Displacement of a cis-Olefin from a trans-Olefin Complex: CpRu(CO) 2(trans-olefin)+

Article abstract of DOI:10.1021/om7005535

Ruthenium(II) - olefin complexes CpRu(CO)₂(η²- trans-olefin)⁺ (Cp = η²-C₅H₅; olefin = trans-3-hexene, trans-2-pentene, trans-3-octene, trans-4-octene, trans-5-decene) have been synthesized and characterized by IR, ¹H NMR, and ¹³C NMR spectroscopies. The reactions of these complexes with a wide range of ligands (L) result in the formation of CpRu(CO) ₂(L)₊ and the release of both cis- and trans-olefins: [CpRu(CO)₂(trans-olefin)]BF₄ + L → [CpRu(CO) ₂(L)]BF₄ + cis/trans-olefin. The relative amounts of cis- and trans-olefin released are controlled by several factors: identity and amount of the incoming ligand L, identity of the olefin, temperature, and solvent. For 4-substituted pyridines, the cis/trans ratio increases as the electron-donating ability of the 4-substituent increases: F₃C (18/82) < H (67/33) < CH₃ (74/26) < CH₃O (76/24). Increases in temperature, solvent polarity, and olefin side-chain length reduce the cis/trans ratio. A mechanism is proposed to account for the isomerization of trans-olefin ligands to their cis isomers during the substitution process.

Full text of DOI:10.1021/om7005535

Organometallics 2007, 26, 5111-5118
5111
Displacement of a cis-Olefin from a trans-Olefin Complex:
CpRu(CO)2(trans-olefin)+
Kevin M. McWilliams and Robert J. Angelici*
Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011-3111
ReceiVed June 6, 2007
Ruthenium(II)-olefin complexes CpRu(CO)2(η2-trans-olefin)+ (Cp ) η5-C5H5; olefin ) trans-3-hexene,
trans-2-pentene, trans-3-octene, trans-4-octene, trans-5-decene) have been synthesized and characterized
1
by IR, H NMR, and 13C NMR spectroscopies. The reactions of these complexes with a wide range of
ligands (L) result in the formation of CpRu(CO)2(L)+ and the release of both cis- and trans-olefins:
[CpRu(CO)2(trans-olefin)]BF4 + L f [CpRu(CO)2(L)]BF4 + cis/trans-olefin. The relative amounts of
cis- and trans-olefin released are controlled by several factors: identity and amount of the incoming
ligand L, identity of the olefin, temperature, and solvent. For 4-substituted pyridines, the cis/trans ratio
increases as the electron-donating ability of the 4-substituent increases: F3C (18/82) < H (67/33) < CH3
(74/26) < CH3O (76/24). Increases in temperature, solvent polarity, and olefin side-chain length reduce
the cis/trans ratio. A mechanism is proposed to account for the isomerization of trans-olefin ligands to
their cis isomers during the substitution process.
Scheme 1. Equilibrium Data for Four Different Olefins
Introduction
In a recent paper,1 we reported a kinetic and mechanistic
investigation of the substitution of a cis- or trans-3-hexene
ligand in Cp′Ru(CO)2(η2-3hx)+ by PPh3 (eq 1).
Cp′Ru(CO)2(η2-3hx)+ + PPh3 f
Cp′Ru(CO)2(PPh3)+ + 3hx (1)
For Cp′ ) η5-C5H5(Cp), 3hx ) cis-3-hexene (c3hx)
For Cp′ ) η5-C5Me5(Cp*), 3hx )
cis- or trans-3-hexene (c3hx or t3hx)
At 40.0 °C in CDCl3 solution, the reaction of CpRu(CO)2(η2-
c3hx)+ follows a rate law that is dominated by a term (with k1
) 1.96 × 10-6 s-1) that is independent of the PPh3 concentra-
tion. This first-order term suggested a mechanism involving a
rate-determining dissociation of the cis-3-hexene followed by
In all of the above reactions, the liberated olefin retains the
same cis or trans isomeric structure that was present in the
reacting Cp′Ru(CO)2(η2-3hx)+ complex. In contrast to these
reported results, we observed that the trans-3-hexene ligand in
CpRu(CO)2(η2-t3hx)+ is substituted by PPh3 and other ligands
to give CpRu(CO)2(PPh3)+, but the liberated olefin was a
mixture of c3hx and t3hx (eq 2).
+
a rapid reaction of the unsaturated CpRu(CO)2 intermediate
with PPh3. The analogous Cp*Ru(CO)2(η2-c3hx)+ complex also
reacts predominately by a dissociative mechanism, but the rate
(k1 ) 21.8 × 10-6 s-1) is 11 times faster than for the CpRu-
(CO)2(η2-c3hx)+ complex, which suggests a steric acceleration
by the larger Cp* ligand. The reaction of the trans-3-hexene
complex Cp*Ru(CO)2(η2-t3hx)+ with PPh3 follows only a
dissociative path, and the rate (k1 ) 208 × 10-6 s-1) is 9.5
times faster than that of the analogous cis-3-hexene complex
Cp*Ru(CO)2(η2-c3hx)+. The much faster rate of t3hx dissocia-
tion, as compared with c3hx, was attributed to repulsions
between the Cp* ligand and an ethyl group in the trans-3-hexene
ligand, which must have an ethyl group directed toward the Cp*
ligand in all orientations of the coordinated t3hx; in contrast,
both ethyl groups of the c3hx ligand in Cp*Ru(CO)2(η2-c3hx)+
are likely to be directed away from the Cp*.
CpRu(CO)2(η2-t3hx)+ + PPh3 f
CpRu(CO)2(PPh3)+ + c3hx and t3hx (2)
The liberation of c3hx is surprising for at least two reasons:
(1) common mechanisms for olefin substitution do not explain
the observed olefin isomerization, (2) the formation of c3hx
from t3hx is a process that is thermodynamically unfavorable.
Thermodynamic data for several cis T trans isomerizations
(Scheme 1) illustrate quantitatively (at the stated temperatures)
the greater stability of trans-olefins.
In this paper, we describe investigations of reactions of CpRu-
(CO)2(η2-trans-olefin)+ complexes with PPh3 and a variety of
other ligands (L) to give the CpRu(CO)2(L)+ complex5 and the
* To whom correspondence should be addressed. Phone: 515-294-2603.
Fax: 515-294-0105. E-mail: angelici@iastate.edu.
(1) McWilliams, K. M.; Ellern, A.; Angelici, R. J. Organometallics 2007,
26, 1665.
(2) Golden, D. M.; Egger, K. W.; Benson, S. W. J. Am. Chem. Soc.
1964, 86, 5416.
10.1021/om7005535 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/21/2007

5112 Organometallics, Vol. 26, No. 20, 2007
McWilliams and Angelici
Figure 2. View down the Ru-olefin bond showing the inequiva-
lency of the trans ethyl groups.
solution, as rapid dissociation and reassociation would make
the CH2 protons equivalent. The presence of only one methyl
signal in the room-temperature spectrum indicates that the olefin
is rotating rapidly about the metal-olefin bond, as a nonflux-
ional trans-olefin would exhibit two methyl signals due to the
inequivalence of the two ethyl groups (Figure 2). An 1H NMR
spectrum recorded at -35 °C showed that the olefin was still
rotating at low temperature, as no broadening of the peaks from
the olefin was observed. In the 13C NMR spectrum of 1, two
peaks for the CO ligands are observed at 197.02 and 192.58
ppm, which is consistent with the asymmetry imposed by the
trans-olefin. The resonance for the olefinic carbons 3 and 4 is
observed at 85.15 ppm, which is significantly upfield shifted
from that of the free olefin (131.30 ppm). Peaks for the
methylene and methyl carbon atoms appear at 32.89 and 18.12
ppm, respectively.
