1,3-Dimethyl-4-(diphenylphosphino)imidazolium Triflate: A Functionalized Ionic Liquid with Ambivalent Coordination Capability

Article abstract of DOI:10.1021/acs.organomet.5b00722

Simply using 1-methylimidazole as the starting material, the functionalized ionic liquid 1,3-dimethyl-4-(diphenylphosphino)imidazolium triflate ([3]OTf) has been prepared, from which the corresponding 4-phosphino-substituted N-heterocyclic carbene 4 was generated. The coordination capability of 3 and 4 toward a variety of transition-metal centers has been studied, as well as their electron-donor character through an evaluation of the TEP parameter. 3 behaves as a cationic phosphine ligand, whereas 4 shows a strong preference to coordinate to transition metals through the carbene carbon atom, leading to the obtention of mononuclear complexes with a free phosphine arm which act as metalloligands, allowing for the modular formation of homo- and heterodinuclear transition-metal complexes.

Full text of DOI:10.1021/acs.organomet.5b00722

Article
pubs.acs.org/Organometallics
1,3-Dimethyl-4-(diphenylphosphino)imidazolium Triflate: A
Functionalized Ionic Liquid with Ambivalent Coordination Capability
Javier Ruiz,* Alejandro F. Mesa, and Daniel Sol
́
́
Departamento de Quımica Organica e Inorganica, Facultad de Quımica, Universidad de Oviedo, E-33006 Oviedo, Spain
́
́
S
* Supporting Information
ABSTRACT: Simply using 1-methylimidazole as the starting
material, the functionalized ionic liquid 1,3-dimethyl-4-
(diphenylphosphino)imidazolium triflate ([3]OTf) has been
prepared, from which the corresponding 4-phosphino-
substituted N-heterocyclic carbene 4 was generated. The
coordination capability of 3 and 4 toward a variety of
transition-metal centers has been studied, as well as their
electron-donor character through an evaluation of the TEP
parameter. 3 behaves as a cationic phosphine ligand, whereas 4
shows a strong preference to coordinate to transition metals
through the carbene carbon atom, leading to the obtention of
mononuclear complexes with a free phosphine arm which act
as metalloligands, allowing for the modular formation of homo- and heterodinuclear transition-metal complexes.
INTRODUCTION
■
1,3-Dialkylimidazolium salts are currently receiving a great deal
of attention, owing to their use as ionic liquids for novel media
in organic synthesis and catalysis1 and as precursors of N-
heterocyclic carbenes (NHCs).2 Recently, imidazolium salts
containing functional groups have been used for task-specific
applications,3 such as separation of CO2 from gas streams,4
supports for organic synthesis,5 extraction of metal ions,6
construction of nanostructures,7 and ion conductive materials.8
Particularly, phosphino-functionalized imidazolium salts, most
of them containing the phosphino group connected to a
nitrogen atom of the imidazolium cycle through a carbon
spacer, have been extensively employed in the formation of
chelating or pincer NHC-phosphine ligands9 and as ionophilic
phosphines for ionic-liquid biphasic catalysis.10 In recent
pioneering works, the groups of Bertrand11 and Gates12 have
described the synthesis of 4-phosphino-substituted 1,3-diary-
limidazol-2-ylidenes and proved their suitability for the
synthesis of several dimetallic transition-metal complexes.13
Subsequently our group managed to isolate 4,5-diphosphino-
substituted imidazolium salts and use them for generating
mixed diphosphine-NHC ligands.14,15 In related studies, 4-
phosphorylimidazolium and 4,5-bis(phosphoryl)imidazolium
salts have also been prepared, some of them being remarkable
examples of room-temperature ionic liquids, as well as their
corresponding NHC-transition-metal complexes.16
Figure 1. Parent 1,3-dimethylimidazolium triflate ([1]OTf) and its
diphenylphosphino-functionalized derivatives [2]OTf and [3]OTf
(this work). OTf = CF3SO3 .
−
isomer 1,3-dimethyl-2-(diphenylphosphino)imidazolium triflate
([2]OTf) as well as with the parent unsubstituted imidazolium
salt ([1]OTf).
RESULTS AND DISCUSSION
■
As summarized in Scheme 1, the salt 1,3-dimethyl-4-
(diphenylphosphino)imidazolium triflate ([3]OTf) has been
prepared by using a one-pot procedure starting from 1-
methylimidazole (A). This is first reacted with BuLi and ClPPh2
to afford the phosphine B, which in a following step is treated
with MeOTf to give the 2-phosphinoimidazolium salt [2]-
OTf,17 resulting from chemoselective methylation at the iminic
nitrogen atom. Isomerization of 2 to 3 is carried out by
treatment with LiHMDS and quenching with water. [3]OTf
was obtained as colorless crystals in high yield. Undoubtedly,
deprotonation of 2 should afford initially the corresponding
In this paper we describe the synthesis of the functionalized
ionic liquid 1,3-dimethyl-4-(diphenylphosphino)imidazolium
triflate ([3]OTf; Figure 1), which contains one of the simplest
imidazolium scaffolds, and the study of its properties and
coordination capabilities together with those of the correspond-
ing NHC derivative. A comparison has been made with its
Received: August 21, 2015
© XXXX American Chemical Society
A
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maintained to some extent in solution in view of the relatively
high chemical shift of the C2−H proton in the H NMR
spectrum.
