Unsymmetrical dicarbenes based on N-heterocyclic/mesoionic carbene frameworks: A stepwise metalation strategy for the generation of a dicarbene-bridged mixed-metal Pd/Rh complex

Article abstract of DOI:10.1021/om3004543

A pair of linked imidazolium/triazolium salts have been prepared using copper-catalyzed azide-alkyne cycloaddition (CuAAC or click chemistry) and methylation protocols, producing a precursor for bidentate N-heterocyclic carbene (NHC)/mesoionic carbene (MIC) ligands, representing a rare example of an NHC/MIC hybrid. Metalation of one-half of this dicationic species using the basic ligand-containing [Pd(OAc)₂] in the presence of potassium iodide or half an equivalent of [Rh(μ-OMe)(COD)]₂ yields NHC-anchored/pendent triazolium species of Pd or Rh, respectively. The pendent Pd species can be further functionalized through iodide substitution by various monophosphines, which preferentially adopt a cis or trans arrangement depending on the bulk of the anchored NHC substituent. Combining these internal-base and pendent strategies, the pendent MIC(H)⁺ arm of the trans-triethylphosphine-functionalized Pd species can be metalated by [Rh(μ-OMe)(COD)]₂, resulting in the generation of a hybrid NHC/MIC-bridgedmixed-metal Pd/Rh species. This complex represents the first example of a hybrid unsymmetrical dicarbene bridging two different metals.

Full text of DOI:10.1021/om3004543

Article
pubs.acs.org/Organometallics
Unsymmetrical Dicarbenes Based on N-Heterocyclic/Mesoionic
Carbene Frameworks: A Stepwise Metalation Strategy for the
Generation of a Dicarbene-Bridged Mixed-Metal Pd/Rh Complex
Matthew T. Zamora,† Michael J. Ferguson,†,‡ Robert McDonald,†,‡ and Martin Cowie*,†
‡
†Department of Chemistry and X-ray Crystallography Laboratory, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
S
* Supporting Information
ABSTRACT: A pair of linked imidazolium/triazolium salts
have been prepared using copper-catalyzed azide−alkyne
cycloaddition (CuAAC or “click” chemistry) and methylation
protocols, producing a precursor for bidentate N-heterocyclic
carbene (NHC)/mesoionic carbene (MIC) ligands, represent-
ing a rare example of an NHC/MIC hybrid. Metalation of one-half of this dicationic species using the basic ligand-containing
[Pd(OAc)2] in the presence of potassium iodide or half an equivalent of [Rh(μ-OMe)(COD)]2 yields NHC-anchored/pendent
triazolium species of Pd or Rh, respectively. The pendent Pd species can be further functionalized through iodide substitution by
various monophosphines, which preferentially adopt a cis or trans arrangement depending on the bulk of the anchored NHC
substituent. Combining these “internal-base” and “pendent” strategies, the pendent MIC(H)+ arm of the trans-triethylphosphine-
functionalized Pd species can be metalated by [Rh(μ-OMe)(COD)]2, resulting in the generation of a hybrid NHC/MIC-bridged
mixed-metal Pd/Rh species. This complex represents the first example of a hybrid unsymmetrical dicarbene bridging two
different metals.
position (Figure 1c).13 Since this discovery, a number of groups
have targeted these species owing to their impressive electron-
INTRODUCTION
Since the discovery of a free, isolable N-heterocyclic carbene
■
(NHC) by Arduengo in 1991,1 the use of carbene ligands has
donating properties. In addition to being adjacent to only one
risen tremendously, especially in homogeneous catalysis,2−7
electron-withdrawing group, the zwitterionic character of these
carbenes places more electron density on the carbene carbon,
extending their already well-established presence in organo-
making it a better donor.10,14
metallic chemistry.8,9 The intense recent interest in NHCs and
related species has led to several variations of this ligand, a
consequence of their highly tunable nature. However, until 2001,
all imidazol-2-ylidene-based NHCs (whether free or bound to
metals) invariably had their lone pair situated on the C-2 carbon
(Figure 1a). NHCs having the carbene functionality at C-4
These “wrong-way” carbenes have been referred to as NHCs
as a consequence of their lineage; however, since no reasonable
resonance forms containing a carbene can be drawn for the free
ligands without additional charges,15,16 they have been described
as “abnormal” NHCs (aNHCs).10,14−16 The fact that these
compounds require mesoionic17 resonance forms to represent
the carbene character (i.e., a lone pair on carbon) led Bertrand to
suggest that they be grouped into a category known as mesoionic
carbenes (MICs).18 Subsequently, Bertrand et al. isolated a
variety of free MICs, such as aNHCs,12 and “remote” NHCs
(rNHCs, in which the stabilizing heteroatoms are located at
positions β to the carbene as opposed to the α position).19−24
Other research groups have focused on other MICs, such as 2,3-
substituted tetrazol-3-ylidenes,25 2,4-substituted tetrazol-5-yli-
denes,26−28 or 1,2,3-triazol-5-ylidenes.29−36
Figure 1. (a) Conventional NHC, (b) “wrong way” NHC, and (c)
“wrong way” NHC Ir complex.
Our interest in dicarbene ligands as bridging groups in both
homo-37,38 and heterobinuclear38,39 complexes led us to examine
the synthesis of unsymmetrical dicarbenes, only three examples of
which were known at the time this work began,40−42 none of
which bridged two different metals. As a result, we initiated a
study on the synthesis of hybrid, unsymmetrical NHC/MIC
dicarbenes and their use as bridges in mixed-metal complexes to
(Figure 1b, or C-5 depending on the nature of R and R′10) had
not been considered as likely alternatives until a computational
report by Crabtree and Eisenstein,11 which suggested that free
“wrong-way” C-4 carbenes should be isolable, having their lone-
pair-containing HOMO at only slightly higher energy than that
of “normal” NHCs.12
Shortly after this communication, Crabtree reported the
internal-base metalation of a pyridine-functionalized imidazo-
lium species at the C-5 carbon rather than the expected C-2
Received: May 23, 2012
© XXXX American Chemical Society
A
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Scheme 1. Proposed “Pendent Strategy” for Generation of Dicarbene-Bridged Mixed-Metal Systems
further develop this area. With two different metals combined
into one catalyst, heterobimetallic complexes, such as these, can
potentially function as tandem catalysts,7,43,44 in which the pair of
metals mediate two mechanistically different catalytic processes
in one pot with high atom economy. One of our previously
reported di-NHC-bridged Pd/Rh species39 is currently being
studied as a potential Suzuki−Miyaura/transfer hydrogenation
tandem catalyst, and we sought to compare this reactivity with
that of other mixed-metal complexes linked by other types of
dicarbenes, such as di-MICs38 or NHC/MICs, the latter of which
is the topic of this work. In dicarbene-bridged tandem catalysts, it
seems unlikely that symmetric dicarbenes, having the same
carbene unit bound to each metal, will be optimal in promoting
the required differing reactivity at the different metals. For this
reason, we sought to develop unsymmetrical dicarbenes to give
greater flexibility in tuning the electronic and steric environments
at each metal.
Figure 2. Labeling schemes for the free dication, pendent, and bridging
NHC/MIC-based systems.
RESULTS AND COMPOUND CHARACTERIZATION
■
Our strategy for generating dicarbene-bridged, mixed-metal
complexes involves the stepwise incorporation of the two metals,
first generating a carbene-anchored/pendent-cation, involving
the first metal, followed by metalation of the pendent group by
the second metal (a “pendent strategy”).38,39 In this manuscript,
we report our studies on the preparation of mixed NHC/MIC
dicarbene (imidazol-2-ylidene/1,2,3-triazol-5-ylidene) proli-
gands and the use of an internal-base strategy for the controlled
stepwise metalation of the dicationic precursors. However, unlike
symmetrical precursors to di-NHCs or di-MICs, the two ends of
the mixed dicarbene precursors have different acidities, and
therefore, the order of metal atom incorporation dictates the
nature of the NHC or MIC attachment in the bridge. On the
basis of the acidities45 of the two species (vide infra), metalation
of the imidazolium end seemed most likely to occur first
(Scheme 1), and certainly in our previous studies, we have
observed that, while the acetate complexes [Pd(OAc)2] and
[Rh(μ-OAc)(COD)]2 are capable of the stepwise deprotonation
and accompanying metalation of diimidazolium groups,39 these
complexes have failed with related ditriazolium groups.38
additionally use the label a in the numbering scheme to indicate
the Me/Me/Bn combination, the label b for Me/Me/Dipp, and c
to denote the tBu/Me/Dipp group of substituents (Dipp = 2,5-
diisopropylphenyl).
Hybrid Dicationic Precursors to Dicarbenes. Albrecht
and Bertrand have reported the synthesis of an MIC (Scheme 2)18,47
by coupling an aryl azide with phenylacetylene (PhCCH)
using “click” chemistry48−53 to form a 1,2,3-triazole, followed by
alkylation at N-3 to generate a cationic triazolium ring, which can
later be deprotonated to form the MIC. In a subsequent report by
Elsevier et al.,54 the preparation of various triazolyl-function-
alized NHCs, in which the triazolyl group functioned as a
pendent hemilabile N donor, was outlined in which an azide was
coupled with the pendent propargyl arm (−CH2CCH) of an
imidazolium salt. Inspired by both of these studies, we began
investigating the synthesis of the desired hybrid NHC/MIC
precursors by combining these two methodologies. From our
perspective, we were more interested in N-alkyl NHCs (in order
to draw direct comparisons to our previous work39); therefore, a
slightly different procedure was developed. In addition, we
wanted to extend the synthetic strategy to the transformation of
the triazole moiety into a cationic triazolium species, which could
be subsequently transformed into an MIC. Our synthesis
(Scheme 3) produces a series of new organic compounds, as is
briefly outlined below.
Throughout this report, we use the abbreviations R1Im(H)-
Trz(H) for the NHC(H)+/MIC(H)+ dicationic dicarbene
R2
R3
precursors, κ1-R1ImTrz(H) for the monodentate NHC-
R2
R3
anchored, pendent-triazolium NHC/MIC(H)+ species, and
μ-R1ImTrz or κ2Cx,Cy-R1ImTrz for bidentate hybrid NHC/
R2
R2
R3
R3
MIC dicarbene bridges or chelates, respectively, which are a
slight modification to the nomenclature for symmetric di-NHCs
and di-MICs used by us previously38,39 and originally suggested
by Green et al.,46 as shown in Figure 2. In these abbreviations, the
imidazole substituent (R1) on the imidazolium/NHC ring
appears first, followed by either the dicationic ring (Im(H)Trz-
(H)), anchored-NHC/pendent-triazolium (κ1-ImTrz(H)), or
bridging NHC/MIC (ImTrz) notation, and finally two stacked
symbols designating the substituents on the triazolium/MIC ring
at the N-3 (R2) and N-1 (R3) positions, respectively. We will
Compounds 2 were produced in near-quantitative yields (2a
had been prepared previously55−57) by the reaction of the N-alkyl
imidazoles (1)58,59 with propargyl bromide in refluxing aceto-
1
nitrile. The products are easily identified by their H NMR
spectra, in which the signal characteristic of the acidic
imidazolium proton is observed as an overlapping doublet of
doublets (or “pseudotriplet”) at ca. δ 9.6, due to equal coupling
to both imidazolium backbone protons. In addition, the spectral
B
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Scheme 2. Reported “Click” Synthesis of a 1,2,3-Triazol-5-ylidene, a Type of MIC
Scheme 3. Synthesis of Dicationic Imidazolium/Triazolium Dicarbene Precursors
parameters of 2a are as previously noted.55−57 Reaction of these
propargyl imidazolium salts with either benzyl azide
(BnN3)60−62 or 2,6-diisopropylphenylazide (DippN3)63 in the
presence of catalytic amounts of copper(I) iodide and triethyl-
amine yields the 1,2,3-triazolyl compounds (3), for which all
1H and 13C{1H} resonances are typical for systems involving
both imidazolium and triazolyl groups.41,64−69 In the cases
involving the bulkier Dipp group (3b, 3c), the 1H and 13C{1H}
resonances representing the methyl groups of each iso-propyl
substituent are in slightly different environments (both closely
spaced resonances at ca. δ 1.1), indicating a barrier to rotation
about the Ar−iPr bond. Furthermore, the resonances corre-
sponding to carbon atoms in the Dipp ring (3b, 3c) also show
evidence for inhibited Ar−iPr bond rotation (two different iPrMe
clean formation of the desired [MeIm(H)Trz(H) ][Br][OTf]
Me
Dipp
(4b) and [tBuIm(H)Trz(H) ][Br][OTf] (4c) products of the
Me
Dipp
general NHC(H)+/MIC(H)+ formulation. Formation of the
desired product is easily monitored by the emergence of a new
signal in the 1H NMR spectrum at ca. δ 4.5, indicating
methylation of the triazolyl moiety (at N-3). Once again, the
other resonances in the H NMR spectrum shift only slightly,
with the exception of the now-acidic triazolium proton, which
moves to higher frequency (ca. δ 8.7).
