 to give the
analogous complex 6c. 6a -c all failed to react with CO,
PPh3, and excess PhCtCH, which indicates the dif-
ficulty of η3 to η1 conversion of the allyl ligand, owing
to the tethering effect of the pyridine ligand.
It is well-known that terminal alkynes (RCtCH)
insert into metal hydrides to form vinyl complexes. The
mechanism behind this apparent insertion could be
much more complicated, however. At least three types
of mechanisms were previously proposed (Scheme 6):
(a) a direct metal hydride insertion into an alkyne to
afford a vinyl ligand,22 (b) a concerted intraligand 1,2-
hydrogen shift in the RCtCH unit to yield a vinylidene
ligand, followed by a hydride insertion, where the
hydride behaves as a spectator for this rearrangement,23
or (c) a RCtCH oxidative addition to the metal followed
by a 1,3-hydrogen shift from the metal to the ligand to
A likely mechanism for the formation of 5 involves
the substitution of the acetone ligand in 1 by the â-C-H
bond of CH2dCHC(O)Me to form an agostic intermedi-
ate, followed by a C-H breaking to give a Ir(III)
dihydrogen complex. The pendant carbonyl group might
substitute the dihydrogen ligand to give 5. No H2
acceptor was used in this reaction, since only 1 equiv of
CH2dCHC(O)Me was provided, and molecular hydrogen
is proposed to be a coproduct; this is thermodynamically
feasible, probably owing to the formation of a stable
iridafuran.
(22) The initially formed metal vinyl complexes are cis with respect
to metal and hydrogen, but they can rearrange to the trans isomers
probably via η2-vinyl intermediates.4a,b
2.3. Alk yn e In ser tion in to 1. Terminal alkynes
RCtCH (R ) Bu, Ph) react with 1 in acetone or 2 in
CH2Cl for 10 h to afford 6a ,b in high yields (Scheme 5).
(23) (a) Li, X.; Incarvito, C. D.; Crabtree, R. H. J . Am. Chem. Soc.
2003, 125, 3698. (b) Silvestre, J .; Hoffmann, R. Helv. Chim. Acta 1985,
68, 1461. (c) Wakatsuki, Y.; Koga, N.; Yamazaki, H.; Morokuma, K. J .
Am. Chem. Soc. 1994, 116, 8105. (d) Cadierno, V.; Gamasa, M. P.;
Gimeno, J .; Pe´rez-Carren˜o, E.; Garc´ıa-Granda, S. Organometallics
1999, 18, 2821. (e) Akita, M.; Ishii, N.; Takabuchi, A.; Tanaka, M.;
Moro-oka, Y. Organometallics 1994, 13, 258. (f) De Angelis, F.;
Sgamellotti, A.; Re, N. Organometallics 2002, 21, 2715.
(21) (a) Bleeke, J . R.; New, P. R.; Blanchard, J . M. B.; Haile, T.;
Rohde, A. M. Organometallics 1995, 14, 5127. (b) Castarlenas, R.;
Esteruelas, M. A.; Mart´ın, M.; Oro, L. A. J . Organomet. Chem. 1998,
564, 241.

C-C Coupling in an Iridium(III) Alkyl
Organometallics, Vol. 23, No. 14, 2004 3383
Sch em e 6
Sch em e 7
form a vinylidene, followed by another insertion of this
vinylidene into the M-H bond to yield a vinyl ligand, a
route in which the hydrides on the metal are not
spectators.24 In paths b and c, the well-known alkyne
to vinylidene rearrangement is involved.25
The mechanism was better understood by a deuter-
ium labeling experiment involving 1 equiv of PhCtCD
and 1. Comparison of the 1H NMR spectrum of this
product with that of 6b shows that deuterium scrambles
extensively, with 9% present at Ir-H, 14% at H-9, 30%
at H-8, 36% at H-6, and 12% at H-7. This result makes
paths a and b unlikely, because no deuterium scram-
bling is expected. In contrast, in path c, the hydride is
not a spectator and naturally leads to the scrambling
of the deuterium to the H-8 and H-9 positions. Since
the deuterium also scrambles to other positions, the
mechanism must be more complex, and a plausible
sequence is proposed in Scheme 7. C-H oxidative addi-
tion of RCtCH to this electron-rich Ir(III) could afford
an Ir(V) or an Ir(III) dihydrogen intermediate 7.25,26 At
this stage, either the H or D on the Ir can undergo a
1,3-shift to give a vinylidene followed by a hydride/
deuteride insertion to form a D-scrambled vinyl ligand.24a
By analogy with previous reports,26,28 7 can also be in a
rapid equilibrium with 8, an agostic Ir(III) intermediate,
leading to the deuterium scrambling into both methyl
groups (N(CH3)2). Reductive elimination of the vinyl and
the D-scrambled alkyl in 9 could afford an Ir(I) species
similar to the Ir(I) intermediate in Scheme 3. A C-H
or C-D activation of this Ir(I) could afford a stable Ir-
(III) allyl compound with deuterium fully scrambled.
