Synthesis and Catalytic Properties of Dirhodium Paddlewheel Complexes with Tethered, Axially Coordinating Thioether Ligands

Article abstract of DOI:10.1021/acs.inorgchem.8b02627

Novel mixed-ligand rhodium(II) paddlewheel complexes incorporating tethered axial thioether ligands have been synthesized and characterized. The thioether moiety is essential for high yields and the suppression of byproducts in cyclopropanation reactions using an electron-deficient diazoacetate. Crystal structures, UV-vis analysis, and cyclic voltammetry experiments shed light on the catalytic performance of the complexes.

Full text of DOI:10.1021/acs.inorgchem.8b02627

Communication
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Synthesis and Catalytic Properties of Dirhodium Paddlewheel
Complexes with Tethered, Axially Coordinating Thioether Ligands
Bradley G. Anderson,† Derek Cressy,† Jay J. Patel,† Caleb F. Harris,‡ Glenn P. A. Yap,§ John F. Berry,‡
and Ampofo Darko*,†
†Department of Chemistry, University of Tennessee, 1420 Circle Drive, Knoxville, Tennessee 37996, United States
§Department of Chemistry and Biochemistry, University of Delaware, 236 Brown Laboratory, Newark, Delaware 19716, United
States
‡Department of Chemistry, University of WisconsinMadison, 1101 University Avenue, Madison, Wisconsin 53706, United States
S
* Supporting Information
al.,24 but hemilabile thioether ligands25,26 have not been
explored and offer the potential for a reactive Rh(II) complex
while providing an electron donor with the ability to remotely
affect the reactivity of the transient rhodium carbene.
ABSTRACT: Novel mixed-ligand rhodium(II) paddle-
wheel complexes incorporating tethered axial thioether
ligands have been synthesized and characterized. The
thioether moiety is essential for high yields and the
suppression of byproducts in cyclopropanation reactions
using an electron-deficient diazoacetate. Crystal struc-
tures, UV−vis analysis, and cyclic voltammetry experi-
ments shed light on the catalytic performance of the
complexes.
To demonstrate the applicability of this axial coordination
method, both carboxylate- and carboxamidate-type27 ligands
bearing tethered donor groups were synthesized. Rh(II)
compounds bearing phenylthiocarbamoyl benzoate ligand
128,29 (PhTCB, Scheme 1) and methylthiooxazolidinate ligand
430 [(S)-MeTOX, Scheme 1] were synthesized from ligand-
exchange reactions with Rh2(OAc)4. For ligand 1, the acidity of
the carboxylate ligand allowed Corey’s base-promoted reaction
in tetrahydrofuran to be employed (Scheme 1, top).31 A gem-
dimethyl group was incorporated to enhance the chelate rigidity
and promote axial coordination in PhTCB via the Thorpe−
hodium(II) paddlewheel complexes [Rh(II)] are known
Rfor promoting effective transformations through the
decomposition of α-diazocarbonyl compounds and in situ
generation of rhodium carbenoids.1−8 These carbenes can
undergo a variety of transformations such as cyclopropanation
and C−H and X−H (X = O, N, S, Si) insertion reactions.9−13
Bridging ligands surrounding the bimetallic core of the Rh
catalyst play an important role in the reactivity and selectivity of
the complexes and are largely the focus of Rh(II) design.14 The
axial sites of the complexes serve as sites of electrophilic
reactivity and, as such, are often occupied by weakly
coordinating solvent molecules that are easily displaced.14
Efforts to tune Rh(II) catalysis through axial coordination have
been limited by the weaker interaction of axial ligands compared
to the bridging ligands. Large excesses of the axial ligand15 or
strong σ-donor ligands16,17 are required to observe significant
effects, but this comes at a cost: when ligands block both axial
sites, inert off-cycle complexes result.18 Also, coordination of a
strong σ-donor ligand at one Rh axial site likely decreases the
electrophilicity of the distal Rh axial site via electronic
