Interionic structure of ion pairs and ion quadruples of half-sandwich ruthenium(II) salts bearing a-diimine ligands

3930

Organometallics 2007, 26, 3930-3946

Interionic Structure of Ion Pairs and Ion Quadruples of

Half-Sandwich Ruthenium(II) Salts Bearing r-Diimine Ligands

Daniele Zuccaccia,^†Gianfranco Bellachioma,^†Giuseppe Cardaci,^†Gianluca Ciancaleoni,^†

Cristiano Zuccaccia,^†Eric Clot,*^,‡and Alceo Macchioni*^,†

Dipartimento di Chimica, UniVersita` degli Studi di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy, and

Institut Charles Gerhardt UniVersite´ Montpellier 2 and CNRS, Case Courrier 1501,

Place Euge´ne Bataillon, 34095 Montpellier Cedex 5, France

ReceiVed April 2, 2007

The interionic structure of complexes [Ru(η⁶-Arene){(2-R-C₆H₄)NdC(Me)-C(Me)dN(2-R-C₆H₄)}-

Cl]X was investigated by an integrated experimental (PGSE diffusion and NOE NMR spectroscopy and

X-ray single-crystal studies) and theoretical (DFT and ONIOM calculations) approach. PGSE NMR

experiments indicated that ion pairing is the main aggregative process in CD₂Cl₂and solvents with higher

relative permittivity. They also showed that the tendency to ion pairing for isodielectric solvents is higher

when the latter are protic. NOE interionic contacts were observed in 2-propanol-d₈even for BARF^-

salts. Ion pairing was favored by more coordinating counterions and an increase in concentration. An

equilibrium between ion pairs and ion quadruples was observed by PGSE measurements in chloroform-d

and benzene-d₆. Such equilibrium is shifted toward ion quadruples by an increase in the concentration or

when least coordinating counterions are used. For small fluorinated counterions, NOE studies located

the anion in ion pairs above the plane containing the CdN imine moieties. ONIOM calculations found

that this anion-cation orientation was at least 35.9 kJ/mol lower in energy than a second orientation

with the anion close to cymene, which, in some cases, was observed in the solid state. NOE investigations

on complexes with BPh₄^-counterion did not allow a single orientation capable of explaining the observed

NOEs to be found. X-ray studies showed that one cation is surrounded by two anions. ONIOM calculations

found that these two anion-cation orientations have similar energies. X-ray and NOE NMR data strongly

-

suggest that ion quadruples with BPh₄anions are constituted by an alternation of cations and anions.

Interionic NOE intensities are almost invariant on passing from ion pairs to ion quadruples with small

fluorinated counterions. X-ray studies suggested at least four possible structures of ion quadruples differing

in both disposition and orientation of the ionic moieties. Three structures considered by ONIOM

calculations were similar in energy, but more stable than the separated ion pairs.

latter can be facilitated by the establishment of “inter-ion-pair”

hydrogen bonds⁶or π-π stacking interactions.^7,8Looking at

ion pairs as globally neutral species, the association of two ion

pairs to form an ion quadruple differs little from the association

of two neutral and polarized molecules to form a dimer.⁹

It would be extremely important to correlate the structure of

ion pairs and ion quadruples in solution with their reactivity.

In recent years the interionic structure of several transition-metal

complex ion pairs has been determined by means of NOE

(nuclear Overhauser effect)¹⁰and PGSE (pulsed field gradient

spin-echo)¹¹NMR experiments, but a clear correlation with

their reactivity has been found only in a few cases.^12,13On the

other hand, almost nothing is known about the interionic

structure of ion quadruples in solution.

Introduction

The ion-pairing¹phenomenon plays a crucial role in transi-

tion-metal chemistry.^2,3Many chemical reactions are mediated

by ionic (very often cationic) transition-metal complexes, and

a proper choice of counterion and solvent is critical in order to

maximize activity and selectivity.²A particularity of transition-

metal ion pairs is that the counterion can occupy one of the

coordinating sites or remain in the second coordination sphere,

affording inner-sphere ion pairs (ISIPs) or outer-sphere ion pairs

(OSIPs), respectively.²In favorable conditions, i.e., elevated

concentration in solvents with low relative permittivity, OSIPs

may aggregate, forming ion quadruples.^4,5The formation of the

* Corresponding authors. E-mail: clot@univ-montp2.fr; alceo@unipg.it.

^†Universita` degli Studi di Perugia.

Herein we report the interionic structure of ion pairs and ion

quadruples of [Ru(η⁶-Arene){(2-R-C₆H₄)NdC(Me)-C(Me)d

N(2-R-C₆H₄)}Cl]X complexes¹⁴investigated through an inte-

^‡Universite´ Montpellier 2.

(1) Marcus, Y.; Hefter, G. Chem. ReV. 2006, 106, 4585-4621.

(2) Macchioni, A. Chem. ReV. 2005, 105, 2039-2073, and references

therein.

(3) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391. Bochmann,

M. J. Organomet. Chem. 2004, 689, 3982.

(4) Beck, S.; Geyer, A.; Brintzinger, H.-H. Chem. Commun. 1999, 2477-

2478.

(5) Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M.-C.; Roberts, J.

A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448-1464. Song, F.;

Lancaster, S. J.; Cannon, R. D.; Schormann, M.; Humphrey, S. M.;

Zuccaccia, C.; Macchioni, A.; Bochmann, M. Organometallics 2005, 24,

1315-1328.

(6) Zuccaccia, D.; Macchioni, A. Organometallics 2005, 24, 3476-3486.

(7) Macchioni, A.; Romani, A.; Zuccaccia, C.; Guglielmetti, G.; Querci,

C. Organometallics 2003, 22, 1526. Zuccaccia, D.; Bellachioma, G.;

Cardaci, G.; Zuccaccia, C.; Macchioni, A. Dalton Trans. 2006, 1963.

(8) Hamidov, H.; Jeffery, J. C.; Lynam, J. M. Chem. Commun. 2004,

1364.

(9) Zuccaccia, D.; Clot, E.; Macchioni, A. New J. Chem. 2005, 29, 430-

433.

(10) Macchioni, A. Eur. J. Inorg. Chem. 2003, 195, and references

therein.

Publication on Web 06/23/2007

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3931

Scheme 1

anti isomer when X^-) BPh₄or the syn isomer when X^-

)

-

grated experimental and theoretical approach based on NOE

and PGSE NMR, X-ray, and DFT and ONIOM calculations.

This approach allowed an in-depth evaluation of the presence

and structure of ion pairs and ion quadruples in solution as a

function of the counterion and solvent, and the energetics of

ion quadruple formation from the association of two ion pairs.

BF₄^-, PF₆^-, or CF₃SO₃^-. Pure anti isomers with X^-) BF₄

,

-

PF₆^-, and CF₃SO₃and syn isomer with X^-) BPh₄were

-

synthesized through anion metathesis using AgX (X^-) BF₄

,

PF₆^-, CF₃SO₃^-) in methylene chloride and NaBPh₄salts in

methanol, respectively. Solutions of pure anti or syn isomers

were left for several days in all the solvents used. Even at

temperatures close to the solvent boiling points there was no

appreciable formation of the other isomer.

Results

Synthesis. [Ru(η⁶-Arene){(2-R-C₆H₄)NdC(Me)-C(Me)d

N(2-R-C₆H₄)}Cl]X complexes {1X, Arene ) p-cymene, R )

H, X ) BF₄^-, PF₆^-, BPh₄^-, and BARF^-[B(3,5-(CF₃)₂-

C₆H₃)₄^-]; 2X syn and anti, Arene ) p-cymene, R ) Me, X )

BF₄^-, and BPh₄^-; 3X syn and anti, Arene ) p-cymene, R )

Intramolecular Characterization in Solution and Confor-

mational Analysis of Cymene Rotation through NOE NMR

Experiments. All complexes 1-4 were characterized in solution

1

by H, ¹³C, and ¹⁹F NMR spectroscopies. Data are reported in

the Experimental Section. Numbering of carbon and proton

resonances is illustrated in Scheme 1. The higher symmetry of

the syn isomer makes the two sides of the N,N-ligand, 2/2′ and

3/3′ cymene protons, magnetically equivalent. This reduces the

number of observed NMR signals as well as the availability of

spatial reporters in the cationic moiety. As a consequence, the

results related to the anti isomer will have a dominant position

in the following descriptions of the arene orientations and

relative anion-cation positions.

From ¹H, ¹³C, ¹H-COSY, ¹H-NOESY, ¹H,¹³C-HMQC NMR,

and ¹H,¹³C-HMBC NMR spectroscopies all proton and carbon

resonances belonging to the different fragments were easily

grouped. On the other hand, the distinction between the

resonances of the two sides of the N,N and cymene ligands

and the determination of the preferred conformers of cymene

were two strictly interlocked and difficult issues. Nevertheless,

they were settled as detailed in the following sections.

Et, X ) BF₄^-, PF₆^-, BPh₄^-, and CF₃SO₃^-; 4X syn and anti,

-

Arene ) p-cymene, R ) i-Pr, X ) BF₄^-, PF₆^-, and BPh₄

;

5X, Arene ) benzene, R ) H, X ) PF₆and BPh₄^-} were

synthesized by the reaction of [Ru₂(η⁶-Arene)₂Cl₂(µ-Cl)₂] with

the appropriate ligand in (a) methanol at room temperature by

-

adding a large excess of NaBPh₄or (b) methylene chloride with

-

an equimolar quantity of MX (M ) Tl or Ag, X^-) BF₄

,

PF₆^-, CF₃SO₃^-; M ) Na, X^-) BARF^-).¹⁵

When R * H, the two anti or syn isomers illustrated in

Scheme 1, derived from the relative orientation of ortho-R-aryl

substituents, were observed in solution. The other possible syn

isomer, having R substituents directed toward the chlorine, never

formed. This was probably due to the steric repulsions between

R and Cl. The anti/syn ratio was always close to 2 independent

of the counterion nature and solvent utilized in the synthetic

procedures. Fractionated crystallizations of the anti/syn mixtures

from methylene chloride/n-hexane solutions afforded the pure

Complex 3BPh₄anti. As reported in Figure 1, the ¹H-

NOESY spectrum shows that the intensities of the dipolar

interactions between two cymene protons (labeled 2 and 3′ from

the intraligand assignment) and 11 or 11′ protons are about twice

as high as the analogous ones of the other two cymene protons

(2′ and 3). On the contrary, resonances 16 and 16′ (CH₂protons

of Et substituents) show that the dipolar interactions with 2′

and 3 were higher than with 2 and 3′. These observations are

consistent with the preferential presence of the two conformers

in solution reported in Figure 1, in which the cymene orients

the Me and i-Pr groups toward the 11′ and 11 protons or Vice

Versa, i.e., toward the least hindered regions of space. Since

the 11-2 and 11-3′, and 16-3 and 16-2′, NOEs have the

same intensities, the two conformers are equally populated.

(11) For reviews on the application of PGSE NMR to investigate

intermolecular interactions: 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. 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. Pregosin, P. S. Prog. Nucl. Magn. Reson. Spectrosc.

2006, 49, 261.

(12) Gruet, K.; Clot, E.; Eisenstein, O.; Lee, D. H.; Patel, B.; Macchioni,

A.; Crabtree, R. H. New J. Chem. 2003, 27, 80. Appelhans, L. N.; Zuccaccia,

D.; Kovacevic, A.; Chianese, A. R.; Miecznikowski, J. R.; Macchioni, A.;

Clot, E.; Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 2005, 127, 16299.

Binotti, B.; Carfagna, C.; Zuccaccia, C.; Macchioni, A. Chem. Commun.

2005, 92-94. Binotti, B.; Bellachioma, G.; Cardaci, G.; Carfagna, C.;

Zuccaccia, C.; Macchioni, A. Chem.-Eur. J. 2007, 13, 1570.

(13) Martinez-Viviente, E.; Pregosin, P. S. Inorg. Chem. 2003, 42, 2209.

Algarra, A. G.; Basallote, M. G.; Fernandez-Trujillo, M. J.; Llusar, R.;

Safont, V. S.; Vicent, C. Inorg. Chem. 2006, 45, 5774.

As far as the distinction between the resonances of the two

sides of the N,N ligand is concerned, the ¹H-NOESY spectrum

shows that the 14-17 dipolar interaction has a significantly

higher intensity than the 14′-17′ one (Figure S1). This suggests

that 17′ spends less time close to 14′ compared to the time 17

spends close to 14. This is probably due to the ability of 16′

protons to form a weak H-interaction with chlorine. The 17′

(14) Preliminary results were previously reported: Zuccaccia D.; Sabatini

S.; Bellachioma G.; Cardaci G.; Clot, E.; Macchioni A. Inorg. Chem. 2003,

42, 5465.

(15) Tom Dieck, H.; Kollvitz, W.; Kleinwachter, I. Organometallics

1986, 5, 1449.

3932 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

Figure 3. Four sections of the ¹H-NOESY NMR spectrum (400.13

MHz, 296 K, methylene chloride-d₂) of the complex 4BPh₄anti.

The F2 traces (direct dimension) relative to the 17′ and 17

resonances are reported at the bottom. * denotes the resonance of

a small amount of [Ru₂(η⁶-p-cymene)₂(µ-Cl₃)]BPh₄.

Figure 1. Two sections of the ¹H-NOESY NMR spectrum (400.13

MHz, 296 K, methylene chloride-d₂) of the complex 3BPh₄anti.

The F2 traces (direct dimension) relative to the 11 and 11′

resonances are reported at the bottom.

group has to be the one directed far away from chlorine (Figure

S2). Interestingly, 17′ also interacts dipolarly with 5 but with

an intensity about 4 times less than 17.

2-4BPh₄syn Complexes. Only weak dipolar interactions

between the protons of R substituents and 5 and isopropyl

protons of cymene are observed in the ¹H-NOESY NMR

spectra; in contrast, 2 and 3 protons show strong NOEs of

comparable intensities with R protons. This suggests that cymene

orients the alkylic groups almost parallel to the N arms in order

to avoid steric interactions with the R substituents.

