Ruthenium hydride complexes with a heteroscorpionate ligand derived from methane: 2-Phenoxy-bis(pyrazol-1-yl)methane. The hemilabile role of the ligand in substitution and proton transfer reactions

Article abstract of DOI:10.1016/j.poly.2003.11.023

The complex [RuH(κ³-bpzmPhO)(cod)] (1) was synthesized by the reaction of [RuH(cod)(NH₂NMe₂)₃][BPh ₄] with the potassium salt of 2-phenoxy-bis(pyrazol-1-yl)methane (bpzmPhOK). This ligand adopts a κ³-N,N,O coordination on the metal center that is reminiscent of the situation usually observed in trispyrazolylborate complexes. Complex 1 exists in solution as a mixture of two diastereoisomers that are in equilibrium. The reaction of 1 with different phosphines (PMe₃, PMe₂Ph, PMePh₂ and PPh ₃) has been studied. The reaction product depends not only on the nature of the phosphine but also on the complex:L ratio and the temperature. Diphosphine derivatives of stoichiometries [RuH(κ¹-O-bpzmPhO) (cod)L₂] (L=PMe₃, PMe₂Ph) and [RuH(κ ³-bpzmPhO)L₂] (L=PMe₃, PMe₂Ph, PMePh₂, PPh₃) were prepared. Similarly, tetraphosphine derivatives of formula [cis-O,H-RuH(κ¹-O-bpzmPhO)L ₄] (L=PMe₃, PMe₂Ph) were obtained. The complex with PMe₂Ph can be transformed into the respective trans isomer by heating the solution. The reaction of 1 with five equivalents of PMe ₃ gives rise to a pentaphosphine derivative with complete decoordination of the anionic bpzmPhO ligand. This ligand exhibits hemilabile behavior that involve a reversible coordination of the pyrazole fragments. Proton transfer reactions from HBF₄ to 1 have also been studied both in acetone-d₆ and in methanol-d₄. In all of these processes the proton is selectively transferred to the oxygen of the bpzmPhO ligand, which remains coordinated through at least the N-donor centers. Three hydride derivatives are formed in these reactions and they differ either in the relative orientation of the ligands or in the coordination of the OH group of the ligand.

Full text of DOI:10.1016/j.poly.2003.11.023

Polyhedron 23 (2004) 361–371
www.elsevier.com/locate/poly
Ruthenium hydride complexes with a heteroscorpionate
ligand derived from methane:
2-phenoxy-bis(pyrazol-1-yl)methane. The hemilabile role of
the ligand in substitution and proton transfer reactions
a
Agustın Caballero , M. Carmen Carrion , Gustavo Espino , Felix A. Jalon
a
b
a,
*
ꢀ
ꢀ
Blanca R. Manzano
ꢀ
ꢀ
,
a
a
Departemento de Quꢀımica Inorgnica, Org. y Bioquim, Facultad de Quꢀımicas, Universidad de Castilla-La Mancha,
Avda. Camilo J. Cela, 10, E-13071 Ciudad Real, Spain
b
Facultad de Ciencias y de CyTA, Universidad de Burgos, Plaza Misael Ba~nuelos s/n, E-09001 Burgos, Spain
Received 3 June 2003; accepted 5 September 2003
Dedicated to Dr. Swiatoslaw Trofimenko in recognition of his outstanding contribution and dedication to Inorganic Chemistry
Abstract
The complex [RuH(j3-bpzmPhO)(cod)] (1) was synthesized by the reaction of [RuH(cod)(NH2NMe2)3][BPh4] with the potas-
sium salt of 2-phenoxy-bis(pyrazol-1-yl)methane (bpzmPhOK). This ligand adopts a j3-N; N; O coordination on the metal center
that is reminiscent of the situation usually observed in trispyrazolylborate complexes. Complex 1 exists in solution as a mixture of
two diastereoisomers that are in equilibrium. The reaction of 1 with different phosphines (PMe3, PMe2Ph, PMePh2 and PPh3) has
been studied. The reaction product depends not only on the nature of the phosphine but also on the complex:L ratio and the
temperature. Diphosphine derivatives of stoichiometries [RuH(j1-O-bpzmPhO)(cod)L2] (L ¼ PMe3, PMe2Ph) and [RuH(j3-
bpzmPhO)L2] (L ¼ PMe3, PMe2Ph, PMePh2, PPh3) were prepared. Similarly, tetraphosphine derivatives of formula [cis-O,H-
RuH(j1-O-bpzmPhO)L4] (L ¼ PMe3, PMe2Ph) were obtained. The complex with PMe2Ph can be transformed into the respective
trans isomer by heating the solution. The reaction of 1 with five equivalents of PMe3 gives rise to a pentaphosphine derivative with
complete decoordination of the anionic bpzmPhO ligand. This ligand exhibits hemilabile behavior that involve a reversible coor-
dination of the pyrazole fragments. Proton transfer reactions from HBF4 to 1 have also been studied both in acetone-d6 and in
methanol-d4. In all of these processes the proton is selectively transferred to the oxygen of the bpzmPhO ligand, which remains
coordinated through at least the N-donor centers. Three hydride derivatives are formed in these reactions and they differ either in the
relative orientation of the ligands or in the coordination of the OH group of the ligand.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Heteroscorpionates; Ruthenium; Hydrides; Phosphine complexes; Hemilabile ligands
1. Introduction
and tris(pyrazol-1-yl)methane compounds potentially
offer analogous coordination modes to those found in
the classical scorpionates [2]. In contrast with the clas-
sical systems, the methane derivatives are neutral and
consequently the metal–ligand interaction is weaker.
The introduction of charged groups in the spacer carbon
is an interesting possibility in terms of improving the
coordination ability of these ligands and, on the other
hand, involves the possibility of introducing a hemilabile
role for this ligand in the resulting complexes.
Homo- and heteroscorpionate borate ligands have
been widely used in coordination chemistry [1]. In recent
years analogues of the boron-based scorpionates have
1
been prepared and used as ligands. For instance, bis-
* Corresponding author. Fax: +34-926-295318.
ꢀ
E-mail address: felix.jalon@uclm.es (F.A. Jalon).
For an approach, see Chapter 1.9 of [1].