communication through the Rh−Rh bond, affecting the
reactivity of the complex.18−22
Scheme 1. Ligand-Exchange Reactions
To combat this, our research focuses on tethering Lewis base
moieties to the bridging ligand scaffold of Rh paddlewheel
complexes in an effort to control and probe the beneficial aspects
of their coordination. Described herein are new ligands
incorporating chelated, axially coordinating thioether donor
groups that can modulate the electron density about the Rh2
core, enhancing the catalytic activity in cyclopropanation
reactions with an electron-deficient diazoester. Similar ligand
design strategies have been examined by Bera et al.23 and Ball et
Received: September 15, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02627
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
Ingold effect.32 Soxhlet conditions3 were required to achieve
ligand exchange with 4 (Scheme 1, bottom). Using 1 equiv of
ligand, reactions predominantly formed monosubstituted Rh
complexes (2 and 5, Scheme 1), with smaller amounts of cis and
trans isomers of the disubstituted compounds (3a, 3b, 6a, and
6b, Scheme 1). While ligand-exchange reactions have not been
optimized, the axial tether prevented the formation of tri and
tetrasubstituted Rh species in both instances, an issue that
previously complicated the synthesis of mixed-ligand Rh(II)
complexes.33,34
Crystals of Rh(OAc)3MeTOX (5) and trans-Rh-
(OAc)2(PhTCB)2 (3b) were obtained and analyzed by single-
crystal X-ray diffraction, which confirmed axial coordination and
chelation of the thioether donor groups (Figure 1). The crystal
Figure 2. UV−vis spectra of Rh complexes recorded in DCE.
Rh2(OAc)4 was substituted with Rh2(OPiv)4 because of solubility
issues.
The electrochemical characteristics of Rh(II) complexes can
be correlated with the reactivity and selectivity in diazo-
mediated transformations,40,41 with electron-rich complexes
having lower redox potentials, lower reactivities, and higher
selectivities than electron-poor complexes. Electrochemical
relationships for axially coordinating ligands have been limited
to correlating the reactivity in Rh(II,III)-catalyzed oxidation
reactions.42 Nevertheless, it is useful to compare these
characteristics to approximate the electrophilicity of our
complexes.
Figure 1. (a) Solid-state structure of [Rh2(OAc)3MeTOX]·2MeCN,
with 50% probability ellipsoids. Solvent molecules and H atoms
omitted for clarity. Terminal S1 and Rh2 atoms denote the oligomeric
nature of the structure. (b) Solid-state structure of trans-
[Rh2(OAc)2(PhTCB)2], with 50% probability ellipsoids. Only one of
the two molecules in the asymmetric unit is shown, with H atoms
omitted for clarity.
The cyclic voltammograms of all of the complexes showed
4+/5+
reversible Rh2
couples between 404 and 870 mV versus
ferrocenium/ferrocene depending on the ligand architecture
(Figure S2). Interestingly, the Rh24+/5+ E1/2 value of 2 was 36 mV
higher than that of its monobenzoate control complex
Rh2(OAc)3OBz (Figure S2; 870 mV compared to 834 mV),
meaning that the presence of the axial tether in complex 2 should
result in a more electrophilic catalyst compared to
Rh2(OAc)3OBz. Trends based on σ donation alone would
have suggested a cathodic shift for complex 2, implying that the
tethered thioether ligand also has π-acceptor character.43,44 The
more electron-rich axial thiomethyl donor for complex 5 reduces
the redox potential to 603 mV (Figure S2), below that for
complex 2. Irreversible ligand-centered redox events linked to
the number of axially coordinating ligands were observed in the
cases of 2, 3a, and 3b. The strength of the axial binding must also
be a factor because 5, 6a, and 6b do not follow this trend (Figure
S2).
To assess the axial tether concept in catalysis, complexes were
screened for their ability to catalyze the cyclopropanation of
alkene substrates with methyl-p-nitrophenyldiazoacetate (8).
