Synthesis and structural studies of cationic bis- and tris(pyrazol-1-yl)methane acyl and methyl complexes of ruthenium(II): Localization of the counterion in solution by NOESY NMR spectroscopy

Article abstract of DOI:10.1021/om980631q

Complex fac-Ru(PMe₃)(CO)₃(Me)I (1) reacts with tris- and bis(pyrazol-1-yl)methane, in the presence of NaBPh₄, affording cis-[Ru(PMe₃)(CO)₂(COMe)(η²-pz ₃-CH)]BPh₄ (2) and cis-[Ru(PMe₃)(CO)₂(COMe)(pz₂-CH ₂)]BPh₄ (4), respectively. Complexes 2 and 4 decarbonylate leading to [Ru(PMe₃)(CO)(COMe)(η³-pz₃-CH)]BPh ₄ (3) and a mixture of three methyl stereoisomers of cis-[Ru(PMe₃)(CO)₂(Me)(pz₂-CH ₂)]BPh₄ (5-7), respectively. The byproduct of the synthesis of 1, fac,cis-Ru(PMe₃)(CO)₃(I)2 (8), reacts with bis(pyrazol-1-yl)methane affording cis-[Ru(PMe₃)(CO)₂(I)(pz₂-CH ₂)]BPh₄ (9). The stereochemistry of the complexes, the dynamic processes existing between them, and the interionic structures of all of the cationic complexes were investigated by the phase-sensitive ¹H. NOESY NMR spectra in CD₂Cl₂. The solid-state crystal structure of 4, obtained by single-crystal X-ray studies, was compared from the intramolecular and interionic point of views with that in solution with the help of 3-21G* ab initio and AMI-SM2 semiempirical quantum mechanical and docking mechanic calculations. In particular, the differences of interaction energy of the six solid-state ion pairs determined by the cation and the six symmetry-related anions surrounding it were estimated. The main result is that the averaged preferred position of the counterion in solution corresponds to the ion-pair electrostatically (ΔE_el > 2.5 kcal/mol) and sterically (ΔE_st > 3.7 kcal/mol) favored in the solid state.

Full text of DOI:10.1021/om980631q

Organometallics 1998, 17, 5549-5556
5549
Syn th esis a n d Str u ctu r a l Stu d ies of Ca tion ic Bis- a n d
Tr is(p yr a zol-1-yl)m eth a n e Acyl a n d Meth yl Com p lexes of
Ru th en iu m (II): Loca liza tion of th e Cou n ter ion in
Solu tion by NOESY NMR Sp ectr oscop y
Alceo Macchioni,*,† Gianfranco Bellachioma,† Giuseppe Cardaci,†
Gabriele Cruciani,† Elisabetta Foresti,‡ Piera Sabatino,‡ and Cristiano Zuccaccia†
Dipartimento di Chimica, Universita` di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy,
and Dipartimento di Chimica “G. Ciamician”, Universita` di Bologna, Via Selmi 2,
40126 Bologna, Italy
Received J uly 24, 1998
Complex fac-Ru(PMe3)(CO)3(Me)I (1) reacts with tris- and bis(pyrazol-1-yl)methane, in
the presence of NaBPh4, affording cis-[Ru(PMe3)(CO)2(COMe)(η2-pz3-CH)]BPh4 (2) and cis-
[Ru(PMe3)(CO)2(COMe)(pz2-CH2)]BPh4 (4), respectively. Complexes 2 and 4 decarbonylate
leading to [Ru(PMe3)(CO)(COMe)(η3-pz3-CH)]BPh4 (3) and a mixture of three methyl
stereoisomers of cis-[Ru(PMe3)(CO)2(Me)(pz2-CH2)]BPh4 (5-7), respectively. The byproduct
of the synthesis of 1, fac,cis-Ru(PMe3)(CO)3(I)2 (8), reacts with bis(pyrazol-1-yl)methane
affording cis-[Ru(PMe3)(CO)2(I)(pz2-CH2)]BPh4 (9). The stereochemistry of the complexes,
the dynamic processes existing between them, and the interionic structures of all of the
1
cationic complexes were investigated by the phase-sensitive H NOESY NMR spectra in
CD2Cl2. The solid-state crystal structure of 4, obtained by single-crystal X-ray studies, was
compared from the intramolecular and interionic point of views with that in solution with
the help of 3-21G* ab initio and AMI-SM2 semiempirical quantum mechanical and docking
mechanic calculations. In particular, the differences of interaction energy of the six solid-
state ion pairs determined by the cation and the six symmetry-related anions surrounding
it were estimated. The main result is that the averaged preferred position of the counterion
in solution corresponds to the ion-pair electrostatically (∆Eel > 2.5 kcal/mol) and “sterically”
(∆Est > 3.7 kcal/mol) favored in the solid state.
In tr od u ction
actions with the organometallic moiety are difficult to
obtain. This prompted us to search for a different
approach to investigate organometallic ion pairs in
solution based on NMR. We developed a method5 that
allows the determination of the interionic structures6
of cationic organometallic complexes in solution based
on the detection of interionic contacts, i.e., dipolar
interactions between nuclei belonging to the counterion
and to the organometallic moieties, in the NOESY or
HOESY NMR spectra. The main result of this method
is the possibility to understand which is the averaged
position of the counterion with respect to the organo-
metallic moiety. For compounds having the general
formula trans-[M(PMe3)2(CO)(COMe)(NkN)]X (M ) Fe
Cationic organometallic complexes have been increas-
ingly used intensively in homogeneous catalysis. In
particular, a noninnocent role is now attributed to the
counterion in activating or preventing catalytic pro-
cesses such as olefin polymerizations,1 CO-olefin copo-
lymerizations,2 Diels-Alder reactions.3 It is generally
accepted that the counterion has to be large and weakly
coordinating4 in order to enhance the chemical reactivity
of metal complexes and obtain a better catalyst. On the
other hand, direct information concerning the coordi-
nating capacity of the counterion and its specific inter-
† Universita` di Perugia.
‡ Universita` di Bologna.
(5) (a) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G.;
Terenzi, S. Organometallics 1996, 15, 4349. (b) Macchioni, A.; Bella-
chioma, G.; Cardaci, G.; Gramlich, V.; Ru¨egger, H.; Terenzi, S.;
Venanzi, L. M. Organometallics 1997, 16, 2139.
