Unsymmetrical Saturated Ketones Resulting from Activations of Hydrocarbon C(sp3)-H and C(sp2)-H Bonds Effected by CpW(NO)(H)(η3-allyl) Complexes

Article abstract of DOI:10.1021/acs.organomet.5b00537

C-H activations of a C(sp²)-H bond in benzene or a C(sp³)-H bond in mesitylene at 80°C under CO pressure in undried solvents without rigorous exclusion of air and moisture can be effected with the 18e complexes CpW(NO)(H)(η³-CH₂CHCMe₂) (1), CpW(NO)(H)(η³-CH₂CHCHMe) (2), and CpW(NO)(H)(η³-CH₂CHCHPh) (3) (Cp = η⁵-C₅Me₅). These activations are regiospecific and afford in the case of complex 1 good yields of the unsymmetrical saturated ketones 4-methyl-1-phenylpentan-1-one (5) and 1-(3,5-dimethylphenyl)-5-methylhexan-2-one (8), respectively, in which the alkyl groups result from hydrogenation of the allyl ligand in the organometallic reactant. Complex 2 reacts similarly, but complex 3 only produces the ketone from its reaction with CO in benzene. Theoretical calculations indicate that the key mechanistic feature of these conversions is the formation of a 16e η²-alkene complex which is generated by the regiospecific migration of the hydride ligand onto the tertiary carbon of the allyl ligand. The 16e CpW(NO)(η²-CH₂ = CHCHMe₂) and CpW(NO)(η²-MeCH = CHPh) intermediate complexes formed in this manner by complexes 1 and 3, respectively, have been trapped as the corresponding 18e CO adducts CpW(NO) (CO)(η²-CH₂ = CHCHMe₂) (10) and CpW(NO) (CO)(η²-MeCH = CHPh) (11). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two isomers of 11 have been established by single-crystal X-ray crystallographic analyses. This new and facile method of synthesizing saturated unsymmetrical ketones via C-C bond formation not only is atom economical but also is part of a complete synthetic cycle, since CpW(NO)(CO)₂ (4) is the final organometallic product formed in all cases, and it can be readily reconverted to the hydrido allyl reactants 1-3 in three steps via CpW(NO)Cl₂. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00537

Article
pubs.acs.org/Organometallics
Unsymmetrical Saturated Ketones Resulting from Activations of
Hydrocarbon C(sp3)−H and C(sp2)−H Bonds Effected by
Cp*W(NO)(H)(η3‑allyl) Complexes
Rhett A. Baillie, Guillaume P. Lefevre, Russell J. Wakeham, Aaron S. Holmes, and Peter Legzdins*
̀
Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
S
* Supporting Information
ABSTRACT: C−H activations of a C(sp2)−H bond in benzene or a C(sp3)−
H bond in mesitylene at 80 °C under CO pressure in undried solvents without
rigorous exclusion of air and moisture can be effected with the 18e complexes
Cp*W(NO)(H)(η3-CH2CHCMe2) (1), Cp*W(NO)(H)(η3-CH2CHCHMe)
(2), and Cp*W(NO)(H)(η3-CH2CHCHPh) (3) (Cp* = η5-C5Me5). These
activations are regiospecific and afford in the case of complex 1 good yields of
the unsymmetrical saturated ketones 4-methyl-1-phenylpentan-1-one (5) and
1-(3,5-dimethylphenyl)-5-methylhexan-2-one (8), respectively, in which the
alkyl groups result from hydrogenation of the allyl ligand in the organometallic
reactant. Complex 2 reacts similarly, but complex 3 only produces the ketone
from its reaction with CO in benzene. Theoretical calculations indicate that
the key mechanistic feature of these conversions is the formation of a 16e η2-
alkene complex which is generated by the regiospecific migration of the
hydride ligand onto the tertiary carbon of the allyl ligand. The 16e Cp*W(NO)(η2-CH2CHCHMe2) and Cp*W(NO)(η2-
MeCHCHPh) intermediate complexes formed in this manner by complexes 1 and 3, respectively, have been trapped as the
corresponding 18e CO adducts Cp*W(NO) (CO)(η2-CH2CHCHMe2) (10) and Cp*W(NO) (CO)(η2-MeCHCHPh)
(11). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state
molecular structures of two isomers of 11 have been established by single-crystal X-ray crystallographic analyses. This new and
facile method of synthesizing saturated unsymmetrical ketones via C−C bond formation not only is atom economical but also is
part of a complete synthetic cycle, since Cp*W(NO)(CO)2 (4) is the final organometallic product formed in all cases, and it can
be readily reconverted to the hydrido allyl reactants 1−3 in three steps via Cp*W(NO)Cl2.
(H)(η3-CH2CHCHPh) (3) that result in the liberation of
INTRODUCTION
■
unsymmetrical ketones via the formation of new C−C bonds.4
The selective functionalization of C−H bonds continues to
attract interest from synthetic, biological, and theoretical
RESULTS AND DISCUSSION
chemists, since recent advances in this field have begun to
realize some of the early promise of this chemistry for the
straightforward conversion of relatively simple substrates into
more complex chemical entities.1 Our recent contributions to
this chemistry have involved the development of several 18e
Cp*W(NO)(CH2CMe3)(η3-allyl) (Cp* = η5-C5Me5) com-
pounds for the selective single activations of terminal C−H
bonds of hydrocarbon substrates to produce isolable η1-
hydrocarbyl complexes.2 The newly formed hydrocarbyl ligands
in these latter compounds may then be functionalized and
released by a variety of reagents.2 We have now begun to
extend our investigations to encompass the C−H activating
abilities of the related 18e hydrido allyl complexes Cp*W-
(NO)(H)(η3-allyl)3 and in so doing have discovered some
unprecedented chemistry effected by three of these com-
pounds. Consequently, we now wish to report examples of the
activations of hydrocarbon C(sp3)−H and C(sp2)−H bonds
under CO pressure by Cp*W(NO)(H)(η3-CH2CHCMe2) (1),
Cp*W(NO)(H)(η3-CH2CHCHMe) (2), and Cp*W(NO)-
■
Chemical Conversions. The new chemistry that we have
discovered is summarized in Scheme 1. It involves the synthesis
of unsymmetrical saturated ketones via a C−H activation
followed by the formation of two new C−C bonds.