In 2, the two methylene peaks appear as multiplets at 2.15
and 1.64 ppm and are coupled to each other. A doublet at 1.93
ppm may be assigned to the methyl group attached directly to
the olefin carbon (C2), while the other methyl signal appears as
a triplet at 1.17 ppm. In the 13C NMR spectrum, the two CO
resonances are observed at 197.11 and 192.58 ppm, and the
olefinic carbon peaks appear upfield at 86.89 (C3) and 79.94
(C2) ppm. Due to the asymmetry of the trans-2-pentene ligand
in 2, the NMR results do not indicate whether or not the olefin
is rotating rapidly. However, considering that the olefins in
compounds 1, 4, and 5 were all found to be rotating rapidly on
the NMR time scale at room temperature, it seems likely that
this is also the case for 2.
Figure 1. Structures of compounds 1-5. Carbon and hydrogen
labels correspond to NMR assignments given in the Experimental
Section.
liberated cis- and/or trans-olefin. A mechanism is proposed to
account for the isomerization of the coordinated trans-olefin to
its cis isomer during the substitution process.
Results
Synthesis and Structural Characterization of the [CpRu-
(CO)2(trans-olefin)]+BF4- Complexes. These complexes were
all prepared in 75-85% yields by the abstraction of Cl- from
CpRu(CO)2Cl in the presence of the desired olefin (eq 3).
AgBF4, CH2Cl2
CpRu(CO)2Cl + olefin
8
-AgCl
[CpRu(CO)2(η2-olefin)]BF4
(3)
1, olefin ) t3hx ) trans-3-hexene
2, olefin ) t2pt ) trans-2-pentene
3, olefin ) t3oct ) trans-3-octene
4, olefin ) t4oct ) trans-4-octene
5, olefin ) t5dec ) trans-5-decene
The 1H NMR spectrum of 3 shows a multiplet for the olefinic
protons at 4.88 ppm and three multiplets at 2.25, 1.69, and 1.56
ppm for methylene protons. As in the 13C NMR spectrum of 2,
3 exhibits two peaks for the CO ligands (197.06, 192.55 ppm)
and two peaks for the olefinic carbons (85.91 (C3), 83.96 (C4)
The general structures of the synthesized compounds are shown
in Figure 1. Compounds 1 and 3-5 were isolated as light tan
solids, whereas compound 2 was isolated as a dark brown solid.
All of the compounds are stable toward air and moisture in the
solid state for at least 8 weeks and are also stable in solution
for several days when exposed to air. Compounds 1-5 all have
ν(CO) bands in their IR spectra at 2078 and 2035 cm-1. These
values are approximately 27 cm-1 higher than those in the
starting complex, CpRu(CO)2Cl (2055, 2003 cm-1).
1
ppm). The H and 13C NMR spectra of 4 and 5 have features
similar to those of the other complexes, which indicate rapid
rotation of the olefin at room temperature on the NMR time
scale.
Displacement of the Olefin in the [CpRu(CO)2(trans-
1
In the room-temperature H NMR spectrum of 1, there is a
olefin)]+BF4 Complexes. Although the reaction of Cp*Ru-
-
marked shift upfield from 5.46 ppm to 4.86 ppm for the olefinic
protons upon coordination to the metal, which is also observed
for all of the other complexes (2-5) and for CpRu(CO)2(η2-
olefin)+ complexes reported in the literature.5,6 Two multiplets
at 2.23 and 1.64 ppm in the 1H NMR spectrum of 1 are assigned
to the methylene protons, and a single triplet peak at 1.17 ppm
(CO)2(t3hx)+ with PPh3 gave Cp*Ru(CO)2(PPh3)+ and free
t3hx,1 the same reaction with CpRu(CO)2(t3hx)+ gave CpRu-
(CO)2(PPh3)+ and both cis- and trans-3-hexene. It was the
surprising formation of cis-3-hexene that led to the present study
of reactions (eq 4) of CpRu(CO)2(trans-olefin)+ complexes with
1
is assigned to the methyl protons. H-1H COSY experiments
[CpRu(CO)2(trans-olefin)]BF4 + L f
showed that the two methylene peaks are coupled to each other,
indicating that the two methylene protons on the same carbon
are different from one another. The presence of two methylene
peaks also shows that the olefin remains bound to the metal in
[CpRu(CO)2(L)]BF4 + cis- and trans-olefin (4)
a variety of ligands (L). It was evident that the coordinated t3hx
was isomerizing partially to c3hx during the substitution
reaction. In order to determine whether free t3hx isomerizes on
its own to c3hx under the conditions of the reaction, an NMR
tube containing free t3hx dissolved in CD2Cl2 was flame-sealed
and placed in a constant-temperature bath at 50 °C. After 7 days,
the 1H NMR spectrum showed no indication of c3hx formation,
eliminating thermal isomerization as a pathway for the formation
(3) Steele, W. V.; Chirico, R. D. J. Phys. Chem. Ref. Data 1993, 22,
377.
(4) Knorr, R. Chem. Ber. 1980, 113, 2441.
(5) Jungbauer, A.; Behrens, H. Z. Naturforsch., B 1978, 33, 1083.
(6) (a) Fischer, E. O.; Vogler, A. Z. Naturforsch., B 1962, 17, 421. (b)
Clayton, H. S.; Moss, J. R.; Dry, M. E. J. Organomet. Chem. 2003, 688,
181.

Displacement of a cis-Olefin from a trans-Olefin Complex
Organometallics, Vol. 26, No. 20, 2007 5113
Table 1. cis/trans Ratios of 3-Hexene Obtained from
Reactions of CpRu(CO)2(t3hx)+ According to Eq 4 at 25 °C
in CD2Cl2
would give still higher cis/trans ratios, but the reactions would
be even slower than the 50 days already required at 25 °C for
the reaction of PPh3.
entry
ligand (L)a
pKa reaction time (h) cis/trans ratiob
Kinetic studies of the reactions of 1 with PPh2Me and
4-picoline using ligand/1 ratios from 30 up to 70 were conducted
at 50 °C in CD2Cl2 under pseudo-first-order conditions. The
rates of reactions of both ligands did not depend on the
concentration of L, giving similar rate constants at all concentra-
tions; the k1 values averaged 3.1 × 10-5 s-1 for PPh2Me and
2.2 × 10-5 s-1 for 4-picoline (see Supporting Information).
While the rates do not depend on the ligand concentration, the
rate constant for PPh2Me is slightly higher than that for
4-picoline, which suggests some type of association between
the complex and L. Inspection of Table 2 shows that many of
the other ligands, such as 4-methoxypyridine, 2-picoline, and
PPh3, react at about the same rate, as indicated by their 48 h
completion time. On the other hand many of the ligands, such
as quinaldine, take longer than 48 h to react fully with 1. These
ligands are generally more bulky than those that react within
48 h.
c
1
2
3
4
5
6
7
8
PPh3
2.73
4.57
6.50
8.65
9.70
1200
312
144
144
480
1440
720
1440
960
1440
1440
1440
1440
480
44/56
43/57
0/100
0/100
13/87
0/100
0/100
0/100
78/22
6/94
PPh2Mec
c
PPhMe2
d
PMe3
PCy3
c
d
P(OMe)3
P(OEt)3
d
c
P(OPh)3
9
pyridinec
5.23
0.90
2.60
10
11
12
13
14
2-bromopyridinee
2-benzoylpyridinee
20/80
27/73
34/66
83/17
2-hydroxypyridinec 0.75
3-bromopyridinee
4-methoxypyridined 6.62
2.91
a 50-fold concentration as compared with that of CpRu(CO)2(t3hx)+ (1).
b The cis/trans ratios were determined at the indicated times when all of
CpRu(CO)2(t3hx)+ (1) had reacted. Only reactions 10-13 were stopped
before 1 had reacted completely. c Moderate amount of decomposition.
d Large amount of decomposition. e Small amount of decomposition.