(1) (a) Chen, Y.-X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1997,
119, 2582. (b) J ia, L.; Yang, X.; Stern, C. L.; Marks, T. J . Organome-
tallics 1997, 16, 842. (c) Chen, Y.-X.; Stern, C. L.; Yang, X.; Marks, T.
J . J . Am. Chem. Soc. 1996, 118, 12451. (d) Yang, X.; Stern, C. L.;
Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10015.
(2) (a) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267. (b) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996,
96, 663. (c) Milani, B.; Vicentini, L.; Sommazzi, A.; Garbassi, F.;
Chiarparin, E.; Zangrando, E.; Mestroni, G. J . Chem Soc., Dalton
Trans. 1996, 3139.
(3) (a) Evans, D. A.; Murry, J . A.; von Matt, P.; Norcross, R. D.;
Miller, S. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 798. (b) Carmona,
D.; Cativiela; C.; Garcia-Correas, R.; Lahoz, F. J .; Lamata, M. P.; Lopez,
J . A.; Lopez-Ram de Viu, M. P.; Oro, L. A.; San J ose´, E.; Viguri, F.
Chem. Commun. 1996, 1247.
(6) For references on interionic studies of organic salts which
catalyze phase-transfer reactions see: (a) Pochapsky, T. C.; Wang, A.-
P.; Stone, P. M. J . Am. Chem. Soc. 1993, 115, 11084. (b) Pochapsky,
T. C.; Stone, P. M. J . Am. Chem. Soc. 1990, 112, 6714. (c) Pochapsky,
T. C.; Stone, P. M. J . Am. Chem. Soc. 1991, 113, 1460. For references
on interionc studies of organolithium ion pairs, see: (d) Hoffman, D.;
Bauer, W.; Schleyer, P. v. R. J . Chem Soc., Chem. Commun. 1990, 208.
(e) Bauer, W.; Mu¨ller, G.; Pi, R.; Schleyer, P. v. R. Angew. Chem., Int.
Ed. Engl. 1986, 25, 1103. (f) Bauer, W.; Klusener, P. A. A.; Harder, S.;
Kanters, J . A.; Duisenberg, A. J . M.; Brandsma, L.; Schleyer, P. v. R.
Organometallics 1988, 7, 552. (g) Bauer, W.; Clark, T.; Schleyer, P. v.
R. J . Am. Chem. Soc. 1987, 109, 970. (h) Bauer, W.; Feigel, M.; Mu¨ller,
G.; Schleyer, P. v. R. J . Am. Chem. Soc. 1988, 110, 6033.
(4) Strauss, S. H. Chem. Rev. 1993, 93, 927.
10.1021/om980631q CCC: $15.00 © 1998 American Chemical Society
Publication on Web 11/14/1998

5550 Organometallics, Vol. 17, No. 25, 1998
Macchioni et al.
Ch a r t 1
Sch em e 1
and Ru), we found that the counterion interacts in
methylene chloride specifically with protons belonging
to the NkN ligands and to the PMe3 groups. In no case
were there contacts between the NMR-active nuclei of
the counterion and the COMe protons. These observa-
tions were done both for “organic” counterions (X )
BPh4) and “inorganic” counterions (X ) BF4). It is
evident that the specific averaged position of the coun-
terions cannot be explained on the basis of only a
maximization of the van der Waals interactions but
must also involve an electrostatic gain.
In this paper, we report the synthesis of other new
cationic compounds, shown in Chart 1, derived from the
reaction of fac-Ru(PMe3)(CO)3(Me)I7 (1) with bis- and
tris(pyrazol-1-yl)methane ligands. Different from the
above-mentioned compounds, the acyl compounds de-
carbonylate affording a mixture of methyl complexes
that are in slow equilibrium in solution compared to the
NMR time scale. The phase-sensitive 1H NOESY NMR
spectra allows the dynamical processes, the stereochem-
istry of the various stereoismers, and the more interest-
ing interionic structures of the cationic complexes to be
investigated. A comparison between the solid-state
structure of complex 4 (obtained by X-ray single-crystal
studies) and that in solution carried out with the help
of semiempirical and ab initio quantum mechanical and
mechanical calculations is also reported. The semiem-
pirical and ab initio quantum mechanical calculations
allowed us to evaluate the electron density on both ionic
fragments. The mechanic calculations led to the energy
interaction values of six ion pairs determined by the six
symmetry-related anions surrounding the cation in the
solid state.
solution.7 Even in the solid state, it slowly decomposes
and is usually stored as a mixture of acyl complexes
under CO atmosphere.
Complex 1 can easily ionizise the Ru-I bond. It also
undergoes methyl migration on a cis CO and dissocia-
tion of a Ru-CO bond. A maximum of three coordina-
tion sites can be potentially left free.
The reaction of complex 1 with pz3-CH (pz ) pyrazol-
1-yl ring) in the presence of NaBPh4 affords the acyl
η2-complex 2, according to Scheme 1, where one of the
pz rings remains uncoordinated.
By dissolving complex 2 in CH2Cl2 and bubbling in
the solution N2, it is possible to allow the coordination
of the third pyrazolyl ring, forming the η3-complex 3.
Complex 3 is a very stable complex that is not sensitive
to moisture, does not react with CO to give back complex
2, and does not undergo further decarbonylation.
The reaction of complex 1 with pz2-CH2 in the pres-
ence of NaBPh4 affords only one acyl complex (4) (see
Scheme 2) whose stereochemistry in solution and in the
solid state has been clarified by 1H NOESY NMR
spectroscopy and X-ray single-crystal studies, respec-
tively (see below).
Resu lts a n d Discu ssion
Syn th esis. The oxidative addition of MeI on Ru-
(PMe3)(CO)4 affords a mixture of acyl complexes that
easily decarbonylate by bubbling N2 in the solution
leading to the methyl complex 1 that is unstable in
(7) (a) Reichenbach, G.; Cardaci, G.; Bellachioma, G.; J . Chem. Soc.,
Dalton Trans., 1982, 847. (b) Bellachioma, G.; Cardaci, G.; Macchioni,
A.; Madami A. Inorg. Chem. 1993, 32, 554.
