RhIAr/AuIAr′ Transmetalation: A Case of Group Exchange Pivoting on the Formation of M?M′ Bonds through Oxidative Insertion

Article abstract of DOI:10.1002/anie.201813419

By combining kinetic experiments, theoretical calculations, and microkinetic modeling, we show that Pf/Rf (C₆F₅/C₆Cl₂F₃) exchange between [AuPf(AsPh₃)] and trans-[RhRf(CO)(AsPh₃)₂] does not occur by typical concerted Pf/Rf transmetalation via electron-deficient double bridges. Instead, it involves asymmetric oxidative insertion of the Rh^I complex into the (Ph₃As)Au?Pf bond to produce a [(Ph₃As)Au?RhPfRf(CO)(AsPh₃)₂] intermediate, followed by isomerization and reductive elimination of [AuRf(AsPh₃)]. Interesting differences were found between the LAu?Ar asymmetric oxidative insertion and the classical oxidative addition process of H₂ to Vaska complexes.

Full text of DOI:10.1002/anie.201813419

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: RhIAr/AuIAr' Transmetalation, a Case of Group Exchange
Pivoting on Formation of M–M' Bonds via Oxidative Insertion
Authors: Pablo Espinet, Marconi N. Peñas-Defrutos, Camino
Bartolomé, and Maximiliano García-Melchor
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201813419
Angew. Chem. 10.1002/ange.201813419
Link to VoR: http://dx.doi.org/10.1002/anie.201813419
http://dx.doi.org/10.1002/ange.201813419

10.1002/anie.201813419
Angewandte Chemie International Edition
COMMUNICATION
RhIAr/AuIAr' Transmetalation, a Case of Group Exchange Pivoting
on Formation of M–M' Bonds via Oxidative Insertion
M. N. Peñas-Defrutos,[a] C. Bartolomé,[a] M. García-Melchor,[b] and P. Espinet*[a]
Abstract: By combining kinetic experiments, theoretical calculations
and microkinetic modelling, we show that the Pf/Rf (C6F5/C6Cl2F3)
exchange between [AuPf(AsPh3)] and trans-[RhRf(CO)(AsPh3)2]
does not occur through the typical concerted Pf/Rf transmetalation
via electron deficient double bridges. Instead, it involves asymmetric
oxidative insertion of the RhI complex into the (Ph3As)Au–Pf bond
producing a [(Ph3As)Au–RhPfRf(CO)(AsPh3)2] intermediate, followed
by isomerization and reductive elimination of [AuRf(AsPh3)].
Interesting differences are found between the LAu–Ar asymmetric
oxidative insertion and the classical oxidative addition process of H2
to Vaska's complexes.
mechanism.5 We also discovered a dramatic mechanistic switch
in the Ar/X exchange between SnIVPh(nBu)3 and [AuIXL]
complexes: the typical concerted mechanism involving Ar/X
mixed bridges operates when X = Cl, whereas an oxidative
addition/reductive elimination (OA/RE) pathway via a formally
AuII–SnIII intermediate takes over when X = vinyl.6 A similar
OA/RE mechanism involving AuI–PdII intermediates had been
earlier proposed (based on kinetic studies) for the [AuArL]
catalyzed trans to cis-[PdAr2L2] isomerization, the first
homogeneous Au catalysis ever reported.7
In the present work, we investigate the reversible Pf/Rf aryl
exchange between linear [AuPf(AsPh3)] (1) and square-planar
trans-[RhRf(CO)(AsPh3)2] (2) to yield [AuRf(AsPh3)] (3) and
trans-[RhPf(CO)(AsPh3)2] (4) (eqn. 2; X-ray structures of 1, 2,
and 4 are given in SI). Kinetic and density functional theory
(DFT) calculations uncover an unexpected mechanism operating
in this apparently simple system.
