Wingtip substituents tailor the catalytic activity of ruthenium triazolylidene complexes in base-free alcohol oxidation

Article abstract of DOI:10.1039/c3dt32939a

A series of Ru^II (η⁶-arene) complexes with 1,2,3-triazolylidene ligands comprising different aryl and alkyl wingtip groups have been prepared and characterized by NMR spectroscopy, microanalysis, and in one case by X-ray diffraction.

Full text of DOI:10.1039/c3dt32939a

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Wingtip substituents tailor the catalytic activity of
ruthenium triazolylidene complexes in base-free
Cite this: DOI: 10.1039/c3dt32939a
alcohol oxidation†
Daniel Canseco-Gonzalez and Martin Albrecht*
A series of RuII (η6-arene) complexes with 1,2,3-triazolylidene ligands comprising different aryl and alkyl
wingtip groups have been prepared and characterized by NMR spectroscopy, microanalysis, and in one
case by X-ray diffraction. All complexes are active catalyst precursors for the oxidation of alcohols to the
corresponding aldehydes/ketones without the need of an oxidant or base as additive. The wingtip
groups have a direct impact on the catalytic activity, alkyl wingtips providing the most active species
while aryl wingtip groups induce lower activity. An N-bound phenyl group was the most inhibiting
wingtip group due to cyclometalation. Arene dissociation was observed as a potential catalyst deactiva-
tion pathway.
Received 7th December 2012,
Accepted 17th January 2013
DOI: 10.1039/c3dt32939a
www.rsc.org/dalton
catalyzed alcohol oxidation,9 both homogeneously and
heterogeneously.10
Introduction
Carbonyls such as ketones and aldehydes are synthetically
Oxidant-free dehydrogenation of alcohols is comparatively
prevalent functional groups because of their outstanding rare, despite the obvious attractiveness of such a procedure in
versatility for derivatization. Amongst the various procedures terms of waste, atom-economy, and possibly functional group
to prepare carbonyl compound, they are accessible from alco- tolerance. The recent quest for hydrogen as an alternative that
hols as abundant precursors through selective oxidation pro- does not impact the global carbon cycle has strongly stimu-
cedures.1 Oxidation of alcohols to aldehydes and ketones has lated research into acceptorless alcohol (and amine) dehydro-
been achieved by oxidation with high-valent chromium or genation processes.11 Ruthenium-catalyzed protocols for the
manganese oxides,2 or by Oppenauer-type oxidation involving dehydrogenation of primary and secondary alcohols have been
the metal-catalyzed hydrogen transfer from the substrate to a developed for example by the groups of Beller, Milstein, and
sacrificial ketone such as cyclohexanone.3 Milder and often Williams.12 In some cases, however, the formed product
more selective methods were developed by Dess and Martin remains in the metal coordination sphere and is thus predis-
using hypervalent iodine,4 and by Ley with the introduction of posed for further coupling to yield esters and acetals.13 We
perruthenate as catalyst in the presence of an N-oxide as termi- recently observed that a ruthenium(II) cymene complex con-
nal oxidant.5 A drawback of these systems is the stoichio- taining a triazolylidene ligand14 affords a catalyst precursor
metric utilization of an oxidant, thus providing significant that readily oxidizes benzyl alcohol (BnOH) to benzaldehyde
quantities of (sometimes toxic) side-products and a low atom- with concomitant release of H2.15 We have now expanded our
economy of the overall reaction. Much effort has therefore investigation of this clean oxidation process and have prepared
been devoted in recent years to use more benign oxidants such a series of different triazolylidene complexes. Variation of the
as H2O2 and O2 as terminal oxidants,6 leading to substantial wingtip groups at the triazolylidene C4 and N1 positions from
progress in particular in ruthenium-7 palladium-,8 and copper- aryl groups to mixed aryl/alky systems and to exclusively alkyl
substituents revealed a direct correlation between the ligand
framework and the catalytic activity of the complexes.
School of Chemistry & Chemical Biology, University College Dublin, Belfield,
Dublin 4, Ireland. E-mail: martin.albrecht@ucd.ie; Fax: +353 17162501;
Tel: +353 17162504
Results and discussion
†Electronic supplementary information (ESI) available: Synthetic procedures for
the triazolium salts and the silver carbene complexes, time-conversion profiles
Synthesis of the complexes
for alcohol oxidation, and crystallographic data of 3e. CCDC 914595. For ESI and
The triazolium salts 1a–j were conveniently accessible through
conventional copper-catalyzed click cycloaddition of the
crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt32939a
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upfield shift from δH 5.47 and 5.33 ppm in the [RuCl2-
(cymene)]2 precursor to 5.35(1) and 5.02(1) ppm in complexes
3a–c. Introduction of a phenyl group at C4 increases the
upfield shift by some 0.2 ppm and the cymene protons reso-
nate at δH 5.12(1) and 4.84(2) ppm in complexes 3d–f. In both
sets of complexes, the length of the alkyl substituents has no
detectable impact on the resonance frequency. A mesityl group
at C4 affects the high-field doublet stronger (δH 5.16 and
4.98 ppm for 3g), suggesting steric interactions between the
mesityl group and the cymene. Such interactions are expected
to be more pronounced when both wingtip groups are bulky
aryl groups, and indeed the cymene resonances are scattered
over a broad range for the diaryl-substituted triazolylidene
complexes 3h and 3i (δH 5.13 and 4.23 ppm, and 5.00 and
1
4.62 ppm, respectively). The H NMR pattern of complex 3j is
Scheme 1 Synthesis of triazolylidene ruthenium complexes 3.
distinctly different and is characterized by a desymmetrization
of the N-bound phenyl group due to cyclometalation, as briefly
communicated.19,20 Similarly, the resonance frequency of the
appropriate azide and alkyne,16 followed by chemoselective tertiary proton of the iPr group of cymene correlates with the
methylation of the N3 position by using MeI (Scheme 1). set of wingtip substituents. With alkyl wingtips on N1 and C4,
Ruthenation of these triazolium salts was accomplished by the septet appears around δH 2.9 ppm, while aryl substituents
transmetalation according to established procedures.13a,15,17 induce an upfield displacement by 0.05–0.4 ppm.
