Chiral Heterobimetallic Bismuth–Rhodium Paddlewheel Catalysts: A Conceptually New Approach to Asymmetric Cyclopropanation

Article abstract of DOI:10.1002/anie.201900265

Cyclopropanation reactions of styrene derivatives with donor–acceptor carbenes formed in situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuth–rhodium complex 5 a endowed with N-phthalimido tert-leucine paddlewheel ligands rather than by its homobimetallic dirhodium analogue 1 a. This virtue is likely the result of two synergizing factors: the conical shape of 5 a translates into a narrower calyx-like chiral binding site about the catalytically active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic core be matched by proper directionality of the ligand sphere.

Full text of DOI:10.1002/anie.201900265

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Chiral Heterobimetallic Bismuth-Rhodium Paddlewheel Catalysts:
A Conceptually New Approach to Asymmetric Cyclopropanation
Authors: Alois Fürstner, Lee R. Collins, Sebastian Auris, and Richard
Goddard
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201900265
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10.1002/anie.201900265
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Chiral Heterobimetallic Bismuth-Rhodium Paddlewheel Catalysts: A Conceptually New Approach to
Asymmetric Cyclopropanation
Lee R. Collins, Sebastian Auris, Richard Goddard, and Alois Fürstner*
Dedicated to Professor Walter Thiel on the occasion of his 70th birthday
Abstract: Cyclopropanation reactions of styrene derivatives with donor/acceptor carbenes formed in
situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuthrhodium
complex 5a endowed with N-phthalimido tert-leucine paddlewheel ligands rather than by its
homobimetallic dirhodium analogue 1a. This virtue is likely the result of two synergizing factors: the
conical shape of 5a translates into a narrower calyx-like chiral binding site about the catalytically
active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates
and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation
proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic
core be matched by proper directionality of the ligand sphere.
Our group has recently published the first structure of a chiral dirhodium carbene complex in the
solid state.1,2 We had chosen [Rh2(PTTL)4] (1a) as precatalyst for its excellent pedigree in asymmetric
catalysis (Scheme 1).3,4,5 The derived electrophilic donor-acceptor carbene complex 3 was found to
adopt an ,,,-conformation: all N-phthalimido substituents of the tert-leucine derived
paddlewheel ligands are oriented toward the same side, thus crafting a chiral calyx about one of the
two rhodium atoms; the immediate environment about the second rhodium center formed by the
four tert-butyl groups is essentially “achiral”.6,7 Detailed spectroscopic studies showed that this
*
Dr. L. R. Collins, S. Auris, Dr. R. Goddard, Prof. A. Fürstner
Max-Planck-Institut für Kohlenforschung
45470 Mülheim/Ruhr (Germany)
Email: fuerstner@kofo.mpg.de
Supporting Information for this article can be found under https://doi.org/10.1002/anie.201900265 and
10.1002/ange.201900265
1
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conformation is well retained in solution at low temperature, as is necessary to maintain the integrity
of this highly reactive and sensitive complex.1
Scheme 1. Top: Preparation and reactivity of the dirhodium donor/acceptor carbene 3, the structure
of which was solved by crystallographic means and NMR spectroscopy; bottom/left: structure of 3 in
the solid state (the carbene unit was removed to show the conformation of the paddlewheel ligands
about the dirhodium core);1 bottom right: schematic drawing of the possible basic conformers that a
chiral dirhodium tetracarboxylate complex can adopt; complex 3 is essentially a manifestation of the
C4 symmetric extreme10
Although these experimental data describe the ground state, it is tempting to assume that the overall
shape of the complex is preserved in the stereodetermining transition state passed through in the
reaction of 3 with styrene as a prototypical substrate; this would lead to the formation of
cyclopropane 4a, which is indeed the major product.1 For the correct prediction of the relative and
2
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absolute stereochemistry, it also seems legitimate to consider in more detail why the level of
asymmetric induction is modest (78% ee).8 In contrast to other conceivable basic conformers that
such paddlewheel complexes might adopt (Scheme 1), an essentially C4 symmetric “all up” array
exposes two notably different rhodium faces:9,10 Although our X-ray data showed that the achiral
pore of 3 between the tert-butyl groups is narrower than the aperture of the chiral calyx, it remains
large enough that CH2Cl2 can enter and coordinate to Rh2 (see Scheme 1).1 If a diazo derivative
