Stable crystalline annulated diaminocarbenes: Coordination with rhodium(i), iridium(i) and catalytic hydroformylation studies

Article abstract of DOI:10.1039/b905729c

Stable annulated diaminocarbene ligands 7,9-bis(2,4,6-trimethylphenyl)-6b, 9a-dihydroace naphtha[1,2-d]imidazolin-2-ylidene and 7,9-bis(2,6- diisopropylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolin-2-ylidene; designated as (BIAN-SIMes, 5a,) and (BIAN-SIPr, 5b), respectively, have been prepared. The base dependent decomposition of imidazolinium salts via ring opening at the backbone was also observed. The corresponding rhodium(i) and iridum(i) complexes (η⁴-1,5-COD)M(BIAN-SIMes)Cl and (η⁴-1,5-COD)M(BIAN-SIPr)Cl; M= Rh (6a, 6b) and Ir (7a, 7b) have been synthesised by the reaction of free carbene with [M(η⁴-1,5- COD)(μ-Cl)]₂; where M= Rh, Ir. The cationic Ir(i) complexes [(η⁴-1,5-COD)Ir(BIAN-SIMes)Py]BF₄8a and [(η⁴-1,5-COD)Ir(BIAN -SIPr)Py]PF₆8b have also been synthesised. Compounds 4b, 5a, 6a, 6b, 7b and 8b have been structurally characterised. The catalytic activities for the rhodium(i) complexes 6a and 6b were evaluated for the hydroformylation of 1-octene.

Full text of DOI:10.1039/b905729c

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N-Heterocyclic Carbenes
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www.rsc.org/dalton | Dalton Transactions
Stable crystalline annulated diaminocarbenes: coordination with rhodium(I),
iridium(I) and catalytic hydroformylation studies†
Sarim Dastgir,*‡a Karl S. Coleman,b Andrew R. Cowleya and Malcolm L. H. Green*a
Received 30th March 2009, Accepted 26th June 2009
First published as an Advance Article on the web 23rd July 2009
DOI: 10.1039/b905729c
Stable annulated diaminocarbene ligands 7,9-bis(2,4,6-trimethylphenyl)-6b,9a-dihydroace
naphtha[1,2-d]imidazolin-2-ylidene and 7,9-bis(2,6-diisopropylphenyl)-6b,9a-dihydroacenaphtho-
[1,2-d]imidazolin-2-ylidene; designated as (BIAN-SIMes, 5a,) and (BIAN-SIPr, 5b), respectively, have
been prepared. The base dependent decomposition of imidazolinium salts via ring opening at the
4
backbone was also observed. The corresponding rhodium(I) and iridum(I) complexes (h -1,5-COD)-
4
M(BIAN-SIMes)Cl and (h -1,5-COD)M(BIAN-SIPr)Cl; M= Rh (6a, 6b) and Ir (7a, 7b) have been
4
synthesised by the reaction of free carbene with [M(h -1,5-COD)(m-Cl)]2; where M= Rh, Ir. The
4
4
cationic Ir(I) complexes [(h -1,5-COD)Ir(BIAN-SIMes)Py]BF4 8a and [(h -1,5-COD)Ir(BIAN
-SIPr)Py]PF6 8b have also been synthesised. Compounds 4b, 5a, 6a, 6b, 7b and 8b have been
structurally characterised. The catalytic activities for the rhodium(I) complexes 6a and 6b were
evaluated for the hydroformylation of 1-octene.
a change in the substituent (p-donor/acceptor) attached to the
Introduction
imidazole ring.16
The pioneering work on the coordination chemistry of N-
heterocyclic carbenes (NHCs) was independently reported by
Wanzlick et al.1 in 1968 and Ofele et al. in 1970 but it was
We have continued our interest in the organometallic chemistry
of N-heterocyclic carbenes,17–21 and now we report the synthesis
of the first two members of a bulky acenaphthylene-annulated
backbone substituted imidazolin-2-yilidene ligand D (Fig. 1).
Such ligand modification on monodentate imidazolin-2-yilidene
systems could alter the coordination behaviour of these ligands by
their greater steric bulk away from the coordination site, which may
provide the opportunity for small molecule activation and catalyst
fine tuning since a slight change in the steric properties can play a
very significant role. During the course of our investigation some
annulated N-heterocyclic carbene ligands were reported,12–14,22,23
but their attempted synthesis to deprotonate the imidazolinium
salts failed to generate the N-heterocyclic carbene cleanly.22,23
2
¨
almost two decades later when the first stable imidazole-2-ylidene
(NHC) was successfully isolated by Arduengo et al. in 1991.3 Since
this significant breakthrough, the chemistry of NHCs have put
this valuable class of potent ligands at the forefront of current
research. In general, NHCs have been considered as strong Lewis
bases and weak p-acceptors, consequently making their complexes
more stable towards degradative cleavage.4,5 However, it is worth
mentioning that the extent of p-back bonding abilities in NHCs
have been revised extensively in recent literatures.4–8 Unlike phos-
phines for which the wide spectrum of compounds with tuneable
sterics and electronics are known,9 the tunability in NHCs is more
restricted due to their confined architectures. Although a broad
range of architectures containing annulated NHCs have been
synthesised, these modifications are limited to the unsaturated
carbenes, presumably due to the more ubiquitous dimerisation
for saturated carbenes to produce enetetramines.10–14 Studies on
the annulated backbone substituted NHCs11–15 have demonstrated
that the s-donating ability of NHCs varies substantially with
Fig. 1 Examples of N-heterocyclic carbene compounds.
aInorganic Chemistry Laboratory, University of Oxford, South Parks Road,
Oxford, UK OX1 3QR. E-mail: malcolm.green@chem.ox.ac.uk, sarim.
dastgir@lmh.oxon.org; Fax: +44 (0)1865 272690; Tel: +44 (0)1865
272600
Results and discussion
bDepartment of Chemistry, University of Durham, South Road, Durham,
UK DH1 3LE
Synthesis and characterization of the imidazolinium salts
[(BIAN-SIMes)(H)]BF4 (3a) and [(BIAN-SIPr)(H)]BF4 (3b)
† Electronic supplementary information (ESI) available: Experimental
details. CCDC reference numbers 719732 (4b), 719731 (5a), 719730 (6b)
719729 (6a), 719728 (7b), 719727 (8b). For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/b905729c
‡ Present address: Department of Chemistry, York University, 4700 Keele
Street, Toronto, ON, Canada M3J 2Z3. Tel: +1 416 736 2100 Ext. 77720;
Fax: +1 416 736 5936
The imidazolium salts 3a and 3b were synthesised in good yields
(60–75%) from Ar-BIAN;24,25 where Ar = 2,4,6-trimethylphenyl
3a and 2,6-diisopropylphenyl 3b, by reduction with LiAlH4
followed by cyclisation with triethylorthoformate in the presence
of NH4BF4 and an acid catalyst. (Scheme 1) The detailed synthetic
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7203–7214 | 7203
©

ring opening at the backbone was observed with the formation of
corresponding amines; [N-(acenaphthylene-1-yl)-N-N-bis(2,4,6-
trimethylphenyl)formamidine,4a] and [N-(acenaph-thylene-1-yl)-
N-N-bis(2,6-diiso-propylphenyl)formamidine, 4b] in high yields
(>80%). (Scheme 2) After optimizing the conditions, the depro-
tonation of the imidazolium salt 3a was successfully achieved by
◦
KOtBu in THF at -78 C for 30 min. The reaction mixture was
then warmed to room temperature and stirred for one hour. After
work-up, the diaminocarbene 5a was isolated as an off-white solid
in 79% yield. Whereas the diaminocarbene BIAN-SIPr 5b was
synthesised by the careful de◦protonation of imidazolium salt 3b
with nBuLi in pentane at -78 C for 10 min. The reaction mixture
was warmed to room temperature and stirred for 2 h. After work-
up, the diaminocarbene 5b was obtained as an off-white solid
(90% yield). (Scheme 2) The isolated diaminocarbenes BIAN-
SIMes 5a and BIAN-SIPr 5b appeared to be stable under nitrogen
both in solution and in solid state. The diaminocarbene BIAN-
SIMes 5a and the decomposition product; formamidine 4b were
characterised by X-ray diffraction. The detailed synthetic protocol
is provided in the Experimental.
