Ruthenium Complexes Stabilized by Bidentate Enamido-Phosphine Ligands: Aspects of Cooperative H2 Activation

Article abstract of DOI:10.1021/acs.inorgchem.5b00672

Four bidentate, hybrid ligands (^R(NP)^R′H) featuring imine-nitrogen and alkyl-phosphine donors linked by a cyclopentyl ring were synthesized. The ortho position of the aryl group attached to nitrogen is varied such that R is Me or Prⁱ; additionally, the groups decorating phosphorus (R′) are varied between Bu^t or Prⁱ. The addition of each ligand to RuHCl(PPrⁱ₃)₂(CO) in the presence of KOBu^t generates four enamido-phosphine complexes RuH{^R(NP)^R′}(PPrⁱ₃)(CO) that were characterized by NMR spectroscopy, elemental analyses, and, in the case of R = Prⁱ and R′ = Bu^t or Prⁱ, X-ray crystallography. Depending on R′, the reaction of RuH{^R(NP)^R′}(PPrⁱ₃)(CO) with H₂ generates varying amounts of the imine-phosphine complex RuH₂{^R(NP)^R′H}(PPrⁱ₃)(CO). Insights into the mechanism of H₂ activation by these enamido derivatives were explored using RuH{^Pr(NP)^Pri}(PPrⁱ₃)(CO), for which an intermediate was identified as the dihydrogen-dihydride complex, RuH₂(H₂){^Pri(NP)^PriH}(PPrⁱ₃)(CO), on the basis of the T_1,min value of 22 ms for the ¹H NMR resonance at δ -7.2 at 238 K (measured at 400 MHz). The N donor of the enamine tautomeric form of the ligand is protonated by H₂ or D₂ and dissociates from Ru. Tautomerization of the enamine to the imine form of the dissociated arm is involved in formation of the final product.

Full text of DOI:10.1021/acs.inorgchem.5b00672

Article
pubs.acs.org/IC
Ruthenium Complexes Stabilized by Bidentate Enamido-Phosphine
Ligands: Aspects of Cooperative H2 Activation
Truman C. Wambach and Michael D. Fryzuk*
Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
S
* Supporting Information
ABSTRACT: Four bidentate, hybrid ligands (R(NP)R′H) featuring imine-nitrogen
and alkyl-phosphine donors linked by a cyclopentyl ring were synthesized. The
ortho position of the aryl group attached to nitrogen is varied such that R is Me or
Pri; additionally, the groups decorating phosphorus (R′) are varied between But or
Pri. The addition of each ligand to RuHCl(PPri3)2(CO) in the presence of KOBut
generates four enamido-phosphine complexes RuH{R(NP)R′}(PPri3)(CO) that
were characterized by NMR spectroscopy, elemental analyses, and, in the case of R
= Pri and R′ = But or Pri, X-ray crystallography. Depending on R′, the reaction of
RuH{R(NP)R′}(PPri3)(CO) with H2 generates varying amounts of the imine-
phosphine complex RuH2{R(NP)R′H}(PPri3)(CO). Insights into the mechanism of
H2 activation by these enamido derivatives were explored using RuH{Pr(NP)Pri}-
(PPri3)(CO), for which an intermediate was identified as the dihydrogen−dihydride
complex, RuH2(H2){Pri(NP)PriH}(PPri3)(CO), on the basis of the T1,min value of 22
ms for the 1H NMR resonance at δ −7.2 at 238 K (measured at 400 MHz). The N
donor of the enamine tautomeric form of the ligand is protonated by H2 or D2 and dissociates from Ru. Tautomerization of the
enamine to the imine form of the dissociated arm is involved in formation of the final product.
Scheme 1
INTRODUCTION
■
Until recently, ligands were designed to be ancillary in nature,
in other words, to remain innocent during any transformation
at the metal center by providing the appropriate steric and
electronic environment without getting involved in the actual
process. However, ligand systems that can participate in
reactions are a topic of current interest.1−5 A simple example
of ligand-based reactivity is hemilability, which occurs when a
donor of a multidentate ligand dissociates during a trans-
formation to provide an open coordination site. Other
examples are noninnocent or redox active ligands, wherein
electrons can be stored on the ligand and are available for use
by the complex. Of importance to this work are cooperative
ligands that react in concert with a metal center to activate
small molecules.1
other types of ligand cooperativity that involve activation of
small molecules at a remote site of the ligand, not necessarily
the backbone of the ligand that links the different donors.11−14
Linker reactivity is a key feature of the catalytic reactivity of
numerous pyridine-based metal−ligand systems. For example, 3
and 4 are involved in the catalytic acceptorless dehydrogenation
of primary alcohols to form esters15 and the reverse reaction,
hydrogenation of esters to form primary alcohols.9 Numerous
other pyridine-based linker reactive ligands are known,10,16−18
and coordination of this ligand architecture to a variety of late
transition metals generates complexes that display linker
reactivity. Importantly, in several cases, the enamido-phosphine
unit (bolded in 3, Scheme 1) cooperates with a metal, such that
Scheme 1 depicts two specific types of ligand cooperativity
that can be distinguished: donor reactivity6−8 and linker
reactivity.9,10 In the iridium example, addition of dihydrogen to
dihydride 1 results in the formation of the amine-trihydride 2
by heterolytic cleavage of H2 across the iridium-amido unit,
which we define as an example of donor reactivity. In the
ruthenium example 3, the heterolytic activation of H2 also
occurs, but in this case, a proton (H+) is transferred to the
backbone of the ligand, and the hydride (H−) coordinates to
the Ru(II) center in 4. In both cases, H2 is activated by the
ligand and the metal center acting in a cooperative fashion, but
the difference is which part of the ligand is protonated, the
donor in 1 → 2, or the linker in 3 → 4. Other nomenclature
has been developed to describe similar reactivity,4 and there are
Received: March 26, 2015
© XXXX American Chemical Society
A
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functionalization of the linker with a proton9,10,19,20 or other
electrophile21−25 occurs without the formation of any
observable intermediates. Computational evidence for select
systems suggests that concerted proton transfer to the linker of
the ligand occurs.20,26−30
We recently reported our studies on replicating the linker
reactivity shown for the transformation of 3 to 4; however,
instead of using the tridentate pyridine-based pincer ligand we
focused our attention on a simplified, bidentate enamido-
phosphine system, which is easily accessible by deprotonation
of readily available imine-phosphine ligands. As shown in eq 1,
positions of the N-aryl group (R = Pri or Me), and the
substituents on the phosphine donor (R′ = Pri or But), are
varied to explore the impact these modifications have on ligand
cooperativity (Scheme 2). The short form descriptors of the
ligands reported here are R(NP)R′. In solution, the imine-
phosphine and enamine-phosphine tautomers each display
unique singlets in their 31P{1H} NMR spectra, which allows
easy determination of the amount of each tautomer. When R′ is
Pri the equilibrium between the two tautomers slightly favors
the enamine form over the imine tautomer. When R′ is But the
equilibrium is shifted almost entirely toward the enamine. The
most sterically demanding ligand in this work is 5c, and it exists
exclusively as the enamine tautomer.
The reaction of 5a−d with RuHCl(PPri3)2(CO) in the
presence of 1 equiv of potassium tert-butoxide (KOBut) forms a
dark red solution in every case. 31P{1H} NMR spectroscopy
shows two doublet resonances with large coupling constants
indicative of trans disposed phosphines for the enamido-
ruthernium complexes 6a−d. After the reaction is complete and
after workup, analytically pure complexes are obtained in
acceptable yields (∼42%). The multinuclear NMR spectra of
6a−d are all consistent with C1 symmetric, five-coordinate
complexes.
we discovered that the cyclopentyl-based enamido-phosphine
derivative coordinated to Ir(I) (A in eq 1) could engage in
processes that replicated the heterolytic cleavage of H2 in a
cooperative manner to generate B.31
When concentrated pentane solutions of 6a or 6c were
cooled to −35 °C, crystals of both compounds were obtained
and analyzed by X-ray diffraction. ORTEP representations of 6a
and 6c are shown in Figures 1 and 2, respectively. For both 6a
and 6c, the hydride ligand could be located and freely refined.