Thus, reaction with Ag2O produced the silver carbene com-
Comparison of the 13C NMR data and in particular of the
plexes 2a–j, which were isolated but not fully characterized due carbenic C5 resonance provides interesting trends. With alkyl
to their tendency to degrade. Analysis by 1H NMR spectroscopy wingtip groups on C4 and N1, a carbene resonance at δC 161.0(2)
revealed the complete disappearance of the aromatic triazo- ppm is observed for complexes 3a–c. No specific correlation
lium proton around 8.9–9.8 ppm along with minor shifts of between the length of the alkyl chain and the chemical shift
the wingtip group signals as a consequence of the new chem- was observed. Replacing the C-bound alkyl group with a
ical environment. The diarylated silver carbene complexes phenyl substituent (complexes 3d–f) increases the shielding of
were considerably more stable. Crystals suitable for X-ray diffr- the carbene resonance slightly, δC 160.7(2) ppm. The upfield
action were obtained for 2j, however, the refinement did not shift is counterintuitive when considering the electron-with-
converge and showed a triazolylidene ligand that was strongly drawing character of aryl groups and thus implies a significant
disorder through a 180° rotation about the Ag–Ctrz bond. steric contribution to the NMR frequency. In line with such a
While this disorder hampered further refinement and pre- notion, the carbene resonance is gradually shifting to higher
cludes analysis of geometrical data, the X-ray diffraction analy- field when increasing the length of the N-bound alkyl substitu-
sis unambiguously showed a monomeric [AgI(trz)] complex as ent from Me to Et to nBu (δC 160.9, 160.5, and 160.4 ppm,
opposed to a cationic [Ag(NHC)2]+ structure as observed in respectively). Furthermore, introducing a mesityl rather than a
many NHC silver complexes.18
phenyl substituent at C4 pronounces the high-field shift
Carbene transfer from complexes 2a–j to [Ru(p-cymene) (δC 158.8 ppm for 3g). With aryl substituents both on N1 and
Cl2]2 yielded triazolylidene ruthenium(II) complexes 3a–i in C4, the steric interactions are further altered and as a conse-
good to excellent yields (70–99% apart from 3a), whereas 3j quence, the NMR frequency does not follow any trend
was obtained in 35% yield only (Scheme 1). Generally, bulkier (δC 163.0 and 161.0 ppm for 3h and 3i, respectively). In its
wingtip groups prolonged the reaction time for transmetala- entirety, these chemical shift values underline the caution that
tion. Complexes 3a–c with alkyl wingtip groups were better needs to be applied when correlating 13C NMR frequencies
soluble in chlorinated solvents and toluene than those with with ligand donor properties.21
aromatic substituents. All complexes were stable towards
moisture and air both in solution and in the solid state for crystal of 3e as a representative example. The molecular struc-
several months.
ture (Fig. 1) confirmed the expected connectivity pattern and
An X-ray diffraction analysis was performed of a single
Successful transruthenation was indicated by the character- shows the typical three-legged piano-stool geometry with two
istic NMR data. Specifically, formation of complexes 3a–j was chlorides and the triazolylidene ligand as the three ‘legs’. The
supported by the presence of resonances due to the cymene Ru–Ctrz bond is 2.061(4) Å, which is slightly shorter than in an
group and the triazolylidene ligand in equimolar ratio. The analogue of 3b containing hexamethylbenzene rather than
two doublets of the aryl protons of cymene shift to higher field cymene as ancillary ligand,15 yet it is comparable to related
upon triazolylidene coordination and provide a diagnostic [RuCl2(arene)(NHC)] complexes.22 Also, the Ru–Ccentroid dis-
probe for the nature of the triazolylidene wingtip groups. tance to the cymene ligand is relatively short, 1.684(2) Å. The
Thus, alkyl wingtip groups on both C4 and N1 induce a small phenyl substituent is almost perpendicular to the heterocyclic
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Table 1 Oxidation of benzyl alcohol catalyzed by triazolylidene ruthenium
complexesa
ð1Þ
[Ru]
Ntrz–R
C
trz–R′
Conv’n 1 h
Conv’n 16 h
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
4
Et
Bu
Hex
Me
Et
Bu
Bu
Mes
Mes
Ph
Me
Et
Bu
Bu
Hex
Ph
Ph
Ph
Mes
Ph
Mes
Ph
Ph
55%
45%
55%
35%
49%
57%
52%
16%
41%
14%
31%
53%
60%
37%
<2%
13%
87%
>98%
>98%
55%
74%
82%
84%
36%
63%
31%
54%
69%
79%
95%
17%
15%
Fig. 1 ORTEP representation of 3e (50% probability, hydrogens omitted for
clarity). Selected bond lengths (Å) and angles (°): Ru(1)–C(1) 2.061(4), Ru(1)–
Cl(1) 2.4183(11), Ru(1)–Cl(2) 2.466(12), Ru(1)–Ccentroid 1.684(2); C(1)–Ru(1)–Cl(1)
87.06(10), C(1)–Ru(1)–Cl(2) 89.95(13), Cl(1)–Ru(1)–Cl(2) 83.70(4).
Ph
Ph
Hex
Bu
Hex
[RuCl2(cym)]2
[RuCpCl(PPh3)2]
a Conditions: benzyl alcohol (0.2 mmol), [Ru] (0.01 mmol, 5 mol%),
toluene (2 mL), 110 °C.
Several trends evolve from this catalyst evaluation.
(i) The triazolylidene ligand imparts the catalytic activity
as related commercial ruthenium complexes such as
[RuCl2(cym)]2 or [RuCpCl(PPh3)2] are considerably less compe-
tent than complexes 3.
(ii) Variation of the remote substituents at N3 from methyl
to ethyl has no detectable impact on the catalytic performance
(cf. 3d–f vs. 3k–m). While the essentially identical performance
of these systems is not surprising, these runs underpin the
reproducibility of the catalytic activity and the well-defined
nature of the most competent species.
(iii) In contrast to remote substitution, the catalytic activity
is markedly affected by the type of wingtip substituents at the
triazolylidene ligand. Generally, the presence of alkyl wingtip
groups improves catalytic activity and longer alkyl chains
induce better performance than shorter ones. This latter trend
is supported by the increasing activity in the series 3a < 3b <
3c for complexes containing alkyl wingtip groups only, and
also in the series 3d < 3e < 3f for complexes containing a
phenyl wingtip at C4 and an alkyl substituents at N1.
Scheme 2 Synthesis of complexes 3k–m.
carbene plane. The tertiary proton of the cymene iPr group is
located exactly on top of the center of the phenyl substituent
(distance H to centroid 2.68 Å), suggesting an edge-to-face type
hydrogen bond interaction. This interaction might be pre-
served in solution (cf. NMR shifts above).
For comparative reasons, complexes 3k–m were prepared as
analogues of 3d–f. These complexes contain an ethyl rather
than a methyl substituent at N3 (Scheme 2). The synthesis
mirrors that of complexes 3d–f with the exception that EtI was
used for the alkylation of the corresponding triazoles rather
than MeI. The spectroscopic trends were identical and com-
plexes 3k–m are characterized by two diagnostic doublets due
to the cymene ligand (δH 5.12 and 4.86 ppm), and a low-field
13C NMR resonance for the ruthenium-bound triazolylidene
carbon at δC 160.5( 1) ppm.
(iv) The presence of a C-bound phenyl group has a minor
impact on initial rates (cf. conversion after 1 h for the series
Catalytic alcohol oxidation
The ruthenium complexes 3a–m are catalyst precursors for the 3a–c vs. 3d–f), though it compromises the long term stability
oxidant- and base-free oxidation of alcohols to ketones and of the catalytically active species and leads to incomplete con-
aldehydes. The catalytic efficiency was evaluated by using version after 16 h. No significant difference was noted when
BnOH as a model substrate (eqn (1)). Gradual oxidation to replacing the phenyl wingtip group in 3f with a mesityl substi-
benzaldehyde was observed upon heating this substrate in tuent (3g).
toluene in the presence of catalytic quantities of the triazolyli-
(v) The unfavorable influence of aryl wingtip groups is
dene ruthenium complex. Benzaldehyde formation was moni- further illustrated when considering the catalytic activity of
tored over time,† and conversions after 1 h and after 16 h are complexes comprising aryl wingtip groups on both N1 and C4
compiled in Table 1.
