Oxidative addition of chlorohydrocarbons to a rhodium tris(pyrazolyl)borate complex

Article abstract of DOI:10.1021/acs.organomet.5b00131

The reactive fragment [Tp′Rh(PMe₃)], generated from the thermal precursor Tp′Rh(PMe₃)(Me)H, is found to cleave the C-Cl bonds of chlorohydrocarbons under mild conditions. Reaction with chloromethane gives clean formation of an initial C-H activation product, which rearranges to form the C-Cl activation product at 30 C. Reaction with dichloromethane or benzyl chloride gives a mixture of C-Cl activation products as well as products from chlorination. Reaction with chlorocyclohexane gives a mixture of intermediates from C-H activation, which react further upon heating to give a C-Cl cleavage product as well as the β-chloride elimination product Tp′Rh(PMe₃)(Cl)H plus cyclohexene. Complete conversion from a C-H activation product to a C-Cl activation product was observed in the reaction with 1,2-dichloroethylene, where β-elimination is circumvented. Activation of 1-chlorobutane, 1,2-dichloroethane, or 1,4-dichlorobutane gives a mixture of C-Cl activation products as well as Tp′Rh(PMe₃)(Cl)H plus olefin. Similar to the case for activation of methylene chloride, C-Cl activation and hydride/chloride exchange was observed in the reaction with benzyl chloride, where C-H activation was not seen. The reaction with chlorobenzene gives isomeric species resulting from C-H activation, which react further to give the corresponding chloride derivatives upon heating. Reaction with pentachlorobenzene gives a cyclometalated product from C-H bond cleavage in the phosphine ligand. These reactions are compared and contrasted with related photoreactions with the [Tp′Rh(CNneopentyl)] analogue, where C-H activation is solely observed in most cases. Mechanistic studies suggest the spectator ligand dependent reactivity relies greatly on the dissociation energy of the Tp′Rh-L bond.

Full text of DOI:10.1021/acs.organomet.5b00131

Article
pubs.acs.org/Organometallics
Oxidative Addition of Chlorohydrocarbons to a Rhodium
Tris(pyrazolyl)borate Complex
Yunzhe Jiao, William W. Brennessel, and William D. Jones*
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
*
S Supporting Information
ABSTRACT: The reactive fragment [Tp′Rh(PMe )], generated from
3
the thermal precursor Tp′Rh(PMe )(Me)H, is found to cleave the C−Cl
3
bonds of chlorohydrocarbons under mild conditions. Reaction with
chloromethane gives clean formation of an initial C−H activation
product, which rearranges to form the C−Cl activation product at 30 °C.
Reaction with dichloromethane or benzyl chloride gives a mixture of
C−Cl activation products as well as products from chlorination. Reaction
with chlorocyclohexane gives a mixture of intermediates from C−H
activation, which react further upon heating to give a C−Cl cleavage product as well as the β-chloride elimination product
Tp′Rh(PMe )(Cl)H plus cyclohexene. Complete conversion from a C−H activation product to a C−Cl activation product was
3
observed in the reaction with 1,2-dichloroethylene, where β-elimination is circumvented. Activation of 1-chlorobutane, 1,2-
dichloroethane, or 1,4-dichlorobutane gives a mixture of C−Cl activation products as well as Tp′Rh(PMe )(Cl)H plus olefin.
3
Similar to the case for activation of methylene chloride, C−Cl activation and hydride/chloride exchange was observed in the
reaction with benzyl chloride, where C−H activation was not seen. The reaction with chlorobenzene gives isomeric species
resulting from C−H activation, which react further to give the corresponding chloride derivatives upon heating. Reaction with
pentachlorobenzene gives a cyclometalated product from C−H bond cleavage in the phosphine ligand. These reactions are
compared and contrasted with related photoreactions with the [Tp′Rh(CNneopentyl)] analogue, where C−H activation is solely
observed in most cases. Mechanistic studies suggest the spectator ligand dependent reactivity relies greatly on the dissociation
energy of the Tp′Rh−L bond.
2
4
INTRODUCTION
well as in the related DFT calculations by Hall. The selec-
■
tivity can be different, as seen in the reactions of the rhodium
Selective C−H activation of functionalized substrates has
attracted much attention recently due to the possibility for
I
analogue (PNP)Rh with haloarenes, giving exclusive C−Hal
25
1
−3
bond addition. The absence of C−H activation is consistent
incorporation of versatile functional groups such as halo,
4
,5
6−8
with dominating thermodynamic factors relative to small kinetic
cyano, and hydroxo
in organic synthesis. In these cases,
26
selectivities, as indicated by DFT calculations.
the functionalities remain unreactive under suitable conditions,
allowing the targeted C−H bonds to be cleaved to form more
complicated organic molecules. However, competitive C−X
In comparison with activations of aryl halides, oxidative
additions of alkyl halides are less common. A typical activation
of a C−Hal bond by Ir(I) is the oxidative addition reaction of
(
X = CN, Cl, Br, I, OTf) bond activation can take place, especially
27
an alkyl halide to Vaska’s complex. Cundari calculated CH −H
3
when it involves breaking a weak C−X bond or forming a
9
−18
vs CH −X preferences where X = N, O, F, P, S, and Cl using an
3
strong M−X bond.
Therefore, investigation of the factors
Ir(PH ) (H) model, finding a significant thermodynamic
3
2
that control the preference of bond cleavage is crucial to the
design of optimal routes in transition-metal-catalyzed processes.
Halohydrocarbons are among the most commonly accessible
functionalized feedstocks, which have been involved in many
oxidative addition reactions of C−H and/or C−Hal bonds with
unsaturated metal centers. There are a number of experimental
and computational studies focusing on the C−Hal bond
preference for C−X activation but a kinetic preference for
28
C−H activation. Our group investigated the activation of
chloroalkanes using a rhodium tris(pyrazolyl)borate spe-
2
9,30
cies.
[Tp′Rh(CNneopentyl)] has been used for selective
C−H activations of alkanes, alkenes, arenes, and alkynes.
Even in reactions with functionalized hydrocarbons, C−H activa-
tion was still preferred to C−X activation (X = Cl, CN), although
the latter would usually lead to a much more robust product.
Similar to the case for the isonitrile derivative, highly regio-
31−35
1
0
9,10,19−21
cleavage by zerovalent d metals.
metals have been extensively reported for activation of C−H
Recently, the group
9
bonds in the presence of C−Hal bonds. For example, Milstein
has described an exclusive activation of the ortho C−H bonds
in chloro- and bromobenzene via the cationic pincer complex
selective cleavage of C−H bonds by [Tp′Rh(PMe )] was also
observed in the activation of substrates with functional groups.
3
36,37
+
22
[
(PNP*)Ir] . The kinetically favored C−H activation and
thermodynamic preference for C−Hal activation of PhCl was
Received: February 16, 2015
Published: April 15, 2015
23
I
observed by Ozerov using an analogous (PNP)Ir system as
©
2015 American Chemical Society
1552
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Article
For example, in the activation of fluoroalkanes and fluoroarenes, the
3
6,38
C−F bond remained unreactive to [Tp′Rh(PMe )],
although it
3
39
was cleaved in perfluoropyridine. In both examples, the halogen
substituent gave additional stabilization to the resulting product
X
Tp′Rh(L)(R )(H) (L = CN-neopentyl, PMe ) on the basis
3
of the relative distance between the substituent and the metal
center, consistent with an inductive effect.
29,34,36
To compare
the influence of the spectator ligand in these reactions, we report
here the activation of a wide range of chlorohydrocarbons using
the analogous fragment [Tp′Rh(PMe )]. Some interesting
3
results on selectivity control of C−H vs C−Cl cleavage have
been uncovered.
RESULTS AND DISCUSSION
■
Reactions with Chloroalkanes. Thermolysis of
Tp′Rh(PMe )(Me)H (1) or irradiation of Tp′Rh(PMe )H
3
3
2
(
2) at ambient temperature generates the active fragment
[
Tp′Rh(PMe )], which has been found to react with various
3
38
types of C−H bonds of alkanes, alkenes, arenes, and alkynes.
It has been reported that thermal exchange of 1 with CH F
3
resulted in the formation of the C−H activation product
Tp′Rh(PMe )(CH F)H, which underwent reductive elimina-
3
2
38
Figure 1. 31P{ H} NMR spectra for the activation of methylene
chloride by [Tp′Rh(PMe )]: (a) thermolysis of 1 in CH Cl after 18 h
at room temperature followed by replacement of CH Cl by C D ; (b)
1
tion of CH F in benzene at 67 °C. Similarly, reaction of 1
3
with CH Cl after several days at room temperature cleanly
3
2
2
3
forms the C−H activation product Tp′Rh(PMe )(CH Cl)H
2
2
6
6
3
2
photolysis of 2 in CH Cl2 after 20 min at −20 °C followed by
replacement of CH Cl by C D .
2
(3) (eq 1), which contains a characteristic hydride resonance at
2
2
6
6
1
δ −17.479 with typical coupling constants ( J
= 24 Hz,
Rh−H
2
1
J
= 29 Hz) (cf. for (Tp′Rh(PMe )(CH )H: J
=
P−H
4 Hz, J
3
3
Rh−H
2
2
= 34 Hz). The two methylene hydrogen atoms
P−H
are diastereotopic with an H−H coupling constant of ∼7 Hz.
Addition of carbon tetrachloride to 3 gave the air-stable
derivative Tp′Rh(PMe )(CH Cl)Cl (3-Cl), the structure of
3
2
which was determined by X-ray analysis. 3 was expected to
reductively eliminate chloromethane in benzene, like other
Tp′Rh(PMe )(R)H complexes. However, the known species
3
3
8
Tp′Rh(PMe )(CH )Cl (1-Cl) was the only product formed
3
3
after 1 month at room temperature (τ = 10.0 days at 30 °C;
1
/2
Figure 2. ORTEP drawing of the molecular structure of 3-Cl. All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
50% probability level.
⧧
−1
ΔG = 26.20(1) kcal mol ). As the reaction took place in neat
benzene-d6 and Tp′Rh(PMe )(C D )D was not observed,
3
6
5
isomerization of 3 to 1-Cl must therefore proceed via an
intramolecular pathway. A competition experiment showed
2
9
a kinetic preference for benzene over chloromethane by
chloride. Other products that formed were assigned as the
0
.3 kcal mol− in the C−H activation barriers (eq 2). In
1
two known species Tp′Rh(PMe )MeCl (1-Cl, 17%) and
3
38
comparison to methane with a kmethane/k
ratio of 1/2.55,
Tp′Rh(PMe )Cl (2-Cl , 11%). 3-Cl can also be generated
benzene
3
2
2
activation of chloromethane is slightly faster than activation of
by photolysis of 2 in methylene chloride at low temperature
(eq 4, Figure 1b). Oxidative addition of the C−Cl bond of
methane (1.5×). With [Tp′Rh(CNneopentyl)], chloromethane
29
40−45
46
reacted 2.5 times faster than methane.
dichloromethane
and chloroform to rhodium(I) has
Reaction of 1 with methylene chloride resulted in a
nonhydridic major product after standing overnight at 22 °C
been observed previously. 29
2
From a previous report, photolysis of Tp′Rh(CNR)(η -
PhNCNR) (R = neopentyl) in 1-chlorobutane gave
Tp′Rh(PMe )(CH (CH ) Cl))H with no activation of the
(
eq 3). The structure was confirmed as Tp′Rh(PMe )(CH Cl)
3
2
Cl (3-Cl) from C−Cl bond activation (72%) by NMR
spectroscopy and X-ray crystallography (Figures 1a and 2).