For the P-donor ligands, PPh3 reacts with 1 to give the free
olefin with a cis/trans ratio of 44/56; PPh2Me gives the same
ratio (43/57), but PCy3 gives a much smaller ratio (13/87) (Table
1). The smaller and more basic phosphines, PPhMe2 and PMe3,
attack the olefin, initially forming an η1-complex, CpRu(CO)2-
[CH(Et)CH(Et)PR3]+, as established by 1H NMR studies, which
exhibit two upfield multiplets for the formerly olefinic protons
(4.86 ppm) at 3.02 and 2.78 ppm for PR3 ) PPhMe2 and at
2.98 and 2.49 ppm for PR3 ) PMe3. These values are similar
to those of CpFe(CO)2[CH2CH2PPh3]+, which exhibits two
upfield multiplets at 3.34 and 1.42 ppm.7 In CpRu(CO)2[CH-
(Et)CH(Et)PPhMe2]+, overlapping triplets at 0.92 and 0.91 ppm
indicate the inequivalence of the two ethyl groups of the olefin
after phosphine attack has occurred. These η1-complexes of both
PPhMe2 and PMe3 give only free trans-3-hexene and CpRu-
(CO)2(PR3)+ within 144 h at 25 °C. The phosphites react with
1 to yield only free trans-3-hexene. Among the P-donor ligands
(entries 1-8 in Table 1), those that give the highest cis/trans
ratios are moderately basic (PPh3, PPh2Me). Those that are less
basic (P(OR)3) or more basic (PPhMe2, PMe3) give much lower
cis/trans ratios.
Pyridine gives a much higher cis/trans ratio (78/22 at 25 °C
and 67/33 at 50 °C) than any of the P-donor ligands. For the
reactions of 1 with substituted pyridines at 50 °C, the ortho-
substituted pyridines, 2-bromopyridine (3/97), 2-benzoylpyridine
(14/86), 2-methoxypyridine (20/80), and 2-picoline (58/42), all
give lower cis/trans ratios than pyridine (67/33). The meta-
substituted pyridine, 3-bromopyridine (22/78), yields a ratio
higher than that of 2-bromopyridine but still much lower than
pyridine. The highest ratios are obtained with the pyridines,
4-picoline (74/26) and 4-methoxypyridine (76/24), that have
electron-donating para-substituents, while 4-CF3pyridine gives
a low ratio (18/82). On the basis of the data from the para-
substituted pyridine reactions, it is obvious that substituents that
increase the basicity of the nitrogen, such as the methyl group
in 4-picoline (pKa ) 5.98) and the methoxy group in 4-meth-
oxypyridine (pKa ) 6.62), increase the cis/trans ratio as
compared with pyridine (pKa ) 5.23). Conversely, the electron-
withdrawing CF3 group in 4-CF3-pyridine reduces the basicity
of the nitrogen, resulting in a lower yield of the cis-olefin. These
electronic effects also appear to influence the cis/trans ratios
obtained from reactions of the ortho-substituted pyridines where
of c3hx. To examine the possibility that the reacting ligand (L)
catalyzes the isomerization, 50-fold excesses of PPh3 and
4-picoline were added to NMR tubes containing t3hx in CD2-
Cl2. The tubes were flame-sealed under inert gas and placed in
a 50 °C water bath. As no c3hx was observed in either tube
after at least a week, the PPh3 and 4-picoline ligands did not
catalyze the isomerization. To test for the possibility that the
isomerization occurs in the complex or is catalyzed by a product
of metal complex decomposition, an NMR tube loaded with
CpRu(CO)2(t3hx)+ (1) dissolved in CD2Cl2 and flame-sealed
under inert gas was heated in a 50 °C water bath. After one
week, 1 was still present in solution with no evidence for the
formation of c3hx or release of free t3hx; this experiment also
showed the considerable thermal stability of the olefin complex.
These experiments show that the formation of free c3hx from
coordinated t3hx must occur during the substitution reaction
(eq 4).
In Tables 1 and 2 are shown percent ratios of cis- and trans-
3-hexene that are formed in reactions (eq 4) of CpRu(CO)2-
(t3hx)+ (1) with various ligands at 25 and 50 °C, respectively,
in CD2Cl2 using large excesses of the ligand (L). Due to the
long reaction times at 25 °C and the high temperature of the 50
1
°C experiments, considerable decomposition is seen in the H
NMR spectra of many of the reactions. This decomposition is
attributed to both breakdown of the ligand in the deuterated
solvent and the formation of several Ru products, as evidenced
by the presence of multiple Cp peaks. Approximate amounts
of decomposition for each reaction are noted in Tables 1 and
2. The reactions were run long enough (Tables 1 and 2) such
that all of the CpRu(CO)2(t3hx)+ (1) had reacted, except where
the reaction time was excessively long, as in entries 10-13 in
Table 1. In an experiment wherein 1 was reacted with a 50-
fold excess of PPh3 at 50 °C and the cis/trans ratio was
determined after 12, 24, or 48 h, it was found that the cis/trans
ratio is the same after the reaction is approximately 25%, 50%,
and 100% complete, respectively.
It is notable that the reaction times at 50 °C (Table 2) are
much shorter than those at 25 °C (Table 1) by several hundred
hours for the same ligand, and the cis/trans ratio for every ligand
is lower at 50 °C than at 25 °C. The cis/trans ratios for the
reactions of PPh3 and pyridine were determined at several
temperatures between 25 and 50 °C in order to document in
greater detail the decreasing cis/trans ratio as the temperature
is increased (Table 3). In principle, an even lower temperature
(7) Lennon, P.; Madhavarao, M.; Rosan, A.; Rosenblum, M. J. Orga-
nomet. Chem. 1976, 108, 93.

5114 Organometallics, Vol. 26, No. 20, 2007
McWilliams and Angelici
Table 2. cis/trans Ratios of 3-Hexene Obtained from Reactions of CpRu(CO)2(t3hx)+ According to Eq 4 at 50 °C in CD2Cl2
entry
ligand (L)
excess of L
pKa
reaction time (h)
cis/trans ratioa
b
b
b
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
PPh3
PPh3
PPh3
10×
50×
100×
10×
50×
100×
50×
pure
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
50×
2.73
2.73
2.73
5.98
5.98
5.98
5.23
5.23
0.90
2.60
3.06
6.00
2.91
48
48
48
48
48
48
48
48
96
96
96
48
72
48
48
48
48
0.5
12
72
72
144
144
144
192
96
96
48
48
8/92
29/71
31/69
45/55
74/26
73/27
67/33
40/60
3/97
4-picolineb
4-picolineb
4-picolineb
pyridineb
pyridine
2-bromopyridinec
2-benzoylpyridinec
2-methoxypyridineb
2-picolinec
14/86
20/80
58/42
22/78
18/82
76/24
0/100
32/68
0/100
0/100
55/45
44/56
0/100
68/32
32/68
30/70
25/75
32/68
48/52
15/85
3-bromopyridinec
4-CF3pyridinec
4-methoxypyridined
(BnNEt3)Brc
6.62
(BnNEt3)Clc
piperidined
11.3
9.2
DMAPd
N-methylmorpholined
quinolined
7.38
4.90
2.48
6.95
5.42
4.9
pyrazoled
imidazoled
quinaldined
indolined
2,2′-bipyridyld
4,4′-dimethyl-2,2′-bipyridyld
benzophenone imined
2,2′,4,4′-tetramethyl-3-pentanone imined
a The cis/trans ratios were determined at the indicated times when all of CpRu(CO)2(t3hx)+ (1) had reacted. b Moderate amount of decomposition. c Small
amount of decomposition. d Large amount of decomposition.
