A diruthenium μ-methylene complex

Article abstract of DOI:10.1021/om0010417

The reaction of [Ru₂(μ-CO)(CO)₄(μ-dppm)₂] (1; dppm = Ph₂PCH₂PPh₂) with CH₂N₂ gives the μ-methylene complex [Ru₂(μ-CH₂)(CO)₄(μ-dppm)₂] (2), and complex 2 reacts with CO to regenerate complex 1 with loss of ketene. Complex 2 reacts with HBF₄ or CF₃SO₃H at low temperature to form the fluxional μ-methyl complex [Ru₂(μ-CH₃)(CO)₄ (μ-dppm)₂]⁺ (3) Variable-temperature ¹H, ¹³C, and ³¹P NMR studies establish that the μ-CH₃ group has an unsymmetrical coordination mode with an agostic hydrogen and is fluxional. At room temperature, the reaction of 2 with formic acid gives an equimolar mixture of complex 1 and [Ru₂(μ-H)(H)(μ-CO)(CO)₂(μ-dppm)₂] (4), which is an active catalyst for the decomposition of formic acid to hydrogen and carbon dioxide, and the reaction is shown to occur via the intermediate complexes 3 and [Ru₂(μ-H){μ-C(O)Me}(HCOO)(CO)₃ (μ-dppm)₂]⁺ (5). The reaction of 2 with acetic acid at room temperature gives in sequence the complexes [Ru₂{μ-C(O)-Me}(OAc)(CO)₃(μ-dppm)₂] (6) and [Ru₂(μ-H){μ-C(O)Me}(OAc)(CO)₃ (μ-dppm)₂]⁺ (7) before loss of methane occurs with formation of [Ru₂(μ-OAc)(CO)₄(CO)₄ (μ-dppm)₂]⁺ (8). Complex 2 reacts with methyl triflate to give ethylene and [Ru₂(μ-H)(μ-CO)(CO)₃ (μ-dppm)₂]⁺ (9), as the triflate salt, probably via an intermediate with an ethylruthenium group. In the presence of HBF₄, complex 2 is an efficient precatalyst for the ring-opening polymerization of norbornene.

Full text of DOI:10.1021/om0010417

1882
Organometallics 2001, 20, 1882-1888
A Dir u th en iu m µ-Meth ylen e Com p lex
Yuan Gao, Michael C. J ennings, and Richard J . Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
Received December 6, 2000
The reaction of [Ru2(µ-CO)(CO)4(µ-dppm)2] (1; dppm ) Ph2PCH2PPh2) with CH2N2 gives
the µ-methylene complex [Ru2(µ-CH2)(CO)4(µ-dppm)2] (2), and complex 2 reacts with CO to
regenerate complex 1 with loss of ketene. Complex 2 reacts with HBF4 or CF3SO3H at low
temperature to form the fluxional µ-methyl complex [Ru2(µ-CH3)(CO)4(µ-dppm)2]+ (3).
1
Variable-temperature H, 13C, and 31P NMR studies establish that the µ-CH3 group has an
unsymmetrical coordination mode with an agostic hydrogen and is fluxional. At room
temperature, the reaction of 2 with formic acid gives an equimolar mixture of complex 1
and [Ru2(µ-H)(H)(µ-CO)(CO)2(µ-dppm)2] (4), which is an active catalyst for the decomposition
of formic acid to hydrogen and carbon dioxide, and the reaction is shown to occur via the
intermediate complexes 3 and [Ru2(µ-H){µ-C(O)Me}(HCOO)(CO)3(µ-dppm)2]+ (5). The reac-
tion of 2 with acetic acid at room temperature gives in sequence the complexes [Ru2{µ-C(O)-
Me}(OAc)(CO)3(µ-dppm)2] (6) and [Ru2(µ-H){µ-C(O)Me}(OAc)(CO)3(µ-dppm)2]+ (7) before loss
of methane occurs with formation of [Ru2(µ-OAc)(CO)4(µ-dppm)2]+ (8). Complex 2 reacts with
methyl triflate to give ethylene and [Ru2(µ-H)(µ-CO)(CO)3(µ-dppm)2]+ (9), as the triflate salt,
probably via an intermediate with an ethylruthenium group. In the presence of HBF4,
complex 2 is an efficient precatalyst for the ring-opening polymerization of norbornene.
Ch a r t 1
In tr od u ction
Transition-metal alkylidene complexes are of interest
as reagents or intermediates in catalysis or as models
for proposed intermediates in catalytic reactions. For
example, µ-alkylidene groups can model intermediates
in the Fischer-Tropsch reaction,1 and terminal alkyl-
idene groups are important in olefin metathesis chem-
istry.2 Ruthenium is one of the most active metals in
Fischer-Tropsch catalysis,3 and ruthenium alkylidene
complexes are among the most versatile metathesis and
cyclopropanation catalysts.4 Hence, there is considerable
interest in alkylidene complexes of ruthenium. This
article reports the synthesis of a new (µ-methylene)-
diruthenium complex, [Ru2(µ-CH2)(CO)4(µ-dppm)2]
(dppm ) Ph2PCH2PPh2), and a study of its reactivity.
Some related (µ-methylene)diruthenium complexes are
shown in Chart 1,5 and there is also much interest in
the chemistry of Ru2(µ-CH2) groups that can exist on
ruthenium metal surfaces.6
Resu lts a n d Discu ssion
Syn th esis of [Ru 2(µ-CH2)(CO)4(µ-d p p m )2]. Com-
plex 2 was synthesized by reaction of [Ru2(µ-CO)(CO)4-
(µ-dppm)2] (1)7 with diazomethane in toluene at 50 °C,
(5) (a) Akita, M.; Knox, S. A. R.; Moro-Oka, Y.; Nakanishi, S.; Yates,
M. I. J . Organomet. Chem. 1998, 569, 71. (b) Akita, M.; Hua, R.; Oku,
T.; Tanaka, M.; Moro-Oka, Y. Organometallics 1996, 15, 4162. (c) Akita,
M.; Hua, R.; Oku, T.; Moro-Oka, Y. Organometallics 1996, 15, 2548.