The requisite 18e hydrido reagents 1−3 may be conveniently
prepared in various isomeric forms from Cp*W(NO)Cl2 by
two sequential metathesis steps.3 In solution complex 1 exists as
two coordination isomers in an 83/17 ratio, differing with
respect to the endo/exo orientation of the allyl ligand. In
contrast, complexes 2 and 3 each exist as four coordination
isomers, all differing in the attachments of their allyl ligands,
which can have either an endo or exo orientation with the
methyl or phenyl groups being either proximal or distal to the
nitrosyl ligand.3 All reactions of 1−3 have been performed with
mixtures of these isomers, whose solution molecular structures
Received: June 19, 2015
Published: August 10, 2015
© 2015 American Chemical Society
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Scheme 1. Synthetic Cycle for Forming Unsymmetrical
Saturated Ketones
Scheme 3. Reactions Involving Mesitylene
are consistent with the regiospecific nature of the hydro-
carbon−CO reaction depicted in Scheme 1 (vide infra).
The formation of the unsymmetrical ketones shown in
Scheme 1 involves one-pot C−H activation of the hydrocarbon
followed by 1,1-CO insertion and coupling to the allyl ligand
which has been hydrogenated by the hydride ligand and an H
atom from the C−H activation. The organometallic final
product in all cases is the well-known dicarbonyl nitrosyl
complex Cp*W(NO) (CO)2 (4).5 Most notably, these
conversions may be effected with undried solvents and without
rigorous exclusion of moisture and air, since both the
organometallic reactant and product are oxidatively and
hydrolytically stable. To date benzene (Scheme 2) and
mesitylene (Scheme 3) have been utilized as prototypical
C(sp2)−H and C(sp3)−H bond containing R−H substrates to
obtain the ketones indicated in unoptimized yields under the
specified experimental conditions.
generated by complexes 1 and 3. Thus, the reaction of 1 with
CO in benzene affords only a single ketone, 4-methyl-1-
phenylpentan-1-one (5) (Scheme 2), a fact that can be
explained by the solution isomers of 1, both of which have
the methyl substituents of the allyl ligand proximal to the
hydride ligand. The tertiary allyl carbon is the site of the allyl−
hydride coupling, a feature that is reflected in the CHMe2
terminus of the single organic product, 5. In contrast, the same
reaction of 2 produces two ketones, 2-methyl-1-phenylbutan-1-
one (6a) and 1-phenylpentan-1-one (6b) (Scheme 2). Again,
the solution isomers of complex 2 are consistent with this
result, since 2 exists as four isomers in solution with the methyl
substituent of the allyl ligand being proximal to the hydride
ligand for two isomers and proximal to the nitrosyl ligand for
the other two isomers. These Cp*W(NO)(H)(η3-allyl)
complexes also possess σ−π distorted allyl ligands, which
result in their having unequal C−C bond lengths. The shorter
C−C linkage with the greater sp2 character C terminus is
situated trans to the nitrosyl in each complex.3 It is this carbon
that is the site of coupling with the hydride ligand.6 In other
words, the substituents on the allyl ligand influence how it is
coordinated to the metal center, and the σ−π distortion of the
bound allyl ligand determines how it couples with the hydride
ligand. These features are illustrated in Figure 1 to account for
the production of the two ketones 6a,b, the higher yield of 6b
An interesting feature of the reactions presented in Scheme 1
is the degree of regioselectivity, particularly for the ketones
Scheme 2. Reactions Involving Benzene
Figure 1. (a) Isomers of 2 with the methyl substituent of the allyl
ligand proximal to the nitrosyl produce ketone 6a. (b) Isomers of 2
with the methyl substituent proximal to the hydride ligand produce
ketone 6b.
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being reflective of the fact that principal isomers of 2 have the
methyl group of the allyl ligand situated proximal to the hydride
ligand.3
resulting from hydride migration to the other allyl carbons have
not been detected in the final reaction mixtures. Further
support for the existence of a 16e η2-alkene intermediate comes
from the trapping of the Cp*W(NO)(η2-CH2CHCHMe2)
(A) and Cp*W(NO)(η2-MeCHCHPh) intermediates
formed by complexes 1 and 3, respectively, by CO as the
corresponding 18e adducts Cp*W(NO)(CO)(η2-CH2
CHCHMe2) (10) and Cp*W(NO)(CO)(η2-MeCHCHPh)
(11). These trapping reactions are described in the following
paragraphs.
The reaction of 1 with CO in pentane does not afford a
ketone resulting from pentane activation. Instead, the 18e CO
adduct of the intermediate A can be isolated from the final
reaction mixture (Scheme 5). Evidently A cannot effect the C−
The reaction of 3 with CO in benzene produces a single
ketone, 7 (Scheme 2), that does not follow the isomer trend
observed for complexes 1 and 2. This difference is probably an
electronic effect due to the phenyl substituent on the allyl
ligand. The two possible 16e η2-alkene intermediate complexes
that 3 can generate contain either η2-MeCHCHPh or η2-
CH2CHCH2Ph ligands. The reactive intermediate that
contains the conjugated η2-trans-β-methylstyrene is likely
favored on electronic grounds and is consistent with the
formation of ketone 7.
The reactions of 1 and 2 with CO in mesitylene
(summarized in Scheme 3) parallel the reactions in benzene.
Complex 1 gives a single organic product, namely 1-(3,5-
dimethylphenyl)-5-methylhexan-2-one (8), while complex 2
affords the two ketones 1-(3,5-dimethylphenyl)-3-methylpen-
tan-2-one (9a) and 1-(3,5-dimethylphenyl)-hexan-2-one (9b).
