From ion pairs to ion triples through a hydrogen bonding-driven aggregative process

Article abstract of DOI:10.1021/om700775u

Complexes [Ru(arene)(κ³-dpk-OR]X (dpk = 2,2′-dipyridylketone) were synthesized, and their interionic structure was investigated through an integrated approach based on diffusion and NOE NMR experiments and X-ray single-crystal studies. PGSE NMR results indicated that the highest aggregation tendency occurred for complex 2BF₄ (arene = p-cymene and R = OH) that showed aggregation numbers consistent with the main presence of 2₂BF₄⁺ ion triples (N⁺ = 1.9 and N^- = 1.1, in CD₂Cl₂ at 0.5 mM). X-ray investigations indicated that a [1 × 1] network of HBs is present involving the two OH moieties of the two cationic fragments belonging to the two independent ion pairs of the asymmetric unit. This dication is likely the central moiety of 2₂BF₄⁺ ion triples. According to ¹⁹F,¹H-HOESY NMR interionic studies, the counterion was close to two pyridyl rings belonging to two different cations undergoing a π-π-stacking interaction in CD₂Cl₂ exactly as observed in the solid state. All of the other complexes having an alyphatic OR-tail showed a much smaller aggregation tendency, leading to ion pairs even when OR = OCH₂CH₂OH. In the latter case, X-ray studies showed that the terminal OH underwent an intracationic HB with the oxygen atom coordinated at the ruthenium.

Full text of DOI:10.1021/om700775u

Organometallics 2007, 26, 6099-6105
6099
From Ion Pairs to Ion Triples through a Hydrogen Bonding-Driven
Aggregative Process
Daniele Zuccaccia,† Elisabetta Foresti,‡ Stefania Pettirossi,† Piera Sabatino,‡
Cristiano Zuccaccia,† and Alceo Macchioni*,†
Dipartimento di Chimica, UniVersita` di Perugia, Via Elce di Sotto, 8 - 06123 Perugia, Italy, and
Dipartimento di Chimica “Giacomo Ciamician”, UniVersita` di Bologna,
Via Selmi, 2 - 40126 Bologna, Italy
ReceiVed July 31, 2007
Complexes [Ru(arene)(κ3-dpk-OR]X (dpk ) 2,2′-dipyridylketone) were synthesized, and their interionic
structure was investigated through an integrated approach based on diffusion and NOE NMR experiments
and X-ray single-crystal studies. PGSE NMR results indicated that the highest aggregation tendency
occurred for complex 2BF4 (arene ) p-cymene and R ) OH) that showed aggregation numbers consistent
+
with the main presence of 22BF4 ion triples (N+ ) 1.9 and N- ) 1.1, in CD2Cl2 at 0.5 mM). X-ray
investigations indicated that a [1 × 1] network of HBs is present involving the two OH moieties of the
two cationic fragments belonging to the two independent ion pairs of the asymmetric unit. This dication
+
is likely the central moiety of 22BF4 ion triples. According to 19F,1H-HOESY NMR interionic studies,
the counterion was close to two pyridyl rings belonging to two different cations undergoing a π-π-
stacking interaction in CD2Cl2 exactly as observed in the solid state. All of the other complexes having
an alyphatic OR-tail showed a much smaller aggregation tendency, leading to ion pairs even when OR
) OCH2CH2OH. In the latter case, X-ray studies showed that the terminal OH underwent an intracationic
HB with the oxygen atom coordinated at the ruthenium.
hydrogen bonding (HB), readily form dimers,12,13 trimers, and,
in favorable conditions, nanometric aggregates.14
Introduction
It is increasingly evident that noncovalent interactions may
alter the structure and reactivity of organometallic compounds.1,2
Ion pairing3 has been deeply investigated, particularly by means
of NOE4 and diffusion NMR5 experiments, because its effects
on the chemistry of transition-metal salts are well-recognized.6-8
Less attention has been dedicated to the aggregation of neutral
“molecular entities” even if, in principle, they may play a role
at least in two important catalytic reactions: the polymerization
of olefins catalyzed by metallocene or post-metallocene ion
pairs9 and the transfer hydrogenation of ketones occurring
through a bifunctional mechanism.10,11 In the former case, ion
pairs are the neutral “molecular entities” that have been
demonstrated to aggregate forming ion quadruples; in the latter,
monomers are the neutral “molecular entities” that, especially
when they have peripheral functionalities suitable to undergo
The aggregation of transition-metal ion pairs to form ion
quadruples usually occurs in solvent with a relative permittivity
(ꢀr) equal to or lower than that of chloroform mainly driven by
the interaction between the permanent dipolar moments of ion
pairs.15,16 Consequently, a higher tendency to form ion qua-
druples is observed for large and least coordinating anions that,
once paired with a given cation, lead to an ion pair having a
higher dipole moment.16 The association of neutral organome-
tallics becomes relevant if HBs can establish in the second-
coordination sphere. In such cases, dimers and higher aggregates
can persist even in solvent with medium to high ꢀr.12,14 We
thought that it could be of interest to investigate the aggregation
tendency of ion pairs having a pendant peripheral group whose
capability to undergo hydrogen bonding could be easily tuned.
(9) Beck, S.; Geyer, A.; Brintzinger, H.-H. Chem. Commun. 1999, 2477.
Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M.-C.; Roberts, J. A.;
Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448. Song, F.; Lancaster, S. J.;
Cannon, R. D.; Schormann, M.; Humphrey, S. M.; Zuccaccia, C.; Mac-
chioni, A.; Bochmann, M. Organometallics 2005, 24, 1315. Alonso-Moreno,
C.; Lancaster, S. J.; Zuccaccia, C.; Macchioni, A.; Bochmann, M. J. Am.
Chem. Soc. 2007, 129, 9282.
(10) Shvo, Y.; Czarkie, D.; Rahamim, Y.; Chodash, D. F. J. Am. Chem.
Soc. 1986, 108, 7400. Menashe, N.; Shvo, Y. Organometallics 1991, 10,
3885.
(11) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97. Ya-
makawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1446. Noyori,
R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 7931.
(12) Zuccaccia, D.; Clot, E.; Macchioni, A. New J. Chem. 2005, 29, 430.
(13) Pelagatti, P.; Carcelli, M.; Calbiani, F.; Cassi, C.; Elviri, L.; Pelizzi,
C.; Rizzotti, U.; Rogolino, D. Organometallics 2005, 24, 5836. Pelagatti,
P.; Bacchi, A.; Calbiani, F.; Carcelli, M.; Elviri, L.; Pelizzi, C.; Rogolino,
D. J. Organomet. Chem. 2005, 690, 4602.
* To whom correspondence should be addressed. Phone: +39 075
5855579. Fax: +39 075 5855598. E-mail: alceo@unipg.it.
† Universita` di Perugia.
‡ Universita` di Bologna.
(1) Das, S.; Incarvito, C. D.; Crabtree, R. H.; Brudvig, G. W. Science
2006, 312, 1941.
(2) Thomas, C. M.; Ward, T. R. Chem. Soc. ReV. 2005, 34, 337. Kra¨mer,
R. Angew. Chem., Int. Ed. 2006, 45, 858. Roelfes, G.; Feringa, B. L. Angew.
Chem., Int. Ed. 2005, 44, 3230.
