Structure, bonding, and ligand-based reactions of zwitterionic boratoiridium(I) complexes with oxazolinyl scorpionate ligands

Article abstract of DOI:10.1016/j.ica.2009.06.017

New tris(4,4-dimethyl-2-oxazolinyl)phenylboratoiridium(I) scorpionate-type compounds [Ir(To^M)L₂] (L₂ = η⁴-C₈H₁₂ and (CO)₂) and electrophiles form adducts that contain a bidentate IrTo^M-coordination and an N-electrophile interaction of the third oxazoline instead of the oxidative addition product. The adduct with lithium chloride gives a unique heterobimetallic Li-O-oxazoline-N-Ir bridging structure that has been identified through X-ray crystallography. Density functional theory calculations provide thermodynamic data, orbital symmetries, and orbital energies that explain the formation of the observed iridium(I) products.

Full text of DOI:10.1016/j.ica.2009.06.017

Inorganica Chimica Acta 362 (2009) 4517–4525
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Structure, bonding, and ligand-based reactions of zwitterionic boratoiridium(I)
complexes with oxazolinyl scorpionate ligands
Andrew V. Pawlikowski, Tristan S. Gray, George Schoendorff, Benjamin Baird, Arkady Ellern,
*
Theresa L. Windus, Aaron D. Sadow
Iowa State University and Ames Laboratory, Ames, IA 50011-3111, USA
a r t i c l e i n f o
a b s t r a c t
New tris(4,4-dimethyl-2-oxazolinyl)phenylboratoiridium(I) scorpionate-type compounds [Ir(ToM)L2]
Article history:
(L2 = g
4-C8H12 and (CO)2) and electrophiles form adducts that contain a bidentate IrToM-coordination
Received 31 January 2009
Received in revised form 28 May 2009
Accepted 2 June 2009
and an N–electrophile interaction of the third oxazoline instead of the oxidative addition product. The
adduct with lithium chloride gives a unique heterobimetallic Li–O-oxazoline-N–Ir bridging structure that
has been identified through X-ray crystallography. Density functional theory calculations provide ther-
modynamic data, orbital symmetries, and orbital energies that explain the formation of the observed irid-
ium(I) products.
Available online 13 June 2009
Dedicated to Prof. Swiatoslaw Trofimenko.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Iridium compounds
Scorpionate
Oxazoline
1. Introduction
and the electrophiles MeOTf and MeI provide N-methylated oxaz-
olinium species [Ir(j
2-ToP-Me)L2]+ rather than oxidative addition
Oxidative addition reactions of monovalent Rh and Ir scorpio-
nates yield racemic [M(Tp)R(X)L] compounds (Tp = tris(pyrazol-
yl)borate, Chart 1 [1]; M = Rh, Ir; R = hydrocarbyl; X = hydride,
halide; L = neutral ligand) that contain a stereogenic metal center
[2]. The configuration of the metal stereocenter and peripheral ste-
reocenters on the hydrocarbyl R group could be controlled by chi-
ral ligands. However, few diastereoselective C–H bond activation
reactions have been reported with TpRh(I)- or TpIr(I)-type com-
pounds. Notable examples include the diastereoselective activa-
tion of a fused menthylpyrazole group on an optically active
products. Interestingly, reactions of Group 9 Tp-type scorpionates
with protons show either metal- or ligand-based reactivity [7].
For example, mixtures of [TpRh(CO)2] and [HOEt2][BF4] give a pyr-
azolyl-protonated rhodium(I) product, whereas the heavier irid-
ium congener forms an iridium(III)-hydride [7]. Additionally, a
tetrahedral tris(carbene)boratocobalt(II) chloride complex reacts
with H+ to give a protonated carbene [8]. In contrast, [Tp*Rh(CO)2]
(Tp* = HB(N2C3HMe2)3) and MeI react to give the acetyl compound
[Tp*Rh(CO)(COMe)I] via the unobserved Rh(III) oxidative addition
product [9]. Likewise, the cationic compound [Rh(tris-ox)(g4
-
Tp ligand [3], and cyclometalation of a diisopropylamine ligand
C8H12)]+ is oxidized by CsBr3 to give [RhBr3(tris-ox)] (tris-
ox = 1,1,1-tris(4S-isopropyl-2-oxazolinyl)ethane) [10].
i
that
gives
racemic
[TpMe2Cl
]
RhH(NH( Pr)CHMeCH2)
(TpMe2Cl = HB(4-Cl-3,5Me2N2C3)3) in high diastereoselectivity
(>95%) [4]. Stereoselective C–H bond oxidative additions could be
an important component of hydrocarbon functionalization medi-
ated by scorpionate compounds [5], providing impetus for investi-
gating oxidative addition reactions of new chiral scorpionate
compounds, as well as comparing related optically active and achi-
ral ligands.
Tris(oxazolinyl)boratoiridium(I) compounds were further ex-
plored to clarify their reactivity in the context of this Group 9 scor-
pionate chemistry. In this contribution, achiral ToMIr(I) compounds
(ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) and their
interactions with electrophiles are reported. Although enantiopure
IrToP-based compounds are amorphous as determined by line-
widths of solid state CPMAS NMR experiments [6], the achiral
IrToM compounds described here are crystalline and therefore
amenable to X-ray diffraction studies for structural analysis. Inter-
Therefore, we recently prepared the optically active scorpionate
compounds [Ir(ToP)L2] (ToP = tris(4S-isopropyl-2-oxazolinyl)phe-
nylborate, Chart 1; L2 =
g
4-C8H12 or (CO)2) to study stereoselective
estingly, the reaction of Li[ToM] and [Ir(
l
-Cl)(g
4-C8H12)]2 produces
-ToM)–
oxidative addition reactions [6]. However, reactions of [Ir(ToP)L2]
an unusual heterobimetallic complex that contains a [Li–(
l
Ir] interaction through N–Ir, N–Li, and O–Li bonds. The N–Ir inter-
actions are persistent in solution, as verified by 15N NMR chemical
shift data obtained using 1H–15N heteronuclear multiple bond cor-
* Corresponding author. Tel.: +1 515 294 8069; fax: +1 515 294 0105.
E-mail address: sadow@iastate.edu (A.D. Sadow).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.06.017

4518
A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
Ph
B
A few examples of O-coordinated oxazole-metal interactions (par-
Ph
B
H
B
ticularly benzoxazole, A in Fig. 2) have been proposed, and a euro-
pium(III) compound O-coordinated by 2-(20-pyridyl)-1,3-
benzoxazole has been crystallographically characterized [12]. The
configuration of divalent cobalt, nickel, copper, and zinc O-coordi-
nated benzoxazole compounds was assigned using their metal–
O
O
O
O
O
O
N
N
N
N
N
N
N
N
N
N
N
N
oxygen stretching frequencies (mM–O) in the far infrared [13], and
EPR studies supported oxygen binding in a related copper(II) com-
plex [14]. The dimeric [Pd(oxalato)(benzoxazole)]2 apparently in-
ToP
Chart 1.
