Synthesis and reactivity of a diruthenium diazoalkane complex

Article abstract of DOI:10.1021/om0102293

Reaction of [Ru₂(μ-CO)(CO)₄(μ-dppm)₂], 1, dppm = Ph₂PCH₂PPh₂, with N₂CHCO₂Et gives the complex [Ru₂(μ-NNCHCO₂Et)(CO)₄ (μ-dppm)₂], 2, in which the diazoalkane acts as a novel 2-electron ligand bridging a metal-metal bond. Complex 2 reacts with phenylacetylene, with displacement of a carbonyl ligand, to give [Ru₂(μ-CO)(CO)₂{μ-NN(CHCO₂Et)(CPh=CH)} (μ-dppm)₂], 3a, which contains a new type of metallacycle formed by coupling of the diazoalkane and alkyne ligands at the diruthenium center. Protons attack complex 2 first at the NCH center to give the alkyldiazonium complex [Ru₂(CO)₄(μ-NNCH₂CO₂Et) (μ-dppm)₂]⁺, 4, and then, with the strong acid H[BF₄], at the Ru-Ru bond to give the dicationic complex [Ru₂-(μ-H)(CO)₄(μ-NNCH₂CO₂Et) (μdppm)₂]²⁺, 5. Complex 2 is a precatalyst for the decomposition of formic acid to give CO₂ and H₂, and the chemistry leading to the active catalyst is described.

Full text of DOI:10.1021/om0102293

3500
Organometallics 2001, 20, 3500-3509
Syn th esis a n d Rea ctivity of a Dir u th en iu m Dia zoa lk a n e
Com p lex
Yuan Gao, Michael C. J ennings, and Richard J . Puddephatt*
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
Hilary A. J enkins
Department of Chemistry, St. Mary’s University, Halifax, Nova Scotia, Canada B3H 3C
Received March 22, 2001
Reaction of [Ru2(µ-CO)(CO)4(µ-dppm)2], 1, dppm ) Ph2PCH2PPh2, with N2CHCO2Et gives
the complex [Ru2(µ-NNCHCO2Et)(CO)4(µ-dppm)2], 2, in which the diazoalkane acts as a novel
2-electron ligand bridging a metal-metal bond. Complex 2 reacts with phenylacetylene, with
displacement of a carbonyl ligand, to give [Ru2(µ-CO)(CO)2{µ-NN(CHCO2Et)(CPhdCH)}(µ-
dppm)2], 3a , which contains a new type of metallacycle formed by coupling of the diazoalkane
and alkyne ligands at the diruthenium center. Protons attack complex 2 first at the NCH
center to give the alkyldiazonium complex [Ru2(CO)4(µ-NNCH2CO2Et)(µ-dppm)2]+, 4, and
then, with the strong acid H[BF4], at the Ru-Ru bond to give the dicationic complex [Ru2-
(µ-H)(CO)4(µ-NNCH2CO2Et)(µ-dppm)2]2+, 5. Complex 2 is a precatalyst for the decomposition
of formic acid to give CO2 and H2, and the chemistry leading to the active catalyst is described.
Ch a r t 1
In tr od u ction
Transition-metal diazoalkane complexes are of inter-
est as intermediates in the formation of alkylidene
complexes and in catalytic transfer of alkylidene groups,1
but also because they can exhibit several unusual
coordination modes2 and may model intermediates in
the fixation of dinitrogen to give organonitrogen com-
pounds.3 There are still relatively few complexes in
which a diazoalkane bridges between two metal atoms,
and most of these are with early transition metals. In
these complexes, the diazoalkane usually acts as a
4-electron ligand, with structure A or B (Chart 1).2
There appear to be no structurally characterized ex-
amples of binuclear complexes with 2-electron bridging
diazoalkane ligands of type C (Chart 1). In the case with
diazoalkane ) ethyl diazoacetate, there are several
resonance forms possible for a 2-electron donor (e.g.,
D1-D3 in Chart 1) and extended π-conjugation is
possible as shown in D4 (Chart 1, participation by metal
d(π) orbitals is also likely but is not shown).2 The
binuclear rhodium complex [Rh2(CO)2(µ-dppm)2(µ-N2-
CHCO2Et)], dppm ) Ph2PCH2PPh2, (Chart 1, E) may
be of this bonding type, based on its spectroscopic data,
but it does not contain a metal-metal bond.4
(1) (a) Sutton, D. Chem. Rev. 1993, 93, 995. (b) Doyle, M. P. Chem.
Rev. 1986, 86, 919. (c) Herrmann, W. A. Angew. Chem., Int. Ed. Engl.
1978, 17, 800. (d) Hillhouse, G. L.; Haymore, B. L. J . Am. Chem. Soc.
1982, 104, 1537. (e) Galardon, E.; Le Maux, P.; Simonneaux, G.
Tetrahedron 2000, 56, 615. (f) Baratta, W.; Herrman, W. A.; Kratzer,
R. M.; Rigo, P. Organometallics 2000, 19, 3664. (g) Noels, A. F.;
Demonceau, A. J . Phys. Org. Chem. 1998, 11, 602. (h) Nishiyama, H.;
Itoh, Y.; Matsumoto, H.; Park, S. B.; Itoh, K. J . Am. Chem. Soc. 1994,
116, 2223.
(2) (a) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. Rev. 1995, 139,
281. (b) Dartiguenave, M.; Menu, M. J .; Deydier, E.; Dartiguenave,
Y.; Siebald, H. Coord. Chem. Rev. 1998, 178-180, 623.
(3) (a) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115. (b) Harada,
Y.; Mizobe, Y.; Ishii, Y.; Hidai, M. Bull. Chem. Soc. J pn. 1998, 71, 2701.
(4) Woodcock, C.; Eisenberg, R. Organometallics 1985, 4, 4.
This paper reports the first example of a diruthenium
µ-diazoalkane complex, establishes that the diazoalkane
serves as a 2-electron ligand, and describes a study of
the reactivity of this compound. It has previously been
shown that a diruthenium µ-methylene complex, [Ru2-
(µ-CH2)(CO)4(µ-dppm)2], is formed by reaction of CH2N2
with [Ru2(µ-CO)(CO)4(µ-dppm)2], 1.5
(5) Gao, Y.; J ennings, M. C.; Puddephatt, R. J . Organometallics
2001, 20, 1882.
