Strongly Coordinating Ligands to Form Weakly Coordinating Yet Functional Organometallic Anions

Article abstract of DOI:10.1021/jacs.9b10234

Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we describe the implementation of strongly coordinating dianionic carboranyl N-heterocyclic carbenes (NHCs) to create organometallic -ate comple

Full text of DOI:10.1021/jacs.9b10234

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Article
Strongly Coordinating Ligands to Form Weakly
Coordinating yet Functional Organometallic Anions
Steven P. Fisher, Scott G. McArthur, Varun Tej, Sarah E. Lee, Allen L. Chan, Isaac Banda, Aaron Gregory,
Kevin Berkley, Charlene Tsay, Arnold L. Rheingold, Gregorio Guisado-Barrios, and Vincent Lavallo
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b10234 • Publication Date (Web): 05 Dec 2019
Downloaded from pubs.acs.org on December 5, 2019
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Strongly Coordinating Ligands to Form Weakly Coordinating
yet Functional Organometallic Anions.
Steven P. Fisher,† Scott G. McArthur,† Varun Tej,† Sarah E. Lee,† Allen L. Chan,† Isaac Banda,†
Aaron Gregory,† Kevin Berkley,† Charlene Tsay,† Arnold L. Rheingold,§ Gregorio Guisado-
Barrios,‡ Vincent Lavallo*,†
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†Department of Chemistry, University of California, Riverside, California, 92521, United States
‡Institute of Advanced Materials (INAM), Universitat Jaume I, Avda. Vicente Sos Baynat s/n, Castellón, E-12071,
Spain
§Department of Chemistry and Biochemistry, University of California–San Diego, La Jolla, California 92093,
United States
KEYWORDS (Weakly Coordinating Anions, Carborane Anions, Gold Catalysis, Carbocations, Silylium
Ions)
ABSTRACT: Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we
describe the implementation of strongly coordinating dianionic carboranyl N-Heterocyclic Carbenes (NHCs) to create organometallic
ate complexes of Au(I) that serve both as WCAs and functional catalysts. These organometallic WCAs can be utilized to form both
+
+
heterobimetallic (Au(I)-/Ag(I)+; Au(I)-/Ir(I)+) and organometallic/main group ion pairs (Au(I)-/(CPh3 or SiEt3 ). As the parent
+
unfunctionalized dianionic carboranyl NHC complex 3 is unstable in most solvents when paired with CPh3 , novel synthetic
methodology was devised to create polyhalogenated carboranyl NHCs, which show superior stability towards electrophilic
substitution and cyclometalation chemistry. Additionally, the WCAs containing polyhalogenated carboranyl NHCs are among the
most active catalysts reported for the hydroamination of alkynes. This investigation has also produced the first examples of low
coordinate Au(III) center with two cis accessible coordination sites and the first true dianionic carbene. These studies pave the way
for the design of functional ion pairs that have the potential to participate in tandem or cooperative small molecule activation and
catalysis.
H
C
1-
2-
1-
INTRODUCTION
N
N
N
N
C
C
C
C
Weakly coordinating anions (WCAs)1 are indispensable tools
for the study of extremely reactive cationic species, ranging
from main group to transition metal compounds. With respect
to main group chemistry they have allowed for the isolation of
fundamentally important reactive intermediates, such as
carbocations and silylium “like” salts,2-3 and have been utilized
to facilitate or catalyze4 important organic transformations.5-8
Similarly, in transition metal chemistry WCAs are commonly
found as counterions for cationic metal complexes with an
unsaturated coordination sphere, which are essential for many
homogeneous catalytic processes. In a classical sense, WCAs
have little function other than to be spectators for reactive
cations, ideally being inert to decomposition. Among the
different classes of WCAs, polyhalogenated 12-vertex
carborane anions ([HCB11HaXb]1-; a = 0 or 5 and b = 6 or 11)
C
C
Au
S
3
2
1
Figure 1. The parent 12-vertex closo-carborane anion 1, its NHC
derivative 2, and its anionic Au(I) complex 3. Unlabeled vertices = BH.