1
The 13C{1H} NMR spectra of compounds 4 are essentially
identical to those of their precursors (3), with the exception of
the emergence of a new signal at ca. δ 39.2 (for the methyl group
on N-3), and a slight shift of the triazole carbons (CTrz, δ 128 to δ
133) and Cquat (δ 140 to δ 139). It is worth noting that the C−H
coupling constants for the carbon attached to the imidazolium
acidic proton, the carbon attached to the triazolium acidic proton
(CTrz), and one of the carbons in the imidazolium backbone are
abnormally large, such that they are absent in 13C{1H} attached
proton test (APT) NMR experiments (which uses a database of
“normal” 1JC−H values to assign “up” or “down” signal intensity).
Furthermore, the C−H coupling constant for the diisopropyl-
i
environments at ca. δ 24, but only one PrC−H environment,
suggesting that N−Dipp rotation is not inhibited).
As noted earlier, Bertrand et al. had established routes to MICs
via alkylation18 of a triazole group and subsequent deprotonation
to afford the mesoionic species. Although successful methylation
of the triazolyl ring at N-3 by reaction with iodomethane (CH3I)
at elevated temperatures had been reported,31,32,41,47,70−72 we
were unable to methylate our systems in this manner under a
variety of conditions (others had also failed).18,73−75 However,
the triazolyl-functionalized imidazolium salts (3) could be
methylated using methyl trifluoromethanesulfonate (MeOTf),
as explained below. Because alkylation was carried out using
phenyl carbon para to the triazolium ring is so large (1JC−H
210 Hz) that it appears in the opposite phase than expected (with
CH2/Cquat resonances).
The X-ray structure determination for the bis(triflate)
analogue of compound 4b, shown in Figure 3, further confirms
the structural assignments determined on the basis of spectral
data. Although it was reasonably clear from the spectroscopy that
methylation occurred only at the N-3 position (since the MeTrz
resonance in the 1H NMR spectrum displays an NOE correlation
signal with the bridging methylene protons at ca. δ 5.8, while
≈
+
CH3 , the substituent R2 appears as a methyl group in all cases.
Attempts to prepare the sterically less-bulky benzyl-
substituted product 4a did not yield the methylated product
cleanly. It appears that the benzyl group is not sufficiently bulky
to afford regioselective methylation at N-3 (when using MeOTf)
and results in an equal mixture of both N-2- and N-3-methylated
isomers, as determined by 1H NMR spectroscopy, which displays
two sets of resonances for both products, with the most obvious
being two pairs of acidic imidazolium (δ 9.20 and δ 9.15) and
triazolium (δ 9.00 and δ 8.89) signals, as well as two new methyl
resonances (δ 5.62 and δ 5.51). Attempts to convert the N-2-
methylated compounds to the N-3 products by heating a sample
of both were unsuccessful. Crowley et al. reported regioselective
methylation at N-3 using “Meerwein’s salt” (Me3OBF4) in the
synthesis of their di-MIC precursors that contained benzyl
substituents at N-1.73 However, this methylating agent was not
regioselective in our attempts. In the systems reported herein, the
Dipp substituent allows selective methylation at N-3, resulting in
i
none of the Pr resonances on the Dipp group display any
interaction with this group), its N-3 attachment is unambigu-
ously established with this structure determination.
NHC-Anchored/Pendent-Triazolium Complexes of Rh.
As proposed earlier, NHC/MIC dicarbene-bridged complexes
involving two different metals can be accessed via metalation of a
carbene-anchored/pendent-cation complex, of the type shown in
Scheme 1, using a different metal in the second metalation step.
We had already shown that a stepwise metalation strategy could
be employed to generate di-NHC-bridged Rh2,37 Ir/Rh, and Pd/
Rh39 complexes via metalation of mononuclear, anchored species
by [Rh(μ-OAc)(COD)]2. With the dicationic NHC/MIC pre-
Me
Dipp
cursors in hand (namely, [MeIm(H)Trz(H) ][Br][OTf] 4b
C
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in refluxing acetonitrile did not produce the desired NHC-
MIC(H)+ species but, instead, generated a mixture of products,
1
as determined by H NMR spectral analysis (we were able to
conclude that both ends of the dication were being metalated, as
demonstrated by the disappearance of both acidic signals).
During purification attempts, we were able to isolate one product
of this mixture as a chelated-NHC/MIC Rh(III) species with one
OAc− ligand still coordinated (complexes 5b, and 5c, Scheme 4).
Unfortunately, the quantity of 5b isolated was insufficient for
obtaining useful NMR data. These compounds are NHC/MIC
analogues of a di-NHC species previously reported in 2002.77
The X-ray structure determination for the compound 5b,
shown in Figure 4, confirms the chelating arrangement of the
dicarbene, as suggested by the absence of resonances
1
corresponding to acidic protons in the H NMR spectrum.
The rhodium atom in 5b has a distorted octahedral geometry
with a chelated NHC/MIC group and mutually trans-iodo
ligands. The Rh−NHC (Rh−C(4) = 1.968(2) Å) and Rh−MIC
(Rh−C(1) = 1.969(2) Å) bond lengths are virtually identical and
are typical for Rh(III) systems.77 In general, MICs tend to have
shorter metal−MIC bond distances than analogous metal−NHC
cases,31,39 but with an already contracted Rh−NHC bond (owing
to the high oxidation state of Rh); a bond shorter than observed
is probably unfavorable owing to crowding in this six-coordinate
species. Both Rh−acetate bonds (Rh−O(1) and Rh−O(2)) are
essentially identical (2.160(1) and 2.166(1) Å), suggesting no
significant difference in trans influence of the two carbenes in this
system.
Me
Figure 3. Three-dimensional representation of [MeIm(H)Trz(H) ]-
Dipp
[OTf]2 (4b) showing the numbering scheme. Thermal ellipsoids are
shown at the 20% probability level, except for hydrogen atoms, which
are shown artificially small. Relevant parameters (distances in Å and
angles in deg): C(2)−C(3) = 1.347(3), N(2)−C(1) = 1.323(2), N(1)−
C(1) = 1.330(2), C(6)−C(7) = 1.364(2), N(5)−C(6) = 1.359(2),
N(4)−N(5) = 1.321(2), N(3)−N(4) = 1.328(2), N(3)−C(7) =
1.351(2); N(1)−C(1)−N(2) = 108.5(2), N(3)−C(7)−C(6) =
106.0(2), N(4)−N(3)−C(9)−C(14) = 92.3(2).
The internal angles at C(4) (104.3(2)°) and C(1) (102.4(2)°)
are typical for NHC and MIC complexes, which are smaller than
the angles of the respective carbons in the protio ligand 4b
(NHC(H)+ = 108.5(2)°, MIC(H)+ = 106.0(2)°, Figure 3), but
are still larger than in cases of free carbenes of these types (NHC
= ca. 102°, MIC = ca. 100°).1,18 This trend of decreasing angles at
carbon (X2C:−H+ > X2C:−MLn > X2C:) is consistent with
increasing s character in the lone-pair-containing orbital on
carbon. As was observed for 4b, the aryl ring of the Dipp group
adopts an orientation almost perpendicular to the Trz plane
(torsion angle: N(2)−N(1)−C(11)−C(16) = 84.1(2)°), in
which both isopropyl groups lie adjacent to the mutually trans-
iodides, causing them to bend away from these groups (I(1)−
Rh−I(2) = 171.778(8)°). The entire dicarbene is almost planar,
deviating from planarity only slightly at the CH2 linker (torsion
angles: C(3)−N(4)−C(4)−Rh = 7.7(3)° and Rh−C(1)−
C(2)−C(3) = 0.5(3)°).
and [tBuIm(H)Trz(H) ][Br][OTf] 4c), we attempted to use
Me
Dipp
this acetate-containing Rh complex to first metalate half of the
dicationic species 4, in order to form the desired anchored/
pendent product. 1,2,3-Triazol-5-ylidene-type MICs have been
shown to be significantly better electron donors than 1,3-
dialkylimidazol-2-ylidene-type NHCs (based on lower νC−O(trans)
values for carbene-containing carbonyl complexes);18,47,76 there-
fore, it was assumed that the MIC(H)+ end would be much less
acidic than the NHC(H)+ side. Furthermore, in our experience,
acidic protons in the carbene precursors that resonate at higher
frequencies tend to correspond to groups that are more acidic,
suggesting that the imidazolium end would be metalated first to
generate an NHC-anchored/pendent-MIC(H)+ species of Rh,
which could presumably be further metalated by a different basic
ligand-containing metal precursor (M ≠ Rh).
However, reaction of both methyl- (4b) and tert-butyl-substi-
tuted (4c) complexes with half an equivalent of [Rh(μ-OAc)(COD)]2
Scheme 4. Reactions of Dicationic Species 4 with Basic Ligand-Containing Rh Precursors
D
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Because all attempts using [Rh(μ-OAc)(COD)]2 failed to
generate the [RhI(COD)(κ1-R1ImTrz(H) )][I] systems of
Me
Dipp
interest, we attempted metalation using [Rh(μ-OMe)(COD)]2,
containing the stronger methoxide base, allowing the use of
milder conditions. Accordingly, reaction of our imidazolium/
triazolium precursors (4b and 4c) with one-half equivalent of the
methoxide-bridged dimer successfully generates the desired Rh-
bound NHC/MIC(H)+ species 6b or 6c (see Scheme 4), with
only mild heating in acetonitrile.
The 1H NMR spectral parameters for the pair of products (6b
t
(R1 = Me) and 6c (R1 = Bu)) display many similarities to the
NHC-anchored/pendent-imidazolium complexes of Rh, re-
ported by us previously,37,39 but also include some important
differences resulting from the triazolium arm. Compounds 6
show typical resonances for the CH2 groups in the coordinated
COD ligands (between ca. δ 1.0 and 2.6), as well as signals for the
olefinic CH groups cis (ca. δ 3.6) and trans (ca. δ 5.2) to the
NHC. The olefinic protons that are cis or trans to the carbene can
be differentiated since only the cis protons display an NOE
correlation signal with the resonance for the methyl (6b) or tert-
butyl protons (6c). Both resonances for the cis protons overlap
to form a broad singlet, whereas individual multiplets can be seen
for each trans proton.
Figure 4. Three-dimensional representation of [RhI2(κ2O,O′-OAc)-
Me
Dipp
(κ2C2,C5‑MeImTrz
)], 5b, showing the numbering scheme.
Thermal ellipsoids are as described in Figure 3, except for hydrogen
atoms, which are shown artificially small. Relevant parameters
(distances in Å and angles in deg): Rh−C(1) = 1.969(2), Rh−C(4) =
1.968(2), Rh−O(1) = 2.160(1), Rh−O(2) = 2.166(1); N(1)−
C(1)−C(2) = 102.42(16), N(4)−C(4)−N(5) = 104.3(2), C(1)−
Rh−C(4) = 87.79(8), O(1)−Rh−O(2) = 60.86(5), N(4)−C(3)−
C(2) = 111.9(2), O(1)−C(9)−O(2) = 119.4(2), I(1)−Rh−I(2) =
171.778(8), N(2)−N(1)−C(11)−C(16) = 84.1(2), Rh−C(1)−
C(2)−C(3) = 0.5(3), C(3)−N(4)−C(4)−Rh = 7.7(3),
C(1)−Rh−O(1)−C(9) = −177.3(1), C(4)−Rh−O(2)−C(9) =
176.5(1).
The pendent structure of compounds 6 is easily confirmed by
the presence of only one acidic (HTrz) proton in the high-
1
frequency region of the H NMR spectrum as a sharp singlet.
Furthermore, the “pseudotriplets” observed for the imidazolium
backbone protons have simplified into doublets due to the
absence of the 4JH−H coupling to the acidic imidazolium proton
of the precursor. The AB quartet observed for the methylene
Figure 5. (a) Spectral expansion of 1H CSSF/TOCSY and (b) 1H-coupled 13C NMR experiments on 6b.
E
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linker, rather than a singlet, suggests that the NHC unit adopts
the usual orientation in which it is bound perpendicular to the
square plane of the metal. In this orientation, the plane bisecting
the linking CH2 group is unsymmetrical on each side, having an
iodo ligand on one side, and one-half of the COD ligand on the
other.
for the Dipp carbon and a simple doublet for the triazolium
carbon) allowed us to distinguish these two signals.
NHC-Anchored/Pendent-Triazolium Complexes of Pd.
