Allylic C-H bond activation and functionalization mediated by tris(oxazolinyl)borato rhodium(i) and iridium(i) compounds

Article abstract of DOI:10.1039/c1dt10249d

Allylic C-H bond oxidative addition reactions, mediated by tris(oxazolinyl)borato rhodium(i) and iridium(i) species, provide the first step in a hydrocarbon functionalization sequence. The bond activation products To^MMH(η³-C₈H₁₃) (M = Rh (1), Ir (2)), To^MMH(η³-C₃H₅) (M = Rh (3), Ir (4)), and To^MRhH(η³-C₃H ₄Ph) (5) (To^M = tris(4,4-dimethyl-2-oxazolinyl) phenylborate) are synthesized by reaction of Tl[To^M] and the corresponding metal olefin chloride dimers. Characterization of these group 9 allyl hydride complexes includes ¹H-¹⁵N heteronuclear correlation NMR experiments that reveal through-metal magnetization transfer between metal hydride and the trans-coordinated oxazoline nitrogen. Furthermore, the oxazoline ¹⁵N NMR chemical shifts are affected by the trans ligand, with the resonances for the group trans to hydride typically downfield of those trans to η³-allyl and tosylamide. These group 9 oxazolinylborate compounds have been studied to develop approaches for allylic functionalization. However, this possibility is generally limited by the tendency of the allyl hydride compounds to undergo olefin reductive elimination. Reductive elimination products are formed upon addition of ligands such as CO and CN^tBu. Also, To^MRhH(η³-C ₈H₁₃) and acetic acid react to give To ^MRhH(κ²-O₂CMe) (8) and cyclooctene. In contrast, treatment of To^MRhH(η³-C₃H ₅) with TsN₃ (Ts = SO₂C₆H ₄Me) gives the complex To^MRh(η³-C ₃H₅)NHTs (10). Interestingly, the reaction of To ^MRhH(η³-C₈H₁₃) and TsN ₃ yields To^MRh(NHTs)(H)OH₂ (11) and 1,3-cyclooctadiene via β-hydride elimination and Rh-H bond amination. Ligand-induced reductive elimination of To^MRh(η³- C₃H₅)NHTs provides HN(CH₂CHCH₂)Ts; these steps combine to give a propene C-H activation/functionalization sequence.

Full text of DOI:10.1039/c1dt10249d

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PAPER
Allylic C–H bond activation and functionalization mediated by
tris(oxazolinyl)borato rhodium(I) and iridium(I) compounds
Hung-An Ho, Tristan S. Gray, Benjamin Baird, Arkady Ellern and Aaron D. Sadow*
Received 14th February 2011, Accepted 31st March 2011
DOI: 10.1039/c1dt10249d
Allylic C–H bond oxidative addition reactions, mediated by tris(oxazolinyl)borato rhodium(I) and
iridium(I) species, provide the first step in a hydrocarbon functionalization sequence. The bond
3
3
activation products ToMMH(h -C8H13) (M = Rh (1), Ir (2)), ToMMH(h -C3H5) (M = Rh (3), Ir (4)), and
ToMRhH(h -C3H4Ph) (5) (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) are synthesized by
3
reaction of Tl[ToM] and the corresponding metal olefin chloride dimers. Characterization of these group
9 allyl hydride complexes includes 1H-15N heteronuclear correlation NMR experiments that reveal
through-metal magnetization transfer between metal hydride and the trans-coordinated oxazoline
nitrogen. Furthermore, the oxazoline 15N NMR chemical shifts are affected by the trans ligand, with
3
the resonances for the group trans to hydride typically downfield of those trans to h -allyl and
tosylamide. These group 9 oxazolinylborate compounds have been studied to develop approaches for
allylic functionalization. However, this possibility is generally limited by the tendency of the allyl
hydride compounds to undergo olefin reductive elimination. Reductive elimination products are formed
3
upon addition of ligands such as CO and CNtBu. Also, ToMRhH(h -C8H13) and acetic acid react to give
2
3
ToMRhH(k -O2CMe) (8) and cyclooctene. In contrast, treatment of ToMRhH(h -C3H5) with TsN3
(Ts = SO2C6H4Me) gives the complex ToMRh(h -C3H5)NHTs (10). Interestingly, the reaction of
3
3
ToMRhH(h -C8H13) and TsN3 yields ToMRh(NHTs)(H)OH2 (11) and 1,3-cyclooctadiene via
b-hydride elimination and Rh–H bond amination. Ligand-induced reductive elimination of
3
ToMRh(h -C3H5)NHTs provides HN(CH2CH CH2)Ts; these steps combine to give a propene
C–H activation/functionalization sequence.
study outside of catalytic conversions. Investigations of these two
Introduction
steps in stoichiometric systems, en route to catalysis, is important
for understanding steric and electronic effects on selectivity and
reactivity that may also lead to new transformations.
Selective transformations of metal-carbon bonds are central
components of many catalytic conversions, including hydrocarbon
functionalizations. However, metal hydrocarbyl species derived
from C–H bond activation steps are not always easily trans-
formed into desired functionalized products. For example, the
In particular, facile late transition-metal-mediated allylic C–
H bond oxidative additions could complement recent ad-
vances in palladium-, molybdenum-, and copper-catalyzed allylic
oxidations.7,8 The electrophilic-type C–H bond activations in these
catalyses are mechanistically distinct from the classic two-electron
oxidative additions of low valent group 9 compounds, particularly
Cp*IrH2(PMe3),1a,b Cp*RhL2,1c,9 and Tp*RhL2,1f,10 where the
ancillary ligands’ fac-coordinating and electron-donating prop-
erties significantly influence the metal center’s reactivity. These
low valent metal centers also mediate stoichiometric oxidative
additions of allylic C–H bonds. A classic example involves
reaction of IrCl(N2)(PPh3)2 and allylbenzene which provides the
Ir(III) allyl hydride.11 Fac-coordinating ancillary ligands were
later shown to facilitate allylic C–H bond activations. For
example, reaction of K[Tp] (Tp = tris(pyrazolyl)hydridoborate)
5
organometallic compounds (L2X)MR(H)L¢ (L2X = Cp* = h -
C5Me5 , Tp* = (tris(3,5-dimethylpyrazolyl)hydridoborate); M =
Rh, Ir; L = CO, PMe3), obtained from C–H bond oxidative
addition under mild photochemical conditions, undergo C–H
reductive elimination without functionalization.1 A few of these
compounds undergo functionalization of the hydrocarbyl moiety,
including bromination after transmetalation to mercury,1b oxida-
tive bromination,1d and an olefin insertion.1g This limitation, fortu-
nately, has not hindered the development of a range of catalytic hy-
drocarbon functionalization reactions that may or may not utilize
C–H bond oxidative addition,2 including borylation,3 oxidation,4
dehydrogenation,5 and hydroarylation.6 Still, sequences of C–H
bond activation and hydrocarbyl elaboration are often difficult to
2
and 0.5 equiv. of [Ir(m-Cl)(h -C8H14)2]2 affords the iridium allyl
3
hydride TpIrH(h -C8H13) along with the byproducts C8H12 and
KCl.12 This transformation is highly sensitive to the reaction
conditions, as the interaction of Na[Tp] and 0.5 equiv. of
Department of Chemistry and U.S. DOE Ames Laboratory, Iowa State
University, Ames, IA 50011, USA. E-mail: sadow@iastate.edu
6500 | Dalton Trans., 2011, 40, 6500–6514
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2
[Ir(m-Cl)(h -C8H14)2]2 results in vinylic C–H bond activation
group (endo/exo) and its cis/trans disposition to coordinated
oxazoline ligands. In 1H-15N HMBC experiments, correlations
between the M-H and the trans-disposed oxazoline nitrogen (i.e.,
yielding TpIrH(s-C8H13)(h -C8H14).13 In a later report, the latter
2
compound is converted into the former upon thermolysis.14
2
1
Although KTp* and [Ir(m-Cl)(h -C8H14)2]2 gives a mixture of
through-metal H-15N magnetization transfer) further define the
five or more products, in the presence of 2-butene the allylic C–
coordination sphere and configuration of the metal center. We
have investigated reactions of these allyl hydride compounds to
develop hydrocarbon functionalization strategies. These attempts
to transform the metal allyl hydrides have uncovered an interesting
Rh–H bond amination reaction that provides allylic amination
products after C–N bond reductive elimination.
3
H bond oxidative addition species anti-exo-Tp*IrH(h -C4H6) is
formed.14 Iridium(III) allyl hydrides are also formed in related
metalations of electron-rich Li[BP3] (BP3 = PhB(CH2PPh2)3).15
In addition to the thermal allylic C–H bond oxidative ad-
t
t
ditions, photolysis of Tp*Rh(CNCH2 Bu)(PhN
C
NCH2 Bu)
in liquid propylene generates the allylic C–H bond activation
product Tp*RhH(h -CH2CH CH2)(CNCHtBu).16 Irradiation
1
Results
3
of Cp*Rh(CH2 CHMe)2 yields Cp*Rh(h -C3H5)H.17
Thus, an allylic C–H bond functionalization scheme might
involve a p-allyl Rh(III) or Ir(III) species as a reactive intermediate.
While this appears reasonable based on known rhodium- and
iridium-catalyzed allylic substitution chemistry,18,19 examples of
nucleophilic attack upon p-allyl compounds obtained from C–
H bond activation are uncommon. In fact, reductive elimination
Synthesis and characterization of rhodium and iridium allyl
hydrides supported by ToM
3
Our initial attempts to prepare ToRMH(h -C8H13) were based on
reports of allylic C–H bond oxidative addition that accompanied
2
a salt metathesis reaction of [Ir(m-Cl)(h -C8H14)2]2 with K[Tp] or
Li[BP3].12,15 Unfortunately, reactions of Li[ToM] or Li[ToP] and
3
of olefin from (L2X)MH(h -C3H4R) (L2X = Cp*, Tp*, BP3) is a
2
[M(m-Cl)(h -C8H14)2]2 (M = Rh, Ir) give complex mixtures in
dominant reaction pathway, as is the case for the s-hydrocarbyl
compounds. The elimination reactions provide access to highly
reactive, low valent, coordinatively unsaturated late metal com-
plexes, but limit the functionalization of the allyl moiety.17,20 We
sought to utilize this mild C–H bond oxidative addition reaction as
an alternative to electrophilic allylic functionalization (eqn (1)).21
benzene, THF, methylene chloride and acetonitrile at 60 ◦C, and
far upfield resonances that might be attributed to metal hydride
complexes were observed to have very low intensities. Only starting
materials are observed after 24 h at ambient temperature. Allylic
C–H bond activation may be sensitive to counterions present in the
2
reaction,14 so the reaction of K[ToM] and [Ir(m-Cl)(h -C8H14)2] was
tested. Although these two reagents react at room temperature
(unlike Li[ToM]), we were unable to isolate or characterize the
products.
