or activated zinc dust at room temperature gives initially a deep
brown solution, which changes to red-brown after heating for a
few hours; filtration gives a very air-sensitive, orange-red solu-
tion. The brown-black oily residue obtained after evaporation
phosphine complexes are consistent with the assigned geom-
etries. For the methylphosphine complexes trans-[Ru(acac)2L2]
(L = PMe3, PMe2Ph or PMePh2), the PMe resonance appears
as a 1:2:1 triplet in both the 1H and 13C NMR spectra as a con-
sequence of the expected strong coupling between the equiv-
alent, mutually trans 31P nuclei19–21 (for example, 2JPP values of
308 and 229 Hz have been reported for isomers of the type
[RuCl2(CO)2(But2PH)2] in which the secondary phosphine
ligands are trans22). For the complexes cis-[Ru(acac)2L2]
1
to small volume shows in its H NMR spectrum in d6-benzene
two sharp 3 H singlets at δ 1.78 and 1.96 due to acac methyl
protons and a sharp 1 H singlet at δ 5.20 due to the γ-CH
proton, consistent with the presence of a cis-Ru(acac)2 group
attached to two identical ligands. In addition to a symmetrical
multiplet at δ 5.62 due to residual free cyclooctene, there is a
2 H multiplet of similar appearance at δ 3.80, which we assign
to the olefinic protons of co-ordinated cyclooctene. The ca. 2
ppm shift to low frequency is similar to those observed for
[Ru(NH3)5(η2-C2H4)]2ϩ (δ 3.57),8 cis-[Ru(H2O)4(η2-C2H4)2]2ϩ
(δ 3.81),4 and [Ru(H2O)5(η2-C2H4)]2ϩ (δ 5.04)4 (cf. δ 5.46 for free
C2H4). There are also well resolved multiplets at δ 1.6–1.8 and
2.4 assignable to the CH2 protons of co-ordinated cyclooctene,
which are distinguishable from broad singlets at δ 1.42 and 2.06
due to the corresponding resonances of free cyclooctene.
1
(L = PMe3 or PMePh2) the PMe resonance in the H NMR
spectrum consists of a filled-in doublet as a consequence of the
2
much smaller value of JPP (probably ca. 20–30 Hz); in cis-
[Ru(acac)2(PMe2Ph)2] the PMe resonance appears as a pair of
filled-in doublets because the PMe groups are diastereotopic.
As in the cases of planar bis(tertiary phosphine) complexes
of palladium(II) and platinum(II),21,23 the corresponding 13C
resonances are less diagnostic, consisting of a triplet (L =
PMe3), a pair of triplets (L = PMe2Ph), and a doublet of doub-
lets with a pair of weak outer lines (L = PMePh2). The CH2
resonance in the 13C NMR spectra of the complexes
[Ru(acac)2(PEt3)2] is a 1:2:1 triplet for the trans isomer and a
doublet of doublets with weak outer lines for the cis.
1
The H NMR data are consistent with the presence in solu-
tion of cis-[Ru(acac)2(η2-C8H14)2] 1, the co-ordinated cyclo-
octene of which clearly does not exchange rapidly with free
cyclooctene on the NMR timescale. Although on one occasion
a yellow-brown crystalline solid of this formula was isolated by
cooling the reaction residue to 0 ЊC overnight, the procedure
was not reproducible. Attempts to remove the excess of
cyclooctene in vacuo caused the appearance of additional peaks
at δ 1.73 (s), 2.04 (s) due to acac CH3, δ 5.09 (s), 5.12 (s) due to
acac γ-CH, and δ 4.64 (symmetrical multiplet) due to co-
ordinated cyclooctene. These signals disappeared when more
cyclooctene was added and the original spectrum was reformed;
hence the new peaks may be due to species such as
[Ru(acac)2(η2-C8H14)(solv)] (solv = H2O or THF). Experiments
in progress indicate that the ethene analogue of compound 1
can be generated by a similar procedure and that it is stable
enough to be isolated.13 If the preparation is carried out with
norbornadiene in place of cyclooctene the known complex
[Ru(acac)2(η4-nbd)]14 can be isolated in ca. 50% yield.
The trans to cis isomerisations of [Ru(acac)2L2] (L = PMe2Ph
or PMe3) require more forcing conditions (refluxing xylene and
mesitylene, respectively) than those of other members of the
series. The isolated products contain a small amount of a
carbonyl complex, probably cis-[Ru(acac)2(CO)L], which can
be detected in the mass spectra and by the ν(CO) band at ca.
1940 cmϪ1 in the IR spectra. The CO may be formed by degrad-
ation of the acac ligands, although this has not been proved.
