X-ray diffraction, PGSE diffusion, and related NMR studies on a series of Cp*-based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) allyl complexes

Article abstract of DOI:10.1021/om060448u

The new ruthenium (IV) allyl complexes [Ru(Cp*)Cl(DMF) (η³-CH₂-CH-CHPh)](PF₆) (2b) and [Ru-(Cp*)Cl(t-BuCN)(η³-CH₂-CH-CHPh)](PF ₆) (2c) have been prepared and their structures determined. These results are compared with the analogous X-ray data for [Ru(Cp*)Cl(CH ₃CN)(η³-CH₂-CH-CHPh)]-(PF ₆),[Ru(Cp*){OC(O-t-Bu)O}(η³-CH ₂-CH-CHPh)](PF₆),[Ru(Cp*)(CH₃CN) ₂(η³-CH₂-CH-CHPh)]-(PF₆) ₂ and [Ru(Cp*)(DMF)₂(η³-CH ₂-CH-CHPh)](PF₆)₂. In all of the structures, the Ru-((η³-CH₂-CH-CHPh) moiety is markedly distorted such that Ru-CPh(allyl) separation is much longer than the remaining two Ru-C(allyl) distances. The DMF and acetonitrile ligands are shown to exchange on the NMR time scale via both variable-temperature and 2-D exchange spectroscopy. Pulsed gradient spin-echo (PGSE) diffusion and ¹H,¹⁹F HOESY NMR methods show that there is relatively little ion pairing in these salts in DMF and acetonitrile solutions. The PF₆ anions take up specific positions with respect to the Ru(IV) cations.

Full text of DOI:10.1021/om060448u

4520
Organometallics 2006, 25, 4520-4529
X-ray Diffraction, PGSE Diffusion, and Related NMR Studies on a
Series of Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh)
Allyl Complexes
Ignacio Ferna´ndez and Paul S. Pregosin*
Laboratory of Inorganic Chemistry, ETH HCI, Ho¨nggerberg CH-8093 Zu¨rich, Switzerland
Alberto Albinati* and Silvia Rizzato
Department of Structural Chemistry (DCSSI), UniVersity of Milan, 20133 Milan, Italy
ReceiVed May 22, 2006
The new ruthenium (IV) allyl complexes [Ru(Cp*)Cl(DMF)(η3-CH2-CH-CHPh)](PF6) (2b) and [Ru-
(Cp*)Cl(t-BuCN)(η3-CH2-CH-CHPh)](PF6) (2c) have been prepared and their structures determined.
These results are compared with the analogous X-ray data for [Ru(Cp*)Cl(CH3CN)(η3-CH2-CH-CHPh)]-
(PF6), [Ru(Cp*){OC(O-t-Bu)O}(η3-CH2-CH-CHPh)](PF6), [Ru(Cp*)(CH3CN)2(η3-CH2-CH-CHPh)]-
(PF6)2, and [Ru(Cp*)(DMF)2(η3-CH2-CH-CHPh)](PF6)2. In all of the structures, the Ru-((η3-CH2-
CH-CHPh) moiety is markedly distorted such that Ru-CPh(allyl) separation is much longer than the
remaining two Ru-C(allyl) distances. The DMF and acetonitrile ligands are shown to exchange on the
NMR time scale via both variable-temperature and 2-D exchange spectroscopy. Pulsed gradient spin-
echo (PGSE) diffusion and 1H,19F HOESY NMR methods show that there is relatively little ion pairing
in these salts in DMF and acetonitrile solutions. The PF6 anions take up specific positions with respect
to the Ru(IV) cations.
as 1,5-COD5 complexes. In all these reactions, a ruthenium-
(IV) allyl complex is thought to be a common intermediate.
We have recently reported that, for the allylic alkylation
reaction, the source of the observed branched-to-linear regio-
selectivity has an electronic origin.6 These conclusions were
based on studies of two Ru(IV) allyl complexes: [Ru(Cp*)Cl-
(CH3CN)(η3-CH2-CH-CHPh)](PF6), 2a, and the carbonate
complex [Ru(Cp*){OC(OBut)O}(η3-CH2-CH-CHPh)](PF6), 3.
We have subsequently prepared7 two new dicationic species,
4a,b, and these and other complexes are shown in Scheme 1.
Interestingly, while the monocations 2a and 3 are useful in
C-O,6c C-N,6d and C-C allylation reactions, via the use of
oxygen, nitrogen, and carbon nucleophiles, respectively (see
Introduction
Ruthenium complexes have been described as useful catalysts
in an increasing number of processes.1 Ru-catalyzed allylic
alkylation2 and amination reactions,3 among others, have
attracted significant interest due to the recognized regioselec-
tivity in favor of branched products when starting from allylic
precursors of the type R-CHdCH-CH2-X (X ) chloride,
acetate, carbonate). The most commonly used catalyst precursor
contains a Ru-Cp* fragment, e.g., [Ru(Cp*)(CH3CN)3](PF6),
1. Increasingly, a variety of derivatives of 1 are in use as
catalysts, and these include chelating nitrogen ligands4 as well
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10.1021/om060448u CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/16/2006

Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) Allyl Complexes
Organometallics, Vol. 25, No. 19, 2006 4521
Scheme 1
a more comprehensive understanding of these salts and may
mirror the source of their effectiveness in the differing catalytic
reactions.
