Reactions of anilines and benzamides with a 14-electron iridium(I) bis(phosphinite) complex: N-H oxidative addition versus lewis base coordination

Article abstract of DOI:10.1021/om051070n

Anilines react with (POCOP)Ir(C₆H₅)(H) (12; POCOP = 2,6-(OPtBu₂)₂C₆H₃) to yield equilibrium mixtures of 12, the Ir(I) σ-complexes (POCOP)Ir(NH ₂Ar) (13), and the Ir(III) oxidative addition adducts (POCOP)Ir(H)(NHAr) (14). Quantitative studies of these equilibria for a series of anilines were carried out. Anilines possessing electron-withdrawing groups favor the Ir(III) oxidative addition adduct over the Ir(I) σ-complex. Low-temperature studies using p-chloroaniline show that the Ir(I) σ-complex is the kinetic product of the reaction and is likely the precursor to the Ir(III) oxidative addition adduct. Reductive elimination of complexes 14 in the presence of ethylene led to the corresponding anilines and the ethylene complex (POCOP)Ir(C₂H₄). Kinetic analysis of these reactions for 14e-g bearing electron-withdrawing aryl groups (Ar- = p-CF₃C₆F₅-, C₆F₅-, 3,5-(CF₃)₂C₆H₃-) shows the rate is independent of ethylene concentration. The ΔG? values for these reductive eliminations fall in the range of 21-22 kcal/mol. X-ray analysis establishes 14f (Ar- = C₆F₅-) as a square-pyramidal complex with the hydride occupying the apical site. Reaction of 12 with benzamides 21a,b yields quantitatively the Ir(III) oxidative addition adducts (POCOP)Ir(H)(NHC(O)Ar) (22). X-ray analysis of 22b (Ar- = C₆F ₅-) shows significant interaction of the carbonyl oxygen with Ir in the site trans to hydride. The barrier to reductive elimination of 22a, 29 kcal/mol, is substantially higher than for complexes 14e-g.

Full text of DOI:10.1021/om051070n

1664
Organometallics 2006, 25, 1664-1675
Reactions of Anilines and Benzamides with a 14-Electron Iridium(I)
Bis(phosphinite) Complex: N-H Oxidative Addition versus Lewis
Base Coordination
Alison Cartwright Sykes, Peter White, and Maurice Brookhart*
Department of Chemistry, The UniVersity of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
ReceiVed December 15, 2005
Anilines react with (POCOP)Ir(C6H5)(H) (12; POCOP ) 2,6-(OPtBu2)2C6H3) to yield equilibrium
mixtures of 12, the Ir(I) σ-complexes (POCOP)Ir(NH2Ar) (13), and the Ir(III) oxidative addition adducts
(POCOP)Ir(H)(NHAr) (14). Quantitative studies of these equilibria for a series of anilines were carried
out. Anilines possessing electron-withdrawing groups favor the Ir(III) oxidative addition adduct over the
Ir(I) σ-complex. Low-temperature studies using p-chloroaniline show that the Ir(I) σ-complex is the kinetic
product of the reaction and is likely the precursor to the Ir(III) oxidative addition adduct. Reductive
elimination of complexes 14 in the presence of ethylene led to the corresponding anilines and the ethylene
complex (POCOP)Ir(C2H4). Kinetic analysis of these reactions for 14e-g bearing electron-withdrawing
aryl groups (Ar- ) p-CF3C6H4-, C6F5-, 3,5-(CF3)2C6H3-) shows the rate is independent of ethylene
concentration. The ∆Gq values for these reductive eliminations fall in the range of 21-22 kcal/mol.
X-ray analysis establishes 14f (Ar- ) C6F5-) as a square-pyramidal complex with the hydride occupying
the apical site. Reaction of 12 with benzamides 21a,b yields quantitatively the Ir(III) oxidative addition
adducts (POCOP)Ir(H)(NHC(O)Ar) (22). X-ray analysis of 22b (Ar- ) C6F5-) shows significant interaction
of the carbonyl oxygen with Ir in the site trans to hydride. The barrier to reductive elimination of 22a,
29 kcal/mol, is substantially higher than for complexes 14e-g.
could impact the rapidly growing number of metal-catalyzed
transformations of amine and related compounds, including
hydroaminations of alkenes, styrenes, dienes, and alkynes.17-20
Some of these transformations appear to involve oxidative
addition of N-H bonds,21,22 while the mechanisms of many
other transformations are unknown, but some could involve an
N-H oxidative addition step.
An early instructive example of oxidative addition of N-H
bonds to late transition metal centers was reported by Merola,
who showed that the N-H bonds of pyrroles and indoles
oxidatively add to the Ir(I) moiety (COD)(PMe3)3Ir+, to yield
the 18-electron, octahedral Ir(III) species illustrated in eq 1.23
Introduction
Carbon-hydrogen bond activation by late transition metal
complexes has received intense scrutiny over the past two
decades since the classic work of Bergman,1 Jones,2 and
Graham.3 Fundamental studies, including kinetics, thermo-
dynamics, and selectivities of the oxidative-addition reactions
of C-H bonds to a variety of transition-metal centers together
with theoretical investigations, have appeared.4,5 More recently,
these reactions have been incorporated into catalytic cycles, and
there are now numerous useful catalytic organic transformations
based on C-H bond activation reactions.6-12
Although N-H and C-H bonds exhibit similar homolytic
bond strengths, much fewer investigations of late-metal activa-
tion of N-H bonds have been carried out.13-16 Such studies
* To whom correspondence should be addressed. E-mail:
mbrookhart@unc.edu.
(1) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982, 104, 352.
(2) Jones, W. D.; Feher, F. Organometallics 1983, 2, 562.
(3) Hoyano, J. K.; McMaster, A. D.; Graham, W. A. G. J. Am. Chem.
Soc. 1983, 105, 7190.
(4) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879.
(5) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154.
The Goldman, Jensen, and Kaska groups have shown that
the 14-electron complex (PCP)Ir (1; PCP ) 2,6-(CH2-
PtBu2)2C6H3), generated from treatment of the dihydride (PCP)-
Ir(H)2 with acceptors such as tert-butylethylene, readily oxida-
(6) Crabtree, R. H. Dalton Trans. 2001, 2951.
(7) Crabtree, R. H. Dalton Trans. 2003, 3985.
(16) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem.
Res. 2002, 35, 44.
(8) Lersch, M.; Tilset, M. Chem. ReV. 2005, 105, 2471.
(9) Jun, C.-H.; Lee, J. H. Pure Appl. Chem. 2004, 76, 577.
(10) Ishiyama, T. Kagaku to Kogyo (Tokyo) 2003, 56, 1237.
(11) Kakiuchi, F.; Chatani, N. AdV. Synth. Catal. 2003, 345, 1077.
(12) Labinger, J. A.; Bercaw, J. E. Nature (London) 2002, 417, 507.
(13) Hartwig, J. F.; Andersen, R. A.; Bergman, R. G. Organometallics
1991, 10, 1875.
(17) Utsunomiya, M.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 2702.
(18) Hartwig, J. F. Pure Appl. Chem. 2004, 76, 507.
(19) Beller, M.; Breindl, C.; Eichberger, M.; Hartung, C. G.; Seayad, J.;
Thiel, O. R.; Tillack, A.; Trauthwein, H. Synlett 2002, 1579.
(20) Utsunomiya, M.; Kuwano, R.; Kawatsura, M.; Hartwig, J. F. J. Am.
Chem. Soc. 2003, 125, 5608.
(21) Uchimaru, Y. Chem. Commun. 1999, 1133.
(22) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. J. Am. Chem. Soc.
1988, 110, 6738.
(14) Glueck, D. S.; Winslow, L. J. N.; Bergman, R. G. Organometallics
1991, 10, 1462.
(15) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163.
(23) Ladipo, F. T.; Merola, J. S. Inorg. Chem. 1990, 29, 4172.
10.1021/om051070n CCC: $33.50 © 2006 American Chemical Society
Publication on Web 03/03/2006

