Synthesis and reactivity of a Ru(i) dimer devoid of π-acid ligands

Article abstract of DOI:10.1039/b902759a

Zinc reduction of [(Cym)RuCl₂]₂ gives [(Cym)RuCl]₂, (Cym = 1,4-MeⁱPrC₆H₄), whose reactivity is evaluated. This Ru^I dimer with two bridging chlorides shows no reactivity towards H

Full text of DOI:10.1039/b902759a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and reactivity of a Ru(I) dimer devoid of p-acid ligands†
Amy G. Walstrom, Maren Pink, Xiaofan Yang and Kenneth G. Caulton
Received 10th February 2009, Accepted 11th May 2009
First published as an Advance Article on the web 19th June 2009
DOI: 10.1039/b902759a
Zinc reduction of [(Cym)RuCl2]2 gives [(Cym)RuCl]2, (Cym = 1,4-MeiPrC6H4), whose reactivity is
evaluated. This RuI dimer with two bridging chlorides shows no reactivity towards H2, N2, N2O or
methyl triflate, but does add HCl to form (Cym)2Ru2HCl3. Attempts to form a monomeric monovalent
1
ruthenium complex with dppm, Ph2PCH2PPh2, gives disproportionation to (Cym)RuCl2(h -dppm) and
2
(Cym)Ru(h -dppm). With terpyridyl, the analogous disproportionation behavior is observed, to form
2+
Ru(terpy)2 and a zero valent product, which decomposed before it could be isolated. The molecular
orbitals, from a DFT calculation, of [(Cym)RuCl]2 show the LUMO to be in a sterically crowded region
of the molecule, and thus helps to account for the reactivity targeted for small and more nucleophilic
reagents, while the HOMO is accessible to reaction with HCl.
especially electron rich chlorides, to one or both Cl; for the
cation fragment which has lost one Cl, only one water molecule is
retained.
We have determined the crystal structure of this molecule,
crystallized from benzene (Fig. 1), and find it to be the identical
phase as that reported.2 There are no significant differences from
the previously reported structure, so we merely comment that it
has a folded Ru2Cl2 quadrilateral, which leaves one side of each Ru
Introduction
A recent publication1 reported the identification of a side product
of reaction of [(Cym)RuCl2]2 (Cym = 1,4-MeiPrC6H4) with a
Ga(I)Cp* reagent as the dimer [(Cym)RuCl]2, 1, containing a
metal–metal bond and thus diamagnetic for the d7 electron
configuration. We ourselves have formed this as a side product of
other research, and we desired to provide some more convenient
synthesis of this species as a useful new source of anhydrous
Ru, in a reduced oxidation state. This synthon might be useful
because it incorporates (a) a somewhat unusual oxidation state,
carrying reducing power, (b) a metal–metal bond, which may keep
together the two metals in any derived product, (c) the potential2,3
to disproportionate to Ru0 and RuII and (d) the leaving group
character of cymene, which means that this reagent is, at heart,
a synthon for the simple anhydrous unit Ru2Cl2. Our interest
in a molecule devoid of carbonyl ligands relates to maximizing
metal reducing power by avoiding electron withdrawing p-acid
ligands. We report here on a convenient synthesis of [(Cym)RuCl]2,
together with a survey of its reactivity characteristics, including
efforts to break the usual constraint4–13 of dimeric RuI species and
to access monomeric RuI.
˚
open to reagent attack (Fig. 1). In spite of the length (2.6022 A) of
the Ru–Ru bond, the NMR spectrum of this molecule is normal
for a diamagnetic species, and shows no signs of population of a
triplet spin state. The molecule is surprisingly poorly soluble in
hydrocarbon solvents like benzene and toluene.
Results
Synthesis of [(Cym)RuCl]2
Fig. 1 ORTEP drawing of the non-hydrogen atoms of [(Cym)RuCl]2,
showing selected atom labelling. The unlabelled atoms are carbon.
