Dynamic Ligand Reactivity in a Rhodium Pincer Complex

Article abstract of DOI:10.1002/chem.201501453

Ligand cooperativity provides (transition) metal complexes with new reactivities in substrate activation and catalytic reactions, but usually the ligand acts as an internal (Bronsted) base, while the metal acts as a (Lewis) acid. We describe the synthesis and stepwise activation of a new phosphane-pyridine-amide ligand PNN^H2 in combination with Rh^I. The ligand is susceptible to stepwise proton and hydride loss from the nitrogen arm (imine formation) and deprotonation at the pyridylphosphine arm (dearomatization), giving rise to amine complex 1, amido species 2, imine complex 3 and dearomatized compound 4. Complex 4 bears a dual-mode cooperative PNN′ ligand containing both a (nucleophilic) basic methine fragment and a reactive (electrophilic) imine moiety. The basic ligand arm enables substrate deprotonation while the imine ligand arm enables reversible "storage" of the activated (nucleophilic) form of a sulfonamide substrate at the ligand. In combination with metal-based reactivity, this allows for the mono-alkylation of o-toluenesulfonamide with iodomethane. Compounds 1, 3 and 4 are structurally characterized. We also report the first structurally characterized example of an aminal in the coordination sphere of rhodium, complex 5, [Rh(CO)(PNN′′)], formed by sequential N-H activation of sulfonamide by the dearomatized ligand PNN′ and follow-up nucleophilic attack of anionic sulfonamide onto the imine fragment.

Full text of DOI:10.1002/chem.201501453

DOI: 10.1002/chem.201501453
Full Paper
&
Pincer Complexes |Hot Paper|
Dynamic Ligand Reactivity in a Rhodium Pincer Complex
[a]
[b]
[a]
[a]
[a]
Zhou Tang, Edwin Otten, Joost N. H. Reek, Jarl Ivar van der Vlugt,* and Bas de Bruin*
Dedicated to Professor David Milstein in recognition of his inspirational contributions to the field of cooperative catalysis
Abstract: Ligand cooperativity provides (transition) metal
complexes with new reactivities in substrate activation and
catalytic reactions, but usually the ligand acts as an internal
philic) imine moiety. The basic ligand arm enables substrate
deprotonation while the imine ligand arm enables reversible
“storage” of the activated (nucleophilic) form of a sulfona-
mide substrate at the ligand. In combination with metal-
based reactivity, this allows for the mono-alkylation of o-tol-
uenesulfonamide with iodomethane. Compounds 1, 3 and 4
are structurally characterized. We also report the first struc-
turally characterized example of an aminal in the coordina-
tion sphere of rhodium, complex 5, [Rh(CO)(PNN’’)], formed
by sequential NÀH activation of sulfonamide by the dearom-
atized ligand PNN’ and follow-up nucleophilic attack of
anionic sulfonamide onto the imine fragment.
(
Brønsted) base, while the metal acts as a (Lewis) acid. We
describe the synthesis and stepwise activation of a new
H2
phosphane-pyridine-amide ligand PNN
in combination
I
with Rh. The ligand is susceptible to stepwise proton and
hydride loss from the nitrogen arm (imine formation) and
deprotonation at the pyridylphosphine arm (dearomatiza-
tion), giving rise to amine complex 1, amido species 2, imine
complex 3 and dearomatized compound 4. Complex 4 bears
a dual-mode cooperative PNN’ ligand containing both a (nu-
cleophilic) basic methine fragment and a reactive (electro-
Introduction
have attracted much attention due to the broad substrate
[
6–8]
scope.
A common feature of most reported cooperative
Pincer-type transition-metal complexes have been extensively
studied and applied in a wide range of bond activation and
catalytic reactions, due to their high stability and synthetic ver-
ligand concepts is the function of an internal (Brønsted) base,
which reversibly accepts protons from substrates, while the
metal functions as a (Lewis) acid.
[
1]
satility. Recently, the introduction of metal–ligand bifunction-
Examples of metal-ligand cooperativity that extends beyond
substrate activation via a Lewis acidic metal and Brønsted
basic ligand site are rare. Most of those are limited to substrate
activation by simultaneous binding of the substrate to
a vacant (transition) metal site and to a hydrogen-bond donor
[2]
al substrate activation has further boosted applications of
pincer metal complexes and have opened up new opportuni-
ties for catalyst design. Cooperative ligands assist the metal
center in bond-breaking and bond-making processes by direct-
[
2a]
[9]
[10]
ly participating in substrate activation or product formation.
or acceptor, with a borane ligand as a hydride mediator, or
radical-type activation with transition metal complexes bearing
This cooperative effect provides the metal complexes with
new reactivities to promote reactions using more environ-
[
11]
redox-active ligands. To the best of our knowledge, using
a reactive Schiff-base functionality in the ligand framework to
reversibly “store” an activated substrate in the periphery of the
active (transition) metal site in order to enable subsequent
coupling with another substrate is thus far not reported using
[3]
ment-benign reagents and conditions and also provides op-
portunities to replace noble metals with more abundant base
[
4]
metals. Various ligand designs, both pincers and otherwise,
have proven efficient for metal–ligand bifunctional substrate
[5]
[12]
activation and cooperative catalysis. Among them, proton-re-
sponsive donor-appended picolyl- and lutidyl-based systems
cooperative catalysis. This approach of cooperative substrate
activation is demonstrated for the selective mono-methylation
I
of sulfonamides using a Rh(PNN) system (Figure 1), designed
to encompass both nucleophilic and electrophilic reactivity in
the ligand framework. We describe a series of stoichiometric
reactions that form a hypothetical catalytic cycle when com-
bined. Some unwanted side-reactions prevent true catalytic
turnover in one-pot reactions, but the described approach
may be able to accelerate other catalytic reactions.
[
a] Z. Tang, Prof. Dr. J. N. H. Reek, Dr. Ir. J. I. van der Vlugt, Prof. Dr. B. de Bruin
Homogeneous, Bio-inspired & Supramolecular Catalysis
van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam
Science Park 904 (The Netherlands)
E-mail: j.i.vandervlugt@uva.nl
b.debruin@uva.nl
[
b] Dr. E. Otten
We argued that ligands that contain both a Brønsted basic
site and an imine functionality might enable new modes of co-
operative substrate activation processes. Therefore, a new PNN
ligand platform that offers several reactive sites was designed.
Stratingh’ Institute, University of Groningen
Nijenborgh 8, Groningen (The Netherlands)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501453.
Chem. Eur. J. 2015, 21, 12683 – 12693
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H3
ionic carbonyl complex [Rh(CO)(PNN ]PF (1) (Scheme 2). The
6
complex exhibits a sharp doublet at 96.4 ppm (J
155.8 Hz)
Rh-P
31
in the P NMR spectrum. The signals for the two isopropyl CÀ
H protons appear as broad multiplets at 4.50 and 3.24 ppm in
1
the H NMR spectrum, indicating a stable coordination mode
of the pyramidal tertiary amine donor to rhodium and hin-
dered rotation of the diisopropylphenyl group around the CÀN
bond.
Figure 1. Concept of sequential proton-nucleophile reactivity combined
within one dual-mode reactive pincer scaffold.
It is known that sec-aminomethylpyridine ligands (s-AMP),
when bound in their amido form to a transition metal, have
a tendency to lose a hydride (or the overall equivalent of one
proton and two electrons) from the methylene group, resulting
Scheme 2. Synthesis of amine complex 1.
[13,14]
in oxidation to the imine form,
which is then electrophilic
and thus susceptible to coupling with a nucleophile. This fea-
ture could provide an opportunity for ligand-assisted sequen-
tial proton and nucleophile transfer chemistry when combined
with PMP-derived dearomatization reactivity (PMP=phosphi-
nomethylpyridine; Figure 1). We herein describe the coordina-
H2
Synthesis of the amido derivative 2, [Rh(CO)(PNN )]PF ,
6
H
+
imine-complex 3, [Rh(CO)(PNN )] and its dearomatized de-
rivative 4, Rh(CO)(PNN’)
I
tion chemistry of such a hybrid PNN-ligand to Rh and demon-
Addition of one equivalent of potassium tert-butoxide (KOtBu)
to a C D suspension of 1 led to a doublet at 88.1 ppm (Dd=
strate the multiple activation and monoalkylation of a primary
sulfonamide as a test-case for this new concept.
6
6
31
À8.3) in the P NMR spectrum, with a remarkably smaller JRh-P
of 129.7 Hz (DJ=À26.1) compared to that of complex 1, in
[
16]
agreement with the presence of a stronger donor trans to P.
1
The H NMR spectrum showed no -NH signal, which supports
Results and Discussion
formulation of this complex as the neutral amido complex
H2
Rh(CO)(PNN ) (2) (Scheme 2). Complex 2 is not stable at room
H3
Synthesis of amine-complex 1, [Rh(CO)(PNN )]PF6
temperature, and transforms into other species, see below. Stir-
ring a mixture of in situ formed amido-complex 2 (generated
by deprotonation of 1 using 1 equiv KOtBu) and sodium bicar-
H3
PNN ligand PNN was prepared using a modified literature
[15]
procedure (Scheme 1), involving sequential phosphorylation
and amination of 2,6-bis(chloromethyl)pyridine with di-tert-bu-
tylphosphine borane and 2,6-diisopropylaniline, respectively.
bonate (NaHCO ) in THF overnight led to unexpected forma-
3
tion of a major brown product (3) and a minor dark blue prod-
uct (4) after work-up (Scheme 3).