Scheme 1 Synthesis of imidazolinium salts.
protocol of their synthesis, crystal structures and corresponding
palladium(II) complexes is published elsewhere.26
1
The H NMR spectrum of carbene 5a shows a set of three
distinctive signals for the mesityl CH3 protons at d 1.74, 2.21 and
2.41 ppm, respectively, while the H NMR spectrum of carbene
5b shows two set of two doublets at d 0.53, 0.87, 1.06 and
Synthesis and characterization of diaminocarbenes BIAN-SIMes
(5a) and BIAN-SIPr (5b)
1
1.14 ppm, respectively. This may be attributed to the hindered
The solvent, as well as the base, play a vital role in the clean
deprotonation of imidazolium salts. The choice of an appropriate
solvent and the corresponding base for the synthesis of NHCs
may be restricted due to the insolubility of the imidazolium
salts and/or the decomposition of NHCs once it has been
generated.27 It is also noteworthy that a slight change to the
imidazolium architecture has a dramatic effect on the deproto-
nation behaviour. (Scheme 2) Our initial attempts to generate
the free carbenes BIAN-SIMes, 5a and BIAN-SIPr, 5b under
standard conditions with KN(SiMe3)2, KOtBu and potassium
pentalate in THF at -78 ◦C failed but instead an unexpected
1
rotation around N-aryl bond in the imidazole ring. In the 13C{ H}
NMR (C6D6) spectrum a weak downfield carbene resonances
(–NC(carbene)N–) at d 247.3 (5a) and d 241.9 (5b) ppm were observed
and found to be in a good comparison with the chemical shift
values reported for Arduengo’s cyclic diaminocarbene SIMes
(d 243.8 ppm) and SIPr (d 244.0 ppm).28 The lower population
of the carbene pp-orbital in the cyclic diamino carbene 5a and
5b results in downfield chemical shifts (approximately 24 ppm
1
downfield on average) in 13C{ H} NMR, when compared with
the corresponding values observed for Arduengo’s unsaturated
carbene IMes (d 219.5 ppm) and IPr (d 220.6 ppm).29–33 As
expected no significant change in the chemical shift values for
the backbone (–NCCN–) carbons was observed for 5a and 5b
when compared with imidazolinium ion 3a and 3b.26 Full 1H and
13C NMR assignments for carbenes 3a and 3b are given in the
Experimental.
Structural study
Single crystals of the BIAN-SIMes 5a (Fig. 2) suitable for
X-ray diffraction study were grown from a saturated solution of
benzene at room temperature. An ORTEP view of the molecule 5a
is depicted in Fig. 2. The structure was solved in the space group
C2/c using the direct-methods program SIR92,34 which located
all non-hydrogen atoms. Subsequent full-matrix least-squares
refinement was carried out using the CRYSTALS program suite.35
Coordinates and anisotropic thermal parameters of all non-
hydrogen atoms were refined. Hydrogen atoms were positioned
geometrically after each cycle of refinement. A 3-term Chebychev
polynomial weighting scheme was applied. Refinement converged
satisfactorily to give R = 0.0482, wR = 0.0584. The X-ray
structural analysis reveals that the unit cell contains one molecule
of diaminocarbene 5b located on a site with no crystallographic
symmetry, but having an approximate local mirror plane with
Scheme 2 Synthesis of N-heterocyclic carbene (base/reaction solvent,
temperature); (i) KOtBu/THF, -78 ◦C (3a); (ii) nBuLi/pentane, -78 ◦C
(3b); (iii) KOtBu/THF, -78 ◦C (3b); (iv) KN(SiMe3)2]/THF, -78 ◦C
(3a and 3b); (v) potassium pentalate/THF, -78 ◦C (3a and 3b); (vi)
nBuLi/THF, -78 ◦C (3b).
7204 | Dalton Trans., 2009, 7203–7214
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The Royal Society of Chemistry 2009
©

˚
but of the same order as that observed for 3a (1.495 A) and are
consistent with the single bond character between these bonds.
˚
˚
The longer 0.0526 A (5.26 pm) C2–C3 bond in 5a (1.558 A)
when compared with Arduengo’s cyclic diaminocarbene28 (SIMes)
˚
(1.505 A) is due to the presence of bulky naphthyl group at
the backbone C2–C3. The average N1(2)–C2(3)–C3(2) bond angle of
101.47◦ is shorter than the one observed for 3a (102.42◦) is
consistent with the loss of p-delocalization over nitrogen atoms
bound to carbene carbon in carbene 5a. The N1–C2–C3–N2 torsion
angle is 1.29◦ wider relative to 3a is also an indicative of the
loss of p-delocalization over the N–C–N bonds and consistent
with the carbene formation. The angle between the best planes of
the dihydroimidazole ring and the naphthyl group is 60.93◦. The
angle between the best planes of the dihydroimdazole ring and the
phenyl rings C15–C14–C19 and C24–C23–C28 are 78.22◦ and 63.22◦,
respectively, and consistent with loss of p-delocalization due the
carbene formation. The remaining bond lengths and angles are
unexceptional and lie within the range expected. Complete details
of the single-crystal X-ray analysis are given in the ESI.†
Crystals of the N-(acenaphthylene-1-yl)-N-N-bis(2,6-diisopro-
pylphenyl)formamidine, 4b (Fig. 3) suitable for X-ray diffraction
study were grown from a saturated solution of diethyl ether at
-78 ◦C. An ORTEP view of the molecule 4b is depicted in Fig. 3.
Crystallographically interesting structures of molecule 4b shows
the presence of two conformers with respect to rotation about
the tertiary nitrogen atom and the imine carbon atom. In both
conformers the atoms of the acenaphthylene, amine nitrogen
atoms and imine groups are all approximately co-planar with the
two isopropyl groups approximately perpendicular to these planes.
Details of the single-crystal X-ray analysis are given in the ESI.†
Fig. 2 ORTEP diagram of the molecular structure of the BIAN-SIMes 5a
at 40% probability (solvent molecule C6H6 have been omitted for clarity).
the solvent molecule on a crystallographic two-fold axis. A
comparison of selected bond length and angles for imidazolinium
ion 3a and diaminocarbene 5a along with the related structural
parameters for 1,3-dimesitylimidazolinium chloride28 and 1,3-
dimesitylimidazolin-2-ylidene28 are given in Table 1.
More interestingly, the N1–C1–N2 angle at the carbene centre
(106.09◦)◦is 1.4◦ larger than Ardu◦engo’s cyclic diamino carbene
(104.7(3) )28 and approximately 7.7 shorter relative to imidazolin-
ium ion 3a (113.8(3)◦). The average C1–N1 and C1–N2 bond length
˚
˚
(1.347 A) observed for 5a is increased by 0.0328 A (3.28 pm) from
˚
the average value of 1.314 A observed for 3a but of the same
order as that observed for Arduengo’s cyclic diamino carbene
28
˚
(1.349 A). This increase in the bond length is due to the loss of
p-delocalization over the N1–C1–N2 bonds and also an indicative
of carbene formation. This increase in bond lengths for average
C1–N1 and C1–N2 bonds is also consistent with the Arduengo’s
Synthesis and characterization of rhodium(I) complexes
4
˚
cyclic diaminocarbene, where an increase of 0.03 A (3.0 pm) was
The rhodium(I) complexes (h -1,5-COD)Rh(BIAN-SIMes)Cl 6a
4
observed.28 The average N1(2)–C2(3) bond length observed for 5a
and (h -1,5-COD)Rh(BIAN-SIPr)Cl 6b were synthesised by the
4
˚
˚
(1.493 A) is 0.012 A (1.2 pm) is significantly larger than the
reaction of the free carbenes with [Rh(h -1,5-COD)(m-Cl)]2 in
28
˚
corresponding bond lengths (1.481 A) observed for the SIMes
toluene at -78 ◦C. (Scheme 3) After work-up, the rhodium(I)
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) in carbenium ion 3a and diaminocarbene 5a
Property
[(BIAN-SIMes)(H)]BF4 3aa
BIAN-SIMes 5a
[(SIMes)(H)]Clb
SIMesc
˚
Bond lengths/A
C1–N1(2)
N1(2)–C2(3)
C2–C3
1.315(4), 1.313(4)
1.496(4), 1.494(4)
1.560(4)
1.348(2), 1.346(2)
1.491(2), 1.496(2)
1.558(2)
1.327(5), 1.310(5)
1.498(6), 1.487(6)
1.518(7)
1.352(5), 1.345(5)
1.475(5), 1.487(5)
1.505(6)
N1(2)–Cmes
1.442(4), 1.442(4)
1.434(2), 1.435(2)
1.432(5), 1.437(6)
1.427(5), 1.437(5)
Bond angles (q)/◦
N1–C1–N2
C1–N1(2)–C2(3)
113.8(3)
106.09(14)
113.1(4)
104.7(3)
110.7(2), 110.7(2)
102.3(2), 102.5(2)
126.9(2), 121.2(2)
113.2(2), 112.5(2)
115.51(14),115.37(14)
101.51(13),101.43(13)
124.01(14), 123.18(14)
113.97(14)114.30(14)
109.7(4), 110.6(4)
103.0(4), 103.3(4)
127.0(4), 126.2(4)
—
115.0(3), 114.6(3)
101.6(4), 101.9(4)
122.9 (3), 122.5(3)
—
N
1(2)–C2(3)–C3(2)
C1–N1(2)–Cmes
N1(2)–C2(3)–C4(8)
Torsion angle/◦
N1–C2–C3–N2
0.68
1.97
—
—
a Ref. 36. b Ref. 37. c Ref. 28.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7203–7214 | 7205
©

Fig. 3 ORTEP diagram of the two crystallographically distinct molecules of amine 4b at 40% probability (hydrogen atoms have been omitted for clarity).
