Thermal Activation of Hydrocarbon C-H Bonds Initiated by a Tungsten Allyl Complex

Article abstract of DOI:10.1021/ja037076q

Gentle thermolysis of the allyl complex, Cp*W(NO)(CH ₂CMe₃)(η³-H₂CCHCMe₂) (1), at 50 °C in neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane, mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of Cp*W(NO)-(CH₂SiMe₃)(η ³-H₂CCHCMe₂) (2), Cp*W(NO)(CH ₂C₆H₃-3,5-Me₂)(η ³-H₂CCHCMe₂) (3), and Cp*W(NO)-(C ₆H₅)(η³-H₂CCHCMe₂) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes indicate an inherent preference of the system for the activation of stronger arene sp² C-H bonds. For example, C-H bond activation of p-xylene leads to the formation of Cp*W(NO)(CH₂C ₆H₄-4-Me)(η³-H₂-CCHCMe ₂) (5) (26%) and Cp*W(NO)(C₆H ₃-2,5-Me₂)(η³-H₂CCHCMe ₂) (6) (74%). Mechanistic and labeling studies indicate that the transient C-H-activating intermediates are the allene complex, Cp*W(NO)(η²-H₂C=C=CMe₂) (A), and the η²-diene complex, Cp*W(NO)(η²-H ₂C=CHC(Me)=CH₂) (B). Intermediates A and B react with cyclohexene to form Cp*W(NO)(η³-CH ₂C(2-cyclohexenyl)CMe₂)(H) (18) and Cp*W(NO)-(η ³-CH₂CHC)(Me)CH₂C_βH(C ₄H₈)C_αH (19), respectively, and intermediate A can be isolated as its PMe₃ adduct, Cp*W(NO)(PMe₃)(η²-H₂C=C=CMe ₂) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-2-ene results in the formation of a species that undergoes η³ → η¹ isomerization of the dimethylallyl ligand following the initial C-H bond-activating step to yield Cp*W(NO)(η³-CMe₂CMeCH₂)(η ¹-CH₂CHCMe₂) (21). Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H bond-activation reactions. For instance, 1 in cyclohexane converts to Cp*W(NO)(η³-C₆H₉)(H) (22) with dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric complexes, Cp*W(NO)(η³-C ₇H₁₁)(H) (23a,b). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been established by X-ray crystallographic analyses.

Full text of DOI:10.1021/ja037076q

Published on Web 11/14/2003
Thermal Activation of Hydrocarbon C-H Bonds Initiated by a
Tungsten Allyl Complex
Stephen H. K. Ng, Craig S. Adams, Trevor W. Hayton, Peter Legzdins,* and
Brian O. Patrick
Contribution from the Department of Chemistry, UniVersity of British Columbia,
VancouVer, British Columbia, Canada V6T 1Z1
Received July 4, 2003; E-mail: legzdins@chem.ubc.ca
Abstract: Gentle thermolysis of the allyl complex, Cp*W(NO)(CH2CMe3)(η3-H2CCHCMe2) (1), at 50 °C in
neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates
that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane,
mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of Cp*W(NO)-
(CH2SiMe3)(η3-H2CCHCMe2) (2), Cp*W(NO)(CH2C6H3-3,5-Me2)(η3-H2CCHCMe2) (3), and Cp*W(NO)-
(C6H5)(η3-H2CCHCMe2) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes
indicate an inherent preference of the system for the activation of stronger arene sp2 C-H bonds. For
example, C-H bond activation of p-xylene leads to the formation of Cp*W(NO)(CH2C6H4-4-Me)(η3-H2-
CCHCMe2) (5) (26%) and Cp*W(NO)(C6H3-2,5-Me2)(η3-H2CCHCMe2) (6) (74%). Mechanistic and labeling
studies indicate that the transient C-H-activating intermediates are the allene complex, Cp*W(NO)(η2-
H2CdCdCMe2) (A), and the η2-diene complex, Cp*W(NO)(η2-H2CdCHC(Me)dCH2) (B). Intermediates A
and B react with cyclohexene to form Cp*W(NO)(η3-CH2C(2-cyclohexenyl)CMe2)(H) (18) and Cp*W(NO)-
(η3-CH2CHC)(Me)CH2CâH(C4H8)CRH (19), respectively, and intermediate A can be isolated as its PMe3
adduct, Cp*W(NO)(PMe3)(η2-H2CdCdCMe2) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-
2-ene results in the formation of a species that undergoes η3 f η1 isomerization of the dimethylallyl ligand
following the initial C-H bond-activating step to yield Cp*W(NO)(η3-CMe2CMeCH2)(η1-CH2CHCMe2) (21).
Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H
bond-activation reactions. For instance, 1 in cyclohexane converts to Cp*W(NO)(η3-C6H9)(H) (22) with
dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric
complexes, Cp*W(NO)(η3-C7H11)(H) (23a,b). All new complexes have been characterized by conventional
spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been
established by X-ray crystallographic analyses.
Introduction
select systems has been significantly advanced toward efficient,
catalytic functionalizations.2
Interest in C-H bond activations at transition-metal centers
continues unabated because these processes hold the promise
of leading to efficient and catalytic methods for the selective
conversion of hydrocarbon feedstocks into functionalized
organic compounds.1 Considerable progress in this regard has
been made in the past 20 years, and numerous metal-containing
complexes have been discovered to effect intermolecular C-H
bond activations, often selectively and under relatively mild
conditions.2 Notable examples include (1) late transition-metal
complexes that oxidatively add C-H linkages to the metal
center, (2) transition-metal, lanthanide, and actinide complexes
that facilitate C-H activation via M-C σ-bond metathesis, and
(3) early- to mid-transition-metal complexes that add C-H
bonds across MdN and MdC linkages. A fundamental under-
standing of the discrete C-H activation processes has been
acquired for many of these complexes, and the chemistry of
Our contributions to this area of chemistry began with our
recent discovery that Cp*M(NO)(hydrocarbyl)2 complexes (Cp*
) η5-C5Me5) of molybdenum and tungsten exhibit hydrocarbyl-
dependent thermal chemistry.3 Thus, gentle thermolysis of
appropriate Cp*M(NO)(hydrocarbyl)2 precursors (M ) Mo, W)
results in loss of hydrocarbon and the transient formation of
16-electron organometallic complexes such as Cp*M(NO)-
(alkylidene), Cp*M(NO)(η2-acetylene), and Cp*M(NO)(η2-
benzyne). These intermediates first effect the single activation
of hydrocarbon C-H bonds intermolecularly via the reverse of
the transformations by which they were generated. Some of the
new product complexes formed in this manner are stable and
may be isolated. Others are thermally unstable under the
experimental conditions employed and react further to effect
double or triple C-H bond activations of the hydrocarbon
substrates. We now report the thermal chemistry of the related
(1) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 2437.
(2) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507 and references therein.
(3) Pamplin, C. B.; Legzdins, P. Acc. Chem. Res. 2003, 36, 223.
9
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Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
Scheme 1
Figure 1. Solid-state molecular structure of Cp*W(NO)(CH2SiMe3)(η3-
H2CCHCMe2) (2) with 50% probability thermal ellipsoids shown. Selected
interatomic distances (Å) and angles (deg): W1-N1 ) 1.760(5), W1-
C11 ) 2.182(6), W1-C12 ) 2.433(6), W1-C13 ) 2.874(6), W1-C16 )
2.217(6), C11-C12 ) 1.46(1), C12-C13 ) 1.348(9), N1-O1 ) 1.237(7),
W1-N1-O1 ) 170.7(5), C11-C12-C13 ) 124.9(7), W1-C11-C12 )
81.2(4), C12-C13-C14 ) 125.6(7), C14-C13-C15 ) 113.5(7).
tungsten allyl complex, Cp*W(NO)(CH2CMe3)(η3-H2CCHCMe2)
(1), which loses neopentane at 50 °C and forms an allene
complex and an η2-diene complex as reactive intermediates.
Both of these intermediates effect a variety of hydrocarbon C-H
bond activations, some of which are without precedent in the
chemical literature. To the best of our knowledge, this work
constitutes the first confirmed examples of metal-allene and
metal-diene species functioning in this manner. A portion of
this work has been communicated previously.4
The dimethylallyl ligand in 2 adopts an endo configuration
in the solid state (Figure 1). This configuration is identical to
that extant in its solution structure as determined by selective
NOE NMR spectroscopic data10 and is probably a manifestation
of minimization of the intramolecular steric interactions between
the methyls on the allyl ligand and the rapidly rotating methyl
groups of the trimethylsilylmethyl ligand. Another interesting
feature is the orientation of the dimethylallyl ligand so that the
most substituted carbon atom of its three-carbon allyl backbone,
that is, C(13), is situated trans to the NO ligand. This orientation
can be attributed to the electronic asymmetry at the tungsten
center resulting from the different acceptor characteristics of
the NO and the alkyl ligands.11 This electronic asymmetry also
results in markedly different W-C(allyl) distances which range
from 2.182(6) Å for W-C(11) to 2.874(6) Å for W-C(13) in
2. Finally, the substituted allyl ligand is also oriented so as to
maximize the π-interaction between the nonbonding orbital of
the allyl ligand and the metal center.12
Results and Discussion
Single C-H Bond Activations Initiated by 1. (A) Activa-
tion of Tetramethylsilane, Mesitylene, and Benzene. Scheme
1 summarizes the C-H bond activations discovered during the
course of this study that afford one principal organometallic
product following exclusive reaction with a single C-H bond
of the hydrocarbon substrate.
Thermolysis of 1 in neat tetramethylsilane at 50 °C for 6 h
results in the quantitative formation of the alkyl-allyl complex,
Cp*W(NO)(CH2SiMe3)(η3-H2CCHCMe2) (2). Complex 2 is
thermally stable in tetramethylsilane under these conditions, and
the known bis(alkyl) complex, Cp*W(NO)(CH2SiMe3)2, is not
formed on prolonged reaction times. A single-crystal X-ray
crystallographic analysis has been performed on 2, and the
resulting ORTEP diagram is shown in Figure 1. The solid-state
molecular structure of 2 exhibits a strong σ-π distortion of
the dimethylallyl ligand as evidenced by its long C(11)-C(12)
(1.46(1) Å) and short C(12)-C(13) (1.348(9) Å) linkages,
suggestive of more single- and double-bond character, respec-
tively.5 NMR data indicate that this distortion persists in
solutions. Thus, the 13C{1H} NMR spectrum of 2 in C6D6
exhibits a resonance at 101.9 ppm (allyl-CH) characteristic of
an sp2-like carbon and a signal at 39.3 ppm (allyl-CH2)
indicative of an sp3-like terminal carbon. Other chiral transition-
metal allyl complexes display similar spectroscopic and solid-
state properties that are reflective of σ-π distortions of this
type.6-9
The thermal reaction of 1 in mesitylene results only in the
formation of Cp*W(NO)(CH2C6H3-3,5-Me2)(η3-H2CCHCMe2)
(3) (Scheme 1). The exclusive activation of benzylic sp3 C-H
bonds during this transformation is similar to the behavior
exhibited by other previously studied Cp*W(NO)-containing
(7) Frohnapfel, D. S.; White, P. S.; Templeton, J. L. Organometallics 1997,
16, 3737.
(8) Villanueva, L. A.; Ward, Y. D.; Lachicotte, R.; Liebeskind, L. S.
Organometallics 1996, 15, 4190.
(9) Adams, R. D.; Chodosh, D. F.; Faller, J. W.; Rosan, A. M. J. Am. Chem.
Soc. 1979, 101, 2570.
(10) Direct evidence for endo- versus exo-allyl conformations using selective
NOE NMR spectroscopy is sometimes not available, and logical inferences
must be made to ascertain the solution structure. For example, irradiation
of the signal due to the central allyl H atom leading to an NOE enhancement
of the Cp* methyl H atoms signal is direct evidence for an exo
configuration. However, its absence, and hence the implication of an endo
configuration, must be confirmed by irradiation of the trans Me group signal
that should exhibit an NOE enhancement of the Cp* ring signal.
(11) Faller, J. W.; DiVerdi, M. J.; John, J. A. Tetrahedron Lett. 1991, 32, 1271.
(12) Schilling, B. E. R.; Hoffman, R.; Faller, J. W. J. Am. Chem. Soc. 1979,
101, 592.
(4) Ng, S. H. K.; Adams, C. S.; Legzdins, P. J. Am. Chem. Soc. 2002, 124,
9380.
(5) Bent, H. A. Chem. ReV. 1961, 61, 275.
(6) Ipaktschi, J.; Mirzaei, F.; Demuth-Eberle, G. J.; Beck, J.; Serafin, M.