The reaction of [(Cym)RuCl2]2 in THF with powdered zinc under
argon gives complete conversion within 12 h at 23 ◦C to a poorly
soluble product, which matches the H NMR spectra reported
for [(Cym)RuCl]2. The spectra show a cymene ring with mirror
symmetry. The ESI-MS shows mainly singly charged ions of the
parent ion, but also containing water molecules (derived from
ESI solvent), presumably attached by hydrogen bonding to the
1
Reactivity
[(Cym)RuCl]2 should have some reactivity associated either with
its redox character, or even through heterolytic splitting of the
Ru–Ru bond yielding equimolar RuII and Ru0. Although the
metals are saturated, one side of the RuCl2 plane is sterically
open to access by reagents for a chloride bridge-splitting reaction.
In fact, there is no reaction, at 23 ◦C in C6D6, on addition
of 1 atm of N2, H2, N2O and of equimolar SiHMe3, even
after heating 24 h at reflux. Attempts to heterolytically split
coordinated H2, in any unfavorable equilibrium forming an H2
Department of Chemistry, Indiana University, Bloomington, IN, USA.
E-mail: caulton@indiana.edu; Fax: +1 812 855 8300; Tel: +1 812 855 4798
† Electronic supplementary information (ESI) available: 1H NMR spectra
of the terpy complexes and details of the X-ray determination. CCDC
reference numbers 719526. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b902759a
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6001–6006 | 6001
©

adduct, by addition of NEt3 also returned unreacted starting Ru
reagent. The complex is recovered unchanged after treatment with
equimolar Me3SiO3SCF3, where chloride-by-triflate replacement
was sought; this suggests that the bridging chlorides are not very
nucleophilic, apparently due to their formal positive charge. In
addition, in hopes of either coordinating N2 to the Ru2 species
during reduction, or even effecting disproportionation of Ru into
(Cym)Ru(N2)2 and (Cym)RuCl2(N2), the synthetic reaction with
Zn was repeated under 1 atm N2. The product was unchanged, as
[(Cym)RuCl]2. We therefore turned to electrophilic and oxidizing
reagents, which revealed that reducing power is indeed the center
of the reactivity of this Ru(I) compound.
HCl. Adding HCl(etherate) (one mole per mole Ru2) yields
primarily a diamagnetic product which has one set of cymene
signals, with no two ring hydrogens equivalent, indicating Ru
Scheme 1
i
2
to be a chiral center. Consistent with this, the Pr methyls are
shows production of this same (Cym)Ru(h -dppm), together
with lesser amounts of a Cs symmetry (by 1H and 31P NMR
spectra) product characterized as (Cym)Ru(h -ZnCl4)(h -dppm)
by independent synthesis of this molecule from anhydrous ZnCl2
and (Cym)RuCl2(h -dppm); this Lewis acid/base reaction is faster
also inequivalent. The molecule is a hydride, giving a singlet
at -10 ppm. The color lightens in the reaction, and the major
product is benzene soluble. No H2 evolution is visible, nor is
there a resonance due to dissolved free H2. The identity of this
product provides evidence that the reactivity of the Ru(I) dimer is
both electron rich (oxidizable) and Brønsted basic. Although the
product has no mirror plane bisecting the cymene ring, the two
ends of the molecule are symmetry related. A possible product
structure is shown as 2, but it could also have the cymenes trans.
1
2
1
than the reduction reaction, which is why it is formed competitively
during the zinc metal reduction.
2RuI → RuII + Ru0
(1)
a
(b) Pyridine-based chelates. In an attempt to form
monomeric 4-coordinate mer-(imine)3RuICl species, 2,2¢:6¢,6¢¢
terpyridine (terpy, Scheme 2, R = H) was reacted with the RuI
dimer, anticipating that this tridentate donor would replace an
arene. When terpy was combined with the RuI dimer in a 2 : 1 ratio
at room temperature in deuterobenzene, there was no reaction
between the two, even after a week of stirring. At 50 ◦C, the color
changed from blood red to brown after 12 h, and a dark brown
precipitate was observed. 1H NMR showed that the precipitate was
diamagnetic and contained no p-cymene, confirming the leaving
group behavior of cymene. X-Ray quality crystals were grown
from CH2Cl2 and showed that two terpy molecules surrounded
one RuII center, with two outer sphere chloride anions (Fig. 2).15–18
In fact, this molecule has been made previously14 from
[CymRuCl2]2 and H2 in the presence of base, and the structures
of two different polymorphs of (Cym)2Ru2HCl3 determined. The
structure reported has the cymenes trans, and the cell constants
for our product are identical to one of those already published.