NMR Interionic Structure in Solution. (a) PGSE Mea-

1

surements. H and ¹⁹F-PGSE NMR experiments were carried

out for complexes 1X and 3X in different solvents, with a

relative permittivity (ꢀ_r) ranging from 2.27 (benzene-d₆) to 32.66

(methanol-d₄), using tetrakis(trimethylsilyl)silane (TMSS) as

internal standard. PGSE measurements allow the translational

self-diffusion coefficients (D_t) for both cationic (D_t⁺) and anionic

(D_t^-) moieties to be determined (Table 1). From the measured

self-diffusion coefficients (D_t), the average hydrodynamic radius

(r_H) of the diffusing particles were derived by taking advantage

of the Stokes-Einstein equation, eq 1:

Figure 2. Two sections of the ¹H-NOESY NMR spectrum (400.13

MHz, 296 K, methylene chloride-d₂) of the complex 3BPh₄anti.

The F2 trace (direct dimension) relative to the 5 resonance is

reported at the bottom. * denotes the multiplet of proton 6

superimposed with that of 16.

methyl group is forced to orient far away from the plane that

contains N,N,Cl atoms, and the steric repulsion minimization

leads to the selection of the orientation where 17′ is more distant

from cymene as reported in Figure 2. The latter feeble criterion

for distinguishing R from R′ (based on the differential 14/17

and 14′/17′ NOE intensities) is strengthened by the observations

that both 16 and 17 protons afford appreciably stronger NOEs

with 5 cymene protons than do the 16′ and 17′ protons (Figure

2).

4BPh₄anti Complex. The dipolar interactions of 2 and 3′

with 11 or 11′ are more intense for this complex than the

analogous ones of the other two cymene protons 2′ and 3.

Different from 3BPh₄anti, the intensities of the 2′-17′ and

3-17 NOEs are twice as great as those of 2′-17 and 3-17′

(Figure 3). This indicates that the staggered conformation with

the i-Pr group oriented toward the 11 proton is more populated

than the other (Figure 3).

kT

cπηr_H

D_t)

(1)

where k is the Boltzman constant, T is the temperature, c is a

numerical factor, and η is the solution viscosity (Table 1). D_t

data were treated by taking all the methodological precautions

described in our recent paper.⁶From the average hydrodynamic

radii of the aggregates, assumed to be spherical, their volumes

(V_Hand V_H^-) were obtained.

+

In order to evaluate the average level of aggregation in

solution, V_H⁺and V_H^-can be contrasted with the hydrodynamic

volume of ion pairs (V_H^IP). We have previously shown that in

some cases^5,16the van der Waals volume (V_VdW) of ion pairs,

known from the solid state or from calculations, is a good

descriptor of V_H^IP, while in other cases, it underestimates V_H

.

IP

(16) Ciancaleoni, G.; Di Maio, I.; Zuccaccia, D.; Macchioni, A. Orga-

nometallics 2007, 26, 489. Claudio Pettinari, C.; Pettinari, R.; Marchetti,

F.; Macchioni, A.; Zuccaccia, D.; Skelton, B. W.; White, A. H. Inorg. Chem.

2007, 46, 896.

Once the preferential cymene conformer in solution is known,

the two R substituents can be easily distinguished. In fact, the

17 methyl group that shows the strongest NOE with the 5 Me

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3933

Table 1. Diffusion Coefficients (10¹⁰D_tm²s^-1), Hydrodynamic Radius (r_H, Å), c Factor, Hydrodynamic Volume (V_H, Å³), and

Aggregation Number (N) for Compounds 1 and 3 as a Function of Solvent and Concentration (C, mM)

+

-

D_t⁺

D_t^-

r_H

c⁺

r_H

c^-

V⁺

V^-

N⁺

N^-

C

1BF₄(V_H⁰) 546)

1

2

3

4

5

6

7

chloroform-d

CD₂Cl₂

7.38

6.40

10.8

10.2

10.1

9.8

7.41

6.76

13.5

11.1

10.8

10.2

24.0

5.66

5.93

5.12

5.22

5.34

5.36

5.47

5.3

5.4

5.3

5.4

5.3

5.63

5.68

4.30

4.93

5.04

5.17

3.48

5.3

5.1

5.3

4.5

759

873

567

595

637

645

685

747

767

333

501

536

578

176

1.4

1.6

1.0

1.1

1.2

1.3

1.4

0.6

0.9

1.0

1.1

0.3

30.6

50.0

0.08

1.0

1.3

10.0

5.0

CD₂Cl₂

acetone-d₆

12.9

1PF₆(V_H⁰) 566)

8

9

benzene-d₆

CD₂Cl₂

6.89

6.82

6.46

5.45

4.28

11.6

10.9

28.0

21.0

17.8

7.54

14.8

5.28

5.48

6.12

6.52

5.13

5.36

5.11

5.26

5.55

5.62

5.93

5.05

5.2

5.3

5.4

5.5

5.3

5.4

5.2

5.3

5.4

5.1

5.32

5.46

5.88

6.48

4.72

5.00

3.17

3.14

3.7

5.2

5.3

5.4

5.5

5.2

5.3

4.2

4.3

4.6

4.7

5.3

4.1

613

690

959

1160

565

645

559

610

716

744

873

540

630

681

851

1139

440

523

133

130

210

228

720

137

1.1

1.2

1.7

2.1

1.0

1.1

1.0

1.1

1.3

1.5

1.0

1.1

1.2

1.5

2.0

0.8

0.9

0.2

0.4

1.3

0.2

0.13

5.0

38

85

0.12

3.0

0.019

0.45

18

62

30.1

2.6

6.41

5.19

4.24

10.4

9.96

14.0

13.3

12.1

10.9

10

11

12

13

14

15

16

17

18

19

CD₂Cl₂

acetone-d₆

chloroform-d

methanol-d₄

3.79

5.56

3.20

6.98

7.57

1BPh₄(V_H⁰) 936)

20

21

22

23

24

25

26

27

28

29

30

31

chloroform-d

CD₂Cl₂

acetone-d₆

6.11

5.96

10.8

9.79

9.14

8.46

7.85

7.62

6.08

6.09

10.5

10.0

9.28

8.56

7.95

7.74

15.7

14.3

13.8

12.7

6.72

6.80

5.5

5.3

5.4

5.5

5.3

5.4

6.68

5.5

5.3

5.4

5.5

5.1

5.2

1271

1317

533

693

792

869

877

904

634

716

743

804

1248

1237

565

659

767

851

855

877

432

520

536

599

1.4

0.6

0.7

0.9

1.0

0.7

0.8

0.9

1.3

0.6

0.7

0.8

0.9

0.5

0.6

1.6

7.8

0.012

0.29

1.8

13.3

40.0

47.5

0.2

2.0

8

6.67

5.13

5.40

5.68

5.88

5.89

5.94

4.69

4.99

5.04

5.23

5.035.21 (5.21

5.49

5.75

5.92

5.94

6.00

5.33

5.55

5.62

5.77

13.3

12.6

12.0

11.1

31

1BARF (V_H⁰) 1313)

32

33

34

35

36

37

38

CD₂Cl₂

2-propanol-d₈

acetone-d₆

benzene-d₆

11.8

9.56

8.90

8.33

7.45

1.44

11.7

12.0

3.72

4.94

5.47

5.95

5.5

5.56

5.46

8.82

5.3

5.4

5.5

5.0

5.3

5.4

5.7

6.03

5.5

5.6

5.2

5.4

5.7

504

685

882

700

623

681

2835

918

969

1166

969

809

813

0.4

0.5

0.7

0.5

2.1

0.7

0.9

0.7

0.6

2.1

0.004

6.14

6.53

6.1

5.78

5.79

8.78

1.0

32.0

30.1

0.17

2.1

5.1

8.39

1.66

12.2

12.8

3.7414

2874

3BF₄anti (V_H⁰) 616)

39

40

41

42

43

44

45

46

47

48

benzene-d₆

chloroform-d

CD₂Cl₂

2-propanol-d₈

acetone-d₆

5.14

6.73

8.86

2.01

1.94

1.84

1.75

11.8

3.80

7.08

5.15

7.15

9.94

2.65

2.34

2.06

1.94

19.5

4.63

11.1

6.50

6.00

5.66

5.26

5.40

5.60

5.84

5.83

5.35

5.29

5.5

5.3

5.5

4.9

5.0

5.1

5.3

5.0

5.2

6.49

5.5

5.3

5.4

4.5

4.7

4.9

5.1

4.8

4.7

4.5

1150

904

759

609

659

735

833

830

641

620

1145

775

575

346

440

578

662

246

423

237

1.9

1.5

1.2

1.0

1.1

1.2

1.4

1.0

1.9

1.3

0.9

0.6

0.7

0.9

1.1

0.4

0.7

0.4

34.1

34.0

34.1

0.2

5.71

5.16

4.36

4.72

5.17

5.41

3.89

4.66

3.84

3.2

19.8

39.6^a

34.1

34.0

ethanol-d₆

methanol-d₄

3BPh₄anti (V_H⁰) 1006)

49

50

51

52

benzene-d₆

chloroform-d

CD₂Cl₂

5.87

4.90

7.83

6.00

4.85

8.03

12.6

6.56

7.64

6.13

5.80

5.5

5.7

5.6

5.5

6.46

7.68

6.02

5.12

5.5

5.7

5.5

5.3

1182

1867

964

1129

1897

913

1.2

1.9

1.0

0.8

1.1

1.9

0.9

0.6

0.4^a

31.0

43.0

31.8

acetone-d₆

10.8

817

562

3CF₃SO₃anti (V_H⁰) 646)

53

54

55

chloroform-d

2-propanol-d₈

methanol-d₄

6.17

1.74

7.08

6.41

1.94

10.6

6.33

5.49

5.28

5.5

5.1

6.12

5.14

3.98

5.5

5.0

4.6

1062

693

616

960

568

264

1.6

1.1

1.0

1.5

0.9

0.4

31.3

31.0

31.5

^aSaturated solution.

A much more reliable procedure for evaluating the level of

aggregation is based on comparing V_Hwith the hydrodynamic

volume at the lowest concentration value (V_H⁰).¹⁷It seems that

M) and/or by using solvents where it is supposed that the

molecules are less aggregated. Trends of V_Hversus C were

determined for 1BF₄(Table 1, entries 3-6), 1BPh₄(Table 1,

entries 22-27), and 1BARF (Table 1, entries 32-34) in CD₂-

Cl₂and for 1BPh₄in acetone-d₆(Table 1, entries 28-31). The

lowest measured value for the hydrodynamic volume of 1⁺was

504 Å³observed in a 0.004 mM solution of 1BARF in CD₂Cl₂

IP

V_VdWdescribes V_Hwell only if the molecules are nearly

spherical in shape and do not have inlets. One can determine

IP

0

whether V_VdWis a good descriptor of V_Hby measuring V_H

through diffusion measurements at low concentration (ca. 10^-5

3934 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

(Table 1, entry 32). The latter was taken as V_Hfor 1⁺. From

0

-

measurements in acetone-d₆, the V_Hfor BPh₄and BARF^-

counterions were determined to be 432 (Table 1, entry 28) and

0

809 Å³(Table 1, entry 36), respectively. V_Hfor small

counterions was considered equal to V_VdW(62 Å³for PF₆^-, 42

Å³for BF₄^-, and 72 Å³for CF₃SO₃^-). V_H⁰of 1X ion pairs was

derived by adding the volumes of the single ions (Table 1). It

0

can be seen that the determined V_Hof 1⁺is ca. 1.35 times

higher than V_VdW(372 Å³). Since 3⁺has a shape similar to that

0

of 1⁺, its V_H(574 Å³) was derived by scaling V_VdW(424 Å³)

by the same factor (1.35). V_H⁰of 3X ion pairs was obtained by

0

adding the volume of the counterion to V_Hof 3⁺(Table 1).

The ratios (N⁺and N^-, respectively) between the hydrody-

namic volume (V_H⁺and V_H^-, respectively) and V_H⁰for the ion

pairs are reported in Table 1. They represent a sort of

aggregation number.¹⁸Since a distribution of ionic species is

present in solution, the N⁺or N^-indicates the apparent average

aggregation number of the ionic moieties. For example, if both

of them are equal to 1 or 2, this means that ion pairs or ion

quadruples, i.e., “(Ru⁺X^-)₂”, are the predominant species in

solution, respectively. The interpretation of the N values is less

intuitive when there is a significant presence of odd aggregates

in solution, i.e., when N < 1 or N⁺* N^-, due to the different

volumes of the single ionic fragments. In such cases, N values

can be discussed considering the volumes of the free ions.

Theoretical N values for the free ions in our complexes are as

follows: N⁺) 0.92 and N^-) 0.08 for 1BF₄, N⁺) 0.89 and

N^-) 0.11 for 1PF₆, N⁺) 0.54 and N^-) 0.46 for 1BPh₄, N⁺

) 0.38 and N^-) 0.62 for 1BARF, N⁺) 0.93 and N^-) 0.07

for 3BF₄anti, N⁺) 0.57 and N^-) 0.43 for 3BPh₄anti, and

N⁺) 0.89 and N^-) 0.11 for 3CF₃SO₃anti. If N⁺and/or N^-

in Table 1 are larger than the previously indicated aggregation

number, then ion pairing and/or aggregation occurs. It should

be noted that the N values reported in Table 1 are lower than

those reported earlier¹⁴because, in that case, they were

Figure 4. Aggregation number for the cation (N⁺) and anion (N^-)

of complex 3BF₄anti as a function of the solvent relative

permittivity (ꢀ_r).

concerning the effect of solvent on aggregation is that, when ꢀ_r

is kept constant, the aggregation tendency increases in protic

solvents. This is clearly shown in Figure 4, where N⁺and N^-

for complex 3BF₄anti as a function of ꢀ_rare reported. The N⁺

values are identical (Table 1, entries 45 and 46), but the N^-

values are 1.1 and 0.4 in 2-propanol-d₈and acetone-d₆,

respectively, while the ꢀ_rvalues are almost the same.