Results and Discussion
Preparation and Characterization. The complex Ru(IV)
salts 2-4 have been prepared by oxidative addition reactions
of either a chloro or carbonato substrate, in the appropriate
solvent, e.g., see eq 3. One can also use an oxidative addition
approach to afford 2a and then use a solvent exchange reaction,
as indicated by the right-hand side of eq 3. All of these complex
salts, see Scheme 1, have been characterized via NMR, mass
spectral, and microanalytical studies, together with selected
X-ray results. The complexes 2a (80:20) and 2c (82:18) reveal
two isomers in solution; however, in other salts, e.g., 2b, only
one isomer is detected. We believe these two complexes are
due to the presence of endo and exo isomers; that is, the central
CH bond can point toward or away from the Cp* ligand, on
the basis of 2-D NOESY measurements (see Figure 1). The
Overhauser measurements show that the two terminal anti-allyl
protons afford substantial NOE cross-peaks arising from the Cp*
methyl groups, whereas an NOE to the central allyl proton
resonance, from the Cp* methyl groups, is either absent or very
weak. Further, one finds NOEs between the allyl phenyl protons
and, for example, the DMF ligand, suggesting that these two
are close in space and thus that the geometric isomer shown
(DMF or acetonitrile proximate to the phenyl group) represents
eq 1), the dication 4a, in acetonitrile solution, affords a novel
selective Friedel-Crafts catalyst,7 which gives allylation of the
phenyl ring (e.g., eq 2).
We report here two new ruthenium(IV) allyl complexes, 2b,c,
and present X-ray crystallographic, diffusion, and NMR studies
for a number of these and other salts. We are specifically seeking
information with respect to (a) subtle structural distortions within
the allyl ligand, (b) the structural influence of the solvent mol-
ecules acetonitrile and DMF, and (c) anion (PF6)/cation inter-
actions within these ruthenium(IV) allyl complexes. X-ray
crystallography and NMR studies are ideally suited for the first
two points. PGSE (pulse gradient spin-echo) NMR diffusion
studies8 are now increasingly in use to recognize ion-pairing
interactions in solution.9,10 When the PGSE studies are combined
with 1H,19F HOESY11,12 measurements, which describe the
relative positions of the (fluorine-containing) anion, relative to
the cation, one has a useful probe for point “c”, the question of
ionic interactions. These various physical studies should provide
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P. S.; Schmid, T. M.; Consiglio, G. Magn. Reson. Chem. 2004, 42, 795-
800. (d) Kumar, P. G. A.; Pregosin, P. S.; Bernardinelli, M. V. G.; Jazzar,
R. F.; Viton, F.; Ku¨ndig, E. P. Organometallics 2004, 23, 5410-5418. (e)
Schott, D.; Pregosin, P. S.; Jacques, B.; Chavarot, M.; Rose-Munch, F.;
Rose, E. Inorg. Chem. 2005, 44, 5941-5948. (f) Schott, D.; Pregosin, P.
S.; Veiros, L. F.; Calhorda, M. J. Organometallics 2005, 24, 5710-5717.
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(12) (a) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G.;
Terenzi, S. Organometallics 1996, 15, 4349-4351. (b) Bellachioma, G.;
Cardaci, G.; Gramlich, V.; Macchioni, A.; Valentini, M.; Zuccaccia, C.
Organometallics 1998, 17, 5025-5030. (c) Bellachioma, G.; Cardaci, G.;
D′Onofrio, F.; Macchioni, A.; Sabatini, S.; Zuccaccia, C. Eur. J. Inorg.
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A.; Zuccaccia, C.; Zuccaccia, D.; Orabona, I.; Ruffo, F. Organometallics
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Larive, C. K. Concepts Magn. Reson. 2004, 20A, 24-41. (f) Pregosin, P.
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4522 Organometallics, Vol. 25, No. 19, 2006
Ferna´ndez et al.
1
Figure 1. Section of the phase-sensitive H,1H NOESY spectrum of 2b at ambient temperature, showing the relatively strong contacts
from the Cp* methyl groups to the terminal allyl anti protons H-1b and H-3. There is also a modest contact to the syn allyl proton H-1a
and no contact to the central allyl proton. These data suggest that the endo configuration is the correct structure (CD2Cl2, 500 MHz).
Table 1. 1H and 13C NMR Allyl Chemical Shifts for the
Ru(IV) Cp* Allyl Salts 2-4
H-1a H-1b H-2 H-3 H-5 C-1 C-2 C-3
C-5
C-7
2aa 3.06 4.41 6.01 4.84 7.76 67.5 93.7 91.0 129.6 130.5
2bb 2.68 4.51 5.91 4.94 7.31 64.4 95.9 92.3 129.4 130.7
2cb 2.76 4.49 5.94 4.56 7.51 68.2 94.3 91.3 129.5 131.3
3c
3.52 4.66 6.36 5.11 7.74 65.8 99.9 90.2 129.2 130.5
4aa 3.41 4.87 6.59 5.31 7.90 66.3 94.1 103.3 129.9 130.5
4ba 3.64 4.70 6.48 5.49 7.72 66.0 96.9 98.4 131.5 131.6
a In Me2CO-d6. b In CD2Cl2. c In DMF-d7.
in Table 2. The immediate coordination sphere of the ruthenium
cations contain a chloride donor, the η3-CH2-CH-CHPh allyl
ligand, the π-bound Cp*, and an oxygen-bound DMF molecule
for 2b, or a nitrogen bound tert-butylcarbonitrile molecule for
2c. In both cations, the allyl ligand adopts the endo configuration
with respect to the Cp*, as found in solution and in other
published related examples.13b-e The allyl C(Ph) terminal carbon
is proximate to the coordinated solvent in both structures.
Therefore, this structure corresponds to that of the major isomer
in solution. The Ru to Cp* distances (centroid of the Cp ring)
are 1.868(1) and 1.859(2) Å for 2b and 2c, respectively. The
methyl groups of the Cp* are bent out of the plane defined by
the five Cp* ring carbon atoms, away from the Ru atom. The
PF6 counterions in 2b,c show short, nonbonding contacts in the
range 2.5-2.6 Å (< van der Waals radii) to the H atoms of the
Cp* methyl groups.
