Axially chiral dimeric Ir and Rh complexes bridged by flexible NHC ligands

Article abstract of DOI:10.1016/j.ica.2011.11.034

A family of Ag complexes of the type [{BnN(CH₂CH ₂^RIm)₂}Ag]·[AgX₂] (X = I, ^RIm = 1-methylimidazole (3a); X = Cl, ^RIm = 1-tert-butylimidazole (3b), 1-benzylimidazole (3c) or 1-methylbenzimidazole (3d)) or [{BnN(CH₂CH₂CH₂^RIm) ₂}Ag]·[AgCl₂] (^RIm = 1-methylimidazole (4a), 1-tert-butylimidazole (4b), 1-benzylimidazole (4c) or 1- methylbenzimidazole (4d)) with a flexible unsaturated linker connecting the two NHC ligands has been prepared. These silver complexes undergo facile transmetalliation with [Ir(COD)Cl]₂ to generate the bimetallic species (COD)ClIr{BnN(CH₂CH₂^RIm) ₂}IrCl(COD) (^RIm = 1-methylimidazole (5a), 1-tert-butylimidazole (5b), 1-benzylimidazole (5c) or 1-methylbenzimidazole (5d)) or (COD)ClIr{BnN(CH₂CH₂CH₂ ^RIm)₂}IrCl(COD) (^RIm = 1-methylimidazole (6a), 1-tert-butylimidazole (6b), 1-benzylimidazole (6c) or 1-methylbenzimidazole (6d)) with a bridging bidentate NHC ligand. A similar reaction can be performed using [Rh(COD)Cl]₂ to generate the analogous Rh species (COD)ClRh{BnN(CH₂CH₂CH₂^RIm) ₂}RhCl(COD) (^RIm = 1-methylimidazole (7a), 1-benzylimidazole (7c) or 1-methylbenzimidazole (7d)). Complexes 5d, 6d and 7d were characterized by X-ray crystallography. All of our new Rh and Ir species possess axial chirality and are prepared as a mixture of isomers. However, crystals of 5d, 6d and 7d contain only one diastereomer. Dissolution of the diastereometrically pure crystals results in epimerization and the formation of an equilibrium mixture. Our new Ir complexes are active catalysts for both olefin and transfer hydrogenation and we present a comparison of their catalytic activity based on the linker length of the ligand.

Full text of DOI:10.1016/j.ica.2011.11.034

Inorganica Chimica Acta 380 (2012) 399–410
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Inorganica Chimica Acta
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Axially chiral dimeric Ir and Rh complexes bridged by flexible NHC ligands
⇑
John M. Ashley, Joy H. Farnaby, Nilay Hazari , Kelly E. Kim, Eddie D. Luzik Jr., Robert E. Meehan,
Eric B. Meyer, Nathan D. Schley, Timothy J. Schmeier, Amit N. Tailor
The Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520, USA
a r t i c l e i n f o
a b s t r a c t
A family of Ag complexes of the type [{BnN(CH2CH2RIm)2}Ag]Á[AgX2] (X = I, RIm = 1-methylimidazole (3a);
X = Cl, RIm = 1-tert-butylimidazole (3b), 1-benzylimidazole (3c) or 1-methylbenzimidazole (3d)) or
[{BnN(CH2CH2CH2RIm)2}Ag]Á[AgCl2] (RIm = 1-methylimidazole (4a), 1-tert-butylimidazole (4b), 1-benzyl-
imidazole (4c) or 1-methylbenzimidazole (4d)) with a flexible unsaturated linker connecting the two
NHC ligands has been prepared. These silver complexes undergo facile transmetalliation with [Ir(COD)Cl]2
to generate the bimetallic species (COD)ClIr{BnN(CH2CH2RIm)2}IrCl(COD) (RIm = 1-methylimidazole (5a),
1-tert-butylimidazole (5b), 1-benzylimidazole (5c) or 1-methylbenzimidazole (5d)) or (COD)ClIr{BnN(CH2
CH2CH2RIm)2}IrCl(COD) (RIm = 1-methylimidazole (6a), 1-tert-butylimidazole (6b), 1-benzylimidazole
(6c) or 1-methylbenzimidazole (6d)) with a bridging bidentate NHC ligand. A similar reaction can be per-
formed using [Rh(COD)Cl]2 to generate the analogous Rh species (COD)ClRh {BnN(CH2CH2CH2RIm)2}RhCl
(COD) (RIm = 1-methylimidazole (7a), 1-benzylimidazole (7c) or 1-methylbenzimidazole (7d)). Complexes
5d, 6d and 7d were characterized by X-ray crystallography. All of our new Rh and Ir species possess axial
chirality and are prepared as a mixture of isomers. However, crystals of 5d, 6d and 7d contain only one
diastereomer. Dissolution of the diastereometrically pure crystals results in epimerization and the forma-
tion of an equilibrium mixture. Our new Ir complexes are active catalysts for both olefin and transfer hydro-
genation and we present a comparison of their catalytic activity based on the linker length of the ligand.
Ó 2011 Elsevier B.V. All rights reserved.
Article history:
Available online 25 November 2011
Young Investigator Award Special Issue
Keywords:
NHC ligands
Rhodium and iridium compounds
Axial chirality
Transfer hydrogenation
Olefin hydrogenation
1. Introduction
metal centers [42–45]. Representative examples of each of these
types of complex are shown in Fig. 1. At this stage, reactivity studies
Over the last 20 years the coordination chemistry of N-heterocy-
clic carbenes has been explored in significant detail [1–7]. A wide
range of different NHC ligands have now been prepared, including
numerous systems which incorporate NHCs in chelate [8–11], pin-
cer [8,12] and tripodal [9,10,13,14] scaffolds. It has been shown that
these ligands coordinate to most transition metals and the resulting
complexes have been utilized in a number of catalytic reactions
[1,2,10–12,15]. In general, it is believed that NHCs are extremely
are not as extensive as structural studies, however these bimetallic
and multimetallic systems are catalysts for hydrosilylation reac-
tions [26,30,42,46], hydrogen transfer reactions [46], the hydrofor-
mylation of olefins [24,38], and the cyclization of acetylenic
carboxylic acids [43].
Currently the handful of reports describing bimetallic Ir and Rh
complexes with saturated linkers [19–23], are restricted to systems
which contain an unsubstituted alkyl chain as the linker. Recently
both Douthwaite and our group have reported bidentate NHC
ligands with flexible amine linkers (Fig. 2) [47–49]. Douthwaite
has described ligands with a two carbon linker (a) (linker length
is defined as the number of carbons between the imidazole and
the central amine) while our group has prepared species with a
three carbon linker (b). Depending on the length of the linker and
the size of the amine substituent, when these ligands coordinate
to PdCl2(MeCN)2, the ligand either binds in a tridentate pincer
fashion with coordination of the central amine or as a bidentate
trans-spanning ligand with no coordination of the central amine
[47–49]. In both cases the resulting complexes are active catalysts
for the Heck and Suzuki reactions. As part of our studies exploring
the coordination chemistry of ligands of the type a and b we were
interested in preparing Rh and Ir complexes supported by these
ligands. Here, we describe the synthesis of dimeric Ir and Rh
strong
r-donors and weak p-acceptors, although there is some
dispute on the latter point [16–18]. Surprisingly, given the plethora
of NHC ligands that have been designed for monomeric species, re-
ports of bimetallic complexes are less common. The vast majority
of reports of bidentate and polydentate NHC supported bimetallic
species involve Rh or Ir. Broadly speaking these complexes fall into
four main classes: (i) species with bidentate carbenes containing
flexible saturated linkers [19–23], (ii) species with bidentate carb-
enes containing semi-rigid unsaturated linkers [24–38], (iii) species
with bidentate carbenes containing completely rigid linkers, often
described as ‘Janus’ type carbenes [39–41]; and (iv) species with
three or more NHC ligands, which often contain more than two
⇑
Corresponding author.
E-mail address: nilay.hazari@yale.edu (N. Hazari).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.034

400
J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
Fig. 1. Representative examples of the four different types of carbene linkers utilized to make multinuclear Ir and Rh complexes.
imidazolium salts 1a, 1c and 1d were prepared in good yield using
an SN2 reaction between the appropriate free imidazole and bis(2-
chloroethyl)benzylamine. This reaction was significantly slower
when 1-methylbenzimidazole was used as the substrate and both
a high concentration and an elevated temperature were required
to obtain a satisfactory yield. In the case of the methyl substituted
imidazolium salt 1a, the ClÀÀ salt was extremely hygroscopic and
was converted into the PF6 salt to allow for easy handing in air.
Treatment of 1c and 1d with Ag2O generated the silver salts 3c
and 3d (Eq. (À1)), as reported earlier for 1b and 2a–2d. In the case
of 1a the PF6 was first converted into the IÀ salt (see Supporting
information for X-ray structure) before being treated with Ag2O to
generate the silver species 3a. The new silver salts were
characterized by 1H and 13C NMR spectroscopy and have similar
spectroscopic properties to those previously reported. Although
they were not characterized by X-ray crystallography, it is likely that
the ligand binds in a bidentate fashion to one cationic Ag center, with
an AgCl2À or AgI2À anion, as described for 2d [49].
a
b
Fig. 2. Bidentate carbene ligands with flexible amine containing linkers [47–49].
complexes supported by ligands a and b. The resulting species pos-
sess axial chirality and are unusual amongst Rh and Ir species
bridged by a flexible bidentate NHC ligand because they contain a
functional group in the linker. Furthermore, we demonstrate that
our complexes are active catalysts for both olefin and transfer
hydrogenation and present a comparison of their catalytic activity
based on the linker length of the ligand.
Reaction of the silver salts 3a–3d and 4a–4d with [IrCl(COD)]2
resulted in facile transmetallation and the formation of the new di-
meric Ir complexes 5a-5d and 6a-6d, respectively (Eq. (2)). When a
similar reaction was performed between the representative silver
salts 4a, 4c and 4d and [RhCl(COD)]2 the analogous Rh complexes
7a, 7c and 7d were obtained (Eq. (2)). All of the Rh and Ir com-
plexes were fully characterized. If two equivalents of the silver
salts were reacted with [IrCl(COD)]2 or [RhCl(COD)]2, one
2. Results and discussion
2.1. Ligand synthesis and preparation of Ir and Rh complexes
As part of a previous study we prepared the imidazolium salts
2a–2d [49], while Douthwaite had previously reported an analogous
species to 2b with a two carbon linker 1b [47,48]. Using an analo-
gous synthetic route to that described by Douthwaite, the
X-
N
N
( )
( )
N
n
n
N
N
N
Ag2O
R
R
( )
Ag
( )
(1)
Nn
Nn
-
AgX2
CH2Cl2,rt
X-
N
N
R
R
For imidazole
n=1, X=I, R= Me (3a)
For imidazole
n=1, X=PF6, R=Me (1a)
n=1, X=Cl, R=tBu (3b),Bn (3c)
n=1, X=Cl, R=tBu (1b), Bn (1c)
n=2, X=Cl, R=Me (4a),t Bu (4b), Bn (4c)
For benzimidazole
n=2, X=Cl, R=Me (2a),tBu (2b), Bn (2c)
For benzimidazole
n=1, X=Cl, R=Me (3d)
n=1, X=Cl, R=Me (1d)
n=2, X=Cl, R=Me (4d)
n=2, X=Cl, R=Me (2d)

J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
401
Scheme 1. Synthesis of Ir complexes 5b and 6b from the free carbenes 8b and 9b.
equivalent of the silver salt remained unreacted, consistent with
the proposed coordination of one equivalent of the ligand per
equivalent of the Ir dimer. In some cases the yields of the Rh and
Ir complexes (after purification by column chromatography) were
relatively low and an alternative synthetic method was pursued.