Notably, both structures are distorted from an idealized
geometry, but are approximately square pyramidal. For the
PPri derivative, 6a, the N1−Ru1−C32 bond angle is
155.36(5)°, and the corresponding angle in 6c (N1−Ru1−
C100) is more linear at 164.25(6)°, no doubt due to the large
tert-butyl substituents on the latter. The H50−Ru1−C32 angle
is 84.1(7)° for 6a, and the corresponding angle in 6c is 85(1)°.
The above angles are noteworthy as DFT calculations
performed on a related Ru enamido-phosphine complex,
which could not be characterized by X-ray analysis, suggest
that upon switching from an amido phosphine35 to an
enamido-phosphine donor a square-based pyramidal structure
is favored over a trigonal bipyramidal geometry.20 The
structures of 6a and 6c are consistent with this proposal, as
are the large, negative chemical shifts (ca. −24 ppm) of the
hydride ligands of 6a and 6c observed by 1H NMR
spectroscopy.
While this iridium(I) system was found to add and release
H2, these systems did not catalyze the acceptorless dehydrogen-
ation (AD) of alcohols due to the formation of a variety of
stable, catalytically inactive iridium derivatives upon reaction
with primary and secondary alcohols. In contrast to the
ruthenium system in Scheme 1, the H2 addition and loss
resulted in a change in formal oxidation state at the metal
center from Ir(I) to Ir(III) (A to B), and most importantly, H2
loss (B to A) required addition of CO. What we also discovered
was that the N-arylimine donor was prone to dissociation and
putative enamine intermediates also did not bind to the iridium
center during ligand induced H2 loss.
We report here an update on our continued efforts to explore
a simplified cooperative ligand that can replicate key aspects of
the pyridine-based pincer ligands in Scheme 1. We also examine
modifications of the same imine-phosphine scaffold with a
Ru(II) precursor and its reactions with dihydrogen. What we
have discovered is that while the final product appears to match
linker reactivity in terms of product outcomes, the details of the
process are more consistent with a stepwise transformation that
involves a donor reactive pathway that is kinetically accessible
followed by tautomerization to generate the final product.
The bond lengths and angles of the enamido-phosphine unit
are nearly identical for both 6a and 6c; however, some subtle
differences occur in the bond lengths around the coordination
sphere of the two ruthenium centers. The Ru1−N1 bond
length is slightly longer for the PBut derivative; for example, for
SYNTHESIS OF RUTHENIUM
ENAMIDO-PHOSPHINE COMPLEXES
■
The synthesis of cyclopentyl-linked imine phosphine ligands
has been reported by us and others.31−34 In this work, the ortho
Scheme 2
B
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minimal, as reflected by the CO ligand. Interestingly, the CO
stretch for 3 is also 1899 cm−1, which is virtually identical to the
series of derivatives reported here. Given the differences in H2
activation for complexes 6a−d as compared to each other and
to 3, it is clear that electronic effects at ruthenium are
apparently not that important for cooperative H2 activation for
6a−d.
REACTIVITY OF RUTHENIUM
ENAMIDO-PHOSPHINE COMPLEXES WITH
DIHYDROGEN
■
As monitored by 1H, 1H{31P}, and 31P{1H} NMR spectroscopy,
exposing solutions of 6a−d to 1−4 atm of H2 forms products
consistent with 7a−d (Scheme 3).
Scheme 3
Figure 1. ORTEP drawing of the solid-state molecular structure of 6a
with probability ellipsoids at 50%. Hydrogen atoms are omitted for
clarity, with the exception of H50, which was found in the difference
map. Selected bond lengths (Å) and angles (deg): Ru1−N1 2.1287(2),
Ru1−P1 2.3273(6), Ru1−P2 2.4081(6), Ru1−C32 1.8196(2), N1−
C1 1.3796(2), C1−C2 1.3643(2), C2−P1 1.7629(2), C32−O1
1.1640(2), N1−C1−C2 125.42(2), C1−C2−P1 113.52(2), N1−
Ru1−P1 81.47(4), C32−Ru1−P1 88.62(5), N1−Ru1−P2 106.42(4),
P1−Ru1−P2 166.600(2), N1−Ru1−C32 155.36(5), C32−Ru1−H50
84.1(7).
Carefully controlling hydrogen pressure, solvent volume, and
headspace volume allows addition of reproducible amounts of
dihydrogen to samples of 6a−d, which allows the effects of
changing the sterics of the ligands on the H2 addition process
to be ascertained. The least sterically demanding variant (6b)
proceeds to completion with H2 to form two products in a
2.4:1.0 ratio. The two products likely correspond to
diastereomers due to the presence of the chiral center on the
ligand and the chiral ruthenium center; that is, the α-CH unit
can be syn or anti to the carbonyl ligand. The presence of these
1
two diastereomers for 7b complicates the solution H NMR
data enough that assignment of the resonances for the minor
1
diastereomer was not attempted. Importantly, H−13C HSQC
allows for assignment of 13C resonances as α-CH protons for
both the major and minor isomer; therefore, the imine
tautomeric form of the ligand is bound to Ru in both cases
(see Supporting Information). A major and minor diastereomer
1
also form when 6d reacts with H2. Trace resonances in the H
NMR spectra of 7a and 7c are consistent with small amounts of
a second diastereomer. The selectivity for one diastereomer
over the other is apparently governed by the sterics on the N-
aryl moiety, as only small amounts of a second diastereomer
appear in the H NMR spectra of 7a and 7c, which have the
bulkier ortho-isopropyl substituents.
Figure 2. ORTEP drawing of the solid-state molecular structure of 6c
with probability ellipsoids at 50%. Hydrogen atoms are omitted for
clarity, with the exception of H50, which was found in the difference
map. Selected bond lengths (Å) and angles (deg): Ru1−N1 2.1427(2),
Ru1−P1 2.3576(4), Ru1−P2 2.4217(4), Ru1−C100 1.8228(2), N1−
C1 1.3774(2), C1−C2 1.372(2), C2−P1 1.7703(2), C100−O1
1.169(2), N1−C1−C2 125.24(2), C1−C2−P1 113.94(1), N1−
Ru1−P1 81.05(3), C100−Ru1−P1 90.21(5), N1−Ru1−P2
106.19(3), P1−Ru1−P2 169.060(2), N1−Ru1−C100 164.25(6),
C100−Ru1−H50 85(1).
1
When the alkyl groups decorating phosphorus (R′) are
changed from isopropyl to tert-butyl, the rate of dihydrogen
addition is much slower, and the reactions never reach
1
completion despite an observable (by H NMR spectroscopy)
excess of H2 1and extended reaction times. Identification of 7c,d
is based on H NMR resonances consistent with the hydride
ligands observed for complexes 7a,b; the low concentrations of
7c,d relative to the respective starting materials are such that
obtaining 13C NMR data was not attempted and no further
characterization was possible.
The reaction of 6a with H2 proceeds to completion over the
course of approximately 12 h at room temperature. The
resulting complex 7a is isolated as a pale yellow, crystalline solid
after workup, in one diastereomeric form. In the 31P{1H} NMR
spectrum of 7a, new resonances at δ 74.5 and 92.9 are
6a this bond distance is 2.1287(2) Å, and lengthens to
2.1427(2) Å for 6c. The oxygen−carbon bond length of the
carbonyl group attached to ruthenium is 1.1641(2) Å for 6a
and 1.169(2) Å for 6c; therefore, changing from PPri2 to PBut2
groups has little influence on the length of the CO triple bond
of the carbonyl ligand. The CO stretching frequencies of 6a−d
are very similar and range from 1893 to 1899 cm−1 (see
Supporting Information, Table S1), which indicates that the
difference in electronic influence of these ligands on Ru is
C
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observed, with a P−P coupling constant (2JPP = 252.3 Hz) that
Scheme 4
is consistent with trans disposition of the two phosphine
1
ligands. Two signals in the hydride region of the H NMR
spectrum at δ −18.4 and −5.5 are observed. Additionally, a
resonance assigned to the α-CH proton that results from the
overall heterolytic cleavage of H2 at δ 3.1 can be identified.
Multinuclear NMR studies as well as deuterium labeling
experiments confirm that the linker α-CH of 7a originates from
added H2.
Dissolving 7a in a minimal amount of pentane and cooling
the mixture to −35 °C resulted in formation of X-ray quality
crystals. Figure 3 shows an ORTEP representation of 7a. The
never isolated as a pure material, several spectroscopic features
are consistent with the dihydride dihydrogen complex (8)
shown in Scheme 4.