Organometallics 1997, 16, 3965.
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A R T I C L E S
Ng et al.
Figure 2. Solid-state molecular structure of Cp*W(NO)(CH2C6H3-3,5-
Me2)(η3-H2CCHCMe2) (3) with 50% probability thermal ellipsoids shown.
Selected interatomic distances (Å) and angles (deg): W1-N1 ) 1.753(4),
W1-C20 ) 2.187(5), W1-C21 ) 2.391(5), W1-C22 ) 2.961(5), W1-
C11 ) 2.239(4), N1-O1 ) 1.240(5), C20-C21 ) 1.454(8), C21-C22 )
1.365(6), C11-C12 ) 1.493(6), W1-N1-O1 ) 171.1(4), W1-C20-C21
) 79.3(3), W1-C11-C12 ) 120.5(3), C20-C21-C22 ) 125.5(5), C21-
C22-C24 ) 123.5(4), C23-C22-C24 ) 115.2(4).
Figure 3. Solid-state molecular structure of Cp*W(NO)(C6H5)(η3-H2-
CCHCMe2) (4) with 50% probability thermal ellipsoids shown. Selected
interatomic distances (Å) and angles (deg): W1-N1 ) 1.762(3), W1-C7
) 2.218(4), W1-C8 ) 2.363(4), W1-C9 ) 2.768(4), W1-C1 ) 2.186(3),
N1-O1 ) 1.224(4), C7-C8 ) 1.439(6), C8-C9 ) 1.365(5), W1-N1-
O1 ) 169.5(3), W1-C1-C6 ) 121.4(2), C7-C8-C9 ) 124.8(4), W1-
C7-C8 ) 77.3(2), C8-C9-C10 ) 124.3(4), C10-C9-C11 ) 113.5(3).
systems,13 and it is a result of the mesitylene methyl groups
hindering access of the tungsten center to the arene’s sp2 C-H
bonds. The ORTEP diagram of the solid-state molecular
structure of 3 is shown in Figure 2.
are formed in an approximate 1:3 ratio which persists even after
3 times the normal reaction time of 6 h. The distribution of
products indicates a tendency of this system to preferentially
The exo conformation adopted by the dimethylallyl ligand
in 3 in the solid state is consistent with its apparent solution
structure as deduced from selective NOE NMR spectroscopic
data.10 This conformation is in contrast to the endo configuration
observed in solution for complex 1 and the solution- and solid-
state molecular structures of 2. Theoretical calculations per-
formed on similar asymmetric allyl transition-metal complexes
reveal that there is a minimal energy difference between the
idealized endo and exo conformers,12 thus suggesting that the
two different orientations observed for complexes 1, 2, and 3
are the result of intramolecular steric factors operative in the
various molecules. As outlined for 2 (vide supra), the solid-
state molecular structure of 3 (Figure 2) also exhibits the
customary intramolecular metrical parameters reflective of the
electronic asymmetry existing at the metal center. Indeed, these
features are common to all of the chiral allyl nitrosyl complexes
characterized structurally during this work.
The thermal reaction of 1 in benzene affords exclusively the
phenyl dimethylallyl product, Cp*W(NO)(C6H5)(η3-H2CCHCMe2)
(4) (Scheme 1). A single-crystal X-ray crystallographic analysis
has been performed to confirm the identity of the final
organometallic product, and the ORTEP diagram of 4 is shown
in Figure 3. Not surprisingly, the interatomic distances and
angles of 4 are comparable to those extant in the solid-state
molecular structures of 2 and 3.
activate aromatic C-H bonds over benzylic ones, a trend
commonly seen with many C-H-activating transition-metal
complexes.13 The customary rationalization of this selectivity
involves the thermodynamics of the bond-breaking and bond-
forming steps. Although the bond-dissociation energy for an
sp2 C-H bond is greater than that for an sp3 C-H bond, the
resulting metal-carbon interaction is stronger for a M-C(sp2)
linkage than for a M-C(sp3) bond.15-19
The thermolyses of 1 in m- or o-xylene result in similar
transformations. The thermal reaction with m-xylene affords
three products, Cp*W(NO)(CH2C6H4-3-Me)(η3-H2CCHCMe2)
(7), Cp*W(NO)(C6H3-2,4-Me2)(η3-H2CCHCMe2) (8), and Cp*W-
(NO)(C6H3-3,5-Me2)(η3-H2CCHCMe2) (9) (eq 2). Not surpris-
ingly, the ratio of the final products is comparable to that
observed for the benzylic- and aromatic-activated complexes 5
and 6 (see eq 1).
(B) Activations of Xylenes and Toluene. The thermal
reaction of 1 in p-xylene at 50 °C results in the formation of
two organometallic products in essentially quantitative yields
(eq 1). The product generated upon activation of a benzylic sp3
C-H bond of p-xylene, Cp*W(NO)(CH2C6H4-4-Me)(η3-H2-
CCHCMe2) (5), and that from the activation of an aromatic sp2
C-H bond, Cp*W(NO)(C6H3-2,5-Me2)(η3-H2CCHCMe2) (6),14
(14) A single-crystal X-ray crystallographic analysis of 6 has been performed.
Its solid-state structural features are similiar to those exhibited by other
p-xylene aryl C-H-activated tungsten nitrosyl complexes.
(15) Johansson, L.; Ryan, O. B.; Romming, C.; Tilset, M. J. Am. Chem. Soc.
2001, 123, 6579.
(16) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J. E. J.
Am. Chem. Soc. 1987, 109, 1444.
(17) Jones, W. D.; Hessell, E. T. J. Am. Chem. Soc. 1993, 115, 554.
(18) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91.
(19) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984, 106, 1650.
(13) Adams, C. S.; Legzdins, P.; Tran, E. Organometallics 2002, 21, 1474.
9
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Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
ments that the pure benzyl products of conversions 1-4 do not
convert to the aryl products under the experimental conditions
employed. Consistently, the isolated aryl products also do not
convert to the benzyl products. However, we have been unable
to isolate any one of the individual aryl products to determine
whether it interconverts with its aryl isomers. All attempts at
isolation afford a mixture of aryl products in the proportions
specified in eqs 1-4.
The thermal reaction of 1 with o-xylene also affords three
organometallic products, Cp*W(NO)(CH2C6H4-2-Me)(η3-H2-
CCHCMe2) (10), Cp*W(NO)(C6H3-2,3-Me2)(η3-H2CCHCMe2)
(11), and Cp*W(NO)(C6H3-3,4-Me2)(η3-H2CCHCMe2) (12) (eq
3).
Mechanistic Investigations of Single C-H Bond Activa-
tions Initiated by 1. The thermolysis of 1 in benzene-d6 at 50
°C (the temperature employed throughout these studies) results
in the elimination of neopentane and the formation of several
new organometallic complexes, the isomeric Cp*W(NO)-
(C6D5)(η3-CH2CDCMe2) (4a-d6), Cp*W(NO)(C6D5)(η3-CH2-
CHCMe(CH2D)) (4b-d6), and Cp*W(NO)(C6D5)(η3-CH2CHC-
(CH2D)Me) (4c-d6). Reactant 1 is consumed via a pseudo first-
order process with an observed rate constant of 2.2(1) × 10-4
s-1 (R2 ) 0.999). The magnitude of this rate constant is
comparable to that found for the related rate-limiting loss of
neopentane from Cp*W(NO)(CH2CMe3)2 at 70 °C.20
Complexes 4a-c-d6 have been identified from their 2H{1H}
and 1H NMR spectroscopic data which also provide the product
ratios shown in Scheme 2. Deuterium incorporation into the
dimethylallyl ligands of the final products in the manner shown
suggests that reactive intermediates such as an allene or a diene
complex are generated via hydrogen abstraction from the
dimethylallyl ligand in 1 to form a transition-state entity that
eventually eliminates neopentane. The activation of a benzene
C-D bond could then proceed via the microscopic reverse
processes to afford the final labeled allyl phenyl complexes.
However, an independently prepared sample of the trans-diene
complex, Cp*W(NO)(η4-trans-H2CdCHC(Me)dCH2) (17), is
unreactive in benzene-d6 under the customary thermolysis
conditions. Consequently, 17 is most likely not an intermediate
involved in the formation of 4b,c-d6. Furthermore, no incorpora-
tion of deuterium into the Cp* ring is evident from the 2H{1H}
NMR spectrum of the final reaction mixture, thereby eliminating
the possibility of a C-H activation pathway via oxidative
addition of a tucked-in Cp*-methyl C-H bond.21
The most striking feature of the product ratios obtained with
o-xylene is the markedly decreased proportion of the benzylic
C-H-activated species 10. This trend of decreasing benzylic
C-H activation in different xylene solvents (i.e., para > meta
> ortho) is similar to that seen for the related Cp*W(NO)-
(alkylidene) complexes.13 This feature is probably a manifesta-
tion of the steric hindrance imposed on the sp3 C-H bonds by
the adjacent methyl group in o-xylene and less overall hindrance
of the sp2 C-H bonds, both factors subsequently increasing the
preference for the formation of the aromatic-activated com-
plexes.
The thermolysis of 1 in toluene leads to the formation of all
four products of single C-H bond activation, Cp*W(NO)-
(CH2C6H5)(η3-H2CCHCMe2) (13), Cp*W(NO)(C6H4-2-Me)(η3-
H2CCHCMe2) (14), Cp*W(NO)(C6H4-3-Me)(η3-H2CCHCMe2)
(15), and Cp*W(NO)(C6H4-4-Me)(η3-H2CCHCMe2) (16) (eq
1
4). Complexes 14-16 were characterized as a mixture by H
NMR spectroscopy, and thus many of the resonances expected
for each individual compound were not discernible due to
overlapping signals.
Again, the product ratios observed for complexes 13-16 are
invariant with time, and the proportion of aryl:benzyl species
(i.e., 70:30) is similar to those observed for products from
activation of the various C-H bonds of m- and p-xylene (vide
supra). We have also established by independent NMR experi-
(20) Adams, C. S.; Legzdins, P.; Tran, E. J. Am. Chem. Soc. 2001, 123,
612.
(21) Schock, L. E.; Brock, C. P.; Marks, T. J. Organometallics 1987, 6, 232.
9
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A R T I C L E S
Ng et al.
Scheme 2
Figure 4. Solid-state molecular structure of Cp*W(NO)(η3-CH2C(2-
cyclohexenyl)CMe2)(H) (18) with 50% probability thermal ellipsoids shown.
Selected interatomic distances (Å) and angles (deg): W1-N1 ) 1.774(5),
W1-C11 ) 2.258(5), W1-C12 ) 2.333(5), W1-C13 ) 2.407(5), N1-
O1 ) 1.227(6), C11-C12 ) 1.434(7), C12-C13 ) 1.405(7), C17-C18
) 1.326(7), W1-N1-O1 ) 167.1(4), C11-C12-C13 ) 118.7(5), C12-
C13-C14 ) 122.2(4).
Scheme 3
Figure 5. Solid-state molecular structure of Cp*W(NO)(η3-CH2CHC)(Me)-
CH2CâH(C4H8)CRH (19) with 50% probability thermal ellipsoids shown.
Selected interatomic distances (Å) and angles (deg): W1-N1 ) 1.773(5),
W1-C11 ) 2.232(5), W1-C12 ) 2.290(5), W1-C13 ) 2.568(6), N1-
O1 ) 1.232(6), C11-C12 ) 1.426(9), C12-C13 ) 1.381(8), W1-N1-
O1 ) 170.1(5), C11-C12-C13 ) 122.0(6).
The incorporation of deuterium at both methyl positions of
the dimethylallyl ligand can be rationalized by the mechanism
shown in Scheme 3, which is supported by the room-temperature
EXSY NMR spectrum of 4 in C6D6 that exhibits cross-peaks
attributable to exchange of the methyl groups of the allyl
ligand. The proposed pathway hinges on the ability of the σ-π
distorted η3-allyl fragments to break the two-electron bond,
rotate about the remaining single bond to exchange the terminal
allyl substituents, and then revert back to the original η3-endo
or -exo configuration. Such processes do have literature
precedents.22-25
CH2C(2-cyclohexenyl)CMe2)(H) (18) and Cp*W(NO)(η3-CH2-
CHC)(Me)CH2CâH(C4H8)CRH (19) (eq 5).
Reaction Products Indicative of Allene and Diene Inter-
mediates. The thermal reaction of 1 in cyclohexene leads to
the formation of two allyl-containing products, Cp*W(NO)(η3-
(22) Becconsall, J. K.; Job, B. E.; O’Brien, S. J. Chem. Soc. A 1967, 423.