ToM
Tp
volves
a
unique Pd–N-benzoxazole-O–Pd bridging structure
M–O and M–N [15]. In oxazoline
(structure B in Fig. 2) based on its
m
m
coordination chemistry, oxygen–metal interactions are less com-
mon. A trimeric lithium compound 2-(20-lithiophenyl)-4,4-di-
methyl-2-oxazoline was proposed to contain an oxygen–lithium
interaction, although N-coordination was not excluded [16]. Re-
cently, a zirconium(IV)-mediated oxazoline ring opening was sug-
gested to involve a Zr–O interaction [17].
relation (HMBC) experiments. Additionally, the X-ray data is
compared with model structures obtained from density functional
theory (DFT) calculations. These computational studies indicate
that the observed N-methylated and N-protonated oxazolinium
species are the thermodynamic products and thus favored
in
comparison
to
the
oxidative
addition
products
We have not found analogous examples of M-(
l
-Tp)-M0 or
[Ir(E)(ToM)L2]+ (E = H, Me).
M-(l
-pyrazolyl)-M0 structures from intact classic scorpionates in
the literature, although functionalized scorpionates have recently
provided heterobimetallic structures useful for building coordina-
tion networks, investigating Mꢀ ꢀ ꢀM0 electronic interactions, and
developing new catalytic reactions [18].
2. Results and discussion
2.1. Synthesis and characterization of tris(2-
oxazolinyl)boratoiridium(I) compounds
The structure of 1 is particularly interesting in the context of
salt metathesis reactions of polydentate anionic ligands. Presum-
The compound [(g l-j j l-
4-C8H12)Ir( 2-N1,N2-ToM- 2-N3,O2)Li(
Cl)]2 (1; N1, N2, N3, and O2 designate nitrogen- and oxygen-centers
ably the reaction of optically active Li[ToP] and 0.5 [IrCl(g4
-
C8H12)]2 that yields LiCl-free [Ir(ToP)( 4-C8H12)] [6] proceeds
g
in oxazoline rings 1, 2, and 3) is obtained upon heating a benzene
through structures in which oxazoline groups bond simultaneously
with both metal centers before the eventual extrusion of LiCl. Like-
wise, reactions of KTp and metal halides likely involve unobserved
heterobimetallic intermediates. Thus, compound 1 may be viewed
as an intermediate in salt metathesis reactions of polydentate li-
gand anions and metal halides. In the case of achiral Li[ToM], the
salt elimination is not completed under the reaction conditions,
by refluxing in tetrahydrofuran, by heating in non-polar solvents
(to precipitate LiCl), or by Soxhlet extraction. However, ligand sub-
stitution reactions and stronger electrophiles than Li+ will induce
LiCl extrusion (see below).
solution of Li[ToM] [11] and 0.5 equiv. of [Ir(
reflux for 18 h (Eq. (1)).
l
-Cl)(g
4-C8H12)]2 to
O
Ph
N
B
Ir
O
Cl
Li
N
Li
2 Li[ToM
[IrCl(η4-C8H12)]2
]
O
+
benzene
N
N
Ir
O
N
Cl
18 h, reflux
O
B
N
Ph
1
64%
O
Although 1 is C1-symmetric in the solid state, solution state
NMR data (in benzene-d6, methylene chloride-d2, and tetrahydro-
furan-d8) are consistent with Cs-symmetry. In the 1H NMR spec-
trum of 1 in tetrahydrofuran-d8, the oxazoline methyl resonances
appeared as three singlet resonances at 1.18, 1.24 and 1.46 ppm,
and three resonances assigned to ring methylene moieties were
observed as a singlet (3.5 ppm, 2 H) and two coupled diastereotop-
ic doublets (4.18 and 4.26 ppm, 4 H, 2JHH = 7.7 Hz) from one unique
and two equivalent oxazoline rings, respectively. The spectrum for
a C1-symmetric structure (not observed in solution) would contain
six singlet resonances and six doublets for oxazoline CH3 and CH2
groups. Thus, two of the three oxazolines are related by a mirror
ð1Þ
The solid state structure of 1 was established by X-ray crystal-
lography as an interesting heterobimetallic dimer in which the
[ToM] anion is a bridging bidentate ligand for one iridium and
one lithium center (Fig. 1). The pseudo-square planar iridium cen-
ters are coordinated by nitrogen from two oxazoline rings and by
1,5-cyclooctadiene. The nitrogen of the third oxazoline ring inter-
acts with a lithium cation, and that four-coordinate lithium center
is also bonded to the oxygen of the second oxazoline ring. Thus,
that oxazoline interacts with both iridium and lithium in a Li–O-
oxazoline-N–Ir bridging structure. The final two coordination sites
of the lithium cation are taken by two inversion-related chloride
ions that bridge to the symmetry-equivalent lithium cation in
the other half of the dimer. This configuration gives a (LiCl)2 planar
parallelogram (<Li1–Cl1–Li1#, 78.0(4)°; <Cl1–Li1–Cl1#, 102.0(4)°;
the <Li1–Cl1–Li1#–Cl1# dihedral angle is 0°), and the crystallo-
graphic inversion center that relates the two halves of the dimer
is located at the center of the parallelogram. The Ir–N distances
are identical within error (Ir1–N1, 2.107(5) and Ir1–N2,
2.107(6) Å) indicating that the lithium-oxygen interaction does
not affect the iridium–nitrogen bond distances. In this crystalline
phase, all three oxazoline groups are unique and 1 is C1-symmetric,
whereas in solution two oxazoline rings are related by a mirror
plane (see NMR discussion below).
plane that is coincident with the third oxazoline ring. A 1H–15
N
HMBC experiment helped identify the solution state coordination
mode of the [ToM] ligand in 1; two 15N NMR resonances at
ꢁ145.9 and ꢁ181.4 ppm (referenced to nitromethane and acquired
in tetrahydrofuran-d8) correspond to one unique and two equiva-
lent oxazoline nitrogen, respectively. The latter resonance was as-
signed to the iridium-coordinated oxazoline nitrogen based on its
crosspeaks with the two diastereotopic doublets in the 1H NMR
spectrum. The chemical shift of the former 15N NMR resonance
(ꢁ145.9 ppm) is 18 ppm upfield from that of uncoordinated 4,4-di-
methyl-2-oxazoline (ꢁ127.9 ppm) and substantially downfield
from the two oxazoline nitrogen that are coordinated to iridium
(ꢁ182 ppm, 36 ppm difference).
The structure of 1 contains the first crystallographically charac-
terized O-coordinated oxazoline, and it is further highlighted by a
unique heterobimetallic M-N-oxazoline-O-M0 bridging interaction.