10.1021/om0102293 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/11/2001

Synthesis of a Diruthenium Diazoalkane Complex
Organometallics, Vol. 20, No. 16, 2001 3501
Ta ble 1. Selected Bon d Dista n ces a n d An gles in 2
Bond Distances (Å)
Ru(1)-Ru(2)
Ru(1)-P(2)
Ru(2)-P(4)
Ru(1)-C(6)
Ru(2)-C(8)
Ru(2)-N(1)
N(2)-C(1)
C(2)-O(1)
C(3)-O(2)
C(5)-O(5)
C(7)-O(7)
2.8550(4)
2.3472(9)
2.3671(9)
1.914(4)
1.889(4)
2.075(3)
1.328(5)
1.201(5)
1.440(6)
1.137(5)
1.145(5)
Ru(1)-P(1)
Ru(2)-P(3)
Ru(1)-C(5)
Ru(2)-C(7)
Ru(1)-N(1)
N(1)-N(2)
C(1)-C(2)
C(2)-O(2)
C(3)-C(4)
C(6)-O(6)
C(8)-O(8)
2.3507(9)
2.3621(10)
1.908(4)
1.895(4)
2.094(3)
1.270(4)
1.433(6)
1.365(5)
1.549(9)
1.136(5)
1.129(5)
Bond Angles (deg)
P(1)-Ru(1)-P(2)
P(1)-Ru(1)-N(1)
P(3)-Ru(2)-N(1)
Ru(1)-N(1)-Ru(2)
C(2)-C(1)-N(2)
C(6)-Ru(1)-N(1)
C(8)-Ru(2)-N(1)
178.47(3)
90.13(8)
86.03(8)
46.50(8)
119.74(3)
P(3)-Ru(2)-P(4) 161.92(4)
P(2)-Ru(1)-N(1)
P(4)-Ru(2)-N(1)
C(1)-N(2)-N(1)
90.06(3)
85.58(8)
124.6(3)
C(5)-Ru(1)-N(1) 101.22(15)
162.51(16) C(7)-Ru(2)-N(1) 140.24(14)
120.15(16)
electron rule, the µ-NNCHCO2Et ligand is expected to
act as a 2-electron ligand in complex 2.
F igu r e 1. A view of the structure of complex 2. Thermal
The ethyl diazoacetate ligand is very roughly planar
(the twist away from planarity is clear in Figure 1), and
it is also roughly coplanar with the Ru2(CO)4 atoms. The
distances Ru(1)-N(1) ) 2.094(3) Å and Ru(2)-N(1) )
2.075(3) Å suggest single bonds and appear inconsistent
with bonding mode A (Chart 1), for which the MdN
bond is expected to be short.2,10 The ethyl diazoacetate
is bent at N(2) with the angle C(1)-N(2)-N(1) ) 124.6-
(3)°, suggesting sp2 hybridization at N(2), but N(2) is
clearly not coordinated to ruthenium and the bonding
mode B of Chart 1 is ruled out. The distances N(1)-
N(2) ) 1.270(4) Å, C(1)-N(2) ) 1.328(5) Å, and C(1)-
C(2) ) 1.433(6) Å and C(2)-O(1) ) 1.201(5) Å are all
shorter than expected for single bonds. Together with
the approximate planarity of these atoms, the pattern
of bond distances supports the presence of NNCCO
conjugation, with Ru-N single bonds, as depicted in D4
(Chart 1). The representation as 2 in eq 1 is clearly
oversimplified, since it represents only one canonical
form (D1 in Chart 1).
ellipsoids are shown at the 25% probability level.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of [Ru 2(µ-η1:η1-
NNCHCO2Et)(CO)4(µ-d p p m )2], 2. The reaction of
ethyl diazoacetate with complex 1 occurred according
to eq 1 to give the product [Ru2{µ-NNCHCO2Et}(CO)4-
(µ-dppm)2], 2, as a brown-red, air-stable solid that was
isolated in 56% yield. The reaction of eq 1 is reversible,
The Ru2P2C2 atoms of the Ru2(µ-dppm)2 unit are in
the extended boat conformation with the two methylene
carbon atoms directed above the Ru2P4 plane, toward
the diazoalkane ligand. The conformation is probably
determined by the need to minimize steric effects
between the phenyl substituents of the dppm ligands
and the carbonyl and diazoalkane ligands (Figure 1).
The distortion of PRuP angles from linearity is much
greater at Ru(2) [P(3)-Ru(2)-P(4) ) 161.92(4)°] than
at Ru(1) [P(1)-Ru(1)-P(2) ) 178.47(3)°]. It is also
noteworthy that the Ru-P bonds are longer but the
Ru-C bonds and Ru-N bond are slightly shorter at Ru-
(2) compared to Ru(1) (Table 1), but it is not clear if
these differences are caused by electronic or steric
effects.
The spectroscopic data for 2 are consistent with the
solid structure. The IR spectrum contains four peaks
for the four terminal carbonyl ligands at ν(CO) ) 1974,
1955, 1929, and 1900 cm-1. The ethyl diazoacetate
ligand gave a peak at 1632 cm-1 for ν(CdO) and a peak
at 1574 cm-1 for ν(CdN). The stretching frequency for
and reaction of 2 with excess CO gave back complex 1.
Complex 2 appears to be the first example of a diru-
thenium diazoalkane complex, and it was characterized
by its spectroscopic properties and by an X-ray structure
determination.
The molecular structure of 2 is shown in Figure 1,
and selected bond lengths and angles are listed in Table
1. As shown in Figure 1, the complex contains a
trans,trans-Ru2(µ-dppm)2 unit, with four terminal car-
bonyl ligands and a bridging ethyl diazoacetate ligand.
The distance Ru-Ru ) 2.8550(4) Å is typical for a single
Ru-Ru bond6-9 and similar to that found in complex 1
(Ru-Ru ) 2.903(2) Å in the acetone solvate).6 Therefore,
the reaction of eq 1 occurs by simple displacement of
µ-CO by µ-NNCHCO2Et, and on the basis of the 18-
(6) Kuncheria, J .; Mirza, H. A.; J enkins, H. A.; Vittal, J . J .;
Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1998, 285.
(7) Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J . Inorg. Chem. 1993,
32, 1327.
(8) Engel, D. W.; Moodley, K. G.; Subramony, L.; Haines, R. J . J .
Organomet. Chem. 1988, 349, 393. Ferrence, G. M.; Fanwick, P. E.;
Kubiak, C. P.; Haines, R. J . Polyhedron 1997, 16, 1453.
(9) Kuncheria, J .; Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J . J .
Organomet. Chem. 2000, 593-594, 77.
(10) Curtis, M. D.; Messerle, L.; D’Errico, J . J .; Butler, W. M.; Hay,
M. S. Organometallics 1986, 5, 2283.

3502 Organometallics, Vol. 20, No. 16, 2001
Gao et al.
ν(CdO) ) 1632 cm-1 for the ethyl diazoacetate ligand
of 2 is significantly lower than that in the free ligand,
which has ν(CdO) ) 1730 cm-1. This difference is
caused by the conjugation in 2, with a contribution from
the canonical form D3 in Chart 1, leading to a CO bond
order less than two. A similar rationale was offered for
the reduced value of ν(CdO) ) 1610 cm-1 in E (Chart
1).4
4-Tolyl. The reaction of excess PhC≡CH with complex
2 in a dichloromethane solution for 3 h gave the complex
[Ru 2 (µ-CO)(CO)2 {µ-N N (CH CO2 E t )(CP h dCH )}(µ-
dppm)2], 3a , according to eq 4. When monitored by
In solution, complex 2 was fluxional, as shown by
variable temperature NMR studies. At room tempera-
ture, the spectra were broad but consistent with the
expected Cs symmetry for complex 2. Thus, the 31P{H}
NMR spectrum of 2 contained two multiplets at δ ) 26.3
and 33.0, and the 1H NMR spectrum contained a singlet
at δ ) 5.8 (NCH) and multiplets at δ ) 4.3 (CH2) and
1.5 (CH3) for the ethyl diazoacetate ligand and two
partly overlapped multiplets centered at δ ) 3.1 for the
CH2 protons of the dppm ligands. The 13C{H} NMR
spectrum of a 13CO-labeled sample of 2 showed four
resonances at δ ) 198, 198.4, 210, and 214.8 for the four
carbonyl ligands.