Table 3. cis/trans Ratios of 3-Hexene Obtained from
Reactions of CpRu(CO)2(t3hx)+ According to Eq 4 at
Various Temperatures in CD2Cl2
is probably due to the electron-donating methyl groups at the 4
and 4′ positions. The two imines, benzophenone imine and
2,2′,4,4′-tetramethyl-3-pentanone imine, react with 1 to give cis/
trans ratios of 48/52 and 15/85, respectively. The much lower
ratio for 2,2′,4,4′-tetramethyl-3-pentanone imine may be at-
tributed to the steric bulk of this ligand.
reaction
time (h)
cis/trans
entry
temp (°C)
ligand (L)a
pKa
ratiob
c
44
45
46
47
48
49
50
51
25
30
40
50
25
30
40
50
PPh3
PPh3
PPh3
PPh3
2.73
2.73
2.73
2.73
5.23
5.23
5.23
5.23
1200
525
96
44/56
41/59
36/64
29/71
78/22
79/21
75/25
67/33
c
The chloride anion in (BnNEt3)Cl reacts with 1 to give a
32/68 cis/trans ratio as well as generating CpRu(CO)2Cl. The
bromide anion in (BnNEt3)Br, on the other hand, reacts with 1
to give solely trans-3-hexene and CpRu(CO)2Br. Two ligands
containing sulfur donor atoms, thiophene and diethyl sulfide,
did not react with 1 at 25 °C even after 336 h.
c
c
48
pyridinec
pyridinec
pyridinec
pyridinec
960
525
96
48
a 50-Fold concentration as compared with that of CpRu(CO)2(t3hx)+ (1).
b The cis/trans ratios were determined at the indicated times when all of
CpRu(CO)2(t3hx)+ (1) had reacted. c Moderate amount of decomposition.
In order to determine whether or not other trans-olefins in
CpRu(CO)2(η2-trans-olefin)+ can be isomerized to the cis-olefin
upon displacement by various ligands, complexes of 2-pentene
(2), trans-3-octene (3), trans-4-octene (4), and trans-5-decene
(5) were reacted with selected phosphine and pyridine ligands
(Table 4). Compounds 2 and 3 react with PPh3 to give cis/trans
ratios of 17/83 and 26/74, respectively, which are slightly lower
than that obtained for 1 (29/71). Similarly, 2 and 3 react with
4-methoxypyridine to give ratios (75/25 and 71/29, respectively),
that again are slightly lower than for 1 (76/24). On the other
hand, the reactions of 4 and 5 with PPh3 give only the trans-
olefin. However, 4 and 5 do react with 4-picoline to give both
cis- and trans-olefins, as evidenced by two peaks in the 1H NMR
spectrum at 5.48 and 5.44 ppm for 4 and 5.47 and 5.43 ppm
for 5, but exact cis/trans ratios could not be determined due to
overlapping peaks. The larger sizes of the n-propyl and n-butyl
groups in trans-4-octene and trans-5-decene in 4 and 5 are
presumably responsible for the poor trans-to-cis conversion,
especially when reacted with a bulky ligand such as PPh3. For
complexes 2 and 3, at least one of the alkyl groups in the olefin
is a relatively small methyl or ethyl. It is interesting that the
trans-3-octene, with ethyl and n-butyl groups, in 3 reacts with
PPh3 to give some of the cis-olefin, while the trans-4-octene,
the electron-withdrawing Br group gives the lowest ratio (3/
97), and the electron-donating and relatively small CH3 group
gives the largest ratio (58/42).
Considering the effectiveness of pyridines at achieving high
cis/trans 3-hexene ratios, other nitrogen-containing ligands were
tested at 50 °C. Ligands with high pKa values (piperidine, 11.3;
p-dimethylaminopyridine, DMAP, 9.2) or low pKa values
(pyrazole, 2.48) did not yield any of the cis-olefin during the
course of the reactions but instead gave multiple Cp peaks in
the 1H NMR spectra as well as very dark solutions with
piperidine and p-dimethylaminopyridine. Heterocyclic ligands
with moderate pKa values gave a wide range of cis/trans
ratios: imidazole (68/32), N-methylmorpholine (55/45), quino-
line (44/56), quinaldine (32/68), and indoline (30/70). The
polycyclic ring structures of quinoline, quinaldine, and indoline
increase the steric bulk around the nitrogen donor atom, which
is perhaps the basis of the lower cis/trans ratios than those for
the smaller heterocycles. The 2,2′-bipyridyl (25/75) and 4,4′-
dimethyl-2,2′-bipyridyl (32/68) ligands with aryl groups in the
ortho position of the pyridine give lower ratios than pyridine
(67/33). The slightly higher ratio for 4,4′-dimethyl-2,2′-dipyridyl

Displacement of a cis-Olefin from a trans-Olefin Complex
Organometallics, Vol. 26, No. 20, 2007 5115
Table 4. cis/trans Ratios of Olefin Obtained from Reactions of CpRu(CO)2(trans-olefin)+ According to Eq 4 at 50 °C in CD2Cl2
entry
compound
olefin
liganda
pKa
cis/trans ratiob
c
c
c
c
c
52
53
54
55
56
57
58
59
60
61
62
1
2
3
4
5
1
2
3
1
4
5
trans-3-hexene
trans-2-pentene
trans-3-octene
trans-4-octene
trans-5-decene
trans-3-hexene
trans-2-pentene
trans-3-octene
trans-3-hexene
trans-4-octene
trans-5-decene
PPh3
PPh3
PPh3
PPh3
PPh3
2.73
2.73
2.73
2.73
2.73
6.62
6.62
6.62
5.98
5.98
5.98
29/71
17/83
26/74
0/100
0/100
76/24
75/25
71/29
73/27
e
4-methoxypyridined
4-methoxypyridined
4-methoxypyridined
4-picolinec
4-picolinec
4-picolinec
e
a 50-Fold concentration as compared with that of CpRu(CO)2(trans-olefin)+. b The cis/trans ratios were determined at the indicated times when all of
CpRu(CO)2(trans-olefin)+ had reacted. c Moderate amount of decomposition. d Large amount of decomposition. e Exact ratio could not be determined due
1
to peak overlap in the H NMR spectrum but is estimated to be 50/50 based on inspection.
1
Table 5. cis/trans Ratios of 3-Hexene Obtained from
Reactions of CpRu(CO)2(t3hx)+ According to Eq 4 at 50 °C
in Various Solvents
reaction, there was no H NMR evidence for the formation of
the η1-adduct, CpFe(CO)2[CH(Me)CH(Me)PPh3]+.