C−Cl activation of CH Cl was also observed during irradiation
3
2
2 3
C−Cl bond at −20 °C. However, reaction of 1 with
1-chlorobutane at room temperature afforded a mixture of 2-Cl
and the stable product 4-Cl in a 2.4/1 ratio after 3 days (eq 5).
2
2
of Tp′Rh(CNR)(PhNCNR) (R = neopentyl) in methylene
1
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Tp′Rh(PMe )(1-chlorocyclohexyl)H resulting from α-C−H
3
activation, one with the chlorine “up” (between two pyrazole
rings), and one with the chlorine “down” (between the
phosphine and hydride ligands). Hindered rotation around
the rhodium−cyclopentyl bond was seen previously in
The NMR spectra of 4-Cl were consistent with those of
38
Tp′Rh(PMe )(c-pentyl)H. Their stabilities relative to the
Tp′Rh(PMe )(n-butyl)Cl, which was independently synthe-
3
3
labile complexes 5a and 1 is also consistent with this assign-
ment, as seen in Tp′Rh(CN-neopentyl)(CHClR)H derivatives
sized from the reaction of 2-Cl and n-BuMgCl Grignard
2
reagent. NMR resonances of 4-Cl resemble those of the known
29
3
8
with α-chloro substituents.
alkyl chloride species Tp′Rh(PMe )(n-pentyl)Cl. The for-
3
5b,c can convert to 5-Cl and 2-Cl in a 1/3 ratio after 1 h at
mation of 2-Cl as the major product suggested the existence of
the C−H addition adduct Tp′Rh(PMe )(CH(CH Cl)-
7
0 °C (Figures 3c and 4c). These observations, especially the
3
2
major quantity of 2-Cl, indicate that C−H activation is
kinetically favored over C−Cl activation. However, the C−H
activation products are too reactive to be observed, as the
subsequent positional isomerization and rapid β-Cl elimination
(cyclohexene was observed by GC-MS) dominates over
isomerization to the C−Cl oxidative addition product. Like
4-Cl, 5-Cl can also be independently synthesized from the
CH CH )H (4), which underwent fast β-chloride elimination
2
3
to give 2-Cl. Additional evidence to support this assumption is
1
the observation of 1-butene in the reaction by GC-MS and H
NMR spectroscopy.
Activation of secondary C−H bonds was seen in the reaction
of 1 with chlorocyclohexane at room temperature, which led to
the formation of a mixture of three hydridic species (5a−c), the
C−Cl activation product Tp′Rh(PMe )(c-hexyl)Cl (5-Cl), and
reaction of 2-Cl
2
and (c-hexyl)MgCl. The structure of 5-Cl
3
2-Cl in a ratio of 2/1/6 (eq 6, Figures 3a and 4a). On
was characterized by NMR spectroscopy and X-ray analysis
(
Figure 5).
Reactions with Dichloroalkanes. Previously, C−Cl bonds
were observed to remain inert during photolysis of Tp′Rh(CN-
2
neopentyl)(η -PhNCNR) in 1,4-dichlorobutane. Different
results were found here in the activation of nongeminal
dichlorohydrocarbons at [Tp′Rh(PMe )]. Reaction of 1 with
3
1
,2-dichloroethane after 3 days at room temperature gave
the new non-hydridic product 6′-Cl as well as the two
known species 2-Cl and 2-Cl in a 1/2.8/2.6 ratio (eq 7).
2
1
Chloroethylene and ethylene were seen by GC-MS and H
NMR spectroscopy. The pure form of 6′-Cl was isolated and
1
identified as Tp′Rh(PMe )(η -CHCH )Cl by NMR spec-
3
2
troscopy and X-ray analysis (Figure 6). Note that the formation
of Tp′Rh(PMe )(CH CH Cl)Cl (6-Cl) from C−Cl cleavage of
3
2
2
1
,2-dichloroethane was not seen in this reaction.
The 1H NMR spectrum of 6′-Cl displays the geminal
methylene resonances as two doublets at δ 5.24 and 5.66. The
methine hydrogen has a characteristic splitting pattern of an
overlapping dddd at δ 7.95 due to coupling with rhodium,
phosphorus, and the two neighboring methylene hydrogen
atoms. These typical resonances corresponded to a singlet
at δ 122.43 for the methylene carbon and a doublet of doublets
Figure 3. 1H NMR spectra for the reaction of 1 with chloro-
cyclohexane: (a) after 1 day at room temperature; (b) on heating at
13
1
at δ 147.99 for the methine carbon in the C{ H} NMR
spectrum. The 31P{ H} NMR spectrum of 6′-Cl shows a
doublet at δ 1.415 with a rhodium−phosphorus coupling con-
stant of 126 Hz.
30 °C after 16 h; (c) on heating at 70 °C after 1 h. The asterisks
1
denote the two isomeric residues Tp′Rh(PMe )(furanyl)H from the
3
preparation of 1.
monitoring of the reaction at different temperatures, 5a and the
starting material signals disappeared after 16 h at 30 °C, while
The crystal structure of 6′-Cl reveals an octahedral
3
coordination sphere around the rhodium center with a κ -Tp′
hydride resonances for 5b,c remained at δ −17.301 (J
=
=
ligand. The C(16)−C(17) distance is 1.270(3) Å, indicating
the presence of a double bond. Correspondingly, the Rh−
Rh−H
2
2
4 Hz, J
= 31 Hz) and δ −17.879 (J
= 26 Hz, J
Rh−H P−H
P−H
2
9 Hz) (in chlorocyclohexane), corresponding to the two sets
C(16) distance (2.019(2) Å) is typical for a Rh−C(sp ) bond
2
t
of doublet signals at δ 4.29 (J = 151 Hz), δ 3.28 (J = 153 Hz)
(cf. Rh−C(sp ) distance in Tp′Rh(PMe )(CHCH Bu)Br:
3
31
1
38
in the P{ H} NMR spectrum (Figures 3a,b and 4a,b).
2.008(2) Å ). The proposed mechanism for formation of
5a is assigned as arising from C−H activation at the 3- or
4-position of the chlorocyclohexane, as it goes away quickly.
5b,c can be assigned as the two α-chloro rotamers of
these products is shown in eq 8. The reaction of 1 with
dichloroethane initially proceeds via C−H activation and C−Cl
activation to give two transient species 6 and 6-Cl. 6-Cl is
1
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Figure 4. 31P{ H} NMR spectra for the reaction of 1 with chlorocyclohexane: (a) after 1 day at room temperature; (b) on heating at 30 °C after
1
1
6 h; (c) on heating at 70 °C after 1 h. The asterisks denote the two isomeric residues Tp′Rh(PMe )(furanyl)H from the preparation of 1.
3
Figure 6. ORTEP drawing of the molecular structure of 6′-Cl. All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
5
0% probability level.
Figure 5. ORTEP drawing of the molecular structure of 5-Cl. All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
fragment to give the C−Cl cleavage product 6′-Cl. The
reaction was more complicated than that seen with the
isocyanide analogue [Tp′Rh(CN-neopentyl)], which gives
exclusive formation of Tp′Rh(CN-neopentyl)HCl in the
50% probability level.
29
photolysis with 1,2-dichloroethane.
Activation of 1,4-dichlorobutane gave a mixture of the
products 7-Cl and 2-Cl in a 1.2/1 ratio (eq 9). The structure of
7
-Cl was confirmed as Tp′Rh(PMe )((CH ) Cl)Cl from C−Cl
3
2 4
29
thermally labile, and β-chloride elimination occurs rapidly to
oxidative addition by solid-state X-ray analysis (Figure 7). As
give the stable complex 2-Cl and ethylene. Conversion of 6
expected from β-Cl elimination, 4-chloro-1-butene was
observed by GC-MS and by H NMR spectroscopy. Although
no direct C−H activation product was observed, internal C−H
oxidative addition was assumed to be an initial or a competitive
2
1
could follow an intramolecular C−Cl activation to give 6-Cl
and/or undergo a similar β-Cl elimination to form 2-Cl. The
released chloroethylene is rapidly seized by the reactive Rh
1
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Figure 8. ORTEP drawing of the molecular structure of 8-Cl (cis). All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
Figure 7. ORTEP drawing of the molecular structure of 7-Cl. All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
5
0% probability level.
50% probability level.
(
Figure 8, modeled as an isomeric disorder of cis to trans in
step in comparison to C−Cl activation, followed by rapid
β-chloride elimination to give the stable species 7-Cl and
a 87/13 ratio).
Reactions with Chloroarenes. Similar to the case for
2
-Cl.
activation of methylene chloride, reaction of 1 with benzyl
chloride led to formation of 1-Cl, 2-Cl , and the new non-
hydridic species 9-Cl in nearly equal amounts (eq 11). The new
Additionally, reaction of 1 in cis-1,2-dichloroethylene over-
2
night gave an initial product distribution of three non-hydridic
2
species (8-η , 8-Cl-cis, and 8-Cl-trans) and the hydridic species
8
in a 1.0/2.9/1.1/2.8 ratio (eq 10). The observation of a minor
31
1
product contains a P{ H} resonance at δ −0.85 with a Rh−P
coupling constant of 131 Hz, typical for species of the type
Tp′Rh(PMe )(R)Cl. 9-Cl was isolated and the structure
3
quantity of 2-Cl (18%) is from the side reaction in preparing
, as the possibility of β-chloride elimination can be excluded
confirmed by X-ray analysis as the C−Cl oxidative addition
1
product Tp′Rh(PMe )(benzyl)Cl (Figure 9). The resonances
3
3
8
in this case. 8 may be assigned as the C−H adduct
for the two diastereotopic benzylic hydrogens appear as a
Tp′Rh(PMe )(C(Cl)CHCl)H with a hydride resonance as
3
1
2
a triplet at δ −17.55 ( J
P{ H} resonance at δ 3.21 ( J
= J
= 25 Hz) as well as a
= 138 Hz). Additional
Rh−H
P−H
3
1
1
1
Rh−P
evidence for this assignment comes from the observation that 8
can convert to 8-Cl-cis and 8-Cl-trans with a half-life of ∼2 h at
⧧
−1
7
0 °C (ΔG = 26.5 kcal mol ), comparable to the reductive
t
38
⧧
elimination rate of Tp′Rh(PMe )(CHCH Bu)H (ΔG =
3
2
−1
2
8.0 kcal mol ).
In comparison to the complexes Tp′Rh(PMe )(X)(Y), the
3
3
1
1
2
P{ H} resonance of 8-η shows a characteristic downfield
I
shift (for Rh ) at δ 12.40, as well as a large coupling constant of
53 Hz, leading to its assignment as the π-bound rhodium
1
2
31
1
complex Tp′Rh(PMe )(η -CHClCHCl) (cf. P{ H} for
3
2
37
Tp′Rh(PMe )(η -H CCCCH ): δ 10.66, J = 160 Hz ). As
3
3
3
2
expected, complete conversion of 8 and 8-η to form 8-Cl-cis
and 8-Cl-trans was observed after 2 days at 70 °C in neat
cis-1,2-dichloroethylene. Heating of the initial product mixture
in neat C D also led to growth of 8-Cl-cis and 8-Cl-trans
6
6
without formation of Tp′Rh(PMe )(C D )D, indicating an
3
6
5
2
intramolecular pathway for rearrangement of 8 and 8-η to
-Cl-cis and 8-Cl-trans. 8-Cl-cis and 8-Cl-trans were cocrystal-
8
Figure 9. ORTEP drawing of the molecular structure of 9-Cl. All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the
50% probability level.
lized, and their structures were confirmed as the C−Cl cleavage
products Tp′Rh(PMe )(HCCHCl)Cl by X-ray analysis
3
1
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doublet of doublets at δ 4.528 (2JRh−H = 3 Hz, J
Article
2
36
= 11 Hz)
= 3 Hz,
P−H
Tp′Rh(PMe )(2-C H F)H, which appears at δ −16.32.