Doublet resonances at δ 80.1 and 41.2 assigned to 8 are
observed by 31P{1H} NMR spectroscopy. The P−P coupling
constant (2JPP = 195.8 Hz) confirms that the phosphine ligands
1
remain trans to one another. Certain resonances in the H
NMR spectrum are especially diagnostic. For example, a sharp
singlet at δ 8.9 is assigned as the N−H proton of 8. A broad
resonance at δ −7.2 that integrates to four protons relative to
the signal at δ 8.9 is also observed. Measuring the relaxation
time of this upfield resonance at 400 MHz in a solution of 5%
CH2Cl2 in d8-toluene as a function of temperature gives a T1,min
value of 22 ms at 238 K. This relaxation time is comparable to
T1,min values reported for two similar dihydrogen dihydride
complexes: RuH2(H2)(CO)(PPri3)2 (T1,min = 15 ms at 200 K,
measured at 200 MHz)38 and RuH2(H2)(CO)(PCp3)2 (T1,min
= 42 ms at 233 K measured at 500 MHz).39 The abbreviation
PCp3 in this case corresponds to tricyclopentylphosphine.
Despite several attempts, decoalescence of the hydride
ligands from the dihydrogen ligand was never observed using
the conditions employed. Complete disappearance of the
dihydrogen−dihydride signal occurred at temperatures below
213 K, and the lowest temperature at which meaningful spectra
could be recorded was 173 K. Further cooling to 153 K did not
Figure 3. ORTEP drawing of the solid-state molecular structure of 7a
with probability ellipsoids at 50%. All of the hydrogen atoms except α-
CH proton and hydrides are omitted for clarity. The α-CH proton and
hydrides were located in the difference map. Selected bond lengths
(Å) and angles (deg): Ru1−N1 2.306(3), Ru1−P1 2.2923(2), Ru1−
P2 2.3310(2), Ru1−C32 1.872(6), N1−C1 1.293(6), C1−C2
1.510(6), C2−P1 1.854(5), C32−O1 1.172(6), N1−C1−C2
122.3(4), C1−C2−P1 109.1(3), N1−Ru1−P1 80.82(9), C33−Ru1−
P1 100.50(2), N1−Ru1−P2 107.77(9), P1−Ru1−P2 161.99(4), N1−
Ru1−C33 101.33(2).
ruthenium center is bound to two hydride ligands that are cis
disposed to one another. The α-CH proton of the ligand is
disposed anti to the carbonyl moiety. Interestingly, another
molecule corresponding to 7a is present in the asymmetric unit
of the crystal structure. Both molecules in the asymmetric unit
feature the S enantiomer of the imine-phosphine ligand
coordinated to ruthenium. The other enantiomer of 7a, with
the R form of the ligand coordinated to ruthenium, is also
present in the crystal lattice; the c-glide plane of the space
group (P21/c) generates it. Overall, the most notable feature of
the solid-state structure is the cis disposition of the two hydride
ligands. In comparison, trans hydrides are observed for the
pyridine-based pincer ligated ruthenium complex (4) and
related compounds (Scheme 1).9,10,20,36,37 As will be discussed
below, this change in the relative disposition of the hydrides
was the first clue that the mechanism of H2 addition is different
for our system in comparison to 3.
1
give any return of signal intensity, and very broad H NMR
resonances were observed, possibly due to freezing of the
solvent.
Deuterium labeling studies support the assignment of 8 as a
dihydrogen dihydride complex. For instance, exposing 6a to D2
shows rapid deuterium scrambling into the broad resonance at
δ −7.2 corresponding to 8. This is consistent with a highly
fluxional dihydrogen−dihydride species.38−41 A key feature of 8
is the protonated enamine that is dissociated from the
ruthenium center, wherein the N−H proton results from
added H2. Consistent with this proposal, the resonance at δ 8.9
is not observed when D2 gas is used in place of H2 (see
Supporting Information). An additional observation made
during these experiments is the 1H NMR resonance that
corresponds to the hydride ligand of the starting material 6a
disappears much more quickly than the other diagnostic
resonances of 6a. This suggests that 6a and 8 are in equilibrium
since the hydride of 6a exchanges for a deuteride under D2.
Monitoring the conversion of 6a to 7a under approximately
1
3.6 atm (6.5 equiv) of dihydrogen by H and 31P{1H} NMR
spectroscopy revealed that an intermediate species, 8, forms
after less than 20 min and goes on to form 7a (Scheme 4) over
a period of 5.4 h (95% complete). While this intermediate was
D
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The reverse reaction (Scheme 5), the loss of H2 from 7a to
form 6a, occurs slowly at room temperature under an
bubbler, gave no catalytic turnover. Analysis of the reaction
mixture by 31P{1H} NMR spectroscopy showed free PPri3,
consistent with decomposition. Lowering the temperature to 60
°C allowed for catalytic dehydrogenation of isopropanol and
cyclohexanol (Table 1, entries 2 and 4). Monitoring 0.9
turnovers of AD converting isopropanol to acetone in an
Scheme 5
1
evacuated J. Young tube by H NMR spectroscopy shows
hydride resonances that are consistent with 7a. The relative
concentrations of 6a and 7a vary somewhat during AD;
however, full conversion to 7a was not observed. The ratio of
6a:7a is approximately 1:1.2 after 0.9 turnovers, suggesting 7a
can release H2 under these conditions.
Attempts to dehydrogenate benzyl alcohol to benzyl
benzoate at 60 °C under similar conditions to those used for
secondary alcohol dehydrogenation were unsuccessful. Initial
attempts gave ∼1% conversion to benzyl benzoate. Recorded
31P{1H} NMR spectra of the reaction mixture prior to heating
show release of PPri3 and formation of a variety of products.
Addition of 1 equiv of pyridine relative to ruthenium had little
effect on the catalytic performance (∼2% conversion); likewise,
addition of 1 equiv of PMe3 to 6a had little effect (∼3%
conversion).
atmosphere of nitrogen. Evacuating the headspace of a J.
Young NMR tube containing a solution of 7a, and heating this
mixture to 60 °C, gives full conversion of 7a to 6a overnight.
Unfortunately, no intermediates were detected by 31P{1H} or
1H NMR spectroscopy. Monitoring H2 loss as a function of
time shows only resonances for the dihydride starting material
7a and the enamido-phosphine hydride product 6a, although
signals of the latter are broadened, presumably due to some
reactivity with hydrogen that is released into the headspace of
the NMR tube.
EFFORTS TOWARD CATALYTIC
DEHYDROGENATION OF ALCOHOLS
Having established the ability of these complexes to reversibly
add and release H2, attempts to apply this reactivity to the
catalytic acceptorless dehydrogenation (AD) of isopropanol,
cyclohexanol, and/or benzyl alcohol (Scheme 6) were made.
■
CONCLUSION
■
The synthesis and reactivity of a series of bidentate enamido-
phosphine ligands coordinated to ruthenium extend the linker
reactivity previously reported for 3 and related com-
pounds9,10,20,36 to new systems. Variation of the groups
decorating the N and P donor atoms of the bidentate ligands
explored here shows that the sterics of the phosphorus donor
have a profound impact on the reactivity of 6a−d with H2. The
reactivity of 6a with H2 is reversible, a potentially important
feature of an AD catalyst. Monitoring the reactivity of 6a with
primary and secondary alcohols demonstrates that it is a
catalyst precursor for secondary alcohol dehydrogenation.
Attempts to use 6a as AD catalysts for benzyl alcohol
dehydrogenation were unsuccessful, likely due to the thermal
instability of putative intermediates, such as 8. Perhaps the
most intriguing feature of these studies is the reactivity of 6a
with H2. Identification of dihydrogen−dihydride 8 as an
intermediate, which forms during conversion of 6a to 7a,
demonstrates that N-donor dissociation and tautomerization of
the dissociated arm of the ligand between enamine and imine
forms are involved in linker reactivity for this system. The
mechanism for linker reactivity described in this Article is a
unique alternative to what is commonly reported for other
tridentate and tetradentate metal−ligand systems, where linker
reactivity occurs via a concerted mechanism.