Figure 2. Section of the 1H,1H phase-sensitive NOESY spectrum
of 2c at ambient temperature showing the exchange between the
central allyl proton H-2 of the two isomers (CD2Cl2, 500 MHz).
the correct structure. The two isomers observed are in exchange
on the NMR time scale, as indicated by 2-D exchange spec-
troscopy (see Figure 2). Moreover, for 2b, we observe exchange
between the complexed DMF and traces of free DMF in solu-
tion. Table 1 gives selected 1H and 13C data for the major com-
ponents in 2-4. Exchange of Cl- for either DMF or CH3CN
results in marked high-frequency shifts in all four allyl protons.
We suggest that these changes are due to local anisotropic effects
Whereas the Ru-Cl separations, 2.389 and 2.412 Å, and the
Ru-O or Ru-N bond lengths, 2.113(2) and 2.068(2) Å, for
since (with one exception, see below) the appropriate allyl 13
C
(13) (a) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1-S83. (b) Gemel,
C.; Kalt, D.; Mereiter, K.; Sapunov, V. N.; Schmid, R.; Kirchner, K.
Organometallics 1997, 16, 427-433. (c) Kondo, H.; Yamaguchi, Y.;
Nagashima, H. Chem. Commun. 2000, 1075-1076. (d) Hermatschweiler,
R.; Ferna´ndez, I.; Breher, F.; Pregosin, P. S. Organometallics 2006, 25,
1440-1447. (e) A recent calculation supports this isomer as the more
favored: Bi, S.; Ariafard, A.; Jia, G.; Lin, Z. Organometallics 2005, 24,
680-686.
chemical shifts do not change markedly. Interestingly, the
methylene allyl carbon resonance is found at much lower
frequency than the terminal methine allyl carbon signal.
X-ray studies on [Ru(Cp*)Cl(η3-CH2-CH-CHPh)(DM-
F)](PF6), 2b, and [Ru(Cp*)Cl(η3-CH2-CH-CHPh)((CH3)3-
CCN)](PF6), 2c. Figures 3 and 4 show views of the Ru(IV)
allyl cations. Selected bond distances and bond angles are given

Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) Allyl Complexes
Organometallics, Vol. 25, No. 19, 2006 4523
Scheme 2. Ruthenium-Carbon Allyl Bond Distances (Å),
in the Various Salts, 2 to 4
Figure 3. Structure of the cation [Ru(Cp*)Cl(η3-CH2-CH-
CHPh)(DMF)]+ in 2b. Thermal ellipsoids are drawn at 50%
probability; PF6 anion is omitted for clarity.
2.320(3) Å. In the cation of 2c, the distances are Ru(1)-C(1L),
2.177(2) Å, Ru(1)-C(2L), 2.166(2) Å, and Ru(1)-C(3L),
2.313(2) Å. Obviously, the separations from the two terminal
allyl carbons, C(1) and C(3), are different by ca. 0.13-0.15 Å,
suggesting very different bond strengths to these carbon atoms.
This conclusion is also supported by the observed 13C data given
in Table 1. In a recent structural report2c Bruneau and co-workers
find for Ru(CH3CN)(η3-CH3CH-CH-CH2)(Br)Cp* Ru-C
bond lengths of 2.280(5), 2.165(5), and 2.208(4) Å, with the
largest value for the RuCH(CH3) distance and the smallest for
the central allyl carbon. Although not quite so marked, once
again the value for the substituted allyl carbon is consistent with
the observed trend.
Scheme 2 shows a comparison of the Ru-C allyl bond
lengths for all of our Cp*Ru(η3-PhCH-CH-CH2) cationic
derivatives. All of the structures reveal strongly asymmetrically
bound allyl moieties, with the bis-acetonitrile cation having the
largest Ru-C3 bond length, ca. 2.38 Å. The substitution of a
chloride by a DMF molecule, i.e., going from 2b to 4b, does
not affect the Ru-C3 bond distance; however, substituting chlo-
ride by acetonitrile (2a to 4a) significantly affects the Ru-C3
bond length.
During an earlier preparation of the neutral Ru(IV) Cp allyl
complex RuCpCl2(η3-CH2-CH-CH2) a small amount of a
crystalline material precipitated from acetone solution (see
Experimental Section). The solid-state structure of this material
was determined and found to be the dinuclear Ru(III) species
[Ru(Cp)Cl(µ-Cl)]2, 5. A view of this molecule is shown in
Figure 5, and selected bond lengths and bond angles are given
in the caption.
Figure 4. Structure of the cation [Ru(Cp*)Cl(η3-CH2-CH-
CHPh)(CH3)3CCN)]+ in 2c. Thermal ellipsoids are drawn at 50%
probability; PF6 anion is omitted for clarity.
Table 2. Bond Lengths (Å) and Angles (deg) for 2b and 2c
2b
2c
Ru-O(1)
Ru-Cl
2.113(2)
2.3886(8)
2.193(3)
2.258(3)
2.256(3)
2.227(3)
2.175(3)
2.164(4)
2.157(3)
2.320(3)
84.76(6)
Ru-N(1A)
Ru-Cl
2.068(2)
2.4115(6)
2.269(2)
2.268(2)
2.199(2)
2.199(2)
2.212(2)
2.177(2)
2.166(2)
2.313(2)
81.69(6)
Ru-C(1)
Ru-C(2)
Ru-C(3)
Ru-C(4)
Ru-C(5)
Ru-C(1L)
Ru-C(2L)
Ru-C(3L)
O(1)-Ru-Cl
Ru-C(1)
Ru-C(2)
Ru-C(3)
Ru-C(4)
Ru-C(5)
Ru-C(1L)
Ru-C(2L)
Ru-C(3L)
N(1A)-Ru-Cl
2b and 2c, respectively, are as expected,13a the three Ru-C(allyl)
distances are worthy of note. For the two cations, the termi-
nal allyl Ru-C bond lengths are markedly different. In the
cation of 2b, the Ru-(C(allyl) distances are Ru(1)-C(1L),
2.164(4) Å, Ru(1)-C(2L), 2.157(3) Å, and Ru(1)-C(3L),
The five Ru-C(Cp) separations in 5, and in 2b,c as well
(see Table 2), are clearly significantly different, although there
seems no obvious reason for this in these three structures. We
also note that, in the Cp* rings, the C-C bond distances are
not equivalent, showing a trend that associates the shortest

4524 Organometallics, Vol. 25, No. 19, 2006
Ferna´ndez et al.