(3h–3i). Initial activities are comparably moderate and final
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product yields are the lowest in the series tested. Wingtip C–H formation of free cymene was detected by the characteristic ali-
bond activation and ensuing cylcometalation may constitute a phatic signals at δH 2.71 (septet), 2.15 (s), and 1.15 (d), while
plausible catalyst deactivation pathway. Such a process has pre- the pertinent aromatic doublets overlapped with residual
cedents both for phenyl and for mesityl substituents,19,23 and protio signals of the reaction solvent (toluene-d8). No for-
may be induced by steric constraints (cf. NMR discussion mation of free triazolylidene or any triazolium salt was
above). Cyclometalated species are catalytically less competent observed, however, which may point to the formation of col-
as demonstrated by the low conversions observed with the loidal ruthenium stabilized by a triazole derivative.26 After
preformed ruthenacycle 3j and may thus account for the 16 h, only benzaldehyde and free cymene were detectable with
incomplete conversion when using phenyl-substituted triazoly- integrals that suggest quantitative conversion of BnOH and 3c,
lidenes (3d–m).
respectively (anisole as internal standard). During the initial
(vi) The low activity of complex 3i containing the triazolyli- stages of the reaction, two complexes were identified in
dene analogue of IMes apparently disagrees with a carbene addition to 3c in small concentrations (ca. 5% and 15% rela-
dissociation step as observed in other catalytic processes.24 tive to 3c, respectively) by the appearance of diagnostic doub-
The di(mesityl)-substituted triazolylidene is arguably the most lets in the 4.9–5.4 ppm range. The minor of these two species
stable free carbene of the series evaluated here14b because is asymmetric and features four different Hcym resonances,
acidic α-hydrogens in the wingtip substituents are absent. whereas the major species is symmetric and displays only two
Hence this complex should lead to the lowest catalyst deactiva- Hcym signals.27 Their relative ratio as well as their proportion
tion rate if carbene dissociation were relevant.
to complex 3c remained approximately constant over the
A potential catalyst activation step may involve the ancillary course of the reaction. Based on the gradual but consistent
cymene ligand, either through edge-to-face hydrogen bonding drift of the BnOH methylene signal from δH 4.32 ppm to
to the substrate or through substitution by BnOH (or the 4.30 ppm within the first hour of reaction, the asymmetric
solvent).25 We evaluated this hypothesis by synthesizing species was tentatively assigned to a cationic ruthenium
complex 4, viz. the benzene analogue of the most active cata- (cymene) complex containing a triazolylidene ligand, a chlo-
lyst precursor 3c (eqn (2)).
ride, and a rapidly exchanging BnOH (B, Scheme 3),28 while
the symmetric species may feature a two-legged piano-stool
geometry including a triazolylidene and a chloride ligand only
(A, Scheme 3).29 No resonances in the hydridic region were
observed in the spectra. Based on this assumption, the rate-
limiting step of the dehydrogenation process would consist of
either alcohol deprotonation or β-hydrogen elimination.
Attempts to synthesize the surmised intermediate by substitut-
ð2Þ
Complex 4 displayed similar catalytic activity to 3c, though ing one chloride in 3c by a BnOH ligand, mediated by AgBF4,
initial activities are lower (37% vs. 55%, cf. Table 1). Slower have failed thus far.
initial performance is inconsistent with hydrogen bonding of
The catalytic scope was evaluated with the best performing
the substrate, which should be easier with benzene with less catalyst precursors, 3b and 3c, using different primary ali-
shielded C–H bonds than cymene. Moreover, the higher ten- phatic and benzylic alcohols (Table 2). Aliphatic alcohols are
dency of benzene compared to cymene to dissociate from the converted substantially slower than BnOH and afford 30–60%
ruthenium coordination sphere disagrees with a catalyst acti- of the corresponding aldehyde (entries 1–3). While the initial
vation step involving the arene ligand. Easier dissociation of rate of oxidation was identical for all three n-alcohols (23%
benzene from complex 4 was confirmed NMR spectroscopi- conversion after 1 h), catalyst deactivation occurred at different
cally by heating toluene-d8 solutions of 3c and 4 to 110 °C for later stages of the reaction and led to the observed range of
16 h in the absence of any substrate. Only traces of free final conversions. Similar effects were observed with benzylic
cymene were noted from 3c (<3%) while substantial benzene alcohols that contain a functional group on the aromatic ring
dissociation was identified by the diagnostic 1H NMR signal at (entries 4–6). Initial rates with 3,4-dimethoxybenzyl alcohol
δH 7.13 ppm when heating complex 4 (ca. 20% by NMR and 4-bromobenzyl alcohol were comparable to those
integration).
Further insight into the catalytic process was obtained from
a catalytic experiment in deuterated toluene. A substantially
larger ruthenium loading (25 mol%) was used in order to
identify the fate of complex 3c during the reaction. Interest-
ingly, the rate of product formation was not accelerated with
this higher ruthenium concentration (41% conversion after
0.5 h, 56% after 1 h), suggesting that the effective concen-
tration of the catalytically active species is not increased. Over
the first hour of reaction, the concentration of 3c was decreas-
Scheme 3 Postulated activation pathway with formation of intermediates A
ing to 33% in an exponential decay, and proportionally, and B.
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Table 2 Conversions of different alcohols with catalyst precursor 3ca
Conclusions
Entry
1
Substrate
Product
Conversionb
62%
A series of triazolylidene ruthenium(II) complexes were pre-
pared as catalyst precursors for the base- and oxidant-free
dehydrogenation of alcohols to the corresponding carbonyl
compounds. Variation in the triazolylidene ligand framework
allowed trends to be established. Specifically, aryl wingtip
groups induce lower activity than alkyl groups, and longer
alkyl substituents lead to slightly better performance than
shorter alkyl chains. As a particular case, the N-bound phenyl
group undergoes spontaneous CPh–H bond activation and
affords a cyclometalated complex with low catalytic activity in
alcohol oxidation. Primary and secondary benzylic alcohols
gave the corresponding aldehydes and ketones in good to
excellent yields, while aliphatic alcohols were insufficiently
converted, which may provide opportunities for selective oxi-
dation. The absence of base and oxidant is appealing in terms
of atom economy and experimental setup and should allow for
wide functional group tolerance. Future work should be
directed towards lowering the reaction temperature and cata-
lyst loading. A deeper mechanistic understanding of the dehy-
drogenation process will be pivotal to achieve these goals and
to make the process widely applicable.