Complex 4 is also insensitive to moisture but in CH2-
Cl2 solution it undergoes spontaneous decarbonylation

Bis- and Tris(pyrazol-1-yl)methane Complexes
Organometallics, Vol. 17, No. 25, 1998 5551
Sch em e 2
reaching an equilibrium with a mixture of three methyl
complexes 5-7 in the ratio 1:1.6:0.1 at 25 °C. By
warming the solution to 38 °C, the equilibrium is
completely shifted toward the methyl complexes. Com-
plexes 5-7 equilibrate in solution, and any attempt to
separate them was unsuccessful. The stereochemistry
of complexes 5-7 has been clarified by 1H NOESY NMR
spectroscopy (see below). The acyl complex 4 is regained
by dissolving the methyl mixture in CH2Cl2 under CO
atmosphere for 2 h.
Both the coordination of the third pyrazolyl ring in
the case of the reaction of 1 with pz3-CH and the
possibility to decarbonylate complex 4 to obtain the
methyl complexes 5-7 derive from the lower electron
density on ruthenium complexes respect to the analo-
gous ones deriving from trans-Ru(PMe3)2(CO)2(Me)I5b
due to the presence in complex 1 of only one phosphine.
This weakens the Ru-CO bond and allows the decar-
bonylation.
One of the byproduct of the oxidative addition of MeI
to complex 1 is complex 8 that can react with pz2-CH2
in the presence of NaBPh4 affording complex 9 owing
to the ionization of one Ru-I bond and dissociation of a
Ru-CO bond.
Ch a r a cter iza tion a n d Str u ctu r e. (a ) Solu tion s.
In tr a m olecu la r Str u ctu r e. Characterization of com-
plexes 2-9 in this phase was carried out with IR and
1H, 13C, and 31P NMR spectroscopies.
with the protons of the phosphine and of the COMe
group and must be H-3. The remaining resonance at
7.62 ppm is due to H-3′′. The other protons of the rings
are assigned by the “intraring” contacts.
The stereochemistry of complex 4 derives from the
observation in the 1H NOESY NMR spectrum of two
“contacts” between both H-3 and H-3′ protons and the
protons of PMe3 that ensure that the two pyrazolyl rings
are both in the relative cis position with respect to PMe3.
Furthermore, the fact that they are not equivalent leads
to the stereochemistry reported in Chart 1.
The stereochemistry of the methyl complexes 5 is
straightforward obtained because of the equivalence of
the two pyrazolyl rings. The stereochemistry of complex
6 is derived from considerations similar to the previous
ones. In fact, one of the H-3 shows a contact only with
the protons of Me, while H-3′ shows contacts with the
protons of Me and of PMe3. The only possible structure
is reported in Chart 1. The determination of the third
methyl complex 7 having very low concentration can
also be done considering that it is the only other possible
one having the two CH2 protons inequivalent.
The two protons of the CH2 groups in complexes 4-7
and 9 are inequivalent and their assignment is done
based on the presence of contacts with the protons of
the apical groups. The frequencies of resonance of these
protons are relatively low (4.5-5.5 ppm) indicating a
shielding of the aromatic groups of the tetraphenylbor-
ate.4a This is confirmed by the interionic contacts.
The IR spectra of complexes show bands in the
carbonyl region between 2080-1940 and 1645-1600
cm-1, relative to the CO and COMe stretchings, respec-
tively. When complexes contain two carbonyl groups
(2, 4-7, and 9), we observe two stretching bands having
similar intensity. This ensures that the two carbonyl
groups are in the relative cis position.
1
It is interesting to notice that the phase-sensitive H
NOESY spectrum of the methyl mixture shows some
cross-peaks with the same sign of the diagonal indicat-
ing the presence of exchange processes. In particular,
there are exchange cross-peaks between (a) the methyl
groups belonging to the two methyl complexes 5 and 6;
(b) the H-3 belonging to the two methyl stereoisomers
5 and 6; and (c) the methyl group of complex 6 with the
COMe group of 4 present in very low quantity. These
observations are explainable only by assuming the
formation of one or more unsaturated intermediates.
The assignment of carbon resonances was carried out
in some cases by 1H,13C inverse correlation experiments
with gradients or considering that the order of reso-
The characterization of complex 2 is not complete
because, in solution, it transforms into complex 3. In
complex 3, all three pyrazolyl rings are nonequivalent
owing to the different trans substituents. Consequently,
1
there are nine resonances both in the H and the 13C
NMR spectra. The assignment of the H-3 protons,
1
which fall at higher frequency, is easily done by the H
NOESY NMR spectrum considering that only the H-3′
(7.89 ppm) (for numeration see Chart 1) does not show
any contact with the protons of the phosphine and must
belong to the pyrazolyl ring trans to PMe3. Further-
more, only the resonance at 8.41 ppm shows contacts
1
nances in 13C is the same as in H spectra.
In ter ion ic Str u ctu r es. The interionic structures of
complexes 3-6 and 9 were investigated in CD2Cl2 by
1
the phase-sensitive H NOESY NMR spectra by detect-

5552 Organometallics, Vol. 17, No. 25, 1998
Macchioni et al.
1
F igu r e 1. Two sections of H NOESY spectrum of com-
pound 4, recorded at 400.13 MHz in CD2Cl2, showing the
interionic contacts between the PMe3 group and o-H, m-H,
and p-H protons, and between CH2 and o-H protons.
1
F igu r e 2. Section of H NOESY spectrum of compound
9, recorded at 400.13 MHz in CD2Cl2, showing the specific
interionic contact between the H-1 and o-H, and intramo-
lecular contact between H-1 and H-5.
-
ing contacts between protons belonging to the BPh4
and those of the organometallic moieties. The informa-
tion derived from the detection of nuclear dipolar
interactions in solution allows the determination of the
averaged interionic structures.
Complex 3 shows interionic contacts between the H-5
protons and the o-H (strong) and between the protons
of the PMe3 group and the m-H (weak). In complex 4
there are interionic contacts between CH2 and PMe3
(weak) protons and o-H, m-H, and p-H (see Figure 1).
The intensity of cross-peaks of the section relative to
PMe3 groups in Figure 1 have been multiplied 32 times.
