A missing relative: A Hoveyda-Grubbs metathesis catalyst bearing a peri-substituted naphthalene framework

Article abstract of DOI:10.1021/om300052b

Molecular scaffolds of polycyclic aromatic hydrocarbons can serve as unique tools to control the molecular and electronic structure of coordination compounds. Herein, we report the synthesis and properties of a Hoveyda-Grubbs metathesis catalyst bearing a chelating benzylidene ligand assembled on peri-substituted naphthalene. In contrast to other reported naphthalene-based complexes (Barbasiewicz, M. and Grela, K.Chem. Eur. J. 2008, 14, 9330-9337), it exhibits a very fast initiation behavior, attributed to a distorted molecular structure and reduced π-electron delocalization within the chelate ring.

Full text of DOI:10.1021/om300052b

Article
pubs.acs.org/Organometallics
A Missing Relative: A Hoveyda−Grubbs Metathesis Catalyst Bearing
a Peri-Substituted Naphthalene Framework
Michał Barbasiewicz,* Krzysztof Grudzien, and Maura Malinska
́
Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
S
* Supporting Information
ABSTRACT: Molecular scaffolds of polycyclic aromatic
hydrocarbons can serve as unique tools to control the
molecular and electronic structure of coordination com-
pounds. Herein, we report the synthesis and properties of a
Hoveyda−Grubbs metathesis catalyst bearing a chelating
benzylidene ligand assembled on peri-substituted naphthalene.
In contrast to other reported naphthalene-based complexes
(Barbasiewicz, M.; Grela, K. et al. Chem. Eur. J. 2008, 14,
9330−9337), it exhibits a very fast initiation behavior,
attributed to a distorted molecular structure and reduced π-electron delocalization within the chelate ring.
ell-defined homogeneous metathesis catalysts are
ubiquitous tools for the construction of carbon−carbon
metathesis reactions.13 Thus, factors influencing the initiation
W
process control the rate of the main metathesis reaction14 and
give a chance to improve the catalytic performance.15
multiple bonds in modern synthetic chemistry.1 Evolving from
phosphane complexes2 toward N-heterocyclic carbenes3 and
benzylidene ligands bearing chelating arms of oxygen,4 sulfur,5
nitrogen,6 phosphorus,7 and selenium,8 the class of catalysts is
still a subject for development by both conceptual and trial and
error attempts. The parent o-isopropoxy-substituted benzyli-
dene complex 1, introduced by Hoveyda,4a was developed in
numerous ways, and structure−activity correlations effecting
diminished activity (latent systems)9 and improved perform-
ance10,11 were discovered. Although the detailed mechanistic
picture is complicated, it is believed that the family of ether-
chelated complexes (1 and 2; Chart 1)12 is characterized by an
olefin-dependent rate-determining initiation process, where
active 14-electron species are released and propagate in
Following these efforts,4b,c the nitro derivative 2, displaying
fast initiation behavior, was introduced by Grela.10 The
withdrawing properties of the nitro group present in the
position para to the iPrO substituent were postulated to
facilitate dissociation of the chelate ring by reducing electron
density on the coordinating oxygen atom. In turn, an improved
activity of the ortho-substituted complex 3 was explained by
steric effects which cause an out-of-plane distortion of the
isopropyl substituent and destabilization of the Ru···O bond.11
A different picture was presented by Barbasiewicz and Grela et
al.,9 in systematic studies of the naphthalene-based complexes
4. Striking activity differences between the isomeric catalysts
were observed in the model metathesis reactions of N,N-
diallyltosylamine, where the complex 4b initiated at 0 °C while
4a,c required refluxing toluene (111 °C) to give a similar
activity profile. This observation inspired the synthesis of
related polycyclic complexes and led to the conclusion that the
effect can be attributed to the degree of cyclic electron
delocalization in the chelate rings controlled by the topology of
ligands. In a way similar to that for polyaromatic hydrocarbons,
phenanthrene (5) and anthracene (6) differ with respect to
their π-electron distribution; complexes 4 assembled on the
naphthalene core in an angular (variants I and II) or linear
(variant III) fashion, differ in the properties of the chelate rings
(Chart 2).
Chart 1. Selected Metathesis Catalysts Bearing a Chelating
iPrO Group
According to the Clar rule9 the electronic structure of
phenanthrene consists of highly aromatic external rings with
completed electron sextets and an “empty” character of the
middle ring with a double-bond-like character of the C9−C10
Received: January 23, 2012
Published: March 26, 2012
© 2012 American Chemical Society
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alcohol 12 was oxidized with PCC and subjected to the Wittig
reagent in two variants, as presented in Scheme 1.
