Hydrophenylation of ethylene using a cationic Ru(ii) catalyst: Comparison to a neutral Ru(ii) catalyst

Article abstract of DOI:10.1039/c4sc01665c

Charge neutral Ru(ii) complexes of the type TpRu(L)(NCMe)Ph [Tp = hydridotris(pyrazolyl)borate; L = CO, PMe₃, P(OCH₂)₃CEt or P(OCH₂)₂(OCCH₃)] have been previously reported to catalyze the hydrophenylation of ethylene (Organometallics, 2012, 31, 6851-6860). However, catalyst longevity for the TpRu(L)(NCMe)Ph complexes is inhibited by competitive ethylene C-H activation. For example, ethylene C-H activation limits catalysis using TpRu(P(OCH₂)₃CEt)(NCMe)Ph to a maximum of 20 turnover numbers for conversion of benzene and ethylene to ethylbenzene. In contrast, reaction of the cationic Ru(ii) complex [(HC(pz⁵)₃)Ru(P(OCH₂)₃CEt)(NCMe)Ph][BAr′4] [HC(pz⁵)₃= tris(5-methyl-pyrazolyl)methane; BAr′4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate] (0.025 mol% relative to benzene) in benzene with C₂H₄(15 psi) at 90 °C gives 565 turnover numbers of ethylbenzene after 131 hours. The production of 565 turnovers of ethylbenzene corresponds to an approximate one-pass 95% yield with ethylene is the limiting reagent and is a 28-fold improvement compared to the charge neutral catalyst TpRu(P(OCH₂)₃CEt)(NCMe)Ph. Under identical conditions, the activity of [(HC(pz⁵)₃)Ru(P(OCH₂)₃CEt)(NCMe)Ph][BAr′4] is only 1.3 times less than TpRu(P(OCH₂)₃CEt)(NCMe)Ph, but the increased stability of the cationic Ru(ii) catalyst allows reactivity at much higher temperatures (up to 175°C) and significantly enhanced rates. This journal is

Full text of DOI:10.1039/c4sc01665c

Chemical
Science
View Article Online
View Journal | View Issue
EDGE ARTICLE
Hydrophenylation of ethylene using a cationic Ru(II)
catalyst: comparison to a neutral Ru(II) catalyst†
Cite this: Chem. Sci., 2014, 5, 4355
a
a
a
b
*
*
Samantha A. Burgess, Evan E. Joslin, T. Brent Gunnoe, Thomas R. Cundari,
Michal Sabatc and William H. Myersd
Charge neutral Ru(II) complexes of the type TpRu(L)(NCMe)Ph [Tp ¼ hydridotris(pyrazolyl)borate; L ¼ CO,
PMe3, P(OCH2)3CEt or P(OCH2)2(OCCH3)] have been previously reported to catalyze the
hydrophenylation of ethylene (Organometallics, 2012, 31, 6851–6860). However, catalyst longevity for
the TpRu(L)(NCMe)Ph complexes is inhibited by competitive ethylene C–H activation. For example,
ethylene C–H activation limits catalysis using TpRu(P(OCH2)3CEt)(NCMe)Ph to a maximum of 20
turnover numbers for conversion of benzene and ethylene to ethylbenzene. In contrast, reaction of the
cationic Ru(II) complex [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] [HC(pz5)3 ¼ tris(5-methyl-pyrazolyl)-
methane; BAr40 ¼ tetrakis[3,5-bis(trifluoromethyl)phenyl]borate] (0.025 mol% relative to benzene) in
benzene with C2H4 (15 psi) at 90 ꢀC gives 565 turnover numbers of ethylbenzene after 131 hours. The
production of 565 turnovers of ethylbenzene corresponds to an approximate one-pass 95% yield with
ethylene is the limiting reagent and is a 28-fold improvement compared to the charge neutral
catalyst TpRu(P(OCH2)3CEt)(NCMe)Ph. Under identical conditions, the activity of [(HC(pz5)3)-
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] is only 1.3 times less than TpRu(P(OCH2)3CEt)(NCMe)Ph, but the
increased stability of the cationic Ru(II) catalyst allows reactivity at much higher temperatures (up to
175 ꢀC) and significantly enhanced rates.
Received 5th June 2014
Accepted 2nd July 2014
DOI: 10.1039/c4sc01665c
www.rsc.org/chemicalscience
dialkyl arenes, and direct synthesis of vinyl arenes using
oxidative hydroarylation.17,18,22–36 Examples of catalysts that are
Introduction
active for unactivated hydrocarbons (e.g., benzene and ethylene)
are limited, but catalysts based on Pd, Ru, Ir, Re and Pt have
been reported.17,22–36
Our group has previously reported TpRu(L)(NCMe)Ph [Tp ¼
hydridotris(pyrazolyl)borate; L ¼ CO, PMe3, P(OCH2)3CEt or
P(OCH2)2(OCCH3)] complexes for catalytic ethylene hydro-
phenylation.36,38,40–42 These studies have indicated a trend in the
catalytic efficiency as the donor ability of the ligand “L” is
Alkyl arenes are produced on a large scale from arenes and
olens using acid-based catalysts (either zeolites or Friedel–
Cras catalysts).1–5 In recent years, substantial advances have
been made in transition metal-catalyzed functionalization of
C–H bonds.6–16 Transition metal catalyzed olen hydroarylation
provides a complementary route for the alkylation of aromatic
substrates that can proceed by a pathway that is different from
acid catalyzed aromatic alkylation.17–36 For some transition
metal mediated olen hydroarylation reactions, olen insertion
into a metal–aryl bond is followed by aromatic C–H activation
and liberation of alkylated aromatic arene (Scheme 1).17,18,37
Potential benets of this method include the selective produc-
tion of linear alkyl arenes when using a-olens, selective
synthesis of mono-alkyl arenes, regioselective synthesis of
aDepartment of Chemistry, University of Virginia, Charlottesville, Virginia 22904, US
bDepartment of Chemistry, Center for Advanced Scientic Computing and Modeling
(CASCaM), University of North Texas, Denton TX 76203, US. E-mail: tbg7h@
virginia.edu; t@unt.edu
cNanoscale Materials Characterization Facility, Department of Materials Science and
Engineering, University of Virginia, Charlottesville, Virginia 22904, US
dDepartment of Chemistry, University of Richmond, Richmond, Virginia 23173, US
† Electronic supplementary information (ESI) available: Crystallographic data
(CIF), 1H NMR spectral data and representative kinetic plot. See DOI
10.1039/c4sc01665c
Scheme 1 Catalytic cycle for transition metal catalyzed olefin
hydroarylation that incorporates olefin insertion and aromatic C–H
activation.
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4355

View Article Online
Chemical Science
Edge Article
Scheme 2 Formation of the complexes TpRu(L)(h3-C3H4Me) [L ¼ CO, PMe3, P(OCH2)3CEt, and P(OCH2)2(OCCH3)], which are inactive for
ethylene hydrophenylation, results from ethylene C–H activation.
varied.17,39 For more strongly donating ligands (e.g., PMe3, catalyst with low TON (#20).39,41 Under optimized conditions, the
P(OCH2)3CEt), ethylene C–H activation competes with catalytic new cationic Ru(II) catalyst provides an increase in TON by a factor
ethylene hydrophenylation and results in the formation of of nearly 30-fold compared to TpRu(P(OCH2)3CEt)(NCMe)Ph
TpRu(L)(h3-C3H4Me) and catalyst deactivation (Scheme 2).38,39,41 (Scheme 3). Although the new cationic Ru(II) complex is slightly
As a result, the more electron-rich TpRu(L)(NCMe)Ph less active than its TpRu variant, its increased thermal stability
complexes are relatively poor catalysts for olen hydroarylation. allows reactions to be carried out at higher temperatures at which
Table 1 shows a summary of turnover numbers (TONs) for much faster catalysis is accessible.
hydrophenylation of ethylene using a series of TpRu(L)(NCMe)
Ph complexes. Ru(III/II) potentials (vs. NHE), which have been
used to compare the impact of L on the electron density of
TpRu(L)(NCMe)Ph catalyst precursors, are also shown in Table
1.17,39 Based on these results, it is anticipated that less electron-
rich Ru(II) complexes would provide catalysts that give higher
TONs than TpRu(L)(NCMe)Ph complexes.
One strategy to access less electron-rich Ru(II) catalysts,
compared to TpRu(L)(NCMe)Ph complexes, is to produce cationic
variants. For example, replacement of anionic Tp with charge-
neutral poly(pyrazolyl)alkanes provides a method to generate
cationic complexes that are structurally similar to TpRu(L)(NCMe)
Ph but less electron-rich.43 To test this strategy, we have
synthesized a cationic Ru(II) catalyst that is similar to TpRu-
(P(OCH2)3CEt)(NCMe)Ph, a known ethylene hydrophenylation
Table 1 Comparison of Ru(III/II) potentials and TONs for ethylene
hydrophenylation using TpRu(L)(NCMe)(Ph) [L
P(OCH2)3CEt or P(OCH2)2(OCCH3)] complexes17,39
¼
CO, PMe3,
E1/2 (V
vs. NHE)
L
TONa
PMe3
0.29
0.54
0.69
1.03
0b
20b
P(OCH2)3CEt
P(OCH2)2(OCCH3)
CO
90b
415c
Scheme 3 Previously reported TpRu(P(OCH2)3CEt)(NCMe)Ph gives 20
TONs of ethylbenzene at 90 ꢀC whereas the catalyst described in this
work, [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ], gives 565 TONs of
ethylbenzene.
a
90 ꢀC, 15 psi C2H4, and 0.025 mol% catalyst. b Catalyst deactivates by
forming TpRu(L)(h3-C3H4Me).
decomposition products are unknown.
The identity of the catalyst
c
4356 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014