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1665
tively adds C-H bonds of alkanes and arenes.24,25 Such species
are highly active for catalytic transfer dehydrogenation of
alkanes and can also be used for synthesis of enamines through
transfer dehydrogenation of tertiary amines.26 Goldman and
Hartwig have recently observed that the (PCP)Ir complex 1
oxidatively adds the N-H bond of aniline to produce the Ir-
(III) anilino hydride 2, as shown in eq 2.27 In benzene, adduct
simple coordination.28 Treatment of 7 with ammonia gives the
Ir(III) amido hydride in high yields at 25 °C (eq 5).
Our laboratory29-31 has investigated the chemistry of more
electron-deficient Ir pincer complexes based on the bis-
(phosphinite) ligand POCOP ()2,6-(OPtBu2)2C6H3). The highly
active 14-electron complex 10 can be conveniently generated
in situ by treatment of the hydrido chloride 9 with sodium tert-
butoxide (eq 6). Generation of 10 in a cyclooctane/tert-
2 equilibrates with the phenyl hydride complex 3. The equi-
librium favors the anilino hydride complex with Keq ) 105 at
22 °C (eq 3).
butylethylene mixture produces a highly active catalyst system
for transfer dehydrogenation and production of cyclooctene and
cyclooctadiene (eq 7). Detailed mechanistic studies of this
system have complemented the studies of Goldman on 1 and
provided interesting contrasts, suggesting that the phosphinite
POCOP system prefers the Ir(I) oxidation state relative to the
PCP systems.29-31
In this paper we report the reaction of a series of substituted
anilines and benzamides with the phosphinite pincer complex
10. In the case of the anilines, the Ir(III) oxidative addition
adduct, the Ir(I) σ-complex, or a mix of these products is formed,
depending on the nature of the para substituent. Rates of
reductive elimination of the Ir(III) species have been measured,
as well as the equilibria in benzene between the aniline adducts
and the phenyl hydride. Information on the mechanism of
reductive elimination was attained through the study of low-
temperature reactions of both the p-chloroaniline and the
p-methoxyaniline complexes.
Attempted oxidative addition of the better σ-donor ammonia
results in the Ir(I) ammonia complex 4. The amido hydride 5
can be independently generated by dehydrochlorination of 6 at
-78 °C. Warming to 25 °C resulted in conversion to ammonia
complex 4, indicating that thermodynamically the ammonia
complex is favored over the amido hydride (eq 4). When a more
Results and Discussion
(I) Reaction of (POCOP)Ir Pincer complexes with Various
Anilines (11a-g). (a) Equilibration of (POCOP)Ir(H)(C6H5)
(12) with (POCOP)Ir(NH2Ar) (13) and (POCOP)Ir(H)-
NHAr) (14). Reactions of anilines shown in Chart 1 with the
Chart 1. Anilines of Varying Electron-Withdrawing and
-Donating Ability (11a-g)
electron-donating saturated backbone is incorporated in the
pincer ligand, oxidative addition of ammonia occurs rather than
(24) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J.
Am. Chem. Soc. 1999, 121, 4086.
(25) Kanzelberger, M.; Singh, B.; Czerw, M.; Krogh-Jespersen, K.;
Goldman, A. S. J. Am. Chem. Soc. 2000, 122, 11017.
(26) Zhang, X.; Fried, A.; Knapp, S.; Goldman, A. S. Chem. Commun.
2003, 2060.
14-electron (POCOP)Ir pincer complex 10 were carried out
(28) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science (Washington, DC)
2005, 307, 1080.
(27) Kanzelberger, M.; Zhang, X.; Emge, T. J.; Goldman, A. S.; Zhao,
J.; Incarvito, C.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 13644.
(29) Goettker-Schnetmann, I.; Brookhart, M. J. Am. Chem. Soc. 2004,
126, 9330.

1666 Organometallics, Vol. 25, No. 7, 2006
Sykes et al.
Scheme 1. Equillibria between (POCOP)Ir(H)(Ph) (12), (POCOP)Ir(NH2Ar) (13), and (POCOP)Ir(H)(NHAr) (14)
Table 1. Equilibrium Constantsa for 12 + NH2Ar h 13 +
Benzene h 14 + Benzene at 25 °C
aniline (11)
K1
K2
K3 ()K1K2)
a
b
c
d
e
f
1130
456
188
55
c
b
b
18
19
55
260
2190
2770
0.04
0.1
1
c
c
c
c
g
c
a Equilibrium values are based on an average of two to three runs.
b Concentration of 14a too low to detect. c Concentrations of 13e-g too low
to detect.
by treatment of the hydrochloride complex 9 with NaOtBu and
anilines 11a-g in benzene at room temperature for 1.5 h. The
phenyl hydride complex 12 is in rapid equilibrium with 1031
and thus reacts with the aniline to form either the σ-complex
13 or the oxidative addition adduct 14. The three species 12-
14, depicted in Scheme 1, are all in equilibrium at 25 °C. 31P
NMR spectroscopy was used to determine the ratios of the three
species. Complex 12 exhibits a 31P shift at 182 ppm,31 while
the Ir(I) σ-complexes show resonances in the 173.4-173.6 ppm
range and 31P signals of the Ir(III) oxidative addition adducts
Figure 1. ORTEP diagram of 14f. Only the hydrogens on iridium
and nitrogen are shown for clarity. Key bond distances (Å) and
bond angles (deg): Ir(1)-N(1) ) 2.145, N(1)-C(2) ) 1.348,
Ir(1)-C(22) ) 2.013, Ir(1)-P(1) ) 2.294, Ir(1)-P(2) ) 2.309;
C(22)-Ir(1)-N(1) ) 177.32, P(1)-Ir(1)-N(1) 99.20, P(2)-Ir(1)-
N(1) 101.42, Ir(1)-N(1)-C(2)-C(7) ) 32.5, H-Ir(1)-N(1)-H
177.31.
1
occur in the 171.7-173.3 ppm range. The H NMR data, as
well as a crystal structure of 14f (see below), confirm the
structural assignments of these species. The σ-complexes exhibit
a broad 2H resonance around 5.2 ppm, distinct from the ArNH2
resonance for free anilines, indicating that these species are
1
exchanging slowly on the NMR time scale. The ArNHIr H
signals for the oxidative addition adducts appear in the 3.0-
5.6 ppm range and are paired with a Ir-H triplet (JPH ) 12.6-
13.5 Hz) at high fields (-34.1 to -42.2 ppm range). The Ir
hydride signal for 12 cannot be detected at room temperature,
due to rapid exchange with benzene via complex 10.31
pentane at -35 °C was carried out. An ORTEP diagram of the
structure, including key bond distances and angles, is shown in
Figure 1. The complex is square pyramidal, with the hydride
in an apical position. There is an empty coordination site trans
to the hydride. The dihedral angle Ir(1)-N(1)-C(2)-C(7) is
32.5°, indicating the arene ring sits approximately perpendicular
to the square plane and the filled p orbital on nitrogen lies
parallel to the square plane. The N-H bond lies anti to the
Ir-H bond (H-Ir(1)-N(1)-H dihedral angle 177.3°), and thus,
there can be no N-H- - -H-Ir interaction as seen in related
systems.32
It is worth noting that the crystal structure of 14f is
representative of the (POCOP)IrIII complexes of the electron-
withdrawing anilines 14e-g. The 1H resonance of the hydride
in these complexes falls between -41 and -43 ppm, which
seems to be characteristic of hydride shifts in these (POCOP)Ir
pincer complexes when there is an empty coordination site trans
to the hydride. However, for the (POCOP)IrIII complexes of
the less electron-withdrawing anilines 14b-d the chemical shift
for the hydride falls between -33.3 and -35.9 ppm. This
surprisingly downfield chemical shift might be indicative of a
change in orientation of the aniline substituent, where the
The equilibrium constants K1, K2, and K3, measured by 31P
NMR spectroscopy at 25 °C, are summarized in Table 1. For
the electron-rich p-methoxyaniline 11a, only the Ir(I) σ adduct
13a can be observed. As the substituents become more electron-
withdrawing, the Ir(III) oxidative addition adduct becomes
increasingly favored. For example, a 1:1 ratio of Ir(III):Ir(I) is
now observed for p-chloroaniline 11d. For even less electron-
rich anilines 11e-g, the Ir(I) species can no longer be
spectroscopically detected and K2 cannot be measured. The
equilibrium constants K3 between the aryl hydride and Ir(III)
complexes can still be determined, since benzene is in large
excess relative to aniline and 12 can be detected. The reasons
for the trends in these substituent effects will be discussed below.
To confirm the structures of the anilino hydrides, a single-
crystal X-ray diffraction analysis of a crystal of 14f grown from
(30) Goettker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem.
Soc. 2004, 126, 1804.
(31) Goettker-Schnetmann, I.; White, P. S.; Brookhart, M. Organome-
tallics 2004, 23, 1766.
(32) Crabtree, R. H. Science (Washington, D.C.) 1998, 282, 2000.