Counterion Effect on Aggregation. The results of PGSE

NMR measurements performed for complexes 1X (X^-) BF₄

,

-

PF₆^-, BPh₄^-, and BARF^-) in CD₂Cl₂at similar concentrations

are reported in Table 1, entries 5, 13, 24, and 33. They indicate

that the ion-pairing tendency follows the order BF₄^-(N⁺) 1.2,

N^-) 1.0) ≈ PF₆^-(N⁺) 1.1, N^-) 0.9) > BPh₄^-(N⁺) 0.9,

N^-) 0.8) > BARF^-(N⁺) 0.5, N^-) 0.7). The effect of the

counterion on the tendency to form ion quadruples from ion

pairs can be deduced from the PGSE results for 3X anti in

calculated by the ratio of V_Hand V_VdW

.

chloroform-d [Table 1, entries 40, 50, and 53; BPh₄(N⁺

)

-

All of the measurements indicated a certain level of aggrega-

tion that was found to be quite insensitive to the size of the

ortho-R groups (compare entries 1 with 40 or 26 with 51 in

Table 1). The level of aggregation was, however, affected by

the choice of the solvent, counterion, and concentration.

Solvent Effect on Aggregation. The tendency to aggregate

for all complexes decreases as ꢀ_rincreases. In solvents that have

a ꢀ_rhigher than that of chloroform-d, N⁺and N^-are very often

less than 1 and, consequently, free ions and ion pairs are the

predominant species. In chloroform-d (Table 1, entries 1-2,

18, 20-21, 40, 50, and 53) and benzene-d₆(Table 1, entries

8-11, 38, 39, and 49), N⁺and N^-assume the same values that

significantly exceed 1, which clearly indicates that ion pairs

associate forming ion quadruples. In 2-propanol-d₈and acetone-

d₆, having an intermediate values of ꢀ_r, the complexes with small

counterions show N⁺values that are slightly greater than 1

(Table 1, entries 7, 14-17, 42-45, 54), while the N^-values

are less than 1. It is difficult to say if this is due to a partial

formation of “Ru₂X⁺” ion triples or to the hydrodynamic

properties of such solvents. Perhaps, the most important finding

1.9, N^-) 1.9) > CF₃SO₃^-(N⁺) 1.6, N^-) 1.5) ≈ BF₄^-(N⁺

) 1.5, N^-) 1.3)] and 1X in benzene-d₆[Table 1, entries 9

and 38; BARF^-(N⁺) 2.1, N^-) 2.1) > PF₆(N⁺) 1.2, N^-

-

) 1.2)]. For both complexes the least coordinating counterions

favored the formation of ion quadruples.

Concentration Effect on Aggregation. As expected, the

aggregation tendency increases with the concentration, but the

nature of the counterion and solvent are critical. For instance,

-

complexes with small counterions (BF₄^-, PF₆^-, and CF₃SO₃

)

in CD₂Cl₂afford complete ion pairing already at ca. 1 mM

(Table 1, entry 4). In contrast, complex 1BPh₄leads to complete

ion pairing at ca. 15 mM (Figure 5, Table 1 entries 22-27),

while 1BARF never reaches complete ion pairing even at 32

mM (Table 1, entries 34). As stated before, complete ion pairing

is observed in chloroform-d and benzene-d₆even at the lowest

investigated concentration. An increase of concentration in such

solvents causes the aggregation of ion pairs into ion quadruples.

The case of complex 1PF₆in benzene-d₆is reported in Figure

5: complete formation of ion quadruples occurs at ca. 80 mM.

A comparison of the concentration trends in acetone-d₆and

2-propanol-d₈confirms that the latter has a greater tendency to

undergo ion pairing. This can be noted by looking at entries

14-17 and 42-45 in Table 1. While ion pairing is complete in

2-propanol-d₈at ca. 20 mM (Table 1, entry 44), in acetone-d₆

(Table 1, entry 16) it is only marginal at the same concentration.

(b) NOE Measurements. The relative anion-cation orienta-

tions in solution for complexes 1-4X were determined by

detecting dipolar interionic interactions in the ¹⁹F,¹H-HOESY

(17) Zuccaccia, D.; Pirondini, L.; Pinalli, R.; Dalcanale, E.; Macchioni,

A. J. Am. Chem. Soc. 2005, 127, 7025. Kang, H.; Facchetti, A.; Zhu, P.;

Jiang, H.; Yang, Y.; Cariati, E.; Righetto, S.; Ugo, R.; Zuccaccia, C.;

Macchioni, A.; Stern, C. L.; Liu, Z.; Ho, S.-T.; Marks, T. J. Angew. Chem.,

Int. Ed. 2005, 44, 7922. Menozzi, E.; Busi, M.; Massera, C.; Ugozzoli, F.;

Zuccaccia, D.; Macchioni, A.; Dalcanale, E. J. Org. Chem. 2006, 71, 2617.

(18) (a) Pochapsky, S. S.; Mo, H.; Pochapsky, T. J. Chem. Soc., Chem.

Commun. 1995, 2513. (b) Mo, H.; Pochapsky, T. J. Phys. Chem. B 1997,

101, 4485. (c) Zuccaccia, C.; Bellachioma, G.; Cardaci, G.; Macchioni, A.

Organometallics 2000, 19, 4663.

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3935

Figure 5. Aggregation number for the cation (N⁺) and anion (N^-) of complexes 1BPh₄in CD₂Cl₂(left) and 1PF₆in benzene-d₆(right) as

a function of the concentration (C).

(X^-) BF₄^-, PF₆^-, CF₃SO₃^-, BARF^-) and ¹H-NOESY (X^-)

Table 2. Relative NOE Intensities Determined by

Arbitrarily Fixing the Intensity of the NOE(s) between the

BPh₄^-) NMR spectra at room temperature (296 K). The

Anion Resonances (o-H in the case of BPh₄^-) and the Imine

following solvents differing in both relative permittivity (ꢀ_r) and

Methyls (8 and 8′) at 1

nature were taken into account: benzene-d₆(ꢀ_r^25°C) 2.27),

8/8′

16

17

11′

2/3

7/7′

5

chloroform-d (ꢀ_r^20°C) 4.81), methylene chloride-d₂(ꢀ_r^25°C

8.93), isopropanol-d₈(ꢀ_r^25°C) 19.92), acetone-d₆(ꢀ_r^25°C

)

1

2

3

4

5

6

7

3BF₄anti^a

3BF₄anti^b

3BF₄syn^b

1

1.23 0.46 1.78 0.17 0.10 0.25

1.50 0.76 1.68 0.51 0.16 0.58

20.56), ethanol-d₆(ꢀ_r^25°C) 24.55), methanol-d₄(ꢀ_r^25°C) 32.66),

nitromethane-d₃(ꢀ_r^25°C) 35.94), and dimethylsulfoxide-d₆

(ꢀ_r^25°C) 46.45).

1.42 0.61

0.28 0.13 0.24

3CF₃SO₃anti^c

3BPh₄anti^c

3BPh₄anti^a

3BPh₄syn^c

0.97 1.38 1.39 0.60 0.46 0.75

0.85 0.54

0.79 0.49

1.33 0.72

d

1.47 0.38 0.70

1.92 0.44 0.92

1.60 0.40 1.11

Interionic NOEs were not detected in nitromethane-d₃. In all

other cases, anion-cation dipolar interactions were observed

with intensities that decreased as ꢀ_rincreased and, interestingly,

were higher for protic solvents when pairs of solvents with

similar ꢀ_rvalues were compared. In fact, NOEs were much more

intense in isopropanol-d₈(ꢀ_r^25°C) 19.92) than in acetone-d₆

b

c

^aIn CD₂Cl₂at 286 K. In benzene-d₆at 296 K. In chloroform-d at 296

d

K. Difficult to quantitatively evaluate due to the overlapping of cationic

and anionic resonances.

results: in CD₂Cl₂where there is a predominance of ion pairs

(Table 2, entry 1) and in benzene-d₆where ion quadruples are

predominant (Table 2, entry 2). In the former case, BF₄is

located above the plane containing the CdN imine moieties

and is shifted toward the less hindered N arm having the Et

group pointing toward the chlorine atom. Although BF₄is

confined in such a position by the two aryls of the N,N ligand

that are almost perpendicular to the plane bearing the CdN

groups, it can still interact weakly with cymene protons. Few

changes are observed in NOE intensities on passing from CD₂-

Cl₂(ion pairs, entry 1 in Table 2) to benzene-d₆(ion quadruples,

entry 2 in Table 2): NOEs with Et and cymene (all except 7/7′)

protons have a higher intensity in ion quadruples than in ion

pairs. Having normalized the NOE intensity between F nuclei

of the counterion and 8/8′ protons to 1, it is clear that in ion

quadruples there is an average shift of the counterions toward

cymene. In the syn isomer (Table 2, entry 3) the anion is located

in a more central position with respect to the N,N ligand that

now has equally hindered arms.

(ꢀ_r^25°C) 20.56);¹⁹they were observed in methanol-d₄(ꢀ_r^25°C

)

32.66) but were not detected in the almost isodielectric

-

nitromethane-d₃(ꢀ_r^25°C) 35.94).²⁰

The preferred relative anion-cation orientations that can be

deduced from the observed interionic NOEs depend little on

the R substituents and solvent, while they are affected greatly

by the nature of the counterion. In particular, two different

situations were observed for small (BF₄^-, PF₆^-, CF₃SO₃^-) and

large (BPh₄^-, BARF^-) counterions.

-

Interionic NOEs when X^-) BF₄^-, PF₆^-, or CF₃SO₃^-. For

anti compounds, strong contacts were observed between F atoms

of the counterion and 8, 8′, 11′, and R resonances. Weak contacts

were detected with all cymene resonances and with 12′ and 14,

while the anion did not show any interaction with R protons

pointing toward the chloride. The only difference for syn

compounds was the lack of interaction between X^-and 11.

A quantitative analysis of interionic NOE intensities was

carried out taking into account that the volumes of the cross-

peaks are proportional to (n_In_S/n_I+ n_S), where n_Iand n_Sare

the number of equivalent I and S nuclei, respectively.^10,21,22The

main results are reported in Table 2. In particular, two limiting

situations were considered for 3BF₄anti based on the PGSE

Very few differences were observed in the NOE intensities

for the various fluorinated anions, which indicates that the latter

are located in the same position. One of the few differences

-

was that while BF₄showed a stronger interaction with CH₂

(19) Evans, D. F.; Gardam, P. J. Phys. Chem. 1968, 72, 3281. Evans,

D. F.; Thomas, J.; Nadas, J. A.; Matesich, M. A. J. Phys. Chem. 1971, 75,

1714.

(20) Miller, R. C.; Fuoss, R. M. J. Phys. Chem. 1953, 75, 3076.

(21) Macchioni, A.; Magistrato, A.; Orabona, I.; Ruffo, F.; Ro¨thlisberger,

U.; Zuccaccia, C. New J. Chem. 2003, 27, 455.

than with CH₃of the Et′ substituent in 3 anti (Table 2, entry

-

1), the contrary was observed with CF₃SO₃(Table 2, entry

4). This is not necessarily due to a variation in the position of

the anion. It can be explained by considering that while the

head of the triflate anion (SO₃) is located in the same position

(22) Macura, S.; Ernst, R. R. Mol. Phys. 1980, 41, 95.

3936 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

ranging from 159.0° to 173.3° and from 156.9° to 173.0° for

N′- and N-aryl substituents, respectively. The latter form an

angle with the RuNN′ plane that ranges from 49.2° to 80.5°.

Cymene orientation was evaluated by measuring the C1-

cymene centroid-Ru-Cl torsion angle considering clockwise

angles with a positive sign: 1BPh₄, 31.7°; 2BF₄syn, 72.3°;

3BPh₄anti, 12.2°; and 4BPh₄anti, -11.2°. Compound 1BPh₄

exhibits an almost ideal staggered orientation of cymene with

a torsion angle that approaches 30°; the isopropyl group of

cymene is directed between the N and N′ arms. In 3BPh₄anti

and 4BPh₄anti an intermediate situation between staggered and

eclipsed cymene orientation is reached, probably due to the

increased steric interactions. The isopropyl group of cymene is

directed between the N and N′ arms, as in 1BPh₄. A completely

different situation occurs in 2BF₄syn: the isopropyl and methyl

cymene groups are oriented along the N,N-axis due to the steric

hindrance introduced by the ortho diimine substituents that are

both pointed toward the cymene.

Interionic Structure. Analogous to what is observed in

solution, the solid-state interionic structure is also strongly

affected by the nature of the anion. Some common features can

be found in the interionic structures of 1BPh₄, 3BPh₄anti, and

4BPh₄anti. Each cation is surrounded by two anions (Figure

8). One is positioned on the side of the cymene ligand and

orients a phenyl ring almost coplanarly with the cymene ring

to give π-π stacking interactions (A in Figure 8, left). The

angle between the two rings is 11.2° (1BPh₄), 16.1° (3BPh₄

anti), and 27.2° (4BPh₄anti), while the mean slip angle between

the normal of the cymene plane and the centroid vector of the

phenyl ring is 28.4° (1BPh₄), 11.3° (3BPh₄anti), and 12.8°

(4BPh₄anti), and the centroid to centroid distance is 3.94

(1BPh₄), 3.87 (3BPh₄anti), and 4.08 Å (4BPh₄anti). In addition,

there is a CH-π interaction between one hydrogen atom of

the cymene ring and another phenyl group of the anion. The

other anion is positioned on the side of the N,N ligand and shows

contacts between the three hydrogen atoms of the imine methyls

and the phenyl group (B in Figure 8, left). No significant

intercationic interactions are present. Consequently, there is an

alternation of cations and anions, with the latter bridging two

differently oriented cations.

In complex 2BF₄syn the cation is surrounded by four anions

(A, B, C, and D in Figure 8, right). Two of them are much

closer than the others (A, Ru-B 5.80 Å, and B, Ru-B 6.05 Å,

in Figure 8, right). One is adjacent to the cymene group on the

opposite side of the Cl (A in Figure 8, bottom). The fluorine

atoms of the anion moiety show interactions as short as 2.50 Å

with cymene hydrogen atoms. The other anion is located above

the NdC-CdN moiety (B in Figure 8, right) and shows several

short F‚‚‚H contacts.

Figure 6. ¹⁹F,¹H-HOESY NMR spectrum (376.65 MHz, 296 K,

2-propanol-d₈) of complex 1BARF. * denote the residues of

nondeuterated solvent.

as BF₄^-, its tail (CF₃) is pointed far away from the R-diimine

carbon plane toward the methyl group of the R substituent.