(3) Marcus, Y.; Hefter, G. Chem. ReV. 2006, 106, 4585.
(4) Macchioni, A. Eur. J. Inorg. Chem. 2003, 195 and references therein.
(5) For reviews on the application of PGSE NMR to investigate
intermolecular interactions: Binotti, B.; Macchioni, A.; Zuccaccia, C.;
Zuccaccia, D. Comments Inorg. Chem. 2002, 23, 417. Pregosin, P. S.;
Martinez-Viviente, E.; Kumar, P. G. A. Dalton Trans. 2003, 4007. Pregosin,
P. S.; Kumar, P. G. A.; Ferna´ndez, I. Chem. ReV. 2005, 105, 2977. Pregosin,
P. S. Prog. Nucl. Magn. Reson. Spectrosc. 2006, 49, 261.
(6) Macchioni, A. Chem. ReV. 2005, 105, 2039 and references therein.
(7) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391. Bochmann,
M. J. Organomet. Chem. 2004, 689, 3982.
(14) Ciancaleoni, G.; Di Maio, I.; Zuccaccia, D.; Macchioni, A. Orga-
nometallics 2007, 26, 489.
(15) Zuccaccia, D.; Sabatini, S.; Bellachioma, G.; Cardaci, G.; Clot, E.;
Macchioni, A. Inorg. Chem. 2003, 42, 5465.
(8) Binotti, B.; Bellachioma, G.; Cardaci, G.; Carfagna, C.; Zuccaccia,
C.; Macchioni, A. Chem.-Eur. J. 2007, 13, 1570.
(16) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Ciancaleoni, G.;
Zuccaccia, C.; Clot, E.; Macchioni, A. Organometallics 2007, 26, 3930.
10.1021/om700775u CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/02/2007

6100 Organometallics, Vol. 26, No. 25, 2007
Zuccaccia et al.
Scheme 1
with dpk in the appropriate protic solvent (H-OR), at room
temperature, by adding a large excess of MX (NaBPh4 or NH4-
PF6) that caused their precipitation (Scheme 1). Complexes 3PF6
and 5PF6 were preferably synthesized by the anion metathesis
reaction of 3BPh4 and 5BPh4 and an equimolar amount of TlPF6
in acetone, due to their higher solubility in methanol and
HOCH2CH2OH. Complex [Ru(η6-p-cymene)(κ2-N,N-dpk)Cl]-
BF4 (1BF4) was isolated by the reaction of [Ru2(η6-p-cymene)2-
Cl2(µ-Cl)2] with dpk in methylene chloride in the presence of
2 equiv of AgBF4. The reaction of 1BF4 with H-OR, under
the appropriate experimental conditions, afforded another
pathway to obtain complexes 2BF4, 3BPh4, and 5-7BPh4
(Scheme 1). When the reaction of [Ru2(η6-p-cymene)2Cl2(µ-
Cl)2] with dpk was carried out in CD2Cl2, an intermediate (I)
was observed that partial NMR characterization indicated to
contain the κ2-N,O-dpk moiety (Scheme 1). Consequently,
complexes I and 1 seem to be the kinetic and thermodynamic
products of the reaction, respectively, and it cannot be excluded
that the transformation of 1 into 2, 3, and 5-7 proceeds through
I. Dissolving complex 2 in methanol or HOCH2CH2OH did not
lead to the conversion in complexes 3 and 5; the latter complexes
were stable for days in water.
Herein, we report on the synthesis and characterization of
complexes [Ru(arene)(κ3-dpk-OR)]X (dpk ) 2,2′-dipyridylke-
tone, Scheme 1) having a suitable OR-tail for hydrogen bonding.
Dpkhasbeenusedasligandinseveralcoordinationcompounds17-22
because it is a versatile ligand that can afford κ2-N,N-,23 κ2-
N,O-,24 and also anionic κ3-N,N,O-25 coordination at the metal.
Addition of a nucleophile to the carbonyl of κ2-N,N-coordinated
dpk can be used to generate gem-diols κ2-dpkH-OH26 by the
reaction with water or semi-acetal κ2-dpkH-OR or κ2-dpkH-
NR by the reaction with alcohols,27 amines,28 or pyrazoles.29 In
the presence of an M-X (X ) halogen) moiety, κ3-N,N,O-
coordination mode of dpk is obtained with a suitable -OR or
-NR tail, through the elimination of HX.25
All complexes 1-7 were characterized in solution by 1H, 13C,
31P, 19F NMR spectroscopies (Experimental Section). The solid-
state structures of complexes 2BF4 and 5BPh4 were solved by
X-ray diffractometric studies.
Intramolecular NMR Characterization in Solution. The
1
assignment of all H and 13C NMR resonances of complexes
1-7 was carried out by crossing together the information
1
1
1
1
coming from H, 13C, H-COSY, H-NOESY, H,13C-HMQC,
and 1H,13C-HMBC NMR experiments. Data are reported
in the Experimental Section. In the 13C NMR spectrum of
complex 1, the resonance of the carbonyl moiety fell at a
chemical shift value (185.46 ppm) lower than that of the free
dpk ligand (192.95 ppm); this is consistent with a carbonyl
moiety not coordinated at the metal center. In contrast, when
dpk coordinates at the metal as an N,O-ligand, a deshielding of
the carbon nucleus of CdO is observed; the latter resonates
above 200 ppm in similar complexes.30,31 In 2-7, no carbon
resonance at ppm values higher than 165 ppm was observed,
while a new quaternary carbon appeared at ca. 105 ppm. This
carbon showed long-range correlation with proton 14 (Figure
1) that, in turn, correlates with carbon 12, in perfect agreement
with the proposed structure.
Results and Discussion
Synthesis. Complexes [Ru(arene)(κ3-dpk-OR)]X (2BF4, R )
H, arene ) p-cymene; 3BPh4, R ) Me, arene ) p-cymene;
3PF6, R ) Me, arene ) p-cymene; 4PF6, R ) Me, arene )
hexamethylbenzene; 5BPh4, R ) CH2CH2OH, arene ) p-
cymene; 5PF6, R ) CH2CH2OH, arene ) p-cymene; 6BPh4, R
) Et, arene ) p-cymene; 7BPh4, R ) i-Bu, arene ) p-cymene)
were synthesized by the reaction of [Ru2(η6-arene)2Cl2(µ-Cl)2]
X-ray Studies. (a) Intramolecular Structure. The solid-
state structures of compounds 2BF4 and 5BPh4 were determined
through single-crystal X-ray diffractometric investigations. Both
complexes exhibit a three-legged piano stool pseudo-octahedral
geometry where the arene occupies three adjacent sites of the
octahedron and dpk-OR- the other three. Intramolecular bond
lengths and angles fall in the typical ranges observed for
analogous compounds and will not be discussed here.32 Both
complexes contain two independent anion/cation pairs in the
asymmetric unit; in addition, two solvent molecules (CH2Cl2)
are present in 2BF4 and one in 5BPh4. In the latter complex,
each cation exhibits an intramolecular H bonding between the
Ru-coordinated oxygen atom and the terminal OH group with
(17) Bock, H.; Van, T. T. H.; Scho¨edel, H.; Dienelit, R. Eur. J. Org.
