Incorporation of phenyl-substituted pentadienyl ligands in (pentamethylcyclopentadienyl)ruthenium complexes t

Article abstract of DOI:10.1039/b003001p

The reactions of the [Ru(C5Mej)Cl]4 tetramer with 2, 4-diphenylpenta-l, 3-diene or 3-phenyl- or 1, 5-diphenyIsubstituted pentadienyl anions lead to the incorporation of the expected phenyl-substituted pentadienyl ligands into the respective symmetric Ru(C

Full text of DOI:10.1039/b003001p

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Incorporation of phenyl-substituted pentadienyl ligands in
(pentamethylcyclopentadienyl)ruthenium complexes†
Vichien Kulsomphob,a Gregory C. Turpin,a Kin-Chung Lam,*b Chris Youngkin,a
Wimonrat Trakarnpruk,a Pat Carroll,*c Arnold L. Rheingold*b and Richard D. Ernst*a
a Department of Chemistry, University of Utah, 315 S. 1400 E., Rm. DOCK, Salt Lake City,
UT 84112-0850, USA
b Department of Chemistry, University of Delaware, Newark, DE 19716, USA
c Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
Received 13th April 2000, Accepted 7th July 2000
Published on the Web 18th August 2000
The reactions of the [Ru(C5Me5)Cl]4 tetramer with 2,4-diphenylpenta-1,3-diene or 3-phenyl- or 1,5-diphenyl-
substituted pentadienyl anions lead to the incorporation of the expected phenyl-substituted pentadienyl ligands
into the respective symmetric Ru(C5Me5)(Pdl) products (Pdl = 2,4-Ph2C5H5; 3-PhC5H6; 1,5-Ph2C5H5). The reaction
of the tetramer with a mixture of 2-methyl-4-phenylpenta(-1,3- or -2,4-)dienes led to the Pdl = 2-Me-4-PhC5H5
complex. In contrast, the reaction of the tetramer with 3-phenylpenta-1,3-diene led to simple incorporation of
the η4-diene ligand. Structural confirmation of the formulations of the four η5-pentadienyl complexes has been
achieved, allowing for a number of comparisons to be made regarding the structural effects of phenyl substitution
on the (1,5), (2,4) and 3 positions of the open dienyl ligand.
Introduction
Metal pentadienyl compounds have proven to be interesting
in terms of their structures and bonding,1 as well as reaction
chemistry2 and potential applications.3 In many of these
aspects, the ability to incorporate a wide variety of substituents
would clearly be advantageous, whether for probing the effects
of such substituents on physical properties, or to expand upon
the range of targets that can be prepared from them synthetic-
ally. To date, Ru(C5Me5)(Pdl) complexes (Pdl = various penta-
dienyl groups) have been found capable of tolerating a number
of different substituents, including alkyl, CF3 and siloxy groups4
(trialkylsilyl substituents having been incorporated in other
systems).5 Aromatic substituents should be of particular inter-
est, owing to the possibility of conjugation with the pentadienyl
fragment, and of coordinating additional metal centers to the
complex.6 Indeed, a few, typically highly specialized, phenyl-
substituted pentadienyl complexes of chromium,7 rhodium,8
iron9 and rhenium10 have previously been described, although
general systematic routes to symmetrically mono- and di-
substituted complexes have not been developed. Herein we
report the syntheses and full characterizations of Ru(C5Me5)-
(Pdl) complexes having symmetrically (Pdl = 1,5-Ph2C5H5, 1;
2,4-Ph2C5H5, 2; 3-PhC5H6, 3) or unsymmetrically (Pdl = 2-Me-
4-PhC5H5, 4) disposed phenyl substituents.
ence of K2CO3 [eqn. (1)]. In this reaction it is likely that a
K CO
2
3
1
–
4 [Ru(C5Me5)Cl]4 ϩ 2,4-Ph2-1,3-C5H6
Ru(C5Me5)[2,4-Ph2C5H5] (1)
Ru(C5Me5)Cl(η4-diene) complex is first formed, such as 5, from
which HCl may be extracted by virtue of the presence of an
endo-oriented methyl group on a diene terminus.11
Results and discussion
Diene and symmetric dienyl complexes
The preparation of Ru(C5Me5)(1,5-Ph2C5H5) 1 from the reac-
tion of [Ru(C5Me5)Cl]4 with the 1,5-diphenylpentadienyl anion
has been previously described.4a The other possible sym-
metrically disubstituted complex, Ru(C5Me5)(2,4-Ph2C5H5) 2,
can be prepared in variable yield (35–65%) from the reaction of
[Ru(C5Me5)Cl]4 with 2,4-diphenylpenta-1,3-diene in the pres-
Such methyl group orientations are a normal consequence
of a 2,4-disubstitution pattern in a pentadiene or pentadienyl
fragment,1,12 and formal deprotonations have been found to
be quite facile in a number of complexes similar to 5.4,13 As
a related 3-phenylpenta-1,3-diene complex would instead be
expected to have an exo-oriented methyl group, its conversion
to an η5-dienyl complex should not occur so readily. In fact, a
similar reaction of the tetramer and this diene led to the antici-
pated Ru(C5Me5)Cl(η4-3-PhC5H6) complex 6, one of many
† Dedicated to Professor Herbert Schumann on the occasion of his
65th birthday.