View Article Online
Edge Article
Chemical Science
Fig. 1 ORTEP diagram of [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Cl (5-
Cl) (35% probability with hydrogen atoms and chloride omitted).
During crystallization from CH2Cl2, bromide counterion was replaced
with chloride. Selected bond lengths (A˚) Ru–P1, 2.1889(9); P1–O1,
1.602(3); P1–O2, 1.614(3); P1–O3, 1.624(3); Ru–C1, 2.069(4); Ru–N1,
2.133(3); Ru–N3, 2.172(3); Ru–N5, 2.071(3); Ru–N7, 2.023(3); N7–C25,
1.140(5). Selected bond angles (deg): O3–P1–O2, 100.93(15); O1–P1–O3,
101.1(1); O1–P1–O2, 101.7(2); N7–Ru–C1, 89.4(1); P1–Ru–N7,
92.19(9); C1–Ru–P1, 89.3(1); Ru–N7–C25, 178.0(3).
Scheme 4 Synthesis of [(HC(pz0)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Br (1)
and [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6). For the conver-
sion of 4 to 1 “Ligand” is HC(pz0)3. For the conversion of 4 to 5, “Ligand”
is HC(pz5)3.
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Br (5) in 87% isolated
yield (Scheme 4). A crystal of 5 suitable for X-ray diffraction was
obtained (Fig. 1). The structure reveals a pseudo octahedral
coordination sphere. The O–P–O bond angles of the phosphite
are 101.7(2)ꢀ, 101.1(1)ꢀ and 100.9(2)ꢀ. The O–P–O bond angles
Results and discussion
We have previously reported that heating the Ru(II) cation
[(C(pz)4)Ru(P(OCH2)3CEt)(NCMe)Me]+ (pz ¼ pyrazolyl) results in
intramolecular C–H activation of a pyrazolyl 5-position C–H
bond.44 As a result, [(C(pz)4)Ru(P(OCH2)3CEt)(NCMe)Me]+ is
inactive for catalytic hydrophenylation of benzene.44 Thus, we
synthesized the 3,5-dimethyl variant [(HC(pz0)3)Ru(P(OCH2)3-
CEt)(NCMe)Ph][BAr40 ] (1) [HC(pz0)3 ¼ tris(3,5-dimethylpyrazolyl)-
methane] to protect against C–H activation of the pyrazolyl
5-position C–H bond (Scheme 4). Cyclic voltammetry of
[(HC(pz0)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (1) shows
a
reversible wave [Ru(III/II)] at 0.82 V (vs. NHE), which is approxi-
mately a +0.28 V shi compared to TpRu(P(OCH2)3CEt)(NCMe)
Ph (0.54 V vs. NHE).41 Complex 1 was investigated as a ꢀcatalyst
ꢀ
for ethylene hydrophenylation between 90 C and 125 C with
15 to 25 psi of ethylene. No production of ethylbenzene or
styrene was observed.
Assuming that the steric bulk of the HC(pz0)3 ligand is
responsible for the inability of complex 1 to catalyze ethylene
hydrophenylation, we prepared [(HC(pz5)3)Ru(P(OCH2)3-
CEt)(NCMe)Ph][BAr40 ] (6) [HC(pz5)3 ¼ tris(5-methylpyrazolyl)-
methane] which incorporates the 5-methyl variant of the ligand
(Scheme 4). The addition of Ph2Mg[THF]2 (0.8 equivalents) to a
heterogeneous mixture of (h6-p-cymene)Ru(P(OCH2)3CEt)Br2 (2)
in THF gives (h6-p-cymene)Ru(P(OCH2)3CEt)(Br)Ph (3) in a 95%
isolated yield.44 Heating (h6-p-cymene)Ru(P(OCH2)3CEt)(Br)Ph
(3) in NCMe at 70 ꢀC for 3.5 h leads to the formation of putative
(NCMe)2Ru(P(OCH2)3CEt)(Br)Ph (4). Complex 4 has not been
Fig. 2 Catalytic hydrophenylation of ethylene (15 psi) using 0.01 mol%
(relative to benzene) [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
isolated.44 The reaction of 4 with HC(pz5)3 at 70 ꢀC gives at 90, 105, 150 and 175 ꢀC.
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4357

View Article Online
Chemical Science
Edge Article
for previously reported TpRu(PPh3)(P(OCH2)3CEt)Cl [101.4(1)ꢀ,
In order to directly compare the activity of complex 6 to
101.3(1)ꢀ,
100.8(1)ꢀ]
and
TpRu(PPh3)(P(OCH2)3CEt)OTf TpRu(P(OCH2)3CEt)(NCMe)(Ph), the turnover frequency (TOF) for
[102.43(8)ꢀ, 102.78(8)ꢀ, and 99.88(8)ꢀ] are in good agreement ethylene hydrophenylation catalyzed by 6 was calculated aer 4 h
with those of complex 5. The Ru–P bond distances of the of reaction at 90, 105, 150 and 175 ꢀC (Table 2). For reactions at 90
previously reported complexes TpRu(PPh3)(P(OCH2)3CEt)Cl and ꢀC and 105 ꢀC, catalyst deactivation at 4 h is minimal (see Fig. 2).
TpRu(PPh3)(P(OCH2)3CEt)OTf are 2.202(1) A and 2.212(1) A, However, at 150 and 175 ꢀC some catalyst deactivation occurs aer
˚
˚
respectively, which are comparable to the Ru–P [2.1889(9) A] 4 h. Thus, the calculated TOFs at 150 and 175 ꢀC are lowerꢃli4mits
˚
bond distance for the cationic complex 5.41
on catalyst activity. The TOF using 6 at 90 C is 3.6 ꢂ 10 sꢃ1
ꢀ
A metathesis reaction of 5 with NaBAr40 gave [(HC(pz5)3)- (Table 2). Under the same conditions, at 90 ꢀC a TOF of 4.8 ꢂ 10ꢃ4
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) in 97% isolated yield sꢃ1 is observed for TpRu(P(OCH2)3CEt)(NCMe)Ph.39 Thus, TpRu-
(Scheme 4). The E1/2 [Ru(III/II)] of complex 6 is 0.83 V versus NHE. (P(OCH2)3CEt)(NCMe)Ph is only 1.3 times more active than
The efficiency of complex 6 (0.01 mol%) as a catalyst for complex 6 at 90 ꢀC (Table 2). The increased stability of 6 compared
ethylene hydrophenylation was investigated at several different to TpRu(P(OCH2)3CEt)(NCMe)Ph allows catalysis at higher
temperatures using 15 psi of C2H4 (Fig. 2). The reactors were temperatures. At 150 ꢀC, the TOF using 6 (ꢁ2 ꢂ 10ꢃ2 sꢃ1) is ꢁ42
recharged with 15 psi ethylene aer each time point recorded. times greater than the TOF using TpRu(P(OCH2)3CEt)(NCMe)Ph at
The highest turnovers (TOs) of ethylbenzene (ꢁ400) were 90 ꢀC. Attempted catalysis using TpRu(P(OCH2)3CEt)(NCMe)Ph at
ꢀ
obtained aer 36 h at 150 C, aer which the catalyst is deac- temperatures greater than 100 ꢀC leads to rapid deactivation with
tivated. Using the ideal gas law, the maximum theoretical minimal ethylbenzene product (<20 TONs).41
number of TO with 15 psi of ethylene is ꢁ600.
For
TpRu(L)(NCMe)Ph
complexes
with
L
¼
Under optimized conditions (0.025 mol% catalyst, 15 psi P(OCH2)2(OCCH3), P(OCH2)3CEt or PMe3, catalyst deactivation
C2H4 and 90 ꢀC), TpRu(P(OCH2)3CEt)(NCMe)Ph gives only occurs though ethylene C–H activation to form a Ru–vinyl
20 TONs of ethylbenzene.39,41 For a direct comparison of cata- complex, which undergoes olen insertion and isomerization to
lytic hydrophenylation of ethylene using 6 versus TpRu- form h3-allyl complexes (Scheme 1).17,39 Also, for
(P(OCH2)3CEt)(NCMe)Ph, complex 6 (0.025 mol% relative to TpRu(L)(NCMe)Ph catalysts, TONs increase as the donating
benzene) was heated in benzene at 90 ꢀC with 15 psi of ethylene. ability of L decreases.39 We have interpreted experimental and
Aer 131 h, 565 TONs of ethylbenzene are produced using computational studies to determine that increased donor
complex 6, which is ꢁ95% yield based on ethylene (eqn (1)). For ability of L retards the rate of ethylene insertion, which allows
this reaction, ethylene was not recharged at any time point olen C–H activation to compete with olen hydroarylation.17,39
between 0 h and 131 h, this represents a 28-fold improvement The catalyst deactivation products are TpRu(L)(h3-C3H4Me)
compared to TpRu(P(OCH2)3CEt)(NCMe)Ph.39
complexes.17,39 Likewise, the 1H NMR spectra of the non-volatile
material from catalytic reactions using 6 show resonances
consistent with an h3-allyl complex. Characteristic allyl peaks
include a triplet of triplets at 4.47 ppm (3JAC ¼ 7 Hz) (for labels
see Experimental section), a doublet of triplets at 2.56 ppm
2
(3JAC ¼ 7 Hz, JAB ¼ 2 Hz), a doublet of quartets at 1.86 ppm
3
(3JCD ¼ 12 Hz, JDMe ¼ 6 Hz) and a doublet of doublets at 0.80
ppm (3JBC ¼ 11 Hz, 2JAB ¼ 2 Hz). The resonance due to the allyl
methyl is observed as a doublet (3JDMe ¼ 6 Hz) at 1.54 ppm. The
allyl complex [(HC(pz5)3)Ru(P(OCH2)3CEt)(h3-C3H4Me)][BAr40 ]
(7) was independently synthesized by heating a solution of
(1)
ꢀ
complex 6 in THF at 105 C under 215 psi C2H4.
Thus, the deactivation of complex 6 occurs by a similar
pathway to TpRu(L)(NCMe)Ph [L ¼ CO, P(OCH2)3CEt, PMe3 and
P(OCH2)2(OCCH3)] complexes (Scheme 5). For TpRu(PMe3)(NCMe)
Ph, the formation of the vinyl complex occurs from
Table 2 Comparison of TOF for ethylbenzene production for catalytic ethylene hydrophenylation using Ru(II) complexes
Catalyst
Temp (ꢀC)
TOF (sꢃ1
)
rel TOF
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ]a
TpRu(P(OCH2)3CEt)(NCMe)Pha
90
90
105
150c
175c
3.6 ꢂ 10ꢃ4
4.8 ꢂ 10ꢃ4
3.2 ꢂ 10ꢃ3
2.0 ꢂ 10ꢃ2
2.1 ꢂ 10ꢃ2
1
1.3
9
56
58
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ]b
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ]b
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ]b
TOF calculated aer 4 h at 90 ꢀC with 15 psi C2H4 and mol% of catalyst. b TOF calculated aer 4 h with 15 psi C2H4 and 0.01 mol% of catalyst.
Catalyst deactivation is signicant, and TOF is a lower limit.
a
c
4358 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014