(23) Benn, R.; Rufinska, A.; Schroth, G. J. Organomet. Chem. 1981, 217,
91.
(24) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M.
C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc.
1987, 109, 203.
(25) Abrams, M. B.; Yoder, J. C.; Loeber, C.; Day, M. W.; Bercaw, J. E.
Organometallics 1999, 18, 1389.
Single-crystal X-ray crystallographic analyses have been
performed on 18 and 19, and the resulting ORTEP diagrams
are shown in Figures 4 and 5, respectively. Interestingly, both
complexes show less pronounced structural manifestations of
9
15214 J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003

Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
Scheme 4
Figure 6. Solid-state molecular structure of Cp*W(NO)(PMe3)(η2-H2Cd
CdCMe2) (20) with 50% probability thermal ellipsoids shown. Selected
interatomic distances (Å) and angles (deg): W1-N1 ) 1.795(4), W1-
C11 ) 2.205(4), W1-C12 ) 2.148(5), W1-P1 ) 2.4660(12), N1-O1 )
1.224(5), C11-C12 ) 1.436(7), C12-C13 ) 1.324(7), W1-N1-O1 )
175.0(4), N1-W1-C11 ) 91.00(18), C12-W1-C11 ) 38.49(18), C11-
C12-C13 ) 134.0(5), C12-C13-C14 ) 121.8(5), C12-C13-C15 )
124.3(5).
Scheme 5
observation, taken in conjunction with labeling studies conducted
on this system (vide supra), suggests that the two reactive
intermediates, A and B, are simultaneously generated thermally
from 1 via two different mechanisms, both involving intramo-
lecular hydrogen abstraction from the dimethylallyl ligand.
Trapping of the Allene Intermediate. The thermal reaction
of 1 in neat trimethylphosphine yields the base-stabilized adduct
of the dimethylallene complex, Cp*W(NO)(PMe3)(η2-H2CdCd
CMe2) (20) (eq 6), which has been isolated in 24% yield.
Interestingly, there is no evidence in the 1H NMR spectrum of
the final reaction mixture suggesting the presence of a phos-
phine-stabilized η2-diene species.
the electronic asymmetry at their tungsten centers than do the
other allyl complexes isolated during this work.
The most plausible rationale for the origin of these products
involves two pathways originating at 1 that generate two
different reactive intermediates, the allene complex, Cp*W(NO)-
(η2-H2CdCdCMe2) (A), and the diene complex, Cp*W(NO)-
(η2-H2CdCHC(Me)dCH2) (B) (Schemes 4 and 5, respectively).
This reactivity exhibited by the purported allene intermediate
is not surprising, given the numerous examples in the literature
of metal-mediated C-C bond coupling of allenes with other
unsaturated organic species.26-30
The ORTEP diagram of 20 shown in Figure 6 confirms that
one of the reactive intermediates responsible for the C-H bond-
activating chemistry of 1 is the η2-dimethylallene complex. The
most notable feature of the solid-state molecular structure of
20 is the nonlinear nature of the allene ligand framework, a
feature that has also been documented for other η2-allene
complexes.30,32-40 The C(11)-C(12)-C(13) angle of 134.0(5)°
On the basis of previous studies performed on similar
systems,31 we originally thought that 19 could also be derived
from a C-C bond-coupling reaction between a trans-diene
complex and an incoming cyclohexene molecule. However, the
thermolysis of the independently synthesized trans-diene com-
plex 17 in excess cyclohexene results in no reaction. This
(32) Racanelli, P.; Pantini, G.; Immirzi, A.; Allegra, G.; Porri, L. Chem. Commun.
(26) Wu, I. Y.; Tsai, J. H.; Huang, B. C.; Chen, S. C.; Lin, Y. C. Organometallics
1993, 12, 3971.
1969, 361.
(33) Binger, P.; Langhauser, F.; Wedeman, P.; Gabor, B.; Mynott, R.; Kruger,
(27) Doxsee, K. M.; Juliette, J. J. J.; Zientara, K.; Nieckarz, G. J. Am. Chem.
Soc. 1994, 116, 2147.
C. Chem. Ber. 1994, 127, 39.
(34) Clark, H. C.; Dymarski, M. J.; Payne, N. C. J. Organomet. Chem. 1979,
(28) Yin, J.; Jones, W. M. Tetrahedron 1995, 51, 4395.
(29) Murakami, M.; Itami, K.; Ito, Y. J. Am. Chem. Soc. 1997, 119, 7163.
(30) Choi, J. C.; Sarai, S.; Koizumi, T.; Osakada, K.; Yamamoto, T. Organo-
metallics 1998, 17, 2037.
(31) Christensen, N. J.; Legzdins, P.; Einstein, F. W. B.; Jones, R. H.
Organometallics 1991, 10, 3070.
165, 117.
(35) Lentz, D.; Willemsen, S. Organometallics 1999, 18, 3962.
(36) Werner, H.; Schneider, D.; Schulz, M. J. Organomet. Chem. 1993, 451,
175.
(37) Pu, J.; Peng, T.-S.; Arif, A. M.; Gladysz, J. A. Organometallics 1992, 11,
3232.
9
J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003 15215

A R T I C L E S
Ng et al.
is among the most acute yet found for acyclic allene com-
plexes,41 and it is a manifestation of the considerable back-
donation of electron density from the metal center to the η2-
allene π* orbitals. The ability of Cp′W(NO)(PR3) fragments to
function as strong π-bases has been previously documented,42
and in 20 it results in the lengthening of C(11)-C(12) (1.436(7)
Å) relative to that in the uncoordinated dimethylallene (1.324-
(7) Å). This elongation suggests a decrease in the C(11)-C(12)
bond order from formally two to almost one. This view is further
1
supported by evidence gathered from H and 13C{1H} NMR
spectroscopic data. The large upfield shifts observed for the
methylene carbon (δ 7.7) and hydrogen (δ 0.67, 1.97) signals
are consistent with the terminal carbon having considerable sp3
character.43 This upfield shift is also evident for the central
carbon atom signal (δ 165.7), while the remaining assignable
resonances are relatively unchanged from those exhibited by
free dimethylallene.
Formation of an η1-Dimethylallyl Complex. In an attempt
to obtain additional evidence supporting the existence of the
diene reactive intermediate, the thermolysis of 1 was effected
in 2,3-dimethyl-2-butene with the anticipation that two products
would be formed that would implicate the two suggested reactive
intermediates in a manner similar to that found in the reaction
with cyclohexene (vide supra). However, in this instance,
Cp*W(NO)(η3-Me2CCMeCH2)(η1-CH2CHCMe2) (21) is formed
exclusively (eq 7). A single-crystal X-ray crystallographic
analysis has been performed to ascertain the connectivity of
the atoms in this organometallic complex, and the resulting
ORTEP diagram of 21 is shown in Figure 7. This alternate allyl
complex presumably results from the activation of a methyl
C-H bond of 2,3-dimethyl-2-butene followed by a subsequent
isomerization which leaves the more electron-rich 1,1,2-tri-
methylallyl group as the η3 ligand and the 3,3-dimethylallyl
group as the η1-ligand in the solid state (eq 7). The mono-
Figure 7. Solid-state molecular structure of Cp*W(NO)(η3-Me2CCMeCH2)-
(η1-CH2CHCMe2) (21) with 50% probability thermal ellipsoids shown.
Selected interatomic distances (Å) and angles (deg): W1-C11 ) 2.236(5),
C11-C12 ) 1.500(6), C12-C13 ) 1.342(7), W1-C21 ) 2.219(5), W1-
C16 ) 2.403(5), W1-C17 ) 2.696(5), C21-C16 ) 1.438(7), C16-C17
) 1.375(7), N1-O1 ) 1.221(5), C17-C16-C21 ) 119.9 (5), C11-C12-
C13 ) 130.3(5), W1-C11-C12 ) 113.3(3), W1-N1-O1 ) 170.9(4),
C14-C13-C15 ) 114.4(4), W1-C21-C16 ) 79.0(3).
a feature indicative of the loss of metal-to-ligand electron density
transfer that exists in the η3-allyl mode.
Multiple C-H Bond Activations Initiated by 1. (A)
Activation of Cyclohexane. Reaction of 1 with cyclohexane
leads to the formation of the cyclohexenyl-hydrido complex,
Cp*W(NO)(η3-C6H9)(H) (22) (eq 8), which has been character-
ized by conventional spectroscopic techniques.44 This transfor-
mation constitutes a novel mode of multiple C-H activations
of cyclohexane, a relatively inert solvent that has frequently
been used to study the C-H activations of other hydro-
carbons.45-47 In addition to complex 22, GC-MS data suggest
that a coupled organic product, a dimethylpropylcyclohexane,
is also present in the final reaction mixture. This product could
possibly result from coupling between a coordinated cyclohex-
enyl group and an alkyl fragment derived from the precursor
dimethylallyl ligand.
hapticity of the dimethylallyl ligand is indicated by its orientation
away from the metal center and the C(11)-C(12) and C(12)-
C(13) bond lengths of 1.500(6) and 1.342(7) Å typical of a C-C
single and double bond, respectively. Another clear indication
of the loss of its previous η3 coordination mode is the W(1)-
C(11)-C(12) bond angle of 113.3(3)° which is reflective of
principally sp3 character at C(11). Consistently, the most notable
aspect of the 1H NMR spectrum of 21 in C6D6 is the significant
downfield shift of the signal due to the â-hydrogen of the η1-
allyl fragment (δ 5.82) from its previous values (δ 3.54-4.43),
For comparison, the well-studied bis(alkyl) complex, Cp*W-
(NO)(CH2CMe3)2, reacts with cyclohexane in a completely
different manner. Its thermolysis in the presence of an excess
of trimethylphosphine in cyclohexane at 70 °C for 40 h results
(38) Yasuoka, N.; Morita, M.; Kai, Y.; Kasai, N. J. Organomet. Chem. 1975,
90, 111.
(39) Lee, L.; Wu, I. Y.; Lin, Y. C.; Lee, G. H.; Wang, Y. Organometallics
1994, 13, 2521.
(44) Preliminary single-crystal X-ray crystallographic analysis of 22 has
confirmed the atomic connectivity shown in eq 8. However, the quality of
the diffraction data collected precludes meaningful discussion of its metrical
parameters.
(40) Okamoto, K.; Kai, Y.; Yasuoka, N.; Kasai, N. J. Organomet. Chem. 1974,
65, 427.
(41) Yin, J.; Abboud, K. A.; Jones, W. M. J. Am. Chem. Soc. 1993, 115, 3810.
(42) The exceptionally strong π-donor ability of the related Cp*W(NO)(PPh3)
fragment has been documented, see: Burkey, D. J.; Debad, J. D.; Legzdins,
P. J. Am. Chem. Soc. 1997, 119, 1139.
(45) McGhee, W. D.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 4246.
(46) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am. Chem. Soc. 1988,
110, 8731.
(47) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J. Am. Chem. Soc.
1996, 118, 591.
(43) Gibson, V. C.; Parkin, G.; Bercaw, J. E. Organometallics 1991, 10, 220.
9
15216 J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003

Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
in the formation of two base-stabilized complexes, Cp*W(NO)-
(dCHCMe3)(PMe3) and Cp*W(NO)(η2-cyclohexene)(PMe3).48
However, in the absence of a suitable Lewis base, decomposition
occurs. In contrast, the thermal reaction of 1 in cyclohexane in
the presence of excess trimethylphosphine results in the
exclusive formation of the PMe3-stabilized allene complex 20.
(B) Activation of Methylcyclohexane. Two principal prod-
ucts are formed in the reaction between 1 and methylcyclohex-
ane, the two isomeric species, Cp*W(NO)(η3-C7H11)(H) (23a,b)
(eq 9).
the C-H activations effected by this system have been the
subjects of theoretical studies.50
There is no evidence for the formation of the bis(trimethyl-
silylmethyl), the benzyl-aryl, or the bis(mesityl) Cp*W(NO)-
containing complexes upon reaction of 1 in tetramethylsilane,
toluene and xylenes, or mesitylene, respectively. This observa-
tion indicates that the dimethylallyl ligand in the products
resulting from single C-H bond activation is not prone to
elimination from the metal’s coordination sphere to form
reactive alkylidene and benzylidene species which have been
demonstrated to have C-H-activating abilities.13,20 However,
the formation of the allyl-hydrido complexes 22 and 23a,b by
thermolysis of 1 in cyclic alkanes must involve the ejection of
the dimethylallyl moiety at some point, presumably via an initial
η3 f η1 isomerization of the type that has been shown to occur
during the formation of the η1-dimethylallyl ligand in complex
21. Furthermore, the reaction of 1 with methylcyclohexane gives
an indication of the selectivity of the C-H-activating intermedi-
ate complexes for different sp3 C-H bonds. The exclusive
formation of the exocyclic allyl complexes 23a,b suggests the
preference of A and B to activate primary C-H bonds, a feature
commonly observed for other metal-based alkane C-H-activat-
ing complexes.