(d) Frohlich, R.; Gimeno, J .; Gonzalez-Cueva, M.; Lastra, E.; Borge,
J .; Garcia-Granda, S. Organometallics 1999, 18, 3008. (e) Shelby, Q.
D.; Lin, W. B.; Girolami, G. S. Organometallics 1999, 18, 1904. (f)
Bottcher, H. C.; Bruhn, C.; Merzweiler, K. Z. Anorg. Allg. Chem. 1999,
625, 586. (g) Lee, K.; Wilson, S. R.; Shapley, J . R. Organometallics
1998, 17, 4113. (h) Lin, Y. C.; Calabrese, J . C.; Wreford, S. S. J . Am.
Chem. Soc. 1983, 105, 1679. (i) Doherty, N. M.; Fildes, M. J .; Forrow,
N. J .; Knox, S. A. R.; Macpherson, K. A.; Orpen, A. G. J . Chem. Soc.,
Chem. Commun. 1986, 1355.
(1) (a) Fischer, E. O.; Maasbol, A. Angew. Chem., Int. Ed. Engl. 1964,
3, 580. (b) Brady, R. C. I.; Pettit, R. J . J . Am. Chem. Soc. 1980, 102,
6181. (c) Anderson, R. B. The Fischer-Tropsch Synthesis; Academic
Press: New York, 1984. (d) Geoffroy, G. L.; Bassner, S. L. Adv.
Organomet. Chem. 1988, 28, 1.
(2) (a) Noels, A. F.; Demonceau, A. J . Phys. Org. Chem. 1998, 11,
602. (b) Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565. (c) Grubbs, R.
H.; Chang, S. Tetrahedron 1998, 54, 4413.
(3) (a) Maitlis, P. M.; Long, H. C.; Quyoum, R.; Turner, M. L.; Wang,
Z. Q. J . Chem. Soc., Chem. Commun. 1996, 1. (b) Quyoum, R.; Berdini,
V.; Turner, M. L.; Long, H. C.; Maitlis, P. M. J . Catal. 1998, 173, 355.
(4) (a) Kanaoka, S.; Grubbs, R. H. Macromolecules 1995, 28, 4707.
(b) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc. 1996,
118, 100. (c) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J . Am. Chem.
Soc. 1997, 119, 3887. (d) Dias, E. L.; Grubbs, R. H. Organometallics
1998, 17, 2758. (e) Ivin, K. J .; Mol, J . C. Olefin Metathesis and
Metathesis Polymerization; Academic Press: New York, 1997.
(6) (a) Kis, A.; Kiss, J .; Solymosi, F. Surf. Sci. 2000, 459, 149. (b)
Ciobica, I. M.; Frechard, F.; van Santen, R. A.; Kleyn, A. W.; Hafner,
J . J . Phys. Chem. B 2000, 104, 3364.
(7) Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J . Inorg. Chem. 1993,
32, 1327.
10.1021/om0010417 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/17/2001

A Diruthenium µ-Methylene Complex
Organometallics, Vol. 20, No. 9, 2001 1883
as shown in eq 1. Most syntheses of µ-methylene
complexes from diazomethane have been carried out at
lower temperatures in order to avoid decomposition of
diazomethane to nitrogen and polymethylene.8,9 How-
ever, complex 1 failed to react with CH2N2 at 0 °C and,
when it was warmed to room temperature, rapid
decomposition of diazomethane occurred to give poly-
methylene. The ruthenium complex present was shown
to be very largely unchanged complex 1; therefore, the
decomposition of diazomethane is catalytic. The com-
plete conversion of 1 to 2 was successfully achieved at
50 °C, although much polymethylene was again pro-
duced by parallel decomposition of diazomethane. The
polymer could be easily separated by filtration; thus,
this is a reasonable synthesis of 2, though a large excess
of diazomethane is needed. Complex 2 was isolated as
a yellow solid that decomposed only slowly in air at room
temperature.
Complex 2 gives a sharp singlet at δ 39.6 in the 31P-
{1H} NMR spectrum, indicating a symmetrical struc-
ture. The 1H NMR spectrum of 2 displays a quintet
resonance at δ 5.2, with 3J (PH) ) 10 Hz, and the 13C
NMR spectrum gave a peak at δ 88. These chemical
shifts are on the borderline for bridging CH2 groups in
complexes containing a metal-metal bond (δ(1H) 5-11;
δ(13C) 100-210) and those with no metal-metal bond
(δ(1H) 1-5; δ(13C) -37 to +65), probably as a result of
the relatively long Ru-Ru distance in 2 (see below).8
Two resonances characteristic of terminal carbonyls
were observed in the 13C NMR spectrum (δ 214, 208),
and four terminal carbonyl bands were observed in the
IR spectrum (νCO 1970, 1926, 1902, 1878 cm-1). Two
resonances were observed for the CHaHb protons of the
CH2P2 groups. The NMR data show that complex 2 is
not fluxional, unlike the parent 1, which undergoes
rapid exchange of carbonyl environments by a merry-
go-round mechanism.7 The µ-CH2 group serves to lock
the structure of 2. Finally, the structure of 2 was
confirmed by an X-ray diffraction study. A view of the
structure is shown in Figure 1, crystal data are given
in Table 1, and selected bond lengths and angles are
summarized in Table 2.
F igu r e 1. View of the structure of [Ru2(µ-CH2)(CO)4(µ-
dppm)2] (2) (25% thermal ellipsoids).