These NMR data contrast the solution structures of 1 and the
optically active, LiCl-free derivative [Ir(ToP)( 4-C8H12)]; in the lat-
g
ter, the three 4S-isopropyloxazoline groups are equivalent due to a

A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
4519
Ir1
N1
N2
O2
B1
Cl1
O1
O3
N3
Li1
Li1
O1
Cl1
N3
O3
B1
O2
N1
N2
Ir1
Fig. 1. ORTEP diagram of [(
g
4-C8H12)Ir(
l
-j
2-N1,N2-ToM
-
j
2-N3,O2)Li(
l-Cl)]2 (1). Hydrogen atoms and a co-crystallized tetrahydrofuran molecule are not shown (for clarity),
and the ellipsoids are drawn at 50% probability. Bond distances: Ir1–N1, 2.107(5) and Ir1–N2, 2.107(6) Å.
designates bonding to the nitrogen on the third oxazoline ring,
Eq. (2)) rather than formation of an iridium-carbon bond.
[OTf]
O
N
O
N
Me
N
M'
M
M
O
MeOTf
-LiCl
A
B
O
0.5
1
R
R
N
Ir
Ph
B
Fig. 2. (A) O-coordinated benzoxazole, oxazole, or oxazoline, and (B) bridging M–
Ox–M0 benzoxazole/oxazole/oxazoline structures.
N
O
2
63%
rapid exchange process(es) [6]. However, the CPMAS 15N NMR
spectrum (Cross-polarization Magic Angle Spinning) of the chiral
ð2Þ
In benzene-d6, a small amount of precipitate (likely LiCl) formed
iridium compound revealed it is composed of a mixture of j2
-
and
j
3-isomers in the solid state. The 15N chemical shift of the
2-isomer of [Ir(ToP)(g4
upon addition of MeOTf to 1, and Cs-symmetric 2 was the only
product detected by 1H NMR spectroscopy. A new resonance at
3.12 ppm (3 H) was assigned to an N-methyl oxazoline moiety
based on its integrated intensity and its downfield chemical shift.
Furthermore, an intense crosspeak in the 1H–15N HMBC spectrum
showed coupling between the methyl moiety and an oxazoline
nitrogen (15N NMR: ꢁ208.0 ppm). This 15N NMR chemical shift
for the N–Me in 2 is far upfield from 4,4-dimethyl-oxazoline
uncoordinated oxazoline nitrogen in the
j
-
C8H12)] (ꢁ147 ppm) is similar to that of uncoordinated 4S-isopro-
pyl-2-oxazoline (ꢁ150 ppm).
The Li–O-oxazoline interaction of 1 in solution is either com-
pletely disrupted or the two oxazoline rings are exchanging rapidly
on the 1H NMR timescale. The low temperature 1H NMR spectrum
of 1 (toluene-d8, 190 K) is broad but the resonances do not coalesce
at or above this temperature. Thus, the lithium–oxygen interaction
is labile at least to 190 K.
(ꢁ127.5 ppm), the lithium-coordinated oxazoline in
1
(ꢁ145.9 ppm), as well as the iridium-coordinated oxazoline nitro-
gen of 2 and 1 at ꢁ175.0 and ꢁ181.4 ppm, respectively.
Given its lithium–oxazoline interactions, we were curious to
investigate reactivity of 1 with electrophiles and toward ligand
substitution. We speculated that oxidative addition would be more
likely with 1 because the third oxazoline is blocked by coordina-
tion to a cationic lithium center. Nonetheless, addition of MeOTf
to 1 at room temperature results in oxazoline N-methylation and
Oxazoline N-methylation in 2 was confirmed by a single crystal
X-ray diffraction study that also verified bidentate IrToM-coordina-
tion (Fig. 3). The two iridium–nitrogen bond distances are identical
within 3r (Ir1–N1, 2.105(6); Ir1–N2, 2.140(6)) and identical to the
Ir–N distances in 1. Although the phenyl group and the iridium
center are disposed syn, the ipso carbon of the phenyl group is
loss of LiCl producing [Ir(j g
2-ToM-N3-CH3)( 4-C8H12)][OTf] (2) (N3

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A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
oxazoline groups and a cyclooctadiene ligand, and the chemical
shifts are different from those of the lithium chloride adduct 1.
The reaction of 1 and CO could provide additional information
about substitution chemistry of iridium in this bimetallic system.
We considered that the lithium-, proton-, or methyl-oxazoline
interactions might facilitate [ToM-E] substitution rather than
C8H12 replacement, since the charge-neutral [ToM-E] could be a
better leaving group than anionic ancillary ligands such as [ToM]
or Tp. Conversely, cyclooctadiene substitution might affect the
oxazoline–lithium interaction by increasing the electrophilicity of
the iridium center. The mCO of the desired [Ir(ToM)(CO)2] product
are valuable for identifying the coordination geometry of the
[ToM] ligand. In analogy to [TpM(CO)2] systems [2], photochemical
carbonyl dissociation from [Ir(ToM)(CO)2] will access reactive spe-
cies. Finally, the smaller CO compounds are easier to model com-
putationally, and frequency calculations can be used to compare
calculated structures with experimental spectroscopic properties
(see below).
O3
B1
N3
O2
N2
N1
Ir1
C15
O1
Fig. 3. ORTEP diagram of [Ir(
j
2-ToM-Me)(
g
4-C8H12)][OTf] (2). Centroids are drawn
co-crystallized
When a benzene-d6 solution of 1 was exposed to carbon mon-
oxide, the resulting 1H NMR spectrum contained broad singlets
for the methyl (1.10 ppm) and methylene groups (3.50 ppm). We
were surprised to find that degassing this mixture after short reac-
tion times (ca. 1 h) resulted in regeneration of compound 1. How-
ever, when 1 was stirred for 18 h under a CO atmosphere, a
precipitate formed (presumably LiCl) and irreversible substitution
of 1,5-cyclooctadiene provided the pale yellow LiCl-free dicarbonyl
compound [Ir(ToM)(CO)2] (4) in 77% yield. In contrast to 1, the
[ToM] ligand of 4 appeared C3-symmetric in its 1H, 13C and 15N
NMR spectra. For example, only one 15N signal is detected at
ꢁ167.3 ppm in a 1H-15N HMBC experiment. The infrared spectrum
at 50% probability. Hydrogen atoms, OTfꢁ counterion, and
a
tetrahydrofuran molecule are omitted for clarity. Distances (Å): Ir1–N1, 2.105(6);
Ir1–N2, 2.140(6); N3–C15, 1.45(1).
approximately 3.43 Å from the iridium center, well outside the
sum of covalent radii (2.17 Å) [19], and the aryl C–C bond distances
are all identical within error.
