Exceedingly Facile Ph-X Activation (X=Cl, Br, I) with Ruthenium(II): Arresting Kinetics, Autocatalysis, and Mechanisms

Article abstract of DOI:10.1002/anie.201501996

[(Ph₃P)₃Ru(L)(H)₂] (where L=H₂ (1) in the presence of styrene, Ph₃P (3), and N₂ (4)) cleave the Ph-X bond (X=Cl, Br, I) at RT to give [(Ph₃P)₃RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph₃P)₃Ru(H)₂] as the reactive species generated upon spontaneous loss of L from 3 and 4. The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2, originating from the initial PhI activation with 3, is roughly as reactive toward PhI as 3 itself; and 2) the Ph-I bond cleavage with the just-produced 2 gives rise to [(Ph₃P)₂RuI₂], which quickly comproportionates with the still-present 3 to recover 2. Both the initial and onward activation reactions involve PPh₃ dissociation, PhI coordination to Ru through I, rearrangement to a η²-PhI intermediate, and Ph-I oxidative addition.

Full text of DOI:10.1002/anie.201501996

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International Edition: DOI: 10.1002/anie.201501996
German Edition: DOI: 10.1002/ange.201501996
Reaction Mechanisms
À
Exceedingly Facile Ph X Activation (X = Cl, Br, I) with
Ruthenium(II): Arresting Kinetics, Autocatalysis, and Mechanisms**
Fedor M. Miloserdov, David McKay, Bianca K. MuÇoz, Hamidreza Samouei,
Stuart A. Macgregor,* and Vladimir V. Grushin*
Abstract: [(Ph3P)3Ru(L)(H)2] (where L = H2 (1) in the
are particularly challenging substrates because of the strength
[2]
À
À
presence of styrene, Ph3P (3), and N2 (4)) cleave the Ph X
and low reactivity of the Ar Cl bond. High-cost bulky,
À
bond (X = Cl, Br, I) at RT to give [(Ph3P)3RuH(X)] (2) and
PhH. A combined experimental and DFT study points to
[(Ph3P)3Ru(H)2] as the reactive species generated upon
spontaneous loss of L from 3 and 4. The reaction of 3 with
excess PhI displays striking kinetics which initially appears
zeroth order in Ru. However mechanistic studies reveal that
this is due to autocatalysis comprising two factors: 1) complex
2, originating from the initial PhI activation with 3, is roughly
electron-rich phosphine ligands are usually required for Ar
Cl oxidative addition to Pd0, which is most widely used in
cross-coupling reactions.[2,3] Activation of chloroarenes as
well as aryl bromides and iodides with metals besides Pd and
Ni are rare.[2,4,5]
By far the lowest-cost platinum-group metal, ruthenium,
À
is highly attractive for Ar X activation. However, examples
of such reactions are rare, especially under mild conditions.
Carbonyl- and PPh3-ligated Ru complexes can cleave the less
À
as reactive toward PhI as 3 itself; and 2) the Ph I bond
À
cleavage with the just-produced 2 gives rise to [(Ph3P)2RuI2],
which quickly comproportionates with the still-present 3 to
recover 2. Both the initial and onward activation reactions
inert C X bonds of iodo- and bromobenzene and -toluene,
but only at 1258C.[6] With bulky electron-rich Cy3P co-ligands,
[7a,b]
À
Ru can activate the Ph I bond at ambient temperature,
but the Ar Cl bond requires 808C.[7c] In general, ruthenium-
À
involve PPh3 dissociation, PhI coordination to Ru through I,
2
À
rearrangement to a h -PhI intermediate, and Ph I oxidative
addition.
catalyzed arylation reactions with chloroarenes occur only at
120–1508C.[8] Herein we report unprecedentedly facile (room
temperature) activation of iodo-, bromo-, and even chlor-
obenzene with simple PPh3-based Ru complexes, with no
need to employ electron-rich bulky phosphine ligands. The
E
fficient activation of inert bonds is a major goal of
organometallic chemistry and catalysis with metal com-
plexes.[1] The C X (X = Cl, Br, I) bond of unactivated
Ph I bond cleavage reaction displays striking apparent zero-
À
À
haloarenes is especially targeted because of their key role in
organic synthesis. Most economically attractive aryl chlorides
order kinetics that we show to arise from a masked autoca-
talysis. We detail a combined experimental and computa-
À
tional mechanistic study of this unconventional Ph X bond
activation, which is expected to be significant for future
progress in the area.