exchanged despite the large excess of nitrile. This suggests
a relatively slow dissociation of DMF from the 18e Ru(IV)
dication. However, at 353 K, the temperature at which the
Friedel-Crafts C-C bond making catalysis is run (eq 2), the
exchange of the two DMF solvent molecules took place within
1 min. This supports the validity of assuming that 4a is indeed
the relevant catalyst precursor.
The crystallographic data for 2b, 2c, and 5 hinted at some
differences in the Ru-C(Cp*) separations. Consequently,
variable-temperature NMR measurements were performed for
complex 2b in the range 298-155 K, and these are shown in
Figure 7. The rotation of the Cp* is still rapid at 155 K since
we find no significant broadening of the Cp* methyl resonance;
however, the rotation of the allyl phenyl ring about the C(ipso)-
C(Ph) bond is now restricted on the NMR time scale at ca.
163 K. The nonequivalent resonances for two ortho and meta
protons are clearly visible. Further, one of the two nonequivalent
DMF methyl groups experiences a low-frequency shift (∆δ )
-0.2 ppm), and we assign this to an anisotropic effect due to
the proximate allyl phenyl group. Consequently, the source of
the difference in the Ru-C separations, observed from the X-ray
data, remains unclear.
Figure 5. Dinclear Ru(III) Cp complex 5. Ru-Ru ) 2.7748(6)
Å, Ru-Cl(1) ) 2.3591(8) Å, Ru-Cl(1′) ) 2.3788(8) Å, Ru-Cl-
(2) ) 2.3851(8) Å, Ru-C(1) ) 2.229(3) Å, Ru-C(2) ) 2.207(3)
Å, Ru-C(3) ) 2.167(3) Å, Ru-C(4) ) 2.156(3) Å, Ru-C(5) )
2.195(3) Å, Cl(1)-Ru-Cl(2) ) 87.87(3)°, Ru-Cl(1)-Ru′ )
71.70(2)°.
separations with the longest Ru-C distances. This observation
is consistent with a subtle interplay of electronic and steric
factors associated with the change in the ligands.
Diffusion NMR and HOESY Studies. It seemed likely that
a comparison of mono- vs dicationic salts might reveal differ-
ences in how the PF6 anions interact with the organometallic
cations. As in previous studies, we measure the experimental
diffusion constants (D-values) via pulsed gradient spin-echo
(PGSE) methods and then calculate the corresponding hydro-
dynamic radii, rH, via the Stokes-Einstein equation (eq 4).
The Ru to Cp distance (to the centroid of the Cp ring in 5),
at 1.830(3) Å, is somewhat shorter than that measured for 2b,c
(1.859(2) and 1.861(1) Å, respectively). This difference is likely
due to the differing steric effects associated with Cp* relative
to Cp. We presume that complex 5 is formed via a slow radical
process involving loss of the allyl ligand. Complex 5 is worthy
of note in that allyl chloride derivatives are occasionally used
in organic allylation chemistry.
rH ) kT/6πηD
(4)
D ) diffusion constant and η ) viscosity
Solution NMR Studies. Since the bis-DMF salt, 4b, was used
as a catalyst precursor, in acetonitrile solution, it was of interest
to monitor the rate of DMF/acetonitrile exchange. Figure 6
It is assumed that, when a relatively large cation and a relatively
small anion reveal similar D-values, this indicates substantial
ion pairing. The use of the constant “6” in eq 4 has been
criticized,14 so that in Table 3 we show both conventional (using
6) and corrected, r, constants. The factor c can vary from 4
1
shows the curve derived from H NMR data for this exchange
process (using the appearance of free DMF as a monitor), at
room temperature in CD3CN solution. Surprisingly, after 1 h
at probe ambient temperature, only 84% of the DMF had
Figure 6. Solvent exchange of the bis-DMF complex [RuCp*(η3-CH2-CH-CHPh)(DMF)2](PF6), 4b, to afford the bis-acetonitrile complex
[RuCp*((η3-CH2-CH-CHPh)(CH3CN)2](PF6), 4a. Salt 4b was dissolved in CD3CN, and the appearance of free DMF was monitored by
1H NMR spectroscopy (y0 ) 57.16157; A1 ) 13.68922; t1 ) 0.2404; A2 ) 29.50985; t2 ) 1.37759).

Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) Allyl Complexes
Organometallics, Vol. 25, No. 19, 2006 4525
1
Figure 7. Variable-temperature H NMR spectra for a sample of 2b. The change in the aromatic region (a) stems from the restricted
rotation around the C(ipso)-C(Ph) bond, whereas the pronounced low-frequency shift of one of the DMF methyl groups (b) is assigned to
an anisotropic effect (500 MHz, CD2Cl2).
(slip boundary conditions14) to 6 (stick boundary conditions14)
and stems from semiempirical estimations derived from the
microfriction theory proposed by Wirtz and co-workers,14 in
which c is expressed as a function of the solute-to-solvent ratio
of radii. For the 2 mM measurements, the table gives three rH
values: using c ) 6, a corrected c, and an rx estimated using
the program Chem3D.
