Easy preparation of Cp*-functionalized N-heterocyclic carbenes and their coordination to rhodium and iridium

Article abstract of DOI:10.1039/b901195a

A simple high-yielding method for the preparation of a tetramethylcyclopentadienyl-NHC ligand is described. This ligand has been successfully coordinated to Rh and Ir. A related Cp*-NHC ligand with a -CH₂CMePh- linker between the Cp*and the NHC is also described, together with its coordination to Rh and Ir. This latter ligand, affords the orthocyclometallation of the phenyl ring yielding a constrained structure in which the ligand is tridentate. All the complexes have been fully characterized and their crystal structures are described. Preliminary catalytic results on the β-alkylation of secondary alcohols and N-alkylation of aniline with primary alcohols are also reported.

Full text of DOI:10.1039/b901195a

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N-Heterocyclic Carbenes
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Westfälische Wilhelms-Universität, Münster, Germany
Published in issue 35, 2009 of Dalton Transactions
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PAPER
www.rsc.org/dalton | Dalton Transactions
Easy preparation of Cp*-functionalized N-heterocyclic carbenes and their
coordination to rhodium and iridium†
Andre´ Pontes da Costa,a Mercedes Sanau´,b Eduardo Peris*c and Beatriz Royo*a
Received 21st January 2009, Accepted 5th May 2009
First published as an Advance Article on the web 12th June 2009
DOI: 10.1039/b901195a
A simple high-yielding method for the preparation of a tetramethylcyclopentadienyl-NHC ligand is
described. This ligand has been successfully coordinated to Rh and Ir. A related Cp*-NHC ligand with
a -CH2CMePh- linker between the Cp* and the NHC is also described, together with its coordination
to Rh and Ir. This latter ligand, affords the orthocyclometallation of the phenyl ring yielding a
constrained structure in which the ligand is tridentate. All the complexes have been fully characterized
and their crystal structures are described. Preliminary catalytic results on the b-alkylation of secondary
alcohols and N-alkylation of aniline with primary alcohols are also reported.
Introduction
The easy access to N-heterocyclic carbenes and their potential ap-
plication in a large number of homogeneously-catalyzed processes,
has led to a rapid development in the design of an almost unlimited
number of NHC-containing architectures. NHCs are known to be
compatible with a wide set of functionalities, including pyridines,
Scheme 1
alcohols, phosphines, arenes, aryls, ethers, oxazolines, amines
and other donor groups.1 Among these NHC-based ligands,
the scope of their catalytic applications, we thought that the
6
1
5
1
those containing h -arene-h -carbene,2 h -indenyl-h -carbene3 or
multistep and low-yielding procedure to the preparation of the
ligand in A, could be an inconvenient that needed to be addressed.
Here we report a new synthetic method that allows one to
easily prepare an h-(tetramethylcyclopentadienyl)-NHC ligand
and simplifies the multistep process needed for the preparation of
our previously described ligand. Together with the description of
the new synthetic protocols, we have described the intramolecular
C-H activation processes that allows the preparation of the
h -cyclopentadienyl-h -carbene4 are limited to a very few recent
examples, despite their obvious interest in the preparation of stable
and rigid molecules.
5
1
After the pioneering studies by Bergman and co-workers on
the application of Cp*Ir(phosphine) complexes in C-H activation
processes,5,6 several works appeared showing that the replacement
of the phosphine by NHC ligands, may sometimes result in
an enhancement of the catalytic activities.7–9 An early approach
to more stable ‘Cp*Ir(phosphine)’ complexes consisted of the
preparation of complexes bearing chelating cyclopentadienyl-
phosphine ligands,6 an idea that was also applied by us to obtain
a Cp*Ir(III)-related complex that contained the first chelating
tetramethylcyclopentadienyl-NHC ligand, in which the Cp* ring
and the NHC were connected by a -CH2CHPh- linker (A,
Scheme 1).4
5
tethered h -Cp*-NHC metal complexes, one of which shows
an unusual rigid tridentate coordination form. The preliminary
catalytic applications of the new complexes are also described.
Results and discussion
The salt 1 was prepared by a one-pot synthesis route,10 starting
from the easily accessible 2-(2,3,4,5-tetramethylcyclopentadienyl)-
ethylamine,11 glyoxal and formaldehyde, yielding 2-(2,3,4,5-
tetramethylcyclopentadienyl)ethylimidazole, that further reacts
with MeI to provide the imidazolium iodide 1 with an overall
yield of ca. 66% (Scheme 2).
Compound A proved to be an excellent catalyst for a number
of reactions implying hydrogen-borrowing processes,4 a fact that
confirmed the applicability of the tethered ligand. In order to
extend the use of Cp*-NHC ligands to other metals and widen
aInstituto de Tecnolog´ıa Qu´ımica e Biolo´gica da Universidade Nova de
Lisboa, Quinta do Marqueˆs, EAN, Apt. 127, 2781-901, Oeiras, Portugal.
E-mail: broyo@itqb.unl.pt
bDepartamento de Qu´ımica Inorga´nica, Universitat de Valencia, Av. Dr
Moliner s/n, 46100, Burjassot, Valencia, Spain
cDepartamento de Qu´ımica Inorga´nica y Orga´nica, Universitat Jaume
I, Avenida Vicente Sos Baynat s/n, 12071, Castello´n, Spain. E-mail:
eperis@qio.uji.es
† Electronic supplementary information (ESI) available: Ortep diagram
of compound 6. CCDC reference numbers 717566–717569. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b901195a
Scheme 2 Synthesis of 1.
