Synthesis and properties of the 16-electron complex [(C5Me5)RuCl(PMeiPr2)] and of half-sandwich ruthenium hydrido complexes containing bulky monodentate phosphine ligands

Article abstract of DOI:10.1016/s0022-328x(00)00176-5

The 16-electron complex [(C₅Me₅)RuCl(PMeⁱPr₂)] (1) was obtained by reaction of [{(C₅Me₅)RuCl}₄] with PMeⁱPr₂ in petroleum. This compound appears to be in equilibrium with the dimer [{(C₅Me₅)Ru(PMeⁱPr₂) }2(|>C1)J as inferred from low-temperature NMR studies. The 18-electron complex [(C₅Me₅)RuCl(PMeⁱPr₂)₂] was formed upon addition of PMeⁱPr₂ to 1. The related species [(C₅H₅)RuCl(PMeⁱPr₂)₂] (2) was obtained by reaction of [(C₅H₅)RuCl(PMeⁱPr₂)(PPh ₃)] with PMeⁱPr₂, followed by column chromatography. A range of Ru^IV dihydrides [(C₅R₅)RuH₂(PR₃) ₂][BPh₄] (R = Me, H; PR₃ = PMeⁱPr₂, PEt₃) have been prepared and characterised. The corresponding monohydrido complexes [(C₅R₅)RuH(PR₃)₂] were obtained by deprotonation of the cationic dihydrides. Protonation at low temperature of either of these monohydrido complexes yielded back the corresponding dihydrido derivative, except in the case of [(C₅Me₅)RuH(PEt₃)₂], for which the metastable cationic dihydrogen complex [(C₅Me₅)Ru(H₂)(PEt₃) ₂]⁺ was obtained and characterised by NMR spectroscopy. This compound rearranges to its dihydrido tautomer as the temperature is raised, and a kinetic study of such process was accomplished. Interestingly, the only isolable dinitrogen adduct of the type [(C₅R₅)Ru(N₂)(PR₃) ₂][BPh₄] among all possible combinations of phosphines and cyclopentadienyl ring substituents was [(C₅Me₅)Ru(N₂)(PEt₃) ₂][BPh₄].

Full text of DOI:10.1016/s0022-328x(00)00176-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 609 (2000) 161–168
Synthesis and properties of the 16-electron complex
[(C5Me5)RuCl(PMeiPr2)] and of half-sandwich ruthenium hydrido
complexes containing bulky monodentate phosphine ligands
Manuel Jime´nez Tenorio, M. Carmen Puerta *, Pedro Valerga
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Qu´ımica Inorga´nica, Facultad de Ciencias, Uni6ersidad de Ca´diz,
Apartado 40, 11510 Puerto Real, Ca´diz, Spain
Received 30 January 2000; received in revised form 3 March 2000
Abstract
The 16-electron complex [(C5Me5)RuCl(PMeiPr2)] (1) was obtained by reaction of [{(C5Me5)RuCl}4] with PMeiPr2 in
petroleum. This compound appears to be in equilibrium with the dimer [{(C5Me5)Ru(PMeiPr2)}2(m-Cl)2] as inferred from
low-temperature NMR studies. The 18-electron complex [(C5Me5)RuCl(PMeiPr2)2] was formed upon addition of PMeiPr2 to 1.
The related species [(C5H5)RuCl(PMeiPr2)2] (2) was obtained by reaction of [(C5H5)RuCl(PMeiPr2)(PPh3)] with PMeiPr2, followed
by column chromatography. A range of RuIV dihydrides [(C5R5)RuH2(PR3)2][BPh4] (R=Me, H; PR3=PMeiPr2, PEt3) have been
prepared and characterised. The corresponding monohydrido complexes [(C5R5)RuH(PR3)2] were obtained by deprotonation of
the cationic dihydrides. Protonation at low temperature of either of these monohydrido complexes yielded back the corresponding
dihydrido derivative, except in the case of [(C5Me5)RuH(PEt3)2], for which the metastable cationic dihydrogen complex
[(C5Me5)Ru(H2)(PEt3)2]+ was obtained and characterised by NMR spectroscopy. This compound rearranges to its dihydrido
tautomer as the temperature is raised, and a kinetic study of such process was accomplished. Interestingly, the only isolable
dinitrogen adduct of the type [(C5R5)Ru(N2)(PR3)2][BPh4] among all possible combinations of phosphines and cyclopentadienyl
ring substituents was [(C5Me5)Ru(N2)(PEt3)2][BPh4]. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium; Half-sandwich complexes; Hydrido complexes; Dihydrogen complexes; Dinitrogen complexes
1. Introduction
Me). This allowed us to establish a correlation between
the value found for w(N2) and the observed stability of
the dihydrogen adducts. The work was extended to
Half-sandwich ruthenium derivatives of the type
[(C5R5)Ru(H2)P2]+ (R=Me, H; P2=two monodentate
phosphine ligands, or one bidentate phosphine ligand)
constitute one of the most important classes of known
dihydrogen/dihydrido complexes [1–4]. We have previ-
ously studied in detail the dihydrogen to dihydrido
tautomerisation process for the systems [(C5R5)Ru-
(H2)(dippe)]+ (R=H, Me; dippe=1,2-bis(diisopropyl-
phosphino)ethane) [5] as part of our studies on the
activation and binding of small molecules by transition
metal complexes containing bulky phosphine ligands.