Given the range of hydrocarbon solvents with which they
have been shown to react to date, the C-H-activating chemistry
of the reactive allene and diene intermediates appears to be quite
extensive. It is also not unreasonable to expect that intramo-
lecular hydrogen abstraction by other metal nitrosyl alkyl allyl
complexes to eliminate alkanes and generate reactive intermedi-
ates will afford similarly diverse chemistry. Our studies designed
to encompass both other hydrocarbon substrates and related
C-H-activating intermediates are currently in progress.
Compounds 23a,b are identical to the principal organometallic
species isolated from the reactions of the intermediate tungsten
neopentylidene and benzylidene species, Cp*W(NO)(dCHCMe3)
and Cp*W(NO)(dCHC6H5), with methylcyclohexane. The
major product, 23a, is formed in greater than 90% yield in all
three cases, and it exhibits an exocyclic endo-η3-allyl linkage
with the terminal CH2 group being cis to the nitrosyl ligand.
The apparent exclusive formation of exocyclic η3-allyl com-
plexes as opposed to the endocyclic species suggests that the
reactive intermediates preferentially activate the thermodynami-
cally stronger primary C-H bonds, much like other metal-based
alkane activation systems.49
Experimental Section
Conclusion
General Methods. All reactions and subsequent manipulations
involving organometallic reagents were performed under anaerobic and
anhydrous conditions either under high vacuum or an inert atmosphere
of prepurified argon or dinitrogen. General procedures routinely
employed in these laboratories have been described in detail else-
where.20,51 All solvents were dried with appropriate drying agents under
dinitrogen or argon atmospheres and were freshly distilled or vacuum
transferred from the appropriate drying agent prior to use. Hydrocarbon
solvents, their deuterated analogues, diethyl ether, and trimethylphos-
phine were dried over sodium or sodium/benzophenone ketyl. Tetra-
hydrofuran was distilled from molten potassium, and dichloromethane
and chloroform were distilled from calcium hydride. All IR samples
were prepared as KBr pellets, and their spectra were recorded on a
BOMEM MB-100 FT-IR spectrometer unless otherwise noted. El-
emental analyses were performed by Mr. P. Borda and Mr. M. Lakha
in the Department of Chemistry at UBC and by Ms. Pauline Maloney
of Canadian Microanalytical Service Ltd. in Delta B.C.
This work constitutes the first definitive demonstration of the
C-H bond-activating ability of a transition-metal allene com-
plex. Similar allene intermediates are believed to form during
thermolyses of alkyl-allyl complexes of iridium at 120 °C, but
these intermediates have not been isolated or characterized and
they are only capable of effecting single C-H bond activa-
tions.45 The studies presented here indicate the concurrent
generation of a diene reactive species which is also evidently
responsible for the C-H bond-activating chemistry initiated by
1. However, cyclohexene is the only hydrocarbon substrate
found to date that reacts with 1 under thermal conditions to
form two different products resulting from the two reactive
intermediates invoked. All other hydrocarbon solvents afford
the same product regardless of which intermediate is involved
in the activation of its C-H bonds. These studies have also
elucidated the scope of single C-H bond activations via thermal
reactions of 1 in the chosen hydrocarbon solvents. The
thermodynamic preference for aromatic C-H activations over
benzylic ones is evident in the product distributions resulting
from the thermolyses of 1 with p- and m-xylene and toluene.
Similar reactions conducted with o-xylene and mesitylene yield
product ratios that suggest that steric factors play a role during
benzylic and aromatic C-H activations initiated by 1. Some of
Unless otherwise specified, all reagents were purchased from
commercial suppliers and were used as received. The (CH2CMe3)2-
Mg‚x(dioxane) alkylating reagent and the requisite Cp*W(NO)(CH2-
CMe3)Cl complex were prepared according to published procedures.52,53
A modified version of the general synthetic method for dialkylmag-
(50) Webster, C. E.; Hall, M. B. 224th ACS National Meeting, Boston, MA,
August 2002; Abstract INOR-013.
(51) Legzdins, P.; Rettig, S. J.; Ross, K. J.; Batchelor, R. J.; Einstein, F. W. B.
Organometallics 1995, 14, 5579.
(52) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organometallics 1991,
10, 2857.
(48) Tran, E.; Legzdins, P. J. Am. Chem. Soc. 1997, 119, 5071.
(49) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc.
Chem. Res. 1995, 28, 154.
(53) Debad, J. D.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organo-
metallics 1993, 12, 2094.
9
J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003 15217

A R T I C L E S
Ng et al.
nesium reagents was employed for the preparation of the dimethyl-
allylmagnesium reagent, and the procedure is described below.
10.2 (C5Me5), 19.5, 30.7 (allyl Me), 34.3 (Npt CMe3), 37.6 (allyl CH2),
39.9 (Npt CMe3), 40.7 (Npt CH2), 101.7 (allyl CH), 107.5 (C5Me5),
147.8 (allyl C). Sel NOE (400 MHz, C6D6) δ irrad. at 4.45, NOE at
1.02, irrad. at 0.67, NOE at 1.02, 1.42, 1.52, and 2.55. Anal. Calcd for
C20H35NOW: C, 49.09; H, 7.21; N, 2.86. Found: C, 49.16; H, 7.03;
N, 2.87.
Preparation of (1,1-Me2C3H3)2Mg‚x(dioxane). 3,3-Dimethylallyl
bromide (Fluka, 10 mL, 0.085 mol) was syringed into a 200-mL two-
neck, round-bottom flask and was diluted with Et2O (100 mL). In a
glovebox, a 500-mL three-neck, round-bottom flask was charged with
magnesium powder (4.2 g, 0.172 mol) and a magnetic stir bar. The
500-mL flask was transferred to a vacuum line, was charged with Et2O
(250 mL), and was fitted with a reflux condenser. Activation of the
magnesium powder was accomplished via addition of sufficient
dibromoethane (∼1-2 mL) using a syringe. The suspension was
allowed to reflux until all of the added dibromoethane had reacted.
The suspension was then cooled in an ice bath to 0 °C, whereupon the
ethereal bromide solution was added dropwise via a cannula over a
3-h period. During this time, the contents of the flask were stirred
rapidly, and the solution remained clear. Upon completion of the
dropwise addition, the mixture was slowly warmed to room temperature.
The transformation of the Grignard reagent into the bis(allyl)magnesium
reagent was conducted in the usual manner.52 (1,1-Me2C3H3)2Mg‚
x(dioxane) was isolated as a snow-white powder (2.7 g, 50%), and
titration with 0.1 M HCl afforded a titer of 127 g/mol.
Representative Procedure for Effecting Preparative Thermolyses
of 1 in Hydrocarbon Solvents. Unless noted otherwise, the following
general procedure was used to prepare new compounds via thermolysis
of 1. A 30-mL bomb was charged with the specified amount of 1, a
magnetic stir bar, and sufficient solvent to obtain an approximately
10% (w/w) orange solution. The solvent was either pipetted directly
into the reaction vessel from a storage bomb inside a glovebox or
vacuum transferred onto the orange microcrystals on a vacuum line.
The sealed bomb was then heated at 50 °C for a period of 6 h in a
VWR Scientific Products Circulating Bath 1160A. During this time,
the deep orange color of the reaction mixture either remained unchanged
or lightened to an orange-yellow. Alternatively, it darkened to a brown
color, whereupon further steps were necessary to extract and isolate
the analytically pure organometallic products. The reaction bomb was
removed from the bath, and the reaction was quenched by placing the
bomb under a flow of cold water or dipping it into a cold bath. The
volatiles were then removed in vacuo, and the resulting residue was
dried under high vacuum for a suitable period of time. It was then
dissolved in C6D6, and the 1H NMR spectrum of this mixture was
recorded to determine the number of principal organometallic products
present and the ratios in which they were formed. Average product
ratios were determined via multiple integrations of like signals in this
1H NMR spectrum. The NMR solvent was then removed, and the
residue was redissolved in the specified solvent or solvent mixtures
for recrystallization of the products. The solutions were then concen-
trated to the point of incipient crystallization and cooled for a suitable
amount of time at -30 °C to induce the deposition of the organometallic
products as crystals. The reported yields are not optimized.
Cp*W(NO)(CH2CMe3)(η3-1,1-Me2C3H3) (1). In a glovebox, a 100-
mL Schlenk tube was charged with a magnetic stir bar and Cp*W-
(NO)(CH2CMe3)Cl (483 mg, 1.15 mmol).54 A 400-mL Schlenk tube
was then charged with a magnetic stir bar and the dimethylallylmag-
nesium reagent (147 mg, 1.16 mmol). On a vacuum line, Et2O (200
mL) from a bomb was cannulated into the Schlenk tube containing the
magnesium reagent with vigorous stirring to ensure its dissolution. The
resulting colorless solution was then frozen by cooling to -196 °C
using a liquid N2 bath. Et2O (50 mL) was added in a similar fashion to
the Schlenk tube containing the solid Cp*W(NO)(CH2CMe3)Cl to obtain
a purple solution which was then cooled to -60 °C with a dry ice/
acetone bath. The purple solution was then cannulated dropwise into
the 400-mL Schlenk tube (maintained at -196 °C) at a slow enough
rate that allowed the added solution to freeze upon contact with the
solidified ethereal solution of the magnesium reagent. Sufficient Et2O
was added to the 100-mL Schlenk tube and subsequently cannulated
into the reaction flask to ensure complete transfer of Cp*W(NO)(CH2-
CMe3)Cl. The liquid N2 bath was replaced with a liquid N2/acetone
bath at -60 °C to enable the ethereal contents to melt slowly. After
being stirred for 5 min, the purple solution changed to a straw-yellow
color which then became a turbid orange after a further 10 min. The
solution was stirred at -60 °C for a total of 45 min, whereupon the
contents were warmed to room temperature to ensure completion of
the reaction. The volume of the mixture was reduced under vacuum to
∼100 mL, and the turbid orange solution was filtered through an
alumina(I) column (2 × 3 cm) which was also rinsed with fresh Et2O
(2 × 10 mL) to obtain a clear bright orange filtrate. The volatiles were
then removed from the filtrate in vacuo to obtain an orange crystalline
powder which was dried at room temperature under high vacuum for
1 h. Analysis of this solid by 1H NMR spectroscopy revealed that
complex 1 was the sole organometallic product. Analytically pure 1
was obtained as orange microcrystals (296 mg, 57%) via crystallization
from a THF/hexanes mixture (5 mL/20 mL) at -25 °C.
Cp*W(NO)(CH2SiMe3)(η3-1,1-Me2C3H3) (2). Complex 2 was
prepared via thermolysis of 1 (75 mg, 0.15 mmol) in tetramethylsilane.
The reaction mixture was then cooled overnight in a freezer (-30 °C)
to obtain orange needles of 2 (47 mg, 61%).
2: IR (cm-1) 1549 (s, νNO). MS (LREI, m/z, probe temperature 80
1
2
°C) 505 [P+, 184W]. H NMR (400 MHz, C6D6) δ -0.78 (d, JHH
)
2
14.09, 1H, SiCH2), -0.59 (d, JHH ) 14.09, 1H, SiCH2), 0.45 (s, 9H,
SiMe3), 0.61 (s, 3H, allyl Me), 1.12 (s, 3H, allyl Me), 1.18 (m, 1H,
allyl CH2), 1.51 (s, 15H, C5Me5), 2.55 (m, 1H, allyl CH2), 4.43 (m,
1H, allyl CH). 13C{1H} NMR (125 MHz, C6D6) δ 2.01 (SiCH2), 4.34
(SiMe3), 10.2 (C5Me5), 19.6, 28.9 (allyl Me), 39.3 (allyl CH2), 101.9
(allyl CH), 106.9 (C5Me5). Sel NOE (400 MHz, C6D6) δ irrad. at 0.61,
NOE at -0.78, 0.45, 1.12, 1.18, 1.51, and 2.55. Anal. Calcd for C19H35-
NOSiW: C, 45.15; H, 6.98; N, 2.77. Found: C, 45.37; H, 6.92; N,
2.90.
Cp*W(NO)(CH2C6H3-3,5-Me2)(η3-1,1-Me2C3H3) (3). Complex 3
was prepared by the thermolysis of 1 (79 mg, 0.16 mmol) in mesitylene.