1
Bimetallic catalysis
generally concerns homogeneous
processes in which two transition metals (TM), or one TM and
2
one group-11 element (M),
cooperate in
a
synthetic
transformation (often C−C coupling) where their two catalytic
cycles are linked by a transmetalation step. [M]–R1 can be an
intermediate previously formed from a main group [MG]–R1
organometallics in a first cycle, which subsequently acts as a
nucleophile towards TM in a second cycle (e.g. in gold assisted
Stille reactions). In that case three metals (e.g. Sn, Au, Pd) are
involved.3 An archetypical transmetalation mechanism is the
R1/X (X = halide) exchange between [M]–R1 nucleophiles and
[TMR2]–X electrophiles via a cyclic transition state structure with
the two metals connected through mixed R1/X bridges (eqn. 1).
The catalytic processes can suffer complications due to the
reversibility of these transmetalations and the existence of
undesired secondary transmetalations.4
Ph3As
CO
Ph3As
Pf
CO
Rh
Rh
Rf
AsPh3
AsPh3
Keq ≈ 1
2
4
(2)
Pf Au AsPh3
Rf Au AsPh3
+
+
1
3
The highly preferred trans disposition of the carbonyl ligand
relative to Ar in the RhI metal center guarantees that formation of
other isomers will not complicate the study. The exchange
reaction (1:1 molar ratio) in dry THF as solvent reached the
equilibrium in ca. 24 hours at 294 K, leading to similar
concentrations of the four species (Keq ≈ 1). This means that the
bond energy difference [(M−CPf) – (M−CRf)] for M = Rh is very
similar to the difference for M = Au, hence resulting in a very
small ΔG0 for the overall equilibrium. The reaction was 19F NMR
monitored, in the region where the Fortho signals of Pf and the
Fpara of the Rf appear (Figure 1). Neither by-products nor
reaction intermediates were detected.
R1
[TMR2]
[M]
X
[TMR2] X + [M] R1
1 + [M]
X
[TMR2]
R
(1)
Transmetalation reactions not only are important in cross-
coupling processes. In fact, they can operate whenever [M]–X or
[M]–R compounds of different (or identical) metals coexist in
solution. Surprisingly, despite their ubiquitous presence and
important consequences therefrom, these exchanges are often
overlooked. For this reason, their mechanisms are poorly
understood. Concerning Rh, we recently reported that the Pf/Rf
2Fortho
RhPf
1Fpara
AuRf
600
transmetalation between [RhIIICp*Pf2] (Pf
=
C6F5) and
[RhIIICp*Rf2] (Rf = C6F3Cl2-3,5) takes place only when triggered
by the catalytic presence of [RhIIICp*Ar(OH)] (Ar = Pf, Rf), which
allows for the formation of mixed Ar/OH bridges in the exchange
400
200
1Fpara
2Fortho
AuPf
RhRf
0
[a]
Mr. Marconi N. Peñas-Defrutos, Dr. Camino Bartolomé, and Prof.
Dr. Pablo Espinet.
IU CINQUIMA/Química Inorgánica, Facultad de Ciencias,
Universidad de Valladolid, 47071-Valladolid (Spain).
E-mails: caminob@qi.uva.es and espinet@qi.uva.es
Dr. Max García-Melchor
–114
–118
f1 (ppm)
–122
Figure 1. Reaction between [AuPf(AsPh3)] (1) and trans-[RhRf(CO)(AsPh3)2]
(2) in THF at 294 K, monitored by 19F NMR until 40% conversion.
[b]
School of Chemistry, Trinity College Dublin, College Green, Dublin
2, Ireland. E-mail: garciamm@tcd.ie
When measuring reaction kinetics, one should be aware that
equilibria are chemical reactions where the starting reagents are
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201813419
Angewandte Chemie International Edition
COMMUNICATION
regenerated by the reverse reaction at increasing rate as the
system approaches the equilibrium. Fortunately, working at 284
K the aryl exchange studied here has an appropriate rate for
very precise monitoring, and the initial rate method can be
applied within margins of negligible influence of the reverse
reaction (consumption of reactants 1 and 2 lower than 10%), to
obtain an experimental value of the initial rate (r0).8 The integrals
of well-separated signals, i.e. the decreasing Fortho signal of
reactant 2 (doublet for Fortho−Rh coupling) and the rising sharp
Fpara signal of product 3, were monitored. Additional experiments
using different Au:Rh ratios confirmed a kinetic reaction order 1
on the concentration of both metal complexes, as expected
(details in SI). Least squares adjustment using these data
(Figure 2a) yielded a reaction rate r0 = 1.08×10−7 mol L−1 s−1. In a
simple process this would correspond to an activation Gibbs
calculations (black lines);13 2) plausible structures, with COPASI-
adjusted energies (grey and hashed lines). The COPASI
adjustment leads to an AsPh3 kinetic dependence [AsPh3]–0.64
,
very close to the experimental value. Since the energy profile is
very symmetric, only the first half is discussed.