We were able to prepare as well the half-sandwich
dinitrogen complexes [(C5R5)Ru(N2)(dippe)]+ (R=H,
systems
containing
hydrotris(pyrazolyl)borate-
(1-) ({HB(pz)3}) and both bidentate [6] and monoden-
tate bulky phosphines [7] as ligands. The complexes
[{HB(pz)3}Ru(H2)(dippe)]+ [6] and [{HB(pz)3}-
Ru(H2)(PR3)2]+ (PR3=PMeiPr2, PEt3) [7] were all
found to be stable species which do not rearrange to
their dihydrido tautomers, at variance with what
occurs for the [(C5R5)Ru(dippe)]+ (R=H, Me)
systems [5]. Stable {HB(pz)3}Ru dinitrogen complexes
were also prepared and characterised. In order to com-
plete this study, we have focused our attention on the
C5Me5 and C5H5 ruthenium systems containing bulky
monodentate phosphines, particularly PMeiPr2, which
can be considered as a monodentate equivalent of the
bulky, strong electron releasing phosphine dippe [7].
* Corresponding author. Tel.: +34-956-016350; fax: +34-956-
016288.
E-mail address: carmen.puerta@uca.es (M.C. Puerta).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00176-5

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M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
The steric and electronic properties of PMeiPr2 have
also allowed the isolation of the 16-electron complex
[(C5Me5)RuCl(PMeiPr2)], which belongs to a family of
stable, yet reactive coordinatively unsaturated deriva-
tives of the type [(C5Me5)RuX(PR3)] (X=halide, OR,
OSiR3, NHPh; PR3=PiPr3, PCy3, PPhiPr2) [8–10].
Only phosphines having large cone angles allow the
isolation of such species. However, from our studies
PMeiPr2 could be exceptional in the sense that com-
plexes containing two of these ligands attached to the
same metal centre, e.g. [(C5Me5)RuCl(PMeiPr2)2], are
also accessible. In this work we describe the synthesis
and properties of [(C5Me5)RuCl(PMeiPr2)] and related
compounds, as well as the study of C5Me5 and C5H5
ruthenium dihydrido/dihydrogen complexes containing
bulky monodentate phosphine ligands.
10]. Other synthetic procedures, such as the reduction
of [{(C5Me5)RuCl2}2] with zinc dust in THF in the
presence of PMeiPr2, have proven to be less effective in
the isolation of the desired pure complex. As its con-
geners containing bulkier phosphines, 1 is a blue, crys-
talline material, very soluble in non-polar solvents and
extremely air-sensitive both in the solid state and in
solution. Thus, exposure to air of solutions of 1 results
in rapid colour change to red–brown, and formation of
phophine oxide plus paramagnetic species as inferred
from NMR spectroscopy. The observed colour change
is consistent with the possible formation of paramag-
netic oligomeric oxoruthenium(III) complexes of the
type [{((C5Me5)RuClx)(m-O)}n], very much like
[((C5Me5)RuCl2)2(m-O)], already described in the litera-
ture [12]. The spectral properties for 1 are consistent
with those reported for other [(C5Me5)RuCl(PR3)] com-
1
plexes. Thus, the H-NMR spectrum of 1 in toluene-d8
at room temperature shows one singlet at 1.39 ppm
attributable to the methyl resonances of the C5Me5
ring, whereas its 31P{1H}-NMR spectrum displays one
sharp singlet at l 31.7 ppm. These features are consis-
tent with a ‘two-legged’ piano stool structure for this
complex, analogous to that found by single crystal
X-ray diffraction for [(C5Me5)RuCl(PiPr3)] [8]. When
the temperature is lowered at 180 K, the 31P{1H}-NMR
resonance broadens and shifts to 32.6 ppm (ca. 1 ppm
downfield), and a new, broad resonance arises at 33.4
ppm (Fig. 1). The original spectrum is restored when
the temperature is raised. We have interpreted this
behaviour in terms of a monomer–dimer equilibrium,
as shown.
2. Results and discussion
2.1. Synthesis and properties of [(C5Me5)Ru-
Cl(PMeiPr2)] and related compounds
The 16-electron complex [(C5Me5)RuCl(PMeiPr2)] (1)
was obtained by treatment of the tetramer
[{(C5Me5)RuCl}4] [11] with the stoichiometric amount
of the corresponding phosphine in petroleum ether, a
procedure which has been successfully used for the
preparation of other related species of the type
[(C5Me5)RuCl(PR3)] (PR3=PCy3, PiPr3, PPhiPr2) [8–
The new, broad resonance observed at 33.4 ppm
should therefore correspond to the dimeric species. The
amount of dimeric product observed is significative
only at very low temperatures, since higher tempera-
tures favour the monomer 1 within this equilibrium for
entropical reasons. In fact, only the monomer appears
to be present at room temperature, and hence the
proposed monomer–dimer equilibrium (which should
be rapid on the NMR time scale) only starts at already
very low temperatures. This is a possible explanation
for the observed downfield shift of the 31P{1H}-NMR
resonance of 1 as the temperature is lowered, although
it could be also interpreted just in terms of the chemical
shift dependence on the temperature over an expanded
Fig. 1. 31P{1H}-NMR spectra of [(C5Me5)RuCl(PMeiPr2)] in toluene-
d8.

