Degradation of the second-generation Grubbs metathesis catalyst with primary alcohols and oxygen - Isomerization and hydrogenation activities of monocarbonyl complexes

Article abstract of DOI:10.1002/ejic.200200702

Reaction of the second-generation Grubbs metathesis catalyst [RuCl ₂(=CHPh)(H₂IMes)(PCy₃)] (2) (H₂IMes = 1,3-dimethyl-4,5-dihydroimidazol-2-ylidene) with primary alcohols in the presence of a base produced the complexes [RuClH(CO)(PCy₃) ₂] (3) and [RuClH(CO)(H₂IMes)(PCy₃)] (5). When benzyl alcohol was used, the ruthenium phenyl complexes [RuClPh(CO)(PCy ₃)₂] (4) and [RuClPh(CO)(H₂IMes)(PCy ₃)] (7) were formed in addition to 3 and 5. Complex 7, characterised by an X-ray structure analysis, was also formed on exposure of 2 to oxygen. The isomerization and hydrogenation activity of 7 was determined and compared with that of 3 and 4. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200200702

FULL PAPER
Degradation of the Second-Generation Grubbs Metathesis Catalyst with
Primary Alcohols and Oxygen ؊ Isomerization and Hydrogenation Activities
of Monocarbonyl Complexes
Maarten B. Dinger[a] and Johannes C. Mol*[a]
Keywords: Ruthenium / Metathesis / Carbene ligands / Alcohols / Isomerization / Hydrogenation
Reaction of the second-generation Grubbs metathesis cata-
lyst [RuCl2(=CHPh)(H2IMes)(PCy3)] (2) (H2IMes = 1,3-di-
methyl-4,5-dihydroimidazol-2-ylidene) with primary alcohols
Mes)(PCy3)] (7) were formed in addition to 3 and 5. Complex
7, characterised by an X-ray structure analysis, was also
formed on exposure of 2 to oxygen. The isomerization and
hydrogenation activity of 7 was determined and compared
with that of 3 and 4.
in the presence of
a base produced the complexes
[RuClH(CO)(PCy3)2] (3) and [RuClH(CO)(H2IMes)(PCy3)] (5).
When benzyl alcohol was used, the ruthenium phenyl com-
plexes [RuClPh(CO)(PCy3)2] (4) and [RuClPh(CO)(H2I-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
[RuClH(CO)(PCy3)2] (3) could be affected by aliphatic pri-
mary alcohols, and we established that the addition of a
suitable base greatly facilitates this reaction. Additionally,
if benzyl alcohol is used in place of the aliphatic alcohol,
the phenyl complex [RuClPh(CO)(PCy3)2] (4) is produced
in good yields. The reactions occur via an alcohol dehydro-
genation pathway, with toluene and an alkane being the
major organic products. Complex 4 was of particular inter-
est because it was also formed when 1 was treated with oxy-
gen, this reaction being especially effective in the solid state,
where the undesirable oxidation of the phosphane ligands
is suppressed.
With the advent of the Grubbs metathesis catalysts
[RuCl2(ϭCHPh)(PCy3)2] (1) and [RuCl2(ϭCHPh)(H2I-
Mes)(PCy3)] (2) olefin metathesis has become an increas-
ingly useful tool for organic transformations.[1] Moreover,
these metathesis catalysts can catalyse a number of other
reactions,[2] and can also be transformed in situ into various
catalytically active species. Single-component tandem ca-
talysis in the presence of 1 and 2 has, so far, included met-
athesis followed by hydrogenation,[3] dehydrogenation,[3c]
and, most recently, isomerization.[4] Relatively little effort,
however, has been made to identify the active species re-
sponsible for the secondary reaction(s), although various
hydride species are thought to be involved.
Complexes 3 and 4 proved to be excellent α-olefin iso-
merization catalysts, producing the β-olefin with high (95%)
selectivity. Extending the first-generation research to the
important second-generation metathesis catalyst 2 was a
natural step. The results of these studies are described here.