View Article Online
Edge Article
Chemical Science
Scheme 5 The possible deactivation pathways for [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) via ethylene C–H activation to form
[(HC(pz5)3)Ru(P(OCH2)3CEt)(h3-C3H4Me)][BAr40 ] (7).
TpRu(PMe3)(h2-C2H4)Ph.17,38 For complex 6, we have not differen-
Ethylene hydrophenylation was carried out at 90 ꢀC with 0.01
tiated whether formation of the putative vinyl complex occurs from mol% complex 6 under different ethylene pressures. Similar to
[HC(pz5)3Ru(P(OCH2)3CEt)(h2-C2H4)Ph][BAr40 ] or [(HC(pz5)3Ru- TpRu(L)(NCMe)Ph catalysts,17,39 higher ethylene pressures
(P(OCH2)3CEt)(h2-C2H4)(CH2CH2Ph)][BAr40 ]. GC-MS analysis of the reduce the TONs and TOF (Fig. 3). A plot of TOF versus C2H4
reaction solution for the conversion of 6 and ethylene to 7 reveals pressure reveals an inverse dependence (Fig. 4), for which
the presence of ethylbenzene. Thus, conversion of [(HC(pz5)3Ru- previous studies of the mechanism of ethylene hydro-
(P(OCH2)3CEt)(h2-C2H4)(CH2CH2Ph)][BAr40 ] to complex 7 is viable. phenylation by TpRu(L)(NCMe)Ph complexes provide a plau-
sible explanation (Scheme 6).17 Initial exchange of coordinated
NCMe with ethylene forms [(HC(pz5)3)Ru(P(OCH2)3CEt)-
(h2-C2H4)Ph][BAr40 ]. Subsequent olen insertion gives
Fig.
Catalytic ethylene hydrophenylation by [(HC(pz5)3)- hydrophenylation using [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ]
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (0.01 mol%, 90 ꢀC) at variable (6) (0.01 mol%) plotted versus C2H4 psi. TOFs were calculated using
4 TOFs for ethylbenzene production for catalytic ethylene
Fig.
3
ethylene pressures.
TOs after 4 h at 90 ꢀC.
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4359

View Article Online
Chemical Science
Edge Article
Scheme 6 Proposed catalytic cycle for ethylene hydrophenylation using [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6).
Table 3 Comparison of TOFs for ethylbenzene production for cata-
reaction of complex 6 with C6D6 and 25 psig C2H4 in THF-d8 at
90 ꢀC. A multiplet is observed a 1.19 ppm for the mono-
deuterated methyl and a multiplet at 2.60 ppm is observed for
the benzylic methylene resonances. GC-MS shows EtPh-d6 as
the major product, and a primary fragment consistent with
–CH2CH2D (m/z ¼ 30) is observed. We compared the TOF for
ethꢀylbenzene production (determined using the TOs aer 4 h at
90 C with 15 psi C2H4) for catalytic reactions performed with
C6D6 to separate experiments using C6H6, and a KIE (kH/kD) of
1.8(3) was determined. This is consistent with rate limiting
benzene C–H activation in the catalytic cycle.
lytic ethylene hydrophenylation using [(HC(pz5)3)Ru(P(OCH2)3-
CEt)(NCMe)Ph][BAr40 ] (6) (0.01 mol%) and variable pressures of C2H4
C2H4 (psi)
TOF (sꢃ1 a
)
15
25
50
100
200
3.07 ꢂ 10ꢃ4
2.54 ꢂ 10ꢃ4
2.39 ꢂ 10ꢃ4
5.88 ꢂ 10ꢃ5
1.82 ꢂ 10ꢃ5
a
TOF calculated aer 4 h at 90 ꢀC and 0.01 mol% of catalyst.
[(HC(pz5)3)Ru(P(OCH2)3CEt)(CH2CH2Ph)][BAr40 ], and coordina-
tion of ethylene forms [(HC(pz5)3)Ru(P(OCH2)3CEt)(CH2CH2Ph)-
(h2-C2H4)][BAr40 ]. For TpRu(L)(NCMe)Ph catalysts, we have
evidence that TpRu(L)(CH2CH2Ph)(h2-C2H4) complexes are the
likely catalyst resting states.17 An inverse dependence of the rate
of catalysis on ethylene concentration is expected since ethylene
removes the active catalyst from the catalytic cycle (Table 3).
For the catalytic reaction of complex 6 with C6D6 and C2H4,
GC-MS and 1H NMR data indicate the primary product is
C6D5CH2CH2D (eqn (2)). Resonances (1H NMR) for
C6D5CH2CH2D can be observed when monitoring a catalytic
(2)
4360 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014