(24) (a) Esteruelas, M. A.; Oro, L. A.; Valero, C. Organometallics
1995, 14, 3596. (b) De los R´ıos, I.; Tenorio, M. J .; Puerta, M. C.; Valerga,
P. J . Am. Chem. Soc. 1997, 119, 6529. (c) Wakatsuki, Y.; Koga, N.;
Werner, H.; Morokuma, K. J . Am. Chem. Soc. 1997, 119, 360. (d) Garcia
Alonso, F. J .; Hoehn, A.; Wolf, J .; Otto, H.; Werner, H. Angew. Chem.
1985, 97, 401.
(26) Ng, S. M.; Lam, W. H.; Mak, C. C.; Tsang, C. W.; J ia, G.; Lin,
Z.; Lau, C. P. Organometallics 2003, 22, 641.
(27) (a) Ge´rard, H.; Eisenstein, O.; Lee, D.-H.; Chen, J .; Crabtree,
R. H. New J . Chem. 2001, 25, 1121. (b) Albeniz, A. C.; Schulte, G.;
Crabtree, R. H. Organometallics 1992, 11, 242.
(28) Crabtree, R. H.; Holt, E. M.; Lavin, M.; Morehouse, S. M. Inorg.
Chem. 1985, 24, 1986.
(25) Reviews: (a) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999,
32, 311. (b) Bruce, M. I. Chem. Rev. 1991, 91, 197.

3384 Organometallics, Vol. 23, No. 14, 2004
Li et al.
Ta ble 3. Selected Bon d Len gth s a n d An gles for
Ta ble 1. Cr ysta llogr a p h ic Da ta for 3b, 5, a n d 6b
Com p lex 5
3b
5
6b
Bond Lengths (Å)
empirical formula
C
52H50BF4Ir-
N2P2
C
50H50BF4Ir-
N2O2P2
C
52H47BCl2-
F4IrN2P2
Ir(1)-P(1)
Ir(1)-P(2)
Ir(1)-O(1)
Ir(1)-N(1)
Ir(1)-C(6)
Ir(1)-C(8)
N(2)-C(1)
2.353(2)
N(2)-C(6)
N(2)-C(7)
O(1)-C(10)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
1.464(11)
1.475(11)
1.289(12)
1.338(13)
1.39(1)
2.361(2)
2.157(6)
2.097(6)
2.061(9)
2.025(9)
1.323(12)
mol wt
radiation, λ (Å)
T (°C)
cryst syst
space group
1043.95
Mo KR (monochromated), 0.710 69 Å
-90 -90
orthorhombic orthorhombic monoclinic
1051.93
1111.83
-90
Pbca (No.
P21212 (No.
P21/c (No.
1.50(2)
61)
18)
14)
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
23.3215(5)
16.2968(4)
24.1017(5)
90
9160.2(2)
8
20.9409(6)
20.9291(9)
10.2731(3)
90
4502.4(2)
4
13.6505(3)
15.9723(4)
21.6001(6)
91.028(1)
4708.7(2)
4
Bond Angles (deg)
P(1)-Ir(1)-P(2)
N(1)-Ir(1)-C(6)
Ir(1)-C(6)-N(2)
Ir(1)-C(8)-C(9)
177.18(9)
79.8(3)
109.3(6)
116.7(7)
Ir(1)-O(1)-C(10)
C(8)-C(9)-C(10)
O(1)-C(10)-C(9)
111.9(6)
115.3(9)
119.3(9)
Dcalcd (g cm-3
)
1.514
30.47
1.552
31.04
1.568
30.79
µ(Mo KR) (cm-1
)
Ta ble 4. Selected Bon d Len gth s a n d An gles for
Com p lex 6b
cryst size (mm)
0.05 × 0.05 × 0.12 × 0.12 × 0.12 × 0.17 ×
0.14 0.19 0.17
total, unique no. of 49 576, 11 335 13 640, 9603 32 059, 10 730
rflns
Bond Lengths (Å)
Ir(1)-P(1)
Ir(1)-P(2)
Ir(1)-N(1)
Ir(1)-C(7)
Ir(1)-C(8)
Ir(1)-C(9)
2.362(1)
2.297(1)
2.181(4)
2.184(5)
2.183(5)
2.345(5)
N(2)-C(1)
N(2)-C(6)
N(2)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
1.355(7)
1.470(7)
1.449(7)
1.421(7)
1.398(7)
1.498(7)
Rint
0.094
0.043
4441
0.052
6152
no. of observns used 4336
no. of params,
restrictions
559, 0
560, 0
550, 0
R,a Rw
0.027; 0.028
0.67
0.038; 0.042
1.15
0.032; 0.033
0.92
b
GOF
min, max resid
-0.70, 0.64
-0.96, 1.69
-0.80, 0.59
Bond Angles (deg)
dens (e Å -3
)
P(1)-Ir(1)-P(2)
107.99(5)
N(1)-Ir(1)-C(7)
76.9(2)
a
b
R ) ∑||Fo| - |Fc||/ ∑|Fo|, for all I > 3σ(I). Rw ) [∑w(|Fo| -
2
1/2
|Fc|)2/∑wFo
] .