(1)
Tl[ToM] is an effective transfer agent for the preparation of
ToMRh(CO)2, where Li[ToM] affords a mixture of products.24c
In contrast to the experiments with Li[ToM] and K[ToM], 1.4
We have been investigating the chemistry of tridentate,
monoanionic tris(oxazolinyl)borates (ToR
=
ToM, tris(4,4-
2
equiv. of Tl[ToM] and [Rh(m-Cl)(h -C8H14)2]2 react on millimolar
dimethyl-2-oxazolinyl)phenylborate; ToR = ToP, tris(4S-isopropyl-
2-oxazolinyl)phenylborate;])22 as easily-accessed chiral analogs23
of the tris(pyrazolyl)borate ligand class and to develop C–H bond
oxidative addition chemistry. However, we initially encountered
difficulties in our attempts to develop oxidative addition reactions
scale in benzene-d6 to provide a single soluble ToM-containing
product and 1 equiv. of cyclooctene at room temperature. The
reaction scale may be increased to 1.8 millimoles, and although
2
a slight excess of [Rh(m-Cl)(h -C8H14)2]2 is required for product
of ToRML2 (M = Ir, Rh; L2 = h -C8H12, (CO)2) and strong
4
isolation, the reaction proceeds to completion after 5 h at room
temperature in benzene providing adequate quantities of product
electrophiles (such as HOTf, MeOTf, and MeI) in which oxazoline-
based additions occur preferentially to metal-centered oxidation.24
Weaker electrophiles (HCCl3, C3H5Br) undergo oxidative ad-
dition to ToMRh(CO)2 and ToPRh(CO)2 under thermal condi-
tions, showing that, despite competitive ligand-based reactivity,
tris(oxazolinyl)borate ligands can provide reactive metal centers.24c
Given the isoelectronic relationship of ToR and Tp (and thus Cp)
ligands and because nCO bands of ToMM(CO)2 and ToPM(CO)2
(M = Rh, Ir) suggest that the tris(oxazolinyl)borate ligands are
slightly more electron donating than tris(pyrazolyl)borates to
group 9 metal centers, C–H bond oxidative addition should be
accessible with tris(oxazolinyl)borate rhodium(I) and iridium(I)
centers. Moreover, allylic bond activation might be facile from
carbonyl-free metal centers.
Here, we report the synthesis of rhodium and iridium allyl
hydride compounds formed by oxidative addition of allylic C–
H bonds. Several compounds were crystallographically charac-
terized, and solution phase NMR spectroscopy including 1H-
15N HMBC (Heteronuclear Multiple Bond Correlation) and
NOESY experiments revealed the configuration of the allyl
3
for the studies described below. Analytically pure ToMRhH(h -
C8H13) (1) is isolated by pentane extraction (3 ¥ 25 mL) from the
evaporated reaction residue in 71% yield (eqn (2)).
(2)
The NMR properties of 1 are described in detail, given
3
the conflicting results associated with TpIrH(h -C8H13) and
2
1
TpIrH(C8H13)(h -C8H14).12,13,14 The H NMR spectrum of 1 con-
1
tained a diagnostic doublet at -24.3 ppm (1 H, JRhH = 11.6 Hz)
that was assigned as a rhodium hydride. The pattern of 1H NMR
resonances for the ToM ligand indicates that 1 is Cs-symmetric,
such that the ring methylene resonances were observed as a singlet
(3.33 ppm, 2 H) and two diastereotopic coupled doublets (3.74
2
and 3.60 ppm, 2 H each, JHH = 8.4 Hz). Three singlets at 1.17,
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1.12 and 0.82 ppm were assigned to the oxazoline methyl groups.
Additionally, a triplet at 5.16 ppm (1 H) and a doublet of doublets
at 3.95 ppm (2 H) were detected. These signals are characteristic
of a p-allyl ligand and rule out vinylic C–H bond activation or an
of Li[ToM] and K[ToM] afford complex mixtures of products.
The structure of the iridium and rhodium h -C8H13 compounds
3
are closely related as indicated by NMR spectroscopy. Thus,
the 1H NMR resonances for the ToM ligand were consistent
with a Cs-symmetric complex, a resonance characteristic of an
iridium hydride was detected at -28.5 ppm, allylic resonances
were observed in the 1H NMR spectrum as a singlet at 4.79 ppm
(2 H) and a doublet of doublets at 3.98 ppm (4 H), and the
expected crosspeaks were detected in a 1H-15N HMBC experiment.
As in 1, the 15N NMR resonance of the oxazoline nitrogen at
-182.6 ppm, assigned as trans to the iridium hydride by symmetry,
exhibited through-bond coupling to the hydride (through the
iridium center). No correlations to the iridium hydride were
observed for the 15N NMR resonance at -190.6 ppm that is
assigned to the oxazolines trans to the allyl ligand.
1
2
h -allyl structure. No JRhH coupling was observed for the allylic
proton resonances, but the 3JHH (8.0 Hz) for the p-allylic protons
was consistent with syn-disposed hydrogen resulting from the allyl
group’s anti-anti conformation, as required for the cyclic ligand.
Crosspeaks in a NOESY experiment were detected between the
methyls on the oxazoline trans to the rhodium hydride and both
the central allyl (Hcentral) and the syn-allyl hydrogen (Hsyn). From
these observations, we assigned the complex’s conformation as
exo as shown in eqn (2) and Fig. 1. We were unable to observe a
crosspeak between the central p-allyl hydrogen and the rhodium
hydride in a NOESY experiment, which suggests the exo structural
assignment.
3
Several ToMMH(h -C3H4R) (M = Rh, Ir; R = H, Ph) compounds
are prepared through related reactions. These compounds each
have distinguishing structural, stereochemical, and reactivity fea-
tures that will be highlighted in the following discussion. The par-
3
ent allyl complex ToMRhH(h -C3H5) (3) is synthesized by reaction
2
of Tl[ToM] and in situ-generated [Rh(m-Cl)(h -C3H6)2]2. Progress
of a micromolar-scale reaction in benzene-d6 was monitored by 1H
NMR spectroscopy; only one conformer (assigned as exo below)
formed after 1 h with complete conversion of Tl[ToM], but after
2 h the exo:endo ratio was 4 : 1 (eqn (3)). Neither reaction times
up to 2 d nor heating at 80 ◦C for 2 h alter this ratio. In contrast,
3
a 7 : 1 mixture of endo and exo Tp*RhMe(h -C3H5) was reported
to isomerize quantitatively to the endo conformer at 60 ◦C.25
Fig. 1 Fisher projection of k -ToMRhH(exo-h -C8H13) (1) showing nOes
between allylic CHs and methyl groups on the oxazoline trans to the
rhodium hydride.
3
3
(3)
1H-15N HMBC experiments provide 15N chemical shift data
and support structural assignments of tris(oxazolinyl)borate
compounds.24 The chemical shifts of the two 15N NMR resonances,
detected at -164.2 and -173.4 ppm, indicate that the oxazoline
nitrogen are coordinated to the rhodium center and ToM is
bonded as a tridentate ligand. The former signal was assigned
to the oxazoline nitrogen trans to the hydride based on through-
bond, through-rhodium coupling between the nitrogen and the
rhodium hydride. Additionally, the oxazoline trans to the rhodium
hydride coincided with the sv-mirror plane, and the 1H-15N HMBC
contained the expected crosspeak between that nitrogen signal and
the singlet methylene resonance. The resonance at -173.4 ppm was
assigned to the nitrogen on the oxazoline groups trans to the p-allyl
ligand off the mirror plane.
1
Exo-3 and endo-3 were identified by the H NMR chemical
shifts of the rhodium hydride at -22.7 and -23.2 ppm as
well as the typical p-allyl resonances. A key crosspeak in the
NOESY spectrum between the rhodium hydride resonance at
-22.7 ppm and the p-allyl C-2 methine proton at 5.1 ppm allowed
assignment of that isomer as endo-3 (eqn (3)). Additionally,
crosspeaks were observed between the allylic syn-CHs and the two
diastereotopic oxazoline methyl groups in a NOESY. In contrast,
the exo conformer exhibited nOes between the anti-CHs and the
3
two diastereotopic oxazolinyl methyl groups. The JHH coupling
constant between the hydrogen on the central carbon and syn
hydrogens of both endo and exo isomers was 7.2 Hz whereas the
3JHH coupling to anti hydrogens was 11.2 and 11.6 Hz for endo and
exo isomers, respectively, further supporting our assignments.
3
h -Coordination of the p-allyl ligand is further supported
1
3
by rhodium-carbon coupling observed in the 13C{ H} NMR
As in the ToMMH(h -C8H13) compounds, the pattern for ToM
spectrum. The resonances at 93.9 ppm (1JRhC = 6.0 Hz, Ccentral
)
resonances in both endo and exo isomers indicated the overall
Cs symmetry. The Rh–H and the oxazoline coordinated trans to
3
and 52.15 (1JRhC = 11.4 Hz) were assigned to the h -C8H13
1
group. Correlations between these resonances and the allylic
the hydride are located on the mirror plane, and their H NMR
1
1H NMR signals were detected in a H-13C HMQC experiment
resonances are assigned based on symmetry. The 15N NMR signals
1
and confirmed the assignments. Finally, a characteristic nRhH
in a H-15N HMBC experiment at -165.6 and -164.8 ppm for
absorption in the IR spectrum of 1 appeared at 2158 cm-1. These
exo and endo isomers, respectively, were corroborated by through-
bond correlations to the rhodium hydride. Further characteriza-
tion included the two nRhH bands in the IR spectrum at 2090
and 2080 cm-1 and single crystal X-ray diffraction. An X-ray
quality crystal was obtained in concentrated toluene at -30 ◦C,
3
data support the formulation of 1 as ToMRhH(exo-h -C8H13).
2
The corresponding reaction of [Ir(m-Cl)(h -C8H14)2]2 and
3
Tl[ToM] in benzene provides the iridium(III) analog ToMIrH(h -
C8H13) (2) in good yield (78%). As in the rhodium system, reactions
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Fig. 2 ORTEP diagrams of (a) endo-ToMRhH(C3H5) (endo-3) and (b) exo-ToMRhH(C3H5) (exo-3) drawn at 50% probability. A toluene molecule and
hydrogen atoms on the ToM ligand are not depicted. The two isomers co-crystallize, but their relative orientation has been altered above to more clearly
illustrate the rhodium centers’ coordination geometry, and this figure does not represent their relative positions in the unit cell. Selected bond distances
˚
(A) for endo-3: Rh1–H1r, 1.67(6); Rh1–N1, 2.107(3); Rh1–N2, 2.109(3); Rh1–N3, 2.298(3); Rh1–C22, 2.160(5); Rh1–C23, 2.099(6), Rh1–C24, 2.139(5).
˚
Selected bond distances (A) for exo-3: Rh2–N4, 2.128(3); Rh2–N5, 2.223(3), Rh2–N6, 2.141(3); Rh2–C46, 2.147(7); Rh2–C47, 2.035(8); Rh2–C48,
2.096(7).
and the unit cell contains both endo and exo isomers as well as
a toluene molecule. The p-allyl groups in both the endo and exo
isomers were refined with restraints, resulting in uncertainty in the
C–C–C angles of 135.8(9) and 135(1)◦, respectively. The rhodium
hydride in the exo isomer was not located although the hydride on
the endo isomer was located objectively and refined isotropically.
Despite these problems, the two isomers are readily distinguished
as shown in Fig. 2.
the central CH, and exo and endo orientations of the phenylallyl
ligand).
(5)
˚
The Rh–N bonds trans to hydride Rh1–N3 (endo: 2.298(3) A)
˚
3
and Rh2–N5 (exo: 2.223(3) A) are longer than the two Rh–N
The four p-allyl protons (h -C3H4Ph) were assigned using
bonds trans to the allyl ligand (endo: Rh1–N1, 2.107(3); Rh1–N2,
2.109(3); exo: Rh2–N4, 2.128(3); Rh2–N6, 2.141(3) A). The Rh–N
a COSY experiment that contained correlations between the
central p-allyl proton resonance (5.62 ppm) and the terminal
syn and anti CH2 (3.22 and 2.84 ppm, respectively) and CHPh
signals (3.98 ppm). The syn and anti JHH were 9.6 and 11.2 Hz,
respectively, where the former coupling constant is unusually high.
˚
distances trans to the allyl ligand in the exo conformer are slightly
longer than the Rh–N distances in the endo conformer.