Scheme 6
These efforts show certain processes inhibit formation of an
active catalyst. Initially, 6a was found to be thermally unstable
under catalytic conditions at temperatures >110 °C, which are
normally used for alcohol dehydrogenation reactivity (Table
1).10 For example, heating 6a in refluxing toluene with
isopropanol, or cyclohexanol under Ar vented to a mercury
Table 1. Reactivity Studies
a
entry
catalyst
time (h)
temp (°C)
substrate
product
acetone
TON
TOF (h‑1)
1
2
3
4
5
6
7
6a
6a
6a
6a
6a
12
12
12
12
16
16
16
115
60
2-propanol
2-propanol
100
0
8.3
7
115
60
cyclohexanol
cyclohexanol
benzylalcohol
benzylalcohol
benzylalcohol
cyclohexanone
benzylbenzoate
benzylbenzoate
benzylbenzoate
50
60
∼1
∼2
∼3
b
6a
60
c
6a
60
a
b
c
Calculated by dividing moles of desired product by moles of 6a. 1 equiv of pyridine was added to 6a prior to addition of substrate and heating. 1
equiv of PMe3 was added to 6a prior to addition of substrate and heating.
E
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= 6.6 Hz, 1H, P−PriCH), 3.4 (sept, 3JHH = 6.9 Hz, 1H, N−PriCH), 3.5
EXPERIMENTAL SECTION
■
3
(sept, JHH = 6.7 Hz, 1H, N−PriCH), 7.1 (m, 3H, N−ArCH). 13C
All procedures and manipulations were performed under an
atmosphere of dry, oxygen-free dinitrogen or argon by means of
standard Schlenk or glovebox techniques. Argon and dinitrogen were
dried and deoxygenated by passing the gases through a column
containing molecular sieves and a Cu catalyst. Dihydrogen and was
dried by passage through activated molecular sieves prior to use. D2
and 13CO gas were purchased from Cambridge Isotope Laboratories
and used as received. Hexanes, toluene, THF, and diethyl ether were
purchased from Aldrich, dried by passage through a tower of alumina,
and degassed by passage through a tower of Q-5 catalyst under
positive pressure of nitrogen. Pentane was dried using Na/K and
benzophenone and collected from a solvent still. Deuterated toluene
and benzene were dried over NaK/benzophenone, trap-to-trap
distilled, and freeze−pump−thaw degassed three times. Potassium
tert-butoxide was purchased and purified by sublimation. Isopropanol,
cyclohexanol, and benzylalcohol were dried over sodium, then distilled
into a Kontes sealed flask and freeze−pump−thaw degassed.
Diisopropyl amine was distilled and freeze−pump−thaw degassed.
Cyclopentanone, 2,6-dimethylaniline, 2,6-diisopropylaniline, and n-
butyl lithium were purchased and used as received. RuCl3 hydrate was
purchased from Pressure Chemical Company and used as received.
RuHCl(PPri3)2(CO)42 was synthesized by a literature procedure. ATR
(attenuated total reflectance) FTIR (Fourier transform infrared
spectroscopy) spectra were recorded on a PerkinElmer Frontier
FTIR spectrometer. NMR (nuclear magnetic resonance) spectra were
recorded on Bruker Avance II 300 MHz or Bruker Avance 400 MHz
spectrometers unless otherwise noted. Chemical shifts for 31P nuclei
3
APT NMR (C6D6, 100.6 MHz, 298 K): δ 18.1 (d, JPC = 3.5 Hz P−
PriCH3), 18.5(5) (d, 3JPC = 2.4 Hz, P−PriCH3), 18.6 (d, 2JPC = 2.4 Hz,
3
P−PriCH3), 18.7 (s, P−PriCH3), 19.6 (d, JPC = 4.0 Hz, P−PriCH3),
20.1 (s, P−PriCH3), 23.0, (s, N−PriCH3), 23.3 (s, N−PriCH3), 23.5
3
1
(d, JPC = 28.9 Hz, P−PriCH), 24.0 (s, N−PriCH3), 25.1 (d, JPC
=
27.1 Hz, P−PriCH), 25.2 (s, N−PriCH3), 26.0 (dd, 3JPC = 1.9 Hz, 1JPC
= 14.8 Hz, P−PriCH), 28.2 (s, N−PriCH), 28.7 (s, N−PriCH), 28.8
(d, 3JPC = 6.2 Hz, γ-CH2), 29.5 (m, δ-CH2), 33.1 (d, 3JPC = 16.6 Hz, β-
1
CH2), 84.4 (d, JPC = 41.6 Hz, α-C), 122.6 (s, N−p-ArCH), 123.4 (s,
N−m-ArCH), 124.3 (s, N−m-ArCH), 142.8 (s, N−ArCPri), 143.3 (s,
N−ArCPri), 156.4 (s, N−CAr), 187.5 (dd, JPC = 4.3 Hz, JPC = 33.3
Hz N−Cenamido), 207.3 (v t, 2JPC = 14.9 Hz, Ru−CO). ATR-FTIR νCO
(cm−1): 1899. Anal. Calcd for C33H59NOP2Ru: C, 61.09; H, 9.17; N,
2.16. Found: C, 61.19, H, 9.45, N, 2.11.
3
2
RuH{Me(NP)Pri}(PPri3)(CO) (6b). (Yield after recrystallization: 0.063 g,
26%.) 31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ 47.4 (d, JPP
=
2
243.9 Hz, 1P, Ru−PPri3), 59.1 (d, 2JPP = 243.9 Hz, 1P, Ru−Pligand). 1H
2
2
NMR (C6D6, 400 MHz, 298 K): δ −25 (dd, JPH = 18.0 Hz, JPH
=
20.5 Hz, 1H, Ru−H), 0.97 (dd, 3JHH = 7.2 Hz, 3JPH = 12.4 Hz, 9H, P−
PriCH3), 1.1 (dd, JHH = 7.1 Hz, JPH = 12.7 Hz, 9H, P−PriCH3),
1.1(6) (dd, 3JHH = 6.0 Hz, 3JPC = 10.8 Hz, 3H, P−PriCH3), 1.2(2) (dd,
2JHH = 6.9 Hz, 3JPH = 15.9 Hz, 3H, P−PriCH3), 1.3 (dd, 3JHH = 6.9 Hz,
2
2
3JPH = 15.7 Hz, 3H, P−PriCH3), 1.4 (dd, JHH = 7.0 Hz, JPH = 16.6
3
3
Hz, 3H, P−PriCH3), 1.7 (dq, JHH = 6.8 Hz, JPH = 13.4 Hz, 3H, P−
PriCH), 1.9 (m, 2H, β-CH2), 2.1 (m, 3H, γ-CH2/P−PriCH), 2.2 (s,
3H, N−CH3), 2.3 (s, 3H, N−CH3), 2.3(5) (m, 1H, δ-CH2), 2.4 (m,
3
3
1H, δ-CH2), 2.7 (m, 1H, P−PriCH3), 6.7 (v dd, 3JHH = 7.2 Hz, 3JHH
=
1
were referenced to 85% H3PO4 in H2O (0 ppm). H nuclei were
7.6 Hz, 1H, N−p-ArCH), 7.0 (v d, J = 7.4 Hz, 2H, N−m-ArCH). 13C
referenced to resonances of the residual protonated solvents relative to
tetramethylsilane (0 ppm), and 13C spectra were referenced to the
solvent carbon resonance(s). Elemental analysis was performed at the
facilities of the Chemistry Department of the University of British
Columbia. Gas chromatography−mass spectrometry (GC−MS)
analyses were performed on an Agilent 6890N instrument using an
Agilent HP-5MS column (30 m length, 0.25 mm diameter, 0.25 μm
3
APT NMR (C6D6, 100.6 MHz, 298 K): δ 18.3 (d, JPC = 3.2 Hz P−
PriCH3), 18.8 (d, 3JPC = 5.3 Hz, 2× P−PriCH3), 19.4 (d, 2JPC = 4.0 Hz,
P−PriCH3), 19.9 (s, P−PriCH3), 20.0 (s, N−CH3), 20.1 (s, N−CH3),
20.6 (s, P−PriCH3), 23.2 (d, JPC = 31.9 Hz, P−PriCH), 25.5 (s, P−
1
PriCH), 25.6 (dd, 3JPC = 2.1, 1JPC = 15.2 Hz, P−PriCH), 28.7 (d, 3JPC
=
2
6.4 Hz, δ-CH2), 29.7 (br s, γ-CH2), 31.4 (d, JPC = 16.7 Hz, β-CH2),
1
1
84.7 (d, JPC = 41.2 Hz, α-C), 123.2 (s, N−p-ArCH), 127.5 (s, N−m-
film). Quantitative H NMR spectra recorded using 1,3,5-trimethox-
ArCH), 127.7 (s, N−m-ArCH), 135 (s, N−ArCMe), 135.0 (s, N−
ybenzene as an internal standard were recorded using a relaxation
delay time (d1) of 57 s. Caution! All reactions that resulted in a pressure
of 1.5 atm or greater within a sealed vessel upon warming to room
temperature were performed with great care, and always manipulated
behind a blast shield. Pressurized NMR tubes were allowed to warm to
room temperature in a safe location and used with caution; protective eye
wear was warn at all times.