˚
˚
The Ru–Ru distance is 2.96 A, or an increase of 0.36 A compared
to [(Cym)RuCl]2. This is consistent with loss of a Ru–Ru bond in
this (RuII)2 species. It is noteworthy that the Ru–Cl distances are
˚
all 2.41 A, hence, and atypically, not longer to the bridging halide.
˚
In [(Cym)RuCl]2 the four Ru–Cl distances are all 2.43 A.
Reaction with Lewis bases
(a) Bidentate phosphine. Reaction of dppm, Ph2PCH2PPh2,
with [(Cym)RuCl]2 occurs within time of mixing in benzene to
give complete conversion to a 1 : 1 mixture of two diamagnetic
compounds, hence not monomeric RuI. One of the products has an
Scheme 2
1
AX 31P{ H} NMR pattern with a small (28 Hz) JPP’ value, and the
1
cymene ring hydrogen H NMR is consistent with Cs symmetry.
A trisubstituted terpyridine ligand was also investigated for
better solubility as well as simpler NMR properties: the terpy
where R = tert butyl in Scheme 2. This reaction, also performed
in a 2 : 1 ratio of ligand to dimer at room temperature in
deuterobenzene, showed no reaction and ultimately required
temperatures as high as 90 ◦C to generate an intense orange
precipitate in good yields. Upon dissolving the precipitated orange
solid in CD2Cl2, the 1H NMR spectrum showed that the product
contained only coordinated tri-tert-butyl terpy signals of C2
1
This product (Scheme 1) was confirmed to be (Cym)RuCl2(h -
dppm) by independent synthesis of this molecule from reaction of
[(Cym)RuCl2]2 with dppm and comparison of its NMR spectra.
Since this is divalent metal, the second product, with a singlet 31
P
NMR spectrum and hence Cs symmetry, based on the cymene
ring proton NMR, is expected to be zero valent metal, and
2
1
thus (Cym)Ru(h -dppm), eqn (1). Reaction of (Cym)RuCl2(h -
dppm) with zinc powder in THF (there is no reaction in benzene)
6002 | Dalton Trans., 2009, 6001–6006
This journal is
The Royal Society of Chemistry 2009
©

unambiguous and is identical to that in Fig. 2. The product is thus
[(tBu3-terpy)2Ru]Cl2. ESI-MS shows signals for the parent cation,
supporting the X-ray study. This shows that this terpy derivative
reacts in a similar manner to terpy, and gives the analogous
compound.
Discussion
The modest reducing power of this RuI dimer contrasts to that
of the Cp*Ru moiety, which has a long history19,20 of reactivity
from the species [Cp*RuH2]2. This is perhaps symptomatic of the
fact that Cp* is much more electron donating than cymene in
the isoelectronic (Cym)Ru+ species, not only because of the ring
difference, but also because of the overall charge, which clearly
favors electron richness for the less positive species.
Based on a DFT geometry optimization calculation, Fig. 3
shows a fragment MO analysis of the frontier orbitals resulting
from interacting two (cymene)RuCl fragments. The six MO’s
resulting from the xz, yz and xy orbitals are all occupied and
contribute no net Ru–Ru bonding. The large splitting of orbitals
HOMO107 and LUMO108, a bonding/antibonding pair (Fig. 4),
indicates strong bonding, of sRuRu character, and the double
occupancy of 107 comprises the net single bond. As shown in the
orbital contour diagram, for each Ru it constitutes the third leg of a
three-legged piano stool; it is also a candidate site for electrophilic
attack, and thus also for 1-electron oxidation. However, since
the s orbital is strongly stabilized by this interaction, this
Fig. 2 ORTEP diagram (50% probability) of the non-hydrogen atoms of
Ru(terpy)2 from its chloride salt; unlabelled atoms are carbon. Selected
2+
˚
bond lengths and angles. Ru1–N2 = 1.969(4) A, Ru1–N5 = 1.973(4)
˚
˚
˚
˚
˚
A, Ru1–N6 = 2.064(4) A, Ru1–N1 = 2.066(4) A, Ru1–N3 = 2.070(4)
◦
A, Ru1–N4 = 2.080(4) A; N1–Ru1–N3 = 158.33(18) , N2–Ru1–N1 =
78.97(18)◦, N2–Ru1–N5 = 177.88(17)◦.
symmetry; p-cymene was thus again displaced. Single crystals
were grown by solvent diffusion of benzene into CH2Cl2. While
the quality of these crystals was poor, and the diffraction data
could not be satisfactorily refined, the connectivity of the solid is
Fig. 3 Frontier orbital energy diagram for [(Cym)RuCl]2 showing their primarily metal-based character.
