Synthesis, characterization, and PGSE (1H and 19F) NMR diffusion studies on cationic (η6- arene)Mn(CO) 3+ complexes: Boron counterion, ion pairing, and solvent dependences

Article abstract of DOI:10.1021/ic0506409

The synthesis, characterization, and PGSE (¹H and ¹⁹F) NMR diffusion studies on the cationic [(η⁶-arene) Mn-(CO)₃][X] (arene = anisole, 4-chloroanisole, and 1,3,5-trimethoxybenzene; X = BPh₄ and BArF)

Full text of DOI:10.1021/ic0506409

Inorg. Chem. 2005, 44, 5941−5948
Synthesis, Characterization, and PGSE (1H and 19F) NMR Diffusion
+
Studies on Cationic (η
6- Arene)Mn(CO)3 Complexes: Boron
Counterion, Ion Pairing, and Solvent Dependences
Daniele Schott and Paul S. Pregosin*
Laboratory of Inorganic Chemistry, ETHZ, Ho¨nggerberg CH-8093 Zu¨rich, Switzerland
Be´atrice Jacques, Murielle Chavarot, Franc¸oise Rose-Munch,* and Eric Rose
Laboratoire de Chimie Organique, UMR 7611, UniVersite´ P. et M. Curie,
75252 Paris Cedex 05, France
Received April 26, 2005
The synthesis, characterization, and PGSE (1H and 19F) NMR diffusion studies on the cationic [( 6-arene)Mn-
η
(CO)3][X] (arene
) anisole, 4-chloroanisole, and 1,3,5-trimethoxybenzene; X ) BPh4 and BArF) are reported. The
tetraphenyl borate complexes of anisole and 4-chloroanisole show surprisingly strong ion pairing in dichloromethane
solution, whereas the BArF salts do not. 1H,1H-NOESY data support this anion selectivity. In chloroform solution
one finds the usual strong ion pairing for both anions. The solid-state structure of [(η
6-1,3,5-trimethoxybenzene)-
Mn(CO)3][BPh4] has been determined. 13C NMR and IR data for the new complexes are reported. The observed
IR frequencies are higher for the BArF complexes than for the BPh4 complexes.
Introduction
rapidly becoming the methods of choice for recognizing how
anions and cations interact in solution. This stems, partially,
from the ability to use a multinuclear diffusion approach28
It is now clear that anion effects play a role in the kinetics
of a number of stoichiometric and catalytic processes.1
Specifically, for the Rh(I)-catalyzed Pauson-Khand reac-
tion,2 the Ru(II)- or Cu(II)-catalyzed Diels-Alder3 reaction,
or the Ir(I)-catalyzed hydrogenation of polysubstituted ole-
fins,4 among others,5 the anion associated with the transition
metal cation can markedly affect the rate of reaction. The
source of these effects is often completely unknown and may
be related to coordination effects, ion pairing effects, or both,
among other possible explanations.
(7) Stilbs, P. Prog. NMR Spectrosc. 1987, 19, 1.
(8) Beck, S.; Geyer, A.; Brintzinger, H. H. Chem. Commun. 1999, 2477-
2478.
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4486.
1H and 19F pulsed gradient spin-echo (PGSE) diffusion
studies,6-16 together with NOE measurements,17-27 are
(13) Avram, L.; Cohen, Y. J. Am. Chem. Soc. 2002, 124, 15148-15149.
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* To whom correspondence should be addressed. E-mail: pregosin@
inorg.chem.ethz.ch.
(1) Fagnou, K.; Lautens, M. Angew. Chem., Int. Ed. 2002, 41, 27-47.
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10.1021/ic0506409 CCC: $30.25
Published on Web 07/13/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 16, 2005 5941

Schott et al.
Scheme 1
(i.e.,1H and 19F NMR methods for the cation and anion,
of solubility of these cationic complexes in most of the usual
organic solvents. Moreover, they cannot be purified by
column chromatography which strongly limits their use and
the subsequent development of new reactions. However, in
a recent report, the routine anions, PF6 and BF4, have been
replaced by the TRISPHAT anion, resulting in the new salts
being soluble in organic solvents of modest polarity.35
We report here the preparation and spectroscopic charac-
terization of the new cationic manganese complexes [(η6-
arene) Mn(CO)3][X] (arene ) 4-chloroanisole (1), anisole
(2), and 1,3,5-trimethoxybenzene (3) with X ) BPh4 (b) and
BArF (B[3,5-(CF3)2C6H3]4) (c)) (Scheme 1) as well as PGSE
diffusion studies on these complexes. The latter measure-
ments are designed to shed light on possible differences
caused by ion pairing. Our results represent the first examples
of PGSE measurements on organometallic Mn compounds
and demonstrate a surprising difference between the anions
BPh4 and BArF.
1
respectively, combined with H and 19F HOESY data) to
follow how and where the anions and cations interact. This
approach has also been extended to salts (and compounds)
7
containing other nuclei, including, Li,29 31P,30 29Si,9 35Cl,30
and recently, 195Pt.31 Despite the recent surge in interest, the
applications of the PGSE method to the problems of ion
pairing remain sparse, and there are few systematic studies
for transition metal complexes in different solvents.