3086
J. Chem. Soc., Dalton Trans., 2000, 3086–3093
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b003001p

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Table 1 1H NMR Resonances for selected Ru(C5Me5)(Pdl) complexes
Pdl
δ[H-3]
δ[H-2,4]
δ[H-1,5(exo)]
δ[H-1,5(endo)]
C5Me5
C5H7
3-C6H9
2,4-C7H11
3-PhC5H6
2,4-Ph2C5H5
1,5-Ph2C5H5
2-Me-4-PhC5H5
4.82
—
4.78
—
6.35
4.79
5.62
4.02
3.88
—
4.48
—
4.95
—
2.30
2.30
2.16
2.39
2.73
—
2.28, 2.72
0.32
0.38
0.36
0.54
0.51
2.28
0.19, 0.74
1.72
1.70
1.68
1.65
1.37
1.19
1.52
Table 2 Summary of structure determinations
Compound
1
2
3
4
Chemical formula
M
Crystal system
C27H30Ru
455.56
Monoclinic
Cc
C27H30Ru
455.56
Hexagonal
P63cm
6.34
C21H26Ru
388.53
Monoclinic
P21/c
C22H28Ru
402.56
Rhombohedral
¯
Space group
R3
µ/cmϪ1
7.37
8.59
8.30
a/Å
b/Å
c/Å
11.833(1)
25.685(3)
7.4492(6)
107.750(5)
2156.3(3)
195
24.266(5)
24.266(5)
7.364(2)
120
3755(2)
298
16.169(6)
7.689(2)
14.598(4)
91.33(2)
1814.4(11)
298
36.617(11)
36.617(11)
7.301(3)
90 (γ = 120)
8482(6)
233
β/Њ
V/Å3
T/K
Z
4
8614
1923
0.041
6
3876
1418
0.038
4
3469
3341
0.034
18
4148
2954
0.072
Reflections collected
Independent reflections
R(F)
R(wF)
0.045
0.064
0.049
0.172
examples of Ru(C5Me5)Cl(η4-diene) compounds.14 Character-
ization of the resulting yellow–orange product was achieved
straightforwardly through analytical and spectroscopic data.
Since these, and other, Ru() complexes could have either η4-cis
or η4-trans diene coordination,14,15 it is not completely certain
which mode would hold for 6, although the presence of the
3-phenyl substituent would likely provide a steric influence in
favor of the cis isomer 6a.
Fig. 1 Perspective view of Ru(C5Me5)(1,5-Ph2C5H5) 1.
scopic methods (see Experimental section), and some particu-
larly interesting comparisons may be made from the NMR
spectroscopic data. For each dienyl complex, the presence of
the expected formal mirror plane symmetry was evident, which
in the case of 3 requires at least a rapid partial oscillation
around the dienyl–aryl C–C bond. That a full rotation is also a
facile process can be recognized from the 13C NMR spectra for
complexes 1–4, which reveal a single resonance for the ortho
carbon atoms, and for the meta carbon atoms as well. The 13C
NMR spectra are strikingly similar to those of the correspond-
ing methyl-substituted analogs. Thus, replacement of H by
either Me or Ph leads to significant and surprisingly compar-
able downfield shifts for the attached carbon atoms, the greatest
difference in chemical shifts being ca. 5 ppm for the dienyls’ C-3
resonance of the 3-substituted complexes (3-H, 92.1; 3-Me,
100.9 ppm; 3-Ph, 105.8 ppm). On the other hand, the 1H NMR
spectra are significantly different, with large downfield shifts of
up to ca. 2 ppm resulting from phenyl substitution (Table 1),
whereas methyl substitution leads to nearly no change.
Owing to the reluctance of 6 to undergo loss of HCl, the
preparation of the η5-3-phenylpentadienyl complex 3 required
a direct reaction of [Ru(C5Me5)4Cl]4 with the dienyl anion
[eqn. (2)]. The resulting product, like 1 and 2, is a yellow crystal-
Structural confirmation has been obtained for the symmetric
1,5-diphenyl, 2,4-diphenyl and 3-phenyl substituted Ru(C5-
Me5)(Pdl) complexes, 1–3, as well as for Ru(C5Me5)(2-Me-
4-PhC5H5) (Tables 2–6, Figs. 1–3). Although reasonable
discrepancy indices were obtained for the symmetric structures,
the fair to poor diffracting natures of the diphenyl substituted
complexes have led to relatively poor precision in some of the
1
–
4 [Ru(C5Me5)Cl]4 ϩ K(3-PhC5H6) →
Ru(C5Me5)(3-PhC5H6) (2)
line compound, relatively air-stable in the solid state, but sig-
nificantly more air-sensitive in solution. These compounds have
been characterized through routine analytical and spectro-
J. Chem. Soc., Dalton Trans., 2000, 3086–3093
3087

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Table 3 Selected bond distances (Å) and angles (Њ) for 1
Table 5 Selected bond distances (Å) and angles (Њ) for 3
Ru–C1
Ru–C2
Ru–C3
Ru–C4
2.307(11)
2.170(8)
2.169(9)
2.161(8)
2.197(16)
2.213(8)
2.203(9)
2.149(15)
2.201(8)
2.259(12)
1.453(14)
1.398(11)
1.416(12)
1.427(15)
1.421(12)
1.483(15)
1.397(16)
1.437(16)
1.431(15)
C1–C6
1.468(16)
1.489(18)
1.505(12)
1.499(12)
1.531(15)
1.490(12)
1.455(17)
1.416(12)
1.397(11)
1.373(12)
1.377(13)
1.377(14)
1.378(12)
1.401(12)
1.380(12)
1.366(13)
1.400(14)
1.361(14)
1.399(12)