[*] Dr. F. M. Miloserdov, Dr. B. K. MuÇoz, Dr. H. Samouei,
Prof. V. V. Grushin
Adding 1 equiv of styrene to
a
mixture of
Institute of Chemical Research of Catalonia (ICIQ)
Avgda. Països Catalans 16, 43007 Tarragona (Spain)
E-mail: vgrushin@iciq.es
[(Ph3P)3Ru(H2)(H)2] (1) and PhX (X = I, Br, Cl) in toluene
at room temperature resulted in instantaneous reaction that
produced [(Ph3P)3RuH(X)] (2) and benzene (GC-MS). The
Ru product precipitated out and was isolated in ca. 90%,
90%, and 70–80% yield for X = I (2-I), Br (2-Br), and Cl (2-
Cl), respectively (Scheme 1). The structures of 2-I·CH2Cl2, 2-
Br·2THF, and 2-Cl·C6H6 were confirmed by single-crystal X-
ray diffraction.[9]
Dr. D. McKay, Prof. S. A. Macgregor
Institute of Chemical Sciences, Heriot-Watt University
Edinburgh EH14 4AS (UK)
E-mail: s.a.macgregor@hw.ac.uk
[**] We thank Prof. Alan S. Goldman, Prof. Vladimir I. Bakhmutov, Prof.
Juan A. Casares, Prof. Michael K. Whittlesey, and Prof. Sylviane
Sabo-Etienne for helpful discussions, and Dr. Jordi Benet-Buchholz,
Dr. Eduardo C. Escudero-Adµn, Dr. Marta Martínez Belmonte, and
Dr. Eddy Martin for X-ray studies. The ICIQ Foundation and The
Spanish Government (Grant CTQ2011-25418 and the Severo Ochoa
Excellence Accreditation 2014-2018 SEV-2013-0319) are thankfully
acknowledged for support of this work. F.M.M. is grateful to the
Government of Spain (MICINN) for the FPI Ph.D. Scholarship (BES-
2012-054922). S.A.M. and D.M. thank the EPSRC for support
through award EP/J010677/1.
À
Such facile Ph X (X = Cl, Br) bond cleavage with
a simple PPh3-stabilized RuII species is unprecedented. Free
radicals are unlikely to be involved in this transformation, as
no bibenzyl was seen in reactions performed in toluene and
deuterium incorporation into the benzene product was
insignificant (< 4%, GC-MS) with [D8]THF used as solvent.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201501996.
ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited.
Scheme 1. Room-temperature Ph-X activation with 1–styrene.
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In the absence of styrene, 1 reacted sluggishly even with
PhI: after 1 day at 408C in toluene, the conversion of 1 was
only
35%.
Both
[(Ph3P)4Ru(H)2]
(3)
and
[(Ph3P)3Ru(H)2(N2)] (4) reacted more readily to give 2-I.
Deliberately added PPh3 slowed down these processes. These
À
data suggested that the Ph X bond was activated by the same
reactive species, likely [(Ph3P)3Ru(H)2] (5) produced upon
removal of L from [(Ph3P)3Ru(L)(H)2], where L = H2 (1),
PPh3 (3), or N2 (4). Complex 5 has been convincingly
proposed as a reactive intermediate in various transforma-
tions but never unambiguously characterized in the solid state
or in solution.[10] Attempts to detect 5 by VT 1H and 31P NMR
spectroscopy upon generation from 1 and styrene in [D8]THF
at À788C were unsuccessful. We therefore sought mechanistic
À
data on Ph X activation at 3 through kinetic and computa-
Figure 1. Kinetic profile of the reaction of 3 (0.0051m) with PhI
(1.49m) at 258C (1H and 31P{1H} NMR).
tional studies, focusing on the most reactive substrate, PhI.