M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
163
when the temperature is lowered, corresponding to an
unresolved AB pattern (Fig. 2). This indicates clearly
the presence of two phosphine ligands attached to
ruthenium despite the bulkiness of PMeiPr2, suggesting
the formation of the 18-electron complex [(C5Me5)-
RuCl(PMeiPr2)2].
The inequivalence of the phosphorus atoms within
this complex arises from freezing out conformers
around single RuꢀP and PꢀC bonds, very much as it
has been recently observed for the even more sterically
crowded compound [{HB(pz)3}RuCl(PMeiPr2)2] [7]. At
180 K, one minor signal attributable to [(C5Me5)RuCl-
(PMeiPr2)] is also present in the 31P{1H}-NMR spec-
trum, indicating its co-existence with the coordinatively
saturated species [(C5Me5)RuCl(PMeiPr2)]. The fact
that both [(C5Me5)RuCl(PMeiPr2)] and [(C5Me5)RuCl-
(PMeiPr2)2] can be generated clearly indicates that the
stabilisation of this sort of coordinatively unsaturated
species (at least for PMeiPr2) is solely attributed to
electronic, rather than steric reasons. Furthermore, in
the case of the {HB(pz)3} ligand, more sterically de-
manding than C5Me5, the 16-electron species
[{HB(pz)3}RuCl(PMeiPr2)] has not yet been detected. It
appears that the steric and electronic properties of
PMeiPr2 trace a line between those of bulkier phoshines
like PiPr3, PPhiPr2 or PCy3, and those of smaller phos-
phines like PEt3 or PMe3. [(C5Me5)RuCl(PMeiPr2)2]
was not isolated pure in solid form. All efforts to
isolate it as a solid always yielded a brown oil, contam-
inated with substantial amounts of free PMeiPr2. In
relation to this, we had previously found that displace-
ment of two PPh3 ligands by PMeiPr2 in
[(C5H5)RuCl(PPh3)2] did not take place, and the only
isolated complex upon prolonged heating at 120°C with
excess of PMeiPr2 was the mixed phosphine complex
[(C5H5)RuCl(PMeiPr2)(PPh3)] [14]. We initially at-
tributed this to the fact that due to the steric hindrance,
the derivative [(C5H5)RuCl(PMeiPr2)2] was possibly an
unstable species. However, upon isolation of complexes
such as [{HB(pz)3}RuCl(PMeiPr2)2] [7] and the detec-
tion of [(C5Me5)RuCl(PMeiPr2)2], we suspected that
[(C5H5)RuCl(PMeiPr2)2] (2) should be stable. We pre-
pared 2 by reaction of [(C5H5)RuCl(PMeiPr2)(PPh3)]
with an excess of PMeiPr2 in refluxing toluene, and it
was isolated in the form of orange crystals upon purifi-
cation by column chromatography on silica gel. The
Fig. 2. 31P{1H}-NMR spectra (toluene-d8) of [(C5Me5)RuCl-
(PMeiPr2)] with added PMeiPr2.
range of ca. 100 K. We have found no precedent for
this behaviour for other compounds of the type
[(C5Me5)RuCl(PR3)]. The coordinative unsaturation in
such species is partially mitigated by p-electron dona-
tion from the lone pairs of the halide ligand, helping
therefore in their stabilisation [10]. The other way for
achieving 18-electron configuration if by halide-bridg-
ing dimerisation, a process which is entropically disfa-
voured. However, if the dimer is more stable than the
monomer on enthalpy basis, an equilibrium between
the two species should occur in more or less extent at
low temperature, when DG becomes close to zero, and
this is apparently what happens in our system, at
variance with other ones containing bulkier phosphines.
Bulky phosphines in [(C5Me5)RuCl(PR3)] (PR3=
PiPr3, PCy3, PPhiPr2) complexes are substitutionally
labile, being readily replaced by phosphines like PEt3 or
PMe3, and phosphites like P(OMe)3, both having
smaller cone angles, furnishing the corresponding 18-
electron complexes [(C5Me5)RuCl(PR3)2] (PR3=PEt3
or PMe3) and [(C5Me5)RuCl(P(OMe)3)2], respectively
[13]. In no case has been detected the formation of
[(C5Me5)RuCl(PR3)2] for bulky phosphines such as
PiPr3 or PCy3, this being attributed to steric reasons [8].
We have observed that addition of an excess of
PMeiPr2 to a toluene-d8 solution of [(C5Me5)RuCl-
(PMeiPr2)] causes a colour change to orange–brown. A
new singlet resonance is observed at 30.5 ppm in the
31P{1H}-NMR spectrum, which splits in two signals

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M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
case of 3a, a broadening in the 31P{1H}-NMR reso-
nance is observed, which is again attributed to the
freezing of conformers around RuꢀP and PꢀC as conse-
quence of the bulkiness of the PMeiPr2 ligand and the
steric repulsion within the formally seven-coordinate
complex.