Ru–C1
Ru–C2
Ru–C3
Ru–C4
Ru–C5
Ru–C12
Ru–C13
Ru–C14
Ru–C15
Ru–C16
C1–C2
C2–C3
C3–C4
2.175(5)
2.144(4)
2.198(4)
2.130(5)
2.165(5)
2.184(4)
2.176(4)
2.195(4)
2.199(4)
2.191(4)
1.420(7)
1.426(6)
1.422(6)
C3–C11
C4–C15
1.505(5)
1.421(6)
1.418(6)
1.438(6)
1.427(6)
1.418(5)
1.414(6)
1.494(7)
1.510(6)
1.498(6)
1.519(7)
1.507(7)
C5–C12
C18–C23
C19–C24
C20–C25
C21–C26
C22–C27
C6–C7
C6–C11
C7–C8
C8–C9
C9–C10
C10–C11
C12–C13
C12–C17
C13–C14
C14–C15
C15–C16
C16–C17
C12–C13
C12–C16
C13–C14
C14–C15
C15–C16
C12–C17
C13–C18
C14–C19
C15–C20
C16–C21
Ru–C5
Ru–C18
Ru–C19
Ru–C20
Ru–C21
Ru–C22
C1–C2
C2–C3
C3–C4
C4–C5
C18–C19
C18–C22
C19–C20
C20–C21
C21–C22
C1–C2–C3
C2–C3–C4
124.4(4)
122.1(4)
119.0(4)
118.1(4)
124.3(4)
121.3(2)
118.7(2)
107.2(4)
126.6(5)
126.1(4)
109.0(4)
C12–C13–C18
C14–C13–C18
C13–C14–C15
C13–C14–C19
C15–C14–C19
C14–C15–C16
C14–C15–C20
C16–C15–C20
C12–C16–C15
C12–C16–C21
C15–C16–C21
125.8(4)
125.0(4)
107.0(3)
126.2(4)
126.5(4)
109.0(4)
124.2(4)
126.7(4)
107.8(4)
125.7(4)
126.5(4)
C2–C3–C11
C4–C3–C11
C3–C4–C5
C3–C11–C6
C3–C11–C10
C13–C12–C16
C13–C12–C17
C16–C12–C17
C12–C13–C14
C1–C2–C3
C2–C3–C4
C3–C4–C5
C2–C1–C6
C4–C5–C12
C1–C6–C7
C1–C6–C11
123.2(8)
126.0(8)
123.7(9)
121.2(10)
121.1(11)
117.1(7)
126.1(8)
C5–C12–C13
C5–C12–C17
C18–C19–C20
C19–C20–C21
C20–C21–C22
C21–C22–C18
C22–C18–C19
118.4(8)
124.8(9)
108.1(8)
109.7(10)
108.2(9)
105.6(10)
108.3(8)
Table 6 Selected bond distances (Å) and angles (Њ) for 4
Table 4 Selected bond distances (Å) and angles (Њ) for 2
Ru–C1
Ru–C2
Ru–C3
Ru–C4
Ru–C5
Ru–C11
Ru–C12
Ru–C13
Ru–C14
Ru–C15
C1–C2
C1–C5
C2–C3
C3–C4
C4–C5
C11–C12
2.208(10)
2.208(9)
C12–C13
C12–C22
C13–C14
C14–C15
C14–C16
C1–C6
C2–C7
C3–C8
C4–C9
C5–C10
C16–C17
C16–C21
C17–C18
C18–C19
C19–C20
C20–C21
1.425(14)
1.531(16)
1.423(14)
1.455(13)
1.489(13)
1.497(15)
1.501(14)
1.494(14)
1.520(14)
1.509(15)
1.394(13)
1.394(13)
1.389(14)
1.371(16)
1.391(16)
1.367(14)
2.191(10)
2.177(10)
2.218(10)
2.195(10)
2.142(10)
2.186(9)
Ru–C7
Ru–C8
Ru–C9
C6–C8
C10–C13
Ru–C10
Ru–C11
Ru–C12
2.170(16)
2.158(11)
2.174(16)
1.544(11)
1.439(27)
2.233(20)
2.218(15)
2.171(15)
C11–C14
C12–C15
C7–C8
1.541(25)
1.536(17)
1.428(22)
1.398(16)
1.391(17)
1.378(29)
1.500(23)
C8–C9
C10–C11
C11–C12
C12–C12a
2.172(9)
2.183(10)
1.453(15)
1.382(15)
1.398(14)
1.447(14)
1.439(15)
1.424(16)
C1–C6–C8
C5–C6–C8
C6–C8–C7
C6–C8–C9
C7–C8–C9
C8–C9–C8a
C11–C10–C11a
119.2(7)
120.7(7)
119.6(11)
119.1(12)
120.9(10)
128.4(16)
106.6(19)
C11–C10–C13
C10–C11–C12
C10–C11–C14
C12–C11–C14
C11–C12–C12a
C11–C12–C15
C12a–C12–C15
126.4(11)
111.3(15)
123.9(18)
124.7(13)
105.4(6)
127.8(13)
126.5(13)
C1–C2–C3
C1–C5–C4
C2–C1–C5
C2–C3–C4
C3–C4–C5
C11–C12–C13
C12–C13–C14
108.3(9)
108.9(11)
108.0(10)
107.8(9)
107.0(10)
123.8(11)
125.2(9)
C13–C14–C15
C11–C12–C22
C13–C12–C22
C13–C14–C16
C15–C14–C16
C14–C16–C17
C14–C16–C21
121.8(9)
120.3(10)
115.9(11)
117.9(8)
119.9(9)
122.8(9)
120.5(9)
Within the statistical limits, the Ru–C(C5Me5) bonding for
the three compounds appears similar (Table 7), and not unlike
that in Ru(C5Me5)(3-C6H9) [C6H9 = methylpentadienyl, Ru–
C(av) 2.193(8) Å]. The Ru–C[1,5], –C[2,4] and –C[3] distances
of 2.164(2), 2.126(2) and 2.187(2) Å in Ru(C5Me5)(3-C6H9) are
all shorter than the respective distances in 3, suggesting that
phenyl substitution hinders the extent of metal–pentadienyl
interaction relative to methyl substitution. Such an effect could
easily be steric in origin, although for 1 and 3 the phenyl groups
could significantly stabilize the formally negatively charged 1, 3
and/or 5 positions, thereby reducing the metal–pentadienyl
interaction electronically. In fact, in both 1 and 3, the Ru–C
distances for the phenyl-substituted carbon atoms are signifi-
cantly longer than those for the other carbon atoms, while for 2
this is not the case. Also pertinent in this regard is the fact that
for 1, with two phenyl groups stabilizing the negative charge,
at least the Ru–C[1,2,4,5] distances appear substantially longer
than their counterparts in 2 and 3, presumably reflecting weaker
bonding for complex 1.16a,b
Fig. 2 Molecular structure of Ru(C5Me5)(2,4-Ph2C5H5) 2.
bonding parameters. Nevertheless, there are still a number of
useful comparisons that can be drawn from these data. For
simplicity, pertinent averaged bonding parameters are pre-
sented in Table 7, using brackets to designate general penta-
dienyl positions, e.g., C[1,5] for the terminal carbon atoms of a
pentadienyl ligand.