These organic products are analogous to those formed by 1 and
2 with CO and benzene. The reaction of complex 3 with CO in
mesitylene does not afford the expected ketone or any organic
product. Instead, a single organometallic complex that sheds
some light as to the mechanism operative during these
conversions is produced (vide infra).
Scheme 5. Trapping of Intermediate η2-Alkene Complexes
with CO
Mechanistic Considerations. The probable mechanism of
the conversions involving benzene (Scheme 2) and mesitylene
(Scheme 3) is outlined for complex 1 in Scheme 4, in which the
organic reactants are represented by R−H for simplicity.
H activation of pentane before reacting with CO. Adduct 10
exists as two isomers in a 52/48 ratio that have been
characterized by 1D and 2D NMR spectroscopy, IR spectros-
copy, and mass spectrometry. The η2 coordination of the olefin
ligand to the tungsten center is established by characteristic
183W satellites evident in the 13C NMR spectrum (i.e., major
isomer 10a, δ 37.3 ppm (1JWC = 11.1 Hz, CHCH2), 59.2
ppm (1JWC = 38.8 Hz, CHCH2); minor isomer 10b, δ 25.8
ppm (1JWC = 36.1 Hz, CHCH2), 65.2 ppm (1JWC = 9.9 Hz,
CHCH2)). As shown in Scheme 5, the two isomers probably
differ in the orientation of the CHMe2 substituent on the
bound olefin, as occurs for 11 (vide infra). The infrared nitrosyl
stretching frequency for the mixture of isomers of 10 is 1614
cm−1, the carbonyl stretching frequency is 1951 cm−1, and the
13C NMR spectrum of 10 exhibits signals attributable to
terminal carbonyls at δ 225.5 and 227.7 ppm for 10a,b,
respectively.
Scheme 4. Probable Mechanism of the Conversions
Involving Complex 1
In contrast to complexes 1 and 2, the reaction of 3 with CO
in mesitylene does not lead to ketone formation but rather
affords the trapped η2-alkene complex 11 (Scheme 5). As for
the formation of 10 (vide supra), this outcome again reflects
the kinetic discrimination between the two possible reaction
pathways available to the η2-alkene intermediate complex.
Complex 11 has been isolated as large orange plate crystals, and
it exists as two isomers both in solution (11a, 63%; 11b, 37%)
and in the solid state (11a, 78%; 11b, 22%) (Figures 2 and 3).
The two isomers differ with respect to the orientation of the η2-
trans-β-methylstyrene ligand. The phenyl substituent of the
ligand is proximal to the nitrosyl ligand in both isomers, but the
ligand differs in the exo/endo orientation of its substituents.
The benzylic H is oriented proximal to the C5Me5 ligand in the
major isomer (Figure 2) and distal in the minor isomer (Figure
3). This feature is also evident in the solution structures of the
The key feature of the mechanism outlined in Scheme 4 is
the formation of the 16e η2-alkene complex Cp*W(NO)(η2-
CH2CHCHMe2) (A), which is generated by a hydride shift
to the tertiary carbon of the allyl ligand. This regiospecific
migration is consistent with the solution molecular structures
established for both isomers of 1, in which the two methyl
substituents of the allyl ligand are proximal to the hydride.3
Furthermore, ketones such as CH3CH2CMe2C(O)[CH2(3,5-
Me2C6H3)] and Me2CHCH(Me)C(O)[CH2(3,5-Me2C6H3)]
1
isomers, since the H NMR spectrum of 11 confirms that the
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226.1 ppm for 11a and δ 225.2 ppm for 11b. These
spectroscopic properties are very similar to those exhibited by
the related complexes 10a,b. Once formed, the CO adducts 10
and 11 are thermodynamically stable entities that evidently do
not permit re-entry into the synthetic cycle under the
experimental conditions employed (Scheme 1).
Theoretical Considerations. The results of DFT calcu-
lations on the transformation involving mesitylene and complex
1 (Scheme 3) are summarized in Figure 4 and corroborate the
mechanistic proposals presented in Scheme 4. These
calculations indicate that the first step is indeed the formation
of the transient reactive 16e η2-alkene complex A (computed
barrier 75.7 kJ mol−1, TS1). Complex A can then effect the C−
H activation of one of the mesitylene C(sp3)−H bonds which
also involves concerted migration of a hydrogen atom onto the
ligated CC double bond to lead to the bis(hydrocarbyl) 16e
complex B with a barrier of 59.8 kJ mol−1 (TS2). Complex B is
also stabilized by a β-agostic C−H interaction, as shown in
Scheme 4. Coordination of a CO molecule onto the metal
center in B affords complex C, and rapid migration (TS3) of the
mesityl group onto the W-ligated carbonyl group (computed
barrier for the two steps 15.1 kJ mol−1) results in the formation
of complex D with a stabilization of 16.7 kJ mol−1 with respect
to complex B. Exothermic coordination of a CO molecule onto
the metal in D can then take place, and complex E is thus
obtained with a stabilization of 28.6 kJ mol−1 with respect to D.