Compound 8 is a diazoacetate that has been previously reported
to give low yields of cyclopropanes in Rh(II)-catalyzed
cyclopropanation reactions,45,46 giving mostly undesired homo-
coupled side product 10, unless bulky catalysts are used.47
Under optimal conditions (see Table S1), 2 was found to be the
best catalyst for the transformation, while reactions carried out
with 5 were less successful in yield for cyclopropane 9a, giving
yields comparable to those for Rh2(OAc)4 (Table 1, entries 1−
3). Disubstituted complexes 3a and 3b were also tested and,
despite having sulfur coordinated at both axial sites, out-
performed Rh2(OAc)4 in yield and product ratio (in the case of
3b) for cyclopropane 9a (entries 4 and 5). Complexes 6a and 6b
performed poorly, giving 17% yield of cyclopropane. As a
control, the monobenzoate complex Rh2(OAc)3(OBz) was
tested (entry 7) and displayed poorer yield and similar product
ratios compared to those of 2, demonstrating that the axial tether
structure of 5 adopts an oligomeric structure in the solid state,
with the thiomethyl group binding both intra- and intermolec-
ularly to the axial site of the Rh (Figure S1). This Rh−Rh−X−
Rh−Rh motif has previously been observed with an O35,36 or
halogen,37,38 spanning the Rh paddlewheel units. The Rh−S−
Rh bond is asymmetric, with the intramolecular Rh−S bond
shorter because of the chelate effect (2.484 vs 2.556 Å). By
comparison, 3b crystallizes as monomeric units, with both axial
sites occupied by chelated thiophenyl units (Figure 1b). The
average Rh−S bond length of 3b (2.542 Å) is notably longer
than that of 5 (2.484 Å) because of the stronger σ-donating
ability of the thiomethyl group compared to the thiophenyl
group. The favorable six-membered ring chelate in complex 5
also contributes to a stronger interaction at the axial site.
UV−vis spectra of the complexes in dichloroethane (DCE)
were obtained (Figure 2) to compare the ability of the axial
thioether coordination to affect the electronic transitions within
these Rh paddlewheel complexes and correlate the results to
their reactivity. Axial ligands affect the electronic states of
rhodium carboxylates and amidates because of perturbation of
the Rh−Rh π*-to-σ* HOMO−LUMO transition.39 Shorter
Rh−Lax bonds from strong σ-donors increase the π*-to-σ* gap,
leading to higher energy shifts in the UV−vis. In each case, the
incorporation of a tethered axial thioether causes a shift of this
band to higher energy. The disubstituted complexes caused a
further blue shift from their respective monosubstituted
complexes. When the (S)-MeTOX complexes (5, 6a, and 6b)
are compared to the PhTCB complexes (2, 3a, and 3b), the data
show that (S)-MeTOX has a stronger interaction at the axial site
than PhTCB when incorporated into the Rh paddlewheel
framework.
B
DOI: 10.1021/acs.inorgchem.8b02627
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
Table 1. Cyclopropanation of Alkene Substrates
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02627.
Experimental details, optimization table, X-ray crystal
data, cyclic voltammetry, and NMR spectra (PDF)
Accession Codes
a
b
entry
product
[Rh]
yield (%)
9/10
CCDC 1861873−1861874 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
1
2
3
4
5
6
7
8
9a
9a
9a
9a
9a
9a
9a
9b
9b
9c
9c
[Rh2(OAc)4]
2
5
3a
3b
6a and 6b
[Rh2(OAc)3OBz]
[Rh2(OAc)4]
49
74
46
48
59
17
52
57
78
8
5.4:1
>20:1
5.0:1
9.3:1
16:1
4.5:1
17:1
12:1
>20:1
1:1
c
AUTHOR INFORMATION
Corresponding Author
*E-mail: adarko@utk.edu.
■
c
9
10
11
2
[Rh2(OAc)4]
2
ORCID
28
9:1
a
1
Caleb F. Harris: 0000-0002-6844-8923
John F. Berry: 0000-0002-6805-0640
Ampofo Darko: 0000-0003-1725-4907
Yields are averaged over two runs. Determined by H NMR using
mesitylene as an internal standard. Ratio determined by H NMR.
The ratio calculated was beyond the standard NMR detection limits.
b
1
c
Notes
The authors declare no competing financial interest.
leads to increased yields. While results for the sterically
congested 9c were modest with 2, they were a significant
improvement in yield and 9c/10 ratio over those of Rh2(OAc)4
(entries 10 and 11), further demonstrating the potential of the
ligand to enhance existing Rh paddlewheel complexes.