A critical observation was made during a VT NMR study
of 3 in the presence of PhI (75 equiv) in [D8]THF or
[D8]toluene.[11] A new species, 6, (15%) in equilibrium with
3 was detected (À90 to + 258C) and identified as mer-
[(Ph3P)3Ru(H)2(PhI)] [Eq. (1)]. The best resolved 1H{31P}
NMR spectrum (À408C) displayed two 1:1 doublets from 6
(À8.56 and À16.14 ppm) with J(H-H) = 7.1 Hz. The 31P{1H}
NMR spectrum at the same temperature exhibited a doublet
(57.1 ppm) and a triplet (52.7 ppm) in a 2:1 integral ratio with
À
J(P P) = 17 Hz. The formation of 6 was accompanied by the
formation of 1 equiv of free PPh3 (À5.5 ppm). Neither 6 nor
its analogues were observed in the absence of PhI or upon its
replacement with PhBr or PhCl. These observations along
with the formation of 6 in toluene indicate that PhI in 6 is
coordinated to Ru through the iodine atom, not the p-system
of the aromatic ring.[12] Small amounts of 2-I owing to Ph I
À
activation were observed in these experiments only above
À408C.
Figure 2. ORTEP of [(Ph3P)4Ru2I2(m-I)2] (7) with all H atoms omitted
for clarity and ellipsoids set to 50% probability.
The reaction of 3 with PhI in large excess (300 equiv)
occurring in [D6]benzene at 258C with ca. 95% selectivity to
2-I was monitored to more than 95% conversion (1H NMR)
to reveal a stunning linear dependence: the rate of disappear-
ance of 3 and the formation of 2-I appeared to be concen-
tration independent, that is, zeroth order. As surprisingly,
after its nearly quantitative formation in a seemingly zeroth
order process, 2-I decayed exponentially (Figure 1). As 2-I
disappeared, its deep purple color vanished and the reaction
mixture turned brown. In parallel, the broad 31P{1H} NMR
signal at 57.1 ppm from 2-I was replaced with a broad
resonance at 69.9 ppm, and the peak from free PPh3 at
À5.5 ppm grew in intensity to 2 equiv per Ru at full
conversion of 2-I. The Ru product of the onward reaction
appeared to be [(Ph3P)4Ru2I2(m-I)2] (7), which was formed
quantitatively and structurally characterized (Figure 2).[9,11]
Therefore, 2-I produced in the first step reacted with PhI still
present in excess to give 7 along with PhH and one equiv of
PPh3 (Scheme 2).
Scheme 2. Initial and onward reactions of 3 with PhI (258C).
The method of initial rates was used to determine reaction
À
orders for the first and second Ph I activations. Each process
is positive first order in both PhI and the metal complex (3 or
2-I) and negative first order in PPh3 [Eqs. (2) and (3)].
Although Equation (2) was consistent with PPh3 predissoci-
ation from 3 to give 5 (see above), which reacted with PhI in
a bimolecular fashion, it could not account for the apparent
zeroth order behavior. Furthermore, Scheme 2 and Equa-
tions (2) and (3) were fully consistent with the observed
stoichiometry of the reaction sequence involving stepwise
formation of first 2-I and then 7 from 3 and PhI. However,
none of the conventional kinetic schemes for two consecutive
reactions could fit the highly reproducible, but peculiar
kinetic profile (Figure 1). The seeming zeroth order of
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appearance of 2-I and the apparent lack of its transformation
to 7 until its nearly quantitative formation seemed inexpli-
cable, given similar reaction rates for both steps.