Complex E then undergoes slow reductive coupling (75.9 kJ
mol−1, TS4) to lead to the η2-CO ligated 3-methylbutyl mesityl
ketone complex F. Further reaction with CO affords Cp*W-
(NO) (CO)2 (4) and liberates the ketone 8 in an overall
strongly exothermic process (overall stabilization of 232.9 kJ
mol−1 with respect to the reactants). This exothermicity leads
to an overall nonreversible process which shifts all the
preceding equilibria toward the formation of 8. In other
words, the theoretical calculations confirm that the overall
conversion is very thermodynamically favored and that the rate-
limiting steps are the formation of the η2-alkene complex A and
the subsequent C−H activation of the hydrocarbon substrate
by A. It is also worth noting at this point that the analogous
Cp*W(NO)(CH2CMe3)(η3-allyl) complexes do not exhibit
chemistry similar to that summarized in Scheme 1, presumably
because upon thermolysis they form intermediate η2-diene and/
or η2-allene complexes that effect the subsequent selective C−
H activations.2
Concluding Comments. The syntheses of unsymmetrical
saturated ketones have received considerable attention since
they are reagents that are common to many organic
transformations.7 For instance, a commonly employed method
involves transition-metal-mediated syntheses (e.g., carbon-
ylative Stille reactions), but these customarily employ costly
metals such as palladium or toxic reagents such as alkyl tin
compounds.8 In addition, reactive substrates such as carboxylic
acid derivatives have also been utilized for this purpose,9 as has
cross-coupling between pre-existing ketones.10 For example, a
typical synthesis of unsymmetrical saturated ketones begins
with the derivatization of a carboxylic acid to an acid chloride or
an amide or direct treatment of the acid with an organometallic
reagent (Scheme 6). However, these methods can pose
significant complications due to the reactivity of the substrates
and unwanted side reactions of the products.7
Figure 2. Solid-state molecular structure of 11a with 50% probability
thermal ellipsoids shown. Selected bond lengths (Å) and angles (deg):
W(1)−N(1) = 1.826(4), N(2)−O(2) = 1.200(5), W(1)−C(11)=
1.925(5), C(11)−O(1) = 1.174(6), W(1)−C(13) = 2.288(6), W(1)−
C(14) = 2.254(6), C(12)−C(13) = 1.513(7), C(13)−C(14) =
1.428(9), C(14)−C(15) = 1.498(6); W(1)−N(2)−O(2) = 173.1(4),
W(1)−C(11)−O(1) = 177.1(4), C(12)−C(13)−C(14) = 122.3(5),
C(13)−C(14)−C(15) = 125.4(5).
Figure 3. Solid-state molecular structure of 11b with 50% probability
thermal ellipsoids shown. Selected bond lengths (Å) and angles (deg):
W(1)−C(13A) = 2.27(2), W(1)−C(14A) = 2.30(2), C(12)−C(13A)
= 1.42(2), C(13A)−C(14A) = 1.40(3), C(14A)−C(15A) = 1.50(2);
C(12)−C(13A)−C(14A) = 126(2), C(13A)−C(14A)−C(15A) =
128(2).
signal due to the benzylic H of 11a has a greater upfield shift (δ
2.44 ppm) due to a stronger interaction with the tungsten
center than does the signal for the benzylic H of 11b (δ 4.06
ppm).3 The strong interaction between the tungsten center and
the η2-alkene ligands is also evinced by the lengthened CC
bonds of 1.428(9) and 1.40(3) Å for 11a,b, respectively.
Consistently, the 13C NMR spectrum of 11 contains alkene C
signals at δ 50.8 and 55.5 ppm for 11a and δ 43.8 and 59.8 ppm
for 11b, significantly more upfield in comparison to those for a
free alkene. The infrared stretching frequencies of the nitrosyl
and carbonyl ligands are 1616 and 1956 cm−1, and the 13C
NMR signals for the carbonyl ligands of the isomers occur at δ
The new methodology for preparing such ketones described
in this article complements existing synthetic methods. In
addition, our new method of forming unsymmetrical ketones
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Figure 4. Computed ΔG values for the various species involved during the mesitylene reaction involving complex 1 shown in Scheme 3.
Cp*W(NO)(H)(η3-CH2CHCHMe) (2), and Cp*W(NO)(H)(η3-
Scheme 6. Syntheses of Unsymmetrical Saturated Ketones
CH2CHCHPh) (3) were prepared according to the published
procedures.3 Pentamethylcyclopentadiene was obtained from Boulder
Scientific Co. All other chemicals and reagents were ordered from
commercial suppliers and used as received.
Unless specified otherwise, all IR samples were prepared as Nujol
mulls sandwiched between NaCl plates, and their spectra were
recorded on a Thermo Nicolet Model 4700 FT-IR spectrometer.
Except where noted, all NMR spectra were recorded at room
temperature on Bruker AV-400 (direct and indirect probes) and AV-
600 instruments, and all chemical shifts are reported in ppm and
coupling constants are reported in Hz. 1H NMR spectra were
from unfunctionalized hydrocarbons and CO not only is atom
referenced to the residual protio isotopomer present in CDCl3 (7.27
economical but also, as indicated in Scheme 1, is part of a
ppm) or C6D6 (7.16 ppm). 13C NMR spectra were referenced to
complete synthetic cycle, since the final organometallic product,
CDCl3 (77.0 ppm) or C6D6 (128.39 ppm). For the characterization of
namely Cp*W(NO) (CO)2, can be readily reconverted to the
the organometallic complexes, the two-dimensional NMR experiments
hydrido allyl reactant via Cp*W(NO)Cl2, which is cleanly
{1H−1H} COSY,{1H−13C} HSQC, and {1H−13C} HMBC were
obtained by treatment of the dicarbonyl nitrosyl complex with
performed to correlate and assign 1H and 13C NMR signals and
PCl5.5
establish atom connectivity. Low- and high-resolution mass spectra
(EI, 70 eV) were recorded by Mr. Marshall Lapawa of the UBC mass
spectrometry facility using a Kratos MS-50 spectrometer, and
elemental analyses were performed by Mr. Derek Smith of the UBC
microanalytical facility.