shine,9-10 as they are immune to decomposition via electrophilic
attack or chemical oxidation even in the presence of the most
potent electrophiles and oxidants, as exemplified by the elegant
and pioneering work of Reed.2
Over the last several years our group has begun to
investigate non-classical applications of closo-carborane anions
1 (Figure 1).9,
In one embodiment of this approach, we
11
covalently attach the anions to ligand frameworks, such as
phosphines12-15 and N-Heterocyclic Carbenes (NHCs).16-19 The
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carborane anions are used as bulky and charged alkyl or aryl
surrogates and we have demonstrated the utility of such ligands
absence of 19F and 7Li resonances in the respective NMR
spectra. The structure of the heterobimetallic ion pair 3[Ag+]
was unambiguously determined by multinuclear NMR and a
single crystal X-ray diffraction study (Figure 2, bottom left). In
the solid-state 3[Ag+] forms a dimeric structure where two
WCAs 3 are linked primarily via electrostatic interactions
between two Ag+ cations and the carborane cages of the ligands.
A single molecule of THF binds each Ag+ ion, presumably
resulting from the liberation of coordinated THF from the Li+
countercation of 3[Li+].
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20-22
in catalysis.13-14,
The NHC 2 (Figure 1) is technically a
dianionic carbenoid19 as it, and related species,16, 18 have been
isolated as alkali metal complexes. With respect to the NHC 2,
we have only reported a single anionic Au(I) compound 3 and
disclosed no reactivity or further synthetic elaboration of this
species (Figure 1).17 One way to view complex 3 is that the
entire molecule is in fact a WCA. We envisioned that if 3
behaved as a WCA, perhaps it could also be functional at the
Au center. If this were true, then one might be able to use the
inherent charge of the strongly coordinating ligand to design
complex heterobimetallic, and hybrid organometallic/main
group ion pairs that could display interesting chemistry and
eventually be utilized as platforms for tandem or cooperative
small molecule activation and catalysis. Here we report that in
fact 3, and its polyhalogenated derivatives, vide infra, are
WCAs that can be used to form heterobimetallic ion pairs, such
as Ag+, Ir+, and hybrid organometallic/main group ion pairs
(e.g. trityl and silylium “like” salts), as well as functional
catalysts. Along this journey we also have developed novel
synthetic methods to access the first polyhalogenated
carboranyl NHCs, isolate the first metal free dianionic NHC and
observed an unusual reaction that forms the first low-coordinate
Au(III) compound with two cis accessible coordination sites.
9
With 3[Ag+] in hand we envisioned utilizing it as a halide
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scavenger to form the organometallic carbocation ion pair
+
3[CPh3 ]. When reacting 3[Ag+] with ClCPh3 in acetonitrile
rapid salt metathesis was observed, however analysis of the
supernatant by 1H NMR revealed the presence of HCPh3 and no
+
resonances for CPh3 . We hypothesized that the THF
coordinated to 3[Ag+] was acting as a hydride source,
quenching the trityl cation. To avoid this decomposition
pathway, we first dissolved 3[Ag+] in MeCN to displace the
bound THF and concentrated the mixture to dryness, effectively
removing the THF as indicated by 1H NMR. Subsequent halide
abstraction from ClCPh3 cleanly afforded the trityl salt
+
3[CPh3 ], as indicated by multinuclear NMR analysis.
+
Unfortunately, we observed that 3[CPh3 ] is only stable in
acetonitrile solution, which hampers its broad utilization as a
reagent to create silylium “like” salts or truly coordinatively
unsaturated metal centers, as acetonitrile is a strongly
RESULTS AND DISCUSSION
+
+
+
As salts of Ag+, CPh3 , and SiR3 containing WCAs are the
coordinating solvent. Dissolving 3[CPh3 ] in solvents such as
reagents of choice to induce the abstraction of halides (Ag+ and
dichloromethane, chloroform, or F-C6H5 rapidly leads to a
complex mixture of products, which are extremely challenging
to separate. However, based on characteristic aryl resonances
and high resolution mass spectrometry we are able to tentatively
assign some of the decomposition products as species arising
from the electrophilic arylation of the carborane cage with the
trityl cation, a new reaction that we recently reported.23 In
addition, we were able to inconsistently isolate in pure form an
SiR3 ) and hydrides/alkides (CPh3 ) to install WCAs,1 we
decided to see if it were possible to prepare such species with 3
as a counteranion (Figure 2). To synthesize the Ag salt 3[Ag+],
we reacted a fluorobenzene (F-C6H5) solution of lithium salt
3[Li+] with AgBF4. A precipitate immediately formed which
contained solid 3[Ag+] and LiBF4. Washing the precipitate with
diethyl ether removes the LiBF4 byproduct as confirmed by the
+
+
+
Figure 2. Synthesis of 3[Ag+], 3[CPh3 ], and the formation of the
extraordinary cyclometalated Au(III) boryl NHC chelate 4,
which was unambiguously identified by multinuclear NMR and
a single crystal X-ray diffraction study (Figure 2, bottom right).