Likewise, addition of HOTf to a benzene solution of 1 provides
[Ir(j g
2-ToM-N3-H)( 4-C8H12)][OTf] (3) in 81% yield. X-ray quality
crystals were obtained from evaporation of a concentrated tetrahy-
drofuran solution, and the solid state structure shows that the con-
formation of the [
very similar (compare Figs. 3 and 4). The Ir–N bond distances are
identical (within 3 ) for 1, 2, and 3 showing that the identity of
j
2-ToM-N3-E] (E = H, Me) ligands in 2 and 3 are
of 4 (methylene chloride) contains two sets of
m
CO; an intense pair
(2066 and 1989 cmꢁ1
)
and
a low intensity pair (2029 and
1933 cmꢁ1), which are assigned to the bidentate and tridentate
[ToM] coordination modes, respectively. Bidentate and tridentate
coordination of related tris(N-coordinating) ligands, particularly
tris(pyrazolyl)borates, to d8 metal centers has been investigated
r
the electrophile bonded to a pendent oxazoline does not affect
the iridium–oxazoline bonding. Protonated 3 is Cs-symmetric,
and sharp resonances were observed in the 1H NMR spectrum
(benzene-d6). Thus, the H- and Ir-coordinated oxazolines do not
exchange on the 1H NMR timescale. Additionally, the reaction of
3 and KH in THF-d8 results in deprotonation of the pendent oxaz-
olinium acid, giving a Cs-symmetric product. Resonances in the
1H NMR spectrum of this compound are assigned to inequivalent
using a range of spectroscopic techniques [20], including mCO values
[20a], N1/N2 chemical shift differences observed by 15N NMR spec-
troscopy [20a], 11B NMR chemical shift values [20b], relative ener-
gies of mBH [20c,d], as well as solid state and solution 15N NMR
spectroscopy [6,21]. For comparison [Tp*Ir(CO)2], the most closely
related pyrazolyl borate complex to 4, contains a tridentate
tris(pyrazolyl)borate as suggested by its mCO (2039 and
1960 cmꢁ1) [7a]. However, the unsubstituted [TpIr(CO)2] is a mix-
ture of four- and five-coordinate species [7a].
Compound 4 reacts with the electrophiles MeOTf and HOTf in
benzene to form [Ir(j
2-ToM-N3-E)(CO)2][OTf] (E = Me (5), 53%;
O3
E = H (6), 63%). The 1H NMR and 1H–15N HMBC spectra are consis-
tent with formation of electrophile-oxazoline bonds and overall Cs-
symmetric molecules as described above for the cyclooctadiene
compounds 2 and 3. An X-ray crystal structure of 5 was obtained
from a concentrated benzene solution (Fig. 5). In contrast to the
structures of 2 (and 3), the methylated oxazoline ring is syn with
respect to the iridium center, and the phenyl group is located anti
to iridium.
B1
O2
N3
N2
N1
H3
Ir1
O1
Both iridium dicarbonyl compounds 5 and 6 can be prepared by
reaction of carbon monoxide with 2 and 3, respectively. Thus,
cyclooctadiene is preferentially replaced for CO, and the overall
non-charged (though zwitterionic) [ToM-E] ligands are not
displaced.
2.2. Computational model structures based on dicarbonyl
tris(oxazolin-2-yl)boratoiridium(I)
Fig. 4. ORTEP diagram of [Ir(j g
2-ToM-H)( 4-C8H12)][OTf] (3). Centroids are drawn at
50% probability. Hydrogen atoms (except for the hydrogen on the protonated
oxazoline), the OTfꢁ counterion, and a co-crystallized tetrahydrofuran molecule are
hidden for clarity. Distances (given in Å): Ir1–N1, 2.098(8); Ir1–N2, 2.120(6); N3–
H3 was not refined.
DFT calculations on
tris(oxazolin-2-yl)borate) provide insight into the structures and
a =
model system [Ir(ToX)(CO)2] (ToX

A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
4521
and 1987 cmꢁ1) [6]. This IR data comparison suggests that the
tris(oxazolinyl)borate ligands are bidentate in 4 and [Ir(ToP)(CO)2].
However, structural conclusions from these DFT calculations are in
conflict with our solid state CPMAS 13C and 15N NMR spectroscopic
data that suggest the coordination mode in [Ir(ToP)(CO)2] is triden-
tate [6]. We made multiple attempts to locate a stationary point
corresponding to a five-coordinate iridium complex by starting
with tridentate ToXIr(I) species, but none are found. A constrained
geometry optimization of one five-coordinate model compound, in
which Ir–N distances were fixed at 2.111, 2.020, and 2.080 Å, is
14.2 kcal/mol higher in energy than the four-coordinate minimum
described above. When these Ir–N distance constraints are re-
moved, the structure optimized to the four-coordinate structure
described above. Crystal forces could be responsible for the struc-
tural difference, since C is modeled in the gas phase.
O3
N3
O2
B1
N2
O5
C16
C24
Ir1
N1
C23
O1
O4
The Kohn–Sham orbitals and their relative energies (Fig. 6) in
this model system suggest that the iridium(I) center is (1) not suf-
ficiently electrophilic to form a five-coordinate structure and (2)
less nucleophilic than the uncoordinated oxazoline group. Notably,
the highest occupied (Kohn–Sham) molecular orbital (HOMO) is
Fig. 5. ORTEP diagram of [Ir(j
2-ToM-Me)(CO)2][OTf] (5). Centroids are drawn at 50%
probability. Hydrogen atoms, the OTfꢁ counterion, and a co-crystallized benzene
molecule are hidden for clarity. Distances (given in Å): Ir1–N1, 2.090(8); Ir1–N2,
2.074(8); Ir1–C23, 1.82(2); Ir1–C24, 1.87(1); C23–O4, 1.17(2); C24–O5, 1.12(1);
N3–C16, 1.46(1). Angles given in °: C23–Ir1–C24, 87.1(5); N1–Ir1–N2, 85.9(3); N1–
Ir1–C23, 93.2(4); N2–Ir1–C24 94.0(4).
the C@N
p-bond located on the non-coordinated oxazoline. The
next highest occupied orbitals are the iridium dz2-like orbital
12.1 kcal/mol (0.52 eV) below the HOMO, and the non-coordinated
oxazoline N-lone pair 15.9 kcal/mol (0.691 eV) below the HOMO.
The lowest unoccupied molecular orbital (LUMO) is a mixture of
selectivity observed in the reactions described above. The opti-
mized model compound [Ir(ToX)(CO)2] (C, B3LYP [22], in the gas
phase) is a four-coordinate, square planar iridium compound with
bidentate N,N-[ToX] coordination (Ir–N, 2.106 and 2.107 Å). The
third oxazoline is not coordinated to iridium (Ir–N3, 5.250 Å).
dxy and py orbitals on the metal center, as well as some CO p* char-
acter, that is available to bond to the nonbonding electron pair on
the uncoordinated oxazoline. Although this orbital is directed to-
ward the ‘free’ oxazoline, this bonding is discouraged because the
LUMO is high in energy (97.2 kcal/mol or 4.2 eV above the HOMO)
and the highest filled orbital on the oxazoline (pCN character) has
The Ir–N bond distances in this [Ir(j
2-ToX)(CO)2] structure are
identical (within error) to the distances in 1 determined by X-ray
diffraction. Based on a Hessian calculation, this structure is a local
minimum; in contrast, no minimum energy structure could be lo-
cated for five-coordinate geometries in which the [ToX] ligand is
the wrong symmetry for bonding to the LUMO (r). Clearly, the
HOMO and HOMO-2 on the oxazoline, as well as the HOMO-1 on
iridium, are available for bonding to external electrophiles.