for complex 6a and at d 3.35 (2H) and d 4.59 (2H) ppm for
1
complex 6b. In the 13C{ H} NMR spectrum of 6a the signal for
the C(carbene) is upfield at d 213.3 ppm (JRh–C = 46.2 Hz) relative to
the free diaminocarbene 5a which appears at d 247.3 ppm and
4
consistent with data reported for (h -1,5-COD)Rh(SIMes)Cl38
(d 212.0, JRh–C = 48.1 Hz). No signal for the C(carbene) in rhodium
complex 6b was observed and may be attributed to a slight
fluxional behaviour of the molecule in solution as evidenced by
1
the broader peaks in the H NMR spectrum. The COD CCH for
rhodium complex 6a appears as doublets at d 67.7 (JRh–C = 14.6 Hz,
trans to chlorine) and d 95.9 (JRh–C = 7.4 Hz, trans to carbene) while
the corresponding resonances for rhodium complex 6b appear as
broad singlets at d 69.6 and d 94.9 ppm and further confirms
the fluxional nature of the molecule. These chemical shifts for the
4
COD CCH are also consistent with the reported data for (h -1,5-
4
COD)Rh(SIMes)Cl38 and (h -1,5-COD)Rh(tmiy)Cl39 complexes;
where tmiy = 1,3-bis(4-tolylmethyl)imidazol-2-ylidene.
Structural study
To establish the structure for rhodium complexes 6a and 6b,
a single-crystal X-ray diffraction study was performed on crys-
tals grown from slow diffusion of pentane into a saturated
dichloromethane solution. The ORTEP views of the molecule 6a
and 6b is shown in Fig. 4 and the crystal data is summarised
in Table 4. The absolute configuration of rhodium complexes 6a
and 6b as determined by X-ray analysis confirms the distorted
square planar geometry at the rhodium(I) centre. Interestingly, the
Scheme 3 Synthesis of Rh(I) and Ir(I) complexes.
complexes 6a and 6b were isolated as yellow crystalline solids,
asymmetric unit cell of rhodium complex 6b contains two different
molecules with no crystallographic symmetry and differs slightly
in their conformations. Both molecules have similar geometries
for coordinated diaminocarbenes whereas the cycloctadiene of
one molecule is reflected about the C1Rh1Cl1 plane with respect to
the other molecule. The Flack enantiopole parameter40 gave the
value of 0.01(2) showing the crystal consists of a single enantiomer
despite the achiral nature of the molecule. As expected for cyclic di-
which were characterised by elemental analysis, mass spectrometry
1
(ES+), 1H and 13C{ H} NMR spectroscopy using gCOSY, HMBC,
HMQC, ROESY and TOCSY experiments.
The 1H NMR spectra for complexes 6a and 6b were well
resolved. The chemical shifts observed for the N-aromatic sub-
stituents on the imidazole ring for 6a and 6b indicates the slightly
different chemical environment with hindered rotation on either
side of imidazole ring. The backbone (–NCHCHN–) protons
resonate as a set of singlets at d 5.93 ppm and d 6.02 ppm for
(6a) and d 6.15 ppm (6b), upfield of those observed for carbene
5a (d 5.70) and 5b (d 6.15), respectively. All the COD-CH protons
appear as broad singlet at d 3.32 (2H), 3.41 (1H) and 4.40 (1H) ppm
˚
aminocarbene, the Rh–C(carbene) bond lengths are 2.042(4) A 6a and
˚
2.078(4) A 6b, respectively, confirming the single bond character
of the bond. These observed bond lengths are somewhat longer
than the corresponding bond lengths observed for unsaturated
heterocyclic carbene complexes41–47 but comparable to that found
7206 | Dalton Trans., 2009, 7203–7214
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The Royal Society of Chemistry 2009
©

Fig. 4 ORTEP representation of molecular structure of the rhodium complexes 6a (left) and 6b (right) Thermal ellipsoids drawn at 40% probability.
in analogous diaminocarbene complexes.38 The Rh–C(carbene) for
spectroscopy. At 213 K four doublets (d 0.01 (6H), d 0.88 (6H), d
1.35 (6H), d 1.45 (6H) ppm, respectively) for isopropyl-CH3, two
septets (d 2.33 (2H) and d 4.05 (2H)) for isopropyl-CH groups and
two singlets (d 2.33 (2H) and d 4.05 (2H)) for COD-CH protons
were carefully assigned.
˚
6b is 0.036 A (3.6 pm) longer when compared with 6a and this
may be due to the greater steric interactions of bulky isopropyl
˚
˚
groups. The average Rh–C(COD) distance is 2.114 A 6a and 2.094 A
˚
˚
6b trans to chlorine and 2.205 A 6a and 2.192 A 6b trans to
diaminocarbene, respectively, and found to be consistent with
the greater trans influence of diaminocarbene when compared to
chlorine. A large N1–C2–C3–N2 torsion angle 9.48◦ was observed
for rhodium complex 6a, when compared with 1.97◦ observed for
5a and 3.38◦ for rhodium complex 6b.
1
The H NMR spectrum (CD2Cl2, room temperature) of the
cationic iridium complex 8a shows three resonances (d 1.49 (6H),
d 1.71 (6H) and d 2.63 (6H)) for the mesityl CH3 protons while
five resonances (d 1.49 (6H), d 1.71 (3H), d 2.38(6H), d 2.58 (3H)
and d 2.73 (3H), respectively) for the corresponding mesityl CH3
protons were observed for iridium complex 7a (CD2Cl2, room
temperature). The backbone protons (–NCHCHN–) resonate
downfield at d 6.01 ppm for complex 7a and d 6.10 ppm (233 K,
CD2Cl2) for iridium complex 7b, respectively, when compared with
BIAN-H2IMes 5a, which resonate as singlets at d 5.70 ppm. The
COD-CH protons appear as multiplets at d 3.12–3.20 and d 3.82–
3.98 ppm for complex 7a, singlets (213 K, CD2Cl2) at d 2.33 and
d 4.05 ppm for complex 7b, singlets at d 2.98 and d 3.92 ppm
for cationic iridium complex 8a and singlets at d 3.12 and d
4.22 ppm for cationic complex 8b, respectively. The downfield
signals for COD-CH protons at d 3.82–3.98 7a, d 4.23 7b, d 3.92
8a and d 4.22 8b ppm were assigned to the vinyl hydrogens trans
The angle between the best planes of the dihydroimidazole ring
and the naphthyl group is 58.38◦ 6a and 50.55◦ 6b,respectively. The
angle between the best planes of the dihydroimidazole ring and the
phenyl rings C15–C14–C19 and C24–C23–C28 are 81.44◦ and 68.28◦ for
6a and 79.64◦ and 69.73◦ for 6b, respectively. The angle between
the best planes of the dihydroimidazole ring and the coordination
plane is 77.70◦ 6a and 79.96◦ 6b. The remaining bond lengths and
bond angles are normal and lie within the expected range.
Synthesis and characterization of iridium(I) complexes
4
The reaction of the free carbenes 5a and 5b with [Ir(h -1,5-
1
to carbene with the help of a H-1H ROESY NMR experiment
COD)(m-Cl)]2 in THF at -78 ◦C yields the neutral iridium(I) com-
plexes 7a and 7b, which were isolated as orange-yellow crystalline
solids in high yields 78% 7a and 77% 7b, respectively. (Scheme 3)
Reaction of iridium(I) complexes 7aand 7b with AgBF4 or AgPF6
in the presence of pyridine as a coordinating ligand in CH2Cl2
at room temperature results in formation of cationic iridium(I)
and confirm its similarity with the very well studied Crabtree
catalyst48–51 Ir(COD)(py)L]PF6; where L= tertiary phosphine. This
is also found to be consistent with the longer Ir–C(COD) bond lengths
trans to carbene ligand (vide infra). In the 13C NMR spectrum of
7a the signal for the C(carbene) is upfield at d 201.9 ppm relative to
iridium complex 6a (d 208.4) and free carbene 3a, which appears
at d 247.3 ppm. This characteristic upfield shift of C(carbene) is
consistent with coordination of carbene with the iridium centre.52,53
4
4
complexes [(h -1,5-COD)Ir(BIAN-SIMes)Py]BF4 8a and [(h -1,5-
COD)Ir(BIAN-SIPr)Py]PF6 8b (Py = pyridine), respectively. The
complexes 8a and 8b were isolated as bright red crystalline solids
1
1
The important H and 13C { H} NMR resonances for iridium
complexes 7a, b and 8a, b are summarised in Table 3. Full 1H and
13C assignments are given in the Experimental.