2
3
4
38%
32%
82%c
5
6
48%
67%
7
8
39% (37%)
66% (66%)
9
96%d (81%)
61% (60%)
Experimental section
General
All solvents used for the reaction were purified using an
alumina/catalyst column system (Thermovac Co.). The syn-
thesis of the new triazolium salts and the new carbene silver
complexes are detailed in the ESI.† The carbene ruthenium
complexes 3b,15 3e,14a and 3j19 were synthesized as described
previously. All other reagents are commercially available and
were used as received. Microwave reactions were carried out
using a Biotage Initiator 2.5, operating at 100 W irradiation
power. Unless specified otherwise, NMR spectra were recorded
at 25 °C on Varian Innova spectrometers operating at 300, 400
or 500 MHz (1H NMR) and 75, 100 or 125 MHz (13C{1H} NMR),
respectively. Chemical shifts (δ in ppm, coupling constants J in
Hz) were referenced to residual solvent resonances. Assign-
ments are based on homo- and heteronuclear shift correlation
spectroscopy. Elemental analyses were performed by the
Microanalytical Laboratory at University College Dublin,
Ireland; residual solvents were also identified by 1H NMR
spectroscopy.
10
a Conditions: alcohol (0.2 mmol), 3c (0.01 mmol, 5 mol%), toluene
(2 mL), 110 °C, 16 h. b Values in parenthesis obtained with complex
3b. c Isolated yield: 35%. d Isolated yield: 47%.
measured for BnOH (51% and 47%, respectively, after 1 h), yet
deactivation of the catalytically competent species halts the
reaction and inhibits full conversion.
Under standard conditions, also secondary alcohols were
oxidized to produce the corresponding ketones with moderate
to excellent conversions. The observed trends are similar to
those deduced for primary alcohols. Thus, aliphatic alcohols
such as cyclohexanol were relatively poor substrates (<40%
conversion), whereas benzylic secondary alcohols were con-
verted efficiently, especially when the phenyl group contained
electron-donating groups. Electron-withdrawing groups gave
lower conversions, indicating reduced catalytic rates upon
General procedure for the syntheses of the triazolylidene
ruthenium(II) complexes 3
depletion or pronounced polarization of the electron density To a solution of silver carbene 2 in CH2Cl2 (20 mL) was added
in the α-C–H bond that is activated during the alcohol oxi- [Ru(p-cymene)Cl2]2 (0.5 eq.). The mixture was stirred at room
dation process. This observation is in agreement with β-H temperature for the time indicated and then filtered through
elimination of a putative Ru–OR alkoxide or a Ru–O(H)(R) Celite. All volatiles were removed in vacuo at room temperature.
alcohol complex as rate-limiting step30 and corroborates the The residue was washed with pentane (3 × 25 mL), dried, and
conclusions drawn from in situ NMR analysis.
dissolved in a minimum amount of CH2Cl2 and precipitated
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with Et2O (100 mL). The precipitate was collected and dried (CDCl3 500 MHz): δ 7.62 (m, 2H, HPh), 7.46 (m, 3H, HPh), 5.12
3
3
in vacuo.
(d, JHH = 5.8 Hz, 2H, Hcym), 4.85 (d, JHH = 5.8 Hz, 2H, Hcym),
3
Complex 3a. According to the general method from silver 4.77 (m, 2H, NCH2), 3.71 (s, 3H, NCH3), 2.57 (sept, JHH
=
carbene 2a (138 mg, 0.34 mmol) and [Ru(p-cymene)Cl2]2 6.8 Hz, 1H, CHMe2), 2.03 (quint, 3JHH = 7.4 Hz, 2H, NCH2CH2),
3
(105 mg, 0.17 mmol) in 16 h. The crude solid obtained after 1.84 (s, 3H, Ccym–CH3), 1.48 (sext, JHH = 7.4 Hz, 2H,
3
solvent evaporation was purified by column chromatography NCH2CH2CH2), 1.11 (d, JHH = 6.8 Hz, 6H, CH–CH3), 0.98
3
(SiO2, CH2Cl2–acetone 3 : 1). The brown band was collected, (t, JHH = 7.4 Hz, 3H, CH2CH2CH3). 13C{1H} NMR (CDCl3,
concentrated to 2 mL and treated with cold Et2O (50 mL), 125 MHz): δ 160.8 (Ctrz–Ru), 147.9 (Ctrz–Ph), 132.0, 129.9,
which induced the precipitation of 3a as a brown solid 129.0, 128.0 (4 × CAr), 104.9, 97.0, 84.4, 84.2 (4 × Ccym), 54.8
3
(135 mg, 83%). 1H NMR (CDCl3 500 MHz): δ 5.35 (d, JHH
=
(NCH2), 36.7 (NCH3), 33.1 (NCH2CH2), 30.6 (CHMe2), 22.5
3
5.9 Hz, 2H, Hcym), 5.01 (d, JHH = 5.9 Hz, 2H, Hcym), 4.70 (CH–CH3), 20.2 (NCH2CH2CH2), 18.3 (Ccym–CH3), 13.9
(sbroad, 2H, NCH2CH3), 3.98 (s, 3H, NCH3), 2.97 (m, 2H, Ctrz
CH2), 2.91 (sept, JHH = 7.0 Hz, 1H, CHMe2), 2.02 (s, 3H, Ccym
–
–
(NCH2CH2CH2CH3). Anal. Calcd for C24H33Cl2N3Ru (521.48):
C, 53.83; H, 6.21; N, 7.85. Found: C, 53.55; H, 6.12; N, 7.67.
Complex 3g. According to the general method from silver
3
3
CH3), 1.58 (m, 5H, NCH2CH3, Ctrz–CH2CH2), 1.47 (sext, JHH
=
3
7.4 Hz, 2H, Ctrz–CH2CH2CH2), 1.28 (d, JHH = 7.0 Hz, 6H, CH– carbene 2g (225 mg, 0.46 mmol) and [Ru(p-cymene)Cl2]2
CH3), 0.97 (t, 3JHH = 7.4 Hz, 3H, Ctrz–CH2CH2CH2CH3). 13C{1H} (140 mg, 0.23 mmol) in 16 h. Yield: 186 mg (72%). 1H NMR
3
NMR (CDCl3, 125 MHz): δ 161.2 (Ctrz–Ru), 147.6 (Ctrz–Bu), (CDCl3 500 MHz): δ 7.02 (s, 2H, HMes), 5.16 (d, JHH = 6.0 Hz,
107.6, 97.5, 85.1, 82.6 (4 × Ccym), 50.0 (NCH2), 36.5 (NCH3), 2H, Hcym), 4.99 (d, JHH = 6.0 Hz, 2H, Hcym), 4.77 (t, JHH
32.3 (Ctrz–CH2), 30.9 (CHMe2), 26.2 (Ctrz–CH2CH2), 23.3 (Ctrz
3
3
=
=
3
–
8.0 Hz, 2H, NCH2), 3.62 (s, 3H, NCH3), 2.76 (sept, JHH
CH2CH2CH2), 22.8 (CH–CH3), 18.7 (Ccym–CH3), 16.3 7.0 Hz, 1H, CHMe2), 2.36 (s, 3H, Mes–CH3), 2.13 (s, 6H, Mes–
(NCH2CH3), 14.1 (Ctrz–CH2CH2CH2CH3). No satisfactory CH3), 1.97 (m, 2H, NCH2CH2), 1.92 (s, 3H, Ccym–CH3), 1.46
3
3
elemental analysis could be obtained for this complex.
