Mononuclear rhodium(I) complexes with chelating N-heterocyclic carbene ligands - Catalytic activity for intramolecular hydroamination

Article abstract of DOI:10.1002/ejic.200300172

The mononuclear cationic Rh^I complexes [Rh(cod)(mdd)] ⁺X^- and [Rh(CO)₂(mdd)]⁺X ^- (X = BPh₄, PF₆) containing the chelating bidentate N-heterocyclic carbene ligand 1,1′-methylene - 3,3′-dimethyldiimidazoline-2,2′-diylidene (mdd) have been synthesised and spectroscopically characterised. The complexes [Rh(cod)(mdd)]⁺BPh₄^- and [Rh(CO) ₂(mdd)]⁺PF₆^- have also been characterised by X-ray crystallography. The dicarbonyl complexes catalyse the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200300172

FULL PAPER
Mononuclear Rhodium(
I
) Complexes with Chelating N-Heterocyclic Carbene
Ligands ؊ Catalytic Activity for Intramolecular Hydroamination
Suzanne Burling,[a] Leslie D. Field,*[a] Hsiu L. Li,[a] Barbara A. Messerle,[b] and
Peter Turner[a]
Keywords: Rhodium / Carbene ligands / Homogeneous catalysis / Hydroamination
The mononuclear cationic RhI complexes [Rh(cod)(mdd)]+X−
and [Rh(CO)2(mdd)]+X− (X = BPh4, PF6) containing the che-
lating bidentate N-heterocyclic carbene ligand 1,1Ј-methyl-
ene-3,3Ј-dimethyldiimidazoline-2,2Ј-diylidene (mdd) have
have also been characterised by X-ray crystallography. The
dicarbonyl complexes catalyse the intramolecular hydroam-
ination of 4-pentyn-1-amine to 2-methyl-1-pyrroline.
been synthesised and spectroscopically characterised. The ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
−
−
complexes [Rh(cod)(mdd)]+BPh4 and [Rh(CO)2(mdd)]+PF6
Germany, 2003)
Introduction
tions in the presence of OAcϪ and IϪ gave the mononuclear
complexes, although the rhodium metal was oxidised from
RhI to RhIII [7] and the mechanism for this oxidation is as
yet unknown.
In this paper, we report the successful synthesis and
characterisation of mononuclear RhI complexes with che-
lating bidentate N-heterocyclic carbene ligands and initial
studies into their activity as hydroamination catalysts.
In 1991, Arduengo[1] synthesised and characterised the
first crystalline carbene 1,3-di-1-adamantylimidazol-2-yl-
idene. Since then, there has been a resurgence of interest in
metal complexes containing N-heterocyclic carbene ligands,
fuelled by reports of their ability to increase catalyst activity
in a range of catalytic reactions.[2,3] Our interest in Rh com-
plexes with chelating N-heterocyclic carbene ligands
stemmed from the synthesis of a successful hydroamination
Ϫ
catalyst[4] [Rh(bim)(CO)2]ϩBPh4 1 [bim ϭ bis(N-methyl-
imidazol-2-yl)methane]; a carbene analogue might influence
Results and Discussion
The mononuclear RhI complexes were synthesised using
a modification of the sodium ethoxide method introduced
by Köcher et al.[6] (Scheme 1). [RhCl(cod)]2 was treated
with NaOEt and the product [Rh(OEt)(cod)]2 was washed
with methanol to remove residual chloride. The halide-free
[Rh(OEt)(cod)]2 was reacted with 1,1Ј-methylene-3,3Ј-di-
methyldiimidazolium bis(tetraphenylborate) to form pre-
dominantly the mononuclear Rh carbene complex
the catalytic activity.
Ϫ
[Rh(cod)(mdd)]ϩBPh4 (2; mdd ϭ 1,1Ј-methylene-3,3Ј-di-
methyldiimidazoline-2,2Ј-diylidene). The removal of all
Reactions of RhI precursors such as [RhCl(cod)]2 or
[Rh(OEt)(cod)]2 (cod ϭ 1,5-cyclooctadiene) with bidentate
N-heterocyclic carbenes (or their precursor imidazolium
halide salts) have produced dinuclear complexes where two
rhodium metals are bridged by the bidentate carbene li-
gand.[5,6] These reactions are probably driven by the in-
herent insolubility of the dinuclear products. Similar reac-
[a]
School of Chemistry, University of Sydney,
New South Wales 2006, Australia
Fax: (internat.)ϩ 61-2/9351-5758
E-mail: l.field@chem.usyd.edu.au
[b]
School of Chemical Sciences, University of New South Wales,
New South Wales 2052, Australia
Scheme 1
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184
DOI: 10.1002/ejic.200300172
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3179

S. Burling, L. D. Field, H. L. Li, B. A. Messerle, P. Turner
FULL PAPER
halide from the reaction mixture is the simple and effective
key to the formation of the mononuclear complex rather
than the dinuclear complex containing bridging mdd li-
gands. The reaction, however, was complicated by the for-
mation of an off-white, sparingly soluble by-product which
was difficult to remove. The by-product was identified as
the zwitterionic compound [Rh(cod)(η6-PhBPh3)] by the
four IR bands at 1478, 1458, 1426 and 1395 cmϪ1 charac-
teristic of coordinated tetraphenylborate.[8] Complex 2 was
isolated as a microanalytically pure compound after careful
recrystallisation from acetone. Further reaction of 2 with
carbon monoxide gas formed the Rh dicarbonyl complex
Ϫ
[Rh(CO)2(mdd)]ϩBPh4
(3). The hexafluorophosphate
Ϫ
analogues [Rh(cod)(mdd)]ϩPF6
(4) and [Rh(CO)2-
Figure 1. An ORTEP[10,11] depiction of the cation of [Rh(cod)-
Ϫ
(mdd)]ϩPF6 (5) were synthesised in similar reactions. In
the synthesis of complex 4, it is essential to use halide-free
[Rh(OEt)(cod)]2 to avoid the formation of the dinuclear
complex.