The volume was reduced to 2 mL, and hexanes (10 mL) were added
via a syringe. Cooling of the mixture resulted in the precipitation of 3
as orange microcrystals (57 mg, 66%).
1: IR (cm-1) 1546 (s, νNO). MS (LREI, m/z, probe temperature 150
3: IR (cm-1) 1533 (s, νNO). MS (LREI, m/z, probe temperature 120
1
°C) 489 [P+, 184W]. H NMR (300 MHz, C6D6) δ 0.67 (s, 3H, allyl
1
°C) 537 [P+, 184W]. H NMR (400 MHz, C6D6) δ 1.08 (s, 3H, allyl
Me), 1.02 (obs, 1H, Npt CH2), 1.02 (s, 3H, allyl Me), 1.42 (s, 9H, Npt
Me), 1.17 (s, 3H, allyl Me), 1.46 (s, 15H, C5Me5), 1.52 (obs, 1H, allyl
CMe3), 1.42 (obs, 1H, allyl CH2), 1.53 (s, 15H, C5Me5), 2.69 (m, 1H,
2
1
CH2), 1.79 (d, JHH ) 9.46, 1H, Mes CH2), 2.38 (s, 6H, Mes Me2),
allyl CH2), 4.45 (m, 1H, allyl CH). H NMR (400 MHz, CD2Cl2) δ
2.45 (m, 1H, allyl CH2), 2.80 (d, 2JHH ) 9.46, 1H, Mes CH2), 3.58 (s,
1H, allyl CH), 6.72 (s, 1H, Mes Hpara), 7.38 (s, 2H, Mes Hortho). 13C-
{1H} NMR (125 MHz, C6D6) δ 9.88 (C5Me5), 20.63 (allyl Me), 22.03
(Mes Me2), 27.65 (allyl Me), 28.23 (allyl CH2), 39.69 (Mes CH2), 98.86
(allyl CH), 106.49 (C5Me5), 125.24 (Mes p-CH), 128.70 (Mes o-CH),
152.4 (allyl C), 136.5, 169.2 (Caryl). Sel NOE (400 MHz, C6D6) δ irrad.
at 3.58, NOE at 1.08, 1.52, 2.45, irrad. at 1.08, NOE at 1.17, 1.46,
2
0.88 (d, JHH ) 14.2, 1H, Npt CH2), 0.99 (s, 3H, allyl Me), 1.02 (d,
2JHH ) 14.2, 1H, Npt CH2), 1.06 (s, 9H, Npt CMe3), 1.24 (s, 3H, allyl
Me), 1.61 (m, 1H, allyl CH2), 1.82 (s, 15H, C5Me5), 2.55 (m, 1H, allyl
CH2), 4.40 (m, 1H, allyl CH). 13C{1H} NMR (75 MHz, CD2Cl2) δ
(54) Our previous communication of the chemistry exhibited by 1 (see ref 4)
incorrectly designated the dimethylallyl ligand as 3,3-Me2C3H3.
9
15218 J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003

Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
1.79, 2.80, 3.58, and 7.38. Anal. Calcd for C24H35NOW: C, 53.64; H,
6.56; N, 2.61. Found: C, 53.80; H, 6.61; N, 2.75.
to sit for 30 min to allow evaporation of the THF solvent, and it was
then loaded into a development chamber charged with Et2O (200 mL)
and sealed to minimize solvent loss and ensure maximum vapor
saturation. After 70 min of development, the plate was removed from
the chamber and allowed to dry. No clear separation was evident, but
a definite region where the band was lighter in color was visible. The
alumina above this region was scraped off and stripped of any
organometallic product with THF and subsequently filtered thru a Celite
plug to obtain a yellow solution. Removal of solvent from this solution
and recrystallization of the residue from 1:4 Et2O/hexanes afforded
yellow needles of complex 6 (53 mg, 17%). The alumina below the
lighter region was treated in a similar fashion to obtain orange needles
of complex 5 (24 mg, 8%).
Cp*W(NO)(C6H5)(η3-1,1-Me2C3H3) (4). Complex 4 was formed
during the thermolysis of 1 (48 mg, 0.10 mmol) in benzene. Complex
4 was isolated as yellow microcrystals by recrystallization of the residue
from 4:1 Et2O/hexanes (34 mg, 70%).
4: IR (cm-1) 1562 (s, νNO). MS (LREI, m/z, probe temperature 150
1
°C) 495 [P+, 184W]. H NMR (300 MHz, C6D6) δ 0.82 (s, 3H, allyl
Me), 1.51 (s, 15H, C5Me5), 1.62 (br s, 3H, allyl Me), 1.74 (br m, 1H,
allyl CH2), 2.49 (br m, 1H, allyl CH2), 3.54 (br m, 1H, allyl CH), 6.64
3
(br d, 1H, Ph Hortho), 7.08 (t, JHH ) 7.1, 1H, Ph Hpara), 7.30 (m, 2H,
3
1
Ph Hmeta), 8.39 (d, JHH ) 6.7, 1H, Ph Hortho). H NMR (400 MHz,
CDCl3) δ 0.87 (s, 3H, allyl Me), 1.51 (br s, 3H, allyl Me), 1.76 (s,
5: IR (cm-1) 1553 (s, νNO). MS (LREI, m/z, probe temperature 120
15H, C5Me5), 1.90 (br m, 1H, allyl CH2), 2.42 (br m, 1H, allyl CH2),
3
1
°C) 523 [P+, 184W]. H NMR (400 MHz, C6D6) δ 1.07 (s, 3H, allyl
3.73 (br m, 1H, allyl CH), 6.68 (br d, 1H, Ph Hortho), 6.93 (t, JHH
7.1, 1H, Ph Hpara), 7.12 (q, 3JHH ) 7.0, 2H, Ph Hmeta), 7.86 (d, 3JHH
)
)
Me), 1.15 (s, 3H, allyl Me), 1.46 (s, 15H, C5Me5), 1.46 (obs, 1H, allyl
6.4, 1H, Ph Hortho). 13C{1H} NMR (75 MHz, CDCl3) δ 10.4 (C5Me5),
21.8, 29.4 (allyl Me), 37.6 (allyl CH2), 95.3 (allyl CH), 107.6 (C5-
Me5), 123.4 (Ph Cpara), 126.8, 127.9 (Ph Cmeta), 139.6, 141.9 (Ph Cortho),
148.5 (allyl C), 168.8 (Ph Cipso). Sel NOE (400 MHz, C6D6) δ irrad. at
3.54, NOE at 0.82, 1.51, and 1.74, irrad. at 0.82, NOE at 1.51, 1.63,
3.54, 6.64, 8.39. Anal. Calcd for C21H29NOW: C, 50.92; H, 5.90; N,
2.83. Found: C, 50.61; H, 5.95; N, 2.92.
CH2), 1.80 (m, 1H, 2JHH ) 11.6, Bzl CH2), 2.26 (s, 3H, Pxyl Me), 2.43
2
(m, 1H, allyl CH2), 2.77 (m, 1H, JHH ) 11.6, Bzl CH2), 3.56 (m, 1H
3
allyl CH), 7.13 (obs, 2H, Pxyl m-CH), 7.62 (d, 2H, JHH ) 7.6, Pxyl
o-CH). 13C{1H} NMR (100 MHz, C6D6) δ 9.7 (C5Me5), 20.5 (allyl
Me), 21.0 (Pxyl Me), 27.4 (allyl Me), 35.2 (Bzl CH2), 39.6 (allyl CH2),
98.3 (allyl CH), 106.3 (C5Me5), 124.8 (Pxyl p-CH), 128.0 (obs Pxyl
o-CH), 130.4 (Pxyl m-CH), 149.8 (allyl C). Anal. Calcd for C23H33-
NOW: C, 52.78; H, 6.36; N, 2.68. Found: C, 52.66; H, 6.26; N, 2.75.
Cp*W(NO)(C6D5)(η3-1,1-Me2-allyl-d1) (4a-c-d6). Complexes 4a-
c-d6 were prepared by the thermolysis of 1 (10 mg, 0.02 mmol) in
benzene-d6. Yellow crystals of complexes 4a-c-d6 were obtained via
crystallization of the residue from 4:1 Et2O/hexanes.
4a-c-d6: MS (LREI, m/z, probe temperature 120 °C) 501 [P+, 184W].
1H NMR (400 MHz, C6D6) δ 0.82 (s, 3H, allyl Me), 1.51 (s, 15H,
C5Me5), 1.62 (br s, 3H allyl Me), 1.73 (br m, 1H, allyl CH2), 2.48 (br
m, 1H, allyl CH2), 3.52 (br m, 1H, allyl CH). 2H{1H} NMR (61 MHz,
C6H6) δ 0.78 (allyl Me-d1), 1.61 (allyl Me-d1), 3.52 (allyl CD), 6.60-
8.4 (Ph D).
Reaction Products of Thermolyses of 1 in Toluene and o,m,p-
Xylenes. Thermolyses of 1 in toluene and xylene solvents afforded
final reaction mixtures with multiple organometallic products due to
the activation of different C-H bonds present in the hydrocarbons.
For the various reaction mixtures, the residues remaining after the
reaction solvent had been removed were triturated with pentane (3 ×
10 mL) to alleviate the oily appearance. Solid product was isolated via
crystallization from hexanes. It was then possible to separate the
benzylic C-H-activated product from the aryl C-H-activated species
either via preparative thin-layer chromatography on an alumina(I) plate
(20 × 20 × 0.15 cm) or via column chromatography through an
alumina(I) column (0.5 × 3 cm). The former separation technique was
utilized once for the products from reaction of 1 in p-xylene (vide infra).
The latter technique was employed for the remainder of the product
separations. The products isolated via crystallization were dissolved
in a 1:5 Et2O/hexanes solvent mixture, and the resulting solution was
eluted through the column described above which was prewetted with
the eluting solvent. A yellow eluate resulted which upon concentration
and cooling to - 30 °C overnight deposited solely the aryl C-H-
activated products. Eluting the column with 1:4 Et2O/hexanes gave a
solution consisting of small amounts of both aryl and benzylic C-H-
activated species. Stripping the alumina column with Et2O yielded an
orange solution which upon addition of hexanes and then subsequent
concentration and cooling to -30 °C overnight yielded solely the
benzylic C-H-activated product.
6: IR (cm-1) 1567 (s, νNO). MS (LREI, m/z, probe temperature 120
1
°C) 523 [P+, 184W]. H NMR (500 MHz, C6D6) δ 0.80 (s, 3H, allyl
Me), 1.54 (s, 15H, C5Me5), 1.74 (s, 3H, allyl Me), 1.79 (m, 1H, allyl
CH2), 2.18 (s, 3H, Xyl Me), 2.50 (m, 1H, allyl CH2), 2.80 (s, 3H, Xyl
Me), 3.70 (m, 1H, allyl CH), 6.12 (s, 1H, Xyl o-CH), 6.77 (d, 1H,
3JHH ) 7.4, Xyl CH), 7.25 (d, 1H, 3JHH ) 7.4, Xyl CH). 13C{1H} NMR
(125 MHz, C6D6) δ 10.2 (C5Me5), 21.0 (Xyl Me), 22.6 (allyl Me), 27.6
(Xyl Me), 28.6 (allyl Me), 39.6 (allyl CH2), 96.1 (allyl CH), 107.3
(C5Me5), 124.8 (Xyl CH), 130.4 (Xyl CH), 140.4 (Xyl o-CH), 148.0
(allyl C), 170.3 (Xyl Cipso). Anal. Calcd for C23H33NOW: C, 52.78; H,
6.36; N, 2.68. Found: C, 52.67; H, 6.26; N, 2.66.
Cp*W(NO)(CH2C6H4-3-Me)(η3-1,1-Me2C3H3) (7), Cp*W(NO)-
(C6H3-2,4-Me2)(η3-1,1-Me2C3H3) (8), and Cp*W(NO)(C6H3-3,5-
Me2)(η3-1,1-Me2C3H3) (9). Complexes 7-9 were prepared via the
thermolysis of 1 (100 mg, 0.20 mmol) in m-xylene. The resulting residue
following removal of solvent was an orange/yellow oil. Subsequent
workup and separation of products afforded complex 7 as orange blocks
(15 mg, 14%) and a mixture of complexes 8 and 9 as orange/yellow
microcrystals (40 mg, 37%).