1
in high yields (>75%). The H NMR spectrum (CD2Cl2) of the
iridium complex 7b at room temperature shows the absence of
characteristic resonances for isopropyl protons and the COD-
CH protons appear as broad singlets, suggesting that molecule is
fluxional, via rotation about the Ir–C(carbene) bond. At 273 K peaks
started to appear as broad resonances and complete freezing of
the fluxional process was achieved at 213 K (-60 ◦C). At this
temperature assignment of the NMR data was made with the
Structural study
Single crystals for iridium complex 7b and 8b, suitable for X-ray
study were grown by slow diffusion of pentane into a saturated
dichloromethane solution. The ORTEP views of the molecule
1
1
1
help of H-1H COSY, H-1H TOCSY and H-1H ROESY NMR
This journal is The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7203–7214 | 7207
©

◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for rhodium and iridium complexes
Property
6a
6b
7b
8b
˚
Bond lengths/A
C1–N1(2)
1.342(5), 1.362(5)
1.495(5),1.478(5)
1.555(5)
1.370(6)
1.390(6)
1.351(5), 1.358(5)
1.489(5), 1.495(5)
1.552(6)
1.369(8)
1.365(7)
1.353(4), 1.351(4)
1.487(4), 1.492(4)
1.548(4)
1.390(5)
1.412(5)
1.348(6), 1.376(7)
1.496(7), 1.477(8)
1.538(7)
1.402(17)
1.404(11)
N
1(2)–C2(3)
C2–C3
=
C
C
C(COD,trans to carbene)
C(COD,trans to X)
=
M–C1
2.042(4)
2.078(4)
2.070(3)
2.098(5)
M–X
M–C(COD,trans to X)
M–C(COD,trans to carbene)
2.3836(11)
2.102(4), 2.120(4)
2.189(4), 2.220(4)
2.3821(11)
2.083(5), 2.105(4)
2.189(5), 2.194(4)
2.3587(7)
2.104(3), 2.131(3)
2.158(3), 2.195(3)
2.109(6)
2.156(6), 2.167(7)
2.180(5), 2.171(6)
Bond angles (q)/◦
N1–C1–N2
C1–N1(2)–C2(3)
N1(2)–C2(3)–C3(2)
C1–M–X
107.6(3)
107.3(3)
108.0(2)
107.1(5)
114.0(3), 113.5(3)
101.4(3), 102.5(3)
96.84(10)
114.2(3), 113.0(3)
101.5(3), 102.8(3)
83.53(11)
112.8(2), 113.0(2)
102.6(2), 101.2(2)
82.97(8)
113.4(4), 112.8(5)
101.3(4), 103.1(4)
101.9(2)
C1–M–C(COD,trans to X)
C1–M–C(COD,trans to carbene)
91.18(16), 88.55(15)
154.06(16), 168.41(16)
98.92(18), 101.93(18)
158.29(18), 162.25(18)
101.16(12), 102.98(12)
155.55(13), 163.51(14)
83.5(2), 90.8(3)
165.4(5), 153.9(2)
Torsion angle/◦
N1–C2–C3–N2
9.48
3.38
12.58
13.56
M = Rh (6a, 6b), Ir (7b, 8b); X = Cl (6a, 6b, 7b), pyridine (8b)
7b and 8b are shown in Fig. 5 and 6, respectively, and crystal
˚
data is summarised in Table 4. Selected bond lengths (A) and
bond lengths (◦) are given in Table 2. For iridium complex 8b,
the refinement on the Flack enantiopole parameter40 gave a value
of 0.384(8) showing the crystal to be twinned by inversion. The
structure of the complexes 7b and 8b confirm the coordination is
distorted square planar at the iridium(I) centre, with coordinated
=
C C (cycloctadiene) midpoints as vertexes. The angle between
the best planes of the dihydroimidazole ring and the coordination
plane is 70.14◦ 7b and 60.29◦ 8b, respectively. The iridium–C(carbene)
Fig. 6 ORTEP representation of molecular structure of 8b (thermal
ellipsoids drawn at 40% probability and hydrogen, solvent of crystallisation
(CH2Cl2) and PF6 are omitted for clarity).
˚
˚
distance of 2.070(3) A in 7b and 2.098(5) A in 8b is slightly longer
than the corresponding bond lengths observed for Crabtree’s39 and
Nolan’s saturated carbene-iridium systems.52
These relatively longer bond lengths for the iridium–C(carbene)
bond is presumably due to the greater steric interactions of
diaminocarbene 5b on coordination and also suggests the single
bond character for the cyclic diaminocarbenes. For complex 7b,
Fig. 5 ORTEP representation of molecular structure of 7b (thermal
ellipsoids drawn at 40% probability and hydrogen atoms are omitted for
clarity).
˚
the mean iridium–C(COD) bond distances of 2.176(8) A (trans to
˚
carbene) and 2.117(8) A (trans to chlorine) are in agreement
7208 | Dalton Trans., 2009, 7203–7214
This journal is The Royal Society of Chemistry 2009
©

Table 3 Selected NMR chemical shifts for iridium complexes 7–8
1H NMR Chemical Shifts (d)/ppm
1
13C{ H} NMR Chemical Shifts (d)/ppm
Compound
COD-CH trans to C(carbene)
COD-CH trans to C(carbene)
C(carbene)
7a
7b
8a
8b
3.82–3.89 [m, 2H]
3.92 [m, 2H]
4.23 [s, 2H]
82.4, 83.4
83.5
80.5
208.4
201.9
Not observed
202.6
4.22 [s, 2H]
83.82
Table 4 Crystal structure refinement data for carbene 5a, rhodium complexes 6a and 6b and iridium complexes 7b and 8b
Compound 5a
Compound 6a
Compound 6b
Compound 7b
Compound 8b
Chemical formula
Formula weight
T/K
C34H33N2
469.65
150
0.71073
Monoclinic
C2/c
25.9142(4)
11.0550(2)
19.0937(3)
90
105.1595(8)
90
5279.64(15)
8
1.182
0.068
C39H42ClN2Rh
677.13
150
0.71073
Monoclinic
P21/c
9.0034(2)
17.0287(5)
21.0890(5)
90
93.5968(15)
90
3226.92(14)
4
1.394
0.642
C45H54ClN2Rh
761.29
150
0.71073
Monoclinic
P21
12.5115(2)
12.2042(2)
24.8139(5)
90
90.4245(9)
90
3788.80(12)
4
1.335
0.555
C45H54ClIrN2
850.61
150
0.71073
Monoclinic
P21/c
11.6520(2)
28.9269(3)
11.7784(2)
90
106.6717(5)
90
3803.10(10)
4
1.486
C51H61Cl2F6IrN3P
1124.15
150
0.71073
Monoclinic
Cc
18.6624(3)
15.6085(2)
16.6277(3)
90
90.0100(6)
90
4843.52(13)
4
1.542
˚
l/A
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
D
calcd/Mg m-3
m/mm-1
F000
3.615
1728
0.08 ¥ 0.14 ¥ 0.14
Orange fragment
Semi-empirical from
2.961
2272
0.12 ¥ 0.16 ¥ 0.24
Orange fragment
Semi-empirical from
2008
0.16 ¥ 0.24 ¥ 0.40
Colourless block
1408
0.14 ¥ 0.18 ¥ 0.18
Yellow fragment
1600
0.08 ¥ 0.12 ¥ 0.14
Yellow block
Crystal size/mm
Description of crystal
Absorption correction
Semi-empirical from Semi-empirical from Semi-empirical from
equivalent reflections equivalent reflections equivalent reflections equivalent reflections equivalent reflections
Transmission coefficients
(min/max)
0.97/0.99
0.89/0.91
0.93/0.96
0.60/0.75
0.49/0.72
q range for data collection/◦
Index ranges
5.0 ≤ q ≤ 27.5
-33 ≤ h ≤ 32, 0 ≤
k ≤ 14, 0 ≤ l ≤ 24
32 188
5.0 ≤ q ≤ 27.5
-11 ≤ h ≤ 11, 0 ≤
k ≤ 22, 0 ≤ l ≤ 27
26 281
5.0 ≤ q ≤ 27.5
-16 ≤ h ≤ 16, -15 ≤
k ≤ 13, 0 ≤ l ≤ 32
46 131
5.0 ≤ q ≤ 27.5
5.0 ≤ q ≤ 27.5
-15 ≤ h ≤ 14, 0 ≤ k ≤ -24 ≤ h ≤ 24, 0 ≤ k ≤
37, 0 ≤ l ≤ 15
20, 0 ≤ l ≤ 21
Reflections measured
Unique reflections
Rint
39 394
22 099
6309
7519
14 962
8609
10 569
0.051
0.064
4293
Full-matrix
least-squares on F
404
0.072
10 770
Full-matrix
least-squares on F
916
0.041
6115
Full-matrix
least-squares on F
458
0.047
9261
Full-matrix
least-squares on F
594
Observed reflections (I > 3s(I)) 3638
Refinement method
Full-matrix least-
squares on F
326
Parameters refined
Weighting scheme
Chebychev 3-term
polynomial
1.0758
Chebychev 3-term
polynomial
1.1352
Chebychev 3-term
polynomial
1.0788
Chebychev 3-term
polynomial
1.0769
Chebychev 3-term
polynomial
1.1069
Goodness of fit
R
0.0482
0.0584
-0.32/0.29
0.0386
0.0415
-0.45/0.65
0.0385
0.0385
-0.49/0.35
0.0218
0.0226
-0.62/0.49
0.0378
0.0423
-1.48/1.80
wR
Residual electron density
(min/max)/e A
-3
˚
Flack parameter
Structure details
—
—
—
—
-0.01 (2)
5983, Friedel-Pairs
—
—
0.384 (8)
4865, Friedel-Pairs
3.38◦ observed for imidazolium salt 3b26 and rhodium complex 6b.