In reactions of CpRu(CO)2(η2-t3hx)+ (1) with phosphine
ligands, formation of the PR3 adduct, CpRu(CO)2[CH(Et)CH-
reaction
time (h)
cis/trans
entry
solvent
nucleophilea
pKa
ratiob
1
(Et)PR3]+, is observed in the H NMR spectrum within 5 min
c
63
64
65
66
67
68
69
70
CD2Cl2
CDCl3
DMSO-d6
acetone-d6
CD2Cl2
CDCl3
acetone-d6
CD3OD
PPh3
PPh3
PPh3
PPh3
2.73
2.73
2.73
2.73
5.98
5.98
5.98
5.98
48
48
48
72
48
48
48
48
29/71
26/74
15/85
0/100
74/26
57/43
32/68
9/91
of adding PMe3 or PPhMe2. As in the Fe series, the adducts
are not stable and transform in CH2Cl2 over the course of 144
h at 25 °C to CpRu(CO)2(PR3)+ (7) and free t3hx. In an attempt
to isolate an η1-adduct, 1 was reacted with benzenethiol in the
presence of K2CO3 at 0 °C in CH3CN, as thiols had been shown
to give only η1 adducts when tert-butylmercaptan was reacted
with either CpFe(CO)2(η2-CH2CH2)+ or CpFe(CO)2(η2-CH2-
CHMe)+. A reaction occurred at 0 °C within 2 h to give a
product with ν(CO) bands in the IR spectrum at 2009 and 1946
c
d
d
4-picolinec
4-picolinec
4-picolinee
4-picolined
a 50-Fold concentration as compared with that of CpRu(CO)2(t3hx)+ (1).
b The cis/trans ratios were determined at the indicated times when all of
CpRu(CO)2(t3hx)+ (1) had reacted. c Moderate amount of decomposition.
d Small amount of decomposition. e Large amount of decomposition.
1
cm-1 in CH3CN. The H NMR spectrum obtained in CD2Cl2
showed two upfield multiplets at 3.45 and 3.12 ppm for the
former olefinic protons and two triplets for the methyl groups
at 1.03 and 0.91 ppm. These values support the formulation of
the compound as CpRu(CO)2[CH(Et)CH(Et)SPh] (8), the only
product. A similar Fe complex, CpFe(CO)2[CH2CH2SBut],
exhibits ν(CO) bands at 2012 and 1949 cm-1 in CH3CN solvent
and multiplets for the CH2 groups at 2.55 and 1.48 ppm in C6D6
in the 1H NMR spectrum.7 The previously reported amine
adduct, CpRu(CO)2(CH2CH2NH3)+, exhibits ν(CO) bands at
with two n-propyl groups, in 4 does not give any cis-olefin. In
the reactions of 4-picoline with 4 and 5, the trans-to-cis
conversion occurs despite the bulkiness of the olefins. This may
be due to the smaller size of 4-picoline as compared with PPh3.
The cis/trans-olefin product ratios from reactions (eq 4) of
CpRu(CO)2(t3hx)+ with PPh3 and 4-picoline are highly de-
pendent on the nature of the solvent (Table 5). Reactions in
relatively low polarity and poorly coordinating solvents (CD2-
Cl2 and CDCl3) give the highest cis/trans ratios (entries 63, 64,
67, 68). In polar, coordinating solvents (DMSO-d6, acetone-d6,
and methanol-d6), the cis/trans ratios are considerably lower.
DMSO is sufficiently strongly coordinating that it displaces the
olefin when 1 is dissolved in DMSO. This reaction gives a 15/
85 cis/trans ratio of 3-hexenes, the same ratio that was observed
in the presence of PPh3 (entry 65) in DMSO solvent.
1
2012 and 1950 cm-1, and the H NMR spectrum shows two
multiplets at 3.43 and 1.70 ppm for the methylene groups.8
Although attempts to isolate and purify 8 were unsuccessful,
the IR and 1H NMR spectral data are consistent with a structure
in which PhS- has added to the t3hx ligand. This result together
with evidence for the formation of η1 adducts in reactions of 1
with PMe3 and PPhMe2 suggests a possible pathway for reaction
4 that involves the addition of ligand (L) to the coordinated
olefin in CpRu(CO)2(t3hx)+.
Discussion
In reactions of nucleophiles with metal complexes containing
η2-olefins,9,10 the rate law generally includes first-order de-
pendences on the complex and the nucleophile concentrations,
which suggests a mechanism involving nucleophilic attack on
the η2-olefin. However, in the reactions (eq 4) of CpRu(CO)2-
(t3hx)+, the rates do not depend on the concentration of the
ligand (L ) PPh2Me or 4-picoline), which suggests a mechanism
that is not simple nucleophilic attack of L on the olefin. Also,
the similar rate constants for the reactions of 1 with PPh3 (3.1
× 10-5 s-1) and 4-picoline (2.2 × 10-5 s-1) at 50.0 °C in CD2-
Cl2 solvent suggest that the incoming ligand does not greatly
affect the rate of the reaction. On the other hand, the mechanism
For the purpose of considering possible mechanisms for
reactions (eq 4) of CpRu(CO)2(trans-olefin)+ with various
ligands, it is useful to consider previously reported reactions of
CpFe(CO)2(η2-olefin)+ (olefin ) ethylene, propene, styrene,
trans-2-butene) with various ligands such as alkoxides, amines,
mercaptans, phosphines, and phosphites.7 The reaction of CpFe-
(CO)2(η2-ethylene)+ with PPh3 gives the η1 product CpFe(CO)2-
(CH2CH2PPh3)+, resulting from PPh3 attack on the ethylene.
For the analogous propene and styrene complexes, formation
of the η1 PPh3 adduct competes with displacement of the olefin
to give CpFe(CO)2(PPh3)+ (6), which becomes the sole product
upon warming to 65 °C, as the PPh3 adducts are not stable at
high temperatures. More specific to our studies is the reaction
of the trans-2-butene complex with PPh3, which gives only 6
and free olefin, which was not identified as cis or trans. In this
(8) Behrens, H.; Jungbauer, A. Z. Naturforsch., B 1979, 34, 1477.
(9) (a) Hupp, S. S.; Dahlgren, G. Inorg. Chem. 1976, 15, 2349. (b) Miya,
S.; Kashiwabara, K.; Saito, K. Inorg. Chem. 1980, 19, 98. (c) Plutino, M.
R.; Otto, S.; Roodt, A.; Elding, L. I. Inorg. Chem. 1999, 38, 1233.
(10) Muller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675.

5116 Organometallics, Vol. 26, No. 20, 2007
McWilliams and Angelici
Scheme 2. Mechanism for the Reaction in Eq 4
using a large excess of the ligand L. This result was observed
in the reaction of 1 with a 50-fold excess of PPh3 when the
cis/trans ratio was determined to be the same after 12, 24, and
48 h. At all three times, the cis/trans ratio was 29/71, which is
identical to that in entry 16 (Table 2). In other experiments, 1
was reacted with PPh3 and 4-picoline in CD2Cl2 at 50 °C using
10-, 50-, and 100-fold excesses in order to establish the effect
of ligand concentration on the cis/trans ratio (entries 15-20).
For both PPh3 and 4-picoline, the cis/trans ratio increases as
the ligand concentration increases from 10-fold to 50-fold
excess, but the cis/trans ratio remains relatively unchanged as
the amount of ligand is increased further to 100-fold excess.
This means, in the context of the proposed mechanism, that
the dissociative pathway predominates at a 10-fold excess, as
the low concentration of L results in a relatively slow rate for
the conversion of C to D. At higher concentrations (50- and
100-fold), this step is fast, as compared with k-2, which means
that the cis/trans ratios are controlled by the rates of the k1 and
k2 steps, which are both independent of the concentration of L.
Thus, the dependence of the cis/trans ratios on the concentration
of L can be reasonably explained by the proposed mechanism.
Not only is the cis/trans ratio dependent on the concentration
of the ligand, but the specific identity of the ligand is also
important. On the basis of the data in Table 2, high cis/trans
ratios are favored by ligands whose conjugate acids have pKa
values between 2 and 6. Ligands with pKa values outside of
this range give either very low amounts of the cis-olefin or none
at all. Highly basic amines (methylamine, dimethylamine,
dibenzylamine) gave only decomposition of the metal complex
accompanied by release of the trans-olefin. This is in stark
contrast to CpFe(CO)2(η2-CH2CH2)+, which reacts with both
methylamine and dimethylamine to give the corresponding η1-
amine adducts CpFe(CO)2(CH2CH2NHR2)+.7 These reactions
were conducted at -10 °C or below, which suggests that
decomposition may occur at higher temperatures. This would
be consistent with our temperature studies (Table 3), which
showed a decrease in the cis/trans ratio as the temperature is
increased. In contrast to the decomposition of 1 observed with
strongly basic ligands, weakly basic ligands such as ethyl sulfide
and thiophene do not react at all with 1.