Chem. 1998, 585.
(18) Milani, B; Mestroni, G.; Zangrando, E. Croat. Chem. Acta 2001,
74, 851.
(19) Karimi, B.; Zamani, A.; Clark, J. H. Organometallics 2005, 24, 695.
(20) Zassinovich, G.; Mestroni, G.; Camus, A. J. Organomet. Chem.
1975, 91, 379.
(21) Codard, C.; Duckett, S. B.; Parsons, S.; Perutz, R. N. Chem.
Commun. 2003, 2332.
(22) (a) Papaefstathiou, G. S.; Perlepes, S. P. Comments Inorg. Chem.
2002, 23, 249 and references therein. (b) Abrahams, B. F.; Hudson, T. A.;
Robson, R. Chem.-Eur. J. 2006, 12, 7095. (c) Toyama, M.; Nakahara, M.;
Nagao, N. Bull. Chem. Soc. Jpn. 2007, 80, 937.
(23) (a) Ghumaan, S.; Sarkar, B.; Chanda, N.; Sieger, M.; Fiedler, J.;
Kaim, W.; Lahiri, G. K. Inorg. Chem. 2006, 45, 7955. (b) Zhang, F.;
Prokopchuk, E. M.; Broczkowski, M. E.; Jennings, M. C.; Puddephatt, R.
J. Organometallics 2006, 25, 1583.
(24) Bellachioma, G.; Cardaci, G.; Gramlich, V.; Macchioni, A.; Val-
entini, M.; Zuccaccia, C. Organometallics 1998, 17, 5025.
(25) Hassan, I.; Green, O.; Bakir, M. J. Mol. Struct. 2003, 657, 75.
(26) Osborne, R. R.; Mcwhinnie, W. R. J. Chem. Soc. A 1967, 2075.
(27) Fischer, B.; Sigel, H. J. Inorg. Nucl. Chem. 1975, 37, 2127.
(28) Li, Y.; Xiang, S.; Sheng, T.; Zhang, J.; Hu, S.; Fu, R.; Huang, R.;
Wu, X. Inorg. Chem. 2006, 45, 6577.
(30) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Zuccaccia, C.; Mac-
chioni, A. Dalton Trans. 2006, 1963.
(31) Binotti, B.; Carfagna, C.; Foresti, E.; Macchioni, A.; Sabatino, P.;
Zuccaccia, C.; Zuccaccia, D. J. Organomet. Chem. 2004, 689, 647.
(32) CCDC 654347 and 654348 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif/.
(29) Feller, M. C.; Robson, R. Aust. J. Chem. 1970, 23, 1997.

From Ion Pairs to Ion Triples
Organometallics, Vol. 26, No. 25, 2007 6101
Figure 3. Stick representation of the cation 5+ in the solid state
showing the intracationic O‚‚‚H hydrogen bond (HB).
distance were observed (Figure 2). With reference to these two
cationic moieties, involved both in the HBs and in the π-π-
-
stacking interaction, three BF4 counterions are located in the
next proximities. Two of them (orientations A and B in Figure
2) are located close to the pyridyl rings that undergo the π-π-
stacking interaction (A, Ru-B 5.26 and 8.30 Å; B, Ru-B, 5.41
and 8.53 Å). The other one (orientation C in Figure 2) is between
a pyridyl ring and a cymene moiety of one ruthenium atom
(Ru-B, 5.35 and 11.47 Å).
Complex 5BPh4 shows Ru‚‚‚B contacts of 6.55 and 6.23 Å,
respectively, for the two ionic pairs in the asymmetric unit, a
value quite similar to that found in cis-[Ru(PMe3)(CO)2(COMe)-
(κ2-pz2-CH2]BPh4.34 Considering the whole crystal packing, the
same interaction is significantly longer on the average (8.05
Å): that is, the two closest packed ion pairs were chosen as the
crystallographic asymmetric unit.
In the same complex, in contrast to what was observed for
complex 2BF4, no intercationic HB is present, while an
intracationic HB between the OH functionality and the oxygen
atom coordinated at the ruthenium is present with an O‚‚‚O
distance equal to 2.70 Å (Figure 3).
Figure 1. A section of the long-range 1H,13C-HMBC NMR
correlation recorded for 2BF4 in CD2Cl2, showing the scalar
coupling of H14 with C13 and C12.
NMR Interionic Structure in Solution. (a) PGSE Mea-
surements. The aggregation tendency of complexes 2-5 with
fluorinated counterions was investigated by 1H- and 19F-PGSE
measurements using TMSS [tetrakis-(trimethylsilyl)silane] as
internal standard. PGSE measurements allowed the translational
self-diffusion coefficients (Dt) for both cationic (Dt+) and anionic
(Dt-) moieties (Table 1) to be determined. By applying
(Experimental Section) the Stokes-Einstein equation Dt ) kT/
cπηrH, where k is the Boltzman constant, T is the temperature,
c is a numerical factor, and η is the solution viscosity, the
average hydrodynamic radii for the cationic (rH+) and anionic
(rH-) moieties were measured (Table 1).35 From the average
hydrodynamic radii of the aggregates, assumed to be spherical,
Figure 2. Left: CPK representation of two 2+ cationic moieties
in the solid state showing O‚‚‚O proximities (hydrogen atoms are
omitted for clarity). Right: CPK representation of some counterion
orientations observed in the solid-state structure of 2BF4. Color-
ing: Ru, green; O, red; H, light gray; N, blue; F, light blue; B,
pink; C, gray.
donor‚‚‚acceptor distances ranging around 2.7 Å. The cymene
assumes an eclipsed conformation and orients the i-Pr and Me
groups in a way of perfectly dividing the dpk ligand into two
parts.
+
their volumes (VH and VH-) were obtained. To have an
+
-
immediate idea of the level of aggregation, VH and VH can
be contrasted with the expected volume of the ion pair. We
have recently shown that the latter is well-described by the van
der Waals volume of the ion pair, easily derived from X-ray or
theoretical data, only for molecules not having inlets.36 In other
cases, it is preferable to use the hydrodynamic volume measured
at very low concentration or extrapolated at infinite dilution
(VH0).
(b) Supramolecular Structure. The supramolecular structure
of complexes 2BF4 and 5BPh4 was analyzed focusing the
attention on the possible role of the peripheral OH moiety. In
complex 2BF4, a [1 × 1] network of HBs is present involving
the two OH moieties of the two cationic fragments belonging
to the two independent ion pairs of the asymmetric unit with
O‚‚‚O distances equal to 2.62 and 2.69 Å (Figure 2). Analogous
dimeric structures held together by HBs have been observed
by Puddephatt and co-workers for Pt(II) complexes,33 while also
in fac-[Mn(CO)3(κ3-dpk-OH)] complexes25 a network of hy-
drogen bonds was observed. In addition to HBs, two cationic
moieties also undergo a π-π-stacking interaction between two
pyridyl rings in 2BF4; a 21.5° mean slip angle between the
normal of one pyridyl plane and 3.67 Å centroid-centroid
The trend of VH versus the salt concentration (C) was obtained
for 4PF6 (Table 1, entries 7-12) to determine the hydrodynamic
volume of 4+ at infinite dilution (VH+0).37 4PF6 was selected
(34) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Cruciani, G.; Foresti,
E.; Sabatino, P.; Zuccaccia, C. Organometallics 1998, 17, 5549.