The angle between the best planes of the dihydroimidazole ring
and the naphthyl group at◦the backbone decreases from 59.80◦
for 3b26 to 54.28◦ and 54.72 for 7b and 8b, respectively. Whereas,
the angles between the best planes of the dihydroimidazole ring
and the 2,6-diisopropylphenyl rings are 61.81◦ and 88.07◦ for 7b
and 63.66◦ and 85.78◦ for 8b, respectively. The remaining bond
lengths and bond angles are normal and lie within the expected
range.
4
with the reported Crabtree’s unsaturated carbene-iridium (h -1,5-
COD)Ir(tmiy)Cl39 systems and confirms the greater trans influence
of cyclic diaminocarbenes when compared with chlorine.39 For
iridium complex 8b, the average Ir–C(COD), trans to pyridine bond
˚
distance is 0.014 A shorter than that trans to carbene, due to the
higher trans influence of carbene. This also confirms the 1H NMR
assignments for COD vinyl protons (vide supra). In contrast, very
large torsion angles of 12.58◦ and 13.56. Were observed for iridium
complexes 7b and 8b, respectively, when compared with 2.44◦ and
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7203–7214 | 7209
©

Table 5 Hydroformylation of 1-octene using rhodium complexes 6a and 6b
Entry
Catalyst/mol%
T/◦C
pa/bar
t/h
Aldehydeb l/b (%)
Alcoholb l/b (%)
1
2
3
4
5
6
7
8
6b
1
1
40
100
100
100
100
100
100
100
40
55
55
40
30
30
20
20
12
20
24
22
24
20
24
24
1.45 (20)
1.47 (≥ 99)
0.85 (95)
1.72 (≥ 99)
0.58 (96)
0.75 (96)
0.54 (85)
0.76 (60)
—
—
6a
6b
6a
6b
0.1
0.5
0.1
0.1
0.01
0.1
2.66 (3)
—
2.57 (3)
1.7 (1)
1.57 (10)
0.87 (30)
6a
a CO–H2, 33 : 67. b Conversion to linear and branched aldehydes and alcohols, as determined by GC and an average of two runs.
Scheme 4 Possible side reaction in the hydroformylation of 1-octene.
Catalytic hydroformylation
were isolated and structurally characterised. The rhodium(I) and
iridium(I) complexes were obtained by the reaction of free carbene
with suitable metal precursors. The rhodium(I) complexes show
activity for the hydroformylation of 1-octene.
The rhodium complexes 6a and 6b were tested for the hydro-
formylation of 1-octene and the data is summarised in Table 5.
The catalytic reaction is sensitive to the reaction conditions as
well as the ligand employed. A series of possible side reaction in
the rhodium catalysed hydroformylation of 1-octene is described
below (Scheme 4). The hydroformylation reactions were carried
out in toluene using varying pressures of CO + H2 (33% CO
balanced with H2) at 100 ◦C unless otherwise stated. Cyclohexane
was used as an internal standard. All the reaction conditions
are optimised as reported in Table 5. The greatest yields of
aldehyde at 100 ◦C were obtained with higher pressures of H2/CO
(>20 bar), while the linear versus branched ratio varied from
0.85 to 1.72. The catalytic activities for catalysts 6a and 6b is
comparable (TOF and TON) to that of closely related systems.54–56
No measurable hydrogenation or isomerisation was observed
for catalysts 6a and 6b, as commonly observed for rhodium-
phosphine based catalytic systems which under hydroformylation
conditions produced a mixture of aldehydes.57–61 The detailed
hydroformylation procedure is given in the ESI.†
Experimental
General procedures
All manipulations were performed under dinitrogen using stan-
dard Schlenk vessel techniques or in an inert atmosphere glove
box. All solvents were dried by passage through an alumina
column under a positive pressure of dinitrogen and deoxygenated
by bubbling dry dinitrogen through the dried solvents for twenty
minutes before use. NMR spectra were recorded on either a
Varian Unity Plus 500 (1H at 500 MHz, 13C at 125.7 MHz) or
on a Varian Mercury 300 (1H at 300 MHz, 13C at 75.5 MHz)
spectrometer at room temperature unless otherwise stated. The
spectra were referenced internally relative to the residual protio-
solvent (1H) and solvent (13C) resonances and chemical shifts
were reported with respect to d = 0 for tetramethylsilane.
Electrospray mass spectra were recorded in acetonitrile on a
Micromass LC TOF spectrometer. Microanalyses were performed
by the microanalytical laboratory of the Inorganic Chemistry
Laboratory, University of Oxford. Gas Chromatographs were
recorded using Perkin Elmer XL 1100 instrument with Perkin
Elmer NCI 900 Network Chromatography Interface using fused
silica, non-polar SGE column 25QC2/BP1 1.0.
Conclusion
In conclusion we describe the synthesis and isolation of first two
members of a new family of annulated cyclic diaminocarbenes
ligands BIAN-SIMes, 5a and BIAN-SIPr, 5b, which have been
structurally characterised (5a). Such carbenes were previously
thought to be impossible to synthesise due their rigid tetracyclic
imidazole skeleton. The imidazolinium precursors show the base
selectivity for the synthesis of such carbenes. The decomposition
of imidazolinium salt via the ring opening at the backbone during
carbene synthesis was also observed and decomposition products
All reagents were purchased from Aldrich, metal precursors
from Johnson-Matthey and used as received unless otherwise
stated. The reagents Ar-BIAN,24,25 [(BIAN-SIMes)(H)]BF4,36
[(BIAN-SIPr)(H)]BF4,36 [Rh(COD)Cl]262 and [Ir(COD)Cl]251 were
prepared using published procedures. The bases KOtBu and
7210 | Dalton Trans., 2009, 7203–7214
This journal is
The Royal Society of Chemistry 2009
©

KN(SiMe3)2 were triply sublimed and kept in the inert atmosphere
glove box.
Elemental analysis (%): found (calcd): C 85.89 (86.33), H 8.15
(8.22), N 5.20 (5.27).
Synthesis of (g4-1,5-COD)-7,9-bis(2,4,6-trimethylphenyl)-6b,9a-
dihydroacenaphtho[1,2-d]imidazolin-2-ylidenerhodium(I)
chloride (6a)
Synthesis of 7,9-bis(2,4,6-trimethylphenyl)-6b,9a-dihydroace-
naphtho[1,2-d]imidazolin-2-ylidene (5a)
The imidazolinium salt 3a (0.3 g, 0.◦58 mmol) was suspended
in THF (5.0 mL) and cooled to -78 C. The KOtBu (65.0 mg,
0.60 mmol) was separately dissolved in THF (5.0 mL) and cooled
to -78 ◦C and added dropwise with constant stirring to the
imidazolinium salt over the period of 5.0 min, stirred for 30 min
and gradually warmed to room temperature. The reaction mixture
was further stirred for 1 h, during which time the colour of the
reaction mixture changed from off-white to light orange yellow.
The mixture was then filtered, evaporated to dryness and washed
with pentane (2 ¥ 10 mL) at -78 ◦C and dried in vacuum. The
product was isolated as off white solid. Yield: 0.19 g, 79%.
1H NMR (300 MHz, 291.6 K, C6D6): 7.47 (d, J = 7.5 Hz, 2H,
backbone ring CH), 7.11 (t, J = 7.6 Hz, 2H, backbone ring CH),
6.94 (s, 2H, mesityl-m-CH), 6.78 (s, 2H, mesityl-m-CH), 6.75 (d,
J = 6.9 Hz, 2H, backbone ring CH), 5.70 (s, 2H, –NCHCHN–),
2.41 (s, 6H, mesityl-CH3), 2.21 (s, 6H, mesityl-CH3), 1.74 (s, 6H,
mesityl-CH3).