Scheme 1. Formation of the Imidazolium Cation 3 and Its
Corresponding NHC 4
1
The parent imidazolium salt MeMeIm+OTf− ([1]OTf) is
reported to have a melting point of 39 °C.19 The inclusion of a
diphenylphophino substituent on carbon atom C2 (compound
[2]OTf) considerably increases the melting point value up to
104 °C, whereas changing the position of this group from C2 to
C4 (compound [3]OTf) leads to an appreciably lower melting
point of 86 °C: that is, below the 100 °C threshold which is
generally admitted for considering a salt to be an ionic liquid.1
Compound [3]OTf behaves as an imidazolium-function-
alized phosphine ligand forming a variety of complexes with
transition metals, as summarized in Scheme 2. Thus, the
Scheme 2. Formation of a Variety of Transition-Metal
Complexes Containing the Imidazolium Cation 3 Acting as a
Phosphine Ligand
mesoionic carbene C,18 which is then transformed into carbene
4 after migration of the phosphino substituent.
Compound 4 was detected by 31P{1H} NMR during the
reaction course but could not be isolated, owing to its
exceeding propensity for protonation. Nevertheless, carbene 4
1
could be characterized by H and 13C{1H} NMR spectroscopy
by reaction of a freshly prepared solution of pure crystals of
[3]OTf in C6D6 with LiHMDS in the NMR tube. A high-field
resonance at 203.7 ppm typical of a carbene carbon atom
together with two singlets at 3.37 and 3.70 ppm for the
hydrogen atoms of the two inequivalent methyl substituents are
the most characteristic signals of this new phosphino-
functionalized carbene. Meanwhile, the imidazolium salt
[3]OTf shown a characteristic high-field singlet in the proton
spectrum (9.20 ppm) for the C2−H hydrogen atom. An X-ray
crystal structure analysis of [3]OTf (Figure 2) was carried out,
showing typical bond lengths and angles for imidazolium
cations.2f Short C2−H···O contacts were found within the
crystal ranging from 2.29 to 2.71 Å, proving the existence of
hydrogen bonds with the triflate anion, which should be
treatment of [3]OTf with [AuCl(SMe2)] and [RhCl(COD)]2
at room temperature readily afforded complexes 5 and 6,
respectively, whereas reaction of [3]OTf with the carbonyl
compound [Mo(CO)6] requires several hours of refluxing in
toluene to achieve substitution of a carbon monoxide molecule
to give complex 7. All three compounds were fully
characterized by spectroscopic methods (see the Experimental
Section). The 31P{1H} NMR spectra showed typical low-field
shifts of the phosphorus signal with respect to that of the free
Figure 2. View of the structure of [3]OTf, shown with 50% thermal
ellipsoids. Hydrogen atoms (except C2−H and C5−H) are omitted
for clarity. Selected bond distances (Å) and angles (deg): N1−C2 =
1.327(5), C2−N3 = 1.333(5), N3−C4 = 1.387(5), C4−C5 =
1.364(5), C5−N1 = 1.375(5), C4−P1 = 1.819(4), N1−C1 =
1.461(5), N3−C3 = 1.471(5); N1−C2−N3 = 108.2(4), C2−N3−
C4 = 109.5(3), N3−C4−C5 = 105.6(3), C4−C5−N1 = 107.7 (4),
C5−N1−C2 = 109.0(3), N3−C4−P1 = 122.0(3), C5−C4−P1 =
131.8(3).
1
ligand, whereas the H and 13C{1H} NMR spectra are very
similar to those of 3. Coordination of two phosphine ligands to
B
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the same metal was also easily accomplished by reacting AgOTf
with 2 equiv of 3, giving the tricationic complex 8. This
example illustrates the possibility of forming highly charged
transition-metal Lewis acids using the cationic phosphine 3 as a
ligand for future catalytic applications.20 The 31P{1H} NMR of
8 at room temperature afforded a broad singlet at −13.0 ppm,
owing to dissociation of the phosphine ligand, which is split up
into two doublets when measuring the spectrum at low
temperature due to the coupling of the phosphorus atoms with
107Ag and 109Ag isotopes (1J(P,Ag) = 488 and 562 Hz,
respectively). The presence of two phosphine ligands per silver
atom within the complex was confirmed by an 109Ag{31P}
INEPT NMR measurement21 carried out at low temperature,
giving a triplet signal at 754.2 ppm (one-up/one-down
appearance typical of the A part of an AX2 spin system), due
to the coupling of 109Ag with the two equivalent phosphorus
atoms.
Looking at the ν(CO) frequencies of the carbonyl ligands in
the IR spectrum of complex 7 (2078 (m), 1952 (vs) cm−1), we
come to the conclusion that the phosphine 3 is moderately less
donating than a typical triarylphosphine such as triphenylphos-
phine (bands at 2073 and 1945 cm−1 for the complex
[Mo(CO)5(PPh3)]),22 which is due to the electron-with-
drawing character of the imidazolium substituent at 3. The
same conclusion is gained by analyzing the ν(CO) bands of the
rhodium(I) complex [RhCl(CO)2(3)] (9), which is prepared
by bubbling carbon monoxide into a dichloromethane solution
of 6 (Scheme 2). The average value of these bands in 9 is 2065
cm−1, which accounts for a TEP (Tolman electronic
parameter)23 of 2072 cm−1 for the cationic phosphine 3. This
TEP value is appreciably higher than that of PPh3 (2063 cm−1)
calculated from the complex [RhCl(CO)2(PPh3)]24 and is
similar to those found in phosphite ligands.20a Note that the
TEP parameter is commonly used to evaluate the electron-
donor character of different ligands, in such a way that the
lower the TEP value, the stronger the donor ability of the
ligand.23 The imidazolium cation 2, bearing the phosphino
substituent at carbon atom C2, shows a TEP value of 2082
cm−1,25 being clearly more weakly electron donating than 3,
which emphasizes the strong influence of placing the
phosphino group on different carbon atoms of the imidazolium
cycle. In fact, 2 has also been considered as a NHC-stabilized
phosphenium adduct,26 whereas 3 has features typical of
phosphine ligands.