H3
The product ligand PNN was obtained as a white solid in an
overall yield of 43% by refluxing a diethylamine solution of
The brown species shows a doublet (96.3 ppm (Dd 0.1); J
Rh-P
H3
31
the resulting product PNN ·BH , followed by facile work-up.
149.3 Hz (DJ=À6.5)) in the P NMR spectrum and a doublet
3
H3
1
The reaction of two equivalents of ligand PNN (in MeOH)
of doublets at 8.39 ppm (CH=N) in the H NMR spectrum,
13
with [Rh(CO) (m-Cl)] (in MeOH) resulted in immediate forma-
which correlates with a peak at 168.87 ppm in the C NMR
2
2
1
31
tion of a brownish-yellow solution. Addition of KPF or NH PF
6
spectrum according to 2D H– C HSQC spectroscopy. These
6
4
followed by partial evaporation and filtration afforded the cat-
data indicated formation of the imine complex 3,
H
+
[
Rh(CO)(PNN )] . One possible pathway involves deprotona-
tion of complex 1 by KOtBu to form amido complex 2, fol-
lowed by hydride transfer from the amidomethylene arm of 2
to the proton of NaHCO . In the presence of KPF (generated
3
6
in the first deprotonation step of 1 with KOtBu) this would
yield the PF salt of imine complex 3, with H and insoluble
6
2
KNaCO3 as side products. An alternative, albeit very similar
mechanism leading to formation of complex 3 involves spon-
taneous loss of H2 from complex 2 to form complex 4 (see
below), followed by protonation of 4 to produce complex 3
(
see Scheme 3). In this case, amphoteric NaHCO3 (possibly
combined with some adventitious water) would act as the
H3
Scheme 1. Synthetic route to ligand PNN
Chem. Eur. J. 2015, 21, 12683 – 12693
.
proton donor in the last step (4+KPF +NaHCO !3+
6
3
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H through either a concerted inter- or intramolecular process.
2
The spontaneous loss of H is unusual and this observation
2
nicely demonstrates the complementary reactivity of the two
arms and the synergy between these electronically distinct
moieties. Complex 4 could also be synthesized simply by stir-
ring a CH Cl solution of 1 overnight in the presence of excess
2
2
sodium hydroxide (NaOH).
The corresponding X-ray structures for 3 and 4 are depicted
in Figure 2, together with the structure of complex 1. Yellow
single crystals for complex 1 were obtained by slow diffusion
of pentane into a concentrated solution of 1 in dichlorome-
thane. Brownish-red colored crystals of 3 were obtained from
slow diffusion of diethyl ether into a concentrated solution of
3
in dichloromethane. X-ray structure determination provided
the structures depicted in Figure 2. Both complexes adopt
a nearly perfect square planar geometry around Rh, with the
plane defined by the atoms P , N and N . The N2ÀC1 bond in
1
1
2
3
3
is markedly shorter than in 1 (1.496(4) Š in 1 vs. 1.284(3) Š in
), indicating genuine imine double bond character in 3. Dark-
colored single crystals of 4 were obtained from a concentrated
pentane solution of 4 at À788C. The square planar geometry
around rhodium is maintained in the conversion of 3 to 4. The
short C ÀC and C ÀN bond lengths indicate double bond
Scheme 3. Formation of imine ligand complex 3 from amido complex 2
with NaHCO and subsequent deprotonation to give dearomatized complex
in THF and spontaneous H loss from 2 to form 4 in benzene.
3
4
2
6
7
1
2
character for these bonds in 4.
KNaCO ). In agreement with both possible mechanisms, H was
The short Rh ÀN bond length of 2.0264(14) Š and the alter-
3
2
1
1
detected by GC taking a sample from the headspace after re-
action. An unidentified intermediate species in the reaction of
nating CÀC bond lengths in the heterocycle (not shown) are
consistent with dearomatization of the pyridine fragment. The
Rh ÀN and Rh ÀP bond lengths vary only marginally between
2
to 3 or 4 in the reaction with NaHCO in THF is detectable
3
1
2
1
1
by NMR spectroscopy (see Supporting Information Figure S3,
S4), but this species was not isolated or further characterized.
the cationic amine and imine species and the dearomatized
neutral imine derivative. The N -Rh -P and N -Rh -P angles
2
1
1
2
1
1
1
3
13
When C-labeled NaH CO was used, no formate was detect-
also do not differ substantially, showing the structural integrity
of the overall tridentate scaffold upon multiple proton-transfer
3
13
ed using C NMR spectroscopy, thus excluding carbonate as
[
17]
a hydride acceptor.
Addition of a second equivalent of KOtBu to imine species 3
in THF instantaneously led to a drastic color change from
3
1
brown to dark-blue. The P NMR spectrum indicated complete
conversion to a single species, exhibiting a doublet at
8
9.2 ppm (J
=156.3 Hz), while the pyridine protons are
RhÀP
shifted markedly upfield (5.37–6.35 ppm) in the corresponding
1
H NMR spectrum, thus pointing to “dearomatization”. The CO
À1
stretch of 4 appears at 1950 cm in the IR spectrum (Dn=
À1
À46 cm compared to 1). These observations are consistent
with formulation of this complex as the dearomatized imine
complex 4, Rh(CO)(PNN’), featuring a formal amido nitrogen
trans to CO. The imine CÀH appears as a doublet of doublets
3
at 7.01 ppm, with long-range couplings to rhodium ( J
Rh-H
4
2
5
.8 Hz) and phosphorus ( J =4.6 Hz). The doublet at
P-H
2
.34 ppm ( J =2.9 Hz) is assigned to the methine proton (C=
P-H
CH-P).
Interestingly, complex 4 was also obtained by simply storing
a C D solution of the amido complex 2 at room temperature,
6
6
while dihydrogen (H ) was detected as a byproduct both with
2
1
H NMR spectroscopy (solution phase) and gas chromatogra-
phy (GC) (head-space above the solution) (Supporting Informa-
tion, Figures S1, S2, S27). This reaction involves formal loss of
a hydride from the amido methylene arm and a proton from
the phosphane methylene arm of the same ligand to generate
Figure 2. ORTEP plots (50% probability ellipsoids) of cationic amine complex
1
, imine complex 3 and dearomatized neutral derivative 4. Disorder, coun-
ter-ions, lattice solvent and hydrogen atoms are omitted for clarity, except
for those located on C and C
1
7
.
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Table 1. Selected bond lengths [Š] and angles [8] for complexes 1, 3 and
4.
1
3
4
Rh
Rh
Rh
Rh
1
ÀN
ÀN
1
2
2.057(2)
2.156(3)
2.2337(8)
1.829(3)
1.496(4)
1.496(4)
1.143(3)
84.64(7)
162.84(7)
111.42(18)
100.62(10)
179.11(13)
178.8(3)
2.0427(18)
2.0885(19)
2.2395(7)
1.829(3)
1.284(3)
1.498(4)
2.0264(14)
2.1191(14)
2.2641(5)
1.8198(19)
1.389(2)
1.367(2)
1.157(2)
82.89(4)
160.46(4)
113.65(12)
100.84(6)
178.90(7)
178.36(16)
1
1
ÀP
1
1
ÀC16
N
2
ÀC
1
C
C
6
ÀC
7
28ÀO
1
1.151(3)
83.96(6)
P
P
1
-Rh
-Rh
1
-N
-N
1
1
1
2
161.55(5)
115.13(15)
101.11(8)
179.26(10)
178.8(2)
Rh
Rh
1
-N
-P
2
-C
-C
1
1
1
7
N
1
-Rh
1
-C28
Rh -C28-O
1
1
reaction steps. The methylene groups are located above and
below the Rh-P-N-N plane in 1, whereas complexes 3 and 4
display a virtually flat extended structure, indicative of signifi-
cant p-conjugation. Selected bond lengths and angles for the
three complexes are compared in Table 1.
Figure 3. DFT calculated (BP86/def2-TZVP) frontier orbitals for imine-complex
4
(dearomatized) and 3 (aromatized) (top left: HOMO of 4; top right: LUMO
of 4; bottom: LUMO of 3).
To obtain further insight in the electronic structure of the
dearomatized imine-ligand complex 4, we switched to DFT cal-
culations (BP86/def2-TZVP) (Figure 3). The highest occupied
molecular orbital (HOMO) is found to reside predominantly on
the electron-rich methine carbon of the phosphine arm, in
accord with calculations on other dearomatized pincer com-
dride transfer from a metal-bound or outer-sphere formate to
the imine fragment (the LUMO) to generate an analogue of 2
was not observed. This indicates that the corresponding
H2À
amido-form of the ligand (PNN’ ) is thermodynamically un-
[
13]
stable with respect to the neutral imine-ligand form (PNN’).