Organometallic Mn compounds enjoy wide synthetic
applications. Indeed, the increased reactivity of aromatic
molecules coordinated to electron-deficient metal fragments,
such as M(CO)3 (M ) Cr or Mn+), is associated with
versatile synthetic intermediates in organometallic and
organic chemistry.32 Interestingly, the applications of cationic
manganese complexes remain relatively undeveloped com-
pared to their isoelectronic, neutral chromium counterparts.
The two main reasons for this are as follows: (a) preparation
of the functionalized complexes by direct complexation of
the arenes to the Mn(CO)3 is difficult33 (access to the salts,
[(η6-arene)Mn(CO)3][X]-substituted by electron-withdrawing
or conjugated substituents, has only recently become avail-
able34 using a multistep synthesis strategy) and (b) the lack
Results and Discussion
Syntheses of Complexes 1-3. We are only aware of two
publications concerning [(η6-arene)Mn(CO)3]+ cationic com-
plexes36,37 as tetraphenylborate salts. One of these37 reports
a general method for the introduction of the desired coun-
terion using an anion metathesis reaction and was applied
to the synthesis of complexes of benzene, toluene, and
mesitylene. We chose to prepare the tetrafluoroborate salts
1a-3a as these were easily obtained via a well-known
versatile procedure.38a,b These BF4 salts were soluble in polar
solvents such as acetone and acetonitrile but were only very
(22) Zuccaccia, C.; Macchioni, A.; Orabona, I.; Ruffo, F. Organometallics
1999, 18, 4367-4372.
(23) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Cruciani, G.; Foresti,
E.; Sabatino, P.; Zuccaccia, C. Organometallics 1998, 17, 5549-5556.
(24) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G.; Terenzi,
S. Organometallics 1996, 15, 4349-4351.
(25) Cavallo, L.; Macchioni, A.; Zuccaccia, C.; Zuccaccia, D.; Orabona,
I.; Ruffo, F. Organometallics 2004, 23, 2137-2145.
(26) Binotti, B.; Carfagna, C.; Foresti, E.; Macchioni, A.; Sabatino, P.;
Zuccaccia, C.; Zuccaccia, D. J. Organomet. Chem. 2004, 689, 647-
661.
-
poorly soluble in THF or CH2Cl2. The new anions, BPh4
and BArF-,39 the latter being known for its beneficial effect
(27) Binotti, B.; Macchioni, A.; Zuccaccia, C.; Zuccaccia, D. Comments
Inorg. Chem. 2002, 23, 417-450.
(32) For example, see: (a) Semmelhack, M. F. In ComprehensiVe Orga-
nometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, Chapter 9, p 979. (b)
McDaniel, K. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 6, Chapter 4, p 93. (c) Rose-Munch, F.; Rose, E. Curr.
Org. Chem. 1999, 3, 445-467. (d) Rose-Munch, F.; Rose, E. Eur. J.
Inorg. Chem. 2002, 1269-1283. (e) Rose-Munch, F.; Rose, E. In
Modern Arene Chemistry; Astruc, D., Ed.; Wiley VCH: New York,
2002; Chapter 11, 368-398. (f) Prim, D.; Andrioletti, B.; Rose-Munch,
F.; Rose, E.; Couty, F. Tetrahedron 2004, 60, 3325-3347. (g) Ku¨ndig,
E. P. Top Organomet. Chem. 2004, 7, 1-20. (h) Moonhyun, O.;
Reingold, J. A.; Carpenter, G. B.; Sweigart, D. A. Coord. Chem. ReV.
2004, 248, 561-569.
(28) (a) Goicoechea, J. M.; Mahon, M. F.; Whittlesey, M. K.; Kumar, P.
G. A.; Pregosin, P. S. Dalton Trans. 2005, 588-597. (b) Kumar, P.
G. A.; Pregosin, P. S.; Schmid, T. M.; Consiglio, G. Magn. Reson.
Chem. 2004, 42, 795-800. (c) Kumar, P. G. A.; Pregosin, P. S.; Vallet,
M.; Bernardinelli, G.; Jazzar, R. F.; Viton, F.; Kundig, E. P.
Organometallics 2004, 23, 5410-5418. (d) Pregosin, P. S.; Martinez-
Viviente, E.; Kumar, P. G. A. Dalton Trans. 2003, 4007-4014. (e)
Kumar, P. G. A.; Pregosin, P. S.; Goicoechea, J. M.; Whittlesey, M.
K. Organometallics 2003, 22, 2956-2960. (f) Drago, D.; Pregosin,
P. S.; Pfaltz. A. Chem. Commun. 2002, 286-287. (g) Chen, Y.;
Valentini, M.; Pregosin, P. S.; Albinati, A. Inorg. Chim. Acta 2002,
327, 4-14. (h) Valentini, M.; Ruegger, H.; Pregosin, P. S. HelV. Chim.
Acta 2001, 84, 2833-2853. (i) Geldbach, T.; Pregosin, P. S.; Albinati,
A.; Rominger, F. Organometallics 2001, 20, 1932-1938. (j) Valentini,
M.; Pregosin, P. S.; Ruegger, H. J. Chem. Soc., Dalton Trans. 2000,
4507.
(33) Jackson, J. D.; Villa, S. J.; Bacon, D. S.; Pike, R. D.; Carpenter, G.
B. Organometallics 1994, 13, 3972-3980.
(34) Auffrant, A.; Prim, D.; Rose-Munch, F.; Rose, E.; Schouteeten, S.;
Vaissermann, J. Organometallics 2003, 22, 1898-1913.