À1
ð2Þ
ð3Þ
d½2-IŠ=dt ¼ k1½3Š½PhIŠ½PPh3Š
À1
Àd½2-IŠ=dt ¼ k2½2-IŠ½PhIŠ½PPh3Š
We suspected that autocatalysis[13] might account for this
kinetic discrepancy [Figure 1 versus Eqs. (2) and (3)], and that
2-I does in fact react with PhI once it is formed in the first step.
The negative first order in PPh3 [Eq. (3)] suggests PPh3
À
predissociation from 2-I prior to Ph I activation. Conse-
Figure 3. Plot of concentrations versus time for the reaction of 3
(0.0042m) with PhI (1.49m) at 258C. Data points are from the
experimental measurements. The curves are from the kinetic model
based on Scheme 3.[11]
À
quently, the Ru product of the C I cleavage is most likely
four-coordinate [(Ph3P)2RuI2] (8) that dimerizes to give 7. We
proposed, however, that 8 comproportionates with the as yet
unreacted starting dihydride 3 to revive 2-I in a reaction that
is much faster than both that between PhI and 3 and the
dimerization leading to 7 (Scheme 3).
reactions. The similarity of k1 = 1.24 ” 10À5 minÀ1 (first step)[15]
and k2 = 6.8 ” 10À6 minÀ1 (second step) at 258C fulfills the
above-described condition for the approximate zero-order
decay of 3 and formation of 2-I.[11]
DFT calculations were used to probe the mechanisms of
À
Ph I bond activation at 3 and 2-I using a BP86-D3(benzene)
procedure, as in previous related studies.[16] Profiles for the
À
first and second Ph I activations are shown in Scheme 4.
Starting with 3 (0.0 kcalmolÀ1), PPh3/PhI substitution leads,
via five-coordinate 5, to 6 (+ 10.1 kcalmolÀ1) in which PhI
binds through iodine. Species 6 is more stable than alternative
s-(C,H) and p-bound adducts, consistent with experimental
observations favoring such an I-bound form. To access the
Scheme 3. Autocatalysis in the reaction of 3 with PhI.
À
Ph I activation, 6 must first isomerize (via 5) to p-bound Int2
(+ 23.8 kcalmolÀ1); TS(5–Int2), the TS for PhI binding, lies at
+ 27.8 kcalmolÀ1. Int2 features an asymmetrically bound
À
This mechanistic proposal was confirmed by generating 8
in situ from [(Ph3P)3RuCl2] and NaI in the presence of 3 in
THF and observing the formation of 2-I within the time of
mixing.[11,14] Although k3 (Scheme 3) could not be accurately
determined experimentally, this instantaneous formation of 2-
I indicated that the comproportionation reaction is much
arene (Ru-Cipso = 2.25 Š, Ru Cortho = 2.47 Š), and an elon-
À
À
gated C I bond (2.34 Š cf. 2.14 Š in free PhI). C I bond
cleavage can therefore readily occur, via TS(Int2–Int3) at
+ 25.6 kcalmolÀ1. This nucleophilic displacement of IÀ by the
À1
À
Ru center leads to Int3 (+ 15.5 kcalmol ), a cationic Ru Ph
species that also features an h2-H2 ligand (H H 0.93 Š)
À
À
faster than both Ph I activation processes and therefore the
formed via the reductive coupling of the two hydrides. The
displaced IÀ in Int3 is loosely associated with the H2 ligand
(H···I = 2.70 Š), but moving the anion trans to the Ph ligand
gives a more stable species, Int4 (+ 0.4 kcalmolÀ1). Facile
condition for the proposed autocatalysis (k3 @ k2) is met.