Interionic NOEs When X^-) BPh₄or BARF^-. These

-

anions afforded much stronger NOEs with cymene protons, as

can be seen from Table 2 (entries 5-7). The intensities of the

interionic NOEs with cymene protons are comparable or even

higher than those with 8, 8′, 11′, or Et. The quantitative analysis

of NOE intensities does not allow finding a single anion-cation

orientation that explains the data. However, there must be a

certain level of specific interactions because these large counter-

anions do not show any NOE with the R group pointing toward

the chlorine in the anti isomers. It is remarkable that interionic

NOEs were clearly observed in the ¹⁹F,¹H-HOESY spectrum

of 1BARF in isopropanol-d₈(Figure 6), since BARF^-is

considered as one of the weakest coordinating counterions and

is being used with greater frequency in organometallic chemistry

and homogeneous catalysis.

X-ray Studies. Intramolecular Results. The solid-state

structures of compounds 1BPh₄, 2BF₄syn, 3BPh₄anti, 4BPh₄

anti, and 5PF₆were determined through single-crystal X-ray

diffractometric investigation. All five complexes exhibit a three-

legged piano stool pseudo-octahedral geometry where the arene

occupies three adjacent sites of the octahedron. Intramolecular

bond lengths and angles fall in the typical ranges observed for

analogous compounds and will be discussed only briefly here.²³

As an example of the geometrical features, two ORTEP views

of 4BPh₄anti and 2BF₄syn cations are reported in Figure 7.

Cymene and 2-monosubstituted aryl moieties of the diimine

ligand are roughly coplanar, with angles between the two planes

In complex 5PF₆the closest anion is located as B in complex

2BF₄syn. Since no alkyl substituents are present in the aryl

rings, the counterion can approach the cation closely:²⁴the

Ru-P distance is equal to 5.23 Å, which is considerably shorter

than in 2BF₄syn (Ru-B 6.05 Å).

While an alternation of cations and anions is observed in the

solid state for 1BPh₄, 3BPh₄anti, and 4BPh₄anti, 2BF₄syn

and 5PF₆show anion/cation, cation/cation, and anion/anion

proximities. Figure 9 shows the different types of ion quadruples

that are present in the solid-state structures of 2BF₄syn and

5PF₆.

(24) Zuccaccia, C.; Macchioni, A.; Orabona, I.; Ruffo, F. Organometallics

1999, 18, 4367. Bellachioma, G.; Binotti, B.; Cardaci, G.; Carfagna, C.;

Macchioni, A.; Sabatini, S.; Zuccaccia, C. Inorg. Chim. Acta 2002, 350,

44. Binotti, B.; Carfagna, C.; Foresti, E.; Macchioni, A.; Sabatino, P.;

Zuccaccia, C.; Zuccaccia, D. J. Organomet. Chem. 2004, 689, 647.

(23) CCDC 634218-634222 contain the supplementary crystallographic

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/.

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3937

Figure 7. Two ORTEP (30% ellipsoid probability) views of 4⁺anti (top) and 2⁺syn (bottom) showing the different cymene orientations.

to 180° (3anti_180, δ ) 171.3°; 3syn_180, δ ) 172.5°). For

the anti isomer, the Me and i-Pr groups are slightly displaced

in the quadrants where no ethyl chain is present (Figure 10).

When Me points toward the Cl, the cymene is less symmetrically

positioned with δ amounting to ca. 25° in a staggered-like

conformation (3anti_00, δ ) 24.4°; 3syn_00, δ ) 25.8°).

Interestingly, in the anti isomer, the preferred conformation is

that with both cymene substituents close to the ethyl chains.

Attempts to locate the other conformer with Me and i-Pr in the

Figure 8. Anion orientations observed for 3BPh₄anti (left) and

less bulky quadrants failed, as 3anti_00 was always recovered.

2BF₄syn (bottom, right) in the solid state.

The piano stool geometry introduces a dissymmetry in the

orientation of the cymene ring plane with respect to the five-

In the two top structures in Figure 9, two counterions bridge

membered ring defined by Ru and the diimine ligand, as

the cationic units; intercationic interactions are present in the

illustrated by the values of the Ru-D1-C5 and D1-Ru-D2

remaining ones. Interestingly, two cooperative intercationic Ru-

angles (Table S1, D2 is the centroid of the five-membered Ru-

Cl‚‚‚H (of cymene moiety) interactions (2.81 Å) are present in

N-C-C-N ring). Consequently, for the phenyl rings on the

2BF₄syn (Figure 9, bottom left) with a Ru‚‚‚Ru distance equal

diimine ligands, the side opposite the Cl is closer to the cymene

to 6.84 Å. The closest intercationic contacts in 5PF₆occur

ring. In 3anti_180, the shortest contact H5‚‚‚H16 with the ethyl

chain is 2.48 Å. This value is significantly shorter than

H5‚‚‚H16 in 3anti_00 (3.142 Å) when Me points toward the

Cl. This is in agreement with the experimental observations of

a strong NOE in the former case and a weak one in the latter

(Figure 2).

between Cl and H protons of diimine Me groups (Cl‚‚‚H 2.79

Å) with a Ru‚‚‚Ru distance equal to 7.46 Å.

Theoretical Calculations. Geometry and Conformers of

3⁺. Syn and anti isomers of cation 3⁺were optimized at the

B3PW91 level (see Computational Details). In each case, three

orientations of the cymene ring were considered: Me toward

Cl (3anti_00, 3syn_00), Me opposite Cl (3anti_180, 3syn_180),

and cymene substituents along the N-N axis (3anti_90,

3syn_90). Figure 10 shows the corresponding geometries with

hydrogen atoms omitted for clarity (selected geometrical

parameters are reported in the Supporting Information). The syn

isomer with both ethyl chains toward the Cl is not searched, as

it was not seen experimentally; it is thought to be at high energy

due to steric repulsions between the ethyl groups and Cl.

The ethyl chain on the Cl side has a different conformation

than the one on the other side in the anti isomers. In the latter,

the ethyl chain lies slightly above the phenyl ring toward the

cymene (22.7°, 3anti_00; 17.7°, 3anti_180), whereas the ethyl

chain toward the Cl is perpendicular to the phenyl ring (98.8°,

3anti_00; 93°, 3anti_180). This orientation is due to a stabilizing

interaction that develops between one methylene proton and the

Cl atom, as illustrated by short H‚‚‚Cl contacts (2.488 Å,

3anti_00; 2.513 Å, 3anti_180), and to a minimization of the

steric repulsion.

The geometries of all the isomers are very similar and can

be described as that of a piano stool with cymene as the stool

and the two diimine N atoms and Cl as the legs. The torsional

angle δ ) Cl-Ru-D1-C5 describes the orientation of cymene

with respect to the plane bisecting the diimine ligand (D1 is

the centroid of the cymene benzene ring) and is independent of

the presence of one (anti) or two (syn) ethyl chains on the same

side. When the Me group points away from the Cl, δ is close

There are also several short H‚‚‚H contacts that can be used

to rationalize the NOE observations. For 3anti_180, the short

contact 3.23 Å is between H2 and H11′, together with the

contacts between H5 and both H11 (2.56 Å) and H16 (2.48 Å).

The H3‚‚‚H11 contact is longer (3.678 Å). For 3anti_00, there

are shorter contacts with H11 for H2 (2.854 Å) and H3 (3.022

3938 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

Figure 9. Ion quadruples observed in the solid state for 2BF₄syn and 5PF₆.

Figure 10. Optimized geometries of the various conformers for 3⁺anti and syn. Hydrogen atoms are omitted for clarity.

Table 3. Electronic Energy (E), Corrected Zero-Point Energy (E+ZPE), and Gibbs Free Energy (G) Values (kJ mol^-1) for the

Different Conformers of 3⁺Optimized at the B3PW91 Level

3anti_00

3anti_90

3anti_180

3syn_00

3syn_90

3syn_180

E

3.8

3.9

4.4

22.7

22.9

29.0

0.0

0.3

0.6

0.5

4.2

3.9

4.0

-3.5

-3.9

-5.2

E+ZPE

G

Å), in agreement with the larger NOE intensities that were

observed experimentally (Figure 1).

3anti_180 is very small (3.8 kJ mol^-1). The energy values are

also in agreement with the different orientations of the cymene

ring observed in the X-ray structures (3⁺anti and 2⁺syn); the

actual orientation of cymene is not an energetically costly

process, and crystal packing forces may easily overcome

preferred orientations.

Table 3 displays the relative energies of the various complexes

with 3anti_180 as a reference. Since no significant differences

are observed if the zero-point energy correction is included or

if the Gibbs free energy values are considered, only the

electronic energy values, E, are discussed. Contrary to what is

observed experimentally, the syn isomer, 3syn_180, is calculated

to be more stable than the anti isomer, 3anti_180, albeit by

only 3.5 kJ mol^-1. All the isomers have very similar energies,

and from the calculations there is no strongly preferred

conformer. The close energy values of the conformers with δ

) 90° (3anti_90 and 3syn_90) support a very easy cymene

rotation, as observed in NMR. This is also in agreement with

the observation of two conformers for 3⁺anti as shown in Figure

10; the calculated energy difference between 3anti_00 and

Anion-Dependent Ion Pair Structures. In order to gain

some insight into the structure and energetics of the ion pairs,

ONIOM calculations were carried out. The calculations were

limited to 3X anti in the conformation with Me opposite Cl,

for X^-) BF₄^-and BPh₄^-. For the cation, the Et, the Me, and

i-Pr on cymene were put in the low-level layer, whereas the

-

rest was kept in the high-level layer. For the anion, BF₄was

-

kept in the high-level layer, whereas the phenyl rings on BPh₄

were put in the low-level layer. The high-level layer was treated

at the B3PW91 level. To test the influence of different types of

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3939

Figure 11. ONIOM(B3PW91/HF) geometries of the ion pair structures with BF₄^-and BPh₄^-either on top of diimine or on top of cymene.

The atoms in the low-level partition (HF) are represented with a wire frame, while the atoms in the high-level layer (B3PW91) are represented

with balls and sticks.

Table 4. Relative Energies (kJ mol^-1) of the Different Ion Pairs Calculated at the ONIOM Level with Different Methods for

the Low-Level Layer (ONIOM(B3PW91/UFF) and ONIOM(B3PW91/HF)), Relative Energy (kJ mol^-1) at the B3PW91 Level on

the ONIOM(B3PW91/HF) Geometries with Inclusion of the Solvent Effect (CH₂Cl₂) as a Continuum PCM Model, Formation

Energy E_b(kJ mol^-1) of the Various Ion Pairs from PCM(B3PW91/CH₂Cl₂) Energy Calculations of the Ion Pair, the Cation,

and the Anion in the Geometry They Have in the Ion Pair

3BF₄anti_B

3BF₄anti_A

3BPh₄anti_B

3BPh₄anti_A

ONIOM(B3PW91/UFF)

ONIOM(B3PW91/HF)

PCM(B3PW91/CH₂Cl₂)

E_b(PCM/CH₂Cl₂)

0.0

35.9

62.2

37.2

51.7

0.0

-9.8

4.5

7.1

98.1

36.4

28.2

interactions on the structure and energetics of the ion pair, two

different methods were used to describe the low-level layer:

molecular mechanics with the UFF force field and Hartree-

Fock.

Only the two relative orientations of the anion and the cation

observed in the solid state were considered: anion on top of

the diimine ligand (3BF₄anti_B and 3BPh₄anti_B) and anion

on top of the cymene ring (3BF₄anti_A and 3BPh₄anti_A).

The geometries obtained with ONIOM(B3PW91/HF) calcula-

tions are shown in Figure 11, and the relative energies between

the ion pairs are reported in Table 4.

part the discrepancies between the respective trends both in the

NOE intensities and in the contact values. This is further

confirmed by the results from the ONIOM(B3PW91/UFF)

calculations on 3BF₄anti_B, where F‚‚‚H8 and F‚‚‚H8′ contacts

are still described at the DFT level, whereas the F‚‚‚H11′,

F‚‚‚H5, and F‚‚‚H16 contacts are treated only at the UFF level

and no correct description of the H-bonding interaction is

expected. The F‚‚‚H8 and F‚‚‚H8′ are shorter than in the

ONIOM(B3PW91/HF) calculations (1.973 Å, H8; 1.986 Å, H8′)

and longer for the other contacts (2.462 Å, H11′; 2.710 Å, H5;

2.390 Å, H16). As a consequence, the energy difference between

-

The ONIOM calculations clearly indicate a strongly preferred

ion pair structure with BF₄^-and two ion pairs of similar energy

with BPh₄^-. For BF₄^-, the ion pair structure with the anion

close to the diimine ligand and to the cymene methyl group

(3BF₄anti_B) is significantly more stable than the ion pair

structure with the anion sitting on top of the cymene ligand

(3BF₄anti_A). The energy difference is more pronounced at

the ONIOM(B3PW91/HF) level (62.2 kJ mol^-1) than at the

ONIOM(B3PW91/UFF) level (35.9 kJ mol^-1). Inclusion of the

solvent effects as a continuum still preserves 3BF₄anti_B as

the most stable ion pair structure. The PCM calculations allow

the formation energy of the ion pair to be estimated as the

difference between the ion pair energy and the energies of both

the anion and cation in the ion pair geometry (Table 4). Strictly

speaking, this is not a formation energy because the fragments

are not in their optimized geometry, but it gives a good estimate

of the energy range involved in the ion pair formation process.

In the case of 3BF₄anti_B, the value of 98.1 kJ mol^-1is in

agreement with the ion pair formation being mainly driven by

H-bonding interactions. As a matter of fact several short F‚‚‚H

contacts are present in the ion pair. The shortest contacts are

with the methyl groups on the diimine backbone (2.071 Å, H8;

2.074 Å, H8′), followed by similar contacts with H11′ (2.268

Å), H5 (2.357 Å), and H16 (2.306 Å). These values are in

qualitative agreement with the relative values for the NOE

intensities in the ¹⁹F,¹H-HOESY spectrum for 3BF₄anti (Table

2). In the present ONIOM(B3PW91/HF) calculations, the

F‚‚‚H interactions are described at the DFT level for the

F‚‚‚H8 and F‚‚‚H8′ contacts, whereas the F‚‚‚H contacts with

H11′, H5, and H16 are described at HF. This might explain in

the two ion pair structures with BF₄is smaller because there

is less stabilization through H-bonding interactions.