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for 2
formula, fw
temp
C55.5H46ClO4P4Ru2, 1138.39
150(2) K
wavelength
cryst syst, space group
cell dimens
0.717 03 Å
monoclinic, P21/n
a ) 16.4421(6) Å
b ) 13.4906(5) Å
c ) 23.3300(7) Å
â ) 110.449(1)°
4848.8(3) Å3, 4
1.559 Mg/m3
V, Z
d(calcd)
abs coeff
0.858 mm-1
F(000)
cryst size
θ range
no. of rflns, no. of indep rflns
abs cor
2304
0.16 × 0.13 × 0.10 mm3
2.64-28.27°
54472, 11665
integration
no. of data/restraints/params
11665/0/613
0.903
GOF on F2
R (I > 2σ(I))
R (all data)
R1 ) 0.0378, wR2 ) 0.0650
R1 ) 0.0867, wR2 ) 0.0727
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) in [Ru 2(µ-CH2)(CO)4(µ-d p p m )2]‚0.5CH2Cl2 (2)
Bond Distances
Ru(1)-Ru(2)
Ru(1)-P(3)
Ru(2)-P(4)
Ru(2)-C(5)
Ru(1)-C(4)
Ru(2)-C(1)
C(2)-O(2)
2.8704(3)
2.3166(8)
2.3389(8)
2.150(3)
1.866(3)
1.918(3)
1.159(3)
1.164(3)
Ru(1)-P(1)
Ru(2)-P(2)
Ru(1)-C(5)
Ru(1)-C(3)
Ru(2)-C(2)
C(1)-O(1)
C(3)-O(3)
2.3519(8)
2.3407(8)
2.144(3)
1.914(3)
1.868(3)
1.145(3)
1.155(3)
C(4)-O(4)
As shown in Figure 1, the complex contains a trans,-
trans-Ru2(dppm)2 unit (angles P(2)-Ru(2)-P(4) )
172.20(3)° and P(1)-Ru(1)-P(3) ) 172.67(3)°), with
each ruthenium also bound to two terminal carbonyl
ligands and to the bridging methylene group. The
distance Ru(1)-Ru(2) ) 2.8704(3) Å indicates that there
is also a metal-metal single bond. Hence, each ruthe-
nium has an 18-electron configuration. The µ-CH2 group
symmetrically bridges the two Ru atoms, and the bond
Bond Angles
172.20(3)
87.629(8) C(5)-Ru(1)-P(3)
P(2)-Ru(2)-P(4)
C(5)-Ru(1)-P(1)
C(5)-Ru(2)-P(2)
Ru(2)-C(5)-Ru(1)
C(2)-Ru(2)-C(1)
C(3)-Ru(1)-C(5)
C(2)-Ru(2)-C(5)
C(3)-Ru(1)-P(3)
P(1)-Ru(1)-P(3) 172.67(3)
90.25(8)
86.72(8)
92.24(8)
83.88(9)
106.6(1)
141.5(1)
111.4(1)
90.23(9)
C(5)-Ru(2)-P(4)
C(3)-Ru(1)-C(4) 106.0(1)
C(1)-Ru(2)-C(5) 142.0(1)
C(4)-Ru(1)-C(5) 112.5(1)
C(1)-Ru(2)-P(4)
96.19(9)
parameters are unremarkable (Ru(1)-C(5) ) 2.144(3)
Å,Ru(2)-C(5))2.150(3)Å,Ru(2)-C(5)-Ru(1))83.88(9)°).5,8
The angle Ru-C-Ru is less acute than in most other
µ-methylene complexes with metal-metal bonds (range
75-78°), as a result of the relatively long Ru-Ru bond
(8) (a) Herrmann, W. A. Adv. Organomet. Chem. 1982, 20, 159. (b)
Casey, C. P.; Audett, J . D. Chem. Rev. 1986, 86, 339. (c) Puddephatt,
R. J . Polyhedron 1988, 7, 767.
(9) (a) Kiel, G. Y.; Takats, J . Organometallics 1989, 8, 839. (b)
Brown, M. P.; Fisher, J . R.; Puddephatt, R. J .; Seddon, K. R. Inorg.
Chem. 1979, 18, 2809.

1884 Organometallics, Vol. 20, No. 9, 2001
Gao et al.
Sch em e 1
broad singlet at δ -0.52 which was assigned to the
µ-methyl group. These data suggest a symmetrical
structure, but there is good evidence that the symmetry
is lower as outlined below, with fluxionality leading to
the observation of deceptively simple spectra.
F igu r e 2. NMR spectra of the µ-methyldiruthenium
complex cation 3, present as a mixture of the CH3 and
CH2D isotopomers, at -35 °C (above) and -90 °C (below):
The conversion of a µ-CH2 to a µ-CH3 group by
protonation has been observed before, and methods for
determining the nature of the µ-CH3 group have been
established.10,11 The unsymmetrical bonding of the
µ-CH3 group in 3 (Scheme 1) was clearly established by
using the NMR method introduced by Shapley.11 In
particular, the µ-CH2D group in 3-d, obtained by reac-
tion of 2 with D+ at -35 °C, gave a broad singlet in the
1H NMR spectrum at δ -0.80 compared to δ -0.52 for
the µ-CH3 group in 3 (Figure 2). The large chemical shift
difference (∆δ 0.28 ppm) between µ-CH3 and µ-CH2D is
characteristic for a bridging methyl group with an
agostic interaction between a metal and a C-H bond.10,11
The fluxionality of complex 3 was established by
recording spectra at lower temperature. At -90 °C, the
1
(left) H NMR spectra in the methyl region only; (right)
31P NMR spectra. The spectra illustrate fluxionality ac-
cording to eq 4.
distance, and this angle has an important effect on the
NMR parameters as discussed above.8
The formation of transition-metal µ-methylene com-
plexes using diazomethane is generally believed to go
through an intermediate diazomethane complex.8 In this
study, an intermediate complex was identified at partial
conversion, but it was always present along with 1 and
2 and could not be separated or identified. It was
characterized only by its 31P{1H} NMR spectrum, which
exhibits two multiplets at δ 31 and 36, indicating lower
symmetry than in either 1 or 2.
1
resonances in the H NMR spectrum became broader,
Rea ction of 2 w ith CO. Complex 2 reacted easily
with CO at room temperature to give complex 1 and
ketene, according to eq 2. The ketene was trapped by
especially in the methylruthenium region (Figure 2), but
no splittings were resolved. However, the single 31P
NMR resonance at δ 28.6 at -35 °C had split at -90 °C
to give two well-resolved multiplets at δ 24.6 and 31.0,
indicating a less symmetrical structure for 3 (Figure 2).