reaches Rh2 and gets decomposed to the corresponding metal carbene, a racemic background
reaction will ensue and the ee of the resulting product 4a drops. With this critical aspect in mind, it
becomes clear why previous empirical catalyst optimization exercises had led to complexes such as
[Rh2(PTAD)4] (1b) bearing adamantyl residues in lieu of the tert-butyl groups (Scheme 2), which likely
block the achiral face more efficiently and hence result in higher enantioselectivities in many
applications.11
Scheme 2. Top: Established design concept for chiral dirhodium paddlewheel complexes that tries to
prevent racemic background reactions by steric means; bottom: alternative concept pursued herein
capitalizing on the use of heterobimetallic precatalyts
3
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Outlined herein is a conceptually different approach to catalyst optimization which builds upon
recent insights into structure and bonding in heterobimetallic paddlewheel carbene complexes
(Scheme 2).12,13,14 Specifically, combined experimental, spectroscopic and computational studies
showed that formal replacement of one RhII center in the bimetallic core for BiII enhances the
electrophilic character of the resulting carbenes to a significant extent, although the rate of metal-
carbene formation is manifestly slower.14 More important in the present context is the fact that the
bismuth site seems to lack any notable Lewis acidity and proved incapable of decomposing ethyl
diazoacetate.12-14,15 Even though the ionic radius of bismuth is larger than that of rhodium and the
bismuth center hence certainly more exposed, any deleterious background reaction should cease.
Furthermore, the different radii impart a conical shape on the heterobimetallic core, which likely
translates into a narrower chiral pocket and hence potentially improves the level of asymmetric
induction. As these factors might synergize, it seemed worthwhile to pursue this design concept in
more detail. As shown below, heterobimetallic complexes can indeed outperform their
homobimetallic cousins in catalytic cyclopropanation to a considerable extent, provided that the
directionality of the bismuth-rhodium tetracarboxylate cage finds proper correspondence in the
ligand sphere. This boundary condition, however, is not necessarily met by the design principles
governing contemporary asymmetric dirhodium catalysis. This communication complements a recent
literature report describing preparation and use of a BiRh precatalyst with a different set of chiral
ligands ([BiRh(TBSP)4] (TBSP = tert-butylsulfonylprolinate).16
4
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Scheme 3. Preparation of the chiral heterobimetallic paddlewheel complexes; TFA = trifluoroacetate
Figure 1. Structure of complex 5aEtOAc in the solid state; top: side view of the ,,,-calyx;
bottom: Newman-type projection along the RhBi axis (bottom); hydrogen atoms are omitted for
clarity and anisotropic displacement parameters are shown at the 30% probability level
The targeted heterobimetallic precatalyst 5a and its close relatives 5b,c were prepared in excellent
yield by mixing 7 with the appropriately protected tert-leucine derivative (Scheme 3). Heating of the
mixture in toluene resulted in ligand exchange; to shift the equilibrium, the volatile trifluoroacetic
acid was azeotropically removed by passing the condensing solvent through a Soxhlet extractor filled
with powdered K2CO3 as described in detail in the Supporting Information. The crude material was
5
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then purified by an extractive work up and recrystallization to remove any acidic residues. Whereas
[BiRh(TFA)4] (7), serving as the starting point, is air sensitive and needs to be handled with care,
complexes 5a-c are indefinitely air-stable and easy to work with. Because they are somewhat
hydroscopic, however, it is recommended to keep them dry or dry them prior to use.17
The structure of 5aEtOAc in the solid state (Figure 1) proves that the co-crystallized EtOAc is bound
to rhodium, whereas the bismuth center is unligated. This finding concurs with literature data which
suggest that the BiII atom exhibits hardly any Lewis acidity.12,14 The ligand sphere adopts the ,,,-
conformation, presumably because this arrangement places the tert-butyl groups as the most bulky
substituents at maximum distance from one another; their orientation toward the Bi center follows
from the larger radius of this ion, which provides more space (see below). Since the resulting
structure of 5aEtOAc is similar to that of the actual dirhodium carbene complex 3,1,18 a comparison
seems meaningful as one can take the coordinated EtOAc ligand as a dummy for the reactive carbene
moiety. The BiO bonds (average 2.41 Å) are significantly longer than the Rh2O bonds in 3 (average
2.03 Å), as is the BiRh distance (2.503(1) Å) compared with the Rh1Rh2 distance of 3 (2.400(1) Å).
