PGSE NMR studies on RAPTA derivatives: Evidence for the formation of H-bonded dicationic species

Article abstract of DOI:10.1021/om701131s

The self-aggregation tendency of RAPTA complexes {[Ru(η⁶-p- cymene){PTA(-R)}Cl₂]X, R = H (1BPh₄ and IPF₆) and Me (2BPh₄ and 20Tf), and [Ru(η⁶-p-cymene)(PTA) ₂Cl]X (3BPh₄ and 3BF₄)] in acetone-de was investigated by means of diffusion NMR spectroscopy. On increasing the concentration, the protonated species (1X) undergoes intercationic self-aggregation driven by hydrogen bonding that leads to the formation of 1₂²⁺ dications and a small amount of 1₂X ⁺ ion triples.

Full text of DOI:10.1021/om701131s

Organometallics 2008, 27, 1649–1652
1649
PGSE NMR Studies on RAPTA Derivatives: Evidence for the
Formation of H-Bonded Dicationic Species
Sandra Bolaño,† Gianluca Ciancaleoni,‡ Jorge Bravo,† Luca Gonsalvi,§ Alceo Macchioni,*,‡
and Maurizio Peruzzini§
UniVersidad de Vigo, Facultad de Química, Departamento de Quimica Inorgánica, 36310 Lagoas
Marcosende, Vigo, Spain, Dipartimento di Chimica, UniVersità di Perugia, Via Elce di Sotto, 8,
06123 Perugia, Italy, and CNR-Istituto di Chimica dei Composti Organo Metallici (CNR-ICCOM), Via
Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy
ReceiVed NoVember 12, 2007
tionality in assisting both the hydrogenation reaction of
benzylidene acetone8 and the heterolytic splitting of a molecular
dihydrogen ruthenium complex,9 has been recently demonstrated.
Summary: The self-aggregation tendency of RAPTA complexes
{[Ru(η6-p-cymene){PTA(-R)}Cl2]X, R ) H (1BPh4 and 1PF6)
and Me (2BPh4 and 2OTf), and [Ru(η6-p-cymene)(PTA)2Cl]X
(3BPh4 and 3BF4)} in acetone-d6 was inVestigated by means of
diffusion NMR spectroscopy. On increasing the concentration,
the protonated species (1X) undergoes intercationic self-
aggregation driVen by hydrogen bonding that leads to the
Noncovalent interactions, occurring in the second coordination
sphere of organometallic compounds, are generally recognized
to play a relevant role in their reactivity and structure.10 The
occurrence of weak interactions in solution can be readily
appreciated by NOE intermolecular11 and diffusion12 NMR
studies or, even better, by taking advantage of the complemen-
tary information that these NMR methods allow us to obtain.13
Although the current importance of transition-metal- PTA
complexes is mostly ascribable to the establishment of weak
interactions in polar solvents, to the best of our knowledge, no
intermolecular study involving PTA-metal complexes in solu-
tion has been carried out.
2+
formation of 12 dications and a small amount of 12X+ ion
triples.
Although 1,3,5-triaza-7-phosphaadamantane (PTA) has been
known since 1974,1 its coordination chemistry has undergone
a remarkable increase in interest in the last 15 years.2 This
renewed interest has been mainly due not only to the successful
utilization of PTA-organometallic compounds as water-soluble
catalysts3 but also to their use as luminescent complexes4 and
promising anticancer agents.5 Most of the distinctive features
of PTA, including its high hydrosolubility and ability to form
water-soluble transition-metal complexes, derive from its in-
trinsic tendency to establish hydrogen bonds via the three
N-donor atoms residing in the lower rim of the adamantane
skeleton. In fact, the N-functionality can act as either HB-
acceptor6 (HB ) hydrogen bond) or, when protonated, HB-
donor.7 In this regard, direct involvement of the distal N-func-
Herein, we report the results of a PGSE (pulsed field gradient
spin–echo)14 NMR investigation on the self-aggregation proper-
ties of neutral and cationic arene ruthenium complexes bearing
the PTA ligand and its protonated (PTA-H) and methylated
derivatives (PTA-Me). The aim of this paper is to evaluate the
tendency of such complexes to self-aggregate as a function of
the chemical nature of the compound, possibly individualizing
the weak interactions that are responsible for it. The establish-
ment of several complex equilibria prevented us to carry out
the study in water. Consequently, our analysis was conducted
in acetone which, like water, is enough polar to minimize ion
pairing. Additionally, acetone is an aprotic solvent, much less
polar than water, thus allowing better evaluation of HB
interactions.