Ϫ
(mdd)]ϩBPh4 (2) showing 20% displacement ellipsoids and cod
ligand disorder about a (pseudo) mirror plane (see main text and
Exp. Sect.); atoms labelled with an asterisk are generated from the
unique sites by x, 3/2 Ϫ y, z
The 1H NMR spectra of the cod complexes 2 and 4 show
two separate resonances for the backbone methylene pro-
tons with a geminal splitting of 13.0 Hz, whilst the dicar-
bonyl complexes 3 and 5 show only a singlet for the corre-
sponding protons. The magnetic inequivalence of the meth-
ylene protons in the cod complexes probably arises from
rigidity of the non-planar metallacyclic ring imposed by the
steric bulk of the cod ligand, whereas the methylene protons
in the dicarbonyl complexes are more fluxional and ex-
change rapidly on the NMR timescale. The 13C{1H} NMR
spectra for cod complexes 2 and 4 show the carbene reson-
tadiene ligand. The complex molecule is bisected by a
(pseudo) mirror plane, with the Rh metal and methylene
carbon C(12) located in that plane. The six-membered met-
allacyclic ring as defined by Rh(1), C(9), N(1), C(12), N(1*)
and C(9*) is boat-like with Rh and methylene carbon devi-
˚
˚
ations from the boat plane of 0.94 A and 0.58 A, respec-
˚
tively. The Rh-carbene bond length [2.025(3) A] agrees well
with that found in non-chelated Rh(cod)(carbene) com-
plexes such as [RhCl(cod)(diy)] and [Rh(cod)(diy)2]Cl
(diy
ϭ
1,3-dimethylimidazoline-2-ylidene) [2.023(2)Ϫ
[5,12]
˚
1
2.059(8) A].
˚
The Rh-cod distances [2.171(6)Ϫ2.244(6)
ances at δ ϭ 181 ppm with JRh,C in the range 52Ϫ53 Hz.
A] are also similar to the corresponding distances in
The cod resonances also exhibit coupling to Rh with coup-
ling constant values of about 8 Hz. The carbene resonances
for dicarbonyl complexes 3 and 5 appear at δ ϭ 174 ppm
[RhCl(cod)(diy)] and [Rh(cod)(diy)2]Cl [2.095(2)Ϫ2.205(2)
˚
A].
1
with JRh,Carbene of about 45 Hz, whilst the carbonyl car-
1
Single crystal X-ray diffraction analysis of an orange col-
umnar-like crystal (grown from a methanol/diethyl ether
bons appear at δ ϭ 189 ppm with JRh,CO of 57 Hz. The
assignment of the carbonyl resonances was confirmed when
solutions of the complexes were placed under an atmos-
phere of 13C-labelled CO gas. There is exchange between
bound and free CO and the carbonyl resonances increase
Ϫ
solution) confirmed the structure of [Rh(CO)2(mdd)]ϩPF6
(5). An ORTEP[10,11] depiction of the cation is shown in
Figure 2 and selected bond lengths and angles are listed in
Table 1. The asymmetric unit in the crystal structure of
complex 5 contains the complex molecule and its hexa-
fluorophosphate counterion, both of which are bisected by
a mirror plane passing through Rh(1), C(5), P(1), F(3) and
F(4). The complex has a boat-like metallacyclic ring as de-
fined by Rh(1), C(2), N(1), C(5), N(1*) and C(2*) with Rh
and methylene carbon deviations from the boat plane of
1
in intensity relative to all resonances. The value of JRh,CO
(57 Hz) is somewhat smaller than that for the correspond-
ing bim complexes and other related bidentate nitrogen-do-
nor complexes where the one-bond coupling is typically in
the range 66Ϫ69 Hz.[4,9] Two strong IR stretches for ν(CO)
were observed for complexes 3 and 5 at 2071Ϫ2076 and
2014Ϫ2017 cmϪ1, consistent with the cis geometry of the
complexes.