Complex 5 shows interionic contacts between the PMe3
protons and the m-H and p-H and between the H-5
protons and the o-H. Complex 6 shows only interionic
contacts between H-5 protons and o-H and m-H. Com-
plex 9 shows interionic contacts between the PMe3
protons and the m-H and p-H. Furthermore, a selective
interionic contact between H-1 and o-H protons has been
observed (see Figure 2). In general, in all complexes,
there is a preferential interaction between the more
shielded H-1 and o-H protons. Also, the intramolecular
contact H-5-H-1 is stronger than H-5-H-2 that is not
visible in Figure 2. These findings are perfectly ex-
plainable considering that H-1, which points toward one
phenyl ring of BPh4-, is also closer to H-5 than H-2 (see
scheme inside Figure 2).
F igu r e 3. An ORTEP view of cationic fragment of 4.
phosphine group, while in complex 6 it stays in front of
the face determined by the pyrazolyl rings and the CO
trans to Me. In none of the spectra are there contacts
between the protons of the tetraphenylborate counterion
and the Me and COMe groups.
(b) Cr ysta l a n d Molecu la r Str u ctu r e of Ca tion
-
From the above observations, one can deduce as a
general consideration that in all cases the counterion
spends most of its time close to the pyrazolyl rings, in
agreement with previous results.5 Furthermore, in
complexes 3-5, the counterion is shifted toward the
4 As Its BP h 4 Sa lt. The overall molecular geometry
of cation 4 is shown in Figure 3; Table 1 reports selected
bond distances and angles. The coordination geometry
at the metal center is approximately octahedral, with
mutually cis carbonyl ligands and an equatorial plane

Bis- and Tris(pyrazol-1-yl)methane Complexes
Organometallics, Vol. 17, No. 25, 1998 5553
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 4
Ta ble 2. Sym m etr y Op er a tion s Rela tin g An ion s
(i)
1 - x
x
-y
-z
z
(ii)
(iii)
(iv)
(v)
1 + y
Ω - y
-Ω - y
-y
Bond Lengths (Å)
x
x
Ω + z
Ω + z
-z
Ru-C(1)
Ru-C(2)
Ru-C(3)
Ru-N(1)
Ru-N(3)
Ru-P
N(1)-C(10)
N(1)-N(2)
N(2)-C(8)
N(2)-C(11)
N(3)-C(14)
1.858(7)
1.921(6)
2.056(6)
2.190(5)
2.233(5)
2.401(2)
1.331(7)
1.337(6)
1.346(7)
1.442(7)
1.333(7)
N(3)-N(4)
N(4)-C(12)
N(4)-C(11)
O(1)-C(1)
O(2)-C(2)
O(3)-C(3)
C(3)-C(4)
C(8)-C(9)
C(9)-C(10)
C(12)-C(13)
C(13)-C(14)
1.351(6)
1.351(7)
1.430(7)
1.131(8)
1.125(7)
1.222(8)
1.488(9)
1.350(8)
1.374(9)
1.345(9)
1.368(9)
2 - x
Bond Angles (deg)
C(1)-Ru-C(2)
C(1)-Ru-C(3)
C(2)-Ru-C(3)
C(1)-Ru-N(1)
C(2)-Ru-N(1)
C(3)-Ru-N(1)
C(1)-Ru-N(3)
C(2)-Ru-N(3)
C(3)-Ru-N(3)
N(1)-Ru-N(3)
C(1)-Ru-P
86.8(3)
92.5(3)
84.1(3)
175.5(2)
96.5(2)
90.9(2)
91.0(2)
98.2(2)
176.0(2)
85.6(2)
90.1(2)
C(2)-Ru-P
173.5(2)
90.4(2)
C(3)-Ru-P
N(1)-Ru-P
N(3)-Ru-P
87.02(12)
87.46(14)
122.2(3)
120.9(5)
121.6(3)
119.2(5)
178.1(6)
170.4(6)
N(2)-N(1)-Ru
N(1)-N(2)-C(11)
N(4)-N(3)-Ru
N(3)-N(4)-C(11)
O(1)-C(1)-Ru
O(2)-C(2)-Ru
F igu r e 4. A ball and stick representation of the ionic pair
where the notably shortest Ru‚‚‚B metal contact is found.
The counterion, BPh4-, orients two of its phenyl
groups almost parallel to the two pyrazolyl rings (angles
between the normals to the planes passing through
C(15) to C(20) with pz(2) (N(3) to C(14)) and C(21) to
C(26) with pz(1) (N(1) to C(10)) of 19° and 15°, respec-
tively.
defined by the bis-pyrazolyl ligand, the acyl group, and
one carbonyl. The axial sites are occupied by the second
CO and the phosphine ligands. The cation is clearly
chiral, but the crystal contains the racemic mixture. The
phosphine ligand is slightly bent toward the bis-pyra-
zolyl moiety (P-Ru-N1 87.0(1)° and P-Ru-N3 87.5-
(1)°) while the trans carbonyl ligand bends away from
it (C2-Ru-N3 98.2(2)°, C2-Ru-N1 96.5(2)° and C2-
Ru-C3 83.9°). The P-Ru-C(2) angle is 173.5(2)°.
Hydrogen bond interactions are found exclusively
within the cations, one intramolecular C(10)-H(10)‚‚‚
O3 and one intermolecular one C(4)-H(4)‚‚‚O(3) (sym-
metry operator 1-x, 1-y, -z) with D‚‚‚A distances of
2.94 and 3.49 Å, respectively, and D-H‚‚‚A angles of
115° and 154°.
The two Ru-N bond distances (2.190(5) and 2.233(5)
Å for Ru-N(1) and Ru-N(3), respectively) are slightly
shorter than those reported5b for the parent species
trans-[Ru(PMe3)2(CO)(COMe)(pz2-CH2)]BPh4 (2.218(15)
and 2.257(14) Å) and, like the latter, are significantly
different, with the longer distance always trans to the
better donor acyl ligand. The two pyrazolyl rings show
complete planarity in each ring but are not coplanar
(dihedral angle between the normals to the two planes
55°). The six-membered metallacycle containing the
four nitrogen atoms adopts a half-chair conformation
with the C(11) atom out of the least-squares plane
through the remaining five of 0.79 Å and oriented on
the side of the least hindering axial CO ligand.