1
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.023

362
A. Caballero et al. / Polyhedron 23 (2004) 361–371
H
H
B
½RuHðcodÞðNH2NMe2Þ ꢁ½BPh4ꢁ þ bpzmPhOK
α
3
3
5'
4
C
N
N
N
N
! ½RuHðbpzmPhOÞðcodÞꢁ þ KBPh4
5'
2
N
N
4'
ð1Þ
N
N
N
5
1
þ 3NH2NMe2
ð1Þ
ð2Þ
4'
6
N
3'
O
3'
-
½RuClHðbpzmÞðcodÞꢁ þ bpzmPhOK
! 1 þ KCl þ bpzm
-
Tp
bpzmPhO
Scheme 1.
cod ¼ 1,5-cyclooctadiene, bpzm ¼ bis(pyrazol-1-yl)meth-
In recent years we [3] and others [4] have prepared
ane.
1
bis(pyrazol-1-yl)methane derivatives bearing additional
functionalized groups in the spacer carbon between the
two pyrazoles. The previously described (2-hydroxy-
phenyl)bis(pyrazol-1-yl)methane is an example of this
family of ligands [5]. The ligand is easily prepared by the
Peterson method [6] and offers the possibility of de-
protonating the phenol group, which transforms it into
an anionic compound (bpzmPhOꢀ) that is reminiscent
of the original scorpionates (Scheme 1). However, in the
anionic form the charge is mainly located at the oxygen,
a situation that increases the coordination ability of this
atom. In this way, this potentially NNO-ligand could
stabilize the same complexes as the boron-based scor-
pionates but the different electronic character of the
donor atoms could lead to asymmetrization of the co-
ordination sphere of the metal.
Carrano et al. used the anionic form of this ligand to
prepare Co [5,7], Ni [7a,7b,8], V and Fe [7c], Zn, Cu and
Mn [7a,7b] complexes. The introduction of substituents
in the pyrazole rings or the phenol (or thiol) groups
makes the formation of mononuclear species less fa-
vorable when bulky ancillary ligands are also coordi-
nated to the metal center. As a consequence, in the work
described here we preferred to use the unsubstituted li-
gand to stabilize mononuclear ruthenium compounds
with three main goals in mind: (i) to explore the coor-
dination ability of the three donor atoms of this ligand;
(ii) to analyze the potential hemilability of the ligand in
substitution processes with different phosphines; (iii) to
evaluate the role of the phenoxy group, which is, in
principle, in competition with the hydride ligand bonded
to the Ru center, in proton transfer reactions.
In the hydride region of the H NMR spectrum of
complex 1, two resonances ()3.64 ppm, d, J ¼ 2:9 Hz
and )6.84 ppm, s) are observed (see Table 1). This is due
to the presence of two isomers whose ratio (1a:1b)
changes with the solvent (acetone-d6, 1:1; methanol-d4,
2:1), meaning that the two species are in equilibrium.
1
The assignment of the H NMR resonances of the two
isomers (except the aliphatic cod signals) was made on
1
the basis of NOE and H–1H COSY spectra (acetone-
1
d6). The H and 13C{1H} NMR spectra of isomer 1a
(Tables 1 and 2) show signals for two types of pyrazole
ring and four distinct resonances for the olefinic CH
groups of the cod ligand (C1 symmetry). The hydride
signal at )3.64 ppm exhibits a NOE with two olefinic
protons. Considering all these data, the structure shown
in Scheme 2 is proposed for this compound. Two lines
are observed for the hydride signal and this is unex-
pected. However, it was confirmed that the resonance is
indeed a doublet after the same coupling constant was
observed in spectra acquired using 300, 200 and 80 MHz
spectrometers. In addition, the COSY spectra show a
correlation between this signal and an aliphatic cod
proton (2.21 ppm). The coupling was confirmed when
selective irradiation of the cod signal was observed to
transform the hydride resonance into a singlet. This
coupling can be explained in terms of a distortion of the
octahedral geometry, which has been determined by X-
ray diffraction for other complexes with the RuH(cod)
fragment [9], resulting in the hydride group coming into
close proximity with the cod ligand.
1
The H and 13C{1H} NMR spectra of 1b (Tables 1
and 2) exhibit signals for one type of pyrazole ring and a
cod group with Cs symmetry. This data, along with the
NOE observed between the hydride resonance ()6.84
ppm) and one type of olefinic cod proton (2H), allowed
the structure of this isomer to be determined (see
Scheme 2).
2. Results and discussion
2.1. Synthesis and characterization of complexes 1a and
1b
The reactivity of 1a/b with different phosphines and
the addition of HBF4 was explored and the results of
these studies will be discussed in the following sections.
The new hydride derivative [RuH(bpzmPhO)(cod)]
(1) which is the starting material for the work described
in this paper, can be obtained by reaction of bpzmPhOK
with [RuH(cod)(NH2NMe2)3][BPh4] or [RuClH(bpzm)
(cod)] according to Eqs. (1) and (2), respectively. Re-
action (2) is slightly less convenient because it requires
the separation of the displaced bpzm (see Section 3).