ACKNOWLEDGMENTS
■
We are grateful for financial support from the University of
Tennessee in Knoxville, TN. We also thank the personnel in the
NMR, Biological and Small Molecule Mass Spectrometry Core,
and analytical facilities at the University of Tennessee. We are
grateful to Dr. Gaya Elpitiya for X-ray analysis of trans-
[Rh2(OAc)2(PhTCB)2]. J.F.B. acknowledges the NSF Center
for Selective C−H Functionalization (Grant CHE-1700982) for
financial support.
Some conclusions can be drawn from the data presented.
Yields for cyclopropane 9a are better for complexes incorporat-
ing ligand 1 than the respective complexes from ligand 4,
suggesting that weaker interaction of the axial donor group is
important for optimal performance. The six-membered chelate
coordination of the thioether donor group in 4 means that the
thiomethyl is more tightly bound to the Rh atom, decreasing the
Lewis acidity of the Rh center compared to that of 1. The
electrochemistry data suggest, though, that the presence of a
tethered axially coordinating thioether in carboxylate complexes
results in a more electrophilic catalyst (compare the E1/2 values
and yields for complex 2 and Rh2(OAc)3OBz). A representative
control for complex 5 is needed to extend this trend to mixed
oxazolidinate/carboxylate complexes.48
In conclusion, new heteroleptic Rh complexes incorporating
tethered thioether axial coordination have been synthesized and
characterized. Their catalytic properties were probed in a
cyclopropanation reaction with a diazo compound that is known
for difficult reactivity and poor selectivity with regard to the
suppression of diazo coupling. Our modified rhodium
carboxylates successfully improved the reaction yield and
decreased olefin formation. The modular nature of our design
allows for experimentation with a variety of donor groups and
equatorial ligands, with the goal of designing a new generation of
Rh catalysts that incorporate axial coordination. Exploration
into the scope of the effects of ligands is currently under
investigation in our laboratory.
REFERENCES
■
(1) Davies, H. M. L.; Parr, B. T. Rhodium Carbenes. In Contemporary
Carbene Chemistry; Moss, R. A., Doyle, M. P., Eds.; John Wiley & Sons:
Hoboken, NJ, 2014; p 363.
(2) Cheng, Q. Q.; Doyle, M. P. The Selection of Catalysts for Metal
Carbene Transformations. Adv. Organomet. Chem. 2016, 66, 1−31.
(3) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods
for Organic Synthesis with Diazo Compounds: from Cyclopropanes to
Ylides; Wiley: New York, 1998.
(4) Kornecki, K. P.; Briones, J. F.; Boyarskikh, V.; Fullilove, F.;
Autschbach, J.; Schrote, K. E.; Lancaster, K. M.; Davies, H. M.; Berry, J.
F. Direct Spectroscopic Characterization of a Transitory Dirhodium
Donor-Acceptor Carbene Complex. Science 2013, 342, 351−4.
(5) Snyder, J. P.; Padwa, A.; Stengel, T.; Arduengo, A. J.; Jockisch, A.;
Kim, H. J. A Stable Dirhodium Tetracarboxylate Carbenoid: Crystal
Structure, Bonding Analysis, and Catalysis. J. Am. Chem. Soc. 2001, 123,
11318−11319.
(6) Nakamura, E.; Yoshikai, N.; Yamanaka, M. Mechanism of CH
Bond Activation/CC Bond Formation Reaction between Diazo
Compound and Alkane Catalyzed by Dirhodium Tetracarboxylate. J.
Am. Chem. Soc. 2002, 124, 7181−92.
(7) Werle, C.; Goddard, R.; Philipps, P.; Fares, C.; Fu
̈
rstner, A.
Structures of Reactive Donor/Acceptor and Donor/Donor Rhodium
Carbenes in the Solid State and Their Implications for Catalysis. J. Am.
Chem. Soc. 2016, 138, 3797−3805.
(8) Werle, C.; Goddard, R.; Furstner, A. The First Crystal Structure of
̈
a Reactive Dirhodium Carbene Complex and a Versatile Method for the
C
DOI: 10.1021/acs.inorgchem.8b02627
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
Preparation of Gold Carbenes by Rhodium-to-Gold Transmetalation.