View Article Online
Edge Article
Chemical Science
Fig.
5
Eyring plot of degenerate NCMe/NCCD3 exchange for
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (R2 ¼ 0.96; 70 ꢀC to
95 ꢀC).
TpRu(CO)(NCMe)Ph as the catalyst.36 The same KIE values for
complex 6 and TpRu(CO)(NCMe)Ph are consistent with similar
mechanisms.
Previously, we reported evidence that stoichiometric C–D
activation of C6D6 by TpRu(L)(NCMe)Ph [L ¼ CO, PMe3,
P(OCH2)3CEt or P(OCH2)2(OCCH3)] complexes occurs by the
pathway shown in Scheme 8.17 We expected that the cationic
nature of 6 might result in strong coordination of NCMe
(compared to TpRu(L)(NCMe)Ph complexes), which could slow
the rate of C–D activation of C6D6. The rate of exchange between
coordinated NCCH3 of 6 and free NCCD3 conrms this. The rate
of degenerate NCCH3/NCCD3 exchange for complex 6 was
determined using 1H NMR spectroscopy by heating a solution of
Scheme 7 The reaction of [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph]-
[BAr40 ] (6) with a 1 : 1 molar ratio C6H6 to C6D6 leads to the formation of
four isotopologues of ethylbenzene.
Catalytic ethylene hydrophenylation using complex 6 (0.01
mol%) was also performed using a 1 : 1 molar ratio of C6H6 to
C6D6. Presumably, this leads to the formation of both
[(HC(pz5)3)Ru(P(OCH2)3CEt)(CH2CH2Ph)][BAr40 ] and [(HC(pz5)3)
Ru(P(OCH2)3CEt)(CH2CH2Ph-d5)][BAr40 ] as catalytic intermedi-
ates. These species can react with C6H6 or C6D6 to generate four
isotopologues (Scheme 7). These four ethylbenzene iso-
topologues are the primary products observed by GC-MS from
the reaction in a 1 : 1 mixture of C6D6 and C6H6. Aer heating
for 4 h at 90 ꢀC, a KIE (kH/kD) of 2.11(5) was determined by
comparing the ratios of Mw 111/112 in the GC-MS of the
reaction mixture. This KIE is statistically identical to the KIE
determined by comparison of TOF from catalysis in C6H6 versus
C6D6 (kH/kD) of 1.8(3) (see above). A KIE of 2.1(1) was previously
determined for catalytic hydrophenylation of ethylene using
ꢀ
complex 6 in NCCD3 at 70 C (eqn (3)). A kobs value of 5.7(7) ꢂ
10ꢃ6 sꢃ1 was determined from rst order plots. This rate is
slower by ꢁ5.6 fold than the rate of exchange for TpRu-
(CO)(NCMe)Ph under similar conditions (kobs ¼ 3.2(2) ꢂ 10ꢃ5 sꢃ1
at 70 ꢀC).17 The rate of degenerate NCCH3/NCCD3 exchange for
complex 6 was also determined at 80, 88 and 95 ꢀC. Values
for kobs of 3.3(3) ꢂ 10ꢃ5 sꢃ1, 5.4(3) ꢂ 10ꢃ5 sꢃ1 and 2.48(7) ꢂ
10ꢃ4 sꢃ1, respectively, were determined. An Eyring plot gave
activation parameters of DH‡ ¼ 35(5) kcal molꢃ1 and DS‡
¼
19(13) eu for the NCCH3/NCCD3 exchange reaction (Fig. 5). The
rate of degenerate NCCH3/NCCD3 exchange for a THF-d8 solu-
tion of complex 6 at 95 ꢀC with 10, 20 and 30 equivalents (0.1 M,
0.2 M, and 0.3 M) of added NCCD3 showed statistically identical
rates (kobs ¼ 1.1(1) ꢂ 10ꢃ4 sꢃ1), consistent with a dissociative
mechanism.
(3)
We attempted to compare the rate of stoichiometric C–D
activation of C6D6 by 6 to the rate using TpRu(L)(NCMe)Ph
Scheme 8 Proposed pathway for C–D activation of benzene by
TpRu(L)(NCMe)Ph [L ¼ CO, P(OCH2)3CEt, and P(OCH2)2(OCCH3)].
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4361

View Article Online
Chemical Science
Edge Article
complexes [L
¼
CO, PMe3, P(pyr)3, P(OCH2)3CEt or glovebox or by using standard Schlenk techniques. Glovebox
P(OCH2)2(OCCH3)].17,39 Monitoring (1H NMR spectroscopy) a purity was maintained by periodic nitrogen purges and was
solution of complex 6 in THF-d8 with 30 equivalents of C6D6 at monitored by an oxygen analyzer (O2 (g) < 15 ppm for all
60 ꢀC for two weeks shows ꢁ50% conversion to [(HC(pz5)3)- reactions). Toluene, tetrahydrofuran, pentane and diethyl
Ru(P(OCH2)3CEt)(NCMe)Ph-d5][BAr40 ] and C6H5D. GC-MS anal- ether were dried by distillation from sodium/benzophenone.
ysis of the reaction mixture conrmed C6H5D as the primary Acetonitrile was dried by distillation from CaH2. Hexanes,
organic product. Using an approximate t1/2 of 2 weeks for the benzene and dichloromethane were puried by passage
reaction of 6 with C6D6 gives kobs ꢁ5.7 ꢂ 10ꢃ7 sꢃ1. However, in through a column of activated alumina. Chloroform-d1,
the absence of added NCMe, decomposition of 6 to intractable benzene-d6, acetonitrile-d3, methylene chloride-d2 and THF-
˚
products is competitive with C–D activation of C6D6, which d8 were stored under a N2 atmosphere over 4 A molecular
prohibits a detailed kinetic analysis. Less decomposition of 6 is sieves. 1H and 13C NMR spectra were recorded on a Varian
observed when 1 equivalent of NCMe is added, but the rate of Mercury Plus 300 (126 MHz operating frequency for 13C NMR),
C–D activation is signicantly reduced. Even with added Varian Inova 500 MHz spectrometer (125 MHz operating
NCMe, decomposition is ultimately competitive with activation frequency for 13C NMR), Bruker Avance DRX 600 MHz spec-
of C6D6.
trometer (150 MHz operative frequency for 13C NMR) or
Bruker Avance III 800 MHz spectrometer (201 MHz operative
frequency for 13C NMR). All 1H and 13C NMR spectra are
referenced against residual proton signals (1H NMR) or the
Conclusions
Detailed studies of olen hydroarylation using TpRu(L)(NCMe)Ph 13C resonances of the deuterated solvent (13C NMR). All 31P
[L ¼ CO, PMe3, P(OCH2)3CEt and P(OCH2)2(OCCH3)] catalysts NMR were obtained on a Varian Mercury Plus 300 MHz
led us to propose that cationic Ru(II) variants would provide spectrometer (operating frequency 121 MHz) and referenced
greater TONs. Comparison of the TONs for ethylene hydro- against an external standard of H3PO4 (d ¼ 0). 19F NMR
phenylation by TpRu(P(OCH2)3CEt)(NCMe)Ph and [(HC(pz5)3) (operating frequency 282 MHz) spectra were obtained on a
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) conrms this hypothesis. Varian Mercury Plus 300 MHz spectrometer and referenced
The best TON for TpRu(P(OCH2)3CEt)(NCMe)Ph is 20 (24 h, 90 against an external standard of hexauorobenzene (d ¼
ꢀC, 0.025 mol% catalyst, 15 psi C2H4).39 In contrast, complex 6 ꢃ164.9). Elemental analyses were performed by Atlantic
gives 565 TONs under similar conditions, which is a 28-fold Microlabs, Inc. Electrochemical experiments were performed
improvement upon replacing Tp with a charge neutral tris- under a nitrogen atmosphere using a BAS Epsilon Potentio-
(pyrazolyl)alkane ligand. Consistent with previous studies stat. Cyclic voltammograms were recorded in CH3CN using a
for TpRu(L)(NCMe)Ph complexes that indicate the rate of standard three electrode cell from ꢃ1700 to 1700 mV at
benzene C–H activation is reduced as electron-density is 100 mV sꢃ1 with a glassy carbon working electrode and tet-
decreased,17,39 the reduced electron density of complex 6 relative rabutylammonium hexauorophosphate as the electrolyte.
to TpRu(POCH2)3CEt)(NCMe)Ph leads to a slight decrease (by a All potentials are reported versus NHE (normal hydrogen
factor of 1.3) in catalytic activity. However, the increased electrode) using ferrocene as the internal standard. High
stability of 6 allows catalysis at higher temperatures, which can resolution mass spectra were acquired in ESI mode from
be used to overcome the slightly lower activity for 6 compared to samples dissolved in a 3 : 1 acetonitrile–water solution con-
TpRu(P(OCH2)3CEt)(NCMe)Ph at 90 ꢀC. At 150 ꢀC, complex 6 is taining sodium triuoroacetate (NaTFA). Mass spectra are
an effective catalyst, and the rate is ꢁ42 times faster than using reported for M+ for monocationic complexes or for [M + H+] or
TpRu(P(OCH2)3CEt)(NCMe)Ph at the optimal 90 C.
[M + Na+] for neutral complexes using [Na(NaTFA)x]+ clusters
ꢀ
A TON of ꢁ400 and TOF $ 2 ꢂ 10ꢃ2 sꢃ1 at 150 ꢀC places as an internal standard. In all cases, observed isotopic enve-
complex 6 among the more active and long lived transition lopes were consistent with the molecular composition repor-
metal catalysts for ethylene hydrophenylation.25 Periana, God- ted. Mass spectra were collected on a Waters Xevo G2 QTof or
dard and co-workers have reported that [Ir(m-acac-O,O,C3)(acac- Agilent 6230 TOF. GC-MS was performed using a Shimadzu
O,O)(acac-C3)]2 (acac ¼ acetylacetonate) catalyzes ethylene GCMS-QP2012 Plus system with a 30 m ꢂ 0.25 mm SHRXI-
hydrophenylation with a TON of 455 (3 h) at 180 ꢀC, which 5MS column with 0.25 mm lm thickness using electron
corresponds to a TOF of 4.2 ꢂ 10ꢃ2 sꢃ1
.
45,46 We have previously impact ionization (EI). The preparation, isolation and char-
reported that [(dpm)Pt(Ph)(THF)]+ (dpm
¼
2,60-dipyridyl- acterization of [h6-p-cymene)Ru(Br)(m-Br)]2,47 (h6-p-cymene)-
0
methane) catalyzes ethylene hydrophenylation with a TOF of Ru(P(OCH2)3CEt)(Br)Ph,44 NaBAr4,48 Ph2Mg[THF]2
and
49
ꢁ1.8 ꢂ 10ꢃ2 sꢃ1 (120 ꢀC) with a TON of 469 (100 ꢀC).25 The HC(pz5)3 have been previously reported. (h6-p-cymene)
50
results reported herein suggest even less electron rich Ru(II) Ru(P(OCH2)3CEt)Br2 was prepared using the procedure reported
catalysts than 6 are promising targets.
for the synthesis of (h6-p-cymene)Ru(P(OCH2)3CEt)Cl2 using the
bromide analogue, [(h6-p-cymene)Ru(Br)(m-Br)]2, as the starting
material.51 P(OCH2)3CEt was obtained from a commercial
source and puried by dissolution in hexanes and ltration
through Celite. The ltrate was concentrated to dryness to yield
Experimental section
General considerations
Unless otherwise noted, all synthetic procedures were per- a white solid. All other reagents were used as purchased from
formed under anaerobic conditions in a nitrogen-lled commercial sources.
4362 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014