The table shows D-values for 2 mM acetonitrile or DMF
samples of 2a, 2b, 4a, and 4b (and then a set of data at higher
concentrations for 4a and 4b). From the measured D-value, for
the chloro-DMF cation of 2b, in DMF solution, we estimate
the hydrodynamic radius, rH, to be ca. 4.9 Å, in good agreement
with estimates of the size of this cation, 4.6 Å, from our
crystallographic data. For the 2 mM result from the bis-DMF
cation, 4b, we obtain an rH value of ca. 5.7 Å, a much larger
value. The D-value for the bis-nitrile dication, 4a, in acetonitrile
solution, is also somewhat large at 5.4 Å.
Possibly, the larger rH values for the dications arise due to
some charge-induced aggregation; that is, the 2+ charge on the
cation could increase the tendency toward aggregation. To test
this idea, we have measured the D-values for 4a and 4b at both
10 and 20 mM. The observed concentration dependence for the
bis-DMF dication is small. Indeed, there is no difference
between the 2 and 10 mM solutions. However, for the bis-nitrile
dication, 4a, the D-values decrease 2-3% (and thus the rH
values increase) with each increase in concentration. It seems
likely that for the bis-nitrile salt 4a we are dealing with some
aggregation as a function of concentration. Aggregation at higher
concentrations is now fairly well known.15,16 Different aggrega-
tion states or different ratios of aggregates might affect the
reactivity.
1H,19F HOESY spectroscopy is often helpful in positioning
the anions in three-dimensional space, relative to the cations.
1
Figure 8 shows H,19F HOESY spectra for 2a, 3, and 4a. The
figure shows that, for the monocation 2a, the anion approaches
only the Cp* methyl groups. The situation is similar for the
monocationic carbonate, 3, although there is a weak contact to
the t-Bu methyl groups. However in the bis-nitrile dication, 4a,
in addition to the Cp* methyl interaction, there are now well-
Ion pairing can result in markedly increased rH values;
however, the diffusion data for the PF6 anions from the 2 mM
solutions of 2a, 2b, 4a, and 4b suggest that this is not the case.
The 2.2-2.8 Å rH values for these PF6 anions are suggestive
of well-separated ions and typical of what one finds in polar
solvents of high dielectric constant. The rH values for the PF6
anions in DMF solution are even somewhat smaller than those
normally found in methanol solution.9
(15) (a) Zuccaccia, D.; Clot, E.; Macchioni, A. New J. Chem. 2005, 29,
430-433. Macchioni, A.; Romani, A.; Zuccaccia, C.; Guglielmetti, G.;
Querci, C. Organometallics 2003, 22, 1526-1533 (b) Song, F. Q.; Lancaster,
S. J.; Cannon, R. D.; Schormann, M.; Humphrey, S. M.; Zuccaccia, C.;
Macchioni, A.; Bochmann, M. Organometallics 2005, 24, 1315-1328. (c)
We have not measured the solution viscosities. However, we have measured,
and show in Table 3, the D-values for the solvents, acetonitrile and DMF,
for the three concentrations. These values are not very different and, allowing
for an error of “6” in the last figure, do not support a significant change in
the viscosities of these solutions.
(14) (a) It has been suggested that the factor c () 6 in eq 4) is not valid
for small species whose van der Waals radii are <5 Å (Edward, J. T. J.
Chem. Educ. 1970, 47, 261). This factor can be adjusted by using a
semiempirical approach (see: Chen, H.-C.; Chen, S.-H. J. Phys. Chem.
1984, 88, 5118; Espinosa, P. J.; de la Torre, J. G. J. Phys. Chem. 1987, 91,
3612) derived from the microfriction theory proposed by Wirtz and co-
workers (Gierer, A.; Wirtz, K. Z. Naturforsch., A 1953, 8, 522; Spernol,
A.; Wirtz, K. Z. Naturforsch., A 1953, 8, 532). (b) Zuccaccia, D.; Macchioni,
A. Organometallics 2005, 24, 3476-3486.
(16) Using our data, a reviewer has calculated that 4a,b exist as “ion
triples” containing two cations and one anion. Further, he suggests some
aggregation for 2a,b.

4526 Organometallics, Vol. 25, No. 19, 2006
Ferna´ndez et al.
Table 3. D and rH (Å) Values for the Ru Complexes 2a,b and 4a,b in Acetonitrile and DMF Solutions
b
c
C (mM)
solvent
CH3CN
nucleus
Da
rH
rX
c
rd
2a
2b
2
1H
13.72
24.76
40.34
5.20
4.7
2.6
1.6
4.9
2.2
1.8
1.8
5.4
2.8
1.6
5.5
2.9
1.6
5.6
3.0
1.6
5.7
2.3
1.8
5.7
2.4
1.8
5.8
2.5
1.8
4.5
1.6
5.6
4.7
5.1
3.3
19F
1H (CH3CN)
2
DMF
1H
4.6
1.6
5.5
3.8
5.4
3.5
19F
11.40
14.04
14.51
12.07
23.50
40.35
11.82
22.69
40.40
11.49
21.57
40.28
4.44
11.05
14.48
4.45
10.59
14.56
4.37
1H (DMF)
1H (DMF)
4a
4a
4a
4b
4b
4b
2
10
20
2
CH3CN
CH3CN
CH3CN
DMF
1H
4.6
1.6
5.7
4.9
5.7
3.4
19F
1H (CH3CN)
1H
19F
1H (CH3CN)
1H
19F
1H (CH3CN)
1H
4.8
1.6
5.6
4.0
6.2
3.5
19F
1H (DMF)
1H
10
20
DMF
19F
1H (DMF)
1H
DMF
19F
10.19
14.51
1H (DMF)
a
× 10-10 m2 s-1, 299 K, at 2 mM. (2%. b The viscosity, η, used in the Stokes-Einstein equation is (DMF, 299 K) ) 0.8574 × 10-3; (CH3CN, 299 K)
) 0.3377. The value “6” was used. c Estimated using Chem3D, by averaging the distances between the centroid and the outer hydrogen. d Using the “c”
value shown immediately to the right.
resolved 1H, 19F contacts from the PF6 to the central allyl proton
H-2 and the ortho phenyl protons H-5.16 The Overhauser
contacts in 4a may well result from the necessity of placing
two anions in three-dimensional space such that the anion-
anion repulsion is minimal, To this end, we suggest a structure
such as 6 as a partial contributor to the overall solution structure.