In the 13C NMR at -90 °C there were four CO reso-
nances at δ 194, 197, 203, and 239. The first three
resonances are assigned to terminal carbonyls, but the
chemical shift of the peak at δ 239 is too high to be
assigned to a terminal CO while still being a little lower
than expected for a bridging carbonyl.12 Hence, it is
tentatively assigned to a semibridging carbonyl in 3 (eq
3). The 13C peaks for the carbonyl ligands broadened at
higher temperatures. At -30 °C, only a single broad
resonance at δ 198 was resolved. This peak is formed
by coalescence of the peaks at δ 194 and 203, and at
this temperature the peaks at δ 197 and 239 are too
broad to be observed. The limiting fast exchange spec-
trum could not be obtained due to thermal decomposi-
tion of the sample at higher temperatures. The proposed
reaction with methanol, and the product, methyl ac-
etate, was identified by its 1H NMR spectrum and
confirmed by GC-MS. The reaction is presumed to occur
by carbonyl insertion to give a bridging ketene complex,1d
followed by displacement of ketene by more CO. Related
diruthenium ketene complexes have been observed
directly in a few cases,5h,i but none were detected in this
1
case when the reaction was monitored by H NMR.
Rea ction of 2 w ith HBF 4 or CF 3SO3H. At -10 to
-35 °C, the reaction of HBF4 or CF3SO3H with a
solution of 2 in CD2Cl2 gave the µ-methyl complex cation
[Ru2(µ-CH3)(CO)4(µ-dppm)2]+ (3). Complex 3 decom-
posed when the solution was warmed to room temper-
ature, to give a complex mixture of products; therefore,
it was characterized by NMR at low temperature. At
-35 °C, complex 3 gave a broad singlet at δ 28.6 in the
31P{1H}NMR spectrum (Figure 2), indicating the effec-
(10) (a) Casey, C. P.; Fagan, P. J .; Miles, W. H. J . Am. Chem. Soc.
1982, 104, 1134. (b) Dawkins, G. M.; Green, M.; Orpen, A. G.; Stone,
F. G. A. J . Chem. Soc., Chem. Commun. 1982, 41. (c) Davies, D. L.;
Gracey, B. P.; Guerchais, V.; Knox, S. A. R.; Orpen, A. G. J . Chem.
Soc., Chem. Commun. 1984, 841. (d) Antwi-Nsiah, F.; Cowie, M.
Organometallics 1992, 11, 1992.
(11) (a) Calvert, R. B.; Shapley, J . R. J . Am. Chem. Soc. 1977, 99,
5225. (b) Calvert, R. B. Shapley, J . R. J . Am. Chem. Soc. 1978, 100,
7726.
(12) (a) Gao, Y.; Kuncheria, J .; Yap, G. P. A.; Puddephatt, R. J . J .
Chem. Soc., Chem. Commun. 1998, 2365. (b) Gao, Y.; Kuncheria, J .;
Yap, G. P. A.; Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 2000,
3212.
1
tive equivalence of all phosphorus atoms. The H NMR
spectrum gave two broad multiplets at δ 3.10 and 3.45
due to the CH2P2 protons of the dppm ligands and a

A Diruthenium µ-Methylene Complex
Organometallics, Vol. 20, No. 9, 2001 1885
Sch em e 2
fluxionality of 3 is shown in eq 4 and leads to equiva-
5 as the only observable ruthenium complex (Scheme
2). Complex 5 was stable in the temperature range -10
to 0 °C, but at room temperature it reacted further to
give the final products described above, and then the
catalytic decomposition of formic acid accelerated. No
intermediates were observed during the decay of 5 to
give 1 and 4. Coordination of formate is required to
stabilize complex 4, and no corresponding complex was
formed in the reactions of 2 with the acids HBF4 and
CF3SO3H, which have weakly coordinating anions.
Complex 5 was characterized by NMR spectroscopy.
lence of the pairs of carbonyl ligands labeled a,d and
b,c as well as the phosphorus atoms Pa and Pb. A second
form of fluxionality involving exchange of methyl hy-
drogen atoms between terminal and agostic positions
is clearly too fast to be frozen out even at -90 °C but
may be responsible for the extreme broadening of the
CH3Ru/CH2DRu resonances (no longer resolved) at -90
°C shown in Figure 2.
Rea ction of 2 w ith HCOOH. Complex 2 is a catalyst
precursor for the decomposition of formic acid to carbon
dioxide and hydrogen at room temperature. It was
previously shown that 1 is also an efficient catalyst for
this reaction, but only in acetone solution.12 At room
temperature, the addition of H13COOH to a solution of
2 in CD2Cl2 caused an immediate color change from dull
yellow to orange-yellow, but there was an induction
period of several minutes before gas evolution was
observed along with a further color change to red. The
products 13CO2 and H2 were identified by 13C and 1H
NMR, respectively, and CH4 was also detected by its
1H NMR spectrum. The ruthenium-containing products
were an equimolar mixture of complex 1 and the
coordinatively unsaturated dihydride complex [Ru2(µ-
1
The H NMR spectrum contained two multiplets at δ
4.4 and 3.4 due to the CHaHbP2 protons of the dppm
ligands, a singlet at δ 2.2 due to the CH3 protons of the
acetyl group, and a quintet at δ -11.4 due to the Ru2-
(µ-H) group. The formate proton was obscured, but the
presence of the formate group was confirmed by using
H13COOH in the reaction, when the formate ligand was
identified by a singlet resonance at δ 171 in the 13C-
{1H} NMR spectrum. This assignment was further
confirmed by a 1H13C gHSQC (gradient heteronuclear
single quantum coherence) experiment in which the
formyl hydrogen was located at δ 7.5 (overlapped with
the phenyl hydrogens of dppm ligands). When the
reaction was carried out using 13CO-enriched 2, three
terminal carbonyl resonances were observed in the 13C
NMR spectrum of 5, and a broad singlet at δ 296 was
assigned to the carbonyl carbon atom of the µ-acetyl
group. The methyl carbon of the acetyl group was
1
H)(H)(µ-CO)(CO)2(µ-dppm)2] (4), identified by their H
and 31P NMR spectra.12 The overall reaction to give
these products is shown in Scheme 1 (top).
The formation of equimolar amounts of 1 and 4 is
clearly controlled by the amount of CO available;
complex 4 is known to react rapidly with CO to give 1
and hydrogen, but there is not enough CO available to
give more than 50% conversion (Scheme 1).12 Complex
4 is known to be especially active in the catalytic
decomposition of formic acid,12 and the induction period
for the catalytic reaction is therefore likely to be
associated with its formation from the precursor 2. It
is noteworthy that this system based on complex 2 gives
rapid catalytic decomposition of formic acid in dichlo-
romethane solution, whereas complex 1 is inactive in
this solvent and reacts only stoichiometrically to give
[Ru2(µ-H)(µ-CO)(CO)4(µ-dppm)2]+[HCO2]- as the major
product.12 The importance of the coordinatively unsat-
urated complex 4 in the catalysis is thus clearly
demonstrated in this study.