(35) Zuccaccia, D.; Macchioni, A. Organometallics 2005, 24, 3476.
(36) Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D.; Macchioni, A.
Organometallics 2007, 26, 3624.
(33) Zhang, F.; Broczkowski, M. E.; Jennings, M. C.; Puddephatt, R. J.
Can. J. Chem. 2005, 83, 595.
(37) Zuccaccia, D.; Busetto, L.; Cassani, M. C.; Macchioni, A.; Mazzoni,
R. Organometallics 2006, 25, 2201.

6102 Organometallics, Vol. 26, No. 25, 2007
Zuccaccia et al.
Table 1. Diffusion Coefficients (1010Dt, m2 s-1), Hydrodynamic Radii (rH, Å), Hydrodynamic Volumes (VH, Å3), and Aggregation
Number for Cation (N+) and Anion (N-) of Compounds 2-5X in CD2Cl2 as a Function of Concentration (C, mM)
+
-
+
-
Dt+
Dt-
rH
rH
VH
VH
N+
N-
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
2BF4 (VH0 ) 471)
3PF6 (VH0 ) 512)
8.9
8.2
11.4
10.6
9.7
10.9
9.3
15.4
12.4
11.0
10.7
6.0
6.3
5.0
5.2
5.3
5.4
4.9
4.9
5.2
5.3
5.3
5.4
5.3
5.6
5.1
5.7
4.0
4.6
4.8
4.9
900
1040
523
578
619
659
495
483
575
637
610
663
610
750
542
780
268
405
470
504
1.9
2.2
1.0
1.1
1.2
1.3
0.9
0.9
1.0
1.1
1.1
1.2
1.1
1.4
1.1
1.7
0.5
0.8
0.9
1.0
0.5
1.7a
0.1
0.6
3
9.5
21
4PF6 (VH0 ) 556)
11.2
11.6
10.9
9.9
10.7
8.5
0.008
0.07
0.6
16.7
13.3
11.9
11.8
10.0
11.4
10.4
3.7
4.4
4.6
4.9
4.9
4.7
5.2
217
361
415
477
467
427
575
0.4
0.7
0.7
0.8
0.8
0.8
1.1
10
28
63
1
5PF6 (VH0 ) 541)
9.8
9.4
24
a Saturated solution.
because the presence of the hexamethylbenzene reduces the
aggregation tendency and furnishes an intense resonance due
to the six equivalent methyl groups that allowed PGSE
responsible for the high stability of the ion triples. The formation
of the latter may also be facilitated by the establishment of the
intercationic π-π-stacking interaction between two pyridyl
moieties evidenced in the solid state. A similar intercationic
π-π-stacking interaction has been observed for [Ru(p-cymene)-
(κ2-2-bzpy)Cl]PF6 (bzpy ) 2-benzoylpyridine) whose cation is
isosteric with that of 2BF4.30 As a consequence of the stacking
interaction, [Ru(p-cymene)(κ2-2-bzpy)Cl]PF6 showed a slightly
higher tendency to form ion triples than analogous compounds
not having the possibility to undergo it.30 By the way, contrasting
-0
experiments at micromolar concentration to be performed. VH
for small counterions was considered equal to the van der Waals
volume.16,36 Consequently, VH of 4PF6 ion pair was derived
0
by adding the volumes of the single ions (Table 1). It can be
seen that the determined VH0 of 4+ is ca. 1.46 times higher than
that of the VvdW one. Because 4+ has a shape similar to that of
other complexes, their VH0 values were derived by scaling VvdW
by the same factor (Table 1).
From the ratio between the hydrodynamic volumes (VH) at a
particular concentration and the volumes of ion pairs at infinite
dilution (VH0), the cationic (N+) and anionic (N-) aggregation
numbers were evaluated (Table 1).38 To appreciate the meaning
of N+ and N-, it is important to consider that, if only free ions
were present in solution, N+ and N- should be ca. 0.9 and 0.1.
Complete ion pairing and “ion quadrupoling” would lead to N+
) N- ) 1 and N+ ) N- ) 2, respectively. While if only
“Ru2X+” ion triples and free “X-” were present in solution,
N+ and N- should be ca. 1.9 and 1.0.
+
-
0
the observed VH and VH with VH instead of VvdW, as was
previously done,30 it is found that ion triples form but N values
are not indicative of their exclusive presence. In the actual case,
the establishment of intercationic HBs makes it possible to have
A comparison of the aggregation tendency of different
complexes was carried out in CD2Cl2 (Table 1, entries 1-2,
3-6, 7-12, 13, 14). The aggregation tendency follows the
order: 2BF4 > 3PF6 ≈ 4PF6 ≈ 5PF6. Excluding 2BF4, other
complexes showed almost the same aggregation tendency in
CD2Cl2 similar also to that of other half-sandwich ruthenium-
(II) complexes bearing diamine,35 acylpyridine,30 and diimine
ligands.16 Ion pairing is the main aggregative process, and only
at concentration higher than ca. 10 mM do other associative
processes become active. It has to be noted that also complex
5PF6 that has a terminal OH moiety did not show a particularly
high aggregation tendency, probably because the OH functional-
ity is engaged in an intramolecular HB as observed in the solid-
state structure of 5BPh4 and, consequently, cannot establish
intercationic HBs. In strict contrast, complex 2BF4 containing
the Ru-O-C(Py)2-OH functionality was little soluble in CD2-
Cl2 but showed a remarkable tendency to aggregate. As shown
+
in Table 1 (entry 1), already at 0.5 mM VH is almost twice
that expected for the ion pair (N+ ) 1.9), while VH- is ca. equal
to VH0 (N- ) 1.1). This clearly indicates that 2BF4 is prevalently
+
-
present as ion triples 22BF4 and BF4 in CD2Cl2. It is
reasonable to believe that 22BF4+ has a structure similar to that
observed in the solid state with the two OH‚‚‚O HBs that are
(38) Pochapsky, S. S.; Mo, H.; Pochapsky, T. J. Chem. Soc., Chem.
Commun. 1995, 2513. Mo, H.; Pochapsky, T. J. Phys. Chem. B 1997, 101,
4485. Zuccaccia, C.; Bellachioma, G.; Cardaci, G.; Macchioni, A. Orga-
nometallics 2000, 19, 4663.
Figure 4. 19F,1H-HOESY NMR spectrum (400.13 MHz, 296 K)
of complex 2BF4 in CD2Cl2 at 1.7 mM. * denotes the residues of
non-deuterated solvent and water.