An alternative preparation of 3 is accomplished by treatment of
isolated 1 with propene in benzene-d6. As in the in situ synthesis,
only the exo conformer is formed after 1 h but a mixture of both
conformers is obtained after several hours.
3
3
The JHH between the central allylic CH and the benzylic CH
was 10.4 Hz. A correlation between the RhH and the central
allylic hydrogen was observed in a NOESY experiment, and
these data suggest that the molecule adopts an endo-syn-C3H4Ph
The parent iridium allyl hydride ToMIrH(h -C3H5) (4) is pre-
3
pared by reaction of Tl[ToM] and in situ-generated [Ir(m-Cl)(h -
2
conformation.11 JRhC coupling observed in the 13C{ H} NMR
spectrum also supports the p-allyl-bonding description, as the
central carbon (90.06 ppm, 1JRhC = 3.5 Hz), terminal p-allyl carbon
1
1
C3H5)2]2 (eqn (4)). Only the endo isomer is formed in the iridium
system. A crosspeak between the IrH and the central hydrogen
on the p-allyl ligand in a NOESY experiment facilitated this
assignment.
1
(36.54 ppm, JRhC = 12.25 Hz), and the benzylic p-allyl carbon
(54.52 ppm, 1JRhC = 10.5 Hz) doublet resonances indicate rhodium-
carbon bonding.
Unlike the sv-symmetric h -C3H5 and h -C8H13 ligands, the
dissymmetrical h -C3H4Ph imparts C1 symmetry to 5, and this
was manifested in six oxazoline methyl signals in the H NMR
3
3
3
(4)
1
spectrum. Thus, the three oxazoline rings are inequivalent, and
three signals were observed (-168.2, -172.1 and -179.9 ppm) in
3
1
ToMRhH(h -C3H4Ph) (5) is synthesized by addition of Tl[ToM]
the H–15N HMBC spectrum. The latter resonance was assigned
2
to in situ generated [Rh(m-Cl)(h -C3H4Ph)2]2 (eqn (5)). Only one
isomer was detected in the reaction mixture (four are possible,
with syn and anti dispositions of the phenyl group with respect to
as trans to the hydride based on a crosspeak between that
nitrogen and the rhodium hydride. The two former resonances
were assigned as oxazolines cis to the hydride.
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X-Ray quality crystals were obtained from a concentrated
toluene solution cooled to -30 ◦C, and a single crystal diffraction
3
study confirmed the structure and configuration of endo-syn-h -
5 (Fig. 3). The rhodium-nitrogen distances range from 2.10 to
˚
2.28 A, and the Rh1–N2 distance (trans to hydride) is the longest.
The distance from the rhodium center to the phenyl–substituted
˚
allylic carbon (Rh1–C23, 2.195(4) A) is longer than the distance to
˚
˚
the terminal allylic carbon (Rh1–C30, 2.148(4) A) by 0.047(8) A.
The carbon-carbon distances in the allylic ligand, (C22–C23,
˚
1.416(5) and C22–C30, 1.406(5) A) are, however, equivalent.
Fig. 4 ORTEP diagram of ToMRh(CNtBu)2 (7) drawn at 50% probability.
˚
Hydrogen atoms are omitted for clarity. Selected bond distances (A):
Rh1–N1, 2.094(4); Rh1–N2, 2.087(4); Rh1–C22, 1.881(6); Rh1–C27,
1.884(7). Selected bond angles (◦): N1–Rh1–C22, 174.9(2); N2–Rh1–C27,
178.4(2); N1–Rh1–N2, 85.2(2); C22–Rh1–C27, 84.8(2).
3
Fig. 3 ORTEP diagram of endo-ToMRhH(h -C3H4Ph) (5) drawn at
50% probability. Hydrogens and a disordered toluene molecule are
omitted for clarity. The rhodium hydride was not located. Selected bond
phase IR spectrum (CH2Cl2) showed two oxazoline nCN bands;
an absorption at 1614 cm-1 was assigned to a pendent, non-
coordinated oxazoline group. However, four isocyanide nCN bands
at 2208, 2147, 2103, 2068 cm-1 indicated that at least two isomers
are present in solution.26 Surprisingly, the iridium analogs 2 or 4
and CO afford free olefin and black precipitate even though the
expected product, ToMIr(CO)2, is isolable from the reaction of CO
˚
distances (A): Rh1–N1, 2.101(3); Rh1–N2, 2.280(3); Rh1–N3, 2.132(3);
Rh1–C22, 2.113(4); Rh1–C23, 2.195(4), Rh1–C30, 2.148(4). Selected
angles (◦): N1–Rh1–N2, 87.5(1); N1–Rh1–N3, 84.1(1); N2–Rh1–N3,
84.9(1); C23–C22–C30, 120.6(4).
Reactions of ToMMH(g3-allyl) (1–5; M = Rh, Ir) toward C–E bond
formation
4
and ToMIr(h -C8H12).24b
Our attempts to transform the allyl moiety began with reactions
with nucleophilic reagents, including alcohols and alkoxides,
amines and amides, and 1,3-dicarbonyl reagents and their enolates.
However, the observed products are consistent with C–H reductive
elimination rather than C–O, C–N, or C–C bond formation. For
example, addition of neopentyl alcohol to a benzene-d6 solution
of 1 results in formation of a black precipitate and cyclooctene
after 1 h at 60 ◦C. The same products are obtained when 1 or 2 are
treated with tert-butylamine at 80 ◦C in benzene-d6 after 4 h and
24 h respectively.
(6)
Transformation of compounds 1–5 into cationic species (by
hydride abstraction) might increase the electrophilicity of the
allyl moiety for further reactivity while impeding olefin reductive
elimination (i.e., C–H bond formation is not possible from
In the presence of ligands such as CO or CNtBu that could
potentially react by insertion, 1 or 2 form cyclooctene or propene
and ToMRhL2 (L = CO (6), CNtBu (7); eqn (6)) at room
temperature. For the bis(isocyanide) 7, two signals were observed
[ToMRh(h -C3H5)]+). Additionally, intermediates in many metal-
3
catalyzed allylic substitution reactions are cationic complexes.
Therefore we attempted to prepare cationic [ToMM(h -C3H4R)]+
by abstracting a hydride from 1–5. These reactions do not provide
3
1
in a H-15N HMBC experiment at -159.6 and -201.1 ppm for
isolable species. For example, reaction of 3 and ◦B(C6F5)3 in
◦
the rhodium-coordinated nitrogen in the oxazoline and isonitrile
groups, respectively. A correlation between the tert-butyl protons
and the isocyanide nitrogen distinguished the two 15N NMR
benzene-d6 at 60 C or methylene chloride-d2 at 40 C overnight
affords a mixture of unidentified products. No free olefin was
detected in these reaction mixtures. Interestingly, treatment of
endo-4 with B(C6F5)3 at 80 ◦C in benzene-d6 for 2 days gives a
mixture of endo-4 and exo-4 (1 : 4 ratio).
Protonolysis and reductive elimination occurs upon treatment
of allyl hydride compounds 1–5 with Brønsted acids. For example,
1
signals. As in ToMRh(CO)2,24c the room temperature H NMR
spectrum of ToMRh(CNtBu)2 contained equivalent oxazoline
groups, whereas the solid state structure revealed a bidentate
ToM-rhodium interaction (Fig. 4). Additionally, the solution-
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2
1 and acetic acid react in benzene to give ToMRhH(k -OAc) (8) and
The 1H NMR spectrum of C1 symmetric 9 contained six unique
oxazoline methyl resonances and three 15N signals (-217.6, -191.1
and -181.5 ppm); the upfield resonance was assigned to the
oxazoline nitrogen trans to the bromide. The p-allyl group is
coordinated in an endo-syn conformation, and this assignment
cyclooctene. Reaction with acetic acid-d1 provides a mixture of 8
and ToMRhD(k -OAc) (8-d1) in a 3 : 1 ratio.27 In those experiments,
2
2
8-d1 and cyclooctene-d1 were detected in the H NMR spectrum
of the reaction mixture. Analytically pure product is obtained by
extraction of the reaction mixture with pentane, and crystallization
1
is based on H NMR chemical shifts, coupling constants, and
◦
3
in toluene at -30 C provides X-ray quality crystals (an ORTEP
NOESY experiments as described in detail for ToMRhH(h -
diagram is shown in Fig. 5).
C3H4Ph) above. Thus, the p-allyl configuration is the same for
the starting material and product in eqn (7).
Treatment of a mixture of endo-3 and exo-3 with 1 equiv.
of TsN3 (Ts = SO2C6H4Me) in benzene at room temperature
3
for 24 h affords exo-ToMRh(NHTs)(h -C3H5) (10) in good yield
(82%) as shown in eqn (8). The product 10 corresponds to a
formal insertion of a tosylnitrene into the Rh–H bond, and
bubbles are formed during the reaction. Signals corresponding to
1
propene were not detected in H NMR spectra of the reaction
mixture. The 1H NMR spectrum of 10 contained resonances
3
assigned to the ToM ligand, a h -C3H5 group bisected by a mirror
plane, and a tosyl group. The distinctive hydride resonances
1
of endo-3 and exo-3 were absent in the H NMR spectrum of
isolated 10.
Fig. 5 ORTEP diagram of ToMRhH(k -O2CMe) (8) drawn at 50%
probability. The hydrogen atom bonded to rhodium was found objectively
on the difference Fourier map and is shown. The other hydrogen atoms and
disordered solvent molecules are not included. Selected bond distances
2
(8)
˚
(A): Rh1–H1r, 1.7(1); Rh1–N1, 2.20(1); Rh1–N2, 1.97(1); Rh1–N3,
2.01(1); Rh1–O4, 2.069(9); Rh1–O5, 2.092(9). Selected bond angles
(◦): N1–Rh1–H1r, 177(4); N1–Rh1–N2, 87.7(4); N1–Rh1–N3, 85.8(4);
N2–Rh1–N3, 85.2(5); N2–Rh1–O4, 167.7(4); N3–Rh1–O5, 168.6(4);
O4–R1–O5, 61.8(4).
Notably, compound 10 exists as only one isomer although
the starting material is a mixture. The oxazoline 15N chemical
shifts (-177.6 and -225.4 ppm) were measured with a 1H-
15N HMBC experiment. The former signal was assigned to the
nitrogen in the oxazoline rings coordinated trans to the allyl
group, based on magnetization transfer between nitrogen and the
diastereotopic oxazoline methylene signals. The oxazolines trans
to the allyl moiety are related by, but do not contain, a sv plane
and thus, the 15N NMR assignments are based on symmetry.
Hydride compounds 1–4 are assigned in the same manner, but
in those cases the assignments are corroborated by through-bond
coupling between the Rh–H and the trans oxazoline nitrogen. The
remaining upfield resonance in 10 corresponds to the oxazoline
trans to the amide group.
The 1H NMR spectrum of 8 contained signals from a Cs-
symmetric ToM ligand and characteristic hydride at -13.2 ppm
(1JRhH = 11.6 Hz), and this latter resonance was correlated to
1
the trans oxazoline nitrogen (-154.3 ppm) in a H-15N HMBC
experiment. The 15N NMR signals for the oxazolines trans to
acetate appeared at -221.0 ppm. The same product, 8, is formed
as a minor species upon reaction of phenylallyl hydride 5 and
acetic anhydride in benzene-d6 at 80 ◦C overnight. However,
allylbenzene is the major organic product, and 8 is the only
identifiable rhodium-containing species.