In line with our expectations, these geometric changes translate into a chiral pocket about the
rhodium center in 5a which is more confined than that of 3.1 Specifically, the aperture measures 8.9
Å and 10.0 Å for the two main axes at the height of the coordinated carbonyl O-atom (Rh1O1
2.305(7) Å), whereas the analogous distances in 3 at the level of the coordinated carbene C-atom
(which is actually somewhat closer to rhodium, cf: Rh1C1 2.004(9) Å) are 11.6 Å and 11.8 Å.
Figure 1 clearly shows that there is no steric impediment whatsoever about the Bi-center that would
prevent carbene formation from occurring if this site were catalytically active (note that a typical
metal carbene bond is  2 Å for an element of the sixth row).19
Encouraged by these structural attributes, we tested the catalytic properties of 5a-c in asymmetric
cyclopropanation reactions of substituted styrenes with a prototypical donor/acceptor diazo
derivative as carbene precursor. For the sake of consistency, the reactions were performed in parallel
with the homobimetallic analogue 1a. As expected, complex 5a reacted more slowly than 1a (14 h
6
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versus < 4 h) but gave a substantially better ee (Table 1), whereas complex 5b bearing the more
bulky NTTL substituent proved less selective. In view of the often excellent results with
[RhRh(TCPTTL)4] documented in the literature,20 it first came as a surprise that the performance of
the heterobimetallic analogue 5c endowed with the identical chlorinated ligand set was
disappointing; this outcome, however, became obvious after an X-ray structure of this complex had
been solved (see below).
Table 1. Optimization of the Asymmetric Cyclopropanation of Styrene Derivatives [a]
entry
R
Catalyst
1a
T (°C)
20
Product
4b
ee (%)
67 (68)[b]
73
1
2
3
4
5
6
7
8
9
10
OMe
OMe
OMe
OMe
H
5a
20
4b
5b
20
4b
53
5c
20
4b
4
1a
20
4a
75
H
5a
20
4a
86
H
1a
4a
77
90[c]
25
25
40
40
H
5a
4a
H
1a
4a
79
95[d]
H
5a
4a
[a] unless stated otherwise, the reactions were carried out in pentane using 1 mol% of the indicated catalyst; [b] literature
data in brackets, see ref. 8; [c] in CH2Cl2 as the solvent, the ee was only 76%; [d] an ee of 93% was reached when the
reaction was carried out in CH2Cl2 at 78°C (1 d) and 45°C (1 d), but the conversion remained incomplete ( 80%)
Focusing on 5a as the most promising candidate, we were able to significantly improve the
enantioselectivity of product 4b by lowering the temperature in pentane as the preferred solvent,
whereas the homobimetallic complex 1a responded much less to this change. Reactions with a set of
representative substrates confirmed the trend (Chart 1) in that the use of 5a as precatalyst invariably
led to cyclopropanes with notably higher optical purity than its dirhodium congener 1a, even though
most reactions using 5a had to be carried out at 10°C for solubility reasons, whereas 1a worked at
40°C. It is of note, however, that the substituent on the phenyl ring of the transient push-pull
7
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carbene complexes exerts a strong effect on the level of induction in either catalyst series (compare
4a, 4i and 4j). The superiority of catalyst 5a also extends to the asymmetric cyclopropenation of
phenylacetylene with formation of compound 4k. The absolute stereochemistry of products 4a and
4k was determined by comparison with literature data;21 all other compounds were assigned by
analogy.
Chart 1. Comparison of heterobimetallic and homobimetallic paddlewheel complexes (5a) and (1a) in
[a]
[b]
cyclopropanation/cyclopropenation reactions (1 mol% catalyst loading, pentane):
at 40°C;
10°C
The strikingly different level of asymmetric induction reached with complexes 5a-c as well as their
very different solubility deserve further comment. While the best performing precatalyst 5a slowly
dissolves in common organic solvents such as CH2Cl2 or toluene, the solubility of 5b and 5c is poor.
