Self-aggregation of amino-acidate half-sandwich ruthenium(II) complexes in solution: From monomers to nanoaggregates

Article abstract of DOI:10.1021/om060904e

The aggregation tendency of [RuCl(AA)(Arene)] complexes (1, AA = amino acidate = Gly, Arene = p-cymene; 2, AA = Ala, Arene = p-cymene; 3, AA = N,N′-dimethyl-Gly, Arene = benzene; 3b, AA = N,N′-dimethyl-Gly, Arene = p-cymene; 3c, AA = MAT-dimethyl-Gly, Arene = hexamethylbenzene; 4a, AA = t-Leu, Arene = benzene; 4b, AA = t-Leu, Arene = p-cymene; 4c, AA = t-Leu, Arene = hexamethylbenzene; 5, AA = α,α′-Me₂-Gly, Arene = p-cymene; 6, AA = α,α′-Ph₂-Gly, Arene = p-cymene; 7, AA = Pro, Arene = p-cymene) as a function of the concentration and solvent (CDCl₃, CD₂Cl₂, acetone-d₆, and 2-propanol-d₈) was investigated through diffusion NMR measurements. The equilibrium constant (K) and the standard variation of the free energy (ΔG°) for the aggregation process were determined by applying the Equal K self-aggregation model. The highest level of aggregation was observed for complexes 1, 2, and 4, bearing the NH₂ moiety, which was involved in intermolecular H-bonding. Complex 2 formed aggregates with a hydrodynamic radius (r_H) equal to 20.8 A in CDCl₃ (ΔG°_296K == -7.1 ± 0.7 kcal mol^-1) at a concentration of 124.9 mM, corresponding to an aggregation number (N) of 133. On the other hand, complex 3c did not show any tendency to aggregate (N = 1.1, 0.5 mM in CDCl₃). The aggregation tendency decreased as the steric hindrance of arene (4a > 4b > 4c) and AA (1 ≈ 2 > 5 ≈ 4b > 6) and the polarity and proticity of the solvent increased. For complex 2, -ΔG°(kcal/mol) was 7.1 in CDCl₃ (ε_r = 4.81) > 5.6 in CD₂Cl₂ (ε_r = 8.93) > 3.9 in acetone-d₆ (ε_r = 20.56) > 3.0 in 2-propanol-d₈ (ε_r = 19.92). While the two diastereoisomers of complexes 2 and 4b showed substantially the same tendency to self-aggregate, diastereoisomer (R_Ru, S_N, S _C)-7 showed a remarkably higher aggregation tendency than the other one [(S_Ru, S_N, S_C)-7] throughout the entire concentration range (1.4-178.0 mM) in CDCl₃, indicating that a diastereoselective recognition process is occurring in solution [|Δ(ΔG°_296K)| = 1.8 ± 0.5 kcal mol ^-1].

Full text of DOI:10.1021/om060904e

Organometallics 2007, 26, 489-496
489
Self-Aggregation of Amino-Acidate Half-Sandwich Ruthenium(II)
Complexes in Solution: From Monomers to Nanoaggregates
Gianluca Ciancaleoni, Ilona Di Maio, Daniele Zuccaccia, and Alceo Macchioni*
Dipartimento di Chimica, UniVersita` di Perugia, Via Elce di Sotto, 8, 06123 Perugia, Italy
ReceiVed October 3, 2006
The aggregation tendency of [RuCl(AA)(Arene)] complexes (1, AA ) amino acidate ) Gly, Arene )
p-cymene; 2, AA ) Ala, Arene ) p-cymene; 3, AA ) N,N′-dimethyl-Gly, Arene ) benzene; 3b, AA )
N,N′-dimethyl-Gly, Arene ) p-cymene; 3c, AA ) N,N′-dimethyl-Gly, Arene ) hexamethylbenzene; 4a,
AA ) t-Leu, Arene ) benzene; 4b, AA ) t-Leu, Arene ) p-cymene; 4c, AA ) t-Leu, Arene )
hexamethylbenzene; 5, AA ) R,R′-Me2-Gly, Arene ) p-cymene; 6, AA ) R,R′-Ph2-Gly, Arene )
p-cymene; 7, AA ) Pro, Arene ) p-cymene) as a function of the concentration and solvent (CDCl3,
CD2Cl2, acetone-d6, and 2-propanol-d8) was investigated through diffusion NMR measurements. The
equilibrium constant (K) and the standard variation of the free energy (∆G°) for the aggregation process
were determined by applying the Equal K self-aggregation model. The highest level of aggregation was
observed for complexes 1, 2, and 4, bearing the NH2 moiety, which was involved in intermolecular
H-bonding. Complex 2 formed aggregates with a hydrodynamic radius (rH) equal to 20.8 Å in CDCl3
(∆G°296K ) -7.1 ( 0.7 kcal mol-1) at a concentration of 124.9 mM, corresponding to an aggregation
number (N) of 133. On the other hand, complex 3c did not show any tendency to aggregate (N ) 1.1,
0.5 mM in CDCl3). The aggregation tendency decreased as the steric hindrance of arene (4a > 4b > 4c)
and AA (1 ≈ 2 > 5 ≈ 4b > 6) and the polarity and proticity of the solvent increased. For complex 2,
-∆G°(kcal/mol) was 7.1 in CDCl3 (ꢀr ) 4.81) > 5.6 in CD2Cl2 (ꢀr ) 8.93) > 3.9 in acetone-d6 (ꢀr )
20.56) > 3.0 in 2-propanol-d8 (ꢀr ) 19.92). While the two diastereoisomers of complexes 2 and 4b
showed substantially the same tendency to self-aggregate, diastereoisomer (RRu, SN, SC)-7 showed a
remarkably higher aggregation tendency than the other one [(SRu, SN, SC)-7] throughout the entire
concentration range (1.4-178.0 mM) in CDCl3, indicating that a diastereoselective recognition process
is occurring in solution [|∆(∆G°296K)| ) 1.8 ( 0.5 kcal mol-1].
Recently, we reported preliminary results7 concerning the
remarkable tendency to self-aggregate of Noyori5 and amino
acidate8,9 half-sandwich ruthenium(II) complexes in both aprotic
solvents with low relative permittivity and protic solvents with
medium to high relative permittivity, including 2-propanol,
which is the solvent used in transfer hydrogenation. This is
particularly interesting since these catalysts are supposed to carry
out the activation process in the second coordination sphere
through a bifunctional mechanism.10 From our results it cannot
be excluded that the catalysis is carried out by a noncovalent
dimeric species.
Introduction
Noncovalent interactions occurring in the second coordination
sphere of transition-metal complexes may profoundly alter their
structure and reactivity. This is well-recognized for ionic
compounds1 and is also becoming evident for neutral ones. In
fact, interactions in the second coordination sphere have been
exploited to optimize the recognition process between the
substrate and the catalyst2 and to impart or improve the
enantioselectivity of the catalyst itself.3 It has also been
proposed4,5 that they may be solely responsible for the activation
process without the necessity of substrate-metal interactions
in analogy with enzymatic and organo catalysis.
The presence of functionalities suitable for undergoing
intermolecular noncovalent interactions, in the second coordina-
tion sphere, may also lead to self-aggregation of transition-metal
complexes.6,7 In our opinion, this aspect has been underestimated
given that it can have important consequences on the reactivity.