Figure 3. Molecular structure of the cationic complex 10, shown with
50% thermal ellipsoids. Hydrogen atoms (except C2−H, C5−H,
C12−H, and C15−H) are omitted for clarity. Selected bond distances
(Å) and angles (deg): N1−C2 = 1.329(4), C2−N3 = 1.322(4), N3−
C4 = 1.396(4), C4−C5 = 1.358(5), C5−N1 = 1.373(4), C4−P1 =
1.804(3), N1−C1 = 1.462(4), N3−C3 = 1.460(4), N11−C12 =
1.315(5), C12−N13 = 1.326(4), Rh1−P1 = 2.3029(8), Rh1−P2 =
2.3142(8); N1−C2−N3 = 109.1(3), C2−N3−C4 = 108.9(3), N3−
C4−C5 = 105.7(3), C4−C5−N1 = 108.0 (3), C5−N1−C2 =
108.4(3), N3−C4−P1 = 124.5(2), C5−C4−P1 = 129.5(3).
two donor atoms prone to coordination to a metal center: the
carbene carbon atom and the phosphorus atom.
We have carried out reactions of 4 with different metal
complexes, proving that the first choice for coordination was
always through the carbene carbon atom, owing to its more
strongly electron donating character (Scheme 3). In fact, the
substitution reactions proceed under conditions milder than
those in the case of the imidazolium precursor 3. Thus, reaction
of 4 (which was prepared in situ by reaction of [3]OTf with
KOH) with [Mo(CO)6] took place at room temperature to
afford the neutral pentacarbonyl NHC complex 11. Formation
of the tetracarbonyl dicarbene complex 12 was also feasible by
treatment of [Mo(CO)6] with 2 equiv of 4 in toluene, but in
this case heating of the reaction mixture at 90 °C for 45 min is
needed. In both new molybdenum carbene complexes the
uncoordinated phosphorus atom appears as a singlet around
−33 ppm in the 31P{1H} NMR spectrum, which is almost
identical with that for free NHC 4. The 13C{1H} NMR spectra
of 11 and 12 show as the most noticeable signal singlets at
192.3 and 199.9 ppm, respectively, for the carbene carbon
atoms.
Complex 9 was very unstable in solution, precluding NMR
spectroscopic characterization, as it spontaneously loses CO
and is transformed into the monocarbonyl complex 10
(Scheme 2) containing two phosphine ligands 3 coordinated
to rhodium. Complex 10 features a sole ν(CO) band in the IR
spectrum at 1995 cm−1, whereas the 31P{1H} NMR spectrum
shown a doublet at 16 ppm (1J(Rh,P) = 129.5 Hz) for the two
equivalent, mutually trans phosphine ligands. The signals of the
proton and carbon NMR spectra are very similar to those found
in the free ligand 3. The structure of 10 in the solid state was
definitively stablished by single-crystal X-ray diffraction analysis.
A view of the structure is shown in Figure 3 together with
selected bond distances and angles, from which it can be
appreciated that the imidazolium cycle features structural
parameters very similar to those found in the free imidazolium
salt 3 (Figure 2).
When carbene 4 was reacted with 1/2 equiv of [RhCl-
(COD)]2, coordination of the ligand also occurred through the
carbene carbon atom, producing complex 13, which shows a
singlet in the 31P{1H} NMR spectrum around −33 ppm
characteristic of the uncoordinated phosphorus atom. In
contrast to what was found in the plethora of known stable
carbene complexes of formula [RhCl(NHC)(COD)], com-
pound 13 was highly unstable in solution, most probably due to
the occurrence of an intermolecular nucleophilic attack of the
free diphenylphosphino group to coordinated cyclooctadiene,27
affording a highly insoluble material which so far remains
uncharacterized.28 This result anticipates a differential chemical
behavior of these new phosphino-functionalized NHC
complexes with respect to more conventional NHCs. If a
freshly prepared solution of 13 is immediately treated with CO,
the corresponding dicarbonyl complex 14 is quickly formed
(Scheme 3), allowing for recording the IR spectrum before
decomposition occurs. The average ν(CO) frequency was
found to be 2044 cm−1, which accounts for a TEP value of 2055
Once the coordination capability of 3 was assessed, we
proceeded to study that of its deprotonated form. The 4-
phosphino-functionalized N-heterocyclic carbene 4 contains
C
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Scheme 3. Modular Formation of Mono- and Dimetallic
Complexes Containing the Mixed NHC-Phosphine Ligand 4
Figure 4. Molecular structure of 15, shown with 50% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): N1−C2 = 1.364(2), C2−N3 =
1.368(2), N3−C4 = 1.400(2), C4−C5 = 1.347(2), C5−N1 =
1.375(2), C4−P1 = 1.8144(17), N1−C1 = 1.462(2), N3−C3 =
1.457(2), Mo1−C2 = 2.2635(16), Mo2−P1 = 2.5353(5); N1−C2−
N3 = 102.97(13), C2−N3−C4 = 111.90(14), N3−C4−C5 =
105.53(14), C4−C5−N1 = 107.59 (14), C5−N1−C2 = 112.01(14),
N3−C4−P1 = 126.20(13), C5−C4−P1 = 127.39(14).
respect to the carbon atom C2 (1.153(2) Å) is slightly higher
than that of the carbonyl ligand placed in a trans position with
respect to the phosphorus atom P1 (1.145(2) Å), additionally
reflecting the stronger electron-donor character of the carbene
moiety.