1
located at δ(C) 50.0 by a H13C HSQC experiment. The
chemical shift for the acetyl carbon (δ 296) is in the
range expected for bridging acetyl groups but outside
the normal range of δ(C) 230-260 for terminal acetyl
groups.13 A higher value of this chemical shift indicates
a greater degree of carbene character arising from the
resonance form B (rather than A) of the bridging acetyl
group.13
This reaction was monitored by low-temperature
NMR, and several intermediates were detected. At -35
°C, the reaction of 2 with HCOOH occurred by simple
protonation to give the µ-methyl complex 3, as with the
stronger acids (Scheme 1). Complex 3 reacted slowly
with more formic acid at -35 °C, and rapidly at -10
°C, to give the (µ-acetyl)(µ-hydrido)diruthenium complex
Since no intermediates were observed during the
conversion of 5 to 1 and 4, the mechanism is uncertain.
However, the steps should involve decarboxylation of
(13) (a) Shafiq, F.; Kramarz, K. W.; Eisenberg, R. Inorg. Chim. Acta
1993, 213, 111. (b) J ohnson, K. A.; Gladfelter, W. L. Organometallics
1990, 9, 2101. (c) J effery, J . C.; Orpen, A. G.; Stone, F. G. A.; Went,
M. J . J . Chem. Soc., Dalton Trans. 1986, 173.

1886 Organometallics, Vol. 20, No. 9, 2001
Gao et al.
Sch em e 3
the formate ligand to give CO2 and a second ruthenium
hydride, migration of the methyl group from the acetyl
group onto ruthenium to give a methyl(hydrido)ruthe-
nium complex which can undergo reductive elimination
of methane, and the further decarboxylation of formate.
Rea ction of 2 w ith Acetic Acid . Since the reactions
with formic acid involved catalysis, a study was made
of the reactions of 2 with acetic acid, which is unlikely
to undergo easy decarboxylation and so should give only
stoichiometric chemistry. The results are summarized
in Scheme 2.
Treatment of 2 with 1 equiv of acetic acid in CD2Cl2
at room temperature gave a color change from yellow
to orange-yellow, with formation of the complex [Ru2-
{µ-C(O)Me}(CO)3(OAc)(µ-dppm)2] (6). This complex was
characterized by its NMR spectra. The 31P{1H} NMR
spectrum contained two multiplets at δ 25 and 40, and
the 1H NMR spectrum contained two multiplets at δ 4.2
and 3.8 due to the CH2P2 protons of the dppm ligands.
CO’s). Hence, structure 9 was deduced. The data are
similar to those for the similar complex [Ru2(µ-H)(µ-CO)-
(CO)3(µ-PP)2]+ (PP ) (iPrO)2PNEtP(OiPr)2),15 and this
gives support to the structural assignment. In confirma-
tion, the IR spectrum of 9 contained three peaks at 2045,
1968, and 1926 cm-1 for the three terminal carbonyls
and a peak at 1685 cm-1 for the bridging carbonyl
ligand.
No intermediate was detected by NMR during the
formation of 9 from 2. It is likely that the slow step in
the reaction sequence involves formation of a cationic
ethyldiruthenium complex (shown in Scheme 3 with a
â-agostic interaction, though an R-agostic interaction as
in 3 is also possible) by addition of Me+ to the µ-meth-
ylene group of 2, and this is followed by rapid â-elimina-
tion of ethylene to give complex 9, which is a new
example of a coordinatively unsaturated hydridodiru-
thenium complex.12,15
1
The H NMR spectrum also contained singlets at δ 1.1
and 1.3 due to the methyl protons of the acetate and
acetyl groups, and the corresponding 13C resonances
were at δ 24 and 47, respectively. In a sample prepared
from 13CO-labeled 2, four resonances were observed in
the 13C NMR spectrum at δ 266 (µ-acetyl) and at δ 219,
209, and 196 (terminal CO).
Further treatment of a solution of 6 with another 1
equiv of acetic acid gave complex 7 (Scheme 2). Now a
hydride resonance was observed at δ -11.2. The spectra
were otherwise similar to those of 6 (see Experimental
Section), and there is also a correlation of equivalent
peaks between 7 and the analogous formate derivative
5. For example, in the 13C{1H} NMR spectrum, the
bridging acetyl carbonyl was found at δ 295 and three
terminal carbonyl resonances were observed at δ 200,
196, and 190.
R in g-Op en in g P olym er iza t ion of Nor b or n en e.
Complex 2 does not react with norbornene even on
heating to 75 °C. However, addition of HBF4 or CF3-
SO3H to a CD2Cl2 solution of 2 and norbornene at room
temperature resulted in an immediate color change to
red-yellow, and the solution slowly became viscous as
polymer was formed. The ratio of cis- to trans-vinylene
content in the poly(norbornene) was approximately 4:3
after 48 h, as estimated from the ratio of the corre-
Complexes 6 and 7 were stable for hours at room
temperature in solution but could not be isolated in pure
form. Complex 7 decomposed slowly in solution, with
elimination of methane, to give the known µ-acetate
complex 8 (Scheme 2).15
1
sponding singlet resonances at δ 5.3 and 5.5 in the H
Rea ction of 2 w ith Meth yl Tr ifla te. Treatment of
2 in dichloromethane solution with excess MeOSO2CF3
led to a color change from yellow to deep red over a
period of several hours, with formation of complex 9 and
NMR spectrum.16 The polymerization was slow at room
temperature, but the active catalyst had a long lifetime,
with reaction to give polymer continuing for at least 1
week. The reaction was faster and more stereoselective
when carried out at higher temperature. For example,
in toluene-d8 solution at 75 °C, polymerization was
complete in 5 days, and the ratio of cis/ trans alkene
units in the polynorbornene was >90:10 (eq 5), as
1
ethylene (detected by H NMR and confirmed by GC-
MS) as major product. A minor ruthenium complex
product was detected by its 31P NMR spectrum only
(δ 26) and could not be characterized further. Pure
complex 9 (Scheme 3) was obtained by recrystallization
and was stable to air in the solid state.