As has been the case for methyl-substituted complexes,17
phenyl substituents decrease delocalized C–C(Ph)–C bond
3088
J. Chem. Soc., Dalton Trans., 2000, 3086–3093

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Table 7 Comparison of pertinent structural parameters for 1, 2, 3
and 4
the ruthenium center is 1.611 Å from the plane of Pdl. The longer
Ru–Pdl separation for 1 seems to be the result of some anomal-
ous distortions present in 1 (vide infra), which also appear
reflected by the small interligand angle in 1 [3.7Њ, cf., 8.0Њ for
Ru(C5Me5)(3-C6H9)]. This can further be seen in the values of
the twist angles between the phenyl and pentadienyl planes. The
values for 2 and 3 of ca. 29–34Њ are reasonable, much as would
be expected for biphenyls.20 For 1, however, one observes a
smaller twist, whose actual value is quite dependent on defin-
ition. Both of these observations are direct results of other,
unexpected deformations. The first of these involves a 6–8Њ
asymmetry in the non-ring angles about the ipso carbon atoms
of the phenyl groups, e.g., C1–C6–C(7 vs. 11) and C5–C12–
C(13 vs. 17). Much smaller or negligible distortions (ca. 2Њ) of
this sort are displayed by 2 and 3. The second distortion
involves a flexing of the phenyl groups such that the attached
dienyl carbon atoms (C[1,5]) do not lie in the phenyl planes.
In fact, flexings of 1.6 and 3.7Њ are observed for the two
phenyl groups of 1, in opposite directions (a smaller deform-
ation of 1.4Њ is found for 2, toward ruthenium, while the
distortion in 3 is negligible). Thus, the first phenyl group is
tilted away from the ruthenium center, but the second one
toward it. Quite possibly these deformations relieve steric
interactions between hydrogen atoms sufficiently that less of a
twist is required between the dienyl and each of the two
phenyl planes, perhaps leading to better conjugation between
them. However, it is also possible that the distortions arise
from an effort to optimize C–H–π interactions between the
phenyl groups and the methyl substituents on the C5Me5
ligands, or to optimize intermolecular π–π interactions between
phenyl groups (vide infra). There are in fact some data that
suggest the presence of C–H–π interactions.21 In particular,
one sees significant upfield shifts for the methyl substituents
on the C5Me5 ligands for 1 and 2, but not for 3 (Table 1),
the shift being especially pronounced for 1. Additionally, for
both 1 and 2 one observes significant tilting toward the
C5Me5 ligands by the phenyl groups (Table 7), while for 3
the tilting is minimal. While it is normal for the tilting
of a substituent in the 3 position to be smaller than for the
other positions,17 the magnitude of the phenyl tilting in 2
appears greater than would be expected, in line with the
idea of an attractive C–H–π interaction. Presumably the tilting
in 1 does not need to be as pronounced as alternative modes
of distortion are available to enhance the interaction (vide
supra).
1
2
3
4
Ru–C(Cp*)/Å
Ru–C[1,5]/Å
Ru–C[2,4]/Å
Ru–C[3]/Å
C[1]–C[2]/Å
C[2]–C[3]/Å
2.205(18)
2.252(10)
2.166(6)
2.169(9)
1.440(10)
1.407(8)
2.202(9)
2.189(4)
2.200(7)
2.189(7)
2.157(7)
2.186(9)
1.440(10)
1.424(10)
122.8(7)
125.2(9)
2.813(15)
10.8,15.4
30.4,30.5
8.4
2.170(16) 2.170(4)
2.158(11) 2.137(3)
2.174(16) 2.198(4)
1.428(22) 1.421(4)
1.398(16) 1.424(4)
120.9(10) 124.4(3)
128.4(16) 122.1(4)
2.789(27) 2.774(8)
C[1]–C[2]–C[3]/Њ 123.4(6)
C[2]–C[3]–C[4]/Њ 126.0(8)
C[1] ؒ ؒ ؒ C[5]/Њ
2.847(21)
11.0,10.3
19.6(1.6,12.4) 30.5,29.0
Ph tilta/Њ
12.2,17.4
1.4,1.0
34.1,34.0
7.5
Ph twistb/Њ
Interligand
anglec/Њ
3.7
11.8
Ru–Pdl/Å
Ru–Cp*/Å
1.611
1.836
1.557
1.846
1.553
1.824
1.561
1.837
a The first tilt angle θ is defined by sin(θ) = ∆/d, for which ∆ is the
deviation of the dienyl-bound substituent atom from the dienyl plane,
and d is the C(dienyl)–substituent bond distance. The second tilt angle
is defined by the torsion angle generated by a dienyl-attached substi-
tuent atom and any three carbon atom dienyl chain to which it is
attached. b The first twist angle is equal to the angle between the phenyl
and Pdl planes, while the other values derive from torsion angles involv-
ing two dienyl and two phenyl carbon atoms. For 1 the latter definition
led to two values due to a deformation of the phenyl group, through
which C(1) and C(5) no longer lie in the phenyl group’s plane. c Deter-
mined from the least-squares planes of the two ligands, such that an
angle of 0Њ would reflect a parallel orientation.