(29) Fernandez, I.; Martinez-Viviente, E.; Pregosin, P. S. Inorg. Chem.
2004, 43, 4555-4557.
(30) (a) Martinez-Viviente, E.; Ruegger, H.; Pregosin, P. S.; Lopez-Serrano,
J. Organometallics 2002, 21, 5841-5846. (b) Martinez-Viviente, E.;
Pregosin, P. S. HelV. Chim. Acta 2003, 86, 2364-2378.
(31) Nama, D.; Anil Kumar, P. G.; Pregosin, P. S. Magn. Reson. Chem.
2005, 43, 246-250.
(35) Planas, J. G.; Prim, D.; Rose, E.; Rose-Munch, F.; Monchaud, D.;
Lacour, J. Organometallics 2001, 20, 4107-4110.
(36) Winkhaus, G.; Pratt, L.; Wilkinson, G. J. Chem. Soc. 1961, 3807-
3813.
(37) Lamanna, W. M.; Palazzoto, M. C.; Devoe, R. J.; McCormick, F. B.;
Olofson, J. M.; Siedle, A. R.; Willett, P. S. WO 95/03338, 1995.
5942 Inorganic Chemistry, Vol. 44, No. 16, 2005

+
Cationic (η6-Arene)Mn(CO)3 Complexes
Scheme 2. Syntheses of Complexes 1a-3c
Table 1. IR Spectral Data (neat, cm-1) for Complexes 1b,c-3b,c
Table 2. Crystal Data for Complex 3b
cation
anion
complex
ν(A1)
∆ν(A1)a
ν(E)
∆ν(E)b
formula
fw
cryst syst
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
C36H32BMnO6
626.39
triclinic
10.4965(11)
11.9045(16)
14.029(2)
74.428(15)
88.031(14)
1
BPh4
BArF
BPh4
BArF
BPh4
BArF
1b
1c
2b
2c
3b
3c
2072
2087
2069
2083
2057
2073
15
2012
2036
2013
2029
1989
2012
24
2
3
14
16
16
23
a ∆ν(A1) ) ν(A1, BArF) - ν(A1, BPh4). b ∆ν(E) ) ν(E, BArF) - ν(E,
BPh4).
71.735(10)
1601.2(3)
2
space group
cryst shape
cryst color
Ph1
on the stability of the related complexes,40,41 were introduced
via their sodium salts.
parallelepiped
yellow
4.57
1.30
µ (cm-1
)
The BPh4 and BArF salts were prepared by treating 1a-
3a, dissolved in a minimum of water, by a saturated
methanolic solution of NaX (X) BPh4, BArF). The new
complexes, 1b-3b (X ) BPh4) or 1c-3c (X ) BArF)
precipitated and were isolated as light yellow powders, either
by filtration of the mixture or by extraction in CH2Cl2, in
good to excellent yields (see Scheme 2). The absence of any
F (g cm3)
diffractometer
radiation
KAPPA CCD Enraf Nonius
Mo KR (λ ) 0.71073 Å)
scan type
scan range (deg)
θ limits (deg)
ω /2θ
0.8 gθ g 0.345
2-30
octants collected
no. of data collected
no. of unique data collected
-14, 14; -12, 16; -19, 18
17662
9229
-
residual BF4 anion was confirmed by mass spectrometry
no. of unique data used for refinement 4311(Fo)2 > 3σ(Fo)2
analysis (negative mode): only the new X- counterion was
detected.
merging R
0.12
0.0529
0.0596
a
R1
R2
b,c
It is noteworthy that the new complexes with BPh4 and
BArF as counterions are soluble in CH2Cl2 and THF and
can be purified by silica gel chromatography.
absorption correction
secondary extinction coefficient
GOF
difabs (Tmin ) 0.80, Tmax ) 1.08)
none
1.086
398
-0.468
0.454
no. of variables
IR Spectroscopy. Because IR νCO shifts are known to be
very sensitive to changes in electron density at the metal
and reflect π-back-bonding into the CO π* orbitals,42 we
have recorded the spectra for 1-3 and show these data in
Table 1. The observed IR frequencies are higher for the BArF
complexes than for the BPh4 complexes with the differences
ranging from 14 to 16 cm-1 for the A1 mode frequency and
from 16 to 24 cm-1 for the E mode frequency. Although the
source of this difference is not immediately clear, the data
suggest less π-back-bonding for the BArF salts and thus,
less electron density at the metal than for the BPh4 analogues.
X-ray Study on Complex 3b. Crystals of complex 3b
were grown by slow diffusion of petroleum ether into a
∆Fmin (e/Å3)
∆Fmax (e/Å3)
2
a R1) ∑||Fo| - |Fc||/∑ |Fo|. b R2) [∑w(||Fo| - |Fc||)2/∑wFo ]1/2
.
c Weighting scheme of the form w ) w′[1 - ((||Fo| - |Fc||)/6s(Fo))2]2 with
w′ ) 1/Sr ArTr(X) with coefficients of 0.477, 0.326, and 0.227 for a
Chebyshev series for which X ) Fc/Fc(max)
.
concentrated acetone solution of 3b. Crystal data43,44 are
reported in Table 2, and Figure 1 shows a CAMERON45
view of the salt along with some selected bond lengths and
angles. The Mn(CO)3 moiety exhibits the well-known regular
piano-stool geometry.33 The three Mn-C(CO) bonds are
perfectly eclipsed by the C-O bonds stemming from the
arene carbons bearing the methoxy groups. The six Mn-C
arene bonds have almost the same lengths with the values
ranging from 2.20 to 2.25 Å, in line with those found for
the previously described (1,2,3-trimethoxybenzene) Mn(CO)3
isomeric complex,46 whose values range from 2.14 to 2.28
Å. The three Mn-C(CO) separations fall in the range
1.804(4)-1.816(4) Å. There seems to be no obvious contact
between the two ions with the Mn‚‚‚B distance >7 Å.