7: IR (cm-1) 1560 (s, νNO). MS (LREI, m/z, probe temperature 120
1
°C) 523 [P+, 184W]. H NMR (400 MHz, C6D6) δ 1.06 (s, 3H, allyl
Me), 1.11 (s, 3H, allyl Me), 1.45 (s, 15H, C5Me5), 1.53 (m, 1H, allyl
2
CH2), 1.79 (d, 1H, JHH ) 11.4, Mxyl CH2), 2.38 (s, 3H, Mxyl Me),
2
2.46 (m, 1H, allyl CH2), 2.81 (d, 1H, JHH ) 11.4, Mxyl CH2), 3.54
3
(m, 1H, allyl CH), 6.89 (d, 1H, JHH ) 7.3, Mxyl CH), 7.27 (t, 1H,
3
3JHH ) 7.5, Mxyl CH), 7.54 (d, 1H, JHH ) 7.8, Mxyl CH), 7.58 (s,
1H, Mxyl o-CH). 13C{1H} NMR (100 MHz, C6D6) δ 9.7 (C5Me5), 22.0
(Mxyl Me), 27.5 (allyl Me), 27.8 (Mxyl CH2), 39.6 (allyl CH2), 98.2
(allyl CH), 106.3 (C5Me5), 124.0 (Mxyl CH), 128.0 (obs Mxyl CH),
128.0 (obs Mxyl CH), 131.4 (Mxyl CH), 136.5 (Mxyl C), 153.0 (allyl
C). Anal. Calcd for C23H33NOW: C, 52.78; H, 6.36; N, 2.68. Found:
C, 52.76; H, 6.20; N, 2.71.
8,9: IR (cm-1) 1552 (s, νNO). MS (LREI, m/z, probe temperature
120 °C) 523 [P+, 184W]. Anal. Calcd for C23H33NOW: C, 52.78; H,
6.36; N, 2.68. Found: C, 52.54; H, 6.43; N, 2.83.
8: 1H NMR (400 MHz, C6D6) δ 0.81 (s, 3H, allyl Me), 1.54 (s,
15H, C5Me5), 1.74 (s, 3H, allyl Me), 1.78 (m, 1H, allyl CH2), 2.28 (s,
3H, Xyl Me), 2.49 (m, 1H, allyl CH2), 2.82 (s, 3H, Xyl Me), 3.71 (m,
Cp*W(NO)(CH2C6H4-4-Me)(η3-1,1-Me2C3H3) (5) and Cp*W-
(NO)(C6H3-2,5-Me2)(η3-1,1-Me2C3H3) (6). Complexes 5 and 6 were
formed via the thermolysis of 1 (292 mg, 0.60 mmol) in p-xylene. The
resulting residue following removal of solvent was an orange/yellow
oil. The solid products obtained after workup (vide supra) were
dissolved in a minimal amount of THF, and the resulting solution was
applied to a preparative-TLC plate using a syringe with a 26-gauge
needle to obtain a 10-mm wide orange/yellow band. The plate was left
1H, allyl CH), 6.22 (d, 1H, 2JHH ) 7.4, Xyl CH), 6.82 (d, 1H, 2JHH
)
7.4, Xyl CH), 7.15 (obs, 1H, Xyl CH). 13C{1H} NMR (100 MHz, C6D6)
δ 10.3 (C5Me5), 21.2 (Xyl Me), 23.0 (allyl Me), 28.4 (Xyl Me), 28.7
9
J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003 15219

A R T I C L E S
Ng et al.
(allyl Me), 39.7 (Xyl Me), 96.0 (allyl CH), 107.0 (C5Me5), 124.7 (Xyl
CH), 131.7 (Xyl CH), 139.3 (Xyl CH).
min via a cannula, whereupon the initial deep-red color of the solution
changed to orange/yellow after being stirred at -78 °C for 10 min.
The final mixture was then warmed to 0 °C, and the reaction was
allowed to proceed for 1 h. The solvent was then removed at 0 °C
over a period of 30 min. The residue was extracted with CH2Cl2 (3 ×
10 mL), and the combined extracts were filtered through an alumina-
(I) plug (2 × 3 cm) supported on a frit to obtain an orange filtrate. The
CH2Cl2 was removed from the filtrate under vacuum, and the residue
was recrystallized from a 2:1 Et2O/hexanes mix at -30 °C to obtain
complex 13 as yellow and orange blocks (138 mg, 52%).
9: 1H NMR (400 MHz, C6D6) δ 0.86 (s, 3H, allyl Me), 1.55 (s,
15H, C5Me5), 1.65 (bs, 3H, allyl Me), 1.77 (m, 1H, allyl CH2), 2.28 (s,
3H, Xyl Me), 2.34 (s, 3H, Xyl Me), 2.50 (m, 1H, allyl CH2), 3.56
(bm, 1H, allyl CH), 6.30 (bs, 1H, Xyl CH), 6.71 (s, 1H, Xyl CH), 8.04
(s, 1H, Xyl CH). 13C{1H} NMR (100 MHz, C6D6) δ 10.3 (C5Me5),
21.4 (Xyl Me), 21.6 (Xyl Me), 21.9 (allyl Me), 29.3 (allyl Me), 37.4
(allyl CH2), 95.6 (allyl CH), 107.3 (C5Me5), 125.6 (Xyl CH), 138.3
(Xyl CH), 140.0 (Xyl CH).
Cp*W(NO)(CH2C6H4-2-Me)(η3-1,1-Me2C3H3) (10), Cp*W(NO)-
(C6H3-2,3-Me2)(η3-1,1-Me2C3H3) (11), and Cp*W(NO)(C6H3-3,4-
Me2)(η3-1,1-Me2C3H3) (12). Complexes 10-12 were formed by the
thermolysis of 1 (205 mg, 0.42 mmol) in o-xylene. The resulting residue
following removal of solvent was an orange/yellow oil. Subsequent
workup and separation of products afforded complex 10 as orange
microcrystals (21 mg, 10%) and a mixture of complexes 11 and 12 as
orange/yellow microcrystals (56 mg, 26%).
13: IR (cm-1) 1552 (s, νNO). MS (LREI, m/z, probe temperature
1
120 °C) 509 [P+, 184W]. H NMR (500 MHz, C6D6) δ 1.04 (s, 3H,
allyl Me), 1.14 (s, 3H, allyl Me), 1.43 (s, 15H, C5Me5), 1.55 (br s, 1H,
2
allyl CH2), 1.78 (d, 1H, JHH ) 11.5, Bzl CH2), 2.46 (m, 1H, allyl
2
CH2), 2.81 (d, 1H, JHH ) 11.5, Bzl CH2), 3.52 (m, 1H, allyl CH),
7.03 (t, 1H, 3JHH ) 7.4, aryl p-CH), 7.32 (t, 2H, 3JHH ) 7.4, aryl m-CH),
7.71 (d, 2H, 3JHH ) 7.4, aryl o-CH). 13C{1H} NMR (125 MHz, C6D6)
δ 9.7 (C5Me5), 20.5 (allyl Me), 27.5 (allyl Me), 27.8 (Bzl CH2), 39.8
(allyl CH2), 97.9 (allyl CH), 106.4 (C5Me5), 123.1 (aryl p-CH), 127.7
(aryl m-CH), 130.4 (aryl o-CH), 153.4 (allyl C). Anal. Calcd for C22H31-
NOW: C, 51.88; H, 6.13; N, 2.75. Found: C, 51.95; H, 6.25; N, 2.86.
14-16: IR (cm-1) 1561 (s, νNO). MS (LREI, m/z, probe temperature
150 °C) 509 [P+, 184W]. Anal. Calcd for C22H31NOW: C, 51.88; H,
6.13; N, 2.75. Found: C, 51.84; H, 6.49; N, 2.85.
10: IR (cm-1) 1552 (s, νNO). MS (LREI, m/z, probe temperature
1
150 °C) 523 [P+, 184W]. H NMR (500 MHz, C6D6) δ 0.81 (m, 1H,
allyl CH2), 1.20 (s, 3H, allyl Me), 1.27 (s, 3H, allyl Me), 1.49 (s, 15H,
2
C5Me5), 2.04 (m, 1H, allyl CH2), 2.19 (d, 1H, JHH ) 10.7, Bzl CH2),
2
2.36 (d, 1H, JHH ) 10.7, Bzl CH2), 2.45 (s, 3H, Oxyl Me), 3.98 (m,
1H, allyl CH), 7.05 (m, 1H, Oxyl CH), 7.10 (obs 1H, Oxyl CH), 7.10
(obs, 1H, Oxyl CH), 7.23 (d, 1H, 3JHH ) 7.0, Oxyl CH). 13C{1H} NMR
(125 MHz, C6D6) δ 9.7 (C5Me5), 20.3 (allyl Me), 21.5 (Oxyl Me), 26.9
(allyl Me), 26.9 (Bzl CH2), 103.2 (allyl CH), 106.5 (C5Me5), 125.1
(Oxyl CH), 125.8 (Oxyl CH), 129.0 (Oxyl CH), 130.1 (Oxyl CH). Anal.
Calcd for C23H33NOW: C, 52.78; H, 6.36; N, 2.68. Found: C, 53.02;
H, 6.36; N, 2.92.
11,12: IR (cm-1) 1552 (s, νNO). MS (LREI, m/z, probe temperature
150 °C) 523 [P+, 184W]. Anal. Calcd for C23H33NOW: C, 52.78; H,
6.36; N, 2.68. Found: C, 52.93; H, 6.37; N, 2.61.
14: 1H NMR (400 MHz, C6D6) δ 2.26 (s, 3H, Tol Me), 3.55 (br m,
3
1H, allyl CH), 6.47 (br s, 1H, Tol CH), 6.88 (d, 1H, JHH ) 7.1, Tol
3
3
CH), 7.25 (t, 1H, JHH ) 7.1, Tol CH), 8.21 (d, 1H, JHH ) 7.1, Tol
CH). 13C{1H} NMR (100 MHz, C6D6) δ 10.2 (C5Me5), 21.7 (Tol Me),
95.8 (allyl CH), 106.9 (C5Me5), 124.8 (Tol CH), 128.0 (obs, Tol CH),
139.5 (Tol CH), 141.2 (Tol CH).
15: 1H NMR (400 MHz, C6D6) δ 2.35 (s, 3H, Tol Me), 3.55 (br m,
3
1H, allyl CH), 6.47 (br s, 1H, Tol CH), 6.94 (d, 1H, JHH ) 6.6, Tol
CH), 7.16 (obs, 1H, Tol CH), 8.24 (s, 1H, Tol CH). 13C{1H} NMR
(100 MHz, C6D6) δ 10.2 (C5Me5), 21.9 (Tol Me), 95.8 (allyl CH), 106.9
(C5Me5), 123.5 (Tol CH), 126.9 (Tol CH), 137.2 (Tol CH), 143.1 (Tol
CH).
11: 1H NMR (400 MHz, C6D6) δ 0.85 (s, 3H, allyl Me), 1.55 (s,
15H, C5Me5), 1.59 (s, 3H, allyl Me), 1.76 (obs, 1H, allyl CH2), 2.21
(br s, 6H, 2 Xyl Me), 2.50 (m, 1H, allyl CH2), 3.56 (br m, 1H, allyl
3
16: 1H NMR (400 MHz, C6D6) δ 2.28 (s, 3H, Tol Me), 3.55 (br m,
CH), 6.45 (br s, 2H, 2 Xyl CH), 7.07 (d, 1H, JHH ) 7.4, Xyl CH).
13C{1H} NMR (100 MHz, C6D6) δ 10.3 (C5Me5), 19.6 (Xyl Me), 19.8
(Xyl Me), 24.7 (allyl Me), 28.4 (allyl Me), 37.4 (allyl CH2), 95.9 (allyl
CH), 106.9 (C5Me5), 128.8 (Xyl CH), 137.8 (Xyl CH), 141.7 (Xyl CH).
12: 1H NMR (400 MHz, C6D6) δ 0.88 (s, 3H, allyl Me), 1.55 (s,
15H, C5Me5), 1.65 (br s, 3H, allyl Me), 1.76 (obs, 1H, allyl CH2), 2.18
(s, 3H, Xyl Me), 2.27 (s, 3H, Xyl Me), 2.50 (m, 1H, allyl CH2), 3.56
(br s, 1H, allyl CH), 7.13 (obs, 1H, Xyl CH), 8.17 (obs, 1H, Xyl CH),
8.19 (s, 1H, Xyl CH). 13C{1H} NMR (100 MHz, C6D6) δ 10.3 (C5Me5),
19.5 (Xyl Me), 19.8 (Xyl Me), 21.8 (allyl Me), 29.4 (allyl Me), 37.3
(allyl CH2), 95.8 (allyl CH), 106.9 (C5Me5), 130.2 (Xyl CH), 140.2
(Xyl CH), 143.7 (Xyl CH).