presence in the reaction mixture of free PPh3 released
from [(C5H5)RuCl(PPh3)2] had initially prevented the
substitution of the second PPh3 by PMeiPr2. This prob-
lem was eventually solved by making the overall substi-
tution in two separate steps, leading to the isolation of
the desired complex 2. This compound exhibits all the
typical spectral features expected for half-sandwich
complexes of the type [(C5H5)RuCl(PR3)2], i.e. one
All dihydrides are readily deprotonated by a strong
base such as KOBut furnishing the corresponding neu-
tral monohydrido complexes [(C5Me5)RuH(PR3)2]
(PR3=PMeiPr2 (5a), PEt3 (5b)), [(C5H5)RuH(PR3)2]
(PR3=PMeiPr2 (6a), PEt3 (6b)) and [(C5H5)RuH-
(PMeiPr2)(PPh3)] (6c). All these compounds are highly
air sensitive, and they were isolated as oils in several
instances. All of them display one high-field triplet for
1
singlet for the C5H5 protons in the H-NMR spectrum,
and one singlet in the 31P{1H}-NMR spectrum. At
variance which what was observed for the system
[(C5Me5)RuCl(PMeiPr2)2], in the case of 2 no decoales-
cence was observed at low temperature for the reso-
nance in the 31P{1H}-NMR spectrum, suggesting that
the rotation barrier around RuꢀP and PꢀC bonds is
lower in energy as expected, given the decrease in steric
hindrance when substituting the ligand C5Me5 with
C5H5.
1
the hydrido ligand in their H-NMR spectra, and one
singlet in the 31P{1H}-NMR spectra (except for 6c,
which shows two doublets as expected). Besides, a
strong IR absorption is present at ca. 1950 cm−1
,
attributed to the stretching w(RuH). Our main interest
in these monohydrido complexes was to study their
protonation reaction at low temperature, in an effort to
obtain cationic dihydrogen adducts of the type
[(C5R5)Ru(H2)(PR3)2]+ (R=Me, H). We carried out
the protonation reaction of the monohydrido com-
plexes in an NMR tube in CD2Cl2 at 193 K using
HBF4·OEt2 as acid (excess). Immediately, the sample
2.2. Hydrido complexes
Despite its coordinatively unsaturated character, 1
does not react with hydrogen at room temperature in
toluene or petroleum ether. However, it reacts with H2
and NaBPh4 in MeOH in the presence of an excess of
PMeiPr2 affording the RuIV dihydride [(C5Me5)RuH2-
(PMeiPr2)2][BPh4] (3a). Likewise, the dihydrido deriva-
tives [(C5R5)RuH2(PR3)2][BPh4] (R=Me, PR3=PEt3
(3b); R=H, PR3=PMeiPr2 (4a), PEt3 (4b)) were all
obtained by reaction of the corresponding chloro com-
plex [(C5R5)RuCl(PR3)2] with H2 and NaBPh4 in
MeOH. The mixed-phosphine dihydride [(C5H5)RuH2-
(PMeiPr2)(PPh3)][BPh4] (4c) was also obtained in
analogous fashion starting from [(C5H5)RuCl-
(PMeiPr2)(PPh3)]. All these compounds are crystalline
1
was inserted in the pre-cooled probe and the H- and
31P{1H}-NMR spectra were recorded. We had previ-
ously used this procedure for the study of the
metastable dihydrogen complexes [(C5R5)Ru(H2)-
(dippe)]+ (R=Me, H), which rearrange to their dihy-
drido tautomers as the temperature is raised [5]. Rather
surprisingly, the only products resulting from the pro-
tonation of the monohydrides 5a and 6a–c were the
corresponding cationic RuIV dihydrido complexes, these
being the complex cations in compounds 3a and 4a–c,
respectively. Only in the case of the protonation of 3b,
the dihydrogen derivative [(C5Me5)Ru(H2)(PEt3)2][BF4]
1
solids, which display one high-field triplet in their H-
NMR spectra for the hydrido ligands, which are equiv-
alent. The 31P{1H}-NMR spectra consist of one singlet
for all compounds except 4c, for which a two-doublet
pattern corresponding to an AX spin system is ob-
served. In this particular case, the triplet for the hy-
drido resonance arises from the accidental coincidence
1
(7) was quantitatively generated, as inferred from H-
and 31P{1H}-NMR spectroscopy. This compound ex-
hibits one broad resonance at −9.98 ppm for the
dihydrogen ligand, for which a minimum longitudinal
relaxation time (T1)min of 17.5 ms was measured. A
value of 21.5 Hz was obtained for the coupling constant
1JHD in the isotopomer [(C5Me5)Ru(HD)(PEt3)2][BF4]
(prepared by reaction of 3b with DBF4, generated from
2
of the values of the two coupling constants JHP and
2JHP% within the complex. The long minimum longitudi-
nal relaxation times (T1)min for these hydrides, along
with the null value of the coupling constant JHD for the
corresponding isotopomers is fully consistent with the
formulation as RuIV dihydrides for these species. A
transoid four-legged piano-stool structure, analogous to
that found by X-ray crystallography for [(C5Me5)-
RuH2(dippe)][BPh4] [5], [(C5Me5)RuH2(PMe3)2][BF4]
[4a], or [(C5Me5)RuH2(dppm)][BF4] (dppm=1,1-bis-
(diphenylphosphino)methane) [4b], is hence proposed
on spectral grounds. No dihydride–dihydrogen equi-
librium has been observed when lowering the tempera-
ture for any of these hydrido complexes. Only in the
1
a mixture HBF4·OEt2/D2O 1:3). Both (T1)min and JHD
are consistent with a ‘non-classical’ formulation for
compound 7. As temperature is raised, 7 undergoes
irreversible tautomerisation to its dihydride form 3b. At
room temperature, the conversion into 3b is quantita-
tive. We studied the kinetics of this tautomerisation
process by following the dissappearace of the phospho-
rus resonance for 7 in its 31P{1H}-NMR spectrum, as
we previously did with the related dippe complexes.