Douthwaite had demonstrated that 1b could be deprotonated to
generate the free carbene 8b [48], and we were able to perform a
similar reaction using 2b to form the free carbene 9b (Scheme 1).
The free carbene 9b was unstable for prolonged periods at room
temperature and needed to be stored under N2. Reaction of the free
carbenes 8b and 9b with [IrCl(COD)]2 generated 5b and 6b in high
initial yield and purity, however further purification by column
chromatography was still required, which resulted in modest
yields. This route could not be generalized to imidazoles with other
substituents, as successful deprotonation to generate the free car-
bene was not possible due to the low solubility of the imidazolium
salts, 1a and 1d and 2a and 2d in organic solvents.
Complexes 5d, 6d and 7d were characterized by X-ray crys-
tallography (Figs. 3–5). The structure of 5d clearly shows that
the ligand is bridging between the two Ir centers with no inter-
action between the central amine and either metal center. The
coordination geometry around Ir is the same at both metal cen-
ters and within experimental error the bond lengths and angles
around Ir are identical. The geometric parameters around Ir are
consistent with those reported in other related species
[22,31,34,43] and the NHC ligands are oriented perpendicular
to the coordination plane around Ir. The most interesting aspect
of the solid state structure is that it demonstrates that the mol-
ecule possesses axial chirality around the Ir–NHC bond [50],
with both metal centers being part of a separate center of axial
chirality. The (R,R) diastereomer is shown in Fig. 3, although as
the space group, P2(1)/n, is non-enantiomorphic, each unit cell
contains two molecules of the (S,S) and (R,R) enantiomers. Inter-
conversion between the (R,R) and (S,S) isomers could be
achieved by rotation around both Ir–NHC bonds, while rotation
around one Ir–NHC bond would give the equivalent meso (R,S)
or (S,R) diastereomers.
The solid-state structures of 6d and 7d are iso-structural (with-
in esd) and both molecules possess axial chirality. In both cases the
(R,R) configuration is depicted in Figs. 4 and 5. Unsurprisingly,
there is almost no variation in bond lengths and angles between
the Ir and Rh structures and the structures are superimposable
(see Fig. S1).1 The major difference between the structures with a
three carbon linker and 5d relates to the orientation of the nitrogen
lone pair on the central amine. This results in the inversion of the
direction of the lone pair on nitrogen atom between the two carbon
linked species 5d and the three carbon linked species 6d and 7d.
The 1H and 13C NMR spectra of 5a–5d and 6a–6d were compli-
cated. For example in the 13C spectrum of a pure (by elemental
analysis) amorphous sample of 6d, 16 different resonances corre-
sponding to both the vinylic and aliphatic COD environments and
two different carbene resonances at d 191.5 and 191.6 ppm were
observed. In fact for all complexes 5a–5d and 6a–6d double the ex-
pected number of carbon resonances were obtained and it
appeared that the molecules have no symmetry. However, when
a crystalline sample of 6d was dissolved in CD2Cl2 and a 13C
NMR spectrum recorded immediately, only eight COD environ-
ments and one carbene resonance were initially detected. Subse-
quently, over the course of several hours, eight new COD
resonances and an additional carbene resonance grew in (changes
in the number of linker resonances were also observed). The 1H
NMR spectrum of crystals of 6d showed similar behaviour. When
crystals of 6d were dissolved in CD2Cl2 and the spectrum immedi-
ately recorded, the CH2 protons in the benzyl substituent on the
central amine of the linker appeared as two doublets at d 3.82
and 3.67 ppm (Fig. 6b). However, over 6 h at room temperature a
new singlet grew in at d 3.75 ppm along with the doublets
(Fig. 6c). We believe that equilibration between the (R,R) or (S,S)
and (R,S) diastereomers of 6d accounts for this phenomenon. As
explained above, a crystalline sample of 6d comprises of only the
1
See supporting information for more details.

402
J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
Fig. 3. Molecular structure of 5d. Hydrogen atoms have been removed for clarity.
Selected bond lengths (Å) and angles (°): Ir(1)–Cl(1) 2.352(2), Ir(1)–C(1) 2.001(8),
Ir(1)–C(28) 2.156(9), Ir(1)–C(32) 2.077(9), Ir(1)–C(31) 2.084(9), Ir(1)–C(35) 2.190(9),
Ir(2)–Cl(2) 2.352(2), Ir(2)–C(13) 2.026(8), Ir(2)–C(36) 2.065(9), Ir(2)–C(37)
2.096(10), Ir(2)–C(40) 2.177(8), Ir(2)–C(41) 2.151(9), C(28)–C(29) 1.494(15),
C(28)–C(35) 1.365(15), C(29)–C(30) 1.485(14), C(30)–C(31) 1.512(13), C(31)–C(32)
1.428(14), C(32)–C(33) 1.494(16), C(33)–C(34) 1.488(15), C(34)–C(35) 1.492(14),
Cl(1)–Ir(1)–C(1) 87.5(2), Cl(1)–Ir(1)–C(28) 91.9(3), Cl(1)–Ir(1)–C(31) 165.1(3), C(1)–
Ir(1)–C(28) 156.8(4), C(1)–Ir(1)–C(31) 94.0(3), C(28)–Ir(1)–C(31) 80.9(3).
Fig. 5. Molecular structure of 7d. Hydrogen atoms have been removed for clarity.
Selected bond lengths (Å) and angles (°): Rh(1)–Cl(1) 2.363(2), Rh(1)–C(1)
2.027(10), Rh(1)–C(23) 2.073(11), Rh(1)–C(24) 2.155(9), Rh(1)–C(27) 2.220(11),
Rh(1)–C(28) 2.223(11), Rh(2)–Cl(2) 2.386(3), Rh(2)–C(15) 2.030(11), Rh(2)–C(38)
2.093(10), Rh(2)–C(41) 2.215(12), Rh(2)–C(42) 2.203(12), Rh(2)–C(45) 2.147(11),
C(23)–C(30) 1.517(18), C(24)–C(25) 1.522(16), C(25)–C(26) 1.520(15), C(26)–C(27)
1.491(14), C(27)–C(28) 1.390(15), C(28)–C(29) 1.542(15), C(29)–C(30) 1.543(17),
C(31)–C(32) 1.525(16), C(32)–C(33) 1.386(14), C(32)–C(37) 1.401(16), Cl(1)–Rh(1)–
C(1) 85.8(2), Cl(1)–Rh(1)–C(24) 160.2(3), Cl(1)–Rh(1)–C(27) 90.4(3), C(1)–Rh(1)–
C(24) 96.1(4), C(1)–Rh(1)–C(27) 162.9(4), C(24)–Rh(1)–C(27) 82.0(4).
major change in the benzylic protons, and the growth of a second
set of peaks in the 13C spectrum, several other more subtle changes
occur in the 1H NMR spectrum. For example several new peaks ap-
pear in the aromatic region, and the complexity of the multiplets
corresponding to some of the coordinated COD and linker peaks in-
creases as the second isomer grows in.1
The rate of rotation around the Ir–NHC bond was measured by
monitoring the growth of the singlet at d 3.75 ppm with time. Eyring
analysis indicates that
D
Hà = 52 3 kJ molÀ1 and
D
Sà = À162
15 J molÀ1 KÀ1. The
D
Gà298 value of 101 6 kJ molÀ1 is consistent
with the measured rate of rotation in Rh supported NHC complexes
[51,52]. The large negative entropy is surprising but a similar value
has been reported by Doyle and Lappert [52]. Crystalline samples
ofthethreecarbonlinkedRhspecies 7ddisplayedsimilarNMRprop-
erties to 6d and the rate of equilibration appears to be similar. Unfor-
tunately crystals of 7d could not be grown on a large enough scale to
performan Eyringanalysisand the rate of rotation couldnot beaccu-
rately measured. In contrast dissolutionof a crystallinesample ofthe
two carbon linked species 5d in CD2Cl2 resulted in the observation of
both the R,R and R,S isomers by 1H NMR spectroscopy immediately
after dissolution. The rate was too fast to accurately measure, which
suggests that rotation around the Ir–NHC bond is significantly faster
in the two carbon linked species 5d compared with the three carbon
linked species 6d.
Fig. 4. Molecular structure of 6d. Hydrogen atoms have been removed for clarity.
Selected bond lengths (Å) and angles (°): Ir(1)–Cl(1) 2.3542(17), Ir(1)–C(1) 2.014(7),
Ir(1)–C(30) 2.191(8), Ir(1)–C(31) 2.187(8), Ir(1)–C(34) 2.092(8), Ir(1)–C(35)
2.082(8), Ir(2)–Cl(2) 2.3623(20), Ir(2)–C(15) 2.026(8), Ir(2)–C(40) 2.107(8), Ir(2)–
C(41) 2.110(8), Ir(2)–C(44) 2.163(10), Ir(2)–C(45) 2.181(9), C(30)–C(31) 1.389(11),
C(30)–C(37) 1.510(11), C(31)–C(32) 1.511(10), C(32)–C(33) 1.507(12), C(33)–C(34)
1.525(12), C(34)–C(35) 1.382(13), C(35)–C(36) 1.503(14), C(36)–C(37) 1.546(13),
Cl(1)–Ir(1)–C(1) 86.34(19), Cl(1)–Ir(1)–C(30) 94.47(19), Cl(1)–Ir(1)–C(34) 160.9(2),
C(1)–Ir(1)–C(31) 162.3(3), C(1)–Ir(1)–C(34) 96.6(3), C(31)–Ir(1)–C(34) 81.9(3).