NMR, 3a was shown to be formed almost quantitatively,
and it was isolated as an air-stable, brown-yellow solid
in 60% yield. Complex 3b was synthesized in a similar
manner, but complex 2 did not react with the alkynes
PhCCPh, PhCCMe, EtCCEt, or n-BuCCH. Complex 2
reacted rapidly with the alkynes HCCCO2Me and MeO2-
CCCCO2Me, but complex mixtures of products were
formed. The solid-state structures of 3a and 3b were
established by X-ray diffraction studies, as well as by
spectroscopic methods.
On reducing the temperature to about -10 °C, each
peak observed in the room temperature NMR spectrum
had split into two, with relative intensities of ca. 3:2.
For example, the NCH proton appeared as two broad
1
singlets at δ ) 5.8 and 5.65 in the H NMR spectrum
The molecular structures of 3a and 3b are shown in
Figure 2, and selected bond lengths and bond angles
are listed in Table 2. The complexes 3a and 3b are
isomorphous and isostructural. The structure solutions
were difficult due to disorder as described below. The
second structure determination was carried out in the
frustrated hope of a simpler solution. Since 3b gave
better data, only its structure is discussed. The com-
plexes contain a crystallographic 2-fold axis that passes
through the atoms N(1)N(2)C(16)O(16); the atoms of the
ligand arising from combination of the diazoalkane and
alkyne ligands, except N(1) and N(2), are disordered 50:
50 by the C2 operation. Only one component is shown
for each of 3a and 3b in Figure 2, but it should be clear
that several atoms in the disorder model will appear to
be very close together and were difficult to resolve. A
reasonable solution was obtained in each case, but the
atoms of the ethoxy group were poorly defined and it is
likely that there is additional disorder of these atoms.
As shown in Figure 2, complex 3b contains a tran-
s,trans-Ru2(µ-dppm)2 unit, in a boat conformation simi-
lar to that in 2. Each ruthenium in 3b has one terminal
carbonyl ligand and there is one bridging carbonyl. The
remaining ligand is formed by combination of the ethyl
diazoacetate and 4-tolyl acetylene groups, with N(1)
bridging the two ruthenium atoms and C(1) terminally
bound to one of the ruthenium atoms. The five-
membered ring RuN(1)N(2)C(2)C(1) can be considered
to be formed by regioselective (3 + 2)-cycloaddition of
the alkyne across the RuN(1)N(2) unit in 2, though with
a change in stereochemistry about the NdC bond (eq
4). The distance Ru-RuA ) 3.117(1) Å is longer than
expected for a typical Ru-Ru single bond (2.71-3.02
Å),6-9 but short enough that a weak bond cannot be
discounted. The carbonyl oxygen atom O(2) lies close to
RuA but the distance RuA-O(2) ) 2.60 Å is too long to
represent a covalent bond, and the pattern of bond
angles within the diazoalkane fragment [e.g., N(1)N-
(2)C(11) ) 143.0(8)°] indicates that the RuA..O(2)
and the dppm phosphorus atoms gave two sets of
resonances at δ ) 25.8 and 32.0 and at δ ) 26.0 and
33.0 in the 31P{H} NMR spectrum. No further splitting
occurred on cooling to -90 °C. These data clearly
indicate that complex 2 exists in solution as a 3:2
mixture of two rapidly equilibrating isomeric forms,
each having Cs symmetry. The isomers probably occur
as a result of restricted rotation about the C(1)-C(2)
bond as shown in eq 2. The data do not exclude rotation
about the N(2)-C(1) bond (eq 3), but this is considered
improbable both because there is more double bond
character and because a bigger difference in chemical
shifts of the two isomers would be expected. A similar
isomerization was observed in dimolybdenum com-
plexes, in which the diazoalkane is present as a 4-elec-
tron ligand.10
Rea ction s of Com p lex 2 w ith Alk yn es: Syn th e-
ses of Com p lexes [Ru 2(µ-CO)(CO)2{µ-EtOC(O)C-
(H)N(N)C(R)dCH}(µ-d p p m )2], 3a , R ) P h ; 3b, R )

Synthesis of a Diruthenium Diazoalkane Complex
Organometallics, Vol. 20, No. 16, 2001 3503
Ta ble 2. Selected Bon d Dista n ces a n d An gles in
3a ‚1/2CH2Cl2 a n d 3b
3a
3b
Bond Distances (Å)
3.108(3)
2.344(5)
2.353(4)
1.85(2)
Ru-RuA
3.117(1)
2.340(2)
2.353(2)
1.836(1)
2.093(6)
2.24(2)
2.061(5)
1.26(1)
1.63(2)
1.30(2)
1.40(3)
1.38(3)
1.20(2)
1.44(2)
1.54(3)
1.54(1)
1.143(8)
1.19(1)
Ru-P(1)
Ru-P(2)
Ru-C(15)
Ru-C(16)
Ru-C(1)
2.07(2)
1.99(5)
2.02(1)
1.33(2)
1.63(5)
1.30(4)
1.44(6)
1.45(7)
1.21(5)
1.42(6)
1.49(1)
1.49(5)
1.13(2)
1.21(3)
Ru-N(1)
N(1)-N(2)
N(2)-C(2)
N(2)-C(11)
C(1)-C(2)
C(10)-C(11)
C(10)-O(2)
C(10)-O(1)
C(12)-O(1)
C(12)-C(13)
C(15)-O(15)
C(16)-O(16)
Bond Angles (deg)
173.8(2)
86.4(1)
P(1)-Ru-P(2)
P(1)-Ru-N(1)
P(2)-Ru-N(1)
P(1)-Ru-RuA
P(2)-Ru-RuA
P(1)-Ru-N(1)
P(2)-Ru-N(1)
Ru-N(1)-RuA
C(2)-N(2)-N(1)
C(11)-N(2)-N(1)
Ru-N(1)-N(2)
Ru-C(1)-C(2)
C(1)-Ru-N(1)
N(2)-C(11)-C(10)
C(1)-C(2)-N(2)
C(15)-Ru-N(1)
C(16)-Ru-N(1)
173.92(7)
86.39(5)
89.12(5)
89.59(5)
89.71(5)
86.39(5)
89.12(5)
98.2(3)
104.3(8)
143.0(8)
130.9(1)
109 (1)
75.3(5)
108 (2)
119 (2)
177.1(3)
82.8(2)
89.3(1)
89.8(1)
89.7(1)
86.4(1)
89.3(1)
100 (1)
102 (2)
145 (2)
129.9(5)
118 (4)
76.2(15)
110 (4)
114 (4)
177.1(7)
81.4(7)
Sch em e 1. d p p m Liga n d s Ar e Om itted for Cla r ity
F igu r e 2. Views of the structures of (a) complex 3a and
(b) complex 3b. The organic ligand is disordered by a C2
axis passing through N(1)N(2), and Figures 2a and 2b
roughly represent the two components of the disorder
model.
interaction may be repulsive.11 The atoms O(2)C(10)C-
(11)N(2)N(1)C(2)C(1) are roughly coplanar with the Ru2-
(CO)2(µ-CO) unit, indicative of π-conjugation in the
complex ligand. The stereochemistry about the N(2)d
C(11) bond is opposite from that in the parent complex
2 (similar to 2b in eq 3), but most distances within the
diazoacetate fragment are similar in 2 and 3b. The bond
distance Ru-N(1) ) 2.061(5) Å is slightly shorter than
the Ru-N bonds in 2, while Ru(1)-C(1) ) 2.24(2) Å is
in the range expected for a Ru-C single bond.12
In complex 3b, ignoring any metal-metal bonding,
the stereochemistry about Ru(1) and Ru(1A) is roughly
octahedral and square pyramidal, respectively. Clearly
(12) It is likely that at least some of the atoms N(2)N(1)C(16)O(16)
lie slightly off of the 2-fold axis, but the displacements were not large
enough to allow resolution of the resulting disorder. Extensive discus-
sion of bond parameters involving disordered atoms is not justified.