Unsymmetric dienyl complexes
There are some situations in which electronic effects of a
substituent may not be apparent as a result of a symmetric
disubstitution pattern. For example, stabilization of negative
charge by a phenyl substituent on a terminal carbon atom
should lead to a long–short–long–short pattern in the dienyl’s
carbonframework,asin7.Obviously,however,with1,5-disubsti-
Fig. 3 Perspective view of Ru(C5Me5)(3-PhC5H6) 3.
angles. Thus, in 2 the C[1]–C[2]–C[3] angle is smaller than the
C[2]–C[3]–C[4] angles, while for 3, the reverse trend is observed.
Such angular contractions are common in delocalized species.18
Interestingly, siloxy substituents have been found to bring about
the opposite effect,4b,d apparently by increasing the amount of s
character available for the other bonds of the siloxy-substituted
carbon atom.
Several other parameters related to the ligand planes are of
interest. Due to the combination of the similarity of the Ru–C
bond lengths for the two ligands, and the wider nature of the
ligands Pdl, the metal atoms in these mixed sandwich com-
plexes are required geometrically to lie closer to the pentadienyl
ligand plane. The values for 2 and 3 are similar to those for
Ru(C5Me5)(3-C6H9) (1.557, 1.553 and 1.567 Å for ligands Pdl vs.
1.846, 1.824 and 1.834 Å for C5Me5, respectively), while for 1
tution by phenyl groups one would have cancelling effects at
each bond. Thus it was of interest to obtain complexes with
unsymmetric mono(phenyl)substitution, especially at the 2 pos-
ition, since some 1-phenylpentadienyl complexes have been
reported.7–10 A straightforward synthesis of such a species was
readily accomplished from the reaction of 2-methyl-4-
phenylpentadienes with [Ru(C5Me5)Cl]4 [eqn. (3)]. As in the
1
–
4[Ru(C5Me5)Cl]4 ϩ 2-Me-4-Ph-(1,3 or 2,4)-C5H6 →
Ru(C5Me5)(2-Me-4-PhC5H5) (3)
J. Chem. Soc., Dalton Trans., 2000, 3086–3093
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case of the preparation of 2, these reactions presumably go
through η4-diene intermediates, 8a,b, whose endo-oriented
methyl groups then facilitate loss of HCl, leading to the form-
ation of 4, as a mixture of planar chiral enantiomers. Com-
Fig. 4 Perspective view of Ru(C5Me5)(2-Me-4-PhC5H5) 4.
1
pound 4 was readily characterized, and its H and 13C NMR
spectra were found to be quite as expected based upon those of
Ru(C5Me5)(2,4-C7H11) (C7H11 = dimethylpentadienyl) and 2.
The structural characteristics of 4 (Fig. 4) are generally
similar to those exhibited by 1–3. However, while a change
from Ru(C5Me5)(3-C6H9) (C6H9 = methylpentadienyl) to 3 led
to an apparent enhancement of the Ru–C5Me5 bonding at the
expense of the Ru–Pdl bonding, the change from 4 to 2 (also
involving replacement of Me by Ph) does not seem to bring
about the same effect, but rather perhaps the opposite (Table 7).
Owing to the greater tiltings experienced by substituents in the
2,4 vs. 3 positions (vide supra), one would expect steric problems
involving the phenyl groups to be relieved in 4 relative to 2;
furthermore, the location of phenyl groups at the formally
uncharged 2 and 4 positions would not lead to nearly as much
resonance stabilization of a free dienyl anion’s π system as
would occur for 3 substitution, so that the less stabilized
2-phenyl or 2,4-diphenyl substituted anions would be expected
on an electronic basis to be at least more comparable to, if not
actually better than, their methyl-substituted counterparts
regarding the favorability of their binding to a given metal
center. It therefore appears entirely reasonable that the Ru–
C(Pdl) bonding in 2 could be quite competitive to that in 4 or
even perhaps in Ru(C5Me5)(2,4-C7H11) (C7H11 = dimethylpenta-
dienyl). With respect to substituent tilting, the presence of both
methyl and phenyl substituents in 4 allows for a direct com-
parison of their inherent preferences. Perhaps not surprisingly,
the tilt by the phenyl substituent is greater than that by the
methyl substituent, 10.8 vs. 8.8Њ.
Finally, one can make some general observations regarding
all four phenyl-substituted complexes. Concerning the extent
of conjugation between the phenyl and pentadienyl planes, one
can note that for 1 and 4 the lengths of the C–C bonds connect-
ing the two aromatic systems are, within their uncertainties,
indistinguishable from the value of ca. 1.484 Å observed in a
large number of biphenyl structures.19b The values of 1.505(5) Å
for 3 and 1.544(11) Å for 2 appear slightly to somewhat longer.
However, in those cases it was necessary to refine the phenyl
rings as rigid groups, which could lead to systematic errors in
these distances, rendering them less credible. Thus, it would
appear reasonable to expect all of these species to be fairly
similar to biphenyls in their degrees of conjugation. Interest-
ingly, it has been observed that the inter-ring C–C distances in
biphenyls appear to be independent of the twist between the
two rings.19b
Fig. 5 Solid state packing for Ru(C5Me5)(2,4-Ph2C5H5) 2.
It is of some interest that the presence of the phenyl groups in
2 and 4 has a significant effect on the solid state packing of
these molecules. As can be seen in Figs. 5 and 6, apparently
favorable intermolecular stacking interactions between the
phenyl groups result in interesting modes of association of the
molecules, which may be responsible for the compounds’ adop-
tion of relatively uncommon hexagonal and rhombohedral
space groups. Of course, π–π stacking interactions are com-
monly observed in a variety of compounds,21 and some of the
ways by which these and various C–H–π interactions can lead
to hexagonal and rhombohedral symmetries have been
explicitly described.22
With the development of straightforward routes to the rather
general incorporation of phenyl substituents into metal penta-
dienyl compounds, a fairly complete series of electronically
tuned pentadienyl ligand substituent patterns has now become
available, and the incorporation of phenyl substituents into
pentadienyl ligands has been found to lead to significant spec-
troscopic as well as electronic effects. Structural data suggest
that at least when phenyl substitution occurs on the formally
charged 1, 3 and/or 5 positions, thereby stabilizing the formal
dienyl anion, the metal–pentadienyl bonding is weakened.