From Ion Pairs to Ion Triples
Organometallics, Vol. 26, No. 25, 2007 6103
HBs. In principle, OH could be a good anchor point for
fluorinated counterions. For instance, it has been previously
found that a peripheral NH moiety strongly favors ion pairing
in the [PtMe(dpa)(Me2SO)]PF6 [dpa ) bis(2-pyridyl)amine]
complex, allowing the establishment of interionic HBs.39
Differently from what was observed for complex 2BF4, in
complexes 3-5PF6 the counterion showed strong interionic
NOEs with 8 and 9 pyridyl resonances and 4 and 5 cymene
protons (Figure 5). Weak NOEs were also detected with 1, 2,
and 7 cymene resonances. No interaction was observed between
the counterion and 10 and 11 pyridyl protons and the protons
of the OR-tail, even for complex 5PF6 that contains the OH
-
functionality. All of these observations indicate that PF6 is
located close to the nitrogen of N,N,O ligand. From the PGSE
measurement, we have shown that the ion pair is prevalently
present in solution, so the counterion can interact only with the
pyridyl rings of the nearest ruthenium center.
Conclusions
The aggregation tendency of [Ru(arene)(κ3-dpk-OR)]X com-
plexes strongly depends on the nature of the OR-tail. When R
) H, the complex has the possibility of establishing a [1 × 1]
network of HBs that stabilize the dication. As a consequence,
a rare example of formation of Ru2X+ ion triples driven by
intercationic HB is evidenced in CD2Cl2 by PGSE NMR
experiments. 19F,1H-HOESY NMR experiments further support
the formation of ion triples and allow one to locate the
counterion in ion triples. The anion position in solution is
consistent with that observed in the solid state through X-ray
single-crystal studies.
Complexes bearing R ) alkyl group, not having the pos-
sibility to undergo intercationic HB, do not afford aggregation
higher than ion pairs in CD2Cl2. The same is observed also for
complex with R ) CH2CH2OH that in principle could undergo
intercationic HB. X-ray and NMR studies allow understanding
that the tail is folded back toward the metal center and the
terminal OH is engaged in an intracationic HB with the oxygen
atom coordinated to the ruthenium.
Figure 5. 19F,1H-HOESY NMR spectrum (400.13 MHz, 296 K)
of complex 3PF6 in CD2Cl2 at 3.0 mM. * denotes the residues of
non-deuterated solvent and water.
Experimental Section
RuCl3‚3H2O and dpk were purchased from Sigma. [Ru(η6-arene)-
Cl2]2 dimers were prepared according to Benneth and Smith.40
Compounds 1-7 were prepared under nitrogen using standard
Schlenk techniques. Solvents were freshly distilled (hexane with
Na, Et2O with Na/benzophenone, MeOH and CH2Cl2 with CaH2)
and degassed, by many gas-pump-nitrogen cycles, before use.
a concentration where ion triples are almost exclusively present
(Table 1, entry 1). Increasing the concentration, the aggregation
level of 2BF4 increases, and at the saturated concentration also
ion quadruples (2BF4)2 become significant (Table 1, entry 2).
(b) NOE Measurements. The relative anion-cation orienta-
tions in solution for complexes with fluorinated counterions were
investigated by 19F,1H-HOESY NMR spectroscopy. The ob-
served NOEs remarkably depended on the nature of the OR-
tail.
For complex 2BF4, strong NOE contacts were observed
between F-atoms of the counterion and 8, 9, 10, and 11 pyridyl
resonances (Figure 4); weak NOEs were detected with 1, 2,
and 7 cymene resonances. The intensity trend of NOEs with
pyridyl protons followed the rather peculiar order: 8 > 10 > 9
≈ 11. This is completely consistent with the main presence in
solution of the ion triple 22BF4+, held together by two
intercationic OH‚‚‚H HBs, having the same structure as that
observed in the solid state with the anion located in the
orientation A or B. From this position, the anion can interact
with both pyridyl rings that undergo the π-π-stacking interac-
tion as illustrated in Figure 4. No interaction was observed
between the counterion and the proton of the OH-tail probably
because the OH moiety is already engaged in intermolecular
1
One- and two-dimensional H, 13C, 19F, and 31P NMR spectra
were measured on Bruker DPX 200 and DRX 400 spectrometers.
Referencing is relative to TMS (1H and 13C), CCl3F (19F), and 85%
H3PO4 (31P). NMR samples were prepared by dissolving the suitable
amount of compound in 0.5 mL of solvent.
Synthesis of Complex 1BF4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in CH2Cl2 (5 mL). To the resulting red-brown solution was added
AgBF4 (0.064 g, 0.326 mmol). AgCl formed as a white solid that
was filtered off. n-Hexane was added to the remaining solution,
and a red-brown precipitate was obtained; it was filtered off, washed
with n-hexane, and dried under vacuum. Yield: 80%.1H NMR
3
(acetone-d6, 298 K, J in Hz): δ 1.27 (d, J1-2 ) 6.90, 1), 1.96 (s,
3
3
7), 2.81 (sept, JH2-H1 ) 6.9, 2), 5.74 (d, J5-4 ) 5.7, 5), 5.95 (d,
(39) Romeo, R.; Nastasi, N.; Monsu` Scolaro, L.; Plutino, M. R.; Albinati,
A.; Macchioni, A. Inorg. Chem. 1998, 37, 5460.
(40) Benneth, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans 1974,
233.

6104 Organometallics, Vol. 26, No. 25, 2007
Zuccaccia et al.
3J4-5 ) 5.7, 4), 7.96 (dd, 3J9,10 ) 7.6, 3J9,8 ) 5.2, 9), 8.27 (d, 3J11,10
) 7.6, 11), 8.38 (dd, 3J10,11 ) 3J10,9 ) 7.6, 10), 9.24 (d, 3J8,9 ) 5.2,
8). 13C{1H} NMR (acetone-d6, 298 K): δ 17.46 (s, 7), 21.93 (s,
1), 31.01 (s, 2), 86.33 (s, 3), 86.86 (s, 6), 101.71 (s, 3), 109.05 (s,
5), 127.36 (s, 11), 129.93 (s, 9), 141.11 (s, 10), 153.91 (s, 12),
158.02 (s, 8), 185.46 (s, 13). 19F NMR (acetone-d6, 298 K): δ
-152.32 (br,10BF4), -152.37 (br, 11BF4). Anal. Calcd for C21H22-
BClF4N2ORu: C, 46.56; H, 4.09; N, 5.17. Found: C, 46.51; H,
4.06; N, 5.13.
0.330 mmol) in MeOH (5 mL). The resulting red-orange suspension
was stirred for 3 h at rt until it changed into a yellow solution; a
large excess of NH4PF6 (10 equiv) dissolved in 0.5 mL of MeOH
was added, and a precipitate formed. The solution was filtered, and
the yellow solid was washed with cold MeOH and n-hexane. Yield
1
) 62%. H NMR (CD2Cl2, 298 K, J in Hz): δ 2.25 (s, HMB),
3
3
4
3.55 (s, 14), 7.40 (ddd, J9,10 ) 7.7, J9,8 ) 5.38, J9,11 ) 1.4, 9),
3
3
3
4
7.55 (d, J11,10 ) 7.4, 11), 7.85 (ddd, J10,11 ) J10,9 ) 7.68, J10,8
) 1.3, 10), 8.75 (d, 3J8,9 ) 5.38, 8). 19F NMR (CD2Cl2, 298 K): δ
-71.6 (d, 1JFP ) 711.0). 31P{1H} NMR (CD2Cl2, 298 K): δ -141.0
(sept, 1JPF ) 711.0). Anal. Calcd for C24H29F6N2O2PRu: C, 46.23;
H, 4.69; N, 4.49. Found: C, 46.29; H, 4.66; N, 4.46.