2.2. Reaction of 1a/b with phosphines
The reaction of 1a/b with phosphines of different
basicity and, more importantly, different levels of steric

Table 1
1H NMR data for bpzmPhOK and complexes 1–3a
Derivative
Ru–H
Ha
Phenoxy group
cod/Phosphine (Me)
Pyrazole
0
0
0
H4
H3
H5
cod-Holef
cod-Halk
bpzmPhOK
6.18 (pt)
7.44 (d, J ¼ 2:2)
7.52 (d, J ¼ 2:4)
8.17 (s)
6.88 (td, J ¼ 7:6, 1.9; H5)
6.83 (dd, J ¼ 7:6, 1.9; H3)
6.43 (dd, J ¼ 8:3, 1.2; H6)
6.08 (td, J ¼ 7:6, 1.2; H4)
6.92 (d, J ¼ 7:7, H3)
1a
1b
2b
)3.64 (d, JHH ¼ 2:9)
6.37 (pt)
6.66 (pt)
6.37 (pt)
8.50 (d, J ¼ 2:0)
7.59 (d, J ¼ 2:0)
7.32 (d, J ¼ 2:3)
7.92 (d, J ¼ 2:4)
8.05 (d, J ¼ 2:4)
7.57 (s)
7.47 (s)
8.23 (s)
3.51d (m)
2.93d (m)
2.83 (m)
2.63 (m); 2.52 (m)
2.32 (m); 2.13 (m)
2.05 (m); 1.96 (m)
1.30 (2H, m)
2.72 (m)
6.66 (td, J ¼ 7:1,1.5, H5)
6.16 (d, J ¼ 8:3, H6)
5.95 (t, J ¼ 7:1, H4)
1.83 (m)
3.59d (m,2H)
2.93 (m,2H)
)6.84 (s)
7.96 (dd, J ¼ 2:6,
J ¼ 0:8)
6.92 (d, J ¼ 7:7, H3)
6.76 (td, J ¼ 6:7,1.6, H5)
2.13 (m)
1.78 (m)
1.64 (m)
6.56 (d, J ¼ 8:2, H6)
5.90 (t, J ¼ 6:7, H4)
)1.04
(dd, JHP ¼ 82:1, 28.2)
5.90 (pt, J ¼ 2:1)
5.96 (pt, J ¼ 2:1)
7.54 (bs)
7.11 (bs)
7.02 (d, J ¼ 2:3)
7.00 (d, J ¼ 2:4)
7.65 (d, J ¼ 8:2; H3)
3.68 (m)
2.84 (m)
2.64 (m)
7.44 (pt, J ¼ 7:4; H5)
6.79 (dd, J ¼ 2:0, 7.5; H6)
6.49 (t, J ¼ 7:2; H4)
1.50–2.3
1.19 (d, JHP ¼ 6:9, PMe3)
0.72 (d, JHP ¼ 7:9, PMe3)
c
3b
)0.95
(dd, JHP ¼ 80:5, 28.7)
5.96 (pt, J ¼ 1:8)
6.02 (pt, J ¼ 1:8)
7.13 (d, J ¼ 2:3)
7.15 (d, J ¼ 2:3)
8.47 (s)
8.09 (d, J ¼ 8:4, H3)
7.33 (m, H5)
6.69 (m, H6)
3.93 (m,2H)
2.93 m
2.77 (m)
2.06–2.66
6.57 (pt, J ¼ 7:5; H4)
1.54 (d, JHP ¼ 7:3, PMe)
1.37 (d, JHP ¼ 7:8, PMe)
1.20 (d, JHP ¼ 8:5, PMe)
1.06 (d, JHP ¼ 6:8, PMe)
a Room temperature. H–H coupling if not specified. Solvent, acetone-d6 if not specified. The phenyl resonances of the phosphines in 3 are in the region 6.8–7.7 ppm.
b In benzene-d6.
c Resonances non observed (overlapped).
d Signal showing noe with the hydride.

364
A. Caballero et al. / Polyhedron 23 (2004) 361–371
Table 2
13C{1H} NMR data for bpzmPhOK and complex 1a
Derivative
Ca
Phenoxy group
Pyrazole
cod
olef
C30
C40
C50
alk
bpzmPhOK
140.62
106.10
129.94
76.31
78.48
79.41
155.0 (C1), 131.5 (C5), 129.6 (C3)
119.8 (C4), 118.3 (C6)
130.90 (C5), 130.55 (C3), 124.03 (C6), 110.45 (C4), 61.00; 62.16
69.27; 80.80
131.28 (C5), 130.28 (C3), 125.20 (C6), 108.84 (C4)
1a
1b
143.13
144.25
141.68
106.64 (2C) 131.70
132.62
26.78; 30.82
32.19; 35.54
28.34; 33.20
107.04
132.17
71.58; 73.24
a Room temperature. All signals are singlets. Solvent, acetone-d6.
most suitable for further study. The reactions were
carried out in an NMR tube using benzene-d6 as solvent
and reaction progress was monitored by 1H and
31P{1H} NMR spectroscopy. The product was isolated
when only one species was detected.
H
O
Ru
H
Hα
N
N
C
Ru
N
N
N
O
N
N
C
N
Hα
The discussion that follows is based on the processes
outlined in Scheme 3 and the nature of the reaction
product is essentially dependent on the whole range of
factors described above. It must be emphasized that the
whole series of steps reflected in Scheme 3 is not com-
plete for any of the phosphines used. However, the
scheme is a reasonable general pathway for the reactions
observed.
As shown in Scheme 3, reaction of 1a/b with small
phosphines, i.e., PMe3 and PMe2Ph, is the most versatile
route. A complex:L ratio of 1:2 at room temperature
(step i) led to complexes 2 and 3, which formally can be
1b
1a
Scheme 2.
hindrance (L ¼ PMe3, PMe2Ph, PMePh2, PPh3) in a
range of complex:L ratios and temperatures was studied.
Although all possible stoichiometries were not assessed,
the preliminary results provide evidence that the most
labile functions to be displaced were those on the pyr-
azole groups and the cod ligand. It was therefore de-
cided that complex:L ratios of 1:2 and 1:4 would be the
H
H
C
O
O
N
N
Ru
Ru
N
C
N
H
H
1b
1a
(i) 2 L
pz
pz
pz
H
pz
H
O
C
O
O
L
(iii) 2L
H
H
L
N
Ru
L
(ii)
Ru
Ru
- cod
L
L
N
L
L
L
L = PMe3 (4), PMe2Ph (5),
PMePh2 (6), PPh3 (7)
L = PMe3 (8), PMe2Ph(9)
L = PMe3 (2), PMe2Ph (3)
(v) L
(iv)
pz
pz
bpzmPhO
L
O
H
L
L
L
Ru
Ru
L
L
L
L
L
H
L = PMe3 (11)
Scheme 3.
L = PMe2Ph (10)

A. Caballero et al. / Polyhedron 23 (2004) 361–371
365
considered as the result of the displacement of the pyr-
azole groups from isomer 1a, although the possibility of
a direct reaction of 1b with the phosphines followed by
rapid rearrangement can not be excluded. Interestingly,
when solutions of 2 or 3 were heated at 70 °C, the
elimination of cod was observed with the concomitant
recoordination of the pyrazole groups to give 4 or 5
(step ii). This behavior implies partial decoordination of
the hemilabile ligand, which allows coordination of a
second ligand (phosphine, in our case) that can induce
the displacement of a third one (cod, in this case) with
recoordiantion of the former. To the best of our
knowledge, this behavior is very rarely observed [10].
The main conclusion to be drawn from these results is
that 2 and 3 can be considered as products of kinetic
control while 4 and 5 are the thermodynamically stable
speciesÕ for this stoichiometry. Complex 5 could be iso-
lated whereas 4 appeared in the solutions as the minor
component of a mixture with the tetraphosphine deriv-
ative 8 and unidentified compounds with resonances in
1H and 31P NMR.
nation of bpzmPhO by incoming ligands, as observed in
the reaction with PMe3 to give 11, is an infrequent
process but does have a precedent in the chemistry of
trispyrazolylborate complexes [11].