X-Ray quality single crystals are obtained by vapor diffusion of
pentane into a toluene solution at -30 C. The constitution and
Reaction of 5 and N-bromosuccinimide (NBS) results in
◦
substitution of the hydride for
a bromide ligand giving
ToMRhBr(h -C3H4Ph) (9; eqn (7)). Compound 9 is the only
allyl-containing species observed. For comparison, the treatment
of Cp*Rh(R)(H)PMe3 with bromoform followed by Br2 pro-
vides RBr products,1d and Tp*Rh(H)(C6H13)CO was converted
to Tp*Rh(Cl)(C6H13)CO by reaction with CCl4.1f Additionally,
3
connectivity of 10 was thus confirmed by X-ray crystallography,
3
which also revealed exo-h -allyl group coordination (Fig. 6). There
is no interaction between the oxygen atoms of the SO2C6H4Me
group and the rhodium center. Also, the Rh–Noxazoline distances are
˚
within ~0.02 A for the three oxazolines (Rh-N1, 2.140(3); Rh1–
3
˚
N2, 2.119(3); Rh1–N3, 2.121(3) A) where the oxazoline nitrogen
cationic diimine palladium(II) and platinum(II) h -indenyl com-
(N2) trans (∠N2–Rh1–N4 = 163.0(1)◦) to the amido ligand has
the shortest Rh–N distance.
pounds, obtained from electrophilic allylic C–H bond activation,
react with Br2 to provide indenylbromide.21
Excitingly, the reaction of 10 and CO at 65 ◦C results in
C–N bond reductive elimination and CO coordination to give
ToMRh(CO)2 (6, 81% yield) and allyl(tosyl)amine (eqn (9)). The
organic product, identified by GC-MS and 1H NMR spectroscopy,
is formed in 29% yield. A number of other unidentified organic
products are also present in the reaction mixture.
(7)
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3
Fig. 6 ORTEP diagram of exo-ToMRh(NHTs)(h -C3H5) (10) drawn
Fig. 7 ORTEP diagram of ToMRh(NHTs)(H)OH2 (11). The hydrogen
atoms shown are the H1r (rhodium hydride) and H4n (amide hydrogen),
and the rest are not represented for clarity. The aryl groups were drawn as
ball-and-stick to more clearly illustrate the rhodium center’s coordination
geometry and the connectivity of the complex. Selected bond distances
at 50% probability. Hydrogen atoms are not included to highlight the
heavy atom positions. Selected bond distances (A): Rh1–N1, 2.140(2);
Rh1–N2, 2.119(3); Rh1–N3, 2.121(3); Rh1–N4, 2.085(3); Rh1–C22,
2.181(3); Rh1–C23, 2.145(3); Rh1–C24, 2.181(3). Selected bond angles
(◦): N1–Rh1–N4, 83.8(1); N2–Rh1–N4, 163.0(1); N3–Rh1–N4, 84.4(1);
Rh1–N4–S1, 138.5(2).
˚
˚
(A): Rh1–H1r, 1.88(7); Rh1–N1, 2.234(6); Rh1–N2, 2.016(7); Rh1–N3,
2.064(7); Rh1–N4, 2.088(6); Rh1–O6, 2.101(6). Selected bond angles
˚
(A): N1–Rh1–H1r, 173(2); N2–Rh1–O6, 179.2(3); N3–Rh1–N4, 176.9(3);
Rh1–N4–S1, 131.5(4).
3
nor ToMIr(h -C8H13) afford tractable products upon treatment
with TsN3.
(9)
Discussion
Given the interesting reaction of 3 and TsN3, we investigated the
reactions of TsN3 with the other metal allyl hydride compounds.
The interaction of 1 and TsN3 results in the elimination of
1,3-cyclooctadiene and formation of a C1-symmetric ToMRh-
containing product. The reaction occurs in benzene at room
temperature and is accompanied by significantly more vigorous
N2 evolution than in the corresponding reaction of 3 and TsN3.
The 1H NMR spectrum of the product contained six singlets
corresponding to three inequivalent oxazoline groups in the ToM
ligand, as well as signals from a tosyl group and a rhodium
hydride (-15.75 ppm;1JRhH = 9.2 Hz). Ultimately the product
ToMRhH(NHTs)(OH2) (11, eqn (10)) was identified by X-ray
crystallography (Fig. 7).
Allylic C–H bond activation and rhodium hydride amination
The tris(oxazolinyl)borate ligand itself is important as a spectator
in the C–H bond activation step, as the reaction of Tl[ToP]
(ToP = tris(4S-isopropyl-2-oxazolinyl)phenylborate) and [Rh(m-
2
Cl)(h -C8H14)2]2 provides TlCl and an unstable, hydride-free
{ToPRh}-species that was not isolable. Two equivalents of non-
coordinated cyclooctene are formed, and the product contains
three inequivalent oxazoline groups (suggesting a non-fluxional
six-coordinate Rh(III) compound; eqn (11)). The absence of a
detectable hydride in the product and the loss of cyclooctene argue
against ToPRh-mediated allylic C–H bond activation, although the
identity of the product is not yet established due to its transient
nature.
(10)
(11)
A related transformation was reported in the thermol-
3
ysis of {BP3}IrH(h -C8H13) in the presence of PMePh2
This change in reactivity between C3v-symmetric ToM and C3-
symmetric ToP is unexpected, as the two ligands are isoelectronic
and have similar steric properties. For comparison, KTp and
which gave {BP3}IrH2(PMePh2) and 1,3-cyclooctadiene.20a Both
3
3
{BP3}IrH(h -C8H13) and ToMRhH(h -C8H13) typically react by
olefin elimination at room temperature (e.g., with CO), so the
apparent b-elimination pathway is somewhat surprising. Further-
more, 1 does not eliminate 1,3-cyclooctadiene in the absence of
2
KTp* also react with dissimilar pathways, such that [Ir(m-Cl)(h -
C8H14)2]2 and KTp* give several products,14 whereas the KTp
3
reaction provides TpIrH(h -C8H13).12 The change in reactivity
3
TsN3. Thus, ToMRhH(h -C3H4Ph) appeared to be a promising
between KTp* and KTp can be explained by the greater cone
angle of the former ligand (or its greater electron-donating
properties).28 The similar electronic and steric properties of ToM
compound to react with TsN3, as b-elimination is not possible.
3
3
Unfortunately, neither ToMRhH(h -C3H4Ph), ToMIrH(h -C3H5),
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2
and ToP preclude such a rationalization in the current system.24c
However, a distinction between the compounds may be found
in the ground state structures: ToPIr(CO)2 appears to contain a
tridentate tris(oxazolinyl)borate ligand in the solid state,24a while
ToMIr(CO)2 and ToMRh(CO)2 are coordinated in a bidentate mode
in the solid state.24b,c Thus, the ancillary ligand may control the
ground state structure of the Rh(I) species that mediates C–H
bond oxidative addition. We are currently preparing new chiral
oxazolinylborate rhodium(I) compounds to better assess the role
of the ancillary ligand in these types of thermal allylic C–H bond
activations.
postulated to involve 1,1-insertion of the organoazide to give k -
triazenide species, followed by 1,3-hydrogen migration and N2
extrusion.32 This pathway is distinct from dirhodium-catalyzed
C–H amination, which is proposed to involve a rhodium nitrene;
in that chemistry, rhodium hydride species are not involved.33
A recent report documented the formation of an iridium(III)
tosyl(aryl)amide from an iridium aryl, and this was proposed to
involve an iridium(V) nitrene species.30b Additionally, a nitrene
compound was recently suggested as an intermediate in the
formation of a palladium amido from a palladium alkyl and
a tosyliminoiodinane.34 In our system, formation of a coordi-
nated nitrene would invoke a pentavalent rhodium intermediate
and follow a sequence that might involve Na-coordination of
It is also interesting to consider the effect of the counterion
2
in these steps. For example, reactions of both [Ir(m-Cl)(h -
C8H14)2]2 and [Rh(m-Cl)(h -C8H14)2]2 require Tl[ToM] for selective
tosylazide, N2 elimination to give ToMRh(NTs)H(h -C3H5), and
2
1
ancillary ligand metalation, and neither Li[ToM] nor K[ToM]
intramolecular nitrene insertion (Scheme 1, A). The final two steps
of this sequence could be more rapid than C–H bond reductive
elimination, and this mechanism provides a rationalization for
amide formation occurring more rapidly than olefin elimination,
but invokes a highly reactive Rh imido species.
3
provide ToMMH(h -C8H13) compounds. Metalation/C–H bond
oxidative addition sequences in reactions of Na[Tp] and K[Tp]
2
with [Ir(m-Cl)(h -C8H14)2]2 also show counterion dependence, with
3
K[Tp] providing TpIrH(h -C8H13) in THF,12 and Na[Tp] giving
2
the vinyl C–H activated product TpIrH(s-C8H13)(h -C8H14) in
An alternative pathway (Scheme 1, B) might involve an eighteen
electron rhodium triazenide intermediate that does not require
high valent rhodium. However, this intermediate is preceded
dichloromethane.13 Additionally, th◦e latter compound is converted
to the former by heating at 80–100 C in cyclohexane.14 Although
counterions and solvent may influence allylic vs. vinylic C–H bond
activations, the Na+, K+, or Tl+ ions are not required for this step
as shown by the reaction of isolated rhodium cyclooctenyl 1 and
1
by a terminally-coordinated azide species such as ToMRhH(h -
C3H5)(NgNNTs). One might expect rapid C–H bond reductive
elimination for this intermediate, as is observed in treatment of 1
or 3 with the ligands CO or CNtBu. All three of these reagents
could react by 1,1-insertion, but instead CO and CNtBu promote
reductive elimination. These contradictions are rationalized by
mechanisms involving reversible insertion of TsN3, CO, and
CNtBu into Rh–H, and only the azide insertion product is irre-
versibly trapped by 1,3-coordination, 1,3-hydrogen migration and
N2 elimination. Additional support for the triazenide mechanism
3
propene that provides the parent allyl 3. In contrast, ToMIrH(h -
C8H13) and propene do not react up to 80 ◦C, highlighting a change
in reactivity between rhodium and iridium.
The distinction between rhodium and iridium is further
3
highlighted by exo to endo isomerization of ToMMH(h -C3H5).
The propenyl oxazolinylborato iridium(III) compound is inert.
3
Isomerization of the kinetically favored endo-ToMIrH(h -C3H5)
2
to the thermodynamic mixture of conformers requires treatment
with the Lewis acid B(C6F5)3. In contrast, the kinetic products of
propene C–H bond activation is exo-3, and isomerization to the
thermodynamically favored mixture of endo and exo conformers
occurs over 2 h.
is based on the previous reports (described above) of isolable k -
triazenide ligands forming by insertion of organoazide, as well
as the current limitation of this nitrene insertion chemistry to
tosylazide. Both mechanisms, importantly, involve interaction of
TsN3 and a rhodium species, as TsN3 does not afford free nitrene
spontaneously.
The isomerization and conversions of the rhodium allyl hydride,
in comparison to the inert iridium complexes, may explain the
reactivity of 1 and 3 (versus 2 and 4) with tosylazide. In line
with the isomerization trend, no interaction between TsN3 and
An open coordination site is needed for azide activation; this site
2
could be accessed either by oxazoline dissociation to form a {k -
ToM}RhH(h -allyl) intermediate or via an h -s-allyl isomerization
3
3
ToMIrH(h -C8H13) or ToMIrH(h -C3H5) was detected, whereas rich
chemistry was observed in reactions of the rhodium analogs.