Reaction of 1 with Benzene and CO: Preparation of 4-
Methyl-1-phenylpentan-1-one (5). In a glovebox, a Parr 5500
EXPERIMENTAL SECTION
General Methods. All reactions and subsequent manipulations
involving organometallic reagents were performed under anhydrous
and anaerobic conditions except where noted. All inert gases were
purified by passing them through a column containing MnO and then
through a column of activated 4 Å molecular sieves. High-vacuum and
■
reactor was charged with 1 (0.300 g, 0.716 mmol) and dried benzene
inert-atmosphere techniques were performed either using double-
(ca. 75 mL), producing a yellow solution. The reactor was sealed,
manifold Schlenk lines or in Innovative Technologies LabMaster 100
removed from the glovebox, and then purged three times with carbon
and MS-130 BG dual-station gloveboxes equipped with freezers
monoxide. The reactor was pressurized to 750 psig of CO, and its
maintained at −33 °C. Preparative-scale reactions were performed
with Schlenk or round-bottom flasks; reactions were performed in
contents were stirred and heated at 80 °C for 18 h to produce an
orange solution. The solvent was reduced in volume in vacuo to obtain
thick-walled glass reaction bombs (larger scale) or J. Young NMR
a concentrated reaction mixture that was then purified by column
chromatography on silica, the products being eluted independently
using a gradient of 0−5% ethyl acetate in hexanes. The products of the
reaction were identified as Cp*W(NO)(CO)2 (4; 14 mg, 5% yield)
and 5 (98.2 mg, 78% yield).
tubes (smaller scale), both of which were sealed by Kontes greaseless
stopcocks. Reactions with gases were performed in a Parr 5500
pressure reactor or a Parr 5500 pressure reactor modified with a
sampling arm. If necessary, solvents were dried according to standard
procedures.11 The complexes Cp*W(NO)(H)(η3-CH2CHCMe2) (1),
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removed in vacuo. The crude product was then purified by flash
column chromatography on silica with a gradient 0−100% EtOAc in
hexanes as eluent to give 7 as a yellow oil (0.0276 g, 29% yield).
Characterization data for 4, which agrees well with those previously
5
1
reported: IR (cm−1) 1993 (s, νCO), 1914 (s, νCO), 1655 (s, νNO); H
Characterization data for 7, which agrees well with those previously
reported:15 IR (cm−1) 1694 (s, νCO); MS (LREI, m/z, probe
NMR (400 MHz, C6D6) δ 1.66 (s, 15H, C5Me5).
1
temperature 150 °C) 224 [M+]; H NMR (400 MHz, C6D6) δ 0.87
3
(t, JHH = 7.4, 3H, Me), 1.75−1.89 (m, 1H, CHaHbCH3), 2.09−2.25
(m, 1H, CHaHbCH3), 4.40 (t, 3JHH = 7.3, 1H, CH), 7.12−7.28 (m, 5H,
3
3
Ar) 7.34 (t, JHH = 7.6, 2H, m-aryl H), 7.44 (t, JHH = 7.3, 1H, p-aryl
H), 7.92 (d, JHH = 7.2, 2H, o-aryl H); 13C APT NMR (100 MHz,
3
C6D6) δ 12.4, 27.3, 55.6, 127.1, 128.4, 128.6, 128.8, 129.0, 132.9,
137.2, 139.8, 191.6.
Characterization data for 5, which agrees well with those previously
reported:12 IR (cm−1) 1694 (s, νCO); MS (LREI, m/z, probe
temperature 150 °C) 176 [M+]; ESI-MS theoretical m/z for [M +
H]+ 177.1, found m/z for [M + H]+ = 177.2; MS (LREI, m/z, probe
temperature 150 °C) 176 [M+], 105 [M+ − C5H11], 77 [M+ − C(
Reaction of 1 with Mesitylene and CO: Preparation of 1-(3,5-
Dimethylphenyl)-5-methylhexan-2-one (8). A Parr 5500 reactor
was charged with 1 (0.300 g, 0.716 mmol) and mesitylene (ca. 20 mL).
The reactor was sealed and purged with CO gas and finally pressurized
to 750 psig of CO. The contents were heated to 80 °C while being
stirred for 18 h. The reactor was then cooled, and the gas was carefully
vented. The final dark red reaction mixture was collected, and the
mesitylene was then removed by flash chromatography on silica using
a gradient of 0−5% EtOAc in hexanes. The resulting crude product
was further purified by column chromatography on silica using a
gradient of 0−30% EtOAc in hexanes. The organic product 8 was
obtained in good yield (122 mg, 78%). The organometallic product 45
was also isolated from the reaction mixture (33 mg, 11% yield), but
much of it was lost with the mesitylene during the first separation.
1
3
O)C5H11]; H NMR (400 MHz, CDCl3) δ 0.96 (d, JHH = 5.8, 6H,
Me), 1.619 (m, 2H, CH2), 1.622 (m, 1H, CH), 2.97 (t, 3JHH = 7.7, 2H,
3
3
CH2C(O)), 7.46 (t, JHH3 = 7.4, 2H, m-aryl H), 7.55 (t, JHH
=
7.4,1H, p-aryl H), 7.97 (d, JHH = 7.4, 2H, o-aryl H); 13C{1H} NMR
(100 MHz, CDCl3) δ 22.4, 27.8, 33.2, 36.5, 128.0, 128.5, 132.8, 137.0,
200.6.
Reaction of 2 with Benzene and CO: Preparation of 2-
Methyl-1-phenylbutan-1-one (6a) and 1-Phenylpentan-1-one
(6b). In a glovebox, a Parr 5500 reactor was charged with 2 (0.159 g,
0.392 mmol) and dried benzene (ca. 30 mL), producing a dark yellow
solution. The reactor was sealed, brought out of the glovebox, and
then purged three times with carbon monoxide. The reactor was then
pressurized to 750 psig of CO and was heated to 80 °C for 18 h while
its contents were stirred. The reactor was then brought to room
temperature and vented. The final reaction mixture was transferred to
a round-bottom flask, and the solvent was removed in vacuo. The
crude product was then purified via flash silica column chromatog-
raphy with a gradient of 0−1% EtOAc in hexanes to give the organic
products 6a (0.017 g, 27%) and 6b (0.017 g, 27%), as well as
organometallic product 4 (<5% yield via NMR).
Characterization data for 8: IR (cm−1) 1717 (s, νCO); MS (LREI,
1
m/z, probe temperature 150 °C) 218 [M+]; H NMR (400 MHz,
3
CDCl3) δ 0.85 (d, JHH = 6.3, 6H, CHMe2), 1.39−1.54 (m,
overlapped, 1H, CHMe2), 1.39−1.54 (m, overlapped, 2H,
3
CH2CHMe2), 2.30 (s, 6H, ArMe2), 2.44 (t, JHH = 7.3, 2H, (C
O)CH2CH2CH), 3.61 (s, 2H, ArCH2(CO)CH2), 6.82 (s, 2H, o-aryl
H), 6.90 (s, 1H, p-aryl H); 13C NMR (100 MHz, CDCl3) δ 22.5, 27.7,
32.7, 21.4, 40.1, 50.2, 125.6, 127.3, 128.7, 138.3, 209.2.