M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
165
The process is first-order respect to the concentration of
complex, the rate constants being independent of the
concentration of complex and of acid. From the first-or-
der rate constants measured at different temperatures,
we obtained the activation parameters DH" =1891
kcal mol−1 and DS" = −4.490.1 eu using an Eyring
plot (Fig. 3). These activation parameters lead to an
overall value of DG"298=1991 kcal mol−1 for the tau-
tomerisation process. The observed kinetic and activa-
tion parameters are consistent with an intramolecular
mechanism for the dihydrogen to dihydride rearrange-
ment analogous to that proposed for other
[(C5R5)Ru(H2)P2]+ systems, as shown.
H2 is always the final thermodynamic product, but in
the case of 7, the energy barrier for the rearrangement is
high enough to allow its detection prior to isomerisa-
tion. It results surprising that the homologous dihydro-
gen complex [(C5Me5)Ru(H2)(PMeiPr2)2]+, for which an
even higher energy barrier could be anticipated, is not
observed. We are currently carrying out detailed investi-
gations on the [(C5Me5)Ru(PMeiPr2)2]+ system [15], and
results will be reported in due course.
The combination of C5Me5 and PEt3 is also excep-
tional among the series of studied compounds because it
allowed the isolation of the dinitrogen compound
[(C5Me5)Ru(N2)(PEt3)2][BPh4] (8) as a yellow microcrys-
talline material, just by reaction of [(C5Me5)RuCl-
(PEt3)2] with N2 and NaBPh4 in MeOH. This method
has been successfully used in the preparation of the half-
sandwich iron derivative [(C5H5)Fe(N2)(dippe)]-
[BPh4] [16], but for other ruthenium dinitrogen com-
plexes such as [(C5H5)Ru(N2)(dippe)][BPh4] [5], or
[{HB(pz)3}Ru(N2)(PEt3)2][BPh4] [7] the addition of a sil-
ver salt as halide scavenger was found to be essential in
the synthetic procedure. Compound 8 displays one
strong IR w(NꢁN) band at 2134 cm−1. This frequency
falls in the range for which the corresponding dihydro-
gen adduct is expected to be stable, according to the
criterion proposed by Morris and co-workers (2160\
w(NꢁN)\2060 cm−1) [17]. In this work, it has not been
possible to obtain dinitrogen complexes for any other
combination of C5H5/C5Me5 and phosphine ligands
apart from that for compound 8. Reciprocally, for all
ruthenium dinitrogen compounds prepared by our
group, the corresponding dihydrogen adduct has always
been observed, or even isolated and structurally charac-
terised in some cases. From these results, and as pointed
by Morris criterion, it appears to be a correspondence
between the ability of a ruthenium centre for binding N2
and the stabilisation of the rutheniumꢀdihydrogen
bond.
All attempts to recrystallise compound 8 were unsuc-
cessful. Dinitrogen is released, and most often, the
dioxygen derivative [(C5Me5)Ru(O2)(PEt3)2][BPh4] (9)
was obtained. The moiety {[(C5Me5)Ru(PEt3)2]+} has
an enormous affinity for dioxygen, as it occurs also for
{[(C5Me5)Ru(dippe)]+} [5,18], leading to the irreversible
formation of the dioxygen complex even at trace level
concentrations of O2. Compound 9 is therefore a very
stable material, such like [(C5Me5)Ru(O2)(dippe)][BPh4]
[18] or [(C5Me5)Ru(O2)(dppe)][BPh4] [19], which be-
comes a ‘stability well’ to be considered in most reac-
tions in which the moiety {[(C5Me5)Ru(PEt3)2]+} is
involved.
In this mechanism, initially postulated by Chinn and
Heinekey [2], the dihydrogen complex traverses a rela-
tively high-energy transition state along the pathway to
dihydride, in which the coordination number changes
from six to seven, and homolytic dihydrogen splitting
takes place. The observed small and negative value for
DS" accounts for the lost of rotational freedom of the
dihydrogen ligand when it transforms into a dihydrido
complex [1,2]. This is fully consistent with literature
data, and therefore unexceptional. The most intriguing
feature is the fact that only for C5Me5 and PEt3 as co-
ligands appears feasible the kinetic stabilisation of coor-
dinated dihydrogen at ruthenium in these systems. In all
cases, the metal centre is electron rich and therefore the
dihydrido tautomer resulting from oxidative addition of
3. Experimental
All synthetic operations were performed under a dry
dinitrogen or argon atmosphere following conventional
Fig. 3. Eyring plot for the tautomerisation process [(C5Me5)Ru-
(H2)(PEt3)2]+ (7)“[(C5Me5)RuH2(PEt3)2]+ (3b) in CD2Cl2.