It can be concluded that: (i) the displacement reac-
tions from 1a/b can be controlled by the complex:L ratio
and temperature; (ii) the final product also depends on
the nature of the phosphine; (iii) the ease of substitution
is in the order: pyrazoles > cod > bpzmPhO ligand; (iv)
the bpzmPhO ligand shows a hemilabile behavior in
these reactions.
The most relevant aspects concerning the character-
ization of complexes 2–11 are discussed below.
The stretching vibrations for the terminal Ru–H
bonds were observed in the expected regions of the IR
spectra (1973–2025 cmꢀ1).
Complexes 2–11 were characterized by 1H (except 4 –
which is present as a minor component with 1 and 8),
31P{1H} (see Tables 1, 3 and 4) and 13C{1H} NMR
spectroscopy (except 2–4, which are too unstable or
could not be isolated) (see Table 4).
The resonances in the 1H and 13C{1H} NMR spectra
for the pyrazole rings provide valuable information about
the symmetry of the complexes. For example, the exis-
tence of two distinct pyrazoles is deduced for complexes 2,
3, 5–7 but only one pyrazole is present in 8–11. One of the
most noticeable differences between 2 and 3 and the rest of
the phosphine complexes is the existence of cod reso-
nances. The cod signals in the 1H NMR spectra of 2 and 3
show the expected pattern for a local C1 symmetry and
more than two different olefinic resonances (in fact three
out of the four expected) are observed.
The hydride chemical shifts are very sensitive to the
environment, and particularly to the ligand situated in
the trans position (d, trans to phosphine ca. )1 ppm, 2–
3; trans to a pyrazole group, between )13 to )15.5 ppm,
4–7). The electronic enrichment of the metallic center
induces a corresponding shift to lower frequency of the
hydride resonance for the tetra- and pentaphosphine
derivatives 8–11 and the trans effect of the ligand is also
observed for this series of complexes (d, trans to phos-
phine ca. )8 ppm, 8–9 or ca. )12 ppm, 11; trans to
phenoxy group ca. )18.7 ppm, 10). The expected mul-
tiplicities were observed for the hydride resonances and
the coupling constants were in the expected range (trans
Bulkier phosphines such as PMePh2 and PPh3 did not
react at room temperature but heating the reaction so-
lutions (70 °C) did give the isolable products 6 and 7,
respectively. These compounds are isostructural with
complexes 4 and 5. The fact that speciesÕ of similar
structure to 2 or 3 were not obtained with PMePh2 or
PPh3 could be due to the high temperature required for
the reactions to occur.
The use of a complex:L ratio of 1:4 with the different
phosphines provided the conclusions that only the
smallest phosphines (PMe3 and PMe2Ph) gave tetra-
phosphine derivatives and for PMe2Ph this reaction was
only possible above 50 °C (room temperature for PMe3).
Complexes 8 and 9 were initially obtained in these reac-
tions (step iii). Both the cod and the pyrazole groups were
displaced, with the bpzmPhO remaining coordinated as a
monodentate O-donor ligand. When solutions of 9 were
heated at 70 °C this complex evolved to give the more
symmetrical isomer 10 (step iv), which, despite being the
major component of the mixture, could not be isolated as
a pure species and was characterized only by NMR.
The smallest phosphine, PMe3, was even able to re-
move completely the bpzmPhO ligand from the metallic
center when a complex:L ratio of 1:5 was used at room
temperature (step v), although in this reaction compe-
tition between the two ligands was observed that gave
mixtures of 8 and the pentaphosphine derivative 11. The
analogous isomer to 10 was not observed with PMe3.
However, the formation of this derivative as a transient
intermediate, with a mutually trans disposition of the
bpzmPhO and H ligands (hydride has a high trans in-
fluence), could explain the total displacement of the
phenoxy group in 8 to give 11. Nevertheless, 10 does not
react with an excess of PMe2Ph, even after heating,
possibly due to steric factors. The complete decoordi-
J
PH, 70–100 Hz; cis JPH, ca. 30 Hz).
The 31P{1H} NMR spectra of diphosphine deriva-
tives 2–7 (see Table 4) show two different resonances
with the expected shift to higher frequencies due to the
coordination. The JPP coupling constants are indicative
of a cis-arrangement for both phosphines (JPP ¼ 26–41
Hz). As expected, the tetraphosphine derivatives 8 and 9
give rise to three resonances while only one, although
broad, is observed for 10. A doublet and a quintet, in the
corresponding spectrum, are due to the pentaphosphine
derivative 11.