Interestingly and in stark contrast with the other substrates
tested, complex 4 reacted almost instantaneously with one
molar equivalent of o-toluenesulfonamide (oTsNH ) in CD Cl ,
[
6,8,18,19]
plexes,
with a minor contribution from the dearomat-
ized pyridine. The corresponding lowest unoccupied molecular
orbital (LUMO) is also found to be predominantly ligand-based,
residing mainly on the electron-deficient imine fragment. The
combination of both a ligand-based HOMO, relevant for reac-
tivity toward electrophiles, and a ligand-based LUMO (suscepti-
ble for attack by nucleophiles) is highly unusual, and shows
that the complex is likely to display ligand-based reactivity in
reactions with both electrophilic and nucleophilic substrates.
The LUMO of 3 is also localized mainly at the imine fragment,
with a similar shape as that of 4, which means the imine func-
tionality of 4 is maintained for nucleophilic addition after the
first electrophilic addition (e.g. protonation of the methine).
The reactivity of such “Janus-like” ligands is ill-explored but po-
tentially interesting in the context of cascade catalysis.
2
2
2
as indicated by a color change from deep-blue to light-yellow
(Scheme 4). Spectroscopic data showed that the reaction in-
volved both reactive ligand arms of the complex, leading to
both protonation of the electron-rich methine arm attached to
the P-donor and nucleophilic attack of the deprotonated sulfo-
[
20]
namide to the electrophilic imine functionality. This reactivity
[
21]
is quite remarkable, as sulfonamides are poorly nucleophilic
and thus should not be able to attack the imine functionality
of 4 in a direct “outher-sphere” mechanism. The IR spectrum
À1
showed a CO stretch at 1983 cm , suggestive of rearomatiza-
31
tion of the pyridine ring. Notably, the P NMR spectrum
showed clean conversion to a single species, represented by
a doublet at 94.2 ppm with a coupling constant J
of
Rh-P
1
13
1
49.3 Hz. Likewise, H NMR and C NMR spectroscopy revealed
clean conversion of 4 to 5 (see Experimental Section and Sup-
porting Information). HR-MS spectrometry (m/z 724.2250 for
Reactivity of 4 towards a weakly nucleophilic amine base
+
Complex 4 was found to be inert toward H , benzyl alcohol or
[MÀH ]) indicates the incorporation of the sulfonamide sub-
2
aniline under mild conditions, which is attributed to the rigid
nature of the ligand backbone, in particular the imine frag-
ment. It seems that the extended conjugated p-system of the
strate as well as preservation of the original diisopropylanilidyl
fragment. These combined data support formulation of this
species as the neutral aminal complex 5 (Scheme 4).
À
PNN’ ligand in 4 does not have the required flexibility to ac-
An unexpected rearrangement of the donor atoms has oc-
curred to generate this addition product, with the sulfonamido
nitrogen donor coordinated to Rh, while the original imine-
donor is transformed into a non-coordinated aniline moiety.
commodate a favorable transition state for proton transfer
from a metal bound substrate to the electron-rich methine
arm. Reprotonation of the phosphine arm (the HOMO) with
stronger protic acids such as HCl, formic acid or benzoic acid is
feasible, generating derivatives of 3. However, in case of formic
acid as substrate for example, further reaction involving hy-
1
The aniline NH moiety resonates at 3.75 ppm in the H NMR
3
spectrum, and gives rise to a sharp doublet ( J =10.3 Hz).
HH
3
The relatively large J coupling constant corresponds to an
HH
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Scheme 4. Reversible reaction of o-toluenesulfonamide with complex 4 to
generate aminal complex 5 [Rh(CO)(PNN’’)].
antiperiplanar configuration of the NÀH and the tertiary PyCÀ
H protons, in agreement with the X-ray structure. Amines typi-
cally give rise to broad featureless signals as a result of rapid
exchange with other amines or for example, water. The fact
that the aniline NH moiety is present as a sharp doublet sug-
gests that it is in a rigid configuration and does not undergo
rapid proton exchange with exogenous proton donors (e.g.,
water). Initially we took this as an indication for H-bonding be-
tween the NH moiety and one of the sulfonyl oxygen atoms,
but spectroscopic investigations are inconclusive about the ex-
istence of such an H-bond. NMR spectroscopy did confirm that
the NH moiety adopts a preferred configuration in solution.
Figure 4. ORTEP plot (50% probability ellipsoids) of aminal complex 5. Lat-
tice solvent (CH
and H , belonging to the aminal fragment. Selected bond lengths [Š] and
angles [8]: Rh
.821(3), P
ÀC
1.520(3), Rh
ÀC16 1.155(4), C16ÀO
-Rh -C16 176.37(10), Rh
100.85(10).
2 2 1
Cl ) and hydrogen atoms removed for clarity, except for H
2
1
ÀN
1
2.057(2), Rh
ÀC
1
ÀN
1.499(4), N
1.155(4); N
-C16-O 177.7(2), Rh
3
2.083(2), Rh
ÀC 1.460(3), N
-Rh -P 162.93(6), P
1
-N -C 114.28(15), Rh -
1
ÀP
1
2.2251(8), Rh
1
ÀC16
1
1
7
1.857(3), C
6
7
3
1
2
ÀC
1
1.482(3), C
1
ÀC
2
1
1
3
1
1
1 1 1
-Rh -N
84.43(6), N
-C
1
1
1
1
1
3
1
P
1
7
ing pre-coordination of the sulfonamide process seems most
likely.
1
1
1
1
13
Detailed analysis of the H, H-COSY, H-NOESY, and H C-
HSQC spectra of the complex showed that the NÀH moiety
has stronger NOE contacts with only one of the two isopropyl
moieties. The structure of 5, [Rh(CO)(PNN’)], was further corro-
borated by X-ray structure determination of single crystals
grown from dichloromethane and diethyl ether. The X-ray
structure (Figure 4) indeed shows a highly congested aminal in
[
22]
In dynamic combinatorial chemistry,
imine formation is
often reversible in the presence of water. In analogy, aminal 5
is highly sensitive to the type of solvent used. Upon switching
from CD Cl to dioxane or [D ]THF (Scheme 4) and under mild
2
2
8
31
heating, complex 5 reverts to 4, as monitored by P NMR
spectroscopy. In addition, HR-MS spectra of complex 5 mea-
sured in positive ion mode showed only m/z 555.2033, corre-
sponding to complex 4 plus a proton (calcd m/z 555.2006)
(Supporting Information, Figures S5–S7). The conversion of 5
to 4 in THF and dioxane is most likely a result of the different
solubility of 5 (poorly soluble) and the mixture of 4 and
oTsNH (well soluble) in these solvents. Adventitious H O might
I
the coordination sphere of a square planar Rh center, but no
hydrogen-bond interaction is observed between the NÀH
moiety and the sulfonyl oxygen atoms. The NÀH and the terti-
ary PyCÀH hydrogen atoms are oriented in an antiperiplanar
configuration, with the NH moiety pointing toward one of the
isopropyl groups, in accordance with the NMR data. Apparent-
ly the conformation of the NH moiety observed in the solid
state is also the preferred orientation in solution, and in con-
trast to our initial assumptions this might not be caused by H-
bonding but seems rather a result of the steric congestion
around the NÀH moiety (as revealed by the X-ray structure),
thus leading to slow proton exchange at the amine nitrogen
atom on the NMR time scale. To the best of our knowledge,
this is the first report of a structurally characterized aminal in
the coordination sphere of rhodium. Furthermore, this reaction
constitutes the breaking of two NÀH bonds and the formation
of one CÀH, one CÀN and a novel NÀH bond.
2
2
also play a role. Note that organic aminals are typically unsta-
ble with respect to their precursors, and hence isolation of
complex 5 is highly unusual.
The reversible making and breaking of the aminal CÀN bond
under mild conditions suggests that this complex has potential
in productive CÀN bond functionalization protocols, using the
cooperative ligand system in concert with metal-based activity.
Hence, as proof-of-concept, the coupling of sulfonamides with
iodomethane (MeI) was investigated (Scheme 5). Selective
mono-alkylation of sulfonamides (and amines in general)
under mild conditions, minimizing the generation of undesira-
[
23]
The reaction likely proceeds via initial proton transfer from
the activated sulfonamide to the nucleophilic methine of the
phosphine arm, resulting in rearomatization of the pyridine
ring. This may occur in either an outer-sphere manner (bimo-
lecular process) or via pre-coordination of the sulfonamide to
Rh (unimolecular process). The resulting (rhodium) sulfonami-
do intermediate can then undergo addition to the electrophilic
imine carbon, with a subsequent 1,3-proton shift to generate
the observed aminal. The latter (intermolecular) process involv-
ble waste, is still a challenging task in organic synthesis.
Heating an equimolar mixture of MeI and 5 in CD Cl at 608C
2
2
for 30 min resulted in the formation of complex 3’, an ana-
logue of complex 3 but with iodine as the counter-ion, and
the N-methylsulfonamide product (N,2-dimethylbenzene sulfo-
namide, oTsNHMe) in 21 and 11 % yield, respectively (accord-
1
ing to H NMR spectroscopy). Continued heating for 22 h in-
creased the yield of these two species to 79% and 51%, re-
1
spectively, based on H NMR integration (Supporting Informa-
Chem. Eur. J. 2015, 21, 12683 – 12693
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12687
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Na CO , thus showing that the reaction is mediated by the Rh
2
3
complex. This sequence represents, to our best knowledge,
the first example of such unique new metal–ligand cooperativ-
ity for productive substrate functionalization, although some
recent cooperative substrate functionalisation strategies and
reversible directing group strategies bear some similarities
[
12b,c,24]
with this concept.
