A sterically demanding nucleophilic carbene: 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene. Thermochemistry and catalytic application in olefin metathesis

Article abstract of DOI:10.1016/S0022-328X(00)00260-6

The sterically demanding nucleophilic carbene ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr, 4) has been synthesized. The reaction of [Cp*RuCl]₄ (5; Cp* = η⁵-C₅Me₅) with this ligand affords a coordinatively unsaturated Cp*Ru(IPr)Cl (6) complex. Solution calorimetric results in this system provide information concerning the electron donor properties of the carbene ligand. Steric parameters associated with this ligand are determined from the X-ray crystal structure study. The carbene ligand reacts with RuCl₂(=C(H)Ph)(PCy₃)₂ (1) to yield a mixed carbene-phosphine ruthenium complex RuCl₂(=C(H)Ph)(IPr)(PCy₃) (9). A single-crystal X-ray diffraction study has been performed on 9. The thermal stability of 9 has been studied at 60°C and its catalytic activity has been evaluated for the ring closing metathesis of diethyldiallylmalonate.

Full text of DOI:10.1016/S0022-328X(00)00260-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 606 (2000) 49–54
A sterically demanding nucleophilic carbene:
1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Thermochemistry
and catalytic application in olefin metathesis
Laleh Jafarpour, Edwin D. Stevens, Steven P. Nolan *
Department of Chemistry, Uni6ersity of New Orleans, New Orleans, LA 70148, USA
Received 9 February 2000; received in revised form 22 March 2000
Abstract
The sterically demanding nucleophilic carbene ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr, 4) has been synthe-
sized. The reaction of [Cp*RuCl]4 (5; Cp*=h5-C5Me5) with this ligand affords a coordinatively unsaturated Cp*Ru(IPr)Cl (6)
complex. Solution calorimetric results in this system provide information concerning the electron donor properties of the carbene
ligand. Steric parameters associated with this ligand are determined from the X-ray crystal structure study. The carbene ligand
reacts with RuCl2(ꢀC(H)Ph)(PCy3)2 (1) to yield a mixed carbene–phosphine ruthenium complex RuCl2(ꢀC(H)Ph)(IPr)(PCy3) (9).
A single-crystal X-ray diffraction study has been performed on 9. The thermal stability of 9 has been studied at 60°C and its
catalytic activity has been evaluated for the ring closing metathesis of diethyldiallylmalonate. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Nucleophilic carbene; Thermochemistry; Olefin metathesis
and/or preventing the decomposition of carbenes [4d,
5]. It has been shown that one of the phosphine ligands
can be exchanged with one bulky nucleophilic carbene
ligand such as 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-
ylidene (IMes (2)) to afford a mixed ligand system,
RuCl2(ꢀC(H)Ph)(IMes)(PCy3) (3) [6]. When used in
RCM, the catalyst precursor 3 shows significant activity
and improved thermal stability compared to the parent
complex 1 [6].
In a detailed study, we have examined steric and
electronic properties of various nucleophilic carbene
ligands by solution calorimetry and structural analysis
[6a, 7]. We have also investigated the role of these
ligands as catalyst precursors in ring closing metathesis
(RCM) reactions [6a, 7]. In this paper we present the
synthesis, structural characterization, and thermochem-
istry involving another bulky ligand 1,3-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene (4). The electronic and
steric properties of this ligand are compared to those of
previously reported carbenes [6a, 7] and phosphines.
This ligand is also utilized in the synthesis and catalytic
behavior of very stable analogue to Grubbs’ olefin
metathesis catalyst.
1. Introduction
Tertiary phosphine ligands are useful in controlling
reactivity and selectivity in organometallic chemistry
and homogeneous catalysis [1] however, they often
undergo significant PꢁC degradation at higher tempera-
tures which, in certain catalytic processes, results in the
deactivation of the catalyst [2]. Therefore there is a
need for strongly nucleophilic (electron-rich) ligands
that form stable bonds with metals. Carbene ligands
have proven to behave as phosphine mimics [3].