Chart 2. (a) Isoelectronic Six-π-Electron Systems, Chelate
Ring of Ruthenium Complexes, Furan, and Benzene, and (b)
Complexes Assembled on the Naphthalene Core Inheriting
the π-Electron Properties of the Corresponding Tricyclic
Aromatic Hydrocarbons Phenanthrene (5), Anthracene (6),
and Pleiadiene (7), in Which the Degree of Cyclic Electron
a
Scheme 1. Synthesis of Ligands 8a,b
a
Delocalization in Bold Fragments Decreases in a Series9
a
Legend: (a) NH2OH, TsCl, py; 10 (64%), ref 19; (b) NaOH, H2O,
then NaNO2, HCl, heating, 11 (70%), ref 19; (c) DIBAL, THF, then
HCl; (d) iPrBr, K2CO3, DMF, 12 (80%, in two steps from 11); (e)
PCC, CH2Cl2, 13 (97%); (f) Ph3PCHRBr, t-PeOK/toluene, THF,
96% for R = H (8a), 88% for R = CH3 (8b). DIBAL =
diisobutylaluminium hydride.
Next, the synthesis of complex 14 was attempted under
ligand exchange conditions with the Grubbs second-generation
catalyst 15 and CuCl as a phosphine scavenger (Scheme 2).20
Scheme 2. Synthesis of the Complex 14
a
NHC = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene.
bond. Thus, the angular orientation of the chelate assembled on
the naphthalene framework in complexes 4a,c, similar to that
found in 5 (Chart 2, variants I and II), results in increased
aromatic properties and stabilization of the chelate. In turn, the
linear isomer 4b, related to anthracene (variant III), displays
activity similar to that of the parent Hoveyda−Grubbs complex
1. This is attributed to the properties of 6, for which only one
electron sextet can be completed, and is considered as
“migrating” among three positions, providing only a fraction
of aromatic stabilization per ring. However, a simple analysis of
the naphthalene molecule allows us to distinguish another
assembly of coordinating sites required to form the chelate.
While complexes 4, related to variants I−III, were described
earlier,9 we wondered about a missing isomer16,17 featuring a
peri substitution18 of the naphthalene core with the
coordinating sites placed at different rings (variant IV). The
synthesis and properties of an isomeric Hoveyda−Grubbs type
ruthenium complex bearing a 1,8-substituted naphthalene
ligand (14) are presented in this report.
At the beginning, we synthesized ligand 8 in five steps
starting from desymmetrization of the commercially available
1,8-naphthalic anhydride 9 via a Beckmann rearrangement to
form lactam 10.19 The product was hydrolyzed and diazotized
with sodium nitrite solution to afford lactone 11.19 Then the
lactone was reduced with DIBAL, and the phenolic oxygen
atom was alkylated with isopropyl bromide in a one-pot
procedure to afford 1-hydroxymethyl-8-isopropoxynaphthalene
(12) in 80% yield after chromatographic purification. Then the
In both cases, when starting from styrenes 8a,b, the ruthenium
complex 14 was obtained in practically the same yield: 47 and
44%, respectively. Surprisingly, an alternative protocol17 with
the indenylidene catalyst 1621 at higher temperature, followed
by flash chromatography and crystallization, gave 14 as a green
microcrystalline powder in very good yield: 70%. The complex
was stable as a solid but decomposed slowly in solution at room
temperature in air.
Complex 14 was characterized by 1H and 13C NMR
spectroscopy, IR, and HRMS (ESI).22 NMR data suggested
differences from the parent Hoveyda−Grubbs complex 1,
manifested23 by an abnormal deshielding of the benzylidene
proton and carbon atoms appearing at 18.66 and 313.8 ppm
(CD2Cl2), respectively, as compared to 16.56 and 296.8 ppm in
1 (CDCl3).4a,24 Further structural insights were available from
X-ray studies.25
The complex 14 crystallized in the monoclinic C2 space
group with two molecules in the asymmetric unit. More
detailed information on the refinement of this structure can be
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Table 1. Selected Bond Lengths (Å) of Complexes 1,27 2,9
found in the Supporting Information. In general the molecules
have similar structural parameters, and the final conclusions
apply to both of them. The Ortep representation26 of one
arbitrarily chosen molecule in two projections is presented in
Figure 1. The side view (presented on the left) depicts the
a
4a,9 and 14
bond
14
29
127
4a9
Ru−O
2.253(3)/
2.237(3)
2.287(1)/
2.258(1)
2.256(1)
2.228(1)
RuC
1.820(4)/
1.815(4)
1.825(2)/
1.828(2)
1.829(1)
1.448(2)
1.370(2)
1.833(2)
1.439(2)
1.377(2)
C−CAr 1.457(7)/
1.448(3)/
1.457(3)
1.454(7)
iPrO−CAr 1.406(6)/
1.368(2)/
1.363(2)
1.396(6)
a
Values separated with a slant correspond to parameters of two
molecules present in the asymmetric unit. The RuC bond length
increases and CH−C bond length decreases in the order 14 → 2 →
1 → 4a.
cyclic electron delocalization rather by the simple strength of
the Ru···O interaction.14 Thus, complex 14 was expected to
display a fast initiation behavior associated with reduced
electron delocalization of the benzylidene chelate.