We had already noticed during their synthesis (Scheme 3) that 5b and 5c start to precipitate even
8
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from boiling toluene. Crude 5b could eventually be recrystallized from hot CH2Cl2, but 5c required
refluxing chlorobenzene for this purpose, indicating an exceptional thermal stability. X-ray diffraction
data revealed the reasons for this surprisingly different behavior: the monomeric units of complex 5a
lack short intermolecular contacts, whereas complexes 5b,c both self-assemble into supramolecular
aggregates of considerable beauty. As shown in Figure 2 for 5c (and Figure S-3b for 5b), six such
entities form a capsule via extensive -stacking interactions between the extended N-substituents. In
case of 5c, peripheral halogen bonding interactions1,22,23 between the perchlorinated phthalimide
groups seem to further stabilize the resulting supercluster, which is difficult to disassemble by
solvation.
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Figure 2. Structure of complex 5cEt2O in the solid state. Top: monomeric [BiRh(TCPPTL]4] unit
adopting an “inverted” ,,,-calyx; bottom: projection along the 3-fold axis in the crystal showing
the assembly of six such units to form a supramolecular capsule; for more details, see the SI.
The arguably most striking structural feature of the structures of 5b,c in the solid state, however, is
the fact that the calyx is “inverted” relative to that of 5a: the six bismuth atoms of the hexamer are
all directed inside the capsule, whereas the catalytically active rhodium atoms reside outwards
within the essentially achiral microenvironment created by the tert-butyl substituents. This “,,,-
conformer” is most likely enforced by the increased bulk of the extended phthalimide residues (NTTL,
TCPTTL) in either complex, which are sterically more demanding than the tert-butyl groups and
hence occupy the wider space about the larger Bi cation.The supramolecular assemblies in the solid
1
state notwithstanding, H NMR DOSY data showed that all three heterobimetallic complexes have
basically the same hydrodynamic radius of 7.4 Å in CD2Cl2 as the solvent (see the Supporting
Information). The solubility of 5b,c may be poor, but the small amount that eventually gets dissolved
exists as a monomeric paddlewheel complex in solution. If the “inverted” calyx persists, the chiral
induction is expected to be marginal: this is indeed the case for 5c (Table 1, entry 4), in which the
differential between the size of the tetrachlorophthalimide (TCPTTL) and the tert-butyl substituents
favor the poorly-inducing ,,,-conformer; additional peripheral halogen bonding interactions
further add to its stability. The situation is perhaps less clear-cut for 5b; it is tempting to speculate
that the intermediate ee reached with this catalyst (Table 1, entry 3) reflects a “calyx flip-flop”, in
which the ,,,-conformer observed in the solid state might equilibrate with the more
enantioselective ,,,-conformer. Because of the very poor solubility at low temperature,
however, this aspect could not yet be firmly established by spectroscopic means.
The exploratory study summarized above pursued an unorthodox approach to asymmetric rhodium
carbene chemistry. The new concept capitalizes on the use of heterobimetallic precatalysts that
allow a conceivable racemic background reaction to be avoided. An additional virtue is the conical
shape of the BiRh core which renders the chiral binding site crafted by the chosen amino acid-derived
10
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paddlewheel ligands narrower; these two factors are thought to synergize, as suggested by the much
improved level of asymmetric induction reached with complex 5a in a set of cyclopropanation
reactions. In conceptual terms, however, it is important to recognize that any successful ligand
design mandates that the anisotropy of the conical heterobimetallic core be matched by proper
directionality of the ligand sphere; the comparison of the closely related complexes 5a-c shows that
linear extrapolations of successful concepts from the dirhodium tetracarboxylate estate do not
necessarily meet this stringent condition but may actually be counterproductive. More systematic
investigations are necessary to better understand how to conciliate the auspicious molecular shape
with the necessary (physico)chemical qualities of chiral catalysts of this new type. Work along this
and related lines of research24 is currently in progress.
Acknowledgements
Generous financial support by the MPG is gratefully acknowledged. We thank the analytical
departments of our Institute for excellent support.
For the Table of Contents
Stretched and Bent: Formal replacement of one Rh atom in a classical dirhodium tetracarboxylate
paddlewheel complex by Bi results in a concial shape of the precatalyst: while the wide-open Bi site
does not cause a racemic background reaction, the calyx-like chiral binding pocket about Rh is
11
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narrower and hence more effective. These two virtues likely synergize in asymmetric
cyclopropanation reactions.
Keywords: Bimetallic Catalysts  Bismuth  Carbene Complexes  Cyclopropanation  Rhodium
1
C. Werlé, R. Goddard, P. Philipps, C. Farès, A. Fürstner, Angew. Chem. Int. Ed. 2016, 55, 10760-
10765.