Recently, we[5] and others,[3aϪ3c,6,7] described how the
transformation of the first-generation Grubbs catalyst
[RuCl2(ϭCHPh)(PCy3)2] (1) to the hydride species
[a]
Institute of Molecular Chemistry, Faculty of Science,
Universiteit van Amsterdam
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The
Netherlands
Fax: (internat.) ϩ31-20/5256456
E-mail: jcmol@science.uva.nl
Eur. J. Inorg. Chem. 2003, 2827Ϫ2833
DOI: 10.1002/ejic.200200702
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M. B. Dinger, J. C. Mol
FULL PAPER
The third detected hydride species shows a doublet at δ ϭ
Ϫ7.43 ppm in the 1H NMR spectrum, and was only a
minor product (about 10%). While the large downfield shift
Results and Discussion
Reaction of 2 with Primary Aliphatic Alcohols
When the second-generation catalyst 2 was treated with relative to 3 and 5 suggested a ligand trans to the hydride
2
methanol in the presence of triethylamine, the initially dark group, the JP,H coupling constant of 50.4 Hz is both too
brown solution slowly became dark orange. Catalyst 2 was high for a phosphorus cis and too low for a phosphorus
more active than the first-generation system 1, and the reac- trans to the hydride moiety, indicating a distorted coordi-
tions proceeded readily at lower temperatures than used nation environment. The associated phosphorus resonance
previously for 1 (60 vs. 80 °C).[5] However, 1H and 31P appears at δ ϭ 47.5 ppm in the 31P NMR spectrum, and so
NMR spectroscopy revealed an unexpectedly complex reac- was not separated from those of 3 and 5.
tion in which three different hydrides were produced, in
A fourth, unidentified complex that was definitely not a
marked contrast to 1 where only one hydride species was hydride species shows a phosphorus resonance at δ ϭ
formed.[5] Two of these hydride complexes were identified 51.2 ppm in the 31P NMR spectrum, and represented about
spectroscopically.
20Ϫ25% of the total phosphorus content of the crude reac-
The major reaction product (ഠ30Ϫ40% yield by NMR tion mixture. This peak appeared in a similar location as
spectroscopy), showing a doublet at δ ϭ Ϫ27.8 ppm in the that found for the reaction of 1 with water,[5] and might
1H NMR spectrum, was assigned as the expected mixed- arise from the reaction of 2 with adventitious water in the
ligand hydride species [RuClH(CO)(H2IMes)(PCy3)] (5). reagents/solvents used.
1
The formation of 5 was verified by comparison of H and
Ethanol, 1-propanol and 1-nonanol also gave the hy-
31P NMR spectra with those obtained from the model reac- drides 3 and 5 as the dominant products, but with much
tion of 3 with H2IMes. Unfortunately, repeated attempts to smaller amounts (Ͻ5%) of the unknown hydride. Interest-
isolate complex 5 from either synthetic route were unsuc- ingly, 1-propanol and 1-nonanol gave significantly higher
cessful due to the product’s extremely high solubility in all relative yields of 5; 3:5 was 15:85 for these two alcohols,
common organic solvents, ranging from pentane to meth- compared with 40:60 and 35:65 for methanol and ethanol,
anol. The surprisingly high solubility of 5 — the very respectively. Ethanol, 1-propanol and 1-nonanol also pro-
closely related complex [RuClH(CO)(IMes)(PCy3)] (6) was duced the unknown complex with a 31P NMR peak at δ ϭ
reported to be insoluble in methanol[8] — may be because 51 ppm, and in approximately the same quantities. Such a
it is not a solid at room temperature. Complex 5 could be significant side-product was never observed in otherwise
precipitated from pentane solutions at Ϫ78 °C, but sub- identical reactions of 1, further highlighting the quite differ-
sequent removal of the supernatant by syringe, followed by ent behaviour of 1 and 2 in the alcoholic degradation
warming of the solid to room temperature, gave only a experiments.
highly air-sensitive, oily residue.
The volatile components of the 1-nonanol reaction were
A second hydride (about 25Ϫ30% yield by NMR spec- analysed by GCMS and showed that, as with 1, toluene and
troscopy) shows δ ϭ Ϫ24.2 ppm as a triplet, and was deter- octane were the major constituents, indicative of an alcohol
mined to be complex 3 by comparison with the spectrum dehydrogenation/decarboxylation mechanism.[5] Reaction
of an authentic sample.[5] The formation of complex 3 from with 1-13C enriched ethanol (CH313CH2OH) confirmed
2 is especially noteworthy since it could only have orig- that the hydride complexes were formed by this pathway.
inated from an unexpected H2IMes ligand exchange with Most of the 13C label was incorporated as the carbonyl
PCy3. N-Heterocyclic carbene (NHC) ligands in ruthenium groups in 3 and 5, and the associated hydride signals clearly
systems generally show stronger covalent bonds (more exo- showed additional coupling due to an adjacent spin-active
thermic reaction enthalpies) than phosphanes, and so tend carbon isotope. A third 13C-labeled carbonyl group, which
not to readily dissociate.[9] We were unable to unambigu- showed no splitting from phosphorus (singlet), appeared at
ously identify the reaction by-products, but the observed δ ϭ 204.7 ppm; this complex may possibly be a bis-NHC
ligand exchange must consume the starting material (or complex. Interestingly, the third, unidentified, hydride spec-
products), and should lead to RuCl(H2IMes) and free ies (δ ϭ Ϫ7.43 ppm) showed no additional splitting (re-
H2IMes fragments which could subsequently combine to maining a simple doublet), indicating that it does not con-
produce bis-H2IMes complex(es). While free H2IMes dis- tain a carbonyl group and, therefore, probably does not
placed PCy3 in separate reactions (vide infra), in this case form from an alcohol dehydrogenation pathway.