The distance C(2A)-N(2) ) 1.63(2) appears anomalously long, for
example.
(11) (a) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
J . Am. Chem. Soc. 1982, 104, 1918. (b) J ohnson, K. A.; Vashon, M. D.;
Moasser, B.; Warmka, B. K.; Gladfelter, W. L. Organometallics 1995,
14, 461. (c) Herrero, P. G.; Weberndorfer, B.; Ilg, K.; Wolf, J .; Werner,
H. Angew. Chem., Int. Ed. 2000, 39, 3267.

3504 Organometallics, Vol. 20, No. 16, 2001
Gao et al.
The NMR spectra of 3b are consistent with the solid-
state structure. The 31P{H} NMR spectrum displayed
two multiplets at δ ) 35.5 and 33.5 for the phosphorus
atoms of the dppm ligands. The 1H NMR spectrum
contained two multiplets at δ ) 3.0 and 2.5 for the
CH2P2 protons of the dppm ligands and a singlet
resonance at δ ) 6.3 due to CHdN proton. The RuCHd
C proton resonance was not observed and is presumed
to be obscured by the intense aryl resonances. The
ethoxy reonances were observed at δ ) 2.3 (CH2) and
at δ ) 0.6 (CH3) and are markedly different from those
in complex 2 (δ ) 4.2 and 1.5, respectively). The
difference reflects the different conformations about the
NdC bond, and the ethyl protons of 3b lie in a shielding
zone between phenyl groups, as illustrated in Figure 3.
The ethoxy group in 2 lies beyond this zone, and
therefore normal chemical shifts are observed. There is
greater steric hindrance in 3b than in 2, and 3b does
not exhibit the fluxionality due to rotation of the CO2-
Et group that was shown to occur in 2. The 13C{H} NMR
spectrum for a 13CO-labeled sample of 3b displayed
three carbonyl resonances, a multiplet at δ ) 270 for
the bridging CO and multiplets at δ ) 213.6 and 208.5
for the two terminal carbonyls.
P r oton a tion of Com p lex 2: Syn th esis of [Ru 2(µ-
H)(CO)4{µ-NNCH2CO2Et}(µ-d p p m )2][BF 4]2, 5[BF 4]2.
The reaction of HBF4‚Et2O with complex 2 in CD2Cl2
solution occurred according to eq 5. At -20 °C, the
F igu r e 3. The different conformations of the diazo ligand
in complexes 2 and 3b that lead to large differences in
chemical shifts of the ethoxy protons.
then, Ru should have an 18-electron configuration but
RuA might have a 16-electron or 18-electron configu-
ration. It may be convenient to consider the cycloaddi-
tion involving nucleophilic attack by the lone pair on
N(2) in 2 (and electrophilic attack by ruthenium) on the
alkyne as shown in Scheme 1. The stereochemistry of
the product could then be understood in terms of the
canonical forms 3A (16-e at RuA) and 3B (18-e at RuA).
The representations 3A and 3B of Scheme 1 do not
explicitly show conjugation in the diazoester unit, but
this is likely to be similar to that for 2 (Chart 1), as
indicated by similar values of ν(CdO) ) 1627 and 1632
cm-1 in 3b and 2, respectively.
cationic complex 4[BF 4] was the major product, but at
room temperature, further protonation occurred to give
complex 5[BF 4]2. Complex 4 was identified only by its
spectroscopic properties (see later), but complex 5 was
isolated as the tetrafluoroborate salt and was fully
characterized.

Synthesis of a Diruthenium Diazoalkane Complex
Organometallics, Vol. 20, No. 16, 2001 3505
F igu r e 5. The variable temperature NMR spectra of
1
complex 5: (a and b) the hydride resonance in the H NMR
F igu r e 4. A view of the structure of the dicationic complex
5. The hydride shown bridging the Ru-Ru bond was
located but not refined. There is disorder in the diazo ligand
and in two of the phenyl groups that is not shown (see text).
spectrum at room temperature and at -90 °C, respectively;
(c and d) the carbonyl resonances in the 13C NMR spectrum
at room temperature and at -90 °C, respectively. At low
temperature, separate resonances for 5a and 5b (eq 6) are
observed.
Ta ble 3. Selected Bon d Dista n ces a n d An gles in 5
Bond Distances (Å)
Ru-RuA
2.970(2)
2.400(3)
1.93(1)
2.25(1)
1.12(1)
Ru-P(1)
2.403(3)
1.88(1)
1.90(1)
1.21(2)
1.16(1)
unit were not accurately defined, it is apparent from
Figure 4 that the N2CCO2 atoms are no longer coplanar
in 5 [the dihedral angle N(1)N(2)C(3)C(4) ) -87°], as
expected if conjugation is lost by protonation at carbon
(eq 5). The lack of extended π-conjugation is also clear
from the IR spectrum, which gives a normal value of
ν(CO) ) 1729 cm-1 for the ester carbonyl group, a value
much higher than in the conjugated complex 2, [ν(CO)
) 1632 cm-1].
Ru-P(2)
Ru-C(11)
Ru-N(1)
Ru-C(12)
RuA-N(1)
C(11)-O(11)
N(1)-N(2)
C(12)-O(12)
Bond Angles (deg)
P(1)-Ru-N(1)
P(2)-Ru-P(1)
N(2)-N(1)-Ru
C(11)-Ru-P(1)
82.9(4)
177.61(9)
139(1)
P(2)-Ru-N(1)
Ru-N(1)-RuA
N(2)-N(1)-RuA
C(12)-Ru-P(2)
96.0(4)
91.2(4)
129(1)
89.0(3)
88.9(3)
The structure of 5 was further defined by its NMR
spectra. The 31P{H} NMR spectrum contained two
overlapping signals at δ ) 21.4 and 21.1, and the 13C-
{H} NMR spectrum of a 13CO-enriched sample con-
tained four peaks at δ ) 195.8, 195.0, 190.2 and 188.4,
due to the four terminal carbonyls. The 1H NMR
spectrum contained the expected resonances for the
CH2P2 protons of the dppm ligands [δ ) 3.73 and 3.40]
and ethoxy protons [δ ) 4.45 (CH2) and δ ) 1.40 (CH3)],
and the Ru2(µ-H) group was indicated by a resonance
at δ ) -11.10, which appeared as a quintet due to
coupling 2J (PH). A sharp singlet at δ ) 4.96 was
assigned to the NNCH2 protons and confirmed by the
observation of its correlation with the adjacent carbonyl
carbon atom present at δ ) 168 in the 13C{H} NMR
spectrum by a 1H13C HMBC experiment and to the
directly bound carbon at δ ) 82.5 by a 1H13C HSQC
experiment. Hence protonation of 2 at both the Ru-Ru
bond and the NNCH atom is confirmed.