Complex 9 was characterized by its NMR spectra. The
31P NMR spectrum contained two multiplets centered
1
at δ 30.4 and 36.0, and the H NMR spectrum in the
CH2P2 region displayed two multiplets at δ 3.86 and
3.42 due to the dppm ligands. The hydride was char-
acterized by a quintet resonance at δ -8.8. The 13C{H}
NMR spectrum of the 13CO-labeled product exhibited
four multiplets for the carbonyl ligands at δ 249.4
(bridging CO) and δ 196.6, 196.4, and 195.6 (terminal
deduced by 1H and 13C NMR. The polymer was isolated
in high yield from such reactions. One such sample had
Mn ) 46.4 × 104 and Mw ) 1.27 × 106 and thus the
polydispersity r ) 2.7, which are in the range found with
some mononuclear ruthenium catalysts.17
(14) Sherlock, S. J .; Cowie, M.; Singleton, E.; Steyn, M. D. V.
Organometallics 1988, 7, 1663.
(15) Edwards, K. J .; Field, J . S.; Haines, R. J .; Homann, B. D.;
Stewart, M. W.; Sundermeyer, J .; Woollam, S. F. J . Chem. Soc., Dalton
Trans. 1996, 4171.
(16) (a) Gilliom, L. R.; Grubbs, R. H. J . Am. Chem. Soc. 1986, 108,
733. (b) Petasis, N. A.; Fu, D. K. J . Am. Chem. Soc. 1993, 115, 7208.
(c) Wallace, K. C.; Schrock, R. R. Macromolecules 1987, 20, 450.
(17) Katayama, H.; Urushima, H.; Ozawa, F. J . Organomet. Chem.
2000, 606, 16.

A Diruthenium µ-Methylene Complex
Organometallics, Vol. 20, No. 9, 2001 1887
washed with pentane and dried under vacuum. Yield: 0.12 g,
48%. Anal. Calcd for C55H46O4P4Ru2: C, 60.2: H, 4.2. Found:
C, 60.0; H, 4.4. IR (Nujol, cm-1): νCO 1970, 1926, 1902, 1878.
The reaction mechanism is not clear, but some
features could be determined by low-temperature NMR
studies. The bridging methyl complex 3 was the first
complex observed during this catalytic reaction, being
formed immediately on addition of acid to complex 2 and
norbornene at -60 °C. At -40 °C, complex 3 reacted
with norbornene to give a new complex, which gave a
singlet resonance at δ 24 in the 31P{1H} NMR spectrum
but whose structure could not be deduced. When the
solution was warmed to room temperature, the 31P NMR
spectrum became very complex, indicating the formation
of several complexes. In the 1H NMR spectrum, the
formation of CH4 was observed at this stage and a new
singlet at δ 11.0 was observed. This resonance is in the
range expected for a terminal ruthenium alkylidene
complex, RudCHR, and is at the edge of the range for
bridging alkylidenes (compare δ 5.2 for complex 2).18
Hence, it is possible that the propagation step involves
a terminal rather than a bridging alkylidene.
3
NMR in CD2Cl2 at 20 °C: δ(1H) 5.2 [quin, 2H, J PH ) 10 Hz,
µ-CH2], 3.1 [m, 2H, P-CH-P], 4.1 [m, 2H, P-CH-P]; δ(13C)
44 [CH2P2], 88 [µ-CH2]; for sample prepared from 13CO-labeled
2, δ(13C) 214 [m, terminal CO], 208 [m, terminal CO]; δ(31P)
39.6 [s, dppm].
Rea ction of 2 w ith CO. A stream of CO was bubbled
through a solution of 2 (15 mg, 0.014 mmol) in CD2Cl2 (0.6
mL) in a septum-sealed NMR tube for 10 min, and the tube
was then sealed. After 24 h, analysis by 1H and 31P NMR
showed that most of complex 2 had reacted to give complex 1.
After addition of methanol to this solution, methyl acetate was
detected by both 1H NMR and GC-MS.
[Ru 2(µ-CH3)(CO)4(µ-d p p m )2][BF 4] (3[BF 4]). To a solution
of 2 (15 mg, 0.014 mmol) in CD2Cl2 (0.5 mL) in a septum-sealed
NMR tube at -35 °C was added HBF4‚Et2O (3 mL, 0.021
mmol) using a microsyringe. Complex 3 was observed as the
only ruthenium complex in solution. NMR in CD2Cl2 at -35
°C: δ(1H) 3.1 [m, 2H, P-CH-P], 3.45 [m, 2H, P-CH-P],
-0.52 [br s, 3H, µ-CH3]; δ(31P) 28.6 [br s, dppm]; for a sample
prepared by reaction of HBF4 with 13CO-labeled 2, δ(13C) 198
[br s, terminal CO], 193 [br s, terminal CO]; for a sample
prepared by reaction of HCOOD with 2 at -35 °C, δ(1H) 3.1
[m, 2H, P-CH-P], 3.4 [m, 2H, P-CH-P], -0.52 [br s, µ-CH3],
-0.80 [br s, µ-CH2D]; δ(31P) ) 28.6 [br s, dppm]. NMR in CD2-
Cl2 at -90 °C: δ(1H) 3.1 [br m, 2H, P-CH-P], 3.45 [br m,
2H, P-CH-P], -0.55 [vbr s, 3H, µ-CH3 and µ-CH2D]; δ(31P)
24.6, 31.0 [m, dppm]; for a sample prepared by reaction of
HBF4 with 13CO-labeled 2, at -80 °C, δ(13C) 239 [m, µ-CO],
203 [m, terminal CO], 194 [m, terminal CO], 197 [m, terminal
CO]. The same cation was formed by a similar reaction of 2
with CF3SO3H at -35 °C.
Su m m a r y
The new diruthenium µ-methylene complex [Ru2(µ-
CH2)(CO)4(µ-dppm)2] (2) was synthesized by reaction of
[Ru2(µ-CO)(CO)4(µ-dppm)2] (1) with diazomethane,
CH2N2. Complex 2 has high reactivity toward electro-
philes, apparently by direct reaction at a Ru-CH2 bond.