AuL
Rh
AuL
Rh
AuL
Rh
Pf
CO
L
Rf
CO
L
AuL
Rh
CO
Pf
Rf
CO
L
Rf
Pf
L
Rf
L
Pf
L
TS3
L
L
TS1
TS2
TS2*
22.3
TS1*
20.3
19.3
19.3
18.8
k3
k2
k-1
k-2
I3*
I3
I2
I2*
14.4
AuL
Rh
13.8
AuL
13.1
AuL
13.4
AuL
Rh
L
k1
energy of ΔG‡
= 20.6 kcal mol−1 for a single rate determining
initial
Rf
CO
Pf
CO
L
Pf
CO
L
Rf
CO
step. However this is not a correct interpretation for the more
complex mechanism operating here, as discussed below. The
kinetic effect of added free arsine ligand on the initial reaction
rate was then quantified by measuring the decelerating effect
upon addition of different percentages of AsPh3 (from 5% to
250%), yielding a ligand dependence [AsPh3]–0.53 (Figure 2b).9,10
Rh
Rh
L
Pf
L
Rf
Rf
Pf
L
+ L
+ L
3 + 4
1 + 2
0.0
RfAuL
L
PfAuL
I1*
1.5
I1
CO
L
L
CO
Rh
-1.5
Rh
-2.2
Pf
Rf
L
Figure 3. Gibbs energy profile for the transmetalation reaction between 1 and
2, in THF at 284 K and 1 atm.
ln[AsPh3
]
-8
-6
-4
-2
–2
–6
–4
–8
1.5
–14
E-03
-14
No extra
AsPh3
a
b
5%
Beginning in complexes 1 and 2, DFT simulations found a van
der Waals complex I1 (grey thin line), which is non-existing in
solution in the presence of solvating THF molecules. Otherwise,
being I1 hypothetically more stable than 1 and 2, it should be
observed experimentally. Artifacts of this kind may arise in
simulations in the absence of explicit solvent molecules and
hence, must be discarded (unless experimentally observed) to
calculate ΔG‡.
The process starts with the oxidative addition of the Au–Pf bond
to Rh, via the transition state TS1. This first step requires an
energy barrier of 20.3 kcal mol–1 and gives rise to the octahedral
complex I2, where the Au atom is in the axial position and the Pf
moiety is in the equatorial plane, in cis position to the Rf group.
From I2, calculations indicate that the dissociation of the arsine
ligand in the axial position to afford the 5-coordinate
intermediate I3 is almost thermoneutral. The corresponding
transition state (TS2) is barrierless in gas phase (see Figure
S13) and was not found, which is frequent for L dissociations by
progressive bond elongation (Figure S13). Estimations of
1.2
E-03
–15
-15
25%
0.9
E-04
–16
-16
75%
0.6
E-04
250%
5 mol% free
AsPh3
–17
-17
0.3
E-04
Kinetic order = – 0.53.
–18
-18
0.0
E+00
0
5
10 15
25
20
0 5.00100.00105.0020.00205.000
Reaction time (s·103)
Figure 2. (a) Kinetic plot for the reaction between 1 and 2 in THF at 284K, with
(black circles) and without (grey squares) excess of free arsine (+ 5% AsPh3).
(b) Change in r0 upon addition of different amounts of free AsPh3 at 298 K.