Diffusion studies for [(Arene)Mn(CO)3][X]. Diffusion
(38) (a) Pearson, A. J.; Richards, I. C. J. Organomet. Chem. 1983, 258,
C41-C41. (b) Balssa, F.; Gagliardini, V.; Rose-Munch, F.; Rose, E.
Organometallics 1996, 15, 4373-4382. (c) Abel, E. W.; Wilkinson,
G. J. Chem. Soc. 1959, 1501-1505.
(39) Reger, D. L.; Wright, T. D.; Little, C. A.; Lamba, J. J. S.; Smith, M.
D. Inorg. Chem. 2001, 40, 3810-3814.
(40) Nishida, N.; Takada, N.; Yoshimura, M.; Nosoda, T.; Kobayashi, H.
Bull. Chem. Soc. Jpn. 1984, 57, 2600.
(41) We are aware of only one example of a Mn derivative that has been
synthesized with BArF- as the counterpart. This salt contains the (η5-
diphenylium cyclopentadienyl) (tricarbonyl)manganese cation, see:
Volland, M. A. O.; Kudis, S.; Helmchen, G.; Hyla-Kryspin, I.;
Rominger, F.; Gleiter, R. Organometallics 2001, 20, 227-230.
constants, D, from the H and 19F PGSE measurements in
1
(42) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2952-2956.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5943

Schott et al.
D (and then calculate the rH) values in either water or
methanol as these solvents are normally sufficiently polar
to separate and solvolyse the ions.
Organometallic cations are not routinely soluble in water;
however, both the BF4 salts of 1a and 2a are soluble in
aqueous solution so that their D and rH values for the cations
(D ) 7.04 and rH ) 3.5 Å for 1a and D ) 7.68 and rH )
3.2 Å for 2a) could be determined. These rH values for the
cations are relatively small but reasonable.47 From a metha-
nolic solution of NaBPh4, we find D ) 8.08 and rH ) 5.1 Å
for the BPh4 anion, in good agreement with what we
observed from the X-ray data for 3b. Further, from a
methanolic solution of 3b, the diffusion measurements for
the anion give D ) 7.75 and rH ) 5.4 Å. Alcohols as solvents
may induce some ion pairing,20b,27,31 so we assumed that a
value of ca. 5.1 Å is reasonable for the BPh4 anion. In the
absence of ion pairing, the BArF anion often shows rH values
in the region of 5.8-6.1 Å.28c,f
The data in Table 3 show D and rH values for 2 mM
solutions of 1-3 as their BPh4 and BArF salts, in three
solvents, chloroform, dichloromethane, and acetone. As
expected,28 there is very substantial (often 100%) ion pairing
in chloroform for 1-3. Reasonably enough, the BArF ion
pair is larger in volume than the BPh4 analogues. We
consider the 6.2 Å values for 1b in chloroform to be slightly
large; perhaps these are the result of increased solvation
(hydrogen bonding) from the chloroform to the Cl atom.
In a direct comparison of the BPh4 and BArF salts 1-3
in dichloromethane, the solvent often used in homogeneously
catalyzed reactions, we find that the tetraphenyl borate
complexes show complete ion pairing for 1b and 2b and
substantial ion pairing for 3b, whereas the BArF analogues
appear to have little or no ion pairing. The rH values for the
cations in 1b and 2b, 5.6 Å, are much larger than the
measurements on the cation models described above (3.2-
3.5 Å). We believe this to be the first clear example of this
kind of ion pairing selectivity in tetraphenyl borate anions.
We note that the rH values for the cations in these BArF
salts (4.3-4.7 Å) are much closer to what one might expect
for a solvated cation in dichloromethane, instead of water.
Presumably, the electron-withdrawing trifluoromethyl groups
delocalize the negative charge so that the ion pairing is no
longer very favorable. Moreover, these results are consistent
with the variations observed for the carbonyl stretching
frequencies, which suggest an increase in electron density
at the metal center for the BPh4 complexes.
Figure 1. ORTEP view of the structure of complex 3b with 30% thermal
ellipsoid probability. Selected bond lengths (Å) and selected angles (deg)
are as follows: Mn-C1, 2.253(3); Mn-C3, 2.247(3); Mn-C5, 2.237(3);
Mn-C2, 2.198(3); Mn-C4, 2.201(3); Mn-C6 2.198(3); Mn-C10,
1.816(4); Mn-C11, 1.804(4); Mn-C12, 1.816(4); C10-Mn-C11,
90.0(2); C10-Mn-C12, 91.2(2); and C11-Mn-C12, 91.1(2)
chloroform, dichloromethane, and acetone are given in Table
3.
kT
rH )
6πηD
The hydrodynamic radii, rH, are obtained from the Stokes-
Einstein relationship47 (above) where k is the Boltzmann
constant and η is the viscosity. This calculated rH value
permits a direct comparison between diffusion measurements
in different solvents, as it corrects for the different solvent
viscosities.