Here we report in full the results of a systematic PGSE
(pulsed field gradient spin-echo)11 NMR investigation on the
self-aggregation tendency of [RuCl(AA)(Arene)] compounds.
The nature of arene and amino acidate ligands and solvent has
(6) Burini, A.; Fackler, J. P., Jr.; Galassi, R.; Macchioni, A.; Omary, M.
A.; Rawashdeh-Omary, M. A.; Pietroni, B. R.; Sabatini, S.; Zuccaccia, C.
J. Am. Chem. Soc. 2002, 124, 4570. Macchioni, A.; Romani, A.; Zuccaccia,
C.; Guglielmetti, G.; Querci, C. Organometallics 2003, 22, 1526. Zuccaccia
D.; Sabatini S.; Bellachioma G.; Cardaci G.; Clot, E.; Macchioni A. Inorg.
Chem. 2003, 42, 5465. Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen,
M.-C.; Roberts, J. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448.
Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Zuccaccia, C.; Macchioni, A.
Dalton Trans. 2006, 1963.
* Corresponding author. E-mail: alceo@unipg.it. Fax: +39 075 5855598.
Phone: +39 075 5855579.
(1) Macchioni, A. Chem. ReV. 2005, 105, 2039.
(2) Das, S.; Incarvito, C. D.; Crabtree, R. H.; Brudvig, G. W. Science
2006, 312, 1941.
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R. Angew. Chem., Int. Ed. 2006, 45, 858. Roelfes, G.; Feringa, B. L. Angew.
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433.
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M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1446. Noyori, R.;
Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 7931.
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Chem. Lett. 1998, 6, 491. Katho´, AÅ .; Carmona, D.; Viguri, F.; Remacha,
C. D.; Kova´cs, J.; Joo´, F.; Oro, L. A. J. Organomet. Chem. 2000, 593-
594, 299.
10.1021/om060904e CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/04/2007

490 Organometallics, Vol. 26, No. 3, 2007
Ciancaleoni et al.
Scheme 1
tively, were obtained for complexes 2 and 4 due to the chirality
on the metal center.16 In the case of the reaction with (SC)-
proline, due to the presence of another stereogenic center, i.e.,
the nitrogen atom that always adopts the same configuration as
the asymmetric carbon of the amino acidate ligand,17 the two
diastereoisomers (SRu, SN, SC)-7 and (RRu, SN, SC)-7, respectively,
were obtained.
The equilibrium ratio of the two diasteroisomers depended
on the ligand. The (S)-configuration at the metal was adopted
by the major component of the mixtures, in all cases.17 This
was verified for complex 7 since the chemical shift of the N-H
proton is a good indicator of its orientation.18 In fact, when N-H
points toward the cymene, it resonates about 2-3 ppm at higher
frequency with respect to when it is directed toward the chloride.
PGSE NMR Measurements. The tendency of complexes
1-7 to self-aggregate in solution was investigated by means of
PGSE NMR diffusion measurements. Extensive investigations
were carried out for complex 2, which showed the highest
aggregation tendency, comparable only to that of the analogue
with glycine 1, which, on the other hand, did not dissolve in
most organic solvents. PGSE NMR measurements were then
carried out on the other complexes where the arene and amino
acidate ligands were varied with the aim of selectively turning
on and off the intermolecular interactions that were supposed
to be responsible for the aggregation and, consequently, allowing
them to be identified and quantified.
been varied in order to identify and quantify the noncovalent
interactions that are responsible for the self-aggregation. Nano-
aggregates have been observed in solvents with low relative
permittivity at elevated concentration mainly due to the estab-
lishment of a network of hydrogen bonds. Extended self-
aggregation has seldom been observed in organic compounds,12-14
and the results presented here are a novelty for transition-metal
complexes.15
Using the PGSE NMR measurements, the translational self-
diffusion coefficient (Dt) of the species present in solution was
determined. The latter allowed the hydrodynamic radius (rH)
of the diffusing species to be evaluated by taking advantage of
the Stokes-Einstein equation, eq 1:
kT
cπηrH
Dt )
(1)
Results and Discussion
where k is the Boltzmann constant, T is the temperature, c is a
numerical factor, and η is the solution viscosity. The c factor
substantially depends on the size of the diffusing species; the
correct evaluation is particularly critical for medium- and small-
sized molecules, for which c differs significantly from both 4
(slip boundary condition) and 6 (stick boundary conditions) and
when a large variation of the average dimensions for a given
solute occurs on changing either solvent or concentration.18 This
is exactly the case reported here (Supporting Information), in
that complexes passed from mononuclear species to nano-
aggregates depending on the ligands, solvent, and concentration
(Vide infra). 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 and the van der Waals
volume (VvdW), was derived in order to estimate the average
nuclearity of the noncovalent adduct. For large aggregates (VH
> 3VvdW), N was calculated by the [(VH - VINT)/VvdW] ratio,
Synthesis. Complexes 1-7 (Scheme 1) were synthesized by
the reaction of a suitable amino acid with an appropriate [Ru2(η6-
arene)2Cl2(µ-Cl)2] dimer in MeOH in the presence of an
equivalent of t-BuOK. Starting from the (SC)-enantiopure amino
acid the two diastereoisomers (SRu, SC) and (RRu, SC), respec-
(10) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. ReV.
2004, 248, 2201. Mun˜iz, K. Angew. Chem., Int. Ed. 2005, 44, 6622. Samec,
J. S. M.; Ba¨ckvall, J.-E.; Andersson, P. G.; Brandt, P. Chem. Soc. ReV.
2006, 35, 237.
(11) Hahn, E. L. Phys. ReV. 1950, 80, 580-594. Stejskal, E. O; Tanner,
J. E. J. Chem. Phys. 1965, 42, 288. Stilbs, P. Prog. Nucl. Magn. Reson.
Spectrosc. 1987, 19, 1. Price, W. S. Concepts Magn. Reson. 1997, 9, 299.
Price, W. S. Concepts Magn. Reson. 1998, 10, 197. Johnson, C. S., Jr.
Prog. Nucl. Magn. Reson. Spectrosc. 1999, 34, 203. Valentini, M.; Ru¨egger,
H.; Pregosin, P. S. HelV. Chim. Acta 2001, 84, 2833. Binotti, B.; Macchioni,
A.; Zuccaccia, C.; Zuccaccia, D. Comments Inorg. Chem. 2002, 23, 417.
Macchioni, A. In PerspectiVes in Organometallic Chemistry; Screttas, C.
G., Steele B. R., Eds.; The Royal Society of Chemistry: Cambridge, 2003;
pp 196-207. Pregosin, P. S.; Martinez-Viviente, E.; Kumar, P. G. A. Dalton
Trans. 2003, 4007. Bagno, A.; Rastrelli, F.; Saielli, G. Prog. Nucl. Magn.
Reson. Spectrosc. 2005, 47, 41. Brand, T.; Cabrita, E. J.; Berger, S. Prog.
Nucl. Magn. Reson. Spectrosc. 2005, 46, 159. Cohen, Y.; Avram, L.; Frish,
L. Angew. Chem., Int. Ed. 2005, 44, 520-554. Pregosin, P. S.; Kumar, P.
G. A.; Ferna´ndez, I. Chem. ReV. 2005, 105, 2977.
(12) Kunimura, M.; Sakamoto, S.; Yamaguchi, K. Org. Lett. 2002, 4
(3), 347-350.