The high computed DFT Gibbs energies (wb97xd level in THF,
at the experimental temperature of 284 K and 1 atm) for AsPh3
dissociation from the starting square-planar RhI complex 2 (27.1
kcal mol−1) or from the AuI complex 1 (31.5 kcal mol−1) allow us
to discard these potentially initial routes as the origin of [AsPh3]
dependence. Moreover, the addition of only 5% AsPh3 ligand
already results in a large decrease of the reaction rate by a
factor of 0.52 (Figure 2a), suggesting that added AsPh3 is
operating on some lower concentration intermediate and not on
1 or 2. The data point towards a mechanism far from the rate-
determining step oversimplification, 11 and support that the
kinetics observed must depend on more than one transition
state.
For a closer examination of the problem, multivariant kinetic
analysis using COPASI,12 and DFT calculations were used (see
SI for details). With new data in hand, a reversible reaction path
that fits very well all the experimental observations could be
proposed (Figure 3). The profile combines: 1) computed
transition states and intermediates by means of DFT
coordination transition states in the literature suggest
a
reasonable value about 4.5 kcal mol−1 higher than I3, due to
diffusion cost in solution.14 The value proposed in the profile,
calculated by kinetic COPASI adjustment, is 19.3 kcal mol−1, that
is 5.5 kcal mol−1 higher than I3 (see details in SI). This is an
excellent fitting with the literature expectations. Finally, the
process requires isomerization from the 5-coordinate species I3
to I3* before the rest of the process progresses symmetrically.
The isomerization of 5-coordinate species has been extensively
theoretically studied showing that many reaction pathways are
possible with activation energies within 10 kcal mol-1.15 Using
COPASI, we estimated the energy of the transition state for
(TS3) to be 8.5 kcal mol–1 higher than I3 (ΔG‡ = 22.3 kcal mol−1).
This article is protected by copyright. All rights reserved.

10.1002/anie.201813419
Angewandte Chemie International Edition
COMMUNICATION
It is worth noting that the AsPh3 dissociation barrier for the
octahedral complex I2 is considerably lower than calculated for
the square-planar precursor. This can be rationalized
considering that the trans-influence of the different ligands is
LAu– > Pf– > AsPh3, which is supported by the order of Rh–As
bond distances in complexes 2 and I2: (Rh–Astrans to Au = 2.688 Å
in I2) > (Rh–Astrans to Pf = 2.520 Å in I2) > (Rh–Astrans to As = 2.421
Å in 2). Thus, the M–M bond strongly facilitates the dissociation
of the ligand in trans.
fragments (1 and 2, respectively) from their structure as isolated
species to their “strained” geometries in TS1. On the other hand,
Eint is known as the interaction energy and represents the energy
gain arising from the interaction between the Au and Rh
fragments in TS1. This analysis revealed that Edist for the Au
fragment is substantially larger than that for Rh (32.8 vs 23.8
kcal mol-1), while the most important energy term is Eint (71.3
kcal mol-1). Hence, we next decided to examine in detail the
interactions involved in TS1 via Natural Bond Orbital (NBO) and
second order perturbation theory (SOPT) analyses. NBO
indicates that the Rh–Au bond in TS1 involves the electron
donation of a filled 4d orbital from RhI into an empty 6s orbital of
The large effect on the reaction rate of a small amount of added
AsPh3 is now easily understood observing that the arsine
operates on the dissociative step from I2 to I3 via TS2: the 5% of
arsine relative to the initial concentration of complexes 1 and 2 is, Au, and the back-donation of a filled 5d orbital from Au into an
in fact, an enormous excess relative to the concentrations of I2
or I3 in equilibrium.16 Indeed, the correct interpretation of the
AsPh3/2 ≈ 0.05 concentration ratio (corresponding in fact to
AsPh3/I2 ≈ 1011 at the correct reaction point) indicates that
added AsPh3 is very inefficient at preventing its dissociation from
I2. In other words, AsPh3 trans to Au(AsPh3) behaves as a very
weak ligand (which is consistent with the close energies of I2
and I3), and also as fairly labile (ΔG‡ = 5.5 kcal mol−1 from I2).