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M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
Schlenk or drybox techniques. THF, diethylether and
petroleum ether (b.p. range 40–60°C) were distilled
from the appropriate drying agents. All solvents were
deoxygenated immediately before use. [{(C5Me5)-
RuCl}4] [11], [(C5Me5)RuCl(PEt3)2], [(C5H5)RuCl-
(PEt3)2] and [(C5H5)RuCl(PMeiPr2)(PPh3)] [14] were
prepared according to reported procedures. IR spectra
were recorded in Nujol mulls on Perkin–Elmer 881 or
Perkin–Elmer FTIR Spectrum 1000 spectrophotome-
ters. NMR spectra were taken on Varian Unity 400
MHz or Varian Gemini 200 MHz spectrophotometers.
Chemical shifts are given in ppm from SiMe4 (1H) or
85% H3PO4 (31P{1H}). Microanalyses were taken by Dr
Manuel Arjonilla at the CSIC-Instituto de Ciencias
Marinas de Andaluc´ıa.
3.3. [(C5Me5)RuH2(PMeiPr2)2][BPh4] (3a)
To a solution of 1 (0.15 g, ca. 0.37 mmol) in MeOH,
PMeiPr2 (0.1 ml, excess) was added. Hydrogen was
bubbled through the reaction mixture, which was then
treated with an excess of solid NaBPh4 (0.25 g). A light
brown precipitate was immediately formed. The mix-
ture was stirred under a H2 atmosphere for 15 min.
After this time, the solids were filtered off, washed with
ethanol and petroleum ether and dried in vacuo. The
compound was recrystallised from acetone/ethanol as a
light brown microcystalline material. Yield: 0.24 g,
80%. Anal. Calc. for C48H71BP2Ru: C, 70.2; H, 8.65.
Found C, 69.9; H, 8.73%. IR (Nujol): w(RuH) 2016 br
1
2
cm−1. NMR (CD3COCD3): H: l −9.21 (t, JHP
=
28.7 Hz, RuH2; (T1)min=740 ms at 400 MHz), 2.01 (s,
C5(CH3)5), 1.19 (m, PCH(CH3)2), 1.33 (d, PCH3), 2.07
(m, PCH(CH3)2). 31P{1H}: l 55.7 (s).
3.1. Preparation of [(C5Me5)RuCl(PMeiPr2)] (1)
To a slurry of [{(C5Me5)RuCl}4] (0.54 g, 0.5 mmol)
in petroleum ether, PMeiPr2 (0.3 ml, 2 mmol) was
added. An immediate colour change to purple–blue
was observed, with the concomitant dissolution of the
tetrameric [{(C5Me5)RuCl}4]. The mixture was stirred
for 15 min. Then, the solution was filtered through
Celite, concentrated and cooled to −20°C. Large dark
blue, almost black, crystals were obtained. They were
filtered off and dried in vacuo. Further crops could be
obtained by subsequent concentration and cooling of
the mother liquor. Yield: 0.53 g, 66%. Anal. Calc. for
C17H32ClPRu: C, 50.6; H, 7.93. Found C, 50.3; H,
3.4. [(C5Me5)RuH2(PEt3)2][BPh4] (3b)
To a solution of [(C5Me5)RuCl(PEt3)2] (0.2 g, 0.39
mmol) in MeOH, solid NaBPh4 (0.3 g, excess) was
added while a stream of H2 was bubbled through the
reaction mixture. A white precipitate was formed.
Upon stirring for 10 min, it was filtered off, washed
with ethanol and petroleum ether and dried in vacuo.
Recrystallisation from acetone/ethanol afforded colour-
less crystals of this compound, which were filtered off
and dried in vacuo. Yield: 0.32 g, 95%. Anal. Calc. for
C46H67BP2Ru: C, 69.6; H, 8.52. Found: C, 69.4; H,
1
7.88%. NMR (toluene-d8): H: l 0.65, 0.76, 0.99 (m,
PCH(CH3)2), 1.13 (d, PCH3), 1.93, 2.23 (m,
8.48%. IR (Nujol): w(RuH) 1958 w, 2004 w cm−1
.
PCH(CH3)2), 1.39 (s, C5(CH3)5). 31P{1H}: l 31.7 (s).
NMR (CD3COCD3): H: l −9.47 (t, JHP=28.4 Hz,
RuH2; (T1)min=764 ms at 400 MHz), 2.00 (s,
C5(CH3)5), 1.10 (m, PCH2CH3), 1.80 (m, PCH2CH3).
31P{1H}: l 49.9 (s).
1
2
3.2. [(C5H5)RuCl(PMeiPr2)2] (2)
A solution of [(C5H5)RuCl(PMeiPr2)(PPh3)] (0.8 g,
1.34 mmol) in toluene was treated with an excess of
PMeiPr2 (0.35 ml). The mixture was heated under reflux
for 18 h. At the end of this time, the solvent was
removed in vacuo. The resulting orange oil was dis-
solved in a minimum amount of petroleum ether and
passed through a silica gel chromatographic column in
order to remove PPh3. This was done in the air, an inert
atmosphere being not necessary at this stage. The
column was eluted with petroleum–diethylether (3:1
v/v). The fraction corresponding to the orange band
was collected. Removal of the solvent afforded a yel-
low–orange microcrystalline material. Analytically
pure samples were obtained by recrystalisation from
petroleum ether/diethylether. Yield: 0.46 g, 74%. Anal.