Despite repeated attempts, X-ray quality crystals of species sup-
ported by imidazole, instead of benzimidazole ligands could not be
obtained. In all cases the 1H NMR spectrum of 5a–5c and 6a–6c
displayed two doublets and a singlet for the CH2 protons of the
benzyl group and 16 signals for the COD carbons in the 13C NMR
spectrum. On this basis we believe that these species are formed
as a mixture of diastereomers and the approximate ratio of the iso-
mers is 1:1 (from integration of the 1H NMR spectrum). Presum-
ably, the lower solubility of the (R,R) and (S,S) isomers of 5d, 6d
and 7d allowed them to be crystallized and separated from the
meso (R,S) isomer, but they are clearly not configurationally stable
(R,R) or (S,S) diastereomers (the NMR spectra of these species
would be expected to be equivalent). In the (R,R) or (S,S) diastereo-
mer the benzylic protons are diastereotopic and should appear as
two doublets (Fig. 6a). Immediately after dissolution of crystalline
6d in solution, only these equivalent diastereomers are present.
Over time, presumably through rotation around the Ir–NHC bonds,
some of the (R,R) and (S,S) diastereomers are converted to the
meso (R,S) diastereomer. The benzylic protons in the (R,S) diaste-
reomer are equivalent and should appear as a singlet, which ex-
plains the growth in the peak at d 3.75 ppm. Along with the

J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
403
Fig. 6. (a) Modified Newman projections of 6d looking down the Ir–NHC bond. In the R,R (or S,S) isomer H1 and H2 are diastereotopic, whereas they are equivalent in the S,R
(or R,S). (b) Selected region of the 1H NMR spectrum of crystals of 6d immediately after dissolution in CD2Cl2 at room temperature. (c) Selected region of the 1H NMR spectrum
of crystals of 6d 24 h after dissolution in CD2Cl2 at room temperature. In the case of the R,R isomer, the inequivalence of H1 and H2 gives rise to a pair of doublets. Conversely,
the R,S isomer contains a mirror plane making H1 and H2 equivalent and gives rise to a singlet.
in solution at room temperature. To the best of our knowledge this
is the first example of bimetallic Rh or Ir complexes supported by
NHC ligands in which one isomer of an axially chiral pair has been
separated. Crabtree and Faller have previously reported that di-
meric Rh complexes supported by a bidentate NHC with a flexible
linker give rise to two sets of signals in their 1H NMR spectra, but
were unable to separate the isomers or confirm the structure of
either isomer by X-ray crystallography [20].
Treatment of 5c and 6c with 1 atm of CO at room tempera-
ture, resulted in rapid displacement of the COD ligands and
the formation of the tetra(carbonyl) complexes 10c and 11c
(Eq. (3)). Compounds 10c and 11c were not fully characterized
but were identified using 1H and 13C NMR spectroscopy, high
resolution mass spectrometry and IR spectroscopy. The length
of the linker did not affect the average m(CO) values suggesting
that the size of the linker length does not greatly perturb the
electronic properties of the complexes. Furthermore, the average
m(CO) values are consistent with those observed in monomeric
complexes of the type IrCl(CO)2(NHC) [53], indicating that there
is little electronic effect of having a second metal center in rel-
atively close proximity. Attempts to further compare the elec-
tronic properties of complexes with two carbon and three
carbon linkers using electrochemistry failed, as only broad
1 atm CO
CH2Cl2,rt
( )
N
( )
N
( )
( )
n
n
n
n
3
Bn
N
N
N
N
Bn
Bn
N
N
N
N
Bn ( )
IrCl(COD)
IrCl(CO)2
IrCl(COD)
IrCl(CO)2
n = 1 (10c) (CO)2062,1978cm-1; avg2020cm-1
n = 2 (11c) (CO)2061,1978cm-1; avg2020cm-1
n = 1 (5c)
n = 2 (6c)

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J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
irreversible waves were observed and a solid material deposited
on the electrode.
version, when time course experiments were performed, it was
clear that that the three carbon linked species was faster than
the two carbon linked species at short reaction times as well.
There is also some variation in the rates of reaction when the imid-
azole substituent is changed, suggesting that in agreement with
previous results the reaction is sensitive to the electronic proper-
ties around the metal [59]. Imines are more difficult to reduce than
ketones and we were interested in testing our catalysts for the
transfer hydrogenation of imines. A higher catalyst loading was re-
quired to achieve imine reduction within 24 h at 80 °C (Table 2).
The three carbon linked systems were again faster than the two
carbon linked systems. Overall our bimetallic catalysts are fairly
effective for transfer hydrogenation but the rate of catalysis is
slower than the best catalysts in the literature [58,59]. Notably
our observation that changing from imidazole to benzimidazole
makes a bigger difference to catalytic activity than changing the
linker length is consistent with Crabtree’s hypothesis that elec-
tronic effects make a larger different to catalytic activity than ste-
ric effects [1].
Cationic Ir complexes have been shown to be vastly more effec-
tive catalysts for olefin hydrogenation compared with neutral spe-
cies. Treatment of the representative neutral Ir complexes 5c, 6a
and 6c with KPF6 and PPh3 in CH3CN, resulted in rapid displace-
ment of the Cl ligand with PPh3 on both Ir centers (Eq. (4)). The
resulting complexes 12c, 13a and 13c were fully characterized.
The 1H NMR spectra of these complexes featured both two sets
of doublets and a singlet at the characteristic resonance for the
benzylic protons in the 1H NMR spectrum and all resonances in
the 13C NMR spectrum were doubled. This strongly suggests that
these species were formed as a mixture of diastereomers with an
approximate ratio of 1:1. X-ray quality crystals of these species
could not be obtained.
2.2. Catalysis
Since the early 1970s cationic Ir complexes have been utilized
as homogeneous olefin hydrogenation catalysts [60]. One of the
main pathways for catalyst deactivation involves the formation
of bi and trimetallic Ir polyhydrides [60] and we hypothesized that
by starting with a bimetallic system decomposition pathways
involving the formation of dimeric species might be circumvented.
The phosphine supported dimers 12c and 13c were screened as
olefin hydrogenation catalysts (Table 3). Both complexes were able
to hydrogenate (Z)-cyclooctene to cyclooctane at room tempera-
ture, with no apparent difference in activity between the two car-
bon and three carbon linked system. However, the complexes are
far less active than the best Ir catalysts [60]. Lower conversions
were obtained with more substituted olefins. Only a small amount
Ir(I) and Ir(III) complexes supported by NHC ligands have been
shown to catalyze hydrogen transfer reactions to oxidize alcohols
to aldehydes and ketones and reduce ketones, aldehydes, and imi-
nes to alcohols and amines, respectively [54]. We tested our sys-
tems for hydrogen transfer reactions to gauge the performance
of the bimetallic systems relative to reported catalysts with high
TON [54–59]. Initially we probed the reduction of acetophenone
using standard conditions [59]. Our results demonstrate that our
new complexes are active for transfer hydrogenation (Table 1).
In general it appears that the three carbon linked species are more
efficient catalysts than the two carbon linked species, although
mechanistically it is not clear what factors make a certain linker
length desirable. Consistent with our results at high substrate con-
Table 1
Results for hydrogen transfer between acetophenone and acetone using different bimetallic Ir catalysts.
O
OH
OH
O
[Ir]
KOtBu
+
+
Ph
Ph
CH3
H3C
CH3
CH3
H3C
CH3
iPrOH
Entry
Catalyst
Time (h)
Yield (%)a
1
2
3
4
5b
6b
5d
6d
10
9
36
36
92
92
74
92
a
Yield measured using 1H NMR spectroscopy (average of two runs), no by-products were detected. Reagents and
conditions: 4.16 mmol acetophenone, catalyst loading 0.021 mol%, 0.43 mol% KOtBu, 25 mL PrOH, 80 °C.
i
Table 2
Results for hydrogen transfer between N-benzylideneaniline and acetone using different bimetallic Ir catalysts.
Ph
NPh
OH
NH
O
[Ir]
+
+
KOtBu
Ph
H
Ph
H
H3C
CH3
H3C
CH3
iPrOH
H
Entry
Catalyst
Time (h)
Conversion (%)a
1
2
3
4
5b
6b
5d
6d
4
2
12
12
99
98
75
87
a
Yield measured using 1H NMR spectroscopy (average of two runs), no by-products were detected. Reagents and
conditions: 4.16 mmol N-benzylideneaniline, catalyst loading 0.043 mol%, 0.43 mol% KOtBu, 25 mL PrOH, 80 °C.
i

J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
405
Table 3
Results for catalytic hydrogenation using different bimetallic Ir catalysts.
Entry
Catalyst
Substrate
Time (h)
Temp (°C)
Yield (%)a
1
2
3
4
5
6
7
8
12c
13c
12c
13c
12c
13c
12c
13c
(Z)-Cyclooctene
(Z)-Cyclooctene
(Z)-stilbene
(Z)-stilbene
(E)-stilbene
(E)-stilbene
1-methylcyclohexene
1-methylcyclohexene
4
4
21
25
25
40
40
40
40
40
40
100
100
5b
21
4b
168
168
168
168
12
12
0
0
a
Yield measured using 1H NMR spectroscopy (average of two runs), no by-products were detected.
In this case the (Z)-stilbene was completely isomerized to the thermodynamically more stable (E)-stilbene. Reagents and condi-
b
tions: 0.091 mmol substrate, catalyst loading 2.5 mol%, 1 atm H2, 0.5 mL CD2Cl2.
of (E)-stilbene was converted to bibenzyl and no conversion was
obtained with 1-methylcyclohexene as the substrate. When
(Z)-stilbene was used as the substrate, complete isomerization to
thermodynamically preferred (E)-stilbene occurred prior to any
hydrogenation. At this stage there is little information about the
mechanism of hydrogenation using our bimetallic systems but
we believe the standard pathway of oxidative addition of H2, olefin
coordination, insertion and then reductive elimination is occurring
[61].
4.2. X-ray crystallography
Crystal samples were mounted in MiTeGen polyimide or
Hampton Research nylon loops with immersion oil. The diffraction
experiments were carried out on either a Rigaku SCXMini diffrac-
tometer using filtered Mo K
diffractometer equipped with a Saturn 944+ detector and rotating
anode Cu K source (k = 1.54187 Å). The data frames were processed
a radiation (k = 0.71073 Å) or a Rigaku
a
using Rigaku CrystalClear [66] and corrected for Lorentz and polar-
ization effects. The structures were solved by direct methods [67]
and expanded using Fourier techniques [68]. Non-hydrogen atoms
were refined anisotropically and hydrogen atoms were treated as
idealized contributions. Details of the crystal and refinement data
for complexes 5d, 6d, 7d and [Me(H)CEtN(Bn)EtC.(H)Me]Á2[I] are given
in the supporting information.
3. Conclusions
We have synthesized a series of bimetallic Rh and Ir complexes
bridged by a flexible bidentate NHC ligand containing an amine in
the linker. The new complexes are axially chiral and in several
cases one diastereomer can be isolated selectively through recrys-
tallization. To the best of our knowledge this is the first time a sin-
gle isomer of a species of this type has been isolated in a pure form.