˚
˚
0.88 A and 0.59 A respectively. The Rh-carbene bond
˚
length [2.062(2) A] is similar to that reported for [Rh(CO)-
(diy)2Cl][13] [2.049(4) A and 2.047(4) A]. The Rh-carbonyl
˚
˚
X-ray Crystallography
˚
bond length [1.892(2) A] is marginally longer than those in
A single-crystal X-ray diffraction analysis of an orange
tabular section excised under a polarising microscope from
a contact twinned crystal mass (grown from a concentrated
[D6]acetone solution at 300 K), confirmed the structure of
analogous Rh complexes with N-donor bidentate ligands
[9]
˚
[1.79(1)Ϫ1.868(7) A].
Hydroamination Catalysts
Cationic RhI complexes with chelating N-donor ligands
Ϫ
[Rh(cod)(mdd)]ϩBPh4 (2). An ORTEP[10,11] depiction of
the cation is shown in Figure 1 and selected bond lengths
and angles are listed in Table 1. The structure was modelled are known to catalyse intramolecular hydroamination of
as a pseudo-centrosymmetric structure, with P21/m sym- aminoalkynes,[4] amino alcohols and amino carboxylic ac-
metry broken by a lack of mirror symmetry in the cyclooc- ids.[14] At a catalyst loading of 1.5%, both complexes
3180
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184

Mononuclear Rhodium() Complexes with Chelating N-Heterocyclic Carbene Ligands
FULL PAPER
ϩ
Ϫ
Ϫ
Table 1. Selected bond lengths (A) and angles (°) for [Rh(cod)(mdd)] BPh4 (2) and [Rh(CO)2(mdd)]ϩPF6 (5)
˚
˚
Atoms
Bond lengths (A)
Atoms
Bond angles (°)
Ϫ
[Rh(cod)(mdd)]ϩBPh4
2
Rh(1)ϪC(9)
Rh(1)ϪC(5)
Rh(1)ϪC(6)
Rh(1)ϪC(1)
Rh(1)ϪC(2)
2.025(3)
2.171(6)
2.221(6)
2.243(7)
2.244(6)
C(9)ϪRh(1)ϪC(9*[a]
N(1)ϪC(9)ϪN(2)
)
83.19(19)
103.0(3)
Ϫ
[Rh(CO)2(mdd)]ϩPF6
5
Rh(1)ϪC(1)
Rh(1)ϪC(2)
O(1)ϪC(1)
1.8924(17)
2.0619(16)
1.1373(19)
C(1)ϪRh(1)ϪC(1*[b]
C(2)ϪRh(1)ϪC(2*[b]
N(1)ϪC(2)ϪN(2)
)
)
92.01(9)
83.48(8)
104.3(1)
[a]
[b]
x, 3/2 Ϫ y, z.
x, 1/2 Ϫ y, z.
Figure 2. An ORTEP[10,11] depiction of the cation of
Ϫ
[Rh(CO)2(mdd)]ϩPF6 5 showing 20% displacement ellipsoids.
Atoms labelled with an asterisk are generated from the unique sites
by x, 1/2 Ϫ y, z
Figure 3. Comparative reaction rates for the metal-catalysed cycli-
sation of 4-pentyn-1-amine to 2-methyl-1-pyrroline using
[Rh(CO)2(mdd)]ϩBPh4Ϫ (3) and [Rh(CO)2(mdd)]ϩPF6Ϫ (5)
catalyse the cyclisation of 4-pentyn-1-amine to 2-methyl-1-
pyrroline (76% and 85% conversion, respectively, in 16
hours at 60 °C in [D8]THF solution). Turnover rates[15] at
50% conversion of 6 hϪ1 and 10 hϪ1 were calculated for
complexes 3 and 5 respectively (Scheme 2). The reaction
rate for complex 3 was slower than that observed for the
analogous bisimidazolylmethane complex [Rh(bim)-
Ϫ
Ϫ
[Rh(CO)2(mdd)]ϩBPh4
3
(᭡), [Rh(CO)2(mdd)]ϩPF6
5 (᭿),
[Rh(bim)(CO)2]ϩPF6 6 (᭜), and [Rh(bim)(CO)2]ϩBPh4 1 (᭹);
catalyst loading 1.5% at 60 °C in [D8]THF solution
Ϫ
Ϫ
pentyn-1-amine to 2-methyl-1-pyrroline than the corre-
Ϫ
sponding BPh4 complex 3. The dependence of the turn-
over rate on the counterion has also been noted previously
with related catalysts and this could be the result of signifi-
cant ion pairing in solution.