Calc. for C19H39ClP2Ru: C, 49.0; H, 8.38. Found C,
49.1; H, 8.40%. NMR (C6D6): 1H: l 1.15, 1.18 (m,
PCH(CH3)2), 1.14 (d, PCH3), 1.86 (m, PCH(CH3)2),
4.40 (s, C5H5). 31P{1H}: l 40.0 (s).
3.5. [(C5H5)RuH2(PR3)2][BPh4] (PR3=PMeiPr2 (4a),
PEt3 (4b))
A method analogous to that used in the preparation
of 3b was used for the synthesis of these compounds,
starting either from [(C5H5)RuCl(PMeiPr2)2] (for 4a) or
from [(C5H5)RuCl(PEt3)2] (for 4b).
Compound 4a: Yield: 70%. Anal. Calc. for
C43H61BP2Ru: C, 68.7; H, 8.12. Found C, 68.5; H,
8.22%. IR (Nujol): w(RuH) not observed. NMR
1
2
(CD3COCD3): H: l −9.47 (t, JHP=24.9 Hz, RuH2;
(T1)min=520 ms at 400 MHz), 1.18 (d, PCH3), 1.34–
1.45 (m, PCH(CH3)2), 2.03 (m, PCH(CH3)2), 5.91 (s,
C5H5). 31P{1H}: l 65.5 (s).
Compound 4b: Yield: 72%. Anal. Calc. for
C41H57BP2Ru: C, 73.0; H, 7.79. Found: C, 73.1; H,
7.81%. IR (Nujol): w(RuH) 1994 w, 2022 w cm−1
.
1
2
NMR (CD3COCD3): H: l −10.09 (t, JHP=25.4 Hz,

M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
167
RuH2; (T1)min=500 ms at 400 MHz), 0.96 (m,
PCH2CH3), 1.43 (m, PCH2CH3), 4.85 (s, C5H5).
31P{1H}: l 54.5 (s).
(m, PCH(CH3)2), 1.54, 1.75 (m, PCH(CH3)2), 4.54
(C5H5). 31P{1H}: l 61.7 (s).
Compound 6b: Yield: 55%. Anal. Calc. for
C17H36P2Ru: C, 57.7; H, 10.2. Found C, 57.5; H,
3.6. [(C5H5)RuH2(PPh3)(PMeiPr2)][BPh4] (4c)
10.0%. IR (Nujol): w(RuH) 1940 cm−1
. NMR
1
2
(CD3COCD3): H: l −13.32 (t, JHP=35.6 Hz, RuH),
0.91 (m, PCH2CH3), 1.50 (m, PCH2CH3), 4.70 (s,
C5H5). 31P{1H}: l 53.6 (s).
A procedure identical to that for 4a–b was used for
the preparation of this compound, starting from
[(C5H5)RuCl(PMeiPr2)(PPh3)]. Yield: 60%. Anal. Calc.
for C54H59BP2Ru: C, 77.9; H, 7.16. Found: C, 77.8; H,
3.9. [(C5H5)RuH(PPh3)(PMeiPr2)] (6c)
7.21%. IR (Nujol): w(RuH) 2008 w, 2042 w cm−1
.
1
2
NMR (CD3COCD3): H: l −9.11 (t, JHP=24.6 Hz,
RuH2; (T1)min=320 ms at 400 MHz), 0.94, 1.11 (m,
PCH(CH3)2), 1.25 (d, PCH3), 2.05 (m, PCH(CH3)2),
4.78 (C5H5), 7.22, 7.45, 7.63 (m, P(C6H5)3). 31P{1H}: l
It was obtained as described for compounds 5a–b
and 6a–b, starting from the dihydride 4c. Yield: 88%.
Anal. Calc. for C30H38P2Ru: C, 70.4; H, 7.50. Found:
C, 70.2; H, 7.43%. IR (Nujol): w(RuH) 1944 cm−1
.
2
61.1(d), 64.3 (d), JPP=48 Hz.
1
2
NMR (C6D6): H: l −11.58 (t, JHP=34.4 Hz, RuH),
0.38 (d, PCH3), 0.84, 0.97 (m, PCH(CH3)2), 1.71 (m,
PCH(CH3)2), 4.58 (C5H5), 5.90, 6.12 (m, P(C6H5)).
3.7. [(C5Me5)RuH(PR3)2] (PR3=PMeiPr2 (5a), PEt3
(5b))
2
31P{1H}: l 58.7 (d), 72.8 (d), JPP=32.8 Hz.
To a solution of either 5a or 5b in THF, an excess of
solid KOBut was added. A yellow–orange colour devel-
oped immediately. The mixture was stirred for 15 min
at room temperature. At the end of this time, the
solvent was removed in vacuo, and the residue ex-
tracted with petroleum ether. The resulting solution was
filtered through Celite. Removal of the solvent afforded
a yellow oil, which was re-dissolved in a minimum
amount of petroleum ether, and cooled to −20°C.
Air-sensitive yellow crystals were obtained, which were
isolated by removing the supernatant liquor via can-
nula, and dried thoroughly in vacuo.
3.10. [(C5Me5)Ru(H2)(PEt3)2][BF4] (7)
Compound 7 was obtained and characterised in solu-
tion by protonation of the monohydride 5b inside a 5
mm NMR tube in either CD3COCD3 or CD2Cl2 at 193
K, using a slight excess HBF4·OEt2. Yield: quantitative.