(sext, JHH = 7.4 Hz, 2H, NCH2CH2CH2CH3), 1.07 (d, JHH =
3
Complex 3c. According to the general method from silver 7.0 Hz, 6H, CH–CH3), 0.96 (t, JHH
= 7.4 Hz, 3H,
carbene 2c (188 mg, 0.39 mmol) and [Ru(p-cymene)Cl2]2 NCH2CH2CH2CH3). 13C{1H} NMR (CDCl3, 125 MHz): δ 158.5
(118 mg, 0.19 mmol) in 16 h. The crude solid was purified by (Ctrz–Ru), 145.4 (Ctrz–Mes), 140.5, 139.3, 128.9, 126.3 (4 ×
column chromatography (SiO2, CH2Cl2–acetone 3 : 1). The
CMes), 110.2, 105.1, 86.7, 84.5 (4 × Ccym), 55.8 (NCH2), 35.9
brown band was collected and concentrated to 2 mL. Addition (NCH3), 33.9 (NCH2CH2), 30.5 (CHMe2), 22.4 (CH–CH3), 21.5,
of cold Et2O induced the precipitation of 3c as a brown solid 21.4 (2 × MesCH3), 20.2 (Ccym–CH3), 18.4 (NCH2CH2CH2), 14.2
3
(184 mg, 74%). 1H NMR (CDCl3 500 MHz): δ 5.35 (d, JHH
=
(NCH2CH2CH2CH3). Anal. Calcd for C26H37Cl2N3Ru (563.14) ×
3
5.9 Hz, 2H, Hcym), 5.02 (d, JHH = 5.9 Hz, 2H, Hcym), 4.59 (br, 1/3 CH2Cl2: C, 53.44; H, 6.41; N, 7.10. Found: C, 53.06; H, 6.47;
2H, NCH2), 3.97 (s, 3H, NCH3), 2.96 (m, 2H, Ctrz–CH2), 2.88 N, 7.03.
(m, 1H, CHMe2), 2.01 (s, 3H, Ccym–CH3), 1.98 (m, 2H,
NCH2CH2), 1.42 (m, 4H, CH2 hex), 1.33–1.28 (m, 16H, CH2 hex
Complex 3h. According to the general method from silver
carbene 2h (300 mg, 0.59 mmol) and [Ru(p-cymene)Cl2]2
,
3
CH–CH3), 0.90 (t, JHH = 7.0 Hz, 6H, CH2CH3). 13C{1H} NMR (179 mg, 0.29 mmol) in 2 h. Yield: 239 mg (70%). 1H NMR
(CDCl3, 125 MHz): δ 161.2 (Ctrz–Ru), 147.5 (Ctrz–hex), 107.2, (CDCl3 500 MHz): δ 8.00 (m, 2H, HAr), 7.58 (m, 3H, HAr), 6.90
3
3
97.3, 85.2, 82.7 (4 × Ccym), 54.9 (NCH2), 36.5 (NCH3), 31.8 (s, 2H, HAr), 5.13 (d, JHH = 5.9 Hz, 2H, Hcym), 4.23 (d, JHH
=
(CHMe2) 31.2, 30.9, 30.2, 29.2, 26.8, 26.6, 22.9, 22.8, 22.3 (9 × 5.9 Hz, 2H, Hcym), 3.95 (s, 3H, NCH3), 2.85 (sept, 3JHH = 7.0 Hz,
CH2 hex), 22.7 (CH–CH3), 18.8 (Ccym–CH3), 14.3, 14.2 (2 × 1H, CHMe2), 2.31 (s, 3H, ArCH3), 2.06 (s, 6H, ArCH3), 1.80 (s,
CH3 hex). Anal. Calcd for C25H43Cl2N3Ru (557.19) × 0.5 H2O: 3H, Ccym–CH3), 1.16 (d, JHH = 7.0 Hz, 6H, CH–CH3). 13C{1H}
3
C, 52.99; H, 7.83; N, 7.42. Found: C, 52.68; H, 7.44; N, 7.47.
NMR (CDCl3, 125 MHz): δ 163.0 (Ctrz–Ru), 142.7 (Ctrz–Ph),
Complex 3d. According to the general method from silver 139.5, 135.3, 132.2, 130.4, 130.2, 130.0, 128.9, 128.5 (8 × CAr),
carbene 2d (330 mg, 0.80 mmol) and [Ru(p-cymene)Cl2]2 107.1, 97.2, 88.9, 80.9 (4 × Ccym), 37.7 (NCH3), 30.7 (CHMe2),
(247 mg, 0.40 mmol) in 2 h. Yield: 154 mg (40%). 1H NMR 22.7 (CH–CH3), 21.4, 18.8 (2 × ArCH3), 18.1 (Ccym–CH3). Anal.
(CDCl3 500 MHz): δ 7.63 (m, 2H, HPh), 7.47 (m, 3H, HPh), 5.12 Calcd for C28H33Cl2N3Ru (583.11) × 0.5 CH2Cl2: C, 54.68;
3
3
(d, JHH = 5.9 Hz, 2H, Hcym), 4.86 (d, JHH = 5.9 Hz, 2H, Hcym), H, 5.47; N, 6.71. Found: C, 54.83; H, 5.38; N, 6.81.
3
4.45 (s, 3H, NCH3), 3.72 (s, 3H, NCH3), 2.61 (sept, JHH
6.9 Hz, 1H, CHMe2), 1.86 (s, 3H, Ccym–CH3), 1.13 (d, JHH
=
=
Complex 3i. According to the general method from silver
carbene 2i (94 mg, 0.17 mmol) and [Ru(p-cymene)Cl2]2
3
6.9 Hz, 6H, CH–CH3). 13C{1H} NMR (CDCl3, 125 MHz): δ 160.9 (52 mg, 0.09 mmol) in 16 h. Yield: 82 mg (77%). 1H NMR
(Ctrz–Ru), 148.6 (Ctrz–Ph), 131.9, 129.9, 128.7, 128.0 (4 × CPh), (CDCl3 500 MHz): δ 7.00 (s, 2H, HMes), 6.90 (s, 2H, HMes), 5.00
3
3
104.9, 97.4, 84.2, (3 × Ccym), 42.6, 36.7 (2 × NCH3), 30.6 (d, JHH = 5.9 Hz, 2H, Hcym), 4.62 (d, JHH = 5.9 Hz, 2H, Hcym),
(CHMe2), 22.5 (CH–CH3), 18.4 (Ccym–CH3). Anal. Calcd for 3.65 (s, 3H, NCH3), 2.61 (sept, 3JHH = 7.0 Hz, 1H, CHMe2), 2.38,
C20H25Cl2N3Ru (479.40): C, 50.11; H, 5.26; N, 8.76. Found: 2.33 (2 × s, 3H, Mes–CH3), 2.19, 2.16 (2 × s, 6H, Mes–CH3),
3
C, 49.87; H, 5.22; N, 8.74.
1.80 (s, 3H, Ccym–CH3), 1.06 (d, JHH = 7.0 Hz, 6H, CH–CH3).