3
1H, allyl CH), 6.58 (br s, 1H, Tol CH), 7.08 (d, 1H, JHH ) 6.6, Tol
3
CH), 7.16 (obs, 1H, Tol CH), 8.31 (d, 1H, JHH ) 7.1, Tol CH). 13C-
{1H} NMR (100 MHz, C6D6) δ 10.2 (C5Me5), 21.5 (Tol Me), 95.8
(allyl CH), 106.9 (C5Me5), 128.0 (obs Tol CH), 129.6 (Tol CH), 140.1
(Tol CH), 142.4 (Tol CH).
Cp*W(NO)(η4-trans-H2CdCHC(Me)dCH2) (17). Preparation of
this η4-trans-diene tungsten complex was accomplished by using a
modified version of the previously published procedure and employing
isoprene as the trapping agent.55 Previous research in this group has
shown that the likelihood of forming the cis-isomer was unlikely,
because similar cis-diene complexes that had been prepared spontane-
ously isomerized to the thermodynamically more stable trans form.56-58
In a thick-walled bomb, Cp*W(NO)(CH2SiMe3)259 (401 mg, 0.77 mmol)
was dissolved in pentane (60 mL), and isoprene (3 mL, 30 mmol) was
syringed into the reaction vessel. The resulting mixture was frozen using
a liquid N2 bath, and H2 gas (14 psig) was then introduced. The contents
of the bomb were allowed to warm to room temperature and react while
being stirred overnight. After 16 h, the final mixture was concentrated
and cooled to obtain yellow crystals of 17 (20 mg, 6%).
Cp*W(NO)(CH2C6H5)(η3-1,1-Me2C3H3) (13), Cp*W(NO)(C6H4-
2-Me)(η3-1,1-Me2C3H3) (14), Cp*W(NO)(C6H4-3-Me)(η3-1,1-Me2C3H3)
(15), and Cp*W(NO)(C6H4-4-Me)(η3-1,1-Me2C3H3) (16). Complexes
13-16 were prepared via the thermolysis of 1 (200 mg, 0.41 mmol) in
toluene. After the 6-h reaction period, the resulting solution was a dark
orange/brown color which yielded a brown oil upon solvent removal
under vacuum. Subsequent workup and separation of products afforded
complex 13 and a mixture of complexes 14-16 as orange/yellow blocks
(156 mg, 75%).
Complex 13 was prepared by a method similar to the procedure
published for Cp*W(NO)(CH2C6H5)(CH2CMe3).20 In the glovebox, a
100-mL Schlenk tube was charged with a magnetic stir bar and (1,1-
Me2C3H3)2Mg‚x(dioxane) (103 mg, 0.53 mmol). A 200-mL Schlenk
tube was then charged with a stir bar and Cp*W(NO)(CH2C6H5)Cl (250
mg, 0.53 mmol). On a vacuum line, THF (80 mL) was vacuum
transferred into the Schlenk tube containing the organometallic halide
and into the Schlenk tube with the magnesium reagent (10 mL). The
two resulting solutions were then mixed at -78 °C over a period of 5
17: IR (Nujol, cm-1) 1560 (w, νNO). MS (LREI, m/z, probe
1
temperature 120 °C) 417 [P+, 184W]. H NMR (400 MHz, C6D6) δ
(55) Debad, J. D.; Legzdins, P.; Young, M. A. J. Am. Chem. Soc. 1993, 115,
2051.
(56) Hunter, A. D.; Legzdins, P.; Nurse, C. R. J. Am. Chem. Soc. 1985, 107,
1791.
(57) Hunter, A. D.; Legzdins, P.; Nurse, C. R.; Einstein, F. W. B.; Willis, A.
C.; Bursten, B. E.; Gatter, M. J. J. Am. Chem. Soc. 1986, 108, 3843.
(58) Christensen, N. J.; Hunter, A. D.; Legzdins, P. Organometallics 1989, 8,
930.
(59) Legzdins, P.; Rettig, S. J.; Sanchez, L. Organometallics 1988, 7, 2394.
9
15220 J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003

Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
2
4
1
0.95 (dd, JHH ) 3.91, JHH ) 0.98, 1H, CdCH2), 1.11 (m, 1H, CH),
1.64 (s, 15H, C5Me5), 2.05 (s, 3H, CMe), 2.35 (m, 1H, CHdCH2),
C6D6) δ -21.4 (s, JPW ) 345, PMe3). Sel NOE (400 MHz, C6D6) δ
irrad. at 0.67, NOE at 1.67, 1.97, and 2.44, irrad. at 1.78, NOE at 1.27
and 2.44. Anal. Calcd for C18H32NOPW: C, 43.83; H, 6.54; N, 2.84.
Found: C, 43.65; H, 6.53; N, 2.97.
2
3
2
3.15 (dd, JHH ) 4.16, JHH ) 13.94, 1H, CHdCH2), 3.29 (d, JHH
)
3.67, 1H, CdCH2). 13C{1H} NMR (125 MHz, C6D6) δ 10.2 (C5Me5),
18.5 (CMe), 50.4 (CHdCH2), 55.2 (CdCH2), 80.3 (CH), 103.9
(C(Me)dCH2), 110.2 (C5Me5). Sel NOE (400 MHz, C6D6) δ irrad. at
2.05, NOE at 3.15 and 3.29, irrad. at 1.64, NOE at 0.95, 1.11, 2.35,
and 3.29. Anal. Calcd for C15H23NOW: C, 43.18; H, 5.56; N, 3.36.
Found: C, 43.26; H, 5.39; N, 3.34.
Cp*W(NO)(η3-1,1,2-Me3C3H2)(η1-3,3-Me2C3H3) (21). Complex 21
was prepared by the thermolysis of 1 (66 mg, 0.13 mmol) in
2,3-dimethyl-2-butene. The resulting residue was a bright orange/red
oil which was triturated with hexanes (2 × 10 mL) to obtain red specks
among the oil upon removal of the hexanes in vacuo. The residue was
dissolved in Et2O, and the solution was eluted through an alumina(I)
column (0.5 × 3 cm). The solvent was then removed from the eluate,
and orange blocks of 21 were isolated by recrystallization of the residue
from pentane (26 mg, 38%).
Thermolyses of 17 in Benzene-d6 and Cyclohexene. Thermolyses
of complex 17 were effected in benzene-d6 and cyclohexene at 50 °C
for 6 h to test its thermal stability. After this time, 1H NMR
spectroscopic data (C6D6) indicated that no reaction had occurred.
Cp*W(NO)(η3-CH2C(CHCHdCHC3H6)CMe2)(H) (18) and Cp*W-
(NO)(η3-CH2CHC)(Me)CH2CâH(C4H8)CrH (19). Complexes 18 and
19 were formed by the thermolysis of 1 (106 mg, 0.22 mmol) in
cyclohexene. The volatiles were removed under high vacuum for 1 h,
the resulting residue was dissolved in Et2O, and this solution was
transferred to the top of an alumina(I) column (0.5 × 1 cm) and eluted
with Et2O. The yellow/orange eluate thus obtained was again taken to
dryness under high vacuum. The residue was recrystallized from a
minimal amount of pentane to obtain 18 as a red amorphous solid (19
mg, 35%) and 19 as yellow microcrystals (21 mg, 39%) that could be
separated manually.
21: IR (cm-1) 1577 (s, νNO). MS (LREI, m/z, probe temperature
120 °C) 501 [P+, 184W]. H NMR (400 MHz, C6D6) δ 0.70 (s, 3H,
1
η3-allyl Me), 1.07 (d, JHH ) 4.6, 1H, η3-allyl CH2), 1.33 (s, 3H, η3-
2
allyl Me), 1.56 (obs, 1H, η1-allyl CH2), 1.59 (s, 15H, C5Me5), 1.96 (s,
3H, η1-allyl Me), 1.97 (obs, 1H, η1-allyl CH2), 1.98 (s, 3H, η1-allyl
Me), 2.19 (s, 3H, η3-allyl CMe), 2.48 (d, 2JHH ) 4.6, 1H, η3-allyl CH2),
5.82 (t, 3JHH ) 7.3, 1H, η1-allyl CH. 13C{1H} NMR (100 MHz, C6D6)
δ 9.9 (C5Me5), 18.6 (η1-allyl Me), 18.6 (η1-allyl CH2), 22.6 (η3-allyl
Me), 22.6 (η3-allyl Me), 22.8 (η3-allyl Me), 26.0 (η1-allyl Me), 44.8
(η3-allyl CH2), 106.9 (C5Me5), 133.3 (η1-allyl-CH). Sel NOE (400 MHz,
C6D6) δ irrad. at 1.59, NOE at 0.70 and 1.07. Anal. Calcd for C21H35-
NOW: C, 50.31; H, 7.04; N, 2.79. Found: C, 50.58; H, 7.20; N, 2.89.
Cp*W(NO)(η3-C6H9)(H) (22) and Cp*W(NO)(η3-C7H11)(H) (23a,b).
Complex 22 was formed via thermolysis of 1 (50 mg, 0.10 mmol) in
cyclohexane, and complexes 23a,b were formed via the thermolysis
of 1 (80 mg, 0.16 mmol) in methylcyclohexane. The reaction mixtures
at the end of the 6-h periods were a dark orange/brown color, and the
residues formed upon removal of the solvent were brown oils. The
residues were triturated with hexanes (2 × 10 mL) which were dried
under high vacuum for approximately 1 h to obtain mixtures of dark
specks interspersed in brown oils. These mixtures were then redissolved
in 1:3 Et2O/hexanes solvent mixtures, and the resulting solutions were
eluted through alumina(I) columns (0.5 × 3 cm) to obtain yellow
eluates. The solvent was once again removed in vacuo, and the final
residues were recrystallized from 3:1 pentane/Et2O solvent mixtures
to obtain complexes 23a,b as yellow microcrystals (3.5 mg, 5%), and
complex 22 as yellow blocks (14 mg, 32%). Complexes 23a,b were
identified by comparison of their 1H NMR spectra to those previously
reported.20
18: IR (cm-1) 1558 (s, νNO), 1912 (w, νWH). MS (LREI, m/z, probe
temperature 120 °C) 499 [P+, 184W]. H NMR (400 MHz, C6D6) δ
1
-0.40 (s, 1JWH ) 131, 1H, WH), 0.88 (br m, 1H, CH2C(dCMe2), 1.01
3
(d, JWH ) 1.1, 3H, dCMe2), 1.56 (obs, 1H, C3H6), 1.76 (s, 15H,
C5Me5), 1.75 (obs, 1H, C3H6), 1.86 (obs, 3H, C3H6), 2.01 (br s, 1H,
C3H6), 2.51 (d, 3JWH ) 2.5, 3H, dCMe2), 3.25 (m, 1H, CH2C(dCMe2)),
3.61 (br s, CH(HCdCH)), 5.91 (m, 1H, HCdCH), 6.27 (m, 1H,
HCdCH). 13C{1H} NMR (100 MHz, C6D6) δ 10.6 (C5Me5), 21.0
(C3H6), 25.7 (C3H6), 26.5 (Me), 27.3 (Me), 30.9 (C3H6), 39.8 (CH-
(HCdCH)), 45.8 (CH2C(dCMe2)), 81.9 (dCMe2), 105.1 (C5Me5),
127.1 (CH2C(dCMe2)), 129.2 (HCdCH), 130.1 (HCdCH). Anal. Calcd
for C21H33NOW: C, 50.51; H, 6.66; N, 2.80. Found: C, 50.63; H,
6.92; N, 2.83.
19: IR (cm-1) 1559 (s, νNO). MS (LREI, m/z, probe temperature
100 °C) 499 [P+, 184W]. H NMR (400 MHz, C6D6) δ 1.20 (m, 1H,
1
C4H8), 1.23 (m, 1H, CRH), 1.31 (m, 1H, η3-CH2CHC), 1.38 (obs, 1H,
C4H8), 1.54 (s, 15H, C5Me5), 1.65 (obs, 1H, C4H8), 1.73 (obs, 1H, CâH),
1.76 (obs, 1H, C4H8), 1.79 (obs, 1H, C4H8), 1.82 (m, 1H, C4H8), 1.96
(obs, 1H, CH2Câ), 2.00 (obs, 1H, η3-CH2CHC), 2.08 (s, 3H, Me), 2.25
(m, 1H, C4H8), 2.42 (m, 1H, C4H8), 2.44 (m, 1H, CH2Câ), 3.40 (m,
1H, η3-CH2CHC). 13C{1H} NMR (100 MHz, C6D6) δ 9.7 (C5Me5), 21.8
(C4H8), 24.6 (Me), 32.7 (η3-CH2CHC), 33.1 (C4H8), 33.8 (C4H8), 34.1
(C4H8), 35.4 (CH2Câ), 42.2 (CR), 57.6 (Câ), 93.0 (η3-CH2CHC), 104.8
(C5Me5), 139.2 (η3-CH2CHC). Anal. Calcd for C21H33NOW: C, 50.51;
H, 6.66; N, 2.80. Found: C, 50.74; H, 6.54; N, 2.79.