Furthermore, if k1 ꢀ k2 and changes in [PhI] and [PPh3] are
negligible during the process, the general kinetic equation for
the first step in Scheme 2 (Eq. (4), as derived from the steady-
state approximation for 8) is transformed to Equation (5)
accounting for the apparent zeroth order behavior observed
(Figure 1).[11,15]
À
hydrogenolysis of the Ru Ph bond then occurs via TS(Int4–2-
I) at + 10.4 kcalmolÀ1. The overall rate-limiting TS for the
À1 [17]
À
first Ph I activation is TS(5-Int2) at + 27.8 kcalmol .
À
Once formed, 2-I can effect the second Ph I activation
(Scheme 4, right, where the energy of 2-I is reset to
0.0 kcalmolÀ1). This process again shows an inverse depend-
ence on [PPh3], consistent with initial PPh3/PhI exchange to
form Int5 (+ 21.8 kcalmolÀ1) as an I-bound adduct. Int5
isomerizes to Int6 (+ 26.1 kcalmolÀ1) in which the major
À1
À1
ð4Þ
ð5Þ
d½2-IŠ=dt ¼ k1½3Š½PhIŠ½PPh3Š þ k2½2-IŠ½PhIŠ½PPh3Š
d½2-IŠ=dt ¼ k0ð½3Š þ ½2-IŠÞ ¼ const:
À
To our delight, the model presented in Scheme 3 gave an
excellent fit to the full kinetic profile of the reaction
(Figure 3).[11] Although the starting complex 3 equilibrates
with 6 (Keq = 1.7 Æ 0.3 ” 10À3), this equilibrium [Eq. (1)]
establishes within the time of mixing and is therefore much
interaction is with the ipso carbon (Ru Cipso 2.12 Š) and
À
significant C I bond lengthening is again seen (2.29 Š). Int6
undergoes facile three-centered oxidative addition via
TS(Int6–Int7) at + 27.4 kcalmolÀ1 and forms Int7 (+ 18.2 kcal
molÀ1), which has an unusually short Cipso···H non-bonded
contact of 2.01 Š. Int7 could therefore be viewed as an
À
faster than the rate determining steps of both Ph I activation
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Scheme 4. Reaction pathways [BP86-D3(benzene), kcalmolÀ1] for Ph-I activation at 3 and 2-I, respectively. P=PPh3, selected distances in Š. For
the first Ph-I activation (left), free energies are quoted relative to 3+free PhI set to 0.0 kcalmolÀ1; for the second Ph-I activation (right), 2-I+free
PhI are then reset to 0.0 kcalmolÀ1. Boxed data indicate the free-energy changes associated with the reactions of 8. [a] Reductive elimination
involves an intermediate C,H-bound C6H6 s-complex.[11]
“elongated benzene s-complex”, with a square-pyramidal Ru,
an axial PPh3 ligand, and “C6H6” occupying a basal position
and H-bridged intermediate, [(Ph3P)3Ru(H)(m-H)(m-I)(I)Ru-
(PPh3)2], which then collapses in the presence of PPh3 to two
molecules of 2-I. Whereas the BP86-D3(benzene) procedure
gave good agreement between the experimental and com-
puted barriers, this approach is less successful in describing
these ligand exchange processes. For example [(Ph3P)3RuI2] is
predicted to form in preference to [(Ph3P)4Ru2I2(m-I)2], 7
(boxed data in Scheme 4) and the experimental Keq for Ph3P/
PhI exchange in 3 to give 6 is overestimated (DGcalc =+
10.1 kcalmolÀ1 cf. + 3.8 Æ 0.1 kcalmolÀ1 from experiment).
Extensive functional testing[11] indicates that the M06 func-
tional performs well for such processes, but then this approach
À
À
trans to I . Facile Ph H reductive elimination then forms
[(Ph3P)2RuI2], 8, plus free benzene at À27.8 kcalmolÀ1.