* To whom correspondence should be addressed. Phone: +39 075
5855579. Fax: +39 075 5855598. Email: alceo@unipg.it.
† Universidad de Vigo.
‡ Università di Perugia.
§ CNR-ICCOM.
(1) Daigle, D. J.; Pepperman, A. B.; Vail, S. L. J. Heterocycl. Chem.
1974, 11, 407.
(2) Phillips, A. D.; Gonsalvi, L.; Romerosa, A.; Vizza, F.; Peruzzini,
M. Coord. Chem. ReV. 2004, 248, 955.
(7) Forward, J. M.; Assefa, Z.; Staples, R. J., Jr. Inorg. Chem. 1996,
35, 16.
(3) (a) Akbayeva, D. N.; Gonsalvi, L.; Oberhauser, W.; Peruzzini, M.;
Vizza, F.; Brueggeller, P.; Romerosa, A.; Sava, G.; Bergamo, A. Chem.
Commun. 2003, 264. (b) Bolano, S.; Gonsalvi, L.; Zanobini, F.; Vizza, F.;
Bertolasi, V.; Romerosa, A.; Peruzzini, M. J. Mol. Catal. A 2004, 224, 61.
(c) Frost, B. J.; Mebi, C. A. Organometallics 2004, 23, 5317.
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Assman, B.; Angermaier, K.; Schmidbaur, H. Inorg. Chem. 1995, 34, 2490.
(b) Assefa, Z.; McBurnett, B. G.; Staples, R. J.; Fackler, J. P.; John, P.
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J. P.; Staples, R. J. Inorg. Chem. 1995, 34, 6330.
(8) Mebi, C.; Frost, B. J. Organometallics 2005, 24, 2339.
(9) Rossin, A.; Gonsalvi, L.; Phillips, A. D.; Maresca, O.; Lledós, A.;
Peruzzini, M. Organometallics 2007, 26, 3289.
(10) (a) Binotti, B.; Bellachioma, G.; Cardaci, G.; Carfagna, C.;
Zuccaccia, C.; Macchioni, A. Chem. Eur. J. 2007, 13, 1570. (b) Macchioni,
A Chem. ReV. 2005, 105, 2039. (c) Noyori, R.; Yamakawa, M.; Hashiguchi,
S. J. Org. Chem. 2001, 66, 7931.
(11) Macchioni, A. Eur. J. Chem. 2003, 195 and references therein.
(12) (a) Zuccaccia, C.; Bellachioma, G.; Cardaci, G.; Macchioni, A.
Organometallics 2000, 19, 4663. (b) Valentini, M.; Pregosin, P. S.; Ruegger,
H. Dalton 2000, 24, 4507. (c) Bellachioma, G.; Ciancaleoni, G.; Zuccaccia,
C.; Zuccaccia, D.; Macchioni, A. Coord. Chem. ReV., doi: 10.1016/
j.ccr.2007.12.016.
(5) (a) Scolaro, C.; Chaplin, A. B.; Hartinger, C. G.; Bergamo, A.;
Cocchietto, M.; Keppler, B. K.; Sava, G.; Dyson, P. J. Dalton Trans. 2007,
5065. (b) Ang, W. H.; Daldini, E.; Juillerat-Jeanneret, L.; Dyson, P. J. Inorg.
Chem. 2007, 46, 9048. (c) Dyson, P. J.; Ellis, D. J.; Laurenczy, G. AdV.
Synth. Catal. 2003, 345, 211. (d) Allardyce, C. S.; Dyson, P. J.; Ellis, D. J.;
Heath, S. L. Chem. Commun. 2001, 1396. (e) Dyson, P. International Patent
WO 02/40491 A1(2002).
(6) (a) Darensbourg, D. J.; Decuir, T. J.; Stafford, N. W.; Robertson,
J. B.; Draper, J. D.; Reibenspies, J. H.; Kathó, A.; Joó, F. Inorg. Chem.
1997, 36, 4218. (b) Alyea, E. C.; Ferguson, G.; Kannan, S. Chem. Commun.