3
2
ArCMe), 157.9 (s, N−CAr), 185.7 (dd, JPC = 5 Hz, JPC = 33.3 Hz,
3
2
N−Cenamido), 207.0 (dd, JPC = 15.4 Hz, JPC = 25.1 Hz, Ru−CO).
ATR-FTIR νCO (cm−1): 1894. Anal. Calcd for C29H51NOP2Ru: C,
58.76; H, 8.67; N, 2.36. Found: C, 58.73, H, 8.64, N, 2.37.
RuH{Pri(NP)But}(PPri3)(CO) (6c). (Yield after recrystallization: 0.153 g,
55%.) 31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ 39.5 (d, JPP
=
2
245.7 Hz, 1P, Ru−PPri3), 73.2 (d, 2JPP = 245.7 Hz, 1P, Ru−Pligand). 1H
General Procedure for the Synthesis of RuH{Pri(NP)Pri}(PPri3)-
(CO) (6a), RuH{Me(NP)Pri}(PPri3)(CO) (6b), RuH{Pri(NP)But}(PPri3)-
(CO) (6c), and RuH{Me(NP)But}(PPri3)(CO) (6d). The appropriate
imine-phosphine ligand (0.411 mmol) was combined with RuHCl-
(PPri3)2(CO) (0.200 g, 0.411 mmol) and potassium tert-butoxide
(0.046 g, 0.411 mmol) in a vial fitted with a stir bar in the glovebox.
THF (5 mL) was added, which immediately produced a dark red color
indicative of formation of the desired product. The reaction mixture
was stirred for approximately 4 h and monitored by 31P{1H} NMR
spectroscopy until complete, whereupon the mixture was taken to
dryness and the residue was dissolved in a minimal amount of pentane
(∼5 mL). The pentane solution was filtered through Celite into a
small round-bottom flask, and the pentane and free PPri3 were
removed under vacuum. The crude product was dissolved in a minimal
amount of pentane, and upon cooling to −35 °C overnight analytically
pure crystalline samples of each complex were obtained.
2
2
NMR (C6D6, 400 MHz, 298 K): δ −24.0 (dd, JPH = 18.8 Hz, JPH
=
20.2 Hz, 1H, Ru−H), 0.9 (dd, JHH = 7.2 Hz, 3JPC = 12.1 Hz, 9H, P−
3
PriCH3), 1.1 (m, 12H, N/P−PriCH3), 1.2 (d, JHH = 6.7 Hz, 3H, N−
3
PriCH3), 1.2(8) (d, 3JHH = 6.7 Hz, 3H, N−PriCH3), 1.2(9) (d, 3JHH
=
6.9 Hz, 3H, N−PriCH3), 1.5 (d, JPH = 13.1 Hz, 9H, P−ButCH3), 1.6
3
3
(d, JPH = 12.9 Hz, 9H, P−ButCH3), 1.7 (m, 1H, β-CH2), 1.8(9) (m,
1H, β-CH2), 2.0 (m, 2H, γ-CH2), 2.1 (m, 3H, P−PriCH), 2.5 (m, 1H,
δ-CH2), 2.7 (m, 1H, δ-CH2), 3.4 (sept 3JHH = 6.9 Hz, 1H, N−PriCH),
3.6 (sept 3JHH = 6.7 Hz, 1H, N−PriCH), 7.1 (br s, 3H, N−ArCH). 13
C
APT NMR (C6D6, 100.6 MHz, 298 K): δ 18.9 (s, P−PriCH3), 20.0 (s,
P−PriCH3), 23.4 (s, N−PriCH3), 23.9 (s, N−PriCH3), 25 (s, N−
PriCH3), 25.0 (s, N−PriCH3), 25.7 (d, JPC = 1.8 Hz, JPC = 15.2 Hz,
3
1
P−PriCH), 28.3 (s, N−PriCH), 28.4(7) (s, N−PriCH), 28.5 (m, γ-
CH2), 30.3(5) (d, JPC = 3.8 Hz, P−ButCH3), 30.4 (d, JPC = 4.4 Hz,
2
2
P−ButCH3), 32.3 (m, δ-CH2), 33.5 (d, JPC = 16.4 Hz, β-CH2), 36.0
2
1
1
(d, JPC = 23.7 Hz, P−ButC), 40.9 (d, JPC = 20.6 Hz, P−ButC), 86.7
RuH{Pri(NP)Pri}(PPri3)(CO) (6a). (Yield after recrystallization: 0.097 g,
1
36%.) 31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ 39.5 (d, JPP
=
2
(d, JPC = 38.4 Hz, α-C), 122.9 (s, N−m-ArCH), 123.3 (s, N−m-
245.2 Hz, 1P, Ru−PPri3), 59.8 (d, 2JPP = 245.2 Hz, 1P, Ru−Pligand). 1H
ArCH), 124.3 (s, N−p-ArCH), 143.1 (s, N−ArCPri), 143.6 (N−
ArCPri), 156.6 (N−CAr), 186.7 (dd, JPC = 4.5 Hz, JPC = 33.0 Hz,
N−Cenamido), Ru−CO not observed. ATR-FTIR νCO (cm−1): 1893.
Anal. Calcd for C35H63NOP2Ru: C, 62.10; H, 9.38; N, 2.07. Found: C,
61.93, H, 9.61, N, 2.04.
2
2
2
2
NMR (C6D6, 400 MHz, 298 K): δ −23.3 (dd, JPH = 18.6 Hz, JPH
=
22.1 Hz, 1H, Ru−H), 0.83 (dd, 3JHH = 7.2 Hz, 3JPH = 11.9 Hz, 9H, P−
PriCH3), 1.1−1.3(4) (m, 34H (30H expected, trace PPri3 may explain
slight over integration), N/P−PriCH3), 1.5 (dd, JHH = 7.0 Hz, JPC
=
3
3
16.9 Hz, 3H, P−PriCH3), 1.7 (m, 1H, β-CH2), 2.0 (m, 1H, β-CH2),
2.1 (m, 4H, 3× P−PriCH/γ-CH2), 2.2 (m, 2H, P−PriCH, γ-CH2), 2.3
(m, 1H, δ-CH2), 2.5 (m, 1H, δ-CH2), 2.7 (d. sept, 2JPH = 4.4 Hz, 3JHH
RuH{Me(NP)But}(PPri3)(CO) (6d). (Yield after recrystallization: 0.215g,
55%.) 31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ 46.5 (d, JPP
=
2
242.6 Hz, 1P, Ru−PPri3), 72.4 (d, 2JPP = 242.6 Hz, 1P, Ru−Pligand). 1H
F
DOI: 10.1021/acs.inorgchem.5b00672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2
2
NMR (C6D6, 400 MHz, 298 K): δ −24.8 (dd, JPP = 18.0 Hz, JPP
=
vacuum. After this process, the tube was left submerged in liquid N2,
whereupon the headspace of the NMR tube was backfilled with H2 to
a total pressure of 38.0 mm Hg. The Kontes valve was sealed, and the
NMR tube was flame-sealed such that 210 mm of headspace existed
above the frozen toluene solution. The NMR tube was removed from
liquid N2 and allowed to warm to room temperature in a safe location.