1
NMR (CD3COCD3, 203 K): H: l −9.98 (br, Ru(H2),
1
(T1)min=17.5 ms at 400 MHz, JHD=21.5 Hz), 1.21
(m, PCH2CH3), 2.36 (m, PCH2CH3), 1.95 (s, C5(CH3)5).
31P{1H}: l (203 K) 35.0 (s).
Compound 5a: Yield: 50%. Anal. Calc. for
C24H50P2Ru: C, 57.5; H, 9.98. Found C, 57.5; H,
9.76%. IR (Nujol): w(RuH) 1954 cm−1. NMR (C6D6):
3.11. Kinetics of the dihydrogen to dihydride
isomerisation 7“3b
2
1H: l −14.57 (t, JHP=37 Hz, RuH), 0.95 (d, PCH3),
Samples of 7, prepared as described above, were
immersed into a liquid nitrogen/ethanol bath, in order
to prevent isomerisation during transport and handling.
The sample was removed and introduced into the pre-
cooled probe of the Varian Unity 400 MHz spectrome-
ter at 203 K (the NMR temperature controller was
previously calibrated against a methanol sample, the
reproducibility being 95°C). Once the shims were
adjusted, the probe was warmed to the desired temper-
ature. 31P{1H}-NMR spectra were recorded for at least
three half-lives at regular intervals using the spectrome-
ter software for accurate time control. Peak intensities
were analysed from stacked plots of the 31P{1H}-NMR
spectra. First-order rate constants were derived from
the least-squares best-fit lines of the ln(intensity) versus
time plots. The uncertainty in the isomerisation rate
constants represents one standard deviation (9|)
derived from the slope of the best-fit line. Uncertainties
in the activation enthalpy and entropy were calculated
from the uncertainties in the slope and intercept of the
best-fit lines of the Eyring plots.
0.77, 1.01, 1.12 (m, PCH(CH3)2), 1.61, 1.81 (m,
PCH(CH3)2), 1.89 (C5(CH3)5). 31P{1H}: l 54.3 (s).
Compound 5b: Yield: 58%. Anal. Calc. for
C22H46P2Ru: C, 55.8; H, 9.81. Found: C, 55.6; H,
9.75%. IR (Nujol): w(RuH) 1939 cm−1. NMR (C6D6):
2
1H: l −14.26 (t, JHP=36.8 Hz, RuH), 1.85 (s, C5H5),
0.12 (m, PCH2CH3), 1.10 (m, PCH2CH3). 31P{1H}: l
46.4 (s).
3.8. [(C5H5)RuH(PR3)2] (PR3=PMeiPr2 (6a), PEt3
(6b))
These compounds were obtained by deprotonation of
the corresponding dihydride 4a or 4b using KOBut,
following a procedure identical to that outlined for
5a–b.
Compound 6a: This compound was obtained as an
air-sensitive oil, and it was not analysed. IR (Nujol):
1
w(RuH) 1944 cm−1. NMR (CD3COCD3): H: l −9.15
2
(t, JHP=24.4 Hz, RuH), 1.02 (d, PCH3), 0.93–1.10

168
M. Jime´nez Tenorio et al. / Journal of Organometallic Chemistry 609 (2000) 161–168
3.12. [(C5Me5)Ru(N2)(PEt3)2][BPh4] (8)
Society of Chemistry for the award of a grant for
International Authors (to M.J.T.)
To a solution of [(C5Me5)RuCl(PEt3)2] (0.25 g, ca.
0.5 mmol) in MeOH under dinitrogen, an excess of
solid NaBPh4 (0.3 g) was added. A yellow precipitate
was formed gradually. Upon stirring for 10–15 min,
the precipitate was filtered off, washed with ethanol and
petroleum ether, and dried in vacuo. All attempts to
recrystallise this material led to dinitrogen loss, and
eventual formation of the dioxygen derivative
[(C5Me5)Ru(O2)(PEt3)2][BPh4] (9), described below. As
a consequence, accurate microanalysis figures could not
be obtained. Yield (crude): 0.25 g, 61%. Anal. Calc. for
C46H65BN2P2Ru: C, 67.4; H, 8.01; N, 3.4. Found C,
References
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NMR (CD2Cl2): H: l 1.13 (m, PCH2CH3), 1.90 (m,
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This compound was obtained following a procedure
identical to that used for the dinitrogen derivative 8,
but performing the reaction under air instead of dini-
trogen. Amber crystals of this compound were obtained
upon recrystallisation from acetone/ethanol. Yield:
85%. Anal. Calc. for C46H65BO2P2Ru: C, 67.0; H, 7.97.
1
Found C, 67.0; H, 8.10%. NMR (CDCl3): H: l 1.11
(m, PCH2CH3), 1.74 (m, PCH2CH3), 1.47 s (C5(CH3)5).
31P{1H}: l 22.2 s.
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Am. Soc. Chem., submitted for publication.
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We wish to thank the Ministerio de Educacio´n y
Ciencia of Spain (DGICYT, Project PB97-1357) and
Junta de Andaluc´ıa (Grupo FQM0188) for financial
support. We also thank Johnson Matthey plc for the
generous loan of ruthenium trichloride, and the Royal
.