Synthesis of Complex 2BF4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol),
NaOH (0.013 g, 0.358 mmol), and NaBF4 (0.040 g, 0.358 mmol)
in H2O (5 mL). The resulting red-orange suspension was stirred
for 1 h at rt until it transformed into a yellow suspension. The
solution was filtered, and the yellow solid was washed with cold
Synthesis of Complex 5BPh4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in HOCH2CH2OH (5 mL). The resulting red-orange suspension was
stirred for 3 h at rt until it changed into a yellow solution; a large
excess of NaBPh4 (10 equiv) dissolved in 0.5 mL of HOCH2CH2-
OH was added, and a precipitate formed. The solution was filtered,
and the yellow solid was washed with cold HOCH2CH2OH and
1
H2O and n-hexane. Yield ) 70%. H NMR (acetone-d6, 298 K, J
in Hz): δ 1.36 (d, 3J1-2 ) 6.90, 1), 2.42 (s, 7), 3.13 (sept, 3JH2-H1
) 6.9, 2), 5.91 (d, 3J5-4 ) 5.7, 5), 6.17 (d, 3J4-5 ) 5.7, 4), 7.16 (s,
3
3
4
14), 7.47 (ddd, J9,10 ) 7.7, J9,8 ) 6.0, J9,11 ) 1.3, 9), 7.76 (dd,
3J11,10 ) 7.6, 4J11,9 ) 1.3, 11), 8.03 (dd, 3J10,11 ) 3J10,9 ) 7.7, 4J10,8
) 1.3, 10), 9.36 (d, 3J8,9 ) 6.0, 8). 13C{1H} NMR (acetone-d6, 298
K): δ 17.51 (s, 7), 22.47 (s, 1), 31.26 (s, 2), 81.92 (s, 5), 83.87 (s,
4), 100.68 (s, 6), 103.70 (s, 13), 106.03 (s, 13), 121.24 (s, 11),
124.57 (s, 9), 140.34 (s, 10), 153.46 (s, 8), 163.80 (s, 12). 19F NMR
(acetone-d6, 298 K): δ -152.32 (br,10BF4), -152.37 (br, 11BF4).
Anal. Calcd for C21H23BClF4N2O2Ru: C, 48.20; H, 4.43; N, 5.35.
Found: C, 48.25; H, 4.46; N, 5.33.
1
n-hexane. Yield ) 85%. H NMR (CD2Cl2, 298 K, J in Hz): δ
1.29 (d, 3J1,2 ) 7.0, 1), 2.22 (s, 7), 2.80 (sept, 3J2,1 ) 6.9, 2), 3.73
(m, 15), 4.03 (m, 14), 4.93 (d, 3J16,15 ) 5.1, 5), 5.28 (d, 3J5,4 ) 6.2,
3
3
3
5), 5.49 (d, J4,5 ) 6.2, 4), 6.91 (t, Jp,m ) 7.2, p), 7.03 (dd, Jm,p
) 3Jm,o ) 7.8, m), 7.22 (ddd, 3J9,10 ) 7.8, 3J9,8 ) 5.4, 4J9,11 ) 1.3,
9), 7.37 (br, o), 7.62 (dd, 3J11,10 ) 7.2, 4J11,9 ) 0.5, 11), 7.82 (ddd,
3J10,11 ) J10,9 ) 7.7, J10,8 ) 1.3, 10), 8.72 (d, J8,9 ) 5.45, 8).
13C{1H} NMR (CD2Cl2, 298 K): δ 19.0 (s, 7), 22.8 (s, 1), 31.5 (s,
2), 62.6 (s, 15), 68.4 (s, 14), 81.8 (s, 5), 83.9 (s, 4), 100.5 (s, 6),
105.5 (s, 3), 106.0 (s, 13), 121.9 (s, 11), 122.3 (s, p), 125.0 (s, 9),
126.1 (s, m), 136.4 (s, o), 140.4 (s, 10), 152.7 (s, 8), 160.1 (s, 12),
3
4
3
Synthesis of Complex 3BPh4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in MeOH (5 mL). The resulting red-orange suspension was stirred
for 3 h at rt until it changed into a yellow solution; a large excess
of NaBPh4 (10 equiv) dissolved in 0.5 mL of MeOH was added,
and a precipitate formed. The solution was filtered, and the yellow
solid was washed with cold MeOH and n-hexane. Yield ) 85%.
1H NMR (CD2Cl2, 298 K, J in Hz): δ 1.30 (d, 3J1,2 ) 6.9, 1), 2.24
1
11
164.4 (q, JC ) 49.5, Cipso). Anal. Calcd for C47H47BN2O3Ru:
C, 70.58; H, 5.92; N, 3.50. Found: C, 70.50; H, 5.95; N, 3.52.
B
Synthesis of Complex 5PF6. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in HOCH2CH2OH (5 mL). The resulting red-orange suspension was
stirred for 3 h at rt until it changed into a yellow solution; a large
excess of NH4PF6 (10 equiv) dissolved in 0.5 mL of HOCH2CH2-
OH was added, and a precipitate formed. The solution was filtered,
and the yellow solid was washed with cold MeOH and n-hexane.
Yield ) 63%. Alternatively, 0.123 g (0.154 mmol) of 3BPh4 was
dissolved in 5 mL of acetone. 0.056 g of TlPF6 (0.161 mmol) was
added under nitrogen atmosphere, and TlBPh4 precipitated from
the solution. The solution was filtered and dried under vacuum,
3
3
(s, 7), 2.81 (sept, J2,1 ) 6.9, 2), 3.55 (s, 14), 5.29 (d, J5,4 ) 6.2,
3
3
3
5), 5.47 (d, J4,5 ) 6.2, 4), 6.91 (t, Jp,m ) 7.2, p), 7.03 (dd, Jm,p
) 3Jm,o ) 7.8, m), 7.19 (ddd, 3J9,10 ) 7.7, 3J9,8 ) 5.38, 4J9,11 ) 1.4,
9), 7.40 (br, o), 7.57 (d, 3J11,10 ) 7.4, 11), 7.79 (ddd, 3J10,11 ) 3J10,9
) 7.68, 4J10,8 ) 1.3, 10), 8.71 (d, 3J8,9 ) 5.38, 8). Anal. Calcd for
C46H45BN2O2Ru: C, 71.78; H, 5.89; N, 3.64. Found: C, 71.71; H,
5.84; N, 3.68.
Synthesis of Complex 3PF6. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in MeOH (5 mL). The resulting red-orange suspension was stirred
for 3 h at rt until it changed into a yellow solution; a large excess
of NH4PF6 (10 equiv) dissolved in 0.5 mL of MeOH was added,
and a precipitate formed. The solution was filtered, and the yellow
solid was washed with cold MeOH and n-hexane. Yield ) 65%.
Alternatively, 0.118 g (0.154 mmol) of 3BPh4 was dissolved in 5
mL of acetone. 0.056 g of TlPF6 (0.161 mmol) was added under
nitrogen atmosphere, and TlBPh4 precipitated from the solution.
