Experimental and computational studies of ruthenium(II)-catalyzed addition of arene C-H bonds to olefins

Article abstract of DOI:10.1021/om049404g

Hydroarylation reactions of olefins are catalyzed by the octahedral Ru(II) complex TpRu-(CO)(NCMe)(Ph) (1) (Tp = hydridotris(pyrazolyl)borate). Experimental studies and density functional theory calculations support a reaction pathway that involves initial acetonitrile/olefin ligand exchange and subsequent olefin insertion into the ruthenium-phenyl bond, Metal-mediated C-H activation of arene to form a Ru-aryl bond with release of alkyl arene completes the proposed catalytic cycle. The cyclopentadienyl complex CpRu(PPh ₃)₂(Ph) produces ethylbenzene and styrene from a benzene/ethylene solution at 90°C; however, the transformation is not catalytic. A benzene solution of (PCP)Ru(CO)(Ph) (PCP = 2,6-(CH ₂P^t-Bu₂)₂C₆H ₃) and ethylene at 90°C produces styrene in 12% yield without observation of ethylbenzene. Computational studies (DFT) suggest that the C-H activation step does not proceed through the formation of a Ru(IV) oxidative addition intermediate but rather occurs by a concerted pathway.

Full text of DOI:10.1021/om049404g

Organometallics 2004, 23, 5007-5020
5007
Exp er im en ta l a n d Com p u ta tion a l Stu d ies of
Ru th en iu m (II)-Ca ta lyzed Ad d ition of Ar en e C-H Bon d s
to Olefin s
†
†
†
‡
Marty Lail, Christen M. Bell, David Conner, Thomas R. Cundari,
.
†
§
T. Brent Gunnoe,* and J effrey L. Petersen
Department of Chemistry, North Carolina State University,
Raleigh, North Carolina 27695-8204, Department of Chemistry, University of North Texas,
Box 305070, Denton, Texas 76203-5070, and C. Eugene Bennett Department of Chemistry,
West Virginia University, Morgantown, West Virginia 26506-6045
Received August 2, 2004
Hydroarylation reactions of olefins are catalyzed by the octahedral Ru(II) complex TpRu-
(CO)(NCMe)(Ph) (1) (Tp ) hydridotris(pyrazolyl)borate). Experimental studies and density
functional theory calculations support a reaction pathway that involves initial acetonitrile/
olefin ligand exchange and subsequent olefin insertion into the ruthenium-phenyl bond.
Metal-mediated C-H activation of arene to form a Ru-aryl bond with release of alkyl arene
completes the proposed catalytic cycle. The cyclopentadienyl complex CpRu(PPh
3 2
) (Ph)
produces ethylbenzene and styrene from a benzene/ethylene solution at 90 °C; however, the
t
transformation is not catalytic. A benzene solution of (PCP)Ru(CO)(Ph) (PCP ) 2,6-(CH
2
P -
Bu ) and ethylene at 90 °C produces styrene in 12% yield without observation of
2 2 6 3
) C H
ethylbenzene. Computational studies (DFT) suggest that the C-H activation step does not
proceed through the formation of a Ru(IV) oxidative addition intermediate but rather occurs
by a concerted pathway.
In tr od u ction
methods for C-C bond-forming reactions involving
aromatic molecules include transformations that typi-
cally incorporate aryl halides, and the preparation of
The activation of C-H bonds using transition metal
complexes has received attention due to the chemically
inert nature of the C-H bond.1 The availability of
aromatic compounds renders the development of meth-
ods for catalytic aromatic C-H functionalization an area
of significance. For example, the production of alkyl
8-14
aryl halides often requires multistep syntheses.
-4
Whereas these methodologies have been widely incor-
porated for the synthesis of small organic molecules,
C-C bond-forming reactions of aromatic molecules that
proceed through metal-mediated C-H rather than C-X
5
arenes is performed on a large scale. Simple σ-Lewis
(X ) halide) bond activation would expand the scope of
acid catalysts can be used for the synthesis of alkyl
arenes by activating olefins toward electrophilic addition
to arenes;6 however, due to the formation of species
with carbocationic character, products with linear alkyl
chains cannot be accessed with these traditional cata-
lytic methods. Linear alkyl arenes can be produced in
low yields by Friedel-Crafts alkylation of arenes using
available transformations and reduce the need for aryl
halide syntheses.
,7
Significant advances in catalytic metal-mediated C-H
2,15
activation have been achieved for aromatic systems;
however, such reactions are primarily limited to com-
pounds that possess heteroatomic functionality tethered
to the aromatic ring or carbonylation reactions of
1
-haloalkanes or by acylation of arenes followed by
16-24
heteroaromatic substrates.
Metal-catalyzed conver-
Clemmensen reduction of the carbonyl fragment. Other
(
8) Heck, R. F. In Comprehensive Organic Synthesis; Trost, B. M.,
*
To whom correspondence should be addressed. E-mail:
Fleming, I., Semmelhack, M. F., Eds.; Pergamon Press: Oxford, 1999;
Vol. 4, pp 833-863.
brent_gunnoe@ncsu.edu.
†
North Carolina State University.
University of North Texas.
West Virginia University.
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‡
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§
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0.1021/om049404g CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/10/2004

5
008 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
Ta ble 1. Ca ta lytic Ad d ition of Ar en es to Un sa tu r a ted Su bstr a tes (u n less oth er w ise n oted , r ea ction
con d ition s a r e 90 °C, 25 p si of ga s, 0.1 m ol % of 1, 4 h )
a
mol 1-1 s-1. b Turnovers observed after 24 h are given in parentheses. Trace quantities of 1,3- and 1,4-diethylbenzene are also produced.
c
d
At 250 psi of ethylene. 50 equiv based on 1, after 6 h. f 24 h. g 10 psi.
e
9-42
sion of aromatic compounds and olefins to styrenes have
olefin hydroarylation reactions.3
We now disclose a
been reported,2
5-29
and Pd or Pt systems can catalyze
combined experimental and computational study of a
Ru(II) system that activates the C-H bonds of arenes
including the details of the catalytic addition of arenes
the addition of the C-H bonds of nonfunctionalized
2
9-32
aromatic compounds across unsaturated C-C bonds.
4
3
to unsaturated C-C bonds.
Ru(III) and Au(III) complexes catalyze intra- and in-
termolecular olefin/alkyne hydroarylation.33,34 Catalytic
Resu lts a n d Discu ssion
3
5-38
borylation ofaromaticsubstrateshasalsobeen reported.
Most relevant to the present research are Ir-catalyzed
Ca ta lytic Hyd r oa r yla tion of Olefin s. At elevated
temperatures, TpRu(CO)(NCMe)(Ph) (1) (Tp ) hydri-
dotris(pyrazolyl)borate) serves as a catalyst for the
addition of arene C-H bonds across the CdC bond of
olefins. The results of several reactions are shown in
Table 1. For example, under 25 psi of ethylene pressure,
0.1 mol % of 1 in benzene (90 °C) catalyzes the formation
of ethylbenzene with 51 turnovers after 4 h. Using 0.1
mol % of 1, trace quantities of 1,3- and 1,4-diethylben-
zene are produced without detectable quantities of 1,2-
diethylbenzene. After 4 h, the rate of catalysis begins
to slow; however, 77 turnovers are achieved after 24 h
at 90 °C. Beyond this time, the production of ethylben-
zene significantly decreases. Evidence of styrene forma-
tion has not been obtained for catalytic reactions of
ethylene and benzene using between 0.1 and 1 mol %
of complex 1 when the ethylene pressure is e60 psi. A
recent computational study suggested that at high
ethylene pressures multiple insertions of ethylene will
(
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Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5009
In contrast to Lewis acid-catalyzed Friedel-Crafts
reactions, complex 1 is mildly selective for linear over
branched alkyl benzene product. For example, the
reaction of propene and benzene at 25 psi (90 °C) yields
a 1.6:1 ratio of linear propyl benzene to cumene. In
addition, the formation of trans-â-methylstyrene is
observed in nearly quantitative yield based on complex
Sch em e 1. P r op osed Ca ta lytic Cycle for th e
Ad d ition of Ben zen e to Olefin s (eth ylen e sh ow n )
1
. After 4 h at 90 °C, catalyst activity ceases. The
reaction of 1-hexene and benzene (90 °C, 1 mol % of 1)
results in the production of linear 1-phenylhexane and
branched 2-phenylhexane in a 1.7:1.0 ratio along with
formation of trans-1-phenylhex-1-ene. In contrast to an
4
2
Ir(III) system that catalyzes similar reactions, evi-
dence for the isomerization of 1-hexene to internal
olefins has not been obtained for catalysis with complex
1
. Accordingly, detectable quantities of 3-phenylhexane
are not produced in the catalytic reactions of benzene
with 1-hexene. The combination of 0.1 mol % of 1 in
benzene with isobutylene does not yield new organic
products after 24 h at 90 °C. The reaction of benzene
and acetylene with 1 mol % of 1 yields only trace
quantities of styrene after 24 h at 90 °C.
Complex 1 can also catalyze reactions of monoalkyl-
ated arenes. For example, the combination of 0.1 mol
%
of 1 with ethylbenzene and ethylene results in the
formation of 1,3-diethylbenzene and 1,4-diethylbenzene.
No evidence for the formation of the ortho disubstituted
product 1,2-diethylbenzene is observed. The rate of
conversion of ethylbenzene to diethylbenzenes is ap-
proximately 7 times slower than the rate of conversion
of benzene to ethylbenzene. For example, after 2 h at
to that directly observed in stoichiometric aromatic C-H
47
oxidative addition reactions. Heating (90 °C) a 1:1
molar mixture of 1,4-diethylbenzene and benzene in the
presence of 1 does not result in the formation of
ethylbenzene (after 24 h) as is often observed for
Friedel-Crafts catalysts. The relative rate of reaction
of benzene versus monoalkylated benzene is contrary
to observations made for most Lewis acid-catalyzed
Friedel-Crafts reactions. For example, catalytic addi-
tion of C-H bonds to ethylene using 1 as catalyst is
approximately 7 times more rapid for benzene than
ethylbenzene (based on analysis after 2 h of reaction).
Finally, the lack of catalytic activity for TpRu(CO)2(Me),
a precursor to complex 1, indicates that minor amounts
of impurities from commercial starting reagents are not
responsible for the catalysis.
9
0 °C with 0.1 mol % of 1, 43 turnovers of benzene to
ethylbenzene are observed. For the identical reaction
in ethylbenzene, after 2 h a total of approximately 6
turnovers to 1,3- and 1,4-diethylbenzene are observed.
We have previously reported that TpRu(II) complexes
catalyze radical polymerization reactions of electron-
4
5
deficient olefins. Thus, efficient catalytic hydroaryla-
tion reactions of olefins such as methyl methacrylate,
styrene, or acrylonitrile are not possible due to radical
polymerization side reactions. Attempted hydropheny-
lation of methylvinyl ketone resulted in a previously
4
6
reported thermal cyclodimerization reaction.
Simple Lewis acids are known to catalyze the net
addition of arene C-H bonds across olefin CdC bonds
by activating the olefin toward carbocationic reactivity
P r op osed Ca ta lytic Cycle. A proposed catalytic
cycle is shown in Scheme 1 using ethylene as the olefinic
substrate. The first step in the proposed cycle involves
dissociation of acetonitrile. Heating a CDCl3 solution of
6
,7
(
i.e., electrophilic addition to the arene). However, the
Ru-catalyzed reactions exhibit characteristics that are
inconsistent with classic Friedel-Crafts chemistry. The
primary evidence against the TpRu(II) complex acting
as a Friedel-Crafts catalyst is the mildly selective
production of linear over branched products in the
reactions of benzene with the R-olefins propene and
1
in the presence of CD3CN results in a decrease in the
1
intensity of the resonance ( H NMR) of the coordinated
NCCH3 and the appearance of a singlet consistent with
free NCCH3. In CD3CN at 90 °C the exchange reaction
has a half-life of approximately 15 min. The ability of
the acetonitrile ligand to undergo exchange suggests
that proposed ethylene/acetonitrile ligand exchange is
feasible under catalytic conditions (Scheme 1). The lack
of catalysis with disubstituted olefins (e.g., isobutylene)
is likely explained by steric inhibition of olefin coordina-
tion in this first step.
1
-hexene. In addition, Friedel-Crafts reactions typically
produce 1,2-dialkyl products in addition to 1,3- and 1,4-
dialkyl benzenes. TpRu(CO)(NCMe)(Ph) (1) does not
produce 1,2-diethylbenzene in detectable quantity dur-
ing the reaction of ethylene with ethylbenzene. Presum-
ably, the lack of formation of 1,2-diethylbenzene using
complex 1 as catalyst is due to steric selectivity in the
metal-mediated C-H activation step (see below) similar
Insertion of ethylene into the Ru-phenyl bond (second
step in the proposed catalytic cycle) provides a pathway
for C-C bond formation. Direct evidence for olefin
(
45) Arrowood, B. N.; Lail, M.; Gunnoe, T. B.; Boyle, P. D. Organo-
metallics 2003, 22, 4692-4698.
46) J enner, G.; Rimmelin, J .; Libs, S.; Antoni, F. Tetrahedron 1976,
2, 1107-1111.
(
(47) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1982, 104, 4240-
4242.
3