Our new bimetallic complexes are active catalysts for both transfer
hydrogenation and olefin hydrogenation and the length of the lin-
ker between the metal centers influences the catalytic activity in
the case of transfer hydrogenation reactions. At this stage it is un-
clear why the linker length affects catalysis and further work will
look to understand this interesting phenomenon.
4.3. Synthesis and characterization of compounds
4.3.1. [Me(H)CEtN(Bn)EtC(H)Me]Á2[PF6] (1a)
1-methylimidazole (1.40 g, 17.2 mmol) and BnN(CH2CH2Cl)2
(2.00 g, 8.60 mmol) were mixed with dioxane (20 mL) and heated
at reflux for 18 h with stirring. The pale solid that precipitated out
of the reaction mixture was isolated by filtration, and then quickly
dissolved in methanol (20 mL). (The solid is presumably the Cl salt
of 1a which is extremely hygroscopic.) NH4PF6 (4.77 g, 10.0 mmol)
was then added to the methanol solution and a white solid instantly
precipitated. The solid was isolated by filtration, washed with meth-
anol (2 Â 10 mL) and then dried in vacuo to give 1a as a white solid.
Yield: 4.23 g, 80%.
4. Experimental
4.1. General methods
1H NMR (400 MHz, d6-DMSO): 2.86 (4H, t, CH2CH2NBn,
3JH–H = 6.0), 3.64(2H, s, NCH2Ar), 3.85(6H, s, CH3), 4.26 (4H, t, NCNCH2
CH2, 3JH–H = 6.0), 7.01 (2H, m, C6H5), 7.26 (3H, m, C6H5), 7.54 (2H, br t,
HC@CH), 7.63 (2H, br t, HC@CH), 8.88 (2H, s, NCHN). 13C{1H} NMR
(101 MHz, d6-DMSO): 35.7, 46.4, 52.4, 56.8, 122.5, 123.2, 127.1,
128.2, 128.6, 136.4, 137.9. 19F NMR (376 MHz, d6-DMSO): À70.1 (d,
1JP–F = 711, PF6). HR FT–ICR MS: Found (Calc. for C19H27F12N5P2): m/
z = (M–PF6) 470.1892 (470.1903).
Experiments were performed under air unless otherwise noted.
Solvents were dried by passage through a column of activated alu-
mina followed by storage under dinitrogen. All commercial chemi-
cals were used as received except where noted. Acetophenone,
ammonium hexafluorophosphate, benzyl amine, N-benzylidenean-
iline, 1-methylimidazole, 1-benzylimidazole, 1-methylbenzimida-
zole, silver(I) oxide, potassium tert-butoxide, sodium iodide,
sodium hydride, and triphenylphosphine were purchased from Al-
drich. Deuterated solvents were obtained from Cambridge Isotope
Laboratories. CD2Cl2 and CDCl3 were dried using P2O5 and vacuum
transferred prior to use. NMR spectra were recorded on Bruker
AMX-400 or AMX500 spectrometers at ambient probe tempera-
tures. Chemical shifts are reported with respect to residual internal
protio solvent for 1H and 13C{1H} NMR spectra. All assignments are
based on two dimensional 1H,13C-HMQC and HMBC experiments.
HRMS were recorded at The Mass Spectrometry (MS) and Proteo-
mics Resource of the W.M. Keck Foundation Biotechnology Resource
Laboratory at Yale University. Robertson Microlit Laboratories, Inc.
performed the elemental analyses. Literature procedures were fol-
lowed to prepare the following compounds: 1b [48], 2a–2d [49],
3b [48], 4a–4d [49], 8b [48], 1-tert-butylimidazole [62],
BnN(CH2CH2Cl)2 [63], [Ir(COD)Cl]2 [64] and [Rh(COD)Cl]2 [65].
4.3.2. [Bn(H)CEtN(Bn)EtC(H)Bn]Á2[Cl] (1c)
1-benzylimidazole (1.36 g, 8.60 mmol) and BnN(CH2CH2Cl)2
(1.00 g, 4.30 mmol) were mixed with dioxane (15 mL) and heated
at reflux for 18 h with stirring. The pale solid that precipitated out
of the reaction mixture was isolated by filtration, dissolved in water
and washed with dichloromethane (3 Â 20 mL) and hexane
(3 Â 20 mL). The water was removed by heating to 70 °C under re-
duced pressure to yield 1c an orange glassy solid. Yield: 1.80 g, 76%.
3
1H NMR (400 MHz, D2O): 2.93 (4H, t, CH2CH2NBn, JH–H = 6.0),
3
3.55 (2H, s, NCH2Ar), 4.10 (4H, t, NCNCH2CH2, JH–H = 6.5), 5.22
3
(4H, s, NCNCH2CH2), 6.91 (2H, d, HC@CH, JH–H = 8.0), 7.08 (2H, t,
3
HC@CH, JH–H = 1.6), 7.19–7.23 (4H, m, C6H5), 7.29–7.31 (1H, m,
C6H5), 7.38–7.48 (12H, m, C6H5), 9.07 (2H, s, NCHN). 13C{1H} NMR

406
J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
(101 MHz, D2O): 47.4, 52.8, 52.9, 57.2, 121.9, 122.5, 127.5, 128.5,
128.7, 128.9, 129.4, 129.4, 133.5, 135.0, 138.0. HR FT–ICR MS:
Found (Calc. for C31H35Cl2N5): m/z = (M–Cl) 512.2556 (512.2576).
H = 8.0), 7.32 (2H, t, Ar, JH–H=), 7.38 (2H, t, Ar, JH–H=), 7.44 (2H, d,
Ar, JH–H = 8.0). 13C{1H} NMR (100 MHz, CDCl3): 35.9, 47.5, 53.6,
60.3, 111.0, 111.1, 123.7, 123.7, 127.3, 128.3, 129.0, 133.6, 134.3,
138.4, 192.0.
4.3.3. [MeBz(H)CEtN(Bn)EtC(H)BzMe]Á2[Cl] (1d)
1-methylbenzimidazole (1.32 g, 10.00 mmol) and BnN(CH2CH2
Cl)2 (1.16 g, 4.99 mmol) were mixed with dioxane (5 mL) and heated
at reflux for 48 h with stirring. The pale solid that precipitated out of
the reaction mixture was isolated by filtration, dissolved in water
and washed with dichloromethane (3 Â 20 mL) and hexane
(3 Â 20 mL). The water was removed by heating to 70 °C under re-
duced pressure to yield 1d an orange glassy solid. Yield: 1.60 g, 65%.
4.3.7. (COD)ClIr{MeCEtN(Bn)EtCMe}IrCl(COD) (5a)
The following representative procedure was used for the syn-
thesis of 5a–5d:
[Ir(COD)Cl]2
(10.3 mg,
15
l
mol)
and
[(MeCEtN(Bn)EtC-
Me)Ag]Á[AgI2] (3a) (10 mg, 15
lmol) were dissolved in 2 mL of
dichloromethane. The reaction was stirred for 1 h and the solution
filtered through Celite. The solvent was removed under reduced
pressure and the yellow solid washed with pentane (2 Â 2 mL).
The precipitate was collected as a yellow crystalline solid. The so-
lid was purified using column chromatography (acetone/pentane
(30:70 v/v)). Yield: 10.0 mg, 63%.
3
1H NMR (400 MHz, D2O): 3.20 (4H, t, CH2CH2NBn, JH–H = 5.6),
3.71 (2H, s, NCH2Ar), 3.85 (6H, s, NCNCH3), 4.42 (4H, t, NCNCH2CH2,
3JH–H = 5.4), 7.02–7.71 (13H, m, Ar), 8.61 (2H, s, NCHN). 13C{1H}
NMR (101 MHz, D2O): 32.9, 45.0, 51.9, 57.6, 112.6, 113.2, 126.9,
127.0, 127.7, 128.3, 129.3, 130.9, 131.4, 137.4, 140.7. HR FT–ICR
MS: Found (Calc. for C27H31ClN5) m/z (M–Cl) 460.2209 (460.2268).
1H NMR (500 MHz, CDCl3): 1.52–1.77 (8H, m, COD CH2), 2.09–
2.25 (8H, m, COD CH2), 2.77 (2H, m, COD CH), 2.93–3.06 (4H,
m, COD CH and CH2CH2NBn), 3.18 (2H, m, CH2CH2NBn), 3.87 (2H,
m, CH2C6H5), 3.91 (3H, s, NCH3), 3.92 (3H, s, NCH3), 3.98 (1H, m,
NCNCH2CH2), 4.12 (1H, m, NCNCH2CH2), 4.53 (4H, s br, COD CH),
4.56 (1H, m, NCNCH2CH2), 4.70 (1H, m, NCNCH2CH2), 6.72 (1H, d,
4.3.4. [(MeCEtN(Bn)EtCMe)Ag]Á[AgI2] (3a)
[
Me(H)CEtN(Bn)EtC(H)Me]Á2[PF6] (1a) (129 mg, 0.21 mmol) was
dissolved in acetone (10 mL) and NaI (63.0 mg, 0.42 mmol) was
added with stirring. A white solid immediately precipitated out of
solution. The solid, presumably [Me(H)CEtN(Bn)EtC(H)Me]Á2[I] (see
supporting information for X-ray structure) was isolated via filtra-
tion, dried under reduced pressure and then dissolved in dichloro-
methane (15 mL). Ag2O (53.2 mg, 0.23 mmol) was added to the
reaction mixture and the reaction vessel was covered in aluminum
foil and left to stir for 14 h. The reaction mixture was then filtered
through Celite and the filtrate dried under reduced pressure to give
3a as a white powder. Yield = 75 mg, 38%.
3
3
HC@CH, JH–H = 2.0), 6.74 (1H, d, HC@CH, JH–H = 2.0), 6.91 (1H, d,
3
3
HC@CH, JH–H = 2.0), 6.91 (1H, d, HC@CH, JH–H = 1.5), 7.27–7.38
(5H, m, C6H5). 13C{1H} NMR (126 MHz, CDCl3): 29.1, 29.6, 29.8,
33.0, 33.8, 37.3, 49.0, 49.2, 51.3, 51.8, 55.2, 59.8, 84.2, 84.3, 84.6,
121.2, 121.3, 121.7, 121.9, 127.4, 128.6, 129.2, 139.0, 180.3. HR
FT–ICR MS: Found (Calc. for
C35H49Cl2Ir2N5): m/z = (M–Cl)
960.2880 (960.2935). Despite repeated attempts satisfactory ele-
mental analysis could not be achieved for this compound.