any released H2IMes might also react with the excess al-
Reaction of 2 with Benzyl Alcohol
cohol, thereby limiting its immediate availability for further
reaction. Reaction of the ligand with alcohol is not available
for PCy3, and so the degradation becomes considerably with an excess of benzyl alcohol, in the presence of triethyl-
more complicated than that observed for 1.
amine, several products were observed by 31P NMR spec-
As with aliphatic alcohols, when complex 2 was reacted
Surprisingly, the addition of an NHC ligand has virtually troscopy. This was in sharp contrast to the reaction of 1
no effect on the 31P NMR spectrum of the complexes, ren- with benzyl alcohol under the same conditions, which
dering 31P NMR of less use than usual in monitoring the cleanly generated the phenylruthenium complex 4 in good
reaction outcomes; 3, 5 and 6 show chemical shifts of yield.[5] Again, the main reason for the relatively unsatisfac-
47.6,[5] 46.9, and 47.5[8] ppm, respectively.
tory reaction is the apparently significant lability of the
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Degradation of the Second-Generation Grubbs Metathesis Catalyst with Primary Alcohols and Oxygen
FULL PAPER
H2IMes ligand under the conditions used, which readily electron-rich, thereby increasing the nucleophilicity of the
scrambled with the phosphane. Additionally, whereas no benzylidene group toward an electrophile.[11]
hydride complexes formed with 1, catalyst 2 also produced
Unsurprisingly, complex 7 was more easily prepared, and
hydride complexes. Complexes 3 and 5 represented about in better yield, by reaction of 4 with H2IMes in toluene at
25% and 10% of the total phosphorus-containing com- 100 °C.
plexes, respectively, while 4 and the desired product,
[RuClPh(CO)(H2IMes)(PCy3)] (7), were formed in 5% and
30% yield, respectively. The remaining about 30% was due
to an unknown species that shows a 31P NMR signal at δ ϭ
51.9 ppm. This chemical shift is very similar to that of the
complex(es) formed with aliphatic alcohols, although the
about 0.7 ppm difference implies that it may possibly be a
slightly different species.
Crystal Structure of 7
Red blocks of 7 suitable for X-ray diffraction were grown
by the slow evaporation of a CH2Cl2/MeOH solution in air.
Figure 1 shows the structure of 7, with selected bond
lengths and angles in the caption.
The 1H NMR spectrum revealed that a third hydride
species had again formed, in addition to 3 and 5, but this
species was distinct from that present in the aliphatic al-
cohol reactions, showing a sharp singlet at δ ϭ Ϫ6.59 ppm
that indicates the complete absence of phosphorus ligands
and a substituent trans to the hydride atom. This complex
might be the bis-carbene [RuClH(CO)(H2IMes)2], although
this could not be confirmed synthetically; complex 3, with
excess H2IMes, even at 100 °C, gave only the mono-substi-
tuted complex 5. However, this does not rule out a bis-
NHC complex; the failure of bis-phosphanes to fully substi-
tute with NHCs can be attributed to the lowered lability of
the remaining phosphane after mono-substitution.[6] To
gain further insight we analysed the crude reaction mixture
by FAB/MS. Unfortunately, this yielded little new infor-
mation since only 4 and 7 (and their fragmentation prod-
ucts) were detected.
Figure 1. ORTEP representation of complex 7 with thermal ellip-
soids drawn at the 30% probability level; hydrogen atoms have been
˚
omitted for clarity; selected bond lengths (A) and angles (°): RuϪCl
2.4542(8), RuϪP 2.4499(7), RuϪC(1) 1.805(3), RuϪC(2) 2.039(3),
RuϪC(8) 2.118(3), OϪC(1) 1.142(4), N(1)ϪC(8) 1.335(3),
N(2)ϪC(8) 1.345(4); PϪRuϪCl 89.76(3), ClϪRuϪC(1) 168.6(1),
ClϪRuϪC(2) 102.7(1), ClϪRuϪC(8) 86.05(7), PϪRuϪC(1)
Reaction of 2 with Oxygen
Like complex 1,[5] complex 2 also reacted with oxygen.