An analogous series of NHC-anchored/pendent-triazolium
complexes of palladium can be generated by similar procedures
used to generate NHC-anchored/pendent-imidazolium com-
plexes by Herrmann78 and our group,39 by reacting the dicationic
1
Finally, the H NMR spectrum implies that there is a signi-
NHC(H)+/MIC(H)+ precursors [MeIm(H)Trz(H) ][Br]-
Me
ficant barrier to rotation about the N−Ar bond of the pendent
Dipp
group (in addition to the barrier for Ar−iPr rotation, as also
[OTf] (4b) and [tBuIm(H)Trz(H) ][Br][OTf] (4c) with the
Me
Dipp
i
observed in compounds 4) since there are four separate PrMe
internal-base-containing [Pd(OAc)2] in the presence of KI in hot
doublets at ca. δ 1.1; and three separate resonances for the
protons on the aryl ring, which all show some degree of mutual
coupling. The low-frequency region is somewhat complicated
because of four different doublets representing four different
iPrMe methyl environments in close proximity (Δδ ≈ 0.1 ppm or
acetonitrile (60 °C), resulting in metalation of the imidazolium
end of the dication, and formation of the zwitterionic species
[PdI3(κ1-R1ImTrz(H) )] (R1 = Me, 7b; Bu, 7c, as shown in
Me
Dipp
t
Scheme 5). Interestingly, the reaction does not proceed without
the addition of potassium iodide, at which point the color
changes instantly (orange to dark purple). Albrecht et al.79 have
shown for di-aNHCs that palladation (using [Pd(OAc)2]) is
only possible if the counteranions are sufficiently strongly
coordinating, such as halides, presumably through the generation
of an anion pair involving [PdI2(OAc)2]2−,78,79 followed by
subsequent metalation of the dicarbene precursor. Furthermore,
if a large excess of potassium iodide is not used in the generation
of 7, or if the solution is heated too long, the pendent complex
converts to an undesireable chelate species, [PdI2(κ2C2,C5-R1-
ImTrzDMiepp)] (8), similar to the proposed Suzuki−Miyaura
catalyst reported by Kahn.41 This structure is proposed on the
basis of preliminary spectroscopic evidence, but was not fully
characterized since it was not a target in our studies.
i
50 Hz). Furthermore, the PrC−H environments are also
overlapping and are also masked by the CODalkyl resonances.
However, using a chemical shift selective filter (CSSF), each
i
individual PrC−H shift (δ 2.44, δ 2.51) can be pinpointed and
selectively excited. Combining this technique with a 1D-total
correlation spectroscopy (1D-TOCSY) experiment allows both
spin systems to be separated, which results in simplification of the
iPrMe region, confirming the existence of one set of well-separated
3
doublets (Δδ ≈ 27.7 Hz, JH−H = 6.8 Hz) and another group
of overlapping doublets, appearing as a triplet (Δδ ≈ 6.6 Hz,
3JH−H = 6.7 Hz) (Figure 5a).
The 13C{1H} NMR spectra for complexes 6 display
resonances typical for a coordinated NHC, a pendent triazolium
group, and a Rh-coordinated COD ligand. Specifically, the
Ccarbene resonance appears as a doublet (1JC−Rh = 49 Hz) at ca. δ
185, whereas the rest of the resonances for the carbons in the
NHC and MIC(H)+ have not changed significantly from the
spectra of compounds 4. Evidence for a chelated COD ligand is
demonstrated by the presence of two doublets at ca. δ 98 (1JC−Rh
≈ 7 Hz) representing the olefinic carbons trans to the NHC, as
well as two doublets at ca. δ 73 (1JC−Rh ≈ 14 Hz) for the carbons
in the cis position. As was observed in the 1H NMR spectrum, the
13C{1H} NMR spectra indicate a barrier to rotation about the
N−Ar bond, as well as the Ar−iPr bond, by the existence of 12
different resonances for the Dipp group. Finally, resonances for
the Dipp carbon para to the triazole ring and the carbon attached
to the acidic triazolium proton in 6b are closely spaced (δ 133.3, δ
133.2) and could not be differentiated by 2D gHSQC or
gHMQC NMR experiments (in both cases, the 2D contours
were centered at δ 133.3). A proton-coupled 13C NMR
experiment allowed for differentiation of these two resonances,
because the carbon and hydrogen nuclei at position 4 (Figure 5b)
Despite the propensity for complexes 7 to convert to these
unwanted chelate species 8, the reaction can easily be halted at
1
the pendent stage by careful monitoring of the H NMR
spectrum. Over the course of 1−2 h under gentle heating, one of
the high-frequency acidic resonances (representing the imida-
zolium end of species 4) begins to disappear, while new (slightly
shifted) ligand signals emerge in the spectrum. The final pendent
formulation for complexes 7 is again easily confirmed by the
presence of only one acidic proton in the high-frequency region
of the 1H NMR spectrum as a slightly broad singlet. Unlike the
Rh pendent cases (6), the 1H NMR resonance for the CH2 group
remains as a singlet, owing to the higher symmetry at palladium
(mutually trans-I− ligands). Again, the 1H NMR spectrum
implies that there is a significant barrier to rotation about the
Ar−iPr bond since there are two separate iPr doublets around δ
1.1 (separated by ca. 0.5 ppm).
The 13C{1H} NMR spectra for complexes 7 display signals
similar to the NHC/MIC(H)+ group of the Rh complexes 6.
Although no carbene resonance could be observed in previously
reported Pd triiodo NHC-anchored/pendent-carbene(H)+
complexes,39,78 the Ccarbene resonance can be observed here
upon overnight acquisition on a concentrated sample using a
high-sensitivity cold-dual probe. This resonance appears as a
1
display the same “abnormally large” JC−H behavior of its
precursor 5b. This large C−H coupling (1JC(Dipp)−H = 209.5 Hz as
1
opposed to JC(Trz)−H = 160.7 Hz) in addition to the obvious
difference in coupling patterns (a doublet of doublet of doublets
Scheme 5. Generation of Anchored/Pendent and Chelated NHC/MIC Complexes of Palladium
F
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singlet at ca. δ 162. Evidence for inhibited Ar−iPr bond rotation
As observed in our previous report,39 substitution of the iodo
ligand opposite the carbene can be effected by adding 1 equiv of
PEt3 or PPh3 to acetonitrile solutions of 7 (Scheme 6). Upon
phosphine addition, each solution immediately changes from
dark purple to bright yellow, corresponding to the generation of
i
is also present since two closely separated Pr resonances are
observed (separated by ca. 0.8 ppm).
The X-ray structure determination for the compound 7b,
shown in Figure 6, confirms the pendent structure proposed on
trans-[PdI2(PEt3)(κ1-R1ImTrz(H) )][I] 9trans and trans-
Me
Dipp
Me
[PdI2(PPh3)(κ1-R1ImTrz(H) )][I] 10trans from the triiodo
Dipp
precursors. However, for the sterically less-bulky complex 7b
(R1 = Me), the cis isomers 9bcis and 10bcis are formed together
with the trans isomers, as shown in Scheme 6, in about a 50:50
cis/trans ratio for 9b and about a 35:65 ratio for 10b. Although
sterically less-favored, the cis position is more electronically
preferred owing to the high trans effect of both the NHC and the
PR3 ligands. This site is presumably less accessible in a species
t
having bulky substituents (R1 = Bu) on the NHC’s outer
nitrogen atom. A solution containing a mixture of both isomers
can be completely converted to the thermodynamically favored
cis products (9bcis or 10bcis) with gentle heating in acetonitrile
over the course of 2 h. Owing to this facile isomerization, we were
unable to isolate the kinetic products 9btrans and 10btrans
.
The existence of two products in the less-bulky anchored-
NHC (R1 = Me) is obvious from two singlets in the 31P{1H}
NMR spectrum as well as roughly twice as many signals as
1
expected in the H NMR spectrum. Although most of the
Figure 6. Three-dimensional representation of [PdI3(κ1-MeImTrz-
1
resonances in the H NMR spectrum for both cis and trans
Me
(H) )], 7b, showing the numbering scheme. Thermal ellipsoids are
Dipp
isomers differ only slightly, a few major differences are observed
that can help to distinguish the two. For example, the protons in
the methylene CH2 linker of the cis isomers are in significantly
different environments as a result of the lower symmetry at Pd,
resulting in two doublets (an “AB quartet”) for the linker protons
in the cases of 9bcis and 10bcis, showing mutual coupling, whereas
both protons are represented by a singlet in all trans systems. In
both cis complexes, the combination of front/back asymmetry
and inhibited rotation about both Ar−iPr bonds results in the
inequivalence of all nine proton environments in the Dipp group
(as was observed in 6, in which all Dipp groups became
diastereotopic). As a result, the aryl region is slightly more
complicated, as is the region for iPr groups.
as described in Figure 3, with hydrogen atoms shown artificially small.
Relevant parameters (distances in Å and angles in deg): Pd−C(1) =
1.96(1), I(1)−Pd = 2.604(2), I(2)−Pd = 2.598(2), I(3)−Pd =
2.668(2); I(3)−Pd−C(1) = 176.1(3), I(1)−Pd−I(2) = 172.68(4),
N(1)−C(1)−N(2) = 103.6(8), N(5)−C(7)−C(6) = 106(1); NHC
and Pd square planes’ dihedral angle = 86.1(3), NHC and MIC(H)+
planes’ dihedral angle = 78.8(4), MIC(H)+ and PhDipp planes’ dihedral
angle = 82.1(4).
the basis of spectral data and carbene formation via the NHC
end. The Pd atom has a slightly distorted square-planar geometry
with three coordinated iodo ligands, an anchored-NHC lying
essentially perpendicular to the square plane (94.5(9)°), and a
pendent-MIC(H)+ group. The length of the Pd−Ccarbene bond
(Pd−C(1) = 1.96(1) Å) is significantly shorter than reported
examples having a trans-phosphine (Pd−Ccarbene ca. 2.05 Å),39
but is similar to other Pd−CNHC bonds trans to ligands with a low
trans influence (NHC−Pd(κ2O,O′-OAc) = 1.953(5) Å and
NHC−PdI3 = 1.990(9) Å).78 Again, the aryl ring of the Dipp
group adopts an orientation almost perpendicular to the Trz(H)
plane (82.1(4)°). Furthermore, the planes of the NHC and
MIC(H)+ rings lie in almost perpendicular arrangements
(dihedral angle = 78.8(4)°).
The 13C{1H} NMR spectra for the isolated complexes display
resonances similar to the NHC/MIC(H)+ group of the
zwitterionic complexes 7. Interestingly, although the 13C{1H}
resonance for the carbene carbon is difficult to observe for “PdI3”
adducts,39,78 it is clearly seen in PR3-substituted analogues. The
resonance representing the carbene in these species appears at ca.
δ 165, as a singlet in the case of both cis complexes (showing no
coupling to the cis phosphorus atom) and as a doublet for both
trans systems (2JC−P ≈ 185 Hz). In addition to the extra signals
for the carbons on the phosphine (which can easily be located
Scheme 6. Displacement of Iodo Ligands for Monophosphines in Pd Pendent Complexes
G
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Me
Figure 7. Three-dimensional representation of one independent molecule of cis-[PdI2(PPh3)(κ1-R1ImTrz(H) )][I], 10bcis, showing the numbering
Dipp
scheme. Thermal ellipsoids are as described in Figure 3, with hydrogen atoms shown artificially small. Relevant parameters (distances in Å and angles in
deg): Pd−C(1) = 2.003(4), 1.988(4); Pd−P(1) = 2.268(1), 2.273(1); I(1)−Pd = 2.6569(6), 2.6525(6); I(2)−Pd = 2.6408(6), 2.6434(6); I(2)−Pd−
C(1) = 175.9(1), 174.5(1); I(1)−Pd−P(1) = 175.21(3), 174.50(3); N(1)−C(1)−N(2) = 105.1(3), 104.6(3); N(5)−C(7)−C(6) = 105.8(3),
105.6(3); NHC and Pd square planes’ dihedral angle = 86.25(9), 88.71(9); NHC and MIC(H)+ planes’ dihedral angle = 82.1(2), 80.9(2); MIC(H)+
and PhDipp planes’ dihedral angle = 82.1(1), 75.8(1).
Scheme 7. Synthesis of NHC/MIC-Bridged Pd/Rh Complex via the Pendent Strategy
with 13C{1H,31P} experiments), there are 12 different signals for
the Dipp group.
An NHC/MIC-Bridged Rh/Pd Complex. Although Al-
brecht et al. had shown that [Pd(OAc)2] could metalate 1,2,3-
triazolium species at around 120 °C,31 this reagent failed to
metalate the NHC-anchored/pendent-MIC(H)+ complexes of
Rh (6b and 6c) at temperatures below 100 °C, while at higher
temperatures, only decomposition occurred. This outcome
parallels our earlier failures to effect deprotonation and
accompanying metalation of pendent triazolium groups using
[Pd(OAc)2].38 In this earlier study, the second metalation step,
involving a pendent triazolium group, could be successfully
accomplished using the more basic, methoxide-bridged [Rh(μ-
OMe)(COD)]2 and [Ir(μ-OMe)(COD)]2, suggesting that our
targeted NHC/MIC-bridged complexes of Pd/Rh could be
accessed through metalation of the pendent triazolium groups in
the Pd complexes 7, 9, and 10 using the methoxide-bridged Rh
species. Although this strategy was successful in the reaction of
9ctrans, to yield the mixed-metal product 11, as shown in Scheme 7,
it was surprisingly unsuccessful with the closely related triiodo
Pd complex (7) and with the triphenylphosphine analogue
(10ctrans), both of which gave no product at temperatures below
100 °C and gave only decompositions above this temperature.