(13) (a) Jadzin, J.; Stockhausen, M.; Zywucki, B. J. Phys. Chem. 1987,
91, 754. (b) Ohta, T.; Nakahara, Y. S.; Hattori, K.; Furukawa, I. Chem.
Lett. 1998, 6, 491.
(14) Geringer M.; Gruber, H.; Sterk, H. J. Phys. Chem. 1991, 95, 2525.
(15) For self-aggregation of Ru surfactants: Bowers, J.; Danks, M. J.;
Duncan, W.; Heenan, R. K. Langmuir 2003, 19, 292. Bowers, J.; Amos,
K. E.; Duncan, W.; Heenan, R. K. Langmuir 2005, 21, 5696. Domy´nguez-
Gutierrez, D.; Surtchev, M.; Eiser, E.; Elsevier, C. J. Nano Lett. 2006, 6,
145.
(16) Brunner, H.; Henning, F.; Zabel, M. Z. Anorg. Allg. Chem. 2004,
630, 91, and references therein. Brunner, H.; Zwack, T.; Zabel, M.; Beck,
W.; Boehm, A. Organometallics 2003, 22, 1741, and references therein.
Brunner, H.; Henning, F.; Weber, M.; Zabel, M.; Carmona, D.; Lahoz, F.
J. Synthesis 2003, 1091. For a review: Brunner, H. Angew. Chem., Int. Ed.
1999, 38, 1194. Brunner, H. Eur. J. Inorg. Chem. 2001, 905.
(17) (a) Carmona, D.; Vega, C.; Lahoz, F. J.; Atencio, R.; Oro, L. A.
Organometallics 2000, 19, 2273. (b) Carmona, D.; Lahoz, F. J.; Atencio,
R.; Oro, L. A.; Lamata, M. P.; Viguri, F.; San, Jose, E.; Vega, C.; Reyes,
J.; Joo, F.; Katho, A. Chem.-Eur. J. 1999, 5, 1544. (c) Carmona, D.;
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Amino-Acidate Half-Sandwich Ru(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 491
Table 1. Diffusion Coefficients (Dt, m2 s-1), Hydrodynamic
Radius (rH, Å), Hydrodynamic Volume (VH, Å3), Aggregation
Number (N), and Concentration (C, mM) for Compounds
(SRu,SC)-2 and (RRu,SC)-2 in Different Solvents (Er at 25 °C)
aggregation also depended on the nature of the solvent:
comparing the data for acetone-d6 with those of 2-propanol-d8,
which has about the same dielectric constant, it is clear that the
protic nature of the solvent decreases the tendency of the
ruthenium complexes to self-aggregate (Figure 1).
entry
solvent
1010 Dt
rH
VH
N
C
(SRu, SC)-2
7.95
5.12
3.38 11.1
2.93 12.8
2.07 16.2 17 908
1.46 20.8 37 858 133.0 124.9
12.4
8.67
6.69
4.89
4.43 10.4
3.04 13.0
The significant tendency of complex 2 to aggregate can be
rationalized considering that it can undergo several noncovalent
interactions. H-bond (HB) acceptors (chlorine atom and oxygen
atoms of the carboxylate groups), an HB donor (amino group),
and carbon atoms with a partial positive charge (aromatic C-H,
aliphatic C-H in R-position with respect to the carboxylate
group) are present in 2. Consequently, classical hydrogen
bonding and C-H‚‚‚X interactions19 can be established. In
addition, the arene ligand can be involved in π-π stacking
interactions. All these interactions have been observed in the
solid state of complexes [RuCl(S-Ala)(Arene)] (Arene )
mesitylene20 or benzene21). The case of [RuCl(S-Ala)(mesityl-
ene)], which differs from 2 in that it has a mesitylene ligand in
place of cymene, is shown in Figure 2.
Every Ru unit is surrounded by four other units and undergoes
NH2‚‚‚Cl (distance N‚‚‚Cl ) 3.34 Å) and NH2‚‚‚OdCO
(distance N‚‚‚O ) 2.96 Å) hydrogen bonding, CH‚‚‚Cl and
CH‚‚‚O interactions19 (distance Carene‚‚‚Cl ) 3.79 Å), and π-π
stacking between two arene moieties (mean slip angle between
the normal of one arene plane and the centroid vector ) 15°
and centroid to centroid distance ) 3.63 Å).22 The three-
dimensional repetition of all these interactions affords a network
that determines the supramolecular structure of these complexes.
The marked tendency of complex 2 to aggregate can be justified
by assuming that the above-mentioned intermolecular interac-
tions observed for [RuCl(S-Ala)(Arene)] complexes in the solid
state also occur in solution.
1
2
3
4
5
6
7
8
CDCl3 (4.81a)
5.5
7.7
686
2.9
0.3
1.7
5.7
11.1
39.3
CDCl3 (4.81a)
1927
5713
8702
7.8
21.6
32.3
64.2
CDCl3 (4.81a)
CDCl3 (4.81a)
CDCl3 (4.81a)
CDCl3 (4.81a)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
2-propanol-d8 (19.92)
2-propanol-d8 (19.92)
2-propanol-d8 (19.92)
4.7
6.0
7.5
9.8
445
883
1757
3906
4690
9288
1.9
3.7
7.2
15.0
17.9
37.4 106
48.6 165
2.5
3.0
2.9
3.0
4.3
5.8
2.8
3.5
3.7
0.09
3.9
10.1
27.7
40.2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
2.43 14.7 13 387
15.9
16.9
14.9
14.4
10.7
10.7
1.85
1.62
1.52
5.2
5.5
5.4
5.5
6.3
7.0
5.4
5.8
5.9
601
701
686
0.5
1.3
1.4
3.4
14.0
28b
4.8
26
713
1047
1408
667
830
873
36
(RRu′ SC)-2
8.18
5.49
3.84
3.30 11.4
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
CDCl3 (4.81a)
5.4
7.3
9.9
645
1596
4003
6206
2.7
5.0
15.3
23.4
59.0
0.2
1.3
3.3
5.9
20.7
65.1
0.08
2.8
8.5
20.0
25.1
61.5
CDCl3 (4.81a)
CDCl3 (4.81a)
CDCl3 (4.81a)
CDCl3 (4.81a)
2.14 15.8 16 397
1.53 20.0 33 510 118.0
CDCl3 (4.81a)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
CD2Cl2 (8.93)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
acetone-d6 (20.56)
2-propanol-d8 (19.92)
2-propanol-d8 (19.92)
2-propanol-d8 (19.92)
12.7
9.39
7.40
5.44
4.86
4.6
5.6
6.8
8.8
9.5
418
723
1340
2887
3599
7808
1.8
3.1
5.5
11.3
13.9
29.1
(b) Aggregation of Complexes 3-7. 1H-PGSE NMR
measurements were carried out for complexes 3-7 in order to
establish the relative importance of the three noncovalent
interactions described above. The results are shown in Table 2
(see Supporting Information for a complete list of the 1H-PGSE
NMR experiments). Before discussing in detail the effect of
ligand variation on the aggregation tendency of the complexes,
it is extremely important to note that the N value for complex
3c in CDCl3 (Table 2) and CD2Cl2 (Supporting Information)
was 1.1 and 1.0, respectively. Therefore, it is exclusively present
as a monomer. Due to the absence of N-H HB donors and
positively polarized aromatic C-Hs and to the presence of six
methyl groups in the arene that hinder the π-π interaction, only
the interactions between CH2 and Cl or O could occur in 3c.