Table 3
1H NMR data for complexes 4–11a
Complex
Ru–H
Ha
Phenoxy group
6.3–7.6
Phosphine (Me)
Pyrazole
0
0
0
H4
H3
H5
d
5
)14.64 (t, JHP ¼ 32:3)
5.74 (pt, J ¼ 2:1) 6.94c (bs)
5.54 (pt, J ¼ 2:1) 6.87c (bs)
7.09c (bs)
0.82 (d, JHP ¼ 7:9)
1.19 (d, JHP ¼ 7:6)
1.62 (d, JHP ¼ 8:5)
1.79 (d, JHP ¼ 8:7)
7.11c (bs)
6b
)14.24 (t, JHP ¼ 29:9)
5.84 (bs)
6.32 (bs)
7.82 (d, J ¼ 2:0)
8.15 (d, J ¼ 2:3)
6.61 (td, J ¼ 7:4, 1.4; H5) 1.23 (d, JHP ¼ 7:4)
d
5.91 (pt, J ¼ 7:2; H4)
1.42 (d, JHP ¼ 7:4)
d
d
5.75 (d, J ¼ 7:8; H6)
d
7
)12.95 (dd, JHP ¼ 31:0; 27.9)
5.29 (pt)
5.43 (pt)
6.17 (d, J ¼ 2:1)
6.22 (d, J ¼ 2:1)
6.71 (d, J ¼ 2:4) 7.45 (s)
7.26 (d, J ¼ 2:1)
6.66 (dd, J ¼ 7:4, 1.7; H3)
6.25 (td, J ¼ 7:2, 1.1; H4)
5.94 (dd, J ¼ 8:4, 1.1; H6)
d
8
)7.76 (ddt, JHPtrans ¼ 100:1; JHPcis ¼ 26:4, 29.3)
6.00 (pt)
6.03 (pt)
7.26 (d, J ¼ 2:3)
7.62 (d, J ¼ 1:8)
7.58 (d, J ¼ 2:4) 8.56 (s)
7.29 (d, J ¼ 2:3) 8.85 (s)
7.08 (d, J ¼ 2:3) 8.26 (s)
7.74 (dd, J ¼ 8:4, 1.0; H3) 0.88 (d, JHP ¼ 7:8, 3Me)
7.35 (td, J ¼ 7:8, 2.0; H5) 1.02 (pt, 6 Me)
7.09 (dd, J ¼ 7:8, 1.5; H6) 1.11 (d, JHP ¼ 5:5, 3Me)
6.48 (pt, J ¼ 8:0; H4)
9
)7.91 (ddt, JHP ¼ 95:8, 25.6, 25.2)
7.65 (d, J ¼ 8:2; H3)
0.76 (d, JHP ¼ 7:8, 2Me)
7.44 (dt, J ¼ 7:8, 1.7; H5) 1.26 (pt, 4Me)
6.79 (dd, J ¼ 7:5, 2.0; H6) 1.72 (d, JHP ¼ 5:3, 2Me)
6.49 (pt, J ¼ 8:0; H4)
10
11
)18.67 (q, JHP ¼ 20:8)
5.71 (pt, J ¼ 1:9) 7.19 (d, J ¼ 1:8)
5.97 (pt, J ¼ 2:1) 7.32 (d, J ¼ 2:1)
6.98 (pt, J ¼ 8:2; H5)
1.27 (bs, 8Me)
6.32 (pt, J ¼ 7:4; H4)
d
)11.83 (dc, JHPtrans ¼ 72:4; JHPcis ¼ 24:8)
7.48 (bs)
8.37 (s)
7.23 (d, J ¼ 7:5; H3 or 6
)
0.96 (d, JHP ¼ 5:8, 3Me)
6.58 (pt, J ¼ 7:3; H4 or 5
)
d
a Room temperature. H–H coupling if not specified. All resonances are singlets if not specified . Solvent, benzene-d6 if not specified. The phenyl resonances of the corresponding phosphines in
complexes 5–7, 9 and 10 are in the region 6.8–7.7 ppm. The hydride resonance of 4 appears at )15.46 ppm (t, JHP ¼ 34:3, benzene-d6).
b In DMSO-d6.
c The assignment of H3 and H5 resonances may be reversed.
d Resonances non observed (overlapped).
0
0

A. Caballero et al. / Polyhedron 23 (2004) 361–371
367
Table 4
13C{1H} data for 5–11 and 31P{1H} NMR data for 2–11a
Complex
Ca
Phenoxy group
Pyrazole
C30
Phosphine
13C
C40
C50
31P
5
145.71
147.36
105.55
106.31
131.77
c
80.54
c
171.29 (C1), 131.20,
PMe2Ph: 21.41, (d, JCP ¼ 26:2)
17.36, (d, JCP ¼ 27:2)
36.40 (d, JPP ¼ 41.5)
125.20,120.79 (C2), 109.60
41.78 (d)
c
c
6b
146.07
147.47
108.93
106.58
79.87
170.55 (C1), 125.99, 124.43,
121.42
PMePh2: 17.99 (d, JCP ¼ 25:7)
19.11, (d, JCP ¼ 28:2)
52.62 (d, JPP ¼ 39:0)
60.40 (d)
PMePh2: 127–133.5, m
c
7
8
146.70
148.67
110.27
106.02
132.07
130.06
80.73
75.17
171.07 (C1), 120.5–135.5
134.4–140.7 (m)
78.71 (d, JPP ¼ 34:8)
75.10 (d)
140.31
105.45
128.95
130.63, 128.78, 128.21,
122.32, 111.49
21.37, dt, (JCP ¼ 16:1, 2.3; 3C)
22.59, td (JCP ¼ 3:5; 6C)
18.42 (td, JPP ¼ 16:5,
33.6) 2.60 (dd,
JPP ¼ 26:8, 33.6)
)11.61 (m)
26.93, dc (JCP ¼ 25:7, 3.0; 3C)
9
140.10
104.93
131.01
75.53
168.74 (C1), 126.28, 122.07,
111.43
PMe2Ph: 19.01
(d, JCP ¼ 17:1; 2C)
20.16 (m, 4C)
30.16 (td, JPP ¼ 33:8,
12.8) 16.39 (dd,
JPP ¼ 33:8, 21.4)
)4.57 (m)
c
23.65 (d, JCP ¼ 26:2; 2C)
PMe2Ph: 127–131 (m) c
10
11
139.83
139.69
105.34
104.74
128.67
129.61
75.34
75.96
118.49, 114.88
c
PMe2Ph: 21.30 (bs)
28.43 (d, JCP ¼ 5:8)
PMe2Ph: 132.67 (bs);
130.78 (d, JCP ¼ 17:8)
10.88 (bs)
130.03, 122.92, 118.69,
116.77
19.27 (d, JCP ¼ 15:1; 3C)
)21.28 (q, JPP ¼ 26:3)
)7.76 (d)
24.45 (m, 12C)
a Room temperature. All signals are singlets if not specified. Solvent, benzene-d6 if not specified. 13C{1H} NMR for complexes 2–4 were not
recorded (see text). 31P{1H} NMR data for complexes 2–4: 2, 1.05 (d, JPP ¼ 38:7), )11.24 (d); 3, 6.52 (d, JPP ¼ 34:8), )1.27 (d); 4: )0.50 (d,
JPP ¼ 26:0), )12.14 (d).
b In DMSO-d6.
c Resonances non observed.
2.3. Reaction of 1a/b with HBF4
This reaction was analyzed in acetone-d6 and meth-
anol-d4.
The addition of one equivalent of HBF4 to 1a/b
(equimolecular amount of HBF4 and 1a/b) in acetone-d6
1
was carried out at )80 °C and monitored by H NMR
from )80 to 50 °C. Two hydride singlets in a 4:1 ratio
(12a:12b) were observed at )80 °C (see Fig. 1). A reso-
nance at 9.83 ppm was observed for the major compo-
nent 12a, indicating the protonation of the oxygen atom.