View Article Online
Edge Article
Chemical Science
[(HC(pz0)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Br (1)
added, and the mixture was stirred for ꢁ10 min. The solution
was ltered through Celite, and the ltrate was discarded. The
remaining solid was dissolved in CH2Cl2 and ltered through
Celite. The ltrate was concentrated to ꢁ2 mL, and hexanes
were added to induce precipitation. The precipitate was
collected on a ne porosity frit. The solid was washed with
pentane and dried in vacuo to yield a tan solid (0.360 g, 87%).
X-ray quality crystals of 5 were grown by layering a solution of
complex in CH2Cl2 with pentane. During crystallization, the
bromide was replaced with chloride. 1H NMR (500 MHz,
CD2Cl2) d 8.17 (s, 1H, HC(pz5)3), 7.95, 7.56, 7.15 (each a d, 1H,
The complex (h6-p-cymene)Ru(P(OCH2)3CEt)(Br)Ph (3) (0.285 g,
0.515 mmol) was dissolved in approximately 15 mL of NCMe,
added to a pressure tube and heated for 2 h at 70 ꢀC. The
reaction was brought into the glovebox and allowed to cool to
room temperature. The mixture was ltered through Celite, and
the ltrate was concentrated to dryness yielding (NCMe)3R-
u(P(OCH2)3CEt)(Br)Ph (4). Without any purication, the result-
ing solid was dissolved in ꢁ10 mL of methylene chloride and
added to a pressure tube with a 5 mL methylene chloride
solution of HC(pz0)3 (0.145 g, 0.487 mmol). The reaction was
3
3JHH ¼ 2 Hz, HC(pz5)3 3-position), 6.98 (dd, 2H, JHH ¼ 8 Hz,
ꢀ
heated to 70 C for 2 h. The reaction was brought into the glo-
4JHH ¼ 2 Hz, ortho-phenyl), 6.74 (m, 3H, overlapping meta-
phenyl and para-phenyl), 6.33, 6.17 (each a d, 1H, 3JHH ¼ 2 Hz,
HC(pz5)3 4-position), 6.21 (br s, 1H, HC(pz5)3 4-position), 4.22
(m, 6H, P(OCH2)3CCH2CH3), 2.81, 2.79, 2.77 (each a s, 3H,
vebox and ltered through Celite. The ltrate was concentrated
to dryness. Benzene was added, and the mixture was stirred.
The mixture was ltered through Celite, and the ltrate was
discarded. The remaining solid was eluted with methylene
chloride, concentrated to ꢁ2 mL, and hexanes were added to
induce a precipitate. The precipitate was collected on a ne
porosity frit. The solid was washed with pentane and dried in
vacuo to yield a tan solid (0.207 g, 53% yield). 1H NMR (600
MHz, CD2Cl2) d 7.87 (s, 1H, HC(pz0)3), 7.62 (d, 1H, 3JHH ¼ 8 Hz,
ortho-phenyl), 6.91 (t, 1H, 3JHH ¼ 8 Hz, meta-phenyl), 6.74 (t, 1H,
3JHH ¼ 8 Hz, para-phenyl), 6.60 (t, 1H, 3JHH ¼ 8 Hz, meta-phenyl),
3
HC(pz5)3 5-methyl), 2.36 (s, 3H, NCCH3), 1.22 (q, 2H, JHH ¼ 8
3
Hz, P(OCH2)3CCH2CH3), 0.81 (t, 3H, JHH
¼
8
Hz,
P(OCH2)3CCH2CH3). 13C NMR (151 MHz, CD2Cl2) d 166.1 (d,
2JCP ¼ 19 Hz, ipso of phenyl) 149.2, 146.6, 144.9, 142.6, 141.8,
141.7, 140.2, 125.7, 122.9, 120.8, 108.6, 108.5, 108.4 (each a s,
HC(pz5)3 and phenyl), 122.9 (s, NCCH3), 74.6 (d, JCP ¼ 7 Hz,
2
P(OCH2)3CCH2CH3), 69.5 (s, HC(pz5)3), 35.8 (d, JCP ¼ 31 Hz,
3
P(OCH2)3CCH2CH3), 24.0 (s, P(OCH2)3CCH2CH3) 12.6, 12.1
(HC(pz5)3 methyls, one missing resonance likely due to coinci-
dental overlap), 7.4 (s, P(OCH2)3CCH2CH3), 4.9 (s, NCCH3). 31P
{1H} NMR (121 MHz, CD2Cl2) d 133.1. M+ ¼ C27H35N7O3PRu+
obsd (%), calcd (%), ppm: 635.1589 (32), 635.1594 (35), ꢃ0.8;
636.1592 (41), 636.1587 (44), 0.7; 637.1603 (55), 637.1594 (58),
1.4; 638.1595 (100), 638.1584 (100), 1.7; 639.1611 (30), 639.1610
(30), 0.2; 640.1598 (55), 640.1592 (54), 0.9.
3
6.37 (d, 1H, JHH ¼ 8 Hz, ortho-phenyl), 6.15, 6.04, 5.98 (each
3
a s, 1H, HC(pz0)3 4-positions), 4.22 (d, 6H, JHP ¼ 5 Hz,
P(OCH2)3CCH2CH3), 2.64 (overlapping s, 9H, HC(pz0)3 3,5-
methyl positions), 2.53, 1.97, 1.41 (each a s, 3H, HC(pz0)3
3
3,5-methyl positions), 2.35 (s, 3H, NCCH3), 1.23 (q, 2H, JHH
¼
3
8
Hz, P(OCH2)3CCH2CH3), 0.83 (t, 3H, JHH
¼
8 Hz,
P(OCH2)3CCH2CH3). 13C NMR (151 MHz, CD2Cl2) d 165.3 (d,
2JCP ¼ 19 Hz, ipso of phenyl) 158.9, 156.5, 156.1, 141.2, 140.6,
140.5 (each a s, HC(pz0)3 aromatic C's), 143.5 (phenyl), 141.7
(phenyl), 125.8 (phenyl), 125.2 (phenyl), 124.0 (s, NCCH3), 120.6
(phenyl), 109.9, 109.6, 109.3 (each a s, HC(pz0)3 4-position), 74.5
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Br (5) (0.360 g, 0.503
mmol) was suspended in THF (ꢁ10 mL) in a round bottom ask
to form a heterogeneous mixture. NaBAr40 (0.057 g, 0.064 mmol)
in THF (ꢁ5 mL) was slowly added, and a homogenous solution
resulted. The reaction was stirred at room temperature for 1.5 h
during which time it turned grey. The solution was ltered
through Celite, and the ltrate was concentrated to dryness. The
solid was reconstituted in Et2O and ltered through Celite. The
ltrate was concentrated to dryness to yield a golden solid
(0.729 g, 97%). 1H NMR (500 MHz, CD2Cl2) d 7.95 (s, 1H,
HC(pz5)3), 7.93, 7.60, 7.23 (each a d, 1H, 3JHH ¼ 2 Hz, HC(pz5)3 5-
2
(d, JCP ¼ 7 Hz, P(OCH2)3CCH2CH3), 68.8 (s, HC(pz0)3), 35.6 (d,
3JCP ¼ 31 Hz, P(OCH2)3CCH2CH3), 24.0 (s, P(OCH2)3CCH2CH3)
15.8, 14.0, 13.1, 12.3, 11.9, 11.8 (each a s, HC(pz0)3 methyls), 7.5
(s, P(OCH2)3CCH2CH3), 4.8 (s, NCCH3). 31P{1H} NMR (121 MHz,
CD2Cl2) d 137.4. CV (NCMe): E1/2 ¼ 0.82 V. HR-MS: [M+] obsd
(%), calcd (%), ppm: 677.2058 (34), 677.2064 (35), ꢃ0.9;
678.2056 (43), 678.2058 (44), ꢃ0.3; 679.2061 (55), 679.2064 (59),
ꢃ0.4; 680.2049 (100), 680.2055 (100), ꢃ0.9; 681.2086 (32),
681.208 (32), 0.9; 682.2064 (55), 682.2063 (55), 0.1.
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph]Br (5)
position), 7.72 (br s, 8H, BAr40 ortho position), 7.56 (br s, 4H, BAr40
3
The complex (h6-p-cymene)Ru(P(OCH2)3CEt)(Br)Ph (3) (0.320 g, para position), 6.97 (d, 2H, JHH ¼ 7 Hz, ortho-phenyl), 6.82 (t,
0.577 mmol) was dissolved in CH3CN (ꢁ20 mL), added to a 2H, 3JHH ¼ 7 Hz, meta-phenyl), 6.78 (m, 1H, para-phenyl), 6.29,
3
pressure tube and heated for 3.5 h at 70 C. The reaction was 6.20 (each a d, JHH ¼ 2 Hz, HC(pz5)3 4-position), 6.22 (s, 1H,
ꢀ
allowed to cool to room temperature. The mixture was ltered HC(pz5)3 4-position), 4.22 (m, 6H, P(OCH2)3CCH2CH3), 2.62 (s,
through Celite, and the ltrate was concentrated to dryness 3H, HC(pz5)3 5-methyl position), 2.60 (overlapping s, 6H,
yielding the putative complex (NCMe)3Ru(P(OCH2)3CEt)(Br)Ph HC(pz5)3 5-methyl position), 2.30 (s, 3H, NCCH3), 1.20 (q, 2H,
3
(4). The resulting solid was taken up in CH2Cl2 (ꢁ10 mL) and 3JHH ¼ 8 Hz, P(OCH2)3CCH2CH3), 0.80 (t, 3H, JHH ¼ 8 Hz,
added to a pressure tube with HC(pz5)3 (0.178 g, 0.695 mmol) in P(OCH2)3CCH2CH3). 13C NMR (151 MHz, CD2Cl2) d 165.5 (d, 2JCP
CH2Cl2 (ꢁ10 mL). The solution was heated to 70 C overnight ¼ 16 Hz, ipso of phenyl), 162.3 (four line pattern, 1JCB ¼ 50 Hz,
ꢀ
aer which it was ltered through Celite. The volatiles were BAr40 ), 149.4, 146.7, 145.2, 141.7, 140.8, 140.6, 126.0, 122.9,
removed from the ltrate under reduced pressure. Benzene was 121.1, 109.0, 108.9, 108.6 (each a s, HC(pz5)3, phenyl, and
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4363