Ta ble 2. Selected Bon d Len gth s a n d An gles for
Com p lex 3b
Bond Lengths (Å)
Ir(1)-P(1)
Ir(1)-P(2)
Ir(1)-N(1)
Ir(1)-C(6)
2.300(2)
2.317(2)
2.140(8)
2.020(8)
N(2)-C(1)
N(2)-C(6)
N(2)-C(16)
1.397(8)
1.348(8)
1.469(8)
Bond Angles (deg)
P(1)-Ir(1)-P(2)
N(1)-Ir(1)-C(6)
164.51(5)
77.6(2)
Ir(1)-C(6)-N(2)
Ir(1)-C(6)-C(7)
115.8(4)
125.5(6)
Cases where hydride is not a spectator in an alkyne to
vinylidene rearrangement are rather rare, and most
studies have been theoretical.23,24
3. Cr ysta l Str u ctu r es of 3b, 5, a n d 6b
Single crystals of 3b, 5, and 6b suitable for X-ray
diffraction analysis were obtained by slow diffusion of
diethyl ether into CH2Cl2 solutions. X-ray diffraction
data for single crystals was measured on a Nonius
Kappa CCD diffractometer. Data collection was carried
out at -90 °C, using graphite-monochromated Mo KR
radiation (λ ) 0.710 69 Å). The crystal parameters and
other experimental details of the data collection are
summarized in Table 1. A complete list of the details of
the crystallographic analysis in given in Supporting
Information. Metrical data for 3b, 5, and 6b are given
in Tables 2-4, respectively.
The structure determination of 3b was straightfor-
ward, and the space group was determined from the
systematic absences. The cell for 5 had two similar
distances, which suggested the possibility of a tetragonal
system; however, Rint was ∼0.33 for this system. The
ultimate solution of the structure showed that the space
group was the fairly unusual P21212, which only con-
tains one enantiomer. The correct enantiomer for the
crystal chosen was determined by inverting the coordi-
nates, which gave R ) 0.057 and Rw ) 0.067 versus that
F igu r e 1. ORTEP diagram of the cation of 3b, showing
50% probability ellipsoids. The hydrides are shown in
calculated positions.
for the correct enantiomer of R ) 0.038 and Rw ) 0.042.
The structure for 6b contained a disordered methylene
chloride. A suitable model for the disorder was difficult
to obtain, and the program SQUEEZE in the program
PLATON29,30 was used to correct for the residual density
from methylene chloride.
An X-ray single-crystal study of 3b reveals its octa-
hedral structure (Figure 1): the Ir-C-N-C-N unit
defines a plane perpendicular to the P-Ir-P axis. The
Ir-CR distance of 2.020 Å is consistent with predomi-
nant single-bond character, while the CR-N bond
distance of 1.348 Å indicates substantial multiple-bond
character, as expected from the resonance form gener-
ally preferred by Fischer carbenes (Scheme 3). Planar
geometry about the carbene carbon and π-π stacking
(29) Spek, A. L. J . Appl. Crystallogr. 2003, 36, 7.
(30) Vandersluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46,
194.

C-C Coupling in an Iridium(III) Alkyl
Organometallics, Vol. 23, No. 14, 2004 3385
between them. The ipso carbon in each PPh3 ligand is
no longer a virtual triplet, as in the case for 3a ,b and 5
(see Experimental Section). The reduced P-Ir-P bond
2
angle results in a small J PP and a suppressed virtual
coupling, and this is also consistent with a cis triphen-
ylphosphine arrangement in solution.
4. Exp er im en ta l Section
All reactions were carried out under argon, although most
of the products proved to be air stable. Acetone was used
without any treatment. PhCHdCH2, PhCtCH, nBuCtCH,
PhCtCPh, PhCtCD, methyl vinyl ketone, and PhCH2CHd
CH2 were purchased from Aldrich without purification. 1H and
13C NMR spectra were recorded on Bruker 400 or 500
spectrometers. 31P NMR spectra were recorded on Bruker 400
spectrometers with an external 85% H3PO4 standard. Elemen-
tal analyses were performed at Atlantic Microlabs.
4.1. tr a n s-Dih yd r id obis(tr ip h en ylp h osp h in e)(1-(m eth -
yl(2-pyr idyl)am in o)-3-ph en ylpr op-1-yliden e-N,C)ir idiu m -
(III) Tetr a flu or obor a te (3a ). To a Schlenk tube charged with
2 (150 mg, 0.162 mmol) and CH2Cl2 (3 mL) was added styrene
(102 mg, 0.973 mmol) via syringe. The light yellow solution
was stirred for 2 h at 21 °C and was then concentrated to ca.
0.5 mL under reduced pressure, followed by slow addition of
diethyl ether (15 mL). A light yellow precipitate appeared and
was filtered and washed with diethyl ether (2 × 15 mL).
Analytically pure 3a was obtained by drying under vacuum
F igu r e 2. ORTEP diagram of the cation of 5, showing 50%
probability ellipsoids.