The combined DFT plus experimental energy profile in Figure 3
illustrates how the RhIRf/AuIPf exchange occurs through
different coordination geometries (square-planar, octahedral and
square pyramidal), different oxidation states for the Rh and Au
centers, and an isomerization process via 5-coordinate
intermediates. Geometrical details of the evolution from the
initial square-planar RhI complex 2 (including I1 for comparison)
anti-bonding orbital mainly constituted by a hybrid sd orbital from
Rh (Figures 5a,b). The sum of the two (mostly the first one, see
donor-acceptor interaction energies by SOPT in Figures 5a,b
and Table S4) contributes to make the Rh–Au bond. NBO
analysis also suggests that the Au center does not participate in
the formation of the Rh–Pf bond. This interaction is initiated
instead by electron donation from a hybrid sp orbital of the Pf
group to an empty hybrid sd orbital from Rh (Figure 5c). In short,
our analysis supports that the formation of the Rh–Au bond
using electron density from Rh prepares the formation of the Pf–
Rh bond by polarizing the electron density of the Au–Pf bond
towards the Pf ipso carbon atom. In other words, the oxidative
addition is the result of an asymmetric oxidative insertion of the
electron donor Rh: into the Pf–AuL bond.
are summarized in Figure 4. It clearly shows
a parallel
approximation of the Pf–AuL bond over the L–Rh–L axis, which
induces progressive closure of the L–Rh–L angle and
concomitant elongation of the Pf–AuL bond in TS1. This
eventually results in the cis-addition of the Pf and AuL groups to
complex 2, giving rise to the octahedral complex I2. At this point
the high trans-influence of the AuL group facilitates dissociation
of the AsPh3 ligand in trans, giving the 5-coordinate I3 from
which isomerization occurs. The formation of the two other
possible octahedral isomers arising from approximation of the
Pf–AuL bond along the Rf–Rh–CO direction (two possible
orientations) was also considered but were discarded based on
their high computed activation energies (more than 10 kcal mol-1
higher than TS1, see SI for details).
I1
TS1
I2
I3
Pf
AuL
CO
LAu
LAu
Pf
AuL
CO
CO
L
CO
L
L
Rh
L
Rh
Pf
Rf
Rh
Pf
Rf
Rh
L
Rf
L
Rf
L
Au-Rh = 3.579 Å
Au-Pf = 2.057 Å
Rh-Pf = 3.649 Å
Rh-Rf = 2.115 Å
Au-Rh = 2.671 Å
Au-Pf = 2.436 Å
Rh-Pf = 2.269 Å
Rh-Rf = 2.155 Å
Au-Rh = 2.602 Å
Au-Pf = 3.278 Å
Rh-Pf = 2.103 Å
Rh-Rf = 2.145 Å
Au-Rh = 2.599 Å
Au-Pf = 3.602 Å
Rh-Pf = 2.070 Å
Rh-Rf = 2.107 Å
Figure 4. Evolution of bond distances along the reaction pathway. Sum of
covalent radii: Au-Rh = 2.78 Å; Au-C = 2.09 Å; Rh-C = 2.15 Å.
Figure 5. Isosurfaces (isovalue = 0.05 e– bohr3) of selected NBOs in TS1.
Above: a)+b) electron-donation between Rh and Au to form the Rh–Au bond; it
can alternatively be defined as Rh-to-Au donation (a) + Au-to-Rh back-
donation (b). Below: c) electron donation from the Pf– group forming the C–Rh
bond, while breaking the C–Au bond. Donor-acceptor interactions in each
NBO, ENBO (in kcal mol-1), obtained from second order perturbation theory
(SOPT) are also presented. H atoms are omitted and AsPh3 is drawn as AsC3
for better observation.
To gain a deeper insight into the energy contributions in TS1, we
performed an activation-strain analysis,17 where the total energy
is decomposed as E = Edist + Eint. The first term, Edist, is the so-
called distortion energy and accounts for the energy cost
associated with the geometric distortion of the Au and Rh
This article is protected by copyright. All rights reserved.