Significant twisting exists between the phenyl and pentadienyl
ligands, which would seem to hinder conjugation and com-
munication between the π systems; however, the fact that such
interactions do occur in similarly twisted biphenyls suggests
that conjugation effects in phenylpentadienyl ligands are not
3090
J. Chem. Soc., Dalton Trans., 2000, 3086–3093

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added to the stirred ether solution, whose composition was
monitored by GC. After ca. 10 h, dehydration of the alcohol
was complete, and small portions of aqueous sodium hydro-
gensulfite were added, until the iodine had been reduced to
iodide. The diethyl ether solution was then dried over MgSO4,
and the ether removed in vacuo, providing a mixture of the
dienes in a yield of 78%. Vacuum transfer of the dienes yielded
a product of ca. 95% purity. Further purification is possible,28
but was found unnecessary for the subsequent reaction with
[Ru(C5Me5)Cl]4. Spectroscopic data were identical to those
previously reported.28
(Pentamethylcyclopentadienyl)(3-phenylpentadienyl)-
ruthenium(II), Ru(C5Me5)(3-PhC5H6), 3
To a solution of 0.35 g of [Ru(C5Me5)Cl]4 (1.4 mmol of Ru) in
30 mL of THF at Ϫ78 ЊC, a solution of 0.40 g (1.4 mmol) of the
potassium salt of the 3-phenylpentadienyl anion in 20 mL of
THF was slowly added. The resulting red solution was stirred
at Ϫ78 ЊC for 30 min and thereafter slowly warmed to room
temperature. The red solution was stirred overnight, and the
solvent removed in vacuo. The crude product was extracted with
3 × 25 mL of pentane, and the mixture was filtered through
alumina. After concentration to a volume of ca. 5–10 mL, the
yellow solution was cooled to Ϫ90 ЊC, yielding a yellow air-
stable (as solid) crystalline compound (mp 59–60 ЊC, 31%
yield).
Fig. 6 Solid state packing for Ru(C5Me5)(2-Me-4-PhC5H5) 4.
precluded. Of course, such could also be the case for phenyl-
substituted cyclopentadienyl ligands; however, to date most
such species have contained adjacent phenyl groups,23 which
would further diminish if not prevent conjugation with the
ligand fragment. In any event, the fact that there are significant
differences between the natures of the pentadienyl positions
(e.g., the charged 1,5 vs. 3 vs. uncharged 2,4 carbon atoms) leads
to an added dimension and potentially greater diversity in
properties for the open pentadienyl systems. It can be expected
that much remains to be learned through comparative physical
studies on variously substituted pentadienyl complexes, and
additional efforts in these directions are continuing.
Anal. Calc. for C21H26Ru: C, 66.45; H, 6.91. Found: C, 64.82;
1
H, 7.01%. H NMR (toluene-d8, ambient): δ 7.1–7.4 (m, 5H,
Ph), 4.48 (t, 2H, H-2,4, J = 8.8 Hz), 2.39 (dd, 2H, Hexo-1,5,
J = 2.3, 8.9 Hz), 1.65 (s, 15H, C5Me5), 0.54 (dd, 2H, Hendo-1,5,
J = 2.3, 8.9 Hz). 13C NMR (toluene-d8, ambient): δ 142.7 (s,
Ph), 128.2 (d, Ph, J = 159 Hz), 126.9 (d, Ph, J = 159 Hz), 123.8
(d, Ph, J = 159 Hz), 105.8 (s, C-3), 90.1 (s, C5Me5), 82.7 (d, C-2,
J = 157 Hz), 44.6 (t, C-1, J = 156 Hz), 10.6 (q, C5Me5, J = 122
Hz). Mass spectrum (EI, 17 eV) [m/z (relative intensity)]: 379
(100), 365 (51), 363 (30), 351 (4), 231 (10), 189 (6), 128 (6), 91
(3%).
Experimental
All procedures were carried out under a nitrogen atmosphere
using standard Schlenk apparatus and techniques. Solvents
were dried and deoxygenated under a nitrogen atmosphere
using sodium benzophenone ketyl. Phenylacetaldehyde was
obtained commercially, and converted to phenylcrotonaldehyde
and subsequently to 3-phenylpenta-1,3-diene by reported pro-
cedures;24 2,4-diphenylpenta-1,3-diene was also prepared by a
reported procedure from dypnone,25 except that the use of flash
chromatography (silica column, 3 cm diameter × 10 cm, hexane
eluent) allowed for higher yields (up to ca. 65%). [Ru(C5-
Me5)Cl]4 and Ru(C5Me5)(1,5-Ph2C5H5) 1 were also prepared as
previously described.7 Spectroscopic studies were carried out
as reported earlier,26 while analytical data were obtained from
Robertson or E ϩ R Laboratories.
(Pentamethylcyclopentadienyl)(2,4-diphenylpentadienyl)-
ruthenium(II), Ru(C5Me5)(2,4-Ph2C5H5), 2
To a THF solution containing 0.30 g of [Ru(C5Me5)Cl]4 (1.1
mmol of Ru) and 0.30 g of K2CO3 (2.2 mmol) was slowly added
0.50 g of 2,4-diphenylpenta-1,3-diene (2.2 mmol). The red–
brown solution was stirred for 24 h, during which time it turned
to yellow. The solvent was removed from the yellow solution.
The residue was extracted with 2 × 30 mL of pentane, and the
mixture was filtered through Celite. The yellow filtrate was con-
centrated to a volume of ca. 5–10 mL and cooled to Ϫ90 ЊC,
yielding yellow air-stable (as solid) crystals (mp 59–60 ЊC, 37–
65% yield). Anal. Calc. for C27H30Ru: C, 71.18; H, 6.64. Found:
ꢀ-Phenylcrotonaldehyde
1H NMR (neat): δ 9.54 (s, 1H, CHO), 7.1–7.4 (m, 5H, C6H),
6.83 (q, 1H, vinyl, J = 7.2 Hz), 1.99 (d, 3H, Me, J = 7.2 Hz).