When the toluene solution melted, the time was recorded as the start
18.8 Hz, 1H, Ru−H), 1.0 (dd, JHH = 7.2 Hz, 3JPH = 12.7 Hz, 9H, P−
3
PriCH3), 1.1 (dd, JHH = 7.2 Hz, JPH = 12.5 Hz, 9H, P−PriCH3), 1.5
(d, 3JPH = 13.2 Hz, 9H, P−ButCH3), 1.5(1) (d, 3JPH = 12.8 Hz, 9H, P−
ButCH3), 1.7 (m, 3H, P−PriCH), 1.8 (v t, J = 2.2 Hz, 2H, β-CH2), 2.1
(m, 2H, γ-CH2), 2.2 (s, 3H, N−CH3), 2.4 (s, 3H, N−CH3), 2.5 (m,
3
3
3
1H, δ-CH2), 2.6 (m, 1H, δ-CH2), 6.9 (t, JHH = 6.9 Hz, 1H, N−p-
ArCH), 7.0 (v d, JHH = 7.4 Hz, 2H, N−m-ArCH). 13C APT NMR
3
1
of the reaction. After 30 min, a quantitative H NMR spectrum was
(C6D6, 100.6 MHz, 298 K): δ 20.0 (s, P−PriCH3), 20.2 (s, P−
PriCH3), 20.3 (s, 2× N−CH3), 25.0 (dd, 4JPC = 1.8 Hz, 1JPC = 15.5 Hz,
P−PriCH), 28.8 (d, 3JPC = 6.0 Hz, γ-CH2), 30.1 (v t, 2JPC = 3.8 Hz, 2×
recorded. The tube was allowed to sit for 2 days, and then
characterization by multinuclear NMR spectroscopy was performed.
RuH2{Pri(NP)PriH}(PPri3)(CO) (7a). The reaction is complete after 12
h using the above conditions. Multinuclear NMR data are reported
above in the synthesis of 7a.
P−ButCH3), 31.8 (d, JPC = 16.4 Hz, β-CH2), 32.4 (v t, JPC = 1.9 Hz,
2
δ-CH2), 35.2 (dd, 3JPC= 1.3 Hz, 1JPC = 22.9 Hz, P−CBut), 42.2 (d, 1JPC
= 21.0 Hz, P−CBut), 86.5 (d, JPC = 39.4 Hz, α-C), 123.1 (s, N−p-
1
RuH2{Me(NP)PriH}(PPri3)(CO) (7b). After 2 days, two products are
observed in a 2.4:1.0 ratio by 31P{1H} NMR. The compound with 2JPP
= 251.9 Hz is present in higher concentration than the compound with
2JPP = 248.7 Hz. 31P{1H} NMR (d8-toluene, 161.9 MHz, 298 K): δ
ArCH), 127.7 (s, 2× N−m-ArCH), 134.2 (s, N−ArCMe), 135.4 (s,
3
2
N−ArCMe), 158.0 (s, N−CAr),184.5 (dd, JPC = 4.0 Hz, JPC = 32.4
Hz, N−Cenamido), 207.2 (dd, 2JPC = 13.7 Hz, 2JPC = 15.2 Hz, Ru−CO).
ATR-FTIR νCO (cm−1): 1895. Anal. Calcd for C31H55NOP2Ru: C,
59.98; H, 8.93; N, 2.26. Found: C, 59.99, H, 9.06, N, 2.51.
2
2
2
72.4 (d, JPP = 248.7 Hz), 73.3 (d, JPP = 251.9 Hz), 89.7 (d, JPP
=
248.7 Hz), 95.4 (d, 2JPP = 251.9 Hz). 1H NMR (d8-toluene, 400 MHz,
298 K): Only resonances assigned to the major isomer are listed, all
the resonances except for the hydrides were identified with the aid of a
1H−13C HSQC NMR spectrum. There are many overlapping signals
present. The data follow: δ −17.5 (ddd, 2JHH = 6.6 Hz, 2JPH = 18.3 Hz,
Synthesis of RuH2{Pri(NP)PriH}(PPri3)(CO) (7a). Compound 6a
(0.100 g, 0.204 mmol) was taken into hexanes (5 mL) in a thick
walled glass vessel fitted with a Kontes valve. The mixture was freeze−
pump−thaw degassed three times using high vacuum. The headspace
of the reaction vessel, frozen in liquid nitrogen, was backfilled with
dihydrogen. The Kontes valve was sealed, and the reaction was allowed
to warm to room temperature behind a blast shield. Upon warming to
room temperature, the reaction gradually lightened in color. After 24
h, a pale red-yellow solution is observed. At this time, the reaction was
refrozen in liquid nitrogen, and the hydrogen pressure was released by
carefully opening the Kontes valve to a Schlenk line connected to a
mercury bubbler. Hexanes were removed under vacuum, and a
minimal amount of pentane was added to dissolve all of the solids.
This mixture was stored at −35 °C overnight and generated small
clusters of colorless crystals (yield, 0.046 g, 46%). 31P{1H} NMR
(C6D6, 161.9 MHz, 298 K): δ 74.5 (d, 2JPP = 252.3 Hz, 1P, Ru−PPri3),
2JPH = 28.2 Hz, 1H, trans-N−Ru−H), −5.6 (ddd, 2JHH = 6.8 Hz, 2JPH
=
21.5 Hz, 2JPH = 31.9 Hz, 1H, trans-CO−Ru−H), 1.3−1.5 (m, 21H, P−
PriCH3), 1.5−1.6 (m, 11H, P−PriCH3, 2× β-CH2), 1.6(3) (m, 2H, γ-
CH2/δ-CH2), 1.8 (m, 2H, γ-CH2/δ-CH2), 2.0 (s, 3H, N−CH3),
2.0(1)−2.2 (m, 5H, P−PriCH), 2.6 (s, 3H, N−CH3), 3.4 (dd, J = 9.0
Hz, J = 20.3 Hz, 1H, α-CH), 6.9−7.0 (m, 2H, N−ArCH), 7.1 (m, 1H,
N−ArCH). 13C APT NMR (d8-toluene, 100.6 MHz, 298 K): δ 18.1
(d, JPC = 7.5 Hz, P−PriCH3),18.3 (s, N−CH3), 18.9 (s, N−CH3),
2
19.4 (d, JPC = 4.3 Hz, P−PriCH3), 20.7 (m, P−PriCH3, signal
2
obscured by d8-toluene CD3 signal, identified by 1H−13C HSQC), 20.9
(d, JPC = 2.8 Hz, P−PriCH3), 21.1 (s, P−PriCH3), 21.4 (s, P−
2
PriCH3), 23.7 (dd, 3JPC = 2.4 Hz, 1JPC = 12.0 Hz, P−PriCH), 25.3 (v t,
2
1
92.9 (d, JPP = 252.3 Hz, 1P, Ru−Pligand). H NMR (C6D6, 400 MHz,
298 K): δ −18.4 (ddd, 2JHH = 6.7 Hz, 2JPH = 18.4 Hz, 2JPH = 28.8 Hz,
2JPC = 6.8 Hz, β-CH2), 26.2 (d, JPC = 16.9 Hz, P−PriCH), 27.5 (d,
1
3JPC = 5 Hz, γ-CH2), 31.1 (dd, JPC = 2.1 Hz, JPC = 24.3 Hz, P−
PriCH), 35.3 (s, P−PriCH), 55.2 (d, 1JPC = 11.9 Hz, α-CH2), 124.5 (s,
N−ArCH), 127.9 (s, N−ArCH), 129.1 (s, N−ArCH), 152.1 (s, N−
ArCCH3), 191.3 (m, N−Cimine), 209.63 (m, Ru−CO). Resonances for
N−CAr and N−ArCMe not observed, potentially due to poor S/N.
RuH2{Pri(NP)ButH}(PPri3)(CO) (7c). After 2 days, only signals assigned
3
1
1H, trans-N−Ru−H), −5.5 (ddd, 2JHH = 6.7 Hz, 2JPH = 22.1 Hz, 2JPH
=
32.2 Hz, 1H, trans-CO−Ru−H), 1.2 (m, 33H, N/P−PriCH3), 1.3 (d,
3JHH = 7.2 Hz, 3H, N−PriCH3), 1.4 (d, 3JHH = 7.2 Hz, 4H, N−PriCH3/
γ-CH2), 1.4(6) (m, 1H, δ-CH2), 1.6 (m, 4H, 2× β-CH2/δ-CH2/γ-
CH2), 1.7 (d, 3JHH = 6.6 Hz, 3H, N−PriCH3), 1.9 (m, 2H, P−PriCH3),
2.0 (m, 3H, P−PriCH3), 3.0 (sept 3JHH = 6.72 Hz, 1H, N−PriCH), 3.2
(v dd, J = 10.3 Hz, J = 20.1 Hz, 1H, α-CH), 3.7 (sept. 2JHH = 6.76 Hz,
1
to the expected product could be detected by H NMR spectroscopy.