The structure of the dication 5 is shown in Figure 4,
and selected distances and angles are in Table 3. The
structure solution was again complicated by disorder.
A crystallographic C2 axis passes through the center of
the Ru2(µ-dppm)2 ring, and the N(1)N(2)CH2CO2Et
atoms are disordered over equivalent positions by the
2-fold rotation. There is probably also further disorder
of the ethoxy group which was not resolved. Hence the
CH2CO2Et group is poorly defined.
Complex 5 contains a trans,trans-Ru2(µ-dppm)2 unit,
in a boat conformation similar to that in 2 and 3, and
there are four terminal carbonyl ligands and the bridg-
ing N2CH2CO2Et ligand. A hydride ligand bridges the
Ru-RuA bond and was tentatively located but not
refined [Figure 4, Ru-H ) 1.6 Å, RuA-H ) 1.7 Å, Ru-
H-RuA ) 125°]. The Ru-Ru distance [2.970(2) Å] is
markedly longer than that in the parent complex 2
[2.8550(4) Å] but still suggests the presence of a weak
RuRu single bond.6,7,9,13 Protonation of metal-metal
bonds usually leads to a significant increase in M-M
bond distance.13 Two BF4- ions were identified for each
diruthenium complex ion, thus confirming the dicationic
nature of 5. Although the atoms of the N2CH2CO2Et
The IR spectrum of 5 displays four peaks at 2097,
2074, 2048, and 2030 cm-1 for the four terminal carbo-
nyl ligands. In addition, there was a band assigned to
ν(NdN) ) 1548 cm-1, in the accepted range for diazo-
nium complexes.2
Complex 5 exhibited fluxional behavior in solution at
room temperature, and this was frozen out below -60
°C. At -90 °C, two isomers were present in almost equal
amounts, each displaying a hydride resonance signal in
the 1H NMR spectrum and four terminal carbonyl
(13) (a) Alcock, N. W.; Raspin, K. A. J . Chem. Soc. A 1968, 2108.
(b) Kauffmann, Th.; Beissner, G.; Koppelmann, E.; Kuhlmann, D.;
Schott, A.; Schrecken, H. Angew. Chem., Int. Ed. Engl. 1968, 7, 131.
(c) J ohnson, K. A.; Gladfelter, W. L. Organometallics 1992, 11, 2534.
(d) Hursthouse, M. B.; J ones, R. A.; Abdul Malik, K. M.; Wilkinson, G.
J . Am. Chem. Soc. 1979, 101, 4129.

3506 Organometallics, Vol. 20, No. 16, 2001
Gao et al.
resonances in the 13C{H} NMR spectrum (Figure 5).
Interestingly, the two isomers have different sym-
metries. One isomer, 5a , has apparent Cs symmetry.
resonance in the regions for either CHdN or CH2N
groups. It is tentatively suggested that it may contain
a HCH‚‚‚NEt3 hydrogen bond, leading to a very broad
resonance. These data clearly confirm that protonation
of 2 is kinetically controlled to give 4, while deprotona-
tion of 5 occurs at carbon to give 7.
1
Thus, it gives a single CH2O resonance in the H NMR
at δ ) 4.30 and two CH2P2 resonances at δ ) 3.65 and
2.70. The other isomer, 5b, appears to have no sym-
metry (C1). Thus, it gives two resonances due to dias-
tereotopic CHaHbO protons of the ethoxy group and two
pairs of CH2P2 resonances at δ ) 5.60, 3.65 and 5.20,
3.85 with the assignments confirmed by the 1H-1H
correlated spectrum (COSY). This low symmetry form
5b is likely to resemble the solid-state structure (Figure
4) in which the carboxyl group and N(1)N(2)C(3) planes
are roughly orthogonal and therefore there is no mirror
plane. The more symmetrical isomer 5a has effective
Cs symmetry, and the conformation is probably similar
to that in complex 2. The rotation about the C(3)-C(4)
bond needed to interconvert 5a and 5b (eq 6) is
Th e Rea ctivity of Com p lex 2 to F or m ic Acid . At
room temperature, the addition of an excess of formic
acid to a solution of 2 in CD2Cl2 caused an immediate
color change from brown-red to orange. After an induc-
tion period, the evolution of a gas, identified as a
mixture of CO2 and H2, was observed. Once started, the
gas evolution was complete in a few minutes to leave a
wine-red solution. No formic acid remained at this stage,
and two known complexes 1 and [Ru2(µ-H)(H)(µ-CO)-
(CO)2(µ-dppm)2], 8,14 were the only ruthenium com-
plexes present, in about equal amounts, in the final
solution. It is apparent from the above observations that
catalytic decomposition of HCOOH to give CO2 + H2
occurred.14 The ethyl diazoacetate ligand in 2 was
converted to ethyl acetate, which was identified by its
NMR spectrum. Complex 8 is known to be an active
catalyst for decomposition of formic acid in dichlo-
romethane solution (complex 1 is also a catalyst but only
in acetone solution), so the induction period is presumed
to be associated with formation of complex 8.14 The
stoichiometric reaction can be described by eq 7. It is
presumably restricted due to steric effects, since C(3)-
C(4) multiple bond character is not expected in 5.
When complex 5 was dissolved in acetone-d6, slow
exchange of the NCH2 protons with deuterium from the
solvent occurred. The resonance at δ ) 4.96 (NCH2)
decayed and a new isotopically shifted resonance at δ
) 4.90 (NCHD) grew; over long periods, both decayed
as the NCD2 group was formed. This shows that the
protonation is reversible at the NdCH center of 2 (eq
5). Reaction of complex 5 with the base triethylamine
at -15 °C gave a new complex, 6, which was only
partially characterized but which certainly maintained
a Ru2(µ-H) group having δ ) -8.9. On warming,
complex 6 formed an equilibrium with another complex,
7, whose formation from 5 involves selective deproto-
nation at carbon (eq 5). Complex 7 is therefore an isomer
of complex 4. The diazo and diazonium isomers 4 and 7
are readily distinguished by their NMR properties,
particularly by the absence or presence of a hydride
resonance and of CHdN or CH2N resonances, respec-
tively (Table 4). Complex 6 failed to give a resolved
likely that the ethyl acetate is formed by decomposition
of transient EtO2CCH2NNH with elimination of N2, by
analogy to the known reaction of alkyldiazenes.15
The catalytic reaction proceeded much faster when
carried out in acetone-d6, and the final ruthenium
complexes were again 1 and 8. However, ethyl acetate
was formed in low yield and a second unidentified
organic product was formed as the major product.
The reaction of formic acid with complex 2 was
studied by a variable temperature NMR experiment in
order to identify reaction intermediates. At a temper-
Ta ble 4. Com p a r ison of th e NMR P r op er ties of
Com p lexes 2, 4, 5, 6, a n d 7
2
4
5
6
7
δ(CHN) 5.8a
δ(CH2O) 4.3
4.5b
4.2
1.2
4.96b
4.45
1.40
3.4, 3.7
-11.1
92.5b
c
5.9a
4.4
1.5
3.5, 3.7
-11.5
112a
(14) (a) Gao, Y.; Kuncheria, J .; J enkins, H. A.; Puddephatt, R. J .;
Yap, G. P. A. J . Chem. Soc., Dalton Trans. 2000, 3212. (b) Gao, Y.;
Kuncheria, J .; Yap, G. P. A.; Puddephatt, R. J . Chem. Commun. 1998,
2365.