Scheme 3. Slipping of MLn Fragment along Olefin π-Bond
by Distance ∆
must account for the fact that the cis/trans 3-hexene product
ratios in the reactions are different for PPh3 and 4-picoline. It
must also account for the observation that the double bond does
not migrate along the carbon chain of the olefin during the trans-
to-cis isomerization process. We propose the mechanism shown
in Scheme 2 for these reactions.
Among the ligands (L) that give significant amounts of the
cis-olefin product, both electronic and steric properties of the
ligand influence the cis/trans ratio. For reactions of 1 with the
series of para-substituted pyridines, the cis/trans ratio decreases,
using a 50-fold excess of ligand, as the substituent becomes
less electron-donating (Table 2): MeO (76/24) > Me (74/26)
> H (67/33) > CF3 (18/82). This is the expected trend from
the proposed mechanism where the k3 step would be faster for
the more nucleophilic pyridines, which would lead to higher
yields of the cis-olefin.
This mechanism involves two olefin substitution pathways;
both are first order in the complex and independent of the ligand
(L) concentration. The k1 pathway is a simple dissociation of
the trans-olefin followed by rapid addition of L to the
unsaturated Ru intermediate. This pathway gives only the trans-
olefin product. The k2 pathway begins with a rate-determining
slippage of the η2-olefin to give a dipolar η1-olefin intermediate
C, which can either return to A or undergo attack by L on the
side of the olefin opposite the Ru to give olefin adduct D.
Rotation around the C-C bond in D places the L group near
the metal, where it can transfer to the Ru and release the cis-
olefin. Rotation around the C-C bond converts D to E and
also moves the trans R groups to a cis arrangement, thereby
setting up the release of the cis-olefin in the final step (E f
F). In this mechanism, the relative rates of the k1, k2/k-2, and
k3/k-3 steps control the cis/trans-olefin product ratio. In the
following paragraphs is a more detailed discussion of the
mechanism and the experimental observations that pertain to
this mechanism.
Pyridines with ortho substituents uniformly give lower cis/
trans 3-hexene ratios than para- or meta-substituted pyridines
(Tables 1 and 2). The steric effect of an ortho-substituent would
be expected to reduce the rate of attack in the k3 step of the
proposed mechanism, which would result in a lower cis/trans
ratio.
The size of the R groups in the trans-olefin (RHCdCHR)
ligand also plays a major role in determining the amount of
cis-olefin that is produced in the reaction of 1 with PPh3 (Table
4). Those olefins (trans-3-hexene, trans-2-pentene, and trans-
3-octene) with at least one ethyl or methyl R group give similar
cis/trans ratios, whereas olefins (trans-4-octene and trans-5-
decene) with larger R groups (n-propyl or n-butyl) yield none
of the cis-olefins. Such an effect of large R groups is not sur-
The mechanism in Scheme 2 predicts that the cis/trans ratio
will remain the same throughout the course of the reaction when

Displacement of a cis-Olefin from a trans-Olefin Complex
Organometallics, Vol. 26, No. 20, 2007 5117
analysis performed on the CpFe(CO)2 fragment,13 which is
+
prising because they would decrease the rate of ligand addition
to C in the k3 step, especially with bulky ligands such as PPh3.
However, if the ligand is the less bulky 4-picoline, both
compounds 4 and 5 react to yield some of the cis-olefin (entries
61, 62). An exact cis/trans ratio could not be obtained for these
latter two reactions due to overlap of the cis- and trans-olefin
peaks, but the ratio is estimated to be about 50/50 based on
inspection. Therefore, even internal olefins with large R groups
can yield cis-olefin if the correct incoming ligand is chosen.
Although PPh3 and PCy3 react with 1 at rates that are similar
to pyridine, PMe3 and PPhMe2 react much more rapidly (within
5 min) to give the η1 complexes CpRu(CO)2[CH(Et)CH(Et)-
analogous to our system, showed that this fragment should
strongly activate olefins toward nucleophilic attack. Experi-
mental support for this activation was found in the higher
reactivity of CpFe(CO)2[η2-CH2dCH(OMe)]+, in which the
olefin is unsymmetrically bonded to the Fe, as compared with
that of CpFe(CO)2(η2-CH2dCH2)+.14 In the mechanism in
Scheme 2, the olefin-slipping step (k2) is proposed to be rate-
determining, which has not been suggested for other reactions
involving nucleophilic attack on coordinated olefins.
Although the mechanism in Scheme 2 reasonably accounts
for the experimental results, the most important result of these
studies is the observation that the simple process of substituting
a trans-olefin in a metal complex by another ligand may result
in the formation of the free cis-olefin. This represents a new
pathway for the trans-to-cis isomerization of olefins that may
occur in transition metal complex-catalyzed reactions of olefins,
where substituting ligands are often present in solution. How-
ever, it should be noted that this isomerization does not occur
in all olefin substitution reactions. Even the reaction (eq 1) of
Cp*Ru(CO)2(t3hx)+ with PPh3 liberates only trans-3-hexene,
which can be explained by the much faster rate of t3hx
dissociation in the sterically crowded Cp* complex (208 × 10-6
s-1 at 40.0 °C) by the k1 pathway, as compared with the rate of
t3hx substitution in the analogous Cp complex 1 (27 × 10-6
s-1 at 50.0 °C).1 Also, the reaction (eq 1) of CpRu(CO)2(c3hx)+
with PPh3 gives only cis-3-hexene,1 which is more difficult to
understand because the rate of c3hx dissociation (k1 ) 1.96 ×
10-6 s-1 at 40.0 °C) is slower than the substitution in the t3hx
complex 1 (27 × 10-6 s-1 at 50.0 °C); this suggests that the
olefin slippage step (k2) in the mechanism (Scheme 2) is slower
for c3hx than t3hx. Moreover, many substituting ligands (L)
(Tables 1 and 2) produce no or little cis-olefin. The lack of
olefin isomerization in these reactions shows that the trans-to-
cis isomerization observed in the present study depends
sensitively on the metal complex, the specific trans-olefin, and
the substituting ligand L.
1
PR3]+, which were identified by their H NMR spectra. The
much greater rate of these reactions means that they must
proceed by a mechanism that is different than either the k1 or
k2 pathways in Scheme 2. These highly basic and sterically small
ligands are likely to react by direct nucleophilic attack on the
coordinated olefin to give the η1 complex. The CpRu(CO)2-
[CH(Et)CH(Et)PR3]+ complexes convert at 25 °C over a period
of about 144 h to CpRu(CO)2(PR3)+ and the free trans-olefin.
Although it is not clear how these η1-intermediate complexes
yield the trans-olefin, they cannot follow the E f F pathway,
which would be expected to give the cis-olefin.
Conclusions
Reactions (eq 4) of the η2-trans-olefin complexes CpRu(CO)2-
(η2-trans-olefin)+ with pyridine and phosphine ligands (L) to
give CpRu(CO)2(L)+ and free cis- and trans-olefins is surprising
because as much as 83% of the trans-olefin isomerizes to the
thermodynamically less stable cis isomer during the substitution
process. The driving force for this trans-to-cis isomerization
must be the greater stability of the CpRu(CO)2(L)+ product as
compared with the CpRu(CO)2(η2-trans-olefin)+ reactant. This
isomerization is also not accompanied by migration of the
double bond along the hydrocarbon chain. In other metal com-
plexes where cis/trans isomerization and double-bond migration
are observed (often catalytic reactions),11 a mechanism involving
a metal hydride intermediate is proposed (and sometimes
detected). In eq 4, H2 or other sources of hydrogen are not
present, and it seems unlikely that the CpRu(CO)2(η2-trans-
olefin)+ complexes themselves would form an allyl-hydride
intermediate CpRu(CO)(H)(η3-allyl)+, which would be expected
to give olefin products in which the double bond has migrated.