Angew. Chem., Int. Ed. 2015, 54, 15452−15456.
din-4(S)-Carboxylate], Rh2(4S-MEOX)4. Recl. Trav. Chim. Pays-Bas
1995, 114, 163−170.
(9) Davies, H. M. L.; Morton, D. Guiding principles for site selective
and stereoselective intermolecular C-H functionalization by donor/
acceptor rhodium carbenes. Chem. Soc. Rev. 2011, 40, 1857−1869.
(10) Doyle, M. P.; Duffy, R.; Ratnikov, M.; Zhou, L. Catalytic Carbene
Insertion into CH Bonds. Chem. Rev. 2010, 110, 704−724.
(11) Ford, A.; Miel, H.; Ring, A.; Slattery, C. N.; Maguire, A. R.;
McKervey, M. A. Modern Organic Synthesis with α-Diazocarbonyl
Compounds. Chem. Rev. 2015, 115, 9981−10080.
(28) Cowan, D. J.; Collins, J. L.; Mitchell, M. B.; Ray, J. A.; Sutton, P.
W.; Sarjeant, A. A.; Boros, E. E. Enzymatic- and Iridium-Catalyzed
Asymmetric Synthesis of a Benzothiazepinylphosphonate Bile Acid
Transporter Inhibitor. J. Org. Chem. 2013, 78, 12726−12734.
(29) Tohnishi, M.; Nakao, H.; Furuya, T.; Seo, A.; Kodama, H.;
Tsubata, K.; Fujioka, S.; Kodama, H.; Hirooka, T.; Nishimatsu, T.
Flubendiamide, a Novel Insecticide Highly Active against Lepidop-
terous Insect Pests. J. Pestic. Sci. (Tokyo, Jpn.) 2005, 30, 354−360.
(30) Lewis, N.; Mckillop, A.; Taylor, R. J. K.; Watson, R. J. A Simple
and Efficient Procedure for the Preparation of Chiral 2-Oxazolidinones
from α-Amino Acids. Synth. Commun. 1995, 25, 561−568.
(31) Lou, Y.; Remarchuk, T. P.; Corey, E. J. Catalysis of
Enantioselective [2 + 1]-Cycloaddition Reactions of Ethyl Diazoacetate
and Terminal Acetylenes Using Mixed-Ligand Complexes of the Series
Rh2(RCO2)n (L*4n). Stereochemical Heuristics for Ligand Exchange
and Catalyst Synthesis. J. Am. Chem. Soc. 2005, 127, 14223−14230.
(32) Jung, M. E.; Piizzi, G. gem-Disubstituent Effect: Theoretical
Basis and Synthetic Applications. Chem. Rev. 2005, 105, 1735−1766.
(33) Boruta, D. T.; Dmitrenko, O.; Yap, G. P. A.; Fox, J. M. Rh2(S-
PTTL)3TPAa mixed-ligand dirhodium(II) catalyst for enantiose-
lective reactions of α-alkyl-α-diazoesters. Chem. Sci. 2012, 3, 1589−
1593.
(12) Doyle, M. P. Perspective on Dirhodium Carboxamidates as
Catalysts. J. Org. Chem. 2006, 71, 9253−9260.
(13) Chepiga, K. M.; Qin, C. M.; Alford, J. S.; Chennamadhavuni, S.;
Gregg, T. M.; Olson, J. P.; Davies, H. M. L. Guide to enantioselective
dirhodium(II)-catalyzed cyclopropanation with aryldiazoacetates.
Tetrahedron 2013, 69, 5765−5771.
(14) Cotton, F. A.; Murillo, C. A.; Walton, R. A. Multiple Bonds
between Metal Atoms, 3rd ed.; Springer Science and Business Media:
New York, 2005.
(15) Zhao, L.; Wang, Y.; Ma, Z.; Wang, Y. Dirhodium(II)-Catalyzed
Carbonylation Peroxidation of α,β-Unsaturated Esters: Mechanistic
Insight into the Role of Aryl Aldehydes. Inorg. Chem. 2017, 56, 8166−
8174.
(16) Gomes, L. F. R.; Trindade, A. F.; Candeias, N. R.; Gois, P. M. P.;
Afonso, C. A. M. Intramolecular CH insertion using NHC-di-
rhodium(II) complexes: the influence of axial coordination. Tetrahe-
dron Lett. 2008, 49, 7372−7375.