The ruthenium carbene complex, RuCl2(ꢀC(H)Ph)-
(PCy3)2 (1) developed by Grubbs et al. is a highly
efficient catalyst precursor in ring closing metathesis
(RCM) and its use is widespread in organic and poly-
mer chemistry [4]. Mechanistic studies have shown that
the presence of a bulky tertiary phosphine ligand is
mandatory for stabilizing reactive catalytic intermediate
* Corresponding author. Tel.: +1-504-2866311; fax: +1-504-
2806860.
E-mail address: snolan@uno.edu (S.P. Nolan).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00260-6

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L. Jafarpour et al. / Journal of Organometallic Chemistry 606 (2000) 49–54
2. Results and discussion
the synthesis of 1,3-bis(2,6-diisopropylphenyl)imidazol-
2-ylidene (IPr (4)).
2.1. Ligand synthesis
2.2. The Cp*Ru(L)Cl system
(L=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene,
IPr)
Although a number of 1,3-disubstituted imidazolium
chlorides including the sterically hindered imidazolium
chloride,
1,3-bis(2,4,6-trimethylphenyl)imidazolium
It has been shown that the versatile starting material
[Cp*RuCl]4 [12] (5) (Cp*=h5-C5Me5) rapidly reacts
with sterically demanding phosphines [13] as well as
bulky carbene nucleophile (1,3-bis(2,4,6-trimethyl-
phenyl)imidazol-2-ylidene IMes (2)) [6a] to give deep
blue 16-electron Cp*Ru(L)Cl complexes (L=PR3 and
IMes). Reaction of 5 with 1,3-bis(2,6-diisopropyl-
phenyl)imidazol-2-ylidene (IPr (4)) in THF proceeds
rapidly, and a deep blue color appears instantaneously.
chloride (IMes·HCl) are available by established proce-
dures [8], our numerous trials to synthesize the 1,3-di-
isopropylphenyl substituted product following this
protocol have failed [9]. Herein, we report a modified
procedure for the synthesis of 1,3-bis(2,6-diisopropy-
lphenyl)imidazoliumchloride (IPrHCl). Addition of gly-
oxal to 2,6-diisopropylaniline in absolute ethanol in the
presence of catalytic amount of formic acid leads to the
formation of the diazabutadiene as a yellow solid in
good yields [10]. This compound reacts with para-
formaldehyde and HCl in toluene to form 1,3-bis(2,6-
diisopropylphenyl)imidazoliumchloride (IPrHCl) as an
off-white solid in moderate yields. The carbene nucleo-
phile IPr (4) is formed when IPrHCl is reacted with
potassium tert-butoxide in THF [11]. Scheme 1 presents
A
deep blue crystalline solid formulated as
Cp*Ru(IPr)Cl (6) is isolated in 60% yield upon workup
(Eq (1)).
(1)
1
The H-NMR spectrum of 6 shows the resonances
for the Cp* and the carbene ligand. The reaction
depicted in Eq (1) is quantitative by NMR and there-
fore is suitable for calorimetric investigations [14].
When four equivalents of the carbene (4) react with one
equivalent of the tetramer (5) in THF at 30°C, the
measured enthalpy of reaction is exothermic by −
44.5(0.4) kcal mol−1. Comparing this value to the
previously measured reaction enthalpies involving 5
and PCy3, PiPr3 [15] and IMes (2) [6a] indicates that the
RuꢁL stability decreases in the order shown in Eq (2).
The IMes ligand (2) is by far the strongest binder of the
four with the IPr (4) strength very close to that of PCy3.
Therefore, from an electronic point of view, the IPr
ligand should be very similar to PCy3.
Scheme 1.