For the ion pair with BPh₄^-, the driving forces of the ion

pair formation are either π-stacking interactions between the

-

phenyl rings on BPh₄and cymene or C-H‚‚‚π interactions

-

between the diimine methyl groups and phenyl groups on BPh₄

.

For the ion pair 3BPh₄anti_B, the phenyl ring below the two

diimine methyl groups exhibits two short H‚‚‚centroid distances

of 3.305 Å (H8) and 3.368 Å (H8′), whereas the one facing the

diimine ligand and pointing toward the cymene exhibits a shorter

H‚‚‚centroid distance with H8′ (2.963 Å) than with H8 (3.553

Å) because of the asymmetry imposed by the ethyl chain. These

stacking interactions are all described at the HF level due to

the choice made for the partition. In the ONIOM(B3PW91/UFF)

calculations some of these contacts are shorter (2.84 Å for the

phenyl group below, 2.711 Å for the phenyl group facing)

because these stacking interactions are described by UFF.

The other ion pair with BPh₄^-on top of the cymene (3BPh₄

anti_A) is calculated to be of similar energy (Table 4) because

the ion pair stability is due to the same type of interactions.

The centroid-centroid distance between the two phenyl rings

-

that are almost parallel (cymene and BPh₄phenyl rings) is

4.4 Å, a value indicative of the presence of π-stacking

interactions. The H‚‚‚centroid contacts between H2 and H3 and

the phenyl ring of the side of the cymene ring are also rather

short (3.393 Å, H2; 3.422 Å, H3). The H5‚‚‚centroid contact

with the phenyl ring on top of the cymene is of the same order

of magnitude (3.407 Å). In the case of the ONIOM(B3PW91/

UFF) calculations, these contacts are shorter, with a centroid-

centroid distance of 3.686

Å and H2‚‚‚centroid and

3940 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

Figure 12. The three different structures of ion quadruples considered (Q1, Q2, and Q3) together with a schematic representation that

highlights the basic interaction patterns. On each schematic representation the shortest contact with H involving either F (anion) or Cl is

shown.

Table 5. B3PW91 Relative Energies (kJ mol^-1) in Gas Phase

H3‚‚‚centroid contacts of 2.912 and 3.174 Å, respectively. This

(E_GP) and in CH₂Cl₂(E_PCM) for the Three Quadrupoles, and

overestimation of the stacking interactions is the result of 3BPh₄

Formation Energy in Gas Phase (∆_fE_GP) and in CH₂Cl₂

anti_A being more stable than 3BPh₄anti_B in the ONIOM-

(B3PW91/UFF) calculations, while 3BPh₄anti_B is more stable

in the ONIOM(B3PW91/HF) calculations (Table 4). Neverthe-

less the energy differences are small and the two ion pair

structures are best considered as isoenergetic, in agreement with

(∆_fE_PCM

)

Q1

0.0

-47.2

-20.6

Q2

Q3

E_GP

21.2

9.7

-26.0

-10.9

23.0

3.8

-24.2

-16.8

E_PCM

∆_fE_GP

∆_fE_PCM

1

the H-NOESY experiments where contacts with cymene and

diimine protons were of similar intensities.

-

In contrast to the BF₄anion held in a specific position as

maintain this preferred interaction, as observed in the three

the result of cooperative H-bonding interactions with the fluorine

atoms, the BPh₄^-anion is engaged in less directional and weaker

stacking interactions and thus does not form a single ion pair

with a precise geometry. This is illustrated by the lower value

of the formation energy of the ion pair either at the diimine

(36.4 kJ mol^-1) or at the cymene (28.2 kJ mol^-1). Breaking the

ion pair with BF₄is thus expected to be energetically

demanding, and the formation of higher order aggregates may

need to maintain this favorable motif.

Structure and Energetics of the Quadrupoles. The PGSE

experiments indicated the presence of ion quadruples in solvent

with low relative permittivity such as chloroform and benzene.

To shed more light on the structure and energetics of the various

quadrupoles with small and fluorinated counterions, DFT

calculations were carried out. Due to the size of the system,

only the simplest complex, 5BF₄, was considered. Following

the observations from X-ray solid-state investigations, three

different structures of ion quadruples were considered (Figure

12): Q1 having two bridging BF₄^-anions (observed in the solid

state for 5PF₆, Figure 9 top right), Q2 containing Ru-Cl‚‚‚H-

C(cymene) intercationic interactions (observed in the solid state

for 2BF₄syn, Figure 9 bottom left), and Q3 containing Ru-

Cl‚‚‚H-CH₂(diimine) intercationic interactions (observed in the

solid state for 5PF₆, Figure 9 bottom right). The relative energies

of the quadrupoles in the gas phase and in CH₂Cl₂(PCM single-

point calculations on gas-phase-optimized geometries) are given

in Table 5.

optimized quadrupoles. The most stable situation, Q1, is

obtained when a unique BF₄is engaged in two such interac-

-

tions, leading to the expected cation-anion-cation sequence.

However, such a pattern develops at the expense of the second

anion that finds stabilizing interactions with the η⁶-C₆H₆and

diimine methyl groups slightly above the aforementioned tripole.

The two other quadrupoles preserve the preferred interactions

for each BF₄^-, thus leading to the anion-cation-cation-anion

sequence. The main difference between Q2 and Q3 lies in the

way the two cations interact. In Q2, the chlorine atom is

interacting with H atoms on the η⁶-C₆H₆group in a typical

inverted piano stool geometry. In Q3, the shortest Cl‚‚‚H

contacts are with the diimine methyl groups.

In the gas phase, Q1 is significantly more stable than the

other two quadrupoles, the latter two being of similar energy

(Table 5). Inclusion of solvent effects as a continuum reduces

the energy differences between the various quadrupoles, with

Q1 still the most stable structure. The energy differences are

small enough that the actual geometry in solution or in the solid

state may depend critically on the steric bulk of both the anion

(BF₄^-versus PF₆^-) and the cation (cymene versus benzene and

alkyl chain on phenyl diimine groups).

-

To evaluate the formation energy of the quadrupole, the ion

pair structure, IP, with the present simplified model was

optimized. The latter presents the basic interaction features

obtained for 3BF₄anti_B. The formation energy of the ion pair

was calculated to be 105.2 kJ mol^-1, a value similar to that

obtained for 3BF₄anti_B (98.1 kJ mol^-1). For the quadrupoles,

the formation energy from the neutral ion pair can be evaluated

in the gas phase and in CH₂Cl₂(Table 5). Interestingly, the

The calculations on the ion pairs show the strong interaction

-

of BF₄with both the diimine and cymene ligands. It is thus

expected that the formation of quadrupoles would tend to

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3941

quadrupole formation process is exothermic for all the isomers,

in the gas phase and in solvent. Thus there is an energetic driving

force toward higher order aggregation. The formation energy

of Q1 is significantly lowered in CH₂Cl₂compared to the gas-

phase values because both BF₄^-’s are interacting with both

cations and are partially shielded from the solvent in the

quadrupole. The solvent-anion interaction (even described as

a continuum) in IP is lost in Q1, thus leading to a lower

formation energy. The situation is slightly different for Q2 and

Q3 because the anion occupies a position that is similar in the

ion pair and in the quadrupole. The lowering of the formation

energy is thus less important. The inverted piano stool geometry

corresponds to a chlorine atom that is more buried inside the

quadrupole, and thus the formation energy is more strongly

influenced by the shift from the gas phase to CH₂Cl₂. Neverthe-

less, the formation energy values of the three quadrupoles are

sufficiently similar so as to exclude the preference for anyone

particular geometry. Depending on the actual nature of the

system, the three situations may occur; however a shift toward

Q2 and Q3 is anticipated when the steric bulk of the anion and/

or the cation is increased.

ring.²⁵Recently, Weller and co-workers showed that η⁶-

coordination can also occur for BARF^-.²⁶

1-3X OSIPs aggregate, in benzene-d₆and chloroform-d, to

form ion quadruples. Although a complete study could not be

done due to the insolubility of some salts, an interesting result

was obtained. The counterion effect on the formation of ion

quadruples from ion pairs is the opposite of what occurs on

the formation of ion pairs from free ions. In fact, the tendency

-

to form ion quadruples in chloroform-d and benzene-d₆is BPh₄

> CF₃SO₃≈ BF₄and BARF^-> PF₆^-, respectively. Large

counterions probably do not have the possibility to suitably dock

with the cation, and the resulting OSIPs have a higher dipolar

moment than those with small counterions. This high dipolar

moment may facilitate their aggregation to ion quadruples. In

agreement, the dipole moment of 3BF₄anti with the anion close

to the diimine ligand and 3BPh₄anti (in both A and B

orientations) was estimated to be 15 and 30 D, respectively,

from the PCM calculations on the ONIOM(B3PW91/HF)

geometries.

-

Anion-Cation Orientations in Ion Pairs. The benefit of

using an integrated approach to determine the anion-cation

orientation in 1-3X ion pairs is evident. As stated before, the

PGSE results allow the right combination of solvent and

concentration for having the predominance of ion pairs to be

determined. For example, this occurs for all complexes (except

1BARF) in CD₂Cl₂at ca. 10 mM. For complexes with small

and fluorinated counterions, the quantification of the NOEs

clearly indicated that the anion specifically “sits” over the Nd

C-CdN moiety of the diimine ligand (orientation B). X-ray

studies on 2BF₄syn and 5PF₆showed that this relative anion-

cation orientation is actually present in the solid state with

Ru‚‚‚B and Ru‚‚‚P distances equal to 6.06 and 5.23 Å,

respectively. But another orientation, that for 2BF₄syn has an

even shorter Ru‚‚‚B distance (5.81 Å), is also present with the

anion staying close to cymene (orientation A). Nevertheless,

ONIOM calculations indicated that the energy of orientation B

for 3BF₄anti (3BF₄anti_B in Table 4) is at least 30.0 kJ/mol

less than that of A, which validates the NMR findings.

A completely different situation was observed for 3BPh₄anti.

NOE quantitative analysis of a solution for which the PGSE

measurements indicated the predominance of ion pairs (Table

2, entry 47) did not allow finding a single anion-cation

orientation that explained all data. In the solid state two anion-

cation orientations were observed, one with the anion that

exhibits π-π stacking and CH-π interactions with cymene (B)

and the other with the anion close to the N,N ligand (A).

ONIOM calculations indicated that the two ion pairs having

the anion in orientations A and B had comparable energies,

supporting the idea that both of them are present in solution in

similar abundance.

Discussion

An integrated approach for investigating the aggregation of

transition-metal salts in solution appears to be particularly

promising due to the complementary information obtainable

from the various techniques. PGSE NMR measurements are

crucial for estimating the average size of the ionic adducts in

solution, thus identifying their nature, while NOE NMR

experiments allow the relative orientation(s) of the ionic moieties

within the adducts to be determined. From interionic X-ray

studies, the metric parameters of the interionic adduct can be

evaluated. Several anion cation orientations are present in the

solid state, and even though they may be absent in solution,

they surely provide a good starting point for comparative

considerations. The crucial link between the solid-state structure

of interionic adducts and that observed solution is given by

calculations (ONIOM or DFT).

The PGSE NMR experiments indicate the ionic form in which

complexes 1-3X are present in solution, thus affording the

initial information that is necessary to determine their interionic

structure. The aggregation tendency of complexes 1-3X

depends on the solvent, concentration, and counterion as

described in earlier. Not surprisingly, ion pairing is the main

aggregation process in CD₂Cl₂or in solVents with a ꢀ_rhigher

than that of CD₂Cl₂. However, in addition to the polarity, the

nature of the solvent is also important in determining the

aggregation process. This is clearly demonstrated by comparing

the PGSE results in isodielectric solvents acetone-d₆and

2-propanol-d₈for complex 3BF₄anti: the aggregation tendency

is higher in the latter. Although a little counterintuitive, this

behavior has been observed for NBu₄X salts through conductiv-

ity measurements.^19,20Both concentration and counterion effect

on ion pairing of complexes 1-3X are standard in that ion

pairing is favored by “more coordinating” conterions and an

increase of the concentration. In reality, it would be more correct

to speak about “ion-pairing tendency” than “coordinating

tendency”, since in the ion pairs of complexes 1-3X the

counterion stays on the second coordination sphere of the

saturated cations and, consequently, they are OSIPs. This

distinction is critical, especially for the position in the scale of

BPh₄^-that, when paired with an unsaturated cation, may afford

Structures of Ion Quadruples. As mentioned before, PGSE

NMR experiments indicate that OSIPs of 1-3X complexes

aggregate in low-polarity solvents such as chloroform-d and

benzene-d₆, affording ion quadruples. While all the experimental

data (X-ray and NOE NMR) strongly suggest that ion quad-

-

ruples with BPh₄anions are constituted by an alternation of

cations and anions, they do not provide an explanation for the

structure of ion quadruples with small and fluorinated counte-

rions. Interionic NOE intensities are almost invariant on passing

from ion pairs to ion quadruples, even if a small increase of

interionic NOEs with arene protons suggests an average shift

(25) Strauss, S. H. Chem. ReV. 1993, 93, 927.

(26) Douglas, T. M.; Molinos, E.; Brayshaw, S. K.; Weller, A. S.

Organometallics 2007, 26, 463-465.