A Cs symmetry for the complex was deduced. The fol-
lowing NOEs between different signals (indicated with
arrows in Scheme 4) were observed for 12a ()10 °C): (i)
Ha and H05; (ii) Ha and OH; (iii) the hydride signal and
one olefinic cod resonance; (iv) the hydride signal and
H3 of the phenoxy group. The NOEs of (ii) and (iv)
reflect the fact that the OH group is not coordinated to
the metal center. The low proportion of 12b meant that
Fig. 1. Variable 1H NMR spectra of 12a,b,c in the hydride region.
it was not possible to observe and assign all resonances
for this species. However, it is worth mentioning that a
quartet observed at 4.95 ppm was assigned to a molecule
of Et2O (from the HBF4 solution) coordinated to the Ru
center in this derivative. Considering all these data, the
structures proposed for the two derivatives are indicated
in Scheme 4. Protonation of the phenoxy group and its
decoordination makes possible the formation of these

368
A. Caballero et al. / Polyhedron 23 (2004) 361–371
two complexes, which mainly differ in the relative dis-
position of the phenol group with respect to the hydride.
We must emphasize that a boat-to-boat inversion of
either of these two speciesÕ does not lead to the skeleton
of the other.
species 13c in comparison to 12c in the respective
mixtures.
On the other hand, the hydride (also the Ha proton)
resonances of 13b and c coalesced (see Fig. 2) as a
consequence of the equilibrium that arises due to the
competition for the coordination between the OD group
of the phenol ring and that of methanol. The free energy
When the temperature of the sample was raised, the
resonances of 12b broadened (clearly observed for the
hydride, Ha and Et2O signals). However, the resonances
of 12a remained sharp. At )10 °C, the resonances of 12b
were not observed. At 10 °C, a new and broad hydride
signal appeared (12c) (see Fig. 1). At higher tempera-
tures this signal became less broad and at 50 °C the
approximate ratio 12a:12c was 1:0.8. A decrease in the
temperature to 20 °C indicated that the process is re-
versible. On the basis of these data it is proposed that
12b easily interconverts with 12c in such a way that an
increase in temperature favors the latter derivative. A
Cs symmetry was deduced for 12c. We propose the
structure indicated in Scheme 4 for this derivative and
believe that the equilibrium involves coordination–
decoordination of the Et2O molecule and the OH group.
In fact the stated resonances for the Et2O coordinated
on 12b disappeared when the formation of 12c was
completed. Displacement of the Et2O molecule must be
favored for entropic reasons. In any case, the Ru–O
bond must be labilized by the high trans influence of the
hydride ligand (in both 12b and 12c). Considering the
stated change of the 12a:12b + 12c ratio with tempera-
ture, the transformation of 12a into the pair 12b–12c is
also possible although less rapid than the transforma-
of activation calculated at 0 °C is 55.9 kJ molꢀ1
.
1
The H resonances of 13a at )90 °C are shown in
Table 5.
It can be concluded that the proton transfer from
HBF4 to 1a/b is selective and occurs on the oxygen atom
of the phenoxy group. The previous attack onto the Ru–
H bond (kinetic control) with the formation of a dihy-
drogen compound, acid enough to be transformed onto
the final products (thermodynamic control) can not be
ruled out, although none evidence of such a pathway
can be deduced from the spectra. The acid character of
some dihydrogen complexes of Ru [12] and the kinetic
control of the proton transfer over the Ru–H bonds of
some complexes [13] is well reported.
An isomerization process, at least for isomer 1a, must
take place in these proton transfer processes and gives
products with Cs symmetry. Considering the coordina-
tion mode of the bpzmPhO ligand, the main reaction
products show a j2-NN coordination (a and b) with two
different configurational dispositions that orientate the
phenol group towards (forms a) or away from (forms b)
the hydride ligand. The latter configuration means that
the phenol group has an orientation suitable for coordi-
nation to the metal center (which leads to isomers of type
c) but this coordination is in competition with the solvent
(methanol or ether, isomers of type b). The hydride ligand
apparently does not participate in the process.
1
tion between 12b and 12c. The H NMR resonances of
12a (two temperatures) and 12c (50 °C) are given in
Table 5.
The proton transfer evolved in a similar way when
carried out in methanol-d4, with the formation of
complexes 13a,b,c as depicted in Scheme 4. However,
several differences must be pointed out for this system:
(i) as expected, a signal for the OH group was not
observed in the spectra as a consequence of the rapid
proton exchange with the medium; (ii) the three
products of the reaction were separately observed in
the 1H NMR spectrum at )90 °C in a 4:1:0.5 ratio
(13a:b:c), which implies a relative stabilization of
3. Experimental
3.1. General comments
All manipulations were carried out under an atmo-
sphere of dry oxygen-free nitrogen using standard
Schlenk techniques. Solvents were distilled from the
+
+
+
XO
XO
OX
H
H
α
α
H
C
- S'
S'
C
H
S'
α
N
C
N
N
N
N
Ru
Ru
H
N
N
N
Ru
N
N
N
N
S
H
(a)
(b)
X = H, S = acetone, S' = diethyl ether 12
(c)
X = D, S = S' = methanol-d 13
4
Scheme 4.

A. Caballero et al. / Polyhedron 23 (2004) 361–371
369
Fig. 2. Variable 1H NMR spectra of 13a,b,c in the hydride region.
Note the coalescence of the hydride resonances of 13b and c at 0 °C.
appropriate drying agents and degassed before use.