22: IR (cm-1) 1568 (s, νNO), 1898 (m, νWH). MS (LREI, m/z, probe
temperature 120 °C) 431 [P+, 184W]. H NMR (500 MHz, C6D6) δ
1
1
-0.57 (s, JWH ) 132, 1H, WH), 1.16 (m, 1H, cyclohexenyl CaH2),
1.42 (m, 1H, cyclohexenyl CaH2), 1.69 (s, 15H, C5Me5), 2.46 (m, 1H,
cyclohexenyl CbH2), 2.58 (m, 1H, cyclohexenyl CbH2), 2.62 (m, 2H,
cyclohexenyl CcH2), 2.75 (m, 1H, allyl CxH), 3.59 (m, 1H, allyl CyH),
5.30 (m, 1H, allyl CzH). 13C{1H} NMR (125 MHz, C6D6) δ 10.4
(C5Me5), 19.9 (cyclohexenyl CaH2), 26.6 (cyclohexenyl CcH2), 28.7
(cyclohexenyl CbH2), 61.8 (allyl CyH2), 73.4 (allyl CzH), 93.2 (allyl
CxH2), 103.9 (C5Me5). Anal. Calcd for C16H25NOSiW: C, 44.56; H,
5.84; N, 3.25. Found: C, 44.40; H, 5.76; N, 3.24.
Kinetic Studies. A J. Young NMR tube was charged with 1 (10
mg, 0.020 mmol), benzene-d6 (0.8 mL), and hexamethyldisilane (1 mg,
0.007 mmol) as an inert internal standard, and the contents were mixed
thoroughly. The thermolysis of 1 was monitored by 1H NMR
spectroscopy at 323.0 K with the number of scans set to one. The loss
of starting material versus time was determined by the integration of
the neopentyl CMe3 signal versus the hexamethyldisilane signal, except
for the t ) 0 value which was extrapolated from the plot of starting
material loss versus time. The first-order rate constant for the
decomposition of 1 was determined from the plot of ln(I(t)/I(0)) versus
time. After 4.5 h, the sample was removed from the probe, and the
crystalline product 4a-c-d6 was analyzed by NMR and MS spectro-
scopic techniques.
Cp*W(NO)(PMe3)(η2-H2CdCdCMe2) (20). Complex 20 was
prepared by the thermolysis of 1 (67 mg, 0.14 mmol) in neat
trimethylphosphine. The final residue was triturated with hexanes (2
× 10 mL), the solvent was removed, and the solid was dried for 1 h
under high vacuum. Hexane extracts of this solid were transferred to
the top of an alumina(I) column (0.5 × 3 cm) and were eluted with
Et2O to obtain a yellow eluate. The solvent was once again removed
from the eluate in vacuo, and the final residue was recrystallized from
a 3:1 pentane/Et2O solvent mix to obtain complex 20 as yellow blocks
(16 mg, 24%).
20: IR (cm-1) 1541 (s, νNO). MS (LREI, m/z, probe temperature
120 °C) 493 [P+, 184W]. 1H NMR (400 MHz, C6D6) δ 0.67 (d, 2JHH
)
2
7.31, 1H, allene CH2), 1.27 (d, JHP ) 8.8, 9H, PMe3), 1.67 (s, 15H,
C5Me5), 1.78 (s, 3H, allene Me), 1.97 (br s, 1H, allene CH2), 2.44 (s,
3H, allene Me). 13C{1H} NMR (100 MHz, C6D6) δ 7.7 (allene CH2),
10.4 (C5Me5), 17.3 (d, 2JCP ) 31, PMe3), 25.9 (allene Me), 31.9 (allene
Me), 104.6 (C5Me5), 165.7 (dCdCH2). 31P {1H} NMR (121 MHz,
9
J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003 15221

A R T I C L E S
Ng et al.
Table 1. X-ray Crystallographic Data for Complexes 2, 3, 4, 18, 19, 20, and 21
2
3
4
18
19
20
21
Crystal Data
empirical formula
cryst habit, color
cryst size (mm)
C19H35NOWSi
platelet, orange block, orange
C24H35NOW
C21H29NOW
prism, yellow
0.30 × 0.20 ×
0.20
C21H33NOW
block, yellow
0.90 × 0.20 ×
0.10
C21H33NOW
block, yellow
0.30 × 0.25 ×
0.05
C18H32NOPW
chip, yellow
0.25 × 0.20 ×
0.10
C21H35NOW
prism, yellow
0.45 × 0.35 ×
0.20
0.30 × 0.15 ×
0.40 × 0.30 ×
0.08
0.15
cryst syst
space group
vol (Å3)
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
orthorhombic
Pbca
monoclinic
P21/c
orthorhombic
P212121
2013.0(3)
8.2431(7)
9.2094(9)
26.517(3)
90
90
90
4
orthorhombic
Pbca
monoclinic
P21/c
monoclinic
P21/n
4228.4(3)
15.3944(6)
8.4977(3)
32.326(1)
90
90.753(3)
90
8
4456.2(3)
14.2207(7)
15.9939(7)
19.5926(9)
90
90
90
8
1949.6(1)
12.8869(3)
9.0219(3)
16.7835(7)
90
92.439(2)
90
4
3908.5(5)
14.8888(10)
14.7065(9)
17.8503(12)
90
90
90
8
1969.10(18)
9.1458(5)
13.6500(7)
15.9576(9)
90
98.724(3)
90
4
2055.5(3)
9.1734(7)
16.9621(11)
13.2647(10)
90
95.201(4)
90
4
R (deg)
â (def)
γ (deg)
Z
density (calc) (Mg/m3) 1.500
1.602
52.03
1.687
59.39
1.648
5.75
1.697
5.92
1.664
59.50
1.62
58.05
abs coeff (cm-1
)
54.73
F000
1904.00
2144.00
976.00
992
1984
976
1000
Data Collection and Refinement
measd reflns: total
measd reflns: unique
final R indicesa
12 879
4410
R1 ) 0.036,
wR2 ) 0.071
1.60
41 082
5645
R1 ) 0.031,
wR2 ) 0.038
0.80
13 123
4484
R1 ) 0.038,
wR2 ) 0.066
1.07
4239
3863
R1 ) 0.0246,
wR2 ) 0.049
0.882
4347
3155
R1 ) 0.0331,
wR2 ) 0.0825
0.888
4136
3358
R1 ) 0.0281,
wR2 ) 0.067
0.947
4496
3684
R1 ) 0.0311,
wR2 ) 0.075
0.985
GOF on F2 b
largest diff. peak
and hole (e Å-3
2.01 and
-1.75
3.30 and
-2.01
1.08 and
-1.64
0.92 and
-1.02
2.985 and
-3.000
1.580 and
-2.497
3.379 and
-1.460
)
a R1 on F ) ∑|(|Fo| - |Fc|)|/∑|Fo|; wR2 ) [(∑(Fo - Fc )2)/∑w(Fo )2]1/2; w ) [σ2Fo ]-1
.
b GOF ) [∑(w(|Fo| - |Fc|)2)/degrees of freedom]1/2
.
2
2
2
2
X-ray Crystallography. Data collection for each compound was
carried out at -100 ( 1 °C on a Rigaku/ADSC CCD diffractometer
using graphite-monochromated Mo KR radiation.
included in fixed positions. The final cycle of full-matrix least-squares
analysis was based on 4239 observed reflections and 236 variable
parameters.
Data for 19 were collected to a maximum 2θ value of 55.8° in 0.5°
oscillations with 23.0 s exposures. The structure was solved by direct
methods62 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H11a, H11b, H12a,
H16a, and H21a were refined isotropically, and all other hydrogen atoms
were included in fixed positions. The final cycle of full-matrix least-
squares analysis was based on 4347 observed reflections and 243
variable parameters.
Data for 2 were collected to a maximum 2θ value of 55.9° in 0.5°
oscillations with 27.0 s exposures. The structure was solved by direct
methods60 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H11a, H11b, and
H12 were refined isotropically, and all other hydrogen atoms were
included in fixed positions. The final cycle of full-matrix least-squares
analysis was based on 4156 observed reflections and 221 variable
parameters.
Data for 20 were collected to a maximum 2θ value of 55.8° in 0.5°
oscillations with 20.0 s exposures. The structure was solved by direct
methods62 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H1 and H2 were
refined isotropically, and all other hydrogen atoms were included in
fixed positions. The final cycle of full-matrix least-squares analysis
was based on 4135 observed reflections and 217 variable parameters.
Data for 21 were collected to a maximum 2θ value of 55.7° in 0.5°
oscillations with 20.0 s exposures. The structure was solved by direct
methods62 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H1, H2, H3, H4,
and H5 were refined isotropically, and all other hydrogen atoms were
included in fixed positions. The final cycle of full-matrix least-squares
analysis was based on 4496 observed reflections and 247 variable
parameters.
Data for 3 were collected to a maximum 2θ value of 55.7° in 0.5°
oscillations with 20.0 s exposures. The structure was solved by direct
methods60 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H16, H17, H27,
H28, and H29 were refined isotropically, and all other hydrogen atoms
were included in fixed positions. The final cycle of full-matrix least-
squares analysis was based on 5120 observed reflections and 264
variable parameters.
Data for 4 were collected to a maximum 2θ value of 57.5° in 0.5°
oscillations with 12.0 s exposures. The structure was solved by direct
methods60 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H6, H7, and H8
were refined isotropically, and all other hydrogen atoms were included
in fixed positions. The final cycle of full-matrix least-squares analysis
was based on 4264 observed reflections and 229 variable parameters.
Data for 18 were collected to a maximum 2θ value of 55.7° in 0.5°
oscillations with 35.0 s exposures. The structure was solved by direct
methods62 and expanded using Fourier techniques.61 All non-hydrogen
atoms were refined anisotropically; hydrogen atoms H11a, H11b, and
H22 were refined isotropically, and all other hydrogen atoms were
For each structure, neutral-atom scattering factors were taken from
Cromer and Waber.63 Anomalous dispersion effects were included in
Fcalc;
64 the values for ∆f ′ and ∆f ′′ were those of Creagh and McAuley.65
The values for mass attenuation coefficients are those of Creagh and
Hubbell.66 All calculations were performed using the CrystalClear
software package of Rigaku/MSC,67 the teXsan crystallographic
(60) SIR97: Altomare, A.; Burla, M. C.; Cammalli, G.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
A. J. Appl. Crystallogr. 1999, 32, 115-119.
(63) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystallography;
Kynoch Press: Birmingham, 1974; Vol. IV.
(64) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781-782.
(65) Creagh, D. C.; McAuley, W. J. International Tables for X-ray Crystal-
lography; Kluwer Academic Publishers: Boston, 1992; Vol. C.
(66) Creagh, D. C.; Hubbell, J. H. International Tables for X-ray Crystal-
lography; Kluwer Academic Publishers: Boston, 1992; Vol. C.
(61) PATTY: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. University
of Nijmegen, The Netherlands, 1992.
(62) SIR92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A. J.
Appl. Crystallogr. 1993, 26, 343.
9
15222 J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003

Thermal Activation of Hydrocarbon C−H Bonds
A R T I C L E S
software package of Molecular Structure Corp.,68 or Shelxl-97.69 X-ray
crystallographic data for all seven structures are presented in Table 1,
and full details of all crystallographic analyses are provided in the
Supporting Information.
scholarships to C.S.A. and T.W.H. We also thank Ms. N.
Thompson for assistance with the statistical analyses and Dr.
C. B. Pamplin for technical assistance. P.L. is a Canada Council
Killam Research Fellow.
Acknowledgment. We are grateful to the Natural Sciences
and Engineering Research Council of Canada for support of
this work in the form of grants to P.L. and postgraduate
Supporting Information Available: Kinetic data for the
thermal decomposition of 1 in benzene-d6 at 50 °C (PDF) and
full details of crystallographic (CIF) analyses of complexes 2,
3, 4, 18, 19, 20, and 21. This material is available free of charge
via the Internet at http://pubs.acs.org.
(67) CrystalClear: Version 1.3.5b20; Molecular Structure Corp.: The Wood-
lands, TX, 2002.
(68) teXsan; Molecular Structure Corp.: The Woodlands, TX, 1985 and 1992.
(69) SHELXL97; Sheldrick, G. M. University of Go¨ttingen: Germany, 1997.
JA037076Q
9
J. AM. CHEM. SOC. VOL. 125, NO. 49, 2003 15223