1998, 345.
(13) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Ciancaleoni, G.;
Zuccaccia, C.; Clot, E.; Macchioni, A. Organometallics 2007, 26, 3930.
(14) (a) Hahn, E. L. Phys. ReV. 1950, 80, 580. (b) Stejskal, E. O.; Tanner,
J. E J. Chem. Phys. 1965, 42, 288. (c) Stilbs, P. Prog. Nucl. Magn. Reson.
Spectrosc. 1987, 19, 1. (d) Price, W. S. Concepts Magn. Reson. 1997, 9,
299. (e) Price, W. S. Concepts Magn. Reson. 1998, 10, 197. (f) Johnson,
C. S, Jr. Prog. Nucl. Magn. Reson. Spectrosc. 1999, 34, 203.
10.1021/om701131s CCC: $40.75
2008 American Chemical Society
Publication on Web 03/14/2008

1650 Organometallics, Vol. 27, No. 7, 2008
Notes
Table 1. Diffusion Coefficients (1010Dt+/-, m2 s-1), Average
Scheme 1
Hydrodynamic Volumes for Cations and Anions (VH+/-, Å3), and
Concentrations (C, mM) for 1X, 2X, and 3X Salts in Acetone-d6
(Er ) 20.56)
+
-
entry
Dt+
Dt-
VH
VH
N+
N-
C
1
2
3
4
5
6
7
8
1PF6
12.0
14.9
9.20
10.8
12.4
14.7
9.25
9.39
10.8
11.5
12.5
12.2
10.3
11.7
11.8
7.20
9.64
11.3
11.8
11.9
11.6
11.8
22.0
28.3
11.9
13.3
14.4
15.0
10.8
11.0
12.6
13.5
14.5
14.8
13.1
14.5
16.6
9.58
12.5
14.1
14.3
14.9
23.5
28.4
834
483
1194
1003
739
217
131
660
546
527
487
800
720
638
552
508
469
569
517
342
579
559
539
530
472
163
118
1.5
0.9
1.3
1.0
0.8
0.5
1.0
0.9
0.8
0.7
0.6
0.6
1.3
1.1
1.0
0.9
0.8
0.7
0.7
0.6
1.0
0.9
0.4
0.2
0.7
0.6
0.5
0.5
0.7
0.6
0.5
0.5
0.4
0.4
0.7
0.7
0.4
0.5
0.4
0.4
0.4
0.4
0.2
0.1
4.7a
0.01
40
1BPh4
13
2.4
0.47
65a
51
517
2BPh4
1188
1072
937
826
724
735
1023
865
9
23
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
9.9
1.1
0.1
49
27
8.7
24
2OTf
792
3BPh4
1161
1067
923
843
796
11
4.2
1.6
0.13
3.2a
0.44
16a
7.4
0.9
Results and Discussion
3BF4
839
800
Synthesis. Complexes [Ru(η6-p-cymene){PTA(-H)}Cl2]X
(1X), [Ru(η6-p-cymene){PTA(-Me)}Cl2]X (2X), [Ru(η6-p-
cymene)(PTA)2Cl]X (3X), and [Ru(η6-p-cymene)(PTA)Cl2] (4),
shown in Scheme 1, were synthesized as detailed in the
Experimental Section. In particular, complex 1Cl was prepared
by treating an aqueous solution of complex 4 with aqueous HCl
(0.1 M) solution. 1BPh4 and 1PF6 were synthesized from 1Cl
through anion metathesis in methanol with an excess of NaBPh4
and NH4PF6, respectively. 2OTf was synthesized as described
in the literature.15 2BPh4 was obtained as a yellow solid
dissolving 2OTf in methanol in the presence of a large excess
of NaBPh4. 3Cl was synthesized by the reaction of [Ru2(η6-p-
cymene)2Cl2(µ-Cl)2] with 2 equiv of PTA in refluxing methanol.
Anion metathesis reaction of 3Cl with NaBPh4 and halide
removal using AgBF4 gave 3BPh4 and 3BF4, respectively.
4
13.4
14.0
14.8
579
539
496
1.2
1.1
1.0
a Saturated solution.