Naturally, the formation of heterodimetallic complexes was
also possible by using the above procedure. As an example,
complex 11 was treated with 1/2 equiv of [RuCl2(p-cym)]2 in
CH2Cl2 at room temperature, readily affording complex 16
(Scheme 3), which was fully spectroscopically characterized
(see the Experimental Section for details).
cm−1: that is, very similar to that of the nonfunctionalized
parent carbene ImNMe2 (2054 cm−1)29 and naturally
appreciably lower than that of phosphine 3 (2072 cm−1, see
above), showing its stronger donor character.
Aiming to obtain TEP values of 4 when it is simultaneously
coordinated to two rhodium(I) centers, we prepared the
dimetallic complex 17 by reacting 3 with 1 equiv of
[RhCl(COD)]2 using LiHMDS as proton abstractor (obviously
17 can also be prepared in a similar way by starting from
isolated 6). Among the spectroscopic data of 17, it is worth
noting the presence of a typical low-field doublet (189.7 ppm,
1J(Rh,C) = 51 Hz) for the carbene carbon atom in the 13C{1H}
NMR spectrum, together with a doublet at 9.14 ppm (1J(Rh,P)
= 151 Hz) for the phosphino group in the 31P{1H} NMR
spectrum. The bubbling of CO into a dichloromethane solution
of 17 readily produces complex 18, which showed two ν(CO)
bands in the IR spectrum for each [RhCl(CO)2] fragment. The
average values of these bands were 2059 and 2044 cm−1, which
account for TEP values of 2067 and 2055 cm−1 for the
phosphine and carbene moieties of 4, respectively. Note that
the TEP value of the carbene moiety remains unchanged with
respect to the mononuclear complex 14 containing uncoordi-
nated phosphorus, whereas the TEP value of the phosphine
moiety slightly decreases with respect to that of complex 9
(2072 cm−1), which is logical because the neutral phosphine 4
is more electron donating than the cationic phosphine 3.
Complex 11 can act as a metallophosphine, allowing the
modular formation of dimetallic complexes. Thus, the reaction
of 11 with 1 equiv of [Mo(CO)6] in refluxing toluene afforded
the homodimetallic complex 15. Both carbon and phosphorus
donor atoms are clearly identified in the 13C{1H} NMR (197.3
ppm) and 31P{1H} NMR (16.7 ppm) spectra, while the IR
spectrum in CH2Cl2 shows differentiated bands for the two
inequivalent molybdenum pentacarbonyl fragments, those
corresponding to the carbene complex (2064 and 1931
cm−1) having substantially lower frequencies in comparison
to those of the phosphine complex (2075 and 1948 cm−1),
clearly reflecting the stronger electron-donor character of the
carbene carbon atom with respect to the phosphine group.
Complex 15 can alternatively be prepared by reaction of 7 with
[Mo(CO)6] in the presence of KOH as deprotonating agent.
The crystal structure of 15 was determined by X-ray diffraction
analysis. A view of the structure is presented in Figure 4,
showing the new 4-diphenylphosphino-NHC 4 bridging two
[Mo(CO)5] moieties. The bond distances and angles within
the imidazole cycle are in the expected range for NHCs, which
means slightly longer C2−N bond lengths and a closer N1−
C2−N3 angle than in the imidazolium salt 3.2f The C−O bond
length of the carbonyl ligand located in a trans position with
D
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NMR tube. After a few minutes, carbene 4 was formed quantitatively.
1H NMR (400 MHz, C6D6, 25 °C): δ 7.37−7.29 (m, 5 H, Ph), 7.16−
7.15 (m, 5 H, Ph), 6.01 (s, 1 H, CH), 3.72 (s, 3 H, NMe), 3.39 (s, 3
H, NMe). 13C{1H} NMR (100.61 MHz, C6D6, 25 °C): δ 204.1 (s,
C2), 133.7−128.9 (Ph), 127.4 (s, C5), 36,5 (s, NMe), 36.0 (d, 3J(C,P)
= 8.7 Hz, NMe). 31P{1H} NMR (162.14 MHz, C6D6, 25 °C): δ −34.4
(s, PPh2).
CONCLUSION
■
We have found a one-pot experimental procedure to synthesize
the functionalized ionic liquid 1,3-dimethyl-4-
(diphenylphosphino)imidazolium triflate ([3]OTf; mp 86
°C) and subsequently generate the corresponding 4-phosphi-
no-substituted N-heterocyclic carbene 4, simply starting from
the easily available 1-methylimidazole. The coordination
capability of 3 and 4 toward a variety of transition-metal
centers has been studied, as well as their electron-donor
character through the evaluation of the TEP parameter from
dicarbonyl Rh(I) derivatives. Several mononuclear complexes
of Au(I), Ag(I), Mo(0), and Rh(I) containing 3 as a cationic
phosphine ligand that features electron-donating ability similar
to that of phosphite ligands have been prepared. 4 shows a
strong preference to coordinate to transition metals through
the carbene carbon atom, leading to the obtention of
mononuclear complexes with a free phosphine moiety which
act as metalloligands, allowing for the modular formation of
homo- and heterodinuclear transition-metal complexes.