The Royal Society of Chemistry 2009 Dalton Trans., 2009, 6001–6006 | 6003
This journal is
©

These results prove the validity of cymene as a leaving group
in [(Cym)RuCl]2, being displaced by phosphorus donors and
less easily by imines (i.e. the terpy ligands, but also bipy and
some diimines were evaluated, all with very low conversions after
long times at 90 ◦C in benzene).
Experimental
General
Preparation from a literature source21 was used to synthesize
[RuCl2(p-cymene)]2, and standard Schlenk or glovebox techniques
in inert (argon) atmosphere were used for air sensitive manipu-
lations. All solvents, including deuterated NMR solvents, were
dried over and distilled from Na/benzophenone and stored in
anaerobic conditions. All other reagents were degassed and/or
used as received from commercial vendors. 1H NMR spectra were
recorded on either a Varian Unity I400 (400 MHz) instrument
or a Varian Gemini 300 (300 MHz). Mass spectra were acquired
on a PE-Sciex API III triple quadrupole spectrometer. The zinc
powder used in the reduction of [RuCl2(p-cymene)]2 was stirred in
concentrated HCl to remove the oxide outer surface (~5 min). The
zinc was then filtered under argon, rinsed with water, and then
triple rinsed with THF to wash away any remnant acid or water.
Fig. 4 Selected Kohn–Sham orbitals for [(Cym)RuCl]2 showing primarily
metal-based orbitals, Ru–Ru bond (MO 103), chloride participation, and
lowest orbitals for nucleophilic attack.
may diminish its reducing power; it lacks the high-lying energy
which characterizes a reducing agent. Note also (Fig. 4) the Cl
participation in occupied MO’s 101, 102 and HOMO107.
[RuCl(p-cymene)]2. To a round bottom flask containing 0.20 g
(0.34 mmol) of [RuCl2(p-cymene)]2 in 50 mL of THF, a 10 fold
excess (0.23 g, 3.4 mmol) of zinc powder was added and the
mixture stirred overnight in an argon filled drybox. The resultant
air sensitive, blood red solution was dried in vacuo and the residue
redissolved in C6H6, filtered, and dried again. A 5 mg sample of
the resultant red-black powder was dissolved in C6D6, and the 1H
NMR showed the quantitative conversion to [RuCl(p-cymene)]2.
1H NMR (300 MHz, C6D6): 5.34 (d, A of AB, JH–H = 6 Hz, 2 H,
CH3-C6H4-CH(CH3)2), 5.27 (d, B of AB, JH–H = 5 Hz, 2 H,
CH3-C6H4-CH(CH3)2), 2.13 (septet, JH–H = 7.5 Hz, Hz, 1 H,
CH3-C6H4-CH(CH3)2)), 1.61 (s, 3 H, CH3-C6H4-CH(CH3)2)), 1.08
(d, JH–H = 7.5 Hz, 6 H, CH3-C6H4-CH(CH3)2)). The crystal
used for X-ray diffraction structure determination was grown
by slow evaporation of a benzene solution. This molecule is
highly O2 sensitive, even as a solid. ESI-MS in THF, where M =
[(Cym)RuCl]2: (M + 2H2O)+ at 577.2, (M + H2O)+ at 559.3, M+(v.
weak) at 540.6, (M - Cl + H2O)+ at 523.3 and (M - Cl)+ at 504.3.
The lack of symmetric chloride bridge splitting reactivity
towards nucleophiles (i.e. making two RuCl monomers), even
relatively sterically unencumbered ones, can be traced to the
character of the unoccupied MO 110 (Fig 4). This has the Ru–Cl s*
character needed to effect the typical bridge-splitting behavior of
an M2(m-Cl)2 unit, but the main extent of the LUMO lies between
the two cymene rings syn to the Ru–Ru bond, hence a crowded
place. While this alone might not have predicted a lack of reactivity,
it surely contributes to the experimental fact. Even the location of
the methyl and iPr ring substituents in Fig 1 shows this region to
be a place to avoid, when ring rotation is facile.