The anions lie above and below the cation and thus explain the
complexed DMF ligands for solvent CH3CN. However, the
exchange is rapid at elevated temperature. The resulting Ru-
(IV) bis-acetonitrile species, 4a, which performs Friedel-Crafts
type allylation chemistry, rather than simple O-, N-, or C-
allylation, (a) possesses the longest Ru-C3 bond length, (b)
may aggregate in acetonitrile solution, and (c) has one of the
two PF6 anions fairly close to the complexed η3-CH2-CH-
CHPh allyl ligand. The diffusion data clearly show that the anion
does not reside permanently in this position. Nevertheless, this
position of the anion, plus some aggregation, might result in
sufficient steric hindrance such that aromatic allylation would
be preferred to the more routine attack of the nucleophile at
allyl carbon C3.
Experimental Part
All reactions and manipulations were performed under a N2
atmosphere using standard Sclenck techniques. Solvents were dried
and distilled under standard procedures and stored under nitrogen.
All the standard one- and two-dimensional measurements were
performed on Bruker Avance 300, 400, and 500 MHz spectrometers
using samples of 2-20 mM concentration. Chemical shifts are given
observed contact to the central allyl proton, H-2. The presence
of one of the two anions in the region of the allyl ligand (in
addition to some aggregation) might well have steric conse-
quences with respect to an incoming phenol nucleophile.
Comments. The physical studies reveal that these Ru(IV)
allyl complexes all have markedly distorted allyl ligands, both
in the solid and in the solution states. At room temperature the
dimethyl formamide Ru complex, 4b, slowly exchanges the
1
in ppm and referenced to TMS and CFCl3 for H and 19F, respec-
tively. Elemental analyses and mass spectroscopic studies were
performed at ETHZ.
Crystallography. Red crystals of [Ru(Cp*)Cl(Me2NCHO)(η3-
CH2-CH-CHPh)](PF6) (2b) and [Ru(Cp*)Cl[(CH3)3CCN](η3-
CH2-CH-CHPh)](PF6) (2c), suitable for X-ray diffraction, were
obtained by layering diethyl ether in a CH2Cl2 solution of the

Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) Allyl Complexes
Organometallics, Vol. 25, No. 19, 2006 4527
Figure 8. 19F,1H HOESY spectra of 10 mM samples at ambient temperature of (a) [Ru(Cp*)Cl(CH3CN)(η3-CH2-CH-CHPh)](PF6), 2a,
in CD3CN; (b) [Ru(Cp*)(CH3CN)2(η3-CH2-CH-CHPh)](PF6), 4a, in CD3CN; and (c) [Ru(Cp*)(OCO2tBu)(η3-CH2-CH-CHPh)](PF6),
3, in DMF. In the fluorine dimension only one of the two resonances of the doublet is shown. For 4a, the cross-peak at ca. 2.5 ppm stems
from those acetonitrile ligands, which have not yet exchanged with the deuteroacetonitrile (1H, 400 MHz).
isolated complex and are air-stable. Red, plate-like, crystals of [Ru-
(Cp)Cl2]2 were obtained from acetone solution. The crystals were
mounted on Bruker diffractometers, equipped with CCD detectors,
for the unit cell and space group determinations. The crystals for
the data collection were cooled to 120 K (110 K for 2c) using a
cold nitrogen stream. Selected crystallographic and other relevant
data are listed in Table 4 and in the Supporting Information.
Data were corrected for Lorentz and polarization factors with
the data reduction software SAINT17 and corrected empirically for
absorption using the SADABS program.18 The structures were
solved by Patterson and Fourier methods and refined by full matrix
least-squares19 (the function minimized being ∑[w(Fo - 1/kFc)2]).
For all the structures, no extinction correction was deemed neces-
sary. The scattering factors used, corrected for the real and imagi-
nary parts of the anomalous dispersion, were taken from the
literature.20 All calculations were carried out by using the PC version
of SHELX-9719 and ORTEP programs.21
3622 reflections (θmax e 24.3°). The data were collected by using
ω scans, in steps of 0.3°. For each of the 1515 collected frames,
counting time was 30 s. The least-squares refinement was carried
out using anisotropic displacement parameters for all non-hydrogen
atoms. The H atoms of the allylic moiety were found from differ-
ence Fourier maps and refined using isotropic temperature factors,
while the contribution of the remaining hydrogens, in their calcu-
lated positions (C-H ) 0.96 (Å), B(H) ) 1.2B(Cbonded) (Å2)), was
included in the refinement using a riding model.
Structural Study of [Ru(Cp*)Cl[(CH3)3CCN](η3-CH2-CH-
CHPh)](PF6) (2c). The space group was determined from the
systematic absences, while the low-temperature cell constants were
refined by least-squares, at the end of the data collection, using
9821 reflections (θmax e 25.5°). The data were collected by using
ω scans, in steps of 0.3°. For each of the 1800 collected frames,
counting time was 30 s. The least-squares refinement was carried
out using anisotropic displacement parameters for all non-hydrogen
atoms, while the H atoms were included in the refinement as
Structural Study of [Ru(Cp*)Cl(Me2NCHO)(η3-CH2-CH-
CHPh)]PF6 (2b). The space group was unambiguously determined
from the systematic absences, while the cell constants (at 120 K)
were refined by least-squares, at the end of the data collection, using
-
described above. The PF6 anion showed positional disorder for
several equatorial fluorine atoms. Two different orientations for
the F atoms were clearly shown in the difference Fourier maps; the
resulting disordered model was refined anisotropically (sof’s 0.66
and 0.34, respectively).