Additionally, the charges on atoms in the ToMIr-system can pro-
vide insight into its electronic properties, and these have been
evaluated with Mulliken charges determined for the model com-
pound C. In C, the boron center is negatively charged (ꢁ0.38
tridentate. The calculated mCO for [Ir(j
2-ToX)(CO)2] (corrected)
[23] are 2065 and 1993 cmꢁ1, which compare extremely well with
[Ir(ToM)(CO)2] (4) (2066 and 1989 cmꢁ1) and [Ir(ToP)(CO)2] (2065
Fig. 6. Rendered structures of [Ir(j
2-ToX)(CO)2] (C) illustrating the Kohn–Sham orbitals for a) HOMO-2, b) HOMO-1, c) HOMO, and d) LUMO. The relative energies for each
orbital are given in eV.

4522
A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
electrons) as expected, and the nitrogen in the pendent oxazoline
also has some anionic character (ꢁ0.19 electrons). The iridium cen-
ter contains significant positive character (+0.59 electrons), so the
pCN bond, and this HOMO is consistent with our observed reactiv-
ity. Additionally, the calculations show that oxazoline-methylation
(and likely oxazoline-protonation) is thermodynamically favored
over iridium-based oxidative addition in these compounds. In con-
trast to these results, [Tp*Rh(CO)2] and MeI react via oxidative
description of [Ir(j
2-ToX)(CO)2] as a zwitterionic boratoiridium(I)
complex is reasonable.
*
To better understand the selectivity for oxazoline N-methyla-
tion versus oxidative addition to iridium, the model compounds
addition [9], although [Tp Rh(CO)2] also reacts with HBF4ꢀOEt2
via pyrazolyl protonation [7a]. Additionally, a cationic rhodium
compound containing the neutral tris-ox ligand [Rh(tris-
ox)(C8H12)]+ has been oxidized by CsBr3 to [RhBr3(tris-ox)] [10].
These contrasting results could be attributed to differences in li-
gand (neutral versus anionic), metal center (rhodium versus irid-
ium), or oxidant (CsBr3 versus H+, Me+). Regardless, the mCO for 4
and [Ir(ToP)(CO)2] suggest that the tris(oxazolinyl)borate ligands
are sufficiently electron donating to mediate oxidative addition
of non-polar bonds under photolytic conditions. Our investigations
of stereoselective oxidative additions will be disclosed in due
course.
[Ir(
mized. The calculated structure of the model oxazoline-methylated
compound [Ir(
2-ToX-Me)(CO)2]+ successfully reproduces the bond
lengths and angles of the crystallographically characterized 5. The
Ir–N distances (2.12 Å), Ir–C distances (1.87 Å), the Noxazoline
j j
2-ToX-Me)(CO)2]+ (D) and [IrMe( 3-ToX)(CO)2]+ (E) were opti-
j
–
Cmethyl distance (1.46), and the C@O distances (1.14 Å) in the calcu-
lated structure are all identical with 5 within error. The square
planar geometry of iridium is observed in this calculated structure
and in the X-ray data, and the N–Ir–N angle (87.1°) is only slightly
larger than the experimental value of 85.9(3)° and the N–Ir–C an-
gles are slightly smaller (calculated 91.4° versus experimental
94.0(4) and 93.2(4)°). Thus, there is good structural agreement be-
tween calculated structure D and compound 5. Structural compar-
isons of the optimized geometry for the oxidative addition product
E were not possible since corresponding methyliridium(III) species
could not be prepared. Importantly, D is 12.4 kcal/mol lower in en-
ergy than E (electronic and zero point energy correction). Thus,
these gas phase model compounds predict that the observed oxaz-
oline-methylation product is thermodynamically favored over the
oxidative addition product.
4. Experimental
4.1. General procedures
All manipulations were performed under a dry argon atmo-
sphere using standard Schlenk techniques, or under a nitrogen
atmosphere in a glovebox unless otherwise indicated. Dry, oxy-
gen-free solvents were used throughout. Benzene, toluene, pen-
tane, methylene chloride, and tetrahydrofuran were degassed by
sparging with nitrogen, filtered through activated alumina col-
umns, and stored under N2. Benzene-d6 and tetrahydrofuran-d8
were vacuum transferred from Na/K alloy and stored under N2 in
the glovebox. Lithium tris(4,4-dimethyl-2-oxazolinyl)phenylb-
The (corrected) m
CO for D (2089 and 2022 cmꢁ1) are higher than
the experimental values for 5 (2069 and 1997 cmꢁ1), and we attri-
bute this difference to the approximation of 5 by a gas phase coun-
terion-free cationic species. Although experimental and calculated
mCO deviated slightly, the mCO differences for calculated structures
orate (Li[ToM]) [11] and [Ir( 4-C8H12)]2 [24] were synthe-
l-Cl)(g
sized as previously reported. All other reagents were purchased
from Aldrich and used as received.
[Ir(
and
and [IrMe(
87 cmꢁ1), and the experimental compounds [Ir(ToM)(CO)2] (4)
j
2-ToX)(CO)2] and [Ir(
j
2-ToX-Me)(CO)2]+
(
D
m
COsym = 25 cmꢁ1
2-ToX)(CO)2]
;
D
m
COasym = 30 cmꢁ1), calculated structures [Ir(
3-ToX)(CO)2]+ COsym = 69 cmꢁ1
and DmCOasym =
j
1H, 11B, and 13C{1H} solution NMR spectra were collected on
Bruker DRX-400 or Avance II 700 spectrometers. 15N chemical
shifts were determined by 1H–15N HMBC experiments on a Bruker
Avance II 700 spectrometer with a Bruker Z-gradient inverse TXI
1H/13C/15N 5 mm cryoprobe. 15N chemical shifts were originally re-
corded with respect to liquid NH3 (machine calibration) and recal-
culated to the CH3NO2 chemical shift scale by adding ꢁ381.9 ppm.
Elemental analysis was performed using a Perkin–Elmer 2400 Ser-
ies II CHN/S by the Iowa State Chemical Instrumentation Facility.
j
(D
m
;
and [Ir(ToM-Me)(CO)2][OTf] (5) ( COsym = 3 cmꢁ1; and
DmCOasym =
D
m
8 cmꢁ1) are worth considering. In the calculations, oxazoline
N-methylation produces a smaller effect on the mCO than the
change upon oxidative addition to iridium. The change in the IR
spectrum upon methylation is even smaller for the experimental
[Ir(ToM)(CO)2] compounds.