Conclusions
The facile reaction of the dimer with dppm thus shows that
disproportionation is preferred over production of radical RuI
monomers. The facility of this reaction is surely assisted by the fact
that each ruthenium in [(Cym)RuCl]2 is bonded to two chlorides,
so asymmetric splitting of Ru–Cl bonds as phosphine arrives is
enough to accomplish formation of distinct products. It is the
dimeric and doubly chloride-bridged character of [(Cym)RuCl]2
that facilitates disproportionation.
With these reactivities established, it becomes clear that the
divalent ruthenium product observed with several terpy reagents
is not caused by oxidative reaction of RuI with CH2Cl2, but is
inherent to the dimeric reagent. The slow rate of reaction with
terpy ligands is thus attributed to the lower basicity of bulky terpy
imine nitrogen atoms than of trivalent phosphorus. Moreover,
since terpy alone is unsuitable to satisfy the coordination demands
of Ru0 (five coordinate by five N donors), hence the zero valent
product is subject to decomposition. Note also that the yields of
divalent terpy ruthenium products, ~50%, are consistent with this
being disproportionation chemistry.
Reaction of 1 with 1M HCl in Et2O. To 5 mg (8.62 mmol) of 1
in C6D6, was added 9.8 mL of 1 M HCl in Et2O and the solution
was shaken vigorously as its color turned from blood red to pale
red. Yield: 54%. 1H NMR (300 MHz, C6D6): 5.67 (d, A of AMXY,
JH–H = 6 Hz, 2 H, CH3-C6H4-CH-(CH3)2), 5.54 (d, M of AMXY,
JH–H = 6 Hz, 2 H, CH3-C6H4-CH-(CH3)2), 5.33 (d, Y of AMXY,
JH–H = 6 Hz, 2 H, CH3-C6H4-CH-(CH3)2), 4.79 (d, X of AMXY,
JH–H = 6 Hz, 2 H, CH3-C6H4-CH-(CH3)2), 2.90 (septet, JH–H
=
7.5 Hz, 2 H, CH3-C6H4-CH-(CH3)2), 2.16 (s, 6 H, CH3-C6H4-CH-
(CH3)2), 1.42 (d, JH–H = 7.5 Hz, 6H, CH3-C6H4-CH-(CH3)2), 1.37
(d, JH–H = 7.5 Hz, 6H, CH3-C6H4-CH-(CH3)2), -10.30 (s, 1 H, Ru-
H-Ru). Crystals were grown by layering pentane over a benzene
solution of the compound.
Reaction of (CymRuCl)2 with bis-(diphenylphosphino)methane,
dppm. To 5 mg of (CymRuCl)2 (9.2 mmol) dissolved in 0.5 mL
of C6D6, was added 7.0 mg (18.2 mmol) of dppm, which is
6004 | Dalton Trans., 2009, 6001–6006
This journal is
The Royal Society of Chemistry 2009
©

1
(Cl2Ru(dppm))2. 31P{ H} NMR [162.0 MHz, C6D6] (d/ppm):
a 2 : 1 ligand–dimer ratio. Two products, characterized as
1
2
-6.46 (s). 31P{ H} NMR [162.0 MHz, d8-THF] (d/ppm):
1
(Cym)RuCl2(h -dppm) and (Cym)Ru(h -dppm), are observed
within 20 min in a 1 : 1 ratio as indicated by 31P NMR. Attempted
crystal growth from this stoichiometry reaction, by evaporation
of benzene, resulted only in a black precipitate, apparently due
-6.80 (s). 1H NMR [400.1 MHz, C6D6] (d/ppm): 4.93 (br t, 4.0 Hz,
PC(H2)P). H NMR [400.1 MHz, d8-THF] (d/ppm): 5.07 (br t,
1
4.0 Hz, PC(H2)P).
2
to decomposition of (Cym)Ru(h -dppm), whereas the reaction
Reaction of (Cym)RuCl2(g1-dppm) with Zn powder
with 4 : 1 ligand–dimer ratio, which showed (spectroscopically)
the above products at early reaction time, finally afforded small
yellow crystals of trans-Cl2Ru(dppm)2, by slow (4 d) evaporation
of benzene solvent at room temperature under inert atmosphere;
these were identified by single-crystal X-ray diffraction.