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1667
Scheme 2. Comparison of the Reactions of (PCP)Ir(H)(Ph) (3) and (POCOP)Ir(H)(Ph) (10) with NH2C6H5
hydride and the N-hydrogen are cis to each other with a possible
hydrogen-bonding interaction.32 A corresponding shift in the
ArNH signal occurs on moving from ca. 3.0-4.4 ppm in the
adducts involving electron-withdrawing anilines (14e-g) to 5.6
ppm for the p-chloroaniline adduct 14d.
the arene becomes more electron-withdrawing, the energy of
the py orbital is lowered and the destabilizing interaction is
reduced. This could account for the substituent effect on relative
stabilities. An alternative view is that the electron-withdrawing
substituents stabilize the negative charge on the anilino ligand,
enhancing the electrostatic interaction between the metal and
the anilino group, thus strengthening the Ir-N bond.36,37
(b) Rates of Oxidative Addition of Anilines to (POCOP)
Iridium Pincer Complexes. Low-temperature 1H and 31P
studies showed that in the case of p-chloroaniline (which yields
a 1:1 equilibrium mixture of 13d and 14d) the kinetic product
of reaction with 10 is the σ-complex 13d. Generation of the
tolyl hydride complexes 17 (a mixture of the meta and para
isomers31) in toluene was achieved in the usual way by reaction
of the hydrochloride complex in toluene with NaOtBu. Treat-
ment of this solution with excess p-chloroaniline (10 equiv) at
-50 °C initially yields only the σ complex 13d (eq 8). Slow
When the equilibrium data for reaction with aniline are
compared with those of Goldman and Hartwig,27 it is clear that
the more electron-withdrawing (POCOP) phosphinite Ir system
more strongly prefers the Ir(I) oxidation state relative to the
(PCP)Ir system. At room temperature, the reaction of 1 with
H2NC6H5 favors the oxidative addition product and forms only
the Ir(III) anilino hydride complex. In benzene solution, an
equilibrium is established between (PCP)Ir(H)(NHC6H5) and
(PCP)Ir(H)(C6H5) with a Keq value of 105 favoring the formation
of the iridium anilino complex.27 In the POCOP system, reaction
of 10 with NH2C6H5 favors the Ir(I) σ-complex with an
Ir(I):Ir(III) complex equilibrium ratio of ca. 10:1 (see Scheme
2). These results are also supported by IR data. Comparison of
the IR stretching frequencies of coordinated carbon monoxide
in (POCOP)Ir(CO) (15; νCO 1949 cm-1 31
(16; νCO 1927.7 cm-1 33
shows a higher frequency CtO stretch
)
and (PCP)Ir(CO)
)
for 15 than for 16, indicating that the more electron-withdrawing
ligand leads to a more electron-deficient metal center.
The increasing donor ability of the lone pair of electrons on
the aniline is reflected, as expected, by the increasing stability
of the Ir(I) σ-aniline complexes relative to the Ir(III) phenyl
hydride complex (compare K1 values, Table 1). The stability
of the Ir(III) anilino hydride complexes relative to the Ir(III)
phenyl hydride increases as the arene ring of the aniline becomes
more electron withdrawing (K3 values). This behavior can be
rationalized in two ways. In the d6 Ir(III) complexes 14, all the
dπ orbitals are filled and thus there are unfavorable pπ-dπ
interactions34,35 in 14e-g. The crystal structure of 14f shows
that the Ir-N-C plane lies perpendicular to the Ir(III) square
plane. As illustrated in Figure 2, there is repulsive interaction
formation of the oxidative addition product 14d is observed at
this temperature. While it seems likely that the oxidative addition
occurs directly from the σ complex, we have no direct proof of
this. After formation of the σ complex 13d, the rate of oxidative
addition of the p-chloroaniline to form 14d was measured at
-12 °C via 1H low-temperature NMR spectroscopy. The first-
order rate constant was found to be 4.8 × 10-4 s-1 with
∆Gq ) 19.7 kcal/mol.
Similar low-temperature experiments were conducted with
3,5-bis(trifluoromethyl)aniline (11g). At the highest achievable
concentrations of aniline, a trace of a species tentatively assigned
to the σ complex (δ(31P) 173.2, maximum concentration ca.
Figure 2. The destabilizing interaction between the filled N π
orbital (py) and the filled Ir dxy orbital (apical hydride not shown).
between the filled Ir dxy orbital and the filled N py orbital. As
(33) Krogh-Jespersen, K.; Czerw, M.; Zhu, K.; Singh, B.; Kanzelberger,
M.; Darji, N.; Achord, P. D.; Renkema, K. B.; Goldman, A. S. J. Am. Chem.
Soc. 2002, 124, 10797.
(34) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley: New York, 2001.
(36) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg.
Chem. 1999, 21, 115.
(37) Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J.; Nolan,
S. P. J. Am. Chem. Soc. 1997, 119, 12800.
(35) Caulton, K. G. New J. Chem. 1994, 18, 25.

1668 Organometallics, Vol. 25, No. 7, 2006
Sykes et al.
Scheme 3. Possible Mechanism for Oxidative Addition of 11g
Table 2. Rates of Reductive Elimination of Anilines (11e-g)
from (POCOP)Ir(H)(NHAr) at 9 °C in Toluene
3.0%) could be detected as a transient during reactions carried
out at -37 °C (Scheme 3). These results are consistent with
formation of the σ-complex as the kinetic product, which never
builds up to significant concentrations due to rapid oxidative
addition to form 14g (path A). Again, we cannot rule out direct
formation of 14g from reaction of 10 with 11g (path B).
(c) Rates of Reductive Elimination of Electron-withdraw-
ing Anilines from Five-Coordinate (POCOP) Iridium Pincer
Complexes using Ethylene as a Trapping Ligand. The rates
of reductive elimination of 14e-g were measured by heating
the Ir(III) adducts in the presence of ethylene as a trapping
ligand, L, to form the iridium(I) ethylene adduct 18, as shown
below in eq 9. Complexes 14e-g were chosen for study, since
C2H4
concn, M
k,
av k,
∆Gq,
kcal/mol
Ir(III) complex
104 s-1
104 s-1
14e (0.022 M)
0.087
0.28
4.0
4.4
4.2
20.8
21.1
14f (0.022 M)
14g (0.036 M)
0.022
0.19
1.1
3.0
2.6
2.8
2.8
0.18
0.34
0.42
0.47
0.45
22.1
To determine if these barriers are the true barriers for
reductive elimination of anilines from 14e-g, several mecha-
nistic scenarios, consistent with the observation that the rates
of formation of ethylene complex 18 are independent of ethylene
concentration, were considered. These are summarized in cases
A-C in Scheme 4. In case A, slow reductive elimination leads
directly to 10, followed by fast trapping by ethylene leading to
formation of the ethylene complex 18. In view of the above
experiments with p-chloroaniline, which suggest that the σ-
complex is the precursor to oxidative addition adducts, case A
seems less likely than cases in which reductive elimination
initially leads to the σ-complex. In case B, the σ-complex 13 is
the precursor to 10, which is then rapidly trapped by ethylene.
It is possible that the rate of formation of 13 is rate-determining
(i.e. k2 > k1, k-1) or that 13 and 14 are in equilibrium followed
by slow formation of 10 (k2 < k-1). (In this latter case, the
measured ∆Gq values do not correspond to the true barriers for
reductive elimination of 14e-g.) In case C, formation of 13 is
rate-determining, followed by rapid associative displacement
of the aniline by ethylene.
K2 and K3 are sufficiently large that the Ir(III) complexes can
be prepared cleanly with no contamination by aryl hydride 12
or Ir(I) complexes. The trapping ligand must be chosen so that
the 18-electron Ir(III) six-coordinate complex is not formed. A
survey of several trapping ligands revealed that ethylene was
ideal for this purpose (PMe3 and carbon monoxide form the
octahedral complexes 1938 and 20 prior to reductive elimination;
see below).
To probe whether displacement of anilines from 13 by
ethylene is associative or dissociative, we examined the reaction
of 13a, a system for which the σ-complex 13a can be generated
free of the Ir(III) oxidative addition adduct 14a. Generation of
13a in toluene at room temperature followed by exposure to
ethylene at -8 °C results in quantitative formation of ethylene
complex 18 (eq 11).
The disappearance rates of adducts 14e-g were measured at
9 °C in the presence of excess ethylene and found to be
independent of ethylene concentration (eq 10). Measured rate
constants and free energies of activation are summarized in
Table 2.
The reductive eliminations follow the same trend as the
equilibrium reactions above; the more electron-withdrawing
aniline reductively eliminates more slowly (Table 2). This is
also evident by comparing the free energies of activation, ∆Gq
values, for the reductive eliminations. As the electron-withdraw-
ing ability of the aniline increases, the ∆Gq value also increases
from 20.8 kcal/mol for aniline 11e to 22.1 kcal for 11g.
Using 0.015-0.019 M 13a and excess ethylene concentrations
of 0.25 and 0.48 M, clean first-order kinetics are observed at
-8 °C with measured rate constants of 3.3 × 10-4 and 2.7 ×
10-4 s-1, respectively. No dependence of the rate on ethylene
(38) Formed by reaction of in situ generated 14f followed by addition
of PMe3 at -40 °C. Key NMR resonances include the following: 1H NMR
(400 MHz, C7D8) δ -11.9 (dt, Ir-H, JP-H ) 149.1 Hz (trans), JP-H ) 23.4
Hz (cis); 31P NMR (162 MHz, C7D8) δ 169.6 (m, 2P), -57.1 (m, 1P).