The oxazoline-protonated structure [Ir(
j
2-ToX-H)(CO)2]+ (F) is a
model for the observed product [Ir(
j
2-ToM-H)(CO)2][OTf] (6), and
the optimized structure of F is a minimum on the potential energy
surface. Direct structural comparisons between calculated F and
compound 6 were not made because X-ray data was not available
for 6. However the relative energies obtained from the calculations
are consistent with our experimental observations favoring oxazo-
line protonation, since the minimum for the iridium(III)-hydride
4.2. [(
g l-j j l-Cl)]2. (1)
4-C8H12)Ir( 2-N1,N2-ToM- 2-N3,O2)Li(
A 100 mL Teflon-sealed flask was charged with [Ir(
l
-Cl)(g4
-
C8H12)]2 (0.50 g, 0.74 mmol), 2 equiv. of Li[ToM] (0.58 g, 1.5 mmol),
and 50 mL of benzene. This mixture was heated at 80 °C for 18 h.
The resulting suspension was filtered and the solvent removed
from the filtrate under vacuum to give a red solid. Methylene chlo-
ride (20 mL) was added to the residue, the volume was reduced to
10 mL, and the mixture was filtered to wash away the red compo-
nent of the material. The remaining yellow solid was washed with
pentane (20 mL) and dried under vacuum to afford 0.69 g of 1 as a
yellow powder (0.48 mmol, 64% yield). X-ray quality crystals were
obtained by slow evaporation of a tetrahydrofuran solution of iso-
lated 1. 1H NMR (tetrahydrofuran-d8, 700 MHz): d 0.85 (m, 2 H,
species [Ir(j
3-ToX)H(CO)2]+ (G) is 7.46 kcal/mol higher in energy
than protonated-oxazoline structure F. Thus, 6 is most likely the
thermodynamically favored product.
3. Concluding remarks
Tris(oxazolinyl)boratoiridium(I) scorpionates clearly differ from
isoelectronic tris(pyrazolyl)borates in their interactions with elec-
trophiles. Protonation of TpML2-type compounds provides metal
hydrides in several cases [7], whereas three electrophiles EX (EX = -
C8H12), 1.11 (m, 2 H, C8H12), 1.18 (s, 6 H,
), 1.24 (s,
NCMe2CH2OC
), 1.31 (m, 2 H, C8H12), 1.46 (s, 6 H,
HOTf, MeOTf, and LiCl) interact with [Ir(ToM)L2] to give [Ir( 2-ToM-
j
6 H,
NCMe2CH2OC
E)L2]+ compounds. These oxazoline-electrophile interactions have
been established by 15N NMR HMBC experiments through chemi-
cal shift comparisons and through-bond coupling, as well as
through X-ray crystallography. Our computational results indicate
that the highest energy electron pair resides in a non-coordinated
), 2.05 (m, 2 H, C8H12), 3.50 (s, 2 H,
),
),
),
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
2
3.65 (m, 2 H, C8H12), 4.18 (d, 2 H, JHH = 7.7 Hz,
2
4.22 (m, 2 H, C8H12), 4.26 (d, 2 H, JHH = 7.7 Hz,

A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
4523
3
3
7.07 (t, 1 H, JHH = 7.0 Hz, para-C6H5), 7.17 (t, 2 H, JHH = 7.0 Hz,
1.12 (m, 2 H, C8H12), 1.16 (s, 6 H, H
NCMe2CH2OC
), 1.19 (m, 2 H
meta-C6H5), 7.25 (d, 2 H, JHH = 7.0 Hz, ortho-C6H5). 13C{1H} NMR
3
C8H12), 1.40 (s, 6 H, Ir
NCMe2CH2OC
), 1.91 (m, 2 H, C8H12), 3.19 (s,
(tetrahydrofuran-d8, 150 MHz): d 26.15 (
), 27.68
), 29.42 (C8H12), 30.79
NCMe2CH2OC
2 H,
H
), 3.63 (m, 2 H, C8H12), 3.78 (d, 2 H,
NCMe2CH2OC
(
), 27.86 (
NCMe2CH2OC
NCMe2CH2OC
(C8H12), 59.91 (C8H12), 62.70 (C8H12), 68.53
77.00 ( ), 82.78 ( ), 124.65 (para-C6H5),
2JHH = 8.0 Hz, Ir
2JHH = 8.0 Hz, Ir
), 4.10 (m, 2 H, C8H12), 4.74 (d, 2 H,
NCMe2CH2OC
(
),
NCMe2CH2OC
3
), 7.22 (t, 1 H,
JHH = 7.2 Hz, para-
NCMe2CH2OC
NCMe2CH2OC NCMe2CH2OC
3
C6H5), 7.31 (t, 2 H, JHH = 7.2 Hz, meta-C6H5), 7.38 (d, 2 H,
3JHH = 7.2 Hz, ortho-C6H5), 11.73 (br s, 1 H, NH). 13C{1H} NMR (tet-
126.91 (meta-C6H5), 134.04 (ortho-C6H5). 15N{1H} NMR (tetrahy-
drofuran-d8, 71 MHz): d ꢁ145.9 (N–Li), -181.4 (N–Ir). 11B NMR
(benzene-d6, 128 MHz): d ꢁ15.7. IR (KBr, cmꢁ1):
m
3064 (w),
rahydrofuran-d8, 125 MHz):
d
26.57
(
), 28.62
NCMe2CH2OC
2999 (w), 2964 (s), 2929 (m), 2881 (m), 2835 (w), 1610 (s), 1573
(s), 1463 (m), 1431 (w), 1363 (w), 1280 (s), 1199 (s), 1158 (m),
996 (m), 970 (s), 894 (w), 819 (w), 781 (w), 730 (m). Anal. Calc.
for C29H41BCl2IrLi2N3O3: C, 48.04; H, 5.70; N, 5.80. Found: C,
48.14; H, 5.78; N, 5.46%. mp 250ꢁ254 °C, dec.
(
) and
, 30.61 (C8H12), 31.63 (C8H12),
NCMe2CH2OC
NCMe2CH2OC
33.01 (
), 61.28 (C8H12), 63.75 (
), 64.43
NCMe2CH2OC
NCMe2CH2OC
(C8H12), 70.42
(
), 83.30
(
), 83.96
NCMe2CH2OC
NCMe2CH2OC
(
), 122.00 (SO3CF3), 126.93 (C6H5), 128.53 (C6H5),
NCMe2CH2OC
4.3. [Ir(j g
2-ToM-N3-Me)( 4-C8H12)][OTf] (2)
134.66 (C6H5). 15N{1H} NMR (tetrahydrofuran-d8, 71 MHz):
d
ꢁ206.3 (N–H), ꢁ180.0 (N–Ir). 11B NMR (benzene-d6, 128 MHz): d
ꢁ16.3. 19F NMR (benzene-d6, 376 MHz): d ꢁ78.30. IR (KBr, cmꢁ1):
CH3OTf (1.0 mL, 0.152 M in benzene) was added to a benzene
solution of compound 1 (0.10 g, 0.069 mmol). The solution was
stirred overnight, and the color changed from pale orange to yel-
low–green. The volatile materials were removed under reduced
pressure to give a powder, and the resulting solid 2 (0.075 g,
0.087 mmol, 63%) was washed with pentane (10 mL). Slow evapo-
ration of a concentrated tetrahydrofuran solution of 2 at room tem-
m
3220 (br w), 3091 (w), 3007 (m), 2973 (m), 2929 (m), 2878
(m), 2834 (w), 1603 (m sh), 1581 (s), 1463 (m), 1433 (w), 1390
(w), 1373 (m), 1294 (s), 1250 (s), 1225 (m), 1153 (s), 1032 (s),
1005 (m), 961 (m), 727 (m). Anal. Calc. for C30H42BF3IrN3O6S: C,
43.27; H, 5.08; N, 5.05. Found: C, 43.12; H, 5.37; N, 4.31%.