However, the reactions were much lower yielding. Thus, 2 89.6(1),
PϪRuϪC(2)
94.25(8),
PϪRuϪC(8)
168.81(7),
C(1)ϪRuϪC(2) 88.7(1), C(1)ϪRuϪC(8) 92.5(1), C(2)ϪRuϪC(8)
96.8(1), RuϪOϪC(1) 179.2(3)
reacted with dry air at room temperature in toluene to give,
mainly, tricyclohexylphosphane oxide, and only very low
amounts of 7. Furthermore, the diphosphane product 5 was
also produced. Higher temperatures gave OϭPCy3 as the
The ruthenium occupies a typical distorted square-pyr-
only phosphorus-containing species according to 31P amidal coordination geometry. As in related structures, the
NMR spectroscopy.
halogen is trans to the carbonyl moiety, so that the phos-
In the solid state, the reaction of 2 with oxygen (5 bar) phorus is trans to the other neutral ligand (in this case
was cleaner. Nonetheless, only about 30% of 2 had reacted H2IMes). Somewhat surprisingly, few structures of com-
after 48 h, and, of that, only about 30% was complex 7. The plexes of the type [RuArCl(L)2(CO)] (Ar ϭ aromatic, L ϭ
major product peak in the 31P NMR spectrum appears at phosphane) have been described,[12] and 7 is the first ex-
δ ϭ 48 ppm, possibly due to OϭPCy3, although the lability ample containing an NHC ligand.
of phosphane in the solid state should be relatively low, dis-
Overall, the structure most closely resembles that of the
favouring the formation of this product. At higher pressures hydride complex 6 determined by Nolan,[8] with the phenyl
(50 bar) and 60 °C the complete reaction of 2 was achieved group in 7 residing at the position of the hydride at the apex
over three days to give, after workup, a 29% yield of the of the pyramid. The main distortions from an ideal square-
air-stable, bright pink 7. The fate of the remaining 2 could pyramidal geometry are the PϪRuϪC(8) and ClϪRuϪC(1)
not be determined; a phosphorus-containing material gave angles (both about 169°), which compare with analogous
a
31P NMR peak at δ ϭ 54.4 ppm, but could not be iso- angles of 173.4 and 175.9°, respectively, in 6. The increased
lated. The lower reactivity of 2 compared with 1 towards distortion is most likely due to the higher steric influence
oxygen is foretold by its superior air tolerance; it can even of the phenyl group in 7 relative to the hydrogen in 6. Sur-
be purified by chromatography using non-degassed sol- prisingly, the RuϪC(8) and RuϪP distances in 7 are signifi-
vents.[10] Nonetheless, the NHC ligand, being a better σ- cantly longer (0.035 and 0.083 A, respectively) than in 6;
˚
donor than phosphanes, should render the ruthenium more typically, these bond lengths are not greatly affected when
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M. B. Dinger, J. C. Mol
FULL PAPER
saturated (H2IMes) or unsaturated (IMes) NHC ligands are
From Figure 2, the hydride complex 3 remains the most
present. Conversely, the RuϪCO bond length in 7 is longer active catalyst with respect to turnover number. At lower
˚
(0.021 A) than in 6, concomitant with a shortening (0.038 temperatures, the phenyl-substituted analogue of 3, com-
˚
A) of the CϵO distance. The different electronic influences plex 4, displayed considerably lower activity, and was essen-
of the unsaturated (in 6) and saturated (in 7) NHC ligands tially inactive below 50 °C, possibly because the active spec-
are probably not responsible for these discrepancies. The ies has to be generated in situ Ϫ for both 3 and 4 this active
increased steric demands of the phenyl group are probably species is likely to be [RuClH(CO)(PCy3)].[16] The NHC-
the dominant influence, since the pushing back of the neu- substituted analogue 7 was almost as active as the hydride
tral ligands may result in less-ideal orbital overlaps with the 3. The loss in activity associated with substituting the hy-
metal center. The phenyl ring and one of the mesityl groups dride moiety (in 3) for a phenyl group (in 4) is at least par-
are in close contact, and almost perfectly eclipse one an- tially offset by the increase in activity associated with re-
other. Because the two rings are not quite co-planar, for- placing one of the tricyclohexylphosphane ligands with
ming a butterfly angle of 10.0(2)°, C(2)···C(11) represents H2IMes (in 7). Unfortunately, as mentioned above, the
˚
the minimum distance between the rings at 3.259 A.
H2IMes-substituted hydride 5 could not be obtained in a
sufficiently pure form for comparison.