-

ISIPs more easily than BF₄and PF₆through η²- or η⁶-

coordination and the possible subsequent transfer of an aryl

3942 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

cording to the literature procedures.^15,27RuCl₃‚3H₂O was purchased

from Sigma, and the ruthenium chlorine dimers were prepared

according to Benneth et al.²⁸

of the counterions toward cymene. X-ray studies suggest at least

four possible structures of ion quadruples (Figure 9) differing

in both disposition and orientation of the ionic moieties. Leaving

the counterion in the favorable B orientation, two ion pairs can

aggregate using the counterions as bridges (Ru⁺X^-X^-Ru⁺,

Figure 9 top) or through intercationic interactions (X^-Ru⁺Ru⁺X^-,

Figure 9 bottom). DFT calculations carried out on the simplest

complex (arene ) benzene, R ) H, and X^-) BF₄^-) show that

the aggregation of two ion pairs forming any type of the

considered ion quadruples is an exothermic process. Q1

(Ru⁺X^-X^-Ru⁺) ion quadruple is slightly favored in energy

(Table 5), but the energy differences are so small that they can

be overcome by introducing different arene or R substituents

or counterions. Moreover, the small increase of NOE intensities

of the BF₄^-/cymene protons on passing from ion pairs to ion

quadruples for 3BF₄anti suggests that Q1 is the most probable

structure for ion quadruples, at least in this complex. In fact,

due to the steric hindrance of ortho-Et substituents and cymene,

the association of two ion pairs on the side of the diimine ligand

bearing BF₄^-could cause a slight shift of the counterion toward

cymene.

The preparation of compounds was carried out under nitrogen

using standard Schlenk techniques. The compounds were prepared

using freshly distilled solvents (hexane with Na, Et₂O with Na/

benzophenone, MeOH with CaH₂, CH₂Cl₂and CH₃CN with P₂O₅).

The solvents were also degassed by many gas-pump-nitrogen

cycles before use.

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 deuterated solvent.

Synthesis of Complex 1BPh₄. Method a. A 0.537 g (0.877

mmol) sample of the dimer [Ru(η⁶-arene)Cl₂]₂and 0.404 g (1.754

mmol) of the ligand PhNdC(Me)-C(Me)dNPh were suspended in

5 mL of MeOH. The suspension was stirred for many hours (3-6)

at rt until the color of the solution changed from red-orange to

brown; a large excess of NaBPh₄(10 equiv) in 0.5 mL of MeOH

was added and a precipitate formed. The solution was filtered, and

the solid was washed with cold MeOH and n-hexane. Yield ) 96%.

Slow diffusion of ether into a CH₂Cl₂solution of the complexes

produced red crystals.

Conclusions

Method b. A 0.071 g (0.119 mmol) portion of 1BF₄was

dissolved in 5 mL of MeOH. A large excess of NaBPh₄(10 equiv)

in 0.5 mL of MeOH was added, and a precipitate formed. The

solution was filtered, and the solid was washed with cold MeOH

and n-hexane. Yield ) 96%. Slow diffusion of ether into a CH₂-

Cl₂solution of the complexes produced red crystals. The complex

was obtained with the same procedure but with the use of 1PF₆

instead of 1BF₄.

Herein we have shown how an integrated experimental and

theoretical approach has allowed an in-depth description of the

interionic structure of [Ru(η⁶-Arene){(2-R-C₆H₄)NdC(Me)-

C(Me)dN(2-R-C₆H₄)}Cl]X (1-5X) complexes to be obtained.

PGSE NMR experiments were of crucial importance for

understanding the ionic forms that were mainly present in

solution. Having found the correct conditions (solvent, coun-

terion, and concentration) needed to obtain the predominance

of ion pairs and ion quadruples, their structure was investigated

by combining NOE NMR experiments, X-ray studies, and

calculations (DFT and ONIOM).

¹H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J in Hz): δ 1.10 (d,

³J_H7-H6) 6.9, H7), 2.05 (s, H5), 2.20 (s, H8), 2.55 (sept., H6),

3

4.80 (d, J_H3-H2) 6.4, H3), 4.93 (d, J_H2-H3) 6.4, H2), 6.90 (t,

³J_p-m) 7.1, p), 7.04 (t, J_m-o) J_m-p)7.4, m and H11or H15),

3

7.34 (br, o), 7.56 (dd, ³J_H13-H14) 8.5, ⁴J_H13-H11) 2.0, H13), 7.65

In 1-5X ion pairs with small, fluorinated counterions, there

is a strong preference for the anion to locate above the plane

containing the CdN imine moieties. When ion pairs aggregate

forming ion quadruples (in chloroform-d and benzene-d₆), they

try to maintain such an anion-cation orientation. In cases of

small counterions and substituents, “Ru⁺X^-X^-Ru⁺” ion qua-

druples may form. Otherwise, “X^-Ru⁺Ru⁺X^-” ion quadruples,

stabilized by Ru-Cl‚‚‚H-C intercationic interactions, are

probably favored. In both cases, calculations indicated that the

formation of an ion quadruple from two ion pairs is an

exothermic process.

3

(t, J_H12-H13,H11) J_H12-H11) 8.0, H12), 7.71 (br, H11 or H15).

¹³C{¹H} NMR (CD₂Cl₂, 298 K): δ 20.7 (s, C8), 22.3 (s, C7), 31.4

(s, C6), 88.3 (s, C2), 88.5 (br, C3), 105.5 (s, C1), 110.8 (s, C4),

119.6 (s, C11 or C15), 122.1 (s, p), 122.4 (s, C11 or C15), 125.0

3

(q, J_m-B) 5.23, m), 129.8 8 (s, C12 or C14), 130.0 (s, C13),

130.9 (s, C12 or C14), 136.3 (s, o), 151.3 (s, C10), 164.4 (q, ¹J_C-B

) 49.2, C-ipso), 176.7 (s, C9). Anal. Calcd (%) for C₅₀H₅₀BClN₂-

Ru (826.3): C 72.68, H 6.10, N 3.39. Found: C 72.54, H 6.04, N

3.32.

Synthesis of Complex 1BF₄. Method c. A 0.537 g (0.877 mmol)

sample of the dimer [Ru(η⁶-arene)Cl₂]₂and 0.404 g (1.754 mmol)

of the ligand PhNdC(Me)-C(Me)dNPh were dissolved in 10 mL

of CH₂Cl₂, and 0.345 g of AgBF₄(1.754 mmol) was added under

a nitrogen atmosphere. The solution immediately changed from red

to brown, and a AgCl precipitate formed. The solution was filtered

and dried under vacuum, and a red solid was obtained. Yield )

90%. Slow diffusion of ether into a CH₂Cl₂solution of the

complexes produced red crystals.

-

When BPh₄counterion is used, two anion-cation orienta-

tions are almost isoenergetic in ion pairs. The anion is positioned

(a) on the side of the cymene ligand and orients a phenyl ring

almost coplanarly with the cymene ring to give π-π stacking

interactions or (b) on the side of the N,N ligand and shows

contacts between the three hydrogen atoms of the imine methyls

and the phenyl group. An alternation of anion and cation occurs

in ion quadruples.

Method d. A 0.100 g (0.877 mmol) amount of 1BPh₄was

dissolved in 5 mL of CH₂Cl₂. Then 0.345 g of AgBF₄(1.754 mmol)

was added under a nitrogen atmosphere, and a AgBPh₄precipitate

It should be noted that the tendency to form ion quadruples

from ion pairs increases when “least” coordinating counterions

are used. This leads to a higher charge separation in ion pairs

with a consequent enhanced molecular dipole moment and

aggregation tendency.

(27) (a) tom Dieck, H.; Kinzel, A. Angew. Chem. 1979, 91, 344. (b)

Diercks, R.; Stamp, L.; Kopf, J.; tom Dieck, H. Angew. Chem. 1984, 961,

891. (c) Wu, C.; Swift, H. J. Catal. 1972, 24, 510. (d) Naly, N. A. U.S.

Patent 3446862; Prepr. Am. Chem. Soc., DiV. Pet. Chem. 1972, 17, B95.

(e) tom Dieck, H.; Bruder, H. J. Chem. Soc., Chem. Commun. 1977, 24.

(f) Cotton F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;

Wiley-Interscience: New York, 1988; p 40.

Experimental Section

General Procedures. The synthesis of 1,4-diazabutadiene ligands

(2-R-C₆H₄)NdC(Me)-C(Me)dN(2-R-C₆H₄) was performed ac-

(28) Benneth, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,

233.

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3943

formed. The solution was filtered and dried under vacuum, obtaining

H11(s)), 7.92 (m, H11(a)). Anal. Calcd (%) for C₅₂H₅₄BClN₂Ru

(854.3): C 73.10, H 6.37, N 3.28. Found: C 73.18, H 6.31, N

3.23.

3BPh₄anti. ¹H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J values in

a red solid. Yield ) 98%. Slow diffusion of ether into a CH₂Cl₂

1

solution of the complexes produced red crystals. H NMR (CD₂-

Cl₂, 298 K, 400.13 MHz, J in Hz): δ 1.10 (d, ³J_H7-H6) 6.9, H7),

2.06 (s, H5), 2.37 (s, H8), 2.66 (sept., J_H6-H7) 6.9, H6), 4.94 (d,

3

Hz): δ 1.11 (d, J_H7′-H6) 6.96, H7′), 1.13 (d, J_H7-H6) 6.89,

H7), 1.21 (t, ³J_{H17′-H16′}) 7.51, H17′), 1.46 (t, ³J_17-16) 7.53, H17),

1.90 (s, H5), 2.13 (s, H8′), 2.16 (s, H8), 2.40 (m, H16 and H6),

3

³J_H3-H2) 6.4, H3), 4.97 (d, J_H2-H3) 6.4, H2), 7.43 (br, H11 or

3

4

H15), 7.52 (dd, J_H13-H12) 8.0, J_H13-H11) 1.2, H13), 7.65 (br,

H12 and H11 or H15). ¹⁹F NMR (CD₂Cl₂, 298 K): δ -151.8

(br,¹⁰BF₄), -151.9(br, ¹¹BF₄). Anal. Calcd (%) for C₂₆H₃₀BClF₄N₂-

Ru (593.9): C 52.58, H 5.09, N 4.72. Found: C 52.50, H 5.03, N

4.78.

2

3

2

2.50 (m, J_H16-H16) 14.8, J_H16-H17) 7.47, H16), 2.78 (m, J

_{H16′-H16′}) 14.8, ³J_{H16′-H17′}) 7.4, H16′), 3.00 (m, ²J_{H16′-H16′}) 14.8,

³J_{H16′-H17′}) 7.4, 16′), 4.81 (dd, J_H3′-H2′) 6.27, J_H3′-H5) 1.10,

3

4

3

4

H3′), 4.88 (dd, J_H2-H3) 6.21, J_H2-H6) 1.25, H2), 4.91 (dd,

4

3

³J_H3-H2) 6.19, J_H3-H5) 1.04, H3), 4.96 (dd, J_H2′-H3′) 6.28,

Synthesis of Complex 1PF₆. The 1PF₆complex was obtained

with the same procedures (c and d) as 1BF₄, but TlPF₆was used

⁴J_H2′-H6) 1.26, H2′), 6.84 (dd, J_{H11′-H12′}) 7.71, J_{H11′-H13′}

)

3

4

1.36, H11′), 6.90 (t, ³J_p-m) 7.32, p), 7.03, (t, ³J_m-o,p) 7.41, m),

7.31 (br, o), 7.49 (m, H12 and H12′), 7.54 (m, H13 and H13′),

7.59 (m, H14′), 7.61 (m, H14), 7.88 (dd, ³J_H11-H12) 7.90, ⁴J_H11-H13

) 1.32, H11). ¹³C{¹H} NMR (CD₂Cl₂, 298 K, 100.55 MHz): δ

13.7 (s, 17), 15.1 (s, 17′), 18.7 (s, C5), 21.1 (s, C8), 21.6 (s, C8′),

21.8 (s, C7′), 21.5 (s, C7), 23.2 (s, 16), 25.2 (s, 16′), 31.1 (s, C6),

85.2 (s, C2), 85.9 (s, C2′), 88.9 (s, C3′), 91.1 (s, C3), 103.8 (s,

C1), 114.8 (s, C4), 121.5 (s, C11), 122.1 (s, p), 122.2 (s, C11′),

126.0 (q, m), 127.6 (C12 or C12′), 128.0 (s, C12′ or C12), 129.0

(s, C14′), 129.8 (s, C13 or C13′), 130.1 (s, C13′ or C13), 131.6 (s,

1

instead of AgBF₄. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J in

3

Hz): δ 1.10 (d, J_H7-H6) 6.9, H7), 2.06 (s, H5), 2.37 (s, H8),

3

2.66 (sept., J_H6-H7) 6.9, H6), 4.94 (d, J_H3-H2) 6.4, H3), 4.97

3

(d, J_H2-H3) 6.4, H2), 7.43 (br, H11 or H15), 7.52 (dd, J_H13-H12

) 8.0, ⁴J_H13-H11) 1.2, H13), 7.65 (br, H12 and H11 or H15). ¹³C-

{¹H} NMR (CD₂Cl₂, 298 K): δ 20.7 (s, C8), 22.3 (s, C7), 31.4 (s,

C6), 88.3 (s, C2), 88.5 (br, C3), 105.5 (s, C1), 110.8 (s, C4), 119.6

(s, C11 or C15), 122.1 (s, p), 122.4 (s, C15 or C11), 125.0 (br, m),

129.8 (s, C12 or C14), 130.0 (s, C13), 130.9 (s, C14 or C12), 136.3

1

(s, o), 151.3 (s, C10), 164.4 (q, J_C-B) 49.2, C-ipso), 176.7 (s,

2

C14), 132.4 (s, C15′), 136.3 (q, J_o-B) 2.8, o), 137.2 (s, C15),

1

C9). ¹⁹F NMR (CD₂Cl₂, 298 K): δ -72.1 (d, J_FP) 711). ³¹P

1

149.2 (s, C10), 149.9 (s, C10′), 164.4 (q, J_C-B) 49.2, C-ipso),

NMR (CD₂Cl₂, 298 K): δ -143.2 (sept, ¹J_PF) 711). Anal. Calcd

(%) for C₂₆H₃₀ClF₆N₂PRu (652.0): C 47.89, H 4.64, N 4.30.

Found: C 47.81, H 4.68, N 4.25.

177.8 (s, C9), 178.7 (s, C9′).

3BPh₄syn. ¹H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J values in

3

Hz): δ 1.12 (d, J_H7-H6) 6.96, H7), 1.45 (t, J_17-16) 7.53, 17),

3

Synthesis of Complex 1BARF. Method c. A 0.075 g (0.123

mmol) sample of the dimer [Ru(η⁶-arene)Cl₂]₂and 0.116 g (0.492

mmol) of the ligand PhNdC(Me)-C(Me)dNPh were dissolved

in 5 mL of CH₂Cl₂. Then 0.229 g of NaBARF (0.258 mmol) was

added under a nitrogen atmosphere, and a NaCl precipitate formed.