Of the three Ru-C bond lengths, that relative to the
acyl group, 2.056(6) Å, is strictly comparable to that
found in the above-mentioned trans-[Ru(PMe3)2(CO)-
(COMe)(pz2-CH2)]BPh4, (2.055 Å), while the two metal-
Ccarbonyl distances are quite dissimilar (1.858(7) and
1.921(6) Å for Ru-C(1) and Ru-C(2), respectively),
reflecting the different electronic configurations of the
relative trans ligands. The longer Ru-Cacyl distance
compared with Ru-Ccarbonyl is primarily due to the fact
that the CO ligands interact with two sets of π orbitals.
The plane defined by the acyl ligand is almost coincident
with the equatorial coordination plane (dihedral angle
14°), giving evidence of a delocalized Ru-C(3)-O(3) π
bond.
Solid Sta te ver su s Solu tion In ter ion ic Str u ctu r e
of Com p lex 4. Since the main interest in the structure
was focused on the H‚‚‚H interionic contacts, we have
calculated, in the solid state, a 3.5 Å coordination sphere
around each hydrogen atom. This way, we have evi-
denced the six symmetry-related anions surrounding the
cation and giving the closest contacts with it; the
relative symmetry operations are shown in Table 2.
It is interesting to note that strong interionic contacts
(starting from 2.45 Å) between the PMe3 moiety in the
-
cation and the o-, m-, and p-H atoms of the BPh4
phenyl groups, already observed in solution, are kept
in the solid state. Analogously, the CH2 protons in C(11)
are also involved in contacts with anionic o- and m-H
atoms. In addition, in contrast to what was observed
in solution, in the solid state the acyl protons are also
involved in interactions with o- and m-H atoms, while
the protons of the pyrazolyl rings interact with o-, m-,
and p-H atoms with distances for both kind of contacts
ranging from 2.55 to 3.49 Å. In conclusion, considering
the six pairs, all of the moieties of the cation bearing
protons are close enough to interact with the protons of
at least one anion (distances < 3.5-4 Å) in the solid
state.
It must be underlined that the ionic pair where the
notably shortest Ru‚‚‚B metal contact is found (6.71 vs
8.39 Å av), i.e., the closest packed pair that was chosen
as the crystallographic asymmetric unit exhibits few
and quite long H‚‚‚H contacts because of the almost
parallel orientation of two phenyl rings with respect to
the pyrazolyl rings as reported above (Figure 4).
Finally, the Ru-P distance, 2.403 Å, trans to a
carbonyl group is longer than those found in the above-
mentioned parent species, where the two phosphine
groups are trans to each other.

5554 Organometallics, Vol. 17, No. 25, 1998
Macchioni et al.
the COMe protons and NMR active nuclei of the
counterions.
The estimation of the electrostatic and “steric” energy
of the cation-anion interaction for all six possible pairs
was calculated by docking mechanic calculations. The
numerical data are reported in Table 3. As a general
trend, the counterion prefers to stay close to the “more
organic” side of the molecule, i.e., close to the pyrazolyl
rings. Furthermore, there is indeed a cation-ion pair
(1 in Figure 5) that is more stabilized than the others
both from the electrostatic and steric points of view (∆E
> 7.3 kcal/mol, ∆Eel > 2.5 kcal/mol, ∆Est > 3.7 kcal/
mol). This is the pair chosen as the crystallographic
asymmetric unit reported in Figure 4 and is the
principal ion pair that we find in solution. It must be
said that in solution we also observed a weak interionic
contact between PMe3 protons and o-H, m-H, and p-H
that is not justified simply considering the pair shown
in Figure 4. Of course, several dynamic processes are
active in solution that we cannot consider from the
simplistic assumption that one solid-state pair is strictly
conserved in solution. For example, an inversion of the
six-member metallacycle containing the four nitrogen
F igu r e 5. A schematization of the six symmetry-related
anions surrounding the cation.
Ta ble 3. Rela tive Electr osta tic (∆Eel)a a n d Ster ic
(∆Est)a En er gy of th e Ca tion -An ion In ter a ction s for
All Six P ossible P a ir s Ca lcu la ted by th e DOCK
Meth od Im p lem en ted in SYBYL12
-
atoms is enough to allow the contacts between BPh4
and PMe3 protons. In any case, as a first approxima-
tion, we can assume that dissolving the salt in meth-
ylene chloride allows the solvent to electronically de-
couple the cation from all but one anion. This last anion
is the one that interacts more strongly with the cation
in the solid state.
pair
∆Eel (kcal/mol)
∆Est (kcal/mol)
∆Etot (kcal/mol)
1
2
3
4
5
6
0
0
0
7.3
7.7
8.4
10.1
10.0
3.6
2.5
4.7
6.2
6.2
3.7
5.2
3.7
3.9
3.8
Con clu sion s
a
Intramolecular and interionic structural studies in
The pair 1 cation that is the most stable is taken as reference,
and ∆E values are calculated as Ex - E1 and are, consequently,
all positive.
solution on new acyl and methyl compounds 2-9 have
1
been performed by H NOESY NMR spectroscopy. In
particular, for compound 4, the interionic structure in
solution was compared with that in the solid state with
the help of quantum mechanical and mechanic calcula-
tions. 3-21G* ab initio and AMI-SM2 semiempirical
quantum mechanical calculations indicated that there
is a partial positive charge delocalized on the pyrazolyl
rings and a partial negative charge accumulated on the
oxygen atom of COMe group. By using such a charge
distribution, the energy interaction values of six ion
pairs determined by the six symmetry-related anions
surrounding the cation in the solid state have been
calculated using the DOCK method implemented in
SYBYL. The ion pair where the counterion stays in
front of the bis-pyrazolyl rings (shown in Figure 4) is
favored in the solid state both from the electrostatic
(∆Eel > 2.5 kcal/mol) and steric (∆Est > 3.7 kcal/mol)
points of view. This is the principal ion pair found in
solution based on the detection of interionic contacts in
In a methylene chloride solution and at our concen-
trations, it is known that organometallic complexes are
principally present as tight ion pairs. We wondered if
one of the six pairs selected in the solid state is the
energetically favored ion pair and if this one is that we
found in solution. For this reason, crystallographic
coordinates of the above-mentioned six cation-anion
pairs have been used as input for a calculation of the
sterical and electrostatic energy involved in ion-pair
interactions (Figure 5, Table 3). We first calculated the
charge distribution in separated fragments. Interest-
ingly, from the 3-21G* ab initio and AMI-SM2 semiem-
pirical calculations, we obtained that the positive charge
is not centered on Ru but is mainly delocalized on the
bispyrazolylmethane ligand. This means that the al-
ready favored counterion-cation interaction on the side
of the pyrazolyl rings from the van der Waals point of
view is reinforced by a stronger electrostatic interaction.