Evidently, the latter interactions alone could not afford signifi-
cant aggregation. From a methodological point of view, the fact
that the aggregation number in 3c is equal to 1 indicates that
the hydrodynamic volume is a good descriptor of the van der
Waals volume for this class of compounds, ensuring that the
PGSE NMR measurements are accurate.
3.23 12.3
2.54 14.1 11 767
43.1 104
16.5
18.0
15.2
14.6
18.0
11.1
1.93
1.60
1.55
5.1
5.3
5.4
5.5
5.8
6.7
5.3
5.9
5.9
546
605
645
689
826
1267
606
856
843
2.3
2.6
2.7
2.9
3.5
5.2
2.6
3.6
3.5
0.2
0.7
1.1
2.2
7.2
26b
4.2
24
34
a ꢀr at 20 °C. Saturated solution.
b
where VINT represents the interstitial volume. The latter was
roughly estimated as described in the Experimental Section
assuming a face-centered cubic package of the monomers.
(a) Aggregation of Complex 2 as a Function of Solvent
1
and Concentration. H-PGSE NMR data for the two diaste-
reoisomers (SRu, SC)-2 and (RRu, SC)-2 are reported in Table 1.
The trends of N as a function of the concentration in different
solvents are illustrated in Figure 1. The two diastereoisomers
showed a similar and marked tendency to self-aggregate (Figure
1) that increased by increasing the concentration and decreasing
the relative permittivity (ꢀr) of the solvents. In CDCl3 at the
highest concentration investigated, complex (SRu, SC)-2 afforded
an aggregate with rH ) 20.8 Å and an aggregation number of
133 (Table 1, entry 6). Even at the lowest concentration
investigated, dimers or trimers were prevalently present (entries
1, 7, 14, 20, 23, 29, 36, and 42 in Table 1).
From the data reported in Table 2, it is clear that H-bonding
is the main aggregation motif between those illustrated in Figure
(19) (a) Brunner, H.; Weber, M.; Zabel, M.; Zwack, T. Angew. Chem.,
Int. Ed. 2003, 42, 1859. (b) Brunner, H.; Weber, M.; Zabel, M. Coord.
Chem. ReV. 2003, 242, 3.
(20) Carter, L. C.; Davies, D. L.; Duffy, K. T.; Fawcett, J.; Russell, D.
R. Acta Crystallogr., Sect. C 1994, C50, 1559.
(21) Sheldrick, W. S.; Heeb, S. Inorg Chim. Acta 1990, 168, 93.
(22) For hydrogen bond parameters see: (a) Steiner, T. Angew. Chem.,
Int. Ed. 2002, 41, 48. (b) Jeffrey, G. A. An Introduction to Hydrogen
Bonding; Oxford University Press: Oxford, 1997. For hydrogen bonds with
good metal-bonded halogen acceptors see: (c) Yap, G.; Rheingold, A. L.;
Das, P.; Crabtree, R. H. Inorg. Chem. 1995, 34, 3476. For π-π stacking
parameters see: (d) Janiak, C. J. J. Chem. Soc., Dalton Trans. 2000, 3885.
Hunter, C. A.; Sanders, J. K. J. Am. Chem. Soc. 1990, 112, 5525.
The level of aggregation at the same concentration was
reduced by about a third passing from CDCl3 (ꢀr ) 4.81) to
CD2Cl2 (ꢀr ) 8.93) and by about a tenth passing from CDCl3
(ꢀr ) 4.81) to acetone-d6 (ꢀr ) 20.56) (Figure 1). The level of

492 Organometallics, Vol. 26, No. 3, 2007
Ciancaleoni et al.
Figure 1. Dependence of the aggregation number (N) on the concentration of complex 2 [9 (SRu, SC)-2, b (RRu, SC)-2] in different solvents.
in the aggregation tendency that in 4a (entries 11-16 in Table
2) was comparable to 1 and 2, while substantially decreased in
4b (entries 17-24 in Table 2) and still more in 4c (entries 25,
26 in Table 2). In the second series, 1, 2, 4b, 5, and 6, the
arene was held constant, while the steric hindrance of the amino
acidate ligand gradually increased. The aggregation tendency
decreased as the steric hindrance increased: 1 (CH2) ≈ 2
(CHMe) > 5 (CMe2) ≈ 4b (CHt-Bu) > 6 (CPh2).
Another clear indication of the key role played by NH‚‚‚X
hydrogen bonds can be clearly seen by comparing the aggrega-
tion tendency of complexes 2, 7, and 3b, which bear NH2, NHR
and NMe2 moieties, respectively. Compound 2 showed a
remarkable tendency to aggregate as described above. Complex
7, which still has an N-H fragment, had a marked tendency to
aggregate that was strongly dependent on which diastereoisomer
was considered (Vide infra); the maximum N value was 29.0 at
71.1 mM. Complex 3b, which does not have an N-H moiety,
showed a reduced tendency to aggregate (N ) 2.7 at 114.4 mM).
The effect of changing the arene ligand in complexes 3a-c
was less important than in the 4a-c series. While 3c did not
Figure 2. Noncovalent interactions present in the X-ray single-
aggregate in CDCl3, 3a and 3b showed a comparable aggrega-
crystal structure of RuCl(S-Ala)(Mes) reported by Carter et al.20
tion tendency, and dimers appeared to be the predominant
species. The latter probably formed as a consequence of aromatic
C-H‚‚‚X interactions19 that may have been enforced by π-π
2. The highest level of aggregation was observed for complexes
stacking interactions.
1, 2, and 4, all bearing the NH2 moiety. Nevertheless, steric
effects play an important role in modulating the establishment
of HBs, as can be noted by comparing the aggregation tendency
of two series of compounds. All complexes of the 4a-c series
bear the tert-leucinate ligand, but the arene changes from
benzene to hexamethylbenzene. This caused a dramatic decrease
For complexes 2, 4, and 7, mixtures of two diastereoisomers,
which differed in the configuration on the metal center,19 were
observed in solution (Scheme 2). 1H-PGSE measurements
allowed the individual self-aggregation tendency of the two
diastereoisomers to be evaluated. It was found that the two

Amino-Acidate Half-Sandwich Ru(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 493
Table 2. Diffusion Coefficients (Dt, m2 s-1), Hydrodynamic
Radius (rH, Å), Hydrodynamic Volume (VH, Å3), Aggregation
Number (N), and Concentration (C, mM) for Compounds 1
and 3-7 in CDCl3 (Er ) 4.81 at 20 °C)
entry
compound
1010 Dt
rH
VH
N
C
1
2
3
4
5
6
7
8
1
3a
3a
3b
3b
3b
3b
3b
5.75
10.5
9.5
7.1
4.4
4.7
4.9
5.0
4.9
5.1
5.2
5.5
4.2
6.0
9.3
13.3
6.1
1506
366
440
478
525
502
556
596
686
6.5
1.9
2.2
1.9
2.1
2.0
2.2
2.4
2.7
1.5a
0.9
4.7a
1.8
8.93
8.86
8.74
7.87
7.40
6.51
10.2
6.98
4.18
2.79
6.86
4.29
2.79
7.56
7.60
4.49
3.80
7.91
7.65
4.71
4.01
11.7
11.7
8.37
7.32
5.37
3.22
8.37
7.61
5.97
4.59
1.98
7.70
7.54
4.05
3.06
1.36
12.5
18.6
45.6
58.1
114.4
0.5
0.74
3.62
15.2
0.46
2.33
9.4
9
3b
3c
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
317
896
1.1
3.9
(SRu, SC)-4a
(SRu, SC)-4a
(SRu, SC)-4a
(RRu, SC)-4a
(RRu, SC)-4a
(RRu, SC)-4a
(SRu, SC)-4b
(SRu, SC)-4b
(SRu, SC)-4b
(SRu, SC)-4b
(RRu, SC)-4b
(RRu, SC)-4b
(RRu, SC)-4b
(RRu, SC)-4b
(SRu,SC)-4c
(RRu,SC)-4c
5
3369
9877
928
3136
9877
720
13.4
37.6
4.0
12.6
37.6
2.6
2.8
9.5
13.1
2.3
2.7
8.4
11.3
1.5
1.5
2.3
2.3
4.4
11.8
2.2
2.7
9.08
Figure 3. Dependence of the aggregation number (N) on the
concentration (C) for the two diastereoisomers of 7 in CDCl3.