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1669
Scheme 4
is observed, which implies that dissociation of p-methoxyaniline
from 13a is rate-determining with a free energy of activation,
∆Gq, of 19.8 kcal/mol. This result rules out case C above and
indicates case B as the most likely choice.
(H)(Ar′) (Ar′- ) 3,5-Me2C6H3-) of 14.1 kcal/mol.39 This likely
reflects a stronger Ir-N bond relative to the Ir-C bond.36
(d) Reaction of (POCOP)Ir(H)(NHAr) Complexes (14e,f)
with Carbon Monoxide. Generation of the tolyl hydrides 17
at -78 °C as described above followed by treatment with C6F5-
NH2 (ca. 1.1 equiv) and CO resulted in formation of (POCOP)-
Ir(CO)(H)(NHC6F5) (20f) as the major product via CO trapping
of 14f. (Minor amounts of (POCOP)IrCO (15) are formed,
presumably by CO displacement of aniline from (POCOP)Ir-
(NH2C6F5), since reductive elimination of aniline from either
14f or 20f is very slow at -78 °C.) Removal of toluene and
addition of a minimal amount of pentane at -78 °C resulted in
the precipitation of 20f in low yield. Key NMR parameters of
20f include a 31P signal at 157 ppm and a 1H resonance for the
iridium hydride at -8.6 ppm. The downfield hydride shift is
indicative of ligand coordination trans to the apical hydride. A
solution of 20f in toluene at 25 °C undergoes slow reductive
elimination; (POCOP)Ir(CO) and free pentafluoroaniline are
In examining case B more closely, it is instructive to consider
free energy diagrams for both the p-chloroaniline system 13d/
14d and 14e-g (for simplicity consider 14f as representative
of 14e-g) (Figure 3). In the case of 13d/14d, Keq ) 1; therefore,
barriers for reductive elimination and oxidative addition are the
same, 19.7 kcal/mol. Now consider 14f. Since 14f is somewhat
more stable than 13f, one would expect the ∆Gq value to be
1
slightly greater than 19.7 kcal/mol, e.g. 19.7 + δ, and ∆Gq
-1
to be slightly less, 19.7 - δ′, as shown in Figure 3. Since
(CF3)2C6H3NH2 is a poorer donor than p-methoxyaniline, the
barrier for dissociation from (POCOP)Ir should be somewhat
less than the 19.8 kcal/mol measured for 13a, designated in
Figure 3 as 19.8 - δ′′. It is difficult to predict whether δ′ or δ′′
is larger and thus which transition state, TS1 or TS2, is higher
in energy, but it is likely that the difference is quite small. The
1
visible by H NMR spectroscopy after 18 h.
∆Gq value for 14f cannot exceed 21.1 kcal/mol (see Table 1)
1
X-ray-quality crystals of 20f were obtained through slow
crystallization from pentane at -35 °C. The ORTEP diagram
of 20f (Figure 4) indicates an Ir(III) octahedral complex with
the CO bound in an apical site trans to the hydride and the
aniline ligand trans to Cipso. Since the crystal structure of 14f
showed an empty coordination site in the position trans to the
hydride, CO coordination to this site is consistent with rapid
addition of CO to generate 20f as the kinetic product. Interest-
ingly, there is a change in the orientation of the aniline ligand
upon binding of CO. As mentioned earlier, in 14f the dihedral
angle H-Ir(1)-N(1)-H was 177°, with the hydride and N-H
trans to each other. The dihedral angle H(1)-Ir(1)-N(11)-
H(11) in 20f after CO coordination is now 42°, indicating that
the aniline ligand has rotated ca. 125° and the hydride and N-H
are now nearly cis to each other.
but is certainly greater than 19.7 kcal/mol and thus is narrowly
bracketed. In view of this analysis the ∆Gq values in Table 1
likely reflect fairly accurately the barriers for reductive elimina-
tion of 14e-g.
It is informative to compare the barriers of reductive
elimination observed here, which are in the 21-22 kcal/mol
range, to the barrier of reductive elimination of (POCOP)Ir-
Reaction of (POCOP)Ir(H)(NHAr-pCF3) (14e) with CO was
also investigated. Complex 14e was generated in situ at 25 °C
by treatment of tolyl hydrides 17 with CF3C6H4NH2 (ca. 1.5
equiv) at 25 °C. Cooling the toluene solution to -78 °C and
purging with CO resulted in formation of four complexes. The
major product was the expected CO addition product (POCOP)-
1
Ir(H)(CO)(NHC6H5-p-CF3) (20e). The H and 31P NMR data
support a structure analogous to 20f. Two minor complexes
corresponded to p- and m-tolyl hydride carbonyl complexes
(39) The stability of the aryl hydride complex can be dramatically altered
by incorporation of fluorine substituents in the aromatic ring. In preliminary
experiments we have shown that the reaction of (POCOP)Ir (10) with
2,3,5,6-tetrafluoroaniline yields solely the C-H activation product (POCOP)-
Ir(H)(C6F4NH2). Strengthening of the Re-aryl bond through fluorination
of the aryl ring has been well-documented in earlier studies by Perutz et al.
(Chem. Commun. 2003, 490).
Figure 3. Reaction coordinate diagram for interconversion of 13d
and 14d and conversion of 14f to 18.

1670 Organometallics, Vol. 25, No. 7, 2006
Sykes et al.
22a,b (eq 12). These adducts are substantially more stable than
the anilino hydrides and can be readily isolated as stable solids
at room temperature.
Figure 4. ORTEP diagram of (POCOP)Ir(H)(CO)(NHC6F5) (20f).
Only the hydrogens on iridium and nitrogen are shown for clarity.
Key bond distances (Å) and bond angles (deg): Ir(1)-N(11) )
2.168, N(11)-C(12) ) 1.361, Ir(1)-C(9) ) 2.046, Ir(1)-P(1) )
2.337, Ir(1)-P(2) ) 2.329; H(1)-Ir(1)-N(11)-H(11) ) 42.22,
C(9)-Ir(1)-N(11) ) 173.3, P(1)-Ir(1)-N(11) ) 98.82, P(2)-
Ir(1)-N(11) ) 100.97, Ir(1)-N(11)-C(12)-C(13) ) 139.79.
An X-ray diffraction study was carried out on a crystal of
22b obtained from pentane at -35 °C. The ORTEP diagram is
shown in Figure 6, along with key bond distances and angles.
As for the anilino complexes, the amide nitrogen lies in the
square plane trans to Cipso of the aryl ring of the POCOP ligand.
The N-C-O amide plane is perpendicular to the iridium square
plane with the carbonyl oxygen anti to the axial Ir-H. The Ir-O
bond distance of 2.55 Å suggests weak coordination of the amide
oxygen to the open axial site trans to hydride. It is of interest
to compare the iridium-oxygen bond distance in 22b with Ir-O
distances in the other iridium amide complexes 23,41 24,42 and
25,43 shown in Figure 5. In the 18-electron Ir(III) complexes
23 and 24 the Ir-O distances of 3.401 and 3.412 Å clearly
show no Ir-O interaction. The Ir(III) complex 25 is formally a
16-electron complex in the absence of a Ir-O interaction. The
Ir-O distance of 2.290 Å is considerably shorter than the Ir-O
distances in 23 and 24 and clearly suggests a significant bonding
interaction. The fact that the amide in 25 is an alkyl amide with
a much more basic oxygen then that in the benzamide of 22b
with a strongly electron-withdrawing C6F5 group may in part
account for the shorter Ir-O distance in 25.
(POCOP)Ir(tolyl)(H)(CO). These structures were fully charac-
terized by 2D 1H NMR spectroscopy and independently
generated by treatment of 17 with CO. Distinct 1H NMR signals
for these complexes are the downfield shifts (8.05-8.16 ppm)
of the aryl protons ortho to Ir and the two Ir hydride triplets at
-8.69 and -8.70 ppm. The fourth complex, also verified by
independent synthesis, is (POCOP)Ir(H)(Cl)(CO), from CO
trapping of unreacted starting material. By increasing the
concentration of aniline used, formation of the tolyl complexes
was inhibited. We were unable to crystallize 20e, and column
chromatography resulted in its decomposition.
Complex 20e undergoes reductive elimination at a much
slower rate than the five-coordinate analogue 14e. Heating an
in situ generated toluene-d8 solution of (POCOP)Ir(H)(CO)-
(NHAr-pCF3) (20e) at 63 °C results in the formation of
(POCOP)Ir(CO) and free 4-(trifluoromethyl)aniline. In contrast,
reductive elimination of five-coordinate 14e occurs at 9 °C. A
detailed kinetic analysis of the reductive elimination was not
carried out, due to the difficulties in preparing 20e cleanly and
complications due to the presence of excess product aniline.
However, qualitatively the rate of reductive elimination is
retarded when carried out under 1-3 atm of carbon monoxide.
This is consistent with loss of CO to form five-coordinate 14e
prior to reductive elimination, as might be expected on the basis
of previous work concerning reductive elimination of six-
coordinate Pt(IV) complexes.40
1
The H chemical shifts of the hydride ligands in 22a and
22b also support an axial Ir-O interaction. (POCOP)Ir hydride
complexes with an empty coordination site trans to hydride
exhibit hydride shifts in the -41 ppm range. In six-coordinate
complexes the hydride shifts to much lower values. For example,
in the carbonyl adduct 20f, the 1H shift is -8.56. The
intermediate shifts of the hydrides in 22a and 22b of -30.25
and -35.72 ppm support a significant Ir-O interaction. The
higher field shift of -35.7 ppm in 22b suggests a decreased
Ir-O interaction compared to that in 22a, consistent with a
decreased oxygen basicity due to the strongly electron-
withdrawing C6F5 group.
(II) Reaction of the (POCOP)Ir Pincer Complex with
Benzamides C6H5(CO)NH2 (21a) and C6F5(CO)NH2 (21b).
Reaction of (POCOP)Ir (10; generated by reaction of (POCOP)-
Ir(H)(Cl) (9) with NaOtBu) with NH2(CO)C6H5 (21a) and NH2-
(CO)C6F5 (21b) yields the Ir(III) oxidative addition adducts
(a) Rates of Reductive Elimination of H2N(CO)C6H5 from
(POCOP)Ir(H)(NH(CO)C6H5) Complexes. Since benzamides
form significantly more stable Ir(III) species than their analogous
anilino complexes, the rates of reductive elimination were
measured at 100 °C. Ethylene proved to be a poor choice for a
Figure 5. Comparison of Ir-O bond distances with those in the literature.