1
overnight. Yield: 145 mg (0.141 mmol, 87%). H NMR (CD2-
3
Cl2, 500 MHz, 293 K): δ 7.90 (d, J HH ) 5.4 Hz, 1H, Py), 7.86
3
3
(t, J HH ) 7.5 Hz, 1H, Py), 7.67 (d, J HH ) 8.5 Hz, 1H, Py),
7.40 (m, 30H, PPh3), 7.19 (t, 3J HH ) 7.5 Hz, 2H, -CH2Ph), 7.13-
3
3
(t, J HH ) 7.5 Hz, 1H, -CH2Ph), 6.69 (t, J HH ) 6.0 Hz, 1H,
3
Py), 6.64 (d, J HH ) 7.2 Hz, 2H, CH2Ph), 3.26 (s, 3H, NCH3),
2
2.50 (m, 2H, CH2), 1.74 (m, 2H, CH2), -10.45 (td, J PH ) 20.9
3
2
Hz, J HH ) 5.1 Hz, 1H, Ir-H), -17.52 (td, J PH ) 16.3 Hz,
3J HH ) 5.1 Hz, Ir-H). 13C{1H} NMR (CD2Cl2, 125.8 MHz, 293
K): δ 273.5 (s, IrdC), 160.0 (s), 154.8 (s), 141.1 (s), 140.4 (s),
133.8 (virtual t, 5.9 Hz, Ph3P), 133.6 (virtual t, 28.4 Hz, ipso-
Ph3P), 131.4 (s, PPh3), 129.3 (virtual t, 5.4 Hz, Ph3P), 129.2
(s), 128.8 (s), 127.0 (s), 123.5 (s), 115.3 (s), 49.6 (s, CH2), 39.2
(s, CH2), 37.7 (s, CH3). 31P{1H} NMR (acetone-d6, 161.9 MHz,
273 K): δ 19.2 (s). Anal. Calcd for C51H48BF4IrN2P2: C, 59.48;
H, 4.70; N, 2.72. Found: C, 59.35; H, 4.76; N, 2.72.
F igu r e 3. ORTEP diagram of the cation of 6b, showing
50% probability ellipsoids. Only the ipso carbons on the
triphenylphosphines are shown for clarity.
NMR Sp ectr oscop ic Stu d ies of th e Ra te of th e F or m a -
tion of 3a . In an NMR tube, 2 (20.0 mg, 0.0216 mmol) and
styrene (8 µL, 0.070 mmol) were dissolved in CD2Cl2 (0.7 mL).
1
31P and H NMR spectroscopic analysis at 21 °C showed that
the conversion of 2 was 47.9%, 72.0%, and >97% after 10, 20,
between PhCH2CH2CH2- and PPh3 were also observed
in 3b. These results are comparable to those for an
analogue of 3b in our previously published work.1
Complex 5 is also octahedral, with the N atom in the
pyridine ring trans to the iridafuran carbene/vinyl
carbon, a high trans-effect ligand (Figure 2). The
electron density in the iridafuran is essentially delocal-
ized, as indicated by the presence of the two similar
C-C bond distances (1.34 and 1.39 Å) in the iridafuran.
The Ir-C bond (2.025 Å) in the iridafuran is predomi-
nantly a single bond, as can be seen by comparison with
the Ir-CH2 single bond (2.061 Å).
Complex 6b has a distorted-octahedral shape (Figure
3). The trihapticity of the η3-allyl ligand follows from
the bond distances (Ir-C7 ) 2.184 Å, Ir-C8 ) 2.183 Å,
and Ir-C9 ) 2.345 Å). It is also clear that H-C8 is anti
to H-C9 but syn to H-C7, which is consistent with data
from 1H NMR spectroscopy. The PPh3 ligands are in
different environments, and the P-Ir-P angle is 108°,
which results in very small coupling (2J PP ) 5.9 Hz)
and 75 min, respectively.
4.2. tr a n s-Dih yd r id obis(tr ip h en ylp h osp h in e)(1-(m eth -
yl(2-p yr id yl)a m in o)-4-p h en ylbu t-1-ylid en e-N,C)ir id iu m -
(III) Tetr a flu or obor a te (3b). 3b was synthesized through
a method directly analogous to that for 3a by reacting 2 (137
mg, 0.148 mmol) and allylbenzene (140 mg, 1.19 mmol) in CH2-
Cl2 (3 mL) for 2 h at 21 °C. Yield: 140 mg (0.134 mmol, 91%).
The ethereal solutions were combined, and the ether was
removed carefully under reduced pressure. A light yellow oily
residue (103 mg) was obtained, whose 1H NMR spectrum
shows that the oily residue is a mixture of allylbenzene and
trans-1-phenylpropene in a ratio of 3.5:1. 1H NMR (CD2Cl2,
3
500 MHz, 293 K): δ 7.90 (d, J HH ) 4.5 Hz, 1H, Py), 7.87 (t,
3J HH ) 8.0 Hz, 1H, Py), 7.61 (d, 3J HH ) 7.5 Hz, 1H, Py), 7.20-
3
7.42 (m, 33H, 30 PPh3 + 3 CH2Ph), 6.90 (d, J HH ) 6.9 Hz,
2H, CH2Ph), 6.70 (t, 3J HH ) 6.2 Hz, 1H, Py), 3.15 (s, 3H, NCH3),
3
2.32 (t, J HH ) 7.1 Hz, 2H, CH2CH2CH2), 1.79 (m, 2H, CH2-
CH2CH2), 1.40 (quint, 7.2 Hz, 2H, CH2CH2CH2), -10.49 (td,
3
2
2J PH ) 20.8 Hz, J HH ) 5.3 Hz, 1H, Ir-H), -17.75 (td, J PH
)
15.9 Hz, J HH ) 5.4 Hz, Ir-H). 13C{1H} NMR (CDCl3, 100.6
MHz, 293 K): δ 271.6 (s, IrdC), 159.4 (s), 153.4 (s), 140.9 (s),
3

3386 Organometallics, Vol. 23, No. 14, 2004
Li et al.