10.1002/anie.201813419
Angewandte Chemie International Edition
COMMUNICATION
The geometrical evolution discussed above, in which two ligands
in trans (CO and Rf) remain as mere spectators, is reminiscent
of the classical oxidative addition of H2 to the Vaska's type
complex trans-[MCl(CO)(PPh3)2] (M = Rh, Ir).18 In the latter,
however, the L–M–L axis remains passive while the more
electron poor Cl–M–CO axis undergoes angle bending;19 the
process involves electron donation of the electron pair of the H–
H bond to Rh,20 eventually leading to a different isomer when
back-donation from Rh cleaves the H–H bond.21
DJEI/DES/SFI/HEA Irish Centre for High-End Computing
(ICHEC) is also acknowledged for the provision of computational
facilities and support. M. N. P.-D. gratefully acknowledges the
Spanish MECD for a FPU scholarship.
Keywords: bimetallic catalysis • oxidative addition • gold •
rhodium • transmetalation mechanism
Some concepts used in the text deserve some comment. We
are using the uncommon expression asymmetric oxidative
insertion of Rh into the Au–C bond to define the intimate
oxidation/reduction mechanism of the process, at variance with
the symmetric oxidative addition occurring with H2 on Vaska’s
complexes. The rules to assign formal oxidation numbers
impose that the M–M' bonds should not count because the
electron pair in that bond is supposed to be equally shared
between the two metals (non-polarized bond); with this rule,
complexes I2 would be assigned RhII and Au0 oxidation states,
corresponding to an overall one electron oxidation of RhI by AuI.
In the latter section we have considered the anionic moiety
[(Ph3As)Au:]– because classifying ligands in a trans-influence list
requires to consider them as 2e– donors; within this approach,
the complexes would be assigned RhIII and Au–I. Finally, in
apparent contradiction, in TS1 the Pf–AuL bond is eventually
asymmetrically cleaved providing the Rh center with the
fragments LAu+ and Pf–. This illustrates how assigning oxidation
states may be misleading about the real electron density on the
metal, and about bond polarizations. This is better examined by
looking at the NPA (natural population analysis) charges on Rh
in TS1 and I2 (–1.15 and –1.22 respectively), which show that
RhIII has more negative charge than in the RhI complex 2 (–0.70).
Overall, Rh gains electron density while it is formally being
oxidized. The gold atom shows only minor differences between
the linear molecule and the octahedral intermediate, with similar
slightly positive charges in the range +0.27 to +0.20.
[1]
[2]
a) M. H. Pérez-Temprano, J. A. Casares, P. Espinet, Chem. –Eur. J.
2012, 18, 1864–1884; b) D. R. Pye, N. P. Mankad, Chem. Sci. 2017, 8,
1705–1718.
a) Y. Shi, S. A. Blum, Organometallics, 2011, 30, 1776–1779; b) J.
delPozo, J. A. Casares, P. Espinet, Chem. – Eur. J. 2016, 22, 4274–
4284; c) R. J. Oeschger, P. Chen, J. Am. Chem. Soc. 2017, 139, 1069–
1072.
[3]
[4]
J. delPozo, D. Carrasco, M. H. Pérez-Temprano, M. García-Melchor, R.
Álvarez, J. A. Casares, P. Espinet, Angew. Chem. Int. Ed. 2013, 52,
2189–2193.
For more details and formation of homocoupling products R2–R2, see:
J. del Pozo, G. Salas, R. Álvarez, J. A. Casares, P. Espinet,
Organometallics, 2016, 35, 3604–3611; and references therein.
M. N. Peñas-Defrutos, C. Bartolomé, M. García-Melchor, P. Espinet,
Chem. Commun. 2018, 54, 984–987.
[5]
[6]
D. Carrasco, M. García-Melchor, J. A. Casares, P. Espinet, Chem.
Commun. 2016, 52, 4305–4308.
[7 ]
[8]
A. L. Casado, P. Espinet, Organometallics, 1998, 17, 3677–3683.
The reaction rate when the products formed reaches 10% is
proportional to (0.90)2 – (0.10)2 ≈ 0.8. At that point the rate has
decreased to 80% of r0. The rate constant error within this limit, when
translated to ∆G‡ values, is < 1 kcal mol–1
.
[9]
These experiments were carried out at 298 K due to the lower rate in
the presence of high concentrations of free arsine.