Ϫ
(CO)2]ϩBPh4 (1) (Figure 3), where conversion was com-
plete after 12 hours (turnover rate 17 hϪ1). In contrast, the
reaction rate for complex 5 was significantly faster than that
Conclusions
Ϫ
observed for [Rh(bim)(CO)2]ϩPF6 (6) where the conver-
A synthetic route to mononuclear RhI complexes con-
taining the bidentate bis-carbene ligand 1,1Ј-methylene-
3,3Ј-dimethyldiimidazoline-2,2Ј-diylidene (mdd) has been
developed. The complexes are robust and two Rh com-
plexes containing the mdd ligand have been structurally
characterised. Both complexes show the presence of a boat-
like six-membered metallacycle containing two metal-car-
bon bonds. [Rh(mdd)(CO)2]ϩ is catalytically active for the
intramolecular cyclisation of aminoalkynes and the turn-
over rate is similar to [Rh(bim)(CO)2]ϩ and other related
catalysts for this conversion. Reaction conditions for this
conversion are as yet unoptimised and these results demon-
strate the future potential of rhodium carbenes in a range
of catalytic applications.
sion was only 49% complete after 16 hours (turnover rate 2
h
Ϫ1) at the same catalyst loading under the same reaction
Ϫ
conditions. Complex 6 is the PF6 analogue of 1. The syn-
thesis of 6 is analogous to that reported for the synthesis
of 1.[4]
In comparing the two carbene complexes, the PF6Ϫ com-
plex 5 has a higher turnover rate for the conversion of 4-
Scheme 2
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3181

S. Burling, L. D. Field, H. L. Li, B. A. Messerle, P. Turner
FULL PAPER
(NCH2), 37.2 (NCH3) ppm. 19F NMR ([D6]acetone, 282 MHz):
Experimental Section
1
δ ϭ Ϫ70.9 (d, JP,F ϭ 708 Hz) ppm. 31P NMR ([D6]acetone,
1
121 MHz): δ ϭ Ϫ146.4 (sep, JP,F ϭ 708 Hz). Note: Spectroscopic
All manipulations of metal complexes and air-sensitive reagents
were carried out using standard Schlenk or vacuum techniques or
in a Vacuum Atmospheres nitrogen-filled drybox. RhCl3·H2O was
purchased from Strem and used as received. [RhCl(cod)]2 was pre-
pared by the literature method.[16] 1,1Ј-Methylene-3,3Ј-dimethyldi-
imidazolium dibromide was synthesised by a modification of the
literature procedure for the analogous diiodide salt.[17] All bulk
compressed gases were obtained from BOC Gases. Nitrogen
(Ͼ 99.5%) and carbon monoxide (Ͼ 99.5%) were used as supplied
without further purification.
data (1H and 31P NMR) for this compound have been reported,[18]
although no microanalytical data were included.
Synthesis of [Rh(OEt)(cod)]2: [RhCl(cod)]2 (100 mg, 0.20 mmol) in
methanol (0.6 mL) was treated with NaOEt (0.44 mL of 1  meth-
anol solution, 0.44 mmol) under nitrogen. After stirring for 30 min,
the yellow suspension was filtered. The yellow solid obtained was
washed with methanol and dried. [Rh(cod)(OEt)]2 (102 mg, 98%)
was used directly without further purification.
Synthesis of [Rh(cod)(mdd)]؉ BPh4Ϫ (2): Sodium ethoxide (0.40 mL
of 1  methanol solution, 0.40 mmol) and 1,1Ј-methylene-3,3Ј-di-
methyldiimidazolium bis(tetraphenylborate) (290 mg, 0.36 mmol)
were added to a suspension of [Rh(cod)(OEt)]2 (92 mg, 0.18 mmol)
in methanol (1 mL). The reaction mixture was heated at reflux for
15 minutes and then stirred at room temperature overnight, during
which time the pale-yellow suspension changed to an orange sus-
pension. The resulting precipitate was filtered and washed with
methanol. (Cyclooctadiene)(1,1Ј-methylene-3,3Ј-dimethyldiimida-
zoline-2,2Ј-diylidene)rhodium() tetraphenylborate was recrystal-
lised from acetone as an orange crystalline solid (159 mg, 63%),
m.p. 188 °C (dec). C41H44BN4Rh (706.52): calcd. C 69.7, H 6.3, N
7.9; found C 69.5, H 6.5, N 8.0. 1H NMR ([D6]acetone, 400 MHz):
Tetrahydrofuran and diethyl ether were stored over sodium wire
and distilled under nitrogen from sodium benzophenone ketyl.
Methanol was distilled from magnesium methoxide under nitrogen.
Acetone was distilled from calcium sulfate under nitrogen. Deuter-
ated solvents for NMR purposes were obtained from Merck and
Cambridge Isotopes. Solvents were dried over suitable drying ag-
ents, degassed using three consecutive freeze-pump-thaw cycles and
vacuum distilled immediately prior to use.
Microanalyses were carried out at the Campbell Microanalytical
Laboratory, University of Otago, New Zealand. Electrospray mass
spectra were recorded on a Finnigan LCQ mass spectrometer. In-
fra-red spectra were obtained using a PerkinϪElmer 1600 Series
F.T.I.R. spectrometer as KBr discs.