To verify this hypothesis, we tested complex 14 in two
benchmark RCM reactions and compared its activity with that
of complexes 1, 2, and 4a,b (Figure 2).
Figure 1. ORTEP26 drawings of the complex 14 molecule, represented
by thermal ellipsoids drawn at the 50% probability level (one arbitrary
molecule present in asymmetric unit is shown). Selected bond lengths
(Å) are presented in Table 1.
In accordance with the data reported previously, complex 4a,
bearing a chelate ring assembled on naphthalene in an angular
fashion, remained inactive at 25 °C (the activity of complex 4c
is expectedly the same).9 In turn, complexes 1, 2,10 and 4b
initiated easily, with the nitro catalyst (2) being superior to
both the parent Hoveyda complex (1) and the linear
naphthalene derivative (4b). Expectedly, the complex 14
displayed an excellent activity and at the beginning of reactions
initiated even more quickly than the nitro complex 2. Thus, the
observed initiation rates of the three isomeric naphthalene-
based complexes 4a (blue triangles), 4b (yellow squares), and
14 (red squares) spanned a very wide range from latency
attributed to aromatic stabilization of the chelate in 4a to
overactivity of the complex 14, which suffered from diminished
stability and deactivated at ca. 75% of the substrate conversion
in both cases. Despite the limited stability displayed by catalyst
14, which makes it unsuitable for regular applications,29 the
results of activity studies may give valuable conclusions about
electronic effects present in the chelates. To correlate structural
parameters of 14 with the observed activity, we focused on two
effects: (1) distortion of the molecular structure of the chelate
which possibly weakens the Ru···O coordination and
suppresses cyclic π-electron conjugation as a consequence of
less efficient overlapping of orbitals and (2) suppression of the
cyclic electron delocalization in the chelate controlled by the
structure of the peri-substituted naphthalene ligand, following
the trends demonstrated earlier for complexes 4a−c.9,14
However, the first issue cannot be simply quantified; we
assume that the curvature of the chelate ring, the twist of the
benzylidene RuCH bond, and disturbance of the ruthenium
geometry may facilitate olefin approach and accelerate the
initiation step.13,30 To discuss the latter effect, a short
introduction on the properties of peri-substituted naphthalenes
is required. The peri substitution of the naphthalene core acts
as a clamping framework in which substituents are forced into
close proximity ideally at a distance of ca. 2.5 Å, much shorter
than the separation present in ortho-substituted benzenes (3.1
Å).18 In contrast to chelates represented by variants I−III
(Chart 2) which display strong or moderate π-electron
delocalization, positions 1 and 8 of the naphthalene molecule
complex geometry, which is similar to that of the related
ruthenium complexes 1, 2, and 4. Some interesting structural
properties are noticeable in a front view projection (presented
on the right), oriented along the axis of the benzylidene Ru
CH bond. The chelating ligand is evidently tilted away from the
plane constituted by atoms coordinated directly to the
ruthenium atom: imidazolin-2-ylidene carbon C41, benzylidene
carbon C62, and oxygen O2. The torsion angle C41−Ru−
C62−C63 is reduced from 170.3(1)° in 127 to 153.9(4)°
(−142.4(4)° in the second molecule). The oxygen atom is
slightly out of plane, giving a sum of valence angles around it of
354.3° (356.6°), and the ruthenium atom is pushed out of the
chelate ring plane (C62−C63−C71−C70−O2) by about 0.607
Å (0.738 Å). Breaking of the Cs symmetry is also evident from
the diverse bond lengths to chlorine atoms, ranging from
2.380(1) Å for Ru(1)−Cl(1) to 2.342(1) Å for Ru(1)−Cl(2)
(2.394(1) and 2.350(1) Å for the second molecule). The
observed structural oddities most probably arise from the
unique properties of the peri substitution of the naphthalene
core, substituents of which are forced into close proximity and
oriented in a parallel manner.18 Thus, the six-membered chelate
in complex 1428 must adopt an envelope conformation to
minimize the strain of valence angles (RuCH−CAr and CAr−
iPrO···Ru), and in addition the naphthalene core deplanarizes
by about 12° (C62−C63−C70−O2, torsion angle in both
molecules), opening the gap between coordination sites of the
ligand.
However, even more interesting conclusions can be drawn
from an analysis of the structure of the chelate ring of the
complex 14 and comparison with other Hoveyda-type
complexes. Interesting trends concerning the RuC and 
C−CAr bond lengths were observed within the series 14, 2, 1,
4a (Table 1). The benzylidene RuCH bond elongates, while
the adjacent CH−CAr bond gradually contracts, thus
indicating an increase of the π-electron delocalization and
concomitant equalization of the bond orders within the
chelate.9 As demonstrated by recent theoretical treatments by
Solans-Monfort et al., the key parameter responsible for the
initiation rate of the chelated systems is the length of the 
CH−CAr bond. This bond length is controlled more by the
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1
Figure 2. Reaction profiles of the ring-closing metathesis determined by H NMR: (left) diethyl diallylmalonate (0.5 mol % of catalyst, 25 °C,
CD2Cl2, 0.2 M concentration of substrate); (right) diethyl allylmethallylmalonate (1.0 mol % of catalyst, 25 °C, CD2Cl2, 0.2 M concentration of
substrate).
Figure 3. HOMA34 values calculated for the structures of phenanthrene (5), anthracene (6), pleiadiene (cyclohepta[d,e]naphthalene, 7), isomeric
naphthofurans (17−19), and naphtho[1,8-b,c]pyran (20) optimized with B3LYP/6-311+G(d,p) and nuclear independent chemical shift (NICS)35
values calculated with the GIAO method at the same level.36 X-ray structural data of 7 were taken from ref 32.
seem to be electronically isolated. In the model aromatic
hydrocarbon pleiadiene (7), related to variant IV, the
unsaturated carbon linker (−CHCH−CHCH−), con-
necting peri positions, displays a large bond length alternations
and weakly disturbs the electronic structure of naphthalene.
The isolated character of the diene fragment in 7 was further
supported by theoretical,31 structural,32 and reactivity studies, in
which a Diels−Alder reaction of the diene fragment with maleic
anhydride was demonstrated.33 Thus, in the series of the
catalysts 4a,b and 14, corresponding to a series of tricyclic
hydrocarbons (5−7; Chart 2), electronic delocalization within
the conjugated chelates gradually decreases. In complex 14 it is
even lower than in the parent Hoveyda complex (1), which is
manifested in a higher rate of initiation of the (pre)catalyst. To
support our hypothesis and better assess the π-electron
properties of the chelate rings, we calculated structural and
magnetic properties of isoelectronic model molecules: hydro-
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organic phases were washed with brine and dried with MgSO4. The
mixture was filtered and evaporated in a flask. To the residue were
added 2-bromopropane (6.179 g; 50.2 mmol), K2CO3 (6.91 g; 50.0
mmol), and DMF (25 mL), and the mixture was stirred at 60 °C for
48 h in air. The mixture was poured into water (150 mL) and
extracted with ethyl acetate (3 × 80 mL). The combined organic
phases were washed with brine (100 mL) and dried with MgSO4. The
mixture was filtered, evaporated, and separated with column
chromatography (300 mL of silica; cyclohexane/ethyl acetate 4/1 to
2/1) to give 12 (1.739 g; 8.04 mmol; 80%) as a yellowish oil.
carbons (5−7) and heterocycles represented by naphthofurans
(17−19) and naphtho[1,8-bc]pyran (20) (Figure 3).
The π-electron delocalization in the model compounds was
studied with magnetic and structural aromaticity indexes and
compared with the energetic properties of ruthenium chelates
attributed to the catalytic activity. The structural data of the
model compounds were analyzed with the HOMA (harmonic
oscillator model of aromaticity)34 parameter, which is a
measure of bond length alternation in conjugated structures.
The HOMA values are defined as 0 for the hypothetical
1
Data for 12 are as follows. H NMR (200 MHz, CDCl3): δ 7.69−
7.79 (m, 1H), 7.46 (dd, J = 8.0, 1.5 Hz, 1H), 7.32−7.43 (m, 3H),
6.90−6.96 (m, 1H), 5.06 (s, 2H), 4.87 (sept, J = 2.0 Hz, 1H), 3.38 (s
br, 1H), 1.50 (d, J = 2.0 Hz, 6H). 13C NMR (50 MHz, CDCl3): δ
153.5, 136.8, 136.5, 128.7, 128.0, 125.8, 125.5, 124.5, 121.8, 107.9,
70.8, 67.1, 21.8. MS (EI, m/z, relative intensity): 216 (M•+, 28), 174
(9), 156 (100), 128 (37), 127 (34), 115 (19). Anal. Calcd for
C14H16O2: C, 77.75; H, 7.46. Found: C, 77.73; H, 7.27.
́
cyclohexatriene molecule (Kekule resonance form) and 1 for
the equalized structure of benzene. In the hydrocarbon series
(5−7) the HOMA values of external rings (which correspond
to chelate rings in ruthenium complexes 4 and 14) decrease in
the series +0.87, +0.63, and +0.09, suggesting a large alternation
of bond lengths in the seven-membered ring of 7. Similar
results apply to the heterocyclic series (17−20) and only the
last two structures (19 and 20) display a slightly reversed trend
(+0.14/+0.12; −0.06; +0.05).37 In turn, magnetic properties
expressed by the nucleus independent chemical shift35 values
(NICS, calculated at and 1 Å above the molecular plane of
rings, abbreviated as NICS(0) and NICS(1), respectively)
suggest a gradual change in both series, from the aromatic
properties of external rings of phenanthrene (5; −8.5, −10.7),
naphtho[2,1-b]furan (17; −10.0, −8.6) and naphtho[1,2-
b]furan (18; −9.9, −8.7) toward antiaromatic properties in
pleiadiene (7; +13.9, +8.7) and naphtho[1,8-b,c]pyran (20;
+2.6, +6.5). In general, the aromaticity indexes indicate that
both unsaturated 4π linkers (−CHCH−CHCH− and
−O−CHCH−) binding the peri positions of naphthalene
form rings with suppressed π-electron delocalization and
destabilizing (antiaromatic) properties.38 The same properties
are thus expected for the chelate ring of the catalyst 14, and in
fact the observed activity of complexes 4 and 14 correlate with
properties of the calculated structures. According to our
aromaticity-controlled initiation concept9 the rate-determining
initiation process of the Hoveyda-type catalysts includes
opening of the chelate ring; thus, factors related to stabilization
of the chelates can control the catalyst activity over a broad
range, as was demonstrated for the family of naphthalene-based
complexes.
Synthesis of 13. A flask was charged with 12 (1.739 g; 8.04 mmol)
and CH2Cl2 (150 mL). To the solution was slowly added PCC (2.085
g; 9.67 mmol). The mixture was stirred under air overnight and then
filtered through a pad of silica and eluted with CH2Cl2. After
evaporation 13 was obtained (1.665 g; 7.77 mmol; 97%) as a pale
orange oil, which slowly solidified.
1
Data for 13 are as follows. Mp: 59−61 °C. H NMR (200 MHz,
CDCl3): δ 11.12 (s, 1H), 7.94 (dd, J = 8.0, 1.2 Hz, 1H), 7.85 (dd, J =
1.4, 7.2 Hz, 1H), 7.36−7.55 (m, 3H), 6.97 (dd, J = 1.8, 6.8 Hz, 1H),
4.78 (sept, J = 6.0 Hz, 1H), 1.44 (d, J = 6.0 Hz, 6H). 13C NMR (50
MHz, CDCl3): δ 195.6, 154.1, 135.5, 135.4, 132.9, 127.0, 126.5, 125.6,
124.1, 121.0, 108.6, 71.4, 22.0. MS (EI, m/z, relative intensity): 214
(M•+, 22), 172 (100), 155 (14), 144 (10), 115 (56). Anal. Calcd for
C14H14O2: C, 78.48; H, 6.59. Found: C, 78.25; H, 6.50.
Synthesis of 8a. A flask was charged with methyltriphenylphos-
phonium bromide (0.977 g; 2.73 mmol) and THF (25 mL), and a
solution of potassium tert-amylate (2 mL; 3.4 mmol; 1.7 M solution in
toluene) was added dropwise with stirring. After 15 min the resulting
yellowish suspension was cooled with an ice−water bath and a solution
of 13 (0.484 g; 2.26 mmol) in THF (5 mL) was added dropwise. The
cooling bath was removed, and after 1 h an aqueous solution of NH4Cl
(50 mL, 10% w/w) was added. The mixture was extracted with ethyl
acetate (3 × 50 mL), and the combined organic phases were washed
with brine (50 mL) and dried with MgSO4. The mixture was filtered
and evaporated, and the residue was separated with column
chromatography (150 mL of silica; cyclohexane/ethyl acetate 10/1)
to give 8a (0.460 g; 2.17 mmol; 96%) as a colorless oil.
1
Data for 8a are as follows. H NMR (200 MHz, CDCl3): δ 8.06
In conclusion, we synthesized a missing member of the
naphthalene-based family of the Grubbs−Hoveyda complexes.
In contrast to the naphthalene-based complexes 4, it displays a
very fast initiation behavior, attributed to distorted geometry
around the ruthenium atom and suppressed π-electron
delocalization of the chelate ring. On the basis of the
aromaticity-controlled activity concept,9 the peri-substituted
complex 14 represents a weakly stabilized chelate and extends
the scale of initiation rates controlled by ligand topology toward
systems more active than the parent Hoveyda−Grubbs
complex.
(dd, J = 10.8, 17.4 Hz, 1H), 7.79 (dd, J = 2.0, 7.8 Hz, 1H), 7.36−7.56
(m, 3H), 6.92 (dd, J = 1.6, 7.2 Hz, 1H), 5.48 (dd, J = 2.0, 17.4 Hz,
1H), 5.28 (dd, J = 2.0, 10.8 Hz, 1H), 4.75 (sept, J = 6.0 Hz, 1H), 1.50
(d, J = 2.0 Hz, 6H). 13C NMR (50 MHz, CDCl3): δ 155.2, 141.8,
137.2, 135.9, 128.0, 126.0, 125.8, 125.6, 124.2, 120.8, 112.7, 108.2,
70.9, 21.9. MS (EI, m/z, relative intensity): 212 (M•+, 29), 170 (21),
155 (100), 139 (8), 127 (9), 115 (6). Anal. Calcd for C15H16O: C,
84.87; H, 7.60. Found: C, 84.95; H, 7.73.
Synthesis of 8b. A flask was charged with ethyltriphenylphos-
phonium bromide (1.788 g; 4.82 mmol) and THF (30 mL), and a
solution of potassium tert-amylate (3.6 mL; 6.1 mmol; 1.7 M solution
in toluene) was added dropwise with stirring (cooling with a water
bath was applied to avoid warming). After 20 min the resulting orange
suspension was cooled with an ice−water bath and a solution of 13
(0.858 g; 4.00 mmol) in THF (6 mL) was added dropwise. The
cooling bath was removed, and after 1 h an aqueous solution of NH4Cl
(25 mL; 10% w/w) was added. The mixture was extracted with ethyl
acetate (3 × 75 mL), and the combined organic phases were washed
with brine (100 mL) and dried with MgSO4. The mixture was filtered
and evaporated, and the residue was separated with column
chromatography (250 mL of silica; cyclohexane/ethyl acetate 10/1)
to give 8b (0.797 g; 3.52 mmol; 88%) as a pale yellow oil.
EXPERIMENTAL SECTION
General methods are detailed in the Supporting Information.
■
Synthesis of 12. A Schlenk flask was charged with lactone 11
(1.703 g; 10.01 mmol) and THF (20 mL) and cooled with an ice−
water bath. A solution of DIBAL (21 mL; 21 mmol; 1.0 M solution in
toluene) was added dropwise with stirring. After 15 min the cooling
bath was removed, and after 30 min MeOH (5 mL) was added slowly
and the cooling bath was applied again (slight exothermic effect). The
mixture had gelated. Ethyl acetate (50 mL) and aqueous HCl (30 mL;
1/5 v/v) were added, and the phases were separated. The aqueous
phase was extracted with ethyl acetate (100 mL), and the combined
Data for 8b, as a mixture of E/Z isomers (ca. 1/1), are as follows.
1H NMR (200 MHz, CDCl3): δ 7.66−7.75 (m, 2H), 7.58−7.63 (m,
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1H), 7.22−7.48 (m, 9H), 6.83−6.91 (m, 2H), 5.63−5.91 (m, 2H),
4.60−4.80 (m, 2H), 1.97 (dd, J = 1.8, 6.6 Hz, 3H), 1.77 (dd, J = 1.8,
7.0 Hz, 3H), 1.47 (d, J = 6.0 Hz, 6H), 1.43 (d, J = 6.0 Hz, 6H). 13C
NMR (50 MHz, CDCl3): δ 155.4 (ovl), 137.0, 136.1, 136.0, 135.7,
134.5, 134.3, 128.1, 127.2, 127.0, 125.9, 125.8, 125.53, 125.48, 125.3
(ovl), 124.4, 123.8, 121.2, 120.9, 120.8, 108.3, 108.2, 70.9, 70.8, 22.1,
21.9, 18.5, 14.0. MS (EI, m/z, relative intensity): 226 (M•+, 28), 184
(24), 168 (11), 155 (100), 139 (7), 127 (11). Anal. Calcd for
C16H18O: C, 84.91; H, 8.02. Found: C, 84.71; H, 7.85.
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Synthesis of 14. A Schlenk flask was charged with 8b (0.274 g,
1.21 mmol), toluene (20 mL), CuCl (0.149 g; 1.51 mmol), and 16
(0.948 g, 1.00 mmol) and placed in a preheated oil bath at 80 °C with
stirring. After 20 min the heating bath was removed, most of the
solvent was removed in vacuo, and the residue was placed as a
suspension in a small volume of ethyl acetate on the top of a
chromatographic column (300 mL of silica) and eluted with gradually
changing mixture of cyclohexane and ethyl acetate (6/1 to 1/2). The
first yellowish red fractions were removed, and a green band was
collected (the green product slowly dissolved and was desorbed from
silica). Solvent was evaporated, the residue was dissolved in CH2Cl2 (9
mL), and MeOH (9 mL) was added. Most of the solvents were slowly
removed by evaporation at 220 mbar.39 The resulting suspension was
filtered on a small Schott filter, washed with MeOH (3 × 3 mL), and
dried in vacuo to give 14 (0.477 g; 0.70 mmol; 70%), as a green
microcrystalline solid.
A.; Makal, A.; Wozniak, K.; Kadyrov, R.; Grela, K. Organometallics
́
̇
2009, 28, 2693−2700. (g) Szadkowska, A.; Zukowska, K.; Pazio, A. E.;
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́
1138.
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Organometallics 2006, 25, 3599−3604. (b) Tzur, E.; Szadkowska, A.;
1
Ben-Asuly, A.; Makal, A.; Goldberg, I.; Wozniak, K.; Grela, K.;
́
Data for 14 are as follows. H NMR (500 MHz, CH2Cl2): δ 18.66
̇
Lemcoff, N. G. Chem. Eur. J. 2010, 16, 8726−8737. (c) Zukowska, K.;
(s, 1H), 8.11 (d, J = 7.6 Hz, 1H), 7.55 (d, J = 8.0 Hz, 1H), 7.33 (dd, J
= 8.0, 8.0 Hz, 1H), 7.29 (dd, J = 7.6, 7.6 Hz, 1H), 7.21 (d, J = 8.1 Hz,
1H), 7.08 (s, 4H), 6.67 (d, J = 7.1 Hz, 1H), 5.09 (sept, J = 6.3 Hz,
1H), 3.97−4.18 (m, 4H), 2.63 (s, 6H), 2.49 (s, 3H), 2.38 (s, 3H), 2.31
(s, 6H), 2.16 (d, J = 6.3 Hz, 6H). 13C NMR (125 MHz, CD2Cl2): δ
313.8, 210.1, 152.2, 144.9, 140.4, 139.5, 138.9, 138.1, 137.9, 137.8,
134.9, 131.4, 130.1, 129.8, 126.85, 126.83, 124.3, 122.5, 120.1, 112.5,
79.5, 52.7, 50.9, 21.1, 20.5, 19.9, 18.3. IR (KBr, cm−1): 2912, 1606,
1555, 1503, 1479, 1416, 1379, 1264, 1236, 1221, 1171, 1129, 1089,
1031, 906, 852, 834, 740, 579, 422. HRMS (ESI, m/z): calcd for
C35H40ClN2ORu 641.1873, found 641.1877 (M − Cl)•+. Anal. Calcd
for C35H40Cl2N2ORu: C, 62.12; H, 5.96; N, 4.14. Found:22 C, 60.40;
H, 5.85; N, 3.78.
Szadkowska, A.; Pazio, A. E.; Wozniak, K.; Grela, K. Organometallics
́
2012, 31, 462−469.
(7) Lexer, C.; Burtscher, D.; Perner, B.; Tzur, E.; Lemcoff, N. G.;
Slugovc, C. J. Organomet. Chem. 2011, 696, 2466−2470.
(8) Diesendruck, C. E.; Tzur, E.; Ben-Asuly, A.; Goldberg, I.; Straub,
B. F.; Lemcoff, N. G. Inorg. Chem. 2009, 48, 10819−10825.
(9) Barbasiewicz, M.; Szadkowska, A.; Makal, A.; Jarzembska, K.;
Wozniak, K.; Grela, K. Chem. Eur. J. 2008, 14, 9330−9337.
́
(10) (a) Grela, K.; Harutyunyan, S.; Michrowska, A. Angew. Chem.,
Int. Ed. 2002, 41, 4038−4040. (b) Michrowska, A.; Bujok, R.;
Harutyunyan, S.; Sashuk, V.; Dolgonos, G.; Grela, K. J. Am. Chem. Soc.
2004, 126, 9318−9325.
(11) Wakamatsu, H.; Blechert, S. Angew. Chem., Int. Ed. 2002, 41,
2403−2405.
ASSOCIATED CONTENT
■
(12) Vorfalt, T.; Wannowius, K.-J.; Plenio, H. Angew. Chem., Int. Ed.
2010, 49, 5533−5536.
S
* Supporting Information
Text, figures, tables, and CIF files giving NMR spectra for
compounds 8a,b and 12−14, experimental procedures for the
synthesis of 10 and 11, a complete modeling program citation,
and crystallographic data for compounds 14 and 21. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(13) Thiel, V.; Hendann, M.; Wannowius, K.-J.; Plenio, H. J. Am.
Chem. Soc. 2012, 134, 1104−1114.
(14) Solans-Monfort, X.; Pleixats, R.; Sodupe, M. Chem. Eur. J. 2010,
16, 7331−7343.
(15) The assumption is valid until structure of substrates and reaction
conditions do not cause a change of the rate-determining step. For
structural variations of NHC ligands, which influence properties of
propagating species, see ref 3.
AUTHOR INFORMATION
■
(16) Prof. Christian Slugovc (Graz University of Technology) called
the isomeric complexes 4a−c “unequal siblings” to emphasize their
activity differences in ring-opening metathesis polymerization
(ROMP).17 Obviously, our isomeric complex 14 represents still
another relative of the family, missing until now.
(17) Leitgeb, A.; Szadkowska, A.; Michalak, M.; Barbasiewicz, M.;
Grela, K.; Slugovc, Ch. J. Pol. Sci. A: Polym. Chem. 2011, 49, 3448−
3454.
Corresponding Author
*E-mail: barbasiewicz@chem.uw.edu.pl. Web: http://www.
aromaticity.pl/.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(18) (a) Kilian, P.; Knight, F. R.; Woollins, J. D. Chem. Eur. J. 2011,
17, 2302−2328. (b) Kilian, P.; Knight, F. R.; Woollins, J. D. Coord.
Chem. Rev. 2011, 255, 1387−1413.
■
This work was financed by the Polish Ministry of Science and
Higher Education (Grant No. N N204 152436). M.B. thanks
Prof. Karol Grela for support and the opportunity to perform
an independent research program in the field.
̈
(19) Cammidge, A. N.; Ozturk, O. J. Org. Chem. 2002, 67, 7457−
̈
7464.
(20) Zaja, M.; Connon, S. J.; Dunne, A. M.; Rivard, M.; Buschmann,
N.; Jiricek, J.; Blechert, S. Tetrahedron 2003, 59, 6545−6558.
(21) For the synthesis of complex 16, see: (a) Monsaert, S.;
Drozdzak, R.; Dragutan, V.; Dragutan, I.; Verpoort, F. Eur. J. Inorg.
Chem. 2008, 432−440. (b) Monsaert, S.; De Canck, E.; Drozdzak, R.;
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Organometallics
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(22) Unfortunately, we were unable to obtain a satisfactory
elementary analysis for complex 14.
influences the structure of the naphthalene core, we determined the
structure of 8-hydroxymethyl-1-naphthol (21; intermediate of syn-
thesis of compound 9) by X-ray methods and compared it with that of
complex 14. See the Supporting Information for details.
(39) The evaporation process is a trigger for crystallization; thus,
rotation on a rotary evaporator should be very slow and no heating
bath should be applied. The whole crystallization process takes ca. 2 h,
when most the solvent slowly evaporates and the flask is cold.
(23) In complex 14 the presence of four methyl resonances (in a
2:1:1:2 ratio) of the NHC ligand was observed. For a detailed
discussion of the conformational landscape of similar complexes, see:
Kotyk, M. W.; Gorelsky, S. I.; Conrad, J. C.; Carra, C.; Fogg, D. E.
Organometallics 2009, 28, 5424−5431 and references cited therein.
(24) The strong deshielding of the RuCH− fragment can be
rationalized by reduced overlapping of ruthenium and carbon p-type
orbitals caused by a distortion (twist) of the benzylidene double bond
and close proximity to the aromatic ring of the NHC ligand, in
comparison with the case for complex 1. Reduced π-electron
delocalization between peri positions of naphthalene in complex 14
should cause the opposite effect, however.
(25) Crystals suitable for diffraction experiments were obtained by
layering 0.2 mL of a CH2Cl2 solution of complex 14 (0.015 g) with
MeOH (0.6 mL) in an NMR tube at low temperature (−20 °C).
(26) We wish to acknowledge the use of a free version of Ortep-3 for
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565.
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Thiel, O. R.; Lehmann, C. W. Organometallics 2002, 21, 331−335.
(29) However, complex 14 deactivated within minutes during the
metathesis reaction when tested in nondegassed CD2Cl2 solutions; the
same solution without added olefin was much more stable, and 14 was
detected by TLC after 5 days, on storage at room temperature in air.
See the Supporting Information for details.
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Vincent, M. A. Chem. Commun. 2011, 47, 5428−5430.
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(36) All the calculations were performed using Gaussian 03 on a PC/
Linux workstation: Gaussian 03, Revision E.01; Gaussian, Inc.,
Wallingford, CT; 2004 (for the complete citation see the Supporting
Information). Structures of compounds 5−7 and 17−19 were
optimized using B3LYP with the 6-311+G(d,p) basis set. Only real
values of the analytical harmonic vibrational frequencies confirmed
that the geometries under study correspond to the minimum-energy
structures.
(37) HOMA and NICS values calculated at the same level of theory
for benzene and furan molecules are as follows: benzene, HOMA =
+0.99, NICS(0) = −8.0, NICS(1) = −10.2; furan, HOMA = +0.19,
NICS(0) = −11.9, NICS(1) = −9.4. In the pyran molecule cyclic
electron conjugation is lacking (it is fully conjugated in annulated
system 20 only). Negative values of the HOMA parameter correspond
to systems in which bond alternation is larger than in the model
cyclohexatriene. Negative NICS values correspond to diatropic ring
currents (aromatic), while positive values correspond to paratropic
ring currents (antiaromatic).
(38) Structural distortion of the chelate ring of complex 14 may arise
from its destabilizing (antiaromatic) properties. From the other side
formation of the ring should cause structural changes of the
naphthalene framework. To examine how the formation of the chelate
3177
dx.doi.org/10.1021/om300052b | Organometallics 2012, 31, 3171−3177