Furthermore, the cis complexes (9bcis and 10bcis) displayed a
The X-ray structure determination for 10bcis, shown in
Figure 7, confirms the pendent nature of the NHC/triazolium
group and the cis orientation of the phosphine group, as
proposed on the basis of spectral data. The Pd atom has a slightly
distorted square-planar geometry (I(2)−Pd−C(1) = 175.9(1)°,
I(1)−Pd−P(1) = 175.21(3)°) with two cis-oriented iodo
ligands, an anchored-NHC lying essentially perpendicular to
the square plane (dihedral angle = 86.25(9)°), and a coordinated
phosphine. The Pd−Ccarbene bond (Pd−C(1) = 2.003(4) Å) is
longer than that in 7b (1.96(1) Å), in which an iodo ligand
occupies the trans position, but is shorter than that observed
when a phosphine group is trans (Pd−Ccarbene ca. 2.05 Å).39 The
first difference is presumably a result of steric repulsion between
the adjacent phosphine and carbene ligands, while the second is
undoubtedly a consequence of the high trans influence of the
phosphine ligand. Again, the aryl ring of the Dipp group
adopts an orientation almost perpendicular to the Trz plane
(dihedral angle = 82.1(1)°). Furthermore, the planes of the
NHC and MIC(H)+ rings lie in almost perpendicular
arrangements (dihedral angle = 82.1(2)°).
H
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similar decomposition when reacted with [Rh(μ-OMe)-
(COD)]2. These results parallel our earlier attempts to prepare
di-NHC-bridged complexes of Pd/Rh, for which only the
palladium analogue having the PEt3 group opposite the carbene
successfully yielded the di-NHC-bridged Pd/Rh target.39
Complex 11 is also unstable at higher temperatures and begins
to decompose if the solution is heated for prolonged periods of
time; as a result, careful monitoring of the reaction progress by
1H NMR spectroscopy is usually required to prevent subsequent
decomposition.
product having Pd bound to the NHC end while Rh is attached
to the MIC end. However, metalation of the triazolium group of
the analogous Rh(NHC) complexes (6b or 6c) by [Pd(OAc)2]
to give a species having Pd bound to the MIC was unsuccessful.
Presumably, the lower acidity of the triazolium group does not
allow metalation by the less basic acetate ligands under
conditions mild enough to avoid decomposition. The conditions
reported by Albrecht et al. for metalating triazolium groups using
[Pd(OAc)2], to yield Pd−MIC complexes,31 proved to be too
harsh in our system. Nevertheless, such Rh(NHC)/Pd(MIC)
species should be accessible through reactions of the appropriate
Rh(NHC)/pendent-triazolium species with Pd complexes
having ligands, such as methoxide, that are of sufficient basicity
to result in metalation of the pendent group under conditions
mild enough to prevent subsequent decomposition. Such
strategies for the preparation of a wide range of mixed-metal
products bridged by mixed NHC/MIC dicarbenes should be
successful once the appropriate combination of an NHC-bound/
pendent-triazolium complex of one metal and a base-containing
complex of the other is found.
The capricious nature of these metalations remains puzzling,
however. The use of half an equivalent of [Rh(μ-OMe)(COD)]2
in order to facilitate metalation of the pendent triazolium groups
in complexes 7, 9, and 10 was only successful with the trans-PEt3-
containing species 9ctrans. Interestingly, we had previously also
been successful in generating a closely related di-NHC-bridged
Pd/Rh species only when the NHC-anchored/pendent-
imidazolium Pd precursor was analogous to 9ctrans, containing
a PEt3 ligand trans to the carbene.39 Although we have succeeded
in generating the first NHC/MIC-bridged mixed-metal complex,
it is evident that this “pendent” strategy, although promising,
requires further development, at least with the Pd/Rh
combination, before it can be considered as a general route to
dicarbene-bridged mixed-metal complexes.
Unfortunately, repeated attempts to obtain single crystals of
11, suitable for an X-ray diffraction study, failed; nevertheless, the
spectral data leave little doubt about its formulation. Formation
of the bimetallic species is supported by the emergence of a
slightly shifted resonance for the PEt3 group in the 31P{1H}
NMR spectrum, as well as the disappearance of the high-
frequency resonance in the 1H NMR spectrum (provided in the
Supporting Information) representing the acidic proton on the
triazolium group. Furthermore, the obvious transformation of
the singlet methylene CH2 resonance of 9ctrans in the 1H NMR
spectrum to an AB quartet of 11 is further indication of front−
back asymmetry in the complex, a result of the lower symmetry at
Rh. The 1H NMR resonances for the COD ligands are similar to
those in the Rh pendent complexes (6) noted earlier; however,
they now display an NOE interaction with the ethyl protons from
the PEt3 group attached to Pd. The 13C{1H} NMR spectrum of
11 indicates formation of a new species having two metal−
carbene moieties by the emergence of two new signals in the
typical carbene region; although the doublet (2JP−C = 184.3 Hz)
for the Pd-bound carbene does not shift significantly from that of
the precursor, a new doublet (1JC−Rh = 44.7 Hz) representing the
Rh-bound carbene emerges at δ 173.4. This latter value, which is
at a slightly lower frequency compared with our previous Rh-
NHC noted above,39 is comparable to the other Rh-MIC
complexes reported thus far by Albrecht et al. and Crudden et
al.,31,34 who report the carbene resonance at ca. δ 172.
EXPERIMENTAL SECTION
■
General Comments. Deuterated solvents used for NMR experi-
ments were freeze−pump−thaw degassed and stored under argon over
appropriate molecular sieves. Unless otherwise specified, reactions were
carried out at ambient temperature. Potassium iodide was purchased
from ACP; ammonium carbonate, tert-butylamine, cycloocta-1,5-diene,
2,6-diisopropylaniline, formaldehyde, glyoxal, 1-methylimidazole (1a),
methyltrifluoromethanesulfonate, palladium(II) acetate, propargyl bro-
mide, sodium tetrafluoroborate, triethylphosphine, and triphenylphos-
phine were purchased from Aldrich; triethylamine was purchased from
Anachemia; sodium nitrite and potassium hydroxide were purchased
from Caledon Laboratory Chemicals; sodium azide was purchased from
J.T. Baker Chemical Co.; copper(I) iodide and sodium acetate were
purchased from Fischer Scientific; and rhodium(III) chloride hydrate was
purchased from Pressure Chemical Company. All chemicals were used
without further purification, with the exception of sodium acetate and
potassium iodide, which were purified by repetitive melting under
dynamic vacuum before use. Compound 1c has been reported
previously,59 but was prepared here using tert-butylamine in a
modification to the general procedure for 1-arylimidazoles.58 Com-
pounds 2a,55−57 azidomethylbenzene (BnN3),60,61 2-azido-1,3-diiso-
propylbenzene (DippN3),63 (cycloocta-1,5-diene)(μ-dichloro)-
dirhodium ([Rh(μ-Cl)(COD)]2),80,81 and bis(cycloocta-1,5-diene)(μ-
methoxide)dirhodium ([Rh(μ-OMe)(COD)]2)82 were prepared as
reported previously, and bis(cycloocta-1,5-diene)(μ-diacetato)-
dirhodium ([Rh(μ-OAc)(COD)]2)83 was prepared as previously
reported and recrystallized from ethyl acetate. Caution! Organic azides
are potentially explosive substances that can decompose readily upon
exposure to heat, light, or pressure. Appropriate safety precautions should
be exercised (i.e., proper lab protection, blast shields, etc.) to prevent
serious injury. The 1H and 13C{1H} NMR spectra were recorded on a
DISCUSSION
■
In this work, we set out to design a set of hybrid dicarbenes based
on linked NHC and MIC functionalities for the purpose of
bridging pairs of different metals that could potentially show
subsequent utility in tandem catalysis, wherein the different
metals would display different and orthogonal catalytic roles.
We have succeeded in devising simple routes to NHC/MIC
precursors based on literature precedent by functionalizing an
imidazolium salt with a pendent propargyl arm, and subsequently
using “click” chemistry to transform this group into a triazole.
Methylation transforms the imidazolium/triazole into an
imidazolium/triazolium dication, which can be metalated in a
stepwise manner, through reaction with a base-containing
complex, such as [Rh(μ-OMe)(COD)]2 or [Pd(OAc)2], in the
presence of KI. Metalation first occurs at the more acidic
imidazolium end to give the NHC-bound, pendent-triazolium
Me
complexes, [RhI(COD)(κ1-R1ImTrz(H) )][I] (R1 = Me (6b),
Dipp
tBu (6c)) or [PdI3(κ1-R1ImTrz(H) )] (R1 = Me (7b),
Me
Dipp
tBu (7c)), respectively.
In principle, these two classes of NHC-bound complexes of Rh
and Pd can be used to access isomeric classes, differing with respect
to which end of the NHC/MIC dicarbene the two different metals
(Rh or Pd) are bound. This strategy works well in metalation of the
pendent triazolium functionality of trans-[PdI2(PEt3)(κ1-MeImTrz-
Me
Dipp
(H) )][I] (9ctrans) by [Rh(μ-OMe)(COD)]2, generating the
I
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dual cold probe-equipped Varian DirectDrive 500 MHz, iNova-500,
iNova-400, or Varian iNova-300 spectrometer operating at the
resonance frequencies of the NMR nuclei given below in the
spectroscopic data. Chemical shifts are reported in parts per million
(δ). The 1H and 13C{1H} chemical shifts are referenced to TMS,
19F{1H} chemical shifts are referenced to CFCl3, and 31P{1H} chemical
shifts are referenced to 85% H3PO4 in H2O. The following abbreviations are
used in describing NMR couplings: (s) singlet, (d) doublet, (t) triplet, (q)
quartet, and (br) broad. Resonances within a group are separated by
commas, and separated from other groups by semicolons. The group is
identified in parentheses for the last resonance given for the group. Mass
spectrometric analyses were performed by the departmental Mass
Spectrometry Laboratory using positive ion electrospray ionization on an
Agilent Technologies 6220 Accurate-mass TOF LC/MS.
3JH−H = 7.0 Hz, 3JH−H = 7.0 Hz, iPrCH); 1.01 (d, 6H, 3JH−H = 7.0 Hz), 1.00
(d, 6H, JH−H = 7.0 Hz, PrCH3). 13C{1H} NMR (100.54 MHz,
chloroform-d, 26.5 °C): δ 145.8 (s, 2C, C iPr); 139.9 (s, 1C, CH2CCH);
137.0 (s, 1C, NCHN); 132.6 (s, 1C, NCAr); 131.0 (s, 1C), 123.8 (s, 2C,
CHAr); 127.8 (s, 1C, CHTrz); 123.6 (s, 1C), 122.7 (s, 1C, NCHimid); 44.2
(s, 1C, CH2); 36.9 (s, 1C, NCH3); 28.3 (s, 2C, iPrCH); 24.1 (s, 2C), 23.9
(s, 2C, iPrCH3). HRMS m/z Calcd for C19H26N5 (M+ − Br−): 324.2183.
Found: 324.2183 (M+ − Br−). Anal. Calcd for C19H26BrN5: C, 56.44; H,
6.48, N, 17.32. Found: C, 56.21; H, 6.47; N, 17.12.