We make the assumption that, when the cation and anion
reveal identical D values, whose magnitudes produce rH
values which are substantially greater than those estimated
either by crystallography or calculations,48 then we are
dealing with ion pairing. Further, as an estimate of the rH
value of the solvated cation or anion, we use the measured
(43) Data were recorded at room temperature on a Kappa-CCD Enraf-
Nonius diffractometer with graphite monochromated Mo KR radiation
(I ) 0.71073 Å) and the ω-scan technique. Orientation matrix and
lattice parameters were obtained by least-squares refinement of the
diffraction data of 52 reflections within the range of 5° < θ < 20°.
The index ranges of data collection were -14 e h e 14, -12 e k e
16, and -19 e l e 18. Intensity data were collected in the θ range
2.0-30°, 4311 have (Fo)2 g 3σ(Fo)2. All of the measured independent
reflections were used in the analysis. The structure was solved by
direct methods and refined with a full-matrix least-squares technique
on F using the CRYSTALS44 programs. All non-hydrogen atoms were
refined anisotropically. All hydrogen atoms were either set in calculated
positions and isotropically refined. The values of the discrepancy
indices R1 (R2) for all data were 0.1211 (0.1317), whereas those listed
in Table 1 correspond to the data with I > 3σ(I). The final Fourier
difference map showed maximum and minimum height peaks of 0.454
and -0.468 e Å-3. The values of the number of reflections and number
of variable parameters are 398, and that of the goodness-of-fit (GOF)
is 1.086. The molecular structure was drawn with the program
CAMERON45 and is reported in Figure 1.
Normally, acetone as solvent promotes ion separation,28c,e,49
relative to either dichloromethane or chloroform, and indeed,
we find that, for the BArF salts, 1c-3c, the D and rH values
for the two ions differ significantly. In 1c and 2c, the cations
(44) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487-1492.
(45) Watkin, D. J.; Prout, C. K.; Pearce, L. J. CAMERON; Chemical
Crystallography Laboratory: OXFORD, UK, 1996.
(48) The ionic radii can be estimated from crystallographic data, molecular
models or both. Modern modelling programs, such as Chem 3D, allow
the calculation of the Connolly solvent-excluded volume of a molecule,
(46) Gagliardini, V.; Balssa, F.; Rose-Munch, F.; Rose, E.; Susanne, C.;
Dromzee, Y. J. Organomet. Chem. 1996, 519, 281-283.
(47) It has been suggested that factor 6 in eq 2 is not valid for small species
whose van der Waals radii are <5 Å (Edward, J. T. J. Chem. Educ.
1970, 47, 261; Ue, M. J. Electrochem. Soc. 1994, 141, 3336). To be
consistent and facilitate comparisons we have used eq 2 as shown.
Vcon, which is the volume within the surface created when a probe
sphere, representing the solvent, is rolled over the molecular mode.
M. L. Connolly J. Mol. Graphics 1993, 11. For more information visit
http://connolly.best.vwh.net/. We estimate the rh value of the cation
to be between 3.1 and 3.3 Å. For the BArF anion, we estimate an rh
value of ca. 5.8 Å.
5944 Inorganic Chemistry, Vol. 44, No. 16, 2005

+
Cationic (η6-Arene)Mn(CO)3 Complexes
Table 3. Diffusion Data for Manganese Carbonyl Complexesa-c
a D is ×10-10 m2 s-1; rH is in Å; 2mM solutions. Estimated using the diffusion coefficient of HDO in D2O as the reference. b Viscosity, η (299 K, kg
s-1 m-1): CH2Cl2, 0.414; acetone, 0.306; CDCl3, 0.534. c The size of BPh4 was estimated using a 2mM solution of NaBPh4 at 299 K in MeOD (η )
c
0.523): D ) 8.08, rH ) 5.1 Å. For 3b in MeOD: Dcation ) 9.58, rH ) 4.4 Å; Danion ) 7.75, rH ) 5.4 Å. For 1a in D2O (η ) 0.894): Dcation ) 7.04, rH
) 3.5 Å. For 2a in D2O (η ) 0.894): Dcation ) 7.68, rH ) 3.2 Å.
show an rH value of ca. 4.5 Å which we take to mean that
(allowing for acetone rather than water solvation) there is
little or no ion pairing. However, in 3c, the larger value of
5.2 Å for the cation suggests significant but not complete
ion pairing, and this is supported by a somewhat larger rH
value of 6.5 Å for the BArF anion. The rH values in acetone
for the BPh4 anion are somewhat puzzling. For all three salts,
1b-3b, the diffusion data suggest identical translation for
both the cation and the anion. However, we believe this is
simply a coincidence. The rH values for the anion are
consistent with an isolated BPh4 anion so that it is possible
that the cation is very strongly solvated by the acetone and
thus appears to have the same radius as the anion.
There are a number of related diffusion measurements
known for this type of cationic Binap complex.28b,e The
observed D and rH values are also given in Table 3 and
suggest strong ion pairing in chloroform, significant (but not
complete) ion pairing for this salt in dichloromethane
solution, and separated ions in acetone. Consequently, the
diffusion results for our BPh4 Mn complexes are somewhat
unusual.