1
To a THF solution of (Cym)RuCl2(h -dppm) was added Zn
powder (10 fold excess). Two products, (Cym)Ru(h -dppm) (see
spectra above) and (Cym)Ru(h -ZnCl4)(h -dppm), were observed
to form with equimolar ratio in the early time (3 h of vigorous
agitation).
2
1
2
1
(Cym)RuCl2(g1-dppm). 31P{ H} NMR [162.0 MHz, C6D6]
(Cym)Ru(g1-ZnCl4)(g2-dppm). 31P{ H} NMR [162.0 MHz,
1
(d/ppm): 27.38 (d, JP–P’ = 33.2 Hz) and -27.61 (d, JP–P’
=
1
33.2 Hz). 31P{ H} NMR [162.0 MHz, d8-THF] (d/ppm): 26.87
d8-THF] (d/ppm): 3.95 (s). 1H NMR [400.1 MHz, d8-THF]
(d/ppm): 0.99 (d, 6.8 Hz, CH3(iPr), 6H); 1.42 (s, CH3(cymene),
3 H); 2.83 (sept, 6.8 Hz, CH(iPr), 1 H); 4.60 (dt, JH–H’ = 15.6 Hz,
1
(d, JP–P’ = 29.3 Hz) and -27.44 (d, JP–P’ = 30.1 Hz). H NMR
[400.1 MHz, C6D6] (d/ppm): 0.68 (d, 7.2 Hz, CH3(iPr), 6 H);
1.65 (s, CH3(cymene), 3 H); 2.54 (sept, 7.2 Hz, CH(iPr), 1 H);
4.11 (dd, J1 = 1.6 Hz, J2 = 8.4 Hz, PC(H2)P, 2 H); 4.80 (d,
6.0 Hz, CH(cymene), 2 H); 4.88 (d, 5.6 Hz, CH(cymene), 2 H).
31P decoupling studies established that the CH2 multiplicity was
JH–PP’ = 12.8 Hz, PC(HA)P, 1 H); 5.44 (dt, JH–H’ = 15.2 Hz, JH–PP’
=
10.4 Hz, PC(HB)P, 1 H); 6.50 (d, 6.4 Hz, CH(cymene), 2 H); 6.54
(d, 6.0 Hz, CH(cymene), 2 H).
Reaction of (Cym)RuCl2(g1-dppm) with anhydrous ZnCl2. To
a THF solution of (Cym)RuCl2(h -dppm) and (Cl2Ru(dppm))2,
which was synthesized (as above) from (CymRuCl2)2 (10 mg,
16.3 mmol) and dppm (13 mg, 32.6 mmol), was added anhydrous
ZnCl2 (4.5 mg, 33 mmol). (Cl2Rudppm)2 remained unchanged,
1
due to coordinated and free P. H NMR [400.1 MHz, d8-THF]
1
(d/ppm): 0.78 (d, 6.8 Hz, CH3(iPr), 6H); 1.84 (s, CH3(cymene),
3 H); 2.41 (sept, 6.8 Hz, CH(iPr), 1 H); 3.52 (dd, J1 = 1.6 Hz, J2 =
8.8 Hz, PC(H2)P, 2 H); 5.18 (d, 6.4 Hz, CH(cymene), 2 H); 5.34
(d, 5.2 Hz, CH(cymene), 2 H).
1
but (Cym)RuCl2(h -dppm) was converted to a new species X.
Although many of the chemical shifts duplicated those of
1
(Cym)Ru(g2-dppm). 31P{ H} NMR [162.0 MHz, C6D6]