6960 | Dalton Trans., 2009, 6960–6966
This journal is
The Royal Society of Chemistry 2009
©

In an attempt to obtain an enantiomerically pure chiral Cp*-
NHC ligand, we prepared the imidazolium salt 3 starting from
S-1-(phenylethyl)imidazole as depicted in Scheme 3.4 However,
we observed that the final imidazolium-proligand 3 is a race-
mate, probably as a consequence of the deprotonation of S-
1-(phenylethyl)imidazole with BuLi, which affords the racemic
mixture of the imidazolyl intermediate 2.
steric interaction with the cyclooctadiene ligand, providing two
distinctive rotamers. Further addition of acetic acid facilitates the
C-H activation of the cyclopentadienyl and its h -coordination to
5
the metal, affording the final M(III) species (compounds 5 and 6,
Scheme 4). In this reaction, together with the CH activation of
the pentacyclic fragment, the second step of the reaction implies
the metal-mediated isomerization of the exocyclic double bond
5
of the linker chain, to form the final h -cyclopentadienyl part of
the ligand.
The coordination of 3 to [MCl(cod)]2 (M = Rh, Ir) was
performed via the transmetallation of the in situ pre-formed Ag-
NHC complex to the rhodium or iridium fragments. Further
addition of acetic acid and KI completes the reaction to the final
M(III) species with the coordination of the chelating Cp*-NHC
ligand and formation of compounds 7 and 8 (Scheme 5). The
reaction of the iridium complex 7 with LiOAc in methanol, affords
the orthocyclometallation of the phenyl ring to form compound
9 in almost quantitative yield, as shown in Scheme 5. Although
we have observed this type of aromatic CH activation for related
Cp*Ir(NHC) complexes,9,12 the formation of this rigid terdentate
coordination is unprecedented.
Scheme 3 Synthesis of 3.
Both 1 and 3 served as useful Cp*-NHC chelating precursors
for the preparation of Rh and Ir complexes. The reaction of 1 with
[MCl(cod)]2 (M = Rh, Ir) was performed via the transmetallation
of the in situ pre-formed Ag-NHC complex to the rhodium and
iridium precursors. The first step of this process affords M(I)
species with the monometalated carbene and with uncoordinated
tetramethylcyclopentadienyl moiety. For the Rh complex, we
have isolated the corresponding Rh(I) intermediate 4, which was
characterized by mass spectrometry (molecular peak at 441 ([Cp*-
NHC)Rh(cod)]+) and NMR spectroscopy (Scheme 4). Both 13C
1
and H NMR spectra showed that the isolated species consisted
of two isomers that we were unable to separate. Although we could
not achieve clean NMR spectra for a detailed characterization, we
clearly observed that the 13C NMR spectrum shows two doublets
at 182 and 178 ppm, with a 1JRh-C value of 51 Hz, both suggesting
that 4 is a mixture of two pseudosquare-planar Rh(I) species.
The nature of the two isomers may be ascribed to the restricted
rotation of the NHC ligand about the Rh-C bond due to the
Scheme 5 Coordination of 3 to Ir and Rh.
The identity of all complexes was established by analytical and
spectroscopic methods. The 1H NMR of 5 and 6 showed the
characteristic signals due to the protons of the imidazolylidene
ring. The twofold symmetry of the azole ring is confirmed by
the equivalence of the two pairs of methyl groups, showing two
distinctive signals. The 13C NMR spectra show the signals due to
the M-Ccarbene, at d 150 (5) and 166 (6, 1JRh-C = 55.7 Hz), confirming
the coordination of the NHC.
1
The H NMR of 7 and 8 showed the two doublets due to the
protons of the imidazolylidene ligand, and the four distinctive
signals of the inequivalent methyl groups at the cyclopentadienlyl
ring, as a consequence of the asymmetry of the ligand. The 13C
NMR confirms that the coordination of both the Cp* ring and
the NHC have occurred. Compound 7 shows a signal at 148 ppm,
indicative of a Ir-Ccarbene and in the region of previously reported
Cp*Ir(NHC) complexes.4,8,12–15 The signal due to the metallated
carbene in 8 appears as a doublet at 167 ppm (1JC-Rh = 59.0 Hz).
For both, 7 and 8, five different signals assigned to the five carbons
Scheme 4 Coordination of 1 to Ir and Rh.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6960–6966 | 6961
©

of the cyclopentadienyl ring are clearly observed, confirming the
asymmetry of the system.
The 13C NMR spectrum of 9 confirms that the cyclometallation
of the phenyl ring has occurred. A signal at 159 ppm is due to the
Ir-Cphenyl, while the signal due to the metallated carbene carbon
appears at 147 ppm.
The molecular structures of complexes 5, 6, 8 and 9 were
confirmed by X-ray diffraction methods. Fig. 1, 2, and 3 show
the molecular diagrams of complexes 5, 8 and 9, respectively. The
Ortep diagram of compound 6 can be seen in the ESI† of this
manuscript. Compounds 5 (Fig. 1) and 6 (ESI) are isostructural,
with the only difference that 5 contains an Ir center and 6 is Rh.