H−H
3
6
4
2
3
and a doublet of triplets at δ 5.117 ( J
JH−H = 11 Hz) in the H NMR spectrum. The methylene
= J
Heating the mixture of C−H activation products led to
interconversion between these hydrides, leaving 10a,b as the
Rh−H
2
1
1
carbon displays a doublet of doublets at δ 16.37 ( J
= 8 Hz,
most stable isomers Tp′Rh(PMe
3
)(2-C
6 4
H Cl)H after 6 h at
Continued heating did not afford clean formation
Rh−C
2
13
1
34,36
JP−C = 21 Hz) in the C{ H} NMR spectrum. The resonances
140 °C.
of the single product Tp′Rh(PMe )(Ph)Cl as expected.
at δ 7.010 and 7.552 are assigned to the five hydrogen atoms on
the phenyl ring.
3
Instead, with the consumption of the hydride species, the
series of non-hydridic complexes 10a-Cl−10c-Cl grew up at
140 °C associated with three new sets of doublets at δ −2.17 to
In addition to the aliphatic chlorohydrocarbons, aryl
chlorides were also investigated for reactivities with 1. Reaction
with chlorobenzene at room temperature for 1 day gave
five isomeric sets of hydride-containing species 10a−e, with
hydride resonances at δ −15.988 to −16.884 and correspond-
ing phosphorus signals at δ 2.80−1.83 (Figure 10). 2-Cl is also
31
1
−2.51 (J = ∼125 Hz) in P{ H} NMR (Figure 11). 10a-Cl−
10c-Cl can presumably be attributed to the chloro derivatives
Tp′Rh(PMe
)(C
H
Cl)Cl. Only the two stable rotamers
3
6
4
Tp′Rh(PMe
)(2-C
H
Cl)Cl (10a-Cl and 10b-Cl) were
3
6
4
observed after heating for 2 weeks.
Pentachlorobenzene was selected for examination, as it
contains only one possible C−H activation position. 1 was
completely consumed in pentachlorobenzene after 4 days,
resulting in a mixture of the one non-hydride species 11-Cl
(
76%) as well as a small amount of 2-Cl residue (24%) (eq 12).
The absence of hydride resonances from C−H activation was
probably due to the large steric hindrance from two α-chlorine
atoms. The sole product 11-Cl was characterized as the
2
31
1
cyclometalated structure Tp′Rh(η -CH PMe )Cl. The P{ H}
2
2
resonance of 11-Cl displays a doublet with a large upfield
chemical shift at δ −32.87 and an unusually small Rh−P
coupling constant of 96 Hz. The two phosphine methyl groups
appeared as two doublets at δ 1.789 and 1.864 with J
3 Hz in the H NMR spectrum, which corresponded to two
1
Figure 10. H NMR spectra for reaction of 1 with chlorobenzene at
2
=
P−H
varying temperatures.
1
1
1
1
doublets at δ 8.16 ( J
= 41 Hz) and 10.32 ( J = 22 Hz) in
P−C
P−C
1
seen as the residue from the preparation of 1. 10a−e can be
assigned as the C−H oxidative addition products Tp′Rh-
the 13C{ H} NMR spectrum. The methylene group appeared
2
as two broad doublets at δ 2.101 and 3.093 with J
the H NMR spectrum and a characteristic doublet of doublets
= 8 Hz in
P−H
1
(
PMe )(C H Cl)H by comparison to the hydride resonance of
3
6
4
Figure 11. 31P{ H} NMR spectra for reaction of 1 with chlorobenzene at varying temperatures.
1
1
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1
= 16 Hz, 1JP−C = 21 Hz) in the 13C{ H}
1
at δ −8.96 ( J
hydrocarbons by either exchange with 1 or photolysis of 2.
Even in activation of relatively inert pentane or cyclopentane
substrates, most of 1 remained unreactive prior to decom-
position. To compare the stability of 11 with other hydridic
Rh−C
NMR spectrum. The crystal structure of 11-Cl clearly displays
the η coordination of the P−CH bond to the rhodium center,
rendering a largely distorted octahedral geometry (Figure 12).
2
2
species of Tp′Rh(PMe )(R)H, the first-order rate of reductive
3
elimination from 11 was measured in C D at 30 °C by
6
6
monitoring the disappearance of the hydride resonance in the
1
H NMR spectrum (eq 14). The half-life of 7.5 h suggests that
11 is actually more robust than 1 (τ1/2 = 0.6 h). In light of the
stability of 11, it should have been observed in reactions of 1
with inert alkanes, unless its formation is kinetically disfavored
due to geometrical limitations or exposure to the alkane solvent
(
i.e., an alkane σ complex forms). The hypothesis of forma-
tion of 11 prior to 11-Cl was tested by a control experiment in
which the reaction of 11 with pentachlorobenzene was
monitored under the same conditions as reaction of 1 with
C Cl H. As expected, complete conversion of 11 to 11-Cl was
observed after 1 week. This reaction rate of 11 with penta-
chlorobenzene is comparable to the rate of reaction in eq 12,
suggesting the intermediacy of 11 in the reaction of 1 with
pentachlorobenzene.
6
5
Figure 12. ORTEP drawing of the molecular structure of 11-Cl.
Hydrogen atoms, except on C16, are omitted for clarity. Ellipsoids are
shown at the 50% probability level.
The Rh(1)−Cl(1) distance is 2.34 Å, slightly shorter than that
of 1-Cl (2.36 Å). The restricted three-membered ring contains
Rh(1)−P(1) and Rh(1)−C(16) distances of 2.21 and 2.14 Å,
DFT Study of C−Cl Activation in the Rearrangement
of Tp′Rh(PMe )(CH Cl)H. Density functional theory (DFT)
3
2
calculations were used to determine the reaction pathways and
respectively, both shorter than those of 1-Cl by 0.05 and
transition states for both C−H and C−Cl bond activations
2
0
2
.08 Å, respectively. The similar rhodacycle Tp′Rh(η -C H -
using the model reaction of [Tp′Rh(PMe )] with chloro-
6
4
3
-PMe )H was previously reported via intramolecular C−H
methane. The direct C−H reductive elimination/C−Cl
2
activation from photolysis of Tp′Rh(PPhMe )H or heating of
oxidative addition pathway via two three-centered transition
2
2
3
6
1
Tp′Rh(PPhMe )(C D )D. A search of the Cambridge
states and two high-energy η intermediates is described in
2
6
5
Structural Database shows 30 transition-metal complexes
Figure 13. The calculated energies are consistent with the
experimental observations, in which C−H activation is
kinetically preferred while C−Cl activation is thermodynami-
cally favored. However, the calculated activation barrier for
containing similar M−C−P rings, and only 3 of them contain
4
7−49
Rh−CH −P ring structures.
2
The formation of 11-Cl is interpreted in terms of the
−1
sterically crowded pentachlorobenzene being resistant to
C−Cl activation to form 1-Cl from 3 is uphill by 36.4 kcal mol ,
which is much higher than the experimental value of 26.2 kcal mol−
from the kinetic measurement. Moreover, calculations of a
similar pathway on the reaction of [Tp′Rh(CNMe)] with
chloromethane show little ligand dependence for C−H/C−Cl
selectivities (see the Supporting Information for details), which
is in contrast to the fact that C−Cl activation was not observed
1
reaction with the unsaturated fragment [Tp′Rh(PMe )]
3
generated from 1. Therefore, the neighboring phosphine
C−H bond was recruited for activation, affording the hydride
2
intermediate Tp′Rh(η -CH PMe )H (11). The hydride then
2
2
underwent chlorination by reaction with excess pentachlor-
obenzene to give 11-Cl. To test this proposal, 11 was
independently prepared by reducing 11-Cl with Cp ZrH in
in the rearrangement of Tp′Rh(CNMe)(CH Cl)H at room
2
2
2
29
THF (eq 13). The structure of 11 is representative, with an
temperature or at 80 °C.
Goldman and Choi also found an overestimation of the
activation barrier in their calculations of C−F addition of
50
CH F to a [(PCP)Ir] fragment. The activation barrier was
3
lowered by introducing an indirect pathway where C−H bond
cleavage occurred initially, followed by α-fluorine migration
to form the methylidene fluoride hydride intermediate
(
PCP)Ir(CH )(F)H before giving the C−F activation
2
upfield hydride resonance at δ −21.135 as a doublet of doublets
with a small Rh−H coupling constant of 16 Hz and a slightly
large P−H coupling constant of 35.7 Hz (cf. hydride resonance
product (PCP)Ir(CH )F. On the basis of the analogy between
3
chloromethane and fluoromethane activation, a similar carbene
intermediate is proposed here with related migration transition
states in the pathway from S2 to S1 (Figure 14). The com-
1
2
for 1: δ −18.14 with J
= 24 Hz and J
= 34 Hz).
Rh−H
P−H
3
1
1
Similar to the case for 11-Cl, the P{ H} NMR of 11 possesses
bination of the methylidene complex Tp′Rh(CH )(Cl)H
2
a doublet at δ −35.24 with a small J
value of 113 Hz.
1 was expected to be very labile, as it had never been
(S5) with free trimethylphosphine was found to have a lower
Rh−P
3
2
1
energy than (κ -Tp′)(PMe )Rh(CH )(Cl)H or (κ -Tp′)-
3
2
observed as an intermediate in the C−H activation of other
(PMe )Rh(CH )(Cl)H. The RhCH distance of 1.83 Å is
3
2
2
1
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−
1
Figure 13. Free energy landscape for C−H and C−Cl bond activation of chloromethane with [Tp′Rh(PMe )] (free energies in kcal mol at
3
2
98 K). Gas-phase values are shown in red (italics), and PCM-corrected values are shown in black. All energies are relative to the C−Cl activation
−1
−1
product (S1). The energies of [Tp′Rh(PMe )] + chloromethane are 25.6 kcal mol (gas phase) and 26.1 kcal mol (PCM).
3
−
1
Figure 14. Free energy landscape for the rearrangement reaction of Tp′Rh(PMe )(CH Cl)H to Tp′Rh(PMe )(CH )Cl (free energies in kcal mol
3
2
3
3
at 298 K). Gas-phase values are shown in red (italics), and PCM-corrected values are in black. All energies are relative to the C−Cl activation
product (S1), and intermediates S3 and S4 both include an external PMe .