Compound [5]OTf. To a solution of [3]OTf (30 mg, 0.07 mmol)
in CH2Cl2 (6 mL) was added 1 equiv of [AuCl(SMe2)] (20.5 mg, 0.07
mmol) and the resulting mixture stirred for 15 min. The solution was
filtered, and then the solvent was evaporated to dryness to obtain a
white solid which was washed with hexane (2 × 10 mL). Colorless
crystals of the compound were obtained from THF/hexane. Yield: 31
mg (67%). Anal. Calcd for C18H18N2AuClF3O3PS.THF: C, 35.96; H,
3.57; N, 3.81. Found: C, 35.93; H, 3.49; N, 3.79. 1H NMR (300 MHz,
CD2Cl2, 25 °C): δ 9.32 (s, 1 H, N2CH), 7.78−7.60 (m, 10 H, Ph),
6.83 (s, 1 H, CH), 3.90 (s, 3 H, NMe), 3.85 (s, 3 H, NMe).
13C{1H} NMR (75.46 MHz, CD2Cl2, 25 °C): δ 143.8 (s, C2), 134.9−
130.7 (Ph), 132.5 (d, 2J(C,P) = 12.5 Hz, C5), 125.8 (d, 1J(C,P) = 71.3
1
Hz, C4), 123.9 (d, J(C,P) = 66.7 Hz, Cipso Ph), 37,4 (s, NMe), 36.8
(d, 3J(C,P) = 4.5 Hz, NMe). 31P{1H} NMR (121.48 MHz, CD2Cl2, 25
°C): δ 10.1 (s, PPh2). MS (FAB): m/z 513.0 [M − CF3SO3]+.
Compound [6]OTf. To a solution of [3]OTf (30 mg, 0.07 mmol)
in CH2Cl2 (5 mL) was added 1/2 equiv of [RhCl(COD)]2 (17 mg,
0.035 mmol) and the resulting mixture stirred for 15 min. The
solution was then filtered and the solvent evaporated to dryness to
obtain an orange solid, which was washed with hexane (2 × 10 mL).
Yield: 41 mg (87%). Anal. Calcd for C26H30N2ClF3O3PRhS: C, 46.13;
EXPERIMENTAL SECTION
■
General Considerations. All reactions and manipulations were
performed under an atmosphere of dry nitrogen by standard Schlenk
techniques. Solvents were distilled over appropriate drying agents
under dry nitrogen before use. The IR spectra were measured with
PerkinElmer Spectrum 100 and Paragon 1000 spectrophotometers.
The C, H, and N analyses were performed on a PerkinElmer 240B
elemental analyzer. NMR spectra were recorded on Bruker 300 and
400 MHz spectrometers. Coupling constants J are given in Hz.
Chemical shifts of the NMR spectra were referenced to internal SiMe4
(1H and 13C) or external H3PO4 (31P). All reagents were obtained
commercially and used without further purification.
1
H, 4.11; N, 3.81. Found: C, 46.59; H, 4.14; N, 4.13. H NMR (300
MHz, CD2Cl2, 25 °C): δ 9.21 (s, 1 H, N2CH), 7.61−7.49 (m, 10 H,
Ph), 6.79 (s, 1 H, CH), 5.64 (s, 2H, CH COD), 4.54 (s, 3 H, NMe),
3.82 (s, 3 H, NMe), 3.39 (s, 2H, CH COD), 2.39 (s, 4H, CH2 COD),
2.18−2.01 (m, 4H, CH2 COD). 13C{1H} NMR (75.46 MHz, CD2Cl2,
25 °C): δ 142.0 (s, C2), 134.3−129.8 (Ph), 130.3 (s, C5), 128.4 (d,
1
1J(C,P) = 46.0 Hz, C4), 108.5 (m, CH COD), 73.1 (d, J(C,Rh) =
Compound [2]OTf was prepared as described elsewhere,17 and its
melting point was measured: 104 °C.
12.8 Hz, CH COD), 38,5 (s, NMe), 37.0 (s, NMe), 33.4 (s, CH2
COD), 29.3 (s, CH2 COD). 31P{1H} NMR (121.48 MHz, CD2Cl2, 25
°C): δ 13.1 (d,1J(Rh,P) = 153.9 Hz, PPh2).
Compound [3]OTf. To a solution of 1-methylimidazole (97 μL, d
= 1.03 g/mL, 1.22 mmol) in THF (5 mL) at 193 K was added a
hexane solution of nBuLi (761 μL, 1.6 M, 1.22 mmol) and the
resulting mixture stirred for 1 h. Then, 1 equiv of ClPPh2 (223 μL, d =
1.229 g/mL, 98%, 1.22 mmol) was added to the solution. The mixture
was warmed slowly to room temperature. The solvent was evaporated
to dryness and the residue extracted with CH2Cl2 (5 mL) and filtered.
Addition of methyl triflate (136 μL, d = 1.496 g/mL, 98%, 1.22 mmol)
to the solution and stirring for 30 min caused the formation of
compound [2]OTf, as detected by 31P NMR spectroscopy. The
solvent was evaporated to dryness and the residue dissolved in THF.
Then LiN(SiMe3)2 (1.22 mL of a 1 M hexane solution, 1.22 mmol)
was added to the solution and the mixture stirred for 30 min. The
solvent was eliminated under vacuum, and the residue was successively
washed with hexane (2 × 5 mL), dissolved in CH2Cl2 (10 mL), and
treated with water (10 mL). The mixture was stirred for 1 h, and then
the organic phase was filtered over diatomaceous earth. The solvent
was evaporated to dryness and the resulting residue washed with
hexane (3 × 10 mL) to obtain a white solid corresponding to [3]OTf,
which was filtered and dried under vacuum. Colorless crystals suitable
for X-ray analysis were obtained by slow diffusion of hexane into a
solution of the compound in THF. Yield: 360 mg (70%). Mp: 86 °C.