[RuH(cod)(NH2NMe2)3][BPh4] [14], [RuClH(cod)-
(bpzm)] [15] and the bpzmPhOH ligand [5] were pre-
pared as described in the literature. PMe3 (1 M solution
in toluene), PMe2Ph, PMePh2 and PPh3 were used as
purchased from Aldrich. HBF4 was used as a solution
54 wt% in diethyl ether (Aldrich). Elemental analyses
were performed with a Perkin–Elmer 2400 microana-
lyzer. IR spectra were recorded as KBr pellets with a
Perkin–Elmer PE 883 IR spectrometer. 1H, 31P{1H} and
13C{1H} spectra were recorded on a VARIAN UNITY
300 spectrometer. Chemical shifts (ppm) are given rel-
ative to TMS. Coupling constants are given in Hz.
bs ¼ broad singlet, d ¼ doublet, m ¼ multiplet, pt ¼
pseudo-triplet, q ¼ quintet, t ¼ triplet. COSY spectra:
standard pulse sequence with an acquisition time of
0.214 s, pulse width 10 ms, relaxation delay 1 s, number
of scans 16, number of increments 512. The NOE dif-
ference spectra were recorded with the following ac-
quisition parameters: spectral width 5000 Hz,
acquisition time 3.27 s, pulse width 18 ms, relaxation
delay 4 s, irradiation power 5–10 dB, number of scans
240. For variable temperature spectra the probe tem-
perature (ꢂ1 K) was controlled by a standard unit cal-
ibrated with a methanol reference. Free energies of
activation were calculated [16] from the coalescence
temperature (Tc) and the frequency difference between
the coalescing signals (extrapolated at the coalescence
temperature) with the formula DGzc ¼ aT ½9:972 þ
logðT=dmÞꢁ, a ¼ 1:914 ꢃ 10ꢀ2. The estimated error in the
calculated free energies of activation is ꢂ1.0 kJ molꢀ1
3.2. Preparations
.
3.2.1. bpzmPhOK
This salt was prepared according to a modified
method of that described by Carrano and co-workers
[7b] for the sodium salt. A solution of bpzmPhOH
t
(111.5 mg, 0.4 mmol) and BuOK (56.1 mg, (0.4 mmol)
in THF (15 ml) was stirred during 1 h. The solvent was
evaporated to dryness and the resulting white solid was
washed with diethylether (2 ꢃ 8 ml). Yield: 70%.

370
A. Caballero et al. / Polyhedron 23 (2004) 361–371
3.2.2. [RuH(j3-bpzmPhO)(cod)] (1)
3.2.6. [RuH(j3-bpzmPhO)(PMePh2)2] (6)
To a solution of [RuH(cod)(NH2NMe2)3][BPh4] (200
mg, 0.28 mmol) in THF (30 ml) at room temperature
one equivalent of the ligand bpzmPhOK (78 mg, 0.28
mmol) was added. The mixture was stirred overnight,
and the resulting suspension was filtered off in order to
eliminate the KBPh4 formed. The solution was evapo-
rated to dryness, and the resulting white solid was wa-
shed with hexane (10 ml). Yield: 65%.
Another way to synthesize this complex is starting
from [RuClH(cod)(bpzm)]. To a suspension of [Ru-
ClH(bpzm)(cod)] (125 mg, 0.32 mmol) in THF, one
equivalent of the ligand bpzmPhOK (88 mg, 0.32 mmol)
was added, and the mixture was stirred at room tem-
perature for 10 h. The solution was filtered off in order
to eliminate the KCl formed and evaporated to dryness,
and the resulting white solid was washed with ether
(2 ꢃ 10 ml). Yield: 50%. Anal. Calc. for C21H24N4ORu:
C, 56.11; H, 5.38; N, 12.46. Found: C, 56.11; H, 5.34; N,
12.16%. IR (KBr): 2045 cmꢀ1 (m Ru–H).
To a solution of [RuH(bpzmPhO)(cod)] (1) (200 mg,
0.44 mmol) in toluene (15 ml) two equivalents of the
ligand PMePh2 (165 ll, 0.88 mmol) were added, and the
mixture was heated at 70 °C for 20 min. The pale yellow
solution was evaporated to dryness, and the resulting
yellow solid was washed with 10 ml of hexane. Anal.
Calc. for C39H38N4OP2Ru: C, 63.15; H, 5.16; N, 7.55.
Found: C, 63.25; H, 5.99; N, 7.45%. IR (KBr): 2021
cmꢀ1 (m Ru–H).
3.2.7. [RuH(j3bpzmPhO)(PPh3)2] (7)
To a solution of [RuH(bpzmPhO)(cod)] (1) (125 mg,
0.28 mmol) in acetone (10 ml) two equivalents of PPh3
(146 mg, 0.56 mmol) were added. The mixture was he-
ated at 70 °C for 1 h and a suspension was formed. A
pale yellow solid was obtained after filtration at room
temperature and it was washed with hexane (2 ꢃ 10 ml).
Yield: 80%. Anal. Calc. for C39H38N4OP2Ru: C, 67.97;
H, 4.89; N, 6.47. Found: C, 68.16; H, 4.99; N, 6.24%. IR
(KBr): 1944 cmꢀ1 (m Ru–H).
3.2.3. [RuH(j1-O-bpzmPhO)(cod)(PMe3)2] (2)
The reaction has been done in an NMR tube. To a
solution of [RuH(bpzmPhO)(cod)] (1) (18 mg, 0.04 mmol)
in 0.5 ml of benzene-d6 two equivalents of PMe3 (80 ll, 1
M in toluene, 0.08 mmol) were added. The solution was
stirred at 20 °C and the reaction evolution was monitored
by 1H and 31P{1H} NMR. After that, the solution was put
into a Schlenk and evaporated to dryness, and the re-
sulting yellow solid was washed with hexane (2 ꢃ 10 ml).
Approximate yield: 70%. Anal. Calc. for C27H42
N4OP2Ru: C, 53.90; H, 7.04; N, 9.31. Found: C, 53.90; H,
6.99; N, 9.44%. IR (KBr): 2003 cmꢀ1 (m Ru–H).
3.2.8. [RuH(j1-O-bpzmPhO)(PMe3)4] (8)
The reaction has been done in an NMR tube. To a
solution of [RuH(bpzmPhO)(cod)] (1) (18 mg, 0.04
mmol) in 0.5 ml of benzene-d6 four equivalents of PMe3
(160 ll, 1 M in toluene, 0.16 mmol) were added. The
solution was stirred at 20 °C and the reaction evolution
1
was monitored for 1 h by H and 31P{1H} NMR. After
that, the solution was evaporated to dryness in a
Schlenk. The resulting orange solid was washed with 10
ml of hexane. Approximate yield: 73%. Anal. Calc. for
C25H48N4OP4Ru: C, 46.51; H, 7.49; N, 8.68. Found: C,
46.32; H, 7.58; N, 8.82%. IR (KBr): 1973 cmꢀ1 (m Ru–
H).