3
significantly shorter than the Rh−C single bond. The two other
intermediates Tp′Rh(CH )Cl (S3) and Tp′Rh(CH Cl)H
In the gas phase, the C−Cl activation product (S1) lies
21.6 kcal mol− lower in energy than the C−H activation
product (S2) (Figure 14). Application of a solvation
model (PCM, benzene) slightly increases the selectivity to
22.6 kcal mol− in energy. The two transition states TS1 and
TS2 are close in energy, indicating that thermodynamic factors
play a larger role in favoring C−Cl formation. In comparison to
1
3
2
(
S4) were optimized by removing phosphine from the
corresponding ground states of Tp′Rh(PMe )(CH )Cl (S1)
3
3
1
and Tp′Rh(PMe )(CH Cl)H (S2). By using a potential energy
3
2
surface scan beginning with S3 and increasing one of the C−H
bond distances of Rh−CH , we found a transition state (TS1)
3
−1
for C−H cleavage and connected S3 and S5 in an α-hydrogen
migration. The Rh−H distance of 1.63 Å in the transition state
is only slightly longer than the Rh−H bond distance of
the experimental C−Cl activation barrier (ΔG = 26.2 kcal mol ),
DFT calculations seem to underestimate the barrier as
16.1 kcal mol− in the gas phase (PCM, 14.7 kcal mol ).
Along the reaction coordinate, ligand dissociation is most
responsible to account for the energy gap for C−Cl activation.
Chloride dissociation was not examined, as these reactions were
conducted in benzene solvent, which would strongly disfavor
ion formation.
1
−1
1.55 Å in S5, indicative of a strong Rh−H interaction in TS1.
Similarly, a transition state (TS2) for α-chlorine migration
between rhodium and the methylidene carbon was located
using a potential energy scan that increased the C−Cl distance
beginning with S4 and proceeding to S5. All optimized
stationary points along the reaction pathway are shown in
Figure 15, and selected structural parameters are shown in
Table 1. A complete list of the free energies for each stationary
point is shown in Table 2.
To analyze the ligand influence in C−Cl activation, DFT
calculations have also been conducted in the rearrange-
ment reaction from Tp′Rh(CNMe)(CH )Cl (S6) to Tp′Rh-
3
(CNMe)(CH Cl)H (S7). As shown in Figure 14, the spectator
2
1
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Figure 15. Optimized structures of stationary points on the potential energy surface for the rearrangement reaction of Tp′Rh(L)(CH Cl)H to
2
Tp′Rh(L)(CH )Cl (L = PMe , CNMe ).
3
3
3
Table 1. Optimized Structural Parameters (Å, deg) for the rearrangement reaction of Tp′Rh(L)(CH Cl)H to Tp′Rh(L)(CH )Cl
2
3
a
(
L = PMe , CNMe ).
3 3
b
b
b
c
complex
Rh−C
Rh−Cl
C−Cl
C−H
Rh−H
Cl−Rh−C
H−Rh−C
Rh−N
S1
2.07
2.04
2.05
2.00
1.83
2.08
2.05
1.85
1.86
2.42
3.40
2.36
2.57
2.39
2.41
3.38
2.39
2.45
3.12
1.90
3.09
1.93
2.97
3.18
1.89
2.95
2.61
1.09
2.54
1.10
2.44
2.36
1.09
2.55
1.75
2.38
2.61
1.53
2.56
1.54
1.55
2.63
1.54
1.63
1.53
87.75
29.36
88.90
48.04
88.19
89.91
29.37
87.19
73.05
23.57
89.18
24.42
86.47
87.71
23.35
89.16
59.87
88.43
2.36
2.35
2.26
2.29
2.20
2.26
2.26
2.20
2.29
S2
S3
S4
S5
S6
S7
TS1
TS2
a
b
c
Optimized structural parameters (Å) for free chloromethane: C−H, 1.09; C−Cl, 1.83. Shortest Rh−H distance. Longest Rh−N bond length.
−
1
Table 2. Free Energies (kcal mol ) for Stationary Points in
methylene species has a much higher activation barrier of
34.6 kcal mol− in the gas phase (PCM, 33.5 kcal mol )
relative to that from the phosphine analogue S2, consistent with
the experimentally observed ligand influence. The dissociative
mechanism did not greatly lower the barrier for C−Cl
1
−1
the Rearrangement Reaction of Tp′Rh(L)(CH Cl)H to
2
Tp′Rh(L)(CH )Cl (L = PMe , CNMe ) (B3LYP)
3
3
3
ΔG
gas phase PCM
ΔG
complex
S1
complex
gas phase PCM
−1
activation, as a similar activation barrier (37.4 kcal mol in
the gas phase, 37.4 kcal mol− in benzene) was calculated for
the direct oxidative addition pathway (see the Supporting
Information). The selectivity difference in C−Cl activation is
attributed to the relative ease of ligand dissociation from
Tp′Rh(L)(CH Cl)H (L = PMe vs CNMe).
1
0.00
10.17
37.73
33.09
37.60
31.57
21.60
0.00
8.97
S6
0.00
29.33
56.89
52.26
56.76
50.74
22.34
0.00
27.63
55.89
51.34
56.22
51.68
23.52
S3 + PMe3
TS1+ PMe3
S5 + PMe3
S3 + CNMe
TS1 + CNMe
S5 + CNMe
TS2 + CNMe
S4 + CNMe
S7
37.23
32.68
37.56
33.02
22.57
TS2 + PMe3
2
3
S4 + PMe3
To test the hypothesis of ligand dissociation in Figure 14, we
S2
monitored the kinetics of rearrangement of Tp′Rh(PMe )-
3
(
CH Cl)H (3) in C D at 30 °C with the addition of free
2 6 6
ligand L only participates in the first step of ligand dissocia-
trimethylphosphine. The first trial of adding trimethylphos-
tion from Tp′Rh(L)(CH )Cl. Therefore, the same set of
phine (10 equiv) to 3 led to the formation (73%) of the known
3
2
intermediates (S3−S5) and transition states (TS1 and TS2)
was used together with the free methyl isocyanide to connect
S6 and S7 (Figures 15 and 16). C−Cl cleavage from S7 via the
compound (κ -Tp′)Rh(PMe
)
3
3
as the major product after
4 days. Therefore, only 0.1 equiv of trimethylphosphine was
added in a separate experiment to give a clean conversion
1
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Figure 16. Free energy landscape for the rearrangement reaction of Tp′Rh(CNMe)(CH Cl)H to Tp′Rh(CNMe)(CH )Cl (free energies in
2
3
−1
kcal mol at 298 K). Gas-phase values are shown in red (italics), and PCM-corrected values are shown in black. All energies are relative to the C−Cl
activation product (S6).
1
13
1
31
1
of 3 to 1-Cl. In comparison to the reaction in the absence of
filter and a 270−370 nm low-pass filter. All H, C{ H}, and P{ H}
−7
−1
NMR spectra were collected on either a Bruker Avance 400 or an
Avance 500 MHz spectrometer. All H chemical shifts are reported in
ppm (δ) relative to the chemical shift of residual solvent (benzene-d
added phosphine (k = [8.00(10)] × 10 s ), phosphine
1
addition slows the first-order decay of 3 by a factor of ∼3
−7
−1
6
(
k = [2.93(14)] × 10 s ). The inhibition by free phosphine
1
3
1
(
δ 7.160), CDCl (δ 7.260), or cyclohexane-d (δ 1.400)). C{ H}
3
6
suggests that the spectator ligand must dissociate before or
during the rate-determining step for C−Cl cleavage, although
the inhibition is not as strong as one would expect on the basis
of the calculations.
NMR spectra were referenced to benzene-d (δ 128.00) or CDCl
6
3
4
31
1
(
(
(
δ 77.16). 1 P{ H} NMR spectra were referenced to external H PO
3
δ 0.00). H chemical shifts are given to three decimal places
±0.4 Hz), which is the typical resolution employed while recording
13
1
31
1
these spectra. C{ H} and P{ H} shifts are given to two decimal
places (±1 Hz), which is the typical resolution employed while recording
these spectra. These values can vary slightly with concentration and
temperature. All kinetic plots and least-squares error analysis were done
using Microsoft Excel. Elemental analysis was performed by the
University of Rochester using a PerkinElmer 2400 Series II elemental
analyzer in CHN mode. GC-MS spectra were recorded on a Shimadzu
QP2010 instrument. A Bruker-AXS SMART platform diffractometer
equipped with an APEX II CCD detector was used for X-ray crystal
structure determination. Room temperature is defined as 22 °C.
CONCLUSIONS
■
In summary, we report that the complex Tp′Rh(PMe )(CH )H
3
3
(
1) serves as a thermal precursor to activate C−H and C−Cl
bond of chlorohydrocarbons at ambient temperature. Reactions
of 1 with chloro-substituted hydrocarbons give C−H oxidative
addition complexes as the kinetic products, which can rearrange
to form products from C−Cl cleavage and/or β-chloride
elimination. The mechanism of C−Cl activation in chloro-
methane was investigated by kinetic studies and DFT
calculations. A plausible C−Cl activation pathway is associated
with the generation of a methylidene intermediate after losing
the spectator ligand. The ligand dissociation energy is likely to
be the key factor in determining the activation barrier for C−Cl
bond cleavage.
Computational Details. The crystal structures of 1-Cl and 3-Cl
were used as the starting points for the calculations. The only
simplication used was the replacement of neopentyl isocyanide with
methyl isocyanide for S6 and S7 in Figures 15 and 16 and Tables 1
and 2. This substitution has been used in previous studies and does
52
not have a large impact on the electronics of the rhodium fragment.
The gas-phase structures were fully optimized in redundant internal
5
3
coordinates, with density functional theory (DFT) and a wave
EXPERIMENTAL SECTION
function incorporating Becke’s three-parameter hybrid functional
■
5
4
(
(
B3), along with the Lee−Yang−Parr correlation functional
General Procedures. All operations and routine manipulations
were performed under a nitrogen atmosphere, either on a high-vacuum
line using modified Schlenk techniques or in a Vacuum Atmospheres
Corp. Dri-Lab. Chloromethane was purchased from Aldrich and used
straight from lecture bottles. Dichloromethane was dried over
activated alumina and was distilled prior to use. 1-Chlorobutane was
purchased from Fluka and was dried and degassed prior to use.
Chlorocyclohexane, cis-1,2-dichloroethylene, 1,4-dichlorobutane,
chlorobenzene, pentachlorobenzene, and carbon tetrachloride were
purchased from Aldrich Chemical Co. and dried over 4A molecular
sieves prior to use. 1,2-Dichloroethane was purchased from Fisher
55
LYP). All calculations were performed using the Gaussian09
5
6
package. The Rh, Cl, and P atoms were represented with the
effective core pseudopotentials of the Stuttgart group and the
associated basis sets improved with a set of f polarization functions
for Rh (α = 1.350) and a set of d polarization functions for Cl (α =
5
7,58
0.640) and P (α = 0.387).
The remaining light atoms (C, H, B,
59
and N) were represented by a 6-31G** basis set. The geometry
optimizations were performed without any symmetry constraints, and
the local minima and the transition states were checked by frequency
calculations. For each transition-state structure, the intrinsic reaction
coordinate (IRC) routes were calculated in both directions toward the
corresponding minima. Because of the polarity of the structures, the
solvent effects on their relative stabilities were evaluated by calculating
the free energies of the solvation in terms of the polarizable continuum
model (PCM). The solution-phase structures were also fully optimized
to include the solvent effect in geometries. The self-consistent reaction
Scientific and was dried and degassed prior to use. Benzene-d and
cyclohexane-d12 were purchased from Cambridge Isotopes and
were distilled under vacuum from CaH2 and stored in ampules
6
3
8
with Teflon valves. Preparations of Tp′Rh(PMe )(CH )H (1) and
3
3
5
1
Tp′Rh(PMe )H (2) have been reported.