À
The overall computed barriers for C I activation at 3
(27.8 kcalmolÀ1) and 2-I (27.4 kcalmolÀ1) are in good agree-
ment with experiment (26.6 and 26.9 kcalmolÀ1 respectively)
and reiterate the similar barriers for these two process (that is,
k1 ꢀ k2; Scheme 3). In both cases the energy surface around
PhI association to form a p-bound adduct and the subsequent
À
C I activation is very flat; for 3 the highest point is for
À
association (TS(5–Int2)), whereas for 2-I it corresponds to C
À
À
I cleavage (TS(Int6–Int7)). The nature of the C I bond
fails to capture the similar barriers for two C I activation
cleavage also differs in the two systems: nucleophilic (SN-
type) displacement of IÀ by Ru in TS(Int2–Int3) and a more
conventional concerted oxidative addition in TS(Int6–Int7).
The greater steric bulk around Ru in TS(Int2–Int3) explains
why IÀ is initially expelled from the inner coordination sphere,
whereas the Ru center in TS(Int6–Int7) (with only two PPh3
processes. This complementarity of different DFTapproaches
will be addressed in a future report.
Experimentally, both PhBr and PhCl in excess also react
with 3 at 50–558C to give first 2-Br and 2-Cl in more than 95%
and about 70% yield, respectively. While the onward reaction
of PhBr leads cleanly to stable [(Ph3P)3RuBr2] in equilibrium
with small quantities of the dimer [(Ph3P)4Ru2Br2(m-Br)2],
that of PhCl is less selective. Details of these studies will be
reported separately.
À
À
ligands) permits the formation of new Ru Ph and Ru I
À
bonds. Nonetheless, both C I activations are formally oxida-
tive additions with transfer of two electrons from RuII to the
p-bound PhI. The implied oxidation to RuIV is mitigated by
either the simultaneous reductive coupling of two hydrides (in
In conclusion, it has been found, for the first time, that
RuII complexes devoid of electron-rich bulky phosphines can
À
À
Int3, first C I activation) or the unusually short Ph···H non-
efficiently cleave the Ph X (X = Cl, Br, I) bond under
exceedingly mild conditions. The mechanism of this unusual
À
À
bonding contact (in Int7, second C I activation).
The comproportionation mechanism likely involves facile
Ph X bond activation at Ru has been elucidated. In the
PPh3 dissociation[10] from 18-electron 3 to form 5. H/I
reaction of [(Ph3P)4Ru(H)2] with PhI (or PhBr), a well-
masked autocatalysis is involved, which has been recognized,
thoroughly studied by experimental and computational
À
exchange with [(Ph3P)2RuI2], 8, produced in the second C I
activation (Scheme 3), could then occur, most likely via an I-
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Christ, S. Sabo-Etienne, B. Chaudret, Organometallics 1994, 13,
3800; c) M. E. Cucullu, S. P. Nolan, T. R. Belderrain, R. H.
Grubbs, Organometallics 1999, 18, 1299.
means, and understood in considerable detail. Novel results of
the current study contribute to basic knowledge for further
progress in the area of inert bond activation, catalysis, and
reaction mechanisms.
[8] P. B. Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev. 2012,
112, 5879, and references therein.
[9] CCDC 1051142 (2-I), 1051143 (2-Br), 1051144 (2-Cl), and
1051145 (7) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
Keywords: Ar-X activation · autocatalysis · DFT calculations ·
kinetics · ruthenium
How to cite: Angew. Chem. Int. Ed. 2015, 54, 8466–8470
Angew. Chem. 2015, 127, 8586–8590
[10] H. Samouei, F. M. Miloserdov, E. C. Escudero-Adµn, V. V.
Grushin, Organometallics 2014, 33, 7279.
[11] See the Supporting Information for full details.
[1] See, for example: Activation of Unreactive Bonds and Organic
Synthesis (Ed.: S. Murai), Springer, Berlin, 1999.
[2] For reviews, see: a) V. V. Grushin, H. Alper, Chem. Rev. 1994,
94, 1047; b) V. V. Grushin, H. Alper, Top. Organomet. Chem.