Surprisingly, the cyclooctene ligands of complex 1 are also
displaced at room temperature by an excess of trimethylamine
to give trans-[Ru(acac)2(NMe3)2] as a brownish green solid. The
same compound is obtained more conveniently by zinc amal-
gam reduction of [Ru(acac)3] in aqueous THF in the presence
of an excess of trimethylamine. The EI-mass spectrum shows a
very weak parent ion peak together with peaks arising from the
successive loss of NMe3. The trans configuration follows from
1
Both cyclooctene ligands are displaced from solutions of
complex 1 at room temperature by pyridine, tert-butyl isocyan-
ide, various monodentate P-donors, and triphenylarsine to give
red-brown complexes of the general type trans-[Ru(acac)2L2],
which isomerise to the more stable, more soluble, orange-brown
cis compounds on heating in benzene, toluene or aromatic solv-
ents of higher boiling point. The IR spectra of the complexes
generally show four intense absorptions in the regions 1560–
1570, 1500–1520, 1430–1450 and 1400–1410 cmϪ1, which are
characteristic of bidentate, O-bonded acac.15 Although the IR
spectra in these regions of corresponding trans and cis isomers
do not differ significantly, the isomers are readily identified by
their 1H and 13C NMR spectra, details of which are available as
SUP 57625. As expected, the trans isomers show just one acac
methyl singlet [δ(1H) 1.3–1.7, δ(13C) 27–28], whereas the cis
show two [δ(1H) 1.6–2.1, δ(13C) 27–28]. In addition, the trans
the H NMR spectrum, which shows singlets at δ 1.82 (12 H),
2.16 (18 H) and 5.37 (2 H) in d6-benzene due to the acac methyl,
NMe3 and acac methine protons, respectively. The correspond-
ing resonances in the 13C NMR spectrum are at δ 28.11, 53.93
and 101.32, and there is also a singlet at δ 183.5 due to the
equivalent C᎐O groups. The compound can be sublimed with
᎐
some decomposition at 60 ЊC/10Ϫ4 mmHg to give a brown oil
that slowly solidifies.
Unlike other members of the trans-[Ru(acac)2L2] series, the
NMe3 complex does not undergo trans to cis isomerisation in
refluxing aromatic solvents. It is apparently unreactive towards
cyclooctene and phenylacetylene, and reacts only slowly with
triphenylphosphine to give trans-[Ru(acac)2(PPh3)2]. However,
treatment with CO displaces one of the NMe3 ligands to give
trans-[Ru(acac)2(CO)(NMe3)] as a dark brown solid that smells
strongly of the amine. The presence of a terminal CO ligand is
evident from a very strong ν(CO) band at 1920 cmϪ1 (KBr disc)
[1953 cmϪ1 (C6H12)] in the IR spectrum, a signal at δ 212.2 in the
13C NMR spectrum, and a parent ion peak at m/z 387 in the
FAB-mass spectrum. The EI-mass spectrum did not show this
parent ion peak but did contain peaks at m/z 655, 627 and 599
isomers show just one C᎐O resonance in their 13C NMR spectra
᎐
in the region of δ 184, whereas the cis show two. The spectra of
both trans- and cis-[Ru(acac)2L2] complexes show only one acac
γ-CH resonance in the regions of δ 5.0(1H) and 100 (13C); for a
1
given pair, this resonance is always more shielded in the H
NMR spectrum and less shielded in the 13C NMR spectrum for
the trans than for the cis isomer. The configurations of the cis
and trans isomers of [Ru(acac)2L2] (L = ButNC or PMePh2)
have been confirmed by X-ray crystallographic analysis (see
below).
apparently arising from Ru2(acac)4 fragments. The H NMR
1
spectrum of the compound in d6-benzene shows singlets at
δ 1.71 (12 H), 2.24 (9 H) and 5.08 (2 H) due to the acac methyl,
NMe3, and acac methine protons, respectively, and is therefore
consistent with the formulation. The corresponding peaks in
the 13C NMR spectrum in CD2Cl2 are at δ 27.09, 49.64 and
The 31P-{1H} NMR spectra of the tertiary phosphine com-
plexes [Ru(acac)2L2] show the expected singlets; those of the
trans isomers are always ca. 20 ppm more shielded than those
of the corresonding cis, which is opposite to the trend observed
in cis- and trans-[PtCl2L2].16–18 These data also are available as
SUP 57625. Other features of the NMR spectra of the tertiary
100.48, and the acac C᎐O resonance is at δ 199.0.
᎐
Carbon monoxide also reacts readily at room temperature
with trans-[Ru(acac)2(PPh3)2] to give trans-[Ru(acac)2(CO)-
(PPh3)] as yellow microcrystals, which show a singlet at δ 16.1
in the 31P NMR spectrum. The complex cis-[Ru(acac)2(PPh3)2]
3452
J. Chem. Soc., Dalton Trans., 1999, 3451–3462
Bennett, Martin A.