3
2
All photolysis experiments were performed using a 200 W Hg(Xe)
60
arc lamp purchased from Oriel, which was fitted with a water-filled IR
field (SCRF) calculations using the PCM-UA0 solvation model were
1
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carried out for the gas-phase optimized structures as well as the PCM
optimized structures. The dielectric constant in the PCM calculations
was set to ε = 2.2706 to simulate benzene as the solvent medium used
in the experimental study. Gibbs free energies have been calculated at
Activation of 1-Chlorobutane. A resealable NMR tube was
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
1-chlorobutane. The resulting colorless solution was kept at room
temperature and monitored by NMR spectroscopy. After 3 days, the
2
98.15 K and 1 atm.
Activation of Chloromethane. An ∼40 mg portion of 1
reaction was complete and resulted in a mixture of Tp′Rh(PMe )(Cl)
3
1
31
1
H (70%) and 4-Cl (30%) by H and P{ H} NMR spectroscopy.
1-Butene (56, 55, 41, 39 m/z) was observed as the byproduct of the
(
0.076 mmol) was dissolved in 1 mL of C D and transferred to a
6 12
1
medium-wall Teflon-valved NMR tube, followed by pressurization
with chloromethane at 50 psi. The tube was kept at room temperature,
and the starting material was almost depleted after 1 day, as monitored
by NMR spectroscopy. Some white precipitates formed during the
reaction. The solution phase was separated from the solid phase by
filtration. The NMR spectra of the two portions (liquid and
redissolved solid) display identical resonances indicative of Tp′Rh-
reaction by GC-MS. It was also observed in the H NMR spectrum of
the reaction mixture (∼11% by integration).
Preparation of Tp′Rh(PMe )(n-butyl)Cl (4-Cl). n-Butylmagnesium
3
chloride (40 μL of a 2 M solution in THF, 0.080 mmol) was added
dropwise to 40 mg (0.073 mmol) of 2-Cl in 15 mL of THF. Upon
2
addition of the Grignard reagent, the solution changed from orange to
yellow. The reaction mixture was stirred for 20 min. The reaction
(
PMe )(CH Cl)H (3) (NMR yield: 95%) as the major product.
mixture was quenched with a saturated solution of NH Cl(aq) until all
3
2
4
However, the precipitates contains a small fraction of the known
had reacted to give a clear solution. The volatiles were removed under
vacuum, the resulting residue was dissolved in a minimum amount of
CH Cl , and the solution was filtered through Celite and layered with
species Tp′Rh(PMe )(Cl)H. Treatment of the solution of 3 with CCl
3
4
led to the formation of Tp′Rh(PMe )(CH Cl)Cl (3-Cl) (46%),
3
2
2
2
Tp′Rh(PMe )Cl (2-Cl ) (29%), and Tp′Rh(PMe )(CH )Cl (1-Cl)
hexane for recrystallization. Light orange-yellow crystals were collected
3
2
2
3
3
1
1
(
25%) after 1 week at room temperature. Data for 3 are as follows. H
NMR (500 MHz, C D ): δ −17.479 ( J
Hz, 1 H, RhH), 1.332 (d, J
(39.3 mg, 95%) and dissolved in C D . Data for 4-Cl are as follows. H
6
6
1
2
2
= 23.9 Hz, J
= 9.5 Hz, 9 H, PMe ), 2.097 (s, 3 H,
= 28.6
NMR (400 MHz, C D ): δ 0.875 (m, 4 H, 2 × CH ), 1.103 (d, J
=
6
6
Rh−H
P−H
6
6
2
P−H
2
P−H
3
10.1 Hz, 9 H, PMe ), 1.525 (t, 3 H, CH ), 2.075 (s, 3 H, pzCH ),
3
3
3
pzCH ), 2.115 (s, 3 H, pzCH ), 2.184 (s, 3 H, pzCH ), 2.217 (s, 3 H,
2.094 (s, 3 H, pzCH ), 2.174 (s, 3 H, pzCH ), 2.275 (s, 3 H, pzCH ),
3 3 3
3
3
3
pzCH ), 2.258 (s, 3 H, pzCH ), 2.789 (s, 3 H, pzCH ), 4.794 (dt,
2.677 (s, 3 H, pzCH ), 2.742 (m, 1 H, RhCH ), 2.907 (s, 3 H,
3
3
3
3
2
2
3
3
JRh−H = 2.3 Hz, J
= J
= 6.5 Hz, 1 H, RhCH ), 4.887 (dd,
pzCH ), 4.015 (m, 1 H, RhCH ), 5.552 (s, 1H, pzH), 5.639 (s, 1 H,
3 2
P−H
H−H
2
2J
= 3.6 Hz, J
3
= 7.0 Hz, 1 H, RhCH ), 5.582 (s, 1 H, pzH),
13
1
pzH), 5.693 (s, 1 H, pzH). C{ H} NMR (500 MHz, CDCl ): δ
Rh−H
H−H
2
3
13
1
5.603 (s, 1 H, pzH), 5.708 (s, 1H, pzH). C{ H} NMR (500 MHz,
12.97 (s, 1 C, pzCH
14.17 (s, 1 C, pzCH
3
), 13.08 (s, 1 C, pzCH
3
3
), 13.83 (s, 1 C, pzCH
), 16.17 (s, 1 C, pzCH
3
3
3
),
),
),
C D ): δ 12.70 (s, 1 C, pzCH ), 13.01 (s, 1 C, pzCH ), 13.04 (s, 1 C,
3
), 14.26 (s, 1 C, pzCH
6
6
3
3
1
pzCH ), 15.51 (s, 1 C, pzCH ), 15.66 (s, 1 C, pzCH ), 16.69 (s, 1 C,
16.17 (s, 1 C, n-butyl), 16.73 (d, JP−C = 32.9 Hz, 3 C, P(CH
3
)
3
3
3
1
1
1
2
pzCH ), 19.07 (d, J
= 31.4 Hz, 3 C, P(CH ) ), 38.58 (dd, J =
= 32.0 Hz, 1 C, Rh−C), 106.43 (s, 1 C, pzCH), 106.44
P−C
= 2.7 Hz, 1 C, pzCH), 107.35 (s, 1 C, pzCH), 143.14 (d,
18.12 (dd, JRh−C = 7.4 Hz, JP−C = 20.5 Hz, 1 C, Rh−C), 24.87 (s, 1
3
P−C
3
3
Rh−C
2
1
3.4 Hz, J
C, n-butyl), 34.63 (s, 1 C, n-butyl), 107.71 (s, 1 C, pzCH), 107.80 (d,
4
4
4
(
d, J
JP−C = 4.0 Hz, 1 C, pzCH), 108.83 (s, 1 C, pzCH), 142.72 (d, JP−C =
P−C
4
JP−C = 2.7 Hz, 1 C, pzCq), 143.84 (s, 1 C, pzCq), 144.31 (s, 1 C,
2.5 Hz, 1 C, pzCq), 143.61 (s, 1 C, pzCq), 144.81 (s, 1 C, pzCq),
3
pzCq), 149.29 (s, 1 C, pzCq), 150.04 (s, 1 C, pzCq), 150.56 (s, 1 C,
151.38 (s, 1 C, pzCq), 151.82 (s, 1 C, pzCq), 151.89 (d, JP−C = 4.4
pzCq). 31P{ H} NMR (400 MHz, C D ): δ 4.83 (d, J
1
1
= 147.2 Hz).
31
1
Hz, 1 C, pzCq). P{ H} NMR (400 MHz, C D
J
): δ −0.036 (d,
6
6
Rh−P
6 6
1
Activation of Methylene Chloride. Method A. An ∼10 mg
portion (0.019 mmol) of 1 was synthesized in situ, dissolved in 0.5 mL
of methylene chloride, and transferred to a resealable 5 mm NMR
tube. The reaction was complete after 18 h at room temperature, at
which point the solvent was removed under vacuum and the residue
dissolved in C D . The crude products contained as the major species
Rh−P = 130.6 Hz). Anal. Calcd (found) for C22 40BClN PRh·
H
6
hexane0.14: C, 47.23 (47.23); H, 7.28 (7.27); N, 14.47 (14.42)
(n-hexane seen in NMR spectrum; Figure S7, Supporting Information).
Activation of Chlorocyclohexane. A resealable NMR tube was
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
chlorocyclohexane. The resulting colorless solution was kept at room
temperature and monitored by NMR spectroscopy. After 1 day, the
reaction was almost complete and resulted in a mixture of
6
6
Tp′Rh(PMe )(CH Cl)Cl (3-Cl) (72%) as well as small fractions of
3
2
1
-Cl (17%) and 2-Cl (11%). 3-Cl (7 mg, 66%) was isolated as a light
2
yellow solid and purified by chromatography on silica gel using 5/1
hexane/THF as the eluent. 2-Cl was recrystallized from methylene
chloride/hexanes at room temperature to give light yellow crystals.
Method B. A resealable NMR tube was charged with 5 mg
Tp′Rh(PMe
ratio of 5.8/1/1.9. The reaction mixture was then heated to 70 °C for
)(Cl)H (77%) and 5-Cl
3
)(Cl)H, 5-Cl, and other hydridic species (see text) in a
2 h, resulting in the formation of Tp′Rh(PMe
3
1
31
1
(23%) by H and P{ H} NMR spectroscopy. Cyclohexene (82, 67,
(
0.010 mmol) of 2 and 0.5 mL of CH Cl . The colorless solution was
54, 41, 39 m/z) was observed as the byproduct of the reaction by GC-MS.