3
i
1-(tert-Butyl)-3-((1-(2,6-diisopropylphenyl)-1H-1,2,3-triazol-4-yl)-
methyl)-3-methyl-1H-imidazol-2-ium bromide, [tBuIm(H)TrzDipp][Br]
(3c). The desired product was prepared as described for 3a, using 2c
(2.64 g, 10.9 mmol), 2-azido-1,3-diisopropylbenzene (2.31 g, 11.4
mmol), CuI (0.10 g, 0.53 mmol), and NEt3 (0.98 g, 9.7 mmol). The
solution changed from red/yellow to dark green instantly and was
stirred overnight. The crude product was purified as described for 3a and
isolated as a dark yellow powder (3.257 g, 67%). 1H NMR (498.12 MHz,
chloroform-d, 27.5 °C): δ 10.64 (br s, 1H, NCHN); 8.50 (s, 1H, HTrz);
7.78 (br s, 1H), 7.49 (br s, 1H, NCHimid); 7.44 (t, 1H, 3JH−H = 8.2 Hz),
Preparation of Compounds. 1-(tert-Butyl)3-prop-2-yn-1-yl-1H-
imidazol-2-iumbromide, [tBuIm(H)CH2CCH][Br] (2c). A 20 mL
portion of acetonitrile was added to a flask containing 1-tert-
butylimidazole (16.4 g, 0.132 mol). An approximately 2-fold excess of
an 80 wt % solution (in dioxane) of propargyl bromide (37.0 mL, 0.333
mol) was slowly added to the mixture. The resulting solution was stirred
for 24 h under reflux conditions and cooled to ambient temperature. The
solvent was then removed under reduced pressure, and the crude
product was washed with 5 × 20 mL portions of diethyl ether before
3
7.23 (d, 2H, JH−H = 8.2 Hz, Ar); 6.02 (s, 2H, CH2); 2.08 (qq, 2H,
3JH−H = 7.3 Hz, 3JH−H = 7.3 Hz, iPrCH); 1.69 (s, 9H, NtBu); 1.07 (d, 6H,
3JH−H = 7.3 Hz), 1.06 (d, 6H, 3JH−H = 7.3 Hz, iPrCH3). 13C{1H} NMR
(125.69 MHz, chloroform-d, 26.1 °C): δ 145.8 (s, 2C, C iPr); 140.2 (s,
1C, CH2CCH); 135.7 (s, 1C, NCHN); 132.7 (s, 1C, NCAr); 131.0 (s,
1C), 123.9 (s, 2C, CHAr); 128.1 (s, 1C, CHTrz); 122.6 (s, 1C), 119.4 (s, 1C,
NCHimid); 60.6 (s, 1C, NC(CH3)3); 44.2 (s, 1C, CH2); 30.1 (s, 3C,
NC(CH3)3); 28.4 (s, 2C, iPrCH); 24.2 (s, 2C), 24.0 (s, 2C, iPrCH3). HRMS
m/z Calcd for C22H32N5 (M+ − Br−): 366.2651. Found: 366.2652 (M+ −
Br−). The 1H (Figure S5) and 13C{1H} (Figure S6) NMR spectra of this
compound are given in the Supporting Information.
1
drying in vacuo, giving a brown, viscous oil (25.7 g, 80%). H NMR
(299.97 MHz, acetonitrile-d3, 27.5 °C): δ 9.71 (dd, 1H, 4JH−H = 1.7 Hz,
4JH−H = 1.7 Hz, NCHN); 7.76 (dd, 1H, 3JH−H = 1.7 Hz, 4JH−H = 1.7 Hz),
7.70 (dd, 1H, 3JH−H = 1.7 Hz, 4JH−H = 1.7 Hz, NCHimid); 5.32 (d, 2H,
4JH−H = 2.5 Hz, CH2); 3.13 (t, 1H, 4JH−H = 2.5 Hz, CCH); 1.68 (s, 9H,
NtBu). 13C{1H} NMR (100.58 MHz, acetonitrile-d3, −0.1 °C): δ 135.9
(s, 1C, NCHN); 123.0 (s, 1C), 121.2 (s, 1C, NCHimid); 77.9 (s, 1C, C
CH); 76.0 (s, 1C, CCH); 61.3 (s, 1C, NC(CH3)3); 39.8 (s, 1C, CH2);
29.7 (s, 3C, NC(CH3)3). HRMS m/z Calcd for C10H15N2 (M+ − Br−):
Attempted Synthesis of 1-Benzyl-3-methyl-4-((1-methyl-1H-imi-
dazol-2-ium-3-yl)methyl-1H-1,2,3-triazol-3-ium bromide, [MeIm(H)-
Trz(H)MBne][Br][OTf] (4a). A 10 mL portion of CH2Cl2 was added to a flask
containing 3a (0.074 g, 0.22 mmol). The resulting solution was stirred for 10
min at room temperature, then cooled to −78 °C, followed by the rapid
injection of MeOTf (25 μL, 0.23 mmol) under an inert Ar(g) atmosphere,
resulting in a cloudy discharge above the solution. The solution was allowed
to warm to room temperature and was stirred overnight, wherein the
solution eventually turned dark red. The solvent was removed under
reduced pressure, and the crude product was washed with 5 × 20 mL
portions of n-pentane before drying in vacuo. Analysis of the crude mixture
by a 1H NMR spectrum indicated a mixture of N-2- and N-3-methylated
signals. As a result, the species was not characterized further.
1
163.1230. Found: 163.1229 (M+ − Br−). The H (Figure S1) and
13C{1H} (Figure S2) NMR spectra of this compound are given in the
Supporting Information.
1-((1-Benzyl)-1H-1,2,3-triazol-4-yl)methyl-3-methyl-1H-imidazol-
2-ium bromide, [MeIm(H)TrzBn][Br] (3a). A 30 mL portion of MeOH/
H2O (50:50) was added to a flask containing 2a (0.400 g, 1.99 mmol)
and azidomethylbenzene (0.572 g, 4.30 mmol). The resulting solution
was stirred for 10 min, followed by the rapid addition of CuI (0.096 g,
0.504 mmol) and NEt3 (0.63 mL, 4.5 mmol), at which point the solution
turned dark green. This solution was stirred at room temperature
overnight, followed by filtering and extraction of the product with
chloroform. The solution was dried using MgSO4 and decanted, and the
solvent was removed under reduced pressure, followed by washing of
the crude product with 5 × 20 mL portions of n-pentane before drying in
vacuo, giving a dark yellow oil (0.599 g, 90%). 1H NMR (299.97 MHz,
chloroform-d, 27.5 °C): δ 9.97 (br dd, 1H, 4JH−H = 1.6 Hz, 4JH−H = 1.6
Hz, NCHN); 8.35 (s, 1H, HTrz); 7.67 (br dd, 1H, 3JH−H = 1.6 Hz, 4JH−H
= 1.6 Hz), 7.38 (br dd, 1H, 3JH−H = 1.6 Hz, 4JH−H = 1.6 Hz, NCHimid);
7.33−7.21 (m, 5H, Ph); 5.72 (s, 2H, Im(H)CH2Trz); 5.46 (s, 2H,
NCH2Ph); 3.92 (s, 3H, CH3). 13C{1H} NMR (125.69 MHz,
chloroform-d, 27.7 °C): δ 140.3 (s, 1C, CH2CCH); 136.9 (s, 1C,
NCHN); 134.3 (s, 1C, NCH2CAr); 129.1 (s, 2C), 128.8 (s, 1C), 128.3 (s,
2C, CHAr); 125.2 (s, 1C, CHTrz); 123.4 (s, 1C), 122.7 (s, 1C, NCHimid);
54.3 (s, 1C, NCH3); 41.0 (s, 1C, Im(H)CH2Trz); 36.8 (s, 1C, NCH2Ph).
HRMS m/z Calcd for C14H16N5 (M+ − Br−): 254.1400. Found: 254.1399
(M+ − Br−). The 1H (Figure S3) and 13C{1H} (Figure S4) NMR spectra of
this compound are given in the Supporting Information.
1-(2,6-Diisopropylphenyl)-3-methyl-4-((1-methyl-1H-imidazol-2-
ium-3-yl)methyl-1H-1,2,3-triazol-3-ium bromide trifluoromethane-
Me
sulfonate, [MeIm(H)Trz(H) ][Br][OTf] (4b). The desired product was
Dipp
prepared as described for 4a, using 3b (2.04 g, 5.05 mmol) and MeOTf
(0.83 mL, 7.6 mmol). The crude product was purified as described for 4a
and recrystallized from acetone/diethyl ether as a white microcrystalline
product (1.481 g, 52%). 1H NMR (499.82 MHz, acetonitrile-d3, 27.7 °C):
δ 8.94 (br s, 1H, NCHN); 8.69 (s, 1H, HTrz); 7.70 (dd, 1H, 3JH−H = 2.0
4
3
4
Hz, JH−H = 2.0 Hz), 7.54 (dd, 1H, JH−H = 2.0 Hz, JH−H = 2.0 Hz,
NCHimid); 7.73 (t, 1H, 3JH−H = 7.7 Hz), 7.51 (d, 2H, 3JH−H = 7.7 Hz, Ar);
5.87 (s, 2H, CH2); 4.44 (s, 3H, MeTrz); 3.95 (s, 3H, MeIm); 2.31 (qq, 2H,
3JH−H = 6.8 Hz, 3JH−H = 6.8 Hz, iPrCH); 1.20 (d, 6H, 3JH−H = 6.8 Hz), 1.16
(d, 6H, 3JH−H = 6.8 Hz, iPrCH3). 13C{1H} NMR (100.58 MHz, acetonitrile-
d3, 27.0 °C): δ 145.6 (s, 2C, C−iPr); 138.8 (s, 1C, CH2CCH); 137.6 (s, 1C,
NCHN); 130.6 (s, 1C, NCAr); 133.2 (s, 1C), 124.8 (s, 2C, CHAr); 133.0 (s,
1C, CHTrz); 124.8 (s, 1C), 122.9 (s, 1C, NCHimid); 121.0 (q, 1C, 1JC−F
=
1-((1-(2,6-Diisopropylphenyl)-1H-1,2,3-triazol-4-yl)methyl)-3-
methyl-1H-imidazol-2-ium bromide, [MeIm(H)TrzDipp][Br] (3b). The
desired product was prepared as described for 3a, using 2a (1.27 g, 6.32
mmol), 2-azido-1,3-diisopropylbenzene (1.32 g, 6.49 mmol), CuI (0.14
g, 0.74 mmol), and NEt3 (0.86 g, 8.5 mmol). The solution changed from
red/yellow to dark green instantly and was stirred overnight. The crude
product was purified as described for 3a and isolated as a dark yellow
320.3 Hz, OSO2CF3); 41.5 (s, 1C, CH2); 39.2 (s, 1C, MeTrz); 36.4 (s, 1C,
MeIm); 28.2 (s, 2C, iPrCH); 23.5 (s, 2C), 22.8 (s, 2C, iPrCH3). 19F{1H} NMR
(468.66 MHz, acetonitrile-d3, 27.0 °C): δ −79.3 (s, 3F, OSO2CF3). HRMS
m/z Calcd for C21H29F3N5O3S (M+ − Br−): 488.1938. Found: 488.1936
(M+ − Br−). Anal. Calcd for bis(triflate) salt, C22H29F6N5O6S2: C, 41.44; H,
4.58, N, 10.98. Found: C, 41.48; H, 4.37; N, 10.74. The 1H NMR spectrum
of this compound is given in the Supporting Information (Figure S7).
4-((1-tert-Butyl)-1H-imidazol-2-ium-3-yl)methyl-1-(2,6-diisopro-
1
powder (0.825 g, 32%). H NMR (399.79 MHz, chloroform-d, 26.5
°C): δ 10.15 (br s, 1H, NCHN); 8.37 (s, 1H, HTrz); 7.81 (br s, 1H), 7.54
pylphenyl)-3-methyl-1H-1,2,3-triazol-3-ium bromide trifluorome-
Me
(br s, 1H, NCHimid); 7.40 (t, 1H, 3JH−H = 8.8 Hz), 7.18 (d, 2H, 3JH−H
=
thanesulfonate, [tBuIm(H)Trz(H) ][Br][OTf] (4c). The desired prod-
Dipp
8.8 Hz, Ar); 5.93 (s, 2H, CH2); 4.02 (s, 3H, NCH3); 2.02 (qq, 2H,
uct was prepared as described for 4a, using 3c (3.00 g, 6.72 mmol) and
J
dx.doi.org/10.1021/om3004543 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
MeOTf (2.2 mL, 20.1 mmol). The crude product was purified as
described for 4a and recrystallized from acetone/diethyl ether as a white
microcrystalline product (3.102 g, 76%). 1H NMR (498.12 MHz,
acetonitrile-d3, 26.1 °C): δ 9.12 (br s, 1H, NCHN); 8.75 (s, 1H, HTrz);
7.77 (br s, 1H), 7.74 (br s, 1H, NCHimid); 7.71 (t, 1H, 3JH−H = 8.1 Hz),
7.49 (d, 2H, 3JH−H = 8.1 Hz, Ar); 5.88 (s, 2H, CH2); 4.46 (s, 3H, MeTrz);
2.31 (qq, 2H, 3JH−H = 6.7 Hz, 3JH−H = 6.7 Hz, iPrCH); 1.67 (s, 9H, tBu);
CD2Cl2, 27.7 °C): δ 8.22 (br s, 1H, HTrz); 8.03 (d, 1H, 3JH−H = 2.0 Hz),
7.01 (d, 1H, 3JH−H = 2.0, NCHimid); 7.63 (dd, 1H, 3JH−H = 8.0 Hz, 3JH−H
=
4
8.0 Hz), 7.39 (dd, 1H, 3JH−H = 8.0 Hz, JH−H = 1.3 Hz), 7.36 (dd, 1H,
3JH−H = 8.1 Hz, 4JH−H = 1.3 Hz, Ar); 6.56 (d, 1H, 2JH−H = 16.1 Hz), 6.34
(d, 1H, 2JH−H = 16.1 Hz, CH2); 4.75 (s, 3H, MeTrz); 4.00 (s, 3H, MeIm);
2.51 (qq, 1H, 3JH−H = 6.7 Hz, 3JH−H = 6.7 Hz), 2.44 (qq, 1H, 3JH−H = 6.8
Hz, 3JH−H = 6.8 Hz, iPrCH); 1.19 (d, 3H, 3JH−H = 6.7 Hz), 1.18 (d, 3H,
3JH−H = 6.8 Hz), 1.17 (d, 3H, 3JH−H = 6.7 Hz), 1.12 (d, 3H, 3JH−H = 6.8 Hz,
iPrCH3); 5.24 (m, 1H), 5.12 (m, 1H), 3.60 (br m, 2H), 2.55−0.88 (m, 8H,
COD). 13C{1H} NMR (100.58 MHz, CD2Cl2, 27.7 °C): δ 185.0 (d, 1C,
1JC−Rh = 49.2 Hz, Ccarbene); 146.5 (s, 1C), 146.1 (s, 1C, C−iPr); 142.2 (s,
1C, CH2CCH); 133.3 (s, 1C), 125.1 (s, 1C), 125.0 (s, 1C, CHAr); 131.1
(s, 1C, NCAr); 133.2 (s, 1C, CHTrz); 124.3 (s, 1C), 122.5 (s, 1C,
NCHimid); 44.7 (s, 1C, CH2); 41.1 (s, 1C, MeTrz); 38.2 (s, 1C, MeIm); 29.0
(s, 1C), 28.9 (s, 1C, iPrCH); 25.0 (s, 1C), 24.6 (s, 1C), 24.1 (s, 1C), 24.0 (s,
1C, iPrCH3); 98.3 (d, 1C, 1JC−Rh = 6.7 Hz), 97.1 (d, 1C, 1JC−Rh = 6.4 Hz),
73.4 (d, 1C, 1JC−Rh = 14.2 Hz), 72.8 (d, 1C, 1JC−Rh = 14.2 Hz), 32.8 (s,
1C), 33.6 (s, 1C), 30.1 (s, 1C), 29.7 (s, 1C, COD). HRMS m/z Calcd for
C28H40IN5Rh (M+ − I−): 676.1378. Found: 676.1377 (M+ − I−). Anal.