13.3
5.6
5.7
8.8
9.8
5.4
5.6
8.4
9.3
4.8
4.8
5.2
5.7
7.2
10.2
5.1
5.5
6.3
7.5
8.9
5.4
5.5
8.9
10.9
12.6
0.38
1.37
6.2
768
2806
3990
649
A possible explanation for this differential tendency of the
two diastereoisomers to aggregate can be found by looking at
their structures (Scheme 2). In fact, in (SRu, SN, SC)-7 the N-H
bond is oriented toward the chlorine atom and an N-H‚‚‚Cl-
Ru intramolecular hydrogen bond can be established, making
the N-H moiety less available for intermolecular interactions.
Indeed, the N-H‚‚‚Cl-Ru distance was found to be 2.83 Å in
the solid-state structure of (SRu,SN,SC)-[RuCl(Pro)(benzene)].23
Instead, in the (RRu, SN, SC)-7 diastereoisomer the N-H bond
points toward the cymene and is prone to interact with oxygen
or chlorine atoms of other complexes, forming intermolecular
aggregates.
10.5a
0.32
1.07
4.6
755
2447
3413
463
463
582
7.8a
0.9
0.8
1.6a
3.0
6
6
6
792
1557
4432
559
21.0
70
3.4
(SRu, SN, SC)-7
(SRu, SN, SC)-7
(SRu, SN, SC)-7
(SRu, SN, SC)-7
(SRu, SN, SC)-7
(RRu, SN, SC)-7
(RRu, SN, SC)-7
(RRu, SN, SC)-7
(RRu, SN, SC)-7
(RRu, SN, SC)-7
690
9.9
1068
1774
2903
663
4.1
6.7
10.6
2.6
2.8
10.7
19.0
29.0
34.4
116
178
1.4
The marked difference in the aggregation tendency of the
(SRu,SN,SC)-7 and (RRu,SN,SC)-7 diastereoisomers suggests that
a diastereoisomeric recognition process takes place in solution
that leads to the formation of homochiral adducts.24 This does
not seem to be the case for the (SRu,SC) and (RRu,SC) diastereo-
isomers of complexes with alaninate and tert-leucinate ligands,
which showed the same tendency to self-aggregate. In agreement
with these observations, the solid-state structures of Ru-arene
complexes bearing the alaninate ligands contain both diastereo-
isomers,20,21 while in the one with the prolinate ligand only one
[(SRu,SN,SC)] is present.23 The configuration on the nitrogen that
bears the functionality (N-H) is prevalently responsible for the
formation of intermolecular adducts, in order to obtain diaste-
reoselective self-aggregation and subsequent crystallization.25
Determination of the Thermodynamic Parameters of the
Aggregation Process. The equilibrium constant (K) and,
consequently, the standard variation of the free energy (∆G°)
for the aggregation process were determined for complexes 2,
3b, 4b, and 7 at 296 K. It was assumed that the aggregation
process is well-described by the Equal K (EK) self-aggregation
model.26 Schematizing the self-aggregation process as
702
3.9
2937
5407
8411
13.8
46.6
71.1
a Saturated solution.
Scheme 2
An-1 + A ) An
where A ) [RuCl(AA)(Arene)] and n g 2, the EK model
(23) Kraemer, R.; Polborn, K.; Wanjek, H.; Zahn, I.; Beck, W. Chem.
Ber. 1990, 123, 767.
diastereoisomers of the complexes with the alaninate and tert-
leucinate (4b) ligands (Scheme 2) showed substantially the same
tendency to aggregate. In contrast, the least abundant diastereo-
isomer of the complexes with prolinate [(RRu, SN, SC)-7] showed
a remarkably higher aggregation tendency than the other one
[(SRu, SN, SC)-7] (Figure 3).
(24) (a) Saraswathi, N. T.; Roy, S.; Vijayan, M. Acta Crystallogr., Sect.
B 2003, 59, 641. (b) Harvey, N. G.; Rose, P. L.; Mirajovsky, D.; Arnett, E.
M. J. Am. Chem. Soc. 1990, 112, 3547. (c) Okabayashi, H. F.; Makoto, I.;
O’Connor, C. J. Self-Assembly; Robinson, B. H., Ed.; IOS Press: Amster-
dam, 2003. (d) Hoffmann, F.; Stine, K. J.; Hu¨hnerfuss, H. J. Phys. Chem.
B 2005, 109, 240.
(25) Cooks, R. G.; Zhang, D.; Koch, K. J. Anal. Chem. 2001, 73, 3646.

494 Organometallics, Vol. 26, No. 3, 2007
Ciancaleoni et al.
of the (SRu, SN, SC)-7 and (RRu, SN, SC)-7 diastereoisomers (-3.4
and -5.2 kcal/mol, respectively) are rather different and reflect
their above-mentioned markedly different tendency to self-
aggregate.29 A more incisive consideration can be done by
comparing the ∆G° of (SRu, SN, SC)-7 and (RRu, SN, SC)-7 with
that of 2. The substitution of the H atom of the NH2 moiety
pointing toward cymene with the aliphatic chain of the proline
ring, i.e., passing from 2 to (SRu, SN, SC)-7, leads to a |∆(∆G°)|
of 3.7 kcal/mol. The substitution of the other NH2 proton that
points toward the chlorine, i.e., passing from 2 to (RRu, SN, SC)-
7, has a minor effect on the aggregation, leading to a |∆(∆G°)|
of 1.9 kcal/mol. Finally, the |∆(∆G°)| of 1.4 kcal/mol between
2 and 4b, which both bear the NH2 moiety, indicates that steric
effects can also play an important role.
The aggregation tendency of complex 2 was investigated in
CDCl3, CD2Cl2, acetone-d6, and 2-propanol-d8. The K and ∆G°
values reported in Table 3 clearly indicate that aggregation is
favored by a reduction of the relative permittivity of the solvent.
For the three aprotic solvents taken into account the following
trend was obtained for -∆G°(kcal/mol): 7.1 in CDCl3 (ꢀr )
4.81) > 5.6 in CD2Cl2 (ꢀr ) 8.93) > 3.9 in acetone-d6 (ꢀr )
20.56). This is in line with the fact that the main aggregation
motif is hydrogen bonding, which is known to be disfavored
by an increase in the solvent polarity.30 The observed decrease
of the ∆G° passing from acetone-d6 (∆G° ) 3.9 kcal/mol, ꢀr )
20.56) to 2-propanol-d8 (∆G° ) 3.0 kcal/mol, ꢀr ) 19.92), which
have almost the same polarity, is perfectly reasonable consider-
ing that the protic nature of the latter solvent makes it suitable
to undergo hydrogen bonding with a half-sandwich amino
acidate unit providing those functionalities that are responsible
for aggregation.