Both structures show that the h-(tetramethylcyclopentadienyl)-
NHC ligand is chelating the metal atom, and two chlorine ligands
complete the coordination sphere about the metal. The M-Ccarbene
distance is 2.041 (5, M = Ir) and 2.033 (6, M = Rh). All other
distances and angles are unexceptional and compare well with
related compounds reported in this and other previously published
studies.4,12–14
Fig. 3 Ortep diagram of compound 9, with ellipsoids represent-
ing 30% probability. H atoms are omitted for clarity. Selected bond
˚
distances (A) and angles (deg) are: Ir(1)-C(1) 1.951(17), Ir(1)-C(22)
2.074(18), Ir(1)-C(14) 2.073(17), Ir(1)-C(15) 2.239(18), Ir(1)-C(13)
2.24(2), Ir(1)-C(11) 2.259(18), Ir(1)-C(12) 2.238(19), Ir(1)-I(1) 2.6985(17),
C(1)-Ir(1)-C(22) 83.2(7), C(1)-Ir(1)-I(1) 102.8(6), C(22)-Ir(1)-I(1) 96.2(5).
The two Cp* carbons trans to the NHC ligand display a larger
Ir-C distance, than that shown for the three other carbon atoms
˚
(compare 2.27 and 2.28, with 2.10–2.18 A, respectively as a
consequence of the trans influence of the NHC ligand. This effect
is also observed for all the rest of the structures that we have
determined in this work, and also in other examples published
before.4
The molecular structure of 9 (Fig. 3), shows that the phenyl
substituent at the C(5) atom of the NHC-Cp* linker has or-
thometalated, thus forming a structure with a tridentate coordi-
Fig. 1 Ortep diagram of compound 5, with ellipsoids representing 30%
probability. H atoms are omitted for clarity. Selected bond distances (A)
˚
nation of the ligand. The Ir-Ccarbene distance is 1.95 A, a little shorter
˚
than the similar distances shown by the Ir compounds obtained in
this work and other similar complexes reported in the literature,4
although similar to other Cp*Ir-NHC species with orthometalated
phenyl rings that we have reported previously.12,14 The Ir-C bond
and angles (deg) are: Ir(1)-C(1), 2.041(12); Ir(1)-Cl(1), 2.406(4); Ir(1)-Cl(2),
2.404(3); Ir(1)-C(15), 2.089(11); Ir(1)-C(11), 2.137(11); Ir(1)-C(14),
2.133(13); Ir(1)-C(13), 2.242(11); Ir(1)-C(12) 2.261(10), C(1)-Ir(1)-Cl(1),
92.3(3); C(1)-Ir(1)-Cl(2) 89.2(3), Cl(1)-Ir(1)-Cl(2), 91.82 (16).
˚
distance for the cyclometalated phenyl ring is 2.07 A. The Ccarbene
-
Ir-Cphenyl bite angle is 83.2◦.
In order to test catalytic applicability of the complexes obtained,
we decided to perform a preliminary set of tests using complex 5.
For this purpose, we studied its activity toward hydrogen transfer
and b-alkylation of secondary alcohols with primary alcohols,
using 2-phenylethanol and benzylic alcohol. As shown in Table 1,
the results that we obtained compare well with our previously
published results when we used A.4
Catalyst 5 was also an excellent catalyst in the alkylation of
amines with primary alcohols (Scheme 6), a reaction for which
A and other Cp*Ir(NHC)16 complexes have also shown a good
catalytic activity. In the case of 5, yields on the final product of up
to 93% were achieved, with a low catalyst loading of 0.7 mol% for
the reaction between aniline and benzylic alcohol.
Fig. 2 Ortep diagram of compound 8, with ellipsoids representing
30% probability. H atoms are omitted for clarity. Selected bond dis-
˚
tances (A) and angles (deg) are: Rh-C(1), 2.045(6); Rh-C(14), 2.104(7);
Rh-C(15) 2.141(7); Rh-C(13), 2.181(7); Rh-C(12) 2.266(7); Rh-C(11)
2.279(6); Rh-I(2), 2.7088(18); Rh-I(1), 2.7088(19); C(1)-Rh-I(1) 89.69(18);
C(1)-Rh-I(2) 97.5(2); I(2)-Rh-I(1) 97.86(8).
The molecular structure of 8 (Fig. 2) shows that the
h-(tetramethylcyclopentadienyl)-NHC ligand is chelating the
rhodium atom, and two iodine ligands complete the coordination
˚
sphere about the metal. The Rh-Ccarbene distance is 2.045 A.
Scheme 6 Alkylation of aniline with benzylalcohol.
6962 | Dalton Trans., 2009, 6960–6966
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The Royal Society of Chemistry 2009
©

Table 1 Catalytic b-alkylation of secondary alcohols using 5 and A
successful refinement of the structures. The structure was solved by
direct methods with the aid of successive difference Fourier maps
and were refined using the SHELXTL 6.1 software package.19 All
non-hydrogen were refined anisotropically, except C(5) and C(6) in
compound 5, that were refined isotropically. These two atoms are
probably disordered and cause several problems in the refinement,
like the fact that the distances around them, C(5)-C(6) and C(6)-
C(15) are shorter than expected. Hydrogen atoms were assigned
to ideal positions and refined using a riding model. The diffraction
frames were integrated using the SAINT package.20 Crystals from
compound 9 diffracted very poorly. During the integration process,
reflections showing negative intensities were omitted. Because of
this, some reflections were missed and the completeness was lower
than usual.