1
C, 70.36; H, 6.76%. H NMR (toluene-d8, ambient): δ 7.1–7.6
(m, 10H, Ph), 6.35 (s, 1H, H-3), 2.73 (d, 2H, Hexo-1,5, J = 2 Hz),
1.37 (s, 15H, C5Me5), 0.51 (d, 2H, Hendo-1,5, J = 2 Hz). 13C
NMR (toluene-d8, ambient): δ 144.5 (s, Ph), 128.8 (d, Ph,
J = 159 Hz), 128.2 (d, Ph, J = 159 Hz), 126.9 (d, Ph, J = 159
Hz), 93.1 (d, C-3, J = 155 Hz), 92.9 (s, C-2,4), 90.9 (s, C5Me5),
41.5 (t, C-1,5, J = 157 Hz), 10.1 (q, C5Me5, J = 126 Hz). Mass
spectrum (EI, 17 eV) [m/z (relative intensity)]: 454 (100), 439
(59), 379 (5), 314 (11), 228 (37), 203 (13), 115 (10), 91 (19), 57
(7), 41 (3%).
2,4-Diphenylpenta-1,3-diene
1H NMR: major isomer (neat): δ 7.2–7.5 (m, 10H, Ph), 6.55 (q,
1H, C-3, J = 1.5 Hz), 5.67 (d, 1H, H-1, J = 1.5 Hz), 5.23 (t, 1H,
H-1a, J = 1.5 Hz), 2.12 (d, 3H, Me, J = 1.5 Hz). The minor (ca.
10%) geometric isomer was evidenced in solution by character-
istic peaks at δ 6.24 (t, 1H, J = 1.4 Hz), 5.28 (d, 1H, J = 1.6 Hz),
4.88 (t, 1H, J = 1.5 Hz), 2.19 (d, 3H, J = 1.5 Hz).
2-Methyl-4-phenylpenta-(1,3 and 2,4)-dienes
(ꢁ5-Pentamethylcyclopentadienyl)(ꢁ4-3-phenylpenta-1,3-diene)-
ruthenium(II) chloride, [Ru(ꢁ5-C5Me5)(ꢁ4-3-Ph-1,3-C5H7)Cl] 6
A mixture of these dienes was prepared from the reaction of
mesityl oxide with freshly prepared phenylmagnesium bromide
(commercial solutions gave poorer results), using a procedure
analogous to that used for 2,4-dimethylpenta-1,3-diene.27 After
the reaction had been quenched with aqueous ammonium
chloride, and the organic products extracted with diethyl ether,
GC analysis indicated that some dehydration of the alcohol had
already taken place. A few small crystals of iodine were then
To a THF solution (20 mL) containing [Ru(C5Me5)Cl]4 (0.08 g,
0.3 mmol of Ru) was added an excess of potassium carbonate
and 3-phenylpenta-1,3-diene (0.04 g, 0.3 mmol). The original
dark brown solution immediately turned a clearer yellow–
brown. After 4 h stirring, the solvent was removed in vacuo. The
yellow residue was extracted with 2 × 20 mL pentane and
J. Chem. Soc., Dalton Trans., 2000, 3086–3093
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filtered through Celite. The yellow filtrate was concentrated
in vacuo until incipient crystallization, and cooled to Ϫ20 ЊC,
resulting in the formation of air-stable (as solid) yellow–orange
crystals (0.09 g, 70% yield, mp 95–97 ЊC, decomp.). Refluxing
the mixture for several hours did not result in any new com-
pound. Anal. Calc. for C21H27RuCl: C, 60.64; H, 6.54. Found:
C, 60.66; H, 6.67%. 1H NMR (chloroform-d, ambient): δ 7.66–
7.40 (m, 5H, Ph), 4.60 (dd, 1H, H-2, J = 7.7, 9.5 Hz), 2.97 (dd,
1H, H-1, J = 7.7, 2.3 Hz), 2.11 (q, 1H, H-4, J = 6.8 Hz), 1.80 (d,
CH3, J = 6.8 Hz), 1.60 (dd, 1H, H-1, J = 9.5, 2.3 Hz), 1.42 (s,
15H, C5Me5). 13C NMR (chloroform-d, ambient): δ 137.6 (s,
Ph), 130.7 (d, Ph, J = 158 Hz), 129.1 (d, Ph, J = 158 Hz), 126.8
(d, Ph, J = 158 Hz), 110.1 (s, C-3), 94.9 (s, C5Me5), 83.1 (dd,
C-2, J = 162, 5 Hz), 69.6 (d, C-4, J = 158 Hz), 50.9 (t, C-1,
J = 156 Hz), 15.7 (q, Me, J = 127 Hz), 9.1 (q, C5Me5, J = 128
Hz). IR (Nujol mull): 1732s, 1599w, 1504w, 1261s, 1120w,
1074ms, 1024ms, 893w, 800m, 781m, 705s cmϪ1. Mass spec-
trum (EI, 17 eV) [m/z (relative intensity)]: 544 (49), 543 (47), 542
(35), 467 (14), 145 (15), 144 (89), 143 (19), 129 (100), 128 (23%).
putationally stable results. In the above cases, the Ru
atoms were located from Patterson syntheses. For all structures,
non-hydrogen atoms were anisotropically refined and hydrogen
atoms were treated as idealized contributions. SHELXTL32
(ver. 4.2 and 5.1) software was used in the solution and refine-
ment of 2 and 3.
CCDC reference number 186/2092.
Acknowledgements
Partial support of this research by the NSF and University of
Utah is gratefully acknowledged. We would like to thank a
reviewer for helpful comments.