In the reactions of 1 and 3 with TsN3, C–H bond reductive
elimination is not favored, contrasting the common reaction
pathway for these compounds with Brønsted acids, p-acid ligands
such as CO and CNtBu, and weak s-donors including tert-
butanol and tert-butylamine. In this context, we considered the
possible pathways for the formation of the tosylamido ligand from
tosylazide and rhodium hydride that might preclude C–H bond
reductive elimination.
through the {k -ToM}RhH(s-allyl) species. The initial interactions
3
3
3
of TsN3 and ToMRhH(h -C8H13) are proposed to involve the latter
3
because b-hydrogen elimination to give 1,3-cyclooctadiene and
{k -ToM}RhH(NHTs)(OH2) is more likely to occur from a s-allyl
3
intermediate (Scheme 2). The bulkier cyclooctenyl allyl 1 and TsN3
react more rapidly than the parent allyl 3, and the relative reaction
rates provide further support for a dissociative pathway involving
the allyl group. Finally, b-hydrogen elimination was also reported
3
for a reaction of {BP3}IrH(h -C8H13), where phosphine arm
dissociation is less likely than oxazoline arm dissociation in the
present system. b-Elimination in our system requires interaction
of the two reactants (i.e., tosylazide coordination), as 1 does
not spontaneous form 1,3-cyclooctadiene even upon thermolysis
(which gives cyclooctene). The sequence of steps following the
initial interaction of tosylazide and 1 likely involves b-elimination
subsequent to tosylamide formation, again because CO induces
C–H bond reductive elimination rather than 1,3-cyclooctadiene
elimination.
Additionally, the formation of rhodium tosylamido ligands is
somewhat unexpected because there are no previous reports to
our knowledge of organoazide mediated amination of rhodium-
hydrogen bonds.29 Related reactions of group 9 metal alkyl
compounds and azides give secondary amides (i.e., the formal
insertion of nitrene into Co–Me and Ir–Me bonds).30 Additionally,
organoazides and late metal-hydrogen bonds (e.g., Pt, Re) react
to give N2 and metal amidos.31 These reactions are generally
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3
Scheme 1 Possible mechanisms for the reaction of ToMRhH(h -C3H5) (3) and tosylazide that gives a rhodium tosylamide. Pathway A invokes coordination
of the more nucleophilic Na of the organoazide, followed by N2 elimination to give a highly reactive rhodium nitrene. Pathway B involves end-on tosylazide
coordination, 1,1-insertion, 1,3-hydrogen migration, and nitrogen elimination.
Scheme 2 Proposed mechanism for divergent pathways in reactions of 1 and 3 with tosylazide.
15N NMR chemical shifts of tris(oxazolinyl)borate M(III) (M = Rh,
Ir) compounds
15N NMR chemical shifts have been reported for a series of late
metal compounds with pyridine-type ligands,36 cyclometalated
imidazoles,37 and metal-coordinated oxazolines.22,24,38,39,40 We have
1
also observed through-metal H-15N correlations in ToMMgMe,
31P NMR spectroscopy is routine for structural assignments of
coordination complexes, and 31P NMR chemical shift data are
widely reported.35 In contrast, the low natural abundance and low
gyromagnetic ratio of the 15N nucleus has limited direct detection
methods in 15N NMR spectroscopy for the characterization of
coordination complexes. Indirect 15N NMR detection methods
can bypass this problem and provide chemical shift data, and 2D
heteronuclear correlation spectroscopy is also very powerful for as-
signing structure. A few recent studies have highlighted the power
of 15N NMR measurements (at natural abundance) using het-
eronuclear correlation methods, including identification of the co-
ordination modes of tris(pyrazolyl)borate rhodium compounds.26
ToMAlMe2, as well as in ToMRhCl(CHCl2)CO that demonstrate
that both oxazoline and alkyl ligands are bonded to the same
metal center.24c,39 The through-metal correlations described above
for compounds 1–5 provide information into the metal center’s
configuration.
15N NMR chemical shifts trends could also be useful for
structural assignments, and the series of ToMRhXX¢L compounds
reported here show general trends in 15N NMR shifts that relate
to the transoid ligand. In Table 1, we compare 15N NMR chemical
shift values relative to the trans ligand and M-N distances for the
compounds reported in the current contribution.
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Table 1 15N NMR chemical shift data and M-N distances for oxazoline nitrogen in ToMMXX¢L compounds
M–N distance
trans to H (A)
M–N distance
trans to allyl
15N trans to a
heteroatomic ligand
15N trans to hydride
15N trans to allyl
˚
Compound
3
ToMRhH(h -C8H13) (1)
-164.2
-165.6
-164.8
-179.9
n.a.b
n.a.a
-173.4
n.a.a
n.a.c
endo-ToMRhH(h -C3H5) (endo-3)
2.298(3)
2.223(3)
2.280(3)
n.a.a,b
n.a.b
2.234(6)
2.20(1)
n.a.
-173.8
2.107(3) 2.109(3)
2.141(3) 2.128(3)
2.101(3) 2.132(3)
n.a.a
n.a.c
3
exo-ToMRhH(h -C3H5) (exo-3)
-173.1
n.a.c
3
3
ToMRhH(h -C3H4Ph) (5)
-168.2, -172.1
-191.1, -181.5
-177.6
n.a.c
3
ToMRhBr(h -C3H4Ph) (9)
-217.6 (Br)
ToMRh(NHTs)(h -C3H5) (10)
n.a.b
2.140(2) 2.121(3)
-225.4 (NHTs)
-228.6 (NHTs) -205.8 (OH2)
-221.0 (OAc)
n.a.c
3
ToMRhH(NHTs)OH2 (11)
-154.1
-154.3
-182.6
-184.9
n.a.d
n.a.d
2
ToMRhH(k -O2CMe) (8)
n.a.d
n.a.d
ToMIrH(h -C8H13) (2)
-190.6
-189.5
n.a.a
3
ToMIrH(h -C3H5) (4)
n.a.
n.a.a
n.a.c
3
a An X-ray crystal structure was not obtained. b The compound does not contain a metal hydride. c The compound does not contain a heteroatomic
ligand. d The compound does not contain an allyl group.
The 15N chemical shift of the oxazoline trans to the strong-
field hydride ligand is farthest downfield for compounds 1–4. The
chemical shifts for rhodium complexes are ca. 20 ppm farther
upfield than the corresponding iridium congener. Additionally, the
15N chemical shift of the oxazoline trans to hydride for the C8H13
complexes is systematically 1–2 ppm downfield in comparison
to the shift for the C3H5 complexes. However, the 15N NMR
rhodium triazenide intermediates; we are currently investigat-
ing reactions of other organoazides with tris(oxazolinyl)borato
rhodium compounds to better understand the mechanism
and identify intermediates in the formation of rhodium
amides.
C–N bond formation via reductive elimination from
a
rhodium(III) allyl amide is facilitated by carbon monoxide. The
mechanism for C–N bond formation does not necessarily require
an allylic group (as in iridium-catalyzed allylation chemistry) as
the hydrocarbyl moiety is bonded in a s-only fashion prior to
elimination. Thus, the sequence described here may potentially
be applied to the functionalization of non-allylic hydrocarbon
substrates. This sequence, (a) C–H bond oxidative addition, (b)
azide-mediated amination, and (c) C–N bond reductive elimi-
nation simply requires an accessible coordination site following
the C–H bond activation step. While this open coordination
3
chemical shift of the hydride in ToMRhH(h -C3H4Ph) is not the
farthest downfield in that compound, and it is approximately
15 ppm upfield with respect to the other rhodium allyl com-
pounds. The oxazoline trans to the tosylamide has the farthest
upfield 15N NMR chemical shift, and those trans to weak-field
bromide, water, and acetate ligands also have upfield chemical
shifts.
The hydride ligands have the strongest trans influence, as
shown in Table 1 by their long Rh–N distances. However, 15N
NMR chemical shifts of the oxazolines do not track with the
apparent trans influence of hydride, allyl, and amido ligands. For
example, although the Rh–Noxazoline distances trans to hydride are
3
site is provided by isomerization of ToMRhH(h -C3H5) to the
s-allyl form, dissociation of a hemilabile ancillary ligand could
also provide such an open site. In that case, re-coordination of
the hemilabile ligand might also mediate reductive elimination
and facilitate catalysis. We are currently considering such design
features for the development of new processes.
3
significantly longer than Rh–Noxazoline distances trans to h -allyl
ligands, the chemical shifts range for these two ligands are similar.
Additionally, while the 15N NMR chemical shifts of the oxazoline
trans to tosylamide are 35 ppm upfield of those trans to allyl,
the Rh–Noxazoline distances are similar for groups trans to allyl and
amide ligands.
Experimental
General procedures
Conclusion
All reactions were carried out under an inert atmosphere using
standard Schlenk techniques or in a glovebox. All solvents
were dried and degassed unless otherwise indicated. All reagents
were purchased from Sigma–Aldrich and used without further
We have shown that a tris(oxazolinyl)borate ligand is a suitable
ancillary for rhodium(I)- and iridium(I)-mediated allylic C–H
bond oxidative addition for cyclooctene, propene and allylbenzene
substrates under thermal (non-photolytic) conditions. Thermal
allylic C–H bond activations with iridium(I) tris(pyrazolyl)borate
and tris(phosphino)borate compounds had been previously
been described,12,13,14,15 but examples of rhodium(I)-mediated
allylic C–H bond activation were limited to photochemical
activations.16,17
Our attempts to develop methods for functionalization of
the allyl hydrides have uncovered the first example of (formal)
nitrene insertion into rhodium-hydrogen bonds. The mecha-
nism for this insertion may involve either rhodium nitrene or
2
2
purification. Tl[ToM],24c [Rh(m-Cl)(h -C8H14)2]2,41a [Ir(m-Cl)(h -
41c
C8H14)2]2,41b and TsN3 were prepared according to reported
procedures. All NMR spectra were obtained at room temperature
using Bruker DRX-400 and Avance II-700 spectrometers. 15N
1
NMR chemical shifts were determined by H-15N HMBC exper-
iments recorded on an Avance II-700 spectrometer; the chemical
shift values are reported relative to CH3NO2. 11B NMR spectra
chemical shifts are reported relative to BF3·Et2O. GC-MS data
were obtained on an Agilent 7890 A GC system containing an
HP-5MS capillary column and an Agilent 5975C mass selective
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 6500–6514 | 6509
©

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detector. Elemental analyses were obtained at the Iowa State
Chemical Instrumentation Facility using a Perkin–Elmer 2400
Series II CHN/S. Single crystal X-ray analysis was carried out
on a Bruker APEX2 CCD Diffractometer.
d6, 175 MHz): d 136.66 (ortho-C6H5), 127.06 (meta-C6H5), 125.98
(para-C6H5), 83.20 (CH(CH)2(CH2)5), 81.49 (CNCMe2CH2O),
81.18 (CNCMe2CH2O), 69.46 (CNCMe2CH2O), 69.07
(CNCMe2CH2O), 39.47 (CH(CH)2(CH2)5), 33.62 ((CH)2-
CH2(CH2)3CH2), 30.77 ((CH)3CH2CH2CH2CH2CH2), 30.55
((CH)3CH2CH2CH2CH2CH2), 28.55 (CNCMe2CH2O), 28.50
(CNCMe2CH2O), 28.23 (CNCMe2CH2O). 11B NMR (benzene-d6,
128 MHz): d -17.7. 15N NMR (benzene-d6, 71 MHz): d -182.6
(trans to IrH), -190.6 (cis to IrH). IR (KBr, cm-1): n 2962 (s),
2925 (s, sh), 2253 (m, nIrH), 1589 (s, nCN), 1463 (w), 1355 (w), 1282
(m), 1262 (m), 1200 (m), 1158 (m), 1094 (w), 966 (m), 801 (m),
705 (m). Anal. Calcd. for C29H43BIrN3O3: C, 50.87; H, 6.33; N,
6.14 Found: C, 50.88 H, 6.80 N, 6.38. Mp: 158 ◦C, dec.
ToMRhH(g3-C8H13) (1). Benzene (50 mL) was added to a
2
solid mixture of Tl[ToM] (0.187 g, 0.319 mmol) and [Rh(m-Cl)(h -
C8H14)2]2 (0.160 g, 0.223 mmol) giving a suspension. The resulting
mixture was stirred at room temperature for 5 h and then filtered.