(2)
The X-ray crystallography confirms the formulation
of 6 (Fig. 1). The molecule has a pseudo piano stool
structure with the Cp* ligand h5-bonded to the ruthe-
nium center. Crystallographic data are shown in Table
1 and selected bond lengths and bond angles for 6,
Cp*Ru(IMes)Cl (7) [6a] and Cp*Ru(PCy3)Cl (8) [6a]
are presented in Table 2. We have already defined a
system for quantifying the steric factors in carbenes [7]
which makes use of their fence-like structures. To gauge
the steric factors, the height and the length of the fences
Fig. 1. ORTEP of Cp*Ru(IPr)Cl (6) with elipsoids drawn at 50%
probability.

L. Jafarpour et al. / Journal of Organometallic Chemistry 606 (2000) 49–54
51
Table 1
Crystallographic data for complexes 6 and 9
6
9
Formula
C37H50ClN2Ru
C52H75Cl2N2PRu
fw
Color
Space group
724.42
Blue
Cc
12.2011(6)
31.1928(15)
10.5046(5)
90
94.2270(10)
90
3987.0(3)
4
1.207
0.0281
0.0552
430
29365
9873
931.08
Pink–brown
P2(1)/n
20.4193(18)
11.1326(10)
22.2915(19)
90
107.449(1)
90
4834.1(7)
4
,
a (A)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
Dcalc (g cm−3
)
1.279
a
R
Rw
0.0336
0.0603
823
56 934
11 106
0.75
b
Fig. 2. ORTEP of RuCl2(ꢀC(H)Ph)(PCy3)(IPr) (9) with elipsoids drawn
at 50% probability.
Refined parameters
Data collected
Unique data [I\3|]
Goodnes-of-fit on F2
0.847
RuCl2(ꢀC(H)Ph)(PCy3)2 (1) reacts with IPr (4) in hex-
anes at 60°C to form RuCl2(ꢀC(H)Ph)(PCy3)(IPr) (9) as
brown, air-stable microcrystals in moderate yield (Eq.
(3)). Since the electron donating ability of IPr is similar
to PCy3, the driving force for the exchange reaction is
small and the reaction does not take place at r.t. It is
worth mentioning that even in the presence of excess
IPr ligand, only one PCy3 can be replaced.
a R=S(ꢀꢀFoꢀ−ꢀFcꢀꢀ)/SꢀFoꢀ.
2
b Rw=Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ .
(AL and AH) are compared. A comparison between
relevant bond distances in 6 and 7 indicate that the two
structures are very similar despite their significant dif-
ference in reaction enthalpy (11.1 vs.15.6 kcal mol−1
,
respectively). However, the steric parameters indicate a
significant difference between the two with 6 being
much more sterically demanding than 7 (AH=137.6 in
6 and 70.4° in 7). The metrical parameters also illus-
trate the similarity between the structures of 6 and 8
which is also corroborated by the solution calorimetric
results.
(3)
The 31P{1H}-NMR spectrum of 9 shows one singlet
at 30.33 ppm due to one bound PCy3 ligand. In the
1H-NMR spectrum one can discern the relevant reso-
nances for IPr as well as the very low field signal for the
benzylidene proton at 20.04 ppm. The identity of this
complex was further confirmed by a single-crystal X-
ray diffraction study (Table 1). An ORTEP of 9 and
selected metrical parameters are presented in Fig. 2 and
Table 3.
2.3. The RuCl2(=C(H)Ph)(PCy3)(IPr) complex
2.3.1. Synthesis
We have shown that the IPr ligand (4) is sterically
more demanding than either IMes (2) or PCy3. There-
fore, it is logical to predict that due to its steric bulk,
IPr ligand could be capable of stabilizing the 14-elec-
tron ruthenium intermediate RuCl2(L)(ꢀC(H)Ph) in-
volved in olefin metathesis [4c, 5]. The complex
The coordination geometry around the ruthenium
center is that of a distorted square pyramid with
Cl(1)ꢁRuꢁCl(2) angle of 170.42(2)° which is nearly lin-
Table 2
,
Selected bond lengths (A) and bond angles (°) for Cp*Ru(IPr)Cl (6), Cp*Ru(IMes)Cl (7) and Cp*Ru(PCy3)Cl (8)
Complex
Steric parameters (AL, AH)
RuꢁL
RuꢁCp*
RuꢁCl
CꢁRuꢁCl
CꢁRuꢁCp*
Cp*ꢁRuꢁCl
6
7
8
150.7, 70.4
134.0, 137.6
115.8 a
2.105
2.086
2.383
1.766
1.754
1.771
2.376
2.371
2.378
90.6
140.7
141.5
138.9 b
128.6
129.2
129.9
89.32
91.2 b
a Phosphine cone angle.
b Replace C with P.