3
δ ϭ 7.45 (d, JH,H ϭ 1.8 Hz, 2 H, NCH), 7.34 (m, 8 H, o-H), 7.15
3
3
(d, JH,H ϭ 1.8 Hz, 2 H, NCH), 6.92 (t, JH,H ϭ 7.3 Hz, 8 H, m-
3
2
NMR spectra were recorded on Bruker Avance DPX 300 or DRX
H), 6.77 (t, JH,H ϭ 7.3 Hz, 4 H, p-H), 6.59 (d, JH,H ϭ 13.0 Hz, 1
H, NCH2), 6.26 (d, JH,H ϭ 13.0 Hz, 1 H, NCH2), 5.05 [m, 2 H,
1
400 spectrometers at 300 K. H and 13C NMR chemical shifts (δ/
2
ppm) were referenced to internal solvent resonances. 31P NMR
chemical shifts were referenced to external neat trimethyl phos-
phite, taken to be at δ ϭ 140.85 ppm. 19F NMR chemical shifts
were externally referenced to neat hexafluorobenzene, taken to be
at δ ϭ Ϫ163 ppm.
CH(cod)], 4.87 [m, 2 H, CH(cod)], 3.84 (s, 6 H, NCH3), 2.54 [m, 2
H, CH2(cod)], 2.4Ϫ2.1 [m, 6 H, CH2(cod)] ppm. 13C{1H} NMR
1
([D6]acetone, 101 MHz): δ ϭ 181.1 (d, JRh,C ϭ 52.7 Hz, NCN),
1
164.9 (q, JC,B ϭ 49.6 Hz, ipso-C), 137.0 (o-C), 126.0 (m-C), 123.4
1
(NCH), 122.3 (p-C), 121.8 (NCH), 92.0 [d, JRh,C ϭ 7.8 Hz,
1
CH(cod)], 87.8 [d, JRh,C ϭ 7.8 Hz, CH(cod)], 64.1 (NCH2), 38.0
Synthesis of [mddH2]2؉ 2BPh4Ϫ: Sodium tetraphenylborate (2.0 g,
5.9 mmol) was added to a solution of 1,1Ј-methylene-3,3Ј-dimethyl-
diimidazolium dibromide (1.0 g, 3.0 mmol) in water (20 mL). The
white precipitate formed was isolated by filtration and dried in va-
cuo overnight. 1,1Ј-Methylene-3,3Ј-dimethyldiimidazolium bis-
(tetraphenylborate) was recrystallised from acetone/diethyl ether as
a white solid (1.4 g, 58%), m.p. 218 °C (dec). C57H54B2N4 (816.69):
(NCH3), 31.2 [CH2(cod)], 31.0 [CH2(cod)] ppm. MS (ESϩ,
CH3CN): m/z (%)
ϭ
387 (45) [Rh(cod)(mdd)]ϩ, 361 (25)
[Rh(mdd)(CH3CN)2]ϩ, 320 (100) [Rh(mdd)(CH3CN)]ϩ, 279 (35)
[Rh(mdd)]ϩ.
Ϫ
Synthesis of [Rh(CO)2(mdd)]؉ BPh4 (3): [Rh(cod)(mdd)]ϩBPh4
Ϫ
(2; 50 mg, 71 µmol) was suspended in methanol (1 mL). The mix-
ture was degassed using three freeze-pump-thaw cycles, flushed
1
calcd. C 83.8, H 6.7, N 6.9; found C 83.7, H 6.8, N 6.9. H NMR
([D6]acetone, 400 MHz): δ ϭ 8.75 (s, 2 H, NCHN), 7.75 (d, 3JH,H ϭ with carbon monoxide gas and stirred at room temperature over-
3
1.6 Hz, 2 H, NCH), 7.53 (d, JH,H ϭ 1.6 Hz, 2 H, NCH), 7.48 (m,
night, during which time the orange suspension became a yellow
suspension. The precipitate was isolated by filtration and washed
3
3
16 H, o-H), 6.93 (t, JH,H ϭ 7.3 Hz, 16 H, m-H), 6.77 (t, JH,H
ϭ
7.3 Hz, 8 H, p-H), 6.50 (s, 2 H, NCH2), 3.81 (s, 6 H, NCH3) ppm. with diethyl ether producing dicarbonyl(1,1Ј-methylene-3,3Ј-di-
1
13C{1H} NMR ([D6]acetone, 101 MHz): δ ϭ 164.9 (q, JC,B
ϭ
methyldiimidazoline-2,2Ј-diylidene)rhodium() tetraphenylborate
as a yellow solid (41 mg, 88%), m.p. 170 °C (dec). C35H32BN4O2Rh
49.3 Hz, ipso-C), 138.4 (NCHN), 136.9 (o-C), 126.1 (m-C), 126.0
(NCH), 122.9 (NCH), 122.3 (p-C), 59.8 (NCH2), 37.1 (NCH3) (654.36): calcd. C 64.2, H 4.9, N 8.6; found C 64.2, H 4.7, N 8.7.
3
ppm.