It is now easier to understand why also completely
inorganic counterions (such as BF4-), where we can
assume that the electrostatic interactions are more
important, stay in the same position, in front of the
pyrazolyl rings.5b Another interesting point is that the
oxygen of the acyl group comes out partially negatively
charged. There should be repulsion between this oxy-
gen and the counterion. This agrees perfectly with the
fact that we never observed interionic contacts between
1
the H NOESY NMR spectra. This means that, in the
case of a weak coordinating solvent such as methylene
chloride, the dissolution process corresponds to an
electronically decoupling of the cation from all but the
most stabilized anion in the lattice.
Exp er im en ta l Section
Gen er a l Da ta . Complex 1 was prepared according to the
literature.7 Reactions were carried out in a dried apparatus
under a dry inert atmosphere of nitrogen using standard

Bis- and Tris(pyrazol-1-yl)methane Complexes
Organometallics, Vol. 17, No. 25, 1998 5555
3
3
Schlenk techniques. Solvents were purified prior to use by
conventional methods.8 pz2-CH2 and pz3-CH ligands were
synthesized according to the literature.9 Pyrazole was pur-
chased by Fluka and utilized without further purification.
(d, J HH ) 2.1, H-3′), 7.42 (m, o-H), 7.04 (H-5′), 7.02 (t, J HH
)
3
3
7.4, m-H), 7.01 (H-5), 6.87 (t, J HH ) 7.2, p-H), 6.40 (td, J HH
) 2.5, H-4), 6.36 (t, J HH ) 2.5, H-4′), 4.93(d, J HH ) 15, H-2),
3
2
2
2
4.67 (d, J HH ) 15, H-1), 2.61 (s, COMe), 0.95 (d, J PH ) 9.6,
PMe3); 13C{1H} NMR 243.4 (d, J CP ) 9.7, COMe), 199.1 (d,
2
IR spectra were taken on a 1725 X FTIR Perkin-Elmer
spectrophotometer. One and two-dimensional 1H, 13C, and 31P
NMR spectra were measured on Bruker AC 200, DRX 400,
and DRX 500 spectrometers. Referencing is relative to TMS
and external 85% H3PO4. NMR samples were prepared
dissolving about 20 mg of compound in 0.5 mL of CD2Cl2
bubling for 5 min with dried nitrogen. Two-dimensional 1H
NOESY NMR spectra, with a mixing time 800 ms, were
measured as previously described.10
2J CP ) 16.2, CO (cis)), 189.8 (d, 2J CP ) 94.9, CO (trans)), 164.3
(q, 1J BC ) , C-ipso), 147.8 (s, C-3), 146.1 (s, C-3′), 137.5 (s, C-5),
136.4 (s, o-C), 135.8 (s, C-5′), 126.4 (s, m-C), 122.6 (s, p-C),
108.9 (s, C-4′), 108.2 (s, C-4), 62.1 (s, CH2), 51.9 (s, COCH3),
13.7 (d, J CP ) 30.3, PMe3); 31P{1H} NMR -3.31(s); IR (CH2-
2
Cl2) νCO 2063, 1994, νCOMe 1641 cm-1
.
Deca r bon yla tion of Com p lex 4. Complex 4 (100 mg) was
fluxed with N2 at 35 °C in CH2Cl2 (3 mL) for 3h. The methyl
complexes 5-7 were obtained quantitatively by adding n-
hexane to the solution. Anal. Calcd. (found) for (C37H40N4-
BO2PRu): H, 5.61 (5.63); C, 61.81 (61.47); N, 7.75 (7.41).
P r ep a r a tion of cis-[Ru (P Me3)(CO)(COMe)(η3-p z3-CH)]-
BP h 4 (3). Complex 1 (100 mg, 0.32 mmol) and pz3-CH (62
mg, 0.29 mmol) were dissolved in 5 mL of CH3OH. NaBPh4
(large excess) was added, and a white solid precipitated. The
IR spectrum of the solid showed the presence of complexes cis-
[Ru(PMe3)(CO)2(COMe)(η2-pz3-CH)]BPh4 (2) and cis-[Ru(PMe3)
(CO)(COMe)(η3-pz3-CH)]BPh4 (3). The solid was dissolved in
CH2Cl2 (5 mL) and stirred at 35 °C for 2 h, obtaining only the
η3-complex 3. The solvent was removed by bubbling N2 in an
open Schlenck flask, and the residual solid was washed with
cold CH3OH, dried, and crystallized from CH2Cl2/n-hexane
(yield ca. 60%). Spectroscopic chracterization of complex 2:
1
Chracterization of complex 5: H NMR (CD2Cl2, 298 K) 7.60
3
3
(d, J HH ) 2.1, H-3), 7.42 (m, o-H), 7.04 (t, J HH ) 7.4, m-H),
3
3
6.91 (H-5), 6.90 (t, J HH ) 7.2, p-H), 6.36 (t, J HH ) 2.5, H-4),
2
2
5.13 (d, J HH ) 14.6, H-1), 4.56 (d, J HH ) 14.6, H-2), 1.01 (d,
2J PH ) 7.9, PMe3), 0.25 (d, 3J PH ) 4.7, Me); 13C{1H} NMR 243.4
2
2
(d, J CP ) 9.7 COMe), 199.1 (d, J CP ) 16.8, CO (cis)), 189.8
(d, 2J CP ) 94.9, CO (trans)), 164.3 (q, 1J BC ) 48.1, C-ipso), 147.8
(s, C-3), 146.1 (s, C-3′), 137.5 (s, C-5), 136.4 (s, o-C), 135.8 (s,
C-5′), 126.4 (s, m-C), 122.2 (s, p-C), 108.9 (s, C-4′), 108.2 (s,
C-4), 62.1 (s, CH2), 51.9 (s, COMe), 13.7 (d, 2J CP ) 30.3, PMe3);
3
1H NMR (CD2Cl2, 298 K) 8.36 (d, J HH ) 2.2, H-3), 8.04 (d,
3
3
3J HH ) 2.2, H-3′), 8.41 (d, J HH ) 2.2, H-3′′), 6.38 (t, J HH
)
31P{1H} NMR -17.36 (s); IR (CH2Cl2) νCO 2042, 1985 cm-1
.