5
010 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
Sch em e 2. Or ien ta tion of th e Olefin CdC Bon d
P a r a llel to th e Ru -P h Bon d Op tim izes
d π-Ba ck -Bon d in g
F igu r e 1. Dependence of the rate of catalysis on ethylene
pressure for the addition of benzene to ethylene (0.1 mol
%
of 1, 70 °C).
Sch em e 3. Regioselectivity of Olefin In ser tion
Lik ely Dicta tes th e Lin ea r to Br a n ch ed Selectivity
for th e Hyd r op h en yla tion of r-Olefin s
insertion has been obtained from the isolation of TpRu-
CO)(NCMe)(CH2CH2Ph) (2) in approximately 50% yield
upon reaction of TpRu(CO)(NCMe)(Ph) with ethylene
250 psi) in acetonitrile (eq 1). TpRu(CO)(NCMe)(CH2-
(
(
the hydrophenylation of propene and 1-hexene catalyzed
by Ir(III) are nearly identical to that using complex 1
4
0
as catalyst. However, the regioselectivity of propene
hydrophenylation mediated by CpRu(PPh3)2(Ph) of 5:1
(linear:branched ratio, see below) indicates that the
similarity between the Ir(III) catalyst and TpRu(CO)-
CH2Ph) (2) has been independently prepared and char-
acterized (see below).
For the putative complex TpRu(CO)(Ph)(η -olefin)
2
that precedes the insertion step, the presence of the
strong π-acid CO likely results in a preferred olefin
orientation in which the CdC bond is parallel to the
Ru-phenyl bond. In the proposed olefin orientation,
which is supported by DFT calculations (see below),
π-back-bonding interactions are optimized (Scheme 2),
and the CdC bond is aligned for the subsequent
insertion step. Insertions of olefins into late transition
metal-aryl bonds have precedent. For example, the
Heck reaction involves alkene insertion into Pd-aryl
(
NCMe)(Ph) (1) is likely coincidental rather than im-
plicating that electronic factors during insertion dictate
the selectivity. Heck reactions involving the insertion
of R-olefins with alkyl substituents into Pd-Ph bonds,
as well as Ru-catalyzed Heck reactions that incorporate
acrylates, are selective for 2,1-insertion.
Ethylene insertion into the Ru-phenyl bond of TpRu-
CO)(η -H2CdCH2)(Ph) creates an open coordination site
that can bind ethylene to yield the proposed catalyst
resting state TpRu(CO)(η -H2CdCH2)(CH2CH2Ph). The
formation of butylbenzene at high ethylene pressure
(250 psi, see above) indicates that a second insertion of
ethylene is competitive with arene C-H activation un-
der conditions that increase the concentration of the
putative catalyst resting state TpRu(CO)(η -H2CdCH2)-
CH2CH2Ph). Between 15 and 60 psi of ethylene, the
rate of catalytic addition of benzene to ethylene de-
creases with increasing ethylene pressure (Figure 1),
and the inhibition of catalysis upon increasing ethylene
5
1-53
2
(
2
bonds as a key reaction step.8,9 In addition, stoichio-
metric ethylene insertion into Ru(II) phenyl bonds and
4
8-52
Ru(II)-catalyzed Heck reactions have been reported.
For R-olefins, the regioselectivity of olefin insertion
would determine the selectivity of branched versus
linear alkyl arene products, and the observed selectivity
for linear over branched alkyl arenes suggests that 2,1-
insertion (product I in Scheme 3) is slightly favored.
A computational study by Oxgaard and Goddard
suggests that the regioselectivity of R-olefin insertion
2
(
2
2
pressure is consistent with TpRu(CO)(η -H2CdCH2)(CH2-
CH2Ph) as the catalyst resting state. Deriving a rate
law for the proposed steps in catalytic C-H activation
Scheme 4, L ) ethylene) yields eq 2. If k-1[C2H4] > k2-
for TpRu(CO)(Ph)(η -H2CdC(H)Me) is controlled by
steric interactions between the alkyl group of the olefin
and pyrazolyl rings.44 The linear-to-branched ratios for
(
(
48) Faller, J . W.; Chase, K. J . Organometallics 1995, 14, 1592-
1
3
2
600.
(
47-354.
k k [Ru][C H ]
1
2
6
6
49) Ritleng, V.; Pfeffer, M.; Sirlin, C. Organometallics 2003, 22,
Rate )
(2)
k-1[C H ] + k [C H ]
2 4 2 6 6
(50) Ritleng, V.; Sutter, J . P.; Pfeffer, M.; Sirlin, C. Chem. Commun.
000.
[C6H6], then the reaction rate should exhibit an inverse
first-order dependence on ethylene concentration. Simi-
lar to the hydrophenylation of ethylene using 1 as
catalyst, an inverse dependence on ethylene pressure
(
51) Farrington, E. J .; Brown, J . M.; Barnard, C. F. J .; Rowsell, E.
Angew. Chem. Int. Ed. 2002, 41, 169-171.
52) Na, Y.; Park, S.; Han, S. B.; Han, H.; Ko, S.; Chang, S. J . Am.
Chem. Soc. 2004, 126, 250-258.
(

Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5011
Sch em e 5. Ca ta lytic Hyd r oa r yla tion of Eth ylen e
(
2 4 6 6 6 6
C H ) in a 1:1 Ra tio of C H a n d C D P r od u ces
Isotop ic Distr ibu tion s Ba sed on th e Rela tive Ra te
of C-H a n d C-D Bon d Activa tion of Ben zen e
F igu r e 2. Dependence of the rate of benzene addition to
1
-hexene on concentration of 1-hexene (0.1 mol % of 1, 70
a multiplet at 1.1 ppm due to the monodeuterated
methyl group of d6-ethylbenzene as well as a triplet of
triplets (J HH ≈ 7 Hz and J HD ≈ 1 Hz) at 2.4 ppm due to
the methylene group. In addition, approximately 1 equiv
°
C).
Sch em e 4. P r op osed P a th w a y for Ben zen e C-H
Activa tion by Tp Ru (CO)(R)(L) (R ) Me or
CH CH P h a n d L ) NCMe or eth ylen e)
(based on concentration of 1) of PhCH2CH2D is formed
2
2
due to the protio-phenyl group of the catalyst 1.
Additional evidence of the ability of {TpRu(CO)(R)}
R ) alkyl) fragments to initiate arene C-H activation
comes from the stoichiometric reaction of TpRu(CO)-
Me)(NCMe) with benzene. In the presence of acetoni-
trile, the reaction of TpRu(CO)(Me)(NCMe) with ben-
zene produces TpRu(CO)(NCMe)(Ph) (1) and methane.
The formation of methane via C-H activation of ben-
zene is confirmed by the observation of CH3D in reac-
tions performed in sealed NMR tubes using C6D6 (eq
(
(
has been reported for Ir-catalyzed formation of ethyl-
benzene at high ethylene/benzene ratios.40 Unfortu-
nately, attempts to isolate the proposed catalyst resting
state have failed. Monitoring a catalytic reaction at 20
psi of ethylene in an NMR tube reaction allows observa-
tion of a new TpRu system that exhibits resonances
consistent with the proposed resting state; however, the
presence of the catalytic precursor, ethylbenzene, and
catalyst decomposition make definitive assignment of
this complex difficult.
4
). The complex TpRu(PPh3)(NCMe)(H) has been re-
For catalytic reactions of 1-hexene/benzene using
complex 1, at low 1-hexene concentrations the rate of
catalysis increases with increasing concentration of
1
-hexene; however, the reaction rate reaches an apex
at approximately 80 equiv (based on 1) of 1-hexene.
Beyond this point, increasing the concentration of
1
(
-hexene results in a decrease in the rate of catalysis
Figure 2). These results suggest that at low concentra-
tions of 1-hexene the catalyst resting state is TpRu(CO)-
NCMe)(Ph) (1), and IR spectroscopy of a catalytic
ported to initiate H/D exchange between methane and
5
4
deuterated solvents. The rate of conversion of TpRu-
(CO)(Me)(NCMe) and benzene to complex 1 and meth-
ane is suppressed by increasing the concentration of
(
4
3
reaction in progress reveals a CO absorption identical
to that of complex 1. At higher concentrations of
1
acetonitrile. Thus, access to the coordinatively unsat-
urated fragment {TpRu(CO)(R)} (R ) alkyl) is appar-
ently necessary for benzene C-H activation (Scheme 4).
A kinetic isotope effect (KIE) was determined by
analysis of reaction products from a catalytic reaction
of ethylene in a 1:1 ratio of C6H6 and C6D6. The possible
isotopic distributions of products and their molecular
weights are shown in Scheme 5. Comparison of the
ratios of peaks due to Mw 112/111 allows a determina-
tion of the kinetic isotope effect for the carbon-hydrogen
bond-breaking step. The ratio reveals a kinetic selectiv-
ity for C-H activation over C-D activation by 2.1(1).
A control experiment using a 1:1 mixture of C6H6/
C6D6 in the presence of 1 mol % of complex 1 (in
-hexene, the catalyst resting state likely shifts to TpRu-
2
(
CO)(η -H2CdC(Bu)H)(R) (R ) hexylphenyl isomers).
The final step of the proposed catalytic cycle is Ru-
mediated C-H activation with release of alkyl benzene,
and the proposed metal-mediated C-H activation is
consistent with the assertion that the reaction proceeds
via a non-Friedel Crafts mechanism. Performing the
catalytic addition of C6D6 to ethylene (C2H4) using
complex 1 results in the formation of d5-PhCH2CH2D
as indicated by H NMR spectroscopy and mass spec-
trometry (eq 3). For example, the H NMR spectrum of
the catalyst solution (C6D6) after 12 h at 70 °C reveals
1
1
(
53) Heck, R. F. In Organic Reactions; Duaben, W. G., Ed.; J ohn
(54) Ng, S. M.; Lam, W. H.; Mak, C. C.; Tsang, C. W.; J ia, G.; Lin,
Z.; Lau, C. P. Organometallics 2003, 22, 641-651.
Wiley and Sons: New York, 1982; Vol. 27, pp 345-390.

5
012 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
the absence of ethylene) at 90 °C reveals isotopic
scrambling in the benzene. For example, after 2 h the
ratio of molecular weight 78/79 (C6H6/C6H5D) decreased
by 30%. During the same time period, the ratio of C6D6/
C6D5H undergoes an analogous change. These results
indicate that the Ru(II) phenyl complex 1 catalyzes
isotopic scrambling between C6H6 and C6D6 (the abun-
dance of other mixed isotopomers also increases). How-
ever, monitoring the ratios of peaks due to molecular
weights 78/79 (C6H6/C6H5D) and 84/85 (C6D5H/C6D6)
during the catalytic reaction reveals that isotope scram-
bling between C6H6 and C6D6 under ethylene pressure
(25 psi) is negligible. The significant reduction in the
extent of isotopic scrambling between C6H6 and C6D6
in the presence of ethylene indicates that monitoring
the molecular weights of ethylbenzene products under
catalytic conditions provides a reliable method to ap-
proximate the KIE for the catalytic reaction.
2 2
F igu r e 3. ORTEP of TpRu(CO)(NCMe)(CH CH Ph) (2)
(30% probability with hydrogen atoms omitted). Selected
bond lengths (Å): Ru-N7, 2.020(3); Ru-C13, 2.115(4); Ru-
N1, 2.062(3); Ru-N3, 2.138(3); Ru-N5, 2.191(3); Ru-C12,
It is anticipated that the kinetic isotope effect for the
catalytic reaction should be similar to the kinetic isotope
effect for benzene C-H activation by TpRu(CO)(Me)-
1
1
.819(4); N7-C10, 1.128(5); C13-C14, 1.474(6); C14-C15,
.521(7). Selected bond angles (deg): Ru-C13-C14, 119.0(3);
Ru-N7-C10, 170.6(3); Ru-C12-O1, 179.2(4); C12-Ru-
C13,90.85(16);N1-Ru-N3,84.95(12);N1-Ru-N5,86.71(12);
N3-Ru-N5, 83.90(11); C13-Ru-N7, 88.94(14).
(NCMe) to produce methane and TpRu(CO)(Ph)(NCMe).
The reaction of TpRu(CO)(Me)(NCMe) in a 1:1 molar
mixture of C6H6 and C6D6 in a gastight NMR tube at
9
0 °C for 30 min produces resonances for both CH4 and
Ta ble 2. Selected Cr ysta llogr a p h ic Da ta a n d
Collection P a r a m eter s for
CH3D (eq 5). Integration of these two resonances reveals
2 2
Tp Ru (CO)(NCMe)(CH CH P h ) (2)
empirical formula
fw
C20H22BN7ORu
488.33
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/c
11.6082(9)
12.2077(10)
15.9446(14)
90
92.715(2)
90
2257.0(3)
4
R, deg
â, deg
γ, deg
a kinetic isotope effect of 2.5(5). The large deviation is
due, in part, to the poor signal-to-noise that results from
the necessity of analyzing the reaction before significant
isotopic scrambling. GC-MS of the reaction solution
after 30 min of reaction reveals that approximately 10%
of the C6H6 and the C6D6 have undergone isotopic
scrambling. Although analysis at longer time periods
would improve signal-to-noise of the resonances due to
methane, isotopic scrambling would complicate analysis
of the KIE. Even though the isotopic scrambling after
3
V (Å )
Z
Dcalcd, g cm-
R1, wR2 (I > 2σ(I))
GOF
3
1.437
0.0455, 0.1054
1.020
1
nances at 3.38 and 1.93 ppm ( H NMR), and 1H/ C
13
NMR spectra consistent with Cs molecular symmetry.
Oxidative removal of a carbonyl ligand from complex 3
upon addition of Me3NO in refluxing acetonitrile yields
the monocarbonyl product TpRu(CO)(NCMe)(CH2CH2-
Ph) (2) (eq 7). The conversion of 3 to 2 is characterized
3
0 min of reaction does not allow a quantitative deter-
mination of the KIE, the KIEs for the stoichiometric
benzene C-H activation by TpRu(CO)(NCMe)(Me) and
the catalytic hydrophenylation of ethylene are identical
within deviation.
Stu d y of â-Hyd r id e Elim in a tion . The previously
reported dicarbonyl complex [TpRu(CO)2(THF)][PF6]
reacts with PhCH2CH2MgCl to yield TpRu(CO)2(CH2-
CH2Ph) (3) (eq 6).55 Complex 3 has been characterized
by the disappearance of the CO stretching absorptions
due to 3 and the appearance of a single CO absorption
-
1
at 1917 cm . Complex 2 has been characterized by a
single-crystal X-ray diffraction study. The ORTEP of 2
is displayed in Figure 3, and data collection parameters
are listed in Table 2. The structure reveals an asym-
metric complex with an approximately octahedral co-
ordination sphere. The Ru-alkyl carbon bond distance
is 2.115(4) Å.
1
13
by IR and H and C NMR spectroscopy with νCO )
-
1
2
025 and 1954 cm (IR spectrum), methylene reso-
(55) Sørlie, M.; Tilset, M. Inorg. Chem. 1995, 34, 5199-5204.

Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5013
Sch em e 6. P r op osed Rea ction P a th w a y for th e
Sch em e 7. â-Hyd r id e Elim in a tion Tr a n sfor m a tion s
Con ver sion of Tp Ru (CO)(NCMe)(CH
2
CH
2
P h ) (2) to
for Tp Ru (CO)(L)(R) System s
Tp Ru (CO)(NCMe)(Cl) (4)
styrene in catalytic ethylene hydrophenylation reactions
to reversible â-hydride elimination. In CDCl3, TpRu-
Consistent with the proposed catalytic pathway
Scheme 1), the reaction of complex 2 with C6D6 at 90
2
(CO)(H)(η -styrene) is likely trapped by the chlorinated
(
°
(
solvent; however, attempts to prepare and isolate TpRu-
C results in the production of PhCH2CH2D and TpRu-
2
1
(CO)(H)(η -styrene) have failed. The observations of
CO)(NCMe)(Ph-d5) (1-d5) as determined by H NMR
trans-1-phenylhex-1-ene and trans-â-methylstyrene dur-
ing the hydrophenylation of 1-hexene and propene,
respectively, are likely attributable to more facile dis-
sociation of the disubstituted olefins that are formed
from â-hydride elimination (Scheme 7).
spectroscopy (eq 8). In addition, the combination of 1
Rea ction s of Cp Ru (P P h 3)2(P h ) a n d (P CP )Ru -
(
CO)(P h ). To study the generality of the catalytic
reactions, we have begun to synthesize and explore the
catalytic properties of closely related Ru(II) systems. It
has previously been reported that CpRu(PPh3)2(Me) (Cp
)
cyclopentadienyl) undergoes an intramolecular C-H
activation at 90 °C to yield the orthometalated product
2
56,57
mol % of 2 in benzene under 25 psi (90 °C) results in
the catalytic production of ethylbenzene.
CpRu(PPh )(κ -P,C-Ph PC H ) and methane.
CpRu-
3
2
6
4
(PPh ) (Me) is isoelectronic with TpRu(CO)(NCMe)(Me),
3
2
The proposed reaction mechanism for the addition of
benzene to ethylene involves the formation of the
coordinatively unsaturated {TpRu(CO)(CH2CH2Ph)} sys-
tem that would likely be susceptible to a â-hydride
3 2
and loss of phosphine from CpRu(PPh ) (Me) complex
provides the coordinatively unsaturated complex {CpRu-
(PPh )(Me)}, which is isoelectronic to the proposed
3
TpRu(II) species that initiates arene C-H activation.
2
elimination reaction to produce TpRu(CO)(H)(η -sty-
At 70 °C, CpRu(PPh ) (Me) reacts with benzene to yield
3
2
rene); however, styrene formation is not observed during
catalytic hydrophenylation reactions of ethylene at
ethylene pressures up to 60 psi. The lack of observation
of styrene indicates that either â-hydride elimination
is not kinetically competitive or that dissociation of
3 2
the previously reported phenyl complex CpRu(PPh ) -
(Ph) and methane (eq 9). The formation of methane
5
8
2
styrene from TpRu(CO)(H)(η -styrene) has a substantial
activation barrier (i.e., â-hydride elimination is revers-
ible). We sought to explore â-hydride elimination from
the putative intermediate {TpRu(CO)(CH2CH2Ph)} in
more detail using TpRu(CO)(NCMe)(CH2CH2Ph) (2).
Heating (70 °C) a CDCl3 solution of TpRu(CO)(NCMe)-
is confirmed by resonances consistent with CH3D upon
reaction of CpRu(PPh3)2(Me) with C6D6 in a sealed NMR
tube. Dissolution of CpRu(PPh3)2(Ph) in benzene under
25 psi of ethylene at 90 °C results in the production of
ethylbenzene; however, the reaction is not catalytic, as
only 0.12 equiv of ethylbenzene is produced per equiva-
lent of ruthenium. The formation of styrene in 31% yield
is also observed for the CpRu(II) system (eq 10). The
(
CH2CH2Ph) results in the quantitative production (by
H NMR spectroscopy) of styrene, CHDCl2, and TpRu-
CO)(NCMe)(Cl) (4) after 30 min. Complex 4 has been
1
(
independently prepared upon reaction of HCl with
TpRu(CO)(NCMe)(Me) (Scheme 6). The formation of 4
likely occurs via â-hydride elimination to produce
2
{
TpRu(CO)(H)(η -styrene)} followed by dissociation of
styrene and conversion of the Ru-H bond to a Ru-Cl
bond upon reaction with CDCl3 (regardless of reaction
order; Scheme 6). The rapid conversion of complex 2 to
complex 4 indicates that â-hydride elimination is kineti-
cally facile, and we attribute the lack of observation of
more facile production of styrene by the CpRu system
compared with the TpRu system might be explained by

5
014 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
Sch em e 8. Mech a n ism for Ben zen e C-H Activa tion by (Ta b)Ru (NCH)(Me) w ith Ca lcu la ted F r ee En er gy
Differ en ces Given in k ca l/m ol
the ability of Cp to undergo a ring slip to provide a
on complex 5. Although the source of the lack of activity
for olefin hydroarylation using 5 has not been defini-
tively determined, the steric bulk due to the presence
pathway for associative ligand exchange after â-hydride
5
3
elimination. Thus, an η to η ring-slip would provide
an open coordination site for binding of ethylene (or
phosphine), and subsequent dissociation of styrene is
likely to be facile.59 Although the production of olefin
accounts for a portion of the decomposition of the CpRu
t
of four Bu groups as well as the potential for a trans
orientation of coordinated olefin and the phenyl ligand
could contribute to the poor activity. Consistent with
the former, the coordination of Lewis bases (e.g., am-
monia) to the (PCP)Ru(CO)(R) framework is particularly
3
1
complex, P NMR spectroscopy indicates that the fate
of the remaining Ru (∼70%) is dispersed between
multiple uncharacterized complexes. Thus, the CpRu-
6
0
weak.
(PPh3)2(Ph) system apparently decomposes under cata-
lytic conditions. A benzene solution of CpRu(PPh3)2(Ph)
under 25 psi of propene at 70 °C produces less than
stoichiometric quantities of cumene and n-propylben-
zene. Using 5 mol % of CpRu(PPh3)2(Ph), an ap-
proximate 5:1 molar ratio of n-propylbenzene to cumene
is produced (eq 11).
Com p u ta tion a l Stu d ies. In concert with the experi-
mental studies, the catalytic hydroarylation of ethylene
has been studied at the B3LYP/SBK(d) level of theory.
As a model of the full tris(pyrazolyl)borate (Tp) ligand,
-
the tris(azo)borate (Tab) ligand, [HB(-NdNH)3] , was
The reaction of (PCP)Ru(CO)(OTf) (PCP ) 2,6-(CH2Pt-
used. In previous research, Tab was shown to reproduce
the structure and energetics of the full Tp models for
Bu2)2C6H3) with PhLi allows the isolation of (PCP)Ru-
(
6
1
CO)(Ph) (5) (eq 12). We anticipated complex 5 as a
C-H activation potential energy surfaces. In addition,
the parent nitrile HCN was substituted for acetonitrile.
The C-H activation event was broken down into three
steps: benzene coordination, activation of benzene with
elimination of methane, and coordination of HCN to the
resulting phenyl complex (Scheme 8). Oxgaard and
potential catalyst for the hydroarylation reactions since
it has similar features to complex 1. For example, com-
plex 5 possesses a tridentate (six-electron donating)
monoanionic ligand (cf. the ligand Tp) as well as Ru-
CO and Ru-Ph bonds. In addition, an open coordination
site for olefin binding is available since complex 5 is
coordinatively and electronically unsaturated. Complex
(56) Lehmkuhl, H.; Grundke, J .; Mynott, R. Chem. Ber. 1983, 116,
1
59-175.
5
differs from 1 in that the tridentate ligand is coordi-
nated in a meridonal fashion (versus facial for the Tp
(57) Lehmkuhl, H.; Bellenbaum, M.; Grundke, J .; Mauermann, H.;
Kr u¨ ger, C. Chem. Ber. 1988, 121, 1719-1728.
(58) Lehmkuhl, H.; Bellenbaum, M.; Grundke, J . J . Organomet.
Chem. 1987, 330, C23-C26.
ligand) and the metal center is a more proficient π-base
νCO ) 1900 cm- for 5 compared with 1935 cm for 1).
1
-1
(
(
59) O’Connor, J . M.; Casey, C. P. Chem. Rev. 1987, 87, 307-318.
A 0.5 mol % solution of 5 in benzene under 25 psi of
ethylene pressure at temperatures from 90 to 150 °C
failed to produce detectable quantities of ethylbenzene;
however, styrene was observed in 10-15% yield based
(60) Conner, D.; J ayaprakash, K. N.; Cundari, T. R.; Gunnoe, T. B.
Organometallics 2004, 23, 2724-2733.
(61) Bergman, R. G.; Cundari, T. R.; Gillespie, A. M.; Gunnoe, T.
B.; Harman, W. D.; Klinckman, T. R.; Temple, M. D.; White, D. P.
Organometallics 2003, 22, 2331-2337.

Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5015
Sch em e 9. Ca lcu la ted En er getics for Eth ylen e Coor d in a tion to (Ta b)Ru (CO)(P h ), Eth ylen e In ser tion in to
th e Ru -P h Bon d , a n d â-Hyd r id e Elim in a tion w ith En er gy Differ en ces Given in k ca l/m ol
Goddard have recently communicated a computational
study of the catalytic hydrophenylation of ethylene by
TpRu(CO)(NCMe)(Ph); in cases where Oxgaard and
Goddard studied similar reactions, computed enthalpies
were comparable to those obtained with the smaller
model employing Tab and HCN instead of Tp and
MeCN, respectively.44
Ben zen e C-H Activa tion . The displacement of
HCN by benzene is endergonic by 16.1 kcal/mol. Given
a calculated free energy of binding of HCN to {(Tab)-
Ru(Me)(CO)} of 14.9 kcal/mol, this corresponds to bind-
ing free energy to {(Tab)Ru(Me)(CO)} of +1.2 kcal/mol
for benzene and is consistent with the anticipated weak
binding of a π-heteroaromatic system to a closed-shell,
6
d ML5 fragment. Subsequent C-H activation of ben-
zene to produce methane and {(Tab)Ru(CO)(Ph)} is
exergonic by 6.6 kcal/mol with a calculated free energy
barrier of 21.2 kcal/mol. The coordination of nitrile to
F igu r e 4. B3LYP/SBK(d) calculated structure of (Tab)-
Ru(CO)(Ph)(η -ethylene). Atoms of the Tab ligand are
shown in wire frame for clarity.
2
{
(Tab)Ru(CO)(Ph)} is favorable by -13.7 kcal/mol, and
the overall transformation of (Tab)Ru(CO)(Me)(NCH)
and benzene to (Tab)Ru(CO)(Ph)(NCH) and methane is
exergonic by 4.2 kcal/mol. If the overall entropy change
for benzene C-H activation by (Tab)Ru(CO)(Me)(NCH)
is considered negligible, using a bond dissociation
energy of methane of 105 and 113 kcal/mol for benzene
indicates that the Ru-phenyl bond is approximately 12
kcal/mol stronger than the Ru-methyl bond.6
is oriented approximately parallel to the Ru-Ph bond.
Combining the calculated olefin binding free energies
with the HCN dissociation energies yields a free energy
for HCN/ethylene exchange of -3.3 kcal/mol. The more
favorable coordination of ethylene is consistent with the
suggestion that TpRu(CO)(CH2CH2Ph)(η -ethylene) is
the catalyst resting state for the hydrophenylation of
ethylene. The calculated ethylene insertion barrier is
2
2
Eth ylen e In ser tion . In the proposed catalytic cycle,
dissociation of acetonitrile produces {TpRu(CO)(Ph)},
1
5
8.6 kcal/mol, and the insertion process is exergonic by
.5 kcal/mol.
and binding of ethylene yields the intermediate TpRu-
Agostic In ter a ction s a n d Restin g Sta te. The
2
(
CO)(Ph)(η -ethylene). Subsequent ethylene insertion
â-phenethyl complex, (Tab)Ru(CO)(CH2CH2Ph), which
is the product of ethylene insertion into the Ru-Ph bond
of {(Tab)Ru(CO)Ph}, has a weak π-interaction involving
the phenyl substituent, as evidenced by the calculated
short distances between the ruthenium and ipso carbon
provides a route for C-C bond formation, and these
reaction steps were also studied using DFT with {(Tab)-
Ru(CO)(Ph)} (Scheme 9). The free energy of ethylene
binding to (Tab)Ru(CO)(Ph) is -10.4 kcal/mol. The
2
minimized structure of (Tab)Ru(CO)(Ph)(η -ethylene) is
(Ru-C ) 2.75 Å) as well as one of the ortho carbons
(Ru-C ) 2.61 Å). The minimized structure of (Tab)Ru-
(CO)(CH2CH2Ph) is shown in Figure 5. This conforma-
shown in Figure 4. Consistent with predictions based
on dπ back-bonding (see above), the ethylene CdC bond
tion leads to a Ru-CR-Câ-Cipso dihedral angle of -32°.
An alternative conformation with this dihedral angle
(
62) Luo, Y.-R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: Boca Raton, 2003.

5
016 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
Sch em e 10. Tw o P ossible P a th w a ys for
Ru (II)-Med ia ted C-H Activa tion
reports of Ir(III) systems that activate C-H bonds have
prompted speculation on the mechanism of the C-H
bond-breaking step of late transition metal systems for
which oxidative addition would yield an unusually high
F igu r e 5. B3LYP/SBK(d) calculated structure of (Tab)-
Ru(CO)(CH CH Ph). Atoms of the Tab ligand are shown
in wire frame for clarity.
2
2
4
1,67-73
formal oxidation state.
the C-H activation pathway for catalysis using complex
, DFT calculations have been employed for benzene
To assist efforts to discern
equal to 180° was constructed, and geometry optimized
at the same level of theory, resulting in a â-agostic (RuH
1
)
1.93 Å; RuCâ ) 2.44 Å; RuHCâ ) 100°) interaction,
II
C-H activation by the {(Tab)Ru (CO)(Me)} fragment.
Oxidative addition to form the Ru(IV) complex {(Tab)-
Ru (CO)(Me)(H)(Ph)} (followed by reductive elimina-
which was calculated to be only 1.3 kcal/mol higher than
the π-bonded conformation. The binding of ethylene to
IV
{
(Tab)Ru(CO)(CH2CH2Ph)} to form the proposed resting
tion of methane) and a non-oxidative addition reaction
with simultaneous C-H bond-breaking and bond-form-
ing have been considered (Scheme 10).
2
state (Tab)Ru(CO)(CH2CH2Ph)(η -ethylene) is calcu-
lated to be close to thermoneutral with ∆G ) +0.8 kcal/
mol.
Multiple pathways were investigated for the C-H
activation step including oxidative addition of a C-H
bond to {(Tab)Ru(CO)Me} (A), oxidative addition of a
methane C-H bond to {(Tab)Ru(CO)(Ph)} (B), and non-
oxidative addition metathesis of a C-H bond of benzene
with the Ru-CH3 bond of {(Tab)Ru(CO)Me} (C) (Scheme
â-Hyd r id e Elim in a tion . The formation of (Tab)Ru-
CO)(H)(η -styrene) by â-H elimination from the most
2
(
stable conformation of (Tab)Ru(CO)(CH2CH2Ph) has a
calculated free energy barrier of 4.2 kcal/mol and is
exergonic by 2.9 kcal/mol (Scheme 9). Given the likely
assumption that a â-agostic minimum is the immediate
precursor to the â-hydride elimination pathway, the free
energy barrier is reduced and the driving force is
enhanced by the calculated 1.3 kcal/mol energy differ-
ence between the π-coordinated and â-agostic forms of
1
1). Several different starting geometries were inves-
tigated for each of the proposed transition states. In all
cases, the transition states collapsed to C (the non-
oxidative addition transition state). The identity of the
transition state was confirmed by calculation of the
intrinsic reaction coordinate along the imaginary fre-
quency, the primary motion of which corresponded to
transfer of the transannular hydrogen from the methyl
to the aryl carbon. The transition state geometry for
C-H activation of benzene is depicted in Figure 6. The
transannular hydrogen is only slightly closer to the ipso
carbon (1.49 Å) than the methyl carbon (1.52 Å). The
ruthenium carbon distances in the transition state (Ru-
{
(Tab)Ru(CO)(CH2CH2Ph)}. The calculations are con-
sistent with the experimental observation that â-hy-
dride elimination is kinetically facile and reversible for
TpRu(CO)(NCMe)(CH2CH2Ph) (2).
Isola tion of th e Tr a n sition Sta te for C-H Acti-
va tion . Detailed studies of stoichiometric C-H activa-
tions by transition metal centers have revealed two
common reaction pathways. Oxidative addition reac-
tions dominate the chemistry of late transition metal
complexes in low oxidation states, whereas σ-bond
(67) Tellers, D. M.; Yung, C. M.; Arndtsen, B. A.; Adamson, D. R.;
0
Bergman, R. G. J . Am. Chem. Soc. 2002, 124, 1400-1410.
metathesis transformations occur when d transition
(
(
68) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1972.
69) Alaimo, P. J .; Bergman, R. G. Organometallics 1999, 18, 2707-
metal complexes initiate C-H activation.3
,63-66
Recent
2
717.
(
(
63) J ones, W. D.; Feher, F. J . Acc. Chem. Res. 1989, 22, 91-100.
64) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
(70) Hinderling, C.; Feichtinger, D.; Plattner, D. A.; Chen, P. J . Am.
Chem. Soc. 1997, 119, 10793-10804.
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203-219.
(71) Su, M.-D.; Chu, S.-Y. J . Am. Chem. Soc. 1997, 119, 5373-5383.
(72) Strout, D. L.; Zaric, S.; Niu, S.; Hall, M. B. J . Am. Chem. Soc.
1996, 118, 6068-6069.
(65) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51-
5
6.
(
(73) Oxgaard, J .; Muller, R. P.; Goddard, W. A., III; Periana, R. A.
J . Am. Chem. Soc. 2004, 126, 352-363.
66) Rothwell, I. P. Polyhedron 1985, 4, 177-200.

Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5017
Pt-H distance of 1.99 Å.75 Calculations on the transition
state of benzene C-H activation by (acac)2Ir(CH2CH2-
Ph) reveals an Ir-H distance of 1.58 Å, and Goddard
et al. have differentiated this transition state (in which
there is a metal-hydrogen interaction) from a σ-bond
metathesis transition state using the label oxidative
7
3
hydrogen migration.
Su m m a r y a n d Con clu sion s
TpRu(CO)(NCMe)(Ph) (1) catalyzes the hydroaryla-
tion of olefins through a pathway that likely involves
olefin binding and insertion into the Ru-Ph bond
followed by metal-mediated C-H activation. Reactions
that incorporate R-olefins are mildly selective for pro-
duction of linear over branched alkyl benzene products.
Although the yields are poor, the selectivity for the
hydrophenylation of propene using CpRu(PPh3)2(Ph)
(5:1 linear-to-branched ratio) indicates that ligand
architecture can be used to control the regioselectivity
of olefin insertion. For reactions that incorporate eth-
ylene, â-hydride eliminations to ultimately yield free
styrene are not competitive with hydrophenylation, and
this observation is attributed to reversible â-hydride
elimination under catalytic conditions. The reversibility
is likely a result of a relatively strong Ru-styrene bond
due to the metal π-basicity with suppression of associate
F igu r e 6. B3LYP/SBK(d) calculated transition state for
C-H activation of benzene by (Tab)Ru(Me)(CO) (atoms of
the Tab ligand are shown in wire frame for clarity). View
of calculated transition state illustrates the “out-of-plane”
position of the hydrogen atom undergoing transfer.
Sch em e 11. P a th w a ys for C-H Activa tion
In vestiga ted by DF T Stu d ies
exchange due to the coordinative saturation of TpRu-
2
(
CO)(H)(η -styrene). In contrast, following insertion of
an R-olefin into the Ru-Ph bond, â-hydride elimination
and olefin dissociation are competitive with catalytic
hydrophenylation of the olefin. The similarities between
catalytic olefin hydrophenylation using TpRu(CO)(Ph)-
(NCMe) or Ir(III) phenyl complexes reported by Periana
et al. are noteworthy, and computational/experimental
studies indicate the likelihood of closely related reaction
pathways including the C-H activation step.4
However, evidence for â-hydride elimination and olefin
dissociation has not been obtained for the Ir(III) sys-
tems, whereas such reactions have been observed with
the Ru(II) systems reported herein. Similar to our
experimental results with Ru(II), calculations by Ox-
gaard and Goddard suggest that â-hydride elimination
0,41,73
7
3
for Ir(III) is facile and reversible.
Cipso ) 2.23 Å; Ru-CMe ) 2.31 Å) are only slightly longer
DFT studies suggest that the C-H activation steps
of the catalytic cycles do not proceed through a Ru(IV)
oxidative addition intermediate, and the Tp ligand may
deter processes that lead to seven-coordinate Ru(IV)
(ca. 5-6%) than ground state bond lengths.
Although the calculations indicate that the pathway
for benzene C-H activation does not involve an oxida-
tive addition pathway (i.e., no Ru(IV) intermediate was
found), the calculated distance between the Ru metal
center and hydrogen (1.72 Å) in the C-H activation
transition state is relatively short. Calculations by
Oxgaard and Goddard reveal a Ru-H distance of 1.61
Å in the transition state for benzene C-H activation
by TpRu(CO)(CH2CH2Ph).44 Closely related results have
been reported from calculations to probe the mechanism
of C-H activation for TpM(PH3)(Me) (M ) Fe or Ru)
complexes in which the authors suggested that the
reaction pathway is intermediate between oxidative
addition and σ-bond metathesis processes.74 Computa-
tional studies of methane activation by Pt(H2O)Cl2
indicate a similar four-center transition state with a
6
1
64,76,77
systems. As previously discussed,
for C-H ac-
tivations that proceed without an oxidative addition
intermediate a distinction can be made between σ-bond
metathesis and electrophilic aromatic substitution. The
calculated transition state for benzene C-H activation
by {(Tab)Ru(CO)(CH )} reveals that the hydrogen atom
3
undergoing transfer to the methyl ligand is out of the
aromatic plane (Figure 6). The hydrogen atom is cal-
culated to be 0.87 Å removed from the “best” plane of
the aromatic ring with a H-C-Ru angle of 50.3°, and
the “out-of-phase” transannular hydrogen could be
(
75) Siegbahn, P. E. M.; Crabtree, R. H. J . Am. Chem. Soc. 1996,
118, 4442-4450.
76) Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw, J . E. Orga-
(
nometallics 1987, 6, 1219-1226.
(77) Chesnut, R. W.; J acob, G. G.; Yu, J . S.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1991, 10, 321-328.
(
74) Lam, W. H.; J ia, G.; Lin, Z.; Lau, C. P.; Eisenstein, O. Chem.
Eur. J . 2003, 9, 2775-2782.