(15) Ackermann, M. N.; Hallmark, M. R.; Hammond, S. K.; Roe, A.
N. Inorg. Chem. 1972, 11, 3076. It is also possible that nitrogen loss
occurs before the reductive elimination step. A GC-MS study of a
4.20
1.38
2.7, 2.9
-8.9
c
δ(CH3)
1.5
δ(CH2P2) 3.1, 3.1
δ(RuH)
3.6, 3.9
δ(CHN) 110a
86b
δ(P)
26.5, 32.4 26.6,32.9 21.1, 21.4 30.7, 30.9 18.2, 23.6
reaction mixture after
a reaction in acetone solution showed a
a
CHdM/ CH2N. c Not observed. The assignment of CHN reso-
compound present with m/z ) 116, as expected for the diazene or its
isomeric form EtO2CCHdNNH2, as well as at m/z ) 88, for ethyl
acetate.
nances was confirmed by recording the 1H-13C correlated spec-
trum (gHSQC).

Synthesis of a Diruthenium Diazoalkane Complex
Organometallics, Vol. 20, No. 16, 2001 3507
ature below -10 °C, only the complex cation [Ru2(CO)4(µ-
NNCH2CO2Et)(µ-dppm)2]+, 4, as the formate salt, was
observed in solution. Its spectroscopic properties are
identical to those of 4[BF4] (eq 5). The 31P{H} NMR
spectrum of 4 displays two multiplets at δ ) 32.9 and
26.6 for the dppm phosphorus atoms. The 1H NMR
spectrum contained a singlet at δ ) 4.5 for the CH2N
protons, typical ethoxy resonances at δ ) 4.2 [q, CH2]
and δ ) 1.2 [t, CH3], and two resonances for the CH2P2
protons at δ ) 3.9 and 3.6. The 13C{H} NMR spectrum
of a sample prepared from 13CO-labeled 2 contained four
resonances for terminal carbonyl ligands at δ ) 210.9,
210.8, 194.6, and 193.1. The CH2N resonance in the 13C-
{H} NMR spectrum was found at δ ) 86. The NMR
properties are similar to those of complex 5 described
above but without the hydride resonance. Further
protonation of 4 to give 5 was not observed in reactions
with formic acid.
diazine “EtO2CCH2NdNH”. This eliminates N2 to give
ethyl acetate in dichloromethane solution or reacts in
more complex ways in acetone solution.15
When the solution was warmed to 20 °C, the catalysis
began and concentrations of both 9 and 10 decreased.
At the end of the reaction, the chief ruthenium products
were complexes 1 and 8. Complex 1 is formed simply
by deprotonation of complex 9 as the concentration of
formic acid decreases. Complex 8 is formed by decom-
position of 10 under conditions with no free CO to
convert the “Ru2(CO)3(µ-dppm)2” to the pentacarbonyl
derivative 1 or 9. Reaction of “Ru2(CO)3(µ-dppm)2” with
formic acid can give CO2 and complex 8. Once coordi-
natively unsaturated complexes such as 8 are formed,
the catalysis becomes very fast and is complete within
minutes.14 The induction period for catalysis is associ-
ated with the preliminary chemistry.
When the above solution was warmed to 6 °C, complex
4 decomposed to give a new complex, 10, and then the
known complex [Ru2(µ-H)(µ-CO)(CO)4(µ-dppm)2]+, 9.14
Complex 10 was transient; as it decayed, the concentra-
tion of 9 increased until the ratio of concentrations of
10:9 reached roughly 1:1, after which new products were
observed. Complex 10 was characterized by its NMR
spectra since it could not be isolated. The 31P{H} NMR
spectrum of 10 contained two multiplets at 25.8 and
24.4, indicative of the symmetrical trans arrangement
of the dppm ligands in 10. The 1H NMR spectrum
displayed two multiplets at δ ) 4.05 and 3.60 for the
methylene hydrogens of dppm ligands, a singlet at δ )
4.55 for the CH2N protons, and resonances for the
ethoxy group at δ ) 2.6 [q, CH2] and 0.6 [t, CH3]. A new
singlet resonance, attributed to coordinated formate,
was present at δ ) 9.4. There is a marked difference in
chemical shifts of the ethoxy resonances of 10 compared
to those in 2 and 4 and the values are similar to those
in 3, suggesting a change in conformation of the diazo-
nium ligand. Loss of a carbonyl is needed to allow this
conformational change and to provide the fifth carbonyl
present in the other product, complex 9. The overall
reaction to this point is then proposed to occur according
to eq 8, bearing in mind that the structure of 10 is
tentative.
Discu ssion
Complex 2 represents the first example of fully
characterized diruthenium diazoalkane complex and the
diazoalkane in 2 is shown to act as a 2-electron ligand.
This bonding mode has not been structurally character-
ized previously in binuclear diazoalkane complexes,2
and it is suggested that conjugation through the ester
substituent gives added stability in complex 2.
Complex 2 is electron-rich and has a number of
possible sites for electrophilic attack, of which the lone
pair on the angular â-nitrogen atom N(2), the methine
carbon C(3), and the Ru-Ru bond can be considered
prime candidates. In reactions with protons, the first
reaction occurs rapidly at C(3) to give a diazonium
complex and then, with the strong acid H[BF4], slower
attack occurs at the ruthenium-ruthenium bond to give
a bridging hydride. With the weaker acid HCO2H, only
monoprotonation at carbon occurs and then the formate
coordinates with displacement of CO. Then decomposi-
tion by loss of CO2 from formate, and formation of
dinitrogen and ethyl acetate from the reduced diazoal-
kane, occurs.
In contrast to the site of proton attack, the reaction
with the alkynes RCCH, R ) phenyl or 4-tolyl, appear
to involve nucleophilic attack by the lone pair on N(2).
Mechanistically, it is likely that reaction is initiated by
coordination of the alkyne to ruthenium, followed by
nucleophilic attack by nitrogen leading to formation of
a novel metallacycle in complexes 3. Evidently the
2-electron bridging diazoalkane can display a diverse
pattern of reactivity.
Exp er im en ta l Section
All manipulations were carried out in an atmosphere of dry
nitrogen, using either standard Schlenk techniques or a
glovebox. Solvents were dried and distilled prior to use. The
complex [Ru2(µ-CO)(CO)4(µ-dppm)2] was synthesized according
to the literature procedure.7 1H, 13C, and 31P NMR spectra were
recorded using a Varian Inova 600 or 400 or Gemini 300
spectrometer. Mass (and GC-MS) spectra were recorded using
a Finnigan Mat 8200 spectrometer.
Syn th esis of [Ru 2{µ-NNCHCO2Et}(CO)4(µ-d p p m )2], 2.
Ethyl diazoacetate (37 µL, 0.32 mmol) was added to a solution
of [Ru2(µ-CO)(CO)4(µ-dppm)2], 1, (0.27 g, 0.253 mmol) in CH2-
Cl2 (20 mL). The solution color changed from orange-yellow
to red in 20 min. The volume of solution was reduced to 2 mL
Complex 10 is formed by displacement of a carbonyl
ligand from 4 by formate, and it can then lose CO2 from
the formate to make a hydride that can reductively
eliminate with the diazonium group to give the unstable

3508 Organometallics, Vol. 20, No. 16, 2001
Ta ble 5. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for Com p lexes 2, 3a , 3b, a n d 5
Gao et al.