1
2
(Cym)Ru(h -ZnCl4)(h -dppm) above, curiously, X showed a sin-
glet resonance for all four cymene ring protons in THF. If X was
vacuum dried (5 h), then washed with pentane, then Et2O, to
remove any free cymene, X was insoluble in C6D6 (by lack of color
(d/ppm): -11.67 (s). 1H NMR [400.1 MHz, C6D6] (d/ppm): 0.98
(d, 6.8 Hz, CH3(iPr), 6 H); 1.85 (s, CH3(cymene), 3 H); 2.25 (sept,
6.8 Hz, CH(iPr), 1 H); 4.15 (t, 11.2 Hz, PC(H2)P, 2 H); 5.19 (d,
5.6 Hz, CH(cymene), 2 H); 5.22 (d, 5.6 Hz, CH(cymene), 2 H).
31P{ H} NMR [162.0 MHz, d8-THF] (d/ppm): -12.22 (s). H
NMR[400.1MHz, C6D6] (d/ppm):0.98 (d, 6.8 Hz, CH3(iPr), 6 H);
1.85 (s, CH3(cymene), 3 H); 2.25 (sept, 6.8 Hz, CH(iPr), 1 H); 4.15
(t, 11.2 Hz, PC(H2)P, 2 H); 5.19 (d, 5.6 Hz, CH(cymene), 2 H). 1H
NMR [400.1 MHz, d8-THF] (d/ppm): 0.91 (d, 6.8 Hz, CH3(iPr),
6 H); CH3(cymene) not observed, apparently obscured by other
stronger signals in the spectrum; 2.21 (sept, 6.8 Hz, CH(iPr), 1 H);
4.11 (t, 11.2 Hz, PC(H2)P, 2 H); 5.17 (d, 6.0 Hz, CH(cymene),
2 H); 5.20 (d, 5.6 Hz, CH(cymene), 2 H).
1
and absence of detectable H and 31P NMR signals); X is thus
1
1
probably a salt in THF. Completely dissolving this solid residue
in CD2Cl2, chosen to break the accidental degeneracy, reveals
the existence of one single species X¢, without the presence of
any (Cl2Ru(dppm))2. X¢ showed two nondegenerate cymene ring
chemical shifts in CD2Cl2. We conclude that both X and X¢ are
1
2
(Cym)Ru(h -ZnCl4)(h -dppm), with only small solvent-induced
spectroscopic differences.
1
X. 31P{ H} NMR [162.0 MHz, d8-THF] (d/ppm): 3.82 (s). 1H
NMR [400.1 MHz, d8-THF] (d/ppm): 0.98 (d, 6.8 Hz, CH3(iPr),
6 H); 1.37 (s, CH3(cymene), 3 H); 2.34 (sept, 6.8 Hz, CH(iPr),
1 H); 4.57 (dt, JH–H’ = 14.8 Hz, JH–PP’ = 13.2 Hz, PC(HA)P, 1 H);
5.45 (dt, JH–H’ = 15.2 Hz, JH–PP’ = 10.4 Hz, PC(HB)P, 1 H); 6.48 (s,
CH(cymene), 4 H).
1
trans-Cl2Ru(dppm)2. 31P{ H} NMR [162.0 MHz, C6D6]
1
(d/ppm): 6.29 (s). H NMR [400.1 MHz, C6D6] (d/ppm): 4.94
(t, 4.2 Hz, PC(H2)P, 2 H).
Reaction of (Cym)RuCl2 with dppm. To 10 mg [(Cym)RuCl2]2
(16.3 mmol) dissolved in 0.5 mL C6D6, was added 13.0 mg
(32.6 mmol) of dppm. Species (Cym)RuCl2(h -dppm) (see spectra
1
X¢. 31P{ H} NMR [162.0 MHz, CD2Cl2] (d/ppm): 3.56 (s). 1H
NMR [400.1 MHz, CD2Cl2] (d/ppm): 1.09 (d, 7.2 Hz, CH3(iPr),
6 H); 1.50 (s, CH3(cymene), 3 H); 2.48 (sept, 7.2 Hz, CH(iPr),
1 H); 4.56 (dt, JH–H’ = 15.2 Hz, JH–PP’ = 12.8 Hz, PC(HA)P, 1 H);
4.96 (dt, JH–H’ = 15.2 Hz, JH–PP’ = 10.0 Hz, PC(HB)P, 1 H); 6.12 (d,
1
above) started to form within 10 min and gradually precipitated
out after 12 h and was separated and characterized. This product
2
slowly converts, with liberation of free cymene, to [RuCl2(h -
6.4 Hz, CH(cymene), 2 H); 6.20 (d, 6.0 Hz, CH(cymene), 2 H). 31
P
dppm)]2, established to be a dimer by its inequivalent dppm
decoupling studies confirmed that the CH2 multiplicity was due
to P at 3.56 ppm.