The solution was filtered and then n-hexane was added and a brown

solid formed. The solution was filtered again, and the solid was

washed with n-hexane. Yield ) 85%. Slow diffusion of n-hexane

into a CH₂Cl₂solution of the complexes produced brown crystals.

¹H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J in Hz): δ 1.10 (d, ³J_H7-H6

1.80 (s, H5), 2.18 (s, H8), 2.43 (m, 16 and H6), 4.91 (d, J_{H3 -H2}

3

) 6.27, H3), 4.97 (d, J_H2-H3) 6.21, H2), 6.90 (t, J_p-m) 7.32,

p), 7.03, (t, ³J_m-o,p) 7.41, m), 7.31 (br, o), 7.48 (ddd, ³J_H12-H13

)

3

4

3

7.9, J_H12-H11) 7.8, J_{H12 -H14}) 1.5, H12), 7.53 (ddd, J_H13-H12

) 7.9, J_H13-H14) 7.2, J_H13-H11) 1.2, H13), 7.61 (dd, J_H14-H13

3

4

3

4

3

4

) 7.2, J_H14-H12) 1.5, H14), 7.71 (dd, J_H11-H12) 7.8, J_H11-H13

) 1.2, H11). ¹³C{¹H} NMR (CD₂Cl₂, 298 K, 100.55 MHz): δ 13.6

(s, 17), 18.6 (s, C5), 20.9 (s, C8), 22.1 (s, C7), 23.2 (s, 16), 31.1

(s, C6), 85.9 (s, C2), 89.9 (s, C3), 103.6 (s, C1), 115.0 (s, C4),

122.1 (s, C11 and p), 126.0 (q, m), 128.1 (s, C12), 129.0 (s, C14),

129.8 (s, C13), 132.1 (s, C15), 136.2 (q, ²J_o-B) 2.8, o), 149.3 (s,

3

) 7.2, H7), 2.14 (s, H5), 2.35 (s, H8), 2.57 (sept, J_H6-H7) 7.2,

1

H6), 4.86 (d, ³J_H3-H2) 6.3, H3), 4.98 (d, ³J_H2-H3) 6.2, H2), 7.09

C10), 164.6 (q, J_C-B) 49.2, C-ipso), 177.7 (s, C9). Anal. Calcd

3

(%) for C₅₄H₅₈BClN₂Ru (854.3): C 73.50, H 6.63, N 3.17. Found:

C 73.58, H 6.69, N 3.12.

(m, H11), 7.53 (t, J_H13-H14,H12) 7.3, H13), 7.60 (s, p), 7.65 (m,

H12, H14, H15), 7.76 (s, o). ¹⁹F NMR (CD₂Cl₂, 298 K): δ -62.71

(s, CF₃). Anal. Calcd (%) for C₅₈H₄₂BClF₂₄N₂Ru (1370.26): C

50.84, H 3.09, N 2.04. Found: C 50.88, H 3.01, N 2.09.

1

3BF₄anti. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J values in

Hz): δ 1.03 (d, ³J_H7-H6) 6.96, H7), 1.13 (d, ³J_H7′-H6) 6.89, H7′),

3

1.19 (t, J_{H17′-H16′}) 7.51, H17′), 1.46 (t, J_H17-H16) 7.53, H17),

Synthesis of Complex 2-5X (X ) BPh₄, BF₄, PF₆, CF₃SO₃,

BARF). Complexes 2-5X (X ) BPh₄, BF₄, PF₆, CF₃SO₃, BARF)

were obtained with the same procedures (a-d) for 1X by using

the appropriate ligand (2-R-C₆H₄)NdC(Me)-C(Me)dN(2-R-C₆H₄).

In those cases two isomers, anti and syn, were formed in a 2:1

ratio, and the yields ranged from 85% to 95%. Slow diffusion of

n-hexane or ether into a CH₂Cl₂solution of mixtures of the two

3

1.95 (s, H5), 2.27 (s, H8), 2.31 (s, H8′), 2.44 (sept, J_H6-H7(H7′)

)

6.96, H6), 2.65 (m, H16), 2.77 (m, ²J_{H16′-H16′}) 14.8, ³J_{H16′-H17′}

2

3

7.47, H16′), 3.03 (m, J_{H16′-H16′}) 14.8, J_{H16′-H17′}) 7.47, H16′),

3

4.92 (d, J_H2-H3) 6.27, H2), 4.98 (d, J_H3′-H2′) 6.21, H3), 5.03

(m, H3 and H2′), 7.36 (dd, ³J_{H11′-H12′}) 7.7, ⁴J_{H11′-H13′}) 1.4, H11′),

7.41 (ddd, ³J_H12-H11) ³J_H12-H13)7.8, ⁴J_H12-H14) 1.2, H12), 7.50

3

(m, H14′, H13, H13′, and H12′),7.60 (d, J_H14-H13) 7.5, H14),

isomers allowed the anti or syn isomers to be isolated when X^-

)

7.91 (dd, J_H11-H12) 7.8, J_H11-H13) 1.4, H11). ¹³C{¹H} NMR

(CD₂Cl₂, 298 K): δ 13.6 (s, 17), 15.1 (s, 17′), 18.2 (s, C5), 20.9

(s, C7), 21.5 (s, C7′), 21.6 (s, C8), 22.3 (s, C8′), 22.9 (s, 16), 25.2

(s, 16′), 30.8 (s, C6), 84.3 (s, C2), 85.2 (s, C2′), 88.8 (s, C3), 90.9

(s, C3′), 101.6 (s, C1), 114.6 (s, C4), 122.3 (s, C11′), 122.7 (s,

C11), 127.4 (C12), 127.6 (s, C12′), 128.9, 129.6, 129.3 (s,C14,

C13 and C13′), 130.9 (s, C14), 134.0 (s, C15), 136.9 (s, C15′),

149.4 (s, C10), 150.3 (s, C10′), 178.4 (s, C9), 179.7 (s, C9′). ¹⁹F

NMR (CD₂Cl₂, 298 K): δ -151.8 (br, ¹⁰BF₄), -151.9(br, ¹¹BF₄).

3

4

-

BPh₄or X^-) BF₄^-, PF₆^-, and CF₃^-SO₃^-, respectively. In the

selected NMR data, when present, a indicates the anti isomer and

s indicates the syn isomer.

1

2BPh₄. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J in Hz): δ

3

1.07 (d, J_H7′-H6) 6.9, H7′(a)), 1.14 (d, J_H7-H6) 6.9, H7(s)),

3

1.16 (d, J_H7-H6) 6.9, H7(a)), 1.82 (s, H5(s)), 1.88 (s, H5(a)),

2.13 (s, H8′(a)), 2.16 (s, H8(s) and H8(a)), 2.22 (s, 16(s) and 16-

(a)), 2.40 (s, 16′(a)), 2.43 (m, H6(s) and H6(a)), 4.82 (dd, ³J_H3-H2

4

3

1

) 6.1, H3(a)), 4.89, (dd, J_H2′-H6) 1.1, H2′(a)), 4.90 (d, J_H3-H2

3BF₄syn. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J values in

3

4

3

) 6.4, H3(s)), 4.975 (dd, J_H3′-H2′) 6.1, J_H3′-H5) 1.4, H3′(a)),

Hz): δ 1.12 (d, J_H7-H6) 6.96, H7), 1.47 (t, J_17-16) 7.53, 17),

4.98 (d, ³J_H2-H3) 6.3, H2(s)), 5.09 (dd, ³J_H2-H3) 6.2, ⁴J_H2-H6

)

3

1.88 (s, H5), 2.29 (s, H8), 2.33 (sept, J_H6-H7) 6.96, H6), 2.60

1.0, H2(a)), 6.89 (t, ³J_m-p) 7.1, p and H11′(a)), 7.03 (t, ³J_m-o,p

(m, 16), 5.02 (s,H2 and H3), 7.44 (ddd, ³J_H12-H13) 7.9, ³J_H12-H11

) 7.8, ⁴J_H12-H14) 1.5, H12), 7.51 (ddd, ³J_H13-H12) 7.9, ³J_H13-H14

7.4, m), 7.52 (br, o), 7.49 (m, H14 and H12 and H11(s) and H14

and H14′(a) and H13 and H13′(a) and H12 and H12′(a)), 7.73 (m,

4

3

4

) 7.2, J_H13-H11) 1.2, H13), 7.61 (dd, J_H14-H13) 7.2, J_H14-H12

3944 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

3

4

) 1.5, H14), 7.76 (dd, ³J_H11-H12) 7.8, ⁴J_H11-H13) 1.2, H11). ¹³C-

{¹H} NMR (CD₂Cl₂, 298 K, 100.55 MHz): δ 13.6 (s, 17), 18.5 (s,

C5), 20.9 (s, C8), 22.1 (s, C7), 23.1 (s, 16), 31.1 (s, C6), 85.7 (s,

C2), 89.6 (s, C3), 103.4 (s, C1), 114.5 (s, C4), 122.1 (s, C11), 127.7

(s, C12), 129.0 (s, C14), 129.5 (s, C13), 133.2 (s, C15), 149.5 (s,

C10), 178.5 (s, C9). ¹⁹F NMR (CD₂Cl₂, 298 K): δ -151.8 (br,

¹⁰BF₄), -151.9(br, ¹¹BF₄). Anal. Calcd (%) for C₃₀H₃₈BClF₄N₂Ru

(649.9): C 55.44, H 5.89, N 4.31. Found: C 55.51, H 5.81, N

4.37.

H14′), 7.82 (dd, J_{H11′-H12′}) 8.10, J_{H11′-H13′}) 1.23, H11′). ¹⁹F

NMR (CD₂Cl₂, 298 K): δ -151.8 (br, ¹⁰BF₄), -151.9 (br, ¹¹BF₄).

Anal. Calcd (%) for C₃₂H₄₂BClF₄N₂Ru (678.0): C 56.69, H 6.24,

N 4.13. Found: C 56.61, H 6.28, N 4.18.

1

5PF₆. H NMR (CDCl₃, 298 K, 400.13 MHz, J values in Hz):

δ 2.34 (s, 8), 5.27 (s, benzene), 7.71-7.67 (m, 11-15). ¹⁹F NMR

(CD₂Cl₂, 298 K): δ -72.1 (d, J_FP) 711). ³¹P NMR (CD₂Cl₂,

1

298 K): δ -143.2 (sept, ¹J_PF) 711). Anal. Calcd (%) for C₂₂H₂₂-

ClF₆N₂PRu (595.9): C 44.34, H 3.72, N 4.70. Found: C 44.39, H

3.75, N 4.73.

3CF₃SO₃anti. ¹H NMR (CDCl₃, 298 K, 400.13 MHz, J in Hz):

NOE Measurements. The ¹H-NOESY²⁹NMR experiments were

acquired by the standard three-pulse sequence or by the PFG

version.³⁰Two-dimensional ¹⁹F-¹H-HOESY NMR experiments

were acquired using the standard four-pulse sequence or the

modified version.³¹The 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 a 1 s relaxation delay and 800 ms mixing time.

3

δ 1.05 (d, J_H7-H6) 6.8, H7), 1.10 (d, J_H7′-H6) 6.6, H7′), 1.17

3

(t, J_{H17′-H16′}) 7.5, 17′), 1.49 (t, J_H17-H16) 7.0, 17), 1.93 (s,

H5), 2.29 (s, H8), 2.35 (s, H8′), 2.44 (sept, ³J_H6-H7(H7′)) 7.0, H6),

2.80 (m, 16′ and 16), 3.03 (m, ²J_{H16′-H16′}) 14.8, ³J_{H16′-H17′}) 7.5,

3

H16′), 4.90 (d, J_H2-H3) 6.3, H2), 4.98 (m, H3, H3′ and H2′),

3

7.34 (t, J_H12-H11,H13)7.4, H12), 7.43 (m, H14′, H13, and H13′),

7.51 (t, ³J_{H12′-H11,H13}) 7.6 H12′), 7.55 (d, ³J_{H11′-H12′}) 4.6, H11′),

7.72 (d, ³J_H14-H13) 6.9, H14), 7.92 (d, ³J_H11-H12) 7.8, H11). ¹⁹

F

Quantitative H-NOESY and H-¹⁹F-HOESY NMR experiments

were carried out with a relaxation delay of 7 s and a mixing time

of 0.15 s (initial rate approximation).³²

1

NMR (CDCl₃, 298 K): δ -78.7 (br, CF₃). Anal. Calcd (%) for

C₃₁H₃₈ClF₃N₂O₃RuS (712.2): C 55.44, H 5.89, N 4.31. Found: C

55.51, H 5.81, N 4.37.

PGSE Measurements. All the PGSE NMR measurements were

performed by using the standard stimulated echo pulse sequence³³

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 2:

1

4BPh₄anti. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J in Hz):

3

δ 1.10 (d, J_{H18′-H16′}) 6.7, H18′), 1.11 (d, J_H7′-H6) 6.8, H7′),

3

1.18 (d, J_H7-H6) 7.0, H7), 1.30 (d, J_H18-H16) 3.5, H18), 1.42

3

(d, J_{H17′-H16′}) 6.9, H17′), 1.57 (d, J_H17-H16) 6.7, 17), 1.94 (s,

3

H5), 2.14 (s, H8′), 2.16 (s, H8), 2.49 (sept, J_H6-H7) 6.9, H6),

2.74 (sept, ³J_{H16′-H17′(H18′)}) 6.6, H16′), 3.71 (sept, ³J_H16-H17(H18)

)

3

4

6.6, H16), 4.65 (dd, J_H2-H3) 6.0, J_H2-H6) 1.0, H2), 4.67 (dd,

³J_H3′-H2′) 5.9, H3′), 5.20 (dd, ³J_H2′-H3′) 6.2, ⁴J_H2′-H6) 1.1, H2′),

5.26 (dd, ³J_H3-H2) 6.0, ⁴J_H3-H5) 0.7, H3 (a)), 6.80 (dd, ³J_{H11′-H12′}

I

I₀

δ

3

ln ) -(γδ)²D_t∆ - G²

(2)

4

3

) 8.1, J_{H11′-H13′}) 1.2, H11′) 6.90 (t, J_p-m) 7.32, p), 7.03, (t,

(

)

³J_m-o,p) 7.41, m), 7.31 (br, o), 7.46 (m, and H12 or H12′), 7.59

3

(m, H13, H13′ and H14), 7.70 (d, J_{H14′-H13′}) 7.5, H14′), 7.87

where I ) intensity of the observed spin echo, I₀) intensity of the

spin echo without gradients, D_t) diffusion coefficient, ∆ ) delay

between the midpoints of the gradients, δ ) length of the gradient

pulse, and γ ) magnetogyric ratio.