The solution was filtered and dried under vacuum, giving a yellow
1
giving a yellow solid. Yield ) 98%. H NMR (CD2Cl2, 298 K, J
3
3
in Hz): δ δ 1.34 (d, J1,2 ) 6.9, 1), 2.38 (s, 7), 2.93 (sept, J2,1
)
6.9, 2), 3.74 (m, 14), 4.04 (m, 15), 4.52 (7, 3J16,15 ) 5.1, 16), 5.65
3
3
3
(d, J5,4 ) 6.2, 5), 5.84 (d, J4,5 ) 6.2, 4), 7.43 (ddd, J9,10 ) 7.7,
3J9,8 ) 5.38, 4J9,11 ) 1.4, 9), 7.66 (d, 3J11,10 ) 7.4, 11), 7.91 (ddd,
3J10,11 ) J10,9 ) 7.68, J10,8 ) 1.3, 10), 9.08 (d, J8,9 ) 5.38, 8).
3
4
3
19F NMR (CD2Cl2, 298 K): δ -71.6 (d, JFP ) 711.0). 31P{1H}
1
NMR (CD2Cl2, 298 K): δ -141.0 (sept, 1JPF ) 711.0). Anal. Calcd
for C23H26F6N2O3PRu: C, 44.23; H, 4.20; N, 4.49. Found: C, 44.29;
H, 4.23; N, 4.49.
1
Synthesis of Complex 6BPh4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in ethanol (5 mL). The resulting red-orange suspension was stirred
for 3 h at rt until it changed into a yellow solution; a large excess
of NaBPh4 (10 equiv) dissolved in 0.5 mL of ethanol was added,
and a precipitate formed. The solution was filtered, and the yellow
solid was washed with cold ethanol and n-hexane. Yield ) 75%.
1H NMR (CD2Cl2, 298 K, J in Hz): δ 1.30 (d, 3J1,2 ) 7.0, 1), 1.41
(d, 3J15,14 ) 7.1, 15), 2.25 (s, 7), 2.82 (sept, 3J2,1 ) 6.9, 2), 3.81 (q,
solid. Yield ) 98%. H NMR (CD2Cl2, 298 K, J in Hz): δ 1.35
3
3
(d, J1,2 ) 6.9, 1), 2.37 (s, 7), 2.95 (sept, J2,1 ) 6.9, 2), 3.55 (s,
3
3
14), 5.64 (d, J5,4 ) 6.2, 5), 5.77 (d, J4,5 ) 6.2, 4), 7.40 (ddd,
3J9,10 ) 7.7, 3J9,8 ) 5.38, 4J9,11 ) 1.4, 9), 7.60 (d, 3J11,10 ) 7.4, 11),
8.87 (ddd, 3J10,11 ) 3J10,9 ) 7.68, 4J10,8 ) 1.3, 10), 9.05 (d, 3J8,9
)
5.38, 8). 13C{1H} NMR (CD2Cl2, 298 K, J in Hz): δ 18.1 (s, 7),
22.7 (s, 1), 31.7 (s, 2), 50.5 (s, 14), 82.6 (s, 5), 83.1 (s, 4), 99.8 (s,
6), 106.1 (s, 3), 106.6 (s, 13), 121.6 (s, 11), 124.7 (s, 9), 140.0 (s,
10), 153.1 (s, 8), 161.8 (s, 12). 19F NMR (CD2Cl2, 298 K): δ -71.6
(d, 1JFP ) 711.0). 31P{1H} NMR (CD2Cl2, 298 K): δ -141.0 (sept,
1JPF ) 711.0). Anal. Calcd for C22H25F6N2O2PRu: C, 44.37; H,
4.23; N, 4.70. Found: C, 44.31; H, 4.24; N, 4.72.
3
3
3J14,15 ) 7.1, 14), 5.31 (d, J5,4 ) 6.2, 5), 5.49 (d, J4,5 ) 6.2, 4),
3
3
3
6.90 (t, Jp,m ) 7.2, p), 7.03 (dd, Jm,p ) Jm,o ) 7.8, m), 7.20
(ddd, 3J9,10 ) 7.8, 3J9,8 ) 5.4, 4J9,11 ) 1.3, 9), 7.36 (br, o), 7.59 (d,
3J11,10 ) 7.2, 11), 7.80 (ddd, 3J10,11 ) 3J10,9 ) 7.7, 4J10,8 ) 1.3, 10),
Synthesis of Complex 4PF6. [Ru(η6-hexamethylbenzene)Cl2]2
(0.100 g, 0.149 mmol) was added to a solution of dpk (0.061 g,
8.73 (d, J8,9 ) 5.45, 8). 13C{1H} NMR (CD2Cl2, 298 K): δ 15.9
3

From Ion Pairs to Ion Triples
Organometallics, Vol. 26, No. 25, 2007 6105
(s, 15), 18.2 (s, 7), 22.7 (s, 1), 31.7 (s, 2), 59.1 (s, 14), 82.2 (s, 5),
83.0 (s, 4), 99.9 (s, 6), 105.8 (s, 3), 106.7 (s, 13), 121.7 (s, 11),
122.2 (s, p), 124.6 (s, 9), 126.1 (s, m), 136.5 (s, o), 140.1 (s, 10),
PGSE data were treated taking into account all of the method-
ological precautions described in our recent paper.35
The uncertainty of the measurements was estimated by determin-
ing the standard deviation of the slope of the straight lines, obtained
by plotting ln(I/I0) versus G2, by performing experiments with
different ∆ values. The standard propagation of error analysis gave
a standard deviation of approximately 3-4% in hydrodynamic radii
and 10-15% in hydrodynamic volumes. The van der Waals
volumes of 2BF4 and 5BPh4 ion pairs were determined from their
crystal structures; for the other complexes, VvdW was obtained
starting from those of 2BF4 or 5BPh4 by adding or removing the
appropriate moieties according to Bondi.45 The ratios between the
1
11
152.6 (s, 8), 162.2 (s, 12), 164.4 (q, JC ) 49.5, Cipso). Anal.
B
Calcd for C47H47BN2O2Ru: C, 72.02; H, 6.04; N, 3.57. Found: C,
72.12; H, 6.06; N, 3.50.
Synthesis of Complex 7BPh4. [Ru(η6-cymene)Cl2]2 (0.100 g,
0.163 mmol) was added to a solution of dpk (0.066 g, 0.358 mmol)
in isobutanol (5 mL). The resulting red-orange suspension was
stirred for 3 h at rt until it changed into a yellow solution; a large
excess of NaBPh4 (10 equiv) dissolved in 0.5 mL of isobutanol
was added, and a precipitate formed. The solution was filtered, and
the yellow solid was washed with cold isobutanol and n-hexane.
Yield ) 71%. 1H NMR (CD2Cl2, 298 K, J in Hz): δ 1.09 (d, 3J16,15
0+
+
experimentally determined VH and VvdW for 4+ was 1.46. This
factor was used to calculate the VH0+ of other cations from VvdW
The volumes of ion pairs were evaluated adding VvdW to VH .
.