1H NMR (400 MHz, CD2Cl2): 3.00 (4H, t, CH2CH2NBn,
4.3.8. (COD)ClIr{tBuCEtN(Bn)EtCtBu}IrCl(COD) (5b)
This reaction was performed in toluene instead of dichloro-
methane. Yield: 40 mg, 47%.
3JH–H = 6.8), 3.68 (2H, s, NCH2Ar), 3.88 (6H, s, CH3), 4.23 (4H, t,
3
3
NCNCH2CH2, JH–H = 6.8), 6.80 (2H, HC@CH, JH-H = 1.6), 6.88 (2H,
HC@CH, JH–H = 1.6), 7.18–7.31 (5H, m, C6H5). 13C{1H} NMR
1H NMR (400 MHz, CDCl3): 1.27 (4H, m, COD CH2), 1.46 (4H, m,
COD CH2), 1.62 (8H, m, COD CH2), 2.15 (18H, s, NCCH3), 2.70 (2H, m,
CH2CH2NBn), 2.75 (2H, m, CH2CH2NBn), 2.87 (2H, m, COD CH), 3.00
(2H, m, COD CH), 3.82–3.98 (3H, m, NCH2Ar and NCNCH2CH2), 4.18
(1H, m, NCNCH2CH2), 4.41–4.51 (4H, m, COD CH), 5.23 (2H, m,
NCNCH2CH2) 6.92 (2H, d, HC@CH), 6.95 (1H, d, HC@CH), 7.03
(1H, d, HC@CH), 7.31–7.38 (5H, m, C6H5). 13C{1H} NMR (126 MHz,
CDCl3): 29.5, 29.6, 29.7, 29.9, 32.8, 32.8, 33.1, 33.3, 33.7, 33.8,
50.3, 50.8, 51.5, 51.7, 53.6, 53.6, 55.4, 55.6, 58.7, 60.0, 60.3, 79.5,
79.6, 81.8, 81.9, 118.8, 119.1, 121.4, 127.3, 127.3, 128.5, 128.5,
129.1, 129.2, 140.0, 140.1, 179.0, 179.1. HT FT-ICR MS: Found (Calc.
for C41H61Cl2Ir2N5) m/z (M+H) 1080.3609 (1079.2965). Anal. Calc.
for C41H61Cl2Ir2N5: C, 45.63; H, 5.70; N, 6.49. Found: C, 46.22; H,
5.62; N, 6.07%.
3
(126 MHz, d6-DMSO): 38.0, 48.3, 54.0, 57.8, 122.0, 122.1, 126.8,
128.0, 128.5, 138.3, 181.4.
4.3.5. [(BnCEtN(Bn)EtCBn)Ag]Á[AgCl2] (3c)
Under an N2 atmosphere
[
Bn(H)CEtN(Bn)EtC(H)Bn]Á2[Cl] (1c)
(429 mg, 0.78 mmol) was dissolved in dichloromethane (10 mL)
and Ag2O (218 mg, 0.94 mmol) was added. The reaction vessel
was covered in aluminum foil and left to stir for 14 h. The reac-
tion mixture was then filtered through Celite and the filtrate
dried under reduced pressure to give 3c as a white powder.
Yield = 0.40 g, 69%.
1H NMR (400 MHz, CD2Cl2): 2.95 (4H, t, CH2CH2NBn,
3JH–H = 6.8), 3.67 (2H, s, NCH2Ar), 4.13 (4H, t, NCNCH2CH2,
3JH–H = 6.8), 5.29 (4H, s, NCNCH2Ar), 6.92 (2H, d, HC@CH, JH–
3
3
H = 1.6), 6.97 (2H, d, HC@CH, JH–H = 2.0), 7.15–7.16 (2H, m, C6H5),
4.3.9. (COD)ClIr{BnCEtN(Bn)EtCBn}IrCl(COD) (5c)
7.20–7.22 (3H, m, C6H5), 7.27–7.29 (4H, m, C6H5), 7.32–7.36 (6H,
m, C6H5); 13C{1H} NMR (101 MHz, CD2Cl2): 50.8, 55.8, 56.2, 60.0,
121.6, 122.6, 127.9, 128.5, 129.0, 129.0, 129.3, 129.5, 136.6,
138.7, 180.7.
Yield: 177 mg, 78%. 1H NMR (500 MHz, CDCl3): 1.52 (4H, br m,
COD CH2), 1.65 (4H, br m, COD CH2), 2.06 (4H, br m, COD CH2),
2.14 (4H, br m, COD CH2), 2.67 (1H, m, CH2CH2NBn), 2.80–2.94
(3H, m, COD CH and CH2CH2NBn), 3.00–3.25 (4H, m, COD CH and
CH2CH2NBn), 3.88 (3H, m, CH2C6H5 and NCNCH2CH2), 4.13 (1H, m,
NCNCH2CH2), 4.54 (4H, m, COD CH), 4.64 (2H, m, NCNCH2CH2),
5.44 (1H, d, NCNCH2Ar, JH–H = 3.7), 5.47 (1H, d, NCNCH2Ar,
JH–H = 3.8), 5.71 (1H, d, NCNCH2Ar, JH–H = 14.8), 5.76 (1H, d,
4.3.6. [(MeBzCEtN(Bn)EtCBzMe)Ag]Á[AgCl2] (3d)
Under an N2 atmosphere
[
MeBzC(H)EtN(Bn)EtC(H)BzMe]Á2[Cl]
(1d) (0.36 mg, 0.73 mmol) was dissolved in dichloromethane
(60 mL) containing activated molecular sieves and Ag2O (0.54 g,
2.33 mmol) added. The reaction vessel was covered in aluminum
foil and stirred for 4 days. The resultant orange solution was fil-
tered and the filtrate dried under reduced pressure and washed
with pentane to yield 3d as an orange solid. Yield: 0.38 g, 76%.
1H NMR (500 MHz, CD2Cl2): 3.12 (4H, t, CH2CH2NBn,
3JH–H = 7.1), 3.68 (2H, s, NCH2Ar), 4.03 (6H, s, NCNCH3), 4.57 (4H,
3
NCNCH2Ar, JH–H = 14.8), 6.47 (1H, d, HC@CH, JH–H = 1.9), 6.59 (1H,
3
3
d, HC@CH, JH–H = 1.9), 6.84 (1H, d, HC@CH, JH–H = 2.0), 6.99 (1H,
3
d, HC@CH, JH–H = 1.9), 7.22–7.38 (15H, m, C6H5). 13C{1H} NMR
(126 MHz, CDCl3): 29.4, 29.4, 29.7, 29.8, 33.5, 33.5, 33.6, 33.7, 48.3,
48.3, 51.8, 51.8, 52.3, 52.4, 55.0, 55.7, 59.5, 60.3, 84.4, 84.4, 84.4,
84.4, 119.2, 119.5, 122.3, 122.5, 127.2, 127.3, 128.1, 128.1, 128.3,
128.4, 128.8, 128.8, 129.0, 129.1, 136.6, 136.6, 139.1, 139.4, 180.1,
3
t, NCNCH2CH2, JH–H = 7.2), 7.06 (5H, br s, Ar), 7.25 (2H, d, Ar, JH–
180.2. HR FT–ICR MS: Found (Calc. for
C47H57Cl2Ir2N5):

J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
407
for C41H61Cl2Ir2N5: C, 46.64; H, 5.92; N, 6.32. Found: C, 46.39; H,
5.75; N, 6.04%.
m/z = (M+H) 1148.3241 (1148.3369). Anal. Calc. for C47H57Cl2Ir2N5:
C, 46.63; H, 4.77; N, 5.67. Found: C, 46.30; H, 5.01; N, 6.11%.
4.3.13. (COD)ClIr{BnCPrN(Bn)PrCBn}IrCl(COD) (6c)
4.3.10. (COD)ClIr{MeBzCEtN(Bn)EtCBzMe}IrCl(COD) (5d)
Yield: 55 mg, 64%. 1H NMR (500 MHz, CDCl3): 1.45–1.71 (8H, m,
COD CH2), 1.90–2.30 (12H, m, COD CH2 and NCH2CH2CH2N), 2.62
(4H, m, CH2CH2CH2NBn), 2.90 (4H, m, COD CH), 3.65 (2H, m,
NCH2Ar), 4.16 (2H, m, COD CH), 4.50–4.65 (6H, m, COD CH and
Yield: 57 mg, 69%. X-ray quality crystals were grown by slow
evaporation from an acetone/pentane (30:70 v/v) solution.
1H NMR (500 MHz, CDCl3): 1.74 (6H, m, COD CH2), 2.03 (2H, m,
COD CH2), 2.14 (2H, m, COD CH2), 2.28 (4H, m, COD CH2), 2.85 (1H,
m, COD CH2), 2.89 (1H, m, COD CH2), 3.07 (4H, m, COD CH), 3.19
(2H, m, CH2CH2NBn), 3.48 (2H, m, CH2CH2NBn), 4.15 (5H, m and br
s, NCNCH3 and NCH2Ar), 4.15 (3H, s, NCNCH3), 4.51–4.71 (5H, m,
COD CH and NCNCH2CH2), 4.76 (1H, m, NCNCH2CH2), 5.11 (2H, m,
NCNCH2CH2), 7.12–7.52 (13H, m, Ar). 13C{1H} NMR (126 MHz,
CDCl3): 29.0, 29.2, 30.0, 30.4, 31.7, 33.1, 33.2, 34.2, 34.3, 34.4, 46.0,
46.5, 52.1, 52.3, 53.1, 53.1, 53.2, 53.7, 59.4, 60.7, 86.4, 86.6, 87.1,
87.2, 109.5, 109.5, 110.4, 110.5, 122.5, 122.6, 122.8, 122.8, 127.4,
127.5, 128.5, 128.7, 129.3, 129.4, 134.8, 135.0, 135.4, 135.5, 191.7,
191.8. HT FT–ICR MS: Found (Calc. for C43H53Cl2Ir2N5) m/z (M+H)
1096.2914 (1095.2937). Anal. Calc. for C43H53Cl2Ir2N5: C, 47.15; H,
4.88; N 6.39. Found: C, 47.41; H, 4.93; N 6.22%.
3
NCNCH2CH2CH2), 5.53 (1H, d, NCNCH2Ar, JH–H = 1.8), 5.53 (1H, d,
3
3
NCNCH2Ar, JH–H = 1.8), 5.68 (1H, d, NCNCH2Ar, JH–H = 7.3), 5.71
3
3
(1H, d, NCNCH2Ar, JH–H = 7.3), 6.59 (1H, d, HC@CH, JH–H = 2.0),
3
3
6.61 (1H, d, HC@CH, JH–H = 2.0), 6.80 (1H, d, HC@CH, JH–H = 2.0),
3
6.81 (1H, d, HC@CH, JH–H = 2.0), 7.20–7.40 (15H, m, C6H5).