Isomerization Activity of Complexes 3, 4 and 7
Interestingly, at higher temperatures, and especially after
prolonged reaction times, metathesis products (predomi-
nantly tridecene and dodecene, from the cross-metathesis of
1-octene with 2-octene and the self-metathesis of 2-octene,
respectively) were detected in the reactions involving cata-
lyst 7. While these longer chain olefins represented only
about 3Ϫ5% of the reaction products, it is noteworthy that
only the NHC-containing compound initiated only meta-
thesis, i.e. metathesis products have never been observed in
reactions involving 3 and 4.
Figure 3 depicts the relative reaction rates and selectivity
over time for the isomerization of 1-octene into 2-octene at
100 °C. Catalyst 7 is clearly much more active than either
3 or 4. Again, the presumed loss of activity due to the ex-
change of a hydride for a phenyl group is more than com-
pensated for by the addition of the NHC ligand. Indeed,
97% conversion of 100,000 equivalents of 1-octene in the
presence of 7 was achieved in less than 5 minutes, with 95%
selectivity for 2-octene. For each catalyst, the selectivity for
2-octene formation rapidly decreased once all of the 1-oc-
tene had been consumed. Thus, the selectivity after 8 h was
highest for catalyst 4, followed by 3 and finally 7, coinciding
with their relative activities. We had previously determined
that catalyst 4 could not isomerise 2-octene, and so the de-
crease in selectivity is primarily due to decomposition of
the active catalyst into unknown ruthenium complexes that
Previously we reported that complexes 3 and 4, while tot-
ally metathesis inactive, were potent CϭC bond isomeriz-
ation catalysts for α-olefins.[5] Wagener et al. have recently
made a detailed study of the double-bond isomerization ac-
tivity of the first- and second-generation Grubbs catalysts
1 and 2, and compared that with the Mo-based Schrock
metathesis catalyst.[13] Double-bond isomerization is highly
relevant in metathesis chemistry because it is the primary
cause of secondary metathesis products; this is generally
considered to be a major limitation of olefin metathesis.
Nonetheless, double-bond isomerization has also recently
been deliberately exploited in a tandem metathesis-iso-
merization reaction for the synthesis of cyclic enol ethers[4]
in which the metathesis catalysts 1 or 2 were converted by
hydrogen, after metathesis had ceased, into uncharacterised
isomerization catalysts. We decided to determine the iso-
merization activity of complex 7 towards 1-octene, and
compare this with the first-generation systems 3 and 4.
As we recently reported for metathesis catalysed by 1 and
2,[14] additional solvents were unnecessary in the isomeriz-
ation reactions. Because solvents are a major hurdle in the
development of ‘‘green’’ chemistry, any reactions where they
are not required are particularly relevant to this increasingly
timely area.[15] Figure 2 summarises the 1-octene isomeriz-
ation activity of 7 over a range of temperatures. In each
case, the reactions were allowed to proceed to maximal con-
version, and, for comparison, the results for 3 and 4 under
the same conditions are included.
Figure 2. Double-bond isomerization of neat 1-octene (100,000
equivalents) in the presence of catalysts 3, 4 and 7 as a function of
reaction temperature; all reactions were allowed to proceed until 1-
octene was no longer consumed
Figure 3. Double-bond isomerization of neat 1-octene (100,000
equivalents) into 2-octene at 100 °C in the presence of catalysts 3,
4 and 7 as a function of reaction time
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Degradation of the Second-Generation Grubbs Metathesis Catalyst with Primary Alcohols and Oxygen
FULL PAPER
Table 1. Hydrogenation of 1-octene in the presence of catalysts 3, 4 and 7, under various reaction conditions
T (°C) P(H2) (bar) Cat. Equiv. of 1-octene[a] Reaction time (h) Conversion (%) Selectivity (%)[b] Isomerization products (%)[c]
23
23
23
4
4
4
4
4
4
4
4
4
1
1
1
3
4
7
3
4
7
3
4
7
3
4
7
100,000
100,000
100,000
100,000
100,000
100,000
350,000
350,000
350,000
250,000
250,000
250,000
18
18
18
3
3
3
2
2
2
3
99.9
1.6
0.4
100
100
100
100
100
100
0
0
0
0
0
100
100
100
100
100
100
100
100
100
98.7
98.5
99.3
98.3
98.5
99.1
98.5
99.6
99.1
0
84.1
15.6
9.7
40.7
3.2
22.1
18.4
90.2
58.9
95.3
77.8
81.4
3
3
[a]
[b]
[c]
Mol of 1-octene per mol of catalyst. Selectivity towards the formation of octane. Isomerization products: 2-, 3-, and 4-octene.
are also catalytically active toward olefin isomerization but the very high activity of 7 with regard to isomerization (vide
lack the selectivity (and activity) of the parent catalyst.[5] supra), while the hydrogenation activity of 7 towards 2-oc-
The cis to trans ratio of the 2-octene produced for each tene is clearly lower.
catalyst was approximately 30:70.