3
3
2.6, H-4), 6.35 (t, J HH ) 2.6, H-4′), 6.32 (t, J HH ) 2.6, H-4′′),
2.49 (s, COMe), 0.96 (d, 2J PH ) 9.7, PMe3); 13C{1H} NMR 207.6
Characterization of complex 6: 1H NMR (CD2Cl2, 298 K) 7.57
1
3
(s, CO), 164.2 (q, J BC ) 48.6, C-ipso), 146.8 (s, C-3 or C-3′ or
(s, H-3), 7.42 (m, o-H), 7.41 (s, H-3′), 7.15 (d, J HH ) 2.4, H-5),
3
3
C-3′′), 146.6 (s, C-3 or C-3′ or C-3′′), 136.6 (s, o-C), 126.6 (s,
m-C), 123.0 (s, p-C), 134.5 (s, C-5 or C-5′ or C-5′′), 133.7 (s,
C-5 or C-5′ or C-5′′), 133.3 (s, C-5 or C-5′ or C-5′′), 109.1 (s,
C-4 or C-4′ or C-4′′), 108.7 (s, C-4 or C-4′ or C-4′′), 108.3 (s,
7.04 (t, J HH ) 7.4, m-H), 6.98 (d, J HH ) 2.5, H-5′), 6.90 (t,
3J HH ) 7.2, p-H), 6.33 (m, H-4), 6.30 (t, J HH ) 2.5, H-4′), 5.24
3
2
(br d, H-1), 5.11 (br d, H-2), 1.61 (d, J PH ) 10.0, PMe3), 0.04
3
(d, J PH ) 4.8, Me); 31P{1H} NMR 12.02 (s); IR (CH2Cl2) νCO
2
2047, 1985 cm-1. Chracterization of complex 7: 1H NMR (CD2-
C-4 or C-4′ or C-4′′), 50.6 (s, COCH3), 17.4 (d, J CP ) 33.1,
PMe3); 31P{1H} NMR -3.18; IR (CH2Cl2) νCO 2071, 1994, νCOMe
1638 cm-1. Characterization of complex 3: 1 H NMR (CD2Cl2,
2
2
Cl2, 298 K) 4.96 (d, J HH ) 15.2, H-2), 4.64 (d, J HH ) 15.2,
H-1), 0.92 (d, J PH ) 9.2, PMe3), 0.20 (d, J PH ) 6.8, Me).
P r ep a r a t ion of cis-[R u (P Me3)(CO)2(I)(p z2-CH2)]BP h 4
(9). The residual solution of the synthesis of complex 4 was
still fluxed with CO for 1 h and placed in the refrigerator for
12 h at -18 °C. Complex 9 precipited as a pale yellow solid.
For 9: 1H NMR (CD2Cl2, 298 K) 7.63 (d, 3J HH ) 2.2, H-3), 7.45
2
3
3
3
298 K) 8.41 (d, J HH ) 2.2, H-3), 7.89 (d, J HH ) 1.7, H-3′),
3
3
7.62 (d, J HH ) 2.0, H-3′′), 7.42 (m, o-H), 7.24 (d, J HH ) 2.4,
H-5), 7.21 (d, 3J HH ) 2.8, H-5′), 7.20 (d, 3J HH ) 2.7, H-5′′), 7.06
3
3
(t, J HH ) 7.3, m-H), 7.03 (s, C-H), 6.94 (t, J HH ) 7.2, p-H),
3
6.37 (td, J HH ) 2.5, H-4), 6.30 (m, H-4′ and H-4′′), 2.51 (s,
COMe), 1.43 (d, 2J PH ) 9.8, PMe3); 13C{1H} NMR 256.4 (d, 2J CP
3
3
2
1
(m, o-H), 7.02 (t, J HH ) 7.5, m-H), 6.97 (d, J HH ) 2.8, H-5),
) 12.5, COMe), 203.6 (d, J CP ) 19.2, CO), 164.2 (q, J BC
)
3
3
6.86 (t, J HH ) 7.2, p-H), 6.46 (td, J HH ) 2.6, H-4), 6.33 (d,
48.6, C-ipso), 147.5 (s, C-3), 146.4 (s, C-3′), 146.2 (s, C-3′′), 136.6
(s, o-C), 126.6 (s, m-C), 123.0 (s, p-C), 134.8 (s, C-5), 134.3 (s,
C-5′), 133.9 (s, C-5′′), 109.0 (s, C-4′ and C-4′′), 108.4 (s, C-4),
76.7 (s, CH), 47.2 (s, COCH3), 17.2 (d, 2J CP ) 33.4, PMe3); 31P-
2J HH ) 14.2, H-2), 4.63 (d, J HH ) 14.2, H-1), 1.05 (d, J PH
)
2
2
10.5, PMe3); 13C{1H} NMR 195.0 (d, J CP ) 11.3, CO), 164.6
2
1
(q, J BC ) 49.4, C-ipso), 147.3 (s, C-3), 138.0 (s, C-5), 136.7 (s,
{1H} NMR 15.62 (s); IR (CH2Cl2) νCO 1959, νCOMe 1608 cm-1
.
o-C), 126.8 (s, m-C), 123.1 (s, p-C), 109.9 (s, C-4), 63.9 (s, CH2),
13.7 (d, J CP ) 33.8, PMe3); 31P{1H} NMR 10.89 (s); IR (CH2-
2
Anal. Calcd (found) for (C40H42N6BO2PRu): H, 5.45 (5.40); C,
60.80 (60.61); N, 10.71 (10.38).