1999, 3, 193; c) A. F. Littke, G. C. Fu, Angew. Chem. Int. Ed.
2002, 41, 4176; Angew. Chem. 2002, 114, 4350.
[12] For examples of Ru-I-Ar complexes, see: R. J. Kulawiec, R. H.
Crabtree, Coord. Chem. Rev. 1990, 99, 89, and references
therein.
[13] a) K. J. Singh, A. C. Hoepker, D. B. Collum, J. Am. Chem. Soc.
2008, 130, 18008; b) A. C. Hoepker, L. Gupta, Y. Ma, M. F.
Faggin, D. B. Collum, J. Am. Chem. Soc. 2011, 133, 7135.
[14] a) Unlike well-known [(Ph3P)3RuCl2], its iodo counterpart
[(Ph3P)3RuI2] has never been adequately characterized[14b] and
is expected[14c] to be unstable, easily losing PPh3 and dimerizing
to 7. b) N. R. Champness, W. Levason, S. R. Preece, M. Webster,
C. S. Frampton, Inorg. Chim. Acta 1996, 244, 65; c) P. R.
Hoffman, K. G. Caulton, J. Am. Chem. Soc. 1975, 97, 4221.
[15] For the equilibrium between 3 and 6 shifted toward 3.
[16] F. M. Miloserdov, C. L. McMullin, M. Martínez Belmonte, J.
Benet-Buchholz, V. I. Bakhmutov, S. A. Macgregor, V. V.
Grushin, Organometallics 2014, 33, 736.
[17] Alternative mechanisms were shown to be less-accessible; for
example, direct reaction of 6 via concerted oxidative addition
(DG°calc = 31.3 kcalmolÀ1) or nucleophilic attack by a hydride
with concerted displacement of iodide directly onto the Ru
(DG°calc = 32.0 kcalmolÀ1). See the Supporting Information for
full details of these and other processes considered.
[3] Pd0 bearing an anionic analogue of Xantphos can easily activate
aryl chlorides, which is most likely due to the negative charge of
the ligand. See: J. Zhang, A. Bellomo, N. Trongsiriwat, T. Jia, P. J.
Carroll, S. D. Dreher, M. T. Tudge, H. Yin, J. R. Robinson, E. J.
Schelter, P. J. Walsh, J. Am. Chem. Soc. 2014, 136, 6276.
[4] For selected examples of Ar-Cl activation with Rh, see: a) V. V.
Grushin, H. Alper, Organometallics 1991, 10, 1620; b) S. T. H.
Willems, P. H. M. Budzelaar, N. N. P. Moonen, R. de Gelder,
J. M. M. Smits, A. W. Gal, Chem. Eur. J. 2002, 8, 1310; c) V. V.
Grushin, W. J. Marshall, J. Am. Chem. Soc. 2004, 126, 3068; d) S.
Gatard, R. Celenligil-Cetin, C. Guo, B. M. Foxman, O. V.
Ozerov, J. Am. Chem. Soc. 2006, 128, 2808; e) T. M. Douglas,
A. B. Chaplin, A. S. Weller, Organometallics 2008, 27, 2918; f) J.-
I. Ito, T. Miyakawa, H. Nishiyama, Organometallics 2008, 27,
3312.
[5] For facile Ph-Cl activation with Ir, see: C. Douvris, C. A. Reed,
Organometallics 2008, 27, 807.
[6] a) A. J. Deeming, D. M. Speel, Organometallics 1997, 16, 289;
b) H. Grounds, J. C. Anderson, B. Hayter, A. J. Blake, Organo-
metallics 2009, 28, 5289.
[7] a) B. Chaudret, G. Chug, O. Eisenstein, S. A. Jackson, F. J.
Lahoz, J. A. Lopez, J. Am. Chem. Soc. 1991, 113, 2314; b) M. L.
Received: March 3, 2015
Revised: April 28, 2015
Published online: June 2, 2015
8470 www.angewandte.org
ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 8466 –8470