For the above reasons, it appears that the formation of cis-
olefins in eq 4 occurs by a new mechanism (Scheme 2). A key
step (k2) in the proposed pathway to the cis-olefin product
involves rate-determining slippage of the η2-bonded olefin in
A to an η1-dipolar complex (C). Such a slippage was previously
proposed by Roald Hoffman to account for the increased
reactivity of coordinated olefins toward nucleophiles.12 This
activation, which was supported by computational analysis,
stems from slippage of the olefin away from a symmetrical
bonding mode.
Experimental Section
Methods and Materials. All reactions were carried out under
an inert atmosphere of dry argon using standard Schlenk techniques.
Diethyl ether, methylene chloride, and hexanes were purified on
alumina using a Solv-Tek solvent purification system, similar to
that reported by Grubbs.15 The olefins trans-3-hexene (t3hx), trans-
2-pentene (t2pt), trans-3-octene (t3oct), trans-4-octene (t4oct), and
trans-5-decene (t5dec) were purchased from Sigma-Aldrich Chemi-
cal Co. and used as received. All deuterated solvents were purchased
from Cambridge Isotope Laboratories. Solution infrared spectra
were recorded on a Nicolet-560 spectrometer using a NaCl cell
with a 0.1 mm path length. 1H and 13C NMR spectra were recorded
on a Bruker DRX-400 spectrometer using the deuterated solvents
as internal references. Elemental analyses were performed on a
Perkin-Elmer 2400 Series II CHNS/O analyzer. The compound
CpRu(CO)2Cl was prepared according to reported methods.16
General Procedure for Preparations of the [CpRu(CO)2(η2-
olefin)]BF4 Complexes (1-5). To a mixture of dry CH2Cl2 (20
mL) containing AgBF4 (75.6 mg, 0.388 mmol) was added CpRu-
(CO)2Cl (100 mg, 0.388 mmol) and 1.2 mmol of the olefin (olefin
As the extent of slippage (∆) increases, the η2-coordination
of the olefin begins to resemble an η1 σ-complex with the carbon
furthest from the metal building up a positive charge, causing
it to be activated to attack by nucleophiles. Computational
(11) (a) Harrod, J. F.; Chalk, A. J. J. Am. Chem. Soc. 1964, 86, 1776.
(b) Sen, A.; Lai, T.-W. Inorg. Chem. 1981, 20, 4036. (c) Sen, A.; Lai,
T.-W. Inorg. Chem. 1984, 23, 3257. (d) Ertl, G. Handbook of Heterogeneous
Catalyst; VCH Verlagsgesellschaft mbH: Weinheim, Germany, 1997. (e)
Bernas, A.; Maki-Arvela, P.; Kumar, N.; Holmbum, B.; Salmi, T.; Murzin,
D. Y. Ind. Eng. Chem. Res. 2003, 42, 718.
(13) Eisenstein, O.; Hoffman, R. J. Am. Chem. Soc. 1981, 103, 4308.
(14) Chang, T. C. T.; Foxman, B. M.; Rosenblum, M.; Stockman, C. J.
Am. Chem. Soc. 1981, 103, 7361.
(15) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(16) Eisenstadt, A.; Tannenbaum, R.; Efraty, A. J. Organomet. Chem.
1981, 221, 317.
(12) Eisenstein, O.; Hoffman, R. J. Am. Chem. Soc. 1980, 102, 6148.

5118 Organometallics, Vol. 26, No. 20, 2007
McWilliams and Angelici
) t3hx, t2pt, t3oct, t4oct, t5dec). The solution was stirred at room
temperature for 4 to 6 h until the reaction was complete, as indicated
by the disappearance of the ν(CO) bands for CpRu(CO)2Cl in the
IR spectrum. The solution was filtered to remove AgCl and con-
centrated in vacuo to approximately 1 mL. Then, 20 mL of hexanes
was added to precipitate the tan solid product, which was isolated
by filtration and washed with hexanes (3 × 5 mL) to remove excess
olefin. Isolated yields were typically 75-85%. The products were
further purified by recrystallization from CH2Cl2/ether.
(CtO), 192.53 (CtO), 91.74 (C5H5), 84.57 (C5,6), 39.45 (C4,7),
36.19 (C3,8), 22.77 (C2,9), 14.09 (C1,10). IR (CH2Cl2): ν(CO) (cm-1
)
2078 (s), 2035 (s).
Uncoordinated t5dec. 1H NMR (CD2Cl2, 400 MHz, 293 K): δ
5.40 (m, 2H, H5,6), 1.98 (m, 4H, H4,7), 1.33 (m, 8H, H2,3,8,9), 0.89
3
(t, JHH ) 7.2 Hz, 6H, H1,10). 13C{1H} NMR (CD2Cl2, 100 MHz,
293 K): δ 130.92 (C5,6), 32.90 (C4,7), 32.51 (C3,8), 22.82 (C2,9),
14.34 (C1,10).
General Procedure for Reactions of the CpRu(CO)2(trans-
olefin)+ Complexes with Nucleophiles/Ligands Resulting in
Displacement of the Olefin. A 0.010 mmol sample of the complex
(1-5) was placed in a 22 cm NMR tube. The tube was then moved
into a glovebox, and a 0.70 mL aliquot of deuterated solvent (CD2-
Cl2, acetone-d6, CDCl3, CD3OD, or DMSO-d6) was added to the
NMR tube by calibrated syringe. An excess of the nucleophile was
then added (10×-100×) to the NMR tube, which was subsequently
capped with a rubber septum. After removal from the glovebox,
the NMR tube was then flame-sealed and placed in a constant-
temperature bath at 50.0 ( 0.1 °C. The tube was removed from
the bath periodically. and the spectrum was recorded on a Bruker
DRX-400 spectrometer at room temperature using the deuterated
solvent as the internal lock and standard. The tube was then returned
to the bath within a 10 min period. After the bound olefin peak
had disappeared, the NMR tube was opened and attached to a
vacuum line along with an empty NMR tube. After the sample
was frozen with liquid nitrogen, it was evacuated along with the
empty NMR tube. The vacuum was turned off, and the sample tube
was allowed to warm to room temperature, thereby transferring
the liquid into the empty NMR tube that was immersed in liquid
nitrogen. This process transferred the deuterated solvent, the free
olefin(s), and sometimes excess nucleophile to the originally empty
NMR tube. A 1H NMR spectrum of the contents of the tube showed
diagnostic peaks (see above) for the olefinic protons of the free cis
and trans isomers, which were integrated to give the relative
amounts of the cis and trans isomers. All reactions listed were done
in duplicate. The relative amounts of cis and trans isomers that
were obtained from each trial were reproducible to within 3% or
less.
Characterization of Compounds 1-5. [CpRu(CO)2(η2-t3hx)]-
BF4 (1). 1H NMR (CD2Cl2, 400 MHz, 293 K): δ 5.87 (s, 5H, C5H5),
4.86 (m, 2H, H3,4), 2.23 (m, 2H, H2,5), 1.64 (m, 2H, H2,5), 1.17 (t,
3JHH ) 7.6 Hz, 6H, H1,6). 13C{1H} NMR (CD2Cl2, 100 MHz, 293
K): δ 197.02 (CtO), 192.58 (CtO), 91.78 (C5H5), 85.15 (C3,4),
32.89 (C2,5), 18.12 (C1,6). IR (CH2Cl2): ν(CO) (cm-1) 2078 (s),
2035 (s). Anal. Calcd for C13H17BF4O2Ru: C, 39.71; H, 4.37.