We anticipate that the reaction se-
quence shown in Scheme 5 can be extended to other “electro-
phile-nucleophile” combinations, and further (catalytic) cou-
pling reactions with additional substrates might be realized
based on this dual-mode ligand cooperativity.
Elucidation of side-reactions
The reaction shown in Scheme 5 is composed of individual sto-
ichiometric steps. A catalytic reaction involving multiple turn-
overs is prevented by competing side reactions. To shed more
light on the catalyst deactivation pathways, we decided to ex-
plore the formation of side products (in particular deactivated
rhodium complexes) under (pseudo-) catalytic conditions.
Quite remarkably, and contrary to previous observations on
the reactivity of carbon electrophiles with dearomatized pincer
Scheme 5. Hypothetical cycle composed of stoichiometric steps (one turn-
over) involving mono-methylation of o-TsNH with MeI mediated by 4.
2
[
18,25]
ligands,
the addition of MeI to 4 did not result in ligand-
based CÀC coupling at the methine moiety adjacent to the
À
tion, Scheme S2, S3, Figure S8–S12). The formation of complex
’ and oTsNHMe was confirmed by independent synthesis of
phosphine donor. The inertness of the PNN’ fragment is at-
3
tributed to the electron-withdrawing effect of the imine
moiety, which decreases the overall nucleophilicity of the
ligand framework (decrease of the HOMO relative to, for exam-
ple, a dearomatized PNP ligand). MeI also does not oxidatively
the two species and comparing the NMR spectra. The organic
oTsNHMe product is presumably generated by consecutive ox-
idative addition of MeI, forming intermediate 6, and reductive
I
I
CÀN bond formation at Rh (see Scheme 5). Addition of base
add to the Rh center of 4, which may be explained by a stabi-
(
KOtBu) regenerates the dearomatized complex 4, which
lizing push–pull effect (p-donation from the dearomatized pyri-
dine nitrogen lone pair to a Rh d orbital (push) is balanced by
p-back donation from Rh to the p* orbital at CO (pull)). Addi-
tion of N-methyl-phenylsulfonamide to 4 under the same con-
ditions as for the coupling reaction of 5 and MeI did not result
in any addition product. Therefore, neither MeI nor the mono-
alkylated sulfonamide product interfere with the envisioned
catalyst. Hence, neither product inhibition nor inhibition by un-
wanted reactions with the MeI substrate seems to cause any
problems in the envisioned catalytic reaction. However, the
aminal fragment in complex 5 appears susceptible to hydroly-
sis in wet solvent over the course of several days. Under these
conditions, release of free aniline was detected, and NMR spec-
troscopy further pointed to formation of complex 8, which re-
sults from attack of hydroxide to the imine moiety of the pro-
posed imine intermediate 7, which is formed after expulsion of
aniline (Scheme 6).
should be susceptible to renewed attack by sulfonamide and
thereby close the hypothetical catalytic cycle (Scheme 5). This
sequence is composed of the following steps: 1) ligand-aided
splitting of the NÀH bond of sulfonamide by 4, with the elec-
trophilic and the nucleophilic part residing on the P and N arm
of the ligand, respectively. 2) Oxidative addition of MeI to gen-
III
erate a Rh complex (either five- or six-coordinated). 3) Reduc-
tive CÀN bond formation to generate imine-complex 3’ and
the N-methylated sulfonamide product. 4) Deprotonation of
complex 3’ to regenerate the starting complex 4.
As such, the combined reactions closes a catalytic cycle for
mono-alkylation of sulfonamides with MeI, which proceeds via
the discrete and well characterized intermediates 3’, 4 and 5.
III
Attempts to detect the proposed Rh intermediate 6 by in situ
31
P NMR spectroscopy were not successful, and only complexes
5
and 3’ were observed. This is probably due to the transient
nature of 6 on the NMR time-scale due to rapid reductive elim-
ination of oTsNHMe to yield complex 3’. Direct coupling of
MeI with the sulfonamide nitrogen with the sulfonamide with-
The -CH(OH) proton appears as a sharp doublet at 4.30 ppm
3
( J =2.5 Hz), while the -CH(OH) proton shows up at
H-H
3
4
6.12 ppm as a doublet-of doublet ( J =2.4 Hz, J =2.0 Hz),
H-H
P-H
III
out forming a Rh intermediate cannot be completely exclud-
when measured in CD Cl . Upon addition of [D ]MeOH, the
2 2 4
ed, but seems unlikely. Any direct coupling would be expected
to occur on the aniline nitrogen of the aminal, which should
be more nucleophilic than the sulfonamide nitrogen (which is
involved in delocalization to the sulfonyl moiety). No reaction
was observed between oTsNH2 and MeI in the absence of
complex 5 under the same conditions, or in the presence of
-OH signal disappeared. Besides 8, also another side-product, 9
was detected that potentially hinders catalytic turnover. Like 8,
this species also seems to be derived from intermediate 7
(again formed by aniline elimination from the aminal moiety of
5). Complex 9 is formed more rapidly in the presence of an
excess sulfonamide, and bears two sulfonamide fragments
Chem. Eur. J. 2015, 21, 12683 – 12693
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12688
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
versible by switching to a more polar solvent. MeI is success-
fully used as an electrophile to couple with the activated sulfo-
namide, selectively generating the N-methylsulfonamide. This
proof-of-concept coupling reaction demonstrates the viability
of a new type of metal-ligand cooperativity mechanism involv-
ing two electronically distinctly different ligand arms to acti-
vate both NÀH bonds of the sulfonamide substrate. Although
the overall reaction is inhibited when using an excess of the
substrate due to the occurrence of side-reactions, dual-mode
ligand reactivity in general may be a viable approach for catal-
ysis.
Experimental Section
General methods: All reactions were carried out under an argon
atmosphere using standard Schlenk techniques or in a glovebox
unless noted otherwise. With exception of the compounds given
below, all reagents were purchased from commercial suppliers and
used without further purification. 2-(Chloromethyl)-6-((di-tert-butyl-
Scheme 6. Transformation of complex 5 into 8 and 9, upon reaction with
water and excess sulfonamide, respectively.
phosphino)-methyl)pyridine·BH was synthesized according to a re-
3
[15]
(
Scheme 6). Hence, complex 9 was also identified as the major
ported procedure.
Sodium (o-tolylsulfonyl)amide was synthe-
“
resting state” (Æ80%) in a (pseudo) catalytic test-reaction
sized by reacting 2-methylbenzenesulfonamide with stoichoime-
chic sodium methoxide in methanol solution. THF, dioxane, pen-
tane, and diethyl ether were distilled from sodium benzophenone
ketyl under nitrogen. CH Cl , and methanol were distilled from
CaH2 under nitrogen. NMR spectra ( H, P{ H} and C{ H}) were
measured on a Bruker AMX 400 spectrometer at 258C unless
noted otherwise. IR spectra were recorded with a Nicolet Nexus FT-
IR spectrometer. HR-MS were obtained using a time-of-flight JEOL
using five molar equivalents of the sulfonamide substrate. In-
+
terestingly, m/z values corresponding to complex 7[M ] as the
2
2
major peaks were always observed in the ESI-MS spectra of 8
or 9 in positive ion mode (Supporting Information, Figur-
es S71–S72), while 8 or 9 were not detected. This may suggest
reversible sulfonamide addition to the imine arm of the ligand
of 7. The reactive sulfonimine carbon of the proposed inter-
mediate 7 is likely more susceptible to nucleophilic attack than
the aniline-based imine carbon of 3, which is stable in aqueous
conditions. The most likely pathways for conversion of com-
plex 5 into 8 and 9 are shown in Scheme 6, but alternative
mechanisms cannot be excluded.
1
31
1
13
1
AccuTOF LC-plus mass spectrometer (JMS-T100 LP).
H3
Ligand PNN ·BH : An acetonitrile solution (50 mL) of 2-(chloro-
3
methyl)-6-((di-tert-butylphosphino)methyl)pyridine·BH3 (500.0 mg,
1.669 mmol,
1
0
1 equiv),
.752 mmol, 1.05 equiv), potassium iodide (27.7 mg, 0.167 mmol,
.1 equiv) and potassium carbonate (1153 mg, 8.345 mmol,
2,
6-diisopropylaniline
(0.330 mL,
À
5.0 equiv) was refluxed for 20 h. All volatiles were removed under
vacuum, dichoromethane (30 mL) was added and the solution was
washed with brine and dried with sodium sulfate. The pure prod-
uct was obtained after silica column chromatography (hexane/
Finally, the requirement of a strong base like tBuO to de-
protonate 3 and thus regenerate 4 imposes limitations on the
development of catalytic reactions, as these nucleophilic bases
react with the MeI substrate.