PGSE Measurements. The aggregation tendency of RAPTA
complexes 1-4 (Scheme 1) in acetone-d6 was studied by means
of PGSE NMR experiments (Table 1). PGSE NMR14 allows
the translational self-diffusion coefficient (Dt) to be determined;
the latter is related to the hydrodynamic radius (rH) of the
diffusing particle through to the Stokes–Einstein equation (1)
Figure 1. Schematic view of the PTAMe moiety derived from X-ray
data reported in ref 15. The torus generated from the rapid rotation
of the methylated PTA is outlined in gray; r and R are expressed
in Å.
Å3],13,17 VH+0 and VH0(4) was experimentally determined from
the PGSE measurements at the lowest concentrations. The
results were as follows: VH+0(1+) ) 483 Å3, in excellent
kT
cπηrH
Dt )
(1)
0
agreement with its neutral isosteric analogous 4 (VH ) 496
Å3), VH+0(2+) ) 735 Å3 and VH+0(3+) ) 796 Å3 (entries 2,
where k is the Boltzman constant, T is the temperature, c is a
numerical factor, and η is the fluid viscosity. In order to obtain
accurate hydrodynamic dimensions of the diffusing species, Dt
data were treated as described in our recent paper.16 The
hydrodynamic volume (VH) of the aggregates was determined
by rH assuming that they had a spherical shape. Finally, the
aggregation number (N+/-), defined as the ratio of experimental
hydrodynamic volume of cation or anion and the hydrodynamic
volume of the ion pair (VHIP0), was derived.13,16
25, 12, and 20, Table 1).
VH+0(2+) appears to be larger than expected. In fact, the only
chemical difference between 1+ and 2+ is the presence of the
methyl group instead of the hydrogen atom that apparently does
0
not justify a VH difference of 252 Å3. Nevertheless, it has to
be considered that, due to the rapid rotation of PTA around the
Ru-P bond, the methyl group may occupy not only its intrinsic
volume but also that of toroidal shape swept during its rotation.
A simple calculation, carried out starting from the data in the
+0
-0
VHIP0was considered equal to VH plus VH-0. While VH
solid state,15 indicates that this volume amounts to Vtorus
)
was known from previous studies [VH–0(BPh4-) ) 461 Å3,
VH–0(PF6-) ) 74 Å3, VH–0(BF4-) ) 42 Å3, VH–0(OTf-) ) 72
2π2Rr2 ) 197.5 Å3 (Figure 1). The sum VH0(4) + Vtorus ) 694
Å3 is in agreement with the experimental hydrodynamic volume
of 2+ (735 Å3).
(15) Dorcier, A.; Dyson, P. J.; Gossens, C.; Rothlisberger, U.; Scopelliti,
R.; Tavernelli, I. Organometallics 2005, 24, 2114.
(16) Macchioni, A.; Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D. Chem.
Soc. ReV. 2008, 37, 479 and references therein.
(17) Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D.; Macchioni, A.
Organometallics 2007, 26, 3624.

Notes
Organometallics, Vol. 27, No. 7, 2008 1651
Figure 2. Dependence of the cationic and anionic average
hydrodynamic volume (b ) V-, 9 ) V+) on the concentration of
complex 1BPh4.
Figure 3. Noncovalent interactions (Å) present in the X-ray single-
crystal structure of 2Cl, reported by Dorcier et al.15 Distances are
expressed in angstroms, and all of the hydrogen atoms, except those
involved in intermolecular interaction, are omitted for clarity.
Aggregation of 1X. From PGSE data (Table 1, entries 1–6),
it appears that at the lowest concentration values, 1BPh4 (entry
6), and 1PF6 (entry 2) are almost exclusively present as free
has not the possibility to form HBs, it can be supposed that
cation–cation aggregation occurs through the electrostatic
interaction of the methylenic protons having a partial positive
charge and the chlorine atom, as observed in the solid state for
2Cl15 (Figure 3).