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1671
studies. At room temperature benzamide 21a (0.0094 M) and
triphenylphosphine (0.0094 M) in a 1:1 ratio were added to 10
(0.0046 M), generated in the usual manner. 31P NMR analysis
showed the formation of 22a and 26 in a ratio of 2:1. Since
interconversion of these species is slow at 25 °C, this ratio
represents kinetic trapping and differs from the thermodynamic
ratio of ca. 6:1.
When 22a was generated and the reversible reaction (eq 13)
was analyzed in the presence of 10 equiv of 21a and 10 equiv
of PPh3, the half-life for reductive elimination of benzamide
was found to be ca. 1.7 h, corresponding to a ∆Gq value of ca.
29 kcal/mol. This increased barrier to reductive elimination of
benzamide relative to that for anilines is due to stronger binding
of the benzamido fragment to (POCOP)Ir. The Ir-O interaction
as well as a decrease in the repulsive dπ-p interaction as a
result of the electron-withdrawing ability of the acyl moiety
can account for the increased binding energy.
Summary
Reaction of a series of anilines 11a-g with (POCOP)Ir-
(C6H5)(H) (12) leads to equilibrium mixtures of 12, the Ir(I)
σ-complexes (POCOP)Ir(NH2Ar) (13), and the Ir(III) oxidative
addition adducts (POCOP)Ir(H)(NHAr) (14). Previous studies
have shown that 12 undergoes rapid reductive elimination of
benzene to form the 14-electron species (POCOP)Ir (10);
therefore, complexes 13 and 14 arise from reaction of anilines
with 10. Equilibrium constants connecting these three species
have been measured, and several features are apparent. As
expected, as the basicity of the aniline increases, the equilibrium
ratio (13 + benzene):(12 + aniline) increases. Surprisingly,
however, as the basicity of the aniline decreases, the ratio of
the Ir(III) species 14, to Ir(I) species 13 increases, as does the
ratio (14 + benzene):(12 + aniline). The increased stability of
the oxidative addition adducts bearing electron-withdrawing aryl
groups (-p-CF3C6H4, 14e; -C6F5, 14f; 3,5-(CF3)2C6F3-, 14g)
was attributed to decreased repulsion between the filled dπ and
N p orbitals.
Low-temperature NMR experiments employing p-chloroa-
niline show that reaction with 12 forms the Ir(I) σ-complex
(POCOP)Ir(NH2C6H4Cl) (13d) as the kinetic product, which
equilibrates with the oxidative addition adduct 14d at temper-
atures above -50 °C. Complexes 14e-g undergo reductive
elimination at 9 °C in the presence of ethylene to yield
quantitatively (POCOP)Ir(C2H4) (18) and the respective aniline.
Rate measurements demonstrate that these reactions are cleanly
first order and are independent of ethylene concentration.
Mechanistic analysis suggests that the rate-determining step is
formation of the σ-complex followed by loss of the aniline to
form 10, which is rapidly trapped by ethylene. The reductive
elimination barriers of 14e-g fall in the range of 21-22 kcal/
mol and increase with the electron-withdrawing ability of the
aryl groups.
Figure 6. Crystal structure of (POCOP)Ir(H)(NH(CO)C6F5) (22b).
Only the hydrogens on iridium are shown for clarity. Key bond
distances (Å) and bond angles (deg): Ir(1)-N(1) ) 2.171, N(1)-
C(2) ) 1.279, Ir(1)-C(29) ) 2.034, Ir(1)-P(1) ) 2.412, Ir(1)-
P(2) ) 2.359; H(1)-Ir(1)-N(1)-H(2) ) -18.67, C(29)-Ir(1)-
N(1) ) 176.66, P(1)-Ir(1)-N(1) ) 104.30, P(2)-Ir(1)-N(1) )
96.77, Ir(1)-N(1)-C(2)-C(4) ) -175.64.
trapping ligand, since ethylene concentrations were difficult to
control at elevated temperatures. Therefore, triphenylphosphine,
which competes reversibly with benzamide for coordination to
iridium, was used. The equilibrium between (POCOP)Ir(H)-
(NH(CO)Ph) (22a) + PPh3 and (POCOP)Ir(PPh3) + H2N(CO)-
C6H5, as shown in eq 13, was measured at three different
concentrations of PPh3 (0.29, 0.59, and 1.18 M) at 100 °C. From
these data a Keq value of 0.18, favoring 22a, was calculated.
For the more electron-withdrawing pentafluorobenzamide com-
plex 22b, the equilibrium constant decreases to 0.07, consistent
with the substituent effects observed in the aniline equilibrium
Complex 14f is square-pyramidal, with the hydride occupying
the apical site. Trapping 14f with CO forms the 18-electron
complex (POCOP)Ir(H)(CO)(NHC6F5) (20f). X-ray analysis of
a single crystal of 20f indicates that CO has added at the vacant
site trans to hydride. The six-coordinate CO adducts are much
more stable with respect to reductive elimination. Complex 20e
undergoes reductive elimination at 63 °C at rates similar to 14e
reductive elimination at 9 °C. Qualitative rate measurements
suggest CO must dissociate prior to reductive elimination.
Reaction of 12 with benzamides yields quantatively the
Ir(III) oxidative addition adducts (POCOP)Ir(H)(NHC(O)Ar)
(22). X-ray analysis of 22b (Ar ) C6F5) shows significant
(40) Crumpton-Bregel, D. M.; Goldberg, K. I. J. Am. Chem. Soc. 2003,
125, 9442.
(41) Chin, C. S.; Chong, D.; Lee, S.; Park, Y. J. Organometallics 2000,
19, 4043.
(42) Cooper, A. C.; Huffman, J. C.; Caulton, K. G. Inorg. Chim. Acta
1998, 270, 261.
(43) Tellers, D. M.; Ritter, J. C. M.; Bergman, R. G. Inorg. Chem. 1999,
38, 4810.

1672 Organometallics, Vol. 25, No. 7, 2006
Sykes et al.
vt, J ) 11.0 Hz, C(CH3)3), 28.6 (CH3, vt, 2JP-H ) 3.8 Hz, C(CH3)3).
C4 not observed due to low intensity.
(POCOP)Ir(NH2Ar-Me) (13b). The general procedure was
employed using 9 (0.035 mmol, 22 mg), NaOtBu (0.038 mmol,
3.9 mg), and 11b (0.1 mmol, 11 mg).
interaction of the carbonyl oxygen with Ir in the site trans to
hydride. The barrier to reductive elimination of 22a, 29 kcal/
mol, is substantially higher than for complexes 14e-g. The
increased binding energy of the -NH(CO)Ar group to Ir is
ascribed to Ir-O interaction as well as a decrease in the
repulsive dπ-p interaction as a result of the strong electron-
withdrawing ability of the acyl moiety.
Experimental Section
General Considerations. All manipulations were carried out
using standard Schlenk, high-vacuum, and glovebox techniques.
Argon and nitrogen were purified by passage through columns of
BASF R3-11 (Chemalog) and 4 Å molecular sieves. THF was
distilled from sodium benzophenone ketyl under nitrogen. Pentane
and toluene were passed through columns of activated alumina and
deoxygenated by purging with N2. Benzene was dried with 4 Å
molecular sieves and degassed by either freeze-pump-thaw
methods or by purging with argon. Toluene was further treated by
purging with argon to remove nitrogen. Toluene-d8 and benzene-
d6 were dried over 4 Å molecular sieves and stored under argon in
the glovebox. Hydrogen and carbon monoxide were used as
received from National Specialty Gases of Durham, NC. NMR
spectra were recorded on Bruker DRX 400 MHz and AMX 300
and 500 MHz instruments and are referenced to residual protio
solvent peaks. 31P chemical shifts are referenced to an external H3-
PO4 standard. Since there is a strong 31P-31P coupling in the pincer
complexes, many of the 1H and 13C signals exhibit virtual coupling
and appear as triplets. These are specified as vt with the apparent
coupling simply noted as J. IR spectra were recorded on an ASI
ReactIR 1000 spectrometer. Elemental analyses were carried out
by Atlantic Microlab, Inc., of Norcross, GA. All reagents were
purchased from Sigma-Aldrich and used without further purification.
The POCOP bis(phosphinite) ligand and (POCOP)Ir(H)(Cl) (9)
were prepared by literature procedures.30 [IrCODCl]2 can be
purchased from Strem or synthesized using literature procedures.44
(POCOP)Ir(H)(Ph) (12). Complex 12 was generated in situ by
treatment of (POCOP)Ir(H)(Cl) (9) with 1.1 equiv of NaOtBu in
benzene at 75 °C for 30 min.29
1H NMR (400 MHz, C6D6): 13b, δ 6.77-6.96 (7H, aromatic
protons), 5.17 (s, 2H, -NH2), 2.04 (s, 3H, CH3), 1.27 (vt, J ) 6.4
Hz, 36H, 2 × P(tBu)2); the 14b concentration is very low, resulting
1
in the only distinguishing H resonance as the hydride, δ -33.25
(t, JP-H ) 12.7 Hz, 1H, Ir-H). 31P{1H} NMR (121.5 MHz, C6D6):
13b, δ 173.6; 14b, δ 171.3. 13C{1H} NMR (100.6 MHz, C6D6):
13b, δ 167.8 (Cq, vt, J ) 8.7 Hz, C3 and C5), 144.7 (Cq, s, C1′),
135.3 (Cq, s, C4′), 129.4 (CH, s, C2′ and C6′), 127 (Cq, C4), 123.1
(CH, s, C3′ and C5′), 121.2 (CH, s, C1), 103.2 (CH, vt, J ) 5.9
Hz, C2 and C6), 41.1 (Cq, vt, J ) 11.0 Hz, C(CH3)3), 28.5 (CH3,
vt, J ) 3.4 Hz, C(CH3)3), 20.6 (CH3, s, CH3).
(POCOP)Ir(NH2C6H5) (13c)/(POCOP)Ir(H)(NHC6H5) (14c).
The general procedure was employed using 9 (0.024 mmol, 15 mg),
NaOtBu (0.026 mmol, 2.5 mg), and 11c (0.048 mmol, 4.4 µL).
The equilibrating set of complexes 12, 13c, and 14c as well as
10% of unreacted 9 were all present in the sample; thus, the 13C
NMR spectrum was not useful for structural assignments.
1H NMR (400 MHz, C6D6): 13c, δ 6.69-6.96 (aromatic protons),
5.19 (s, 2H, NH2), 1.26 (vt, J ) 6.4 Hz, 36H, P(tBu)2); the
concentration of 14c is very low, resulting in the only distinguishing
1H resonance as the hydride, δ -34.05 (t, J ) 12.6 Hz). 31P{1H}
NMR (162 MHz, C6D6): 13c, δ 173.8; 14c, δ 172.0.
(POCOP)Ir(NH2(p-ClC6H4)) (13d)/(POCOP)Ir(H)(NH(p-Cl-
C6H4)) (14d). The general procedure was employed using 9 (0.024
mmol, 15 mg), NaOtBu (0.026 mmol, 2.5 mg), and 11d (0.048
mmol, 6.1 µL). The equilibrating set 12, 13d, and 14d, as well as
3% of unreacted 9, were present in the NMR sample.
General Procedure for the in Situ Generation of Complexes
13 and 14. (POCOP)Ir(H)(Cl) (2) was placed in a medium-walled
screw-cap NMR tube with 1.1 equiv of NaOtBu in 0.5 mL of
benzene or toluene and heated to 75 °C for 45 min to generate the
aryl hydride complex. The aniline was added to this mixture and
allowed to react for 45 min at room temperature.
(POCOP)Ir(NH2(p-OCH3C6H4)) (13a). The general procedure
was employed using 9 (0.033 mmol, 21 mg), NaOtBu (0.037 mmol,
3.5 mg), and 11a (0.099 mmol, 13.5 mg).
1H NMR (400 MHz, C6D6): δ 6.61-6.97 (m, 14H, aromatic
protons for 13d and 14d), 5.60 (s, 1H, NH), 5.06 (s, 2H, NH2),
1.08, 1.24 (m, 72H, P(tBu)2), -35.94 (t, JP-H ) 13.2 Hz, 1H, Ir-
H). 31P{1H} NMR (162 MHz, C6D6): 13d, δ 173.9; 14d, δ 172.6.
(POCOP)Ir(H)(NH(p-CF3C6H4)) (14e). The general procedure
was employed using 9 (0.032 mmol, 20 mg), NaOtBu (0.032 mmol,
3.1 mg), and 11e (0.08 mmol, 10 µL).
3
1H NMR (300 MHz, C6D6): δ 6.99 (d, JH-H ) 8.7 Hz, 2H, 2′-
and 6′-H), 6.95 (t, 3JH-H ) 7.8 Hz, 1H, 1-H), 6.83 (d, 3JH-H ) 7.8
Hz, 2H, 2- and 6-H), 6.59 (d, JH-H ) 8.7 Hz, 2H, 3′- and 5′-H),
3
5.15 (s, 2H, -NH2), 3.29 (s, 3H, OCH3), 1.28 (vt, J ) 6.5 Hz,
36H, 2 × P(tBu)2). 31P{1H} NMR (121.5 MHz, C6D6): δ 173.6.
13C{1H} NMR (75.5 MHz, C6D6): δ 167.9 (Cq, vt, J ) 8.6 Hz, C3
and C5), 158.2 (Cq, s, C4′), 138.5 (Cq, s, C1′), 124.6 (CH, s, C3′
and C5′), 121.3 (CH, s, C1), 114.1 (CH, s, C2′ and C6′), 103.3
(CH, vt, J ) 5.7 Hz, C2 and C6), 55.2 (CH3, s, OCH3), 41.1 (Cq,
(44) Baghurst, D. R.; Mingos, D. M. P.; Watson, M. J. J. Organomet.
Chem. 1989, 368, C43.
3
1H NMR (500 MHz, C6D6): δ 7.43 (d, JH-H ) 8.5 Hz, 2H, 3′-