Trans to the boryl ligand a B-H agostic “like” interaction
weakly interacts with a Au orbital. Such interactions are well
documented from previous studies in our group15 and others.24-
cyclometalated Au(III) compound 4. Solid-State structures of 3[Ag+]
and 4. Note: the structure of 3[Ag+] was only of sufficient quality to
establish connectivity for an identification. Thermal ellipsoids drawn
at the 50% probability level. i = CHCl3, CH2Cl2, or F-C6H5).
Unlabeled grey and brown atoms are carbon and boron, respectively.
Unlabeled vertices = BH.
25
Cis to the boryl ligand and B-H interaction is a potentially
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labile dimethyl sulfide ligand. Complex 4 is special as it is the
perchlorinated derivative even under forcing conditions. Both
6Br12 and 6I12 can be cleanly converted to the corresponding
dianionic NHC 7Br12 and Li carbenoid 7I12 via reaction with a
strong base. The 13C NMR shifts for the dianionic NHC 7Br12
and the Li carbenoid 7I12 are shifted downfield by about 20 ppm
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only known Au(III) compound with two potentially accessible
cis-binding sites (the orbital where the B-H interaction is and
the orbital coordinated by dimethylsulfide). This is important
because if practical synthetic methods to cleanly afford species
like 4 can be developed it would lead to prototypical Au(III)
systems to explore classical d8 reaction chemistry. While we are
not sure of the mechanism of the formation of 4 we can say that
we do observe triphenylmethane and electrophilic arylation
where trityl liberates a proton.23 Thus far, all attempts to induce
this reaction via hydride abstraction from 3 with external trityl
or protic acids have been unsuccessful.
(7Br12 = 222.2; 7I12 220.6) with respect to the previously
=
reported dianionic Li carbenoid 2 (196.9 ppm). The downfield
shift of these species relative to 2, is likely due to the electron
withdrawing effects of the halogens. We know that 7Br12 is a
metal-free dianionic NHC as its structure was unambiguously
determined by a single crystal X-ray diffraction study. In
contrast, data collection from a poor quality crystal of 7I12
suggests that the iodinated carbene 7I12 is coordinated to Li+.
The difference in coordination chemistry of these ligands with
Li+ is likely due to inductive effects of the more electron
withdrawing Br atoms, which temper the nucleophilicity of the
NHC to some extent.
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In an effort to develop more stable organometallic trityl salts
+
similar to 3[CPh3 ] we envisioned that polyhalogenated
carboranyl NHCs might be immune to such electrophilic
arylation and cyclometalation reactions. Unfortunately,
reaction methodology (amine condensation with glyoxyl
followed by ring closure with p-formaldehyde) analogous to
what we previously reported19 for the synthesis of NHC
precursors was not effective with polyhalogenated carboranyl
amines (ESI pgs S96-S106). To solve this problem, we thought
that it might be possible to directly and selectively
hexahalogenate both carborane cages of the previously reported
imidazolium anion 5 (Figure
3).