CH2 protons in a square pyramidal structure; this shows that the
1
dangling arm of dppm in (Cym)RuCl2(h -dppm) is competitive
2+
for binding to Ru, and thus ultimately displaces the leaving
Ru(terpy)2 ·2Cl-: reaction of [RuCl(p-cymene)]2 with 2,2¢:6¢,6¢¢
1
group cymene. This conversion from (Cym)RuCl2(h -dppm) to
terpyridine (terpy). To 5 mg [RuCl(p-cymene)]2 (9.2 mmol) dis-
solved in C6D6, was added 4.3 mg (18.4 mmol) of terpy, which is
a 2 : 1 ligand to dimer ratio. The blood red reaction mixture was
(Cl2Ru(dppm))2 and free cymene is much faster in THF than in
benzene.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6001–6006 | 6005
©

heated to 50 ◦C for 72 h and then cooled to room temperature
and the resultant deep brown precipitate (46% isolated yield)
4 S. K. Patra and J. K. Bera, Organometallics, 2006, 25, 6054–
6060.
5 M. Grohmann, S. Buck, L. Schaeffler and G. Maas, Adv. Synth. Catal.,
2006, 348, 2203–2211.
1
was separated and redissolved in DMSO-d6 and the H NMR
1
obtained. H NMR (300 MHz, DMSO-d6) (see ESI†) (d/ppm):
6 M. A. Petrukhina, Y. Sevryugina, A. Y. Rogachev, E. A. Jackson and
L. T. Scott, Organometallics, 2006, 25, 5492–5495.
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B. W. Skelton and A. H. White, Inorg. Chem., 2004, 43, 683–
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13 M. O. Albers, D. C. Liles, E. Singleton, J. E. Stead and M. M. d. V.
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14 B. Therrien, S. Frein and G. Suess-Fink, Acta Crystallogr., Sect. E:
Cryst. Struct. Rep. Online, 2004, 60, m1666–m1668.
15 D. C. Craig, M. L. Scudder, W.-A. McHale and H. A. Goodwin,
Aust. J. Chem., 1998, 51, 1131–1139.
16 M. L. Scudder, D. C. Craig and H. A. Goodwin, CrystEngComm.,
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9.13 (m, 2 H, JH–H = 4.5 Hz), 8.86 (m, 2 H, JH–H = 4.4 Hz), 8.55 (m,
1 H), 8.05 (m, 2 H), 7.42 (m, 2 H), 7.33 (m, 2 H). ESI-MS (CH2Cl2):
+
obs. m/z 284.06 (Ru(terpy)22+) and 568.09 (Ru(terpy)2 ).
2+
Ru(tri-tbutylterpy)2 ·2Cl-: reaction of [RuCl(p-cymene)]2 with
4,4¢,4¢¢-tri-tert-butyl-2,2¢:6¢,6¢¢ terpyridine (tri-tbutylterpy). To
3.8 mg [RuCl(p-cymene)]2 (7.0 mmol) dissolved in C6D6, was added
5.5 mg (13.8 mmol) of tri-tbutylterpy, which is a 2 : 1 ligand to
dimer ratio. The blood red reaction mixture was then heated to
90 ◦C for 72 h, then cooled to room temperature and the resultant
bright orange precipitate (48% isolated yield) was separated and
redissolved in CD2Cl2 and the 1H NMR recorded. 1H NMR
(400 MHz, CD2Cl2) (see ESI†) (d/ppm): 9.18 (s, 2 H), 8.88 (s,
2 H), 7.35 (s, 2 H), 7.14 (m, 2 H, JH–H = 7.8 Hz), 1.83 (s, 9 H), 1.37
(s, 18 H). ESI-MS (THF): obs. m/z 453.72 (Ru(tri-tbutylterpy)22+).
Acknowledgements
This work was supported by the U. S. Department of Energy. We
also thank Prof. D. Vicic for samples of donor amines.
18 K. Lashgari, M. Kritikos, R. Norrestam and T. Norrby, Acta Crystal-
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20 H. Suzuki, H. Omori, D. H. Lee, Y. Yoshida, M. Fukushima, M. Tanaka
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21 M. A. Bennett, T. Huang, T. W. Matheson and A. K. Smith, Inorg.
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6006 | Dalton Trans., 2009, 6001–6006
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The Royal Society of Chemistry 2009
©