(17) Ye, Q. S.; Li, X. N.; Jin, Y.; Yu, J.; Chang, Q. W.; Jiang, J.; Yan, C.
X.; Li, J.; Liu, W. P. Synthesis, crystal structures and catalytic activity of
tetrakis(acetato)dirhodium(II) complexes with axial picoline ligands.
Inorg. Chim. Acta 2015, 434, 113−120.
(18) Pirrung, M. C.; Liu, H.; Morehead, A. T. Rhodium Chemzymes:
Michaelis-Menten kinetics in Dirhodium(II) Carboxylate-Catalyzed
Carbenoid Reactions. J. Am. Chem. Soc. 2002, 124, 1014−1023.
(19) Pirrung, M. C.; Morehead, A. T. Saturation Kinetics in
Dirhodium(II) Carboxylate-Catalyzed Decompositions of Diazo
Compounds. J. Am. Chem. Soc. 1996, 118, 8162−8163.
(20) Bilgrien, C.; Drago, R. S.; Vogel, G. C.; Stahlbush, J. Trans
Influence across a Rh-Rh Bond. Effect of a Series of Lewis Bases on the
Stretching Frequency of Coordinated CO. Inorg. Chem. 1986, 25,
2864−2866.
(21) Drago, R. S.; Long, J. R.; Cosmano, R. Comparison of the
Coordination Chemistry and Inductive Transfer through the Metal-
Metal Bond in Adducts of Dirhodium and Dimolybdenum Carbox-
ylates. Inorg. Chem. 1982, 21, 2196−2202.
(22) Drago, R. S.; Long, J. R.; Cosmano, R. Metal Synergism in the
Coordination Chemistry of a Metal-Metal Bonded System:
Rh2(C3H7COO)4. Inorg. Chem. 1981, 20, 2920−2927.
(23) Sarkar, M.; Daw, P.; Ghatak, T.; Bera, J. K. Amide-Functionalized
Naphthyridines on a RhIIRhII Platform: Effect of Steric Crowding,
Hemilability, and Hydrogen-Bonding Interactions on the Structural
Diversity and Catalytic Activity of Dirhodium(II) Complexes. Chem. -
Eur. J. 2014, 20, 16537−16549.
(24) Sambasivan, R.; Zheng, W.; Burya, S. J.; Popp, B. V.; Turro, C.;
Clementi, C.; Ball, Z. T. A tripodal peptide ligand for asymmetric
Rh(II) catalysis highlights unique features of on-bead catalyst
development. Chem. Sci. 2014, 5, 1401−1407.
(25) Liu, Y.; Kean, Z. S.; d’Aquino, A. I.; Manraj, Y. D.; Mendez-
Arroyo, J.; Mirkin, C. A. Palladium(II) Weak-Link Approach
Complexes Bearing Hemilabile N-Heterocyclic CarbeneThioether
Ligands. Inorg. Chem. 2017, 56, 5902−5910.
(26) Romeo, R.; Scolaro, L. M.; Plutino, M. R.; Romeo, A.; Nicolo’, F.;
Zotto, A. D. Ring Closure Kinetics of Bidentate Hemilabile P,N and P,S
Ligands on a Platinum(II) Complex. Eur. J. Inorg. Chem. 2002, 2002,
629−638.
(34) Lindsay, V. N. G.; Charette, A. B. Design and Synthesis of Chiral
Heteroleptic Rhodium(II) Carboxylate Catalysts: Experimental
Investigation of Halogen Bond Rigidification Effects in Asymmetric
Cyclopropanation. ACS Catal. 2012, 2, 1221−1225.
(35) Cotton, F. A.; Dikarev, E. V.; Stiriba, S.-E. Studies of Dirhodium
Tetra(trifluoroacetate). 3. Solid State Isomers of the Compound
Rh2(O2CCF3)4(THF) Prepared by Sublimation. Inorg. Chem. 1999, 38,
4877−4881.
(36) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A.; Stiriba, S.-E.