3
3
140.0 (s), 133.0 (virtual t, 6.0 Hz, Ph3P), 132.7 (virtual t, 28.1
Hz, ipso-Ph3P), 130.5 (s), 128.4 (virtual t, 5.2 Hz, Ph3P), 126.0
(s), 122.4 (s), 122.4 (s), 123.5 (s), 115.6 (s), 46.8 (s, CH2CH2-
CH2), 36.9 (s, NCH3), 35.2 (s, CH2CH2CH2), 31.1 (s, CH2CH2-
CH2). 31P{1H} NMR (CDCl3, 161.9 MHz, 273 K): δ 19.8 (s).
Anal. Calcd for C52H50BF4IrN2P2: C, 59.83; H, 4.83; N, 2.68.
Found: C, 59.56; H, 4.95; N, 2.92.
Ir-CHdCH), 6.28 (t, J HH ) 7.5 Hz, 1H, py), 5.19 (d, J HH
)
3
8.8 Hz, 1H, Py), 4.74 (t, J PH ) 12.4 Hz, 2H, Ir-CH2), 2.18 (s,
3H, NCH3), 1.25 (s, 3H, C(O)CH3). 13C{1H} NMR (CD2Cl2,
125.8 Hz, 293 K): δ 213.2 (s, C(O)Me), 197.3 (t, 9.0 Hz, Ir-
CHdCH), 160.6 (s), 147.4 (s), 139.3 (s), 138.1 (s), 135.0 (virtual
t, 4.9 Hz, PPh3), 131.5 (s), 128.9 (virtual t, 4.8 Hz, PPh3), 127.8
(virtual t, 26.5 Hz, ipso-PPh3), 112.3 (s), 108.3 (s), 37.4 (s,
NCH3), 24.8 (s, C(O)CH3), 19.3 (t, 6.7 Hz, Ir-CH2). 31P{1H}
NMR (CD2Cl2, 161.9 MHz, 273 K): δ 7.0 (s). Anal. Calcd for
C47H44BF4IrN2OP2: C, 56.80; H, 4.46; N, 2.82. Found: C, 56.60;
H, 4.66; N, 2.87.
4.3. Obser va tion of 4 in th e Rea ction betw een 3b a n d
MeCN or CD3CN. In a Schlenk tube, 3b (100 mg, 0.096 mmol)
was dissolved in acetonitrile (4 mL) to give a light yellow or
colorless solution. This solution was stirred at 0 °C for 50 h,
followed by removal of acetonitrile under reduced pressure (ca.
0.1 mmHg) at 0 °C. A light yellow powder (102 mg) was
obtained, giving 1H NMR signals consistent with a mixture of
4.6. Hyd r id obis(tr ip h en ylp h osp h in e)(3-bu tyl-1-((2-p y-
r id yl)m eth yla m in o)a llyl-C,C′,C′′,N)ir id iu m (III) Tetr a flu -
or obor a te (6a ). To a Schlenk tube charged with 1 (215 mg,
0.219 mmol) and acetone (8 mL) was added 1-hexyne (18 mg,
0.219 mmol) via syringe. The colorless solution was then
refluxed for 6 h to give a yellow solution, which was then
concentrated to ca. 0.5 mL under reduced pressure, followed
by addition of diethyl ether (15 mL). A light yellow precipitate
appeared and was filtered and washed with diethyl ether (2
× 15 mL). Analytically pure 6a was obtained by recrystalli-
zation using CH2Cl2 and diethyl ether. Yield: 182 mg (0.180
mmol, 82%). 1H NMR (CD2Cl2, 500 MHz, 293 K): δ 7.1-7.5
(m, 32H, 30 PPh3 + 2 Py), 5.92 (d, J HH ) 8.7 Hz, 1H, Py),
5.84 (td, J HH ) 6.6 Hz, J HH ) 1.0 Hz, 1H, Py), 5.51 (dd, J HH
) 11.4 Hz, J HH ) 4.5 Hz, 1H, H-8), 5.27 (q, J HH ) 5.4 Hz,
3J PH ) 5.4 Hz, 1H, H-7), 2.84 (m, 1H, H-9), 2.75 (s, 3H,
N-CH3), 1.4 (m, 3H, diastereotopic CH2CH2CH2CH3 + CH2CH2-
CH2CH3), 1.0 (m, 2H, CH2CH2CH2CH3), 0.75 (m, 1H, diaster-
1