13C{1H} NMR (126 MHz, CDCl3): 28.6, 28.8, 29.7, 29.8, 29.8, 33.7,
33.8, 33.8, 33.9, 49.1, 49.2, 50.8, 50.9, 51.9, 51.9, 52.1, 52.2, 54.5,
58.9, 58.9, 84.4, 84.5, 84.7, 84.7, 120.2, 121.2, 121.3, 127.2, 128.3,
128.4, 128.4, 128.5, 129.1, 129.2, 129.3, 136.7, 139.9, 140.0,
180.4, 180.5. HR FT-ICR MS: Found (Calc. for C49H61Cl2Ir2N5): m/
z = (M+H) 1176.3613 (1176.3641). Anal. Calc. for C49H61Cl2Ir2N5:
C, 49.78; H, 5.09; N, 5.91. Found: C, 50.05; H, 5.23; N, 5.96%.
4.3.14. (COD)ClIr{MeBzCPrN(Bn)PrCBzMe}IrCl(COD) (6d)
Yield = 36 mg, 71%. X-ray quality crystals were grown by slow
evaporation from an ethyl acetate/pentane (60:40 v/v) solution.
1H NMR (500 MHz, CDCl3): 1.67 (4H, m, COD CH2), 1.79 (4H, m,
COD CH2), 2.04 (2H, m, CH2CH2CH2), 2.24 (8H br m, COD CH2), 2.40
(2H, m, CH2CH2CH2), 2.78 (4H, br m, CH2CH2CH2NBn), 2.90 (2H, m,
COD CH), 3.00 (2H, m, COD CH), 3.75 (2H, see axial chirality section,
NCH2Ar), 4.17 (3H, s, NCH3), 4.17 (3H, s, NCH3), 4.43 (2H, m, NCNCH2
CH2CH2), 4.71 (4H, m, COD CH), 4.98 (2H, m, NCNCH2 CH2CH2), 7.16–
7.51 (13H, m, Ar). R,R-(COD)ClIr{MeBzCPrN(Bn)PrCBzMe}IrCl(COD)
13C{1H} NMR (126 MHz, CDCl3): 26.2, 29.4, 29.8, 33.5, 34.0, 34.5,
46.7, 50.1, 52.4, 52.7, 58.5, 86.5, 86.6, 109.6, 110.4, 122.5, 127.0,
128.4, 129.2, 134.8, 135.7, 140.1, 191.5 R,S-(COD)ClIr{MeBzCPrN(Bn)Pr
CBzMe}IrCl(COD) 13C{1H} NMR (126 MHz, CDCl3): 27.1, 29.2, 30.0,
33.3, 34.1, 34.5, 46.8, 51.0, 52.2, 52.9, 58.5, 86.4, 86.9, 109.6, 110.4,
122.6, 122.7, 127.1, 128.4, 129.2, 134.7, 139.7, 139.8, 191.6. HR FT
ICR MS Found: (Calc. for C45H57Cl2Ir2N5) m/z 1123.3315 (1123.32
50). Anal. Calc. for C45H57Cl2Ir2N5: C, 48.12; H, 5.11; N, 6.23. Found:
C, 47.35; H, 4.96; N, 5.92%.
4.3.11. (COD)ClIr{MeCPrN(Bn)PrCMe}IrCl(COD) (6a)
The following representative procedure was used for the syn-
thesis of 6a–6d:
[Ir(COD)Cl]2 (108 mg, 0.160 mmol) and [(MeCPrN(Bn)PrCMe)Ag]Á
[AgCl2] (4a) (100 mg, 0.160 mmol) were dissolved in dichlorometh-
ane (10 mL). The reaction was stirred for 3 h and then the solution
was filtered through Celite. The solvent was removed under reduced
pressure and the yellow solid washed with pentane (2 Â 2 mL). The
precipitate was collected as a yellow crystalline solid. The solid was
purified using column chromatography (acetone/hexane (30:70 v/
v)). Yield: 95 mg, 58%.
1H NMR (500 MHz, CD2Cl2): 1.45–1.75 (10H, br m, COD CH2 and
NCH2CH2CH2N), 1.96 (2H, m, NCH2CH2CH2N), 2.17 (8H, br m, COD
CH2), 2.59 (4H, m, CH2CH2CH2NBn), 2.88 (2H, br, COD CH), 2.96
(2H, br, COD CH), 3.65 (2H, m, NCH2Ar), 3.91 (6H, s, NCH3), 4.14
(2H, m, COD CH), 4.45 (4H, br, NCNCH2CH2CH2), 4.54 (2H, m,
COD CH), 6.81 (2H, br, HC@CH), 6.85 (2H, m, HC@CH), 7.25 (1H,
3
t, para-C6H5, JH–H = 7.4), 7.33 (2H, m, meta-C6H5), 7.41 (2H, m
ortho-C6H5). 13C{1H} NMR (126 MHz, CDCl3): 28.6, 28.8, 29.5,
29.6, 30.0, 30.1, 33.5, 33.6, 34.0, 34.1, 37.6, 49.0, 49.0, 51.4, 51.5,
51.9, 51.9, 58.8, 84.1, 84.2, 84.2, 84.3, 120.8, 120.8, 121.7, 121.7,
127.1, 128.5, 129.3, 129.3, 139.9, 140.0, 180.1, 180.2. HR FT–ICR
MS: Found (Calc. for C37H53Cl2Ir2N5): m/z = (M+H) 1024.2986
(1024.3015). Anal. Calc. for C37H53Cl2Ir2N5: C, 42.15; H, 4.88; N,
6.38. Found: C, 42.70; H, 5.22; N, 6.85%.
4.3.15. (COD)ClRh{MeCPrN(Bn)PrCMe}RhCl(COD) (7a)
The following representative procedure was used for the syn-
thesis of 7a, 7c and 7d:
[Rh(COD)Cl]2 (50 mg, 0.101 mmol) and [(MeCPrN(Bn)PrCMe)Ag]Á
[AgCl2] (3a) (63 mg, 0.101 mmol) were dissolved in dichlorometh-
ane (10 ml) and the reaction mixture stirred for 1 h. The yellow solu-
tion was filtered through Celite and the filtrate collected. The solvent
was removed under reduced pressure and the resulting solid
washed with pentane (2 Â 10 mL) to give 7a as a yellow crystalline
solid. The solid was purified using column chromatography
(acetone/hexane (30:70 v/v)). Yield: 83 mg, 95%.
4.3.12. (COD)ClIr{tBuCPrN(Bn)PrCtBu}IrCl(COD) (6b)
This reaction was performed in toluene instead of dichloro-
methane. Yield: 38 mg, 38%.
1H NMR (400 MHz, CDCl3): 1.47 (4H, m, COD CH2), 1.61 (4H, m,
COD CH2), 1.84 (18H, s, NCCH3), 1.92 (4H, m, COD CH2 and
CH2CH2CH2), 2.12 (6H, m, COD CH2), 2.30 (2H, m, CH2CH2CH2),
2.61 (4H, CH2CH2CH2NBn), 2.71 (2H, m, COD CH), 2.79 (2H, m,
COD CH), 3.64 (2H, m, NCH2Ar), 4.27 (2H, m, NCNCH2CH2CH2),
4.45 (2H, m, COD CH), 4.52 (2H, m, COD CH), 5.12 (2H, m,
1H NMR (500 MHz, CDCl3): 1.85 (8H, br m, COD CH2), 1.98 (2H,
m, NCH2CH2CH2N), 2.24 (8H, br m, COD CH2), 2.38 (2H, m,
NCH2CH2CH2N), 2.60 (4H, m, CH2CH2CH2NBn), 3.14 (2H, br, COD
CH), 3.23 (2H, br, COD CH), 3.63 (2H, m, NCH2Ar), 3.98 (6H, s,
NCH3), 4.15 (2H, m, COD CH), 4.67 (2H, m, COD CH), 4.90 (4H, br,
NCNCH2CH2CH2), 6.69 (2H, br, HC@CH), 6.75 (1H, d, HC@CH,
2
3
NCNCH2CH2CH2), 6.87 (1H, d, HC@CH, JH–H = 2.1), 6.93 (1H, d,
3JH–H = 1.8), 6.76 (1H, d, HC@CH, JH–H = 1.8), 7.18 (1H, m, para-
2
2
HC@CH, JH–H = 2.1), 6.97 (1H, d, HC@CH, JHÀH = 2.1), 6.98 (1H, d,
C6H5), 7.27 (2H, m, meta-C6H5), 7.37 (2H, m ortho-C6H5). 13C{1H}
NMR (126 MHz, CDCl3): 28.6, 28.8, 28.8, 28.8, 29.3, 29.3, 32.8,
32.8, 33.4, 33.4, 37.9, 49.2, 49.2, 50.7, 50.9, 58.8, 67.6 (d,
HC = CH, JH–H = 2.1), 7.23–7.39 (5H, m, C6H5). 13C{1H} NMR
2
(101 MHz, CDCl3): 28.1, 28.6, 29.5, 29.5, 29.6, 29.7, 32.8, 33.0,
33.2, 33.6, 33.8, 50.4, 50.7, 51.1, 51.2, 51.2, 51.2, 53.3, 52.4, 58.7,
58.9, 59.0, 79.2, 79.4, 81.6, 81.7, 119.5, 119.5, 120.2, 127.0, 128.3,
129.2, 129.2, 139.8, 140.0, 178.9, 179.0. HT FT-ICR MS: Found (Calc.
for C41H61Cl2Ir2N5) m/z (M+H) 1108.3924 (1107.3876). Anal. Calc.
1
1
1JRh-C = 7.6), 67.8 (d, JRh-C = 7.6), 68.3 (d, JRh-C = 14.5), 98.2 (m),
121.0, 121.1, 122.0, 127.1, 128.4, 129.2, 129.3, 139.9, 140.0, 181.8
1
1
(d, JRh-C = 16.1), 182.2 (d, JRh-C = 16.3). HR FT-ICR MS: Found
(calcd for C37H53Cl2N5Rh2): m/z = (M-Cl) 808.2083 (808.2100).

408
J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
Anal. calcd (found) for C37H53Cl2N5Rh2: C, 52.36 (52.60); H, 6.20
(6.33); N, 8.24 (8.29).
4.3.19. Synthesis of 6b using 9b
Under a N2 atmosphere [tBuCPrN(Bn)PrCtBu]Átoluene (9b) (51.1 mg,
0.09 mmol) and [IrCODCl]2 (65.0 mg, 0.09 mmol) were mixed in
toluene (10 mL). The reaction mixture was stirred for 3 h and then
the solution was filtered through Celite. The solvent was removed
under reduced pressure and the yellow solid washed with pentane
(2 Â 2 mL). The precipitate was collected as a yellow crystalline
solid. The solid was purified using column chromatography
(acetone/hexane (30:70 v/v)). Yield: 38 mg, 38%. (Characterizing
data as described above).