mp137–178 °C, dec.
perature
(tetrahydrofuran-d8, 700 MHz): d 0.92 (m, 2 H, C8H12), 1.06 (m,
2 H, C8H12), 1.24 (s, 6 H, Ir ), 1.34 (m, 2 H, C8H12),
provided
X-ray
quality
crystals.
1H
NMR
4.5. [Ir(ToM)(CO)2] (4)
NCMe2CH2OC
), 1.58 (s, 6 H, Ir
A Teflon-sealed flask was charged with 1 (0.35 g, 0.24 mmol)
dissolved in benzene (50 mL). The solution was degassed with
freeze–pump–thaw cycles, the headspace was evacuated, and
carbon monoxide was added. The reaction mixture was stirred vig-
orously for 18 h during which time the color changed to pale yel-
low–green. The volatile materials were removed in vacuo to afford
[Ir(ToM)(CO)2] as a pale yellow powder (0.23 g, 0.37 mmol, 77%). 1H
1.47 (s, 6 H, Me
NCMe2CH2OC
),
NCMe2CH2OC
2.11 (m, 2 H, C8H12), 3.12 (s, 3 H, NCH3), 3.67 (m, 2 H, C8H12),
2
4.19 (d, 2 H, JHH = 8.4 Hz, Ir
), 4.31 (m, 2 H, C8H12),
NCMe2CH2OC
2
4.34 (s, 2 H, Me
), 4.37 (d, 2 H, JHH = 8.4 Hz,
NCMe2CH2OC
3
Ir
), 7.14 (d, 2 H, JHH = 7.0 Hz, ortho-C6H5), 7.21 (t,
NCMe2CH2OC
3
3
1 H, JHH = 7.0 Hz, para-C6H5), 7.17 (t, 2 H, JHH = 7.0 Hz, meta-
NMR (tetrahydrofuran-d8, 700 MHz):
d
1.27 (s, 18 H,
C6H5). 13C{1H} NMR (tetrahydrofuran-d8, 125 MHz):
d
24.19
), 3.93 (s, 6 H,
), 6.91 (t, 1 H,
NCMe2CH2OC
NCMe2CH2OC
3JHH = 7.7 Hz, para-C6H5), 6.97 (t, 2 H, JHH = 7.7 Hz, meta-C6H5),
3
(
), 26.21
(
), 28.15
(
),
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
30.52 (C8H12), 31.51 (C8H12), 32.41 (NCH3), 61.57 (C8H12), 64.57
7.29 (d, 2 H, 3JHH = 7.0 Hz, ortho-C6H5). 13C{1H} NMR (tetrahydrofu-
(C8H12), 71.09
(
), 82.15
(
), 83.98
ran-d8, 150 MHz): d 25.68 (
), 66.08 (
),
), 122.72 (para-C6H5), 124.05 (meta-C6H5),
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
1
(
), 122.17 (q, JFC = 319 Hz, OSO2CF3), 127.01 (para-
77.87 (
NCMe2CH2OC
NCMe2CH2OC
C6H5), 128.62 (meta-C6H5), 134.66 (ortho-C6H5). 15N{1H} NMR (tet-
rahydrofuran-d8, 71 MHz): d ꢁ174.7 (N–Ir), ꢁ208.8 (N–Me). 11B
NMR (tetrahydrofuran-d8, 128 MHz): d ꢁ16.1. 19F NMR (tetrahy-
132.50 (ortho-C6H5), 176.63(CO) 15N NMR (tetrahydrofuran-d8,
71 MHz): d ꢁ167.1. 11B NMR (tetrahydrofuran-d8, 128 MHz): d
ꢁ18.7. IR (CH2Cl2, cmꢁ1):
m 2970 (m), 2931 (w), 2898 (w), 2066
drofuran-d8, 376 MHz): d ꢁ81.8. IR (KBr, cmꢁ1):
m
3036 (w), 2969
(s), 2029 (w), 1989 (s), 1934 (w), 1613 (w), 1566 (m), 1461 (w),
1391 (w), 1364 (m), 1291 (m), 1205 (m), 1166 (w), 989 (m). Anal.
Calc. for C23H31BIrN3O5: C, 43.67; H, 4.94; N, 6.64. Found: C, 43.13;
H, 4.62; N, 6.15%. mp 203–208 °C, dec.
(m), 2934 (m), 2881 (m), 2836 (w), 1599 (m sh), 1577 (s), 1465
(m), 1434 (w), 1389 (w), 1374 (m), 1322 (s), 1299 (s), 1266 (s),
1183 (s), 1169 (s), 1057 (m), 1043 (s), 1032 (s), 957 (m), 897 (w),
804 (w). Anal. Calc. for C31H44BF3IrN3O6S: C, 43.97; H, 5.24; N,
4.96. Found: C, 43.89; H, 5.18; N, 5.38%. mp 173–175 °C, dec.
4.6. [Ir(j
2-ToM-N3-Me)(CO)2][OTf] (5)
4.4. [Ir(j g
2-ToM-N3-H)( 4-C8H12)][OTf] (3)
A 50 mL Schlenk flask was charged with 4 (0.10 g, 0.16 mmol),
benzene (25 mL), and 1.0 mL of MeOTf (0.152 M in benzene). After
the solution was stirred overnight. The volatile materials were re-
moved in vacuo, and the resulting solid was washed with pentane
(10 mL) to give 0.068 g of 5 (0.09 mmol, 53%). 1H NMR (tetrahydro-
Compound 1 (0.20 g, 0.14 mmol) was dissolved in benzene
(25 mL), and a benzene solution of triflic acid (1.8 mL, 0.15 M)
was added. As the mixture was stirred overnight, the color changed
from pale orange to yellow–green. The solvent was then removed
in vacuo, and the resulting solid was washed with pentane (10 mL)
and dried under vacuum to yield 3 (0.19 g, 0.22 mmol, 81%). X-ray
quality crystals were obtained by slow evaporation of a tetrahydro-
furan solution at room temperature. 1H NMR (benzene-d6,
furan-d8, 400 MHz): d 1.45 (s, 6 H, Ir
), 1.51 (s, 6 H,
NCMe2CH2OC
), 3.10 (s, 3 H,
Me
NCMe2CH2OC
), 1.53 (s, 6 H, Ir
NCMe2CH2OC
2
NCH3), 4.41 (d, 2 H, JHH = 8.4 Hz, Ir
), 4.49 (s, 2 H,
NCMe2CH2OC
2
Me
NCMe2CH2OC
), 4.55 (d, 2 H, JHH = 8.4 Hz, Ir
),
400 MHz): d 0.80 (s, 6 H, Ir
NCMe2CH2OC
), 0.88 (m, 2 H, C8H12),
NCMe2CH2OC

4524
A.V. Pawlikowski et al. / Inorganica Chimica Acta 362 (2009) 4517–4525
7.10 (d, 2 H, 3JHH = 6.4 Hz, ortho-C6H5), 7.15–7.22 (m, 3 H, para- and
meta-C6H5). 13C{1H} NMR (tetrahydrofuran-d8, 125 MHz): d 24.12
surface. The corrections for the mCO [23] are similar to those found
for other similar B3LYP calculations [28].