1
ethyl acetate) as a white solid (345.4 mg, 47%). H NMR (400 MHz,
CD Cl ): d=7.60 (t, J=7.7 Hz, 1H ), 7.51 (d, J=7.7 Hz, 1H ), 7.16–
2
2
py4
Py
7
.06 (m, 1HPy + 3H ), 4.11–4.10 (br m, 2H
+1H ), 3.43–3.36
Ar
Py-CH2N
NH
Conclusion
(
m, 2HPh-C(CH3)2H +2HPy-CH2P), 1.30 (d, J=12.6 Hz,18H
,), 1.25 (d,
C(CH3)3
31
1
J=6.9 Hz, 12HCH(CH3)2), 0.85–0.02 ppm (brm, 3HBH3); P{ H} NMR
(161 MHz, CD
CD Cl ): d=155.59 (d, J=2.4 Hz, Cpy6), 155.47 (d, J=0.5 Hz, Cpy2),
We have reported the synthesis of a unique (phosphane)(ami-
1
3
H3
Cl , ppm): d=47.13 ppm (m); C NMR (100 MHz,
2 2
ne)pyridine ligand PNN and its versatile coordination chemis-
I
2
2
try with Rh . This includes selective, stepwise transformations
1
2
40.3 (s, CAr1), 137.08 (s, Cpy4), 132.59 (s, 2CAr2,6), 125.44 (d, J=
.2 Hz, Cpy5), 122.90 (s, 2CAr3,5), 120.99 (d, J=2.0 Hz, Cpy3), 118.67 (s,
H3
from the neutral PNN amine ligand in complex 1, to the
H2À
H’
anionic PNN
amido ligand in complex 2, the neutral PNN
CAr4), 46.87 (s, PyCH N), 32.98 (d, J=25.2 Hz, PyCH P), 29.33 (d, J=
2
2
imine ligand in complex 3 and the anionic “dearomatized”
imine ligand PNN in complex 4. The ligand is capable of se-
lective dual-mode reactivity and is susceptible to both electro-
23.1 Hz, 2PC(CH ) ), 28.28 (d, J=23.1 Hz, 4PC(CH ) ), 28.26 (s,
3 3 3 3
H’À
2ArCH(CH
)
), 22.59 ppm (s, 4ArCH(CH
)
); HRMS (FD, DCM): m/z:
3
2
3
+
2
calcd for 440.3492; found: 440.3496 [M ].
H3
H3
philic and nucleophilic attack. The X-ray structures of 1, 3, and
Ligand PNN : PNN ·BH
3
(400 mg, 0.908 mmol) was dissolved in
freeze-pump-thaw degassed diethylamine (8 mL). All the volatiles
were removed under vacuum after reflux for 20 h. Diethyl ether
4
show subtle but significant differences between these spe-
cies. DFT calculations show that both the HOMO and LUMO of
are ligand-based, which is rather unique. This complex readi-
(
10 mL) was added and degassed water (10 mL) was used to wash
4
the ether solution quickly for 5 times. The ether solution was dried
over sodium sulfate and the solids were filtered off. All volatiles
were removed under vacuum and the ligand was obtained as
ly activates both NÀH bonds of o-toluenesulfonamide in di-
chloromethane, resulting in selective CÀN bond formation to
generate the unique aminal complex 5, which was also struc-
turally characterized. The addition reaction is found to be re-
1
a white solid (352.5 mg, 92%). H NMR (400 MHz, CD Cl ): d=7.55
2
2
(t, J=7.7 Hz, 1Hpy4), 7.30 (d, J=7.8 Hz, 1Hpy3), 7.11–7.09 (m, 1Hpy5
+
Chem. Eur. J. 2015, 21, 12683 – 12693
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12689 ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
1
HAr4), 7.04–7.01 (m, 2HAr3,5), 4.41 (br, 1HNH), 4.09 (s, 2HPy-CH2N), 3.43
a possibility that complex 2 and 4 have (nearly) identical overlap-
(
sept., J=6.9 Hz, 2HPh-C(CH3)2H), 3.08 (d, J=3.1 Hz, 2HPy-CH2P), 1.23 (d,
ping CO stretch frequencies. The two complexes have n of
1954.7 (2) and 1953.4 cm (4) according to DFT calculations at
BP86/def2-TZVP level.
CO
31
1
À1
J=7.7 Hz, 12HCH(CH3)2), 1.17 ppm (d, J=10.9 Hz,18H
NMR (161 MHz, CD Cl , ppm): d=35.61 ppm;
,); P{ H}
C{ H} NMR
C(CH3)3
1
3
1
2
2
(
1
1
(
2
100 MHz, CD Cl ): d=162.26 (d, J=14.4 Hz, CPy2), 157.72 (s, CPy6),
44.39 (s, CAr1), 143.05 (s, 2CAr2,6), 136.72 (s, CPy4), 123.88 (s, CAr4),
23.81 (s, 2CAr3,5), 122.56 (d, J=8.5 Hz, CPy3), 118.82 (s, Cpy5), 56.71
Py-CH N), 32.13 (d, J=23.0 Hz, Py-CH P), 30.1–29.93 (s, 2PC(CH ) ),
2 2 3 3
H
2
2
[
0
0
Rh(CO)(PNN )]PF (3): To a 3 mL THF solution of 1 (40.0 mg,
6
.0570 mmol, 1 equiv) and sodium bicarbonate (NaHCO , 23.9 mg,
.285 mmol, 5 equiv) was added a THF solution of potassium tert-
3
butoxide (tBuOK 1m in THF, 0.0570 mL, 1 equiv). The solution was
stirred overnight, and 3 was obtained as a mixture with 4. The sol-
vent was removed under vacuum. The solids were first washed
with pentane (5”2 mL) and dichloromethane (2 mL) was added.
The solids were filtered off. The DCM solvent was removed under
9.87 (d, J=23.0 Hz, 4PC(CH ) ), 28.02 (s, 2ArCH(CH ) ), 24.42 ppm
3 3 3 2
(
4
s, 4ArCH(CH ) ); HRMS (FD, DCM): m/z: calcd for 426.3164; found:
3
2
+
26.3167 [M ].
H3
H3
[
Rh(CO)(PNN )]PF (1): A 4 mL methanol solution of PNN ligand
6
vacuum. Complex
3 was obtained as a brownish-red solid
(
313.0 mg, 0.734 mmol, 2.05 equiv) was added to a 6 mL methanol
(
14.4 mg, 36%). Crystals suitable for X-ray diffraction were obtained
solution of [Rh(CO) (m-Cl)]2 (139.1 mg, 0.358 mmol, 1 equiv), fol-
2
1
by top-layering a DCM solution of 3 with diethyl ether. H NMR
lowed by addition of NH PF (466.7 mg, 2.863 mmol, 8 equiv). The
4
6
(
7
7
400 MHz, CD Cl ): d=8.39 (dd, J=5.3, 2.8 Hz, 1H
=
N), 8.21 (t, J=
solution was stirred for one hour and the concentrated to 5 mL by
evacuation. The brownish-yellow precipitate was collected by filtra-
tion and washed with a small amount of cold methanol and dried
2
2
PyCH
.8 Hz, 1HPy4), 8.02 (d, J=8.1 Hz, 1HPy3), 7.97 (d, J=7.8 Hz, 1HPy5),
.36 (dd, J=8.9, 6.4 Hz, 1Haniline4), 7.32–7.21 (m, 2Haniline3,5), 3.91 (d,
1
J=9.1 Hz, 2HPyCH2P), 3.36 (sept., J=6.7 Hz, 2HCH(CH3)2), 1.39 (d, J=
in vacuo (413.8 mg, 82.3%). H NMR (400 MHz, CD Cl , 225.1 K): d=
2
2
1
6
9
1
5.1 Hz, 18HC(CH3)3), 1.36 (d, J=6.8 Hz, 6HCH(CH3)2), 1.23 ppm (d, J=
7
7
4
4
.96 (td, J=9.0, 0.9 Hz, 1Hpy4), 7.63 (d, J=7.9 Hz, 1Hpy3), 7.38 (d, J=
31
1
.9 Hz, 6H
6.30 ppm (d, J
); P{ H} NMR (161 MHz, CD Cl , ppm): d=
2 2
.9 Hz, 1Hpy5), 7.33–7.20 (brm, 3Haniline3,4,5), 6.7 (brm, 1H ), 4.93–
CH(CH3)2
NH
1
13
1
=149.3 Hz); C{ H} NMR (100 MHz, CD Cl): d=
2
.83 (brd, J=16.6 Hz, 1HPy-CHHN), 4.62 (dd, 17.3, 9.9 Hz, 1HPy-CHHN),
.56–4.45 (brm, 1HPh-C(CH3)2H), 3.78 (d, J=9.4 Hz, 2HPy-CH2P), 3.30–3.19
RhÀP
90.97 (dd, J=73.9, 16.6 Hz, CO), 168.87 (d, 2.4 Hz, CPyCH N), 165.29
=
31
1
(
t, J=4.3 Hz, CPy2), 153.75 (d, J=2.2 Hz, CPy6), 147.01 (s, Caniline1),
(
br m, 1HPh-C(CH3)2H), 1.59–1.23 ppm (m, 18HC(CH3)3, 12HCH(CH3)2); P{ H}
1
13
1
1
1
2
4
41.89 (s, CPy4), 138.92 (s, 2Caniline2,6), 128.60 (s, Caniline4), 128.06 (d, J=
NMR (161 MHz, CD Cl ): d=96.4 ppm (d, J =155.8 Hz); C{ H}
NMR (100 MHz, CD Cl , 225.1 K, ppm): d=191.01 (dd, J=73.4,
2
2
RhÀP
0.6 Hz, Cpy3), 126.94 (s, Cpy5), 124.32 (s, 2Caniline3,5), 37.38 (d, J=
2
2
2.1 Hz, CPyCH-P), 36.56 (dd, J=20.6, 1.8 Hz, P(CH ) ), 29.36 (d, J=
1
7.2 Hz, CO), 161.67 (t, J=4.0 Hz, CPy2), 160.24 (s, CPy6), 140.85 (s,
Caniline1), 140.54 (s, CPy4), 138.12 (s, Caniline2 or 6), 127.16 (s, 2Caniline3,5),
26.29 (s, Caniline6 or 2), 123.28 (s, Caniline4), 122.20 (d, J=10.8 Hz, CPy3),
3 3
.5 Hz, P(CH ) ), 28.95 (s, CH(CH ) ), 24.12 (s, CH(CH ) ), 22.97 ppm
3 2
3 2
3 2
À1
(
s, CH(CH ) ); IR ( n˜ , CD Cl )=2003 cm ; HRMS (ESI, 243 K, CD Cl ):
3 2 CO 2 2 2 2
1
+
m/z: calcd for 555.2012; found 555.2035 [M ]; elemental analysis
119.52 (s, CPy5), 62.59 (s, PyCH N), 35.90 (d, J=21.8 Hz, PyCH P),
2
2
(
%) calcd for C H F N OP Rh: C 48.01, H 5.90, N 4.00; found: C
28 41 6 2 2
3
5.34 (dd, J=22.9, 2.3 Hz, PC(CH ) ), 28.98–28.22 (m, ArCH(CH ) ,
3
3
3 2
4
8.69, H 5.81, N 4.31.