NOE Experiments. To support the diffusion data on the
Mn complexes in dichloromethane, we have measured 1H,1H
NOESY spectra for the two tetraphenyl borate complexes,
1b and 2b, and show sections of these spectra in Figure 2.
Clearly, for 1b there are strong contacts from the ortho
protons of the tetraphenyl borate anion to the complexed
arene ring protons. In 1b, there is also a strong contact to
the methoxy methyl resonance. In 2b, the strongest cross-
peaks stem from the aromatic signals, but there is no contact
to the methoxy group. One does observe a contact to the
arene para proton, but this is rather weak when compared to
the crosspeaks resulting from the ortho and meta signals.
Perhaps the anion prefers to be remote from the halogen atom
in 1b. NOESY spectra for the salts 1b and 3b in acetone
Since there are not many PGSE data on BPh4 salts
available, we measured the RuCl(p-cymene)(Binap) model
salt, 4, in the same three solvents.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5945

Schott et al.
1
Figure 2. Sections of the H,1H NOESYspectra of (a) 1b and (b) 2b revealing the strong inter-ion NOE’s from the BPh4 ions.
solution show no inter-ion contacts, in keeping with our
interpretation of their diffusion data.
The corresponding 1H,1H NOESY spectrum for BArF salt
2c contains no crosspeak which stems from the BArF anion
(Figure 3). Obviously, this anion occupies a relatively remote
position with respect to the cation, in keeping with the results
from the PGSE measurements.
1
In Tables 4 and 5 we show H and 13C data for 1 and 2.
In dichloromethane solution, we note marked low frequency
changes in the proton resonance positions of the arene of
2b, relative to an acetone solution, and assign these differ-
ences to the anisotropic effects from the proximate tetra-
phenyl borate anion. The analogous 13C changes are rather
modest and consistent with a solvent effect (i.e, the carbonyl
resonances and the arene resonances are all shifted in the
same direction by a modest 1-3 ppm).
We conclude that both the diffusion and NOE results point
to a somewhat unexpected ion pairing selectivity for the two
tetraphenyl borate complexes. The IR data reflect these
differences, although the actual source of the change in the
ν
CO shifts is not clear.50 In any case, the PGSE methodology
has once again proven to be one of the most useful tools for
elucidating how ions interact in solution.
Experimental Section
We have used the viscosities for the nondeuterated solvent, given
in the on-line version of the Chemical Properties Handbook
(McGraw-Hill, 1999, http://www.knovel.com).
(49) Martinez-Viviente, E.; Pregosin, P. S.; Vial, L.; Herse, C.; Lacour, J.
Chem. Eur. J. 2004, 10, 2912-2918.
(50) The interaction between the anion and the cation and the resulting
changes in the IR data may well involve changes in the arene bonding
(the 13C data do reveal a ca. 3 ppm shift for the complexed arene),
rather than a direct interaction with the Mn center. This subject remains
open.
Figure 3. Section of the 1H,1H NOESYspectrum of 2c. There are no
contacts from the BArF to the cation.
5946 Inorganic Chemistry, Vol. 44, No. 16, 2005

+
Cationic (η6-Arene)Mn(CO)3 Complexes
to a described procedure.38c CH2Cl2 was dried and distilled over
CaH2, and all of the complexation reactions were carried out in
the dark under an inert atmosphere. For the anion metathesis,
NaBPh4 was purchased from Avocado, and NaBArF was prepared
according to the procedure described by Reger.39 These anion
exchanges were performed in air. NMR spectra of complexes 1a-
3a were recorded on a Bruker ARX 200 MHz or Avance 400 MHz
spectrometer. 1H and 13C signals of residual acetone were used as
internal standard at δ ) 2.09 and 30.60, respectively. Deuterated
solvents used in the PGSE experiments were dried by distillation
over molecular sieves and stored over molecular sieves under N2.
MS/HRMS were obtained from the University of Lille on an
Applied Biosystems Voyager DE-STR MALDI-TOF MS. Infrared
spectra were measured on a Bruker Tensor 27 spectrometer via
the “single reflection horizontal ATR” method, which allows one
to deposit the pure product on a crystalline diamond surface.
Consequently, the samples are “neat” in that they are not mixed
with a support material.
Table 4. 1H and 13C NMR Data for the Saltsa
1b
1c
δ
assignment
δ
assignment
1H
7.38 ortho-BPh4
meta-arom Mn
7.80 ortho-BArF
7.55 meta-arom Mn
6.95 meta-BPh4
6.79 para-BPh4
6.50 ortho-arom. Mn
4.16 Me-O
-
-
7.69 para-BArF
6.69 ortho-arom. Mn
4.24 Me-O
60.1 Me-O
84.8 ortho-arom Mn
105.2 meta-arom Mn
108.5 quaternary-Cl-arom Mn
119.1 para- BArF
136.2 ortho- BArF
130.8 meta- BArF
13C 58.4 Me-O
82.7 ortho-arom Mn
103.3 meta-arom Mn
106.5 quaternary-Cl-arom Mn
121.6 para-BPh4
125.4 meta-BPh4
136.1 ortho-BPh4
147.1 quaternary-MeO-arom Mn 149.1 quaternary-MeO-arom Mn
164.1 quaternary-BPh4
214.7 CO
163.3 quaternary- BArF
216.3 CO
-
-
126.1 CF3
2b
2c
Diffusion Measurements. All of the measurements were per-
formed on a Bruker Avance spectrometer, 400 MHz, equipped with
a microprocessor-controlled gradient unit and a multinuclear inverse
probe with an actively shielded Z-gradient coil.