The solvent was removed from the filtrate under reduced pressure.
The resulting residue was extracted with pentane (3 ¥ 25 mL),
and the extractions were combined and evaporated to dryness to
3
give analytically pure ToMRh(h -C8H13) (1, 0.134 g, 0.225 mmol,
1
70.6%) as a brown solid in good yield. H NMR (benzene-d6,
3
400 MHz): d 8.45 (d, 2 H, JHH = 7.6 Hz, ortho-C6H5), 7.58 (t,
ToMRhH(g3-C3H5) (3). Propene was bubbled through a solu-
3
3
2 H, JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, JHH = 7.2 Hz,
2
tion of [Rh(m-Cl)(h -C8H14)2]2 (0.500 g, 0.697 mmol) in benzene
3
para-C6H5), 5.16 (t, 1 H, CH(CH)2(CH2)5, J
(dd, 2 H, JHH = 16.4 Hz, JHH = 8.0 Hz, CH(CH)2(CH2)5), 3.74
(d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O), 3.60 (d, 2 H, JHH
8.4 Hz, CNCMe2CH2O), 3.33 (s, H, CNCMe2CH2O),
2.51 (m, H, (CH)3CH2(CH2)3CH2), 2.21 (m, H,
(CH)3(CH2)2CH2(CH2)2), 1.74 (m, 2 H, (CH)3CH2(CH2)3CH2),
1.50 (m, H, (CH)3(CH2)2CH2(CH2)2), 1.45 (m, H,
= 8.0 Hz), 3.95
HH
2
(100 mL) for 10 min to form [Rh(m-Cl)(h -C3H6)2]2. Tl[ToM]
3
3
2
(0.56 g, 0.96 mmol) was added as a solid to the [Rh(m-Cl)(h -
2
2
=
C3H6)2]2 solution at room temperature, and the resulting mixture
was stirred for 1 h. The solution was then filtered, and the volatile
materials in the filtrate were evaporated to dryness. The resulting
residue was extracted with pentane (3 ¥ 50 mL) and stored at
-35 ◦C overnight. The solids were then collected as an analytically
pure, light-brown, flaky powder (0.39 g, 76%). This powder was
then recrystallized from toluene at -30 ◦C to obtain X-ray quality
crystals of co-crystallized exo-3 and endo-3. IR (KBr, cm-1): n
3075 (m), 3035 (m), 2967 (m), 2927 (m), 2899 (m), 2090 (s, nRhH),
2080 (s, nRhH), 1598 (s, nCN), 1567 (m, nCN), 1460 (m), 1382 (m),
1365 (m), 1351 (m), 1275 (m), 1197 (m), 1155 (m), 1021 (w), 992
(m), 975 (m), 902 (m), 703 (m). Anal. Calcd. for C24H35BRhN3O3:
C, 54.67; H, 6.69; N, 7.97. Found: C, 54.71; H, 6.37; N, 7.71.
Mp: 204–206 ◦C, dec. Although the two conformers are not
independently isolated, the NMR spectroscopic data for each is
2
2
1
1
4
(CH)3CH2CH2CH2CH2CH2), 1.17 (s, 6 H, CNCMe2CH2O), 1.12
(s, 6 H, CNCMe2CH2O), 0.82 (s, 6 H, CNCMe2CH2O), -24.27
1
1
(d, 1 H, JRhH = 11.6 Hz, RhH). 13C{ H} NMR (benzene-d6,
175 MHz): d 136.81 (ortho-C6H5), 126.93 (meta-C6H5), 125.75
(para-C6H5), 93.93 (d, JRhC = 6.0 Hz, CH(CH)2(CH2)5), 81.96
1
(CNCMe2CH2O), 80.93 (CNCMe2CH2O), 68.41 (CNCMe2-
1
CH2O), 67.92 (CNCMe2CH2O), 52.15 (d, JRhC = 11.4 Hz,
CH(CH)2(CH2)5),
((CH)3CH2CH2CH2CH2CH2),
CH2CH2), 28.82 (CNCMe2CH2O), 28.57 (CNCMe2CH2O), 28.33
(CNCMe2CH2O). 11B NMR (benzene-d6, 128 MHz): d -18.7. 15
38.41
((CH)3CH2(CH2)3CH2),
29.52
29.49 ((CH)3CH2CH2CH2-
N
1
provided separately to facilitate interpretation. exo-3: H NMR
NMR (benzene-d6, 71 MHz): d -164.2 (trans to RhH), -173.4
(cis to RhH). IR (KBr, cm-1): n 3076 (w), 3040 (w), 2959 (m),
2927 (m), 2843 (m), 2158 (m, nRhH), 1598 (s, nCN), 1462 (m), 1383
(m), 1363 (m), 1275 (m), 1195 (m), 1156 (m), 996 (m), 972 (m),
933 (w). Anal. Calcd. for C29H43BRhN3O3: C, 58.50; H, 7.28; N,
7.06. Found: C, 58.85; H, 7.48; N, 7.10. Mp: 132–135 ◦C, dec.
(benzene-d6, 400 MHz): d 8.46 (d, 2 H, 3JHH = 7.6 Hz, ortho-C6H5),
7.58 (t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, 3JHH = 7.6 Hz,
para-C6H5), 4.91 (m, 1 H, CH(CH2)2), 3.66 (d, 2 H, 2JHH = 8.4 Hz,
2
CNCMe2CH2O), 3.61 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
3
3.34 (s, 2 H, CNCMe2CH2O), 2.91 (d, 2 H, JHH = 7.2 Hz, syn-
3
CH(CH2)2), 2.28 (d, 2 H, JHH = 11.6 Hz, anti-CH(CH2)2), 1.05
ToMIrH(g3-C8H13) (2).
A
100 mL Schlenk flask was
(s, 6 H, CNCMe2CH2O), 1.02 (s, 6 H, CNCMe2CH2O), 0.79 (s,
charged with Tl[ToM] (0.24 g, 0.41 mmol), [Ir(m-Cl)(h -C8H14)2]2
(0.19 g, 0.21 mmol) and benzene (50 mL). The mixture was
stirred for one day and then was filtered. The filtrate was
evaporated, and the resulting yellow solid was washed with
pentane (10 mL). The filtrate was dried in vacuo to yield 2
as a light brown solid (0.22 g, 0.32 mmol, 78%). 1H NMR
6 H, CNCMe2CH2O), -23.20 (d, 1 H, JRhH = 10.0 Hz, RhH).
2
1
1
13C{ H} NMR (benzene-d6, 175 MHz): d 136.71 (ortho-C6H5),
126.97 (meta-C6H5), 125.78 (para-C6H5), 93.41 (d, 1JRhC = 7.0 Hz,
CH(CH2)2), 81.82 (CNCMe2CH2O), 80.53 (CNCMe2CH2O),
69.00 (CNCMe2CH2O), 67.74 (CNCMe2CH2O), 32.99 (d,
1JRhC = 10.5 Hz, CH(CH2)2), 28.72 (CNCMe2CH2O), 28.38
(CNCMe2CH2O), 28.11 (CNCMe2CH2O). 11B NMR (benzene-
d6, 128 MHz): d -18.4. 15N NMR (benzene-d6, 71 MHz): d -165.6
(trans to RhH), -173.1 (cis to RhH). endo-3: 1H NMR (benzene-
3
(benzene-d6, 400 MHz): d 8.42 (d, 2 H, JHH = 7.2 Hz, ortho-
3
C6H5), 7.58 (t, 2 H, JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H,
3JHH = 7.2 Hz, para-C6H5), 4.79 (t, 1 H, CH(CH)2(CH2)5, 3J
3
3
3
= 8.0 Hz), 3.98 (dd, 2 H, JHH = 17.0 Hz, JHH = 8.0 Hz,
d6, 400 MHz): d 8.56 (d, 2 H, JHH = 6.8 Hz, ortho-C6H5), 7.63
HH
2
3
3
CH(CH)2(CH2)5), 3.77 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
(t, 2 H, JHH = 7.6 Hz, meta-C6H5), 7.41 (t, 1 H, JHH = 7.2 Hz,
2
3.61 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O), 3.32 (s, 2 H,
para-C6H5), 5.10 (m, 1 H, CH(CH2), 3.64 (d, 2 H, 2JHH = 8.4 Hz,
CNCMe2CH2O), 3.47 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
3.29 (s, 2 H, CNCMe2CH2O), 3.01 (d, 2 H, JHH = 7.2 Hz, syn-
CH(CH2)2), 2.51 (d, 2 H, JHH = 11.2 Hz, anti-CH(CH2)2), 0.94
2
CNCMe2CH2O), 2.60 (m,
2
H, (CH)3CH2(CH2)3CH2),
3
2.37 (m, H, (CH)3(CH2)2CH2(CH2)2), 1.72 (m,
1
2
H,
3
(CH)3CH2(CH2)3CH2), 1.61 (m, 1 H, (CH)3(CH2)2CH2(CH2)2),
1.45 (m, 4 H, (CH)3CH2CH2CH2CH2CH2), 1.17 (s, 6 H,
CNCMe2CH2O), 1.08 (s, 6 H, CNCMe2CH2O), 0.80 (s, 6 H,
(s, 6 H, CNCMe2CH2O), 0.79 (s, 6 H, CNCMe2CH2O), 0.76
1
(s, 6 H, CNCMe2CH2O), -22.74 (s, br, 1 H, RhH). 13C{ H}
1
CNCMe2CH2O), -28.54 (s, 1 H, IrH). 13C{ H} NMR (benzene-
NMR (benzene-d6, 175 MHz): d 136.77 (ortho-C6H5), 127.05
6510 | Dalton Trans., 2011, 40, 6500–6514
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1
(meta-C6H5), 125.81 (para-C6H5), 88.28 (d, JRhC = 7.0 Hz,
(s, 3 H, CNCMe2CH2O), 0.72 (s, 3 H, CNCMe2CH2O), 0.39
1
CH(CH2)2), 80.11 (CNCMe2CH2O), 79.97 (CNCMe2CH2O),
69.53 (CNCMe2CH2O), 67.36 (CNCMe2CH2O), 37.46 (d,
1JRhC = 10.5 Hz, CH(CH2)2), 28.38 (CNCMe2CH2O), 27.85
(CNCMe2CH2O), 27.63 (CNCMe2CH2O). 11B NMR (benzene-
d6, 128 MHz): d -17.7. 15N NMR (benzene-d6, 71 MHz): d -164.8
(trans to RhH), -173.8 (cis to RhH).