(17) BrukerAXS, SAINT, Integration Software; Bruker Analytical X-ray
Systems: Madison, WI, 1995.
Structural Study of [Ru(Cp*)Cl2]2 (5). Space group and cell
constants were determined at 120 K. The values of the cell param-
eters were refined at the end of the data collection using 1012
reflections (θmax e 22.5°). The data were collected by using ω scans,
in steps of 0.3°. For each of the 1860 collected frames, counting
time was 30 s. The least-squares refinement was carried out using
(18) Sheldrick, G. M. SADABS, Program for Absorption Correction;
University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(19) Sheldrick, G. M. SHELX-97, Structure Solution and Refinement
Package; Universita¨t Go¨ttingen, 1997.
(20) International Tables for X-ray Crystallography; Wilson, A. J. C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol. C.
(21) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

4528 Organometallics, Vol. 25, No. 19, 2006
Ferna´ndez et al.
Table 4. Experimental Data for the X-ray Study of 2b, 2c, and [RucpCl2]2
2b
2c
[RucpCl2]2
formula
mol wt
C22H31ClF6NOPRu
606.97
C24H33ClF6NPRu
617.00
C10H10Cl4Ru2
474.12
data coll. T, K
diffractometer
cryst syst
space group (no.)
a, Å
120 (2)
110 (2)
Bruker APEX
monoclinic
P21/n (14)
8.4912(4)
14.6540(6)
21.1911(9)
97.822(1)
2612.3(2)
4
1.569
8.20
120(2)
Bruker APEX
monoclinic
P21/c (14)
8.2667(6)
17.441(1)
17.372(1)
101.083(2)
2458.0(3)
4
Bruker SMART
monoclinic
C2/c (15)
6.988(2)
12.489(3)
14.649(3)
99.121(5)
1262.3(5)
4
b, Å
c, Å
â, deg
V, Å3
Z
F
calcd, g cm-3
1.640
8.72
2.495
32.05
µ, cm-1
radiation
Mo KR (graphite monochrom., λ ) 0.71073 Å)
θ range, deg
no. data collected
no. indep data
no. obsd reflns (no)
1.67 < θ < 26.62
19 469
5120
1.69 < θ < 26.03
18 232
5144
2.82< θ < 25.01
5262
1106
1012
4163
4692
2
2
[|Fo| > 2.0σ(|F| )]
no. of params refined (nv)
Rint
326
388
73
0.0475
0.0399
0.0926
1.026
0.0287
0.0312
0.0818
1.049
0.0287
0.0175
0.0201
1.016
R (obsd reflns)a
Rw2 (obsd reflns)b
GOFc
2
2
2
2 2
2
2
a R ) ∑(|Fo - (1/k)Fc|)/∑|Fo|. b Rw ) [∑w(Fo - (1/k)Fc )2/∑w|Fo | ]. c GOF ) [∑w(Fo - (1/k)Fc )2/(no - nv)]1/2
.
anisotropic displacement parameters for all non-hydrogen atoms.
The contribution of the hydrogen atoms, in their calculated positions
(C-H ) 0.96(Å), B(H) ) 1.2B(Cbonded)(Å2)), was included in the
refinement using a riding model.
a red solid, which was filtrated and dried under vacuum, 102 mg
(88%). A dichloromethane solution of this solid was then layered
with diethyl ether and stored at -30 °C during 24 h, affording
1
crystals of 2b, suitable for X-ray diffraction. H NMR (CD2Cl2,
298 K, 400 MHz): δ 1.58 (15H), 2.15 (3H, J 0.8 Hz), 2.68 (1H,
J 9.6 Hz), 3.01 (3H), 4.51 (1H, J 6.4 Hz), 4.94 (1H, J 11.2 Hz),
5.91 (1H, J 11.2, 9.6, 6.4 Hz), 7.30 (2H, J 8.4, 1.2 Hz), 7.38 (2H,
J 8.4, 7.6 Hz), 7.58 (1H, J 7.6, 1.2 Hz), 7.76 (1H). 13C NMR (CD2-
Cl2, 298 K, 400 MHz): δ 9.6 (CH3), 33.2 (CH3), 39.6 (CH3), 64.4
(H2Callyl), 92.3 (HCallyl), 95.9 (HCallyl), 106.6 (C), 129.4 (HCAr),
130.2 (HCAr), 130.7 (HCAr), 134.4 (Cipso), 166.2 (Cdmf). MALDI
MS: m/z 389.1 (M+), 353 (M+ - Cl - PhCHCHCH2).
[Ru(Cp*)Cl[(CH3)3CCN](η3-CH2-CH-CHPh)](PF6) (2c). tert-
Butylcarbonitrile (2 mL) was added to an oven-dried Schlenk con-
taining [RuCp*Cl(CH3CN)(ηPhCH-CH-CH2)](PF6), 2a (60 mg,
0.104 mmol). The reaction mixture was stirred for 2 h, after which
the solution was slowly concentrated under vacuum, 58 mg (91%).