3b and 4 in a ratio of 1:16. Data for 4 are as follows. H NMR
(500 MHz, CD3CN, 273 K): δ 7.72 (d, 3J HH ) 5.6 Hz, 1H), 7.20-
3
3
7.55 (m, H), 7.14 (t, J HH ) 7.2 Hz, 1H), 6.88 (d, J HH ) 7.2
3
3
Hz, 2H), 6.24 (t, J HH ) 5.6 Hz, 1H), 5.84 (d, J HH ) 8.8 Hz,
1H), 3.94 (m, 1H, Ir-CH), 2.31 (s, 3H, N-CH3), 1.96 (s, CH3-
CN-Ir), 1.84 (ddd, J HH ) 14.0 Hz, J HH ) 10.8 Hz, J HH
3
3
3
)
5.2 Hz, diastereotopic CH2CH2CH2Ph), 1.44-1.58 (m, 3H, CH2-
CH2CH2Ph + CH2CH2CH2Ph), 1.24 (m, 1H, diastereotopic
CH2CH2CH2Ph), 1.09 (m, 1H, diastereotopic CH2CH2CH2Ph),
2
2
-16.27 (dd, J PH ) 16.5 Hz, J PH ) 13.4 Hz, 1H, Ir-H). 1H-
3
{31P} NMR (400 MHz, CD3CN, 273 K): δ 7.72 (d, J HH ) 5.6
3
3
4
3
3
3
3
Hz, 1H), 7.20-7.55 (m, H), 7.14 (t, J HH ) 7.2 Hz, 1H), 6.88
3
3
(d, J HH ) 17.2 Hz, 2H), 6.24 (t, J HH ) 5.6 Hz, 1H), 5.84 (d,
3J HH ) 8.8 Hz, 1H), 3.94 (dd, J HH ) 8.6 Hz, J HH ) 3.4 Hz,
3
3
1H, Ir-CH), 2.31 (s, 3H, N-CH3), 1.96 (s, CH3CN-Ir), 1.84
3
3
3
3
(ddd, J HH ) 14.0 Hz, J HH ) 10.8 Hz, J HH ) 5.2 Hz,
diastereotopic CH2CH2CH2Ph), 1.44-1.58 (m, 3H, CH2CH2-
CH2Ph + CH2CH2CH2Ph), 1.24 (m, 1H, diastereotopic CH2CH2-
CH2Ph), 1.09 (m, 1H, diastereotopic CH2CH2CH2Ph), -16.27
(s, 1H, Ir-H). 13C NMR (125.77 MHz, CD3CN, 273 K): δ 161.9
(s), 147.4 (s), 143.6 (s), 138.1 (s), 134.9 (dd, 10.0 Hz, 1.0 Hz,
PPh3), 134.4 (dd, 9.5 Hz, 1.1 Hz, PPh3), 132.2 (dd, 46.3 Hz,
3.3 Hz, ipso-PPh3), 131.4 (d, 2.4 Hz, PPh3), 131.2 (d, 2.1 Hz,
PPh3), 129.7 (dd, 51.2 Hz, 3.1 Hz, ipso-PPh3), 129.2 (s, PPh3),
129.1 (s, PPh3), 129.0 (s), 128.9 (s), 126.4 (s), 119.8 (s, CH3CN),
112.2 (s), 108.2 (s), 45.6 (dd, 13.7 Hz, 4.3 Hz, CH2CH2CH2Ph),
37.2 (t, 5.4 Hz, Ir-C), 36.8 (s, N-CH3), 35.6 (s), 32.8 (s), 1.83
(s, CH3CN). 31P NMR (161.9 MHz, CD3CN, 0 °C): δ 17.41 (d,
eotopic CH2CH2CH2CH3), 0.70 (t, J HH ) 7.3 Hz, CH2-
CH2H2CH3), -20.9 (dd, J PH ) 20.6, 14.8 Hz, Ir-H). 13C{1H}
2
NMR (acetone-d6, 100.6 MHz, 293 K): 162.9 (d, 3.4 Hz, Py),
151.6 (d, 2.6 Hz, Py), 139.2 (s, Py), 135.0 (d, 10.4 Hz, PPh3),
134.5 (d, 54.2 Hz, ipso-PPh3), 134.0 (d, 52.7 Hz, ipso-PPh3),
133.6(d, 10.2 Hz, PPh3), 132.3 (d, 2.1 Hz, para-PPh3), 131.4
(s, para-PPh3), 130.0 (d, 10.4 Hz, PPh3), 129.7 (d, 10.7 Hz,
2
PPh3), 113.6 (s, Py), 108.9 (s, Py), 90.1 (s, C-8), 82.0 (dd, J PC
2
2
) 30.2 Hz, J PC ) 3.7 Hz, C-7), 75.8 (d, J PC ) 26.3 Hz, C-9),
39.3 (d, 3.9 Hz, NCH3), 35.8 (d, 6.1 Hz, C-10), 33.2 (s, C-11),
23.3 (s, C-12), 14.4 (s, C-13). 31P{1H} NMR (CD2Cl2, 161.9 MHz,
293 K): δ 13.1 (s), 7.9 (s). Anal. Calcd for C49H50BF4IrN2P2:
C, 58.39; H, 5.00; N, 2.78. Found: C, 58.12; H, 5.04; N, 2.83.
2
2J PP ) 382.1 Hz), 9.20 (d, J PP ) 382.1).