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1673
and 5′-H), 6.82 (t, 3JH-H ) 7.8 Hz, 1H, 1-H), 6.73 (d, 3JH-H ) 8.0
5.1 mg, 0.010 M), and benzene (4 mL) were added. The reaction
mixture was stirred for 1.5 h. An aliquot was removed and analyzed
by 31P NMR. The equilibrium constants were calculated on the basis
of the concentrations of all the species in solution, (K1 ) 1014, K2
) n/a). A second aliquot was removed after another 1 h to ensure
the reaction was at equilibrium. The reaction was repeated with an
increase in the concentration of 11a to 0.05 M (K1 ) 1189, K2 )
n/a). No 14a could be detected.
Reaction of (POCOP)Ir(H)(C6H5) (12) and p-CH3C6H4NH2
(11b). The general procedure for 11a was followed using 9 (0.069
mmol, 43.45 mg), NaOtBu (0.9 equiv, 0.062 mmol, 6.0 mg), 11b
(0.20 mmol, 21.43 mg, 0.050 M), and benzene (4 mL) (K1 ) 462,
K2 ) 0.04). The reaction was repeated with an increase in the
concentration of 11b to 0.10 M (K1 ) 448, K2 ) 0.04).
Reaction of (POCOP)Ir(H)(C6H5) (12) and C6H5NH2 (11c).
The general procedure for 11a was followed using 9 (0.075 mmol,
46.9 mg), NaOtBu (0.9 equiv, 0.067 mmol, 6.47 mg), 11c (0.2
mmol, 0.18 µL, 0.050 M), and benzene (4.0 mL) (K1 ) 188, K2 )
0.07). The reaction was repeated with an increase in the concentra-
tion of 11c to 0.10 M (K1 ) 189, K2 ) 0.08).
3
Hz, 2H, 2- and 6-H), 6.46 (d, JH-H ) 8.5 Hz, 2H, 2′- and 6′-H),
4.37 (s, 1H, NH), 1.108 (vt, J ) 7.5 Hz, 18H, P(tBu)2), 1.046 (vt,
J ) 7.0 Hz, 18H, P(tBu)2), -40.265 (t, JP-H ) 13.3 Hz, 1H, Ir-
H). 31P{1H} NMR (162 MHz, C6D6): δ 173.3. 19F NMR (376.5
MHz, C6D6): δ -59.1. 13C{1H} NMR (125.8 MHz, C6D6): δ 168.0
(Cq, vt, JC ) 5.5 Hz, C3 and C5), 164.0 (Cq, s, C1′), 127.0 (Cq, q,
3
1JF-C ) 238.9 Hz, CF3), 126.4 (CH, q, JF-C ) 3.6 Hz, C3′ and
C5′), 126.3 (CH, s, C1), 123.7 (Cq, br, C4), 117.1 (CH, s, C2′ and
2
C6′), 112.7 (Cq, q, JF-C ) 32.2 Hz, C4′), 104.8 (CH, t, JP-H
)
5.2, C2 and C6), 42.7 (Cq, vt, J ) 10.8 Hz, C(CH3)3), 38.9 (Cq,
vt, J ) 12.8 Hz, C(CH3)3), 28.0 (CH3, vt, J ) 3.2 Hz, C(CH3)3),
27.6 (CH3, vt, JP-H ) 3.2 Hz, C(CH3)3).
(POCOP)Ir(H)(NHC6F5) (14f). Simultaneously, 9 (0.034 mmol,
21 mg), NaOtBu (0.037 mmol, 3.6 mg), 11f (0.068 mmol, 12.4
mg), and benzene-d6 (0.5 mL) were added to a medium-walled
screw-cap NMR tube and heated to 75 °C for 1 h.
Reaction of (POCOP)Ir(H)(C6H5) (12) and p-ClC6H4NH2
(11d). The general procedure for 11a was followed using 9 (0.074
mmol, 46.15 mg), NaOtBu (0.9 equiv, 0.066 mmol, 6.4 mg), 11d
(0.392 mmol, 50 mg, 0.10 M), and benzene (4 mL) (K1 ) 50, K2
) 1). The reaction was repeated with an increase in the concentra-
tion of 11d to 0.15 mol/L (K1 ) 60, K2 ) 1).
Reaction of (POCOP)Ir(H)(C6H5) (12) and p-CF3C6H4NH2
(11e). The general procedure for 11a was followed using 9 (0.138
mmol, 86.6 mg), NaOtBu (0.9 equiv, 0.124 mmol, 11.9 mg), 11e
(0.08 mmol, 12.9 mg, 0.010 M), and benzene (8 mL) (K3 ) 272).
The reaction was repeated with an increase in the concentration of
11e to 0.050 M (K3 ) 259). No 13e could be detected.
Reaction of (POCOP)Ir(H)(C6H5) (12) and C6F5NH2 (11f).
The general procedure for 11a was followed using 9 (0.038 mmol,
23.75 mg), NaOtBu (0.9 equiv., 0.0343 mmol, 3.3 mg), 11f (0.0721
mmol, 13.2 mg, 0.009 M), and benzene (8 mL) was added (K3 )
2010). The reaction was repeated with an increase in the concentra-
tion of 11f to 0.012 M (K3 ) 2300). No 13f could be detected.
Reaction with (POCOP)Ir(H)(C6H5) (12) and 3,5-(CF3)2-
C6H3NH2 (11g). The general procedure for 11a was followed using
9 (0.158 mmol, 99.05 mg), NaOtBu (0.9 equiv, 0.142 mmol, 13.65
mg), 11g (0.08 mmol, 18 mg, 0.010 M), and benzene (8 mL) (K3
) 2700). The reaction was repeated with an increase in the
concentration of 11g to 0.050 M (K3 ) 2850). No 13g could be
detected.
1H NMR (500 MHz, C6D6): δ 6.82-6.72 (m, 3H, 1-, 2-, 6-H),
3.01 (s, 1H, NH), 1.09-1.03 (m, 36H, P(tBu)2), -42.15 (t, JP-H
)
13.5 Hz, 1H, Ir-H). 31P{1H} NMR (162 MHz, C6D6): δ 172.8.
19F NMR (376.5 MHz, C6D6): δ -167.3 (m), -168.9 (m), -187.3
(m). 13C{1H} NMR (125.8 MHz, C6D6): δ 168.5 (Cq, vt, J ) 5.5
Hz, C3 and C5), 140.4-135.8 (m, Cq, Ar-F5: C2′, C6′, C3′, C5′,
and C4′), 126.7 (CH, s, C1), 122.6 (Cq, t, C4), 104.9 (CH, t, JP-H
) 5.3 Hz, C2 and C6), 42.6 (Cq, vt, J ) 11.1 Hz, C(CH3)3), 39.1
(Cq, vt, J ) 12.6 Hz, C(CH3)3), 27.7 (CH3, vt, J ) 3.2 Hz,
C(CH3)3), 27.2 (CH3, vt, J ) 3.0 Hz, C(CH3)3), C1′ not observed
due to low intensity.
(POCOP)Ir(H)(NH(3,5-(CF3)2C6H3)) (14g). The general pro-
cedure was employed using 9 (0.035 mmol, 22 mg), NaOtBu (0.039
mmol, 3.7 mg), and 11g (0.07 mmol, 10.9 µL).
1H NMR (500 MHz, C6D6): δ 6.98 (s, 1H, 4′-H), 6.87 (s, 2H, 2′-
and 6′-H), 6.81 (t, 3JH-H ) 7.9 Hz, 1H, 1-H), 6.73 (d, 3JH-H ) 7.9
Hz, 2H, 2- and 6-H), 3.74 (s, 1H, NH), 1.06 (vt, J ) 7.4 Hz, 18H,
Low-Temperature Oxidative Addition of p-Chloroaniline to
10. In a screw cap NMR tube, 10 was generated by reaction of 9
(0.023 mmol, 15 mg) with NaOtBu (0.023 mmol, 2.3 mg) in 0.4
mL of toluene-d8 at 100 °C for 1 h. The reaction mixture was cooled
to -78 °C in a dry ice/acetone bath, and 0.1 mL of a 2.3 M solution
of p-chloroaniline (0.23 mmol) was added via syringe. The reaction
mixture was warmed in the NMR probe until the solution consisted
solely of 13c, after which the oxidative addition was monitored at
-12 °C. A data plot is included in the Supporting Information.
Kinetic Analysis of the Reductive Elimination Reactions of
14e-g. In a screw-cap NMR tube, 10 was generated by reaction
of 9 (0.023 mmol, 15 mg) with NaOtBu (0.023 mmol, 2.3 mg) in
0.5 mL of toluene-d8 at 100 °C for 1 h. Anilines 11e-g were added
to the solution of 10 and allowed to react for 45 min. The NMR
tube was cooled to -78 °C in a dry ice/acetone bath, followed by
addition of ethylene to the reaction mixture via syringe. The NMR
tube was warmed to 9 °C in the probe, and the reductive elimination
P(tBu)2), 0.99 (vt, J ) 6.8 Hz, 18H, P(tBu)2), -41.77 (t, JP-H
)
13.5 Hz, 1H, Ir-H). 31P{1H} NMR (162 MHz, C6D6): δ 174.0
(d). 19F NMR (376.5 MHz, C6D6): δ -63.2. 13C{1H} NMR (125.8
MHz, C6D6): δ 168.5 (Cq, vt, J ) 5.6 Hz, C3 and C5), 161.4 (Cq,
2
s, C1′), 132.0 (Cq, q, JF-C ) 31.4 Hz, C3′ and C5′), 127.0 (CH,
1
s, C1), 125.5 (Cq, q, JF-C ) 273.3 Hz, CF3), 124.5 (Cq, m, C4),
115.7 (CH, m, C2′ and C6′), 105.0 (CH, t, vt, J ) 5.2 Hz, C2 and
3
C6), 102.4 (CH, septet, JF-C ) 4.0 Hz), 42.8 (Cq, vt, J ) 10.9
Hz, C(CH3)3), 38.7 (Cq, vt, J ) 12.8 Hz, C(CH3)3), 28.0 (CH3, vt,
J ) 3.2 Hz, C(CH3)3), 27.3 (CH3, vt, J ) 3.1 Hz, C(CH3)3).
General Procedure for Determining the Equilibrium Con-
stants K1, K2, and K3 (Scheme 1). Samples were prepared as
described below in benzene. Molarities of species were determined
1
by carefully measuring the final volume of the solution. Both H
and 31P spectra were used to determine ratios of species. 31P spectra
were taken with a delay time of 15 s to ensure the integrals were
accurate on the basis of the 5 × T1 value of 14f.
1
was monitored by H NMR spectroscopy. A plot of kinetic data
for 14f is included in the Supporting Information.
Reaction of (POCOP)Ir(H)(C6H5) (12) and p-CH3OC6H4NH2
(11a). To a vial in the glovebox under argon, 9 (0.088 mmol, 55.35
mg), NaOtBu (0.8 equiv, 0.07 mmol, 6.0 mg), 11a (0.041 mmol,
Kinetic Analysis of the Dissociation of H2NC6H4-pOMe (11a)
from 13a. (POCOP)Ir(H)(Cl) (9; 10 mg, 0.016 mmol), NaOtBu
(1.7 mg, 0.018 mmol), and toluene-d8 (0.4 mL) were heated for 1