The resulting crude was washed with CH2Cl2/diethyl ether, affording
an orange solid, which was filtrated and dried under vacuum. A
dichloromethane solution of this solid was then layered with diethyl
ether and storaged at RT during 16 h, affording bright orange crys-
tals of 2c, suitable for X-ray diffraction. 1H NMR (CD2Cl2, 298 K,
500 MHz): δ 1.18 (9H), 1.72 (15H), 2.76 (1H, J 9.5 Hz), 4.49
(1H, J 6.5 Hz), 4.56 (1H, J 11.0 Hz), 5.94 (1H, J 11.0, 9.5, 6.5
Hz), 7.48-7.54 (4ArH), 7.62 (1ArH). 13C NMR (CD2Cl2, 298 K,
500 MHz): δ 9.8 (CH3), 27.6 (CH3), 68.2 (H2Callyl), 91.2 (HCallyl),
94.3 (HCallyl), 106.7 (C), 129.5 (CAr), 129.9 (CAr), 131.3 (CAr),
135.1 (Cipso), 137.5 (Cnitrile). Anal. Calcd for C24H33ClF6NPRu: C
46.72, H 5.39, N 2.27. Found: C 46.48, H 5.48, N 2.38. ESI-MS:
m/z 427.1 (M+), 389.1 (M+ - (CH3)3CCN), 272.0 (M+ - (CH3)3-
CCN - PhCHCHCH2).
Diffusion NMR. All the diffusion measurements were performed
on a 400 MHz Bruker Avance spectrometer equipped with a
microprocessor-controlled gradient unit and an inverse multinuclear
probe with an actively shielded Z-gradient coil. The shape of the
gradient pulse was rectangular, and its strength varied automatically
in the course of the experiments. The measurements were carried
out without spinning. The sample temperature was calibrated, before
the PGSE measurements, by introducing a thermocouple inside the
bore of the magnet. The calibration of the gradients was carried
out via a diffusion measurement of HDO in D2O, which afforded
a slope of 2.022 × 10-4. We estimate the experimental error in the
D-values to be (2%. All of the data leading to the reported D-values
afforded lines whose correlation coefficients were >0.999, and
8-12 points have been used for regression analysis. To check
reproducibility, three different measurements with different diffusion
parameters (δ and/or ∆) were always carried out. The gradient
strength was incremented in 8% steps from 10% to 98%. A
measurement of 1H and 19F T1 was carried out before each diffusion
experiment, and the recovery delay set to 5 times T1.
In the 1H-PGSE experiments δ was set to 2 ms. The number of
scans varied between 80 and 128 per increment with a recovery
delay of 5 to 10 s. Typical experimental times were 4-5 h.
For 19F, δ was usually set from 1.5 to 3 ms. Eight to 16 scans
were taken with a recovery delay of 10 to 20 s, and a total experi-
mental time of ca. 2-4 h.
The 1H,1H NOESY spectra were acquired using a 1 s relaxation
delay and 800 ms of mixing time. The 19F,1H HOESY measure-
ments were carried out with a doubly tuned (1H, 19F) TXI probe.
A mixing time of 800 ms was used, and 32-64 scans were taken
for each of the 512 t1 increments recorded. The delay between
increments was set to 2 s.
[RuCp*Cl(Me2NCHO)(η3-CH2-CH-CHPh)]PF6 (2b). Di-
methylformamide (2 mL) was added to an oven-dried Schlenk
containing [RuCp*Cl(CH3CN)(η3-CH2-CH-CHPh)](PF6), 2a
(100 mg, 0.174 mmol). The reaction mixture was stirred for 2 h,
after which the solution was slowly concentrated under vacuum.
The resulting crude was washed with CH2Cl2/diethyl ether, affording
Accidental Preparation of [RuCpCl2]2. [RuCp(CH3CN)3](PF6)-
(5) (50 mg, 0.115 mmol) was added to a solution of allyl chloride
(0.10 mL, 1.22 mmol) dissolved in 4 mL of acetone. The resulting
solution was stirred at room temperature for 12 h. Addition of
diethyl ether afforded 30.4 mg (95%) of the intended allyl Ru(IV)
product. An NMR solution of this Ru(IV) species in acetone-d6
was allowed to stand for 7 days and gave a small crop of orange
crystals, which were shown to be the cited decomposition product
[RuCpCl2]2. [RuCpCl2(CH2CHCH2)] was formed as an orange
powder. 1H NMR (CD3NO2, 298 K, 300 MHz): δ 5.73 (5H, Cp),

Cp*-Based Ru(IV)(Cp*)(η3-CH2-CH-CHPh) Allyl Complexes
Organometallics, Vol. 25, No. 19, 2006 4529
4.77 (1H, J 10.5, 6.0 Hz), 4.21 (1H, J 6.0 Hz), 3.91 (2H, J 10.5
Hz); (CD3NO2, 298 K, 75 MHz): δ 101.83 (CH), 96.21 (C), 67.48
(CH2). Anal. Calcd for C8H10Cl2Ru: C 34.55; H 3.62. Found: C
34.63; H 3.68. ESI-MS: m/z 301.0 (RuCl(CH3OH)5), 197.2 (RuCp-
(CH3OH)), 139.2 (RuCl).
COST Action D24 “Sustainable Chemical Processes: Stereo-
selective Transition Metal-Catalysed Reactions” is also kindly
acknowledged.
Supporting Information Available: Experimental details and
a full listing of crystallographic data, including tables of positional
and isotropic equivalent displacement parameters, anisotropic dis-
placement parameters, calculated positions of the hydrogen atoms,
bond distances, bond angles, and torsional angles for compounds
2b, 2c, and 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. P.S.P. thanks the Swiss National Science
Foundation, the “Bundesamt fu¨r Bildung und Wissenschaft”,
and the ETHZ for financial support. A.A. thanks MURST for
a grant (PRIN 2004). I.F. thanks the Junta de Andalucia for a
research contract. We also thank Johnson Matthey for the loan
of precious metals. The support and sponsorship arranged by
OM060448U