View Article Online
Chemical Science
Edge Article
(d, 3JCP ¼ 29 Hz, P(OCH2)3CCH2CH3), 33.3 (d, 2JCP ¼ 5 Hz, allyl-
CH2CHCHCH3), 23.8 (s, P(OCH2)3CCH2CH3), 18.4 (s, allyl-
CH2CHCHCH3), 11.5, 11.5, 11.5 (each a s, HC(pz5)3-CH3
groups), 7.3 (s, P(OCH2)3CCH2CH3). 31P{1H} NMR (121 MHz,
CD2Cl2) d 139.8. 19F NMR (282 MHz, CD2Cl2) d ꢃ64.2. M+
¼
[C23H34N6O3PRu]+obsd (%), calcd (%), ppm: 569.1502 (12),
569.1501 (15), 0.3; 572.1483 (33), 572.1485 (36), ꢃ0.3; 573.1477
(41), 573.1477 (44), 0.0; 574.1482 (56), 574.1484 (57), ꢃ0.4;
575.1471 (100), 575.1474 (100), ꢃ0.6; 576.1500 (27), 576.1500
(26), ꢃ0.1; 577.1480 (57), 577.1482 (54), ꢃ0.4.
Chart
1
Allyl coupling diagram for [(HC(pz5)3)Ru(P(OCH2)3CEt)-
(h3-C3H4Me)][BAr40 ] (7).
Rate of stoichiometric C6D6 activation by [(HC(pz5)3)-
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (0.014 g,
0.0095 mmol), C6D6 (26 mL, 0.29 mmol) and hexamethyldisilane
(HMDS) (1 mL, 0.005 mmol, as an internal standard) were
combined in 1 mL of THF-d8. To three separate screw-cap NMR
tubes 300 mL of this solution were added. The tubes were heated
NCCH3, 1 resonance missing due to coincidental overlap), 135.4
(s, BAr40 ), 129.6 (q, 1JCF ¼ 32 Hz, BAr40 C–CF3), 125.2 (q, 1JCF ¼ 273
Hz, BAr40 , CF3), 118.0 (s, BAr40 ), 74.7 (d, JCP ¼ 7 Hz,
2
3
P(OCH2)3CCH2CH3), 69.1 (s, HC(pz5)3), 35.8 (d, JCP ¼ 31 Hz,
P(OCH2)3CCH2CH3), 24.0 (s, P(OCH2)3CCH2CH3), 11.8, 11.3
(HC(pz5)3 methyl, one missing due to coincidental overlap), 7.4
(s, P(OCH2)3CCH2CH3), 4.7 (s, NCCH3). 31P{1H} NMR (121 MHz,
CD2Cl2) d 134.3. 19F NMR (282 MHz, CD2Cl2) d ꢃ63.2. CV
(NCMe): E1/2 ¼ 0.83 V. Anal. calcd for C59H47BF24N7O3PRu C,
47.22; H, 3.16; N, 6.73. Found: C, 47.34; H, 3.42; N, 6.47. M+ ¼
1
ꢀ
to 60 C in a temperature-controlled oil bath. H NMR spectra
using a 12.8 s pulse delay time were periodically acquired.
Relative to the internal standard, HMDS, the rate of the reaction
was monitored by integration of the ortho-phenyl resonance
(6.96 ppm). Changes were observed in the P(OCH2)3CEt reso-
nances over time.
C
27H35N7O3PRu+ obsd (%), calcd (%), ppm: 635.1591 (32),
635.1594 (35), ꢃ0.5; 636.1579 (42), 636.1587 (44), ꢃ1.3; 637.1588
(57), 637.1594 (58), ꢃ1.0; 638.1576 (100), 638.1584 (100), ꢃ1.3;
639.1616 (30), 639.1610 (30), 1.0; 640.1585 (57), 640.1592
(54), ꢃ1.1.
Degenerate NCCH3/NCCD3 exchange for [(HC(pz5)3)-
Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
[(HC(pz5)3)Ru(P(OCH2)3CEt)(h3-C3H4Me)][BAr40 ] (7)
In a 1 mL volumetric ask [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)-
Ph][BAr40 ] (6) (0.016 g, 0.011 mmol) was dissolved in CD3CN.
Hexamethyldisilane (HMDS) (1 mL, 0.005 mmol) was added as
an internal standard. The solution was divided between three J.
Young NMR tubes (300 mL per tube). The tubes were placed into
a temperature calibrated Varian 500 MHz spectrometer probe
(equilibrated at 88 ꢀC). The temperature was determined using
80% ethylene glycol in DMSO-d6 and the following equation
provided by Bruker Instruments, Inc. VT-Calibration Manual: T
(K) ¼ (4.218 – D)/0.009132, where D is the shi difference (ppm)
between CH2 and OH resonance of ethylene glycol. The reaction
was monitored by 1H NMR spectroscopy using automated data
acquisition. Eight scans were acquired for each spectrum. The
delay time was set to 12.8 s, and the acquisition time was set to
2.2 s. Each spectrum required 2 minutes to complete and the
acquisition of a new data point began every 30 minutes. The
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (0.785 g,
0.0523 mmol) was dissolved in THF (ꢁ10 mL) in a stainless steel
pressure reactor. The reactor was purged three times with C2H4
and then charged with 200 psig C2H4. The reactor was placed in
a temperature-regulated aluminum block set to 105 ꢀC. Aer 54
h of heating, the reactor was removed from the aluminum
block, cooled to room temperature and degassed. The yellow
solution was ltered through a pad of Celite. The ltrate was
reduced to dryness in vacuo to give a low-density yellow-brown
1
solid (0.063 g, 83%). H NMR (600 MHz, CD2Cl2) d 8.05 (s, 1H,
3
HC(pz5)3), 7.90, 7.82 (each a d, JHH ¼ 2 Hz, 1H, HC(pz5)3
5-position), 7.73 (br s, 8H, BAr40 ortho position), 7.57 (br s, 4H,
BAr40 para position), 7.02 (s, 1H, HC(pz5)3 5-position), 6.31, 6.26
3
(each a dd, JHH ¼ 1 Hz, 1H, HC(pz5)3 4-position), 6.21 (s, 1H,
3
3
HC(pz5)3 4-position), 4.47 (tt, JBC ¼ 11 Hz, JAC ¼ 7 Hz, see
Chart 1 for designations, 2H, allyl Hc), 4.09 (d, 3JCP ¼ 5 Hz, 6H,
P(OCH2)3CCH2CH3), 2.65, 2.63, 2.61 (each a s, 3H, HC(pz5)3 5-
methyl position), 2.56 (dt, 3JAC ¼ 7 Hz, 2JAB ¼ 2 Hz, 1H, allyl HA),
ꢀ
ꢀ
ꢀ
exchange reaction was repeated at 70 C, 80 C and 95 C only
1
the tubes were heated in a temperature-controlled oil bath. H
NMR spectra using a 12.8 s pulse delay time were periodically
acquired. All reactions were monitored through at least three
half-lives.
3
3
1.86 (dq, JCD ¼ 12 Hz, JDMe ¼ 6 Hz, 1H, allyl HD), 1.54 (d,
3
3JDMe ¼ 6 Hz, 3H, allyl CH3), 1.13 (q, JHH ¼ 8 Hz, 2H,
P(OCH2)3CCH2CH3), 0.80 (dd, 3JBC ¼ 11 Hz, 2JAB ¼ 2 Hz, 1H, allyl
HB), 0.76 (t, 3JHH ¼ 8 Hz, 3H, P(OCH2)3CCH2CH3). 13C NMR (201
Dependence of degenerate NCCH3/NCCD3 exchange for
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) on NCCD3
Concentration
MHz, CD2Cl2) d 162.3 (four line pattern, JCB ¼ 50 Hz, BAr40 ),
1
149.0, 146.9, 141.8, 141.3, 140.9, 140.9, 108.8, 108.7, 108.5, (each
0
a s, HC(pz5)3), 135.4 (s, BAr4), 129.7 (q, JCF ¼ 32 Hz, BAr40 In a 1 mL volumetric ask [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)-
1
0
C–CF3), 118.1 (s, BAr4), 125.2 (q, JCF ¼ 273 Hz, BAr40 CF3), 88.2 Ph][BAr40 ] (6) (0.016 g, 0.011 mmol) was dissolved in THF-d8. 10
(allyl-CH2CHCHCH3), 74.9 (d, 2JCP ¼ 7 Hz, P(OCH2)3CCH2CH3), equivalents (0.3 mmol, 0.1 M), 20 equivalents (0.2 mmol, 0.2 M)
69.0 (s, HC(pz5)3), 55.0 (d, 2JCP ¼ 3 Hz, allyl-CH2CHCHCH3), 35.6 or 30 equivalents (0.3 mmol, 0.3 M) of NCCD3 was added.
1
4364 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014