Figure 4. Dependence of N(N - 1) on the concentration for
complex 4b in CDCl3.
Table 3. Equilibrium Constants (K) and Free Energies of
the Aggregation Process (∆G°) for Compounds 2, 3b, 4b, 5,
and 7 in Different Solvents
solvent
(ꢀ at 25 °C)
10-2
(M-1
K
)
-∆G°
entry
compound
(kcal mol-1
)
1
2
3
4
5
6
7
8
2
2
2
2
3b
4b
CDCl3 (4.81a)
CD2Cl2 (8.93)
1700 ( 170
145 ( 14
7.8 ( 0.8
1.7 ( 0.2
7.1 ( 0.7
5.6 ( 0.6
3.9 ( 0.4
3.0 ( 0.3
acetone-d6 (20.56)
2-propanol-d8 (19.92)
CDCl3 (4.81a)
0.25 ( 0.02 1.9 ( 0.2
CDCl3 (4.81a)
156 ( 16
3.2 ( 0.3
76 ( 8
5.7 ( 0.6
3.4 ( 0.3
5.2 ( 0.5
(SRu, SN, SC)-7 CDCl3 (4.81a)
(RRu, SN, SC)-7 CDCl3 (4.81a)
a ꢀr at 20 °C.
assumes that (a) the entropy change of the equilibrium reactions
is constant and (b) the enthalpy change is independent of the
value of n. Under these assumptions, a single K describes the
system, and the concentration (C) can be written as
Conclusions
The intermolecular interactions responsible for the self-
aggregation of [RuCl(AA)(Arene)] complexes were identified
1
and quantified through H diffusion NMR measurements by
C ) [A] + 2[A2] + ... + i[Ai] + ... ) [A]/(1 - K[A])2 (1)
varying the properties of ligands and solvent. The complexes
showed a remarkable tendency to self-aggregate, forming
nanosized adducts under favorable conditions (solvents with low
relative permittivity, elevated concentration, little encumbered
ligands). A key role was played by the N-H functionality of
AA that allowed the establishment of intermolecular H-bonds.
When N-H was present, dimers (or higher aggregates) were
always predominant even at the lowest investigated concentra-
tion. The orientation of the N-H moiety also appeared to be
important and led to an interesting diastereoisomeric intermo-
lecular recognition process. This was clearly shown by the
different self-aggregation tendency of the two diastereoisomers
(SRu,SN,SC)-[RuCl(Pro)(p-cymene)] and (RRu,SN,SC)-[RuCl(Pro)-
(p-cymene)]. In addition, the former, having the N-H moiety
engaged in an intramolecular H-bond with the chloride, showed
a significantly smaller tendency to self-aggregate than the latter.
while the total concentration of aggregates (CA) can be written
as
CA ) [A] + [A2] + ... + [Ai] + ... ) [A]/(1 - K[A]) (2)
The aggregation number N can be expressed as the ratio C/CA.
By combining this definition of N with eqs 1 and 2 the following
equation is obtained:
N(N - 1) ) KC
(3)
Plotting N(N - 1), derived from PGSE NMR measurements,
versus C led to linear trends that were fitted with eq 3. Values
of the equilibrium constant were obtained from the slope of
the linear fit (Figure 4) (Supporting Information). Table 3
summarizes the results of the fits for different complexes. ∆G°
was estimated from the K values (Table 3).
Experimental Section
A comparison between the ∆G° values for 2 and 3b in CDCl3
(entries 1 and 5 in Table 3) allows the weight of the hydrogen
bonding involving the NH2 moiety to be determined. |∆(∆G°)|
is equal to 5.3 kcal/mol and is consistent with the energy of
two “classical” HBs in chloroform.27,28 ∆G° for the aggregation
All reagents were purchased from Sigma-Aldrich and used
without any further purification. [Ru(η6-arene)2Cl2]2 was prepared
(28) Yajima, T.; Maccarrone, G.; Takani, M.; Contino, A.; Arena, G.;
Takamido, R.; Hanaki, M.; Funahashi, Y.; Odani, A.; Yamauchi, O. Chem.-
Eur. J. 2003, 9, 3341.
(26) (a) Ts’O, P. O. P.; Melvin, I. S.; Olson, A. C. J. Am. Chem. Soc.
1963, 85, 1289. (b) Martin, R. B. Chem. ReV. 1996, 96, 3043, and references
therein.
(27) Rivas, J. C. M.; Salvagni, E.; de Rosales, R. T. M. Dalton Trans.
2003, 17, 3339.
(29) Hu¨nenberger, P. H.; Granwehr, J. K.; Aebischer, J.-N.; Ghoneim,
N.; Haselbach, E.; van Gunsteren, W. F. J. Am. Chem. Soc. 1997, 119,
7533.
(30) Reichardt, C. SolVents and SolVent Effect in Organic Chemistry;
Wiley-VCH: Weinheim, 2003.

Amino-Acidate Half-Sandwich Ru(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 495
according to Bennett et al.31 Compounds 1-7 were synthesized
according to the literature,32 using the standard Schlenk technique,
and fully characterized through one- and two-dimensional NMR
techniques. Solvents were freshly distilled (n-hexane with Na, Et2O
with Na/benzophenone, MeOH with CaH2, CH2Cl2 with P2O5) and
degassed, by many gas-pump-nitrogen cycles before use.
All complexes were characterized through 1H, 13C, 1H-COSY,
3H, NMe), 2.18 (d, 1H, 2J ) 14.8 Hz, H8). Anal. Calcd for C10H14-
ClNO2Ru: C, 37.92; H, 4.46; N, 4.42. Found: C, 38.0; H, 4.8; N,
4.1.
Synthesis of Complex 3b. The procedure was equivalent to that
1
described for complex 1. Yield: 61%. H NMR (CDCl3, 298 K,
400.13 MHz, J in Hz): δ 5.41 (d, 1H, 3J ) 5.9 Hz, H2), 5.38 (m,
3
2
2H), 5.33 (d, 1H, J ) 6.0 Hz), 3.58 (d, 1H, J ) 14.6 Hz, H8),
1
1
1H-NOESY, H,13C-HMQC NMR, and H,13C-HMBC NMR ex-
periments recorded on a Bruker DRX 400 spectrometer. Referencing
was relative to TMS. NMR samples were prepared by dissolving
a suitable amount of compound in 0.5 mL of solvent.
3
4.04 (m, 1H, NH), 3.14 (s, 3H, NMe2), 3.00 (sept, 1H, J ) 7.0
Hz, H6), 2.92 (s, 3H, NMe2), 2.43 (d, 1H, 2J ) 14.8 Hz, H8), 2.27
(s, 3H, H1), 1.36 (m, 6H, H7). Anal. Calcd for C14H22ClNO2Ru:
C, 45.10; H, 5.95; N, 3.76. Found: C, 46.3; H, 6.3; N, 3.5.