1674 Organometallics, Vol. 25, No. 7, 2006
Sykes et al.
h. at 100 °C in a J. Young NMR tube to generate the tolyl hydride
complexes 17. p-Methoxyaniline (11a; 3.5 mg, 0.024 mmol) and
1,3,5-trimethoxybenzene (0.1 mL, 0.11 M solution in toluene-d8)
was added to the NMR tube. After the NMR sample was freeze-
pump-thawed, ethylene (10-20 equiv, 3.6-7.2 mL at 23 °C) was
introduced via a gastight syringe at liquid-nitrogen temperature.
The reaction was then monitored via low-temperature NMR
spectroscopy at -8 °C. A plot of kinetic data is included in the
Supporting Information.
(POCOP)Ir(H)(NHC6F5)(CO) (20f). In a Schlenk flask, 9 (101
mg, 0.16 mmol), NaOtBu (17 mg, 0.18 mmol), 11f (33 mg, 0.18
mmol), and toluene (5 mL) were added and stirred at room
temperature for 1 h. The reaction mixture was cooled to -78 °C,
and then CO was purged through the solution until the color
lightened. The toluene was removed under vacuum, and the product
was extracted with pentane. The pentane was reduced under vacuum
until the product began to precipitate. The pentane was then cooled
to -78 °C, and the precipitate was filtered and washed with cold
pentane (60 mg, 46% yield).
Procedure for Monitoring the Reaction of Benzamide Com-
plex 22b with PPh3. A stock solution was prepared using 9 (92.5
mg, 0.148 mmol), NaOtBu (71.0 mg, 0.74 mmol), 22b (161.6 mg,
0.74 mmol), and toluene-d8 (6.0 mL). Aliquots of the stock solution
(0.6 mL, 0.021 M) were placed in three J. Young tubes with known
amounts of PPh3 (0.126, 0.252, 0.378 mmol). The reaction mixtures
were heated to 100 °C overnight, after which the reactions were
stopped by placing the NMR tubes in cold water. The Keq value
was calculated by measuring the ratios of 22b and 26 by 31P NMR.
Keq ) 0.067.
(POCOP)Ir(PPh3) (24). In a Schlenk flask 9 (104 mg, 0.166
mmol), NaOtBu (17.6 mg, 0.183 mmol), PPh3 (46 mg, 0.174 mmol),
and toluene (10 mL) were combined and stirred overnight. Toluene
was removed under vacuum until the product precipitated. The
product was filtered, washed with cold toluene, and dried under
1
vacuum to yield an orange solid (74 mg, 52% yield). H NMR
(500 MHz, C6D6): δ 8.06 (t, 6H, PPh3), 6.9-7.1 (m, 12H, aromatic
protons), 1.072 (vt, JP-H ) 6.8 Hz, 36H, P(tBu)2). 31P{1H} NMR
(162 MHz, C6D6): δ 181.2 (d, JP-P ) 5.2 Hz), 15.8 (t, JP-P ) 5.5
Hz). 13C{1H} NMR (100.6 MHz, C6D6): δ 166.4 (Cq, vt, JP-C
)
6.5 Hz, C3 and C5), 141.5, 135.7, 133.7, 129, 127.0, 125.7 (CH, s,
C1), 102.7 (CH, t, vt, C2 and C6), 41.0 (Cq, vt, JP-H ) 11.6 Hz,
C(CH3)3), 28.7 (CH3, s). Anal. Calcd for C40H54O2P3Ir (851.99):
C, 56.39; H, 6.39. Found: C, 56.19; H, 6.37. Crystallographic data
are included in the Supporting Information.
Kinetic Analysis of the Reductive Elimination of Benzamide
22a. A stock solution (0.06 M) of (POCOP)Ir(H)(NH(CO)C6H5)
(23a) was prepared under Ar by stirring (POCOP)Ir(H)(Cl) (9; 75.1
mg, 0.12 mmol), NaOtBu (12.7 mg, 0.132 mmol), benzamide 22a
(16.0 mg, 0.132 mmol), and toluene-d8 (2 mL) until the solution
turned pale orange. The excess benzamide and NaOtBu were filtered
out through a 0.02 µm syringe filter. In a screw-cap NMR tube, 10
equiv of 22a (15 mg, 0.124 mmol), 10 equiv of PPh3 (32.5 mg,
0.124 mmol), the stock solution of 23a (0.21 mL, 0.06 M), and
toluene-d8 (0.4 mL) were added. The reaction mixture was heated
to 100 °C in the NMR probe, and over time the disappearance of
3
1H NMR (500 MHz, C6D6): δ 6.74 (t, JH-H ) 8.0 Hz,1H, 1-H),
3
6.59 (d, JH-H ) 8.0 Hz, 2H, 2- and 6-H), 2.33 (s, 1H, NH), 1.20
(vt, JP-H ) 7.7 Hz, 18H, P(tBu)2), 1.11 (vt, JP-H ) 7.3 Hz, 18H,
P(tBu)2), -8.56 (t, JP-H ) 17.9 Hz, 1H, Ir-H). 31P{1H} NMR (162
MHz, C6D6): δ 57.6. 19F NMR (376.5 MHz, C6D6): δ -163.3
(bs), -169.0 (t), -186.7 (septet). 13C{1H} NMR (125.8 MHz,
C6D6): δ 179.4 (Cq, CdO), 163.8 (Cq, vt, JP-C ) 3.7 Hz, C3 and
C5), 140.4-135.8 (m, Cq, Ar-F5: C2′, C6′, C3′, C5′, and C4′),
126.8 (CH, s, C1), 106.0 (CH, t, vt, JP-H ) 4.8 Hz, C2 and C6),
43.0 (Cq, vt, JP-H ) 12.6 Hz, C(CH3)3), 40.6 (Cq, vt, JP-H ) 11.4
Hz, C(CH3)3), 28.1 (CH3, vt, JP-H ) 2.9 Hz, C(CH3)3), 27.2 (CH3,
vt, JP-H ) 2.4 Hz, C(CH3)3). C4 and C1′ were not observed, due
to low intensity. IR (C6D6): 2022 cm-1. Anal. Calcd for
C29H41O3P2N1F5Ir (800.80): C, 43.50; H, 5.16; N, 1.75. Found:
C, 43.70; H, 5.25; N: 1.71.
1
23a signals was monitored via H NMR. A plot of kinetic data is
included in the Supporting Information.
(POCOP)Ir(H)(NH(CO)(Ph) (22a). (POCOP)Ir(H)(Cl) (9; 100
mg, 0.16 mmol), NaOtBu (18.4 mg, 0.192 mmol), H2N(CO)C6H5
(21a; 23.2 mg, 0.192 mmol), and 5.0 mL of benzene were added
to a Schlenk flask, and the mixture was stirred for 1.5 h until the
color changed to a light orange. The solution was filtered though
a 0.2 µm syringe filter, and the benzene was sublimed at 0 °C to
yield a yellow-orange solid (71.6 mg, 63% yield).
Reductive Elimination of p-(Trifluoromethyl)aniline from
(POCOP)Ir(H)(CO)(NHC6H4-pCF3) (20e). In a J. Young NMR
tube, tolyl complexes 17 were generated by heating the reaction
mixture of (POCOP)Ir(H)(Cl) (9; 15 mg, 0.024 mmol), NaOtBu
(2.3 mg, 0.024 mmol), and 0.5 mL of toluene-d8 for 1 h at 100 °C.
The reaction mixture was cooled to room temperature. The addition
of p-(trifluoromethyl)aniline (11e; 6.0 µL, 0.048 mmol) formed
complex 14e. After the reaction mixture was freeze-pump-thawed,
a gastight syringe was used to add sufficient CO at liquid-N2
temperature to generate pressures of 1, 2, and 3 atm of CO in the
1
headspace at 25 °C. The reaction was monitored at 63 °C by H
NMR spectroscopy.
1H NMR (500 MHz, C6D6): δ 7.64-7.62 (m, 2H, 2′- and 6′-H),
7.12-7.07 (m, 3H, 3′-, 4′, and 5′-H), 6.87-6.79 (m, 3H, 1-, 2-,
and 3-H), 5.90 (bs, 1H, NH), 1.40 (vt, JP-H ) 6.9 Hz, 18H, P(tBu)2),
1.28 (vt, JP-H ) 7.0 Hz, 18H, P(tBu)2), -30.25 (t, JP-H ) 13.2
Hz, 1H, Ir-H). 31P{1H} NMR (162 MHz, C6D6): δ 164.2. 13C-
{1H} NMR (125.8 MHz, C6D6): δ 176.4 (Cq, t, JP-C ) 1.3 Hz,
CO), 166.6 (Cq, vt, JP-C ) 6.0 Hz, C3 and C5), 138.4 (Cq, s, C1′),
130.1 (CH, s, C4′), 128.3 (CH, s, C3′ and C5′), 126.3 (CH, s, C2′
and C6′), 124.1 (CH, s, C1), 118.5 (C4), 104.5 (CH, t, JP-C ) 5.4
Hz, C2 and C6), 42.5 (Cq, vt, JP-H ) 12.0 Hz, C(CH3)3), 39.9
(Cq, vt, JP-H ) 11.8 Hz, C(CH3)3), 28.8 (CH3, vt, JP-H ) 3.3 Hz,
C(CH3)3), 27.6 (CH3, bvt, JP-H ) 2.2 Hz, C(CH3)3). Anal. Calcd
for C29H46O3P2NIr (710.85): C, 49.00; H, 6.52; N, 1.97. Found:
C, 49.22; H, 6.59; N, 2.00.
Procedure for Monitoring the Reaction of Benzamide Com-
plex 22a with PPh3. A stock solution of (POCOP)Ir(H)(NH(CO)-
Ar) was prepared in the glovebox under Ar by stirring (POCOP)-
Ir(H)(Cl) (9; 112.7 mg, 0.18 mmol), NaOtBu (20.7 mg, 0.22 mmol),
benzamide 21a (26.2 mg, 0.22 mmol), and toluene-d8 (3.0 mL)
until the solution turned pale orange: ca. 30 min. The excess
benzamide and NaOtBu were filtered out through a 0.02 µm syringe
filter. The concentration of the stock solution (0.063 M) was
1
measured via H NMR using 2.0 µL of mesitylene as a standard.
Aliquots (0.5 mL) of the stock solution were added to three J.
Young NMR tubes containing known amounts of PPh3 (0.147
mmol, 0.294 mmol, 0.588 mmol). The NMR tubes were heated to
100 °C for 3 days, after which the reaction was stopped by placing
the NMR tubes in cold water. The Keq value was calculated by
measuring the ratios of 22a and 26 by 31P NMR. Keq ) 0.18.
(POCOP)Ir(H)(NH(CO)(C6F5) (22b). (POCOP)Ir(H)(Cl) (9;
100 mg, 0.16 mmol), NaOtBu (18.4 mg, 0.192 mmol), H2N(CO)-