Complex 3f. According to the general method from silver 13C{1H} NMR (CDCl3, 125 MHz): δ 161.0 (Ctrz–Ru), 142.8 (Ctrz
–
carbene 2f (140 mg, 0.32 mmol) and [Ru(p-cymene)Cl2]2 Mes), 138.7, 138.3, 136.2, 134.4, 130.2, 129.7, 129.0, 128.6 (8 ×
(95 mg, 0.16 mmol) in 2 h. Yield: 161 mg (99%). 1H NMR
CMes), 102.5, 95.0, 86.8, 85.2 (4 × Ccym), 36.2 (NCH3), 30.3
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(CHMe2), 22.5 (CH–CH3), 21.3, 20.6, 18.8, 18.2 (4 × Mes–CH3), CH2Cl2 (40 mL) were stirred at room temperature for 48 h and
17.8 (Ccym–CH3). Anal. Calcd for C31H39Cl2N3Ru (625.16) × then filtered through Celite. The crude residue was purified by
H2O: C, 57.85; H, 6.42; N, 6.53. Found: C, 57.58; H, 6.07; column chromatography (SiO2, CH2Cl2–acetone 3 : 1). The red
N, 6.60.
band was collected and concentrated to 5 mL. Addition of cold
Complex 3k. According to the general method from silver Et2O induced the precipitation of 4 as a brown solid (110 mg,
1
carbene 2k (150 mg, 0.35 mmol) and [Ru(p-cymene)Cl2]2 38%). H NMR (CDCl3 500 MHz): δ 5.48 (s, 6H, Hbenzene), 4.59
3
(108 mg, 0.18 mmol) in 2 h, affording 3k as a red powder (t, JHH = 7.7 Hz, 2H, NCH2(CH2)4CH3), 3.97 (s, 3H, NCH3),
1
3
(70 mg, 80%). H NMR (CDCl3 500 MHz): δ 7.63 (m, 2H, HPh), 3.05 (sbroad, 2H, Ctrz–CH2(CH2)4CH3), 1.97 (q, JHH = 7.7 Hz,
3
7.47 (m, 3H, HPh), 5.12 (d, JHH = 5.9 Hz, 2H, Hcym), 4.86 (d, 2H, NCH2CH2(CH2)3CH3), 1.60 (sbroad, 2H, CH2 hex), 1.43 (m,
3JHH = 5.9 Hz, 2H, Hcym) 4.46 (s, 3H, NCH3), 4.03 (q, JHH
=
4H, CH2 hex), 1.33 (m, 8H, CH2 hex) 0.91 (m, 6H, N(CH2)5CH3).
3
7.3 Hz, 2H NCH2), 2.58 (sept, JHH = 6.8 Hz, 1H, CHMe2), 1.84 13C{1H} NMR (CDCl3, 125 MHz): δ 158.2 (Ctrz–Ru), 147.8 (Ctrz
–
3
(s, 3H, Ccym–CH3), 1.34 (t, 3JHH = 7.3 Hz, 3H, NCH2CH3) 1.13 (d, hex), 85.99 (Cbenzene), 54.9 (NCH2, Hex), 36.5 (NCH3), 31.8
3JHH = 6.8 Hz, 6H, CH–CH3). 13C{1H} NMR (CDCl3, 125 MHz): (NCH2CH2(CH2)3CH3), 31.7, 31.2, 30.5, 29.8, 29.2, (5 × CH2,
δ 160.5 (Ctrz–Ru), 147.9 (Ctrz–Ph), 132.2, 129.8, 128.7, 127.9 Hex), 26.8 (Ctrz–CH2(CH2)4CH3), 26.2, 22.8, 22.7, 22.3 (4 × CH2,
(4 × CPh), 104.6, 97.3, 84.2, 84.1 (4 × Ccym), 45.4 (NCH2), 42.6 Hex), 14.3, 14.2 (2 × CH3, Hex). Anal. Calcd for C21H35Cl2N3Ru
(NCH3), 30.6 (CHMe2), 22.5 (CH–CH3), 18.4 (Ccym–CH3), 14.8 (501.49): C, 50.29; H, 7.03; N, 8.38. Found: C, 49.69; H, 6.85;
(NCH2CH3). Anal. Calcd for C21H27Cl2N3Ru (493.43): C, 51.12; N, 8.12.
H, 5.52; N, 8.52. Found: C, 50.93; H, 5.39; N, 8.28.
Complex 3l. According to the general method from silver
General procedure for alcohol oxidations
carbene 2l (175 mg, 0.40 mmol) and [Ru(p-cymene)Cl2]2
(123 mg, 0.20 mmol) in 2 h. Yield: 90 mg (89%). 1H NMR
A mixture of the alcohol (0.2 mmol) and the appropriate ruthe-
nium complex 3 or 4 (0.01 mmol), and anisole (0.2 mmol) or
hexamethylbenzene (0.2 mmol, for the oxidation of para-
methoxy-1-phenethyl alcohol) as internal standard was
refluxed in toluene (2 mL) in a closed vial. Aliquots were taken
at specific times, diluted with CDCl3 and analyzed by H NMR
(CDCl3 500 MHz): δ 7.62 (m, 2H, HPh), 7.45 (m, 3H, HPh), 5.12
3
(d, JHH = 5.9 Hz, 2H, Hcym), 4.89–4.85 (m, 4H, 2Hcym, 2H,
3
3
NCH2) 4.02 (q, JHH = 7.3 Hz, 2H, NCH2), 2.57 (sept, JHH
=
6.9 Hz, 1H, CHMe2), 1.83 (s, 3H, Ccym–CH3), 1.62 (t, 3JHH = 7.3 Hz,
1
3
3H, NCH2CH3), 1.33 (t, JHH = 7.3 Hz, 3H, NCH2CH3), 1.11 (d,
3JHH = 6.9 Hz, 6H, CH–CH3). 13C{1H} NMR (CDCl3, 125 MHz): δ
160.5 (Ctrz–Ru), 147.2 (Ctrz–Ph), 132.2, 129.7, 128.9, 127.9 (4 ×
spectroscopy.
CPh), 104.9, 96.8, 84.4, 84.0 (4 × Ccym), 50.2, 45.5 (2 × NCH2),
Crystallographic details
30.5 (CHMe2), 22.5 (CH–CH3), 18.3 (Ccym–CH3), 16.2, 14.8 (2 ×
NCH2CH3). Anal. Calcd for C22H29Cl2N3Ru (507.46): C, 52.07;
H, 5.76; N, 8.28. Found: C, 51.78; H, 5.63; N, 8.01.