Synthesis of Complex 1. [RuCl2(p-cymene)]2 (0.100 g, 0.163
mmol), glycine (0.0244 g, 0.326 mmol), and potassium tert-butoxide
(0.0365 g, 0.326 mmol) were dissolved in the minimal amount of
methanol and stirred for 30 min. The volume of the deep red
solution was reduced, and dichloromethane was added. Potassium
chloride precipitated and was filtered off. Addition of diethyl ether
to the red solution caused the precipitation of the desired product.
The latter was filtered and dried under vacuum to give an orange
solid, which was stored under nitrogen. Yield: 70%. 1H NMR (2-
propanol-d8, 298 K, 400.13 MHz, J in Hz): δ 6.45 (m, 1H, NH),
Synthesis of Complex 3c. [RuCl2(hexamethylbenzene)]2 (0.100
g, 0.150 mmol), glycine (0.0309 g, 0.300 mmol), and potassium
tert-butoxide (0.0337 g, 0.300 mmol) were dissolved in the minimal
amount of methanol and stirred for 30 min. The volume of the
deep red solution was reduced, and dichloromethane was added.
Potassium chloride precipitated and was filtered off. Addition of
diethyl ether to the red solution caused the precipitation of the
desired product. The latter was filtered and dried under vacuum to
give an orange solid, which was stored under nitrogen. Yield: 70%.
1H NMR (CD2Cl2, 298 K, 400.13 MHz, J in Hz): δ 3.47 (d, 1H,
2J ) 14.4, H8), 2.90 (s, 3H, NMe2), 2.72 (s, 3H, NMe2), 2.28 (d,
2J ) 14.8, H8), 2.12 (s, 18H, C6Me6). Anal. Calcd for C16H26ClNO2-
Ru: C, 47.93; H, 6.54; N, 3.49. Found: C, 46.5; H, 7.0; N, 3.6.
3
3
3
5.70 (d, 1H, J ) 5.4), 5.65 (d, 1H, J ) 5.6), 5.51 (d, 1H, J )
3
5.7), 5.45 (d, 1H, J ) 5.5), 4.03 (m, 1H, NH), 3.08 (m, 2H, 8),
3
2.94 (sept, 1H, J6-7 ) 6.8, H6), 2.23 (s, 3H, H1), 1.35 (m, 6H,
H7). Anal. Calcd for C12H22ClNO2Ru: C, 41.80; H, 5.60; N, 4.06.
Found: C, 40.9; H, 5.8; N, 3.9.
Synthesis of Complex 4a. The procedure was equivalent to that
described for complex 3a. Yield: 80%. 1H NMR (acetone-d6, 298
K, 400.13 MHz, J in Hz) (SRu, SC)-4a: δ 6.87 (m, 1H, NH), 5.71
(s, 6H, C6H6), 3.05 (d, 3J ) 6.5, 1H, H8), 2.54 (m, 1H, NH), 1.04
Synthesis of Complex 2. The procedure was equivalent to that
1
described for complex 1. Yield: 75%. H NMR (CDCl3, 298 K,
1
(s, 9H, But). H NMR (acetone-d6, 298 K, 400.13 MHz, J in Hz)
(RRu, SC)-4a: δ 5.69 (s, 2H, C6H6), 5.60 (m, 0.3H, NH), 4.46 (m,
3
0.3H, NH), 3.08 (d, J ) 6.4, 0.3H, H8), 1.09 (s, 3H, But). Anal.
Calcd for C12H18ClNO2Ru: C, 41.80; H, 5.26; N, 4.06. Found: C,
42.3; H, 5.8; N, 3.8.
Synthesis of Complex 4b. The procedure was equivalent to that
1
described for complex 1. Yield: 75%. H NMR (2-propanol-d8,
298 K, 400.13 MHz, J in Hz) (SRu, SC)-4b: δ 7.01 (m, 1H, NH),
5.73 (d, 1H, 3J ) 6.0, H3), 5.62 (d, 1H, 3J ) 5.8, H2), 5.59 (d, 1H,
400.13 MHz, J in Hz), (SRu, SC)-2: δ 7.63 (m, 1H, NH), 5.73 (m,
3
3
3J ) 5.8, H4), 5.47 (m, 1.7H), 3.00 (dd, 1H, J ) 6.6, J ) 11.3,
3
2.4H), 5.60 (d, 1H, JH3-H4 ) 5.6, H3), 5.52 (m, 2.7H), 3.50 (m,
H8), 2.88 (m, 3.2H), 2.24 (s, 3H, H1), 1.32 (m, 8.4H), 1.13 (s, 9H,
1H, H8), 2.90 (m, 1.7H, H6), 2.52 (m, 1H, NH), 2.21 (s, 3H, H10),
3
3
But); (RRu, SC)-4b: δ 5.71 (d, 0.7H, J ) 5.6, H3), 5.66 (d, J )
3
1.43 (d, 3H, JH7-H6 ) 6.7, H7), 1.33 (m, 10.2H). 13C{1H} NMR
3
5.9, H3), 5.55 (d, 0.7H, J ) 5.5, H4), 5.47 (m, 1.7H), 5.24 (m,
0.7H, NH), 2.88 (m, 3.2H), 2.25 (s, 1.8H, H1), 1.32 (m, 8.4H),
(CDCl3, 298 K, 100.55 MHz): δ 182.5 (C9), 101.4 (C2), 96.1 (C5),
82.8 (C4), 81.2 (C3), 81.1 (C3), 80.5 (C4), 53.4 (C8), 31.4 (C6),
23.3 (C7), 18.8 (C10). 1H NMR (CDCl3, 298 K, 400.13 MHz, J in
Hz), (RRu, SC)-2: δ 5.95 (m, 0.7H, NH), 5.73 (m, 2.4H), 5.67 (d,
1.15 (s, 5.4H, But).
Synthesis of Complex 4c. The procedure was equivalent to that
1
described for complex 3c. Yield: 82%. H NMR (2-propanol-d8,
3
0.7H, JH3-H4 ) 5.2, H4), 5.52 (m, 2.7H), 3.69 (m, 0.7H, NH),
298 K, 400.13 MHz, J in Hz) (SRu, SC)-4c: δ 6.53 (m, 1H, NH),
3.15 (m, 1.5H), 2.88 (m, 1H, NH), 2.10 (s, 18H, C6Me6). 1H NMR
(2-propanol-d6, 298 K, 400.13 MHz, J in Hz) (RRu, SC)-4c: δ 4.40
(m, 0.5H, NH), 3.88 (m, 0.5H, NH), 3.15 (m, 1.5H), 2.21 (s, 6H,
C6Me6). Anal. Calcd for C18H30ClNO2Ru: C, 50.40; H, 7.05; N,
3.27. Found: C, 51.9; H, 8.0; N, 2.9.
3.30(m, 0.7H, H8), 2.90 (m, 1.7H, H6), 2.24 (s, 2.1H, H10), 1.47
3
(d, 2.1H, JH7-H6 ) 6.7, H7), 1.33 (m, 10.2H). 13C{1H} NMR
(CDCl3, 298 K, 100.55 MHz): δ 183.9 (C9), 101.3 (C2), 96.4 (C5),
83.1 (C4), 82.7 (C3), 81.0 (C3), 82.2 (C4), 51.8 (C8), 31.4 (C6),
21.6 (C7), 19.9 (C7), 18.7 (C10).
Synthesis of Complex 3a. [RuCl2(benzene)]2 (0.100 g, 0.200
mmol), N,N-dimethylglycine (0.0412 g, 0.400 mmol), and potassium
tert-butoxide (0.0448 g, 0.400 mmol) were dissolved in the minimal
amount of methanol and stirred for 30 min. The volume of the
deep red solution was reduced, and dichloromethane was added.