2
For the first structures of non-chiral electrophilic dirhodium carbene complexes in the solid
state, see: a) C. Werlé, R. Goddard, A. Fürstner, Angew. Chem. Int. Ed. 2015, 54, 15452-15456;
Angew. Chem. 2015, 127, 15672-15676; b) C. Werlé, R. Goddard, P. Philipps, C. Farès, A.
Fürstner, J. Am. Chem. Soc. 2016, 138, 3797-3805; see also: c) D. J. Tindall, C. Werlé, R.
Goddard, P. Philipps, C. Farès, A. Fürstner, J. Am. Chem. Soc. 2018, 140, 1884-1893.
3
a) S. Hashimoto, N. Watanabe, S. Ikegami, Tetrahedron Lett. 1990, 31, 5173-5174; b) N.
Watanabe, T. Ogawa, Y. Ohtake, S. Ikegami, S. Hashimoto, Synlett 1996, 85-86; c) S. Kitagaki,
M. Anada, O. Kataoka, K. Matsuno, C. Umeda, N. Watanabe, S. Hashimoto, J. Am. Chem. Soc.
1999, 121, 1417-1418; d) H. Tsutsui, T. Abe, S. Nakamura, M. Anada, S. Hashimoto, Chem.
Pharm. Bull. 2005, 53, 1366-1368.
4
F. G. Adly, Catalyts 2017, 7, 347.
5
a) M. P. Doyle, D. C. Forbes, Chem. Rev. 1998, 98, 911-935; b) H. M. L. Davies, R. E. J. Beckwith,
Chem. Rev. 2003, 103, 2861-2904; c) A. Ford, H. Miel, A. Ring, C. N. Slattery, A. R. Maguire, M.
A. McKervey, Chem. Rev. 2015, 115, 9981-10080; d) H. Lebel, J.-F. Marcoux, C. Molinaro, A. B.
Charette, Chem. Rev. 2003, 103, 977-1050; e) A. DeAngelis, R. Panish, J. M. Fox, Acc. Chem.
Res. 2016, 49, 115-127; f) Z. Zhang, J. Wang, Tetrahedron 2008, 64, 6577-6605; g) S.-F. Zhu, Q.-
L. Zhou, Acc. Chem. Res. 2012, 45, 1365-1377; h) H. M. L. Davies, J. R. Manning, Nature 2008,
451, 417-424.
6
Various geometries had previously been considered; for a discussion, see ref. 1. Based on the
structure of [Rh2(PTTL)4]EtOAc, it was first proposed by Fox and coworkers that an “all up”
conformation might be relevant for asymmetric cyclopropanations, see: a) A. DeAngelis, O.
Dmitrenko, G. P. A. Yap, J. M. Fox, J. Am. Chem. Soc. 2009, 131, 7230-7231; b) A. DeAngelis, D.
12
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T. Boruta, J.-B. Lubin, J. N. Plampin, G. P. A. Yap, J. M. Fox, Chem. Commun. 2010, 46, 4541-
4543.
7
The relevance of the chiral crown conformation originally proposed by Fox et al. was
subsequently considered (but also partly challenged) by other authors, see: c) V. N. G. Lindsay,
W. Lin, A. B. Charette, J. Am. Chem. Soc. 2009, 131, 16383-16385; d) A. Ghanem, M. G.
Gardiner, R. M. Williamson, P. Müller, Chem. Eur. J. 2010, 16, 3291-3295; e) J. T. Mattiza, J. G.
G. Fohrer, H. Duddeck, M. G. Gardiner, A. Ghanem, Org. Biomol. Chem. 2011, 9, 6542-6550; f)
T. Goto, K. Takeda, N. Shimada, H. Nambu, M. Anada, M. Shiro, K. Ando, S. Hashimoto, Angew.
Chem. Int. Ed. 2011, 50, 6803-6808; Angew. Chem. 2011, 123, 6935-6940; g) Y.-S. Xue, Y.-P. Cai,
Z.-X. Chen, RSC Advances 2015, 5, 57781-57791.
8
9
F. G. Adly, M. G. Gardiner, A. Ghanem, Chem. Eur. J. 2016, 22, 3447-3461.
The conformers with C2 or D2 symmetry comprise two equivalent Rh atoms, whereas the
conformers with C4 or C1 symmetry expose two different Rh centers to a reaction partner.