PC(CH ) ), 25.22 (s, ArCH(CH ) ), 24.7822 (s, ArCH(CH ) ), 24.2522 (s,
3
3
3 2
3 2
ArCH(CH ) ), 22.2522 ppm (s, ArCH(CH3)2); IR ( n˜ CO
, CD Cl )=
2 2
3
À1
2
[Rh(CO)(PNN)] (4): Complex 4 was obtained by adding THF solu-
tion of potassium tert-butoxide to the reaction mixture used to
synthesize complex 3, until 3 was fully converted to 4 as moni-
tored by P NMR. The mixture after solvent evaporation was ex-
tracted with 2 mL pentane for three times. The solvent of the com-
bined pentane solution was removed under vacuum and a dark
blue solid was obtained (29.8 mg, 94%). Dark-blue colored crystals
suitable for X-ray diffraction were obtained by storing a concentrat-
1
996 cm ; HRMS (ESI, 243 K, DCM): m/z: calcd for 557.2168;
+
found: 557.2161 [M ]; elemental analysis calcd for (%)
C H F N OP Rh.2H O: C 45.54, H 6.41, N 3.79; found: C 45.85, H
31
28
43
6
2
2
2
6
.22, N 3.79.
H2
[
1
Rh(CO)(PNN )] (2): Method I: To a 1.5 mL THF solution of
(10.0 mg, 0.0179 mmol, 1 equiv) was added a THF solution of po-
tassium tert-butoxide (1m in THF, 0.0179 mL, 1 equiv). The solution
was stirred for 5 min and the solids were filtered off. The solvent
was removed under vacuum. Complex 2 was obtained as a mixture
with two other species; Method II: To a 0.3 mL C D suspension of
1
ed pentane solution of 4 at À788C. H NMR (400 MHz, C D ): d=
6
6
7
9
6
1
1
8
.07 (m, 3H
), 6.89 (dd, J=4.6, 2.8 Hz, 1H
PyCH N
=
), 6.22 (d, J=
Ar3,4,5
.2 Hz, 1HPy3), 6.01 (ddd, J=8.9, 6.4, 1.9 Hz, 1HPy4), 5.26 (d, J=
.3 Hz, 1HPy5), 3.66 (sept., J=6.8 Hz, 2HC(CH3)2H), 3.44 (s, 1HPyCH-P),
.47 (d, J=6.8 Hz, 6HCH(CH3)2), 1.42 (d, J=13.8 Hz, 18HC(CH3)3),
6
6
1
(5.0 mg, 0.0071 mmol, 1 equiv) was slowly added a 0.2 mL C D6
6
solution of potassium bis(trimethylsilyl)amide (KHMDS, 1.4 mg,
.0073 mmol, 1.02 equiv). The mixture was stirred for 5 min and
31
1
.07 ppm (d, J=6.9 Hz, 6HCH(CH3)2); P{ H} NMR (161 MHz, C D ): d=
6
6
0
1
13
1
9.21 ppm (d, J =156.4 Hz); C{ H} NMR (100 MHz, C D ): d=
Rh-P
6
6
the insoluble solids were filtered off and the filtrate was directly
transferred to a NMR tube which was sealed afterwards. H NMR
1
195.35 (dd, J=70.7, 15.4, CO), 168.58 (d, J=1.4 Hz, HC=N), 167.85
dd, J=16.6, 3.8 Hz, Cpy2), 154.69 (s, Cpy6), 148.57 (s, CAr1), 139.38 (s,
(
(
400 MHz, C D ): d=7.39–7.36 (m, 1Haniline3,5), 7.28 (dd, J=8.3,
6 6
2
1
Caniline2,6), 131.14 (s, Cpy4), 127.10 (s, Caniline4), 123.64 (s, 2Caniline3,5),
22.75 (d, J=18.9 Hz, Cpy3), 108.99 (s, Cpy5), 68.98 (d, J=53.2 Hz,
6
6
.9 Hz, 1Haniline4), 6.69 (t, J=7.7 Hz, 1Hpy4), 6.44 (d, J=7.9 Hz, 1Hpy3),
.35 (d, J=7.7 Hz, 1Hpy5), 5.29 (s, 2HPy-CH2N), 4.61 (sept, 6.8 Hz, 2HPh-
Py=CH-P), 36.25 (dd, J=26.2, 1.5 Hz, C(CH ) ), 29.73 (d, J=5.0 Hz,
3
3
C(CH3)2H), 2.91 (d, 2HPy-CH2P), 1.71 (d, J=6.8 Hz, 6HCH(CH3)2), 1.50 (d, J=
3
1
1
C(CH ) ), 28.41 (s, CH(CH ) ), 24.21 (s, CH(CH ) ), 23.22 ppm (s,
3 3 3 2 3 2
7
(
.0 Hz, 6HCH(CH3)2), 1.10 ppm (d, J=13.4 Hz, 18HC(CH3)3); P{ H} NMR
À1
1
CH(CH ) ); IR ( n˜ )=1950(CD Cl ), 1954 cm (C D ); HRMS (CSI,
3 2 CO 2 2 6 6
161 MHz, C D , ppm): d=88.1 (d, JRh-P =129.7 Hz); HRMS (ESI,
6 6
+
+
243 K, C D ): m/z: calcd for 555.2006; found: 555.2033 [M+H ]; el-
6 6
2
43 K, C D ): m/z: calcd for 557.2163; found: 557.2176 [M+H ].
6 6
1
3
1
emental analysis (%) calcd for C H N OPRh.H O: C 58.74, H 7.39, N
28 40 2 2
*
Due to its inherent instability, no reliable C{ H} NMR data were
obtained for complex 2. Attempts to record IR spectra of complex
in C D in a solution KBr cell led to detection of a CO stretch fre-
4
.89; found: C 59.01, H 8.13, N 4.61.
2
[Rh(CO)(PNN’] (5): CD Cl (0.5 mL) was added to a vial containing
6
6
2
2
À1
quency of 1954 cm in several IR measurements, thus indicating
fast formation of 4 from 2 in the KBr IR cell. The observation is in
agreement with the observed H2 loss from complex 2 to form
complex 4 (5.0 mg, 9.0 mmol, 1 equiv) and o-toluenesulfonamide
(1.5 mg, 9.0 mmol, 1 equiv), and the solution was stirred for 5 min.
The solution was used directly for spectroscopic measurements.
Yellow crystals suitable for X-ray diffraction were obtained by stor-
1
complex 4 revealed by H NMR. In the KBr IR cell the transforma-
1
tion seems to be accelerated somehow. However, there is also
ing a CD Cl /diethyl ether solution of 5 at À208C. H NMR
2
2
Chem. Eur. J. 2015, 21, 12683 – 12693
www.chemeurj.org
12690
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
(
400 MHz, CD Cl ): d=8.16 (dd, J=7.8, 1.6 Hz, 1HTs6), 7.40 (td, J=
ative, 243 K, CD Cl ): m/z: calcd for 718.1051; found: 718.1452
2
2
2
2
+
7
1
7
1
2
.8 1.0 Hz, 1HPy4), 7.28 (d, J=7.4 1.5 Hz, 1HPy3), 7.23 (td, J=7.8,
.6 Hz, 1HTs4), 7.16 (t, J=7.5 Hz, 1HTs5), 7.10 (d, J=7.4 Hz, 1HTs3),
.01–6.95 (m, 3Haniline3,4,5), 6.29 (d, J=7.7 Hz, 1HPy5), 5.83 (dd, J=
[MÀH ]; HRMS (ESI, positive ion mode, 243 K, CD Cl ): m/z: calcd
2
2
+
for 549.0848; found: 549.0747 [M ] (complex 7).