4.7. Hyd r id obis(tr ip h en ylp h osp h in e)(3-p h en yl-1-((2-
p yr id yl)m et h yla m in o)a llyl-C,C′,C′′,N)ir id iu m (III) Tet -
r a flu or obor a te (6b). 6b was synthesized as a light yellow
powder in 78% yield by a method analogous to that for 6a
4.4. Mea su r em en t of Keq in Eq 2. In an NMR tube
changed with 3b (20 mg, 0.019 mmol) was quickly added CD3-
CN (0.6 mL). 1H NMR spectra of this sample were taken
between 21 and 50 °C. Enough time (1 day at 21 °C and 5 h at
50 °C) was allowed to ensure that equilibrium was reached.
Only the hydride region of each spectrum was analyzed for
[4-d3]/[3b] ratio. The [4-d3]/[3b] ratio at equilibrium was found
to be 7.94, 5.72, 4.51, 3.73, 3.09, and 2.56 at 21.0, 29.0, 35.0,
40.0, 45.0, and 50.0 °C, respectively, which corresponds to Keq
) 0.415, 0.299, 0.236, 0.195, 0.161, and 0.134, respectively
([CD3CN] ) 19.147 mol/L). Plotting ln Keq against T-1 gives
1
using 1 and 1 equiv of phenylacetylene. H NMR (acetone-d6,
3
500 MHz, 293 K): δ 7.54 (d, J HH ) 5.0 Hz, 1H), 7.34-7.49
3
(m, 10H), 7.15-7.30 (m, 15 H), 7.08 (d, J HH ) 7.5 Hz, 2H,
3
Ph), 7.00-7.04 (m, 6H), 6.94 (t, J HH ) 7.2 Hz, 1H), 6.82 (t,
3J HH ) 7.5 Hz, 2H, Ph), 6.59 (dd, J HH ) 12.2 Hz, J HH ) 4.5
3
3
3
3
Hz, 1H, H-8), 6.17 (d, J HH ) 8.7 Hz, 1H), 5.99 (t, J HH ) 6.4
Hz, 1H), 5.71 (dd, 3J PH ) 9.6 Hz, 3J HH ) 4.4 Hz, 1H, H-7), 4.08
3
3
(dd, J HH ) 12.1 Hz, J PH ) 7.8 Hz, 1H, H-9), 2.93 (s, 3H,
N-CH3), -20.41 (dd, 2J PH ) 21.0 Hz, 2J PH ) 15.0 Hz, 1H, Ir-
H). 1H{31P} NMR (acetone-d6, 400 MHz, 293 K): δ 7.54 (d,
∆H° ) -30.8 kJ /mol and ∆S° ) -112 J /(mol K) with R2
0.9999.
)
3
4.5. Bis(tr ip h en ylp h osp h in e)(((2-p yr id yl)m eth yla m i-
n o)m eth yl-N,C)(2-oxobu t-3-en -4-yl-O,C)ir id iu m (III) Tet-
r a flu or obor a te (5). In a Schlenk tube, 1 (165 mg, 0.168
mmol) was dissolved in acetone (6 mL) to give a light yellow
solution, to which was added methyl vinyl ketone (12.0 mg,
0.171 mmol) via syringe. The solution was then refluxed for 6
h, during which time it turned orange; this solution was then
concentrated to ca. 1 mL. under reduced pressure, followed
by addition of diethyl ether (15 mL). A yellow precipitate
appeared and was filtered and washed with diethyl ether (2
× 10 mL). Analytically pure 5 was obtained by drying under
vacuum overnight. Yield: 121 mg (0.122 mmol, 73%). 1H NMR
(CD2Cl2, 500 MHz, 293 K): δ 10.76 (d, 1H, 3J HH ) 8.4 Hz, Ir-
CHdCH), 8.45 (d, 3J HH ) 5.7 Hz, 1H, Py), 7.20 (m, 30H, PPh3),
3J HH ) 5.0 Hz, 1H), 7.15-7.50 (m, 25 H), 7.08 (d, J HH ) 7.5
3
Hz, 2H, Ph), 7.0-7.04 (m, 6H), 6.94 (t, J HH ) 7.2 Hz, 1H),
6.82 (t, 3J HH ) 7.5 Hz, 2H, Ph), 6.59 (dd, 3J HH ) 10.9 Hz, 3J HH
3
3
) 4.5 Hz, 1H, H-8), 6.17 (d, J HH ) 8.7 Hz, 1H), 5.99 (t, J HH
3
3
) 6.4 Hz, 1H), 5.71 (d, J HH ) 4.4 Hz, 1H, H-7), 4.08 (d, J HH
) 12.2 Hz, 1H, H-9), 2.93 (s, 3H, N-CH3), -20.41 (s, 1H, Ir-
H). 13C{1H} NMR (acetone-d6, 125.8 MHz, 293 K): δ 163.0 (d,
1.0 Hz, Py), 151.8 (d, 2.8 Hz, Py), 139.4 (s, Py), 137.7 (d, 3.1
Hz, ipso-Ph), 134.6 (d, 10.6 Hz, PPh3), 134.2 (d, 55.4 Hz, ipso-
PPh3), 133.7 (d, 10.3 Hz, PPh3), 133.2 (d, 50.7 Hz, ipso-PPh3),
132.1 (s, para-PPh3), 131.5 (s, para-PPh3), 129.8 (d, 10.4 Hz,
PPh3), 129.4 (s, Ph), 128.1 (s, Ph), 126.9 (s, Ph), 113.7 (s, Py),
109.0 (s, Py), 87.2 (s, C-8), 79.8 (d, 31.9 Hz, C-7), 76.2 (d, 25.4
Hz, C-9), 39.4 (d, 2.94 Hz, N-CH3). 31P{1H} NMR (acetone-
d6, 161.9 MHz, 293 K): δ 15.8 (d, 5.9 Hz), 9.7 (d, 5.9 Hz). Anal.