1H NMR ([D6]acetone, 400 MHz): δ ϭ 7.56 (d, JH,H ϭ 1.8 Hz, 2
3
H, NCH), 7.35 (m, 9 H, NCH and o-H), 6.91 (t, JH,H ϭ 7.3 Hz,
Synthesis of [mddH2]2؉ 2PF6Ϫ: A solution of 1,1Ј-methylene-3,3Ј-
dimethyldiimidazolium dibromide (2.6 g, 7.7 mmol) in water
(15 mL) was added to a solution of potassium hexafluorophos-
phate (2.9 g, 15 mmol) in water (50 mL). The precipitate was iso-
lated by filtration, washed with diethyl ether and dried in vacuo
overnight to give 1,1Ј-methylene-3,3Ј-dimethyldiimidazolium bis-
(hexafluorophosphate) as a white solid (2.8 g, 77%), m.p. 200 °C.
C9H14F12N4P2 (468.24): calcd. C 23.1, H 3.0, N 12.0; found C 23.1,
H 3.2, N 11.7. 1H NMR ([D6]acetone, 300 MHz): δ ϭ 9.37 (s, 2 H,
NCHN), 8.05 (s, 2 H, NCH), 7.84 (s, 2 H, NCH), 7.02 (s, 2 H,
NCH2), 4.10 (s, 6 H, NCH3) ppm. 13C{1H} NMR ([D6]acetone,
8 H, m-H), 6.77 (t, 3JH,H ϭ 7.3 Hz, 4 H, p-H), 6.21 (s, 2 H, NCH2),
3.93 (s, 6 H, NCH3) ppm. 13C{1H} NMR ([D6]acetone, 101 MHz):
1
1
δ ϭ 189.0 (d, JRh,C ϭ 57.0 Hz, CO), 173.6 (d, JRh,C ϭ 45.2 Hz,
1
NCN), 164.9 (q, JC,B ϭ 49.3 Hz, ipso-C), 137.0 (o-C), 126.0 (m-
C), 124.1 (NCH), 123.2 (NCH), 122.2 (p-C), 63.8 (NCH2), 38.9
(NCH3) ppm. MS (ESϩ, CH3CN): m/z (%)
ϭ 361 (18)
[Rh(mdd)(CH3CN)2]ϩ, 335 (26) [Rh(CO)2(mdd)]ϩ, 320 (100)
[Rh(mdd)(CH3CN)]ϩ, 279 (53) [Rh(mdd)]ϩ. IR: ν˜ ϭ 2071s (νCO),
2014s (νCO) cmϪ1
.
Ϫ
Synthesis of [Rh(cod)(mdd)]؉ PF6 (4): Sodium ethoxide (0.45 mL
75 MHz): δ ϭ 139.1 (NCHN), 126.0 (NCH), 123.2 (NCH), 60.1 of 1  methanol solution, 0.45 mmol) and 1,1Ј-methylene-3,3Ј-
3182  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184

Mononuclear Rhodium() Complexes with Chelating N-Heterocyclic Carbene Ligands
FULL PAPER
dimethyldiimidazolium
0.40 mmol) were added to
(100 mg, 0.20 mmol) in methanol (1 mL). The reaction mixture was (d, 1JRh,C ϭ 56.6 Hz, CO), 173.6 (d, 1JRh,C ϭ 45.4 Hz, NCN), 124.1
bis(hexafluorophosphate)
(190 mg,
3JH,H ϭ 1.8 Hz, 2 H, CH3NCH), 6.41 (s, 2 H, NCH2), 4.01 (s, 6
a
suspension of [Rh(OEt)(cod)]2 H, NCH3) ppm. 13C{1H} NMR ([D6]acetone, 101 MHz): δ ϭ 189.0
stirred at room temperature for three days, during which time the
yellow suspension became an orange suspension. The resulting pre-
cipitate was filtered and washed with methanol. (Cyclo-
octadiene)(1,1Ј-methylene-3,3Ј-dimethyldiimidazoline-2,2Ј-
diylidene)rhodium() hexafluorophosphate was recrystallised from
acetone as an orange-red crystalline solid (142 mg, 67%), m.p. 203
°C (dec). C17H24F6N4PRh (532.28): calcd. C 38.4, H 4.5, N 10.5;
found C 38.5, H 4.8, N 10.4. 1H NMR ([D6]acetone, 300 MHz):
(CH3NCH), 123.3 (CH2NCH), 63.9 (NCH2), 38.9 (NCH3) ppm.
1
19F NMR ([D6]acetone, 282 MHz): δ ϭ Ϫ67.7 (d, JP,F ϭ 710 Hz)
1
ppm. 31P NMR ([D6]acetone, 121 MHz): δ ϭ Ϫ143.1 (sep, JP,F
ϭ
710 Hz) ppm. MS (ESϩ, MeOH): m/z (%)
[Rh(CO)2(mdd)]ϩ. MS (ES-, MeOH): m/z (%) ϭ 145 (100) [PF6Ϫ].