+
-
ions. For both salts, VH and VH increase by increasing the
concentration, but with different rates. Focusing on the most
soluble 1BPh4 salt, VH+ and VH- span from 517 and 487 Å3 to
1190 and 660 Å3, respectively, as the salt concentration increases
-
–0
(Figure 2). While the observed VH deviates little from VH
,
Aggregation of 3X. In 3X derivatives, the positive charge is
formally centered on the metal. Consistently, a slightly smaller
tendency to ion pairing is observed in 3BPh4 compared to 2BPh4
(entries 9 and 16 in Table 1). Instead, the tendency of 3BPh4 to
form dications is a little higher than that of 2BPh4, but clearly
lower than that of 1BPh4. It is not trivial to understand why
3BPh4 should have a higher tendency to form dications than
2BPh4. A possible explanation can be found by analyzing
the solid-state structure of complex [CpRu(PTA){PTA(-H)}
Cl]PF6 · 3H2O18 bearing two PTA ligands. Short intercationic
contacts are present between the partial positively charged
methylenic hydrogens belonging to the two PTA ligands and a
chlorine atom (Figure 4). Such cooperative electrostatic interac-
tions could be active also for 3BPh4 and persist in solution
allowing the dication to be formed.
VH+ becomes more than 2-fold VH+0 (Figure 2). This data cannot
be explained by the ion-pairing phenomenon alone that, in the
actual case with anion and cation having about the same
volumes, would always lead to equal VH and VH-. On the
+
contrary, they suggest the formation of a substantial amount of
+
+
12 dications and a bit of 12BPh4 ion triples. The latter are
+
necessary to explain the observed value of VH that exceeds
that of the dication (Table 1, entry 3). Also, 1PF6 has a great
tendency to form dicationic species (Table 1, entry 1), but its
low solubility precluded a complete study. It is reasonable to
believe that the cation–cation aggregation is driven by the
formation of hydrogen bonds between the good HB donor group
(N-H+) and one of the available HB acceptors (Cl and/or N).
Aggregation of 2X. In order to prove the effective influence
of the aminic proton on the aggregative process, the RAPTA-
methylated complex 2BPh4 was synthesized, where one of the
nitrogen atoms of the PTA ligand bears a methyl group. 2BPh4
shows a marked decreased tendency to undergo cation–cation
In conclusion, weak organometallic cation–cation interactions
in solution have been previously documented in the literature.
They were found in half-sandwich ruthenium(II) complexes
bearing diamine (NH. . .Cl HB),19 diimine (C-H. . .Cl electro-
static interaction),13 2,2′-dipyridylketone (O-H. . .O HB + π-π
stacking),20 2-benzoylpyridine (π-π stacking),21 and palladium
phenantroline complexes (π-π stacking).22 Despite this, only
in the latter case multicationic aggregates were the predominant
species in solution, while in other cases quadrupoles13,19 or ion
triples20,21 were prevalently formed. Herein, we have shown
that protonated RAPTA complexes have a remarkable tendency
to form dications through intercationic HBs. The choice of
acetone as solvent is crucial to highlight the formation of
dications since it minimizes ion pairing.
+
aggregation. The maximum VH value reached at the highest
concentration (Table 1, entry 7) is the same than that of 1BPh4
(Table 1, entry 3), but this corresponds to a lower cationic
+0
aggregation since VH for 2BPh4 is much higher, as seen
before. In addition, the anion participates to the aggregation to
a larger extent (Table 1). These results indicate, on one side,
that the absence of the N-H hydrogen donor depresses the
intercationic aggregation. On the other side, a certain tendency
to ion pairing is observed for 2BPh4 that is probably favored
by the peripheral location of the cationic charge. Changing the
-
-
anion from BPh4 to CF3SO3 does not lead to a significant
modification of the aggregation tendency (entries 9 and 14 in
-
Table 1). The growth of VH with the concentration is fast,
(18) Mebi, C. A.; Frost, B. J. Organometallics 2005, 24, 2339.
(19) Zuccaccia, D.; Macchioni, A. Organometallics 2005, 24, 3476.
(20) Zuccaccia, D.; Foresti, E.; Pettirossi, S.; Sabatino, P.; Zuccaccia,
C.; Macchioni, A. Organometallics 2007, 26, 6099.
according to the small VH-0 of triflate and its greater ability to
form ion pairs with respect to tetraphenylborate. At the same
+
time, the observation of VH values significantly higher than
+0
(21) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Zuccaccia, C.;
Macchioni, A. Dalton Trans. 2006, 1963.