Catalyst
Time (h)
Conversion (%)
5
5
3
6
70
80
5
24
3
6
>99
70
90
A
A
A
24
>99
a 1 mmol of benzylic alcohol and 1 mmol of 1 phenylethanol, 1 mmol
(100 mol%) of KOH, 0.3 mL of toluene, 1 mol% cat. Temperature:
110 ◦C. Conversions determined by 1H NMR spectroscopy.
Synthesis of Cp*-CH2-CH2-NHCMeI, 1
An aqueous solution of formaldehyde (190 mL of 33% wt
in water, 2.53 mmol) was added dropwise to neat 2-(2,3,4,5-
tetramethylcyclopentadienyl)ethylamine (418 mg, 2.53 mmol) at
Conclusions
In this work we have described a convenient and high-yielding
method for the preparation of a precursor of a Cp*-NHC ligand
with the simple -CH2CH2- linker between the Cp* and the NHC
ring. This precursor can be easily coordinated to Rh and Ir
by transmetallation from the corresponding preformed Ag-NHC
complex. We also described the preparation of another Cp*-
NHC ligand precursor with a -CH2CMePh- linker, which was
also coordinated to Rh and Ir. Both, the synthetic procedures to
the ligand precursor, and the metallation methodologies to the
(Cp*-NHC)M complexes constitute valuable protocols that can
be extended to the preparation of complexes with other transition
metals.
The preliminary studies on the catalytic activity of the Ir
complex 5, shows that this species displays a good activity in the
alkylation of secondary alcohols and amines with benzylic alcohol.
Further studies in order to widen the catalytic applications of these
species, and also in the preparation of enantiomerically pure chiral
catalysts of this type, are underway.
0
◦C. The mixture was stirred until completely formation of a
white solid (10–15 min.). Then, ammonium carbonate (121.6 mg,
1.27 mmol), an aqueous solution of glyoxal (290 mL of 40 % wt in
water, 2.53 mmol) and 5–10 mL of methanol were subsequently
added and the mixture stirred at room temperature overnight.
Then, the reaction mixture was treated with brine and extracted
with hexane. The organic layer was dried over sodium sulfate
anhydrous and evaporated to dryness. The remaining crude
brown oil was redissolved in acetone, and iodomethane (720 mL,
11.6 mmol) was added. Stirring was continued for 24 h at room
temperature. The solvent was removed under vacuum to yield
1 (600 mg, 66%) as a yellow solid. The product was washed
several times with diethyl ether and dried under vacuum. dH
(400 MHz, CDCl3) 9.87 (1H, br s, CHimid), 7.47 (1 H, br s, CHimid),
3
7.28 (1 H, br s, CHimid), 5.18 (1 H, t, JH-H = 7.7 Hz, CH linker),
4.97 (2 H, d, 3JH-H = 7.7 Hz, CH2 linker), 4.10 (3H, s, N-CH3), 2.45
3
3
(1H, q, JH-H = 7.2 Hz, CHCp*), 2.10 (1 H, q, JH-H = 7.0 Hz,
CHCp*), 1.73 (3 H, s, CH3 Cp*), 1.63 (3 H, s, CH3 Cp*), 1.04 (3 H, d,
3JH-H = 7.2 Hz, CH3 Cp*), 0.99 (3H, d, 3JH-H = 7.0 Hz, CH3 Cp*); dC
(100 MHz, CDCl3) 161.7 (CCp*), 150.3 (CCp*), 136.6 (CHImid), 130.1
(CCp*), 123.6 (CHImid), 121.3(CHImid), 104.7 (CHlinker), 51.5 (CHCp*),
49.0 (CH2 linker), 42.41 (CHCp*), 37.38 (N-CH3), 22.2 (CH3 Cp*), 19.33
(CH3 Cp*), 13.40 (CH3 Cp*), 10.33 (CH3 Cp*); m/z (Electrospray) 231.1
[M - I]+.
Experimental
Materials and methods
NMR spectra were recorded on
a Bruker Advance III
400 MHz and a Varian Innova 500 MHz spectrometers us-
ing CDCl3 as solvent. Elemental analyses were performed in
our laboratories at ITQB. Electrospray mass spectra (ESI-
MS) were recorded on a Micromass Quattro LC instru-
ment. 1,2,3,4-Tetramethylfulvene,17 S-1-(phenylethyl)imidazole18,
2-(2,3,4,5-tetramethylcyclopentadienyl)ethylamine,11 were synthe-
sized according to literature procedures. All other reagents are
commercially available and were used as received.