Anal. Calcd for C18H18N2F3O3PS: C, 50.23; H, 4.22; N, 6.51. Found:
Compound [7]OTf. To a solution of [3]OTf (0.1 g, 0.23 mmol) in
toluene (10 mL) was added 1 equiv of [Mo(CO)6] (61 mg, 0.23
mmol). The mixture was heated at 108 °C for 6 h. The solvent was
then evaporated to dryness to form a white solid, which was washed
with hexane (2 × 10 mL). Yield: 58 mg (37%). Anal. Calcd for
C23H18N2F3MoO8PS: C, 41.46; H, 2.72; N, 4.20. Found: C, 42.09; H,
1
2.43; N, 4.11. H NMR (400 MHz, CD2Cl2, 25 °C): δ 9.34 (s, 1 H,
N2CH), 7.59 (br, 5 H, Ph), 7.57 (s, 5 H, Ph), 7.28 (s, 1 H, CH),
4.00 (s, 3 H, NMe), 3.50 (s, 3 H, NMe). 13C{1H} NMR (100.61 MHz,
2
CD2Cl2, 25 °C): δ 209.0 (d, J(C,P) = 25.5 Hz, CO trans), 205.3 (d,
2J(C,P) = 8.6 Hz, CO cis), 143.8 (s, C2), 132.8−130.3 (Ph), 37,4 (s,
NMe), 37.2 (s, NMe). 31P{1H} NMR (121.48 MHz, CD2Cl2, 25 °C):
δ 21.9 (s, PPh2). IR (CH2Cl2): ν(CO) 2078 (m), 1952 (vs) cm−1. MS
(FAB): m/z 519.0 [M − CF3SO3]+.
Compound [8](OTf)3. To a solution of [3]OTf (0.1 g, 0.23 mmol)
in CH2Cl2 (5 mL) was added 1/2 equiv of AgOTf (30 mg, 0.12
mmol) and the resulting mixture stirred for 24 h. The solution was
filtered and the solvent evaporated to dryness, giving a white residue,
which was washed with hexane (2 × 10 mL) to afford a white solid.
Yield: 105 mg (76%). 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 9.07 (s,
2 H, N2CH), 7.64−7.49 (m, 20 H, Ph), 6.69 (s, 2 H, CH), 3.82 (s, 6
H, NMe), 3.71 (s, 3 H, NMe). 13C{1H} NMR (75.46 MHz, CD2Cl2,
25 °C): δ 142.5 (s, C2), 134.6 (d, 2J(C,P) = 17.8 Hz, o-Ph), 133.3 (s,
1
C, 50.74; H, 4.31; N, 6.00. H NMR (300 MHz, CD2Cl2, 25 °C): δ
9.20 (s, 1 H, N2CH), 7.47−7.36 (m, 10 H, Ph), 6.52 (s, 1 H, CH),
3.83 (s, 3 H, NMe), 3.71 (s, 3 H, NMe). 13C{1H} NMR (75.46 MHz,
2
3
1
p-Ph), 131.1 (d, J(C,P) = 7.1 Hz, C5), 130.6 (d, J(C,P) = 10.5 Hz,
CD2Cl2, 25 °C): δ 141.3 (s, C2), 135.6 (d, J(C,P) = 21.6 Hz, C4),
1
2
m-Ph), 125.5 (d, J(C,P) = 37.3 Hz, C4), 37,0 (s, NMe), 36.5 (s,
134.3−128.8 (Ph), 129.0 (d, J(C,P) = 6.8 Hz, C5), 36,9 (s, NMe),
NMe). 31P{1H} NMR (121.48 MHz, CD2Cl2, 25 °C): δ −13.0 (br,
PPh2), 31P{1H} NMR (121.48 MHz, CD2Cl2, − 80 °C): δ −13.0 (d,
1J(109Ag,P) = 562 Hz; d 1J(107Ag,P) = 488 Hz, PPh2). 109Ag{31P}
35.5 (d, 3J(C,P) = 9.6 Hz, NMe). 31P{1H} NMR (121.48 MHz,
CD2Cl2, 25 °C): δ −34.2 (s, PPh2). MS (FAB): m/z 281.2 [M −
CF3SO3]+.
INEPT NMR (CD2Cl2, − 80 °C): δ 754.2 (t, J(109Ag,P) = 558 Hz).
1
Generation of Carbene 4. A solution of the salt [3]OTf in C6D6
was treated with 1 equiv of LiN(SiMe3)2 (1 M hexane solution) in an
MS (FAB): m/z 669.0 [M − 3CF3SO3]+.
E
DOI: 10.1021/acs.organomet.5b00722
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Compounds [9]OTf and [10](OTf)2. Carbon monoxide was
bubbled through a solution of [6]OTf (60 mg, 0.083 mmol) in
CH2Cl2 (5 mL) for 5 min. Immediate formation of the dicarbonyl
compound [9]OTf was evidenced by the ν(CO) bands in the IR
spectrum of the solution: 2106 (s), 2023 (vs) cm−1. This
spontaneously evolves to the monocarbonyl derivative [10](OTf)2
on standing in solution. Orange crystals of [10](OTf)2 suitable for X-
ray crystallography were obtained by slow diffusion of hexane into a
solution of the compound in CH2Cl2. Yield: 25 mg (58%). Anal. Calcd
for C37H36N4ClF6O7P2RhS2: C, 43.27; H, 3.53; N, 5.45. Found: C,
43.53; H, 3.14; N, 5.30. 1H NMR (300 MHz, CD2Cl2, 25 °C): δ 9.22
(s, 2 H, N2CH), 7.81−7.74 (m, 10 H, Ph), 7.63−7.57 (m, 10 H, Ph),
6.81 (s, 2 H, CH), 3.91 (s, 6 H, NMe), 3.86 (s, 6 H, NMe).