In the solid state, the ,,,-conformer adopted by 3 is not strictly C4 symmetric because the
aperture of the chiral binding site has a longer and a shorter dimension; in CD2Cl2 solution at
50°C, however, a single set of resonances was recorded, suggesting that this slight distortion
averages out on the NMR time scale.
10
11
12
R. P. Reddy, G. H. Lee, H. M. L. Davies, Org. Lett. 2006, 8, 3437-3440.
BiRh paddlewheel complexes were originally described in: a) E. V. Dikarev, T. G. Gray, B. Li,
Angew. Chem., Int. Ed. 2005, 44, 1721-1724; b) E. V. Dikarev, B. Li, H. Zhang, J. Am. Chem. Soc.
2006, 128, 2814-2815; c) A. S. Filatov, M. Napier, V. D. Vreshch, N. J. Sumner, E. V. Dikarev, M.
A. Petrukhina, Inorg. Chem. 2012, 51, 566-571; see also: d) T. L. Sunderland, J. F. Berry, Dalton
Trans. 2016, 45, 50-55; e) T. L. Sunderland, J. F. Berry, J. Coord. Chem. 2016, 69, 1949-1956.
For a first application in synthesis, see: J. Hansen, B. Li, E. Dikarev, J. Autschbach, H. M. L.
Davies, J. Org. Chem. 2009, 74, 6564-6571.
13
14
L. R. Collins, M. van Gastel, F. Neese, A. Fürstner, J. Am. Chem. Soc. 2018, 140, 13042-13055.
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15
Some -acidity, however, is manifest in the structure of [BiRh(TFA)4] co-crystallized with
pyrene, in which the Bi atom engages in 6-coordination with this ligand, cf: E. V. Dikarev, B. Li,
A. Y. Rogachev, H. Zhang, M. A. Petrukhina, Organometallics 2008, 27, 3728-3735.
a) Z. Ren, T. L. Sunderland, C. Tortoreto, T. Yang, J. F. Berry, D. G. Musaev, H. M. L. Davies, ACS
Catal. 2018, 8, 10676-10682; b) another chiral Bi-Rh complex is described in ref. 12b, but no
applications were reported.
16
17
Water eventually coordinates to the Rh center as shown, for example, by the structure of
[BiRh(esp)2]H2O in the solid state, which is contained in the Supporting Information of ref. 14
It is also comparable to the structure of 1aEtOAc, see ref. 6
18
19
For pertinent examples see the following and literature cited therein: G. Seidel, A. Fürstner,
Angew. Chem. Int. Ed. 2014, 53, 4807-4811; Angew. Chem. 2014, 126, 4907-4911.
For [RhRh(TCPTTL)4] and related complexes, see: a) M. Yamawaki, H. Tsutsui, S. Kitagaki, M.
Anada, S. Hashimoto, Tetrahedron Lett. 2001, 43, 9561-9564; b) T. Goto, K. Takeda, M. Anada,
K. Ando, S. Hashimoto, Tetrahedron Lett. 2011, 52, 4200-4203; c) H. Tsutsui, Y. Yamaguchi, S.
Kitagaki, S. Nakamura, M. Anada, S. Hashimoto, Tetrahedron: Asymmetry 2003, 14, 817-821.
a) K. M. Chepiga, C. Qin, J. S. Alford, S. Chennamadhavuni, T. M. Gregg, J. P. Olson, H. M. L.
Davies Tetrahedron 2013, 69, 5765-5771; b) H. M. L. Davies, G. H. Lee, Org. Lett. 2004, 6, 1233-
1236.
20
21
22
23
V. N. G. Lindsay, A. B. Charette, ACS Catal. 2012, 2, 1221-1225.
G. Cavallo, P. Metrangolo, R. Milani, T. Pilati, A. Priimagi, G. Resnati, G. Terraneo, Chem. Rev.
2016, 116, 2478-2601.
24
For other recent contributions to carbene chemistry, see: a) A. Fürstner, J. Am. Chem. Soc.
2019, 141, 11-24; b) A. Guthertz, M. Leutzsch, L. M. Wolf, P. Gupta, S. M. Rummelt, R.
Goddard, C. Farès, W. Thiel, A. Fürstner, J. Am. Chem. Soc. 2018, 140, 3156-3168; c) A. G.
Tskhovrebov, R. Goddard, A. Fürstner, Angew. Chem. Int. Ed. 2018, 57, 8089-8094.
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