5
018 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
indicative of a sp2 to sp3 rehybridization of the ipso
carbon that would be consistent with an electrophilic
substitution pathway. Alternatively, the out-of-plane
hydrogen could reflect progress along the reaction
coordinate and incipient Ru-C bond formation with the
arene. The distinction between oxidative addition, σ-bond
metathesis, oxidative hydrogen migration, and electro-
philic aromatic substitution could have important im-
plications for reactivity, and in order to probe this issue
in more detail, we are currently studying the electronic
influence of substituents on the arene.
position), 6.20 (1H, t, Tp CH 4 position), 6.11 (1H, Tp CH 4
position), 3.03 (2H, m, Ru-CH
NCCH ), 1.55 (2H, m, Ru-CH CH
δ): 207.0 (Ru-CO), 149.5 (ipso of Ru-phenyl), 143.5, 142.1,
40.0, 135.4, 134.7, 134.6, 128.2 (ortho, meta, and para of
phenyl, Tp 3 and 5 positions), 124.7 (Ru-NCCH ), 105.7, 105.4,
05.3 (Tp 4 positions), 42.6 (Ru-CH CH Ph), 17.3 (Ru-CH CH
Ph), 4.3 (Ru-NCCH ). Anal. Calcd for C20 ORu: C 49.07,
H 4.53, N 20.04. Found: C 49.00, H 4.59, N 20.13.
Tp Ru (CO) (CH CH P h ) (3). A 50 mL round-bottom flask
was charged with 0.375 g of [TpRu(CO) THF][PF ] (0.643
2 2 6 5
CH C H ), 2.26 (3H, s, Ru-
1
3
1
3
2
2 6 5 3
C H ). C{ H} NMR (CDCl ,
1
3
1
2
2
2
2
-
3
H22BN
7
2
2
2
2
6
mmol) and 25 mL of benzene to yield a heterogeneous slurry.
While stirring, 5 equiv of phenethylmagnesium chloride (1.0
M in THF) were added dropwise to the benzene solution. Upon
addition of the phenethylmagnesium chloride a homogeneous
solution formed along with a color change from pale blue to
honey gold. Analysis by IR spectroscopy revealed a change in
Exp er im en ta l Section
Gen er a l Meth od s. All procedures were performed under
inert atmosphere of dinitrogen in a Vacuum Atmospheres
glovebox or using standard Schlenk techniques. The glovebox
atmosphere was maintained by periodic nitrogen purges and
-
1
CO absorption frequency from νCO ) 2069 and 2006 cm to
-
1
ν
CO ) 2025 and 1954 cm . Excess Grignard reagent was
monitored by an oxygen analyzer {O
reactions}. Benzene, THF, and hexanes were purified by reflux
over sodium followed by distillation. Pentane and methylene
2
(g) < 15 ppm for all
deactivated upon addition of distilled water. The organic layer
was separated from the aqueous layer. The aqueous layer was
then extracted with methylene chloride (3 × 50 mL). The
organic fractions were combined, and the volatiles were
removed under reduced pressure to yield a golden brown oil.
chloride were refluxed over P
Acetonitrile was dried over CaH
Benzene-d , CD Cl , CD CN, and CDCl
three freeze-pump-thaw cycles and stored over 4 Å molecular
2
O
5
followed by distillation.
and collected via distillation.
were degassed by
2
-1 1
IR (THF): νCO 2025, 1954 cm . H NMR (C
7.25, 7.22, 7.20, 7.18, 7.12 (11 H, overlapping d’s and t’s, Tp
CH 3 and 5 position, Ru-CH CH C H ), 5.71 (1H, t, Tp CH 4
6 6
D , δ): 7.36, 7.32,
6
2
2
3
3
1
13
sieves. H and C NMR spectra were recorded on a Varian
Mercury 400 MHz or a Varian Mercury 300 MHz spectrometer.
Resonances due to the Tp ligand are listed by chemical shift
and multiplicity only (all coupling constants for the Tp ligand
are 2 Hz). Gas chromatography was performed on a Hewlett-
Packard 5890 GC using either a J &W SE-30 or an HP-5
capillary column (30 m × 0.25 mm HP-5 column with 0.25 µm
film thickness) and an FID detector. Chromatograms were
produced using either a Hewlett-Packard 3396A integrator or
Perkin-Elmer TotalChrom 6.2 software. GC-MS was per-
formed using a HP GCD system with a 30 m × 0.25 mm HP-5
column with 0.25 µm film thickness. Lecture bottles of ethylene
2
2
6
5
position), 5.68 (2H, t, Tp CH 4 position), 3.38 (2H, m,
1
3
1
Ru-CH
2
CH
2
C
6
H
5
), 1.93 (2H, m, Ru-CH
2 2 6 5
CH C H ). C{ H}
NMR (C
6
D
6
, δ): 201.97 (CO), 147.6 (ipso of phenyl), 143.6,
142.2, 135.0, 134.6, 128.5, 128.3, 122.5 (phenyl and Tp 3/5
position), 106.2, 105.9 (Tp 4 position), 44.5 (Ru-CH CH ),
18.8 (Ru-CH CH ).
2
2 6 5
C H
2
2 6 5
C H
Tp Ru (CO)(NCMe)(Cl) (4). TpRu(CO)(NCMe)(Me) (0.150
g, 0.377 mmol) was dissolved in 30 mL of methylene chloride.
HCl (0.377 mL, 1.0 M in diethyl ether, 0.377 mmol) was added
dropwise to the stirring solution at room temperature. Evolu-
tion of a gas was observed. An IR spectrum of the reaction
solution revealed the disappearance of the CO absorption at
(99.5%) and propylene (99.0%), 1-hexene, and decane were
-
1
-1
obtained from Sigma Aldrich Chemical Co. and used as
received. Ethylene (99.5%) was also received in a gas cylinder
from MWSC High-Purity Gases and used as received. All IR
spectra were acquired using a Mattson Genesis II FTIR as thin
films on KBr plates or as solutions. Pressure tube reactions
were performed in either an ACG Lab-Crest glass pressure
tube with Swagelock hardware or a Parr Instruments high-
pressure reactor. Cumene was obtained from Sigma Aldrich
1919 cm and the appearance of an absorption at 1968 cm .
The volatiles were removed under reduced pressure to give a
pale yellow solid. The solid was washed with 10 mL of pentane
and collected via vacuum filtration through a fine-porosity frit
1
(0.111 g, 0.265 mmol, 71%). H NMR (CDCl
3
, δ): 8.08, 7.74,
7.72, 7.68, 7.52 (each 1H, each a d, Tp CH 3/5 position), 6.33,
6.20, 6.16 (each 1H, each a t, Tp CH 4 position), 2.36 (3H, s,
1
3
1
Ru-NCCH
144.5, 141.8, 136.1, 135.8, 134.9 (Tp 3 and 5 positions), 123.0
(Ru-NCCH ), 106.7, 106.6, 106.2 (Tp 4 positions), 4.5 (Ru-
5 12
NCCH ). Anal. Calcd for C12 13BClN ORu(C H )0.15 (Note: A
3 3
). C{ H} NMR (CDCl , δ): 201.3 (Ru-CO), 145.1,
and dried over CaH
2
prior to use. The preparation, isolation,
5
5
and characterization of [TpRu(CO)
2
(THF)][PF
6
], TpRu(CO)-
3
4
3
43
57
(
NCMe)(Ph) (1), TpRu(CO)(NCMe)(Me), CpRu(PPh
3
)
2
(Me),
3
H
7
5
8
1
CpRu(PPh
3
)
2
(Ph), and (PCP)Ru(CO)(OTf) have been previ-
H NMR spectrum of the analysis sample indicates the
6
0
ously reported.
Tp Ru (CO)(NCMe)(CH
Ph) (3) was dissolved in 20 mL of acetonitrile, and 1 equiv of
Me NO (based on amount of [TpRu(CO) (THF)][PF ], 1.800
presence of pentane in a 1/6.7 molar ratio with complex 4; a
1
CH
2
P h ) (2). TpRu(CO)
2
(CH
2
CH
2
-
H NMR spectrum of 4 is included in the Supporting Informa-
2
tion): C 35.66, H 3.47, N 22.83. Found: C, 35.70, H, 3.29, N,
22.75.
3
2
6
mmol, 0.1352 g) was added to the solution. The solution was
refluxed for 1 h. IR spectroscopy revealed the disappearance
(P CP )Ru (CO)(P h ) (5). In a 100 mL round-bottom flask,
(PCP)Ru(CO)(OTf) (0.1619 g, 0.2409 mmol) was dissolved in
approximately 50 mL of THF. Phenyllithium (0.265 mmol, 1.8
M in ether) was added dropwise using a microsyringe. Upon
addition of phenyllithium, a change in color from orange to
dark red was observed. The volatiles were removed under
reduced pressure, and the resulting solid was dissolved in
approximately 30 mL of cyclopentane. After filtration through
a fine-porosity frit the volatiles were removed under reduced
pressure. The resulting dark red solid was dried in vacuo and
collected (0.0663 g, 0.1105 mmol, 46%). IR (solution cell
-
1
of absorptions at νCO ) 2025 and 1954 cm and the appear-
-
1
ance of a single CO absorption at νCO ) 1917 cm . The
volatiles were removed under reduced pressure to give a light
yellow residue. The residue was dissolved in toluene and eluted
on a column of neutral alumina. Two bands were observed,
the first being dark yellow and the second being pale yellow.
The second band was isolated. Toluene was removed by
evacuation, yielding a pale yellow residue. Hexanes were
added to the residue. After stirring overnight, a white solid
-
1
1
3
was isolated by vacuum filtration (0.153 g, 0.313 mmol, 17%).
2 2
THF): νCO 1900 cm . H NMR (CD Cl , δ): 7.46 (1H, d, J HH
1
3
H NMR (CDCl
3
, δ): 7.73, 7.67, 7.60, 7.54 (6H total 1:3:1:1
) 8 Hz, phenyl ortho), 7.22 (2H, d, J HH ) 8 Hz, PCP 3 and 5
3 3
3
ratio, each a d, Tp CH 3/5 position), 7.34 (2H, d, J HH ) 8 Hz
position), 7.02 (1H, t, J HH ) 8 Hz, PCP 4), 6.58 (1H, d, J HH
3
3
phenyl ortho), 7.27 (2H, t, J HH ) 8 Hz, phenyl meta), 7.13
) 8 Hz, phenyl ortho), 6.50 (1H, t, J HH ) 8 Hz, phenyl meta
3
3
(
1H, t,
J
HH ) 8 Hz, phenyl para), 6.24 (1H, t, Tp CH 4
or para), 6.37 (1H, t, J HH ) 7 Hz, phenyl meta or para), 6.19