The carbene 5a (0.53 g, 1.28 mmol) in toluene (5.0 mL) was
dropwise added to a stirred solution of [Rh(COD)Cl]2 (0.30 g,
0.61 mmol) in toluene (5.0 mL) at -78 ◦C and mixture was stirred
for 10 min, warmed to room temperature and stirred for further
3 h. The colour of the reaction mixture changed to orange yellow
and the reaction mixture was then filtered through Celite and the
volatiles were in vacuo. The crude was washed with pentane (2 ¥
5.0 mL) to give the product as yellow solid which was further
extracted with warm ether (3 ¥ 10.0 mL). Evaporation of diethyl
ether solution gave an orange yellow crystalline solid. Yield: 0.61 g,
81%.
1H NMR (300 MHz, 293 K, C6D6): 7.76 (d, J = 7.5 Hz, 1H,
backbone ring CH), 7.74 (d, J = 7.8 Hz, 1H, backbone ring CH),
7.38 (m, 2H, backbone ring CH), 7.12 (s, 1H, mesityl-m-CH), 7.08
(s, 1H, mesityl-m-CH), 7.03 (s, 1H, mesityl-m-CH), 6.91 (s, 1H,
mesityl-m-CH), 6.86 (d, J = 6.9 Hz, 1H, backbone ring CH), 6.81
(d, J = 6.9 Hz, 1H, backbone ring CH), 6.02 (s, 1H, –NCHCHN–
), 5.93 (s, 1H, –NCHCHN–), 4.40 (s + br, 2H, COD-CH), 3.41
(s + br, 1H, COD-CH), 3.32 (s + br, 1H, COD-CH), 2.82 (s, 3H,
mesityl-CH3), 2.54 (s + br, 3H, mesityl-CH3 + 1H, CODCH2),
2.39 (s + br, 6H, mesityl-CH3 + 1H, COD CH2), 1.87 (s, 3H,
mesityl-CH3), 1.43–1.82 (m + br, 6H, COD-CH2), 1.41 (s, 3H,
1
13C{ H} NMR (75.5 MHz, 293 K, C6D6): 247.3 (s, C(carbene)),
136.4, 138.3, 141.6 (s, C(Backbone ring aromatic)), 131.9, 135.4, 136.8, 138.0
(s, C(Mesityl aromatic)), 129.5, 129.7 (s, C(Mesityl-m-CH)), 120.7, 124.8, 128.1
(s, C(Backbone ring aromatic CH)), 71.6 (s, –NCHCHN–), 18.4, 19.9, 21.1 (s,
C(Mesityl-CH )).
3
Mass Spectrometry (ES+, C6H6): m/z = 431.2501 [M + H]+,
mesityl-CH3).
(100%).
1
13C{ H} NMR (75.5 MHz, 293 K, C6D6): 213.3 [d, JRh–C
=
Elemental analysis (%): found (calcd): C 85.98 (86.47), H 6.92
(7.02), N 6.34 (6.51).
46.2, Rh–C(carbene)], 137.7, 137.8, 137.9, 139.4, 139.5, 139.9 [s,
C(aromatic)], 131.5, 134.3, 134.8, 137.1, 137.2, [s, C(aromatic)], 128.5,
128.6, 130.1, 130.3 [s, mesityl CH], 121.6, 121.8, 125.3, 125.4,
127.9, [s, C(Backbone ring aromatic CH)], 97.1 (d, J = 7.1 Hz, C(COD-CH)), 70.8,
71.1 (s, –NCHCHN–), 95.9 (d, J = 7.4 Hz, C(COD-CH)), 67.7 (d, J =
14.6 Hz, C(COD-CH)), 67.0 (d, J = 14.6 Hz, C(COD-CH)), 28.1, 32.5 (s +
br, C(COD-CH2)), 19.2, 19.3, 20.4, 21.1, 21.3 (s, C(Mesityl-CH3)).
Mass Spectrometry (ES+, CH3CN): m/z = 641.2415 [M-Cl]+,
(100%),
Synthesis of 7,9-bis(2,6-diisopropylphenyl)-6b,9a-dihydro-
acenaphtho[1,2-d]imidazolin-2-ylidene (5b)
To a stirred suspension of imidazolium tetrafluoroborate 3b
(0.26 g, 0.43 mmol) in pentane (15.0 mL) at -78 ◦C was added
dropwise a solution of 1.6 M nBuLi in hexane (0.27 mL, 0.43 mmol)
with the help of syringe, stirred for 10 min and gradually warmed
to room temperature. The reaction mixture was further stirred for
2 h at room temperature, during which time the mixture changed
from off-white to light orange with the dissolution of imidazolium
precursor in pentane. The mixture was then filtered, evaporated to
dryness and washed with pentane at -78 ◦C and dried in vacuum.
The product was isolated as off white solid. Yield: 0.19 g, 90%.
1H NMR (300 MHz, 293 K, C6D6): 7.18 (d, J = 8.21 Hz, 2H),
6.73–7.10 (m + br, 8H), 6.36 (d, J = 6.9 Hz, 2H), 5.38 (s, 2H,
Elemental analysis (%): found (calcd): C 68.91 (69.18), H 6.32
(6.25), N 4.19 (4.14).
Synthesis of (g4-1,5-COD)-7,9-bis(2,6-diisopropylphenyl)-6b,9a-
dihydroacenaphtho[1,2-d]imidazolin-2-ylidenerhodium(I)
chloride (6b)
The carbene 5b (0.63 g, 1.22 mmol) in toluene (5.0 mL) was
dropwise added to a stirred solution of [Rh(COD)Cl]2 (0.28 g,
0.58 mmol) in toluene (5.0 mL) at -78 ◦C and mixture was stirred
for 10 min, warmed to room temperature and stirred for further
3 h, during which time reaction mixture changed to pale yellow.
The reaction mixture was then filtered through Celite and solvent
was removed in vacuo. It was then washed with pentane (2 ¥
5.0 mL) to give the product as yellow solid. The crude product was
then dissolved in CH2Cl2 (2.0 mL) and precipitated with pentane
(10.0 mL), filtered and dried in vacuum. The product was obtained
as pale yellow crystalline solid. Yield: 0.68 g, 78%.
i
–NCHCHN–), 3.19 (sept, J = 6.9 Hz, 2H, Pr-CH), 2.28 (sept,
J = 6.9 Hz, 2H, iPr-CH), 1.14 (d, J = 6.9 Hz, 3H, iPr-CH3), 1.06
(d, J = 6.7 Hz, 6H, iPr-CH3), 0.87 (d, J = 6.7 Hz, 6H, iPr-CH3),
0.53 (d, J = 6.8 Hz, 6H, iPr-CH3).
1
13C{ H} NMR (75.5 MHz, 293 K, C6D6): 241.9 (s, C(carbene)),
137.4, 146.5, 148.8 (s, C(Phenyl aromatic)), 131.7, 136.3, 140.8 (s, back-
bone C(aromatic)), 124.7 (s, C(Backbone ring aromatic CH)), 123.7, 123.8 (s + br,
C(Phenyl CH)), 121.0 (s, C(Backbone ring aromatic CH)), 73.9 (s, –NCHCHN–),
28.7, 29.1 (s, iPr-CH), 21.9, 23.4, 25.2, 26.6 (s, iPr-CH3).
Mass Spectrometry (ES+, C6H6): m/z = 515.3409 [M + H]+,
(100%).
1H NMR (300 MHz, 291.8 K, CD2Cl2): 7.71 (d, J = 8.3 Hz,
2H, backbone ring CH), 7.50 (d, J = 4.6 Hz, 4H, phenyl-p-CH),
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7203–7214 | 7211
©

7.29 (t, J = 7.6 Hz, 2H, backbone ring CH), 7.22 (t, J = 4.5 Hz,
2H, phenyl-p-CH), 6.51 (s + br, 2H, backbone ring CH), 6.15 (s,
2H, –NCHCHN–), 4.59 (s + br, 2H, COD-CH), 4.25 (s + br, 2H,
(0.78 g, 1.53 mmol) in THF (5.0 mL) was ◦then added dropwise
and mixture was stirred for 10 min at -78 C and then warmed
to room temperature, stirred for 3 h. The colour of the reaction
mixture changed to orange-yellow. The reaction mixture was
filtered through Celite and reduced to dryness. Addition of ice
cold pentane (5.0 mL) gave the product as yellow solid. The crude
product was then extracted with warm pentane (5 ¥ 10 mL) and
evaporation of yellow pentane solution gave the product as orange-
yellow crystalline solid. Yield: 1.05 g, 87%.
i
iPr-CH), 3.35 (s + br, 2H, COD-CH), 2.53 (s + br, 2H, Pr-CH),
1.85 (m, 2H, COD-CH2), 1.68 (m, 2H, COD-CH2), 1.58 (d, J =
6.4 Hz, 6H, iPr-CH3), 1.44 (d, J = 6.8 Hz, 6H, iPr-CH3), 1.40–1.55
(m, 4H, COD-CH2), 1.03 (d, J = 5.6 Hz, 3H, iPr-CH3), 0.09 (s +
br, 6H, iPr-CH3).