13C{1H} NMR (75.46 MHz, CD2Cl2, 25 °C): δ 185.7 (s, CO), 142.6
(s, C2), 136.7−130.3 (Ph), 131.1 (s, C5), 127.8 (d, 1J(C,P) = 50.6 Hz,
C4),, 37,6 (s, NMe), 37.2 (s, NMe). 31P{1H} NMR (121.48 MHz,
CD2Cl2, 25 °C): δ 16.0 (d, 1J(Rh,P) = 129.5 Hz, PPh2).). IR
(CH2Cl2): ν(CO) 1995 (vs) cm−1.
(18 mg, 0.029 mmol) and the resulting mixture stirred for 15 min. The
solvent was evaporated to dryness under vacuum, affording an orange
solid which was washed with hexane (2 × 10 mL). Yield: 39 mg, 82%.
1H NMR (300 MHz, CD2Cl2, 25 °C): δ 7.82−7.75 (m, 5 H, Ph), 7.78
(s, 1 H, CH), 7.53−7.46 (m, 5 H, Ph), 5.24 (d, 3J(H,H) = 5.8 Hz, 2
3
H, p-cym), 5.05 (d, J(H,H) = 5.8 Hz, 2 H, p-cym), 3.89 (s, 3 H,
NMe), 3.31 (s, 3 H, NMe), 2.72 (m, 1 H, CHMe2), 1.79 (s, 3 H, Me),
1.07 (d, 3J(H,H) = 6.9 Hz, 6 H, CHMe2). 13C{1H} NMR (75.46 MHz,
CD2Cl2, 25 °C): δ 212.4 (s, CO trans), 207.0 (s, CO cis), 196.9 (s,
2
C2), 138.3 (d, J(C,P) = 23.7 Hz, C5), 134.1−126.7 (Ph), 131.6 (d,
1J(C,P) = 48.5 Hz, C4), 112.3 (s, p-cym), 97.2 (s, p-cym), 89.8 (d,
2
2J(C,P) = 1.8 Hz, p-cym), 87.6 (d, J(C,P) = 5.5 Hz, p-cym), 41,0(s,
NMe), 31.0 (s, CHMe2), 22.0 (s, CHMe2), 18.0 (s, Me). 31P{1H}
NMR (121.48 MHz, CD2Cl2, 25 °C): δ 4.2 (s, PPh2). IR (CH2Cl2):
ν(CO) 2064 (m), 1929 (vs) cm−1.
Compound 17. To a solution of [3]OTf (30 mg, 0.07 mmol) in
THF (5 mL) was added 1 equiv of [RhCl(COD)]2 (34 mg, 0.07
mmol). Then LiN(SiMe3)2 (70 mL of a 1 M hexane solution, 0.07
mmol) was added to the solution and the mixture stirred for 15 min.
The solution was then filtered and the solvent evaporated to dryness
to obtain an orange solid, which was washed with hexane (2 × 10 mL).
Yield: 44 mg (82%). Anal. Calcd for C33H41N2Cl2PRh2: C, 51.25; H,
5.34; N, 3.62. Found: C, 50.59; H, 4.81; N, 3.53. 1H NMR (300 MHz,
CD2Cl2, 25 °C): δ 7.45−7.217 (m, 10 H, Ph), 6.83 (s, 1 H, CH),
5.56 (s, 2H, CH COD), 4.96 (s, 2 H, CH COD), 4.47 (s, 3 H, NMe),
4.02 (s, 3 H, NMe), 3.49 (s, 1 H, CH COD), 3.37 (s, 2 H, CH COD),
3.00 (s, 1 H, CH COD), 2.39 (s, 8H, CH2 COD), 1.98 (s, 4H, CH2
COD), 1.95 (s, 4H, CH2 COD). 13C{1H} NMR (75.46 MHz, CD2Cl2,
Compound 11. To a solution of [3]OTf (0.1 g, 0.23 mmol) in
toluene (10 mL) was added 1 equiv of [Mo(CO)6] (61 mg, 0.23
mmol) and an excess of KOH (0.20 g, 3.56 mmol). The resulting
suspension was stirred for 24 h. The solution was then filtered, and
subsequently the solvent was evaporated to dryness. The residue was
extracted with hexane (2 × 5 mL). The solution was filtered and then
evaporated to dryness to give a white solid. Yield: 40 mg (33%). Anal.
Calcd for C22H17N2MoO5P: C, 50.97; H, 3.31; N, 5.41. Found: C,
50.44; H, 3.62; N, 5.01. 1H NMR (300 MHz, CD2Cl2, 25 °C): δ 7.43−
7.33 (m, 10 H, Ph), 6.35 (s, 1 H, CH), 3.78 (s, 3 H, NMe), 3.77 (s,
3 H, NMe). 13C{1H} NMR (75.46 MHz, CD2Cl2, 25 °C): δ 212.6 (s,
CO), 207.3 (s, CO), 192.9 (s, C2), 134.4−129.5 (Ph), 129.8 (s, C5),
1
25 °C): δ 189.7 (d, J(C,Rh) = 51 Hz, C2), 138.4−128.7 (Ph), 130.5
2
1
(d, J(C,P) = 19.2, C5), 125.8 (d, J(C,P) = 54.5 Hz, C4), 106.9−
106.3 (CH COD), 99.0 (t, J = 6.7 Hz, CH COD), 73.1 (d, 1J(C,Rh) =
13.3 Hz, CH COD), 71.2 (d, 1J(C,Rh) = 13.3 Hz, CH COD), 68.8 (t,
J = 15.6 Hz, CH COD), 39,6 (s, NMe), 38.3 (s, NMe), 33.3 (s, CH2
COD), 29.5 (s, CH2 COD), 29.4 (s, CH2 COD). 31P{1H} NMR
(121.48 MHz, CD2Cl2, 25 °C): δ 9.1 (d,1J(Rh,P) = 151.5 Hz, PPh2).