Ru(II)-Catalyzed Addition of C-H Bonds to Olefins
Organometallics, Vol. 23, No. 21, 2004 5019
2
(
1H, t, 3J HH ) 8 Hz, phenyl meta or para), 3.74 (2H, dt, J HH
leaving a yellow residue. A portion of the residue was dissolved
2
1
)
)
(
17 Hz, J PH ) 8 Hz, P-CH
9 Hz, CH ), 1.03-0.976 (36H, m, PCP Bu). C{ H} NMR-
, δ): 208.9 (t, J PC ) 9 Hz, CO), 192.0 (t, J PC ) 6 Hz,
2
), 3.55 (2H, dt, J HH ) 17 Hz, J PH
in C
6
D
6
, and a H NMR spectrum was acquired. The spectrum
t
13
1
2
revealed two diamagnetic TpRu complexes including ap-
proximately 50% of TpRu(CO)(NCMe)(CH CH Ph) (2). The
2
2
C
6
D
6
2
2
2
RuC), 157.4 (t, J PC ) 10 Hz, Ph ipso), 151.9 (vt, N ) 10 Hz,
PCP Ar or Ph), 146.0, 140.7, 125.9, 125.0 (each a s, each a
PCP or Ph with one overlap), 121.0 (vt, N ) 16 Hz, PCP Ar or
Ph), 119.4 (s, PCP or Ph), 38.2 (vt, N ) 15 Hz, PC), 37.7 (vt,
second product is observed only at high ethylene pressures and
remains uncharacterized.
Con ver sion of Cp Ru (P P h
A thick-walled screw-cap pressure tube was charged with 0.204
g of CpRu(PPh (Me) (0.280 mmol) and 15 mL of benzene. The
3 2 3 2
) (Me) to Cp Ru (P P h ) (P h ).
N ) 20 Hz, CH
vt, N ) 5 Hz, CH
for C31 Ru: C, 62.08, H, 8.07. Found: C, 63.01, H, 8.10
2
), 36.6 (vt, N ) 14 Hz, PC), 31.3, 29.4 (each a
3 2
)
31 1
3
6 6
). P{ H} NMR (C D , δ): 77.4. Anal. Calcd
tube was placed in an oil bath and heated to 70 °C for 48 h.
The reaction vessel was removed from the oil bath, cooled to
room temperature, and purged into an inert atmosphere
glovebox. The volatiles were removed under reduced pressure,
leaving a dark amber residue. Washing of the residue with
hexanes resulted in the formation of solid that was collected
H
48OP
2
1
13
(
Note: H and C NMR spectra revealed a small amount of
1
13
cyclopentane in the analysis sample; H and C NMR spectra
of 5 have been included in the Supporting Information).
Ca ta lytic Rea ction s. A representative catalytic reaction
is described. TpRu(CO)(NCMe)(Ph) (1) (0.021 g, 0.046 mmol)
was dissolved in 4.1 mL (0.0456 mol) of benzene. To the
homogeneous solution was added decane (0.269 mL, 1.38
mmol) as an internal standard. The solution was placed in a
thick-walled glass reaction vessel and charged with 25 psi of
ethylene pressure. The tube was then placed in an oil bath
heated to 90 °C. Periodically the tube was removed from the
oil bath and plunged into an ice bath. A 0.1 mL aliquot of the
reaction solution was removed under a purge of dinitrogen,
and the tube was quickly returned to the oil bath and ethylene
pressure was restored. Samples (∼1 µL) were removed from
the aliquot and analyzed by GC-FID. With application of the
appropriate correction factor (determined from regression plots
of at least three sets of standard samples), the peak areas of
the sample injection were used with the internal standard to
calculate product yields.
1
via vacuum filtration. Analysis of the solid by H NMR
spectroscopy revealed clean formation of CpRu(PPh ) (Ph).
3 2
X-r a y Diffr a ct ion St u d y of Tp R u (CO)(NCMe)(CH
CH P h ) (2). Complex 2 was recrystallized by slow evaporation
of a diethyl ether solution. A pale yellow crystal of TpRu(CO)-
NCMe)(CH CH Ph) was covered in the perfluoropolyether
2
-
2
(
2
2
PFO-XR75 (Lancaster) and sealed under nitrogen in a glass
capillary. The crystal was optically aligned on the four-circle
of a Siemens P4 diffractometer equipped with a graphite
monochromatic crystal, a Mo KR radiation source (λ ) 0.71073
Å), and a SMART CCD detector held at 5.084 cm from the
crystal. Four sets of 20 frames each were collected using the
ω-scan method with a 10 s exposure time. Integration of these
frames followed by reflection indexing and least-squares
refinement produced a crystal orientation matrix for the
monoclinic unit cell. Data collection consisted of the measure-
ment of a total of 1650 frames in five different runs covering
a hemisphere of data. The program SMART (version 5.6) was
used for diffractometer control, frame scans, indexing, orienta-
tion matrix calculations, least-squares refinement of cell
Deter m in a tion of Kin etic Isotop e Effect. TpRu(CO)-
NCMe)(Ph) (1) (0.0511 g, 0.111 mmol) was dissolved in an
equimolar solution of C (0.49 mL, 5.5 mmol) and C (0.53
(
6
H
6
6 6
D
mL, 5.5 mmol). The solution was placed in a glass thick-walled
pressure tube and placed under 25 psi ethylene. The pressur-
ized tube was placed in an oil bath heated to 90 °C. After 2 h,
the pressure tube was removed from the oil bath and plunged
into an ice bath. Aliquots were removed under a purge of
dinitrogen and analyzed by GC/MS. Triplicate comparisons of
the scaled isotopic abundance of fragment 111 to 112 (adjusted
to account for fragmentation) were used to determine the
kinetic isotope effect of 2.1(1). Repeating these experiments
demonstrated reproducibility.
Kin etic Stu d y of Ca ta lytic Rea ction s. A sample deter-
mination of the rate of the formation of ethylbenzene catalyzed
by TpRu(CO)(NCMe)(Ph) (1) at 70 °C is given. A stock solution
consisting of 0.069 g (0.149 mmol) of TpRu(CO)(NCMe)(Ph)
1) in 13.33 mL (0.149 mol) of benzene was made. Decane
0.087 mL, 0.45 mmol) was added as an internal standard.
Stock solution (2.0 mL) was added to a thick-walled glass
pressure tube. The tube was placed under 15 psi ethylene
pressure and heated to 70 °C in an oil bath. Periodically, the
tube was removed from the oil bath and plunged into an ice
bath. An aliquot of the solution was removed under a purge
of dinitrogen, and the tube was placed under ethylene pressure
and quickly returned to the oil bath. The aliquot was analyzed
in triplicate by GC/FID.
78
parameters, and the data collection. All 1650 crystallographic
raw data frames were read by the program SAINT (version
5
/6.0) and integrated using 3D profiling algorithms. The
resulting data were reduced to produce a total of 15 685
reflections and their intensities and estimated standard devia-
tions. An absorption correction was applied using the SADABS
routine available in SAINT. The data were corrected for
Lorentz and polarization effects as well as any crystal decay.
Data preparation was carried out by using the program
XPREP, which gave 5140 unique reflections (Rint ) 4.58%) with
indices -15 e h e 15, -15 e k e 15, -20 e l e 19. The
1
monoclinic space group was determined to be P2 /c (No. 14).
The structure was solved by a combination of direct methods
(
(
78
and Fourier methods with the use of SHELXTL6.1. Idealized
positions for the hydrogen atoms were included as fixed
contributions using a riding model with isotropic temperature
factors set at 1.2 (aromatic protons) or 1.5 (methyl protons)
times that of the adjacent carbon. The position of the B-H
proton was refined with a fixed isotropic temperature factor
set at 1.2 times that of the boron atom. The positions of the
methyl hydrogen atoms were optimized by a rigid rotating
group refinement with idealized tetrahedral angles. Full-
matrix least-squares refinement, based on the minimization
Tp Ru (CO)(NCMe)(Me) in C
sphere, a screw-cap NMR tube was loaded with 0.020 g (0.050
mmol) of TpRu(CO)(NCMe)(Me) in 0.5 mL of C . The tube
6
D
6
. Under nitrogen atmo-
2
2 2
-1
2
2
2
of ∑w
i
|F
o
- F
c
| , with w
i
) [σ (F
o
) + (0.0627P) + 0.0000P],
2
2
where P ) (Max(F
o
, 0) + 2F
c
)/3, converged to give final
6
D
6
discrepancy indices of R1 ) 0.0455, wR2 ) 0.1054 for 3462
reflections with I > 2σ(I). The goodness of fit (GOF) value was
was placed in an oil bath heated to 90 °C. After 1 h of heating,
the tube was removed from the bath and allowed to cool to
room temperature. A H NMR spectrum was acquired reveal-
1
.020. A correction for secondary extinction was not applied.
1
The maximum and minimum residual electron density peaks
ing the production of CH
CO)(NCMe)(Ph-d ).
Rea ction of Tp Ru (CO)(NCMe)(P h ) w ith Eth ylen e in
Aceton itr ile. An acetonitrile solution (∼35 mL) of TpRu(CO)-
NCMe)(Ph) (1) (0.118 g, 0.256 mmol) was placed under 250
3
D (0.14 ppm, 1:1:1 triplet) and TpRu-
3
in the final difference Fourier map were 1.063 and -0.558 e/Å ,
(
5
respectively. The linear absorption coefficient, atomic scatter-
ing factors, and anomalous dispersion corrections were calcu-
(
(78) SMART, SAINT, and XPREP programs are part of the Bruker
psi of ethylene. The solution was heated to 90 °C for a period
of 6 h. The volatiles were removed under reduced pressure,
AXS crystallographic software package for single-crystal data collec-
tion, reduction, and preparation.

5
020 Organometallics, Vol. 23, No. 21, 2004
Lail et al.
lated from values from the International Tables for X-ray
Crystallography.79
analyses. The energy Hessian was calculated at all stationary
points to characterize them as minima (no imaginary frequen-
cies) or transition states (one and only one imaginary fre-
quency). The quoted energies include zero-point, enthalpy, and
entropic corrections determined from unscaled vibrational
frequencies calculated at the B3LYP/SBK(d) level of theory.
All energetic determinations were done at 298.15 K and 1 atm.
Geometries of all isolated stationary points are given as
Supporting Information.
Com p u ta tion a l Meth od s. Quantum calculations were
8
0
carried out using the Gaussian 98 package. The B3LYP
hybrid functional was employed for all calculations.81 Heavy
atoms were described with the Stevens relativistic effective
core potentials (ECPs) and valence basis sets (VBSs).8
2,83
The
valence basis sets of main group elements were augmented
with a d polarization function. This ECP/VBS combination,
termed SBK(d), has been validated for the calculation of a wide
variety of transition metal properties in previous studies.8
4,85
Ack n ow led gm en t. T.R.C. acknowledges support by
the Office of Energy Sciences, Office of Science, United
States Department of Energy, for support of this re-
search through Grant No. DE-FG02-97ER14811. T.B.G.
acknowledges support by the Office of Basic Energy
Sciences, Office of Science, United States Department
of Energy, for support of this research through Grant
No. DE-FG02-03ER15490 and the Alfred P. Sloan
Foundation (Research Fellowship). M.L. acknowledges
GlaxoSmithKline for support through a graduate re-
search fellowship. Prof. Bruce Novak kindly provided
the use of a high-pressure Parr reactor. Mass spectra
were obtained at the Mass Spectrometry Facility for
Biotechnology (NCSU). Partial funding for the facility
was obtained from the North Carolina Biotechnology
Center and the National Science Foundation. The
authors also wish to thank the National Science Foun-
dation (NSF) for support of C.M.B. under the Chemistry
Research Experiences for Undergraduates (REU) Pro-
gram (CHE-0097485).
As a model of the full (tris-pyrazolyl)borate (Tp) ligand, the
-
tris(azo)borate (Tab) ligand, [HB(-NdNH)
3
] , was used. In
previous research, Tab was shown to faithfully reproduce the
structure and energetics of the full Tp models for C-H
6
1
activation potential energy surfaces.
All stationary points were fully optimized without symmetry
constraint. Several conformations of the different ligands were
investigated by torsion about the appropriate metal-ligand
bonds; the lowest energy conformers found are used in the
(79) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, 1974; Vol. IV, p 55 (Present distributor, D. Reidel,
Dordrecht).
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Su p p or tin g In for m a tion Ava ila ble: Cartesian coordi-
nates for all optimized minima are given. Complete tables of
crystal data, collection and refinement data, atomic coordi-
(
81) Becke, A. D. J . Chem. Phys. 1993, 98, 5648-5652.
(82) Stevens, W. J .; Basch, H.; Krauss, M. J . Chem. Phys. 1984, 81,
nates, bond distances and angles, and anisotropic displacement
6
026-6033.
83) Stevens, W. J .; Krauss, M.; Basch, H.; J asien, P. G. Can. J .
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84) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
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1
coefficients for TpRu(CO)(NCMe)(CH
2
13
CH
2
Ph) (2). H NMR
(
spectra of complexes 4 and 5 and a C NMR spectrum of
complex 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
(
OM049404G