H
[Rh(CO)(PNN )]I (3’): 55% Hydriodic acid (HI, 2.0 mL, 0.0146 mmol,
0.5, 3.1 Hz, 1HPyCHN), 3.75 (d, J=10.4 Hz, 1H ), 3.55 (d, J=8.9 Hz,
NH
2 equiv) was added to a CD Cl2 solution (0.5 mL) of complex 4
2
HPyCH2P), 3.03 (sept. J=7.0 Hz, 2HCH(CH3)2), 2.66 (s, 3H ), 1.40 (d,
TsÀCH3
1
(4.0 mg, 0.0072 mmol, 1 equiv) in a NMR tube. H NMR (400 MHz,
J=14.3 Hz, 9HP(CH3)2), 1.34 (d, J=14.2 Hz, 9HP(CH3)2), 1.13 (d, J=
6
(
(
CPy6), 161.91 (dd, J=5.8, 3.3 Hz„ CPy2), 143.85 (s, Cquant-Ar), 143.11 (s,
Cquant-Ar), 138.57 (s, Cquant-Ar), 137.94 (s, CPy4), 136.65 (s, Cquant-Ar),
1
(
CPy3), 82.72 (s, PyCHN), 36.01 (dd, J=20.2, 4.5 Hz, PyCH P), 35.21
(
2
2
negative ion mode, 243 K, CD Cl ): m/z: calcd for 724.2209; found:
7
m/z: calcd for 555.2006; found: 555.2033 [M+H ].
CD Cl ): d=8.60 (dd, J=5.4, 2.7 Hz, 1HPyCH=N), 8.32–8.30 (m, 1HPy4
+
2
2
3
1
1
.8 Hz, 9H CH(CH3)2), 0.87 ppm (d, J=6.7 Hz, 9H CH(CH3)2).); P{ H} NMR
1HPy3), 8.20–8.19 (m, 1HPy5), 7.37–7.28 (m, 3HAr3,4,5), 4.13 (dd, J=8.9,
2.1 Hz, 2HPyCH2P), 3.37 (sept., J=6.8 Hz, 2HCH(CH3)2), 1.41 (d, J=
15.0 Hz, 18HC(CH3)3), 1.36 (d, J=6.8 Hz, 6HCH(CH3)2), 1.23 ppm (d, J=
1
13
1
161 MHz, CD Cl ): d=94.24 ppm (d, J =149.3 Hz); C{ H} NMR
2 2 Rh-P
100 MHz, CD Cl ): d=193.63 (dd, J=73.6, 17.8 Hz, CO), 165.08 (s,
2
2
31
1
6.9 Hz, 6H
CH(CH3)2); P{ H} NMR (161 MHz, CD Cl , ppm): d=96.72 (d,
2 2
1
13
1
JRh-P =149.2 Hz); C{ H} NMR (100 MHz, CD Cl ): d=168.87 (d,
2
2
31.63 (s, CTs3), 130.29 (s, CTs4), 128.81 (s, CTs6), 125.11 (s, CTs5), 124.24
s, Caniline4), 123.36 (s, Caniline3,5), 121.05 (d, J=10.7 Hz, CPy5), 118.69 (s,
2.4 Hz, CPyCH=N
147.01 (s, Caniline1
Caniline4), 128.06 (d, J=10.6 Hz, Cpy3), 126.94 (s, Cpy5), 124.32 (s,
2Caniline3,5), 37.38 (d, J=22.1 Hz, C ), 36.56 (dd, J=20.6, 1.8 Hz,
), 165.29 (t, J=4.3 Hz, CPy2), 153.75 (d, J=2.2 Hz, CPy6),
), 141.89 (s, CPy4), 138.92 (s, 2Caniline2,6), 128.60 (s,
2
dd, J=22.0, 1.7 Hz, PC(CH ) ), 28.74 (dd, J=10.3, 4.8 Hz, PC(CH ) ),
3 3 3 3
PyCHÀP
7.51 (s, ArCH(CH ) ), 24.19 (s, ArCH(CH ) ), 23.35 (brs, ArCH(CH ) ),
3 2 3 2 3 2
P(CH ) ), 29.36 (d, J=4.5 Hz, P(CH ) ), 28.95 (s, CH(CH ) ), 24.12 (s,
3 3 3 2 3 2
À1
1.44 ppm (s, CH3 Ts-Me); IR ( n˜ CO, CD Cl )=1983 cm ; HRMS (ESI,
À1
2
2
CH(CH ) ), 22.97 ppm (s, CH(CH ) ); IR( n˜ , CD Cl )=2003 cm
;
3 2 3 2 CO 2 2
2
2
HRMS (ESI, 243 K, DCM): m/z: calcd for 555.2012; found: 555.2094.
+
24.2250 [MÀH ]; HRMS (ESI, positive ion mode, 243 K, CD Cl ):
13
2
2
*The CO carbon resonance signal was not observable in C NMR
+
spectra, but this complex is only used to confirm the expected
product formation in the coupling reaction (Scheme S1). The other
H1
[
0
Rh(CO)(OH PNN )] (8): A wet THF solution of complex 5 (6.5 mg,
13
peaks in C NMR are identical to those of complex 3, which are
.0179 mmol, 1 equiv) in an NMR tube was left standing for two
compared and mentioned in Figure S62.
weeks, whereafter a light yellow precipitate had formed. The solu-
tion was decanted and the yellow solid was washed four times
with small amounts of THF and then dried under vacuum. H NMR
N,2-Dimethylbenzene sulfonamide (oTsNHMe): To a MeOH solu-
tion (4 mL) of sodium (o-tolylsulfonyl)amide (53.3 mg, 0.276 mmol,
1 equiv) was added iodomethane (MeI, 20.6 mL, 0.331 mmol,
1.2 equiv), the solution was stirred for 16 h. The volatiles were re-
moved by rota-evaporation. CD Cl was directly added to dissolve
1
(
400 MHz, CD Cl ): d=8.21 (dd, J=7.9, 1.3 Hz, 1HTs6), 7.76 (t, J=
2 2
7
7
1
2
(
(
.8 Hz, 1HPy4), 7.40 (d, J=7.8 Hz, 1HPy3), 7.34–7.31 (m, 1HPy5 +1HTs4),
.25–7.18 (m, 1HTs5 +1HTs3), 6.12 (m, 1HPyCHN), 4.29 (d, J=2.5 Hz,
HOH), 3.56 (dd, J=9.2, 5.2 Hz, 2HPyCH2P), 3.03 (sept. J=7.0 Hz,
2
2
out the product. After filtration, the filtrate was taken for NMR and
HRMS measurements. oTsNH and oTsNMe were found as impuri-
HCH(CH3)2), 2.87 (s, 3H
), 1.36 (d, J=14.3 Hz, 9HP(CH3)2), 1.36 ppm
TsÀCH3
2
2
3
1
1
1
d, J=14.2 Hz, 9H
); P{ H} NMR (161 MHz, CD Cl ): d=94.36
ties in 15% and 27%. H NMR (400 MHz, CD Cl ): d=7.92 (dd, J=
2 2
P(CH3)2
13
2
2
1
1
d, J =151.1 Hz); C{ H} NMR (100 MHz, CD Cl ): d=193.69 (d,
8.3, 1.5 Hz, 1HAr6), 7.49 (td, J=7.5, 1.5 Hz, 1HAr4), 7.36–7.32 (m,
Rh-P
2
2
13
1
J=73.7, 18.5 Hz, CO), 166.30 (d, J=1.0 Hz, CPy6), 161.25 (dd, J=5.9,
.0 Hz, CPy2), 142.36 (s, CAr1), 139.54 (s, CPy4), 137.69 (s, CAr2), 132.48(s,
CAr5), 131.00 (s, CAr4), 128.97 (s, CAr6), 125.45 (s, CAr3), 121.92 (d, J=
2HAr3,5), 2.62 (s, 3HArCH3), 2.59 ppm (s, 3HNCH3); C{ H} NMR (100 MHz,
3
CD Cl , ppm): d=137.44 (s, CAr1), 137.19 (s, CAr2), 133.14 (s, CAr4),
2
2
132.96 (s, CAr3), 130.04 (s, CAr6), 126.51 (s, CAr5), 29.31 (s, CNCH3),
1
2
4
0.4 Hz, CPy3), 121.64(s, CPy5), 90.15 (s, PyCH(OH)NTs), 36.56 (d, J=
0.0 Hz, PyCH P), 36.03 (td, J=18.9, 1.7 Hz, PC(CH ) ), 29.25 (d, J=
20.42 ppm (s, CArCH3); HRMS (FD, DCM): m/z: calcd for 184.0510;
found: 185.0522 [M ].