MS (FAB): m/z 773.3 [M]+.
3
40,4 (s, NMe), 38.9 (d, J(C,P) = 12.5 Hz, NMe). 31P{1H} NMR
(121.48 MHz, CD2Cl2, 25 °C): δ −33.4 (s, PPh2). IR (CH2Cl2):
ν(CO) 2063 (m), 1928 (vs) cm−1. MS (FAB): m/z 518.0 [M]+.
Compound 12. To a solution of [3]OTf (0.1 g, 0.23 mmol) in
toluene (10 mL) was added 1/2 equiv of [Mo(CO)6] (31 mg, 0.12
mmol) and an excess of KOH (0.20 g, 3.56 mmol). The resulting
suspension was heated at 90 °C for 45 min. The solution was then
filtered and the solvent evaporated to dryness. The residue was washed
with hexane (2 × 10 mL) to give a pale yellow solid. Yield: 36 mg
(40%). 1H NMR (300 MHz, CD2Cl2, 25 °C): δ 7.46−7.27 (m, 20 H,
Ph), 6.27 (s, 2 H, CH), 3.56 (s, 6 H, NMe), 3.47 (s, 6 H, NMe).
13C{1H} NMR (75.46 MHz, CD2Cl2, 25 °C): δ 220.0 (s, CO), 212.0
(s, CO), 200.5 (s, C2), 134.6−128.0 (Ph), 129.1 (s, C5), 39,7 (s,
Generation of Compound 18. Complex 18 was readily formed
by bubbling carbon monoxide through a solution of 17 in CH2Cl2 for
5 min. 31P{1H} NMR (121.48 MHz, CH2Cl2/D2O capillary; 25 °C): δ
1
11.0 (d, J(Rh,P) = 128.8 Hz, PPh2). IR (CH2Cl2): ν(CO) 2100 (s),
2084 (s), 2018 (s), 2004 (vs) cm−1.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00722.
■
3
NMe), 38.0 (d, J(C,P) = 11.7 Hz, NMe). 31P{1H} NMR (121.48
S
MHz, CD2Cl2, 25 °C): δ −33.9 (s, PPh2). IR (CH2Cl2): ν(CO) 1994
(m), 1868 (vs), 1830 (s) cm−1. MS (FAB): m/z 770.1 [M]+.
Compound 13. 1P{1H} NMR (121.48 MHz, CH2Cl2/D2O
capillary, 25 °C): δ −33.7 (s, PPh2).
Compound 14. IR (CH2Cl2): ν(CO) 2084 (s), 2003 (vs) cm−1.
Compound 15. A solution containing compound 11 (20 mg,
0.039 mmol) and 1 equiv of [Mo(CO)6] (10 mg, 0.039 mmol) in
toluene (6 mL) was heated at 108 °C for 1 h. The solvent was then
evaporated to dryness under vacuum and the residue extracted with
hexane (2 × 5 mL). The solution was then filtered and evaporated to
dryness to afford a white solid. Crystals of 15 suitable for X-ray analysis
were formed by slow diffusion of hexane into a dichloromethane
solution of the compound. Yield: 27 mg, 93%. Anal. Calcd for
C27H17N2Mo2O10P: C, 43.11; H, 2.28; N, 3.72. Found: C, 42.86; H,
2.42; N, 3.52. 1H NMR (300 MHz, CD2Cl2, 25 °C): δ 7.57 (br, 10 H,
Ph), 7.09 (d, 3J(H,P) = 1.7 Hz, 1 H, CH), 3.91 (s, 3 H, NMe), 3.53
(s, 3 H, NMe). 13C{1H} NMR (75.46 MHz, CD2Cl2, 25 °C): δ 212.3
NMR spectra for the new compounds (PDF)
Crystallographic data for compounds [3]OTf, [10]-
(OTf)2, and 15 (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.R.: jruiz@uniovi.es.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
2
(s, CO trans), 210.0 (d, J(C,P) = 24.3 Hz, CO trans), 206.9 (s, CO
This work was supported by the Spanish Ministerio de
2
cis), 205.8 (d, J(C,P) = 8.7 Hz, CO cis), 197.9 (s, C2), 133.5−128.7
́
Economia y Competitividad (Project CTQ2012-32239) and
2
1
(Ph), 132.9 (d, J(C,P) = 14.5 Hz, C5), 125.9 (d, J(C,P) = 28.8 Hz,
C4), 41,0 (s, NMe), 40.8 (d, 3J(C,P) = 2.0 Hz, NMe). 31P{1H} NMR
(121.48 MHz, CD2Cl2, 25 °C): δ 16.7 (s, PPh2). IR (CH2Cl2): ν(CO)
2075 (m), 2064 (m), 1948 (vs), 1931 (vs) cm−1. MS (FAB): m/z
755.8 [M]+.
by the Principado de Asturias (Project FC-15-GRUPIN14-
011). D.S. thanks the Principado de Asturias for a scholarship.
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DOI: 10.1021/acs.organomet.5b00722
Organometallics XXXX, XXX, XXX−XXX