1H, N−PriCH), 7.0 (dd, JHH = 1.0 Hz, JHH = 7.5 Hz, 1H, N−m-
4
3
Allowing the reaction to proceed for 8 days gave approximately 40%
conversion to 7c. 31P{1H} NMR (d8-toluene, 161.9 MHz, 298 K): δ
76.0 (d, 2JPP = 251.5 Hz, 1P, Ru−PPri3), 116.0 (d, 2JPP = 251.5 Hz, 1P,
3
4
ArCH), 7.1 (v t, JHH = 7.6 Hz, 1H, N−p-ArCH), 7.1 (dd, JHH = 1.0
Hz, JHH = 7.7 Hz, 1H, N−m-ArCH). 13C APT NMR (C6D6, 100.6
3
1
MHz, 298 K): δ 18.3 (d, 2JPC = 7.4 Hz, P−PriCH3), 19.1 (d, 2JPC = 5.7
Hz, P−PriCH3), 19.2 (s, P−PriCH3), 21.0 (m, P−PriCH3), 21.1 (d,
Ru−Pligand). H NMR (d8-toluene, 400 MHz, 298 K): δ −18.2 (ddd,
2
2
2JHH = 6.7 Hz, JPH = 18.7 Hz, JPH = 26.7 Hz, 1H, trans-N−Ru−H),
1
2
2JPC = 3.7 Hz, P−PriCH3), 21.5 (d, JPC = 3.5 Hz, P−PriCH3), 23.8
2
−5.7 (v dt, JHH = 6.7 Hz, JPH = 25.4 Hz, 1H, trans-CO−Ru−H).
RuH2{Me(NP)ButH}(PPri3)(CO) (7d). After 2 days approximately 10%
conversion is observed. Only one product is detected by 31P{1H}
NMR. The 1H NMR spectrum shows a major and minor set of
resonances corresponding to new products. The ratio between the
major to the minor isomers is ∼1:4. 31P{1H} NMR (d8-toluene, 161.9
MHz, 298 K): δ 74.0 (d, 2JPP = 250.8 Hz, 1P, Ru−PPri3), 117.9 (d, 2JPP
= 250.7 Hz, 1P, Ru−Pligand). 1H NMR (d8-toluene, 400 MHz, 298 K):
δ −17.5 (ddd, 2JHH = 7.7 Hz, 2JPH = 19.3 Hz, 2JPH = 27.6 Hz, 1H, Ru−
(dd, JPC = 2.4 Hz, JPC = 11.5 Hz, P−PriCH), 24.2 (s, N−PriCH3),
3
1
24.7 (s, N−PriCH3), 25.2 (s, N−PriCH3), 25.5 (dd, 4JPC = 1.4 Hz, 3JPC
= 4.5 Hz, δ-CH2), 25.7 (s, N−PriCH3), 26.5 (dd, 3JPC = 2.7 Hz, 1JPC
=
16.7 Hz, P−PriCH), 26.9 (s, N−PriCH), 27.4 (s, N−PriCH), 27.6 (d,
3JPC = 4.2 Hz, γ-CH2), 31.2 (dd, JPC = 2.3 Hz, JPC = 30.6 Hz, P−
3
1
PriCH), 33.0 (d, JPC = 5.5 Hz, β-CH2), 55.7 (d, JPC = 11.0 Hz, α-
CH), 123.6 (s, N−m-ArCH), 125.1 (s, N−p-ArCH), 125.5 (s, N−m-
ArCH), 137.8 (s, N−ArCPri), 139.2 (s, N−ArCPri), 150.7 (s, N−
2
1
2
2
2
3
2
Hminor), −17.3 (ddd, JHH = 7.0 Hz, JPH = 19.0 Hz, JPH = 27.0 Hz,
CAr), 193.5 (dd, JPC = 2.6 Hz, JPC = 9.8 Hz, N−Cimine), 208.9 (v t,
1H, Ru−Hmajor), −14.7 (dd, JPH = 15.7 Hz, 2JPH = 20.1 Hz, 1H, Ru−
2
3JPC = 9.7 Hz, Ru−CO). ATR-FTIR νCO (cm−1): 1881. Anal. Calcd
H), −7.4 (br s, 4H, Ru−(H2)(H)2), −5.9 (m, 1H, Ru−Hminor), −5.8
for C33H61NOP2Ru: C, 60.90; H, 9.45; N, 2.15. Found: C, 61.26; H,
9.52; N, 2.25.
2
2
(dd, JHH = 6.9 Hz, JPH = 25.7 Hz, 1H, Ru−Hmajor).
Formation of RuH2(H2){Pri(NP)PriH}(PPri3)(CO) (8). Reaction per-
formed under H2. Compound 6a (0.020 g, 0.031 mmol) was dissolved
in C6D6 (0.5 mL). This solution was transferred to a flame sealable
NMR tube attached to a Kontes valve with a ground glass joint. The
mixture was freeze−pump−thaw degassed three times using high
vacuum and left submerged in liquid nitrogen. The headspace of the
NMR tube was backfilled such that a meter stick attached to a column
of mercury read 38.0 mm Hg. The Kontes valve was closed, and the
General Procedure for Monitoring Formation of
RuH2{Pri(NP)PriH}(PPri3)(CO) (7a), RuH2{Me(NP)PriH}(PPri3)(CO)
(7b), RuH2{Me(NP)PriH}(PPri3)(CO) (7c), and RuH2{Me(NP)PriH}-
(PPri3)(CO) (7d) under H2. 6a, 6b, 6c, or 6d (0.031 mmol) was
dissolved in d8-toluene (0.50 mL) in a flame sealable NMR tube
attached to a Kontes valve by a ground glass joint. The d8-toluene
contained 1,3,5-trimethoxybenzene as an internal standard. The
mixture was freeze−pump−thaw degassed three times using high
G
DOI: 10.1021/acs.inorgchem.5b00672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
NMR tube was flame-sealed. The tube was removed from liquid
nitrogen and allowed to warm to room temperature in a safe location.
Within 20 min, the mixture mostly corresponds to 8, such that
meaningful multinuclear NMR spectra could be recorded. No attempts
were made to isolate this intermediate as a pure solid. 31P{1H} NMR
mixture. The Schlenk flask was connected to a reflux condenser under
a flow of Ar. The reaction vessel was lowered into a 60 °C oil bath.
The reaction was vented to the Ar manifold of the Schlenk line, which
was attached to a mercury bubbler. Before heating, and after 16 h, a
small aliquot (0.5 mL) of the reaction mixture was sampled for analysis
by NMR spectroscopy.
2
(C6D6, 161.9 MHz, 298 K): δ 80.1 (d, JPP = 195.8 Hz) and 41.2 (d,
No Additive. Prior to heating, 31P{1H} NMR (C6D6, 161.9 MHz,
298 K): δ 19.6 (s, P−Pri3), 57.5 (s), 60.8 (s), 79.8 (s), 94.3 (s).
After heating to 60 °C, 31P{1H} NMR (C6D6, 161.9 MHz, 298 K):
δ 19.6 (s, P−Pri3), 57.5 (s), 61.5 (s), 78.5 (d, 2JPP = 196.6 Hz), 80.3 (d,
2JPP = 196.6 Hz), 94.2 (s). 1H NMR (d8-toluene, 400 MHz, 298 K): δ
−8.6 (td, 3JHH = 5.4 Hz, 2JPH = 23.1 Hz, Ru−H), −8.4 (td, 2JHH = 5.4
1
2JPP = 195.8 Hz). H NMR (C6D6, 400 MHz, 298 K): δ −7.2 (br s,
3
3
4H, Ru−(H2)H2), 1.0 (dd, JHH = 7.3 Hz, JPH = 13.8 Hz, 3H, P−
PriCH3), 1.1 (dd, 3JHH = 7.1 Hz, 3JPH3 = 13.4 Hz, 18H, P−PriCH3), 1.2
(m, 12H, N/P−PriCH3), 1.3 (d, JHH = 6.8 Hz, 3H, N−PriCH3),
3
3
1.3(5) (d, JHH = 6.8 Hz, 3H, N−PriCH3), 1.4 (d, JHH = 6.8 Hz, 3H,
N−PriCH3), 1.5 (m, 2H, γ-CH2), 1.9 (td, JHH = 6.8 Hz, JPH = 13.8
Hz, 3H, P−PriCH), 2.0 (m, 1H, P−PriCH), 2.1 (t, 3JHH = 7.3 Hz, 2H,
β-CH2), 2.2 (td, 3JHH = 6.7 Hz, 3JPH = 13.4 Hz, 1H, P−PriCH), 2.5 (t,
3
2
2
Hz, JPH = 22.7 Hz, Ru−H) 2.1 (s, mesitylene-CH3), 3.3 (s, benzyl
alcohol-OH), 4.3 (s, benzyl alcohol-CH2), 5.0 (s, benzyl benzoate-CH2),
6.6 (mesitylene-ArCH), 7.0−7.1 (ArCH). On the basis of integration of
the CH2 resonances of benzyl benzoate and benzyl alcohol, ∼1%
conversion occurred over 16 h.