Synthesis of Cp*-CH2-CPhMe-NHC, 2
An hexane solution of n-BuLi (4 mL of 1.6 M in hexane, 6.4 mmol)
was added dropwise to a solution of S-1-(phenylethyl)imidazole
(990 mg, 5.75 mmol) in dried THF (25 mL) at -90 ◦C. After stirring
for 30 minutes, tetramethylfulvene was added, and the reaction
mixture was allowed to reach room temperature and stirred for
onehour. Methanol was then added and the volatiles were removed
under vacuum. The crude oil was purified by flash chromatography
(hexane/ethyl acetate, 1:4) affording compound 2 (750 mg, 43%)
as a yellow oil. dH (400 MHz, CDCl3): 7.45 (1 H, br s, CHimid),
7.28–7.08 (5 H, m, CHPh), 7.00 (1 H, br s, CHimid), 6.78 (1 H, br s,
X-Ray diffraction studies
Single crystals of 5, 6 (ESI†), 8, and 9 were mounted on a glass
fiber in a random orientation. Data collection was performed at
room temperature on a Siemens Smart CCD diffractometer using
˚
graphite monochromated Mo Ka radiation (l = 0.71073 A) with
2
a nominal crystal to detector distance of 4.0 cm. Space group
assignment was based on systematic absences, E statistics and
CHimid), 3.30 (1 H, d, JH-H = 14.0 Hz, CH2 linker), 2.93 (1 H, d,
2JH-H = 14.0 Hz, CH2 linker), 1.71-16.4 (15 H, m, CH3 linker+ CH3 Cp*),
Dalton Trans., 2009, 6960–6966 | 6963
This journal is
The Royal Society of Chemistry 2009
©

0.70 (3 H, d, 3JH-H = 7.6 Hz, CH3 Cp*); dH (100 MHz, CDCl3) 146.8
(CPhenyl), 141.6 (CCp*), 140.3 (CCp*), 136.3 (Cimid-H), 136.0 (CCp*),
133.3 (CCp*), 129.0 (Cimid-H), 128.7 (CPhenyl-H), 127.6 (CPhenyl-H),
125.5 (CPhenyl-H), 118.6 (Cimid-H), 64.1 (Clinker), 49.7 (CCp*-H), 37.1
(Clinker-H2), 28.4 (Clinker-CH3), 15.4 (CCp*-CH3), 12.3 (CCp*-CH3),
11.4 (CCp*-CH3), 11.2 (CCp*-CH3).
chromatography (CH2Cl2/acetone) yielding 5 (70 mg, 24%) as an
orange solid. dH (500 MHz, CDCl3) 6.91 (1 H, br s, CHImid), 6.77
(1 H, br s, CHImid), 4.13 (2 H, m, CH2 linker), 4.08 (3 H, s, NCH3),
2.51 (2 H, m, CH2 linker), 1.7 (6H, br s, CH3 Cp*), 1.6 (6 H, br s,
CH3 Cp*). dC (125 MHz, CDCl3) 150.3 (Ccarbene-Ir), 124.1 (CHImid),
121.3 (CHImid), 105.1 (CCp*), 83.8 (CCp*), 77.5 (CCp*), 77.2 (CCp*),
50.6 (CH2 linker), 39.8 (NCH3), 29.9 (CH2 linker), 21.2 (CH3 Cp*), 9.88
(CH3 Cp*), 8.7 (CH3 Cp*); m/z (Electrospray): 457.2 [M - Cl]+.
Synthesis of Cp*-CH2-CPhMe-NHCMeI, 3
X-Ray crystal structure data. C15H21Cl2IrN2, M = 492.44
monoclinic, space group Pn, a = 7.9908(5), b = 13.1311(9), c =
Iodomethane (780 mL, 12.5 mmol) was added to a solution of
2 (750 mg, 2.5 mmol) in methanol (5 mL). The reaction was
stirred at room temperature for 12 hours and all the volatiles
were evaporated affording a yellow solid, which was washed
several times with dried diethyl ether to yield compound 3 in
quantitative yield. (Found: C, 58.46; H, 6.69; N, 6.29. Calc for
C22H29IN2: C, 58.93; H, 6.25; N 6.52%); dH(400 MHz, CDCl3)
9.96 (1 H, br s, CHimid), 7.53 (1 H, br s, CHimid), 7.39–7.22 (5 H, m,
CHPh), 6.89 (1 H, br s, CHimid), 4.19 (3 H, s, N-CH3), 3.35 (1 H, d,
2JH-H = 14.2 Hz, CH2 linker), 3.13 (1 H, d, 2JH-H = 14.2 Hz, CH2 linker),
1.70 (3 H, s, CH3 Cp*), 1.68 (3 H, s, CH3 Cp*), 1.52 (3 H, s, CH3 Cp*),
◦
3
˚
˚
8.6289(6) A, b = 116.0640(10) , V = 813.34(9) A , Z = 2, crystal
dimensions: 0.06 ¥ 0.14 ¥ 0.531 mm3, Mo Ka radiation, 298(2) K,
4917 reflections, 2241 independent, (m = 8.528 mm-1), Rint
=
0.0334, refinement (on F2) with SHELXTL (version 6.1), 176
parameters, 3 restraints, R1= 0.0308 (I > 2s(I)) and wR2 (all
data) = 0.0790, GOF = 1.248, max/min residual electron density:
-3
˚
2.107/-1.129 e A . CCDC 717567.