The reaction with protic acids leads to formation of an
asymmetric Ru2(µ-CH3) group in complex 3. The fate of
the cation 3 depends on the nature of the acid and has
been investigated with noncoordinating BF4-, coordi-
-
nating MeCO2-, and coordinating and reactive HCO2
.
NMR Stu d ies of th e Rea ction of 2 w ith F or m ic Acid .
To a solution of 2 (10 mg, 0.009 mmol) in CD2Cl2 (0.5 mL) in
a septum-sealed NMR tube at -35 °C was added formic acid
(3 µL, 0.06 mmol). Complexes observed and characterized
during this study are as follows, as a function of temperature.
In each case there is evidence for easy reversible
migration of the µ-CH3 group to a carbonyl ligand to
give a bridging acetyl complex. Later, the methyl group
is converted to methane, and this is thought to occur
by migration to ruthenium followed by C-H reductive
elimination. The µ-methyl complex cation 3 is a catalyst
precursor for the ring-opening polymerization of nor-
bornene.
[Ru 2(µ-CH3)(CO)4(µ-d p p m )2][HCOO] (3[HCOO]). This
compound was formed at -35 °C. The spectra are as described
above for 3[BF4].
[R u 2 [µ-C (O )C H 3 ](C O )3 (µ-H )(H C O O )(µ-d p p m )2 ]-
[HCOO] (5[HCOO]). This compound was formed at -10 °C.
NMR at -10 °C: δ(1H) 8.3 [s, HCO2-], 7.5 [HCO2Ru], 4.4 [m,
2H, P-CH-P], 3.4 [m, 2H, P-CH-P], 2.2 [s, 3H, µ-C(O)CH3],
Exp er im en ta l Section
2
-11.4 [quin, 1H, J P-H ) 11 Hz, RuH]; δ(31P) 16.8 [m, dppm],
All manipulations were carried out under a dry nitrogen
atmosphere using either standard Schlenk techniques or a
glovebox and with freshly dried solvents. [Ru2(µ-CO)(CO)4(µ-
dppm)2] (1) was synthesized according to the literature pro-
cedure.7 NMR spectra were recorded by using Varian Inova
600 and 400 and Gemini 300 MHz spectrometers. Mass spectra
were recorded using a Finnigan MAT 8200 spectrometer.
Polymer molecular weights were determined in THF solution
by GPC using standard polystyrene samples as references.
Syn th esis of [Ru 2(µ-CH2)(CO)4(µ-d p p m )2] (2). To a solu-
tion of [Ru2(µ-CO)(CO)4(µ-dppm)2] (1; 0.25 g, 0.234 mmol) in
toluene (35 mL) at 50 °C was added a solution of diazomethane
in ether (prepared by distillation of ether (30 mL) containing
Diazald (1 g))19 over a period of 1 h. A yellow solution with a
suspension of yellow polymeric material was formed. The
solution was heated for a further 30 min at 50 °C, the volume
was reduced under vacuum, and the mixture was filtered to
remove polymeric material. The volume of the resultant
solution was reduced to 2 mL, and pentane (80 mL) was then
added to precipitate the product as a yellow solid, which was
25.0 [m, dppm]; for a sample prepared from the reaction of
H13COOH with 13CO-labeled 2 in CD2Cl2, δ(13C) 296 [br s,
2
2
µ-COCH3], 2006 [t, J PC ) 28 Hz, terminal CO], 196 [t, J PC
)
2
28 Hz, terminal CO], 190 [t, J PC ) 28 Hz, terminal CO], 171
[s, HCOORu], 166 [s, HCO2-].
Com p lex 1 a n d [Ru 2(µ-CO)(CO)3(µ-H)(H)(µ-d p p m )2] (4).
These compounds were present at 22 °C in equimolar amounts
and were characterized by comparison of spectra with authen-
tic samples.12 Formic acid (and formate) was completely
decomposed after 1 h at 22 °C, and CH4, CO2, and H2 were
detected by NMR.
Stu d ies of th e Rea ction of 2 w ith Acetic Acid . [Ru 2[µ-
C(O)CH3)(CO)3(CH3COO)(µ-d p p m )2] (6). To a solution of 2
(10 mg, 0.009 mmol) in CD2Cl2 (0.5 mL) at room temperature
was added acetic acid (0.5 µL, 0.009 mmol). Complex 6 was
the only product observed. NMR in CD2Cl2 at 20 °C: δ(1H)
4.2 [m, 2H, P-CH-P], 3.8 [m, 2H, P-CH-P], 1.3 [s, 3H, C(O)-
CH3], 1.1 [s, 3H, CH3COO]; δ(31P) 25.5 [m, dppm], 39.6 [m,
dppm]; for sample prepared from the reaction of CH3COOH
with 13CO-labeled 2 in CD2Cl2, δ(13C) 266 [br s, C(O)CH3], 219
(18) Nguyen, S. T.; J ohnson, L. K.; Grubbs, R. H. J . Am. Chem. Soc.
1992, 114, 3974.
(19) Arnett, F. Organic Syntheses; Wiley: New York, 1943; Collect.
Vol. II, p 165.
2
2
[t, J PC ) 66 Hz, terminal CO], 209 [t, J PC ) 61 Hz, terminal
2
CO], 196 [t, J PC ) 61 Hz, terminal CO]. The complex
decomposed on attempted isolation.

1888 Organometallics, Vol. 20, No. 9, 2001
Gao et al.
[R u 2[µ-C (O )C H 3](C O )3(µ-H )(O Ac )(µ-d p p m )2][O Ac ]
(7[OAc]). To a solution of 2 (10 mg, 0.009 mmol) in CD2Cl2
(0.5 mL) at room temperature was added acetic acid (1 µL,
0.018 mmol). Complex 7 was the only observed ruthenium
product. NMR in CD2Cl2 at 20 °C: δ(1H) 4.5 [m, 2H, P-CH-
P], 3.6 [m, 2H, P-CH-P), 2.3 [s, 3H, C(O)CH3], 2.0 [s,
MeCO2-], 1.1 [s, 3H, CH3COORu], -11.2 [quin, 1H, 2J PH ) 11
Hz, RuH]; δ(31P) 17.8 [m, dppm], 24.3 [m, dppm]; for sample
prepared from the reaction of CH3COOH with 13CO-labeled 2
in CD2Cl2, δ(13C) 295 [br s, C(O)CH3], 200 [m, terminal CO],
196 [m, terminal CO], 190 [m, terminal CO]. The complex
decomposed on attempted isolation.