Indeed,
the
imidazolium anion can be selectively brominated or iodinated
utilizing Br2 or ICl, to form 6Br12 and 6I12, respectively. While
the iodination stops at hexahalogenation at each cluster, likely
for steric reasons, the selective hexabromination requires
Figure 3. Synthesis of the hexahalogenated imidazoliums 6Br12 and
6I12 and the corresponding metal free dianionic NHC 7Br12 and the
analogous carbenoid 7I12. Solid state structure of 7Br12 two Li+
countercations coordinated by four THF molecules omitted for clarity,
thermal ellipsoids drawn at 50% probability level. Unlabeled grey,
brown, light brown and white atoms are carbon, boron, bromine and
hydrogen, respectively.
rigorous spectroscopic monitoring as to not over functionalize
the clusters. Chlorination leads to an intractable mixture of over
halogenated products, which do not converge to the
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Given the observed coordination chemistry above, we were
correlation NMR analysis, high resolution mass spectrometry
and a X-ray diffraction study (Figure 4).
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initially concerned that these NHC ligands might be labile or
form unstable complexes when bound to a transition metal
element. Gratifyingly, we observed clean metalation with Au(I)
to afford the thermally and air stable complexes 8X12[Li+]
(Figure 4). These salts are stable in solution to at least 100 oC,
as indicated by NMR analysis.
After demonstrating the potential of these silver salts to act
as halide abstracting reagents for transition metal complexes,
we next sought to apply these reagents to the formation of main
group cations. Reaction of the heterobimetallic Ag+ salts
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9X12[Ag+] with ClCPh3 in DCM rapidly induced the
Figure 4. The synthesis of the silver and iridium salts 9X12[Ag+]
an 10X12[Ir+], respectively (top) (X = Br or I). Solid-state
structures of 9Br12[Ag+] an 10Br12[Ir+] (bottom left and right,
respectively). Thermal ellipsoids drawn at the 50% probability
level. Carbon = unlabeled grey atoms, boron = brown, bromine =
light brown, hydrogen atoms omitted for clarity.
precipitation of AgCl and formation of the corresponding trityl
+
salts 11X12[CPh3 ], the identity of which was unambiguously
determined by multinuclear NMR spectroscopy and in the case
+
of 11Br12[CPh3 ], a single crystal X-ray diffraction study
(Figure 5). In the solid-state
To quantify the steric parameters of the new polyhalogenated
NHC ligands we calculated their percent buried volumes
(%Vbur).26 Compared to the previously reported hydride
substituted ligand 2,17 which is significantly bulkier (%Vbur
47.2) than Arduengo’s diadamantyl substituted NHC (%Vbur
=
=
39.8), these ligands are larger (%Vbur for 7Br12 and 7I12 = 48.7
and 49.4, respectively).
Subsequently, we performed salt metathesis with AgBF4 and
the salts 8X12[Li+], which cleanly afforded the heterobimetallic
Ag+ salts 9X12[Ag+]. The identity of 9Br12[Ag+] was
unambiguously determined by multinuclear NMR analysis and
a single crystal X-ray diffraction study. In the solid state
9Br12[Ag+] forms a beautiful polymeric structure where the
monomeric units of the WCAs are linked together by B-Br---
Ag+---Br-B linkages. The corresponding iodinated species was
too insoluble to obtain solution state NMR data or single
crystals for X-ray diffraction but its identity can be inferred
from subsequent reactions with ClCPh3, vide infra.
+
Figure 5. Synthesis of the trityl 11X12[CPh3 ] and silylium salts
+
12X12[SiEt3 ]. i = ClCPh3. Thermal ellipsoids drawn at the 50%
probability level. Carbon = unlabeled grey atoms, boron = brown,
bromine = light brown, hydrogen atoms omitted for clarity.
In order to probe if the silver salts 9X12[Ag+] could act as
halide scavengers towards other transition metals, we
investigated the reaction of these species with (ClIrCOD)2.
Specifically, we targeted the formation of the classical Ir cation
[6-C6H6IrCOD+].27-28 We found that while 9I12[Ag+] does not
react, likely for solubility reasons, 9Br12[Ag+] rapidly reacted
with (ClIrCOD)2 with a drop of benzene in dichloromethane
solvent (Figure 4). After filtration of the AgCl and
concentration of the solution the Au-/Ir+ ion pair 10Br12[Ir+]
was isolated in 90% yield. The structure of 10Br12[Ir+] was
unambiguously determined via multi nuclear and 2-D
the closest interaction between the weakly coordinating
+
organometallic anion and the carbocation of 11Br12[CPh3 ] is
2.927 Å, which is out of range for any kind of covalent
interaction. Importantly, hexahalogenation of the ligand
substituents completely prevents any cyclometalation
+
chemistry, as evidenced by the compatibility of 10X12[CPh3 ]
in any solvent that trityl is tolerant of.