δ
assignment
δ
assignment
1H
7.37 ortho-BPh4
6.94 meta-BPh4
6.79 para-BPh4
7.09 meta-arom Mn
6.38 ortho-arom Mn
6.23 para-arom Mn
4.17 Me-O
7.80 ortho-BArF
-
-
7.69 para-BarF
The gradient shape was rectangular and its length was of 1.75
ms. Its strength was increased by steps of 4% during the course of
the experiment. The time between midpoints of the gradients was
167.75 ms for all experiments. The experiments were carried out
at a set temperature of 299 K within the NMR probe. Cation
6.52 meta-arom Mn
6.52 ortho-arom Mn
6.38 para-arom Mn
4.24 Me-O
13C 59.5 Me-O
84.4 ortho-arom Mn
59.6 Me-O
84.8 ortho-arom Mn
107.0 meta-arom Mn
91.5 para-arom Mn
119.2 para-BArF
136.3 ortho-BArF
130.8 meta-BArF
1
diffusion rates were measured using the H signal from the MeO
106.7 meta-arom Mn
91.1 para-arom Mn
123.1 para-BPh4
127.0 meta-BPh4
137.7 ortho-BPh4
group, and anion diffusion was obtained from the 1H signal of the
ortho proton of the aromatic ring attached to boron. In the case of
3c in CD2Cl2, the anion diffusion was also measured using the 19
F
151.4 quaternary-MeO-arom Mn 151.8 quaternary-MeO-arom Mn
signal for comparison. The error coefficient for the D values is (
0.06.
Preparation of [(η6-Arene)Mn(CO)3][BF4] (1a-3a). Com-
plexes 1a-3a were prepared following previously described
complexation procedures38a,b by reaction of the arene with a mixture
of BrMn(CO)5 and AgBF4 in dichloromethane.
165.7 quaternary-BPh4
217.3 CO
151.8 quaternary-BArF
217.3 CO
123.5 CF3
a 1H (400 MHz) and 13C (100 MHz) NMR spectra were recorded in d6-
acetone at 299 K.
[(η6-1-Chloro-4-methoxybenzene)Mn(CO)3][BF4]
(1a).
Table 5. 1H and 13C NMR Data for the Saltsa
Yield: 55%. 1H NMR (200 MHz, acetone-d6): δ 4.23 (s, 3H, OMe),
2b (50mM)
assignment
2b (2mM)
assignment
6.67 (d, 3J ) 7.6 Hz, 2H, H3,5), 7.53 (d, 3J ) 7.6 Hz, 2H, H2,6). 13
C
δ
δ
NMR (100 MHz, acetone-d6): δ 60.1 (OMe), 84.8 (C3,5), 105.4
(C2,6), 108.2 (C1), 149.2 (C4), 216.2 (Mn(CO)3+). IR (ATR Diamant,
cm-1): ν 2021 (Mn(CO)3+), 2077 (Mn(CO)3+).
1H
7.53
7.07
6.90
5.36
4.58
4.69
3.52
ortho-BPh4
meta-BPh4
para-BPh4
7.50
7.08
6.90
5.73
4.94
5.05
3.68
ortho-BPh4
meta-BPh4
para-BPh4
meta-arom Mn
ortho-arom Mn
para-arom Mn
Me-O
[(η6-Anisole)Mn(CO)3][BF4] (2a). Yield: 77%. 1H NMR (200
MHz, acetone-d6): δ 4.24 (s, 3H, OMe), 6.36 (t, 3J ) 6.7 Hz, 1H,
meta-arom Mn
ortho-arom Mn
para-arom Mn
Me-O
3
3
H4), 6.51 (d, J ) 6.7 Hz, 2H, H2,6), 7.22 (t, J ) 6.7 Hz, 2H,
H3,5). 13C NMR (100 MHz, acetone-d6): δ 59.5 (OMe), 84.7 (C2,6),
91.4 (C4), 107.0 (C3,5), 151.7 (C1), 217.3 (Mn(CO)3+). IR (ATR
Diamant, cm-1): ν 2004 (Mn(CO)3+), 2071 (Mn(CO)3+).
[(η6-1,3,5-Trimethoxybenzene)Mn(CO)3][BF4] (3a). Yield: 70%.
1H NMR (200 MHz, acetone-d6): δ 4.25 (s, 9H, OMe), 6.20 (s,
3H, H2). 13C NMR (100 MHz, acetone-d6): δ 59.8 (OMe), 66.2
(C2), 151.6 (C1), 218.4 (Mn(CO)3+). IR (ATR Diamant, cm-1): ν
2013 (Mn(CO)3+), 2067 (Mn(CO)3+).