[10] For a related case of arsine dependence in Pd see: M. H. Pérez-
Temprano, J. A. Casares, A. R. de Lera, R. Álvarez, P. Espinet, Angew.
Chem. Int. Ed. 2012, 51, 4917–4920.
[11] S. Kozuch, S. Shaik, Acc. Chem. Res. 2011, 44, 101–110.
[12] S. Hoops, S. Sahle, R. Gauges, C. Lee, J. Pahle, N. Simus, M. Singhal,
L. Xu, P. Mendes, U. Kummer, Bioinformatics, 2006, 22, 3067–3074.
[13] To be more precise (see SI) COPASI produces changes in I2 and I3
(less than 1 kcal mol–1) when the reversibility condition is imposed.
[14] a) C. L. McMullin, J. Jover, J. N. Harvey, N. Fey, Dalton Trans. 2010,
39, 10833–10836; b) C. L. McMullin, N. Fey, J. N. Harvey, Dalton Trans.
2014, 43, 13545–13556.
In conclusion, the RhIAr/AuIAr' transmetalation studied here
does not follow the traditional Ar/Ar' double-bridged mechanism,
but involves an oxidation/reduction mechanism. Moreover this is
also an unusual one in that it is initiated by donation of an
electron pair from Rh to Au, which eventually triggers the
transfer of [Ar:]– to Rh. Interestingly, the different electronic
characteristics of the polar Ar–AuL and the non-polar H–H
bonds on Vaska's type complexes induce formation of different
octahedral isomers.
[15] R. Asatryan, E. Ruckenstein, J. Hachmann, Chem. Sci. 2017, 8, 5512–
5525.
[16] For a related case see: C. Bartolomé, Z. Ramiro, M. N. Peñas-Defrutos,
P. Espinet, ACS Catal. 2016, 6, 6537–6545.
[17] a) S. I. Gorelsky, D. Lapointe, K. Fagnou, J. Am. Chem. Soc. 2008, 130,
10848. b) M. García-Melchor, S. I. Gorelsky, T. K. Woo. Chem. – Eur. J.
2011, 17, 13847–13853; c) F. M. Bickelhaupt, K. N. Houk. Angew.
Chem. Int. Ed. 2017, 56, 10070–10086.
[18] L. Vaska, J. W. DiLuzio, J. Am. Chem. Soc., 1962, 84, 679–680.
[19] C. E. Johnson, R. Eisenberg, J. Am. Chem. Soc. 1985, 107, 3148–
3160.
Experimental Section
[20] A. Didieu, A. Strich, Inorg. Chem. 1979, 18, 2940–2943.
[21] J. J. Low, W. A. Goddard III, J. Am. Chem. Soc. 1984, 106, 6928–6937.
Experimental and computational details are given in the SI.
Acknowledgements
The authors thank the financial support from the Spanish
MINECO (projects CTQ2016-80913-P and CTQ2017-89217-P),
the Junta de Castilla
y León (project VA051P17). The
This article is protected by copyright. All rights reserved.

10.1002/anie.201813419
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
Text for Table of Contents
M. N. Peñas-Defrutos, C. Bartolomé,*
M. García-Melchor,* P. Espinet*
Rh
Au
Nucleophilic attack of Rh(I) to gold
triggers the asymmetric oxidative
insertion of Rh into the Au–Aryl bond,
which is the unexpected mechanism
behind the Aryl/Aryl' exchange
Au
As
Cl
C/Ph
F
O
Rh
Page No. – Page No.
RhIAr/AuIAr' Transmetalation, a Case
of Group Exchange Pivoting on
Formation of M–M' Bonds via
Oxidative Insertion
Oxidative Insertion TS
between the two metals.
Ar'
[Au]
Ph3As
CO
Ph3As
CO
Rh
+
Rh
+
Ar [Rh]
Ar
AsPh3
Ar'
AsPh3
Ar'
[Rh]
Ar' Au AsPh3
[Au]
Ar Au AsPh3
Ar
Double Aryl Bridges TS
Layout 2:
COMMUNICATION
Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
Text for Table of Contents
22
22
This article is protected by copyright. All rights reserved.