View Article Online
Edge Article
Chemical Science
Hexamethyldisilane (HMDS) (1 mL, 0.005 mmol) was added as were degassed and sampled under N2. The reaction mixture was
an internal standard. The solution was divided between three analyzed by GC-MS using peak areas of the products and the
J. Young NMR tubes (300 mL per tube). The tubes were pres- internal standard to calculate product yields. GC-MS data
surized with 25 psig N2. The tubes were heated to 95 ꢀC in a indicate the major product is C6D5CH2CH2D. The MS spectrum
temperature-controlled oil bath. 1H NMR spectra using a 12.8 s for ethyl benzene contains parent peaks at m/z 91 and 106. The
pulse delay time were periodically acquired. All reactions were major peak for the ethyl fragment is observed at 29. For the
monitored through at least three half-lives.
catalytic reaction using C6D6, parent peaks in the mass spec-
trum are observed at 106 and 112 m/z, which is consistent with
the formation of C6D5CH2CH2D. In addition, enrichment of m/z
of 30 is observed for ethyl chain supporting formation of
CH2CH2D. The kH/kD was determined by dividing the ratio
average (data collected in triplicate) peak areas for ethylbenzene
to internal standard for a catalytic reaction under identical
conditions (0.01 mol% complex 6, 90 C, 4 h) in C6H6 by the
ratio of peak areas of the average C6D5CH2CH2D integrations to
internal standard for the three runs using C6D6.
Representative catalytic reaction
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (0.017 g, 0.011
mmol) was dissolved in 10 mL of C6H6 (with decane added as an
internal standard). The solution was stirred for 5 minutes to
ensure homogeneity before transferring 3 mL each to three
stainless steel pressure reactors. The reactors were charged with
15 psi of C2H4 followed by N2 to give a total pressure of 120 psig.
The reactors were placed in a temperature-regulated aluminum
block set to 105 ꢀC. Aer 4, 16, 36, 60, and 84 h the reactors were
degassed, sampled under N2 and then re-pressurized before
returning to the aluminum block. The reaction mixture was
analyzed by GC-MS using peak areas of the products and the
internal standard to calculate product yields. Ethylbenzene
production was quantied using linear regression analysis of
gas chromatograms of standard samples. A set of ten known
standards consisting of 1 : 5, 3 : 5, 5 : 5, 7.5 : 5, 10 : 5, 50 : 5,
100 : 5, 150 : 5, 300 : 5, 500 : 5 molar ratios of ethylbenzene to
decane in methylene chloride were prepared. A plot of peak area
ratios versus molar ratios gave a regression line.
ꢀ
Method 2. [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
(0.012 g, 0.0079 mmol) was dissolved in 3.5 mL of C6D6 and
3.5 mL of C6H6 (with decane added as an internal standard).
The solution was stirred for 5 minutes to ensure homogeneity
before transferring 2 mL each to three stainless steel pressure
reactors. The reactors were charged with 15 psi of C2H4 followed
by N2 to give a total pressure of 120 psig. The reactors were
placed in a temperature-regulated aluminum block set to 90 ꢀC.
Aer 4 h the reactors were degassed and sampled under N2. The
reaction mixture was analyzed by GC-MS. A KIE was determined
by dividing the intensities for Mw ¼ 111 by the intensities for
Mw ¼ 112.
Monitoring ethylene hydrophenylation using C6D6 by 1H NMR
spectroscopy
Acknowledgements
[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6) (0.010 g,
0.0067 mmol) was dissolved in THF-d8 (300 mL) in a J. Young
NMR tube. C6D6 (59 mL 0.67 mmol) was added to the tube using
a microsyringe. The tube was pressurized with 25 psig of C2H4
and placed in a temperature regulated oil bath set to 90 ꢀC. The
reaction was monitored periodically by 1H and 31P NMR
spectroscopy. Resonances for C6D5CH2CH2D were observed by
1H NMR spectroscopy. A multiplet at 1.19 ppm is observed for
the mono-deuterated methyl and a multiplet at 2.60 ppm is
observed for the benzylic methylene resonances of
C6D5CH2CH2D. Unfortunately, the resonance at 2.60 ppm
overlaps with the 5-position methyl resonances of coordinated
HC(pz5)3, which prevents a detailed analysis of splitting. GC-MS
analysis shows two major peaks with m/z of 96 and 112, which is
consistent with production of C6D5CH2CH2D. The ethyl frag-
ment is consistent with predominant –CH2CH2D.
The authors acknowledge support from The Office of Basic
Energy Science, U.S. Department of Energy, under award
numbers DE-SC0000776 (T.B.G.) and DE-FG02-03ER15387 for
(T.R.C.). The authors acknowledge support of the National
Science Foundation (CHE-1126602) for the purchase of an X-ray
diffractometer at the University of Virginia. The authors would
like to thank Gordon Fujimoto and Besnik Bajrami at Waters
Corporation in Beverly, MA for collection of HRMS data.
Notes and references
1 I. M. Gerzeliev, S. N. Khadzhiev and I. E. Sakharova, Pet.
Chem., 2011, 51, 39–48.
2 C. Perego and P. Ingallina, Green Chem., 2004, 6, 274–279.
3 D. J. Macquarrie, in Catalytic Asymmetric Friedel–Cras
Alkylations, ed. M. Bandini and A. Umani-Ronchi, Wiley-
VCH, Weinheim, Germany, 2009.
4 A. M. G. A. Olah, Hydrocarbon Chemistry, Wiley-Intersciences,
New York, 2nd edn, 2003.
5 P. P. C. Perego, in Advances in Nanoporous Materials, Elsevier
B. V., Great Britain, 2009, vol. 1, pp. 97–149.
6 Activation and Functionalization of C-H Bonds, ed. K. I.
Goldberg and A. S. Goldman, American Chemical Society,
Washington, DC, 2004.
7 N. Kuhl, M. N. Hopkinson, J. Wencel-Delord and F. Glorius,
Angew. Chem., Int. Ed., 2012, 51, 10236–10254.
Determination of kinetic isotope effect
Method 1. [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr40 ] (6)
(0.017 g, 0.011 mmol) was dissolved in 7 mL of C6D6 (with
decane added as an internal standard). The solution was stirred
for 5 minutes to ensure homogeneity before transferring 2 mL
each to three stainless steel pressure reactors. The reactors were
charged with 15 psi of C2H4 followed by N2 to give a total
pressure of 120 psig. The reactors were placed in a temperature-
ꢀ
regulated aluminum block set to 90 C. Aer 4 h the reactors
This journal is © The Royal Society of Chemistry 2014
Chem. Sci., 2014, 5, 4355–4366 | 4365