Studies of Dirhodium(II) Tetra(trifluoroacetate). 5. Remarkable
Examples of the Ambidentate Character of Dimethyl Sulfoxide. Inorg.
Chem. 2000, 39, 1748−1754.
(37) Amo-Ochoa, P.; Jimenez-Aparicio, R.; Perles, J.; Torres, M. R.;
Gennari, M.; Zamora, F. Structural Diversity in Paddlewheel
Dirhodium(II) Compounds through Ionic Interactions: Electronic
and Redox Properties. Cryst. Growth Des. 2013, 13, 4977−4985.
(38) Yang, Z.; Fujinami, T.; Ebihara, M.; Nakajima, K.; Kitagawa, H.;
Kawamura, T. Halide-Bridged Zigzag Chain of Tetrakis(acetamidato)-
dirhodium Cationic Radical Assisted by Hydrogen Bond. Chem. Lett.
2000, 29, 1006−1007.
(39) Berry, J. F. The role of three-center/four-electron bonds in
superelectrophilic dirhodium carbene and nitrene catalytic intermedi-
ates. Dalton Trans 2012, 41, 700−713.
(40) Pirrung, M. C.; Morehead, A. T. Electronic Effects in
Dirhodium(II) Carboxylates. Linear Free Energy Relationships in
Catalyzed Decompositions of Diazo Compounds and CO and Isonitrile
Complexation. J. Am. Chem. Soc. 1994, 116, 8991−9000.
(41) Doyle, M. P.; Ren, T. The influence of ligands on dirhodium(II)
on reactivity and selectivity in metal carbene reactions. Progress in
Inorganic Chemistry, Vol 49 2007, 49, 113−168.
(42) Bui, N. N.; Hong, J. T.; Ho, X. H.; Mho, S. I.; Jang, H. Y.
Correlation of Electrochemical Characteristics and Catalytic Activity of
Rh2(OAc)4 in the Presence of Various Phosphines. Bull. Korean Chem.
Soc. 2008, 29, 1624−1626.
(43) Jacobsen, H.; Kraatz, H. B.; Ziegler, T.; Boorman, P. M. A New
Look at an Old Ligand - Surprises with Thioethers - a Density
Functional-Study. J. Am. Chem. Soc. 1992, 114, 7851−7860.
(44) Kraatz, H. B.; Jacobsen, H.; Ziegler, T.; Boorman, P. M. pi.-
Acidity of thioethers and selenoethers: truth or fiction? A comparative
density functional study. Organometallics 1993, 12, 76−80.
(45) Ovalles, S. R.; Hansen, J. H.; Davies, H. M. L. Thermally Induced
Cycloadditions of Donor/Acceptor Carbenes. Org. Lett. 2011, 13,
4284−4287.
(27) Doyle, M. P.; Dyatkin, A. B.; Protopopova, M. N.; Yang, C. I.;
Miertschin, C. S.; Winchester, W. R.; Simonsen, S. H.; Lynch, V.;
Ghosh, R. Enhanced Enantiocontrol in Catalytic Metal Carbene
Transformations with Dirhodium(II) Tetrakis[Methyl 2-Oxooxazoli-
(46) Qu, Z. H.; Shi, W. F.; Wang, J. B. A Kinetic Study on the Pairwise
Competition Reaction of α-Diazo Esters with Rhodium(II) Catalysts:
D
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Inorganic Chemistry
Communication
Implication for the Mechanism of Rh(II)-Carbene Transfer. J. Org.
Chem. 2001, 66, 8139−8144.
(47) Chen, P.-A.; Setthakarn, K.; May, J. A. A Binaphthyl-Based
Scaffold for a Chiral Dirhodium(II) Biscarboxylate Ligand with α-
Quaternary Carbon Centers. ACS Catal. 2017, 7, 6155−6161.
(48) Welch, C. J.; Tu, Q.; Wang, T. B.; Raab, C.; Wang, P.; Jia, X. J.;
Bu, X. D.; Bykowski, D.; Hohenstaufen, B.; Doyle, M. P. Observations
of rhodium-containing reaction intermediates using HPLC with ICP-
MS and ESI-MS detection. Adv. Synth. Catal. 2006, 348, 821−825.
E
DOI: 10.1021/acs.inorgchem.8b02627
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