3JHH = 6.7 Hz, 2H, δ-CH2), 3.6 (sept, JHH = 6.8 Hz, 2H, N−PriCH),
3
7.0(9) (m, 2H, N−m-ArCH), 7.1 (m, 1H, N−p-ArCH), 8.9 (s, 1H,
Nenamine−H).
Formation of RuD2(D2){Pri(NP)PriD}(PPri3)(CO) (8). Reaction per-
formed under D2. Similar conditions to those used to observe
formation of RuH2(H2){Pri(NP)PriH}(PPri3)(CO) (8) were used.
31P{1H} NMR (C6D6, 161.9 MHz, 298 K): No notable changes from
Addition of PMe3. The conditions described above were repeated;
however, PMe3 (5 μL, 0.041 mmol) was added to the mixture of 6a
(0.020g, 0.041 mmol) dissolved in a 1.0 M solution of mesitylene in
d8-toluene (2.0 mL).
Prior to heating to 60 °C, 31P{1H} NMR (d8-toluene, 161.9 MHz,
298 K): δ 19.6 (s, P−Pri3), 61.5 (s), 94.3 (s).
1
reactions using H2 are observed. H NMR (C6D6, 400 MHz, 298 K):
The signals at δ −7.2 (br s, 4H, Ru−(H2)H2) and 8.9 (s, 1H, Nenamine
−
After heating to 60 °C, 31P{1H} NMR (d8-toluene, 161.9 MHz, 298
H) are changed from the spectrum recorded using H2 gas. Integration
2
K): δ 19.6 (s, P−Pri3), 57.5 (s), 61.3 (s), 78.5 (d, JPP = 196.6 Hz),
3
of these resonances relative to a resonance at δ 2.5 (t, JHH = 6.7 Hz,
2
1
80.3 (d, JPP = 196.6 Hz), 94.2 (s). H NMR (d8-toluene, 400 MHz,
2H, δ-CH2) that does not incorporate deuterium gives the ratio
11:1:75, Ru−(H2)H2:Nenamine-H:δ-CH2.
2
2
298 K): δ −8.6 (td, JHH = 5.4 Hz, JPH = 23.1 Hz, Ru−H), −8.4 (td,
2JHH = 5.4 Hz, 2JPH = 22.7 Hz, Ru−H). Chemical shifts similar to those
reported above for benzyl alcohol, benzyl benzoate, and mesitylene are
observed here. On the basis of integration of the CH2 resonances of
benzyl benzoate and benzyl alcohol ∼3% conversion has occurred over
16 h.
General Procedure for the Catalytic Dehydrogenation of
Isopropanol to Acetone and Cyclohexanol to Cyclohexanone
Using RuH{Pri(NP)Pri}(PPri3)(CO) (6a). A three neck flask (100 mL),
fitted with a small stir bar and a reflux condenser connected to an Ar
manifold vented to a mercury bubbler was used as the reaction vessel.
In the glovebox, the three neck flask was charged with 6a (0.040 g,
0.062 mmol) dissolved in toluene (2.00 mL). Using Schlenk
techniques, the appropriate alcohol (6.2 mmol) was added. The
three neck flask was lowered into a 60 °C oil bath and heated for
approximately 12 h. After this period, the reaction mixture was
sampled and analyzed by GC/MS. The trace showed complete
consumption of isopropanol, and formation of acetone. By similar
methods, it was determined approximately 50% of the cyclohexanol
had been converted to cyclohexanone after 12 h.
Addition of Pyridine. The conditions described above were
repeated; however, pyridine (3.3 μL, 0.041 mmol) was added to the
mixture of 6a (0.020g, 0.041 mmol) dissolved in 1.0 M mesitylene in
d8-toluene (2.0 mL).
Prior to heating to 60 °C, 31P{1H} NMR (d8-toluene, 161.9 MHz,
298 K): δ 5.6 (s), 19.6 (s, P−Pri3), 21.5 (s), 22.4 (s), 23.1 (s).
After heating to 60 °C, 31P{1H} NMR (d8-toluene, 161.9 MHz, 298
1
K): δ 19.6 (s), 57.5 (s), 61.7 (s), 75.2 (s), 94.2 (s). H NMR (d8-
toluene, 400 MHz, 298 K): Chemical shifts similar to those reported
above for benzyl alcohol, benzyl benzoate, and mesitylene are observed
here. On the basis of the integration of the CH2 resonances of benzyl
benzoate and benzyl alcohol ∼2% conversion has occurred over 16 h.
Monitoring dehydrogenation of isopropanol to acetone by RuH-
{
Pri(NP)Pri}(PPri3)(CO) (6a) by NMR. 6a (0.020 g, 0.031 mmol)
was dissolved in d8-toluene (0.5 mL) in a J. Young NMR tube.
Isopropanol (0.024 mL, 0.31 mmol) was added to this mixture. The
NMR tube was heated to 60 °C in the sealed tube overnight. Some
conversion of isopropanol to acetone was detected under these
conditions (3%). At room temperature, the headspace of the J. Young
tube was evacuated. The J. Young tube was sealed under vacuum and
lowered into a 60 °C oil bath for 2 h. More acetone formation was
observed (5%). Monitoring the reaction while evacuating the
headspace every hour showed an increase in percent conversion to
acetone with time: 8% after 4 h to 9% after 9 h. The ratio between 6a:
7a varies but is approximately 1:1.2. The multinuclear NMR data
reported below corresponds to the final reaction mixture. 31P{1H}
NMR (d8-toluene, 161.9 MHz, 298 K): δ −19.5 (s,1P), 19.9 (s, 1P,
PPri3), 39.5 (d, 2JPP = 245.4 Hz, 1P, Ru−PPi36a), 59.8 (d, 2JPP = 254.5
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis of the ligands including NMR data, summarized X-
ray crystallographic, and IR spectral data. Crystallographic data
are also provided in CIF format. The Supporting Information is
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.inorgchem.5b00672.
AUTHOR INFORMATION
Corresponding Author
*E-mail: fryzuk@chem.ubc.ca.
■
2
Hz, 1P, Ru−Pligand6a), 74.6 (d, JPP = 252.5 Hz, 1P, P−RuPri37a), 93.0
2
1
Notes
(d, JPP = 252.5 Hz, 1P, Ru−Pligand7a), 95.4 (s, 1P). H NMR (d8-
toluene, 400 MHz, 298 K): δ −23.4 (t, 2JPH =20.2 Hz, Ru−H6a), −18.6
(ddd, 2JHH = 6.6 Hz, 2JPH = 18.3 Hz, 2JPH = 25.5 Hz, Ru−H7a), −16.0
(d, 3JPH = 22.2 Hz, Ru−H), −5.6 (ddd, 2JHH = 6.6 Hz, 2JPH = 21.9 Hz,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank NSERC of Canada for funding in the form of a
Discovery Grant to M.D.F.
■
2JHH = 29.0 Hz, Ru−H7a), 1.0 (d, JHH = 6.1 Hz, PriOH-CH3), 1.6 (s,
3
acetone), 1.7 (s, PriOH−OH), 3.7 (m, PriOH-CH).
General Procedure for Attempted Catalytic Dehydrogen-
ation of Benzyl Alcohol to Benzyl Benzoate Using RuH-
{Pri(NP)Pri}(PPri3)(CO) (6a). In the glovebox in a Schlenk flask (50
mL) fitted with a small stir bar, 6a (0.020 g, 0.041 mmol) was
dissolved in a 1.0 M solution of mesitylene in d8-toluene (2.0 mL). On
the Schlenk line, benzyl alcohol (0.42 mL, 5 mmol) was added to the
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