Found: C, 40.07; H, 4.77.
1
Uncoordinated t3hx. H NMR (CD2Cl2, 400 MHz, 293 K): δ
5.46 (m, 2H, H3,4), 2.01 (m, 4H, H2,5), 0.98 (t, 3JHH ) 7.6 Hz, 6H,
H
1,6). 13C{1H} NMR (CD2Cl2, 100 MHz, 293 K): δ 131.30 (C3,4),
26.31 (C2,5), 14.34 (C1,6).
1
Uncoordinated c3hx. H NMR (CDCl3, 400 MHz, 293 K): δ
5.35 (m, 2H, H3,4), 2.05 (m, 4H, H2,5), 0.97 (t, 3JHH ) 7.6 Hz, 6H,
H
1,6). 13C{1H} NMR (CDCl3, 400 MHz, 293 K): δ 131.08 (C3,4),
20.55 (C2,5), 14.48 (C1,6).
[CpRu(CO)2(η2-t2pt)]BF4 (2). 1H NMR (CD2Cl2, 400 MHz, 293
K): δ 5.87 (s, 5H, C5H5), 4.98 (m, 2H, H2,3), 2.15 (m, 1H, H4),
1.93 (d, 3JHH ) 5.2 Hz, 3H, H1), 1.64 (m, 1H, H4), 1.17 (t, 3JHH
)
7.6 Hz, 3H, H5). 13C{1H} NMR (CD2Cl2, 100 MHz, 293 K): δ
197.11 (CtO), 192.58 (CtO), 91.77 (C5H5), 86.89 (C3), 79.94
(C2), 32.80 (C4), 24.90 (C1), 17.91 (C5). IR (CH2Cl2): ν(CO) (cm-1
)
2078 (s), 2035 (s). Anal. Calcd for C12H15BF4O2Ru: C, 38.02; H,
3.99. Found: C, 37.69; H, 3.99.
1
Uncoordinated t2pt. H NMR (CD2Cl2, 400 MHz, 293 K): δ
5.43 (m, 2H, H2,3), 1.99 (m, 2H, H4), 1.64 (m, 3H, H1), 0.95 (t,
3JHH ) 7.6 Hz, 3H, H5). 13C{1H} NMR (CD2Cl2, 100 MHz, 293
K): δ 133.72 (C3), 124.14 (C2), 26.19 (C4), 18.19 (C1), 14.33 (C5).
1
[CpRu(CO)2(η2-t3oct)]BF4 (3). H NMR (CD2Cl2, 400 MHz,
293 K): δ 5.86 (s, 5H, C5H5), 4.88 (m, 2H, H3,4), 2.25 (m, 2H,
Kinetic Studies of the Reactions of CpRu(CO)2(t3hx)+ with
PPh3 and 4-Picoline. A 0.010 mmol sample of complex 1 was
placed in a 22 cm NMR tube. The tube was then moved into a
glovebox, and a 0.70 mL aliquot of CD2Cl2 was added to the NMR
tube by calibrated syringe. An excess of the nucleophile was then
added (30×-70×) to the NMR tube, which was subsequently
capped with a rubber septum. After removal from the glovebox,
the NMR tube was then flame-sealed and placed in a Bruker DRX-
400 spectrometer maintained at a constant temperature of 50.0 (
0.1 °C. Spectra were recorded on the Bruker DRX-400 spectrometer
at specific intervals using the deuterated solvent as the internal lock
and standard. The olefin methyl peaks were integrated using XWIN-
NMR software. Rate constants, kobs, were obtained from the slopes
of first-order least-squares plots of ln(1 + [product]/[reactant])
versus time.17 All trials were done in duplicate.
H
2,5), 1.69 (m, 1H, H2), 1.56 (m, 3H, H5,6), 1.41 (m, 2H, H7), 1.18
(t, JHH ) 7.2 Hz, 3H, H1), 0.93 (t, JHH ) 7.2 Hz, 3H, H8). 13C-
{1H} NMR (CD2Cl2, 100 MHz, 293 K): δ 197.06 (CtO), 192.55
(CtO), 91.76 (C5H5), 85.91 (C3), 83.96 (C4), 39.40 (C5), 36.14
(C6), 32.93 (C2), 22.70 (C7), 18.15 (C1), 14.10 (C8). IR (CH2Cl2):
ν(CO) (cm-1) 2078 (s), 2035 (s). Anal. Calcd for C15H21BF4O2Ru:
C, 42.77; H, 5.03. Found: C, 41.82; H, 4.61.
3
3
Uncoordinated t3oct. 1H NMR (CD2Cl2, 400 MHz, 293 K): δ
5.42 (m, 2H, H3,4), 1.99 (m, 4H, H2,5), 1.33 (m, 4H, H6,7), 0.96 (t,
3JHH ) 7.6 Hz, 3H, H1), 0.89 (t, 3JHH ) 7.2 Hz, 3H, H8). 13C{1H}
NMR (CD2Cl2, 100 MHz, 293 K): δ 132.43 (C3), 129.94 (C4),
32.85 (C5), 32.49 (C6), 26.22 (C2), 22.82 (C7), 14.42 (C1), 14.34
(C8).
1
[CpRu(CO)2(η2-t4oct)]BF4 (4). H NMR (CD2Cl2, 400 MHz,
293 K): δ 5.86 (s, 5H, C5H5), 4.90 (m, 2H, H4,5), 2.24 (m, 2H,
3,6), 1.56 (m, 6H, H2,3,6,7), 0.99 (t, 3JHH ) 7.2 Hz, 6H, H1,8). 13C-
Acknowledgment. This project was supported by the
National Research Initiative of the USDA Cooperative State
Research, Education, and Extension Service, grant number 2003-
35504-12846.
H
{1H} NMR (CD2Cl2, 100 MHz, 293 K): δ 197.09 (CtO), 192.51
(CtO), 91.74 (C5H5), 84.59 (C4,5), 41.65 (C3,6), 27.43 (C2,7), 13.87
(C1,8). IR (CH2Cl2): ν(CO) (cm-1) 2078 (s), 2035 (s).
Uncoordinated t4oct. 1H NMR (CD2Cl2, 400 MHz, 293 K): δ
5.41 (m, 2H, H4,5), 1.96 (m, 4H, H3,6), 1.37 (m, 4H, H2,7), 0.89 (t,
3JHH ) 7.2 Hz, 6H, H1,8). 13C{1H} NMR (CD2Cl2, 100 MHz, 293
K): δ 130.93 (C4,5), 35.33 (C3,6), 23.41 (C2,7), 14.01 (C1,8).
Supporting Information Available: Table of rate constants for
reactions in eq 4. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
[CpRu(CO)2(η2-t5dec)]BF4 (5). H NMR (CD2Cl2, 400 MHz,
OM7005535
293 K): δ 5.86 (s, 5H, C5H5), 4.88 (m, 2H, H5,6), 2.25 (m, 2H,
H
4,7), 1.56 (m, 6H, H3,4,7,8), 1.41 (m, 4H, H2,9), 0.93 (t, 3JHH ) 7.2
(17) Vecchi, P. A.; Ellern, A.; Angelici, R. J. Organometallics 2005,
24, 2168.
Hz, 6H, H1,10). 13C{1H} NMR (CD2Cl2, 100 MHz, 293 K): δ 197.09