Calcd for C28H40I2N5Rh: C, 41.86; H, 5.02, N, 8.72. Found: C, 41.81; H,
5.10; N, 8.66. The 1H NMR spectrum of this compound is given in the
Supporting Information (Figure S8).
3
3
i
1.18 (d, 6H, JH−H = 6.7 Hz), 1.15 (d, 6H, JH−H = 6.7 Hz, PrCH3).
13C{1H} NMR (125.27 MHz, acetonitrile-d3, 26.1 °C): δ 145.6 (s, 2C,
C−iPr); 138.9 (s, 1C, CH2CCH); 135.4 (s, 1C, NCHN); 130.6 (s, 1C,
NCAr); 133.1 (s, 1C), 124.8 (s, 2C, CHAr); 133.2 (s, 1C, CHTrz); 123.3
1
(s, 1C), 121.2 (s, 1C, NCHimid); 121.1 (q, 1C, JC−F = 319.4 Hz,
OSO2CF3); 61.0 (s, 1C, NC(CH3)3); 41.5 (s, 1C, CH2); 39.3 (s, 1C,
MeTrz); 28.6 (s, 3C, NC(CH3)3); 28.4 (s, 2C, iPrCH); 23.5 (s, 2C), 22.9
(s, 2C, iPrCH3). 19F{1H} NMR (468.66 MHz, acetonitrile-d3, 27.0 °C): δ
−79.2 (s, 3F, OSO2CF3). HRMS m/z Calcd for C24H35F3N5O3S (M+ −
Br−): 530.2407. Found: 530.2411 (M+ − Br−). Anal. Calcd for
C24H35BrF3N5O3S: C, 47.21; H, 5.78; N, 11.47. Found: C, 46.99; H,
5.68; N, 11.15.
First Attempted Synthesis of Methylene[(3-methyl-1H-imidazole-
2-ylidene)iodido(η2,η2-cycloocta-1,5-diene)rhodium(I)][1-(2,6-diiso-
propylphenyl)-3-methyl-1H-1,2,3-triazol-3-ium iodide, [RhI(COD)-
Me
(κ1-MeImTrz(H) ][I][OTf] (6b). A 10 mL portion of acetonitrile was
Dipp
Methylene[(3-tert-butyl-1H-imidazole-2-ylidene)iodido(η2,η2-cy-
added to a solid mixture containing 4b (0.042 g, 0.074 mmol), [Rh(μ-
OAc)(COD)]2 (0.021 g, 0.039 mmol), and KI (0.061 g, 0.37 mmol)
under an inert Ar(g) atmosphere. The resulting slurry was stirred for 19 h
under reflux conditions and cooled to room temperature. The solvent
was then removed under reduced pressure, and the crude product was
redissolved in 10 mL of CH2Cl2. A 45 mL portion of diethyl ether was
added to precipitate a dark red solid, and the solution was filtered via
canula. The solvent was removed under reduced pressure, giving 0.0010
g of a mixture of products, as determined by 1H NMR (none of which
appeared to be the desired product). The solution was layered with
diethyl ether, and the product 5b was crystallized in very low yield
through slow mixing of the solvents. 1H NMR (299.97 MHz, CD2Cl2,
27.5 °C): δ 7.58 (t, 1H, 3JH−H = 7.4 Hz), 7.36 (d, 2H, 3JH−H = 7.4 Hz,
cloocta-1,5-diene)rhodium(I)][1-(2,6-diisopropylphenyl)-3-methyl-
Me
1H-1,2,3-triazol-3-ium] iodide, [RhI(COD)(κ1-tBuImTrz(H) )][I] (6c).
Dipp
The desired product was prepared as described for 6b, using 4c (0.514 g,
0.842 mmol), [Rh(μ-OMe)(COD)]2 (0.201 g, 0.415 mmol), and KI
(0.699 g, 4.21 mmol). The solution was heated at reflux for 12.75 h, and
changed from yellow to orange. The crude product was purified as
1
described for 6b and isolated as a yellow powder (0.619 g, 87%). H
NMR (299.97 MHz, CD2Cl2, 27.5 °C): δ 8.15 (s, 1H, HTrz); 7.63 (d, 1H,
3JH−H = 2.0 Hz), 6.50 (d, 1H, 3JH−H = 2.0, NCHimid); 7.70 (dd, 1H, 3JH−H
8.0 Hz, 3JH−H = 8.0 Hz), 7.40 (d, 1H, 3JH−H = 8.0 Hz), 7.35 (d, 1H, 3JH−H
=
=
8.0 Hz, Ar); 6.60 (d, 1H, 2JH−H = 16.8 Hz), 6.35 (d, 1H, 2JH−H = 16.8 Hz,
CH2); 4.69 (s, 3H, MeTrz); 2.54 (qq, 1H, 3JH−H = 6.5 Hz, 3JH−H = 6.5
Hz), 2.43 (qq, 1H, 3JH−H = 6.8 Hz, 3JH−H = 6.8 Hz, iPrCH); 1.21 (d, 3H,
3JH−H = 6.5 Hz), 1.19 (d, 3H, 3JH−H = 6.8 Hz), 1.18 (d, 3H, 3JH−H = 6.5
Hz), 1.10 (d, 3H, 3JH−H = 6.8 Hz, iPrCH3); 1.80 (s, 9H, tBu); 5.25 (m,
1H), 5.02 (m, 1H), 3.72 (br s, 2H), 2.55−1.00 (m, 8H, COD). 13C{1H}
NMR (100.58 MHz, CD2Cl2, 27.7 °C): δ 182.4 (d, 1C, 1JC−Rh = 47.8 Hz,
Ccarbene); 147.1 (s, 1C), 146.8 (s, 1C, C−iPr); 142.8 (s, 1C, CH2CCH);
132.0 (s, 1C), 126.1 (s, 1C), 125.7 (s, 1C, CHAr); 132.1 (s, 1C, NCAr); 133.0
(s, 1C, CHTrz); 125.2 (s, 1C), 122.3 (s, 1C, NCHimid); 45.2 (s, 1C, CH2);
41.5 (s, 1C, MeTrz); 29.1 (s, 1C), 28.7 (s, 1C, iPrCH); 61.5 (s, 1C), 29.5 (s,
3C, tBu); 25.0 (s, 1C), 24.6 (s, 1C), 24.1 (s, 1C), 24.0 (s, 1C, iPrCH3); 98.0
3
3
Ar); 7.30 (d, 1H, JH−H = 1.5 Hz), 7.17 (d, 1H, JH−H = 1.5 Hz,
NCHimid); 5.60 (s, 2H, CH2); 4.25 (s, 3H, MeTrz); 4.05 (s, 3H, MeIm);
2.96 (qq, 2H, 3JH−H = 6.4 Hz, 3JH−H = 6.4 Hz, iPrCH); 1.74 (s, 3H, OAc);
1.39 (d, 6H, 3JH−H = 6.4 Hz), 1.02 (d, 6H, 3JH−H = 6.7 Hz, iPrCH3). The
amount of crystalline material was insufficient to obtain a useful 13C{1H}
NMR spectrum. HRMS m/z Calcd for C22H30IN5O2Rh (M+ − I−):
626.0499. Found: 626.0499 (M+ − I−).
First Attempted Synthesis of Methylene[(3-tert-butyl-1H-imida-
zole-2-ylidene)iodido(η2,η2-cycloocta-1,5-diene)rhodium(I)][1-(2,6-
diisopropylphenyl)-3-methyl-1H-1,2,3-triazol-3-ium] iodide, [RhI-
(d, 1C, 1JC−Rh = 7.0 Hz), 97.5 (d, 1C, 1JC−Rh = 7.1 Hz), 73.6 (d, 1C, 1JC−Rh
=
Me
(COD)(κ1-tBuImTrz(H) )][I] (6c). Preparation of the desired product
Dipp
14.0 Hz), 72.7 (d, 1C, 1JC−Rh = 14.1 Hz), 32.6 (s, 1C), 33.3 (s, 1C), 30.2 (s,
1C), 30.0 (s, 1C, COD). HRMS m/z Calcd for C31H46IN5Rh (M+ − I−):
718.1847. Found: 718.1845 (M+ − I−). Anal. Calcd for C31H46I2N5Rh: C,
44.04; H, 5.48, N, 8.28. Found: C, 44.30; H, 5.66; N, 8.42.
was attempted as described for 6b, using 4c (0.356 g, 0.583 mmol),
[Rh(μ-OAc)(COD)]2 (0.163 g, 0.302 mmol), and KI (0.492 g, 2.96
mmol). The resulting slurry was stirred for 19 h under reflux conditions
and cooled to room temperature. The crude product was purified as
described for 6b and isolated as a black, amorphous material, giving
0.243 g of a mixture of products, as determined by 1H NMR
spectroscopic methods (none of which were the desired product),
most likely containing 5c, analogous to 5b.