52
L. Jafarpour et al. / Journal of Organometallic Chemistry 606 (2000) 49–54
ear and close to the value for 3 (168.62°). The
ing catalysis in metathesis-active ruthenium systems.
Owing to its large steric bulk, IPr ancillary ligand
prevents/slows bimolecular carbene decomposition in
the olefin metathesis 14-electron ruthenium intermedi-
ate, resulting in significant activity and thermal stability
compared to phosphine containing catalysts.
,
RuꢁC(28) bond distance (1.817(3) A) is shorter than
,
,
that in 3 (1.838(3) A) and 1 (1.851(21) A). The other
,
ruthenium carbene bond length, RuꢁC(13), (2.088(2) A)
is longer than that of 3 (2.069(11) A) which is in
,
agreement with the difference in the reaction enthalpy
between IMes and IPr. It is also much longer than that
of RuꢁC(28) and is in the range of rutheniumꢁcarbon
single bond distances. The isopropyl groups on the
phenyl rings of the IPr ligand are pushed back indicat-
ing a fairly congested environment. This steric conges-
tion may be at the origin of the longer than expected
5. Experimental
5.1. General consideration
,
RuꢁP bond distance in 9 (2.4554(7) vs. 2.419(3) A in 3).
All manipulations involving organoruthenium com-
plexes were performed under argon using standard high
vacuum or Schlenk tube techniques, or in a MBraun
glove box containing less than 1 ppm oxygen and
water. Solvents were dried and distilled under argon
before use employing standard drying agents [16]. Only
materials of high purity as indicated by NMR spec-
troscopy were used in the calorimetric experiments.
NMR spectra were recorded using a Varian Gemini 300
or 400 MHz spectrometer. Calorimetric measurements
were performed using a Calvet calorimeter (Setaram
C-80) which was periodically calibrated using the TRIS
reaction [17] or the enthalpy of solution of KCl in
water [18]. The experimental enthalpies for these two
standard reactions compared very closely to literature
values. This calorimeter has been previously described
[19] and typical procedures are described below. Exper-
imental enthalpy data are reported with 95% confidence
limits.
3. Catalytic activity
The catalytic activity of 9 was tested by using the
standard RCM substrate, diethyldiallylmalonate (Eq.
(4)). When 9 is used as catalyst precursor ring closure is
complete after 15 min at room temperature (r.t.). Under
identical conditions, 3 and 1 show 92 and 85% conver-
sion, respectively [6a].
(4)
We have already illustrated that the carbene complex
3 is much more thermally stable than the phosphine
complex 1 (14 days vs. 1 h at 60°C) [6a]. When a
solution of 9 is heated to 100°C in d8-toluene under an
inert atmosphere, signs of decomposition appear after 2
h. However, at lower temperatures (60°C) the complex
is stable even after 2 weeks of continuous heating. The
stability of 9 is closely related to that found for 3.
5.2. NMR titrations
Prior to every set of calorimetric experiments, an
accurately weighed amount (90.1 mg) of the
organoruthenium complex was placed in a Wilmad
screw-capped NMR tube fitted with a septum, and
THF-d8 was subsequently added. The solution was
titrated with a solution of the ligand of interest by
injecting the latter in aliquots through the septum with
a microsyringe, followed by vigorous shaking. The re-
actions were monitored by 31P{1H}- and 1H-NMR
spectroscopy and the reactions were found to be rapid,
clean and quantitative. These conditions are necessary
for accurate and meaningful calorimetric results and
were satisfied for all organometallic reactions
investigated.