Synthesis of [Cp*-CH2-CH2-NHCMe]RhCl2, 6
3
1.19 (3H, s, CH3 linker), 0.84 (3 H, d, JH-H = 7.4 Hz, CH3 Cp*);
To a solution of 1 (171 mg, 0.48 mmol) in 1,2-dichloroethane
(10 mL), Ag2O (132 mg, 0.57 mmol) was added at room tempera-
ture. After refluxing for 1 h, [Rh(m-Cl)(cod)]2 (100 mg, 0.2 mmol)
was added. The reaction mixture was refluxed for half an hour
and glacial acetic acid (2 mL) was added. Stirring was continued
for 16 h. The volatiles components were removed under vacuum
and the remaining solid was purified by flash chromatography
(CH2Cl2/acetone) yielding 6 (30 mg, 37%) as an orange solid. dH
(500 MHz, CDCl3) 7.00 (1 H, d, 3JH-H = 2 Hz, CHImid), 6.85 (1 H,
dC (100 MHz, CDCl3) 142.7 (CCp*), 142.0 (CCp*), 141.4 (CPhenyl),
136.8 (Cimid-H), 134.1 (CCp*), 132.9 (CCp*), 129.2 (CPhenyl-H), 128.8
(CPhenyl-H), 125.8 (CPhenyl-H), 123.7 (Cimid-H), 120.9 (Cimid-H), 69.1
(Clinker), 50.0(CCp*-H), 37.6 (N-CH3), 36.8 (Clinker-H2), 28.4 (Clinker
-
CH3), 15.3 (CCp*-CH3), 12.0 (CCp*-CH3), 11.8 (CCp*-CH3), 11.0
(CCp*-CH3).
Synthesis of [Cp*-CH2-CH2-NHCMe]RhCl(cod), 4
3
d, JH-H = 2 Hz, CHImid), 4.30 (2 H, m, CH2 linker), 4.00 (3 H, s,
To a solution of 1 (100 mg, 0.28 mmol) in 1,2-dichloroethane
(10 mL), Ag2O (180 mg, 0.78 mmol) was added at room
temperature. After refluxing for 1 h, [Rh(m-Cl)(cod)]2 (70 mg,
0.14 mmol) was added. The reaction mixture was refluxed for
half an hour, then filtered over Celite and evaporated to dryness.
The remaining solid was washed with ether yielding 4 (55 mg,
41%) as a yellow solid. dH (400 MHz, CDCl3) 6.84–6.78 (2 H,
m, CHimid), 5.41 (1 H, m, CH2 linker), 5.2 (1 H, m, CH linker), 5.14
(m, 1H, CH2 linker), 5.01 (2 H, br s, CHcod), 4.07 (3 H, s, N-CH3),
3.32 (2 H, m, CHcod), 2.55 (1 H, m, CHCp*), 2.37 (4H, m, CH2 cod),
NCH3), 2.55 (2 H, m, CH2 linker), 1.77 (6 H, br s, CH3 Cp*), 1.48
(6 H, br s, CH3 Cp*). dC(100 MHz, CDCl3) 166.2 (d, Ccarbene-Rh,
1JC-Rh = 55.7 Hz), 124.7 (CHImid), 121.6 (CHImid), 110.0 (d, CCp*
,
,
1
1JC-Rh = 4.0 Hz), 91.0 (d, CCp*, JC-Rh = 8.0 Hz), 86.7 (d, CCp*
1JC-Rh = 9.6 Hz), 50.6 (CH2 linker), 40.4 (N-CH3), 29.9 (CH2 linker), 21.4
(CH3 Cp*), 9.8 (CH3 Cp*), 9.4 (CH3 Cp*); m/z (Electrospray): 366.8
[M - Cl]+.
X-Ray crystal structure data. C15H21Cl2RhN2·2H2O, M =
439.15, orthorombic, space group P212121, a = 9.1280(10), b =
3
3
˚
˚
2.14 (1 H, q, JH-H = 7.0 Hz, CHCp*), 2.14 (4 H, m, CH2 cod), 1.76
10.8995(12), c = 18.2374(19) A, V = 1814.5(3) A , Z = 4,
crystal dimensions: 0.20 ¥ 0.23 ¥ 0.25 mm3, Mo Ka radiation,
273 (8)K, 9499 reflections, 3706 independent, (m = 1.242 mm-1),
Rint = 0.0573, refinement (on F2) with SHELXTL (version 6.1),
204 parameters, 0 restraints, R1= 0.0377 (I>2s(I)) and wR2 (all
data) = 0.0859, GOF = 1.018, max/min residual electron density:
3
(3 H, s, CH3 Cp*), 1.63 (3 H, s, CH3 Cp*), 1.15 (3 H, two d, JH-H
=
7 Hz, CH3 Cp*), 1.04 (3 H, d, 3JH-H = 7.0 Hz, CH3 Cp*). dC(100 MHz,
1
CDCl3,) 181.7 (two d, Ccarbene-Rh, JC-Rh = 51 Hz), 157.5 + 157.0
(CCp*), 147.1 + 147 (CCp*), 130.53 + 130.46 (CCp*), 122.0 (CHImid),
1
120.1 (CHImid), 110.3 + 110.2 (CHlinker), 98.6 (d, CHcod, JC-Rh
=
-3
˚
7.0 Hz), 68.7-67.9 (m, CHcod), 51.6 (CH Cp*), 49.6 + 49.4 (CH2 linker),
42.4 + 42.3 (CH Cp*), 37.9 (NCH3), 33.4-32.9 + 29.2-28.9 (CH2 cod),
22.1 + 21.9 (CH3 Cp*), 19.5 + 19.4 (CH3 Cp*), 13.4 (CH3 Cp*), 10.4
(CH3 Cp*). m/z (Electrospray) 441.2 [M - Cl]+.