(
), 27.91
(
), 28.18
(
),
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
Acknowledgement
31.14 (NCH3), 71.17 (
), 82.46 (
NCMe2CH2OC
), 82.70
NCMe2CH2OC
We thank the U.S. DOE office of Basic Energy Sciences, through
the Catalysis Science Grant No. AL-03-380-011, the Roy J. Carver
Charitable Trust, and the National Science Foundation (Award
number OCI-0749156) for support. We gratefully acknowledge
Ames Laboratory and Iowa State University for computational re-
sources. Dr. Bruce Fulton is thanked for assistance collecting 15N
NMR spectral data.
1
(
), 122.17 (q, JFC = 319 Hz, OSO2CF3), 127.68 (para-
NCMe2CH2OC
C6H5), 128.74 (meta-C6H5), 133.85 (ortho-C6H5), 173.65 (CO).
15N{1H} NMR (tetrahydrofuran-d8, 71 MHz): ꢁ211.0 (N–Me),
ꢁ181.0 (N–Ir). 11B NMR (tetrahydrofuran-d8, 128 MHz): d ꢁ16.5.
19F NMR (tetrahydrofuran-d8, 376 MHz): d ꢁ81.8. IR (KBr, cmꢁ1):
m
3072 (w), 3006 (w), 2976 (m), 2937 (w), 2069 (s), 1997 (s),
1602 (m), 1575 (s), 1541 (w), 1479 (w), 1461 (m), 1435 (w),
1392 (w), 1297 (s), 1279 (s), 1257 (s), 1224 (w), 1208 (w), 1154
(s), 1031 (s), 956 (m). Anal. Calc. for C28H35BF3IrN3O8S: C,
39.58; H, 4.15; N, 4.95. Found: C, 39.74; H, 4.17; N, 4.89%. mp
145–147 °C.
Appendix A. Supplementary material
Details of DFT optimized atomic coordinates and normal modes,
and X-ray diffraction collection, atomic coordinates, and refined
bond lengths and angles.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2009.06.017.
4.7. [Ir(j
2-ToM-N3-H)(CO)2][OTf] (6)
A flask was charged with [Ir(ToM)(CO)2] (0.1 g, 0.16 mmol) dis-
solved in benzene (25 mL). A benzene solution of triflic acid
(1.0 mL, 0.15 M) was added and the solution was stirred overnight.
All volatile materials were removed in vacuo to provide a yellow
solid, which was washed with pentane (10 mL) and dried under
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vacuum. Compound
0.10 mmol). 1H NMR (tetrahydrofuran-d8, 700 MHz): d 1.43 (s,
6 H, Ir ), 1.50 (s, 6 H, H ), 1.51 (s, 6 H,
6 was isolated in 63% yield (0.080 g,
NCMe2CH2OC
NCMe2CH2OC
), 4.57 (d, 2 H,
Ir
), 4.36 (m, 4 H,
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
3
Ir
), 7.09 (d, 2 H, JHH = 8.8 Hz, ortho-C6H5), 7.13–
7.20 (m, 3 H, para- and meta-C6H5), 11.92 (s, 1 H, NH). 13C{1H}
(b) M. Bovens, T. Gerfin, V. Gramlich, W. Petter, L.M. Venanzi, M.T. Haward, S.A.
Jackson, O. Eisenstein, New J. Chem. 16 (1992) 337;
NMR (tetrahydrofuran-d8, 125 MHz): 26.57 ),
d
(
NCMe2CH2OC
(c) J.S. Wiley, D.M. Heinekey, Inorg. Chem. 41 (2002) 4961.
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9771.
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27.92
(
),
28.50
(
),
63.89
NCMe2CH2OC
NCMe2CH2OC
(
), 70.54
(
), 82.58
(
),
NCMe2CH2OC
NCMe2CH2OC
NCMe2CH2OC
1
83.48 (
NCMe2CH2OC
), 121.93 (q, JFC = 320 Hz, OSO2CF3), 127.46
(para-C6H5), 128.57 (meta-C6H5), 133.78 (ortho-C6H5), 174.20
(CO). 15N{1H} NMR (tetrahydrofuran-d8, 71 MHz): d ꢁ207.1 (N–
H), ꢁ161.4 (N–Ir). 11B NMR (tetrahydrofuran-d8, 128 MHz): d
ꢁ16.6. 19F NMR (tetrahydrofuran-d8, 376 MHz): d ꢁ79.8. IR (KBr,
cmꢁ1):
m 3237 (br w), 2974 (m), 2933 (w), 2880 (w sh), 2067 (s),
1990 (s), 1584 (br s), 1464 (m), 1434 (w), 1392 (w), 1373 (w),
1295 (s), 1248 (s), 1208 (w), 1164 (m), 1043 (m), 1030 (m), 967
(w). Anal. Calc. for C24H32BF3IrN3O8S: C, 36.83; H, 4.12; N, 5.37.
Found: C, 36.61; H, 4.10; N, 5.14%. mp 76–85 °C, dec.
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5. Details of the density functional theory calculations
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suite [25]. Density functional theory (DFT) was employed using
the B3LYP [22] hybrid functional to obtain optimized geometries
and frequencies (see Supplementary material). Energies were also
calculated using DFT with the B3LYP functional and include the
zero point energy correction. The Los Alamos double-f ECP
(LANL2DZ) [26] was used for iridium and the 6ꢁ311+G* [27] basis
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mined using a tolerance of 5 ꢂ 10ꢁ7 for the orbital overlap. Orbitals
with overlap values greater than this threshold were deemed line-
arly dependent and subsequently removed. Additionally, the en-
ergy convergence was tightened to 10ꢁ11 hartree. All structures
reported have positive second derivatives with respect to coordi-
nates, indicating that they are all minima on the potential energy
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4525
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comparison of calculated and experimental mCO for [Cp*Ir(CO)2] were used to
correct the raw values.
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