4. Conclusion
In summary, we have shown that the nucleophilic
carbene IPr acts as a phosphine mimic with reaction
enthalpy similar to that of PCy3 in the Cp*RuCl(L)
system. The IPr ligand is much more sterically demand-
ing than either IMes or PCy3. It is capable of support-
Table 3
,
Selected bond lengths (A) and bond angles (°) for Cl2Ru(=
C(H)Ph)(PCy3)(IPr) (9)
5.3. Calorimetric measurement for reaction between 5
and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene
(IPr (4))
RuꢁC(13)
RuꢁCl(1)
RuꢁC(28)
C(28)ꢁC(29)
RuꢁP
RuꢁCl(2)
C(28)ꢁRuꢁC(13)
2.088(2)
2.3822(7)
1.817(3)
1.478(4)
2.4554(7)
2.4008(7)
97.56(10)
C(13)ꢁRuꢁCl(2)
C(13)ꢁRuꢁP
C(28)ꢁRuꢁCl(2)
C(28)ꢁRuꢁCl(1)
C(28)ꢁRuꢁP
Cl(1)ꢁRuꢁCl(2)
Cl(1)ꢁRuꢁP
83.77(6)
164.60(7)
88.87(9)
99.49(9)
96.64(8)
170.42(2)
93.06(2)
The mixing vessels of the Setaram C-80 were cleaned,
dried in an oven maintained at 120°C, and then taken
into the glove box. A 20–30 mg sample of [Cp*RuCl]4

L. Jafarpour et al. / Journal of Organometallic Chemistry 606 (2000) 49–54
53
was accurately weighed into the lower vessel, it was
closed and sealed with 1.5 ml of mercury. Four ml of a
stock solution of IPr [130 mg of IPr in 16 ml of THF]
was added and the remainder of the cell was assembled,
removed from the glove box and inserted in the
calorimeter. The reference vessel was loaded in an
identical fashion with the exception that no
organoruthenium complex was added to the lower ves-
sel. After the calorimeter had reached thermal equi-
librium at 30.0°C (about 2 h), the reaction was initiated
by inverting the calorimeter. At the end of the reaction,
the vessels were removed from the calorimeter, taken
into the glove box, opened, and analyzed using 1H-
NMR spectroscopy. Conversion to RuCp*(IPr)Cl was
found to be quantitative under these reaction condi-
tions. The enthalpy of reaction, −44.590.4 kcal
mol−1 represents the average of five individual calori-
metric determinations.
mixture turned brown and a white precipitate appeared.
It was then allowed to stir at r.t. for 36 h. The off-white
precipitate was collected by filtration and washed with
THF. Yield=13.1 g (47%) 1H-NMR (400 MHz,
CD2Cl2): l 1.24 (d, J=7.2 Hz, 12 H, CH(CH3)2), 1.27
(d, J=7.2 Hz, 12 H, CH(CH3)2), 2.42 (sep, J=6.8 Hz,
4 H, CH(CH3)2), 7.18 (t, J=7.2 Hz, 2 H, p-C6H3), 7.4
(m, 4 H, m-C6H3), 7.80 (s, 2 H, NCH), 11.00 (s, 1 H,
NC(HCl)N).
5.6. Synthesis of IPr (4)
To a mixture of IPr.HCl (6.5 g, 15 mmol) and
KOtBu (1.78 g, 16 mmol) was added THF (60 ml) at
r.t. The color turned brown immediately and a white
precipitate was formed. The reaction mixture was
stirred for 4 h, the solvent was removed in vacuo and
the residue was taken up in hot toluene (70°C). The
reaction mixture was then filtered through Celite. Evap-
oration of the volatiles afforded a brown solid. Yield=
4.6 g (79%). 1H-NMR (400 MHz, C6D6): l 1.13 (d,
J=9.2 Hz, 12 H, CH(CH3)2), 1.23 (d, J=9.2 Hz, 12 H,
CH(CH3)2), 2.91 (sep, J=9.2 Hz, 4 H, CH(CH3)2),
6.57 (s, 2 H, NCH), 7.11 (m, 4 H, m-C6H3), 7.22 (m, 2
H, p-C6H3).