Reactions with a 14-Electron Ir(I) Bis(phosphinite)
Organometallics, Vol. 25, No. 7, 2006 1675
1
C6F5 (21b; 40.5 mg, 0.192 mmol), and 5.0 mL of benzene were
added to a Schlenk flask, and the mixture was stirred for 1.5 h
until the color changed to a light orange. The solution was filtered
though a 0.2 µm syringe filter, and the benzene was sublimed at 0
°C to yield a yellow-orange solid (101.6 mg, 79% yield).
Hz, C4′), 137.7 (Cq, dm, JF-C ) 252.0 Hz, C3′ and C5′), 125.4
(CH, s, C1), 119.9 (Cq, m, C4), 116.2 (Cq, m, C1′), 104.7 (CH, t,
vt, JP-H ) 5.3 Hz, C2 and C6), 42.8 (Cq, vt, JP-H ) 12.1 Hz,
C(CH3)3), 39.8 (Cq, vt, JP-H ) 12.1 Hz, C(CH3)3), 28.3 (CH3, vt,
JP-H ) 3.3 Hz, C(CH3)3), 27.6 (CH3, vt, JP-H ) 3.1 Hz, C(CH3)3).
Anal. Calcd for C29H41O3P2NF5Ir (800.80): C, 43.50; H, 5.16; N,
1.75. Found: C, 43.70; H, 5.25; N, 1.71.
Acknowledgment. We gratefully acknowledge funding by
the National Institutes of Health (Grant No. GM 28938).
Supporting Information Available: CIF files containing X-ray
crystallographic data for complexes 14f, 20f, 22b, and 26 and
figures giving kinetic plots for the conversion of 13d to 14d, for
the dissociation of 11a from 13a, for the reductive elimination of
11f from 14f, and for the reductive elimination of benzamide from
22a. This material is available free of charge via the Internet at
http://pubs.acs.org.
1H NMR (500 MHz, C6D6): δ 6.87-6.78 (m, 3H, 1-, 2-, 6-H),
5.49 (bs, 1H, NH), 1.44 (vt, JP-H ) 7.0 Hz, 18H, P(tBu)2), 1.22
(vt, JP-H ) 7.0 Hz, 18H, P(tBu)2), -35.72 (t, JP-H ) 13.0 Hz, 1H,
Ir-H). 19F NMR (376.5 MHz, C6D6): δ -141.76 (m), -155.25
(m), -166.61 (m). 13C{1H} NMR (125.8 MHz, C6D6): δ 167.2
(Cq, vt, JP-C ) 5.8 Hz, C3 and C5), 163.0 (Cq, s, CO), 144.5 (Cq,
dm, 1JF-C ) 241.8 Hz, C2′ and C6′), 141.1 (Cq, dm, 1JF-C ) 254.3
OM051070N