0.414/-0.513 e A . CCDC 717568.
The hydrogen atoms of the water molecules could not be located
in the Fourier difference map.
Synthesis of [Cp*-CH2-CPhMe-NHCMe]IrI2, 7
Synthesis of [Cp*-CH2-CH2-NHCMe]IrCl2, 5
A mixture of Ag2O (124 mg, 0.54 mmol) and 3 (200 mg, 0.45 mmol)
was refluxed in 1,2-dichloroethane (15 mL) for 1 h. Then, [Ir(m-
Cl)(cod)]2 (150 mg, 0.22 mmol) was added and the mixture was
refluxed for 30 min, followed by addition of glacial acetic acid
(1 mL). To complete the reaction, the mixture was refluxed
overnight. The suspension was filtered through Celite, the filtrate
was evaporated to dryness and KI (365 mg, 2.2 mmol) and
methanol (10 mL) were added to the remaining residue. The
To a solution of 1 (212 mg, 0.592 mmol) in 1,2-dichloroethane
(10 mL), Ag2O (163 mg, 0.70 mmol) was added at room
temperature. After refluxing for 1 h, [Ir(m-Cl)(cod)]2 (200 mg,
0.298 mmol) was added. The reaction mixture was refluxed for
half an hour and glacial acetic acid (2 mL) was added. Stirring
was continued for 16 h. The volatiles components were removed
under vacuum and the remaining solid was purified by flash
6964 | Dalton Trans., 2009, 6960–6966
This journal is
The Royal Society of Chemistry 2009
©

3
3
mixture was then refluxed for a further 16 h. After cooling, the
solvent was removed in vacuum and the crude solid was purified
by flash chromatography (CH2Cl2/acetone) yielding complex 7
(60 mg, 24%) as an orange solid. dH (400 MHz, CDCl3) 7.27–7.20
(5 H, m, CHPh), 6.89 (1 H, d, 3JH-H = 2.16 Hz, CHimid), 6.84 (1 H, d,
d, JH-H = 2.2 Hz, CHImid), 7.03 (1 H, t, JH-H = 7.5 Hz, CHPh),
6.86 (1 H, m, CHPh), 6.84 (1 H, d, 3JH-H = 2. Hz, CHImid), 3.97 (3
H, s, NCH3), 2.18 (3 H, s, CH3 linker), 2.18 (3 H, s, CH3 Cp*), 2.12
(3 H, s, CH3 Cp*), 1.92 (1 H, d, 2JH-H = 14.9 Hz, CH2 linker), 1.18 (3
H, s, CH3 Cp*), 0.88 (3 H, s, CH3 Cp*). dC (100 MHz, CDCl3) 159.1
(CPhenyl–Ir), 147.2 (Ccarbene–Ir), 144.7 (CPhenyl), 137.9 (CHPhenyl), 128.1
(CHPhenyl), 121.9 (CHPhenyl), 121.8 (CHimid), 120.7 (CHPhenyl), 117.0
(CHimid), 106.6 (CCp*), 103.3 (CCp*), 96.9 (CCp*), 94.2 (CCp*), 75.4
(Clinker), 59.4 (CCp*), 36.6 (NCH3), 34.5 (CH2 linker), 24.1 (CCH3 linker),
9.2 (CCp*–CH3), 9.1 (CCp*–CH3), 8.6 (CCp*–CH3), 8.4 (CCp*–CH3).
3JH-H = 2.16 Hz, CHimid), 4.13 (3 H, s, N-CH3), 2.98 (1 H, d, 2JH-H
=
15.3 Hz, CH2 linker), 2.66 (1 H, d, 2JH-H = 15.3 Hz, CH2 linker), 2.02 (3
H, s, CH3 linker), 1.96 (3H, s, CH3 Cp*), 1.92 (3 H, s, CH3 Cp*), 1.73 (3
H, s, CH3 Cp*), 0.82 (3 H, s, CH3 Cp*). dC (100 MHz, CDCl3) 148.3
(Ccarbene–Ir), 145.4 (CPhenyl), 129.2 (CHPhenyl), 128.1 (CHPhenyl), 126.3
(CHPhenyl), 124.1 (CHimid), 119.9 (CHimid), 105.3 (CCp*), 104.9 (CCp*),
81,9 (CCp*), 81.5 (CCp*), 69.3 (Clinker), 47.1 (N–CH3), 34.3 (CH2 linker),
33.8 (CH3 linker), 11.9 (CH3 Cp*), 11.6 (CH3 Cp*), 10.5 (CH3 Cp*), 9.0
(CH3 Cp*); m/z (Electrospray) 639.3 [M - I]+.