5.4. Synthesis
The compounds RuCl2(ꢀC(H)Ph)(PCy3)2 (1) [4b],
[Cp*RuCl]4 [12] (5) and Cp*Ru(PCy3)Cl (8) [13] were
synthesized according to literature procedures. Experi-
mental synthetic procedures, leading to the isolation of
unreported compounds are described below.
5.7. Synthesis of Cp*Ru(IPr)Cl (6)
5.4.1. Stepwise synthesis of 1,3-bis(2,6-diisopropyl-
phenyl)imidazol-2-ylidene (IPr) (4)
A 50 ml flask was charged with 5 (100 mg, 0.092
mmol), IPr (140 mg, 0.364 mmol) and THF (10 ml).
The clear deep blue solution was stirred at r.t. for 2 h
after which the solvent was removed under vacuum.
The residue was dissolved into 20 ml of warm hexanes,
filtered and the resulting solution was slowly cooled to
−78°C. The dark blue microcrystals were isolated by
cold filtration, then washed with hexanes and finally
dried under vacuum. Yield: 180 mg, 75%. 1H-NMR
(400 MHz, C6D6): l 1.0 (br., 12 H, CH(CH3)2), 1.20 (s,
15 H, Cp*), 1.50 (br., 12 H, CH(CH3)2), 3.40 ( sep,
J=6.8 Hz, 4 H, CH(CH3)2), 6.58 (s, 2 H, NCHCHN),
5.4.1.1. Synthesis of bis(2,6-diisopropylphenyl)diazabu-
tadiene [10]. A 250 ml round-bottom flask was charged
with 100 g (0.56 mol) of 2,6-diisopropylaniline, 31.5 ml
(0.28 mol, 40% in water) of glyoxal and 500 ml of
absolute ethanol. A few drops of formic acid were
added as catalyst. The color of the reaction mixture
turned from colorless to yellow immediately, and a
yellow precipitate appeared after a few hours. The
reaction mixture was stirred for two days and the
yellow solid was collected by filtration and washed with
cold methanol to afford the analytically pure com-
7.2–7.3 (m,
6 H, C6H4ꢁ(CH(CH3)2)2). Calc. for
1
pound. Yield=81.74 g (77.5%) H-NMR (400 MHz,
C49H51ClN2Ru: C, 67.30; H, 7.78; N, 4.24. Found: C,
67.00; H, 7.55; N, 4.25%.
CDCl3): l 1.28 (d, J=7.6 Hz, 24H, CH(CH3)2, 3.03
(sep, J=6.4 Hz, 4H, CH(CH3)2), 7.27 (m, 6H,
(CH(CH3)2)2ꢁC6H3), 8.19 (s, 2H, NCH).
5.8. Synthesis of RuCl2(=C(H)Ph)(PCy3)(IPr) (9)
5.5. Synthesis of IPr·HCl
To a slurry of IPr (110 mg, 0.282 mmol) in hexanes
(20 ml) was added 1 (257 mg, 0.257 mmol). The reac-
tion mixture was heated at 60°C for 3 h and then
cooled to r.t. The volume of the solvent was then
reduced to half and the reaction mixture was cooled to
−78°C. Filtration of the pink precipitate, subsequent
washing with cold hexanes (2×10 ml) and drying
afforded the pink microcrystalline solid in 79% (190
To a solution of bis (2,6-diisopropylphenyl)diazabu-
tadiene (25 g, 66 mmol) in toluene (500 ml) was aded
2.0 g (66 mmol) of paraformaldehyde in solid form.