2
2
cooled to −20 °C in an isopropyl alcohol/N bath and photolyzed for
Preparation of Tp′Rh(PMe )(c-hexyl)Cl (5-Cl). A procedure
3
2
2
0 min. The solvent was removed from the resulting pale yellow
similar to that for 4-Cl was employed, except that cyclohexylmagne-
solution under vacuum to give a mixture of Tp′Rh(PMe )(CH Cl)Cl
sium chloride was used as the Grignard reagent (53% yield). Data for
3
2
1
1
2
(
3-Cl) (67%), Tp′Rh(PMe )(Cl)H (2-Cl) (25%), and 2 (8%) by H
5-Cl are as follows. H NMR (400 MHz, C
10.0 Hz, 9 H, PMe ), 1.227 (m, 2 H, c-hexyl), 1.519 (m, 4 H, c-hexyl),
1.753 (br, 1 H, c-hexyl), 2.005 (m, 2 H, c-hexyl), 2.148 (s, 3 H,
6 6
D ): δ 1.145 (d, JP−H =
3
31
1
1
and P{ H} NMR spectroscopy. Data for 3-Cl are as follows. H
3
2
NMR (500 MHz, C D ): δ 0.975 (d, J = 10.4 Hz, 9 H, PMe3),
6
6
P−H
2
2
5
.054 (s, 3 H, pzCH ), 2.151 (s, 3 H, pzCH ), 2.242 (s, 3 H, pzCH ),
pzCH
pzCH
pzCH
3
3
3
), 2.163 (s, 3 H, pzCH
), 2.637 (s, 3 H, pzCH
), 3.877 (m, 1 H, RhCH), 5.579 (s, 1H, pzH), 5.606 (s, 1 H,
3
), 2.187 (s, 3 H, pzCH
), 2.781 (m, 1 H, c-hexyl), 3.056 (s, 3 H,
3
3
), 2.257 (s, 3 H,
3
3
3
.252 (s, 3 H, pzCH ), 2.609 (s, 3 H, pzCH ), 3.076 (s, 3 H, pzCH ),
3
3
3
2
3
3
.229 (ddd, J
= 2.2 Hz, J
= 6.7 Hz, J = 8.8 Hz, 1 H,
Rh−H
H−H
P−H
1
3
1
RhCH ), 5.531 (s, 1H, pzH), 5.632 (s, 1 H, pzH), 5.646 (s, 1 H, pzH),
pzH), 5.670 (s, 1 H, pzH). C{ H} NMR (500 MHz, C D ): δ 12.88
(s, 1 C, pzCH
(s, 1 C, pzCH ), 16.04 (s, 1 C, pzCH ), 16.06 (d, J = 32.3 Hz, 3 C,
2
6 6
2
3
13
1
6.173 (dd, J
= 3.2 Hz, J
= 6.5 Hz, 1 H, RhCH2). C{ H}
), 13.07 (s, 1 C, pzCH ), 13.80 (s, 1 C, pzCH ), 15.95
3 3 3
Rh−H
H−H
1
NMR (500 MHz, C D ): δ 12.78 (s, 1 C, pzCH ), 12.91 (s, 1 C,
6
6
3
3
3
P−C
pzCH ), 13.34 (s, 1 C, pzCH ), 14.45 (s, 1 C, pzCH ), 15.46 (d,
P(CH ) ), 16.70 (s, 1 C, pzCH ), 28.18 (s, 1 C, c-hexyl), 30.49 (s, 1
3
3
3
3 3 3
1
1
2
JP−C = 33.4 Hz, 3 C, P(CH ) ), 16.24 (s, 1 C, pzCH ), 16.35 (s, 1 C,
C, c-hexyl), 31.19 (s, 1 C, c-hexyl), 31.96 (dd, J
= 6.7 Hz, J
=
P−C
3
3
3
Rh−C
1
2
pzCH ), 37.88 (dd, J
= 9.9 Hz, J = 25.3 Hz, 1 C, Rh−C),
P−C
21.3 Hz, 1 C, Rh−C), 38.00 (s, 1 C, c-hexyl), 40.03 (s, 1 C, c-hexyl),
3
Rh−C
4
4
108.15 (d, J
= 4.5 Hz, 1 C, pzCH), 108.74 (s, 1 C, pzCH), 109.09
107.97 (s, 1 C, pzCH), 108.46 (d, J
= 3.5 Hz, 1 C, pzCH), 110.15
P−C
P−C
4
4
(
s, 1 C, pzCH), 142.46 (d, J
= 2.5 Hz, 1 C, pzCq), 144.47 (s, 1 C,
(s, 1 C, pzCH), 142.71 (d, J
= 2.5 Hz, 1 C, pzCq), 143.20 (s, 1 C,
P−C
P−C
pzCq), 144.63 (s, 1 C, pzCq), 152.01 (s, 1 C, pzCq), 152.81 (d,
pzCq), 144.64 (s, 1 C, pzCq), 151.22 (s, 1 C, pzCq), 151.82 (s, 1 C,
3
31
1
3
31
1
JP−C = 4.5 Hz, 1 C, pzCq), 153.57 (s, 1 C, pzCq). P{ H} NMR (400
pzCq), 152.74 (d, J
= 4.1 Hz, 1 C, pzCq). P{ H} NMR (400
P−C
1
1
MHz, C D ): δ 1.08 (d, J
= 123.3 Hz). Anal. Calcd (found) for
MHz, C D ): δ −0.011 (d, J
= 135.5 Hz). Anal. Calcd (found) for
Rh−P
6
6
Rh−P
6
6
C H BCl N PRh: C, 40.67 (40.89); H, 5.93 (5.89); N, 14.98 (14.91).
C H BClN PRh·0.2(hexane): C, 49.46 (49.28); H, 7.38 (7.25);
24 42 6
19
33
2
6
1
562
DOI: 10.1021/acs.organomet.5b00131
Organometallics 2015, 34, 1552−1566

Organometallics
Article
N, 13.73 (13.56) (n-hexane seen in NMR spectrum; Figure S10,
Supporting Information).
Activation of 1,2-Dichloroethane. A resealable NMR tube was
Tp′Rh(PMe )(trans-HCCHCl)Cl (8-Cl-trans), Tp′Rh(PMe )-
3
3
2
(C(Cl)CHCl)H (8), and Tp′Rh(PMe )(η -HC(Cl)CHCl)
3
2
(8-η ) as well as the residue of 2-Cl with a ratio of 2.9/1.1/2.8/
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
1.0/1.7. The reaction mixture was then heated to 70 °C for 2 days,
1,2-dichloroethane. The resulting colorless solution was kept at room
resulting in the formation of 8-Cl-cis and 8-Cl-trans (2.0/0.6/1
1
31
1
temperature and monitored by NMR spectroscopy. After 3 days, the
relative to 2-Cl) by H and P{ H} NMR spectroscopy. 1 (∼50 mg,
0.095 mmol) was used for a larger scale reaction to isolate 8-Cl-cis and
8-Cl-trans (total yield 25.3 mg, 46%) from 2-Cl by chromatography
on silica gel using 5/1 hexane/acetone as the eluent. Light yellow
crystals were formed by slow evaporation of the THF solution layered
with hexane. The chloroethenyl ligand was modeled as disordered with
two orientations (87/13, cis/trans) in the X-ray structure. Data for 8
reaction was complete and resulted in a mixture of 2-Cl (44%), 2-Cl
2
1
1
(
41%), and Tp′Rh(PMe )(η -CHCH )Cl (6′-Cl) (15%) by H and
3
2
3
1
1
P{ H} NMR spectroscopy. Chloroethylene (62, 27, 26 m/z) and
1
ethylene (28, 27, 26 m/z) were seen by GC-MS and by H NMR
spectroscopy (∼15% C H Cl and ∼10% C H by integration). 1
2
3
2
4
(
6
∼200 mg, 0.380 mmol) was used for a larger scale reaction to isolate
1
′-Cl (36.6 mg, 18%) by chromatography on silica gel using 5/1
are as follows. H NMR (500 MHz, 1,2-dichloroethylene): δ −17.55,
1
2
31
1
hexane/THF as the eluent. 6′-Cl was recrystallized from methylene
(dd, J
= J
= 24.6 Hz). P{ H} NMR (400 MHz): δ 3.205 (d,
Rh−H
P−H
1
2
31
1
chloride/hexanes at room temperature to give light yellow crystals.
JRh−P = 138.3 Hz). Data for 8-η are as follows. P{ H} NMR (400
MHz): δ 12.395 (d, J
follows. H NMR (400 MHz, C D ): δ 1.042 (d, J
1
1
Data for 6′-Cl are as follows. H NMR (500 MHz, C D ): δ 1.09 (d,
6
6
= 152.9 Hz). Data for 8-Cl-cis are as
6
Rh−P
2
1
2
J
= 10.4 Hz, 9 H, PMe ), 2.08 (s, 3 H, pzCH ), 2.11 (s, 3 H,
= 10.5 Hz, 9 H,
P−H
P−H
3
3
6
pzCH ), 2.18 (s, 3 H, pzCH ), 2.29 (s, 3H, pzCH ), 2.70 (s, 3 H,
PMe ), 2.096 (s, 3 H, pzCH ), 2.154 (s, 3 H, pzCH ), 2.210 (s, 3 H,
3
3
3
3 3 3
3
pzCH ), 2.88 (s, 3 H, pzCH ), 5.24 (d,
J
= 16.4 Hz, 1H,
pzCH ), 2.258 (s, 3 H, pzCH ), 2.688 (s, 3 H, pzCH ), 2.840 (s, 3 H,
3 3 3
3
3
H−H
3
RhCHCH ), 5.52 (s, 1 H, pzH), 5.66 (d, JH−H = 8.3 Hz, 1H,
pzCH ), 5.586 (s, 1H, pzH), 5.644 (s, 1 H, pzH), 5.667 (s, 1 H, pzH),
2
3
3
RhCHCH ), 5.57 (s, 1 H, pzH), 5.70 (s, 1 H, pzH), 7.95 (nonet
6.387 (d, J = 6.0 Hz, 1 H, RhCHCHCl), 7.723 (septet 1 H, J =
3.1 Hz, RhCH). C{ H} NMR (500 MHz, C D ): δ 12.81 (s, 1 C,
6 6
2
H−H
13
1
13
1
(
overlapped dddd), 1 H, RhCH). C{ H} NMR (500 MHz, C D ): δ
6
6
1
1
1
1
1
2.76 (s, 1 C, pzCH ), 12.93 (s, 1 C, pzCH ), 13.47 (s, 1 C, pzCH ),
pzCH ), 12.92 (s, 1 C, pzCH ), 13.39 (s, 1 C, pzCH ), 15.46 (s, 1 C,
3
3
3
3 3 3
1
1
5.75 (s, 1 C, pzCH ), 15.98 (d, J
= 33.8 Hz, 3 C, P(CH ) ),
pzCH ), 15.78 (d, J
= 33.7 Hz, 3 C, P(CH ) ), 16.32 (s, 1 C,
P−C 3 3
3
P−C
3
3
3
4
6.17(s, 1 C, pzCH ), 17.69 (s, 1 C, pzCH ), 108.43 (s, 1 C, pzCH),
3
3
pzCH ), 17.12 (s, 1 C, pzCH ), 107.44 (d, J
= 4.6 Hz, 1 C,
3
3
P−C
4
08.01 Hz (d, J
= 4.9 Hz, 1 C, pzCH), 108.85 (s, 1 C, pzCH),
P−C
pzCH), 107.89 (s, 1 C, pzCH), 108.73 (s, 1 C, pzCH), 124.05 (s, 1 C,
4
1
2
22.43 (s, 1 C, CH ), 142.41 (d, J = 2.8 Hz, 1 C, pzCq), 143.96 (s,
C, pzCq), 144.94 (s, 1 C, pzCq), 147.99 (dd, J
2
P−C
CHCl), 136.08 (dd, J
= 13.3 Hz, J
= 28.6 Hz, 1 C, Rh−C),
Rh−C
P−C
1
4
1
= 12.0 Hz,
Rh−C
142.07 (d, J
= 2.5 Hz, 1 C, pzCq), 144.24 (s, 1 C, pzCq), 144.41
(s, 1 C, pzCq), 152.81 (s, 1 C, pzCq), 153.15 (d, J
pzCq), 153.64 (s, 1 C, pzCq). P{ H} NMR (400 MHz, C D ): δ
P−C
2
3
JP−C = 25.1 Hz, 1 C, Rh−C), 151.82 (s, 1 C, pzCq), 152.88 (d,
= 4.3 Hz, 1 C,
P−C
3
31
1
JP−C = 3.8 Hz, 1 C, pzCq), 153.12 (s, 1 C, pzCq). P{ H} NMR (400
31
1
6
6
1
MHz, C D ): δ 1.415 (d, J
= 125.9 Hz). Anal. Calcd (found) for
1
1
6
6
Rh−P
0.61 (d, J
= 118.0 Hz). Data for 8-Cl-trans are as follows. H
Rh−P
C H BClN PRh: C, 44.59 (44.55); H, 6.36 (6.36); N, 15.60 (15.56).
2
20
34
6
NMR (400 MHz, C D ): δ 0.981 (d, J
= 10.6 Hz, 9 H, PMe3),
P−H
6
6
Ethylene (28, 27, 26 m/z) and chloroethylene (62, 27 m/z) were
detected as the byproducts of the reaction by GC-MS.