(s, 3 H, CNCMe2CH2O), -22.48 (s, br, 1 H, RhH). 13C{ H}
NMR (benzene-d6, 175 MHz): d 145.57 (ipso-CH2CHCHPh),
136.74 (ortho-C6H5), 129.43 (meta-CH2CHCHPh), 129.21
(ortho-CH2CHCHPh), 127.09 (meta-C6H5), 125.86 (para-
1
C6H5), 125.54 (para-CH2CHCHPh), 90.06 (d, JRhC = 3.5 Hz,
CH2CHCHPh), 81.39 (CNCMe2CH2O), 79.89 (CNCMe2CH2O),
79.38 (CNCMe2CH2O), 69.91 (CNCMe2CH2O), 68.06
ToMIrH(g3-C3H5) (4). In a 100 mL Schlenk flask, propene
1
(CNCMe2CH2O), 67.56 (CNCMe2CH2O), 54.52 (d, JRhC
=
2
was bubbled through a solution of [Ir(m-Cl)(h -C8H14)2]2 (0.100 g,
1
10.5 Hz, CH2CHCHPh), 36.54 (d, JRhC
= 12.25 Hz,
0.112 mmol) in benzene (30 mL) for 10 min. Tl[ToM] (0.125 g,
0.213 mmol) was added to the solution at room temperature and
stirred overnight. The solution was then filtered and evaporated
to dryness. The residue was washed with pentane (10 mL) and
dried in vacuo to yield the product as a yellow-brown solid
CH2CHCHPh), 28.52 (CNCMe2CH2O), 27.91 (CNCMe2CH2O),
27.59 (CNCMe2CH2O), 27.48 (CNCMe2CH2O), 27.03
(CNCMe2CH2O), 26.89 (CNCMe2CH2O). 11B NMR (benzene-d6,
128 MHz): d -19.7. 15N NMR (benzene-d6, 71 MHz): d -168.17
(cis to RhH), -172.10 (cis to RhH), -179.94 (trans to RhH). IR
(KBr, cm-1): n 3041 (m), 2967 (m), 2927 (m), 2882 (m), 2081
(m, nRhH), 1590 (s, nCN), 1462 (w), 1366 (m), 1351 (m), 1276 (m),
1198 (m), 1177 (m), 1153 (m), 1022 (w), 999 (m), 970 (m). Anal.
Calcd. for C30H39BRhN3O3: C, 59.72; H, 6.52; N, 6.96. Found: C,
60.18; H, 6.11; N, 6.88. Mp: 191–192 ◦C, dec.
1
(0.096 g, 0.16 mmol, 73%). H NMR (benzene-d6, 400 MHz):
3
d 8.43 (d, 2 H, JHH = 7.2 Hz, ortho-C6H5), 7.58 (t, 2 H,
3
3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, JHH = 7.6 Hz, para-
2
C6H5), 4.28 (m, 1 H, CH(CH2)2), 3.68 (d, 2 H, JHH = 8.4 Hz,
2
CNCMe2CH2O), 3.62 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
3
3.33 (s, 2 H, CNCMe2CH2O), 3.07 (d, 2 H, JHH = 6.8 Hz,
3
syn-CH(CH2)2), 2.43 (d, 2 H, JHH = 10.0 Hz, anti-CH(CH2)2),
ToMRh(CNtBu)2 (7). CNtBu (51 mL, 0.46 mmol) was added to
3
1.05 (s, 6 H, CNCMe2CH2O), 1.02 (s, 6 H, CNCMe2CH2O),
a benzene solution of ToMRhH(h -C8H13) (0.138 g, 0.232 mmol).
1
0.76 (s, 6 H, CNCMe2CH2O), -27.64 (s, 1 H, IrH). 13C{ H}
The resulting solution was stirred for 2 h, and then the volatile
materials were evaporated under reduced pressure. The residue was
then washed with ether to give a yellow solid (0.100 g, 0.153 mmol,
NMR (benzene-d6, 175 MHz): d 136.58 (ortho-C6H5), 127.13
(meta-C6H5), 126.05 (para-C6H5), 82.89 (CNCMe2CH2O), 80.76
(CNCMe2CH2O), 79.13 (CH(CH2)2), 70.17 (CNCMe2CH2O),
69.04 (CNCMe2CH2O), 28.44 (CNCMe2CH2O), 28.37
66.2%). 1H NMR (benzene-d6, 400 MHz): d 8.42 (d, 2 H, 3JHH
=
7.2 Hz, ortho-C6H5), 7.48 (t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.25
(t, 1 H, 3JHH = 7.2 Hz, para-C6H5), 3.71 (s, 6 H, CNCMe2CH2O),
(CNCMe2CH2O), 28.26 (CNCMe2CH2O), 16.53 (CH(CH2)2). 11
B
1
NMR (benzene-d6, 128 MHz): d -17.4. 15N NMR (benzene-d6,
71 MHz): d -184.9 (trans to IrH), -189.5 (cis to IrH). IR
(KBr, cm-1): n 3040 (w), 2963 (m), 2926 (m), 2212 (m, nIrH),
1658.5 (w), 1595 (s, nCN), 1461 (w), 1383 (w), 1357 (w), 1282
(s), 1263 (m), 1198 (m), 1160 (w), 1095 (w), 966 (w), 803 (s),
655 (s), 603 (m). Anal. Calcd. for C24H35BIrN3O3: C, 46.75; H,
5.72 N, 6.82. Found: C, 46.23; H, 6.22; N, 6.38. Mp: 144 ◦C,
dec.
1.35 (s, 18 H, CNCMe2CH2O), 0.97 (s, 18 H, CNCMe3). 13C{ H}
NMR (benzene-d6, 175 MHz): d 135.47 (ortho-C6H5), 128.50 (d,
1JRhC = 63.5 Hz, RhCNCMe3), 127.35 (meta-C6H5), 125.37 (para-
C6H5), 79.00 (CNCMe2CH2O), 68.33 (CNCMe2CH2O), 55.98
(CNCMe3), 30.76 (CNCMe2CH2O), 28.70 (CNCMe3). 11B NMR
(benzene-d6, 128 MHz): d -18.0. 15N NMR (benzene-d6, 71 MHz):
d -159.6 (CNCMe2CH2O), -201.1 (CNCMe3). IR (CH2Cl2, cm-1):
n 2962 (m), 2924 (m), 2892 (m), 2865 (w), 2208 (w, nC N), 2147
(s, nC N), 2103 (s, nC N), 2068 (s, nC N), 1614 (m, nC N), 1585 (s,
nC N), 1460 (m), 1431 (w), 1368 (m), 1352 (m), 1274 (m), 1196 (m),
1173 (w), 1162 (w), 1119 (w), 1036 (w), 966 (m). Anal. Calcd. for
C31H47BN5O3Rh: C, 57.15; H, 7.27; N, 10.75 Found: C, 57.00; H,
6.94; N, 10.32. Mp: 216–219 ◦C dec.
ToMRhH(g3-C3H4Ph) (5). Allylbenzene (0.59 mL) and [Rh(m-
2
Cl)(h -C8H14)2]2 (0.159 g, 0.22 mmol) were allowed to react in
2
benzene (10 mL) for 30 min to generate [Rh(m-Cl)(h -C3H5Ph)2]2.
Tl[ToM] (0.26 g, 0.44 mmol) was then added, and the resulting
mixture was stirred overnight. The solids were removed by
filtration and the filtrate was evaporated to dryness. The residue
was washed with pentane (2 ¥ 2 mL) and the resulting solid
was dissolved in toluene (10 mL). The toluene solution was
concentrated to 0.5 mL and the solid was collected as a green
powder (0.160 g, 0.265 mmol, 59.8%). 1H NMR (benzene-d6,
ToMRhH(j2-O2CMe) (8). Acetic acid (0.021 g, 0.346 mmol)
3
and ToMRhH(h -C8H13) (0.103 g, 0.173 mmol) were allowed to
react in benzene (10 mL) at room temperature for 10 min. The
resulting mixture was then evaporated to dryness. The residue
was extracted with pentane (15 mL), dried under vacuum,
and crystallized in toluene at -35 ◦C to give a brown solid
(0.043 g, 0.076 mmol, 44.0%). 1H NMR (benzene-d6, 400 MHz):
3
400 MHz): d 8.51 (d, 2 H, JHH = 7.6 Hz, ortho-C6H5), 7.60 (t,
3
3
2 H, JHH = 7.6 Hz, meta-C6H5), 7.44 (d, 2 H, JHH = 7.6 Hz,
3
3
ortho-CH2CHCHPh), 7.39 (t, 1 H, 3JHH = 7.6 Hz, para-C6H5), 7.11
(t, 2 H, JHH = 7.2 Hz, meta-CH2CHCHPh), 7.09 (t, 1 H, JHH
d 8.40 (d, 2 H, JHH = 7.2 Hz, ortho-C6H5), 7.57 (t, 2 H, JHH
=
3
3
3
=
7.6 Hz, meta-C6H5), 7.38 (t, 1 H, JHH = 7.2 Hz, para-C6H5),
3.78 (s, 2 H, CNCMe2CH2O), 3.52 (d, 2 H, JHH = 8.4 Hz,
CNCMe2CH2O), 3.47 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
2
7.2 Hz, para-CH2CHCHPh), 5.62 (m, 1 H, CH2CHCHPh),
3
2
3.98 (d, 1 H, JHH = 10.4 Hz, CH2CHCHPh), 3.64 (d, 1 H,
2
2JHH = 8.4 Hz, CNCMe2CH2O), 3.48 (dd, 2 H, JHH = 8.4 Hz,
1.59 (s, 3 H, O2CMe), 1.25 (s, 6 H, CNCMe2CH2O), 1.17 (s, 6 H,
CNCMe2CH2O), 3.40 (dd, 2 H, 2JHH = 8.0 Hz, CNCMe2CH2O),
CNCMe2CH2O), 1.11 (s, 6 H, CNCMe2CH2O), -13.23 (d, 1 H,
3
1
3.22 (d, 1 H, JHH = 9.6 Hz, syn-CH2CHCHPh), 3.20 (d, 1 H,
1JRhH = 11.6 Hz, RhH). 13C{ H} NMR (benzene-d6, 175 MHz): d
3
2JHH = 8.4 Hz, CNCMe2CH2O), 2.84 (d, 1 H, JHH = 11.2 Hz,
190.29 (O2CMe), 136.31 (ortho-C6H5), 127.36 (meta-C6H5), 126.38
(para-C6H5), 82.22 (CNCMe2CH2O), 80.33 (CNCMe2CH2O),
68.42 (CNCMe2CH2O), 67.03 (CNCMe2CH2O), 28.38
anti-CH2CHCHPh), 1.02 (s, 3 H, CNCMe2CH2O), 0.91 (s,
3 H, CNCMe2CH2O), 0.83 (s, 3 H, CNCMe2CH2O), 0.76
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(CNCMe2CH2O), 27.66 (CNCMe2CH2O), 23.91 (O2CMe).
11B NMR (benzene-d6, 128 MHz): -18.2. 15N NMR
C6H5), 6.87 (d, 2 H, 3JHH = 8.0 Hz, meta-C6H4Me), 5.60 (m, 1 H,
3
d
CH(CH2)2), 5.17 (d, 2 H, JHH = 12.4 Hz, anti-CH(CH2)2), 4.19
(benzene-d6, 71 MHz): d -154.3 (trans to RhH), -221.0 (cis
to RhH). IR (KBr, cm-1): n 2963 (m), 2927 (m), 2076 (m, nRhH),
1597 (s, nCN), 1470 (s, nCOO), 1387 (w), 1367 (m), 1284 (m), 1263
(m), 1202 (m), 1162 (m), 1026 (w), 999 (w), 968 (m). Anal.
Calcd. for C23H33BRhN3O5: C, 50.66; H, 6.10; N, 7.71. Found: C,
51.05; H, 6.23; N, 7.50. Mp 115–118 ◦C, dec.