View Article Online
Chemical Science
Edge Article
8 D. A. Colby, R. G. Bergman and J. A. Ellman, Chem. Rev., 30 M. A. Bowring, R. G. Bergman and T. D. Tilley,
2010, 110, 624–655. Organometallics, 2011, 30, 1295–1298.
9 C. Cheng, B. G. Kim, D. Guironnet, M. Brookhart, C. Guan, 31 J. Oxgaard and W. A. Goddard, J. Am. Chem. Soc., 2004, 126,
D. Y. Wang, K. Krogh-Jespersen and A. S. Goldman, J. Am.
Chem. Soc., 2014, 136, 6672–6683.
10 S. R. Neufeldt and M. S. Sanford, Acc. Chem. Res., 2012, 45,
936–946.
442–443.
32 J. Oxgaard, R. A. Periana and W. A. Goddard, J. Am. Chem.
Soc., 2004, 126, 11658–11665.
33 A. T. Luedtke and K. I. Goldberg, Angew. Chem., Int. Ed.,
2008, 47, 7694–7696.
11 G. E. Dobereiner, J. Yuan, R. R. Schrock, A. S. Goldman and
J. D. Hackenberg, J. Am. Chem. Soc., 2013, 135, 12572–12575. 34 W. D. Jones, J. A. Maguire and G. P. Rosini, Inorg. Chim. Acta,
12 M. A. Bowring, R. G. Bergman and T. D. Tilley, J. Am. Chem.
Soc., 2013, 135, 13121–13128.
13 Y. J. Lian, R. G. Bergman, L. D. Lavis and J. A. Ellman, J. Am.
Chem. Soc., 2013, 135, 7122–7125.
14 J. M. Howell, W. Liu, A. J. Young and M. C. White, J. Am.
Chem. Soc., 2014, 136, 5750–5754.
15 K. S. L. Chan, M. Wasa, L. Chu, B. N. Laforteza, M. Miura and
J. Q. Yu, Nat. Chem., 2014, 6, 146–150.
1998, 270, 77–86.
35 R. A. Periana, X. Y. Liu and G. Bhalla, Chem. Commun., 2002,
3000–3001.
36 M. Lail, C. M. Bell, D. Conner, T. R. Cundari, T. B. Gunnoe
and J. L. Petersen, Organometallics, 2004, 23, 5007–5020.
37 J. Oxgaard, R. P. Muller, W. A. Goddard III and R. A. Periana,
J. Am. Chem. Soc., 2004, 126, 352–363.
38 N. A. Foley, M. Lail, J. P. Lee, T. B. Gunnoe, T. R. Cundari and
J. L. Petersen, J. Am. Chem. Soc., 2007, 129, 6765–6781.
16 G.-J. Cheng, Y. Yun-Fang, L. Peng, C. Ping, S. Tian-Yu,
L. Gang, Z. Xinhao, K. N. Houk, Y. Jin-Quan and W. Yun- 39 E. E. Joslin, C. L. McMullin, T. B. Gunnoe, T. R. Cundari,
Dong, J. Am. Chem. Soc., 2014, 136, 894–897.
17 N. A. Foley, J. P. Lee, Z. F. Ke, T. B. Gunnoe and T. R. Cundari,
Acc. Chem. Res., 2009, 42, 585–597.
18 J. R. Andreatta, B. A. McKeown and T. B. Gunnoe,
J. Organomet. Chem., 2011, 696, 305–315.
19 J. C. Lewis, R. G. Bergman and J. A. Ellman, Acc. Chem. Res.,
2008, 41, 1013–1025.
20 V. Ritleng, C. Sirlin and M. Pfeffer, Chem. Rev., 2002, 102,
1731–1769.
21 L. A. Goj and T. B. Gunnoe, Curr. Org. Chem., 2005, 9, 671–
685.
M. Sabat and W. H. Myers, Organometallics, 2012, 31,
6851–6860.
40 M. Lail, B. N. Arrowood and T. B. Gunnoe, J. Am. Chem. Soc.,
2003, 125, 7506–7507.
41 N. A. Foley, Z. F. Ke, T. B. Gunnoe, T. R. Cundari and
J. L. Petersen, Organometallics, 2008, 27, 3007–3017.
42 N. A. Foley, M. Lail, T. B. Gunnoe, T. R. Cundari, P. D. Boyle
and J. L. Petersen, Organometallics, 2007, 26, 5507–5516.
43 H. V. R. Dias and C. J. Lovely, Chem. Rev., 2008, 108, 3223–
3238.
44 E. E. Joslin, B. Quillian, T. B. Gunnoe, T. R. Cundari,
M. Sabat and W. H. Myers, Inorg. Chem., 2014, 53, 6270–
6279.
22 B. A. McKeown, N. A. Foley, J. P. Lee and T. B. Gunnoe,
Organometallics, 2008, 27, 4031–4033.
23 B. A. McKeown, H. E. Gonzalez, M. R. Friedfeld, 45 T. Matsumoto, D. J. Taube, R. A. Periana, H. Taube and
T. B. Gunnoe, T. R. Cundari and M. Sabat, J. Am. Chem.
Soc., 2011, 133, 19131–19152.
24 B. A. McKeown, H. E. Gonzalez, M. R. Friedfeld,
H. Yoshida, J. Am. Chem. Soc., 2000, 122, 7414–7415.
46 T. Matsumoto, R. A. Periana, D. J. Taube and H. Yoshida,
J. Mol. Catal. A: Chem., 2002, 180, 1–18.
A. M. Brosnahan, T. B. Gunnoe, T. R. Cundari and 47 M. G. Mendoza-Ferri, C. G. Hartinger, A. A. Nazarov,
M. Sabat, Organometallics, 2013, 32, 2857–2865.
25 B. A. McKeown, H. E. Gonzalez, T. B. Gunnoe, T. R. Cundari
and M. Sabat, ACS Catal., 2013, 3, 1165–1171.
R. E. Eichinger, M. A. Jakupec, K. Severin and
B. K. Keppler, Organometallics, 2009, 28, 6260–6265.
48 N. A. Yakelis and R. G. Bergman, Organometallics, 2005, 24,
3579–3591.
26 B. A. McKeown, H. E. Gonzalez, T. Michaelos, T. B. Gunnoe,
¨
T. R. Cundari, R. H. Crabtree and M. Sabat, Organometallics, 49 K. Luhder, D. Nehls and K. Madeja, J. Prakt. Chem., 1983,
2013, 32, 3903–3913. 325, 1027–1029.
27 D. Karshtedt, A. T. Bell and T. D. Tilley, Organometallics, 50 M. A. Goodman, A. Y. Nazarenko, B. J. Casavant, Z. J. Li,
2004, 23, 4169–4171.
28 D. Karshtedt, J. L. McBee, A. T. Bell and T. D. Tilley,
Organometallics, 2006, 25, 1801–1811.
29 M. E. Cucciolito, A. D'Amora, A. Tuzi and A. Vitagliano,
Organometallics, 2007, 26, 5216–5223.
W. W. Brennessel, M. J. DeMarco, G. Long and
M. S. Goodman, Inorg. Chem., 2012, 51, 1084–1093.
51 E. E. Joslin, C. L. McMullin, T. B. Gunnoe, T. R. Cundari,
M. Sabat and W. H. Myers, Inorg. Chem., 2012, 51, 4791–
4801.
4366 | Chem. Sci., 2014, 5, 4355–4366
This journal is © The Royal Society of Chemistry 2014