2
3a .0.5CH2Cl2
3b
5
formula
fw
cryst sys
space group
a/Å
b/Å
c/Å
C
62H54N2O5P4Ru2
C65.5H50ClN2O5P4Ru2
1306.55
tetragonal
P4(1)2(1)2
15.293(1)
15.293(1)
27.764(2)
90
C66H57N2O5P4Ru2
1284.16
tetragonal
P4(3)2(1)2
15.1244(6)
15.1244(6)
28.2910(15)
90
C59H46B2Cl2F8N2O6P4Ru2
1449.52
1233.09
monoclinic
P2(1)/n
11.9163(6)
22.118(1)
22.351(1)
98.903(1)
5820.1(5)
4
tetragonal
P4(2)2(1)2
18.5555(4)
18.5555(4)
20.0822(4)
90
6914.4(3)
4
1.392
â/deg
V/Å3
6493.2(9)
4
1.337
6471.5(5)
4
1.318
Z
d(calcd)/Mg m-3
T/K
1.407
213(2)
200(2)
223(2)
150(2)
λ/Å
0.710 73
0.678
integration
33 304
0.710 73
0.652
integration
38 214
0.710 73
0.613
integration
32 919
0.710 73
0.674
integration
33 093
abs coeff/mm-1
abs corr
reflns
GOF
1.086
0.927
1.106
1.064
R1, wR2 (I > 2σ(I))
0.047, 0.133
0.078, 0.160
0.058, 0.149
0.082, 0.225
by vacuum, and pentane (80 mL) was then added to precipitate
the brown-yellow product, which was filtered off, washed with
pentane, and then dried under vacuum. Yield: 56%. Anal.
Calcd for C58H50N2O6P4Ru2: C, 58.2; H, 4.2; N: 2.3. Found:
C, 58.1; H, 4.2; N: 1.85. IR (cm-1, Nujol): ν(CO) ) 1974, 1955,
1929, and 1900; ν(CdO) ) 1632; ν(CdN) ) 1574. NMR in CD2-
Cl2 at 20 °C: δ(31P) ) 26.5 [br m, dppm]; 32.4 [br m, dppm];
δ(1H) ) 5.8 [br s, 1H, CHCO(O)Et]; 3.1 [br m, 4H, P-CHaHb-
P]; 4.3 [br m, 2H, -CH2CH3]; 1.5 [br s, 3H, -CH2CH3]; δ(13C) )
214.8, 210, 198.4, 198 [br m, terminal CO]; 167.0 [br s, -C(O)-
OEt]; 110.0 [br s, CHCO(O)Et]; 59.0 [s, -CH2CH3]; 30.0 [br s,
P-CH2-P]; 18.0 [s, -CH2CH3]. NMR in CD2Cl2 at -40 °C:
isomer 2a δ(31P) ) 32.0 [br m, dppm]; 26.0 [br m, dppm]; 5.65
[br s, 1H, CHCO(O)Et]; 4.25 [br s, 2H, -CH2CH3]; 1.55 [br s,
3H, -CH2CH3]; isomer 2b δ(31P) ) 32.0 [br m, dppm]; 25.8 [br
m, dppm ]; δ(1H) ) 5.80 [br s, 1H, CHCO(O)Et]; 4.15 [br s,
2H, -CH2CH3]; 1.32 [br s, 3H, -CH2CH3]. Resonances for the
CH2P2 protons were not fully resolved, with three broad
resonances at δ ) 3.05, 2.9, 2.7 observed. The ratio 2a :2b )
3:2.
color changed immediately to red and then to brown-yellow
in a few minutes. To this solution was layered 2 mL of ether
carefully. Cubic yellow crystals suitable for X-ray diffraction
studies were obtained in 48 h. The crystals were washed with
pentane and dried under vacuum. Yield: 20 mg (48%). Anal.
Calcd for C58H52B2F8N2O6P4Ru2: C, 50.7; H, 3.8; N: 2.0.
Found: C, 50.1; H, 3.9; N: 1.7. The borderline analysis is due
to the fractional presence of dichloromethane. IR (Nujol, cm-1):
ν(CO) ) 2097, 2074, 2048, 2030; ν(CdO of diazoalkane) )
1729, ν(NdN) ) 1548. NMR in CD2Cl2 at 20 °C: δ(31P) ) 21.4
[m, dppm], 21.1 [m, dppm]; δ(1H) ) 4.96 [s, 2 H, -CH2NN];
3.73 [br m, 2H, P-CHaHb-P]; 3.40 [br m, 2H, P-CHaHb-P]; 4.45
[q, 2H, J H-H ) 7 Hz, -CH2CH3]; 1.40 [t, 3H, J H-H ) 7 Hz,
-CH2CH3]; -11.10 [quin, 1H, 2J P-H ) 10 Hz, µ-H]. For a sample
of 13CO-labeled 5, δ (13C) ) 195.8, 195.0, 190.2, 188.4 [br s,
terminal CO]. NMR in CD2Cl2 at -90 °C: resonances for 5a
and 5b overlapped at δ(1H) ) ca. 5 [v br, NCH2] and at δ(31P)
) 21.2 [br m, dppm], 21.8 [br m, dppm]. 5a : δ(1H) ) 3.65,
2.70 [m, each 2H, CHaHbP2]; 4.30 [q, 2H, CH2O]; 1.20 [t, 3H,
CH3]. 5b: δ(1H) ) 5.60, 3.65; 5.20, 3.85 [m, each 1H, CH2P2];
4.60, 4.45 [m, each 1H, CH2O]; 1.20 [t, 3H, CH3]. Resonances
at δ(1H) ) -11.4 and -11.1 [br m, 1H, µ-H]; δ(13C) ) 197,
196.5, 195, 193.6, 190.8, 189.6, 189.6, 189.6, 187.9 [br m,
terminal CO] could not be assigned to a specific isomer.
3
3
Th e Rea ction of 2 w ith CO. A stream of CO was bubbled
through a solution of 2 (15 mg, 0.013 mmol) in CD2Cl2 (0.6
mL) in a rubber septum-sealed NMR tube for 15 min. The
NMR tube was then sealed. After 24 h, only traces of complex
2 remained and complex 1 was formed and identified by its
1H and 31P NMR spectra.
Stu d ies of th e Rea ction of 2 w ith HCOOH. (a ) Room -
Tem p er a tu r e Stu d ies. To a solution of 2 (10 mg, 0.009 mmol)
in CD2Cl2 (0.5 mL) in a septum-sealed NMR tube was added
HCOOH (3 µL, 0.06 mmol). The color of the solution changed
immediately from brown-red to brown. After 3 h, gas bubbling
was observed and the solution color changed to wine-red. The
known complexes 1 and 8 were identified by their 1H and 31P
NMR spectra, and ethyl acetate was identified by its 1H and
13C NMR spectra. Formic acid was absent at this stage.
Syn th esis of [Ru 2(µ-CO)(CO)2{µ-NN(CHCO2Et)(CRCH)}-
(µ-d p p m )2], 3a , R ) P h . PhC≡CH (15 µL, 0.14 mmol) was
added to a stirred solution of 2 (0.1 g, 0.08 mmol) in CH2Cl2
(20 mL). After 3 h the volume was reduced under vacuum to
2 mL and pentane (60 mL) was added to precipitate the brown-
yellow product, which was filtered off, washed with pentane,
and dried under vacuum. Yield: 66%. Anal. Calcd for 3a ‚1/
2CH2Cl2, C65.5H57ClN2O5P4Ru2: C, 59.9; H, 4.4; N: 2.1.