Activation of 1,4-Dichlorobutane. A resealable NMR tube was
1
2
5
.991 (s, 3 H, pzCH ), 2.073 (s, 3 H, pzCH ), 2.141 (s, 3 H, pzCH ),
3 3 3
.241 (s, 3 H, pzCH ), 2.627 (s, 3 H, pzCH ), 2.840 (s, 3 H, pzCH ),
3
3
3
.450 (s, 1H, pzH), 5.482 (s, 1 H, pzH), 5.509 (s, 1 H, pzH), 7.781
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
3
3
4
(
dt, 1 H, J
= 13.1 Hz, J
= J
= 3.5 Hz, RhCH), 8.147 (d,
H−H
Rh−H
P−H
1
,4-dichlorobutane. The resulting colorless solution was kept at room
3
13
1
JH−H = 7.2 Hz, 1 H, RhCHCHCl). C{ H} NMR (500 MHz,
temperature and monitored by NMR spectroscopy. After 2 days, the
C D ): δ 12.57 (s, 1 C, pzCH ), 12.87 (s, 1 C, pzCH ), 13.27 (s, 1 C,
6
6
3
3
reaction was complete and resulted in a mixture of 2-Cl (73%) and
1
pzCH ), 14.90 (s, 1 C, pzCH ), 15.95 (d, J = 34.3 Hz, 3 C,
1
31
1
3
3
P−C
Tp′Rh(PMe )((CH ) Cl)Cl (7-Cl) (27%) by H and P{ H} NMR
3
2 4
P(CH ) ), 16.12 (s, 1 C, pzCH ), 17.06 (s, 1 C, pzCH ), 108.20 (d,
3
3
3
3
spectroscopy. A larger scale reaction of 1 (∼100 mg, 0.190 mmol) led
to the formation of a different ratio of 2-Cl (45%), and 7-Cl (55%).
4
JP−C = 4.5 Hz, 1 C, pzCH), 109.11 (s, 1 C, pzCH), 111.116 (s, 1 C,
pzCH), 129.93 (s, 1 C, CHCl), 136.46 (dd, J
Hz, 1 C, Rh−C), 142.53 (d, J
pzCq), 144.98 (s, 1 C, pzCq), 151.75 (s, 1 C, pzCq), 152.93 (d, J = 4.0
Hz, 1 C, pzCq), 153.49 (s, 1 C, pzCq). P{ H} NMR (400 MHz, C D ):
δ 1.31 (d, J
.4(hexane): C, 44.20 (44.28); H, 6.30 (6.40); N, 13.44 (13.94).
1
2
= 12.4 Hz, J = 27.0
= 2.2 Hz, 1 C, pzCq), 144.24 (s, 1 C,
Rh−C
P−C
7
-Cl (30.4 mg, 27%) was isolated by chromatography on silica gel
4
P−C
using 10/1 hexane/THF as the eluent. 7-Cl was recrystallized from
3
P−C
THF/hexanes at room temperature to give light yellow crystals. Data
31
1
1
6 6
for 7-Cl are as follows. H NMR (500 MHz, C D ): δ 1.084 (d,
1
6
6
= 118.1 Hz). Anal. Calcd (found) for C H BCl N PRh·
2
Rh−P
20 33 2 6
JP−H = 10.2 Hz, 9 H, PMe ), 1.155 (m, 1 H, CH ), 1.419 (m, 1 H,
3
2
0
CH ), 1.812 (m, 2 H, CH ), 2.061 (s, 3 H, pzCH ), 2.100 (s, 3 H,
2
2
3
Activation of Benzyl Chloride. A resealable NMR tube was
pzCH ), 2.160 (s, 3 H, pzCH ), 2.260 (s, 3 H, pzCH ), 2.576 (m, 1 H,
3
3
3
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
benzyl chloride. The resulting colorless solution was kept at room
temperature and monitored by NMR spectroscopy. After the reaction
mixture stood overnight, the reaction was complete and resulted in a
RhCH ), 2.657 (s, 3 H, pzCH ), 2.830 (s, 3 H, pzCH ), 3.132 (m, 2
2
3
3
H, CH ), 3.810 (m, 1 H, RhCH ), 5.557 (s, 1 H, pzH), 5.651 (s, 1 H,
2
2
13
1
pzH), 5.682 (s, 1H, pzH). C{ H} NMR (500 MHz, C D ): δ 12.86
6
6
(
(
s, 1 C, pzCH ), 12.91 (s, 1 C, pzCH ), 13.49 (s, 1 C, pzCH ), 14.59
3 3 3
1
mixture of Tp′Rh(PMe
3
)(benzyl)Cl (9-Cl) (35%), Tp′Rh(PMe
3
)-
s, 1 C, pzCH ), 15.94 (d, J
= 33.1 Hz, 3 C, P(CH ) ), 15.96 (s, 1
3 3
3
P−C
1
2
(CH )Cl (34%), and Tp′Rh(PMe
3
3
)(Cl)H (31%). 1 (∼90 mg, 0.171
C, pzCH ), 16.19 (s, 1 C, pzCH ), 17.20 (dd, J
= 7.9 Hz, J
=
3
3
Rh−C
P−C
mmol) was used for a larger scale reaction to prepare a pure form of
9-Cl (48.1 mg, 47%) by chromatography on silica gel using 5/1
hexane/THF as the eluent. 9-Cl was recrystallized from methylene
2
1.1 Hz, 1 C, Rh−C), 30.05 (s, 1 C, CH ), 35.47 (s, 1 C, CH ), 44.85
2
2
4
(
s, 1 C, CH ), 108.04 (d, J
= 4.1 Hz, 1 C, pzCH), 108.34 (s, 1 C,
2
P−C
4
pzCH), 108.84 (s, 1 C, pzCH), 142.77 (d, J
= 2.6 Hz, 1 C, pzCq),
P−C
chloride/hexanes at room temperature to give orange-yellow crystals.
1
1
44.08 (s, 1 C, pzCq), 144.75 (s, 1 C, pzCq), 151.55 (s, 1 C, pzCq),
1
3
31
1
Data for 9-Cl are as follows. H NMR (400 MHz, C
6
D
6
): δ 0.966 (d,
52.40 (d, J
= 4.5 Hz, 1 C, pzCq), 153.11 (s, 1 C, pzCq). P{ H}
P−C
2
1
JP−H = 10.3 Hz, 9 H, PMe ), 1.936 (s, 3 H, pzCH ), 2.148 (s, 3 H,
3
3
NMR (400 MHz, C D ): δ 0.15 (d, J = 129.7 Hz). Anal. Calcd
6
6
Rh−P
pzCH ), 2.214 (s, 3 H, pzCH ), 2.270 (s, 3 H, pzCH ), 2.673 (s, 3 H,
(
1
found) for C H BCl N PRh: C, 43.81 (44.34); H, 6.52 (6.58); N,
3.93 (13.76). 4-Chlorobutene (90, 55, 41 m/z) was seen as the
3
3
3
22
39
2
6
2
pzCH ), 2.752 (s, 3 H, pzCH ), 4.528 (dd, 1 H, J
= 2.6 Hz,
= 3.5 Hz,
3
3
Rh−H
2
2
2
3
JH−H = 11.2 Hz, RhCH ), 5.117 (dt, 1 H, J
JH−H = 11.2 Hz, RhCH ), 5.443 (s, 1 H, pzH), 5.539 (s, 1 H, pzH),
= J
byproduct of the reaction by GC-MS.
2
Rh−H
P−H
Activation of cis-1,2-Dichloroethylene. A resealable NMR tube
was charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of
cis-1,2-dichloroethylene. The resulting colorless solution was kept at
room temperature and monitored by NMR spectroscopy. After the
mixture stood overnight, the reaction was complete and resulted
2
5.670 (s, 1H, pzH), 7.010 (m, 3 H, Ph), 7.552 (d, 2 H, J = 6.2 Hz, Ph).
1
3
1
C{ H} NMR (500 MHz, C
1 C, pzCH ), 13.61 (s, 1 C, pzCH
1 C, pzCH
D
): δ 12.85 (s, 1 C, pzCH
), 14.86 (s, 1 C, pzCH
), 16.16 (d, JP−C = 32.9 Hz, 3 C, P(CH ), 16.37 (dd, 1 C,
), 12.98 (s,
), 16.12 (s,
3
6
6
3
3
3
1
)
3 3
3
1
2
in a mixture of Tp′Rh(PMe )(cis-HCCHCl)Cl (8-Cl-cis),
JRh−C = 7.9 Hz, J = 21.0 Hz, RhCH ), 17.03 (s, 1 C, pzCH ), 108.46
3
P−C
2
3
1
563
DOI: 10.1021/acs.organomet.5b00131
Organometallics 2015, 34, 1552−1566

Organometallics
Article
(
s, 1 C, pzCH), 108.64 (d, 4JP−C = 4.1 Hz, 1 C, pzCH), 108.76 (s, 1 C,
2.311 (s, 3 H, pzCH ), 2.329 (s, 3 H, pzCH ), 2.424 (s, 3 H, pzCH ),
3
3
3
4
31
1
pzCH), 124.26 (s, 2C, Ph), 130.04 (s, 3 C, Ph), 142.80 (d, J = 2.4 Hz,
5.607 (s, 1H, pzH), 5.700 (s, 1 H, pzH), 5.770 (s, 1 H, pzH). P{ H}
P−C
1
1
C, pzCq), 143.49 (s, 1 C, pzCq), 145.34 (s, 1 C, pzCq), 151.46 (d,
NMR (400 MHz, C D ): δ −35.24 (d, J
= 112.8 Hz).
6
6
Rh−P
2
JRh−C = 1.4 Hz, 1 C, Rh-CH C ), 152.42 (s, 1 C, pzCq), 152.69 (s, 1 C,
Reaction of 11 with Pentachlorobenzene. 11 was prepared as
described above from ∼5 mg (0.0095 mmol) of 11-Cl. A 25 mg
portion of pentachlorobenzene was added to the solution of 11 in
0.5 mL of THF. The reaction mixture was placed in a resealable NMR
2
Ph
3
31
1
pzCq), 153.10 (d, J = 4.4 Hz, 1 C, pzCq). P{ H} NMR (400 MHz,
C D ): δ −0.85 (d, JRh−P = 130.6 Hz). Anal. Calcd (found) for
C H BClN PRh: C, 49.82 (49.48); H, 6.35 (6.42); N, 13.94 (13.33).
Activation of Chlorobenzene. A resealable NMR tube was
charged with a solution of 1 (∼10 mg, 0.019 mmol) in 0.5 mL of chlo-
robenzene. The resulting colorless solution was kept at room
P−C
1
6
6
25
38
6
1
31
1
tube at room temperature and was monitored by H and P{ H}
NMR spectroscopy. The spectra showed no reactivity in the first day.
The decrease of 11 and the growth of 11-Cl were observed in the
following days, and the reaction was clean and complete after 1 week.