Potassium chloride precipitated and was filtered off. Addition of
diethyl ether to the red solution caused the precipitation of the
desired product. The latter was filtered and dried under vacuum to
give an orange solid, which was stored under nitrogen. Yield: 58%.
1H NMR (CDCl3, 298 K, 400.13 MHz, J in Hz): δ 5.40 (s, 6H,
C6H6), 3.32 (d, 1H, 2J ) 14.6 Hz, H8), 2.96 (s, 3H, NMe), 2,75 (s,
Synthesis of Complex 5. The procedure was equivalent to that
1
described for complex 1. Yield: 66%. H NMR (2-propanol-d8,
3
298 K, 400.13 MHz, J in Hz): δ 5.69 (d, 1H, J ) 5.7), 5.65 (m,
3
3
1H, NH), 5.62 (d, 1H, J ) 6.0), 5.51 (d, 1H, J ) 5.7), 5.42 (d,
1H, 3J ) 5.8), 3.45 (m, 1H, H8), 3.14 (d, 1H, 2J ) 10.6 Hz, NH),
3
2.89 (sept, 1H, J ) 6.9 Hz, H6), 2.21 (s, 3H, H1), 1.42 (s, 3H,
3
H10), 1.38 (s, 3H, H10), 1.34 (d, 3H, J ) 6.8 Hz, H7), 1.33(d,
3H, 3J ) 6.9 Hz, H7). Anal. Calcd for C14H22ClNO2Ru: C, 45.10;
H, 5.95; N, 3.76. Found: C, 47.1; H, 5.8; N, 3.95.
Synthesis of Complex 6. The procedure was equivalent to that
1
described for complex 1. Yield: 88%. H NMR (CDCl3, 298 K,
(31) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg.
Synth. 1982, 21, 74.
(32) (a) Dersnah, D. F.; Baird, M. C. J.Organomet. Chem. 1977, 127,
C55-C58. (b) Sheldrick, W. S.; Heeb, S. Inorg. Chim. Acta 1990, 168,
93.
400.13 MHz, J in Hz): δ 7.76 (m, 2H), 7.48 (m, 3H), 7.10 (m,
3
3H), 6.99 (m, 2H), 5.36 (d, 1H, J ) 6.5 Hz), 5.15 (m, 2H), 4.73
3
2
(d, 1H, J ) 6.5 Hz), 3.99 (d, 1H, J ) 10.6 Hz, NH), 2.49 (m,
1H, 6), 1.90 (m, 1H, NH), 1.64 (s, 3H, H1), 1.11 (d, 3H, 3J ) 6.2

496 Organometallics, Vol. 26, No. 3, 2007
Ciancaleoni et al.
3
Hz, H7), 1.07 (d, 3H, J ) 6.2 Hz, H7). Anal. Calcd for C12H22-
The methodology for treating data was described previously.18 All
van der Waals volumes was computed from the crystal structures
using the WebLab ViewerLite 4.0 software packages. The uncer-
tainity 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 ap-
proximately 3-4% in hydrodynamic radii and 10-15% in hydro-
dynamic volumes and aggregation numbers N.
Evaluation of N for Large Aggregates. N was calculated by
the [(VH - VINT)/ VvdW] ratio, where VINT represents the interstitial
volume. It was assumed that molecules had a spherical shape and
a face-centered cubic package. Under these assumptions the packing
density (P) (Voccupied/Vtotal) is 0.7405 for an infinite lattice and there
are N “octahedral” (Ocav) and 2N “tetrahedral” (Tcav) cavities in
the cell.35 While it is not possible to calculate the volume of these
cavities separately, the radius of the largest sphere that can fill the
two types of cavities (rOcav, rTcav) is known.35 From these radii we
deduced the edge and volume of the octahedron (Oinsc) and
tetrahedron (Tinsc) inscribed in the respective spheres. Finally, we
assumed that the ratio V(Tinsc)/V(Oinsc) (0.3210) was equal to the
ClNO2Ru: C, 41.80; H, 5.60; N, 4.06. Found: C, 40.9; H, 5.8; N,
3.9.
Synthesis of Complex 7. The procedure was equivalent to that
described for complex 1. H NMR (CD2Cl2, 298 K, 400.13 MHz,
1
J in Hz) (SRu, SC, SN)-7: δ 5.54 (m, 1.68H), 5.43 (m, 2H), 5.25 (d,
1H, 3J ) 5.7), 4.08 (m, 1H, NH), 3.90 (m, 1H), 3.52 (dd, 3J8-NH
)
3
17.7, J8-10 ) 8.7, H8), 3.12 (m, 1H), 2.88 (m, 1.34H), 2.23 (s,
3H, H1), 1.86 (m, 1.7H), 1.78 (m, 2.34H), 1.34 (m, 8H); (RRu, SC,
SN)-7: δ 8.00 (m, 0.34H, NH), 5.71 (d, 0.34H, 3J ) 5.7), 5.63 (d,
0.34H, 3J ) 5.5), 5.54 (m, 1.68H), 3.75 (m, 0.34H), 3.41 (m,
0.34H), 3.29 (m, 0.34H), 2.88 (m, 1.34H), 2.20 (s, 1H, H1), 1.86
(m, 1.7H), 1.78 (m, 2.34H), 1.34 (m, 8H).
NOE Measurements. The 1H-NOESY33 NMR spectra were
acquired by the standard three-pulse sequence or by the PFG
version.34 The number of transients and the number of data points
were chosen according to the sample concentration and the desired
final digital resolution. Semiquantitative spectra were acquired using
1
a 1 s relaxation delay and 800 ms mixing times. Quantitative H-
NOESY NMR experiments were carried out with a relaxation delay
of 10 s.
ratio V(Tcav)/V(Ocav). Since P ) 0.7405 ) NVvdW/[NVvdW
+
PGSE NMR Measurements. 1H NMR measurements were
performed by using the standard stimulated echo pulse sequence11
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
processed with a line broadening of 1.0 (1H) Hz. The semiloga-
rithmic 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.
NV(Ocav) + 2NV(Tcav)] ) VvdW/[VvdW + 1.6420V(Ocav)], it was
calculated that V(Ocav) ) 0.2134VvdW and V(Tcav) ) 0.06850VvdW
N was estimated by knowing V(Ocav) and V(Tcav) and by evaluating
.
the number of cavities through models.
Acknowledgment. We thank the Ministero dell’Istruzione,
dell’Universita` e della Ricerca (MIUR, Rome, Italy), Programma
di Rilevante Interesse Nazionale, Cofinanziamento 2004-2005
for support.
Supporting Information Available: 1H NMR spectra of new
compounds, complete data of PGSE NMR measurements (Table
S1), and dependence of N(N - 1) on the concentration for
complexes 2 (Figures S1-S4), 3b (Figure S5), 4b (Figure S6), 5
(Figure S7), (SRu, SN, SC)-7 (Figure S8), and (RRu, SN, SC)-7 (Figure
S9). This material is available free of charge via the Internet at
http://pubs.acs.org.
(33) Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. J. Chem. Phys.
1979, 71, 4546.
(34) Wagner, R.; Berger, S. J. Magn. Reson. A 1996, 123, 119.
(35) West, A. Solid State Chemistry and Its Applications; John Wiley &
Sons: New York, 1984.
OM060904E