Found: C, 59.4; H, 4.4; N, 1.9. IR (cm-1, Nujol): ν(CO) ) 1893,
1869, 1661; ν(CdO of the diazoalkane) ) 1627. NMR in CD2-
Cl2 at 20 °C: δ(31P) ) 35.5 [m, dppm]; 33.5 [m, dppm]; δ(1H)
) 6.3 [s, 1H, CHCO(O)Et]; 3.0 [m, 2H, P-CHaHb-P]; 2.5 [m,
2H, P-CHaHb-P]; 2.3 [q, 2H, -CH2CH3]; 0.5 [t, 3H, -CH2CH3].
For a sample of 13CO-labeled 3: δ(13C) ) 277 [m, bridging CO],
213.6, 208.5 [m, terminal CO]. Complex 3b, R ) 4-MeC6H4,
was synthesized similarly. Yield: 62%. Anal. Calcd for 3b‚
1.5CH2Cl2, C67.5H61Cl3N2O5P4Ru2: C, 57.4; H, 4.35; N: 2.0.
Found: C, 57.6; H, 3.6; N: 1.3. NMR in CD2Cl2 at 20 °C: δ-
(31P) ) 35.4 [m, dppm]; 33.8 [m, dppm]; δ(1H) ) 6.3 [s, 1H,
CHCO2Et]; 3.0 [m, 2H, P-CHaHb-P]; 2.5 [m, 2H, P-CHaHb-P];
2.25 [q, 2H, -CH2CH3]; 0.5 [t, 3H, -CH2CH3].
The decomposition of formic acid was complete within 1 h
when a similar reaction was carried out using acetone as the
solvent. The major organic product was not fully characterized.
NMR in acetone-d6 at 20 °C: δ(1H) ) 4.32 [s]; 4.0 [q, J H-H
)
7 Hz]; 1.1 [t, J H-H ) 7 Hz]. δ(13C) ) 152.5, 59.4, 11.8. GC-MS
(M+): m/z ) 116. A sample of EtO2CCHdNNH2 was synthe-
sized according to a literature method for comparison.16 NMR
3
in CD2Cl2 at 20 °C: cis-isomer, δ(1H) ) 1.20 [t, J H-H ) 7 Hz,
3
3H, CH3CH2-]; 4.20 [q, J H-H ) 7 Hz, 2H, CH3CH2-]; 6.42 [s,
1H, -CHNNH2]; 6.85 [br s, -CHNNH2]; δ(13C) ) 14.0 [s, CH3-
CH2-]; 59.8 [s, CH3CH2-]; 120.0 [s, -CHNNH2]; 163.0 [s, CH3-
3
CH2OC(O)-]. trans-isomer: δ(1H) ) 1.20 [t, J H-H ) 7 Hz, 3H,
3
CH3CH2-]; 4.2 [q, J H-H ) 7 Hz, 2H, CH3CH2-]; 7.0 [s, 1H,
Syn th esis of [Ru 2(µ-H)(CO)4{µ-NNCH2CO2Et}(µ-dppm )2]-
[BF 4]2, 5[BF 4]2. To a solution of 2 (35 mg, 0.03 mmol) in CD2-
Cl2 (0.5 mL) in a septum-sealed NMR tube was added HBF4‚
Et2O (10 µL, 0.07 mmol) by using a microsyringe. The solution
(16) Staudinger, H.; Hammet, L.; Siegwart, J . Helv. Chim. Acta
1921, 4, 228.

Synthesis of a Diruthenium Diazoalkane Complex
Organometallics, Vol. 20, No. 16, 2001 3509
-CHNNH2]; 7.05 [br s, -CHNNH2]; δ(13C) ) 23.0 [s, CH3CH2-];
60.8 [s, CH3CH2-]; 128.0 [s, -CHNNH2]; 169.0 [s, CH3CH2OC(O)-
].
Crystals of 3a , 3b, or 5 were grown by diffusion of pentane
(3a , 3b) or ether (5) into a solution of the complex in CH2Cl2.
Crystal data and refinement parameters are listed in Table
5. Data for 2, 3a , and 5 were collected using a Nonius Kappa-
CCD diffractometer using COLLECT (Nonius, 1998) software.
The unit cell parameters were calculated and refined from the
full data set. Crystal cell refinement and data reduction was
carried out using the Nonius DENZO package. The data were
scaled using SCALEPACK (Nonius, 1998). Data for 3b were
collected by using a Siemens P4 diffractometer with XSCANS
software. Refinement was carried out as above. The disordered
C and O atoms in 3a , 3b, and 5 were treated isotropically while
all other heavy atoms were anisotropic. For 3a , 3b, and 5 the
correct choice of absolute structure was confirmed by refine-
ment of the absolute structure factor (BASF ) 0.00 in each
case).
(b) Low -Tem p er a tu r e Stu d ies. A solution in CD2Cl2 was
prepared as above but at -10 °C, and intermediates were
identified by their NMR spectra as follows. [Ru2(CO)4(µ-
NNCH2CO2Et)(µ-dppm)2][HCOO], 4[HCOO], was the only
complex observed at -10 °C. NMR in CD2Cl2: δ(31P) ) 32.9
[m, dppm], 26.6 [m, dppm]; δ(1H) ) 8.1 [s, 1H, HCOO]; 4.5 [s,
3
2H, -CH2NN]; 4.2 [q, 2H, J H-H ) 7.3 Hz, -CH2CH3]; 3.9 [m,
3
2H, P-CH-P]; 3.6 [m, 2H, P-CH-P]; 1.2 [t, 3H, J H-H ) 7.32
Hz]. For a sample prepared from the reaction of HCOOH with
13CO-labeled 2: δ(13C) ) 210.9, 210.8, 194.6, 193.1 [m, terminal
CO]. At 6 °C, the known complex [Ru2(µ-H)(µ-CO)(CO)4(µ-
dppm)2][HCOO], 7[HCOO], was observed as a minor product
and identified by its NMR spectra.14 The major, but transient,
product was tentatively identified as complex 10 (ratio 10:9
) 3:1). NMR in CD2Cl2 at 6 °C: δ(31P) ) 25.8 [br m, dppm],
24.4 [br m, dppm]; δ(1H) ) 4.05 [m, 2H, P-CH-P]; 3.6 [m, 2H,
P-CH-P]; 2.6 [q, J H-H ) 7 Hz, 2H, -CH2CH3]; 0.6 [t, J H-H ) 7
Hz, 3H, -CH2CH3]. When the solution was warmed to 20 °C,
both complexes 10 and 9 disappeared in 20 min. Complexes
[Ru2(µ-H)(H)(µ-CO)(CO)2(µ-dppm)2], 8, and [Ru2(µ-CO)(CO)4-
(µ-dppm)2], 1, were observed in solution and free formic acid
was absent.
Ack n ow led gm en t. We thank the NSERC (Canada)
for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray data
in cif format. This material is available free of charge via the
Internet at http://pubs.acs.org.
X-r a y Str u ctu r e Deter m in a tion s. Crystals of 2 were
grown by slow evaporation of a saturated solution in toluene.
OM0102293