Competition Experiment of Chloromethane/Benzene. A
solution of 2 (8 mg, 0.017 mol) dissolved in 0.3 mL of cyclohexane-
d12 was placed in a resealable NMR tube. A 10 μL portion of benzene
was added and freeze−pump−thaw degassed 3× prior to pressuriza-
1
temperature and at 70 and 140 °C and monitored by H and
3
1
1
P{ H} NMR spectroscopy. The spectra obtained showed a mixture
of activation products, as described in the text. Data for 10a,b are as
1
1
follows. H NMR (400 MHz, C D ): δ −16.840 (dd, J
= 25.3 Hz,
6
6
Rh−H
2
1
2
J
= 29.7 Hz, RhH); δ −16.853 (dd, J
= 24.8 Hz, J
= 29.8
P−H
Rh−H
P−H
3
1
1
1
1
Hz, RhH). P{ H} NMR (400 MHz, C D ): δ 2.80 (d, J
Hz); δ 2.57 (d, J
NMR (400 MHz, C D ): δ −16.884 (dd, J
3
1
δ −15.988 (dd, J
NMR (400 MHz, C D ): δ 1.83 (d, J
are as follows. H NMR (400 MHz, C D ): δ −16.173 (dd, J
2
= 142.8
tion of the tube with chloromethane at 60 psi. A H NMR spectrum of
6
6
Rh−P
1
1
= 142.8 Hz). Data for 10c are as follows. H
the sample was taken to record the mole ratio of the two substrates.
Rh−P
1
2
= 25.3 Hz, J
=
=
6
6
Rh−H
P−H
The sample was irradiated (270−370 nm) for 10 min at 10 °C, and
0.2 Hz, RhH). 31P{ H} NMR (400 MHz, C D ): δ 2.65 (d, J
43.2 Hz). Data for 10d are as follows. H NMR (400 MHz, C D ):
1
1
1
6
6
Rh−P
another H NMR spectrum was immediately collected. The ratio of
1
6
6
C−H activation products was measured by integrating the hydride
1
2
31
1
= 22.7 Hz, J
= 24.7 Hz, RhH). P{ H}
= 140.7 Hz). Data for 10e
resonances in 1H NMR spectrum. k
Ichloromethane)(nchloromethane/nbenzene) = 0.353 × 4.82 = 1.70. ΔΔG
RT ln(kbenzene/kchloromethane) = 0.30 kcal mol .
Rh−H
P−H
/k
= (I
/
=
benzene chloromethane
benzene
1
⧧
6
6
Rh−P
oa
1
1
=
−1
6
6
Rh−H
2
31
1
2.6 Hz, J
= 25.5 Hz, RhH). P{ H} NMR (400 MHz, C D ): δ
P−H 6 6
Kinetics of Elimination Reactions of Chloromethane from
Complex 3 to give 1-Cl. Complex 3 (∼10 mg) was dissolved in
0.6 mL of C D , followed by 0.5 μL of hexamethyldisiloxane added as
1
0
.98 (d, J
= 136.4 Hz). Data for 10a-Cl, 10b-Cl, and 10c-Cl are
Rh−P
31
1
1
as follows. P{ H} NMR (400 MHz, C D ): δ −2.17 (d, J
Hz); δ −2.37 (d, J
Activation of Pentachlorobenzene. A resealable NMR tube
was charged with a solution of 1 (∼10 mg, 0.019 mmol) and
pentachlorobenzene (15 mg, 0.10 mmol) in 0.5 mL THF. The
resulting colorless solution was kept at room temperature and
monitored by NMR spectroscopy. After 4 days, the reaction was complete
and resulted in a mixture of Tp′RhCl(η -CH PMe ) (11-Cl) (76%) and
2
chromatography on silica gel using 5/1 hexane/THF as the eluent.
1
= 124.3
6
6
Rh−P
6
6
1
1
= 124.6 Hz); δ −2.51 (d, J
= 127.1 Hz).
Rh−P
Rh−P
an internal standard. This solution was placed in a resealable NMR
1
31
1
tube and heated in a 30.0 °C heating block. H and P{ H} NMR
spectra were recorded at regular intervals. Kinetic analysis was
performed by integration of the decreasing hydride resonance relative
to the signal for hexamethyldisiloxane. A first-order decay of the con-
centration of 3 was plotted against time to give the rate of reductive
elimination of chloromethane, and Excel was used to determine the
rate constant. The reaction was followed for ∼3 half-lives. For kinetics
with added trimethylphosphine, a separate NMR tube was prepared
2
2
2
-Cl (24%). The pure form of 11-Cl (5.8 mg, 60%) was isolated by
(∼208 mg, 0.395 mmol) was used for a larger scale reaction to
with the same solution as above and 0.1 equiv of PMe before heating.
3
prepare pure 11-Cl (134.4 mg, 67%). 11-Cl was recrystallized from
methylene chloride/hexanes at room temperature to give red-orange
crystals. Data for 11-Cl are as follows. H NMR (400 MHz, CDCl ):
δ 1.789 (d, J
Kinetics of Reductive Elimination Reactions from Complex
1. Complex 11 was prepared from 10 mg of 11-Cl as described
1
1
3
2
2
above. The reaction products were dried and dissolved in 0.6 mL of
C D , followed by 0.5 μL of hexamethyldisiloxane added as an internal
6 6
= 13.3 Hz, 3 H, P(CH ) ), 1.864 (d, J
= 13.5 Hz,
= 8.5 Hz, 1 H,
P−H
3
2
P−H
2
3
H, P(CH ) ), 2.042 (s, 3 H, pzCH ), 2.101 (bd, J
3
2
3
P−H
standard. This solution was transferred into a resealable NMR tube,
which was placed in a preheated NMR spectrometer at 30.0 °C. The
decrease of the hydride resonance of 11 relative to internal standard
CH PMe ), 2.319 (s, 3 H, pzCH ), 2.407 (s, 3 H, pzCH ), 2.418 (s,
3
d, J
2
2
3
3
H, pzCH ), 2.448 (s, 3 H, pzCH ), 2.471 (s, 3 H, pzCH ), 3.093 (br
3 3 3
2
= 8.4 Hz, 1 H, CH PMe ), 5.557 (s, 1H, pzH), 5.821 (s, 1 H,
2 2
P−H
1
13
1
was recorded by H spectroscopy at regular intervals. A plot of the
pzH), 5.908 (s, 1 H, pzH). C{ H} NMR (500 MHz, CDCl ):
3
1
1
concentration of 11 vs time showed a first-order decay to give the rate
of reductive elimination, and Excel was used to determine the rate
constant. The reaction was followed for >2 half-lives.
X-ray Crystal Structure Determinations. Data were collected
on a Bruker SMART APEX II CCD Platform diffractometer at
δ −8.96 (dd, J
= 15.8 Hz, J
= 21.2 Hz, 1 C, Rh−C), 8.16 (d,
P−C
1
Rh−C
1
J
= 40.7 Hz, 1 C, P(CH ) ), 10.32 (d, J
= 22.0 Hz, 1 C,
P−C
P−C
3
2
P(CH ) ), 12.32 (s, 1 C, pzCH ), 12.60 (s, 1 C, pzCH ), 13.95 (s,
1
pzCH ), 16.13 (s, 1 C, pzCH ), 106.33 (d, J = 2.0 Hz, 1 C,
pzCH), 106.59 (s, 1 C, pzCH), 109.65 (s, 1 C, pzCH), 143.32 (s, 1 C,
3
2
3
3
3
C, pzCH ), 14.72 (s, 1 C, pzCH ), 15.54 (d, J = 1.5 Hz, 1 C,
3
3
Rh−C
4
3
3
P−C
1
00.0(1) K. The data collection was carried out using Mo Kα
4
radiation. Data were collected in accord with the parameters in the
Supporting Information. The structures were solved using SIR 97 and
pzCq), 143.56 (d, J
= 1.9 Hz, 1 C, pzCq), 145.91 (s, 1 C, pzCq),
P−C
1
50.97 (s, 1 C, pzCq), 152.02 (br, 1 C, pzCq), 152.64 (s, 1 C, pzCq).
61−64
3
1
1
1
refined using SHELXL-97, SHELXL-2012, or SHELXL-2013.
P{ H} NMR (400 MHz, CDCl ): δ −32.87 (d, J
= 96.2 Hz).
3
Rh−P
All non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were placed in ideal positions and
refined as riding atoms with relative isotropic displacement parameters.
Anal. Calcd (found) for C H BClN PRh: C, 42.34 (42.92); H, 5.92
18
30
6
(
6.08); N, 16.46 (16.05).
2
Preparation of Tp′Rh(η -CH PMe )H (11). A resealable NMR
2
2
tube was charged with a slurry of 11-Cl (10 mg, 0.020 mmol) and
Cp ZrH (21.9 mg, 0.098 mol) in 0.6 mL of THF. The resulting
2
2
ASSOCIATED CONTENT
■
colorless solution was kept at room temperature and monitored by
NMR spectroscopy. The reaction was complete after 1 h, and the
zirconium complexes were removed by chromatography using 5/1
hexane/THF as the eluent. The resulting products contain a mixture
*
S
Supporting Information
Text, figures, tables, and CIF and AVI files giving NMR data,
kinetic data, details of X-ray crystallographic determinations of
-Cl, 5-Cl, 6′-Cl, 7-Cl−9-Cl, and 11-Cl (CCDC deposition
nos. 1020315−1020321), coordinates and energies for
calculated complexes, the complete ref 56, and movie files of
six transition states. This material is available free of charge via
the Internet at http://pubs.acs.org.
2
of Tp′RhH(η -CH PMe ) (11) (67%), Tp′Rh(PMe )(Cl)H (26%),
2
2
3
3
1
and 2 (7%). Data for 11 are as follows. H NMR (400 MHz, C D ):
δ −21.135 (dd, J
m, 1 H, CH PMe ), 1.256 (d, J
= 11.3 Hz, 3 H, P(CH ) ), 1.499 (m, 1 H, CH PMe ), 1.973
s, 3 H, pzCH ), 2.218 (s, 3 H, pzCH ), 2.287 (s, 3 H, pzCH ),
6
6
1
2
= 16.3 Hz, J
= 35.7 Hz, RhH), 0.898
Rh−H
P−H
2
(
(
(
= 11.9 Hz, 3 H, P(CH ) ), 1.418
P−H 3 2
2
2
2
d, J
P−H
3 2 2 2
3
3
3
1
564
DOI: 10.1021/acs.organomet.5b00131
Organometallics 2015, 34, 1552−1566

Organometallics
Article
(
27) Ugo, R.; Pasini, A.; Fusi, A.; Cenini, S. J. Am. Chem. Soc. 1972,
AUTHOR INFORMATION
■
9
(
2
4, 7364−7370.
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(29) Vetter, A. J.; Rieth, R. D.; Brennessel, W. W.; Jones, W. D. J. Am.
Corresponding Author
E-mail for W.D.J.: jones@chem.rochester.edu.
*
Notes
Chem. Soc. 2009, 131, 10742−10752.
The authors declare no competing financial interest.
(
(
30) Vetter, A. J.; Jones, W. D. Polyhedron 2004, 23, 413−417.
31) Choi, G.; Morris, J.; Brennessel, W. W.; Jones, W. D. J. Am.
ACKNOWLEDGMENTS
■
Chem. Soc. 2012, 134, 9276−9284.
The authors thank the U.S. Department of Energy (grant
no. FG02-86ER-13569) for its support of this work. We
acknowledge the Center for Integrated Research Computing at
the University of Rochester for providing the necessary
computing systems and personnel to enable the research
presented in this paper, and the CENTC Elemental Analysis
Facility at the University of Rochester, funded by NSF CHE-
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DOI: 10.1021/acs.organomet.5b00131
Organometallics 2015, 34, 1552−1566