Crystals suitable for single crystal structure analysis were
grown by slow diffusion of pentane into a CH2Cl2 solution of
3e. A suitable crystal was mounted on a Stoe Mark II-Imaging
Plate Diffractometer System (Stoe and Cie, 2002) equipped
with a graphite-monochromator. Data collection was per-
formed at −50 °C using Mo-Kα radiation (λ = 0.71073 Å) with a
nominal crystal to detector distance of 135 mm. The structure
was solved by direct methods using the program SHELXS-97
and refined by full matrix least squares on F2 with
SHELXL-97.31 The hydrogen atoms were included in calculated
positions and treated as riding atoms using SHELXL-97
default parameters. All non-hydrogen atoms were refined ani-
Complex 3m
According to the general method from silver carbene 2m
(140 mg, 0.30 mmol) and [Ru(p-cymene)Cl2]2 (93 mg,
0.15 mmol) in 2 h, yielding 3m as a red-brown powder (69 mg,
1
86%). H NMR (CDCl3 500 MHz): δ 7.62 (m, 2H, HPh), 7.46 (m,
3
3
3H, HPhr), 5.13 (d, JHH = 5.9 Hz, 2H, Hcym), 4.86 (d, JHH
=
=
3
5.9 Hz, 2H, Hcym), 4.78 (m, 2H, NCH2CH2), 4.03 (q, JHH
7.3 Hz, 2H, NCH2CH3), 2.54 (sept, JHH = 6.9 Hz, 1H, CHMe2),
2.05 (quint, JHH = 7.4 Hz, 2H, NCH2CH2), 1.82 (s, 3H, Ccym
3
3
–
sotropically.
A semi-empirical absorption correction was
3
CH3), 1.48 (sext, JHH = 7.4 Hz, 2H, NCH2CH2CH2), 1.33 (t, 2H,
3JHH = 7.3 Hz, NCH2CH3), 1.12 (d, 3JHH = 6.9 Hz, 6H, CH–CH3),
applied using MULscanABS as implemented in PLATON03.32
Complex 3e crystallized with one disordered molecule of
pentane per asymmetric unit and featured partial disorder in
the n-butyl group. CCDC number 914595 contains the sup-
plementary crystallographic data for this paper.
0.99 (t, JHH = 7.4 Hz, 3H, NCH2CH2CH2CH3). 13C{1H} NMR
3
(CDCl3, 125 MHz): δ 160.4 (Ctrz–Ru), 147.2 (Ctrz–Ph), 132.3,
129.7, 128.9, 127.9 (4 × CAr/Ph), 104.5, 96.8, 84.4, 84.2
(4 × Ccym), 54.8 (NCH2CH2), 45.4 (NCH2CH3), 33.1 (NCH2CH2),
30.9 (CHMe2), 22.6 (CH–CH3), 20.2 (NCH2CH2CH2), 18.2
(Ccym–CH3), 14.8 (NCH2CH3), 13.9 (NCH2CH2CH2CH3). Anal.
Calcd for C24H33Cl2N3Ru (535.51): C, 53.83; H, 6.21; N, 7.85.
Found: C, 53.55; H, 6.12; N, 7.67.
Acknowledgements
We thank P. Mathew and A. Neels for growing and measuring
single crystals of 3e. This work was financially supported by
Complex 4
In a one-pot reaction 1c (220 mg, 0.58 mmol), Ag2O (67 mg, Science Foundation Ireland and the European Research
0.29 mmol) and [Ru(benzene)Cl2]2 (144 mg, 0.29 mmol) in Council (ERC StG 208561).
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J. Meuldijk, J. A. J. M. Vekemans, L. A. Hulshof,
H. Kooijman and A. L. Spek, Organometallics, 2006, 25,
873–881.
Notes and references
1 (a) Modern Oxidation Methods, ed. J.-E. Bäckvall, Wiley-
VCH, Weinheim, Germany, 2008; (b) I. E. Marko, 13 (a) J. Zhang, G. Leitus, Y. Ben-David and D. Milstein, J. Am.
P. R. Giles, M. Tsukazaki, A. Gautier, R. Dumeunier,
K. Doda, F. Philippart, I. Chelle-Gegnault, J.-L. Mutonkole,
S. M. Brown and C. J. Urch, in Transition Metals for Organic
Synthesis, ed. M. Beller and C. Bolm, Wiley-VCH, Wein-
Chem. Soc., 2005, 127, 10840–10841; (b) C. Gunanathan,
Y. Ben-David and D. Milstein, Science, 2007, 317, 790–792;
(c) C. Gunanathan, L. J. W. Shimon and D. Milstein, J. Am.
Chem. Soc., 2009, 131, 3146–3147.
heim, Germany, 2008, 437–478; (c) R. Noyori and 14 (a) P. Mathew, A. Neels and M. Albrecht, J. Am. Chem. Soc.,
S. Hashigushi, Acc. Chem. Res., 1997, 30, 97–102.
2 (a) K. Bowden, I. M. Heilbron, E. R. H. Jones and
B. C. L. Weedon, J. Chem. Soc., 1946, 39–45;
(b) J. C. Collins, W. W. Hess and F. J. Frank, Tetrahedron
Lett., 1968, 9, 3363–3366; (c) E. J. Corey and J. W. Suggs,
Tetrahedron Lett., 1975, 16, 2647–2650.
2008, 130, 13534–13535; (b) G. Guisado-Barrios,
J. Bouffard, B. Donnadieu and G. Bertrand, Angew. Chem.,
Int. Ed., 2010, 49, 4759–4762; (c) J. D. Crowley, A. Lee and
K. J. Kilpin, Aust. J. Chem., 2011, 64, 1118–1132;
(d) K. F. Donnelly, A. Petronilho and M. Albrecht, Chem.
Commun., 2013, 49, 1145–1159.
3 C. Djerassi, Org. React., 1951, 6, 207–272.
4 D. B. Dess and J. C. Martin, J. Am. Chem. Soc., 1991, 113,
7277–7287.
5 S. V. Ley, J. Norman, W. P. Griffith and S. P. Marsden, Syn-
thesis, 1994, 639–666.
6 (a) R. A. Sheldon, I. W. C. E. Arends, G. J. ten Brink and
A. Dijksman, Acc. Chem. Res., 2002, 35, 774–781;
15 A. Prades, E. Peris and M. Albrecht, Organometallics, 2011,
30, 1162–1167.
16 (a) V. V. Rostovtsev, L. G. Green, V. V. Fokin and
K. B. Sharpless, Angew. Chem., Int. Ed., 2002, 41, 2596–
2599; (b) F. Himo, T. Lovell, R. Hilgraf, V. V. Rostovtsev,
L. Noodleman, K. B. Sharpless and V. V. Fokin, J. Am.
Chem. Soc., 2005, 127, 210–216.
(b) J. Muzart, Tetrahedron, 2003, 59, 5789–5816; (c) T. Mallat 17 L. Bernet, R. Lalrempuia, W. Ghattas, H. Müller-Bunz,
and A. Baiker, Chem. Rev., 2004, 104, 3037–3058; (d) J. Piera
and J.-E. Bäckvall, Angew. Chem., Int. Ed., 2008, 47, 3506–
3523.
7 (a) S.-I. Murahashi and N. Komiya, in ref. 1a, pp. 241–276;
(b) S. Bähn, S. Imm, L. Neubert, M. Zhang, H. Neumann
and M. Beller, ChemCatChem, 2011, 3, 1853–1864.
8 (a) K. P. Peterson and R. C. Larock, J. Org. Chem., 1998, 63,
L. Vigara, A. Llobet and M. Albrecht, Chem. Commun., 2011,
47, 8058–8060.
18 (a) J. C. Garrison and W. J. Youngs, Chem. Rev., 2005, 105,
3978–4008; (b) I. J. B. Lin and C. S. Vasam, Coord. Chem.