X-ray crystal structure data. C22H26IIrN2, M = 637.55, mon-
oclinic, space group P21n, a = 15.0849(16), b = 8.8037(10), c =
◦
3
˚
˚
16.2181(17) A, b = 98.598(2) , V = 2129.6(4) A , Z = 4, crystal
dimensions: 0.05 ¥ 0.06 ¥ 0.13 mm3, Mo Ka radiation, 278(2)
K, 9969 reflections, 3263 independent, (m = 7.727 mm-1), Rint
=
Synthesis of [Cp*-CH2-CPhMe-NHCMe]RhI2, 8
0.1059, refinement (on F2) with SHELXTL (version 6.1), 241
parameters, 167 restraints, R1= 0.0733 (I > 2s(I)) and wR2 (all
data) = 0.1916, GOF = 0.971, max/min residual electron density:
A mixture of Ag2O (120 mg, 0.52 mmol) and 3 (200 mg, 0.45 mmol)
was refluxed in 1,2-dichloroethane (15 mL) for 1 h. Then, [Rh(m-
Cl)(cod)]2 (116 mg, 0.235 mmol) was added and the mixture was
refluxed for 30 min, followed by addition of glacial acetic acid
(1 mL). The mixture was refluxed overnight and filtered through
Celite, the filtrate was evaporated to dryness and KI (390 mg,
2.35 mmol) and methanol (10 mL) were added to the remaining
residue.
The mixture was then refluxed overnight. After cooling, the
solvent was removed in vacuum and the crude solid was purified
by flash chromatography (CH2Cl2/acetone) yielding complex 8
(110 mg, 51%) as an orange solid. (Found: C, 39.44; H, 4.45;
N, 4.05. Calc for C22H27I2N2Rh: C, 39.08; H, 4.14; N 4.02%); dH
-3
˚
2.914/-1.414 e A . CCDC 717566.
b-Alkylation of 1-phenylethanol with benzylic alcohol
A mixture of 1-phenylethanol and benzylic alcohol (1:1), KOH
(1 eq) and 5 (1% mol) in toluene (0.3 mL) was heated to 110◦ C
1
in a sealed tube. The reaction was monitored by H NMR using
ferrocene as internal standard.
Alkylation of aniline with benzylic acid
A mixture of aniline and benzylic alcohol (1:1), tBuOK (1 eq) and
5 (0.7% mol) in toluene (0.3 mL) was heated to 110◦ C in a sealed
tube. The reaction was monitored by 1H NMR using ferrocene as
internal standard.
(400 MHz, CDCl3) 7.35-7.22 (5 H, m, CHPh), 7.01 (1 H, d, 3JH-H
=
2.0 Hz, CHImid), 6.95 (1 H, d, 3JH-H = 2.0 Hz, CHImid), 4.14 (3 H, s,
2
N-CH3), 3.05 (1 H, d, JH-H = 15.3 Hz, CH2 linker), 2.77 (1 H, d,
2JH-H = 15.3 Hz, CH2 linker), 2.09 (3 H, s, CH3 linker), 1.71 (3 H, s,
CH3 Cp*), 1.63 (3 H, s, CH3 Cp*), 1.42 (3 H, s, CH3 Cp*), 0.51 (3 H, s,
Acknowledgements
1
CH3 Cp*). dC (100 MHz, CDCl3) 166.8 (d, Ccarbene–Rh, JC - Rh- =
-59.0 Hz), 145.6 (CPhenyl), 129.4 (CHPhenyl), 128.3 (CHPhenyl), 126.4
We gratefully acknowledge financial support from FCT of
Portugal, POCI 2010 and FEDER through project PTDC/
QUI/64458/2006 and the MEC of Spain (CTQ2008-04460) and
Bancaixa (P1.1B2007-04). We thank FCT for REDE/1517/
RMN/2005 and REDE/1504/REM/2005. A. Pontes da Costa
thanks FCT for a grant (SFRH/BD/28490/2006). We wish to
acknowledge M. C. Almeida and Dr A. Coelho for providing data
from the Elemental Analyses and Mass Spectrometry Services at
ITQB, and NMR Spectrometry at SCIC (UJI).
(CHPhenyl), 124.9 (CHimid), 121.5 (CHimid), 109.6 (m, CCp*), 90.9 (m,
1
CCp*), 87.4 (d, JC - Rh = 8 Hz, CCp*),70.4 (Clinker), 48.1 (N–CH3),
35.1 (CH2 linker), 33.9 (CH3 linker), 12.7 (CH3 Cp*), 12.4 (CH3 Cp*), 11.4
(CH3 Cp*), 9.9 (CH3 Cp*). m/z (Electrospray) 549.1 [M - I]+.
X-ray crystal structure data. C22H27I2RhN2·CH2Cl2, M =
761.09, triclinic, space group P-1, a = 9.702(10), b = 12.165(12),
◦
˚
c = 12.351(12) A, a = 71.958(19), b = 67.00(2), g = 73.90(2) , V =
3
3
˚
1255(2) A , Z = 2, crystal dimensions: 0.20 ¥ 0.23 ¥ 0.27 mm , Mo
Ka radiation, 293(2) K, 8108 reflections, 5801 independent, (m =
3.366 mm-1), Rint = 0.0245, refinement (on F2) with SHELXTL
(version 6.1), 277 parameters, 0 restraints, R1= 0.0449 (I > 2s(I))
and wR2 (all data) = 0.1841, GOF = 1.097, max/min residual
Notes and references
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Dalton Trans., 2009, 6960–6966 | 6965
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6966 | Dalton Trans., 2009, 6960–6966
This journal is
The Royal Society of Chemistry 2009
©