(dd, ³J_{H11′-H12′}) 8.1, ⁴J_{H11′-H13′}) 1.2, H11′). Anal. Calcd (%) for

C₅₆H₆₂BClN₂Ru (910.4): C 73.88, H 6.86, N 3.08. Found: C 73.80,

H 6.82, N 3.04.

1

4PF₆. H NMR (CDCl₃, 298 K, 400.13 MHz, J values in Hz):

The shape of the gradients was rectangular, their duration (δ)

was 4-5 ms, and their strength (G) was varied during the

experiments. All the spectra were acquired using 32K points and a

spectral width of 5000 (¹H) and 18000 (¹⁹F) Hz and were processed

with a line broadening of 1.0 (¹H) and 1.5 (¹⁹F) Hz. After having

checked that a change in total relaxation time (from 5 to 130 s)

did not affect the measurement results, standard experiments were

carried out with a total recycle time of 5 s. The semilogarithmic

plots of ln(I/I₀) versus G²were fitted using a standard linear

regression algorithm, and an R factor better than 0.99 was always

obtained. Different values of ∆, “nt” (number of transients), and

number of different gradient strengths (G) were used for different

samples.

The self-diffusion coefficient, D_t, that is directly proportional to

the slope of the regression line obtained by plotting log(I/I₀) versus

G²(eq 2) was estimated by measuring the proportionality constant,

using a sample of HDO (5%) in D₂O (known diffusion coefficient

in the range 274-318K)³⁴in the same exact conditions as the

sample of interest using TMS as internal standard.³⁵D_tdata were

treated as described in the literature.⁶

3

δ 1.07 ((d, J_H18-H16) 6.67, H18(a)), 1.08 (d, J_H7′-H6) 6.78,

3

H7′(a)), 1.11 (d, J_H7-H6) 6.93, H7(s)), 1.17 (d, J_H7-H6) 6.98,

3

H7(a)), 1.37 (m, H17 and H18′(a) and H18(s)), 1.52 (d, J_CH3-CH

3

) 6.86, H18(s)), 1.53 (d, J_CH3′-CH′) 6.67, 17′(a)), 1.82 (s, H5-

3

(s)), 2.02 (s, H5(a)), 2.23 (sept, J_H6-H7) 6.84, H6(s)), 2.30

3

(s, H8′(a)), 2.33 (s, H8(s)), 2.34 (s, H8(a)), 2.54 (sept, J_H6-H7

)

6.90, H6(a)), 2.90 (sept, ³J_H16-H17(H18)) 6.67, H16 (s)), 3.08 (sept,

³J_{H16′-H17′(H18′)}) 6.58, H16′(a)), 3.74 (sept, J_H16-H17(H18)) 6.77,

3

H16(a)), 4.61 (dd, ³J_H2′-H3′) 6.02, ⁴J_H2′-H6) 1.02, H2′(a)), 4.74

(dd, ³J_H3-H2) 5.93, H3(a)), 5.06 (d, ³J_H2-H3) 6.25, H2(s)), 5.13

3

4

3

(dd, J_H2-H3) 6.25, J_H2-H6) 1.09, H2(a)), 5.28 (d, J_H8-H2

)

3

4

6.28, H3(s)), 5.41 (dd, J_H3′-H2′) 6.05, J_H3′-H5) 0.70, H3′(a)),

7.34 (m, H12(s) and H12 or H12′(a)), 7.46 (m, H13 and H13′(a)

and H12 or H12′(a)), 7.53 (m, H11(a) and H13(s)), 7.59 (m, H14-

(s) and H14 and H14′(a)), 7.80 (dd, ³J_H11-H12) 8.06, ⁴J_H11-H13

)

3

4

1.22, H11(s)), 7.87 (dd, J_{H11′-H12′}) 8.10, J_{H11′-H13′}) 1.23,

H11′(a)). ¹⁹F NMR (CD₂Cl₂, 298 K): δ -72.1 (d, ¹J_FP) 711). ³¹

P

NMR (CD₂Cl₂, 298 K): δ -143.2 (sept, ¹J_PF) 711). Anal. Calcd

(%) for C₃₂H₄₂ClF₆N₂PRu (736.2): C 52.21, H 5.75, N 3.81.

Found: C 52.28, H 5.71, N 3.85.

1

4BF₄anti. H NMR (CD₂Cl₂, 298 K, 400.13 MHz, J values in

(29) Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. J. Chem. Phys.

1979, 71, 4546.

(30) Wagner, R.; Berger, S. J. Magn. Reson. A 1996, 123, 119.

(31) Lix, B.; So¨nnichsen, F. D.; Sykes, B. D. J. Magn. Reson. A 1996,

121, 83.

(32) Neuhaus, D.; Williamson, M. The Nuclear OVerhauser Effect in

Structural and Conformational Analysis; Wiley-VCH: New York, 2000;

Chapter 4.

(33) Valentini, M.; Ru¨egger, H.; Pregosin, P. S. HelV. Chim. Acta 2001,

84, 2833, and references therein.

(34) (a) Tyrrell, H. J. W.; Harris, K. R. Diffusion in Liquids; Butter-

worth: London, 1984. (b) Mills, R. J. Phys. Chem. 1973, 77, 685.

3

Hz): δ 1.07 (d, J_H18-H16) 6.67, H18), 1.08 (d, J_H7′-H6) 6.78,

H7′), 1.18 (d, ³J_H7-H6) 6.98, H7), 1.34 (d, ³J_CH18-H16) 3.51, H18),

1.40 (d, ³J_CH17′-H16) 3.51, H17′), 1.54 (d, ³J_CH17-H16) 3.51, H17),

2.01 (s, H5), 2.29 (s, H8), 2.32 (s, H8′), 2.50 (sept, ³J_H6-H7) 6.84,

H6), 2.34 (s, H8), 2.90 (sept, ³J_CH-CH3) 6.67, CH(s)), 3.04 (sept,

³J _H16-H17(H18)) 6.58, H16), 3.79 (sept, ³J_{H16′-H17′(H18′)}) 6.58, H16′),

4.66 (d, ³J_H2′-H3′) 6.25, H2′), 4.73 (d, ³J_H3′-H2′) 6.25, H3′), 5.21

3

(d, J_H2-H3) 6.28, H2), 5.40 (d, J_H3′-H2′) 6.05, H3′), 7.38 (m,

H11′,H12, and H12′), 7.52 (m, H13 and H13′), 7.62 (m, H14 and

Half-Sandwich Ru(II) Salts Bearing R-Diimine Ligands

Organometallics, Vol. 26, No. 16, 2007 3945

Table 6. Crystallographic Data for 1BPh₄, 2BF₄syn, 3BPh₄anti, 4BPh₄anti, and 5PF₆

1BPh₄·CH₂Cl₂

2BF₄syn

3BPh₄anti·CH₂Cl₂

4BPh₄anti·CH₃OH

5PF₆

formula

M

T [K]

C₅₁H₅₂BCl₃N₂Ru

911.18

295(2)

C₂₈H₃₄BClF₄N₂Ru

621.90

295(2)

C₅₅H₆₀BCl₃N₂Ru

924.82

295(2)

C₅₇H₆₆BClN₂ORu

942.45

295(2)

C₂₂H₂₂ClN₂RuPF₆

595.91

298(2)

color

red

orange

yellow

orange

cryst syst

space group

a [Å]

b [Å]

c [Å]

orthorhombic

Pbca

14.634(4)

21.829(6)

29.141(4)

90.00

9309(4)

8

1.300

monoclinic

P2₁/a

17.250(5)

11.526(6)

17.310(4)

90.00

113.19(5)

90.00

3163.6(22)

4

orthorhombic

P2₁/b2/c2₁/n

19.726(5)

16.920(5)

28.889(5)

90.00

9642(4)

8

1.274

monoclinic

P2₁/c

15.378(5)

19.605(6)

17.284(5)

90.00

104.61(5)

90.00

5042(3)

4

triclinic

P1h

10.028(5)

10.494(5)

12.573(6)

69.207(4)

73.318(5)

81.083(6)

1182.8(10)

2

R [deg]

â [deg]

γ [deg]

V [Å³]

Z

F

_calcd[g cm^-3

R_int

]

1.306

0.0662

1.035

1.241

0.0621

0.990

1.673

0.0511

1.145

0.0590

0.970

0.0674

1.121

GOF

The measurement uncertainty was estimated by determining the

standard deviation of m by performing experiments with different

∆ values. Standard propagation of error analysis yielded a standard

deviation of approximately 3-4% in the hydrodynamic radius and

10-15% in the aggregation numbers N.

associated basis set⁴¹augmented by a polarization d function (R )

0.640). For the remaining atoms 6-31G(d,p) basis sets were

considered. For the calculations at the HF level in the ONIOM

calculations, the ruthenium and chloride atoms were described by

the Hay and Wadt pseudopotential and the associated basis sets.⁴²

The remaining atoms were represented by 4-31G basis sets. Full

optimizations of geometry without any constraint were performed,

followed by analytical computation of the Hessian matrix to confirm

the nature of the located extrema as minima on the potential energy

surface. The ion pair energies and the formation energy of the ion

pair from separated anion and cation, as well as the relative energies

and formation energies of the quadrupole from the separated ion

pairs, were estimated through PCM calculations⁴³in CH₂Cl₂on

the ONIOM(B3PW91/HF) geometries (ion pair) or B3PW91

geometries (quadrupole). In each case the geometries of the

separated species (cation or anion for ion pair or ion pair for

quadrupole) were not reoptimized but were taken as in the

corresponding aggregate (ion pair or quadrupole).

Computational Details. All calculations were performed with

the Gaussian 03 set of programs³⁶with DFT or the hybrid ONIOM

method.³⁷The cation 3⁺anti and syn were optimized at the

B3PW91 level.³⁸The ion pair complexes for 3X anti (X ) BF₄

and BPh₄) with X close to the diimine methyl groups (3X-B) or

above the cymene ring (3X-A) were optimized at the ONIOM-

(B3PW91/HF) and ONIOM(B3PW91/UFF) levels. The UFF force

field³⁹was used for the molecular mechanics calculations. For the

cationic fragment of 3X anti, the isopropyl and methyl groups on

cymene, as well as the ethyl-substituted phenyl groups of the

diimine ligand, were considered in the low-level layer (HF or UFF).

All of the remaining atoms were treated at the B3PW91 level. The

BF₄was treated at the B3PW91 level, and the phenyl groups on

BPh₄were considered in the low-level layer (HF or UFF).

X-ray Structure. A single crystal of 1BPh₄, 2BF₄syn, 3BPh₄

anti, 4BPh₄anti, and 5PF₆suitable for X-ray diffraction was

obtained as described in the Experimental Section for each complex.

Data were collected on an XCALIBUR (CCD areal) Oxford

Instruments diffractometer, using Mo K graphite-monochromated

radiation (λ ) 0.71073 Å). ω, φ scans and the frame data were

acquired with CRYSALIS (CCD 171) software. The crystal to

detector distance was 65.77 mm. The frames of a single experiment

were processed using CRYSALIS (RED 171) software to give the

respective hkl file corrected for scan speed, background, Lorentz,

and polarization affects. Since there were no apparent variations

in the intensity of the standard reflections of all compounds,

measured periodically, during data collection, no correction for

crystal decomposition was necessary. The data were corrected for

absorption using the semiempirical multiscan sistem.⁴⁴The Laue

symmetry was determined for all compounds, and the investigations

of the observed systematic absences were consistent with the

assigned space groups. All of the data were collected at room

temperature.

In the B3PW91 calculations and in the high-level layer of the

ONIOM calculations, the ruthenium atom was represented by the

relativistic effective core potential (RECP) from the Stuttgart group

(16 valence electrons) and its associated (8s7p5d)/[6s5p3d] basis

set⁴⁰augmented by an f polarization function (R ) 1.235). The

chloride atom was also treated with Stuttgart’s RECPs and the

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N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;

Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;

Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;

Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,

X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;

Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;

Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;

Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,

S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.

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G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;

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03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.

The structures were solved by the direct method using the Sir97⁴⁵

program and refined by the full-matrix least-square method on F²

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3946 Organometallics, Vol. 26, No. 16, 2007

Zuccaccia et al.

using SHELXL-97⁴⁶WinGX⁴⁷. All non-hydrogen atoms were

refined anisotropically. The hydrogen atoms were added at the

calculated positions and refined using a riding model. The final

cycles of full-matrix least-squares refinement against F²were based

on the observed reflections with [F_o> 4σ(F_o)] and were converged

with unweighted and weighted agreement factors of R and R_wand

GOF. Crystals of 1BPh₄, 3BPh₄anti, and 4BPh₄anti showed

internal disorder due to a solvent molecule that cocrystallized with

the complexes. Crystallographic details are summarized in Table

6.

Acknowledgment. This work was supported by grants from

the Ministero dell’Istruzione, dell’Universita` e della Ricerca

(MIUR, Rome, Italy; Programma di Rilevante Interesse Nazio-

nale, Cofinanziamento 2004-2005), COST D24/WG 0014/02

action, Universite´ Montpellier 2 and CNRS.

Supporting Information Available: This material is available

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structure refinement; University of Goettingen: Germany, 1997.

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free of charge via the Internet at http://pubs.acs.org.

OM7003157

Article Doi

Interionic structure of ion pairs and ion quadruples of half-sandwich ruthenium(II) salts bearing a-diimine ligands

DOI: 10.1021/om7003157

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