M e t h y l e n e [ ( 3 - m e t h y l - 1 H - i m i d a z o l e - 2 - y l i d e n e ) -
triiodidopalladium(II)][1-(2,6-diisopropylphenyl)-3-methyl-1H-1,2,3-
Me
triazol-3-ium], [PdI3(κ1-MeImTrz(H) )][I] (7b). A 10 mL portion of
Dipp
acetonitrile was added to a solid mixture containing 4b (0.163 g, 0.287
mmol) and [Pd(OAc)2] (0.070 g, 0.312 mmol), which changed color to
dark purple with the addition of KI (0.302 g, 1.82 mmol) under an inert
Ar(g) atmosphere. The resulting slurry was stirred for 5 h at 80 °C in a
sealed container and cooled to room temperature. The solvent was then
removed under reduced pressure, and the crude product was redissolved
in 10 mL of THF. A 45 mL portion of diethyl ether was added to
precipitate a dark red solid, and the mother liquor was removed via
canula. The resulting precipitate was then washed with 3 × 30 mL
portions of diethyl ether before drying in vacuo, giving a dark red
Methylene[(3-methyl-1H-imidazole-2-ylidene)iodido(η2,η2-cyclo-
octa-1,5-diene)rhodium(I)][1-(2,6-diisopropylphenyl)-3-methyl-1H-
Me
1,2,3-triazol-3-ium] iodide, [RhI(COD)(κ1-MeImTrz(H) )][I] (6b). A
Dipp
10 mL portion of acetonitrile was added to a solid mixture containing 4b
(0.360 g, 0.633 mmol), [Rh(μ-OMe)(COD)]2 (0.155 g, 0.320 mmol),
and KI (0.346 g, 2.08 mmol) under an inert Ar(g) atmosphere. The
resulting solution was stirred for 4.75 h at 80 °C and cooled to room
temperature. The solvent was then removed under reduced pressure,
and the crude product was redissolved in 10 mL of CH2Cl2 and passed
through a bed of Celite via cannula to remove excess KI. The rest of the
solvent was then removed under reduced pressure, and the crude
product was redissolved in 10 mL of CH2Cl2. A 30 mL portion of diethyl
ether was added to precipitate a bright yellow solid, and the mother
liquor was removed via cannula. The resulting precipitate was then
washed with 3 × 30 mL portions of diethyl ether before drying in vacuo,
giving a bright yellow powder (0.422 g, 83%). 1H NMR (499.82 MHz,
1
powder (0.105 g, 44%). H NMR (498.12 MHz, acetonitrile-d3, 26.1
°C): δ 8.78 (br s, 1H, HTrz); 7.73 (br s, 1H), 7.27 (br s, 1H, NCHimid);
3
3
7.69 (t, 1H, JH−H = 7.9 Hz), 7.47 (d, 2H, JH−H = 7.9 Hz, Ar); 6.06
(s, 2H, CH2); 4.80 (s, 3H, MeTrz); 3.88 (s, 3H, MeIm); 2.47 (qq, 2H,
3JH−H = 6.9 Hz, 3JH−H = 6.9 Hz, iPrCH); 1.17 (d, 6H, 3JH−H = 6.9 Hz), 1.12
3
i
(d, 6H, JH−H = 6.9 Hz, PrCH3). 13C{1H} NMR (125.69 MHz,
acetonitrile-d3, 27.7 °C): δ 161.7 (s, 1C, Ccarbene); 145.7 (s, 2C, C−iPr);
K
dx.doi.org/10.1021/om3004543 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
140.3 (s, 1C, CH2CCH); 133.4 (s, 1C), 124.8 (s, 2C, CHAr); 130.8 (s,
1C, NCAr); 133.0 (s, 1C, CHTrz); 124.7 (s, 1C), 123.1 (s, 1C, NCHimid);
43.6 (s, 1C, CH2); 40.8 (s, 1C, MeTrz); 38.3 (s, 1C, MeIm); 28.3 (s, 2C,
iPrCH); 23.9 (s, 2C), 23.1 (s, 2C, iPrCH3). Anal. Calcd for
[C20H28I3N5Pd]·4CH3CN: C, 33.98; H, 4.07; N, 12.74. Found: C,
33.83; H, 4.01; N, 12.65.
7.47 (d, 1H, JH−H = 7.9 Hz, ArDipp); 6.31 (s, 2H, CH2); 4.18 (s, 3H,
MeTrz); 2.22 (br m, 2H, 3JH−H = 6.9 Hz, 3JH−H = 6.9 Hz, iPrCH); 1.18 (d,
3H, 3JH−H = 6.9 Hz), 1.09 (d, 3H, 3JH−H = 6.9 Hz, iPrCH3); 1.92 (s, 9H,
tBu). 13C{1H} NMR (125.69 MHz, acetonitrile-d3, 27.7 °C): δ 159.3 (d,
1C, JC−P = 191.2 Hz, Ccarbene); 144.3 (s, 1C), 144.0 (s, 1C, C−iPr);
139.2 (s, 1C, CH2CCH); 132.6 (s, 1C), 124.3 (s, 2C, CHAr); 131.3 (s,
2
4
Methylene[(3-tert-butyl-1H-imidazole-2-ylidene)-
1C, NCAr‑Dipp); 133.3 (s, 1C, CHTrz); 124.7 (d, 1C, JC−P = 5.0 Hz),
121.1 (d, 1C, 4JC−P = 5.5 Hz, NCHimid); 44.0 (s, 1C, CH2); 40.5 (s, 1C,
MeTrz); 58.5 (s, 1C), 30.7 (s, 3C, tBu); 28.2 (s, 1C), 27.6 (s, 1C, iPrCH);
23.1 (s, 2C), 21.4 (s, 2C, iPrCH3); 131.8 (d, 3C, 1JC−P = 45.7 Hz), 129.4
triiodidopalladium(II)][1-(2,6-diisopropylphenyl)-3-methyl-1H-1,2,3-
Me
triazol-3-ium], [PdI3(κ1-tBuImTrz(H) )][I] (7c). The desired product
Dipp
was prepared as described for 7b, using 4c (0.783 g, 1.28 mmol),
[Pd(OAc)2]2 (0.289 g, 1.29 mmol), and KI (1.204 g, 7.253 mmol). The
solution was heated at reflux for 5 h and allowed to cool to room
temperature. The crude product was purified as described for 7b and
isolated as a dark red powder (0.775 g, 70%). 1H NMR (498.12 MHz,
acetonitrile-d3, 26.1 °C): δ 8.75 (br s, 1H, HTrz); 7.23 (br s, 1H), 7.15 (br
s, 1H, NCHimid); 7.64 (t, 1H, 3JH−H = 8.0 Hz), 7.41 (d, 2H, 3JH−H = 8.0
2
3
(d, 6C, JC−P = 9.1 Hz), 130.1 (d, 6C, JC−P = 1.7 Hz), 134.9 (s, 3C,
PPh3). 13P{1H} NMR (161.84 MHz, acetonitrile-d3, 27.7 °C): δ 17.4 (s,
1P, PPh3). Anal. Calcd for C41H49I3N5PPd: C, 43.58; H, 4.37; N, 6.20.
Found: C, 43.25; H, 4.12; N, 6.02.
Methylene[(3-methyl-1H-imidazole-2-ylidene)-cis-
diiodidotriethylphosphinopalladium(II)][1-(2,6-diisopropylphenyl)-
Hz, Ar); 6.21 (s, 2H, CH2); 4.81 (s, 3H, MeTrz); 2.45 (qq, 2H, 3JH−H
=
3-methyl-1H-1,2,3-triazol-3-ium] iodide, cis-[PdI2(PEt3)(κ1-MeImTrz-
6.9 Hz, 3JH−H = 6.9 Hz, iPrCH); 1.23 (d, 6H, 3JH−H = 6.9 Hz), 1.10 (d, 6H,
3JH−H = 6.9 Hz, iPrCH3); 1.67 (s, 9H, tBu). 13C{1H} NMR (125.69 MHz,
Me
Dipp
(H) )][I] (9bcis). The desired product was prepared as described for
9ctrans, using 7b (0.100 g, 0.121 mmol), and changed color to bright
yellow upon the addition of PEt3 (18 μL, 0.12 mmol). The solution was
stirred for 10 min and then heated at 80 °C in a sealed container for 2 h.
The crude product was purified as described for 9ctrans and isolated as a
acetonitrile-d3, 27.7 °C): δ 163.3 (s, 1C, Ccarbene); 146.6 (s, 2C, C−iPr);
140.5 (s, 1C, CH2CCH); 133.3 (s, 1C), 125.0 (s, 2C, CHAr); 130.7 (s,
1C, NCAr); 133.2 (s, 1C, CHTrz); 124.8 (s, 1C), 124.4 (s, 1C, NCHimid);
44.1 (s, 1C, CH2); 41.2 (s, 1C, MeTrz); 28.1 (s, 2C, iPrCH); 24.2 (s, 2C),
22.8 (s, 2C, iPrCH3); 67.3 (s, 1C), 31.3 (s, 3C, tBu). The 1H (Figure S9)
and 13C{1H} (Figure S10) NMR spectra of this compound are given in
the Supporting Information.
bright yellow powder (0.069 g, 60%). 1H NMR (498.12 MHz,
3
acetonitrile-d3, 26.1 °C): δ 8.72 (s, 1H, HTrz); 7.64 (d, 1H, JH−H
=
1.7 Hz), 7.23 (d, 1H, 3JH−H = 1.7 Hz, NCHimid); 7.74 (t, 1H, 3JH−H = 8.4
Hz), 7.53 (d, 1H, 3JH−H = 8.4 Hz, Ar); 5.52 (d, 1H, 2JH−H = 15.9 Hz),
5.41 (d, 1H, 2JH−H = 15.9 Hz, CH2); 4.24 (s, 3H, MeTrz); 3.83 (s, 3H,
Methylene[(3-tert-butyl-1H-imidazole-2-ylidene)-trans-
3
3
diiodidotriethylphosphinopalladium(II)][1-(2,6-diisopropylphenyl)-
MeIm); 2.38 (qq, 1H, JH−H = 6.9 Hz, JH−H = 6.9 Hz), 2.37 (qq, 1H,
3JH−H = 6.8 Hz, 3JH−H = 6.8 Hz, iPrCH); 1.17 (d, 3H, 3JH−H = 6.9 Hz), 1.13
(d, 3H, 3JH−H = 6. Hz, iPrCH3); 1.95 (dq, 6H, 2JH−P = 9.2 Hz, 3JH−H = 8.2
Hz), 1.05 (dt, 9H, 3JH−P = 16.7 Hz, 3JH−H = 8.2 Hz, PEt3). 13C{1H} NMR
(125.69 MHz, acetonitrile-d3, 27.7 °C): δ 164.3 (s, 1C, Ccarbene); 145.2
(s, 2C, C−iPr); 141.5 (s, 1C, CH2CCH); 133.5 (s, 1C), 125.4 (s, 2C,
CHAr); 132.1 (s, 1C, NCAr); 132.8 (s, 1C, CHTrz); 123.1 (s, 1C), 122.2
(s, 1C, NCHimid); 45.9 (s, 1C, CH2); 40.7 (s, 1C, MeTrz); 38.4 (s, 1C,
MeIm); 28.5 (s, 2C, iPrCH); 22.9 (s, 2C), 23.1 (s, 2C, iPrCH3); 19.3 (d, 3C,
1JC−P = 30.2 Hz), 6.9 (s, 3C, PEt3). 31P{1H} NMR (161.84 MHz,
acetonitrile-d3, 27.7 °C): δ 18.6 (s, 1P, PEt3). HRMS analysis only
3-methyl-1H-1,2,3-triazol-3-ium] iodide, trans-[PdI2(PEt3)-
Me
(κ1-tBuImTrz(H) )][I] (9ctrans). A 10 mL portion of acetonitrile was
Dipp
added to a flask containing 7c (0.353 g, 0.406 mmol). The resulting
slurry was stirred for 10 min, followed by the rapid injection of PEt3
(101 μL, 0.686 mmol) under an inert Ar(g) atmosphere, at which point
the solution changed from dark red to a pale yellow solution almost instantly
and was stirred for another 10 min. The solvent was reduced to 5 mL
under reduced pressure and passed through a bed of Celite via cannula.
The rest of the solvent was then removed under reduced pressure, and
the crude product was redissolved in 5 mL of CH2Cl2. A 100 mL portion
of n-pentane was added to precipitate a solid, which was then washed
with 3 × 30 mL portions of n-pentane before drying in vacuo, giving a
−
detected a chelate product, m/z Calcd for C26H42IN5PPd (M+ − HI2 ):
688.1252. Found: 688.1260 (M+ − I−). Anal. Calcd for C26H43I3N5PPd:
C, 33.09; H, 4.59; N, 7.42. Found: C, 33.31; H, 4.89; N, 7.69.