(d, 2 H, 3JHH = 8.8 Hz, syn-CH(CH2s)2), 3.58 (d, 2 H, 2JHH = 8.0,
2
CNCMe2CH2O), 3.39 (d, 2 H, JHH = 8.4 Hz, CNCMe2CH2O),
3.03 (s, 2 H, CNCMe2CH2O), 1.97 (s, 3 H, C6H4Me), 1.40 (s,
6 H, CNCMe2CH2O), 0.92 (s, 6 H, CNCMe2CH2O), 0.37 (s,
1
6 H, CNCMe2CH2O). 13C{ H} NMR (benzene-d6, 175 MHz):
d 147.44 (ipso-C6H4Me), 140.17 (para-C6H4Me), 136.40 (ortho-
C6H5), 129.34 (meta-C6H4Me), 127.18 (meta-C6H5), 126.71
3
ToMRhBr(g3-C3H4Ph) (9). A benzene solution of ToMRhH(h -
1
(ortho-C6H4Me), 126.32 (para-C6H5), 103.09 (d, JRhC = 5.3 Hz,
C3H4Ph) (0.104 g, 0.172 mmol) and NBS (0.031 g, 0.174 mmol)
was stirred at room temperature overnight. The resulting solution
was evaporated to dryness and washed with pentane (2 mL)
and ether (4 ¥ 1.5 mL). The residue was dried under vacuum
to give a brown solid (0.049 g, 0.072 mmol, 42%). 1H NMR
(methylene chloride-d2, 700 MHz): d 7.91 (d, 2 H, 3JHH = 6.3 Hz,
CH(CH2)2), 82.78 (CNCMe2CH2O), 80.63 (CNCMe2CH2O),
70.07 (CNCMe2CH2O), 69.08 (CNCMe2CH2O), 47.49 (d,
1JRhC = 10.5 Hz, CH(CH2)2), 28.31 (CNCMe2CH2O), 27.58
(CNCMe2CH2O), 27.51 (CNCMe2CH2O), 21.45 (C6H4Me).
1
11B NMR (benzene-d6, 128 MHz): d -18.3. 15N{ H} NMR
(benzene-d6, 71 MHz): d -177.59 (cis to RhNHTs), -255.43 (trans
to RhNHTs). IR (KBr, cm-1): n 3341 (m, nNH), 3000 (m), 2970
(m), 2928 (m), 2885 (m), 1591 (s, nCN), 1462 (m), 1370 (m), 1287
(s, nSO2), 1262 (m), 1203 (s, nSO2), 1158 (m), 1134 (s, nSO2), 1088
(s), 998 (m), 965 (s, nSO2). Anal. Calcd. for C31H42BN4O5RhS: C,
53.46; H, 6.08; N, 8.04. Found: C, 53.90; H, 6.38; N, 7.85. Mp:
200–202 ◦C, dec.
3
ortho-CH2CHCHPh), 7.79 (d, 2 H, JHH = 7.0 Hz, ortho-C6H5),
3
7.39 (t, 1 H, JHH = 7.0 Hz, para-CH2CHCHPh), 7.33 (t,
3
3
2 H, JHH = 7.7 Hz, meta-CH2CHCHPh), 7.21 (t, 2 H, JHH
=
3
7.0 Hz, meta-C6H5), 7.14 (t, 1 H, JHH = 7.0 Hz, para-C6H5),
3
6.54 (m, 1 H, CH2CHCHPh), 5.43 (d, 1 H, JHH = 13.3 Hz,
CH2CHCHPh), 4.45 (d, 1 H, 3JHH = 8.4 Hz, syn-CH2CHCHPh),
3
4.14 (d, 1 H, JHH = 11.9 Hz, anti-CH2CHCHPh), 4.11 (d, 1 H,
2JHH = 7.7 Hz, CNCMe2CH2O), 3.98 (d, 1 H, JHH = 8.4 Hz,
2
3
ToMRh(NHTs)(H)OH2 (11). ToMRhH(h -C8H13) (0.166 g,
2
CNCMe2CH2O), 3.96 (d, 1 H, JHH = 8.4 Hz, CNCMe2CH2O),
0.279 mmol) was added to a solution of TsN3 (0.055 g, 0.279 mmol)
in 10 mL of benzene. The resulting mixture was stirred at room
temperature for 3 h. All volatiles were evaporated, and the residue
was washed with pentane (2 ¥ 2 mL) to give a brown solid (0.126 g,
2
3.92 (d, 1 H, JHH = 7.7 Hz, CNCMe2CH2O), 3.77 (d, 1 H,
2JHH = 7.7 Hz, CNCMe2CH2O), 3.70 (d, 1 H, JHH = 8.4 Hz,
2
CNCMe2CH2O), 1.52 (s,
3 H, CNCMe2CH2O), 1.40 (s,
3 H, CNCMe2CH2O), 1.31 (s, 3 H, CNCMe2CH2O), 1.18 (s,
3 H, CNCMe2CH2O), 0.98 (s, 3 H, CNCMe2CH2O), 0.75 (s,
1
0.187 mmol, 67.0%). H NMR (benzene-d6, 400 MHz): d 8.39
(d, 2 H, 3JHH = 6.8 Hz, ortho-C6H5), 8.19 (d, 2 H, 3JHH = 8.0 Hz,
1
3 H, CNCMe2CH2O). 13C{ H} NMR (methylene chloride-d2,
3
ortho-C6H4Me), 7.56 (t, 2 H, JHH = 7.2 Hz, meta-C6H5), 7.37
175 MHz): d 141.77 (ipso-CH2CHCHPh), 135.85 (ortho-C6H5),
129.38 (meta-CH2CHCHPh), 128.61 (ortho-CH2CHCHPh),
127.04 (para-CH2CHCHPh), 126.59 (meta-C6H5), 125.67
(para-C6H5), 112.29 (CH2CHCHPh), 81.40 (CNCMe2CH2O),
80.74 (CNCMe2CH2O), 80.56 (CNCMe2CH2O), 72.26
(CNCMe2CH2O), 72.12 (CNCMe2CH2O), 70.22 (CNCMe2-
3
3
(t, 1 H, JHH = 7.6 Hz, para-C6H5), 6.88 (d, 2 H, JHH = 8.0 Hz,
2
meta-C6H4Me), 3.79 (d, 1 H, JHH = 8.4 Hz, CNCMe2CH2O),
2
3.73 (d, 1 H, JHH = 8.4 Hz, CNCMe2CH2O), 3.58 (d, 1 H,
2JHH = 8.4 Hz, CNCMe2CH2O), 3.47 (d, 1 H, JHH = 8.4 Hz,
2
2
CNCMe2CH2O), 3.38 (d, 1 H, JHH = 8.4 Hz, CNCMe2CH2O),
3.30 (d, 1 H, 2JHH = 8.8 Hz, CNCMe2CH2O), 2.32 (s, 1 H, NHTs),
1.92 (s, 3 H, C6H4Me), 1.63 (s, 3 H, CNCMe2CH2O), 1.61 (s,
3 H, CNCMe2CH2O), 1.08 (s, 3 H, CNCMe2CH2O), 1.06 (s, 3 H,
CNCMe2CH2O), 0.89 (s, 3 H, CNCMe2CH2O), 0.71 (s, 3 H,
1
CH2O), 64.71 (CH2CHCHPh), 37.34 (d, JRhC = 12.25 Hz,
CH2CHCHPh), 28.18 (CNCMe2CH2O), 27.86 (CNCMe2CH2O),
27.81 (CNCMe2CH2O), 27.45 (CNCMe2CH2O), 26.75
(CNCMe2CH2O), 26.21 (CNCMe2CH2O). 11B NMR (methylene
chloride-d2, 128 MHz): d -18.2. 15N NMR (methylene chloride-
d2, 71 MHz): d -181.5 (cis to RhBr), -191.1 (cis to RhBr),
-217.6 (trans to RhBr). IR (KBr, cm-1): n 3039 (w), 2975 (w),
2883 (w), 1590 (s, nCN), 1466 (w), 1387 (w), 1368 (w), 1286 (m),
1245 (w), 1202 (m), 1028 (w), 1001 (w), 973 (m). Anal. Calcd.
for C30H38BRhN3O3Br: C, 52.81; H, 5.61; N, 6.16; Found: C,
52.86; H, 5.48; N, 5.90. Mp: 215–218 ◦C, dec.
CNCMe2CH2O), -15.75 (d, 1 H, 1JRhH = 9.2 Hz, RhH). 13C{ H}
1
NMR (benzene-d6, 175 MHz): d 142.41 (ipso-C6H4Me), 142.31
(para-C6H4Me), 136.38 (ortho-C6H5), 129.78 (meta-C6H4Me),
127.30 (meta-C6H5), 126.37 (ortho-C6H4Me), 126.31 (para-
C6H5), 82.25 (CNCMe2CH2O), 80.70 (CNCMe2CH2O), 79.70
(CNCMe2CH2O), 69.48 (CNCMe2CH2O), 67.14 (CNCMe2-
CH2O), 66.98 (CNCMe2CH2O), 28.93 (CNCMe2CH2O),
28.79 (CNCMe2CH2O), 27.77 (CNCMe2CH2O), 27.57
(CNCMe2CH2O), 27.53 (CNCMe2CH2O), 27.29 (CNCMe2-
CH2O), 21.51 (C6H4Me). 11B NMR (benzene-d6, 128 MHz): d
3
exo-ToMRh(NHTs)(g3-C3H5)
(10). ToMRhH(h -C3H5)H
(0.101 g, 0.192 mmol) was added to a solution of TsN3 (38 mg,
0.19 mmol) in benzene (10 ml). The resulting solution was stirred
for 24 h. The benzene solvent was evaporated in vacuo, and the
residue was dissolved in a minimal amount of toluene and cooled
to -30 ◦C for crysta◦llization. Orange needles were collected
1
-18.2. 15N{ H} NMR (benzene-d6, 71 MHz): d -154.1 (trans
to RhH), -205.8 (trans to OH2), -228.6 (trans to NHTs). IR
(KBr, cm-1): n 3379 (br, nOH), 3300 (w, nNH), 3042 (w), 2964 (m),
2927 (m), 2889 (m), 2067 (m, nRhH), 1594 (s, nCN), 1495 (w), 1462
(m), 1433 (w), 1388 (w), 1367 (m), 1357 (m), 1289 (s, nSO2), 1267
(s, nSO2), 1205 (s, nSO2), 1160 (m), 1126 (w), 1090 (m), 1028 (w),
991 (m), 969 (s, nSO), 881 (w). Anal. Calcd. for C28H40BN4O6RhS:
C, 49.86; H, 5.98; N, 8.31 Found: C, 49.91; H, 6.01; N, 8.30. Mp:
184–186 ◦C, dec.
3
by filtration at -30 C, giving analytically pure ToMRh(h -
C3H5)NHTs (10) in good yield (0.109 g, 0.157 mmol, 81.7%). 1H
3
NMR (benzene-d6, 400 MHz): d 8.26 (d, 2 H, JHH = 7.2 Hz,
ortho-C6H5), 7.86 (d, 2 H, 3JHH = 8.4 Hz, ortho-C6H4Me), 7.54 (t,
2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.36 (t, 1 H, 3JHH = 7.2 Hz, para-
6512 | Dalton Trans., 2011, 40, 6500–6514
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˚
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Acknowledgements
We thank Dr D. Bruce Fulton for assistance with 15N NMR
measurements. This research was supported by the U.S. De-
partment of Energy, Office of Basic Energy Sciences, Division
of Chemical Sciences, Geosciences, and Biosciences through the
Ames Laboratory. Tristan S. Gray was supported by the US. DOE
Office of Science, Office of Workforce Development for Teachers
and Scientists through the Summer Undergraduate Laboratory
Internship Program at the Ames Laboratory. The Ames Labora-
tory is operated for the U.S. Department of Energy by Iowa State
University under Contract No. DE-AC02-07CH11358. Aaron
D. Sadow is an Alfred P. Sloan Fellow.
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3
probe the pathway for the reaction of ToMRhH(h -C8H13) and acetic
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