Remarkably, the absence of solvent may benefit these re-
actions. Whereas Nolan reported turnover rates for the
hydrogenation [P(H2) ϭ 4 bar) of 1-hexene in benzene at
100 °C of 21,500 and 24,000 (mol product)(mol
catalyst)Ϫ1hϪ1 for 3 and 6, respectively,[8] we attained turn-
over frequencies of well over 100,000 hϪ1 for all the systems
tested at 100 °C, even at only P(H2) ϭ 1 bar.
Hydrogenation Activity of 3, 4 and 7
Hydrogenation of alkenes is an important organic trans-
formation, and can be facilitated by traditional homo-
geneous catalysts such as [RhCl(PPh3)3] (Wilkinson cata-
lyst), [RuClH(PPh3)3] and [RuH(CO)(PPh3)3].[17] More re-
cently, catalyst 3 has been found to be an excellent olefin
hydrogenation catalyst,[8,16,18] and has also been exploited
for the hydrogenation of polybutadiene rubber.[19] Further-
more, the second-generation analogue 6 has recently been
tested for hydrogenation activity, and displayed activity
Conclusions
The chemistry previously developed for the first-genera-
similar to 3 at higher temperatures.[8] Due to the current tion ruthenium metathesis catalyst 1,[5] could be extended
interest in single-component tandem metathesis-hydrogen- to include the second-generation catalyst 2. However, the
ation reactions,[3] we tested the efficacy of catalysts 4 and 7 reactions were complicated by an unanticipated exchange
for the hydrogenation of 1-octene, and compared the results involving the NHC ligand, even at relatively low tempera-
with those of 3 (Table 1). Various reaction conditions were tures (60 °C). The lability of the NHC ligand allowed not
tested, and, again, the reaction proceeds very well in neat only the formation of the desired mixed-ligand systems, but
substrate, i.e. no additional solvents were required for good also the corresponding diphosphane complexes. In theory
conversions and reaction rates.
these complexes could hinder olefin metathesis reactions
From the data in Table 1 catalyst 3 is clearly the most that employ 2 in alcoholic solvents, but the higher tempera-
active catalyst for the hydrogenation of 1-octene. Indeed, tures and relatively long time needed for their formation
only 3 shows appreciable hydrogenation activity at room limits their role in potential side-reactions.
temperature. At 100 °C, 4 and 7 were ‘‘activated’’, and also
Complex 7, a fully air-stable solid, is a highly active iso-
became good hydrogenation catalysts, comparable in ac- merization catalyst Ϫ considerably more active than either
tivity to 3, and gave complete conversion into octane when of the first-generation systems 3 and 4. We tentatively sug-
100,000 equivalents (mol) of 1-octene were reacted.
gest that the higher σ-donation of the NHC ligand (relative
To better test the limits of the catalysts, reactions with to phosphanes), which ultimately renders the second-gener-
lower catalyst loadings were examined. Thus, 350,000 ation metathesis catalysts more active than their first-gener-
equivalents (mol) of 1-octene were hydrogenated in the ation congeners, may also explain their (or their decompo-
presence of 3, 4 or 7 at 100 °C. All the catalysts consumed sition products’) efficacy as isomerization catalysts. We also
the 1-octene completely, but none gave selective conversion found that complexes 4 and 7 are efficient hydrogenation
into octane. Catalysts 3 and 4 showed comparable activity catalysts at higher temperatures, which may aid in the
and selectivity, whereas 7 produced lower amounts of development of single-component tandem metathesis-
octane, with isomerization clearly competing with the hydrogenation of olefins[3a,3b] when employing the second-
hydrogenation. This result is perhaps not surprising given generation metathesis catalysts.
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M. B. Dinger, J. C. Mol
FULL PAPER
P(C6H11)3], 34.5 [d, JC,P ϭ 16.2 Hz, P(C6H11)3], 118.5, 124.3, 125.6,
Experimental Section
129.6, 130.0, 136.2, 136.8, 137.1, 138.2, 139.1, 140.5 (C-Ar), 155.9
2
(d, 2JC,P ϭ 12.0 Hz, i-C C6H5), 205.6 (d, JC,P ϭ 13.7 Hz, Ru-CO),
Unless otherwise stated, all manipulations were performed under
a nitrogen atmosphere on a vacuum line using standard Schlenk
techniques. Complex 1 (Fluka), potassium tert-pentoxide solution
(1.7  in toluene, Fluka), and 1-octene (98%, Aldrich) were ob-
tained from commercial sources. 1,3-Dimesityl-4,5-dihydroimida-
zolinium chloride[20] and the complexes 2,[21] 3,[22] and 4[5] were
prepared by the literature procedures. NMR spectra were recorded
on a Varian Mercury 300 spectrometer, at 300.14, 75.48 and
121.50 MHz for the proton, carbon and phosphorus channels,
respectively. Elemental analyses were performed by H. Kolbe Mi-
kroanalytisches Laboratorium, Germany.