+
-
0+ 37
) 6.7, 16), 1.31 (d, 3J1,2 ) 6.9, 1), 2.09 (m, 3J15,14 ) 6.5, 3J15,16
)
)
3
3
6.7, 15), 2.26 (s, 7), 2.82 (sept, J2,1 ) 6.9, 2), 3.54 (d, J14,15
Crystal Structure Determination of 2BF4 and 5BPh4. Crystal
data for 2: C21H23BF4N2O2Ru‚CH2Cl2, Mw ) 608.22, monoclinic,
P21, a ) 15.781(4), b ) 18.160(2), c ) 9.047(5) Å, â ) 103.98-
(3)°, V ) 2515.97 Å3, F(000) ) 1184, µ ) 0.88 mm-1, Z ) 4,
7969 independent measured reflections. Crystal data for 5: C47H50-
BN2O3Ru‚1/2CH2Cl2, Mw ) 1641.96, a ) 10.240(5), b ) 18.724-
(5), c ) 22.536(5) Å, R ) 75.79(1), â ) 77.62(1), γ ) 80.57(1)°,
3
3
6.5, 14), 5.31 (d, J5,4 ) 5.9, 5), 5.49 (d, J4,5 ) 5.9, 4), 6.90 (t,
3Jp,m ) 7.2, p), 7.03 (dd, Jm,p ) Jm,o ) 7.8, m), 7.20 (ddd, J9,10
3
3
3
3
4
3
) 7.8, J9,8 ) 5.4, J9,11 ) 1.3, 9), 7.36 (br, o), 7.59 (d, J11,10
)
7.6, 11), 7.80 (ddd, 3J10,11 ) 3J10,9 ) 7.6, 4J10,8 ) 1.0, 10), 8.73 (d,
3J8,9 ) 5.3, 8). 13C{1H} NMR (CD2Cl2, 298 K): δ 17.9 (s, 7), 19.7
(s, 16), 22.8 (s, 1), 29.3 (s,15), 31.7 (s, 2), 69.4 (s, 14), 82.2 (s, 5),
83.1 (s, 4), 99.9 (s, 6), 105.8 (s, 3), 106.7 (s, 13), 121.7 (s, 11),
122.2 (s, p), 124.9 (s, 9), 126.0 (s, m), 136.4 (s, o), 140.1 (s, 10),
triclinic, P-1, V ) 4063(2) Å3, F(000) ) 1706.0, µ ) 0.46 mm-1
,
Z ) 4, 29 957 independent measured reflections. Suitable crystals
for the X-ray diffraction studies were grown from CH2Cl2.
Preliminary examination and data collection were carried out at
ambient temperature on a Enraf-Nonius CAD-4 diffractometer for
2BF4 and on a BRUKER AXS SMART 2000 CCD diffractometer
for 5BPh4, using graphite-monochromated Mo KR radiation (λ )
0.71073 Å). The data of 5 were collected using 0.3° wide ω scans
and a crystal-to-detector distance of 5.0 cm and corrected for
absorption empirically using the SADABS routine.46 Data collection
nominally covered a full sphere of reciprocal space with 30 s
exposure time per frame. Both structures were solved by direct
methods and refined on F2 by full matrix least-squares calculations
using the SHELXTL package.47 Thermal vibrations were treated
anisotropically; H atoms were experimentally located but geo-
metrically positioned [C-H 0.93 and 0.97 Å for aromatic and
aliphatic distances; OH 0.82 Å] and refined “riding” on their
corresponding carbon or oxygen atom. Refinement converged at a
final R ) 0.0488 for 7532 Fo > 4σ(Fo) for 588 parameters, wR2 )
0.130, S ) 1.21 for 2; R ) 0.0463 for 11 304 Fo > 4σ(Fo) and 903
parameters, wR2 ) 0.163, S ) 1.15 for 5. Flack parameter for 2
was 0.085 for the correct absolute structure. The final residual
electron density maps showed no remarkable features.
In compound 2, the asymmetric unit contains two crystallo-
graphically independent ion pairs and two solvent (CH2Cl2)
molecules. The isopropyl moiety of the cymene ring is characterized
by large thermal vibrations; however, no satisfactory alternative
model for the disordered atoms could be refined despite repeated
attempts.
Compound 5 also contains two crystallographic independent ion
pairs (BPh4 as a counterion) in the asymmetric unit and one
dichloromethane solvent molecule, treated with half occupancy
because it is disordered.
1
11
152.6 (s, 8), 162.3 (s, 12), 164.3 (q, JC ) 49.5, Cipso). Anal.
B
Calcd for C49H51BN2O2Ru: C, 72.49; H, 6.33; N, 3.45. Found: C,
72.40; H, 6.30; N, 3.48.
NOE Measurements. The 1H-NOESY41 NMR experiments were
acquired by using the standard three-pulse sequence or by the PFG
version.42 Two-dimensional 19F,1H-HOESY NMR experiments were
acquired using the standard four-pulse sequence or the modified
version.43 The number of transients and the number of data points
were chosen according to the sample concentration and to the
desired final digital resolution. Semiquantitative spectra were
acquired using a 1 s relaxation delay and 800 ms mixing times.
1
PGSE Measurements. H and 19F PGSE NMR measurements
were performed by using the standard stimulated echo pulse
sequence44 on a Bruker AVANCE DRX 400 spectrometer equipped
with a GREAT 1/10 gradient unit and a QNP probe with a
Z-gradient coil, at 296 K without spinning.
The dependence of the resonance intensity (I) on a constant
waiting time and on a varied gradient strength (G) is described by
eq 1:
I
I0
δ
3
ln ) -(γδ)2Dt ∆ - G2
(1)
(
)
where I is the intensity of the observed spin echo, I0 is the intensity
of the spin echo without gradients, Dt is the diffusion coefficient,
∆ is the delay between the midpoints of the gradients, δ is the
length of the gradient pulse, and γ is the magnetogyric ratio.
The shape of the gradients was rectangular, their duration (δ)
was 4-5 ms, and their strength (G) was varied during the
experiments. All of the spectra were acquired using 32K points, a
spectral width of 5000 (1H) and 18 000 (19F) Hz, and processed
with a line broadening of 1.0 (1H) and 1.5 (19F) Hz. The
semilogarithmic plots of ln(I/I0) versus G2 were fitted using a
standard linear regression algorithm; the R factor was always higher
than 0.99. Different values of ∆, “nt” (number of transients), and
number of different gradient strengths (G) were used for different
samples.
Acknowledgment. We thank the Ministero dell’Universita`
e della Ricerca (MUR, Rome, Italy) and the Dow Chemical
Co. for support.
Supporting Information Available: Crystallographic data for
complexes 2 and 5 in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
(41) Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. J. Chem. Phys.
1979, 71, 4546.
OM700775U
(42) Wagner, R.; Berger, S. J. Magn. Reson., Ser. A 1996, 123, 119.
(43) Lix, B.; So¨nnichsen, F. D.; Sykes, B. D. J. Magn. Reson., Ser. A
1996, 121, 83.
(44) Valentini, M.; Ru¨egger, H.; Pregosin, P. S. HelV. Chim. Acta 2001,
84, 2833 and references therein.
(45) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(46) Sheldrick, G. M. SADABS; University of Go¨ttingen: Germany, 1996.
(47) Siemens SHELXTL plus Version 5.1 Structure Determination
Package; Siemens Analytical X-ray Instruments Inc.: Madison, WI, 1998.