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+
With the trityl salts 11X12[CPh3 ] in hand we next turned our
attention to the possibility of preparing silylium “like” ions,
featuring organometallic counteranions. The term silylium
“like”, coined by Reed,2 is utilized to indicate that the silylium
orbital is not vacant but contains a weakly interacting ligand of
some sort (e.g. halide lone pairs from a carborane anion, -arene
complexation, C-H -bonding electrons) that engenders the
complex with reactivity one would expect from a free silicon
Au catalysis. Previously we have shown that the combination
of a perchlorinated carboranyl phosphine with Au(I), created
single component zwitterionic systems that display the highest
activity reported for the hydroamination of terminal alkynes
with arylamines (turnover numbers (TONs) approaching
100,000 in some cases).14 We decided to test the Li+ salts of the
WCAs (3[Li+], 8Br12[Li+], 8I12[Li+]) as these countercations
should have minimal effect on the catalysis, particularly as they
are solvated by THF, and likely, amines during the catalysis
under neat conditions (80 oC, 24h). Indeed, as outlined in Table
1
2
3
4
5
6
7
+
cation. Treatment of the highly colored salts 11X12[CPh3 ],
8
9
dissolved in dichlorobenzene (ODCB), with HSiEt3 (1.1 eq)
rapidly quenched the colorful trityl cation (Figure 5). While the
purified white powder of 12Br12[Et3Si+] is soluble enough to
perform complete solution state NMR analysis, 12I12[Et3Si+] was
insoluble. The 1H spectrum of 12Br12[Et3Si+] showed the absence
of the Si-H hydride as well as aromatic resonances for the trityl
cation and signals for triphenylmethane, which suggests hydride
abstraction had occurred. In addition, signals for the NHC, SMe2
ligands, as well as Et resonances for a SiEt3 fragment were
observed. Close examination of the NHC backbone and SMe2
resonances shows two sets of peaks, nearly superimposed,
suggesting that there are two very similar species in solution.
The 13C NMR spectrum show one resonance for the carbene
carbon (178.0 ppm), the backbone carbons (124.5 ppm) and the
dimethylsulfide methyl carbons (25.6 ppm). However, the ethyl
carbons now give rise to two sets of peaks (7.2/6.9 and 7.1/6.1
ppm), indicating two very similar compounds in solution. The
single peaks for the resonances further downfield are likely
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Table 1.
Catalytic activity of weakly coordinating anions
8 13Br
,
12, and
13I
12
N
Ar2
Catalyst
Neat1
NH2
+
Ar2
Ar2
Ph
Ar1
Ar1
Entry Catalyst
Ar1
Catalyst
Loading (%)
Yield (%)
84
TON
1
8[Li+]
Ph
0.1
840
2
3
13Br12[Li+] Ph
Ph
Ph
0.1
0.1
95
95
950
950
13I12[Li+]
8[Li+]
Ph
Ph
4
F-C6H4
0.1
80
800
5
6
7
13Br12[Li+] Ph
F-C6H4
F-C6H4
0.1
0.1
95
94
90
950
13I12[Li+]
8[Li+]
Ph
Ph
940
actually two resonances superimposed by coincidence. The 11
B
MeO-C6H4 0.01
9000
NMR spectrum shows three broad resonances in 1:5:5 ratio,
indicating that the local C5v symmetry of the clusters is retained.
Finally, the 29Si-1H HSQC displays two peaks at 61.3 and 66.1
ppm, further indicating the existence of two compounds in
solution. Reed has observed similar phenomenon for silylium29
and methyl30 “like” cations paired with simple hexahalogenated
trityl salts, and explained this phenomenon via a population of
complexes that differ by coordination mode to the antipodal B-
X and pentahalogenated belt of B-X lone pairs, which have
similar basicities. However, in our case the magnitude of the
29Si shifts are not consistent with simple carborane B-X adducts
(106-112 ppm),30 but suggest the formation of a complex
between the silylium and one of the SMe2 lone pairs.31-33 The
observation of two species perhaps can be explained by
secondary and dynamic interactions with the cage bromides.