2
210.8 [d, JC,P
ϭ
94.9 Hz, Ru-C(N)2] ppm. 31P{1H} NMR
(CD2Cl2): δ ϭ 22.2 ppm. C46H64ClN2OPRu: calcd. C 66.69, H
7.79, N 3.38; found C 66.78, H 7.72, N 3.31.
Isomerization Reactions: Immediately before use, the 1-octene was
passed through a column (20 cm ϫ 1.5 cm) of neutral alumina
(Acros, 50-200 µm), containing 15 g of alumina per 100 mL of oc-
tene, into a Schlenk flask. The 1-octene was then deoxygenated by
a series of degassings (by evacuation of the flask), followed by re-
filling with nitrogen. For each reaction, 20 mL (127 mmol) of 1-
octene was used. The reaction vessel was immersed in an oil bath
and allowed to equilibrate to the desired temperature. An appropri-
ate quantity (six-figure analytical balance) of the catalyst under
investigation was then added to the 1-octene. No additional sol-
vents were used. All reactions were thoroughly stirred, by way of a
magnetic stirrer bar, and were allowed to proceed to completion,
i.e. the reported results are those obtained when 1-octene consump-
tion had ceased. The product distribution of the isomerization reac-
tions was measured by GC/FID (Carlo Erba 8000 Top) using a
ZB-5 (5% phenyl polysiloxane) column (Zebron).
[RuClH(CO)(H2IMes)(PCy3)] (5): Potassium tert-pentoxide solu-
tion (1.7  in toluene, 260 µL, 0.442 mmol) was added to a suspen-
sion of 1,3-dimesityl-4,5-dihydroimidazolinium chloride (0.150 g,
0.437) in toluene (5 mL) and stirred for 10 min. The resulting solu-
tion was transferred, via a steel cannula fitted with a filter, to a
second flask containing a toluene (2 mL) solution of 3 (0.100 g,
0.138 mmol). The mixture was then heated to 100 °C for 3 h. No
colour change was observed. The solvent was removed under re-
duced pressure, leaving an oily residue that was miscible with all
common organic solvents at room temperature. Cooling a concen-
trated pentane solution to Ϫ78 °C produced a yellow solid. The
mother liquor was then carefully removed by syringe and the solid
allowed to warm to room temperature, during which time it slowly
melted. The resultant highly air-sensitive oil was spectroscopically
characterised as complex 5 (ഠ75% purity). IR (toluene): ν˜ ϭ 1896
cmϪ1 (vs, CϵO). 1H NMR (CD2Cl2): δ ϭ 25.37 (d, JHP ϭ 21.3 Hz,
1 H, Ru-H), 2.5Ϫ1.1 (multiple peaks, 51 H, H-aliphatic), 3.17 (br.
s, 2 H, CH2CH2), 3.78 (br. s, 2 H, CH2CH2), 6.80 (br. s, 2 H,
C6Me3H2), 6.99 (br. s, 2 H, C6Me3H2) ppm. 31P{1H} NMR
(CD2Cl2): δ ϭ 46.7 ppm.
Hydrogenation Reactions: 1-Octene was prepared in the manner de-
scribed above for the isomerization reactions. A small quantity of
the catalyst under investigation was introduced into an autoclave
fitted with a glass liner, and the autoclave was subsequently evacu-
ated and flushed with hydrogen. 1-Octene (10 mL) was introduced
by syringe, and the autoclave pressurised with the desired level of
hydrogen; this pressure was maintained throughout the experiment.
The autoclave was heated, where appropriate, by way of an oil bath.
After completion of the reaction, the hydrogen was vented off, and
the solution analysed as for the isomerization reactions.
Crystal Structure Determination of 7: Red blocks of 7 suitable for
X-ray diffraction were grown by the slow evaporation of a CH2Cl2/
MeOH solution. Intensity data were collected on an
EnrafϪNonius CAD-4 diffractometer, using a crystal of dimen-
sions 0.50 ϫ 0.45 ϫ 0.125 mm, with graphite-monochromated Mo-
Kα X-rays (λ ϭ 0.71069) and ω-2θ scan. A total of 7461 unique
reflections in the range 1.6° Ͻ 2θ Ͻ 25° were collected at room
temperature, and these were subsequently corrected for Lorentz ef-
fects, polarization effects, and for linear absorption by a Ψ-scan
method. Crystal data: C46H64ClN2OPRu, FW ϭ 828.48, crystal
[RuClPh(CO)(H2IMes)(PCy3)] (7), Method A: Potassium tert-pent-
oxide solution (1.7  in toluene, 220 µL, 0.374 mmol) was added
to a suspension of 1,3-dimesityl-4,5-dihydroimidazolinium chloride
(0.130 g, 0.379) in toluene (4 mL) and stirred for 10 min. The re-
sulting solution was then transferred, via a steel cannula fitted with
a filter, to a second flask containing a toluene (2 mL) solution of
4 (0.100 g, 0.125 mmol). The mixture was heated to 100 °C for 3 h,
during which time the solution became a brighter orange/red. The
solvent was then removed under reduced pressure, and methanol
subsequently added to the residue. Rapid stirring (1 h) produced a
bright pink precipitate, which was collected by filtration and then
washed with methanol (4 ϫ 10 mL) and pentane (2 ϫ 5 mL) to
give complex 7 as a crimson powder (0.072 g, 70%).
class monoclinic, space group P21/c,
a ϭ 12.2573(8), b ϭ
3
˚
˚
15.6707(12), c ϭ 22.358(4) A, β ϭ 94.686(10)°, Vc ϭ 4280.2(9) A ,
Dc ϭ 1.286 g cmϪ3, Z ϭ 4, F(000) ϭ 1752, µ(Mo-Kα) ϭ 0.502
mmϪ1
.
The structure of 7 was solved using the direct methods option of
SHELXS-97[23] and subsequently refined using SHELXL-97.[24] All
non-hydrogen atoms were assigned anisotropic temperature factors
and all hydrogen atom positions were determined by calculation.
For the methyl groups of the mesityl substituents, where the lo-
cation of the hydrogen atoms was uncertain, the AFIX 137 card
was used to allow the hydrogen atoms to rotate to the maximum
area of residual density, while fixing their geometry. The refinement
converged with R1 ϭ 0.0422 for 6751 data with I Ն 2σ(I), 0.0466
Method B: Finely powdered 2 (0.050 g, 0.059 mmol) was deposited
as a solid in an autoclave that was subsequently pressurised with
oxygen (50 bar) and then heated in an oil bath to 60 °C for 3 days.
After releasing the pressure, workup in the same manner as Method
A gave complex 7 (0.014 g, 29%). IR (KBr): ν˜ ϭ 1901 cmϪ1 (vs,
CϵO). 1H NMR (CD2Cl2): δ ϭ 1.07 [m, 11 H, P(C6H11)3], 1.24
[m, 4 H, P(C6H11)3], 1.54 (s, 3 H, p-Me C6Me3H2), 1.62 [br. s, 14
H, P(C6H11)3], 1.88 [m, 4 H, P(C6H11)3], 2.20 (s, 9 H, o-Me/p-Me
C6Me3H2), 2.63 (s, 6 H, o-Me C6Me3H2), 3.85 (br. s, 4 H,
2
for all data; wR2 ϭ 0.1146 {w ϭ 1/[σ2(Fo ) ϩ (0.0752P)2 ϩ2.3804P]
3
CH2CH2), 5.89 (d, JH,H ϭ 7.50 Hz, 1 H, m-H C6H5), 6.24 (d,
2
where P ϭ (Fo2 ϩ2Fc )/3}, and GoF ϭ 1.046. No parameter shifted
3
3JH,H ϭ 7.20 Hz, 1 H, p-H C6H5), 6.30 (d, JH,H ϭ 7.50 Hz, 1 H,
in the final cycle. The final difference map showed no peaks or
3
m-H C6H5), 6.46 (br. s, 2 H, C6Me3H2), 6.83 (d, JH,H ϭ 7.80 Hz,
Ϫ3
˚
troughs of electron density greater than ϩ1.29 and Ϫ1.02 e·A
1 H, o-H C6H5), 6.88 (s, 2 H, C6Me3H2), 7.14 (d, 3JH,H ϭ 7.20 Hz,
1 H, o-H C6H5) ppm. 13C{1H} NMR (CD2Cl2): δ ϭ 19.3, 19.4 (o-
respectively, both near Ru.
Me/p-Me C6Me3H2), 21.2 (o-Me C6Me3H2), 26.9 [s, P(C6H11)3], CCDC-199892 contains the supplementary crystallographic data
28.4 [d, JC,P ϭ 8.5 Hz, P(C6H11)3], 29.6 [d, JC,P ϭ 16.6 Hz, for complex 7. These data can be obtained free of charge at
2832
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 2827Ϫ2833

Degradation of the Second-Generation Grubbs Metathesis Catalyst with Primary Alcohols and Oxygen
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