3.2.4. [RuH(j1-O-bpzmPhO)(cod)(PMe2Ph)2] (3)
The reaction has been done in an NMR tube. To a
solution of [RuH(bpzmPhO)(cod)] (1) (20 mg, 0.04
mmol) in 0.5 ml of benzene-d6 two equivalents of PMe2Ph
(12.7 ll, 0.08 mmol) were added. The yellow solution was
stirred at 20 °C and the reaction evolution was monitored
over 2 h by 1H and 31P{1H} NMR. After that, the solu-
tion was put into a Schlenk and the solvent was evapo-
rated. The resulting yellow solid was washed with 10 ml of
hexane. Approximate yield: 69%. Anal. Calc. for
C37H46N4OP2Ru: C, 61.23; H, 6.39; N, 7.72. Found: C,
61.45; H, 6.46; N, 7.53%. IR (KBr): 2025 cmꢀ1 (m Ru–H).
3.2.9. [cis-O,H-RuH(j1-O-bpzmPhO)(PMe2Ph)4] (9)
The reaction has been done in an NMR tube. To a
solution of [RuH(bpzmPhO)(cod)] (1) (20 mg, 0.04
mmol) in 0.5 ml of benzene-d6 four equivalents of
PMe2Ph (25.4 ll, 0.16 mmol) were added. The solution
was stirred and heated at 50 °C for 20 min, and the
reaction evolution was monitored by NMR. After that,
the solution was put into a Schlenk and evaporated to
dryness, and the yellow solid was washed with 10 ml of
diethyl ether. Approximate yield: 74%. Anal. Calc. for
C45H56N4OP4Ru: C, 60.46; H, 6.31; N, 6.27. Found: C,
60.40; H, 6.27; N, 6.31%. IR (KBr): 1957 cmꢀ1 (m Ru–
H).
3.2.5. [RuH(j3-bpzmPhO)(PMe2Ph)2] (5)
When a solution of the complex 3 (15 mg, 0.021 mmol)
is heated at 50 °C into an NMR tube in benzene-d6 for 30
min, complex 5 was obtained. After that, the solution was
put into a Schlenk and the solvent was evaporated. The
resulting yellow solid was washed with 10 ml of hexane.
Yield: 95%. Anal. Calc. for C29H34N4OP2Ru: C, 56.40;
H, 5.55; N, 9.07. Found: C, 56.32; H, 5.12; N, 9.05%. IR
(KBr): 1948 cmꢀ1 (m Ru–H).
3.2.10. [trans-O,H-RuH(j1-O-bpzmPhO)(PMe2Ph)4]
(10)
A solution of 9 in 0.5 ml of benzene-d6 in an NMR
tube was heated at 70 °C and the reaction evolution was
monitored by NMR until complete transformation into
10. 10 was spectroscopically characterized by NMR.

A. Caballero et al. / Polyhedron 23 (2004) 361–371
371
[4] P.K. Byers, A.J. Canty, R.T. Honeyman, Adv. Organomet. Chem.
34 (1992) 1.
[5] T.C. Higgs, C.J. Carrano, Inorg. Chem. 36 (1997) 291.
3.2.11. [RuH(PMe3)5] (bpzmPhO) (11)
To a solution of [RuH(bpzmPhO)(cod)] (1) (200 mg,
0.44 mmol) in 20 ml of toluene five equivalents of PMe3
(2.2 ml, 1 M in toluene, 2.2 mmol) were added, and the
mixture was stirred at 20 °C for 30 min. The solution
was evaporated to dryness, obtaining an orange solid.
Complex 11 is not obtained as a single product but only
in a mixture with complex 8. IR (KBr): 1983 cmꢀ1 (m
Ru–H).
[6] (a)
422;
K.I. The, L.K. Peterson, Can. J. Chem. 51 (1973)
(b) K.I. The, L.K. Peterson, E. Kiehlmann, Can. J. Chem. 51
(1973) 2448;
(c) L.K. Peterson, E. Kiehlmann, A.R. Sanger, K.I. The, Can. J.
Chem. 52 (1974) 2367.
[7] (a) T.C. Higgs, N.S. Dean, C.J. Carrano, Inorg. Chem. 37 (1998)
1473;
(b) T.C. Higgs, K. Spartalian, C.J. OÕConnor, B.E. Matzanke,
C.J. Carrano, Inorg. Chem. 37 (1998) 2263;
(c) T.C. Higgs, D. Ji, R.S. Czernuszewicz, B.F. Maizanke, V.
3.2.12. General procedure to the formation of complexes
12a–c and 13a–c
ꢀ
Schunemann, A.X. Trautwein, M. Helliwell, W. Ramırez, C.J.
Carrano, Inorg. Chem. 37 (1998) 2383.
A solution of [RuH(bpzmPhO)(cod)] (1) (18 mg, 0.04
mmol) in 0.5 ml of acetone-d6 or methanol-d4 in a NMR
tube was cooled to )90 °C. A solution of HBF4 ꢄ Et2O
(54 wt%) was added (3.6 ll, 0.04 mmol). This tube was
introduced in the NMR probe previously cooled at
)90 °C. The evolution of the reaction was monitored by
1H NMR with an increasing of temperature up to 50 °C
(increments of 10° except in the proximity of the coa-
lescence temperature where the increments were of 1°).
[8] T.C. Higgs, C.J. Carrano, Inorg. Chem. 36 (1997) 298.
[9] (a) C. Potvin, J.M. Manoli, G. Pannetier, R. Chevalier, J.
Organomet. Chem. 146 (1978) 57;
(b) C. Potvin, J.M. Manoli, G. Pannetier, N. Platzer, J.
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ꢀ
(c) F.A. Jalon, A. Lopez-Agenjo, B.R. Manzano, M. Moreno-
Lara, A. Rodrıguez, T. Sturm, W. Weissensteiner, J. Chem. Soc.,
ꢀ
ꢀ
Dalton Trans. (1999) 4031.
[10] For one example with decoordination and recoordination of
ꢀ
pyrazolylborate ligands see: V. Rodrıguez, I. Atheaux, B. Don-
nadieu, S. Sabo-Etienne, B. Chaudret, Organometallics 19 (2000)
2916.
Acknowledgements
[11] M. Paneque, S. Sirol, M. Trujillo, E. Gutierrez-Puebla, M.A.
Monge, E. Carmona, Angew. Chem., Int. Ed. Engl. 39 (2000)
218.
We are grateful to the Spanish DGES/MCyT (Project
BQU-2002-00286) and the Junta de Comunidades de
Castilla-La Mancha (Project PBI-02-002 ) for financial
support.
[12] (a) S.S. Kristjansdottir, J.R. Norton, in: A. Dedieu (Ed.),
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