3
3
6.90 (t, J HH ) 8.0 Hz, 1H, py), 6.46 (d, J HH ) 8.4 Hz, 1H,

C-C Coupling in an Iridium(III) Alkyl
Organometallics, Vol. 23, No. 14, 2004 3387
Calcd for C51H46BF4IrN2P2: C, 59.59; H, 4.51; N, 2.73. Found:
C, 59.98; H, 4.88; N, 2.66.
5. Con clu sion s
The carbene dihydride complex 2 undergoes insertion
with alkenes to give the carbene dihydrides 3a ,b. CH3-
CN can promote a reversible retro-R-elimination to give
the alkyl hydride 4. Methyl vinyl ketone is an exception,
in that its reaction with 1 gives the cyclometalated
iridafuran derivative 5. The proposed pathway for 3a ,b
involves C-C bond formation by a rare C(sp3)-C(sp3)
reductive elimination. Alkynes also react with 1 or 2
but give tethered η3-allyl complexes 6a ,b via a proposed
pathway that involves C-C bond formation by a C(sp3)-
C(sp2) reductive elimination. The stabilities of 3 and 6
are evidently too high to permit Murai-type catalysis
under the conditions we have examined. Crystal struc-
tures of 3b, 5, and 6b are reported.
4.8. Hyd r id obis(tr ip h en ylp h osp h in e)(2,3-d ip h en yl-1-
((2-pyr idyl)m eth ylam in o)allyl-C,C′,C′′,N)ir idiu m (III) Hexa-
flu or oa n tim on a te (6c). 6c was synthesized as an off-white
powder in 89% yield by a method analogous to that for 6a
-
using the SbF6 analogue of 1 and 1 equiv of diphenylacetyl-
1
3
ene. H NMR (CD2Cl2, 400 MHz, 293 K): δ 7.59 (dd, J HH
)
4
7.3 Hz, J HH ) 1.5 Hz, 2H, Ph), 7.13-7.46 (m, 23H), 7.08 (td,
3J HH ) 7.7 Hz, J PH ) 2.2 Hz, 6H, meta-PPh3), 6.99 (dd, J HH
4
3
3
3
) 7.8 Hz, J PH ) 11.1 Hz, 6H, ortho-PPh3), 6.79 (t, J HH ) 7.3
Hz, 1H, para-Ph), 6.55 (t, J HH ) 7.6 Hz, 2H, meta-Ph), 6.49
3
3
3
(d, J HH ) 7.6 Hz, 2H, ortho-Ph), 6.32 (d, J HH ) 9.3 Hz, 1H,
Py), 5.97 (t, 3J HH ) 6.5 Hz, 1H, Py), 4.87 (t, 3J PH ) 4.7 Hz, 1H,
3
allyl), 4.16 (d, J PH ) 7.0 Hz, 1H, allyl), 3.01 (s, 3H, NCH3),
-19.84 (dd, J PH ) 21.3 Hz, J PH ) 15.4 Hz, 1H, Ir-H). 13C-
{1H} NMR (CD2Cl2, 100.6 MHz, 393 K): δ 161.1 (d, 3.8 Hz),
151.4 (d, 3.1 Hz), 139.1 (s), 136.6 (s), 134.7 (d, 3.1 Hz), 133.8
(d, 10.6 Hz, PPh3), 133.1 (d, 10.0 Hz, PPh3), 132.0 (d, 54.0 Hz,
ipso-PPh3), 131.6 (s), 131.5 (d, 50.0 Hz, ipso-PPh3), 131.2 (d,
2.4 Hz), 130.8 (d, 2.3 Hz), 130.3 (d, 2.4 Hz), 128.9 (d, 10.0 Hz),
128.8 (s), 128.7 (s), 128.5 (d, 10.0 Hz), 127.8 (s), 126.3 (s), 113.0
(s), 112.0 (s, allyl C-8), 107.8 (s), 82.3 (dd, 31.7 Hz, 3.8 Hz,
allyl), 76.1 (dd, 24.4 Hz, 2.4 Hz), 39.2 (s, CH3). 31P NMR (CD2-
2
2
Ack n ow led gm en t. Funding from the U.S. Depart-
ment of Energy, the National Science Foundation, and
the J ohnson Matthey Co. is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables providing
atomic positional parameters, bond distances and angles,
anisotropic thermal parameters, and calculated hydrogen atom
positions for 3b, 5, and 6b. This material is available free of
charge via the Internet at http://pubs.acs.org.
2
Cl2, 161.9 MHz, 393 K): δ 10.90 (d, J PP ) 6.7 Hz), 10.04 (d,
2J PP ) 6.7 Hz). Anal. Calcd for C57H50F6IrN2P2Sb: C, 54.64;
H, 4.02; N, 2.24. Found: C, 54.43; H, 4.01; N, 2.23.
OM049837J