Due to the very low solubility of 12Br12[Et3Si+] we were unable
to further investigate this hypothesis by variable temperature
NMR experiments. Although 12I12[Et3Si+] is completely
insoluble we performed cross polarization magic angle spinning
(CP-MAS) solid-state 29Si NMR analysis and saw a similar
magnitude shift (57 ppm) that does not correspond to HSiEt3,
8
9
13Br12[Li+]
13I12[Li+]
8[Li+]
Ph
MeO-C6H4 0.01
MeO-C6H4 0.01
93
94
65
9300
9400
6500
Ph
10
Mes
Ph
0.01
11
12
13
13Br12[Li+] Mes
Ph
0.01
0.01
0.01
>95
>9500
13I12[Li+]
8[Li+]
Mes
Mes
Ph
>95 (96)a >9500
F-C6H4
70
7000
14
15
16
13Br12[Li+] Mes
F-C6H4
F-C6H4
0.01
0.01
>95
>9500
13I12[Li+]
8[Li+]
Mes
Mes
>95 (85)a >9500
MeO-C6H4 0.01
87
66
8700
17
13Br12[Li+] Mes
MeO-C6H4 0.01
MeO-C6H4 0.001
66000
18
19
13I12[Li+]
8[Li+]
Mes
90
80
90000
8000
Dipp
Ph
0.01
20
21
22
13Br12[Li+] Dipp
Ph
0.01
0.001
0.01
94
75
81
9400
75000
8100
13I12[Li+]
8[Li+]
Dipp
Dipp
Ph
and is of
a similar magnitude to that observed for
12Br12[Et3Si+]. Additionally, 13C resonances for the NHC,
SMe2 and ethyl groups of the Si fragment are observed. Neither
compound is compatible with DCM, as upon contact they
undergo an exothermic reaction indicated by boiling of the
DCM. Although all our attempts to obtain single crystals for an
X-ray diffraction study have been unsuccessful, the NMR
evidence and this chemical incompatibility with DCM is
consistent with the formation of silylium “like” species paired
with weakly coordinating organometallic anions.
F-C6H4
23
24
25
13Br12[Li+] Dipp
F-C6H4
F-C6H4
0.001
0.01
87(78)a 87000
13I12[Li+]
8[Li+]
Dipp
Dipp
68
93
68000
9300
MeO-C6H4 0.01
26
27
13Br12[Li+] Dipp
13I12[Li+]
Dipp
MeO-C6H4 0.01
MeO-C6H4 0.001
93(85)a 93000
88 88000
Given that we had shown that these organometallic anions
are weakly coordinating and suitable for the preparation of
heterobimetallic and organometallic/main group ion pairs, we
next sought to probe if these counteranions were functional in
Reactions performed neat, 80 oC, 24 h, under N2 in Teflon capped vials.
NMR yields. a Isolated yields in brackets. Ph = phenyl, Mes = 2,4,6-trimethyl
phenyl, Dipp= 2,6-diisopropylphenyl.
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1 these weakly coordinating organometallic anions are
Page 6 of 8
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excellent catalysts for such reactions. In some cases, (entries 18,
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CONCLUSIONS
The study above introduces a new paradigm in molecular
design, specifically, using electrostatic interactions to create
complex functional polyatomic ion pairs. Furthermore, we
show that organometallic WCAs can be robust with respect to
chemical decomposition, and at the same time be highly active
catalysts. This strategy has allowed for the isolation of
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organometallic/main group ion pairs Au-/ (CPh3 or SiEt3 ).
These species are intriguing and will likely find applications as
reagents for halide/hydride/alkide abstractions to make various
other ion pairs and/or as platforms for tandem or cooperative
small molecule activation and catalysis.
+
+
(8)
Douvris, C.; Ozerov, O. V., Hydrodefluorination of
Perfluoroalkyl Groups Using Silylium-Carborane Catalysts.