13C
58.7
Me-O
81.4
104.2
88.0
122.6
136.3
126.6
149.3
164.5
214.8
ortho-arom Mn
meta-arom Mn
para-arom Mn
para-BPh4
ortho-BPh4
meta-BPh4
quaternary-MeO-arom Mn
quaternary-BPh4
CO
Anion Metathesis. Complexes 1b-3b and 1c-3c were prepared
from 1a-3a and either NaBPh4 or NaBArF (NaX) according to
the following general procedure. In a 100 mL Erlenmeyer flask
equipped with a magnetic stirring bar, the [(η6-arene)Mn(CO)3][BF4]
complex (0.5 mmol) was dissolved in the minimum amount of water
(50 mL). A concentrated solution of NaX (1.0 equiv) in methanol
(2 mL) was then added. The resulting mixture was stirred for 15
min. The reaction mixture was extracted twice with dichloromethane
(30 mL). The combined organic phases were washed with water
a 1H (400 MHz) and 13C (100 MHz) NMR spectra were recorded in
CD2Cl2 at 299 K. The 1H spectra were recorded at two concentrations, but
the 13C at the higher concentration only.
General Procedures. Mn2(CO)10 was purchased from Aldrich;
AgBF4, anisole, and 1-chloro-4-methoxybenzene were purchased
from Acros Organics, and 1,3,5-trimethoxybenzene was purchased
from Avocado. Anisole and 1-chloro-4-methoxybenzene were
distilled over CaH2 prior to use. BrMn(CO)5 was prepared according
Inorganic Chemistry, Vol. 44, No. 16, 2005 5947

Schott et al.
1
(30 mL), dried over magnesium sulfate, and filtered. Evaporation
of the solvent under reduced pressure produced the [(η6-arene)-
Mn(CO)3][X] complex as a light yellow powder.
119.2 (C para-BArF), 126.1 (q, JCF ) 270 Hz, CF3), 130.8 (q,
2JCF ) 31 Hz, C meta-BArF), 136.3 (C ortho-BArF), 151.5 (C1),
163.3 (q, JCB ) 50 Hz, C-B), 218.4 (Mn(CO)3+). MALDI TOF
1
[(η6-1-Chloro-4-methoxybenzene)Mn(CO)3][BPh4]
(1b).
MS positive mode (m/z): 307.01 ([(η6-1,3,5-trimethoxybenzene)-
Mn(CO)3]+). MALDI TOF MS negative mode (m/z): 863.3
(BArF-).
Yield: 81%. MALDI TOF MS positive mode (m/z): 280.93 ([(η6-
1-chloro-4-methoxybenzene)Mn(CO)3]+). MALDI TOF MS nega-
tive mode (m/z): 319.1 (BPh4-).
Acknowledgment. The support and sponsorship of this
research by COST Action D24 “Sustainable Chemical
Processes: Stereoselective Transition Metal-Catalyzed Reac-
tions” are kindly acknowledged. P.S.P. also thanks the Swiss
National Science Foundation and the ETH Zurich for support
and the Johnson Matthey company for the loan of metal salts.
We thank Dr. P. G. Anil Kumar for the diffusion measure-
ments on 4 and Dr. Heinz Ru¨egger for his advice. We thank
the CNRS for financial support, the Ministe`re de l’Education
Nationale et de la Recherche for an A. C. grant to B. J., Dr.
Patrick Herson (Laboratoire de Chimie Inorganique et
Mate´riaux Mole´culaires, UMR 7071, Universite´ P. et M.
Curie, Paris) for the X-ray study, and Prof. C. Rolando and
Dr. G. Ricart from the Universite´ des Sciences et Techniques
de Lille for the MS and HRMS analyses.
[(η6-1-Chloro-4-methoxybenzene)Mn(CO)3][BArF]
(1c).
Yield: 78%. MALDI TOF MS positive mode (m/z): 280.9 ([(η6-
1-chloro-4-methoxybenzene)Mn(CO)3]+), 224.9 ([(η6-1-chloro-4-
methoxybenzene) Mn(CO)]+). MALDI TOF MS negative mode
(m/z): 863.1 (BArF-).
[(η6-Anisole)Mn(CO)3][BPh4] (2b). Yield: 86%. MALDI TOF
MS positive mode (m/z): 246.99 ([(η6-anisole)Mn(CO)3]+). MALDI
TOF MS negative mode (m/z): 319.2 (BPh4-).
[(η6-Anisole)Mn(CO)3][BArF] (2c). Yield: 87%. MALDI TOF
MS positive mode (m/z): 246.9 ([(η6-anisole)Mn(CO)3]+), 191.0
([(η6-anisole)Mn(CO)]+. MALDI TOF MS negative mode (m/z):
863.1 (BArF-).
[(η6-1,3,5-Trimethoxybenzene)Mn(CO)3][BPh4] (3b). Yield:
93%. 13C NMR (100 MHz, acetone-d6): δ 59.7 (OMe), 66.2 (C2),
122.9 (C para-BPh4), 137.7 (bs, C ortho-BPh4), 126.7 (C meta-
1
BPh4), 151.3 (C1), 165.6 (q, JCB ) 49 Hz, C-B), 218.3 (Mn-
(CO)3+). MALDI TOF MS positive mode (m/z): 307.02 ([(η6-1,3,5-
trimethoxybenzene) Mn(CO)3]+). MALDI TOF MS negative mode
(m/z): 319.2 (BPh4-).
Supporting Information Available: One X-ray crystallographic
file in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
[(η6-1,3,5-Trimethoxybenzene)Mn(CO)3][BArF] (3c). Yield:
92%. 13C NMR (100 MHz, acetone-d6): δ 59.9 (OMe), 66.3 (C2),
IC0506409
5948 Inorganic Chemistry, Vol. 44, No. 16, 2005