Rev., 2007, 251, 642–670.
19 K. F. Donnelly, R. Lalrempuia, H. Müller-Bunz and
M. Albrecht, Organometallics, 2012, 31, 8414–8419.
3185–3189; (b) S. S. Stahl, Angew. Chem., Int. Ed., 2004, 43, 20 For a related reactivity, see: S. Inomata, K. Ogata and
3400–3420. S. Fukuzawa, Dalton Trans., 2013, 42, 2362–2365.
9 For a recent example, see: J. M. Hoover and S. S. Stahl, 21 D. Tapu, D. A. Dixon and C. Roe, Chem. Rev., 2009, 109,
J. Am. Chem. Soc., 2011, 133, 16901–16910. 3385–3407.
10 For examples of heterogeneous systems, see: (a) R. Ben- 22 For representative examples, see: (a) M. Poyatos, E. Mas-
Daniel, P. Alsters and R. Neumann, J. Org. Chem., 2001, 66,
8650–8653; (b) G. Kovtun, T. Kameneva, S. Hladyi,
M. Starchevsky, Y. Pazdersky, I. Stolarov, M. Vargaftik and
I. Moiseev, Adv. Synth. Catal., 2002, 344, 957–964;
(c) Y. Uozumi and R. Nakao, Angew. Chem., Int. Ed., 2003,
42, 194–197; (d) W.-H. Kim, I. S. Park and J. Park, Org. Lett.,
2006, 8, 2543–2545; (e) T. Mitsudome, Y. Mikami, H. Funai,
Marza, M. Sanau and E. Peris, Inorg. Chem., 2004, 43,
1793–1798; (b) R. Cariou, C. Fischmeister, L. Toupet and
P. H. Dixneuf, Organometallics, 2006, 25, 2126–2128;
(c) J. Cai, X. Yang, K. Arumugam, C. W. Bielawski and
J. L. Sessler, Organometallics, 2011, 30, 5033–5037;
(d) F. E. Fernández, M. C. Puerta and P. Valerga, Organo-
metallics, 2012, 31, 6868–6879.
T. Mizugaki, K. Jitsukawa and K. Kaneda, Angew. Chem., 23 (a) K. Hiraki, M. Onishi and K. Sugino, J. Organomet.
Int. Ed., 2008, 47, 138–141.
Chem., 1979, 171, C50; (b) K. Hiraki and K. Sugino, J. Orga-
nomet. Chem., 1980, 201, 469–475; (c) J. Huang,
E. D. Stevens and S. P. Nolan, Organometallics, 2000, 19,
1194–1197; (d) R. F. R. Jazzar, S. A. Macgregor,
M. F. Mahon, S. P. Richards and M. K. Whittlesey, J. Am.
Chem. Soc., 2002, 124, 4944–4945; (e) T. M. Trnka,
J. P. Morgan, M. S. Sanford, T. E. Wilhelm, M. Scholl,
T.-L. Choi, S. Ding, M. W. Day and R. H. Grubbs, J. Am.
Chem. Soc., 2003, 125, 2546–2558; (f) C. M. Crudden and
D. P. Allen, Coord. Chem. Rev., 2004, 247, 2247–2273;
(g) G. D. Frey, J. Schütz, E. Herdtweck and W. A. Herrmann,
Organometallics, 2005, 24, 4416–4426; (h) N. Stylianides,
A. A. Danopoulos, D. Pugh, F. Hancock and A. Zanotti-Gerosa,
11 (a) J. S. M. Samec, J.-E. Bäckvall, P. G. Andersson and
P. Brandt, Chem. Soc. Rev., 2006, 35, 237–248;
(b) T. D. Nixon, M. K. Whittleseay and J. M. J. Williams,
Dalton Trans., 2009, 753–762; (c) G. E. Dobereiner and
R. H. Crabtree, Chem. Rev., 2010, 110, 681–703;
(d) F. Alonso, P. Riente and M. Yus, Acc. Chem. Res., 2011,
44, 379–391.
12 (a) J. Zhang, M. Gandelman, L. J. W. Shimon, H. Rozenberg
and D. Milstein, Organometallics, 2004, 23, 4026–4033;
(b) H. Junge and M. Beller, Tetrahedron Lett., 2005, 46,
1031–1034; (c) G. R. A. Adair and J. M. J. Williams, Tetra-
hedron Lett., 2005, 46, 8233–8235; (d) J. van Buijtenen,
Dalton Trans.
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View Article Online
Dalton Transactions
Paper
Organometallics, 2007, 26, 5627–5635; (i) Z. Liu, T. Zhang
and M. Shi, Organometallics, 2008, 27, 2668–2671;
( j) L. J. L. Häller, M. J. Page, S. A. Macgregor, M. F. Mahon
and M. K. Whittlesey, J. Am. Chem. Soc., 2009, 131,
12080–12084; (c) The cessation of catalytic conversion at
various points of reaction (cf. entries 1–3 in Table 2)
suggests that the colloidal material is, or rapidly becomes,
catalytically inactive.
4604–4605; (k) G. L. Petretto, M. Wang, A. Zucca and 27 Chemical shifts are for the minor species δH = 5.36, 5.13,
J. P. Rourke, Dalton Trans., 2010, 39, 7822–7825;
(l) C. Y. Tang, A. L. Thompson and S. Aldrige, J. Am. Chem.
Soc., 2010, 132, 10578–10591.
5.06, 5.00 (4 × d, 3JHH = 6 Hz, 1H), major species: δH = 5.25,
4.90 (2 × d, 3JHH = 6 Hz, 2H).
28 For a related iridium complex containing an alcohol
ligand, see: A. Bartoszewicz, R. Marcos, S. Sahoo, K. Inge,
X. Zou and B. Martin-Matute, Chem.–Eur. J., 2012, 18,
14510–14519.
24 V. Lavallo and R. H. Grubbs, Science, 2009, 326, 559–
562.
25 (a) J. Takehara, S. Hashiguchi, A. Fujii, S. Inoue, T. Ikariya
and R. Noyori, Chem. Commun., 1996, 233–234; (b) C. Chen, 29 For an example of two-legged ruthenium arene systems,
Y. Zhang and S. H. Hong, J. Org. Chem., 2011, 76, 10005–
10010; (c) L. Delaude, S. Delfosse, A. Richel, A. Demonceau
and A. F. Noels, Chem. Commun., 2003, 1526–1527.
see: A. D. Phillips, K. Thommes, R. Scopelliti, C. Gandolfi,
M. Albrecht, K. Severin, D. F. Schreiber and P. J. Dyson,
Organometallics, 2011, 30, 6619–6632.
26 (a) F. Bernardi, J. D. Scholten, G. H. Fecher, J. Dupont and 30 I. M. Goldman, J. Org. Chem., 1969, 34, 3289–3295.
J. Morais, Chem. Phys. Lett., 2009, 479, 113–116; (b) P. Lara, 31 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
O. Rivada-Wheelaghan, S. Conejero, R. Poteau, K. Philippot
logr., 2008, 64, 112–122.
and B. Chaudret, Angew. Chem., Int. Ed., 2011, 50, 32 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
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Dalton Trans.