IR: ν˜ ϭ 2076s (νCO), 2017s (νCO) cmϪ1
ϭ 335 (100)
.
Synthesis of [Rh(bim)(CO)2]؉PF6Ϫ (6): A solution of bis(N-methyl-
imidazol-2-yl)methane (80 mg, 0.45 mmol) in methanol (5 mL) was
added to a solution of [RhCl(CO)2]2 (88 mg, 0.22 mmol) in meth-
anol (15 mL) at room temperature. The yellow precipitate that
formed initially dissolved after the addition of the ligand was com-
plete. The mixture was stirred for 30 minutes before adding an ex-
cess of potassium hexafluorophosphate (400 mg) in methanol
(10 mL). The resulting precipitate was filtered and washed with
methanol. [Bis(N-methylimidazol-2-yl)methane)dicarbonylrhodi-
um() hexafluorophosphate was recrystallised from acetone as a
dark pink solid (191 mg, 90%), m.p. 262 °C (dec).
C11H12F6N4O2PRh (480.12): calcd. C 27.5, H 2.5, N 11.7; found
3
3
δ ϭ 7.50 (d, JH,H ϭ 1.9 Hz, 2 H, CH2NCH), 7.17 (d, JH,H
ϭ
2
1.9 Hz, 2 H, CH3NCH), 6.61 (d, JH,H ϭ 13.0 Hz, 1 H, NCH2),
2
6.31 (d, JH,H ϭ 13.0 Hz, 1 H, NCH2), 5.05 [m, 2 H, CH(cod)],
4.88 [m, 2 H, CH(cod)], 3.86 (s, 6 H, NCH3), 2.54 [m, 2 H,
CH2(cod)], 2.27 [m, 4 H, CH2(cod)], 2.08 [m, 2 H, CH2(cod)] ppm.
1
13C{1H} NMR ([D6]acetone, 75 MHz): δ ϭ 181.1 (d, JRh,C
ϭ
52.2 Hz, NCN), 123.4 (CH3NCH), 121.9 (CH2NCH), 92.0 [d,
1
1JRh,C ϭ 8.6 Hz, CH(cod)], 87.8 [d, JRh,C ϭ 7.8 Hz, CH(cod)],
64.1 (NCH2), 38.0 (NCH3), 31.2 [CH2(cod)], 31.0 [CH2(cod)] ppm.
1
19F NMR ([D6]acetone, 282 MHz): δ ϭ Ϫ71.0 (d, JP,F ϭ 708 Hz)
1
ppm. 31P NMR ([D6]acetone, 121 MHz): δ ϭ Ϫ146.3 (sep, JP,F
ϭ
1
C 27.6, H 2.2, N 11.4. H NMR ([D6]acetone, 400 MHz): δ ϭ 7.55
708 Hz) ppm. MS (ESϩ, MeOH): m/z (%)
ϭ 387 (10)
3
(d, JH5,H4 ϭ 1.4 Hz, 2 H, H5), 7.42 (d, 2 H, H4), 4.63 (s, 2 H,
[Rh(cod)(mdd)]ϩ, 311 (100) [Rh(mdd)(MeOH)]ϩ, 279 (15)
CH2), 3.97 (s, 6 H, NCH3) ppm. 13C{1H} NMR ([D6]acetone,
[Rh(mdd)]ϩ ppm. MS (ES-, MeOH): m/z (%) ϭ 145 (100) [PF6Ϫ].
1
101 MHz): δ ϭ 185.3 (d, JRh,C ϭ 68.2 Hz, CO), 143.9 (C2), 130.9
(C5), 124.3 (C4), 34.8 (NCH3), 24.4 (CH2) ppm. 19F NMR ([D6]a-
Ϫ
Ϫ
Synthesis of [Rh(CO)2(mdd)]؉PF6 (5): [Rh(cod)(mdd)]ϩPF6 (4;
70 mg, 0.13 mmol) was suspended in diethyl ether (1 mL) and
methanol (1 mL). The suspension was degassed using three freeze-
pump-thaw cycles, flushed with carbon monoxide gas and stirred
at room temperature for 3 days, during which time the orange sus-
pension became a yellow suspension. The precipitate was isolated
by filtration and washed with diethyl ether producing dicar-
bonyl(1,1Ј-methylene-3,3Ј-dimethyldiimidazoline-2,2Ј-diylidene)-
rhodium() hexafluorophosphate as a yellow solid (29 mg, 46%),
1
cetone, 376 MHz): δ ϭ Ϫ67.5 (d, JP,F ϭ 708 Hz) ppm. 31P{1H}
1
NMR ([D6]acetone, 162 MHz): δ ϭ Ϫ135 (sep, JP,F ϭ 708 Hz)
ppm. MS (ESϩ, THF): m/z (%) ϭ 335 (100) [Rh(bim)(CO)2]ϩ. IR:
ν˜ ϭ 2084s (νCO), 2026s (νCO) cmϪ1
.