VH with such a small counterion confirms that a certain
amount of cation–cation aggregation has to occur. Since
2CF3SO3 does not possess any HB donor and, consequently,
(22) Macchioni, A.; Romani, A.; Zuccaccia, C.; Guglielmetti, G.; Querci,
C. Organometallics 2003, 22, 1526.

1652 Organometallics, Vol. 27, No. 7, 2008
Notes
mg, 92.3%): 1H NMR (acetone-d6, 298 K) δ 5.88 (m, 4H, cymene),
5.42-5.18 (m, 4H, NCH2), 4.83–4.22 (m, 6 + 2 H, PCH2+NCH2),
3.11 (s, 3H, CH3N), 2.72 (sept, 1H, JHH ) 6.9 Hz, CH), 2.04 (s,
3H, CH3), 1.21 (d, 6H, JHH ) 6.98 Hz, CH3); 19F NMR (acetone-
d6, 298 K) δ -79.4 (s); 31P{1H}NMR (acetone-d6, 298 K) δ –19.9
(s).
Metathesis reaction of 2OTf with NaBPh4 in MeOH gave the
1
compound 2BPh4 (109.9 mg, 86.2%): H NMR (acetone-d6, 298
K) δ 7.36 (m, 8H, Ph), 6.94 (m, 8H, Ph), 6.70 (m, 4H, Ph), 5.84
(m, 4H, cymene), 5.32–5.13 (m, 4H, NCH2), 4.84–4.22 (m, 6 + 2
H, PCH2 + NCH2), 3.11 (d, 3H, JHH ) 1.9, CH3N), 2.73 (sept,
1H, JHH ) 7.1 Hz, CH), 2.04 (s, 3H, CH3), 1.21 (d, 6H, JHH
6.90 Hz, CH3).
)
Synthesis of [Ru(η6-p-cymene)(PTA)2Cl]X (3X), X ) BPh4,
BF4. A methanolic solution of [Ru(η6-p-cymene)Cl2]2 (200 mg,
0.33 mmol) and PTA (206 mg, 1.32 mmol) was refluxed for 48 h.
The mixture was cooled to room temperature, and the solvent was
removed under reduced pressure to give a solid. The solid obtained
was treated with a saturated solution of NaBPh4 in MeOH, obtaining
3BPh4 (253 mg, 85.0%): 1H NMR (acetone-d6, 298 K) δ 7.35 (m,
Figure 4. Noncovalent interactions (Å) present in the X-ray single-
crystal structure of [CpRu (PTA)(PTAH)Cl]PF6 · 3H2O.18 Distances
are expressed in angstroms. All of the solvent molecules and
hydrogen atoms, apart from those involved in intermolecular
interactions, are omitted for clarity.
8H, Ph), 6.94 (m, 8H, Ph), 6.79 (m, 4H, Ph), 6.54 (d, 2H, JHH
)
6.3 Hz, cymene), 6.36 (d, 2H, JHH ) 6.3 Hz, cymene), 4.74–4.56
(m, 12H, NCH2), 4.56–4.38 (m, 12H, PCH2), 2.70 (sept, 1H, JHH
) 6.8 Hz, CH), 2.18 (s, 3H, CH3), 1.25 (d, 6H, JHH ) 6.90 Hz,
CH3). Anal. Calcd for C46H58BClN6P2Ru: C, 61.1; H, 6.46; N, 9.29.
Found: C, 60.7; H, 6.60; N, 9.08.