+
2
3 3
.8 Hz, 2PC(CH ) ), 21.97 (s, CTs-CH3); IR ( n˜ CO, CD Cl + (trace)
3
3
2
2
X-ray crystallography: X-ray intensities were measured on either
a Bruker Venture D8 (complex 4) or on a Bruker D8 Quest Eco dif-
fractometer equipped with a Triumph monochromator (l=
À1
[
D ]MeOH)=1984 cm ; HRMS (ESI, negative ion mode, 243 K,
4
CD Cl + (trace) [D ]MeOH): m/z: calcd for 565.0803; found:
5
z: calcd for 549.0848; found: 549.0909 [M ] (complex 7).
2
2
4
+
65.0811 [MÀH ]; HRMS (ESI, positive ion mode, 243 K, CD Cl ): m/
2
2
0.71073 Š). Diffraction data were collected at 150(2) K using
a CMOS Photon 50 detector (complexes 1, 3 and 5) or at 100(2) K
using a CMOS Photon 100 detector (complex 4). Intensity data
were integrated with Bruker APEX2 (complex 4) or the Bruker APEX
+
H1
[
Rh(CO)(oTs oTs PNN )] (9): 0.5 mL CD Cl was added to a vial
2 2
containing complex 4 (5.0 mg, 9.0 mmol, 1 equiv) and o-toluenesul-
fonamide (3.9 mg, 22.5 mmol, 2.5 equiv), and the solution was
transferred to a sealed NMR tube. The solution was heated at 508C
[26]
software (complexes 1, 3 and 5). Absorption correction and scal-
[
27]
ing was performed with SADABS.
using direct methods with SHELXS-97 (complex 4) or SHELXL-13
complexes 1, 3 and 5). Least-squares refinement was performed
The structures were solved
[
28]
1
for six hours. H NMR (400 MHz, CD Cl , ppm): d=8.04 (dd, J=8.2,
2
2
(
1
7
2
6
.4 Hz, 1HTs(1)6), 7.85 (d, J=7.9 Hz, 1HTs(2)6), 7.68 (t, J=7.8 Hz, 1HPy4)„
.51–7.47 (1HTs(1)4), 7.49–7.45 (1HPy3), 7.36–7.34 (1HPy5), 7.32–7.28 (m,
HTs(1)3,5), 7.24 (td, J=7.3, 1.5 Hz, 1HTs(2)4), 7.11–7.06 (m, 2HTs(2)3,5),
[28]
with SHELXL-2014 (complex 4) or SHELXL-2013 (complexes 1, 3
and 5) against F of all reflections. Non-hydrogen atoms were re-
2
fined with anisotropic displacement parameters. Heteroatom
bound hydrogen atoms were refined freely with an isotropic dis-
placement parameter, all other hydrogen atoms were included at
calculated positions using a riding model. Geometry calculations
and checking for higher symmetry was performed with the
.03 (brs, 1HPyCHN), 5.77 (brs, 1H ), 3.52 (d, J=9.1 Hz, 2HPyCH2P), 2.66
NH
(
s, 3HTs(1)-CH3), 2.56 (s, 3H
), 1.37 (d, J=14.3 Hz, 9HP(CH3)3), 1.26 (d,
Ts(2)-CH3
1
3
1
J=14.4 Hz, 9HP(CH3)3); P{ H} NMR (161 MHz, CD Cl ): d=94.11 ppm
2
2
1
13
1
(
d, J =151.3 Hz); C{ H} NMR (100 MHz, CD Cl ): d=193.31 (dd,
Rh-P 2 2
J=73.9, 18.1 Hz, CO), 165.26 (s, CPy6), 161.52 (dd, J=73.9, 18.1 Hz,
CPy2), 143.06 (s, C ), 140.11 (s, C ), 139.23 (s, C ), 137.84, (s, C ),
1
[29]
PLATON program.
Crystallographic details for 1: C H N OP Rh, F =702.49, yellow-
Ar
Ar
Ar
Ar
32.80 (s, C ), 132.56 (s, C ), 132.21 (s, C ), 130.84 (s, C ), 129.99
Ar Ar Ar Ar
28 43
2
2
3
w
(
s, CTs(1)6), 128.91 (s, CTs(2)6), 126.03 (s, C ), 125.44 (s, C ), 121.70 (d,
golden rectangles, 0.574”0.118”0.113 mm , monoclinic, P2 /n, a=
Ar
Ar
1
J=10.8 Hz, CPy3), 121.53 (s, CPy5), 78.83 (s, PyCHN), 36.56 (d, J=
11.6022(4), b=13.8309(5), c=21.1322(9) Š, b=94.828(2)8, V=
3
À3
À1
2
1
2
0.1 Hz, PyCH P), 36.09 (d, J=19.7 Hz, PC(CH ) ), 35.76 (dd, J=21.9,
3379.0(2) Š , Z=4, 1 =1.381 gcm , m=0.656 mm . 28807 reflec-
2
3 3
x
À1
.8 Hz, PC(CH ) ), 29.21–19.14 (m, 2PC(CH ) ), 21.40 (s, CTs2-CH3),
tions were measured up to a resolution of 2(sinq/l)max =1.26 Š
.
3
3
3 3
À1
0.78 ppm (s, CTs1-CH3); IR ( n˜ CO, CD Cl )=1985 cm ; HRMS (ESI, neg-
5947 Reflections were unique (Rint =0.0600), of which 4606 were
2
2
Chem. Eur. J. 2015, 21, 12683 – 12693
www.chemeurj.org
12691 ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
observed [I>2s(I)]. 459 Parameters were refined with 307 re-
straints. R1/wR2 [I> 2s(I)]: 0.0340/0.0708. R1/wR2 [all refl.]: 0.0553/
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0
.0782. S=1.030. CCDC 1048612 contains the supplementary crys-
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Crystallographic details for 3: C H N OP Rh PF , F =700.48, red-
2
8
41
2
2
6
w
3
brown block, 0.3”0.2”0.1 mm , triclinic, P 1¯ , a=8.6285(4), b=
1
7
0
2.1541(5), c=16.6555(7) Š, a=69.373(2), b=76.414(2), g=
3
À3
[
[
[
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8.091(2)8, V=1574.24(12) Š , Z=2, 1 =1.407 gcm , m=
x
À1
.704 mm . 45078 Reflections were measured up to a resolution
À1
of 2(sinq/l)max =1.37 Š . 5696 Reflections were unique (Rint
=
0
.0541), of which 4971 were observed [I>2s(I)]. 444 Parameters
were refined with no restraints. R1/wR2 [I>2s(I)]: 0.0267/0.0579.
R1/wR2 [all refl.]: 0.0357/0.0615. S=1.109. CCDC 1048613 contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre.
Crystallographic details for 4: C H N OPRh, F =554.50, dark
2
8
40
2
w
green block, 0.38”0.38”0.12 mm, monoclinic, P2 /c, a=
1
o
1
2
5.1902(6), b=10.4618(4), c=17.4934(6) Š, b=96.1846(18) , V=
3
À3
À1
763.82(18) Š , Z=4, 1 =1.333 gcm , m=0.697 mm . 32777 Re-
x
flections were measured up to a resolution of 2(sinq/l)max
=
À1
1
5
.31 Š . 6546 Reflections were unique (R =0.0269), of which
768 were observed [I>2s(I)]. 308 Parameters were refined with
int
no restraints. R1/wR2 [I>2s(I)]: 0.0256/0.0598. R1/wR2 [all refl.]:
.0324/0.0598. S=1.061. CCDC 1049097 contains the supplementa-
0
1
2790–12794; Angew. Chem. 2012, 124, 12962–12966; m) F. W. Patur-
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180–3183; Angew. Chem. 2008, 120, 3224–3227; n) S. Oldenhof, B. de
ry crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre.
3
Crystallographic details for 5: C H N O PRhS CH Cl , Fw=
3
5
49
3
3
3
2
2
Bruin, M. Lutz, F. W. Patureau, J. I. van der Vlugt, J. N. H. Reek, Chem. Eur.
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8
10.63, yellow block, 0.4”0.2”0.1 mm , monoclinic, P2 /n, a=
1
1
3
1.2583(4), b=13.6561(5), c=25.5029(10) Š, b=102.5430(18)8, V=
3
À3
À1
827.4(2) Š , Z=4, 1 =1.407 gcm , m=0.720 mm . 26791 Reflec-
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Kirchner, Acc. Chem. Res. 2008, 41, 201–213; b) D. Benito-Garagorri, M.
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x
À1
tions were measured up to a resolution of 2(sinq/l)max =1.67 Š
.
6
749 Reflections were unique (Rint =0.0398), of which 5946 were
observed [I>2s(I)]. 438 Parameters were refined with no restraints.
R1/wR2 [I>2s(I)]: 0.0295/0.0767. R1/wR2 [all refl.]: 0.0359/0.0875.
S=1.108. CCDC 1048614 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
DFT calculations: The gas phase geometries of the complexes 3
[
30]
and 4 were optimized with the Turbomole program package
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tesian coordinates of the optimized geometries are supplied as
a separated zip file (.pdb and.xyz format). Orbital plots were gener-
[
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Keywords: amine activation · cooperative reactivity · pincer ·
reactive ligand · rhodium · sulfonamide
Chem. Eur. J. 2015, 21, 12683 – 12693
www.chemeurj.org
12692
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Full Paper
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Received: April 14, 2015
Published online on July 17, 2015
Chem. Eur. J. 2015, 21, 12683 – 12693
www.chemeurj.org
12693
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim