Comparative investigation of ruthenium-based metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands

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Comparative Investigation of Ruthenium-Based Metathesis Catalysts Bearing

N-Heterocyclic Carbene (NHC) Ligands

Alois Fürstner,* Lutz Ackermann, Barbara Gabor, Richard Goddard,

Christian W. Lehmann, Richard Mynott, Frank Stelzer, and Oliver R. Thiel^[a]

Abstract: Exchange of one PCy₃unit of

the classical Grubbs catalyst 1 by N-het-

erocyclic carbene (NHC) ligands leads

to ªsecond-generationº metathesis cata-

lysts of superior reactivity and increased

stability. Several complexes of this type

have been prepared and fully character-

ized, six of them by X-ray crystallogra-

phy. These include the unique chelate

complexes 13 and 14 in which the NHC-

tivity of such catalysts can be easily

adjusted by changing the electronic and

steric properties of the NHC ligands.

The catalytic activity also strongly de-

pends on the solvent used; NMR inves-

tigations provide a tentative explanation

of this effect. Applications of the ªsec-

ond-generationº catalysts to ring closing

alkene metathesis and intramolecular

enyne cycloisomerization reactions pro-

vide insights into their catalytic perform-

ance. From these comparative studies it

is deduced that no single catalyst is

optimal for different types of applica-

tions. The search for the most reactive

catalyst for a specific transformation is

facilitated by IR thermography allowing

a rapid and semi-quantitative ranking

among a given set of catalysts.

Keywords: carbenes

´ imidazol-2-

and the Ru CR entities are tethered to

ylidenes ´ IR thermography ´ meta-

thesis ´ ruthenium

form a metallacycle. A particularly fa-

vorable design feature is that the reac-

Introduction

N

PCy₃

Ru

N

The seminal discovery of

Grubbs that ruthenium car-

bene complexes of type 1 con-

stitute well defined and highly

efficient metathesis pre-cata-

lysts tolerating an array of

Cl

Ru

Ph

Ru

Ph

PCy₃

Ph

PCy₃

1

2

3

little tendency to dissociate from the metal center.^[10]Since

they can be easily endowed with sterically demanding

substituents on their N-atoms, they are able to stabilize the

catalytically relevant intermediates by electronic and steric

means against uni- as well as bimolecular decomposition

pathways. These properties translate into catalysts of greatly

improved reactivity as well as higher stability which outper-

form the parent-complex 1 in many cases. Successful appli-

cations to the formation of tetrasubstituted cycloalkenes,^{[8, 9]}

to ring closing- and cross metathesis reactions of acryl-

ates,^{[11, 12]}to cyclizations of conformationally handicapped

dienes and various natural product syntheses highlight this

notion.^{[13, 14]}Therefore, it is reasonable to anticipate that

NHC-containing ruthenium complexes will set new standards

in this still rapidly expanding field.

functional groups has triggered an avalanche of interest in

this transformation.^{[1, 2]}This groundbreaking development has

inspired many studies aiming at improving access to these

exceedingly useful reagents,^[3]at gaining a deeper under-

standing of their mechanism of action,^[4]at developing

equipotent alternatives,^[5]and at designing catalysts with an

even better application profile.^[6]In this context it is notable

that three independent and almost simultaneous publications

on ªsecond-generationº metathesis catalysts report com-

plexes in which one of the PCy₃groups of 1 is replaced by

an N-heterocyclic carbene (NHC).^[7±9]NHCs are particularly

strong s-donor- but very poor p-acceptor ligands which show

[a] Prof. Dr. A. Fürstner, Dipl.-Chem. L. Ackermann, B. Gabor,

Dr. R. Goddard, Dr. C. W. Lehmann, Dr. R. Mynott,

Dipl.-Chem. F. Stelzer, Dipl.-Chem. O. R. Thiel

Max-Planck-Institut für Kohlenforschung

45470 Mülheim/Ruhr (Germany)

The studies on NHC-containing catalysts reported so far,

however, gravitate toward complexes 2 and 3 bearing

identical substituents on both N-atoms of their saturated or

unsaturated NHC rings.^[15]Herein we report a more compre-

Fax : (49)208-306-2994

E-mail: fuerstner@mpi-muelheim.mpg.de

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Chem. Eur. J. 2001, 7, No. 15

3236±3253

hensive investigation on the preparation, structure, and

reactivity of such ªsecond-generationº metathesis catalysts

including complexes with symmetrically or unsymmetrically

substituted NHC entities, as well as with chelating carbene

ligands, respectively. It will be demonstrated that the resulting

pool of catalysts can be assessed in parallel by IR thermog-

raphy, thus enabling a rapid selection of the optimal

catalyst(s) for a given transformation. Finally, preparative

applications to a representative set of metathesis reactions

and a detailed study on enyne metathesis provide insights into

the specificities of these powerful new tools.

Exposure of the parent Grubbs complex 1 to one of the

N-heterocyclic carbenes 5a ± c (1.1 ± 1.3 equiv) in toluene at

ambient temperature affords the desired catalysts

(Scheme 3).^[7±9]Only in the case of the more sterically

N

R¹

Cl

R²

Ph

PCy₃

Ru

5 or 8

Cl

Ru

PCy₃

Ph

PCy₃

1

2, 9-14

Scheme 3.

Results and Discussion

hindered derivative 10 must the reaction be carried out at

508C to ensure a reasonable rate. In most cases, the replace-

ment of one PCy₃unit of 1 by the NHC can be conveniently

monitored by TLC using n-hexane/ethyl acetate (4:1) as the

eluent. Complexes 2, 9, and 10 thus formed can either be

purified by repeated washing with pentane, or, preferentially,

by routine flash chromatography on silica gel. They are

thermally stable, rather inert towards oxygen and moisture,

and can be stored for extended periods of time without any

appreciable loss of reactivity.

Preparation of the catalysts: Although the synthesis of the

required imidazolium salts,^[16]the N-heterocyclic carbenes

derived thereof,^[16±18]and the ruthenium complexes^[7±9]is

straightforward when following literature routes, some com-

ments are necessary. The symmetrical imidazolium salts 4

(Scheme 1) are obtained by condensation of the correspond-

ing amine, glyoxal and a C-1 synthon (paraformaldehyde,

HC(OEt)₃or ClCH₂OEt) as previously described,^[16±18]where-

as the unsymmetrically substituted derivatives 7 (Scheme 2)

used in this study are prepared by quarternization of N-

mesitylimidazole (6).^[19]

Deprotonation of 4 with tBuOK^[20]in THF affords the

corresponding free carbenes 5 which can be isolated and

stored at low temperature under Ar for several weeks

(Schemes 1 and 2). The chloro-substituted carbene 5c is

obtained on treatment of 5a with CCl₄as outlined by

Arduengo et al.^[17a]

The preparation of complex 11 follows the same route and

is particularly straightforward since the required ligand, that is

1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene,^[21]

is

commercially available. Reaction with the Grubbs catalyst 1

in toluene at ambient temperature furnishes the desired

substitution product 11 in 72% yield. In crystalline form this

compound can be stored under Ar for several weeks, but when

kept in chlorinated solvents it decomposes

rapidly to as yet unidentified products. The

significantly lower stability of 11 in solution as

compared to the other members of this series is a

limiting factor for its preparative utility (see

below).

R²

N

X

R¹

R³

5a,b

4a: R¹= R²= R³= Me

4b: R¹= R²= iPr, R³= H

It is important to note that the procedure

described above involving the isolation of the

free N-heterocyclic carbenes as a separate step is

generally preferred over a more user-friendly

ªin situº method recently outlined in the liter-

ature in which all ingredients, that is the

imidazolium salt, complex 1 and tBuOK, are

mixed together and reacted in n-hexane.^[22]For

example, if applied to the synthesis of 10 this

one-pot procedure produces significant amounts

of by-products thus making the isolation of the

desired complex quite difficult. According to IR

Cl

N

Cl

N

5c

Scheme 1.

and NMR spectroscopic data, at least one of the

contaminants is a ruthenium hydride species

RX

N

X

R

which may be responsible for side reactions (see

below). Despite of this inconvenience, the ªin

6

7

8a: R = (CH₂)₃CH=CH₂

8b: R = (CH₂)₄CH=CH₂

8c: R = (CH₂)₆CH=CH₂

situº protocol was chosen to prepare the olefinic

complexes 12a ± c in order to minimize possible

side reactions between the carbene center and

the alkene groups in the lateral chains of the

NHC derivatives 8a ± c formed from 7a ± c and

tBuOK.^[21b]

8d: R = CH₂CH₂OTBS

8e: R = CH₂CH₂(CF₂)₅CF₃

Scheme 2.

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A. Fürstner et al.

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The unique ability of complexes 12a ± c to metathesize their

own ligands lays the ground for the preparation of compounds

13 and 14 in which the N-heterocyclic carbene and the

Figure 1. Molecular structure of complex 9, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

ªregularº carbene unit Ru CHR are tethered to form a

metallacycle. Specifically, heating a solution of complex 12b

in refluxing pentane or toluene (808C) affords chelate 13 in

75% isolated yield; the course of the reaction can again be

monitored by TLC. The shorter homologue 14 is prepared

analogously starting from complex 12a as the precursor. The

design of these species is based on the idea that they might be

able to regenerate themselves after the productive metathesis

is over and the substrate in solution has been quantitatively

consumed.

N

n

Cl

Ru

PCy₃

Ph

12a: n = 1

12b: n = 2

12c: n = 4

Figure 2. Molecular structure of complex 10, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

N

Cl

Ru

Cl

PCy₃

13

14

Additional unsymmetrically substituted NHC complexes

displaying further structural variations are the silylether

derivative 15 and complex 16 incorporating a perfluoroalkyl

chain.^[23]

N

tBuMe₂Si

N

O

F₃C(F₂C)₅

Cl

Ru

Ph

Cl

Ph

PCy₃

15

16

Figure 3. Molecular structure of complex 11, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

Structure: The crystal structures of 9, 10, 11, 13, 14, and 15

have been determined (Figure 1 ± 6), and allow us to look for

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

correlations between the catalytic activity and structural

properties of this class of compounds. Two related structures

published by others (i.e., X-ray structures of complex 2^[7a]and

a polymorph of complex 10^[15c]) have been included to extend

the basis of this comparison.

In all structures the Ru^IIcenter is pentacoordinate; its

geometry lies between the idealized forms of a trigonal

bipyramid and a square pyramid and is closer to the latter. In

all cases the two chlorine ligands are trans-oriented in the

basal plane of the square pyramid, with the phosphorus atoms

and the imidazolyl carbene carbon atom occupying the

remaining corners. The benzylidene carbene ligand always

occupies the apical position.

A number of interatomic bond and contact parameters

have been extracted from the structures for a more detailed

comparison. These parameters are the averaged Ru-

ligand distances, the Cl-Ru-Cl bond angle, the P-Ru-imida-

zolyl bond angle, the rms deviation of these four ligands

from a least-squares plane, and the distance of the Ru

atom from this plane (Table 1). The dihedral angle between

Figure 4. Molecular structure of complex 13, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

the Cl-Ru-Cl and the carbene double bond (Ru CPh) is

also given. A dihedral angle of 08 corresponds to an

orientation in which the p orbitals are perpendicular to the

Cl-Ru-Cl plane.

The overall geometries of 9, 10, 11, 13, 14, and 15 are

surprisingly similar in the sense that all PCy₃ligands adopt

approximately the same conformation with respect to the

Ru P bond. The NHC ligand is always co-planar with the

carbene and in the case of asymmetrically substituted NHCs

(11, 13, 14, and 15) no rotamer disorder around the C Ru

bond has been observed in the crystal.^[24]While the tethered

carbenes 13 and 14 force the mesitylene group to the side of

the chlorines (Figure 4 and 5), the mesitylene group in 15 is

oriented towards the benzylidene (Figure 6). The distance

between the mesitylene and the benzylidene ring is 3.44 and

both rings are co-planar within 7.98. This p ± p interaction is

preserved to some extent in solution (see below) and can also

be observed in the triazol complex 11 (Figure 3), although in

this case the benzylidene adopts a rather different orientation

as can be seen from Table 1. The angle between the N-phenyl

and the benzylidene ring is 14.08 and the distance between the

two rings is 3.31 . Similar p ± p interactions are found in the

other molecules (with the exception of the polymorph of 10c

reported by Nolan) and are all well within the range observed

for aromatic stacking.^[25]Although the observed preservation

of molecular conformational detail throughout the range of

compounds studied suggests only a small influence of crystal

packing, two points must be noted. In the crystal structure of

11 the phenyl ring attached to C2 in the triazol is disordered

(Figure 3), which might explain the different orientation of

the benzylidene.

Figure 5. Molecular structure of complex 14, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

Secondly and more importantly Nolan et al. report for 10 a

different polymorph (i.e., 10c)^[15c]with rather different

molecular shape. A closer inspection of the crystal packing

of 10a,b prepared in our laboratory reveals Cl ´´´ H contacts

of 2.7 and 2.8 between Cl2 and H2 (one of the hydrogen

atoms in the imidazolyl ring) linked through a 2₁screw-axis in

both independent molecules. In contrast, structure 10c does

not feature this interaction.^[15c]If viewed along the crystallo-

Figure 6. Molecular structure of complex 15, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

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Table 1. Selected bond parameters of the Ru^IIcoordination sphere for 9, 10a,b, 11, 13, 14, 15 and the previously reported 2^[7a]and 10c.^[15c]

Compound

11

10a

10b

10c^[15c]

9

2^[7a]

15

13

14

< Ru Cl >

Ru P

Ru C

2.349(3)

2.440(3)

2.085(9)

1.819(10)

156.94(10)

171.8(3)

46.0

2.373(4)

2.3914(7)

2.3876(11)

2.4160(12)

2.092(5)

2.388(3)

2.4581(5)^[d]

2.4231(7)

2.056(3)

2.3973(16)

2.4214(17)

2.091(6)

2.3848(8)

2.4020(8)

2.076(3)

1.812(3)

168.20(3)

170.98(8)

51.3

2.390(4)

2.049(12)

1.795(11)

168.75(13)

164.0(4)

15.4

2.381(4)

2.067(8)

1.840(13)

168.04(15)

162.1(3)

17.4

2.4554(1)

2.088(2)

1.817(3)

170.42(2)

164.60(1)

38.7

2.419(3)

2.069(11)

1.841(11)

168.62(12)

163.2(3)

18.0

Ru C

1.846(5)

1.835(3)

1.806(6)

Cl-Ru-Cl

C-Ru-P

a [8]^[a]

169.43(4)

163.89(12)

15.0

0.26

0.05

165.240(18)

161.91(7)

16.5

0.33

0.02

174.14(6)

165.99(18)

26.6

0.08

0.04

d^[b][]

0.32

0.15

0.26

0.04

0.29

0.05

0.23

0.06

0.28

0.04

0.21

0.03

planarity^[c]

[a] Dihedral angle between the planes Cl-Ru-Cl and C C Ru. [b] Distance of the Ru atom from the least-squares plane formed by the two chlorine atoms, P

and the imidazolyl carbene carbon atom. [c] Root-mean-square deviation of the four atoms under [b] from the least-squares-plane. [d] The unexpectedly

long averaged Ru Cl bond is due to the fact that 19% of Cl1 and 35% of Cl2 are disordered with Br.

graphic b axis the differences between the two polymorphic

forms of 10a,b are most prominent. In the polymorph 10c

reported by Nolan the molecules form clearly separated

stacks along the b direction. Molecules related by symmetry

interact with these stacks by intersecting one cyclohexyl ring,

employing a 2₁screw-axis passing through the ring (Figure 7).

In 10a,b prepared in our laboratory a completely different

picture is seen. Viewed along the b axis (which is almost

1.5 times as long as in 10c) the two independent molecules

arrange in a one-up/one-down fashion, with a large degree of

overlap (Figure 8). This results in a zig-zag chain along the b

direction which is held together by the H ´´´ Cl interactions

described above. The crystal packing also reveals the for-

mation of two channels parallel to the b axis. A larger

diameter one is centered at x 0.5, z 0.5, and a smaller one

at x 0, z 0. Those channels are filled with disordered

solvent molecules (pentane).

The superposition of these three molecules of 10a ± c shown

in Figure 9 compared with the superposition of the six

remaining ruthenium(ii) carbenes (Figure 10) reveals the

Figure 7. Stereoview of the crystal packing of complex 10c viewed along the b axis, c axis vertical.

Figure 8. Stereoview of the crystal packing of complex 10a,b viewed along the b axis, c axis vertical.

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Ru-Based Metathesis Catalysts

3236±3253

axis. In all the other molecules

of this series, this ring plane is

perpendicular. This observation

is in agreement with the larger

Cl-Ru-Cl bond angle and the

longer Ru Cl bond distances,

compared with 10a and 10b. It

cannot be ruled out that the

different molecular conforma-

tion of 10c results from the

more dense packing (1

3

1.279 Mgm ) compared with

the polymorph of 10a,b pre-

pared

1.179 Mgm ).

in

Mülheim

(1

3

A direct correlation between

the benzylidene Ru bond dis-

tance or the dihedral angle be-

tween the double bond and the

Cl-Ru-Cl plane and any other

geometrical parameter is not

given. This leads to the conclu-

sion that more complex elec-

tronic interactions, in particular

the nature of the NHC ligand

and the ªregularº carbene li-

gand, are responsible for the

geometric interactions. This is

in agreement with the more

trigonal bipyramidal geometry

of the triazolyl complex 11 (Fig-

ure 3) which is not present in the

other molecules. At the other

end of the series is the chelate

complex 13 where the carbene

lacks the possibility of delocal-

izing the metal carbon bond

into the phenyl ring (Figure 4).

Complex 13 is also the repre-

sentative which resembles most

closely octahedral geometry,

with the Ru atom in the plane

of the two chlorines, the phos-

phorus atom and the imidazolyl

carbon atom. The closely related

chelate complex 14, which has a

four carbon bridge instead of

five carbon atoms in 13, adopts a

geometry reflecting the steric

strain caused by the shorter

tether. Hence, the carbene bond

is rotated by 51.38 out of the Cl-

Ru-Cl plane and the NHC li-

gand is twisted by 248 out of the

C1-Ru-C7 plane (Figure 5).

Figure 9. Superposition of the polymorphs of complex 10 using the following color code: 10a (cyan), 10b

(mauve), 10c^[15c](orange).

Figure 10. Superposition of ªsecond-generationº metathesis catalysts bearing NHC ligands. Color code:

Complex 9 (yellow), complex 10 (green), complex 11 (white), complex 13 (magenta), complex 14 (cyan),

complex 15 (white).

Finally, it is worth mentioning that the substitution of the

hydrogens of C4 and C5 of the imidazol ring with chlorine in 9

appears to have no effect on the geometry of the molecule.

Thus, the structure of complex 9 in the solid (Figure 1) and

unusual orientation of the PCy₃. All cyclohexyl rings in the

polymorph 10c reported by Nolan are rotated and the ring

oriented gauche to the two chlorine atoms now adopts a

conformation where the ring plane is parallel to the Ru P

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A. Fürstner et al.

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that of the unsubstituted complex 2 reported by Nolan^[7a]are

virtually identical.

N

Cl

NMR investigationsÐPossible explanation for the pro-

nounced solvent dependence of the catalytic activity of

complex 2: The X-ray structures discussed above suggest that

the p ± p stacking between the benzylidene carbene unit and

the N-aryl substituents on the NHC residues constitutes a

strongly conserved structural element in all the second-

generation metathesis catalysts described herein. It is of

interest to see if this electronic interaction is also operative in

solution because it may affect the reactivity of the benzyli-

dene carbene which, in turn, determines the rate of initiation

of a metathesis reaction.

Ru

Ph

Cl

Ph

PCy₃

3

17

Their synthesis was achieved according to the method

outlined by Grubbs et al.^[8b]through a-elimination of the

corresponding 2-tert-butoxy-4,5-dihydroimidazole precursors.

This procedure works as described for compound 3; we

noticed, however, that increased steric bulk of the N-sub-

stituents leads to a deviation from the regular reaction

pathway and results in the formation of a hydridic by-product

in addition to the desired complex 17 (Scheme 4). A by-

Careful analysis of the NMR spectra of complex 2 in

CD₂Cl₂confirm that the rotation of the NHC ligand around

the C Ru bond is restricted, as has already been report-

ed.^{[24, 26]}More importantly,

however, the spectra also re-

N

veal that the rotation of the

mesityl substituents around the

C N bond is hindered. Two

O H

PCy₃

N

broadened signals are ob-

Cl

Ru

Cl

+ by-products

Ru

Cl

Ph

served in the 600 MHz

¹H NMR spectrum of the me-

sityl protons in CD₂Cl₂. When

the spectra are recorded in

C₆D₆, however, these signals

have coalesced, thus showing

Cl

Ph

PCy₃

1

17

Scheme 4.

that the barrier is lower. Line shape analysis allows one to

product was obtained in pure form by crystallization and was

identified as (PCy₃)₂Ru(H)₂Cl₂(18). Although we could not

directly localize the hydrogen atoms in the X-ray structure of

this complex (see below), an absorption band in the IR

estimate that the exchange rate is ꢀ480 s ¹in CD₂Cl₂whereas

1

it is ꢀ2000 s in C₆D₆, corresponding to an enthalpy differ-

ence for the rotational barrier of ꢀ3.5 Æ 0.4 kJmol ¹at 300 K.

Competing interactions of the N-mesityl group with the

aromatic solvent molecules will reduce the stabilizing effect of

the intramolecular p ± p stacking with the benzylidene

substituent and therefore account for the observed greater

conformational freedom. It is tempting to assume that this

effect explains

1

spectrum (nÄ 1906 cm ) and a characteristic high field signal

in the ¹H NMR spectrum (d 24.38) unequivocally indicate

the presence of hydride ligands. The formation of this species

under conditions used for the preparation of catalyst 17 may

explain why in some cases the isomerization of the olefinic

double bonds of the substrate can compete with productive

RCM.^[28]This undesirable pathway is likely to be caused by

small amounts of metal hydride species formed by decom-

position of or by impurities in the metathesis catalysts.

i) why complex 2 is much more reactive in toluene than in

CH₂Cl₂or ClCH₂CH₂Cl solution,^[28a]

ii) why this positive influence of toluene is observed only for

complexes bearing N-aryl substituents, whereas the activ-

ity of analogues with N-alkyl groups on their NHC ligands

is usually higher in chlorinated media,^[9a]and

iii) why the effect is more pronounced in complex 2 than in

complex 10 in which the motion of the larger isopropyl

residues on the arene disturb the stabilizing p ± p stacking

as can be deduced from a lower rotational barrier around

the C N bond.

cis ± trans Stereoisomerism in (PCy₃)₂Ru(H)₂Cl₂: The molec-

ular structure of 18 (Figure 11) reveals an octahedral geom-

etry with a trans arrangement of the phosphine groups. The

ruthenium atom is situated on a crystallographic inversion

center. The presence of two hydrogen atoms in the complex

that could not be located in difference Fourier maps has been

deduced from spectroscopic data (see above). Complex 18 is

the second known crystal structure of a dihydro-dichloro-

bis(phosphine)-ruthenium(iv) complex. The first example,

(PiPr₃)₂Ru(H)₂Cl₂(19) described by Werner et al.,^[29]how-

ever, is a distorted square antiprism. Chaudret et al.^[30]report

spectroscopic data and theoretical results for the analogous

tricyclohexylphosphine complex (PCy₃)₂Ru(H)₂Cl₂(20)Ða

compound having the same composition as complex 18

described hereinÐwhich are in agreement with the molecular

point group symmetry of 19.

Complexes with ªsaturatedº NHC ligands and the isolation of

a hydridic by-product: In order to provide a more compre-

hensive picture, we have also prepared complexes 3^[8b]and 17

bearing ªsaturatedº NHC units and have compared their

catalytic performance with that of their ªunsaturatedº con-

geners 2 and 10, respectively. It has recently been claimed that

ªsaturatedº NHCs endow the metal center with an even

higher reactivity.^{[8b, 27]}

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

Table 2. Comparison of the reactivity of different NHC complexes in the

cyclization of diene 21 to cycloalkene 22. All reactions have been

performed with 5 mol% of the catalyst in toluene at 808C unless stated

otherwise.

X

see Table 2

X

21a: X = NTs

22a,b

21b: X = C(COOEt)₂

Substrate

Catalyst

t [h]

Yield [%]^[a]

1

2

3

4

5

6

7

8

9

21a

21b

2

9

24

3

24

2

24

95

85^[c]

69^[b]

80

10

11

12a

12b

12c

15

16

2

Figure 11. Molecular structure of complex 18, anisotropic displacement

parameters are drawn at 50% probability, hydrogen atoms omitted for

clarity.

22

48

78

75^[c]

54^[c]

47^[c]

37^[c]

31^[d,e]

10

11

12

While the steric requirements of the two different phos-

phine groups in 18 and 19 are certainly substantially different,

this does not explain the different geometries of the two

complexes. The formation of 18 by a yet unknown mechanism

starts from square pyramidal 1 and thereby leads to the trans-

octahedral complex.^[31]Complexes 19 and 20 on the other

hand are formed from CHCl₃and Ru(H₂)₂(H)₂(PR₃)₂, a

precursor which has already the co-ordinated hydrogen

molecule in place to yield the cis-geometry of the resulting

products. These entirely different syntheses routes may

explain why the hydride complex (PCy₃)₂Ru(H)₂Cl₂exists in

the two distinct diastereomeric forms 18 and 20.

10

3

[a] Isolated Yield unless stated otherwise. [b] In refluxing CH₂Cl₂. [c] GC

Yield. [d] Ref. [8b]. [e] Determined by NMR.

The analogous malonate derivative 21b (X C(COOEt)₂)

is more reluctant toward cyclization. Entries 10 ± 12 show that

the corresponding cycloalkene 22b is formed in moderate

yields only; in this particular case complex 3^{[8b, 27]}bearing the

saturated NHC is by no means superior to the other catalysts

tested.

Care, however, must be taken in generalizing reactivity

trends. This becomes clear by comparing the results discussed

above with those obtained in the macrocyclization of diene 23

to the musk-odored lactone 24^[33](Table 3). Whereas complex

10 with the most crowded NHC was clearly inferior to 2 in the

formation of the five-membered product 22 (Table 2, entries 1

and 3), it performs better than 2 in this particular macro-

cyclization (Table 3, entries 1 and 3). The E/Z-ratio of the

resulting product 24, however, is largely unaffected by the

choice of the catalyst.

Comparative investigation of ªsecond-generationº metathesis

catalysts: With this panel of NHC-containing ruthenium

complexes in hand, we studied their catalytic activity in a

representative set of metathesis reactions, focussing our

efforts on rather demanding cases.^[32]

One of them concerns the formation of the tetrasubstituted

cycloalkene 22a,b which is beyond reach of 1. As can be seen

from Table 2, all NHC-containing complexes effect the

cyclization of 21a (X NTs) to 22a, although appreciable

differences must be noticed. Thus, the triazol-5-ylidene

containing catalyst 11 provides a satisfactory yield of 80%

in just 2 h. Prolonged stirring, however, does not lead to

further conversion, most likely because of the limited lifetime

of complex 11 in solution. In contrast, the N-mesityl

substituted complex 2 is active over much longer periods,

thereby leading to an almost quantitative formation (95%) of

the desired product 22a. Substitution of the backbone of its

NHC ligand with two chlorine atoms has surprisingly little

effect on the reactivity of the resulting complex 9, whereas the

increased steric bulk of the N-substitutents as in 10 turned out

to be disadvantageous. All unsymmetrically substituted NHC

complexes 12, 15, and 16 are able to effect the cyclization of

21a to 22a. However, the catalytic activity of the homologous

series 12a ± c shows a significant dependence of the reactivity

on the tether length between the alkene entity and the metal

core. This effect is likely related to their different capacity to

form chelate complexes such as 13 and 14 in situ and is subject

to further investigation in this laboratory.

Table 3. Comparison of the reactivity of different NHC complexes in the

cyclization of diene 23 to cycloalkene 24. All reactions have been

performed with 2.5 mol% of the catalyst in refluxing CH₂Cl₂.

O

see Table 3

24

23

Catalyst

t [h]

GC Yield [%]

E/Z

1

2

3

4

2

9

10

11

3

5

1

5

83

71

84

78

3.4

3.3

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Another stringent test is the formation of the 14-membered

ring lactone 27 containing a trisubstituted double bond. This

product is far beyond reach of the parent Grubbs catalyst 1,

which effects only a homo-dimerization of 25 at the least

substituted site with formation of an acyclic dimer 26 (Table 4,

entry 1). All NHC-containing catalysts, in contrast, furnish the

desired macrocycle 27 in good yields (entries 2 ± 5).^[34]Entry 5

reveals that complex 3^{[8b, 27]}containing the ªsaturatedº NHC

ligand gives similar results as its ªunsaturatedº congeners.

tion of this rather congested substrate (Table 5, entry 4),

although it is presently not clear to which extent this failure is

due to the limited stability of the complex in solution and/or to

an inherent lack of reactivity toward this particular substrate.

The less congested enyne 28b reacts with exceptional ease

particularly if complex 10 is used as the catalyst. Note that this

preparative result matches the conclusions reached by the IR-

thermographic assay method outlined below.

Taken together, the examples described above unambigu-

ously demonstrate that generalizations concerning

the catalytic potency have to be met with caution.

Table 4. Comparison of the reactivity of different NHC complexes in the conversion of

diene 25 to dimer 26 or the cyclic monomer 27. All reactions have been performed in

refluxing CH₂Cl₂.

More subtle effects including the influence of the

solvent on the reactivity of differently substituted

ruthenium complexes are operative that cannot be

fully rationalized based on our still limited under-

standing of the mode of action of such ªsecond-

generationº catalysts.

O

Enyne metathesis of sterically demanding sub-

strates: Having identified complexes 2 and 9 as

excellent tools for enyne metathesis, we extended

this investigation to a diverse set of sterically

demanding substrates since previous studies on

inter- as well as intramolecular enyne metathesis

reactions deal mainly with unhindered cases.^{[35, 36]}

The results compiled in Table 6 illustrate the

remarkably wide scope of this type of reaction.

Thus, substitutents at the propargylic site are nicely

accommodated and do not lower the yields (en-

tries 1 ± 8). Terminal as well as internal alkynes can

be employed. Various degrees of substitution of the

alkene entities are tolerated and even trisubstituted

olefins are found to undergo efficient cycloisomeri-

see Table 4

O

25

26

27

O

Catalyst [mol%]

t [h]

Product [% Yield]

1

2

3

4

5

1 (10%)

2 (10%)

9 (6%)

10 (6%)

3 (6%)

17

38

80

40

26 (79)^[a]

27 (65)^[b]

27 (60)^[b]

27 (57)^[b]

[a] Isolated Yield. [b] GC Yield.

zation in the presence of complex 2, thereby transferring a

dimethylmethylidene unit (cf. 32 ! 33, 44 ! 45). Note that the

reactions depicted in entries 2 and 4 lead to the formation of

tetrasubstituted alkenes. Catalyst 2 also allows six-membered

rings to be formed (entries 9 and 15) and even the seven-

membered heterocycle 49 is obtained in excellent yield.^[37]The

formation of the related product 55, despite in somewhat

lower yield, is particularly noteworthy as the required

substrate 54 is an electron deficient and highly conjugated

alkyne derivative. To the best of our knowledge, compounds

of this type have not yet been used in enyne metathesis

reactions mediated by metal carbene complexes.^[38]

Enyne cycloisomerization reactions provide another ex-

cellent forum for evaluating differential reactivity. As in the

formation of the tetrasubstituted dihydropyrrole 22a, com-

plex 2 and its chloro-substituted analogue 9 are almost

indistinguishable in their activity toward enyne 28a (Table 5,

entries 1 and 2). It is remarkable, however, that the triazolyl-

substituted complex 11 is unable to effect the cycloisomeriza-

Table 5. Comparison of the reactivity of different NHC complexes in the

cycloisomerization of enyne 28 to diene 29. All reactions have been

performed with 5 mol% of the catalyst in toluene at 808C unless stated

otherwise.

Ph

O

R

Catalyst screening by IR thermographyÐThe enyne meta-

thesis case: Recent investigations have demonstrated that

high precision IR thermography is a useful tool for the rapid

screening of homogeneous and heterogeneous catalysts in

parallel.^{[39, 40]}When applied to RCM, this method allowed the

catalytic activity to be correlated with the heat uptake from

the medium as monitored by the appearance of ªcold spotsº

which are caused, at least in part, by the vaporization of

ethylene formed during the reaction.^[41]In contrast to RCM,

enyne metathesis does not produce any gaseous by-product;

therefore it was of interest to study whether this analytical

technique can be used to monitor this type of transformation

or not.

see Table 5

Ph

R

28a: R = Me

28b: R = H

29a,b

Substrate

Catalyst

t

GC Yield [%]

1

2

3

4

5

6

28a

28b

2

9

10

11

2

18 h

17 h

24 h

60 min

5 min

75

74

58

< 5

85^[a]

88^[a]

10

[a] Isolated yield.

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

Table 6. Cycloisomerization reactions of variously substituted enynes. All reactions were

catalyzed by complex 2 (1 mol%) in toluene at 808C unless stated otherwise.

In order to do so, seven wells of a microtiter

plate were charged with 40 mL of 0.05m sol-

utions of catalysts 1, 2, 3, 9, 10, 11, and 56^{[5i, 42]}in

toluene (this corresponds to ꢀ 0.6 mol% of

catalyst per substrate). Once they are thermo-

Substrate

Product

t [h]

Yield [%]

1

2

1

18

85 (R H)

75 (R Me)^[a]

3

4

0.3

1.5

80 (R H)

PCy₃

Ph

67 (R Me)

Cl

Ru

Cl

PCy₃

5

2.5

77

56

6

7

0.3

20

93 (R Me)

87 (R Ph)^[a]

statically set to 308C, enyne 28b (80 mL, ther-

mostatted to 308C) was added and the course of

the reaction was monitored by the IR camera

mounted above the well plate by taking pictures

every three seconds. Figure 12 shows the pic-

tures after 9, 51, and 60 s which can be analyzed

using the inserted temperature/color code.

Several remarkable features immediately

become apparent. Most notable is the tremen-

dous exothermicity of this reaction (Scheme 5)

when catalyzed by complexes 3 or 10, causing

an increase in temperature (DT_max) of almost

358C. This outcome is in striking contrast to

8

9

1

75^[a]

81^[b]

97^[a]

1

10

0.5

11

12

0.5

12

81 (R H)^[a]

67 (R Me)^[a]

the slight endothermicity of DT_max

ꢀ

18C

previously observed during RCM.^[41]As is

clearly visible, this strong evolution of heat

even affects the temperature profile of the

adjacent wells. Moreover, as the temperature

quickly falls off in the thermographs recorded

after this very short reaction time, it can be

concluded that the transformation of enyne 28b

to diene 29b is almost finished after only 1 min.

This interpretation was confirmed by TLC

control, showing no residual starting material

but only the essentially quantitative formation

of product 29b after 1 min. Finally, Figure 12

shows that complexes 3 and 10 are roughly

equipotent in terms of TOF and are superior to

all other catalysts screened in this assay.

13

14

0.5

16

89 (R H)^[a]

20 (R COOMe)

15

16

14

66^[a]

1.5

81^[a]

A ranking among the remaining catalysts was

achieved in a second experiment choosing a

narrower temperature window that makes more

subtle effects visible. Five vials located suffi-

ciently far apart to minimize mutual heat trans-

fer through the microtiter plate (see above)

were charged with the respective catalyst sol-

utions and enyne 28b as described above and

the course of the reaction was followed by IR

thermography using a higher precision mode. A

prototype picture taken after 210 s (Figure 13)

shows that the reaction is well underway if

catalysts 9 or 2 are used, while the others clearly

stay behind.

17

1

89^[a]

18

19

1.5

4

89

42^[a]

[a] Using 5 mol% of the catalyst. [b] Under reflux in CH₂Cl₂; the product was also

characterized in form of the cycloadduct prepared by Diels ± Alder reaction of diene 39

with dimethyl acetylenedicarboxylate under reflux in toluene (4 h), cf. Experimental Section.

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3245

A. Fürstner et al.

FULL PAPER

Ph

O

catalyst (0.6 mol%)

toluene

Ph

29b

28b

Scheme 5.

These experiments demonstrate that IR thermography is a

convenient and reliable analytical technique for estimating

the potency of metathesis catalysts semi-quantitatively. It

should be stressed, however, that this assay only screens for

reactivity; the fastest catalyst, though, does not necessarily

provide the highest chemical yield (cf. Table 5). Among other

things, the lifetime of the propagating species in solution, that

can vary significantly among the series of catalysts screened,

also affects the yield obtained. This illustrates that several

complementary methods for high throughput screening which

allow different preparatively relevant parameters to be

assessed are necessary before ªcombinatorialº catalysis will

become a mature field.^[40]

Conclusion

The data reported in this paper witness the superiority of

NHC containing ªsecond-generationº metathesis catalysts as

compared to parent-complex 1. Equally noteworthy is the fact

that different NHC ligands turned out to be optimal for

different applications; this shows that no single catalyst

outperforms all others in all possible applications. This

reinforces the notion that our present understanding of the

subtle influences of the substrate on the outcome of a

metathesis event is immature and that great care must be

taken when generalizing the results obtained from single

experiments or a narrow set of test reactions.^[32]

Experimental Section

General: All reactions were carried out under Ar in pre-dried glassware

using Schlenk techniques. The solvents were dried by distillation over the

following drying agents and were transferred under Ar: toluene (Na/K

alloy), CH₂Cl₂(P₄O₁₀), Et₂O (Mg/anthracene), MeOH (Mg), n-pentane,

Figure 12. IR-thermographic screening of the enyne metathesis depicted

in Scheme 5 catalyzed by complexes 1, 2, 3, 9, 10, 11 and 56. Top: after 9 s;

middle: after 51 s; bottom: after 60 s.

Taken together, these two simple

IR-thermographic experiments al-

low the set of ruthenium-based

metathesis catalysts to be ranked

according to their individual initia-

tion rates of enyne metathesis (3 ꢀ

10 ꢁ 9 ꢀ 2 > 1 ꢀ 11 ꢀ 56). Note that

i) this order is in good qualitative

agreement with the results com-

piled in Table 5 (cf. entries 5 and

6) and

ii) even the seemingly ªlessº reac-

tive complexes such as 9 or 2 still

Figure 13. IR-thermographic image recorded over a narrower temperature range (cf. color code) of the

enyne metathesis depicted in Scheme 5 catalyzed by complexes 1, 2, 9, and 11 and 56 after 210 s. The wells

containing the catalyst solutions are sufficiently far apart to minimize mutual heat transfer, compare text.

effect the transformation within

just a few minutes.

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

n-hexane (Na/K). Flash chromatography: Merck silica gel 60 (230 ±

400 mesh). NMR: Spectra were recorded on Bruker AC200, AMX300,

DPX300 or DMX600 spectrometers in the solvents indicated; chemical

shifts (d) are given in ppm relative to TMS, coupling constants (J) in Hz.

IR: Nicolet Magna 750 FT-IR, wavenumbers in cm ¹. MS (EI): Finnigan

MAT 8200 (70 eV), HR-MS: Finnigan MAT 95. Elemental analyses:

Dornis & Kolbe, Mülheim. Equipment for high precision IR thermogra-

phy: Inframetrics Thermacam (Inframetrics Inc., North Billerica, MA,

USA) using the Therma GRAM95 (Inframetrics Inc.) and Dynamite

software (Thermoteknix Systems Ltd., Mount Pleasant, Cambridge, UK)

for data processing and management. All commercially available substrates

were used as received.

C₂₀H₃₃BrN₂OSi (425.48): C 56.46, H 7.82, N 6.58; found: C 56.23, H 8.06,

N 6.98.

Compound 7e (X I): N-Mesitylimidazole (6; 1.29 g, 6.90 mmol) and

1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluoro-8-iodo-octane (3.31 g, 6.98 mmol)

were heated under reflux in toluene (20 mL) for 4 d. Evaporation of the

solvent and crystallization (THF/methyl tert-butylether) of the residue

afforded compound 7e (3.50 g, 77%) as a pale yellow solid. ¹H NMR

(CD₂Cl₂, 300 MHz): d 10.12 (s, 1H), 8.07 (s, 1H), 7.28 (s, 1H), 7.06 (s,

2H), 5.13 (t, J 6.3 Hz, 2H), 3.07 (tt, J 18.6, 6.2 Hz, 2H), 2.36 (s, 3H),

2.08 (s, 6H); ¹³C NMR (CD₂Cl₂, 75 MHz): d 141.7, 137.9, 134.3, 130.5,

129.8, 123.7, 123.4, 122.0 ± 105.0 (m, CF_x), 43.1 (t, J 21.3 Hz), 20.9, 17.5;

IR: nÄ 3120, 3008, 1610, 1566, 1551, 1319, 1236, 1206, 1144, 1121, 1079, 853,

747, 708 cm ¹; MS (ESI): m/z: 1193 [2M I] , 533 [M I] ; elemental

analysis calcd for C₂₀H₁₈F₁₃IN₂(660.25): C 36.38, H 2.75, N 4.24; found: C

36.32, H 2.81, N 4.21.

Novel imidazolium salts

Compound 7a (X Br): N-Mesitylimidazole (6; 1.03 g, 5.56 mmol) and

5-bromo-pent-1-ene (0.83 g, 5.57 mmol) were heated under reflux in

toluene (15 mL) for 16 h. Et₂O (30 mL) was added and the suspension

filtered. Washing of the precipitate with Et₂O and drying afforded

compound 7a (1.53 g, 82%) as a colorless solid. ¹H NMR (CD₂Cl₂,

300 MHz): d 10.54 (s, 1H), 7.89 (s, 1H), 7.28 (s, 1H), 7.04 (s, 2H), 5.84 (m,

1H), 5.07 (d, J 19.0 Hz, 1H), 5.02 (d, J 11.1 Hz, 1H), 4.63 (t, J 6.6 Hz,

2H), 2.34 (s, 3H), 2.30 ± 2.00 (m, 4H), 2.08 (s, 6H); ¹³C NMR (CD₂Cl₂,

75 MHz): d 141.3, 138.3, 136.5, 134.3, 130.8, 129.7, 123.3, 115.9, 49.6, 30.1,

29.5, 20.8, 17.4; IR: nÄ 3087, 3065, 2972, 1641, 1605, 1564, 1548, 1450, 1371,

1205, 1159, 1074, 1039, 991, 919, 892, 866, 780, 673 cm ¹; MS (ESI): m/z:

Metathesis pre-catalysts: Where assignments of the signals [based on

COSY, DEPT and 2D ¹H,¹³C-chemical shift correlated spectra (HSQC and

HMBC)] are given, they are unambiguous and refer to the arbitrary

numbering schemes shown in the inset.

23

22

5

21

20

4

255.2 [M Br] ; elemental analysis calcd for C₁₇H₂₃BrN₂(335.29): C 60.90,

PCy₂

H 6.91, N 8.36; found C 61.05, H 7.06, N 8.22.

Cl

3

2

Ru

Compound 7b (X Br): N-Mesitylimidazole (6; 1.10 g, 5.89 mmol) and

6-bromo-hex-1-ene (95% pure, 1.12 g, 6.51 mmol) were heated under

reflux in toluene (20 mL) for 21 h. Et₂O (50 mL) was added and the

suspension was extracted with H₂O (3 Â 50 mL). The aqueous phase was

washed with Et₂O (3 Â 50 mL), the solvent was evaporated and the residue

dissolved in CH₂Cl₂(150 mL). Drying over Na₂SO₄and evaporating of the

solvent afforded compound 7b (1.42 g, 69%) as a colorless solid. ¹H NMR

(CD₂Cl₂, 300 MHz): d 10.48 (s, 1H), 7.87 (s, 1H), 7.28 (s, 1H), 7.04 (s, 2H),

5.78 (ddt, J 17.0, 10.3, 6.7 Hz, 1H), 5.03 (dq, J 17.0, 1.8 Hz, 1H), 4.96

(dm, J 10.3 Hz, 1H), 4.63 (t, J 7.2 Hz, 2H), 2.34 (s, 3H), 2.20 ± 2.05 (m,

2H), 2.07 (s, 6H), 2.05 ± 1.90 (m, 2H), 1.55 ± 1.40 (m, 2H); ¹³C NMR

(CD₂Cl₂, 75 MHz): d 141.2, 138.1, 137.9, 134.3, 130.8, 129.7, 123.3, 122.9,

115.0, 49.9, 32.8, 29.7, 25.2, 20.8, 17.4; IR: nÄ 3031, 2973, 2930, 2858, 1639,

1608, 1563, 1544, 1486, 1457, 1379, 1204, 1161, 1068, 1036, 995, 907, 855, 758,

1

6

13'

13

N

7'

N

8'

12'

11

10

11'

8

9'

9

10'

7

12

Complex 2: Complex 1 (4.60 g, 5.59 mmol) and carbene 5a (2.43 g,

7.98 mmol) were stirred in toluene (100 mL) under Ar at room temperature

for 1 h. The solvent was evaporated and n-pentane (100 mL) was added.

The precipitate was filtered off, washed with n-pentane and dried in vacuo

to afford complex 2 (3.58 g, 76%) as a violet solid. ¹H NMR (CD₂Cl₂,

600 MHz): d 19.40 (s, 1H, 1-H), 8.90 (br, 1H, 3a-H), 7.40 (t, J 7.3 Hz,

1H, 5-H), 7.15 (br, 1H, 3b-H), 7.13 (t, 2H, 4-H), 7.05 (s, 2H, 10-H), 6.99 (s,

2H, 7-H, 7'-H'), 6.75 (br, 1H, 10'-H), 5.95 (br, 1H, 10'-H), 2.43 (br, 6H, 12-

H), 2.35 (s, 3H, 13-H), 2.21 (m, 3H, 20-H), 2.20 (br, 3H, 12'-H), 1.96 (s, 3H,

13'-H), 1.90 (m, 3H, 12'-H), 1.53 (m, 3H, 23eq-H), 1.51 (m, 6H, 22eq-H),

1.39 (m, 6H, 21eq-H), 1.03 (m, 9H, 22ax-H, 23ax-H), 0.93 (m, 6H, 21ax-H);

¹³C NMR (CD₂Cl₂, 151 MHz): d 295.3 (d, J_CH 147 Hz, C-1), 189.7 (s,

J_CP 83.0 Hz, C-6), 152.1 (s, C-2), 139.5 (s, C-11), 138.8 (s, C-11'), 138.3 (s,

C-9), 137.1 (s, C-8'), 136.4 (s, C-9'), 135.9 (s, C-8), 129.7 (d, J_CH 157 Hz,

C-10), 129.0 (d, C-10'), 128.2 (d, J_CH 158 Hz, C-5), 128.1 (d, C-4), 125.2 (d,

671, 638 cm ¹; MS (ESI): m/z: 269.3 [M Br] ; elemental analysis calcd

(%) for C₁₈H₂₅BrN₂(349.31): C 61.89, H 7.21, N 8.02; found C 61.76, H 7.28,

N 7.94.

Compound 7c (X Br): N-Mesitylimidazole (6; 1.13 g, 6.06 mmol) and

8-bromo-oct-1-ene (1.16 g, 6.06 mmol) were heated under reflux in toluene

(15 mL) for 16 h. Et₂O (30 mL) was added and the suspension filtered.

Washing with Et₂O and drying of the residue in vacuo afforded compound

7c (1.40 g, 61%) as a colorless solid. ¹H NMR (CD₂Cl₂, 300 MHz): d

10.54 (t, J 1.5 Hz, 1H), 7.84 (t, J 1.9 Hz, 1H), 7.28 (t, J 1.9 Hz, 1H),

7.04 (s, 2H), 5.79 (ddt, J 17.2, 10.2, 6.7 Hz, 1H), 4.98 (dm, J 17.2 Hz,

1H), 4.91 (dm, J 10.2 Hz, 1H), 4.61 (t, J 7.2 Hz, 2H), 2.34 (s, 3H), 2.08

(s, 6H), 2.05 ± 1.95 (m, 4H), 1.45 ± 1.30 (m, 6H); ¹³C NMR (CD₂Cl₂,

75 MHz): d 141.2, 138.9, 138.2, 134.3, 130.8, 129.7, 123.3, 122.8, 114.1, 50.1,

33.5, 30.3, 28.6, 28.4, 25.9, 20.8, 17.4; IR: nÄ 3058, 2974, 2929, 2850, 1639,

1608, 1564, 1543, 1486, 1460, 1379, 1203, 1157, 1065, 905, 854, 822, 662,

2

1

¹J_CH 196 Hz, J_CH 12 Hz, J_CP 2.8 Hz, C-7), 124.7 (d, J_CH 196 Hz,

²J_CH 12 Hz, J_CP 1.6 Hz), 31.9 (d, ¹J_CH 127 Hz, J_CP 17 Hz, C-7', C-20),

29.5 (t, ¹J_CH 129 Hz, C-21), 28.2 (t, ¹J_CH 128 Hz, J_CP 10 Hz, C-22), 26.7

1

(t, J_CH 127 Hz, C-23), 21.3 (q, J_CH 127 Hz, C-13), 21.1 (q, J_CH

1

126 Hz, C-13'), 19.7 (q, J_CH 128 Hz, C-12), 18.4 (q, J_CH 127 Hz,

C-12'); ³¹P NMR (CD₂Cl₂, 243 MHz): d 31.9.

¹H NMR (C₆D₆, 600 MHz): d 19.92 (s, 1H, 1-H), 9.30 (br, 1H, H-3), 7.40

(br, 1H, H-3), 7.16 (t, 1H, J 7.3 Hz, 5-H), 6.99 (m, 2H, 4-H), 6.91 (s, 2H,

10-H), 6.23 (d, J 1.8 Hz, 1H, 7'-H), 6.20 (dd, 1H, J_7,7' 1.8 Hz, J_7,P

634 cm ¹; MS (ESI): m/z: 297.2 [M Br] ; elemental analysis calcd for

0.8 Hz, 7-H), 6.20 (br, 2H, H-10'), 2.65 (br, 6H, 12-H), 2.51 (dt, 3H,

J_20,P 11.2, J_20,21ax 9.6 Hz, 20-H), 2.22 (br, 6H, 12'-H), 2.20 (s, 3H, 13-H),

1.85 (s, 3H, 13'-H), 1.66 (br, 6H, H-21_eq), 1.57 (m, 6H, H-22_eq), 1.54 (d, J

12.6 Hz, 3H, H-23_eq), 1.14 (m, 12H, H-21_ax, H-22_ax), 1.06 (m, 3H, H-23_ax);

C₂₀H₂₉BrN₂(377.37): C 63.66, H 7.75, N 7.42; found C 63.48, H 7.82, N 7.35.

Compound 7d (X Br): N-Mesitylimidazole (6; 0.78 g, 4.17 mmol) and (2-

bromo-ethoxy)-tert-butyl-dimethyl-silane (1.00 g, 4.17 mmol) were heated

under reflux in toluene (15 mL) for 16 h. Et₂O (30 mL) was added and the

suspension was extracted with H₂O (3 Â 50 mL). The aqueous phase was

washed with Et₂O (3 Â 50 mL). The solvent was evaporated and the residue

dissolved in CH₂Cl₂(20 mL). Drying over Na₂SO₄and evaporating of the

solvent afforded compound 7d (0.50 g, 28%) as a colorless solid. ¹H NMR

(CD₂Cl₂, 300 MHz): d 10.31 (s, 1H), 7.86 (s, 1H), 7.22 (s, 1H), 7.05 (s, 2H),

4.82 (t, J 4.7 Hz, 2H), 4.09 (t, J 4.7 Hz, 2H), 2.35 (s, 3H), 2.08 (s, 6H),

0.87 (s, 9H), 0.06 (s, 6H); ¹³C NMR (CD₂Cl₂, 75 MHz): d 141.3, 138.1,

134.4, 130.8, 129.7, 124.0, 122.4, 62.1, 52.5, 25.6, 20.8, 18.0, 17.4, 5.8; IR:

nÄ 3034, 2955, 2927, 2855, 1609, 1566, 1547, 1487, 1471, 1447, 1385, 1362,

1259, 1203, 1164, 1110, 1067, 1036, 1007, 937, 829, 812, 780, 731, 668,

¹³C NMR (C₆D₆, 151 MHz): d 295.4 (d, J_CH 148 Hz, C-1), 190.7 (s, J_CP

83.6 Hz, C-6), 152.4 (s, C-2), 139.0 (s, C-11), 138.5 (s, C-9), 138.3 (s, C-11'),

137.3 (s, C-8'), 136.5 (s, C-9'), 136.1 (s, C-8), 129.7 (d, J_CH 157 Hz, C-10),

1

128.9 (d, C-10'), 128.0 (m, C-4), 127.8 (d, C-5), 124.6 (d, J_CH 196 Hz,

²J_CH 12 Hz, J_CP 2.8 Hz, C-7), 124.1 (d, ¹J_CH 196 Hz, ²J_CH 12 Hz, J_CP

1

1.5 Hz, C-7'), 32.1 (d, J_CH 126 Hz, J_CP 17 Hz, C-20), 29.7 (t, J_CH

1

128 Hz, C-21), 28.2 (t, J_CH 124 Hz, J_CP 10 Hz, C-22), 26.6 (t, J_CH

1

128 Hz, C-23), 21.2 (q, J_CH 126 Hz, C-13), 21.0 (q, J_CH 126 Hz,

C-13'), 20.1 (q, J_CH 128 Hz, C-12), 18.7 (q, J_CH 129 Hz, C-12'); ³¹P

1

NMR (C₆D₆, 243 MHz): d 31.8; IR: nÄ 3165, 3131, 2921, 2849, 1608,

1570, 1485, 1445, 1314, 1264, 1242, 1174, 1037, 1005, 898, 848, 740, 701,

1

640 cm ¹; MS (ESI): m/z: 345.2 [M Br] ; elemental analysis calcd for

686 cm

.

Chem. Eur. J. 2001, 7, No. 15

ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001

0947-6539/01/0715-3247 $ 17.50+.50/0

3247

A. Fürstner et al.

FULL PAPER

³¹P NMR (CD₂Cl₂, 243 MHz): d 29.8; IR: nÄ 3166, 3123, 3093, 3060,

23

2962, 2925, 2962, 2849, 1590, 1569, 1445, 1321, 1305, 1173, 1117, 897, 847, 757,

22

21

739, 686 cm ¹; MS (ESI): m/z: 895.7 [M Cl] ; elemental analysis calcd for

5

C₅₂H₇₅Cl₂N₂PRu (931.13): C 67.08, H 8.12, N 3.01; found C 67.05, H 8.20, N

2.96.

20

PCy₂

4

Cl

3

2

Ru

6

Complex 11: Complex 1 (307 mg, 0.37 mmol) and commercially available

1

1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene

(96%,

128 mg,

13'

13

11

0.41 mmol)^[21]were stirred in toluene (15 mL) under Ar at room temper-

ature for 1 h. The solvent was evaporated and the residue was purified by

flash chromatography (n-hexane/Et₂O 4:1 ! 2:1 ! 1:1) affording complex

11 (269 mg, 86%) as a brown solid. ¹H NMR (CD₂Cl₂, 600 MHz): d 19.57

N

8'

11'

8

12'

Cl

10

9'

10'

9

7

7'

12 Cl

Complex 9: Complex 1 (402 mg, 0.49 mmol) and carbene 5c (241 mg,

0.65 mmol) were stirred in toluene (25 mL) under Ar at room temperature

for 1 h. The solvent was evaporated and n-pentane (10 mL) was added. The

precipitate formed was filtered off, washed with n-pentane and dried in

vacuo affording complex 9 (387 mg, 87%) as a violet-brownish solid.

Alternatively the purification can be performed by flash chromatography

(n-pentane/Et₂O 4:1 ! 2:1) affording 9 in 79% yield. ¹H NMR (CD₂Cl₂,

600 MHz): d 19.39 (s, 1H, 1-H), 8.90 (br, 1H, 3a-H), 7.43 (t, 1H, J

7.3 Hz, 5-H), 7.15 (t, 2H, J 7.6 Hz, 4-H), 7.10 (br, 1H, 3b-H), 7.09 (s, 1H,

10-H), 6.80 (br, 1H, 10'-H), 5.95 (br, 1H, 10'-H), 2.41 (br, 6H, 12-H), 2.38

(s, 3H, 13-H), 2.19 (m, 3H, 20-H), 2.18 (br, 3H, 12'-H), 1.97 (s, 3H, 13'-H),

1.87 (br, 3H, 12'-H), 1.53 (m, 3H, 23eq-H), 1.51 (m, 6H, 22eq-H), 1.37 (m,

6H, 21eq-H), 1.03 (m, 9H, 22ax-H, 23ax-H), 0.91 (m, 6H, 21ax-H);

¹³C NMR (CD₂Cl₂, 151 MHz): d 298.0 (d, ¹J_CH 148 Hz, J_CP 9 Hz, C-1),

(d, 1H, J_HP 8.2 Hz, Ru CH), 19.38 (d, 1H, J_HP 6.3 Hz, Ru CH), 8.21 (d,

1H, J 8.4 Hz, o-Ph), 7.90 ± 7.80 (br, 1H), 7.85 (d, J 7.0 Hz, 1H, o-Ph), 7.71

(t, 1H, 7.5 Hz, m-Ph), 7.59 (t, J 6.8 Hz, 1H, m-Ph), 7.57 (m, 1H, p-Ph), 7.55

(m, 1H), 7.50 ± 7.38 (m, 4H), 7.33 ± 7.25 (m, 2H), 7.19 (t, 1H, J 8.2 Hz, m-

Ph), 7.16 (m, 1H, o-Ph), 7.10 (m, 1H), 7.08 ± 7.02 (m, 1H), 7.06 (m, 1H), 7.00

(m, 1H), 6.85 (br, 1H), 2.11 (m, 3H, PCy₃), 1.70 ± 1.50 (m, 15H, PCy₃-H_eq),

1.35 ± 1.00 (m, 15H, PCy₃-H_ax); ¹³C NMR (CD₂Cl₂, 150 MHz): d 291.9

(Ru CH), 192.6 (J_CP 88.6 Hz, Ru CN₂), 191.0 (J_CP 92.4 Hz, Ru CN₂),

154.7 (J_CP 2.8 Hz), 153.8 (J_CP 3.4 Hz), 151.1, 150.9, 142.4, 141.6, 33.0

(J_CP 16.3 Hz, PCH), 32.9 (J_CP 16.1 Hz,PCH), 29.3, 29.3, 28.0 (J_CP

9.7 Hz), 28.0 (J_CP 9.9 Hz), 26.6, 26.6; ³¹P NMR (CD₂Cl₂, 243 MHz): d

24.3, 23.5; IR (KBr): nÄ 3063, 2923, 2849, 1595, 1554, 1495, 1445, 1370,

1201, 1176, 1128, 916, 885, 846, 817, 760, 694, 687 cm ¹; MS (ESI): m/z: 804.2

192.7 (s, ¹J_CP 85.2 Hz, C-6), 152.1 (s, C-2), 140.8 (s, C-11), 140.0 (s, C-11'),

[M Cl] ; elemental analysis calcd for C₄₅H₅₄Cl₂N₃PRu (839.89): C 64.35,

1

139.2 (s, C-9'), 137.1 (s, C-9), 134.1 (s, C-8'), 132.4 (s, C-8), 130.0 (d, J_CH

H 6.48, N 5.00; found: C 64.51, H 6.55, N 4.94.

158 Hz, C-10), 129.2 (d, ¹J_CH 156 Hz, C-10'), 128.7 (d, ¹J_CH 129 Hz, C-5),

128.2 (d, C-4), 119.3 (s, J_CP 2.3 Hz, C-7'), 119.1 (s, J_CP 4.1 Hz, C-7), 31.9

(d, ¹J_CH 129 Hz, J_CP 17.5 Hz, C-20), 29.5 (t, ¹J_CH 128 Hz, C-21), 28.1 (t,

Complex 12a: The imidazolium salt 7a (316 mg, 0.94 mmol), KOtBu

(94 mg, 0.88 mmol) and complex 1 (646 mg, 0.79 mmol) were stirred in

toluene (40 mL) for 3 h under Ar at room temperature. The suspension was

filtered and the solvent evaporated in vacuo. Flash chromatography (n-

pentane/Et₂O 4:1 ! CH₂Cl₂/Et₂O 4:1) afforded complex 12a (263 mg,

¹J_CH 128 Hz, J_CP 10.0 Hz, C-22), 26.5 (t, J_CH 126 Hz, C-23), 21.4 (q,

1

¹J_CH 127 Hz, C-13), 21.2 (q, J_CH 127 Hz, C-13'), 19.8 (q, J_CH 128 Hz,

1

C-12), 18.5 (q, J_CH 127 Hz, C-12'); ³¹P NMR (CD₂Cl₂, 243 MHz): d

1

42%) as a red solid. H NMR (CD₂Cl₂, 200 MHz): d 19.22 (s, 1H), 7.87

31.7; IR: nÄ 3052, 2927, 2847, 1608, 1568, 1559, 1523, 1483, 1444, 1357, 1294,

(br, 2H), 7.50 ± 7.35 (m, 1H), 7.30 ± 7.20 (m, 1H), 7.13 (t, 2H, J 7.5 Hz),

6.85 (d, 1H, J 1.9 Hz), 6.40 ± 6.20 (br, 2H), 5.97 (m, 1H, J 17.1, 10.4 Hz),

5.15 (m, 1H, J 17 Hz), 5.08 (m, 1H, J 10.4 Hz), 4.72 (t, 2H, J 7 Hz),

2.40 ± 2.25 (m, 3H), 2.34 (s, 3H), 2.25 ± 2.10 (m, 2H), 1.93 (s, 6H), 1.95 ± 1.85

(m, 2H), 1.80 ± 1.50 (m, 15H), 1.45 ± 1.00 (m, 15H); ³¹P NMR (CD₂Cl₂,

81 MHz): d 34.0; IR: nÄ 3161, 3124, 2925, 2849, 1639, 1608, 1589, 1490,

1244, 1174, 1037, 899, 854, 818, 747, 734 cm ¹; MS (ESI): m/z: 881.5 [M

Cl] ; elemental analysis calcd for C₄₆H₆₁Cl₄N₂PRu (915.86): C 60.33, H

6.71, N 3.06; found C 60.19, H 6.65, N 3.12.

23

22

5

1445, 1408, 1238, 1173, 1005, 895, 737, 687 cm ¹; MS (ESI): m/z: 795.5 [M] ,

21

20

PCy₂

4

761.5 [M Cl] ; elemental analysis calcd for C₄₂H₆₁Cl₂N₂PRu (796.91): C

Cl

63.30, H 7.72, N 3.52; found C 63.26, H 7.66, N 3.48.

3

2

Ru

6

1

Complex 12b: Imidazolium salt 7b (162 mg, 0.42 mmol), KOtBu (53 mg,

0.47 mmol) and complex 1 (328 mg, 0.40 mmol) were stirred in toluene

(25 mL) for 3 h at room temperature under Ar. The suspension was filtered

and the solvent was evaporated. Flash chromatography (n-pentane/Et₂O

4:1 ! CH₂Cl₂/Et₂O 4:1) afforded complex 12b (132 mg, 41%) as a red

solid. ¹H NMR (CD₂Cl₂, 200 MHz): d 19.23 (s, 1H), 7.86 (br, 2H), 7.42 (t,

1H, J 7.1 Hz), 7.27 (s, 1H), 7.13 (t, 2H, J 7.8 Hz), 6.84 (s, 1H), 6.40 ± 6.20

(br, 2H), 5.89 (ddt, 1H, J 17.1, 10.4, 6.7 Hz), 5.08 (dm, 1H, J 17.1 Hz),

5.02 (dm, 1H, J 10.3 Hz), 4.70 (t, 2H, J 7.5 Hz), 2.40 ± 2.15 (m, 5H), 2.34

(s, 3H), 2.00 ± 1.80 (m, 2H), 1.93 (s, 6H), 1.80 ± 1.50 (m, 15H), 1.45 ± 1.00 (m,

17H); ³¹P NMR (CD₂Cl₂, 81 MHz): d 34.2; IR: nÄ 3161, 3123, 3096,

2925, 2849, 1640, 1490, 1445, 1409, 1240, 1173, 1004, 913, 895, 847, 741,

8'

8

N

13

11'

11

10

13'

12'

9'

9

10'

7

7'

12

14'

14

Complex 10: Complex 1 (485 mg, 0.59 mmol) and carbene 5b (275 mg,

0.71 mmol) were stirred in toluene (30 mL) under Ar at 508C for 2 h. The

solvent was evaporated and n-pentane (10 mL) was added. The precipitate

formed was filtered off at 788C, washed with n-pentane ( 788C) and

dried in vacuo affording product 10 (450 mg, 82%) as a violet solid.

Alternatively, the purification of the crude product can be achieved by flash

chromatography (n-pentane/Et₂O 4:1), affording complex 9 (376 mg, 69%)

as a violet solid. ¹H NMR (CD₂Cl₂, 600 MHz): d 19.62 (s, 1H, 1-H), 7.98

(br, 2H, 3-H), 7.50 (t, J 7.6 Hz, 1H, 11-H), 7.40 (d, J 7.7 Hz, 2H, 10-H),

7.33 (tt, J 7.3, 1.1 Hz, 1H, 5-H), 7.10 (s, 1H, 7-H), 7.05 (s, 1H, 7'-H), 7.05 (s,

2H, 4-H), 6.84 (t, 1H, J 7.5 Hz, 11'-H), 6.79 (m, 2H, 10'-H), 3.55 (sept,

2H, J 6.6 Hz, 12-H), 3.10 (m, 2H, 12'-H), 2.11 (m, 3H, 20-H), 1.50 ± 1.45

(m, 9H, 22eq-H, 23eq-H), 1.40 (d, 6H, J 6.6 Hz, 13-H), 1.37 (m, 6H, 21eq-

H), 1.29 (d, 6H, 13'-H), 1.08 (d, 6H, J 6.8 Hz, 14-H), 1.00 ± 0.95 (m, 15H,

21ax-H, 22ax-H, 23ax-H), 0.95 (d, 6H, J 7.1 H, 14'-Hz); ¹³C NMR

687 cm ¹; MS (ESI): m/z: 775.5 [M Cl] ; elemental analysis calcd for

C₄₃H₆₃Cl₂N₂PRu (810.93): C 63.69, H 7.83, N 3.45; found C 63.78, H 7.89, N

3.42.

Complex 12c: Imidazolium salt 7c (172 mg, 0.46 mmol), KOtBu (51 mg,

0.46 mmol) and complex 1 (281 mg, 0.34 mmol) were stirred in toluene

(20 mL) for 1.5 h at room temperature under Ar. The suspension was

filtered and the solvent was evaporated. Flash chromatography (n-pentane/

Et₂O 4:1) afforded 12c (115 mg, 40%) as a red solid. ¹H NMR (CD₂Cl₂,

200 MHz): d 19.24 (s, 1H), 7.84 (br, 2H), 7.42 (t, 1H, J 7.2 Hz), 7.30 ±

7.20 (br, 1H), 7.12 (t, 2H, J 7.5 Hz), 6.84 (s, 1H), 6.40 ± 6.20 (br, 2H), 5.85

(ddt, 1H, J 17.1, 10.4, 6.7 Hz), 5.02 (dm, 1H, J 17.1 Hz), 4.90 (dm, 1H,

J 10.4 Hz), 4.68 (t, 2H, J 7.7 Hz), 2.40 ± 1.00 (m, 43H), 2.34 (s, 3H), 1.93

(s, 6H); ³¹P NMR (CD₂Cl₂, 81 MHz): d 34.1; IR: nÄ 3160, 3123, 3092,

3056, 2925, 2850, 1640, 1609, 1589, 569, 1489, 1446, 1173, 1004, 913, 896, 847,

1

(CD₂Cl₂, 151 MHz): d 296.7 (d, J_CH 148 Hz, J_CP 9 Hz, C-1), 190.3 (s,

J_CP 83.8 Hz, C-6), 151.6 (s, C-2), 148.7 (s, C-9), 146.2 (s, C-9'), 137.6 (s,

1

C-8'), 136.0 (s, C-8), 131.6 (d, J_CH 132 Hz, C-3), 131.3 (d, J_CH 160 Hz,

1

C-11), 130.0 (d, J_CH 159 Hz, C-11'), 128.2 (d, J_CH 158 Hz, C-5), 128.0

1

(d, J_CH 159 Hz, C-4), 126.3 (d, J_CH 197 Hz, C-7), 126.1 (d, J_CH

1

196 Hz, C-7'), 124.2 (d, J_CH 160 Hz, C-10), 123.7 (d, J_CH 158 Hz,

1

C-10'), 32.2 (d, J_CH 126 Hz, J_CP 17 Hz, C-20), 29.5 (t, J_CH 128 Hz,

741, 687 cm ¹; MS (ESI): m/z: 803.3 [M Cl] ; elemental analysis calcd for

1

C-21), 29.2 (d, C-12), 28.2 (d, C-12'), 28.1 (t, J_CH 127 Hz, J_CP 10 Hz,

1

C₄₅H₆₇Cl₂N₂PRu (838.99): C 64.42, H 8.05, N 3.34; found C 64.56, H 8.14, N

3.42.

C-22), 26.9 (q, C-14), 26.6 (t, J_CH 124 Hz, C-23), 26.3 (q, J_CH 126 Hz,

1

C-14'), 22.9 (q, J_CH 125 Hz, C-13), 22.3 (q, J_CH 125 Hz, C-13');

ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001

3248

0947-6539/01/0715-3248 $ 17.50+.50/0

Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

Complex 13: Complex 12b (30 mg, 0.04 mmol) was heated under reflux in

n-pentane (70 mL) for 1 h. The suspension was filtered and the solvent was

2.30 ± 2.15 (m, 3H), 1.91 (s, 6H, 22-H), 1.80 ± 1.60 (m, 15H), 1.50 ± 1.10 (m,

15H); ³¹P NMR (CD₂Cl₂, 81 MHz): d 32.3; ¹⁹F NMR (CD₂Cl₂,

3

slowly evaporated affording complex 13 (20 mg, 77%) as

a

brown

282 MHz): d 81.1 (t, 3F, J_FF 8.7 Hz, F-16), 113.1 (br, 2F), 121.9

crystalline solid. ¹H NMR (CD₂Cl₂, 200 MHz): d 20.22 (dt, 1H, J 9.8,

4.9 Hz), 7.08 (dm, 1H, J 1.8 Hz), 6.99 (s, 2H), 6.83 (s, 1H), 3.56 (tm, 2H,

J 4.9 Hz), 2.93 (m, 2H), 2.35 ± 2.10 (m, 5H), 2.33 (s, 3H), 2.27 (s, 6H),

1.85 ± 1.60 (m, 17H), 1.55 ± 1.10 (m, 15H); ³¹P NMR (CD₂Cl₂, 81 MHz): d

29.1; IR: nÄ 3123, 2924, 2852, 1609, 1569, 1485, 1462, 1448, 1405, 1387, 1160,

(br, 2F), 122.9 (br, 2F), 123.5 (br, 2F), 126.3 (br, 2F); IR: nÄ 3170,

3130, 3099, 3076, 3060, 2928, 2852, 1611, 1588, 1571, 1490, 1448, 1348, 1239,

1194, 1145, 1122, 1078, 1025, 895, 848, 743, 689 cm ¹; MS (ESI): m/z: 1039.6

[M Cl] ; elemental analysis calcd for C₄₅H₅₆Cl₂F₁₃N₂PRu (1074.87): C

50.28, H 5.25, N 2.61; found C 50.21, H 5.34, N 2.56.

885, 852, 733, 698 cm ¹; MS (ESI): m/z: 706.3 [M] ; elemental analysis

Complex 17: A solution of KOtBu (117 mg, 1.04 mmol) in THF (20 mL)

was slowly added at ambient temperature under Ar to a solution of 2-tert-

calcd for C₃₅H₅₅Cl₂N₂PRu (706.78): C 59.48, H 7.84, N 3.96; found C 59.36,

H 7.88, N 4.02.

butoxy-1,3-bis(2,6-di-isopropylphenyl)-4,5-dihydro-imidazole

(437 mg,

17

16

1.02 mmol) in THF (20 mL). The suspension was stirred at room temper-

ature for 2 h and added to a solution of complex 1 (545 mg, 0.66 mmol) in

toluene (40 mL). The reaction mixture was stirred for 30 min at 808C and

the solvent evaporated in vacuo. Washing of the residue at room temper-

ature with anhydrous methanol (4 Â 10 mL) and drying in vacuo afforded

product 17 (412 mg, 67%) as a violet-brownish solid. ¹H NMR (CD₂Cl₂,

200 MHz): d 19.44 (s, 1H, 1-H), 7.92 (brd, 2H, J 6.8 Hz, 3-H), 7.45 ± 7.25

(m, 5H), 7.03 (t, 2H, J 7.9 Hz, 4-H), 6.75 (s, 2H, 12-H), 4.13 (m, 2H, 12'-

H), 4.06 ± 3.87 (m, 4H, 7-H, 7'-H), 3.52 (sept., 2H, J 6.9 Hz, 12-H), 2.15 ±

2.00 (m, 3H), 1.50 ± 1.40 (m, 9H), 1.48 (d, 6H, J 6.5 Hz), 1.36 (d, 6H, J

6.6 Hz), 1.35 ± 1.30 (m, 6H), 1.21 (d, 6H, J 6.9 Hz), 1.11 (d, 6H, J

6.9 Hz), 1.00 ± 0.90 (m, 15H); ³¹P NMR (CD₂Cl₂, 81 MHz): d 27.1; IR:

nÄ 3063, 2963, 2924, 2848, 1901, 1587, 1462, 1445, 1406, 1382, 1265, 1234,

1172, 1005, 894, 847, 803, 758, 736, 687 cm ¹; MS (ESI): m/z: calcd for

15

14

PCy₂

Cl

1

Ru

5

3

2

8

13

N

4

11

10

9

7

6

12

Complex 14: Complex 12a (25 mg, 0.03 mmol) was heated under reflux in

n-hexane (50 mL) for 45 min. The suspension was filtered and the filtrate

was slowly evaporated affording chelate complex 14 (17 mg, 78%) as a

brown crystalline solid. ¹H NMR (CD₂Cl₂, 600 MHz): d 19.55 (dt, 1H,

3

1-H, J_1,P 13.6 Hz, J_1,2 6.3 Hz), 7.08 (dd, 1H, 6-H, J_6,7 1.8 Hz, J_6,P

C₅₂H₇₇Cl₂N₂PRu: 933.15; found: 897.6 [M Cl] ; HR-MS: calcd: 897.4551;

3

0.7 Hz), 7.00 (s, 2H, 10-H), 6.84 (dd, dd, 7-H, 1H, J_7,6 1.8 Hz, J_7,P

found: 897.4574.

0.9 Hz), 3.83 (dd, 2H, 4-H, ³J > 6.3 Hz, ³J < 6.3 Hz), 3.58 (q, 2H, 2-H,

Enyne metathesis reactionsÐRepresentative procedure. Synthesis of 3-(2-

³J_2,1 6.6 Hz (d), J_2,3 6.6 Hz (t)), 2.32 (s, 3H, 13-H), 2.30 (m, 2H, 3-H),

3

methyl-propenyl)-1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrole

(45a,

2.22 (s, 6H, 12-H), 2.18 (m, 3H, 14-H), 1.81 (m, 6H, 15eq-H), 1.72 (m, 6H,

16eq-H), 1.66 (m, 3H, 17eq-H), 1.51 (m, 6H, 15ax-H), 1.19 (m, 3H, 17ax-

R H): A solution of enyne 44a (R H, 55.5 mg, 0.2 mmol) and complex

2 (8.4 mg, 0.01 mmol) in toluene (20 mL) was stirred at 808C for 30 min.

The solvent was evaporated and the residue purified by flash chromatog-

raphy (hexanes/ethyl acetate 4:1) affording product 45a as a colorless solid

(49.4 mg, 89%). ¹H NMR (300 MHz, CDCl₃): d 7.70 (AA'XX', 2H), 7.28

(AA'XX', 2H), 5.58 (s, 1H), 5.35 (s, 1H), 4.24 ± 4.17 (m, 2H), 4.15 ± 4.08 (m,

2H), 2.37 (s, 3H), 1.75 (s, 3H), 1.72 (s, 3H); ¹³C NMR (75.5 MHz, CDCl₃):

d 143.4, 137.9, 136.3, 134.2, 129.7, 127.4, 120.9, 118.0, 56.2, 54.5, 27.2, 21.5,

19.9; IR (KBr): nÄ 3120, 3065, 2965, 2914, 2843, 1639, 1624, 1595, 1492,

1477, 1452, 1343, 1324, 1302, 1291, 1211, 1162, 1122, 1096, 1069, 1016, 997,

853, 835, 817, 738, 708, 670, 603, 551, 526 cm ¹; MS (EI): m/z (%): 277 (27)

H), 1.16 (m, 6H, 22ax-H); ¹³C NMR (CD₂Cl₂, 150 MHz): d 334.4 (J_CP

159.3 Hz, C-1), 183.1 (J_CP 109.4 Hz, C-5), 138.4 (C-11), 137.0 (C-8), 136.8

(C-9), 129.0 (C-10), 122.5 (J_CP 3.2 Hz, C-6*), 122.2 (J_CP 3.1 Hz, C-7*),

57.4 (C-2), 47.9 (C-4), 32.7 (J_CP 15.0 Hz, C-14), 29.9 (C-15), 28.8 (J_CP

9.8 Hz,C-16), 26.7 (C-17), 24.1 (C-3), 21.0 (C-13), 19.3 (C-12); ³¹P NMR

(CD₂Cl₂, 243 MHz): d 22.8; IR: nÄ 3124, 2921, 2850, 1609, 1562, 1487,

1446, 1407, 1259, 1172, 1005, 888, 851, 730, 700 cm ¹; MS (ESI): m/z: 657.3

[M Cl] ; elemental analysis calcd for C₃₄H₅₃Cl₂N₂PRu (692.76): C 58.95,

H 7.71, N 4.04; found C 59.11, H 7.65, N 4.01.

Complex 15: Imidazolium salt 7d (170 mg, 0.40 mmol), KOtBu (45 mg,

0.40 mmol) and complex 1 (270 mg, 0.33 mmol) were stirred in toluene

(25 mL) for 4 h at room temperature under Ar. The suspension was filtered

and the filtrate was evaporated. Flash chromatography (n-pentane/Et₂O

4:1) of the crude product thus obtained afforded complex 15 (109 mg,

37%) as a violet solid. ¹H NMR (CD₂Cl₂, 200 MHz): d 19.16 (s, 1H), 7.86

(br, 2H), 7.50 ± 7.25 (m, 1H), 7.41 (t, 1H, J 7.1 Hz), 7.12 (t, 2H, J 7.8 Hz),

6.80 (m, 1H), 6.30 (m, 2H), 4.83 (t, 2H, J 4.6 Hz), 4.35 (t, 2H, J 4.6 Hz),

2.45 ± 2.05 (m, 3H), 2.34 (s, 3H), 1.92 (s, 6H), 1.90 ± 1.50 (m, 15H), 1.45 ±

1.05 (m, 15H), 0.94 (s, 6H), 0.09 (s, 6H); ³¹P NMR (CD₂Cl₂, 81 MHz): d

35.4; IR: nÄ 3167, 3129, 3100, 3055, 2925, 2850, 1907, 1609, 1471, 1462, 1445,

1250, 1232, 1118, 1074, 894, 847, 829, 779 cm ¹; MS (ESI): m/z: 851 [M

[M] , 155 (9), 122 (100), 106 (32), 91 (51), 80 (54), 65 (18), 55 (12), 41 (14);

HR-MS (EI): calcd: C₁₅H₁₉NO₂S: 277.1137, found: 277.1132.

2,2-Diphenyl-3-vinyl-2,5-dihydro-furan (29a, R H): ¹H NMR (CDCl₃,

300 MHz): d 7.35 ± 7.22 (m, 10H), 6.23 (ddm, 1H, J 17.8, 11.2 Hz), 6.16

(m, 1H), 5.31 (dm, 1H, J 17.8 Hz), 5.09 (dm, 1H, J 11.2 Hz), 4.77 (s,

2H); ¹³C NMR (CDCl₃, 75 MHz): d 143.7, 143.3, 129.8, 127.9, 127.9, 127.4,

124.9, 117.5, 94.5, 73.2; IR (film): nÄ 3084, 2977, 2945, 2838, 1642, 1597,

1490, 1446, 1064, 990, 912, 758, 699 cm ¹; MS (EI): m/z (%): 248 (38) [M] ,

230 (9), 205 (16), 171 (100), 143 (13), 128 (24), 115 (19), 105 (44), 91 (30), 77

(32); HR-MS: calcd: 248.1201; found: 248.1206.

4-Methyl-2,2-diphenyl-3-vinyl-2,5-dihydro-furan (29b, R Me): ¹H NMR

(CDCl₃, 200 MHz): d 7.50 ± 7.15 (m, 10H), 6.31 (dd, 1H, J 17.8,

11.5 Hz), 5.14 (d, 1H, J 11.5 Hz), 5.02 (d, 1H, J 17.8 Hz), 4.68 (s, 2H),

1.90 (s, 3H); ¹³C NMR (CDCl₃, 50 MHz): d 143.9, 135.4, 135.2, 128.8,

128.0, 127.7, 127.3, 117.9, 96.1, 77.1, 11.1; IR (film): nÄ 3085, 3058, 3024, 2980,

2936, 2913, 2855, 2827, 1653, 1600, 1490, 1446, 1378, 1057, 991, 907, 759,

Cl] ; elemental analysis calcd for C₄₅H₇₁Cl₂N₂OPRuSi (887.10): C 60.93, H

8.07, N 3.16; found C 61.11, H 8.13, N 3.11.

5

4

PCy₃

700 cm ¹; MS (EI): m/z (%): 262 (22) [M] , 247 (5), 229 (8), 205 (14), 185

Cl

2

3

Ru

6

1

(100), 165 (10), 129 (11), 115 (12), 105 (45), 91 (23), 77 (35); HR-MS: calcd:

262.1358; found: 262.1360.

20

19

9

N

7

21

N

17

2-Methyl-2-phenyl-3-vinyl-2,5-dihydro-furan (31a, R H): ¹H NMR

(CD₂Cl₂, 300 MHz): d 7.40 ± 7.24 (m, 5H), 6.22 (ddm, 1H, J 17.9,

11.2 Hz), 6.00 (m, 1H), 5.07 (dm, 1H, J 17.9 Hz), 5.00 (dm, 1H, J

11.2 Hz), 4.73 (s, 2H), 1.76 (s, 3H); ¹³C NMR (CD₂Cl₂, 75 MHz): d

145.3, 145.1, 129.5, 128.5, 127.7, 126.5, 124.9, 116.9, 90.0, 73.5, 24.5; IR

(film): nÄ 3087, 2977, 2838, 1645, 1593, 1493, 1446, 1069, 989, 912, 764,

F

₁₃C₆

10

18

8

22

Complex 16: Imidazolium salt 7e (300 mg, 0.45 mmol), KOtBu (51 mg,

0.46 mmol) and complex 1 (281 mg, 0.34 mmol) were stirred in toluene

(20 mL) for 1.5 h at room temperature. The suspension was filtered, the

filtrate was evaporated and the residue purified by flash chromatography

(n-pentane/Et₂O 4:1 ! CH₂Cl₂) to afford complex 16 (155 mg, 42%) as a

violet solid. ¹H NMR (CD₂Cl₂, 300 MHz): d 19.21 (s, 1H, 1-H), 7.82 (br,

2H, 3-H), 7.44 (t, 1H, J 7.3 Hz, 5-H), 7.26 (s, 1H, 9-H), 7.14 (t, 2H, J

7.7 Hz, 4-H), 6.87 (d, 1H, J 1.9 Hz, 8-H), 6.31 (br, 2H, 19-H), 5.04 (t, 2H,

J 7.0 Hz, 9-H), 3.18 (tt, 2H, J 19.5, 7.0 Hz, 7-H), 2.35 (s, 3H, 21-H),

698 cm ¹; MS (EI): m/z (%): 186 (10) [M] , 171 (100), 153 (8), 143 (35), 128

(31), 115 (17), 109 (14), 105 (7), 91 (7), 77 (20), 51 (13), 43 (18).

1

2,4-Dimethyl-2-phenyl-3-vinyl-2,5-dihydro-furan (31b, R Me): H NMR

(CDCl₃, 200 MHz): d 7.55 ± 7.25 (m, 5H), 6.39 (ddm, 1H, J 17.4,

11.5 Hz), 5.11 (dm, 1H, J 11.5 Hz), 5.05 (dm, 1H, J 17.4 Hz),

Chem. Eur. J. 2001, 7, No. 15

ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001

0947-6539/01/0715-3249 $ 17.50+.50/0

3249

A. Fürstner et al.

FULL PAPER

4.76 ± 4.74 (m, 2H), 1.93 (s, 3H), 1.89 (s, 3H); ¹³C NMR (CDCl₃, 50 MHz):

d 145.7, 136.8, 134.4, 128.4, 127.8, 127.5, 126.6, 116.1, 91.6, 77.4, 24.4, 10.7;

IR (film): nÄ 3088, 3059, 3026, 2978, 2933, 2856, 2827, 1658, 1601, 1494,

54.3, 21.5, 19.9; IR (KBr): nÄ 3088, 2958, 2921, 2840, 1641, 1606, 1596, 1492,

1475, 1457, 1344, 1305, 1290, 1253, 1164, 1100, 1071, 1016, 987, 895, 833, 816,

709, 672, 619, 575, 549 cm ¹; MS (EI): m/z (%): 263 (46) [M] , 222 (9), 155

1446, 1037, 990, 909, 764, 698 cm ¹; MS (EI): m/z (%): 200 (5) [M] , 185

(16), 108 (100), 91 (53), 81 (40), 65 (20), 53 (8), 41 (17); HR-MS (EI): calcd

for C₁₄H₁₇NO₂S: 263.0980, found: 263.0974.

(100), 167 (6), 157 (9), 143 (30), 129 (22), 115 (12), 105 (18), 91 (13), 77 (26),

43 (45); HR-MS: calcd: 200.1201; found: 200.1205.

3-Styryl-1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrole

(43a,

R H,

1

2-Methyl-2-phenyl-3-(2-methyl-prop-2-enyl)-2,5-dihydro-furan

(33):

E:Z 3.4:1): H NMR (300 MHz, CD₂Cl₂): d [E-isomer] 7.75 (AA'XX',

2H), 7.41 ± 7.22 (m, 7H), 6.81 (dd, J 16.5, 0.6 Hz, 1H), 6.37 (d, J 16.4 Hz,

1H), 5.71 (m, 1H), 4.32 (m, 2H), 4.21 (m, 2H), 2.42 (s, 3H); d [Z-isomer]

7.56 (AA'XX', 2H), 7.41 ± 7.22 (m, 5H), 7.12 (m, 2H), 6.59 (d, J 12.0 Hz,

1H), 6.14 (m, 1H), 5.63 (m, 1H), 4.04 (m, 2H), 3.70 (m, 2H), 2.44 (s, 3H);

¹³C NMR (75 MHz, CD₂Cl₂): d [E-isomer] 144.1, 137.6, 136.8, 134.3, 131.6,

130.2, 129.0, 128.4, 127.8, 126.8, 124.0, 121.8, 55.6, 54.1, 21.6; d [Z-isomer,

where resolved] 144.1, 137.8, 136.4, 134.0, 132.3, 130.1, 128.9, 128.3, 127.9,

126.0, 123.7, 55.3, 54.6, 21.6; IR: nÄ 3026, 2922, 2899, 2832, 1596, 1492, 1461,

1450, 1398, 1379, 1345, 1302, 1291, 1263, 1208, 1183, 1163, 1106, 1072, 1016,

985, 960, 828, 812, 792, 752, 722, 708, 693, 670, 603, 572, 546, 529 cm ¹; MS

¹H NMR (CDCl₃, 200 MHz): d 7.55 ± 7.10 (m, 5H), 5.71 (s, 1H), 5.32

(m, 1H), 4.85 (s, 2H), 1.80 (s, 3H), 1.77 (s, 3H), 1.67 (s, 3H); ¹³C NMR

(CDCl₃, 50 MHz): d 145.3, 143.1, 139.4, 128.0, 127.0, 125.7, 120.8, 116.4,

91.2, 74.0, 26.9, 25.0, 20.1; IR (film): nÄ 3086, 2974, 2929, 2837, 1649, 1601,

1493, 1446, 1378, 1071, 763, 698 cm ¹; MS (EI): m/z (%): 214 (18) [M] , 199

(100), 181 (18), 171 (28), 157 (10), 157 (10), 143 (20), 129 (18), 115 (13), 105

(35), 91 (24), 79 (82), 51 (15), 43 (36); HR-MS: calcd: 214.1358, found:

214.1366.

3-Isopropenyl-2-methyl-2-phenyl-2,5-dihydro-furan

(35a,

R Me):

¹H NMR (CD₂Cl₂, 300 MHz): d 7.50 ± 7.38 (m, 2H), 7.35 ± 7.25 (m, 3H),

6.05 (s, 1H), 4.82 (s, 1H), 4.72 (s, 2H), 4.54 (s, 1H), 1.91 (s, 3H), 1.83 (s,

3H); ¹³C NMR (CD₂Cl₂, 75 MHz): d 146.7, 145.3, 136.0, 128.4, 127.6,

126.7, 124.9, 115.2, 90.3, 73.1, 24.4, 22.5; IR (film): nÄ 3087, 3060, 2976, 2836,

1635, 1495, 1447, 1371, 1251, 1237, 1073, 1044, 895, 764, 698 cm ¹; MS (EI):

(EI): m/z (%): 326 (8), 325 (31) [M] , 171 (13), 170 (100), 169 (66), 168 (55),

167 (12), 155 (12), 154 (12), 153 (53), 143 (44), 142 (11), 141 (29), 128 (35),

115 (31), 92 (27), 91 (90), 65 (35), 42 (12), 39 (13); HR-MS (EI): calcd for

C₁₉H₁₉NO₂S: 325.1137, found: 325.1131; elemental analysis calcd for

C₁₉H₁₉NO₂S (325.43): C 70.12; H 5.89; N 4.30; found C 69.94; H 6.11; N

4.06.

m/z (%): 200 (66) [M] , 185 (100), 167 (20), 157 (81), 143 (20), 142 (30), 141

(18), 129 (27), 128 (19), 115 (16), 105 (27), 79 (39), 77 (29), 51 (11), 43 (28);

HR-MS: calcd: 200.1201, found: 200.1202.

3-(1-Methyl-2-phenyl-vinyl)-1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyr-

role (43b, R Me, E:Z 2:1): ¹H NMR (300 MHz, CD₂Cl₂): d [E-

isomer] 7.75 (AA'XX', 2H), 7.44 ± 7.20 (m, 7H), 6.32 (s, 1H), 5.73 (m, 1H),

4.37 (m, 2H), 4.22 (m, 2H), 2.43 (s, 3H), 1.99 (d, J 0.9 Hz, 3H); d [Z-

isomer] 7.54 (AA'XX', 2H), 7.44 ± 7.20 (m, 5H), 7.06 (m, 2H), 6.48 (s, 1H),

5.58 (m, 1H), 4.11 ± 4.03 (m, 2H), 3.75 ± 3.71 (m, 2H), 2.45 (s, 3H), 1.94 (d,

3H, J 1.4 Hz); ¹³C NMR (75 MHz, CD₂Cl₂): d [E-isomer] d 144.1,

140.9, 137.5, 134.2, 130.7, 130.2, 129.6, 128.5, 127.8, 127.3, 123.6, 121.0, 55.9,

54.8, 21.6, 15.3; d [Z-isomer] 144.0, 139.0, 138.2, 133.9, 131.0, 130.0, 129.0,

128.9, 128.3, 127.3, 125.8, 122.6, 55.5, 54.9, 24.3, 19.3; IR: nÄ 3056, 3025,

2950, 2919, 2856, 1597, 1492, 1473, 1444, 1399, 1345, 1305, 1290, 1165, 1099,

1070, 1018, 991, 919, 834, 816, 792, 754, 706, 668, 605, 575, 550 cm ¹; MS

2-Methyl-2-phenyl-3-(1-phenyl-vinyl)-2,5-dihydro-furan (35b, R Ph):

¹H NMR (CD₂Cl₂, 300 MHz): d

7.48 ± 7.45 (m, 2H), 7.37 ± 7.26 (m,

8H), 5.80 (t, J 1.9 Hz, 1H), 5.03 (s, 1H), 4.81 (s, 1H), 4.75 (d, J 1.9 Hz,

2H), 1.87 (s, 3H); ¹³C NMR (CD₂Cl₂, 75.5 MHz): d 146.2, 145.2, 142.9,

142.5, 128.5, 128.4, 128.3, 128.0, 127.8, 127.7, 126.6, 116.6, 90.8, 73.4, 24.6; IR

(neat): nÄ 3083, 3057, 3027, 2978, 2983, 2840, 1720, 1659, 1599, 1573, 1493,

1445, 1370, 1336, 1235, 1183, 1129, 1096, 1071, 1054, 1027, 953, 905, 865, 819,

777, 765, 699, 629, 594, 562, 530 cm ¹; MS (EI): m/z (%): 262 (71) [M] , 247

(100), 229 (25), 219 (69), 204 (20), 185 (13), 171 (13), 155 (4), 141 (89), 128

(15), 115 (44), 103 (77), 91 (49), 77 (52), 63 (8), 51 (19), 43 (32); HR-MS

(EI): calcd for C₁₉H₁₈O: 262.1358, found: 262.1357.

(EI): m/z (%): 340 (16), 339 (66) [M] , 185 (14), 184 (100), 183 (55), 182

2,2,2',2'-Tetramethyl-2,5,2',5'-tetrahydro-[3,3']bifuranyl (37): ¹H NMR

(CD₂Cl₂, 300 MHz): d 5.76 (s, 2H), 4.57 (s, 4H), 1.39 (s, 12H);

(56), 169 (16), 168 (47), 167 (73), 157 (43), 156 (34), 155 (34), 143 (11), 142

(21), 141 (22), 129 (23), 128 (15), 115 (28), 106 (11), 92 (10), 91 (84), 65 (18),

42 (16); HR-MS (EI): calcd for C₂₀H₂₁NO₂S: 339.1293, found: 339.1292;

elemental analysis calcd for C₂₀H₂₁NO₂S (339.46): C 70.77, H 6.24, N 4.13;

found: C 70.58, H 6.30, N 4.06.

¹³C NMR (CD₂Cl₂, 75 MHz): d 139.3, 122.6, 88.8, 72.3, 27.4; IR (KBr):

1

nÄ 3091, 1970, 1836, 1638, 1459, 1364, 1272, 1195, 1145, 1074, 806, 761 cm

;

MS (EI): m/z (%): 194 (27) [M] , 179 (100), 135 (31), 121 (26), 109 (11), 107

(13), 93 (26), 91 (20), 78 (29), 55 (11), 43 (84); HR-MS: calcd: 194.1307,

found: 194.1308.

3-Methyl-2-[1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrol-3-yl]-but-2-eno-

ic acid methyl ester (45b, R CO₂Me): ¹H NMR (300 MHz, CD₂Cl₂): d

7.71 (AA'XX', 2H), 7.35 (AA'XX', 2H), 5.38 (m, 1H), 4.16 (m, 2H), 4.12

(m, 2H), 3.60 (s, 3H), 2.43 (s, 3H), 2.01 (s, 3H), 1.69 (s, 3H); ¹³C NMR

(75 MHz, CD₂Cl₂): d 167.3, 149.7, 144.1, 135.9, 134.5, 130.1, 127.8, 124.3,

122.5, 57.1, 55.6, 51.7, 23.6, 22.7, 21.6; IR: nÄ 3065, 3028, 2989, 2950, 2918,

2867, 1717, 1620, 1598, 1494, 1434, 1399, 1372, 1346, 1306, 1285, 1223, 1163,

1093, 1017, 1007, 985, 921, 885, 816, 777, 760, 709, 669, 603, 549 cm ¹; MS

4-Isopropenyl-3,6-dihydro-2H-pyran (39): ¹H NMR (300 MHz, CD₂Cl₂):

d 5.82 (m, 1H), 4.99 (m, 1H), 4.91 (m, 1H), 4.22 (m, 2H), 3.79 (t, J

5.5 Hz, 2H), 2.28 (m, 2H), 1.90 (m, 3H); ¹³C NMR (75 MHz, CD₂Cl₂): d

142.8, 134.7, 123.2, 110.7, 66.0, 64.7, 26.1, 20.0; MS (EI): m/z (%): 125 (5),

124 (67) [M] , 123 (5), 110 (7), 109 (100), 95 (14), 93 (7), 91 (12), 83 (26), 81

(45), 79 (37), 77 (26), 67 (46), 65 (14), 55 (41), 53 (32), 52 (6), 51 (16), 43

(13), 41 (35), 39 (44), 29 (13), 27 (27). Due to the lability of this diene, the

product was subjected to a Diels ± Alder reaction with dimethyl acety-

lenedicarboxylate (toluene, 4 h, reflux) to afford the corresponding cyclo-

adduct (76% over both steps) which gave the following spectroscopic and

analytical data: m.p. 140 ± 1428C; ¹H NMR (300 MHz, CD₂Cl₂): d 4.00

(dd, J 10.2, 4.2 Hz, 2H), 3.73 (s, 3H), 3.72 (s, 3H), 3.33 ± 3.19 (m, 2H),

3.07 (t, J 10.4 Hz, 1H), 2.99 (d, J 7.2 Hz, 1H), 2.86 (m, 1H), 2.58 (m,

1H), 2.07 (m, 1H), 1.69 (s, 3H); ¹³C NMR (75 MHz, CD₂Cl₂): d 168.4,

167.8, 133.9, 132.4, 126.0, 120.8, 72.4, 69.5, 52.4, 52.3, 41.7, 33.8, 30.3, 17.5;

IR: nÄ 2996, 2970, 2951, 2906, 2871, 2849, 1730, 1714, 1655, 1440, 1406,

1376, 1280, 1271, 1243, 1227, 1188, 1154, 1124, 1102, 1083, 1068, 1024, 968,

(EI): m/z (%): 336 (7), 335 (35) [M] , 180 (24), 148 (27), 121 (11), 120 (100),

93 (15), 91 (39), 77 (11), 65 (12); HR-MS (EI): calcd for C₁₇H₂₁NO₄S:

335.1191, found: 335.1194; elemental analysis calcd for C₁₇H₂₁NO₄S

(335.42): C 60.87, H 6.31, N 4.18; found C 60.94, H 6.26, N 4.10.

5-Isopropenyl-1-(toluene-4-sulfonyl)-1,2,3,6-tetrahydro-pyridine

(47):

¹H NMR (CDCl₃, 300 MHz): d 7.67 (AA'XX', 2H), 7.29 (AA'XX',

2H), 5.87 ± 5.81 (m, 1H), 4.85 (s, 1H), 4.82 (s, 1H), 3.77 ± 3.72 (m, 2H), 3.13

(d, J 5.8 Hz, 2H), 2.39 (s, 3H), 2.33 ± 2.26 (m, 2H), 1.82 (m, 3H); ¹³C NMR

(CDCl₃, 75.5 MHz): d 143.5, 140.5, 133.5, 133.0, 129.6, 127.6, 122.3,

110.4, 45.0, 42.3, 25.5, 21.5, 20.5; IR (KBr): nÄ 3061, 2961, 2925, 2865, 1716,

1642, 1597, 1569, 1494, 1458, 1382, 1364, 1341, 1306, 1241, 1165, 1101, 1018,

911, 898, 839, 790, 759, 666 cm ¹; MS (EI): m/z (%): 267 (3), 266 (22) [M] ,

970, 899, 816, 770, 744, 658, 564, 548 cm ¹; MS (EI): m/z (%): 277 (9) [M] ,

235 (27), 234 (39), 219 (35), 205 (12), 204 (34), 203 (12), 191 (12), 190 (29),

189 (10), 178 (13), 177 (100), 175 (10), 146 (12), 145 (39), 133 (10), 118 (16),

117 (22), 115 (19), 105 (12), 103 (11), 91 (25), 77 (13), 59 (22), 45 (12); HR-

MS (EI): calcd for C₁₄H₁₈O₅: 266.1154, found: 266.1153; elemental analysis

calcd for C₁₄H₁₈O₅(266.29): C 63.15, H 6.81; found C 63.22, H 6.77.

262 (6), 236 (2), 155 (15), 121 (68), 106 (21), 95 (61), 79 (100), 65 (24), 55

(14), 41 (21).

3-Isopropenyl-1-(toluene-4-sulfonyl)-2,5,6,7-tetrahydro-1H-azepine (49):

¹H NMR (CDCl₃, 300 MHz): d 7.64 (AA'XX', 2H), 7.24 (AA'XX',

2H), 5.87 (t, J 6.2 Hz, 1H), 5.11 (s, 1H), 4.93 (s, 1H), 4.06 (s, 2H), 3.39 (t,

J 6.1 Hz, 2H), 2.39 (s, 3H), 2.26 ± 2.18 (m, 2H), 1.83 (d, J 0.8 Hz, 3H),

1.75 ± 1.66 (m, 2H); ¹³C NMR (CDCl₃, 75.5 MHz): d 142.9, 142.3, 139.1,

136.4, 129.7, 129.4, 127.1, 111.7, 50.5, 46.9, 26.4, 26.3, 21.4, 21.3; IR (KBr):

nÄ 3047, 2936, 2852, 1698, 1641, 1599, 1494, 1455, 1337, 1305, 1266, 1240,

3-Isopropenyl-1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrole

(41):

¹H NMR (CDCl₃, 300 MHz): d 7.71 (AA'XX', 2H), 7.29 (AA'XX',

2H), 6.32 (dd, J 17.7, 10.8 Hz, 1H), 5.56 (s, 1H), 4.95 (s, 1H), 4.74 (s, 1H),

4.24 ± 4.15 (m, 4H), 2.39 (s, 3H), 1.82 (s, 3H); ¹³C NMR (CDCl₃,

75.5 MHz): d 143.3, 139.2, 136.5, 134.1, 129.8, 127.4, 120.6, 114.5, 55.5,

3250

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

1160, 1094, 1044, 1018, 928, 906, 881, 816, 737, 708, 657, 596, 548 cm ¹; MS

(EI): m/z (%): 291 (28) [M] , 276 (5), 263 (1), 248 (12), 224 (14), 184 (11),

155 (40), 136 (100), 120 (20), 107 (26), 91 (73), 79 (25), 65 (22), 55 (10), 41

(28); HR-MS (EI): calcd for C₁₆H₂₁NO₂S: 291.1293, found: 291.1295.

(96), 142 (53), 141 (100), 139 (16), 129 (26), 128 (81), 127 (18), 115 (67), 91

(12), 89 (12), 77 (10), 63 (14), 51 (10), 39 (12); HR-MS (EI): calcd for

C₁₄H₁₄O₃: 230.0943, found: 230.0944; elemental analysis calcd for C₁₄H₁₄O₃

(230.26): C 73.03, H 6.13; found C 73.15, H 6.06.

1-(4-{1-[1-(Toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrol-3-yl]-vinyl}-phen-

yl)-ethanone (51): ¹H NMR (CD₂Cl₂, 300 MHz): d 7.90 (AA'XX', 2H),

7.74 (AA'XX', 2H), 7.37 (AA'XX', 2H), 7.31 (AA'XX', 2H), 5.47 ± 5.43 (m,

1H), 5.24 (s, 1H), 5.16 (s, 1H), 4.38 ± 4.32 (m, 2H), 4.23 ± 4.15 (m, 2H), 2.57

(s, 3H), 2.35 (s, 3H); ¹³C NMR (CD₂Cl₂, 75.5 MHz): d 197.7, 145.1, 144.2,

142.6, 138.1, 137.0, 134.3, 130.2, 128.8, 128.5, 127.8, 124.8, 117.0, 56.0, 55.1,

26.8, 21.6; IR (neat): nÄ 3062, 2922, 2854, 1682, 1649, 1604, 1560, 1494,

1427, 1402, 1345, 1306, 1267, 1162, 1097, 1066, 1015, 958, 909, 883, 815, 709,

Crystal Data for 9 ± 11 and 13 ± 15, 18: Single crystals suitable for X-ray

analysis were mounted on glass fibers using perfluoropolyether. X-ray

intensities were measured at 100 K using Mo_Ka(l 0.71073 ) radiation,

employing either a Nonius KappaCCD system and a rotating anode

generator (11, 14, 15, 18) or a Bruker AXS Smart system equipped with a

sealed tube (9, 10, 13). One hemisphere of data was collected in case of the

SMART system and a two-fold redundancy was aimed for in case of the

KappaCCD system. Integrated intensities including Lorentz and polar-

ization corrections were obtained using the SAINT (Bruker AXS) [SAINT

Ver. 6.01, Bruker AXS Inc. Madison, Wisconsin, USA, 1999] and Denzo-

SMN (Nonius)^[44]programs respectively. For further crystal and data

collection details see Table 7.

668, 620, 591, 549 cm ¹; MS (EI): m/z (%): 367 (58) [M] , 222 (19); 212 (50),

196 (18), 170 (74), 155 (43), 91 (100), 65 (25), 43 (87).

3-Isopropenyl-cyclopent-3-ene-1,1-dicarboxylic acid diethyl ester (53):

¹H NMR (300 MHz, CD₂Cl₂): d 5.61 (m, 1H), 4.95 (s, 1H), 4.91 (d, J

0.6 Hz, 1H), 4.17 (q, J 7.1 Hz, 4H), 3.14 (m, 2H), 3.08 (m, 2H), 1.91 (s,

3H), 1.24 (t, J 7.1 Hz, 6H); ¹³C NMR (75 MHz, CD₂Cl₂): d 172.3, 141.8,

139.5, 124.3, 113.3, 61.9, 59.2, 41.4, 40.8, 20.5, 14.2; IR: nÄ 3089, 3062, 2981,

2939, 2907, 2868, 1733, 1634, 1603, 1445, 1385, 1367, 1250, 1183, 1161, 1119,

1068, 1016, 987, 888, 820, 709 cm ¹; MS (EI): m/z (%): 253 (4), 252 (22)

All crystal structures were solved using the SHELXS-97 [G. M. Sheldrick,

Program for the solution of crystal structures, University of Göttingen,

Germany, 1997] program, either by direct methods (9, 13) or interpretation

2

of the Patterson function. The function w(F_o²F_c² was minimized using

full matrix least-squares refinement implemented in the program

SHELXL-97 [G. M. Sheldrick, Program for the refinement of crystal

structures, University of Göttingen, Germany, 1997]. Atomic positions and

anisotropic displacement parameters were included for all non-hydrogen

atoms, with the exception of 9 (cyclohexane solvent and disordered phenyl

substituent) and 10 (all carbon atoms) where isotropic displacement

parameters were employed. Hydrogen atoms were placed at calculated

positions and were allowed to ride on the corresponding parent atom with

isotropic displacement parameters 1.2 times (1.5 times for methyl) of

[M] , 207 (10), 179 (31), 178 (100), 150 (13), 133 (20), 119 (21), 106 (18), 105

(48), 91 (40), 79 (14), 77 (13), 29 (53), 27 (12); HR-MS (EI): calcd for

C₁₄H₂₀O₄: 252.1362, found: 252.1367; elemental analysis calcd for C₁₄H₂₀O₄

(252.31): C 66.65, H 7.99; found C 66.78, H 8.07.

2-(1,3-Dihydro-benzo[c]oxepin-5-yl)-acrylic acid methyl ester (55):

¹H NMR (300 MHz, CD₂Cl₂): d 7.33 ± 7.27 (m, 3H), 7.16 (m, 1H), 6.35

(d, J 1.6 Hz, 1H), 6.17 (t, J 5.1 Hz, 1H), 5.85 (d, J 1.7 Hz, 1H), 4.55 (s,

2H), 4.17 (d, J 5.1 Hz, 2H), 3.60 (s, 3H); ¹³C NMR (75 MHz, CD₂Cl₂):

d 167.1, 143.1, 140.8, 139.0, 138.5, 130.8, 129.2, 128.2, 128.1, 128.0, 127.9,

70.4, 67.1, 52.2; IR: nÄ 3099, 3060, 3022, 2994, 2951, 2916, 2856, 1723, 1618,

1572, 1488, 1448, 1436, 1379, 1361, 1320, 1303, 1271, 1235, 1210, 1149, 1113,

1098, 1057, 1041, 985, 953, 898, 881, 860, 830, 812, 775, 761, 735, 714, 610,

the parent atom.

A

summary of the results is given in

Table 7 (RSjjF_oj jF_cjj/S jF_oj, wR2{S[w(F_o²F_c²²]/S [w(F_o²²]}^1/2

,

GoF{S[w(F_o²F_c²²]/(n p)}^1/2, with n equals number of reflections and

p equals number of parameters).

594 cm ¹; MS (EI): m/z (%): 231 (5), 230 (35) [M] , 202 (20), 197 (11), 187

Crystallographic data (excluding structure factors) for the structures

reported in this paper have been deposited with the Cambridge Crystallo-

(20), 186 (10), 171 (14), 170 (26), 169 (34), 155 (12), 153 (31), 144 (13), 143

Table 7. Crystal data and details of the structure determination for 9 ± 11, 13 ± 15 and 18.

10 11 13

C₄₆H₆₁Cl₄N₂PRu C₅₇H₈₇Cl₂N₂PRu C₄₈H₆₀Cl₂N₃PRu C₃₅H₅₅Cl₂N₂PRu C₃₄H₅₃Cl₂N₂PRu C_47.5H₇₇Cl₂N₂OPRuSi C₃₆H₆₈Cl₂P₂Ru

9

14

15

18

formula

color

M_w[gmol

crystal system

space group

a []

b []

c []

a [8]

b [8]

brown

915.81

red-brown

1003.23

black

881.93

yellow

706.75

brown

692.72

dark red

947.15

yellow

734.81

triclinic

1

]

monoclinic

Cc (no. 9)

12.1730(6)

7.9632(18)

9.7070(5)

monoclinic

P2₁/n (no. 14)

28.3376(9)

14.3007(6)

29.2250(12)

monoclinic

P2₁/c (no. 14)

18.8745(12)

10.9962(8)

20.9943(12)

monoclinic

P2₁/c (no. 14)

18.413(2)

9.9087(11)

18.759(2)

monoclinic

C2/c (no. 15)

40.4367(8)

9.7598(2)

19.0674(6)

triclinic

Å

P1 (no. 2)

P1, (no. 2)

9.7413(2)

15.5112(3)

17.8850(3)

65.7930(10)

84.8880(10)

80.4940(10)

2430.25(8)

2

9.705(10)

10.121(13)

10.719(8)

114.13(4)

108.29(3)

91.48(5)

897.8(16)

1

97.418(2)

107.416(2)

102.700(3)

91.275(4)

117.701(2)

g [8]

V [³]

Z

4448.3(4)

4

1.367

0.663

1912

11300.4(8)

8

1.179

0.436

4288

4250.7(5)

4

1.378

0.570

1848

3421.7(6)

4

1.372

0.688

1488

6662.5(3)

8

1.381

0.705

2912

3

1_calcd[Mgm

]

1.294

0.939

1001

1.359

0.699

392

1

m [mm

]

F(000) [e ]

crystal size [mm]

q range for

data collection

refls. collected

indep. refls.

R_int

0.26 Â 0.16 Â 0.16 0.28 Â 0.24 Â 0.21 0.16 Â 0.08 Â 0.03 0.54 Â 0.40 Â 0.02 0.19 Â 0.09 Â 0.09 0.30 Â 0.13 Â 0.03

0.25 Â 0.10 Â 0.08

1.77 to 33.178

2.04 to 24.008

2.05 to 27.47

2.17 to 27.49

3.41 to 27.828

3.43 to 33.208

2.23 to 27.568

24700

10683

0.0529

8175

36240

15256

0.2060

5291

20661

8670

0.1780

2847

28511

7758

0.1562

5524

25497

7831

0.0779

5907

29616

18425

0.0732

10943

8293

4131

0.0855

3369

obs. refls.

with I > 2s(I)

compl. to q

data/parameters

GoF

33.178/97.6%

10683/490

1.018

24.008/85.9%

15256/599

0.916

27.478/88.9%

8670/471

0.881

27.498/98.6%

7758/373

1.051

27.828/99.1%

7831/382

1.002

27.508/99.6%

18425/514

0.984

27.568/99.7%

4131/187

1.122

R [I > 2s(I)]

wR2 (all data)

flack parameter

0.0544

0.1191

0.07(3)

0.0984

0.2880

±

0.0780

0.2429

±

0.0710

0.2258

±

0.0418

0.1059

±

0.0603

0.1263

±

0.0507

0.1572

±

max. diff. peak/hole [e ³] 1.485/ 0.800

0.824/ 0.886

0.915/ 1.342

2.077/ 5.077

0.812/ 0.461

0.755/ 0.897

1.034/ 2.062

Chem. Eur. J. 2001, 7, No. 15

ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001

0947-6539/01/0715-3251 $ 17.50+.50/0

3251

A. Fürstner et al.

FULL PAPER

graphic Data Centre as supplementary publication no. CCDC ± 154931

(10), CCDC-154932 (18), CCDC-154933 (11), CCDC-154934 (9), CCDC-

154935 (13), CCDC-154936 (15) and CCDC-156357 (14). Copies of the

data can be obtained free of charge on application to CCDC, 12 Union

Road, Cambridge CB21EZ, UK (fax: (44)1223-336-033; e-mail: deposit

@ccdc.cam.ac.uk).

c) U. Frenzel, T. Weskamp, F. J. Kohl, W. C. Schattenmann, O.

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Acknowledgement

Generous financial support by the Deutsche Forschungsgemeinschaft

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Â

(Leibniz award to A.F.) and the Fonds der Chemischen Industrie (Kekule

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Angermund for carrying out AM1 calculations for compounds 28 and 29.

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[20] Alternatively catalytic amounts of tBuOK together with NaH can be

used; this method has the advantage that the progress of carbene

formation can be monitored by measuring the volume of H₂formed,

cf. ref. [17b]. If applicable, we prefer this method for its preparative

convenience over an alternative procedure using NaH in liquid

ammonia as the reaction medium, cf. ref. [18].

[21] a) D. Enders, K. Breuer, G. Raabe, J. Runsink, J. H. Teles, J.-P. Melder,

K. Ebel, S. Brode, Angew. Chem. 1995, 107, 1119 ± 1122; Angew. Chem.

Int. Ed. Engl. 1995, 34, 1021 ± 1023; b) for a detailed description of the

reactivity of this carbene, including its reactions with olefins see: D.

Enders, K. Breuer, J. Runsink, J. H. Teles, Liebigs Ann. 1996, 2019 ±

2028.

[22] L. Jafarpour, S. P. Nolan, Organometallics 2000, 19, 2055 ± 2057.

[23] Complex 16 was designed to make such ªsecond-generationº catalysts

more soluble in supercritical CO₂; applications will be reported in a

separate publication. For the first examples of RCM and ROMP in

scCO₂using the parent-complex 1 see: A. Fürstner, D. Koch, K.

[8] a) M. Scholl, T. M. Trnka, J. P. Morgan, R. H. Grubbs, Tetrahedron

Lett. 1999, 40, 2247 ± 2250; b) M. Scholl, S. Ding, C. W. Lee, R. H.

Grubbs, Org. Lett. 1999, 1, 953 ± 956.

[9] a) L. Ackermann, A. Fürstner, T. Weskamp, F. J. Kohl, W. A.

Herrmann, Tetrahedron Lett. 1999, 40, 4787 ± 4790; b) T. Weskamp,

F. J. Kohl, W. Hieringer, D. Gleich, W. A. Herrmann, Angew. Chem.

1999, 111, 2573 ± 2576; Angew. Chem. Int. Ed. 1999, 38, 2416 ± 2419;

3252

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Chem. Eur. J. 2001, 7, No. 15

Ru-Based Metathesis Catalysts

3236±3253

Langemann, W. Leitner, C. Six, Angew. Chem. 1997, 109, 2562 ± 2565;

Angew. Chem. Int. Ed. Engl. 1997, 36, 2466 ± 2469.

Mori, N. Sakakibara, A. Kinoshita, J. Org. Chem. 1998, 63, 6082 ±

6083; h) J. A. Smulik, S. T. Diver, J. Org. Chem. 2000, 65, 1788 ± 1792

and references therein.

1

[24] In solution, complex 11 gives rise to two sets of signals in the H and

³¹P NMR spectra; 2D EXSY confirm that this effect is due to rotamers

around the Ru NHC bond.

[37] While RCM is driven by the gain in entropy caused by the (gaseous)

by-product (e.g. ethene) released during the course of the reaction,

enyne metathesis is devoid of such an inherent driving force.

Therefore most examples reported so far deal with the formation of

five-membered rings which have the highest intrinsic bias for

cyclization. For some successful applications to larger rings see

ref. [36g].

[25] R. O. Gould, A. M. Gray, P. Taylor, M. D. Walkinshaw, J. Am. Chem.

Soc. 1985, 107, 5921 ± 5927.

[26] T. Weskamp, W. C. Schattenmann, M. Spiegler, W. A. Herrmann,

Angew. Chem. 1998, 110, 2631 ± 2633; Angew. Chem. Int. Ed. 1998, 37,

2490 ± 2493.

[27] C. W. Bielawski, R. H. Grubbs, Angew. Chem. 2000, 112, 3025 ± 3028;

Angew. Chem. Int. Ed. 2000, 39, 2903 ± 2906.

[28] a) For a detailed discussion see ref. [11]. b) Note, that the decom-

[38] Compounds of this type undergo formal enyne metathesis reactions in

the presence of PtCl₂or electron deficient palladacycles as catalysts;

for leading references see: a) N. Chatani, N. Furukawa, H. Sakurai, S.

Murai, Organometallics 1996, 15, 901 ± 903; b) B. M. Trost, M. K.

Trost, J. Am. Chem. Soc. 1991, 113, 1850 ± 1852; c) A. Fürstner, H.

Szillat, B. Gabor, R. Mynott, J. Am. Chem. Soc. 1998, 120, 8305 ± 8314;

d) A. Fürstner, H. Szillat, F. Stelzer, J. Am. Chem. Soc. 2000, 122,

6785 ± 6786.

position of the catalyst also constitutes

a potential source of

ruthenium hydride species; although the decomposition pathways of

the Grubbs catalyst 1 have been studied in some detail, the ruthenium

species formed are not yet clear, cf.: M. Ulman, R. H. Grubbs, J. Org.

Chem. 1999, 64, 7202 ± 7207.

[29] C. Grünwald, O. Gevert, J. Wolf, P. Gonzalez-Herrero, H. Werner,

Organometallics 1996, 15, 1960 ± 1962.

[30] V. Rodriguez, S. Sabo-Etienne, B. Chaudret, J. Thoburn, S. Ulrich, H.-

H. Limbach, J. Eckert, J.-C. Barthelat, K. Hussein, C. J. Marsden,

Inorg. Chem. 1998, 37, 3475 ± 3485.

[31] In this context the reader is referred to a recent report showing that

the Grubbs catalyst 1 converts into (PCy₃)₂RuCl₂H₂upon hydro-

genation in CH₂Cl₂, cf. S. D. Drouin, G. P. A. Yap, D. E. Fogg, Inorg.

Chem. 2000, 39, 5412 ± 5414.

[32] According to our opinion some data reported in the literature are

inadequate for an assessment of the reactivity of NHC containing

catalysts. Complexes of this type were repeatedly applied to a single

substrate such as diethyl diallylmalonate which reacts very smoothly

even with the parent Grubbs carbene 1 and is therefore of limited

value for probing the reactivity of more powerful catalysts.

[33] a) A. Fürstner, K. Langemann, J. Org. Chem. 1996, 61, 3942 ± 3943;

b) A. Fürstner, K. Langemann, Synthesis 1997, 792 ± 803.

[34] Monitoring of this transformation by GC and TLC shows that the

formation of the cyclic monomer proceeds via an initial dimerization

of substrate 25 at the monosubstituted alkene; the resulting dimer 26

is then converted into the cyclic monomer 27. For a more detailed

report on this observation see ref. [13d].

[35] Review: M. Mori, Top. Organomet. Chem. 1998, 1, 133 ± 154.

[36] See ref. [14f, i] and the following for leading references: a) A.

Kinoshita, N. Sakakibara, M. Mori, J. Am. Chem. Soc. 1997, 119,

12388 ± 12389; b) R. Stragies, M. Schuster, S. Blechert, Angew. Chem.

1997, 109, 2628 ± 2630; Angew Chem. Int. Ed. Engl. 1997, 36, 2518 ±

2520; c) A. G. M. Barrett, S. P. D. Baugh, D. C. Braddock, K. Flack,

V. C. Gibson, P. A. Procopiou, Chem. Commun. 1997, 1375 ± 1376;

d) K. Hammer, K. Undheim, Tetrahedron 1997, 53, 10603 ± 10614;

e) A. Kinoshita, M. Mori, Synlett 1994, 1020 ± 1022; f) M. Mori, T.

Kitamura, N. Sakakibara, Y. Sato, Org. Lett. 2000, 2, 543 ± 545; g) M.

[39] Leading references: a) M. T. Reetz, M. H. Becker, K. M. Kühling, A.

Holzwarth, Angew. Chem. 1998, 110, 2792 ± 2795; Angew. Chem. Int.

Ed. 1998, 37, 2647 ± 2650; b) A. Holzwarth, H.-W. Schmidt, W. F.

Maier, Angew. Chem. 1998, 110, 2788 ± 2792; Angew. Chem. Int. Ed.

1998, 37, 2644 ± 2647; c) S. J. Taylor, J. P. Morken, Science 1998, 280,

267 ± 270.

[40] Reviews on combinatorial methods in catalysis: a) B. Jandeleit, D. J.

Schaefer, T. S. Powers, H. W. Turner, W. H. Weinberg, Angew. Chem.

1999, 111, 2648 ± 2689; Angew. Chem. Int. Ed. 1999, 38, 2494 ± 2532;

b) M. T. Reetz, Angew. Chem. 2001, 113, 292 ± 320; Angew. Chem. Int.

Ed. 2001, 40, 284 ± 310.

[41] M. T. Reetz, M. H. Becker, M. Liebl, A. Fürstner, Angew. Chem. 2000,

112, 1294 ± 1298; Angew. Chem. Int. Ed. 2000, 39, 1236 ± 1239.

[42] For preparative applications of this complex see: a) A. Fürstner, O. R.

Thiel, J. Org. Chem. 2000, 65, 1738 ± 1742; b) A. Fürstner, J.

Grabowski, C. W. Lehmann, T. Kataoka, K. Nagai, ChemBioChem

2001, 2, 60 ± 68; c) A. Fürstner, J. Grabowski, C. W. Lehmann, J. Org.

Chem. 1999, 64, 8275 ± 8280; d) A. Fürstner, K. Radkowski, Chem.

Commun. 2001, 671 ± 672.

1

[43] AM1 calculations show that diene 28 is about 35 kcalmol more

stable than enyne 29. This explains the exothermicity observed by the

thermocamera. It is believed, however, that the much more dramatic

evolution of heat in case of complexes 3 and 10 as compared to the

other catalysts screened is partly due to the fact that the heating of the

reaction mixture caused by the incipient reaction increases the

reaction rate, thereby producing even more heat and a yet faster

conversion. Such an ªautocatalyticº effect is absent whenever the

reaction rate is such that heat transfer to the surroundings occurs at

similar rates as the progress of the reaction.

[44] Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307 ± 326.

Received: February 12, 2001 [F3067]

Chem. Eur. J. 2001, 7, No. 15

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Article Doi

Comparative investigation of ruthenium-based metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands

DOI: 10.1002/1521-3765(20010803)7:15<3236::AID-CHEM3236>3.0.CO;2-S

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