4.3.16. (COD)ClRh{BnCPrN(Bn)PrCBn}RhCl(COD) (7c)
Yield: 101 mg, 80%. 1H NMR (400 MHz, CDCl3): 1.79 (8H, m, COD
CH2), 1.98 (2H, m, NCH2CH2CH2N), 2.10–2.35 (10H, m, COD CH2 and
NCH2CH2CH2N), 2.62 (4H, m, CH2CH2CH2NBn), 3.18 (2H, m, NCH2Ar),
3.62 (2H, m, COD CH), 4.19 (2H, m, NCNCH2CH2CH2), 4.69 (2H, m,
NCNCH2CH2CH2), 4.98 (4H, br, COD CH), 5.68 (4H, m, NCNCH2Ar),
6.50 (1H, d, HC@CH, 3JH–H = 1.90), 6.52 (1H, d, HC@CH, 3JH–H = 1.8),
An analogous procedure was used to synthesize 5b using 8b.
3
3
6.73 (1H, d, HC@CH, JH–H = 1.9), 6.76 (1H, d, HC@CH, JH–H = 1.9),
7.12–7.40 (15H, m, C6H5). 13C{1H} NMR (126 MHz, CDCl3): 28.6,
28.8, 29.0, 29.0, 29.1, 29.1, 33.1, 33.1 (br), 33.2, 49.4, 49.4, 50.9,
4.3.20. (CO)2ClIr{BnCEtN(Bn)EtCBn}IrCl(CO)2 (10c)
The following representative procedure was used for the syn-
thesis of 10c and 11c:
1
1
51.0, 53.6, 58.9, 68.1 (d, JRh–C = 5.6), 68.2 (d, JRh–C = 5.6), 68.6 (d,
1JRh–C = 14.1), 98.4 (d, JRh–C = 6.6), 98.5 (d, JRh–C = 6.6), 98.7 (d,
1
1
[(COD)ClIr{BnCEtN(Bn)EtCBn}IrCl(COD)] (5c) (4.5 mg, 3.8
lmol)
1
1JRh–C = 6.4), 98.7 (d, JRh–C = 6.6), 120.6, 121.5, 121.6, 127.1, 128.2,
was dissolved in CD2Cl2 (0.5 mL) in a J. Young NMR tube. The solu-
tion was degassed using three consecutive freeze–pump-thaw cy-
cles and then excess 1 atm CO was added via a dual manifold
Schlenk line. The solution was left to stand for 4 h and the solvent
was then removed under reduced pressure. The resulting solid was
washed with pentane (3 Â 5 mL) to give (CO)2ClIr{BnCEtN(Bn)Et
CBn}IrCl(CO)2 (10c) as a yellow powder in essentially quantitative
yield.
128.4, 128.4, 128.5, 129.1, 129.2, 129.3, 136.8, 140.0, 140.0, 182.5
(d, 1JRh–C = 14.3), 182.7 (d, 1JRh–C = 14.7). HR FT–ICR MS: Found (Calc.
for C49H61Cl2N5Rh2): m/z = (M+H) 996.2461 (996.2492). Anal. Calc.
for C49H61Cl2N5Rh2: C, 58.75; H, 6.09; N, 6.82. Found: C, 59.02; H,
6.17; N, 7.03%.
4.3.17. (COD)ClRh{MeBzCPrN(Bn)PrCBzMe}RhCl(COD) (7d)
1H NMR (400 MHz, CDCl3): 3.10 (4H, m, CH2CH2NBn), 3.82 (2H,
s, NCH2Ar), 4.26 (4H, m, NCNCH2CH2), 5.47 (4H, m, NCNCH2Ar),
6.80 (2H, s br, HC@CH), 7.00 (2H, s br, HC@CH), 7.29–7.36 (m,
15H, C5H5). 13C{1H} NMR (126 MHz, CD2Cl2): 49.7, 55.2, 55.4,
59.7, 121.3, 123.6, 128.7, 128.8, 128.9, 129.0, 129.1, 129.4, 136.2,
Yield = 11 mg, 28%. X-ray quality crystals were grown by slow
evaporation from an acetone/pentane (30:70 v/v) solution.
1H NMR NMR (400 MHz, CDCl3): 1.87–2.15 (10H, br m COD CH2
and CH2CH2CH2), 2.25–2.46 (6H, m, COD CH2 and CH2CH2CH2),
2.51 (4H, m, COD CH2), 2.86 (3H, m, CH2CH2CH2NBn), 3.02 (1H,
ddd, NCH2CH2CH2NBn, J = 12.8, 7.6, 5.1), 3.27 (2H, m, COD CH),
3.38 (2H, m, COD CH), 3.81 (2H, see above, NCH2Ar), 4.30 (3H, s,
NCH3), 4.30 (3H, s, NCH3), 4.52 (2H, m, NCNCH2CH2CH2), 5.04–5.24
(6H, br m, COD CH and NCNCH2CH2CH2), 7.19–7.56 (13H, m, Ar).
13C{1H} NMR (101 MHz, CDCl3): 26.3, 27.2, 28.7, 28.8, 29.3, 29.4,
32.7, 32.9, 33.5, 33.6, 34.9, 47.2, 47.3, 50.2, 51.2, 58.7, 68.4 (d,
168.5, 182.2. IR (Diamond Tip, cmÀ1): 2061.7 (
m
CO), 1978.4
(mCO). HR FT–ICR MS: Found (Calc. for C35H33Cl2Ir2N5O4): m/
z = (M+H) 1044.1146 (1044.1220).
4.3.21. (CO)2ClIr{BnCPrN(Bn)PrCBn}IrCl(CO)2 (11c)
1H NMR (400 MHz, CDCl3): 1.97–2.16 (4H, m, CH2CH2CH2), 2.56
(4H, m, CH2CH2CH2NBn), 3.62 (2H, m, NCH2Ar), 4.32–4.41 (4H, m,
NCNCH2CH2CH2), 5.50 (4H, m, NCNCH2Ar), 6.86 (2H, s, HC@CH),
6.92 (2H, s, HC@CH), 7.32–7.44 (15H, m, C6H5). 13C{1H} NMR
(126 MHz, CD3Cl): 29.1, 51.2, 54.5, 55.3, 59.0, 121.7, 122.7, 127.6,
128.7, 128.8, 128.9, 129.4, 129.5, 129.9, 136.3, 168.7, 180.3. IR
1
1
1JRh–C = 14.6), 68.5 (d, JRh–C = 14.5), 69.0 (d, JRh–C = 14.5), 69.2 (d,
1JRh–C = 14.5), 100.0 (d, JRh–C = 6.3), 100.1 (d, JRh–C = 6.6), 100.2
(d, JRh–C = 6.4). 100.3 (d, JRh–C = 6.4), 109.4, 109.5, 110.3, 122.4,
1
1
1
1
122.4, 122.6, 122.6, 127.1, 127.1, 128.4, 128.5, 129.2, 129.3, 134.7,
1
134.7, 135.6, 140.0, 140.2, 194.9 (d, JRh–C = 18.1), 194.4 (d,
(Diamond Tip, cmÀ1): 2061.5 (
mCO), 1977.7 (
mCO). HR FT-ICR MS:
1JRh–C = 18.2). HR FT–ICR MS Found: (Calc. for C45H57Cl2Rh2N5) m/z
943.2134 (943.2101). Anal. Calc. for C45H57Cl2Rh2N5: C, 57.21; H,
6.08; N, 7.41. Found: C, 57.48; H, 6.93; N, 7.46%.
Found (Calc. for
(682.1543).
C37H37Cl2Ir2N5O4): m/z = (M+H) 682.1514
4.3.22. [(COD)(PPh3)Ir{BnCEtN(Bn)EtCBn}Ir(PPh3)(COD)]Á2[PF6] (12c)
The following representative procedure was used for the syn-
thesis of 12c, 13a and 13c:
4.3.18. [tBuCPrN(Bn)PrCtBu]Átoluene (9b)
Under an N2 atmosphere a 50 mL schlenk flask was charged with
a mixture of [tBu(H)CPrN(Bn)PrC(H)tBu]Á2[Cl] (2b) (0.87 g, 1.73 mmol)
and NaH (0.12 g, 5.04 mmol, 2.9 equivalents) and THF (200 mL) was
added. A solution of KOtBu (0.33 g, 2.93 mmol, 1.7 equivalents) in
THF (20 mL) was then added over 20 min and the reaction mixture
stirred vigorously for 6 h. The solution was filtered on a frit through
dry Celite and the volatiles removed under reduced pressure. The
resultant oil was extracted with toluene (30 mL) and the solution fil-
tered. The toluene was removed under reduced pressure to yield 9b
as orange oil. Yield: 0.89 g, 97%.
[(COD)ClIr{BnCEtN(Bn)EtCBn}IrCl(COD)] (5c) (30.0 mg, 0.027 m
mol) was dissolved in acetonitrile and then triphenylphosphine
(14.0 mg, 0.054 mmol) and KPF6 (9.82 mg, 0.054 mmol) were
added. After 30 min of stirring the solution was deep red with a
white precipitate. The solution was filtered and the filtrate col-
lected. The solvent was removed under reduced pressure and the
resulting solid washing with hexane (2 Â 10 mL) to give 12c as a
red solid. Yield: 40 mg, 80%.
1H NMR (400 MHz, CD3CN): 3.35 (2H, m, NCNCH2CH2CH2), 3.53
(2H, m, NCH2Ar), 3.58 (2H, m, COD CH), 3.71 (2H, br m, COD CH),
4.06 (1H, br m, COD CH), 4.12 (3H, br s, COD CH), 4.42 (2H, m,
NCNCH2CH2CH2), 4.62 (1H, d, NCNCH2Ar, JH–H = 3.8), 4.66 (1H, d,
NCNCH2Ar, JH–H = 3.7), 6.83 (1H, d, HC@CH, 3JH–H = 2.0), 5.50 (1H, d,
NCNCH2Ar, JH–H = 3.1), 5.54 (1H, d, NCNCH2Ar, JH–H = 3.2), 6.83 (1H,
1H NMR (400 MHz, C6D6): 1.56 (18H, s, NCCH3), 1.93 (4H, p, CH2
CH2CH2, JH–H = 5.0), 2.17 (3H, s, C6H5CH3), 2.34 (4H, t, CH2CH2CH2NBn,
3JH–H = 6.8), 3.34 (2H, s, NCH2Ar), 4.01 (4H, t, NCNCH2CH2CH2,
2
3JH–H = 7.3), 6.59 (2H, d, HC@CH, JH–H = 1.6), 6.77 (2H, d, HC@CH,
2JH–H = 1.6), 7.07–7.31 (10H, m, C6H5CH2N, C6H5CH3). 13C{1H} NMR
(126 MHz, C6D6): 21.8 (C6H5CH3), 30.1, 31.8, 49.8, 51.6, 56.0, 59.5,
115.7, 118.8, 126.0 (para-C6H5CH3), 127.4, 128.8 (meta-C6H5CH3),
128.9, 129.6 (ortho-C6H5CH3), 129.7, 138.2 (ipso-C6H5CH3), 140.9,
214 (carbene, located by 1H, 13C HMBC). This compound was too
unstable to obtain elemental analysis.