Cl2) νCO 2076, 2026 cm-1. Anal. Calcd (found) for (C36H37N4-
BIO2PRu): H, 4.50 (4.46); C, 51.11 (50.87); N, 6.79 (6.68).
P r ep a r a tion of cis-[Ru (P Me3)(CO)2(COMe)(p z2-CH2)]-
BP h 4 (4). Complex 1 (151 mg, 0.37 mmol) and pz2-CH2 (66
mg, 0.46 mmol) were dissolved in 5 mL of CH3OH. NaBPh4
(large excess) was added while CO was bubbled in the solution.
Immediately a white solid precipitated. The solution was
stirred for 30 min and put in the refrigerator at -18 °C for 12
h to complete the precipitation. The solid was filtered, washed
with cold CH3OH, dried, and crystallized from CH2Cl2/n-
hexane (yield ca. 60%). Anal. Calcd (found) for (C38H40N4-
BO3PRu): H, 5.39 (5.42); C, 61.05 (60.86); N, 7.47 (7.50). Data
X-r a y Cr ysta llogr a p h y. Crystals of 4 suitable for X-ray
single-crystal study were grown from ethanol/diethyl ether.
Diffraction intensities were collected by the θ-2θ scan method
on a graphite-monochromated Enraf-Nonius CAD-4 diffracto-
2
meter and reduced to Fo values. Structure solved by direct
methods and refined by full-matrix least-squares calculations.
For all computations, SHELXS8611 and SHELXL9311 were
employed. Thermal vibrations for all non-H atoms were
treated anisotropically. All H atoms were found in difference
Fourier maps and refined with adequate constraints (C-H )
0.96 Å). Final difference Fourier map showed residual peaks
lower than 0.51 e Å-3 in the proximity of the Ru atom. Table
4 reports the experimental parameters of data collection and
refinement.
3
for 4: 1H NMR (CD2Cl2, 298 K) 8.48 (d, J HH ) 2.2, H-3), 7.56
(8) Weissberger, A.; Proskauer, E. S. Technique of Organic Chem-
istry; Interscience: New York, 1955; Vol. VII.
(9) (a) J ulia, S.; Sala, P.; del Mazo, J .; Sancho, M.; Ochao, C.;
Elguero, J .; Fayet, J .-F.; Vertut, M.-C. J . Heterocycl. Chem. 1982, 19,
1141. (b) J ulia, S.; del Mazo, J .; Avila, L.; Elguero, J . Org. Prep. Proc.
Int. 1984, 16 (5), 299.
(10) Macchioni, A.; Pregosin, P. S.; Engel, P. F.; Mecking, S.; Pfeffer,
M.; Daran, J .-C.; Vaissermann, J . Organometallics 1995, 14, 1637 and
references therein.
(11) Sheldrick, G. M. SHELXS86 Acta Crystallogr. Sect. A 1990, 46,
467. Sheldrick, G. M. SHELXL93, Program for Crystal Structure
Refinement, University of Gottingen, Germany, 1993.

5556 Organometallics, Vol. 17, No. 25, 1998
Macchioni et al.
Ta ble 4. Cr ysta l Da ta a n d Deta ils of
Mea su r em en ts for 4
permits a real-time approximation of the total intermolecular
energy of all possible nonbonded interactions between pairs
of molecules. More precisely, the total interaction energy is
given by Etot ) ∑(EQ + ELJ ) where EQ is the electrostatic
contribution to the interaction energy of each atom i of one
molecule interacting with all the j atoms of the other molecule,
and where ELJ are the steric attractive and repulsive contribu-
tions of each atom i of one molecule interacting with all the j
atoms of the other molecule. The analytical dissection of EQ
and ELJ into parameters and mathematical formulas may be
found elsewhere.14,15 The atomic charges for the two molecular
structures were obtained using the AMI-SM2 nonpolar
solvent calculation and the 3-21G* ab initio models imple-
mented in Spartan. Since the atomic charges were similar,
the latter method was selected for the docking. In the docking
between the two molecules, positive energies highlight repul-
sive interactions, while negative energies along with their
locations delineate regions of attraction between the two
interacting molecules.
formula
C38H40BN4O3PRu
mol wt
temp
743.6
293
system
space group
a (Å)
monoclinic
P21/c
16.595(3)
10.362(3)
21.309(5)
96.41(3)
3641(2)
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
F(000)
1536
λ (Mo KR) (Å)
µ (Mo KR) (mm-1
ϑ range (deg)
octants explored
measd reflns
0.71069
0.52
2.5-25
(h, +k, +l
6584
)
unique reflns used in the refinement
no. of refined params
GOF on F2
6393
504
0.926
Ack n ow led gm en t. This work was supported by
grants from the Consiglio Nazionale delle Ricerche
(CNR, Rome, Italy) and the Ministero dell’ Universita`
e della Ricerca Scientifica e Tecnologica (MURST, Rome,
Italy).
R1 (on F, I > 2σ(I)
0.049
0.145
wR2 (on F2)
Ca lcu la tion s. The molecular models were performed using
the Sybyl12 and Spartan13 packages. The initial structures
were built starting from the X-ray crystallographic coordinates.
Energy minimization was not performed on the structures.
Simulation of molecular interaction was carried out using
the DOCK command14,15 provided by the Sybyl package, which
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
and equivalent isotropic displacement parameters (Table S1),
all bond lengths and angles (Table S2), anisotropic displace-
ment parameters (Table S3), and H-atom coordinates and
isotropic displacement parameters (Table S4) for 4 (8 pages).
Ordering information is given on any current masthead page.
(12) Sybyl Molecular Modeling Software, version 6.3, TRIPOS Inc.
1699, Manley Road, St. Louis, MI.
(13) Spartan Software, Wavefunction Inc., 18401 V. Karman Av-
enue, Suite 370, IRVINE, CA 92612.
(14) Clark, M.; Cramer, R. D., II; Van Opdenbosh, N. J . Comput.
Chem. 1989, 10, 982.
OM980631Q
(15) Vinter, J . G.; Davis, A.; Sanders, M. R. J . Comput.-Aided Mol.
Des. 1987, 1, 31.