Science 2008, 321, 1188-1190.
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Fisher, S. P.; Tomich, A. W.; Lovera, S. O.; Kleinsasser,
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ASSOCIATED CONTENT
Supporting Information
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Douvris, C.; Michl, J., Update 1 of: Chemistry of the
The Supporting Information is available free of charge on the
ACS Publications website. Contents: Synthetic procedures,
spectroscopic data (NMR, IR, X-ray crystallographic, etc).
Carba-closo-dodecaborate(−) Anion, CB11H12–. Chem. Rev. 2013,
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Fisher, S. P.; Tomich, A.; Guo, J.; Lavallo, V., Teaching
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AUTHOR INFORMATION
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Estrada, J.; Lugo, C. A.; McArthur, S. G.; Lavallo, V.,
Inductive effects of 10 and 12-vertex closo-carborane anions:
cluster size and charge make a difference. Chem. Commun. 2016,
52, 1824-1826.
Corresponding Author
*E-Mail (V.L.): vincent.lavallo@ucr.edu
(13)
Chan, A. L.; Estrada, J.; Kefalidis, C. E.; Lavallo, V.,
Notes
Changing the Charge: Electrostatic Effects in Pd-Catalyzed Cross-
Coupling. Organometallics 2016, 35, 3257-3260.
The authors declare no competing financial interest.
(14)
Lavallo, V.; Wright, J. H.; Tham, F. S.; Quinlivan, S.,
Perhalogenated Carba-closo-dodecaborate Anions as Ligand
Substituents: Applications in Gold Catalysis. Angew. Chem. Int.
Ed. 2013, 52, 3172-3176.
ORCID
Steven P. Fisher: 0000-0002-2519-1873
Gregorio Guisado-Barrios: 0000-0002-0154-9682
Arnold L. Rheingold: 0000-0003-4472-8127
Vincent Lavallo: 0000-0001-8945-3038
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El-Hellani, A.; Kefalidis, C. E.; Tham, F. S.; Maron, L.;
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Complex Supported by a Phosphine with the Parent Carba-closo-
dodecaborate CB11H11– Ligand Substituent. Organometallics 2013.
ACKNOWLEDGMENT
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Jess, E.; Vincent, L., Fusing Dicarbollide Ions with
The authors work like to thank the National Science Foundation
(CHE-1455348) for their financial support. G. G.‐B gratefully
acknowledges MINECO for a “José Castillejo Fellowship”
(CAS16/00128) and MICIU/AEI/FEDER “Una manera de
hacer Europa” ( RTI2018-098903-J-I00 ) for financial support..
N‐Heterocyclic Carbenes. Angew. Chem. Int. Ed. 2017, 56, 9906-
9909.
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Fisher, S. P.; El-Hellani, A.; Tham, F. S.; Lavallo, V.,
Anionic and zwitterionic carboranyl N-heterocyclic carbene Au(I)
complexes. Daltons Trans. 2016, 45, 9762-9765.
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Asay, M. J.; Fisher, S. P.; Lee, S. E.; Tham, F. S.;
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carboranyl NHCs: directing effect of the carborane anion. Chem.
Commun. 2015, 51, 5359-5362.
ABBREVIATIONS
WCA, Weakly Coordinating Anion; NHC, N-Heterocyclic
Carbene; TON, Turnover number.
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El-Hellani, A.; Lavallo, V., Fusing N-Heterocyclic
Carbenes with Carborane Anions. Angew. Chem. Int. Ed. 2014, 53,
4489-4493.
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Page 8 of 8
SYNOPSIS TOC:
.
1
2
3
4
5
6
7
8
-1
Stable Salts
-2
+
Ag+, Ir+, CPh3+, SiEt3
N
N
C
X
X
X
C
X
N
N
C
X
C
X
X
X
C
X
X
C
WCA-
Au
X
X
X
X
X
X
S
X
X
X
X
X
X
Yet
WCA-
Weakly Coordinating Anion
X
X
Powerful Catalysts
Strongly Coordinating Ligand
9
10
11
12
13
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15
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17
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19
20
21
22
23
24
25
26
27
28
29
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31
32
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36
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40
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42
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8
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