1
13C{ H} NMR (75.5 MHz, 293 K, CD2Cl2): 135.9, 148.7 [s + br,
C(Phenyl aromatic)), 132.1, 136.8, 139.4 [s, C(Backbone aromatic)), 124.6, 125.9,
129.2 (s + br, C(Phenyl CH)), 122.9, 125.9, 128.4 (s, C(Backbone ring aromatic CH)),
72.5 (s, –NCHCHN–), 69.6, 94.9 (s + br, C(COD-CH)), 28.4, 29.4 (s,
iPr-CH), 28.5, 32.8 (s, C(COD-CH2)), 22.5, 25.5, 26.1 (s + br, iPr-CH3).
Mass Spectrometry (ES+, CH3CN): m/z = 725.3323 [M - Cl]+,
(100%),
1H NMR (500 MHz, 213 K, CD2Cl2): 7.72 (d, J = 8.3 Hz, 2H,
backbone ring proton), 7.40–7.52 (m + br, 4H, Ph-m-CH + Ph-p-
CH), 7.28 (t, J = 7.62 Hz, 2H, backbone ring proton), 6.45 (d, J =
6.5 Hz, 2H, Ph-m-CH), 6.36 (d, J = 6.4 Hz, 2H, backbone ring
proton), 4.23 (s + br, 2H, COD-CH2), 6.10 (s, 2H, –NCHCHN–),
i
4.05 (d, J = 6.5 Hz, 3H, Pr-CH3), 2.33 (sept, J = 6.5 Hz, 2H,
Elemental analysis (%): found (calcd): C 70.76 (71.00), H 7.25
(7.15), N 3.61 (3.68).
iPr-CH), 2.92 (s + br, 2H, COD-CH2), 1.69 (s + br, 2H, COD-
CH2), 1.45 (d, J = 6.1 Hz, 3H, iPr-CH3), 1.35 (d, J = 6.5 Hz, 3H,
iPr-CH3), 1.19 (m, 4H, COD), 1.02 (m, 2H, COD-CH), 0.88 (d,
J = 6.1 Hz, 3H, iPr-CH3), 0.01 (d, J = 6.5 Hz, 3H, iPr-CH3).
Synthesis of (g4-1,5-COD)-7,9-bis(2,4,6-trimethylphenyl)-6b,9a-
dihydroacenaphtho[1,2-d]imidazolin-2-ylideneiridium(I)
chloride (7a)
1
13C{ H} NMR (75.5 MHz, 293 K, CD2Cl2): 136.7, 138.3, 147.8
(s + br, C(phenyl aromatic)), 130.9, 135.5 (s + br, C(Backbone aromatic)), 128.55,
130.32 (s, C(Phenyl CH)), 123.5, 124.6, 128.1 (s + br, C(Phenyl CH)), 121.8,
124.9, 127.3 (s, C(Backbone ring CH)), 71.6 (s + br, –NCHCHN–), 52.6,
The compound [Ir(COD)Cl]2 (0.37 g, 0.55 mmol) was dissolved
in THF (5.0 mL) and cooled to -78 ◦C. A solution of carbene 5a
(0.50 g, 1.13 mmol) in THF (5.0 mL) was then added dropwise.
i
80.5 (s + br, C(COD-CH)), 32.6 (s + br, C( Pr-CH)), 27.4, 27.6, 28.5 (s +
i
br, C(COD-CH )), 0.0, 23.4, 24.0, 25.1 (s, C( Pr-CH )).
◦
2
3
The solution was stirred for 10 min at -78 C and then warmed
Mass Spectrometry (ES+, CH3CN): m/z = 850.1475 [M]+,
to room temperature, stirred for 3 h. The colour of the reaction
mixture changed to orange yellow. The reaction mixture was then
filtered through Celite and solvent was reduced to dryness. The
addition of ice cold pentane (5.0 mL) gave the product as yellow
solid. The crude product was then extracted with warm diethyl
ether (2 ¥ 5 mL). Evaporation of diethyl ether solution gave the
orange yellow crystals. Yield: 0.66 g, 77%.
(100%)
Elemental analysis (%): found (calcd): C 63.49 (63.54), H 6.71
(6.40), N 3.09 (3.29).
Synthesis of (g4-1,5-COD)(pyridine)-7,9-bis(2,4,6-trimethyl
phenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolin-2-
ylideneiridium(I) tetrafluoroborate (8a)
1H NMR (300 MHz, 291.6 K, CD2Cl2): 7.80 (d, J = 8.2 Hz,
2H, backbone ring CH), 7.41 (m, 2H, backbone ring CH), 7.10
(s + br, 2H, mesityl-m-CH), 6.94 (s + br, 2H, mesityl-m-CH),
6.82 (d, J = 7.0 Hz, 1H, backbone ring CH), 6.79 (d, J = 6.9 Hz,
1H, backbone ring CH), 3.82–3.98 (m, 2H, COD-CH), 6.01 (s, 2H,
–NCHCHN–), 3.12–3.20 (m, 2H, COD-CH), 2.73 (s, 3H, mesityl-
CH3), 2.58 (s, 3H, mesityl-CH3), 2.38 (s, 6H, mesityl-CH3), 1.71
(s, 3H, mesityl-CH3), 1.50–1.63 (m + br, 4H, COD-CH2), 1.49 (s,
3H, mesityl-CH3), 1.21–1.32 (m + br, 4H, COD-CH2).
The iridium complex 6a (0.50 g, 0.65 mmol) and pyridine (80.0 mL,
0.98 mmol) was dissolved in CH2Cl2 (5.0 mL) and a solution of
AgBF4 (0.12 g, 0.65 mmol) in CH2Cl2 (5.0 mL) was added then
dropwise, solution was stirred for 1 h in dark at room temperature.
The precipitated silver chloride was separated by filtration and
volume was reduced to 3.0 mL, pentane (10.0 mL) was added to
precipitate the product. This was then washed with pentane (2 ¥
5.0 mL) and dried in vacuum. The product was obtained as a
bright red solid. Yield: 0.42 g, 73%.
1
13C{ H} NMR (75.5 MHz, 293 K, CD2Cl2): 208.4 (s, Ir–
C(carbene)), 137.7, 137.8, 138.1, 138.2, 139.7, 139.9 (s, C(aromatic)),
131.8, 134.9, 135.2, 135.3, 137.5 (s, C(aromatic)), 128.9, 129.2, 130.1 (s,
C(Mesityl-m-CH)), 122.0, 122.4, 125.7, 128.3, 128.4, (s, C(Backbone aromatic CH)),
82.4, 83.4 (s, C(COD-CH)), 71.4, 71.5(s, –NCHCHN–), 51.7, 52.4 (s,
1H NMR (300 MHz, 291.6 K, CD2Cl2): 8.49 (s + br, 2H, Py
H4), 7.69 (d + br, JHH = 8.0 Hz, 2H, Py H2,6), 7.56 (d, 2H, J =
5.9 Hz, backbone ring CH), 7.27 (t + br, J = 6.9 Hz, 2H, Py H3,5),
7.21 (s + br, 2H, mesityl-m-CH), 7.06 (t + br, J = 6.6 Hz, 2H,
backbone ring CH), 6.77 (s + br, 2H, mesityl-m-CH), 6.50 (d, 2H,
J = 6.9 Hz, backbone ring CH), 6.00 (s, 2H, –NCHCHN–), 3.92
(s + br, 2H, COD-CH), 2.98 (s + br, 2H, COD-CH), 2.63 (s, 6H,
mesityl-CH3), 1.71 (s, 6H, mesityl-CH3 + 2H, COD-CH2), 1.81
(m + br, 2H, COD-CH2), 1.21–1.74 (m + br, 4H, COD-CH2), 1.49
(s, 6H, mesityl-CH3).
C(COD-CH)), 28.8, 33.5, 33.7 [s, C(COD-CH )), 19.5, 19.8, 20.3, 21.2 (s,
2
C(Mesityl-CH )).
3
Mass Spectrometry (ES+, CH3CN): m/z = 729.2792 [M - Cl]+,
(100%).
Elemental analysis (%): found (calcd): C 61.06 (61.12), H 5.50
(5.52), N 3.73 (3.66).
1
13C{ H} NMR (75.5 MHz, 293 K, CD2Cl2: 201.9 (s, Ir–C(carbene)),
Synthesis of (g4-1,5-COD)-7,9-bis(2,6-diisopropylphenyl)-6b,9a-
dihydroacenaphtho[1,2-d]imidazolin-2-ylideneiridium(I)
chloride (7b)
130.1, 130.4 (s, C(Mesityl-m-CH)), 136.3, 137.2, 137.3, 137.8, 138.0 (s,
C(aromatic)), 131.3, 131.5, 133.9, 135.8, 136.2 (s, C(aromatic)), 125.6,
125.8, 139.2, 149.8, 151.1 (s, C(Py-CH)), 121.9, 124.0, 128.2 (s,
C(Backbone ring CH)), 70.9 (s, –NCHNCH–),65.4, 83.5 (s, C(COD-CH)), 29.1,
32.3 (s, C(COD-CH )), 18.59, 18.9, 20.9, 21.0 (s, C(Mesityl-CH )).