Reaction of 2 with Mesitylene and CO: Preparation of 1-(3,5-
Dimethylphenyl)-3-methylpentan-2-one (9a) and 1-(3,5-
Dimethylphenyl)hexan-2-one (9b). In a glovebox, a Parr 5500
reactor was charged with 2 (0.290 g, 0.716 mmol) and dried
mesitylene (ca. 15 mL), producing a dark yellow solution. The reactor
was sealed and was then purged three times with carbon monoxide.
The reactor was finally pressurized to 750 psig of CO, and the
contents were stirred while being heated to 80 °C for 18 h. The
reactor was then cooled to room temperature and vented carefully.
The dark brown crude product was then purified via flash silica column
chromatography with a gradient of 0−5% EtOAc in hexanes to give
the two novel organic products 9a (0.0109 g, 7% yield) and 9b
(0.0632 g, 43% yield) as a yellow oil, as well as the organometallic
product 4 (0.044 g, 15% yield).
Characterization data for 6a, which agrees well with those
previously reported:13 IR (cm−1) 1690 (s, νCO); MS (LREI, m/z,
probe temperature 150 °C) 162 [M+]; 1H NMR (400 MHz, CDCl3) δ
0.91 (t, 3JHH = 7.5, 3H), 1.19 (d, 3JHH = 6.9, 3H), 1.45−1.56 (m, 1H),
3
1.78−1.90 (m, 1H), 3.40 (sext, JHH = 6.7, 1H), 7.44−7.48 (m, 2H),
7.53−7.57 (m, 1H), 7.94−7.97 (m, 2H); 13C{1H} NMR (100 MHz,
CDCl3) δ 11.9, 16.9, 26.6, 42.3, 128.4, 128.7, 132.9, 137.0, 204.6.
Characterization data for 6b:14 1H NMR (400 MHz, CDCl3) δ 0.95
(t, 3JHH = 7.3, 3H), 1.41 (sext, 3JHH = 7.6, 2H), 1.72 (quint, 3JHH = 7.6,
2H), 2.97 (t, 3JHH = 7.4, 2H), 7.44−7.48 (m, 2H), 7.53−7.57 (m, 1H),
7.94−7.97 (m, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ 14.1, 22.6,
26.8, 38.5, 128.2, 128.7, 133.0, 137.3, 200.8.
Reaction of 3 with Benzene and CO: Preparation of 1,2-
Diphenylbutan-1-one (7). In a glovebox, a Parr pressure reactor was
charged with 3 (0.200 g, 0.43 mmol) and benzene (ca. 20 mL). The
pressure reactor was sealed and purged five times with carbon
monoxide and finally pressurized to 750 psi. The reactor was
connected to the mechanical stirrer, and its contents were heated to
80 °C while being stirred for 18 h. The reactor was cooled to room
temperature, and the gas was carefully vented. The final reaction
mixture was transferred to a round-bottom flask, and the volatiles were
Characterization data for 9a: IR (cm−1) 1716 (s, νCO); MS (LREI,
m/z, probe temperature 150 °C) 204 [M+]; MS (HREI-MS, m/z)
calcd for C14H20O 204.15142, found 204.15154; 1H NMR (400 MHz,
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Article
CDCl3) δ 0.84 (t, 3JHH = 7.5, 3H, CH3), 1.06 (d, 3JHH = 6.9, 3H CH3),
1.39 (quint, 3JHH = 7.0, 2H, CH2), 2.29 (s, 6H, ArMe2), 2.58 (sext, 3JHH
= 6.8, 1H, CH), 3.64 (s, 2H, CH2), 6.81 (s, 2H, o-aryl H), 6.89 (s, 1H,
p-aryl H); 13C NMR (100 MHz, CDCl3) δ 11.7, 16.2, 21.4, 26.1, 47.0,
48.6, 127.4, 128.6, 134.2, 138.2, 212.3.
X-ray diffraction analysis were grown by layering CH2Cl2/hexanes at
room temperature in the air.
1
Characterization data for 9b: H NMR (400 MHz, CDCl3) δ 0.87
3
(t, JHH = 7.3, 3H, CH3), 1.26−1.29 (overlapped, CH2), 1.53 (quint,
3
3JHH = 7.5, 2H, CH2), 2.29 (s, 6H, ArMe2), 2.43 (t, JHH = 7.3, 2H,
CH2), 3.59 (s, 2H, CH2), 6.81 (s, 2H, o-aryl H), 6.89 (s, 1H, p-aryl H);
13C NMR (100 MHz, CDCl3) 13.9, 21.4, 22.4, 26.0, 41.8, 50.2, 127.3,
128.7, 134.4, 138.3, 209.1.
Characterization data for 11a (63%): IR (cm−1) 1616 (s, νNO), 1955
(s, νCO); MS (LREI-MS, m/z, probe temperature 150 °C) 495 [M+,
184W]; MS (HREI-MS, m/z, 182W) calcd for C20H25NO182
W
Preparation of Cp*W(NO) (CO)(η2-CH2CHCHMe2) (10). A
Parr 5500 reactor was charged with 1 (0.200 g, 0.477 mmol) and n-
pentane (ca. 100 mL). The reactor was sealed and purged with CO gas
and finally pressurized to 750 psig of CO. The contents were heated to
80 °C while being stirred for 18 h. The reactor was then cooled to
room temperature, and the gas was carefully vented. The final orange
reaction mixture was collected, and the solvent was removed in vacuo
to give a dark orange oily residue. The crude product was purified via
flash column chromatography on silica with a gradient 0−100% EtOAc
in hexanes as eluent. Two isomers of 10 were isolated as an orange
solid (28 mg, 13% yield).