Experimental Section
The PTA ligand and its derivatives1 [Ru2(η6-p-cymene)2Cl2(µ-
Cl)2],23 [Ru(η6-p-cymene)(PTA)Cl2]24 (4), and [Ru(η6-p-cymene)-
(PTA)2Cl]BF4 (3BF4)25 were prepared according to the literature
procedures. All other reagents were supplied by Aldrich and were
used without further purification. The solvents were purified by
conventional procedures.26
A solution of 3BPh4 (80 mg, 0.088 mmol) in 20 mL of CH2Cl2
was treated with AgBF4 (17.94 mg, 0.092 mmol). The white
precipitate of AgBPh4 was filtered off, and the solvent was removed
1
under vacuum, giving the compound 3BF4: H NMR (acetone-d6,
298 K) δ 6.54 (d, 2H, JHH ) 6.4 Hz, cymene), 6.36 (d, 2H, JHH
)
Synthesis of [Ru(η6-p-cymene){PTA(-H)}Cl2]X (1X), X )
BPh4, PF6. Aqueous HCl (0.1 M, 2.2 mL) was added to a solution
of [Ru(η6-p-cymene)(PTA)Cl2] (100 mg, 0.22 mmol) in water, at
room temperature. After 30 min stirring, the solution was concen-
trated under reduced pressure and treated with a saturated solution
of NaBPh4 or NaPF6 in methanol, giving immediately an orange
solid (1BPh4 or 1PF6, respectively). 1BPh4 (159.4 mg, 92.2%): 1H
NMR (acetone-d6, 298 K) δ 7.35 (m, 8H, Ph), 6.94 (m, 8H, Ph),
6.79 (m, 4H, Ph), 5.86 (m, 4H, cymene), 5.16 (s, 6H, NCH2), 4.58
(s, 6H, PCH2), 2.74 (sept, 1H, JHH ) 6.9 Hz, CH), 2.04 (s, 3H,
CH3), 1.22 (d, 6H, JHH ) 6.85 Hz, CH3); 31P{1H}NMR (acetone-
d6, 298 K) δ 22.1 (s). Anal. Calcd for C40H47BCl2N3PRu: C, 61.3;
H, 6.05; N, 5.36. Found: C, 60.9; H, 6.13; N, 5.30. 1PF6 (118.3
mg, 88.2%): 1H NMR (acetone-d6, 298 K) δ 5.86 (m, 4H, cymene),
5.15 (s, 6H, NCH2), 4.60(s, 6H, PCH2), 2.73 (sept, 1H, JHH ) 7.0
Hz, CH), 2.05 (s, 3H, CH3), 1.22 (d, 6H, JHH ) 6.84 Hz, CH3);
19F NMR (acetone-d6, 298 K) δ –72.8 (d, JFP ) 707.9 Hz, PF6);
31P{1H}NMR (acetone-d6, 298 K) δ 22.1 (s), 140 (sept, JPF ) 707.9
Hz, PF6).
6.3 Hz, cymene), 4.74–4.55 (m, 12H, NCH2), 4.56–4.38 (m, 12H,
PCH2), 2.69 (sept, 1H, JHH ) 6.9 Hz, CH), 2.17 (s, 3H, CH3), 1.25
(d, 6H, JHH ) 6.90 Hz, CH3); 19F NMR (acetone-d6, 298 K) δ
-151.84 (10BF4-), -151.89 (11BF4-).
PGSE NMR Measurements.27 1H NMR measurements were
performed by using the standard stimulated echo pulse sequence27
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 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 and a spectral width of 5000 (1H) Hz and 18000
(19F) Hz and processed with a line broadening of 1.0 (1H) Hz 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. The methodology for treating data was
described previously.19 The uncertainty in the measurements was
estimated by determining the standard deviation of the slopes of
the linear regression lines by performing experiments with different
∆ values. The standard propagation of error analysis gave a standard
deviation of approximately 3–4% in Dt and hydrodynamic radii and
10–15% in hydrodynamic volumes and aggregation numbers N.
Synthesis of [Ru(η6-p-cymene){PTA(-Me)}Cl2]X (2X), X )
OTf, BPh4. A mixture of [Ru(η6-p-cymene)Cl2]2 (100 mg, 0.16
mmol) and [PTAMe]OTf (51.38 mg, 0.16 mmol) was refluxed in
MeOH (20 mL) for 24 h. After evaporation of the solvent under
reduced pressure, diethyl ether (30 mL) was added. The precipitated
orange solid was filtered off and dried under vacuum. 2OTf (92.7
Acknowledgment. We thank the DOW Chemical Co., the
Ministero dell’Università e della Ricerca (MUR, Rome,
Italy), and the Xunta de Galicia for support.
(23) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg.
Synth. 1982, 21, 74.
(24) Allardyce, C. S.; Dyson, P. J.; Ellis, D. J.; Heath, S. L. Chem.
Commun. 2001, 1396.
OM701131S
(25) Dyson, P. J.; Ellis, D. J.; Laurenczy, G. AdV. Synth. Catal. 2003,
345, 211.
(26) Perrin, D. D.; Armarego, W. Purification of Laboratory Chemicals,
3a ed.l Butterworth and Heinemann, Oxford, 1988.
(27) Valentini, M.; Rüegger, H.; Pregosin, P. S. HelV. Chim. Acta 2001,
84, 2833 and references therein.