The compound [Ir(COD)Cl]2 (0.49 g, 0.73 mmol) was dissolved
in THF (5.0 mL) and cooled to -78 ◦C. A solution of carbene 5b
2
3
7212 | Dalton Trans., 2009, 7203–7214
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The Royal Society of Chemistry 2009
©

Mass Spectrometry (ES+, CH3CN): m/z = 810.35 [M]+, (100%).
Elemental Analysis (%): found (calcd): C 58.77 (58.92), H 5.34
(5.28), N 4.71 (4.69).
8 D. M. Khramov, V. M. Lynch and C. W. Bielawski, Organometallics,
2007, 26, 6042.
9 C. A. McAuliffe, in Comprehensive Coordination Chemistry, ed.
G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon Press,
Oxford Editon edn., 1987, vol. 2, pp. 989–1066.
10 F. Ullah, M. K. Kindermann, P. G. Jones and J. Heinicke,
Organometallics, 2009, 28, 2441.
11 F. E. Hahn, Angew. Chem., Int. Ed., 2006, 45, 1348.
12 W. A. Herrmann, D. Baskakov, E. Herdtweck, S. D. Hoffmann, T.
Bunlaksananusorn, F. Rampf and L. Rodefeld, Organometallics, 2006,
25, 2449.
13 C. Metallinos, F. B. Barrett, J. L. Chaytor and M. E. A. Heska, Org.
Lett., 2004, 6, 3641.
14 S. Saravanakumar, M. K. Kindermann, J. Heinicke and M. Ko¨ckerling,
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15 F. E. Hahn, L. Wittenbecher, D. Le Van and R. Frohlich, Angew. Chem.,
Int. Ed., 2000, 39, 541.
16 D. Tapu, C. Owens, D. VanDerveer and K. Gwaltney, Organometallics,
2009, 28, 270.
17 K. S. Coleman, H. T. Chamberlayne, S. Turberville, M. L. H. Green
and A. R. Cowley, Dalton Trans., 2003, 14, 2917.
18 K. S. Coleman, S. Dastgir, G. Barnett, M. J. P. Alvite, A. R. Cowley
and M. L. H. Green, J. Organomet. Chem., 2005, 690, 5591.
19 K. S. Coleman, S. Turberville, S. I. Pascu and M. L. H. Green,
Tetrahedron Lett., 2004, 45, 8695.
20 K. S. Coleman, S. Turberville, S. I. Pascu and M. L. H. Green,
J. Organomet. Chem., 2005, 690, 653.
21 S. Dastgir, K. S. Coleman, A. R. Cowley and M. L. H. Green,
Organometallics, 2006, 25, 300.
22 S. Saravanakumar, A. I. Oprea, M. K. Kindermann, P. G. Jones and J.
Heinicke, Chem.–Eur. J., 2006, 12, 3143.
23 H. Tu¨rkmen, O. S¸hin, O. Bu¨yu¨kgu¨ngo¨r and B. C¸ etinkaya, Eur. J. Inorg.
Chem., 2006, 2006, 4915.
Synthesis of (g4-1,5-COD)(pyridine)-7,9-bis(2,6-diisoprop-
ylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolin-2-
ylideneiridium(I) hexafluorophosphate (8b)
The iridium complex 7b (0.80 g, 0.94 mmol) and pyridine (92.0 mL,
1.12 mmol) was dissolved in CH2Cl2 (7.0 mL). A solution of AgPF6
(0.24 g, 0.94 mmol) in CH2Cl2 (5.0 mL) was added then dropwise
and mixture was stirred for 1 h in the dark at room temperature.
Precipitated silver chloride was separated by filtration and volume
was reduced to 3.0 mL, pentane (10.0 mL) was added to precipitate
the product. A bright red solid was filtered, washed with pentane
(2 ¥ 5.0 mL) and dried in vacuum. The product was obtained as
bright red crystalline solid. Yield: 0.86 g, 87%.
1H NMR (300 MHz, 293 K, CD2Cl2): 6.35 (d, J = 8.2 Hz, 2H,
backbone ring proton). 7.55–7.65 (br, 2H, Py H2,6 + 2H phenyl
CH), 7.41–7.52 (br, 1H, Py H4 + 2H phenyl CH), 7.29 (t, J =
6.9 Hz, 2H, backbone ring proton), 6.96–7.09 (br, 2H, Py H3,5 +
2H phenyl CH), 6.35 (d, J = 6.9 Hz, 2H, backbone ring proton),
6.16 (s, 2H, –NCHCHN–), 4.22 (s + br, 2H, COD-CH), 3.63 (sept,
J = 6.7 Hz, 2H iPr-CH), 3.12 (s + br, 2H, COD-CH), 2.10 (br, 4H
COD-CH2 + 2H iPr-CH), 1.65 (d, J = 6.8 Hz, 3H, iPr-CH3), 1.59
(br, 4H, COD-CH2)), 1.55 (d, J = 6.8 Hz, 3H, iPr-CH3), 0.57 (d,
J = 6.1 Hz, 3H, iPr-CH3), 0.02 (d, J = 6.6 Hz, 3H, iPr-CH3).
24 A. Paulovicova, U. El-Ayaan, K. Shibayama, T. Morita and Y. Fukuda,
Eur. J. Inorg. Chem., 2001, 10, 2641.
1
13C{ H} NMR (75.5 MHz, 293 K, CD2Cl2): 202.62 (s, Ir–
25 P. Preishuber-Pflugl and M. Brookhart, Macromolecules, 2002, 35,
C(Carbene)], 126.7, 138.05, 150.93 (s, C(py)), 135.09, 146.64, 148.21
(s, C(Phenyl aromatic)), 131.96, 137.43, 137.54 (s, C(Backbone aromatic)), 128.55,
130.32 (s, C(Phenyl CH)), 126.1–126.38 (br, C(Backbone ring CH) + C(Phenyl CH)),
123.26 (s, C(Backbone ring CH)), 72.19 (s, –NCHCHN–), 66.47, 83.82 [s,
6074.
26 S. Dastgir, K. S. Coleman, A. H. Cowley and M. L. H. Green,
Manuscripts in preparation, 2009.
27 E. Despagent-Ayoub and R. H. Grubbs, J. Am. Chem. Soc., 2004, 126,
10198.
i
C(COD-CH)), 30.22, 31.85 (s, C(COD-CH )), 28.63, 29.47b (s, C( Pr-CH)),
2
28 A. J. Arduengo III, J. R. Goerlich and W. J. Marshall, J. Am. Chem.
i
23.58, 24.66, 25.25, 26.312 [s, C( Pr-CH )).
Soc., 1995, 117, 11027.
3
Mass Spectrometry (ES+, CH3CN): m/z = 815.3959 [M - py]+,
29 R. W. Alder, P. R. Allen, M. Murray and A. G. Orpen, Angew. Chem.,
Int. Ed. Engl., 1996, 35, 1121.
(100%), 815.3959 [M - py + CH3CN]+, 70%).
Elemental analysis (%): found (calcd): C 57.74 (57.79), H 5.62
(5.72), N 3.91 (4.04).
30 A. J. Arduengo, III, R. Krafczyk, R. Schmutzler, H. A. Craig, J. R.
Goerlich, W. J. Marshall and M. Unverzagt, Tetrahedron, 1999, 55,
14523.
31 A. J. Arduengo III, Acc. Chem. Res., 1999, 32, 913.
32 A. J. Arduengo III, S. F. Gamper, M. Tamm, J. C. Calabrese, F.
Davidson and H. A. Craig, J. Am. Chem. Soc., 1995, 117, 572.
33 M. K. Denk, T. Avinash, K. Hatano and A. J. Lough, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 2607.
34 A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
435.
Acknowledgements
We thank the Royal Society for a University Research Fellowship
(K. S. C.), the Ministry of Science and Technology (MOST), the
Government of Pakistan and Lady Margaret Hall, University of
Oxford for Graduate funding (S. D.) and Dr Nick Rees, Central
Research Labs, Department of Chemistry, University of Oxford,
for his help in the NMR studies and for useful discussions.
35 P. W. Betteridge, R. J. Cooper, C. K. Prout and D. J. Watkin, J. Appl.
Crystallogr., 2003, 36, 1487.
36 S. Dastgir, K. S. Coleman, A. H. Cowley and M. L. H. Green,
Organometallics, 2009, manuscript in preparation.
37 A. J. Arduengo III, H. V. R. Dias, R. L. Harlow and M. Kline, J. Am.
Chem. Soc., 1992, 114, 5530.
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7214 | Dalton Trans., 2009, 7203–7214
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©