1
493.13675, found 493.13717; H NMR (400 MHz, C6D63) δ 1.57 (d,
3JHH = 6.5, 3H, CHCH3), 1.59 (s, 15H, C5Me5), 2.44 (d, JHH = 10.5,
3
1H, PhCHCHCH3), 3.52 (dq, JHH = 10.5, 6.5, 1H, PhCHCHCH3),
3
3
6.94 (t, JHH = 7.3, 1H, p-aryl H), 7.03 (d, JHH = 7.3, 2H, o-aryl H)
7.26 (t, 3JHH = 7.8, 2H, m-aryl H); 13C APT NMR (100 MHz, C6D6) δ
10.2 (C5Me5), 21.4 (PhCHCHCH3), 50.8 (PhCHCHCH3), 55.5
(PhCHCHCH3), 105.1 (C5Me5), 124.6 (p-aryl C), 125.4 (o-aryl C),
128.1 (m-aryl C), 147.0 (i-aryl C), 226.1 (W−CO). Anal. Calcd for
C20H25NOW: C, 48.50; H, 5.09; N, 2.83. Found: C, 48.47; H, 5.08; N,
2.83.
Characterization data for 11b (37%): 1H NMR (400 MHz, C6D6) δ
Characterization data for 10a (52%): IR (cm−1) 1951 (s, νCO) 1614
(s, νNO); MS (LREI, m/z, probe temperature 150 °C) 447 [M+, 184W],
3
1.54 (s, 15H, C5Me5), 2.15 (d, JHH3 = 5.8, 3H, CHCH3), 2.29−2.35
(m, 1H, PhCHCHCH3), 4.06 (d, JHH = 11.1, 1H, PhCHCHCH3),
1
3
3
419 [M+ − CO, 184W], 417 [M+ − NO, 184W]; H NMR (600 MHz,
6.88 (t, JHH = 7.1, 1H, p-aryl H), 6.99 (d, JHH = 7.6, 2H, o-aryl H)
7.10 (t, 3JHH = 7.7, 2H, m-aryl H); 13C APT NMR (100 MHz, C6D6) δ
10.0 (C5Me5), 24.1 (PhCHCHCH3), 43.8 (PhCHCHCH3), 59.8
(PhCHCHCH3), 104.8 (C5Me5), 125.2 (p-aryl C), 125.8 (o-aryl C),
128.0 (m-aryl C), 143.9 (i-aryl C), 225.2 (W−CO).
3
C6D6) δ 0.898 (obscured, 1H, CHCH2), 1.24 (d, JHH = 6.3, 3H,
CHMe2), 1.29 (d, 3JHH = 6.3, 3H, CHMe2), 1.60 (s, 15H, C5Me53), 1.65
(obscured, 1H, CHMe2), 1.68 (m, 1H, CHCH2), 2.43 (dd, JHH
=
2
9.8, JHH = 4.4, 1H, CHCH2); 13C APT NMR (150 MHz, C6D6) δ
1
X-ray Crystallography. Data collection was carried out at −173.0
2 °C on a Bruker X8 APEX II diffractometer with graphite-
monochromated Mo Kα radiation.
10.3 (C5Me5), 24.4 (CHMe2), 30.1 (CHMe2), 37.3 (s, JWC = 11.1,
1
CHCH2), 38.6 (CHMe2), 59.2 (s, JWC = 38.8, CHCH2), 104.52
(C5Me5), 225.5 (W−-CO).
Data for 11 were collected to a maximum 2θ value of 55.078° in
0.5° oscillations with 3.0 s exposures. The structure was solved by
direct methods16 and expanded using Fourier techniques. The C12−
C20 fragment was disordered in two orientations with a
0.782(6):0.218(6) occupancy ratio. All non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were placed in calculated
positions. The final cycle of full-matrix least-squares analysis was based
on 4227 observed reflections and 223 variable parameters.
Neutral-atom scattering factors were taken from Cromer and
Waber.17 Anomalous dispersion effects were included in Fc;18 the
values for Δf′ and Δf″ were those of Creagh and McAuley.19 The
values for mass attenuation coefficients were those of Creagh and
Hubbell.20 All refinements were performed using SHELXL-201421 via
the OLEX2 interface.22 X-ray crystallographic data for the structure are
presented in Table S1 in the Supporting Information, as are full details
of the crystallographic analysis.
Characterization data for 10b (48%): 1H NMR (600 MHz, C6D6) δ
0.88 (m, 1H, CHCH2), 0.900 (d, 3JHH = 6.8, 3H, CHMe2), 1.39 (d,
3JHH = 6.6, 3H, CHMe2), 1.60 (s, 15H, C5Me5), 1.969 (m, 1H, CH
CH2), 1.973 (m, 1H, CHCH2), 2.90 (m, 1H, CHMe2); 13C APT
NMR (150 MHz, C6D6) δ 10.4 (C5Me5), 20.5 (CHMe2), 25.8 (s, 1JWC
1
= 36.1, CHCH2), 28.9 (CHMe2), 33.6 (CHMe2), 65.2 (s, JWC
=
9.9, CHCH2), 104.54 (C5Me5), 227.7 (W-CO).