Methylene[(3-methyl-1H-imidazole-2-ylidene)-cis-
diiodidotriphenylphosphinopalladium(II)][1-(2,6-diisopropylphen-
bright yellow powder (0.089 g, 22%). 1H NMR (399.80 MHz,
3
acetonitrile-d3, 26.5 °C): δ 8.52 (s, 1H, HTrz); 7.56 (dd, 1H, JH−H
=
1.9 Hz, 5JH−P = 1.9 Hz), 7.27 (dd, 1H, 3JH−H = 1.9 Hz, 5JH−P = 1.3 Hz,
NCHimid); 7.71 (t, 1H, 3JH−H = 8.0 Hz), 7.49 (d, 2H, 3JH−H = 8.0 Hz, Ar);
6.07 (s, 2H, CH2); 4.43 (s, 3H, MeTrz); 2.39 (qq, 2H, 3JH−H = 6.8 Hz,
yl)-3-methyl-1H-1,2,3-triazol-3-ium] iodide, cis-[PdI2(PPh3)-
Me
Dipp
(κ1-MeImTrz(H) )][I] (10bcis). The desired product was prepared as
3JH−H = 6.8 Hz, iPrCH); 1.18 (d, 3H, 3JH−H = 6.8 Hz), 1.17 (d, 3H, 3JH−H
=
described for 9ctrans, using 7b (0.04 g, 0.05 mmol), and changed color to
bright yellow upon the addition of PPh3 (0.05 g, 0.2 mmol). The
solution was stirred for 10 min and then heated at 80 °C in a sealed
container for 2 h. The crude product was purified as described for 9ctrans
and isolated as a bright yellow powder (0.05 g, 95%). 1H NMR (499.82
6.8 Hz, iPrCH3); 1.15 (d, 3H, 3JH−H = 6.8 Hz), 1.15 (d, 3H, 3JH−H = 6.8
Hz, iPrCH3); 1.87 (s, 9H, tBu); 2.18 (dq, 6H, 2JH−P = 9.5 Hz, 3JH−H = 7.7
Hz), 1.17 (dt, 9H, 3JH−P = 16.2 Hz, 3JH−H = 7.7 Hz, PEt3). 13C{1H} NMR
2
(125.69 MHz, acetonitrile-d3, 27.7 °C): δ 162.4 (d, 1C, JC−P = 186.7
Hz, Ccarbene); 145.6 (s, 2C, C−iPr); 140.9 (s, 1C, CH2CCH); 133.0 (s,
1C), 124.8 (s, 2C, CHAr); 130.7 (s, 1C, NCAr); 133.0 (s, 1C, CHTrz);
123.0 (d, 1C, 4JC−P = 5.8 Hz), 122.0 (d, 1C, 4JC−P = 4.9 Hz, NCHimid);
45.6 (s, 1C, CH2); 39.7 (s, 1C, MeTrz); 28.4 (s, 2C, iPrCH); 59.5 (s, 1C),
MHz, acetonitrile-d3, 27.7 °C): δ 8.51 (s, 1H, HTrz); 7.34 (d, 1H, 3JH−H
=
2.0 Hz), 6.93 (d, 1H, 3JH−H = 2.0 Hz, NCHimid); 7.69 (t, 1H, 3JH−H = 7.5
Hz), 7.47 (d, 2H, 3JH−H = 7.5 Hz, ArDipp); 5.87 (d, 1H, 2JH−H = 16.3 Hz),
5.14 (d, 1H, 2JH−H = 16.3 Hz, CH2); 4.48 (s, 3H, MeTrz); 3.60 (s, 3H,
31.1 (s, 3C, tBu); 23.6 (s, 2C), 23.0 (s, 2C, iPrCH3); 18.4 (d, 3C, 1JC−P
=
3
3
MeIm); 2.41 (qq, 1H, JH−H = 7.0 Hz, JH−H = 7.0 Hz), 2.36 (qq, 1H,
29.4 Hz), 8.2 (s, 3C, PEt3). 31P{1H} NMR (161.84 MHz, acetonitrile-d3,
27.7 °C): δ 8.6 (s, 1P, PEt3). HRMS m/z Calcd for C29H49I2N5PPd (M+
− I−): 858.0844. Found: 858.0849 (M+ − I−). Anal. Calcd for triflate
salt, C30H49F3I2N5O3PPdS: C, 35.75; H, 4.90; N, 6.95. Found: C, 36.01;
H, 5.27; N, 6.90.
3JH−H = 7.0 Hz, 3JH−H = 7.0 Hz, iPrCH); 1.19 (d, 3H, 3JH−H = 7.0 Hz), 1.16
(d, 3H, 3JH−H = 7.0 Hz), 1.16 (d, 3H, 3JH−H = 7.0 Hz), 1.13 (d, 3H, 3JH−H
6.9 Hz, iPrCH3); 7.75 (ddd, 6H, 3JH−P = 12.4 Hz, 3JH−H = 7.7 Hz, 4JH−H
=
=
1.0 Hz), 7.60 (tdd, 3H, 3JH−H = 7.7 Hz, 5JH−P = 2.0 Hz, 4JH−H = 1.0 Hz),
3
3
4
7.51 (ddd, 6H, JH−H = 7.7 Hz, JH−H = 7.7 H, JH−P = 2.2 Hz, PPh3).
Methylene[(3-tert-butyl-1H-imidazole-2-ylidene)-trans-
13C{1H} NMR (125.69 MHz, acetonitrile-d3, 27.7 °C): δ 165.5 (s, 1C,
diiodidotriphenylphosphinopalladium(II)][1-(2,6-diisopropylphen-
C
carbene); 145.7 (s, 1C), 145.5 (s, 1C, C−iPr); 140.1 (s, 1C, CH2CCH);
yl)-3-methyl-1H-1,2,3-triazol-3-ium] iodide, trans-[PdI2(PPh3)-
Me
(κ1-tBuImTrz(H) )][I] (10ctrans). The desired product was prepared as
133.0 (s, 1C), 124.7 (s, 2C, CHAr); 130.7 (s, 1C, NCAr‑Dipp); 133.0 (s, 1C,
CHTrz); 125.4 (s, 1C), 122.4 (s, 1C, NCHimid); 43.5 (s, 1C, CH2); 40.1 (s,
1C, MeTrz); 38.0 (s, 1C, MeIm); 28.4 (s, 1C), 28.3 (s, 1C, iPrCH); 23.9 (s,
Dipp
described for 9ctrans, using 7c (0.141 g, 0.163 mmol) and PPh3 (0.063 g,
0.239 mmol). The solution was stirred for 10 min, and the crude product
was purified as described for 9ctrans, using THF and n-pentane, and
1C), 23.6 (s, 1C), 23.1 (s, 1C), 22.9 (s, 1C, iPrCH3); 131.1 (d, 3C, 1JC−P
=
51.4 Hz), 134.4 (d, 6C, 2JC−P = 11.0 Hz), 128.7 (d, 6C, 3JC−P = 10.8 Hz),
1
isolated as a bright yellow orange powder (0.083 g, 45%). H NMR
4
(399.80 MHz, acetonitrile-d3, 26.5 °C): δ 8.41 (s, 1H, HTrz); 7.81−7.59
131.4 (d, 3C, JC−P = 2.5 Hz, PPh3). 31P{1H} NMR (161.84 MHz,
(br m, 2H, NCHimid); 7.69−7.07 (m, 18H, Ar); (t, 1H, 3JH−H = 7.9 Hz),
acetonitrile-d3, 27.7 °C): δ 24.1 (s, 1P, PPh3). The 1H (Figure S11) and
L
dx.doi.org/10.1021/om3004543 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
13C{1H} (Figure S12) NMR spectra of this compound are given in the
Supporting Information.
ASSOCIATED CONTENT
* Supporting Information
■
S
Diiodidotriethylphosphinopalladium(II)-μ-[(1,1′-methylene(3-
Figures of the 1H NMR spectra of 2c, 3a, 3c, 4b, 6b, 7c, 10bcis,
and 11; figures of the 13C{1H} NMR spectra of 2c, 3a, 3c, 7c, and
10bcis; tables of crystallographic experimental details for 4b, 5b,
7b, and 10bcis; and tables with dihedral angles for 7b and 10bcis.
Atomic coordinates, interatomic distances and angles, aniso-
tropic thermal parameters, and hydrogen parameters for 4b, 5b,
7b, and 10bcis in a CIF file. This material is available free of charge
via the Internet at http://pubs.acs.org.
tert-butyl-1H-imidazole-2-ylidene)(1-(2,6-diisopropylphenyl)-3-
methyl-1H-1,2,3-triazol-5-ylidene)]iodido(η2,η2-cycloocta-1,5-
Me
diene)rhodium(I), [PdI2(PEt3(μ-tBuImTrz )RhI(COD)] (11). A 10 mL
Dipp
portion of acetonitrile was added to a solid mixture containing 9ctrans
(0.504 g, 0.511 mmol), [Rh(μ-OMe)(COD)]2 (0.135 g, 0.279 mmol),
and KI (0.432 g, 2.60 mmol) under an inert Ar(g) atmosphere. The
resulting solution was stirred for 1 h at 80 °C in a sealed container and
cooled to room temperature. The solvent was then removed under
reduced pressure, and the crude product was redissolved in 10 mL of
CH2Cl2 and passed through a bed of Celite via cannula to remove excess
KI. The rest of the solvent was then removed under reduced pressure,
and the crude product was redissolved in 5 mL of THF. A 30 mL portion
of diethyl ether was added to precipitate a bright yellow solid, and the
mother liquor was removed via cannula. The resulting precipitate was
then washed with 3 × 30 mL portions of diethyl ether before drying in
vacuo, giving a bright yellow powder (0.429 g, 70%). 1H NMR (399.80
AUTHOR INFORMATION
Corresponding Author
*E-mail: martin.cowie@ualberta.ca. Fax: +01 7804928231. Tel:
+01 7804925581.
■
Notes
The authors declare no competing financial interest.
MHz, acetonitrile-d3, 26.5 °C): δ 7.56 (dd, 1H, 3JH−H = 1.8 Hz, 5JH−P
=
ACKNOWLEDGMENTS
1.8 Hz), 7.53 (dd, 1H, 3JH−H = 1.8 Hz, 5JH−P = 1.1 Hz, NCHimid); 7.71 (t,
1H, 3JH−H = 8.0 Hz), 7.49 (d, 2H, 3JH−H = 8.0 Hz, Ar); 5.82 (d, 1H, 2JH−H
= 16.0 Hz), 5.31 (d, 1H, 2JH−H = 16.0 Hz, CH2); 4.24 (s, 3H, MeTrz);
2.42 (qq, 2H, 3JH−H = 6.9 Hz, 3JH−H = 6.9 Hz, iPrCH); 1.29 (d, 6H, 3JH−H
= 6.9 Hz), 1.18 (d, 6H, 3JH−H = 6.9 Hz, iPrCH3); 1.81 (s, 9H, tBu); 2.16
(dq, 6H, 2JH−P = 9.4 Hz, 3JH−H = 7.5 Hz), 1.21 (dt, 9H, 3JH−P = 16.0 Hz,
3JH−H = 7.5 Hz, PEt3); 5.59 (br s, 2H, CODtrans); 3.59 (br s, 2H,
CODcis); 1.91−1.11 (m, 8H, CODalk). 13C{1H} NMR (125.69 MHz,
acetonitrile-d3, 27.7 °C): δ 173.4 (d, 1C, 1JC−Rh = 44.7 Hz, Ccarbene(Rh));
161.6 (d, 1C, 2JC−P = 184.3 Hz, Ccarbene(Pd)); 144.7 (s, 2C, C−iPr); 141.3
(s, 1C, CH2CCH); 133.2 (s, 1C), 125.8 (s, 2C, CHAr); 131.3 (s, 1C,
NCAr); 133.2 (s, 1C, CHTrz); 123.5 (d, 1C, 4JC−P = 5.7 Hz), 122.5 (d, 1C,
4JC−P = 4.8 Hz, NCHimid); 45.8 (s, 1C, CH2); 40.1 (s, 1C, MeTrz); 28.1 (s,
■
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) and the University of Alberta for
financial support for this research and NSERC for funding the
Bruker D8 Duo Diffractometer/SMART APEX II CCD
diffractometer and the Nicolet Avatar IR spectrometer. We
thank the Department’s Mass Spectrometry Facility and the
NMR Spectroscopy and Analytical and Instrumentation
Laboratories. Drs. S. Warsink, J. A. Key, L. S. Campbell-Verduyn,
and K. J. Kilpin are acknowledged for their helpful discussions.
We also thank Professor J. C. Vederas and Dr. A. C. Ross for the
generous donation of CuI. M. Miskolzie is acknowledged for
helpful advice related to the NMR investigation. In addition, we
acknowledge support from NSERC and Alberta Innovates−
Technology Futures in the form of postgraduate scholarships
to M.T.Z.
i
t
2C, PrCH); 59.3 (s, 1C), 31.0 (s, 3C, Bu); 23.7 (s, 2C), 23.1 (s, 2C,
iPrCH3); 18.0 (d, 3C, 1JC−P = 29.0 Hz), 8.2 (s, 3C, PEt3). 31P{1H} NMR
(161.84 MHz, acetonitrile-d3, 27.7 °C): δ 9.8 (s, 1P, PEt3). HRMS m/z
Calcd for C37H60I2N5PPdRh (M+ − I−): 1068.0760. Found: 1068.0760
(M+ − I−). Anal. Calcd for C37H60I3N5PPdRh: C, 37.16; H, 5.06; N,
5.86. Found: C, 36.94; H, 5.31; N, 5.81. The 1H NMR spectrum of this
compound is given in the Supporting Information (Figure S13).
X-ray Structure Determinations. General Considerations.
Crystals of 4b, 7b, and 10bcis were grown from concentrated acetonitrile
solutions, and crystals of 5b were grown from slow diffusion of diethyl
ether and pentane into a CH2Cl2 solution of the compound. Data were
collected84 using a Bruker APEX II detector/D8 diffractometer; in
all cases, Mo Kα radiation was used and the crystals were cooled to
−100 °C during data collection. The structures were solved using direct
methods using the program SHELXS-9785 for 4b, 5b, and 10bcis, and
using the program SIR9786 for 7b. The program SHELXL-9785 was used
for structure refinements. Hydrogen atoms were assigned positions on
the basis of the geometries of their attached carbon atoms and were
given thermal parameters 120% of their parent carbons. See Table S1
in the Supporting Information for a listing of crystallographic
experimental data.
REFERENCES
■
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