3
3
d, HC@CH, JH–H = 2.0), 6.86 (1H, d, HC@CH, JH–H = 2.0), 6.99 (1H,
3
3
d, HC@CH, JH–H = 2.0), 7.04 (1H, d, HC@CH, JH–H = 2.0), 7.05 (4H,
m, HC@CH) 7.25–7.60 (41H, m, C6H5 and PPh3). 13C{1H} NMR
(126 MHz, CDCl3): 30.3 (s, br), 31.0, 31.0, 31.1, 31.2, 31.4 (s, br),
2
48.0, 48.1, 53.8, 54.2, 58.7, 58.7, 79.6 (d, JP–C = 6.1), 81.2 (d,

J.M. Ashley et al. / Inorganica Chimica Acta 380 (2012) 399–410
409
2
2
2JP–C = 7.3), 86.4 (t, JP–C = 10.0), 87.0 (d, JP–C = 12.0), 87.1 (d,
2JP–C = 11.8), 122.3, 122.3, 123.4, 123.7, 127.5, 127.6, 127.9 (d,
1JP–C = 5.1), 128.6, 128.7, 128.8, 129.3 (d, 3JP–C = 10.0), 129.4, 130.0,
4.5. Conditions for catalytic reactions
4.5.1. Transfer hydrogenation
The following represents a general procedure for transfer
hydrogenation between acetophenone and acetone:
2
130.0, 130.4, 130.4, 131.5, 133.9 (d, JP–C = 12.0), 134.1, 134.7,
134.8, 138.8, 139.0, 173.8, 173.9. 31P{1H} NMR (162 MHz, CD3CN):
1
À144.6 (sep, PF6, JP–F = 706.4) 17.83 (s, PPh3), 17.86 (s, PPh3). HR
0.021 mol% of a stock solution of the appropriate Ir catalyst in
CH2Cl2 was syringed into a 50 mL round-bottom flask and the
solvent removed. Trimethoxybenzene (15 mg, internal standard),
FT–ICR MS: Found (Calc. for
C83H87Ir2N5P2): m/z = 800.7839
(800.7847). Anal. Calc. for C83H87F12Ir2N5P4: C, 49.38; H, 4.43; N,
3.02. Found: C, 50.70; H, 4.64; N, 3.70%.
KOtBu (2.0 mg, 0.43 mol%), acetophenone (487
lL, 4.16 mmol)
i
and PrOH (25 mL) were then added and the degassed solution
heated under nitrogen at 80ꢀC for the specified time. Aliquots were
taken under a flow of nitrogen gas and concentrated in vacuo be-
fore their 1H NMR spectrum was recorded in CDCl3.
4.3.23. [(COD)(PPh3)Ir{MeCPrN(Bn)PrCMe}Ir(PPh3)(COD)]Á2[PF6] (13a)
Yield: 98 mg, 85%. 1H NMR (300 MHz, CD3CN): 1.47 (2H, br m,
NCH2CH2CH2N), 1.72 (2H, br m, NCH2CH2CH2N), 1.90–2.50 (20H,
br m, COD CH2 and NCH2CH2CH2N), 3.43 (2H, m, NCH2Ar), 3.44
(6H, s, NCH3), 3.59 (2H, br, NCNCH2CH2CH2), 3.76 (4H, br, COD CH),
4.12 (2H, br, NCNCH2CH2CH2), 4.25 (2H, m, COD CH), 4.42 (2H, m,
COD CH), 6.86 (2H, s br, HC@CH), 6.91 (2H, t, HC@CH, JH–H = 2.4),
7.10–7.50 (35H, m, C6H5 and PPh3). 13C{1H} NMR (101 MHz, CD2Cl2):
27.7, 30.8 (d, 3JP–C = 3.0), 30.9 (d, 3JP-C = 2.9), 31.1 (d, 3JP–C = 2.8), 31.2
The following represents a general procedure for transfer
hydrogenation between N-benzylidineaniline and acetone:
0.042 mol% of a stock solution of the appropriate Ir catalyst in
CH2Cl2 was syringed into a 50 mL round-bottom flask and the
solvent removed. Trimethoxybenzene (15 mg, internal standard),
KOtBu (2.0 mg, 0.43 mol%), N-benzylidineaniline (0.754 g,
3
i
(d, JP–C = 3.0), 31.3, 31.4, 31.8, 31.9, 37.7, 49.1, 51.4, 59.2, 80.4 (d,
4.16 mmol) and PrOH (25 mL) were then added and the degassed
2JP–C = 3.4), 81.1, 86.0, 86.1, 86.8 (d, 2JP–C = 2.8), 87.0 (d, 2JP–C = 2.7),
solution heated under nitrogen at 80 °C for the specified time. Ali-
quots were taken under a flow of nitrogen gas and concentrated in
vacuo before their 1H NMR spectrum was recorded in CDCl3.
1
122.0, 122.0, 124.2, 129.0 (d, JP–C = 5.4), 129.1, 129.2, 129.5 (d,
4JP–C = 10.0), 130.5, 131.0, 131.7, 132.5, 134.2 (d, JP–C = 10.8),
3
140.2, 174.1 (d, JP–C = 2.1), 174.1 (d, JP–C = 2.0). 31P{1H} NMR
2
2
1
(162 MHz, CD3CN): À144.3 (sep, PF6, JP–F = 707.1) 18.81 (s, PPh3).
4.5.2. Olefin hydrogenation
The following represents a general procedure for catalytic olefin
hydrogenation reactions:
HR FT–ICR MS: Found (Calc. for C73H83Ir2N5P2): m/z = 738.7687
(738.7691). Anal. Calc. for C73H83F12Ir2N5P4: C, 50.37; H, 4.47; N,
3.28. Found: C, 49.95; H, 4.74; N, 3.60%.
(Z)-Cyclooctene (10 mg, 0.091 mmol) and 2.5 mol% 12c (4.3 mg,
2.3 lmol) were dissolved in CD2Cl2 (0.5 mL) in a J. Young NMR
4.3.24. [(COD)(PPh3)Ir{BnCPrN(Bn)PrCBn}Ir(PPh3)(COD)]Á2[PF6] (13c)
Yield: 49 mg, 70%. 1H NMR (500 MHz, CD2Cl2): 1.55 (2H, m,
CH2CH2CH2), 1.79 (2H, m, CH2CH2CH2), 2.01(10H, m, COD CH2),
2.26 (6H, m, COD CH2), 2.44 (4H, m, BnNCH2CH2CH2), 3.42 (2H, m,
NCH2Ar), 3.67 (2H, m, CH2CH2CH2NCN), 3.77 (2H, m, COD CH), 3.82
(2H, m, COD CH), 4.19 (2H, m, CH2CH2CH2NCN), 2.28 (2H, m, COD
tube. The tube was degassed using three consecutive freeze–
pump-thaw cycles and then 1 atm H2 was introduced using a
dual-manifold Schlenk line. The reaction was monitored using 1H
NMR spectroscopy. In all reactions no by-products were observed
and conversion was estimated by integration of the starting mate-
rial versus the product.
2
CH), 4.37 (1H, d, NCNCH2Ar, JH–H = 2.9), 4.40 (3H, m, COD CH and
NCNCH2Ar), 5.44 (1H, s, NCNCH2Ar), 5.47 (1H, s, NCNCH2Ar), 6.69
(1H, m, HC@CH), 6.94 (2H, m, HC@CH), 7.02 (1H, dd, HC@CH,
2JHÀH = 2.1 and 2.4), 7.23–7.52 (45H, m, C6H5 and PPh3). 13C{1H}
NMR (101 MHz, CD2Cl2): 27.8, 30.2, 30.2, 30.8 (m), 31.8, 31.8, 49.5,
Acknowledgement
We thank Professors Robert H. Crabtree and Jack W. Faller for
insightful discussions. N.D.S. acknowledges funding from the Divi-
sion of Chemical Sciences, Geosciences, and Biosciences, Office of
Basic Energy Sciences of the U.S. Department of Energy through
Grant DE-FG02-84ER13297.
1
1
51.4 (d, JP–C = 2.6), 59.4, 81.0 (m), 86.7 (d, JP–C = 3.6), 86.9 (d,
1
1JP–C = 3.5), 122.2, 128.3, 129.0 (d, JP-C=3.11), 129.2, 129.5, 129.6,
129.7, 130.4, 130.9, 131.8 (d, 1JP–C = 2.1), 134.2, 134.2, 135.1, 140.4,
1
1
174.3 (d, JP–C = 3.0), 174.4 (d, JP–C = 2.9). 31P{1H} NMR (202 MHz,
1
CD2Cl2): À144.4 (sep, PF6, JP–F = 716.8), 18.2 (s, PPh3). HR FT–ICR
Appendix A. Supplementary material
MS: Found (Calc. for C85H91Ir2N5P2): m/z = 814.7994 (814.8004).
Anal. Calc. for C85H91F12Ir2N5P4: C, 47.59; H, 4.61; N, 4.08. Found:
C, 48.50; H, 4.78; N, 3.65%.
X-ray information for 5d, 6d, 7d and
[
Me(H)CEtN(Bn)Et
C.(H)Me]Á2[I], an overlay of the solid state structures of 6d and
7d, a comparison of the 1H NMR spectra of freshly dissolved crys-
tals of 6d versus a solution of crystals that has been standing for
24 h and the Eyring plot for measuring the rate of rotation around
the Ir-NHC bond in 6d is available free of charge via the Internet at
http://pubs.acs.org. Supplementary data associated with this arti-
cle can be found, in the online version, at doi:10.1016/j.ica.
2011.11.034.
4.4. Representative procedure for measuring rate of Ir–NHC rotation in
6d
For a standard kinetics experiment the NMR probe was pre-
heated to the desired temperature prior to introduction of a sam-
ple. Crystals of (COD)ClIr{MeBzCPrN(Bn)PrCBzMe}IrCl(COD) (6d,
4 mg, 3.6
lmol) (prepared by slow evaporation from an ethyl ace-
tate/pentane (60:40 v/v) solution) were dissolved in 700
ll CDCl3
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ies of 1H NMR spectra at different times. In order to generate an
Eyring plot this experiment was repeated at several different
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