Preparation of Cp*W(NO) (CO)(η2-MeCHCHPh) (11). In a
glovebox, a Parr pressure reactor was charged with 3 (0.200 g, 0.43
mmol) and mesitylene (ca. 20 mL). The pressure reactor was sealed
and purged five times with carbon monoxide before being finally
pressurized to 750 psig. The reactor was connected to the mechanical
stirrer, and its contents were heated to 80 °C while being stirred for 18
h. The reactor was cooled to room temperature, and the gas was
carefully vented. The final reaction mixture was transferred to a round-
bottom flask, and the volatiles were removed in vacuo. The crude
product was then purified by flash column chromatography on silica
with a gradient 0−100% EtOAc in hexanes as eluent to give two
isomers of Cp*W(NO)(CO)(η2-MeCHCHPh) (11) as an orange
solid (0.0222 g, 19% yield). Crystals of 11 suitable for a single-crystal
Computational Methods. Density functional theory23 was
applied to determine the structural and energetic features of the
various organometallic complexes described in this article. All
theoretical calculations were performed using Gaussian 09.24 The 6-
31+G(d) basis set25,26 was used for all atoms (C, H, O, N) except W,
which was treated using the Stuttgart pseudopotential and associated
basis set.27 The hybrid exchange correlation functional PBE0 was also
used.28 It mixes 25% of Hartree−Fock exchange into the gradient-
corrected PBE exchange and correlation functional29 and yields
reliable thermochemistry data for reactions involving transition-metal
complexes.30 All structures were calculated without geometrical
constraints, and all stationary points were characterized as minima
or transition states by frequency calculations (i.e., only one negative
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Organometallics 2015, 34, 4085−4092

Organometallics
Article
frequency for a transition state, no negative frequencies for minima).
Solvent effects (n-pentane and benzene) were included in all structure
optimization and frequency calculations using the PCM implicit
solvation model of Tomasi et al. as implemented in the Gaussian
code.31 No explicit solvent modeling was required because of the
extremely low coordinating properties of the hydrocarbon solvents
involved in the modeled reactions. Since all tungsten complexes
investigated were diamagnetic, all corresponding structures were
consequently optimized in the singlet spin state. All charges were
computed using an NBO partition analysis.32 Moreover, connections
between intermediates and several key transition states were checked
using the IRC algorithm.33
(6) Baillie, R. A.; Tran, T.; Thibault, M. E.; Legzdins, P. J. Am. Chem.
Soc. 2010, 132, 15160−15161.
(7) See, for example: (a) Cho, C. S. J. Mol. Catal. A 2005, 240, 55−
60. (b) Fujita, K.; Asai, C.; Yamaguchi, T.; Hanasaka, F.; Yamaguchi,
R. Org. Lett. 2005, 7, 4017−4019. (c) Cho, C. S. Catal. Commun. 2006,
7, 1012−1014.
(8) Palladium-catalyzed reactions: (a) Brunet, J.-J.; Chauvin, R.
Chem. Soc. Rev. 1995, 24, 89−95. (b) Tamaru, Y.; Kimura, M.;
Reactions of Acylpalladium Derivatives with Organometals and
Related Carbon Nucleophiles. In Handbook for Organopalladium
Chemistry for Organic Synthesis; Negishi, E.-I., Ed.; Wiley-Interscience:
New York, 2002; pp 2425−2454. (c) Hartwig, J. F. Organotransition
Metal Chemistry: From Bonding to Catalysis; University Science Books:
Sausalito, CA. 2010; Chapter 19.
ASSOCIATED CONTENT
* Supporting Information
■
(9) Dieter, R. K. Tetrahedron 1999, 55, 4177−4236.
(10) Arisawa, M.; Kuwajima, M.; Toriyama, F.; Li, G.; Yamaguchi, M.
Org. Lett. 2012, 14, 3804−3807.
(11) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Elsevier: Amsterdam, 2003.
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00537.
(12) Compound 5 has been previously reported; see: Ding, B.;
Zhang, Z.; Liu, Y.; Sugiya, M.; Imamoto, T.; Zhang, W. Org. Lett. 2013,
15, 3690−3693.
(13) Compound 6a has been previously reported; see: Li, L.; Cai, P.;
Guo, Q.; Xue, S. J. Org. Chem. 2008, 73, 3516−3522.
(14) Compound 6b has been previously reported; see: Miyoshi, T.;
Miyakawa, T.; Ueda, M.; Miyata, O. Angew. Chem., Int. Ed. 2011, 50,
928−931.
(15) Compound 7 has been previously reported; see: Cheon, C. H.;
Kanno, O.; Toste, F. D. J. Am. Chem. Soc. 2011, 133, 13248−13251.
(16) SHELXT: Sheldrick, G. M. Acta Crystallogr., Sect. A: Found.
Crystallogr. 2008, 64, 112−122.
(17) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV,
Table 2.2A.
X-ray crystallographic data for complex 11 and NMR
spectra of all synthesized unsymmetrical ketones (PDF)
Final thermochemical parameters of the various organo-
metallic complexes subjected to DFT calculations (XYZ)
Crystallographic data for 11 (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail for P.L.: legzdins@chem.ubc.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(18) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781−
782.
We are grateful to The Dow Chemical Company for continuing
financial support of our work under Agreement Number
227046 and to our Dow colleagues, Andy Arthur, Brian
Kolthammer, Billy Bardin, Devon Rosenfeld, and Brandon
Rodriguez, for assistance and helpful discussions. We also thank
Travis Nagle for his contribution during the early stages of
these investigations. R.A.B. acknowledges the NSERC of
Canada for an award of a PGSD postgraduate fellowship.
This research has been enabled by the use of WestGrid
computing resources, which are funded in part by the Canada
Foundation for Innovation, Alberta Innovation, Science BC
Advanced Education, and the participating research institutions.
WestGrid equipment is provided by IBM, Hewlett-Packard, and
SGI.
(19) Creagh, D. C.; McAuley, W. J. International Tables for X-ray
Crystallography; Kluwer Academic: Boston, MA, 1992; Vol. C, Table
4.2.6.8.
(20) Creagh, D. C.; Hubbell, J. H. International Tables for X-ray
Crystallography; Kluwer Academic: Boston, MA, 1992; Vol. C, Table
4.2.4.3.
(21) SHELXL-2014: Sheldrick, G. M. Acta Crystallogr., Sect. A: Found.
Adv. 2015, 71, 3−8.
(22) OLEX2-V1.2.6: Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.;
Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−
341.
(23) Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, U.K., 1989.
(24) Frisch, M. J., et al. Gaussian 09, Revision D.01; Gaussian, Inc.,
Wallingford, CT, 2013.
(25) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys.
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