References
1 R. D. Ernst, Chem. Rev., 1988, 88, 1235.
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1992, 441, 449; J. R. Bleeke, R. J. Wittenbrink, T. W. Clayton, Jr. and
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3 J. T. Spencer and R. D. Ernst, US Pat 5 352 488, 1994; S. J. Severson,
T. H. Cymbaluk, R. D. Ernst, J. M. Higashi and R. W. Parry, Inorg.
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H.-U. Hund, D. Nietlispach and A. Salzer, Organometallics, 1992,
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A. L. Rheingold and T. E. Waldman, Organometallics, 1995, 14,
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540.
(Pentamethylcyclopentadienyl)(2-methyl-4-phenylpentadienyl)-
ruthenium(II), Ru(C5Me5)(2-Me-4-PhC5H5) 4
To a THF solution (40 mL) containing [Ru(C5Me5)Cl]4 (2.50 g,
2.3 mmol) was added an excess of potassium carbonate and a
mixture of 2-methyl-4-phenylpenta-1,3-diene and 2-methyl-4-
phenylpenta-2,4-diene (1.45 g, 9.2 mmol) in 10 mL of THF. The
original dark brown solution turned a clearer yellow–brown
after stirring overnight. The volatiles were removed in vacuo
and the residue was extracted with 3 × 20 mL pentane and
filtered through alumina. The yellow filtrate was concentrated
to a volume of ca. 5 mL and cooled to Ϫ90 ЊC, yielding yellow
air-stable (as solid) crystals (1.70 g, mp 81–82 ЊC, 47% yield).
Higher quality crystals for X-ray analysis were obtained by
slowly cooling a saturated pentane solution to Ϫ30 ЊC. Anal.
Calc. for C22H28Ru: C, 67.15; H, 7.17. Found: C, 66.97; H,
7.26%. 1H NMR (benzene-d6, ambient): δ 7.1–7.5 (m, 5H, Ph),
5.62 (s, 1H, H-3), 2.72 (d, 1H, Hexo-1, J = 2.6 Hz), 2.28 (d, 1H,
Hexo-5, J = 2.3 Hz), 1.83 (s, 3H, Me), 1.52 (s, 15H, C5Me5), 0.74
(d, 1H, Hendo-5, J = 2.3 Hz), 0.19 (d, 1H, Hn-1, J = 2.6 Hz). 13
C
NMR (benzene-d6, ambient): δ 144.5 (s, Ph), 128.7 (d, Ph),
128.6 (d, Ph), 127.1 (d, Ph), 92.7 (s, C-2), 92.5 (d, C-3, J = 159
Hz), 92.1 (s, C-4), 90.7 (s, C5Me5), 46.7 (t, C-5, J = 153 Hz), 40.4
(t, C-1, J = 156 Hz), 26.5 (q, Me, 126 Hz), 10.8 (q, C5Me5,
J = 125 Hz). Mass spectrum (EI, 80 eV) [m/z (relative inten-
sity)]: 396 (40), 395 (40), 394 (100), 393 (89), 392 (96), 391 (83),
390 (45), 389 (32), 388 (21), 387 (10), 381 (22), 380 (12), 379
(56), 378 (30), 377 (50), 376 (32), 375 (20), 374 (14), 373 (11),
233 (11), 232 (11), 231 (13), 230 (11%).
X-Ray structural determinations
Single crystals of the symmetrically substituted compounds
were obtained by slowly cooling their concentrated solutions in
hexane [Ru(C5Me5)(1,5-Ph2C5H5) 1, Ru(C5Me5)(3-PhC5H6) 3]
or diethyl ether [Ru(C5Me5)(2,4-Ph2C5H5) 2] to Ϫ20 ЊC. Crys-
tallographic data are collected in Table 2. The crystals were
mounted in glass capillaries. For 1, systematic absences were
consistent with either the Cc or C2/c space group, but a solution
could only be achieved for the former. Data were processed
using bioteX29 and teXsan30 program packages, while the
structure was solved by direct methods (SIR92).31
8 P. Powell, M. Stephens, A. Muller and M. G. B. Drew,
J. Organomet. Chem., 1986, 310, 255; P. Powell, J. Chem. Res. (S),
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9 W. A. Donaldson and M. Ramaswamy, Tetrahedron Lett., 1989, 30,
1339.
For 2 the crystals were found to possess 6/mmm Laue sym-
10 R. A. Fischer and W. A. Herrmann, J. Organomet. Chem., 1989, 377,
metry. Systematic absences in the data were compatible with
275.
¯
three space groups: P63cm (185), P6c2 (188) or P63/mcm (193).
11 L. Stahl and R. D. Ernst, Organometallics, 1983, 2, 1229.
12 M. Schlosser and G. Rauchschwalbe, J. Am. Chem. Soc., 1978, 100,
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18, 1068; R. Gleiter, I. Hyla-Kryspin, M. L. Ziegler, G. Sergeson,
J. C. Green, L. Stahl and R. D. Ernst, Organometallics, 1989, 8, 298.
Since Z = 6 and the only symmetry element 2 can accommo-
date is a mirror plane, P63cm becomes the only plausible choice.
For 3, 2/m symmetry was indicated and absences uniquely
¯
defined the space group. For 4, 3 Laue symmetry was observed,
¯
¯
compatible with space groups R3, R3, R32, R3m and R3m. The
¯
centrosymmetric R3 yielded chemically reasonable and com-
3092 J. Chem. Soc., Dalton Trans., 2000, 3086–3093

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14 T. D. Tilley, R. H. Grubbs and J. E. Bercaw, Organometallics, 1984,
3, 274; P. J. Fagan, W. S. Mahoney, J. C. Calabrese and I. D.
Williams, Organometallics, 1990, 9, 1843.
15 S. A. Benyunes, M. Green and M. J. Grimshire, Organometallics,
1989, 8, 2268; S. A. Benyunes, J. P. Day, M. Green, A. W.
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