The reaction mixture was heated to 100°C till most of
paraformaldehyde was dissolved. It was then cooled to
40°C and 16.5 ml of HCl (66 mmol, 4 M in dioxane)
was syringed in. The reaction mixture was heated to
70°C for 5 h during which time the color of the reaction
1
mg) yield. H-NMR (400 MHz, C6D6): l 20.04 (s, 1 H,

54
L. Jafarpour et al. / Journal of Organometallic Chemistry 606 (2000) 49–54
RuꢁCH), 7.30 (br, 2 H, o-C6H5), 7.21 (m, 1 H, p-
C6H5), 7.03 (t, J=6.4 Hz, 2 H, p-C6H3(CH(CH3)2),
6.76 (br., 4 H, m-C6H3(CH(CH3)2), 6.68 (s, 2 H,
NCHCHN), 6.65 (m, 2 H, m-C6H5), 3.87(sep, J=6.8
References
[1] (a) G.W. Parshall, S.D. Ittel, Homogeneous Catalysis, Wiley,
New York, 1992. (b) L.H. Pignolet, Homogeneous Cata-
lysis with Metal Phosphine Complexes, Plenum, New York,
1983.
Hz,
1
H, C6H3(CH(CH3)2), 3.43 (m,
1
H,
C6H3(CH(CH3)2), 2.40 (m, 2 H, C6H3(CH(CH3)2), 1.64
(d, J=6.8 Hz, 6 H, C6H3(CH(CH3)2), (d, 6 H,
C6H3(CH(CH3)2), 1.01 (d, 6 H, C6H3(CH(CH3)2), 0.98
(d, 6 H, C6H3(CH(CH3)2), 1.49, 1.16–1.06, 0.90 (all m
PCy3). 31P{1H}-NMR (400 MHz, C6D6): l 30.33 (s).
Anal. Calc. for C52H75Cl2N2PRu: C, 67.08; H, 8.12; N,
3.01. Found: C, 67.37; H, 8.34; N, 2.85%.
[2] J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Finke, Princi-
ples and Applications of Organotransition Metal Chemistry,
2nd, University Science, Mill Valley, CA, 1987.
[3] (a) For a brief review of the first carbene of this type, see:
H.W. Wanzlick, Angew. Chem. Int. Ed. Engl. 1 (1962) 75. For
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5.9. Ring closing metathesis procedure
In the dry box catalyst precursor (5 mol%) was
accurately weighed in a Wilmad screw-capped NMR
tube and dissolved in CD2Cl2 (0.4 ml). Diethyldiallyl
malonate (0.02 g, 0.1 mmol) was added to the solution
and the sealed NMR tube was kept at r.t. Product
formation and diene disappearance were monitored by
integrating the allylic methylene peaks in the proton
NMR spectrum. Product formation was confirmed by
comparison with literature NMR data [4d].
6. X-ray diffraction measurements
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2489.
A single crystal of 6 or 9 was coated with paratone
oil and then sealed in a glass capillary tube. The X-ray
data were collected at low temperature using graphite-
monochromated Mo–Ka radiation on a Siemens P4
automated X-ray diffractometer. The structure was
solved using direct methods (SHELXS-86) and refined by
full matrix least-square techniques. Initial fractional
coordinates for the Ru atom were determined by heavy-
atom methods, and the remaining non-hydrogen atoms
were located by successive difference Fourier calcula-
tions, which were performed with algorithms provided
by SHELXTL IRIS operating on a Silicon Graphics IRIS
Indigo workstation. Crystallographic data can be found
in the Table 1, and selected bond distances and bond
angles are presented in Tables 2 and 3.
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6.1. Supplementary material
[14] Solution calorimetric protocol is similar to that previously re-
ported: S.A. Serron, J. Huang, S.P. Nolan, Organometallics 13
(1998) 534.
Details of crystal structure determination for 6 and 9
(PDF).
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Acknowledgements
The Board of Regents of the State of Louisiana and
the National Science Foundation (CHE-9985213) are
acknowledged for support of this work.
.