X-ray Crystallography
Low-temperature single-crystal diffraction data were collected with
a Bruker SMART 1000 diffractometer using graphite monochrom-
˚
m.p. 200 °C (dec). C11H12F6N4O2PRh (480.13): calcd. C 27.5, H
ated Mo-Kα radiation (λ ϭ 0.71073 A) from a sealed tube. Crystal-
1
2.5, N 11.7; found C 27.7, H 2.8, N 11.6. H NMR ([D6]acetone, lographic details are given in Table 2. Data integration and re-
3
400 MHz): δ ϭ 7.68 (d, JH,H ϭ 1.8 Hz, 2 H, CH2NCH), 7.46 (d,
duction were undertaken with SAINT and XPREP[19] and sub-
Ϫ
Ϫ
Table 2. Crystallographic data for [Rh(cod)(mdd)]ϩBPh4 (2) and [Rh(CO)2(mdd)]ϩPF6 (5)
2
5
Empirical formula
Molecular weight (g molϪ1
Crystal system
C41H44BN4Rh
706.52
C11H12F6N4O2PRh
480.13
Orthorhombic
Pnma (no. 62)
12.416(4)
12.790(4)
10.408(3)
)
Monoclinic
P21/m (no. 11)
10.457(3)
13.108(4)
12.295(4)
95.731(5)
1676.9(9)
2
Space group
˚
a (A)
˚
b (A)
˚
c (A)
β (°)
3
˚
V (A )
Z
1652.7(9)
4
T (K)
150(2)
0.546
100(2)
1.207
µ Mo-Kα (mmϪ1
)
Crystal Size (mm)
T(Gaussian)min,max
2θmax (°)
0.233 ϫ 0.154 ϫ 0.071
0.902, 0.962
56.50
Ϫ13 13, Ϫ17 16, Ϫ16 16
14318
0.324 ϫ 0.121 ϫ 0.120
0.820, 0.946
56.60
Ϫ16 16, Ϫ17 17, Ϫ13 13
16349
hkl range
N
Nind
4005 (Rmerge 0.0310)
3444
1.499
0.0492
0.1325
2079 (Rmerge 0.0321)
1888
1.316
0.0189
0.0549
Nobs [I Ͼ 2σ(I)]
Goodness of fit (all data)
R1 [F, I Ͼ 2σ(I)]
wR2 (F2, all data)
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3183

S. Burling, L. D. Field, H. L. Li, B. A. Messerle, P. Turner
FULL PAPER
[3]
[4]
[5]
[6]
[7]
sequent computations were carried out with the teXsan[20] and
WinGX[21] graphical user interfaces. A Gaussian absorption correc-
tion was applied to the data.[19,22] The structures were solved by
direct methods with SIR97[23] and extended and refined with
SHELXL-97.[24] In general the non-hydrogen atoms were modelled
with anisotropic displacement parameters, and a riding-atom
model with group displacement parameters was used for the hydro-
gen atoms. The crystal structure of complex 2 was modelled as a
disordered (pseudo)centrosymmetric structure in P21/m (no. 11).
An alternative model in P21 (no. 4) had significantly higher re-
siduals at convergence [R1(F) ϭ 0.0591 and wR2(F2) ϭ 0.1656],
and high levels of correlation requiring extensive geometry and dis-
placement restraints. The Flack parameter[25] in P21 refined to
0.49(8) suggesting either an inversion twin or a centrosymmetric
structure. The disordered centrosymmetric model was adopted as
the better model for the crystal structure. The asymmetric unit in
P21/m contains a complex molecule bisected by a (pseudo) mirror
plane, with the metal ion and C(12) atoms located in that plane. A
tetraphenylborate counterion also resides on a mirror plane, with
the B(1), C(14), C(15), C(16), C(17), C(18), C(19), C(20) and C(23)
atoms located in the mirror plane. Two of the phenyl residues of
the counterion have orientational disorder about the boron to qua-
ternary carbon axis. The P21/m symmetry is broken by a lack of
mirror symmetry in the cyclooctadiene ligand, which is disordered
about the mirror plane. The fully occupied non-hydrogen sites were
modelled with anisotropic displacement parameters, and isotropic
displacement parameters were used for the partially occupied non-
hydrogen sites and for the fully occupied boron site. The site occu-
pancies were refined, and then fixed and rounded to the first deci-
mal place.
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data integration and reduction software; Bruker Analytical X-
ray Instruments Inc.: Madison, Wisconsin, USA, 2001.
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[20]
CCDC-186563 (2) and -186564 (5) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
[21]
[22]
bridge CD2 1EZ, UK; Fax: (internat.)
E-mail: deposit@ccdc.cam.ac.uk].
ϩ 44-1233/336-033;
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Acknowledgments
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We thank the Australian Research Council for financial support.
[25b]
G. Bernardinelli, H. D. Flack, Acta Crystallogr., Sect. A
[25c]
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Received March 20, 2003
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[2]
3184
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3179Ϫ3184