[Ru 2(CO)4(µ-OAc)(µ-d p p m )2][OAc] (8[OAc]). To a solu-
tion of 2 (10 mg, 0.009 mmol) in CD2Cl2 (0.5 mL) at room
temperature was added acetic acid (4 µL, 0.072 mmol). After
4 days, complex 8 was observed as the major ruthenium
product by NMR. Methane was also detected. Complex 8 was
characterized by its known NMR spectra.14
(B) Syn th esis of cis-P olyn or bor n en e. To a solution of
norbornene (0.13 g, 1.38 mmol) and 2 (40 mg, 0.036 mmol) in
toluene (30 mL) at 0 °C was added HBF4 (6 mL, 0.042 mmol)
by microsyringe. The solution was stirred and heated to 75
°C for 5 days. Methanol (50 mL) was then added to the viscous
solution to precipitate cis-polynorbornene as a white solid.
Yield: 0.09 g (69%).
(C) NMR Stu d ies of th e F or m a tion of P olyn or bor n en e.
To a solution of 2 (20 mg, 0.018 mmol) and norbornene (10
mg, 0.106 mmol) in CD2Cl2 (0.5 mL) in a septum-sealed NMR
tube at -60 °C was added HBF4 (3 mL, 0.021 mmol). The tube
was then placed into the NMR probe at -90 °C. After 20 min,
the first spectra were recorded and further spectra were
recorded as the temperature was raised. Only complex 3 was
present in the temperature range from -90 to -60 °C. NMR
in CD2Cl2 at -40 °C: δ(31P) 29 [br s, dppm, due to 3], 24 [s,
dppm]; δ(1H) 11 [s]. NMR in CD2Cl2 at 20 °C: δ(31P) 33 [s], 31
[s], 30.6 [s], 29 [s], 28.7 [s], 28.3 [s], 27.2 [s], 25.2 [s], 23.6 [dd];
δ(1H) 10.5 [br s], 0.2 [s, CH4].
Str u ctu r e Deter m in a tion of 2. Crystals of [Ru2(µ-CH2)-
(CO)4(µ-dppm)2]‚1/2CH2Cl2 were grown by slow diffusion of
pentane into a dichloromethane solution. A yellow block
was mounted on a glass fiber. Data were collected at low
temperature (150 K) using a Nonius Kappa-CCD diffracto-
meter with COLLECT (Nonius, 1998) software. The unit cell
parameters were calculated and refined from the full data set.
Crystal cell refinement and data reduction were carried out
using the Nonius DENZO package. The data were scaled using
SCALEPACK (Nonius, 1998), and no other absorption correc-
tions were applied. The crystal data and refinement param-
eters are listed in Table 1.
The SHELXTL 5.1 (G. M. Sheldrick, Madison, WI) program
package was used to solve the structure by direct methods,
followed by successive difference Fourier syntheses. All non-
hydrogen atoms were refined anisotropically. The hydrogen
atoms were calculated geometrically and were riding on their
respective carbon atoms. The solvent molecule was refined
anisotropically without hydrogen atoms in the model. It was
near a center of symmetry and was refined at half-occupancy.
[Ru 2(µ-H)(CO)3(µ-CO)(µ-d p p m )2][OTf] (9[OTf]). To a
solution of 2 (25 mg, 0.023 mmol) in CH2Cl2 (0.5 mL) in an
NMR tube was added excess MeOSO2CF3 (4 mL, 0.035 mmol)
by microsyringe. The color of the solution turned from yellow
to deep red in 4 h. Ether (2 mL) was carefully layered over
the solution, and orange needles of the product formed after
24 h. The crystals were washed with pentane and dried under
vacuum. Yield: 15 mg (52%). Anal. Calcd for
C55H45F3-
Ru2O7P4S: C, 53.6; H, 3.7. Found: C, 53.0; H, 3.9. IR (Nujol,
cm-1): 2045 [terminal CO], 1968 [terminal CO], 1926 [terminal
CO], 1685 [µ-CO]. NMR in CD2Cl2 at 20 °C: δ(1H) 3.86 [m,
2
2H, P-CH-P], 3.42 [m, 2H, P-CH-P], -8.8 [quin, 1H, J PH
) 10 Hz, µ-H]; δ(31P) 30.4 [m, dppm], 36 [m, dppm]; for sample
prepared from the reaction of MeOTf with 13CO-labeled 2 in
CD2Cl2, δ(13C) 249 [m, µ-CO], 197 [m, terminal CO], 196 [m,
terminal CO], 195.6 [m, terminal CO].
P olym er iza tion of Nor bor n en e. (A) Ch a r a cter iza tion
of th e P olym er iza tion P r od u ct. To a solution of complex 2
(10 mg, 0.009 mmol) and norbornene (60 mg, 0.636 mmol) in
toluene-d8 (0.5 mL) in a septum-sealed NMR tube at 0 °C was
added HBF4 (1.5 mL, 0.01 mmol) using a microsyringe. The
NMR tube was then heated to 75 °C, at which point the
mixture slowly became viscous. The monomer (δ(dCH) 6.05)
decayed over 4 days, with formation of predominantly cis-
polynorbornene. The ratio of cis/trans linkages in the polynor-
bornene was 95:5, as determined by integration of the respec-
tive resonances at δ 5.3 and 5.5; in agreement, the 13C NMR
spectrum showed very largely ccc triads (δ 134.1 with only very
minor resonances at δ 133.2, 133.4, and 134.2 due to tcc and
ctc triads.4e,16 When reaction was complete, the polymer
precipitated as a white solid by addition of methanol (2 mL).
Ack n ow led gm en t. We thank the NSERC of Canada
for financial support and Dr. M. J . Irwin (3M Canada)
for the GPC measurements.
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
X-ray data for complex 2. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0010417