Unbridged homo and hetero dinuclear complexes of Group 6 and 8 metals: Synthesis, characterization and comparison of X-ray crystallographic data

Article abstract of DOI:10.1016/S0022-328X(00)00428-9

Several novel compounds of the type Cp/Cp*(CO)₃M-M′(CO)_nCp/Cp* (M = Cr, Mo, W; M′ = Ru, n = 2; M′ = Mo, n = 3; Cp = C₅H₅, Cp* = C₅Me₅) were synthesized, characterized, their structures compared and preliminary reactivity studies were carried out. The main investigations were focused on the molybdenum and ruthenium containing heterobimetallic compounds Cp(CO)₃Mo-Ru(CO)₂Cp (1) as well as Cp(CO)₃Mo-Ru(CO)₂Cp* (2) and Cp*(CO)₃Mo-Ru(CO)₂Cp (3), the latter two representing a 'mixed-metal mixed-ligand' type of complexes with the former (1) having identical ligands on both metal cores. For the first time comparison of properties of unbridged bimetallic complexes with molybdenum and ruthenium metal cores was elaborated. The novel Cp(CO)₃Mo-Mo(CO)₃Cp* (4) consists of two identical metal cores and of 'mixed' ligands. 4 was prepared by treating NaMo(CO)₃Cp with Cp*Mo(CO)₃Br (5) after a route for the synthesis of the latter was established. 1 reacted with halides or AlCl₃, respectively, under cleavage of the metal-metal bond to form Cp(CO)_nMHal (M = Mo, n = 3; M = Ru, n = 2; Hal = Br, I, Cl) but was shown to be inert towards substrates such as CO₂ CO, PPh₃ or CS₂ under the chosen conditions. The corresponding anionic species Cp(CO)_nM^- were obtained when 1 was reacted with alkali metal benzophenyl ketyl.

Full text of DOI:10.1016/S0022-328X(00)00428-9

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Journal of Organometallic Chemistry 612 (2000) 106–116
Unbridged homo and hetero dinuclear complexes of Group 6 and
8 metals: synthesis, characterization and comparison of X-ray
crystallographic data
Thomas Straub* 1, Matti Haukka, Tapani A. Pakkanen* 2
Department of Chemistry, Uni6ersity of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
Received 12 April 2000; accepted 27 June 2000
Abstract
Several novel compounds of the type Cp/Cp*(CO)3MꢀM%(CO)nCp/Cp* (M=Cr, Mo, W; M%=Ru, n=2; M%=Mo, n=3;
Cp=C5H5, Cp*=C5Me5) were synthesized, characterized, their structures compared and preliminary reactivity studies were
carried out. The main investigations were focused on the molybdenum and ruthenium containing heterobimetallic compounds
Cp(CO)3MoꢀRu(CO)2Cp (1) as well as Cp(CO)3MoꢀRu(CO)2Cp* (2) and Cp*(CO)3MoꢀRu(CO)2Cp (3), the latter two represent-
ing a ‘mixed-metal mixed-ligand’ type of complexes with the former (1) having identical ligands on both metal cores. For the first
time comparison of properties of unbridged bimetallic complexes with molybdenum and ruthenium metal cores was elaborated.
The novel Cp(CO)3MoꢀMo(CO)3Cp* (4) consists of two identical metal cores and of ‘mixed’ ligands. 4 was prepared by treating
NaMo(CO)3Cp with Cp*Mo(CO)3Br (5) after a route for the synthesis of the latter was established. 1 reacted with halides or
AlCl3, respectively, under cleavage of the metal–metal bond to form Cp(CO)nMHal (M=Mo, n=3; M=Ru, n=2; Hal=Br,
I, Cl) but was shown to be inert towards substrates such as CO2, CO, PPh3 or CS2 under the chosen conditions. The
corresponding anionic species Cp(CO)nM− were obtained when 1 was reacted with alkali metal benzophenyl ketyl. © 2000
Elsevier Science B.V. All rights reserved.
Keywords: Molybdenum; Ruthenium; Crystal structures; Hetero bimetallic complexes; Carbonyl compounds
and cobalt sulfide compounds supported on alumina
are the standard catalysts for the industrial application,
but there are extensive studies on the development of
mixed-metal clusters that can promote the hydrodesul-
furization, hydrogenation and other processes [3–5].
The major motivation is the expectation that co-opera-
tive effects between different metal atoms may promote
unique patterns of substrate activation. In this respect
clusters containing both molybdenum and ruthenium or
more general, Group 6 and 8 metals, are of special
interest due to their different properties, e.g. the ox-
ophilicity of the former and the hydrogen activation
ability of the latter. A wide range of molybdenum and
ruthenium containing clusters is known and their cata-
lytic activity is reported [3–12]. As poor to moderate
yields and a lack of comprehensive systematic methods
are a general drawback in cluster synthesis, we were
interested in developing a general route to prepare
simple heterobimetallic complexes of molybdenum and
1. Introduction
Dinuclear metal complexes may be considered as
cluster prototypes and may in their chemistry provide
insights to reactions that occur on metal surfaces. Cy-
clopentadienyl molybdenum complexes of this type
have been shown to be useful model systems for the
basic reactions occurring in hydrodesulfurization [1]
which is an important process in the refining of crude
oil [2]. Since crude oil with an increasing sulfur content
will be available in the future, there is particular interest
in the development of new, efficient catalysts and cata-
lyst precursors to remove the sulfur from organic com-
pounds such as thiophene and others. Molybdenum
1 *Corresponding author. Present address: Laboratory of Organic
Chemistry, Department of Chemical Technology, Helsinki University
of Technology, FIN-02015 TKK, Finland. Tel.: +358-9-4515938;
fax.: +358-9-4512538; e-mail: thomas.straub@hut.fi.
2 *Corresponding author e-mail: tapani: pakkanen@joensuu.fi.
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00428-9

T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
107
Na[M(CO)3Cp]+Ru(CO)2CpXTꢀHꢀFꢀ,ꢀDꢁ
ruthenium for the potential use as homogeneous and
heterogeneous catalysts in hydrodesulfurization reac-
tions. Furthermore they could be utilized as building
blocks in the synthesis of higher clusters. Several bridged
complexes of molybdenum and ruthenium are known
[13–16], but only few unbridged species comprising these
two metal centers have been described so far [17–20]. In
this paper we present the straightforward synthesis of
several novel unbridged heterobimetallic group 6-ruthe-
nium complexes with a simple ligation prepared by
metathetical reactions between NaM(CO)3Cp (M=Cr,
Mo, W) and halo-ruthenium precursors [21]. The synthe-
sis of the new homometallic ‘mixed-ligand’ complex
Cp(CO)3MoꢀMo(CO)3Cp* (4) and reactivity studies of
Cp(CO)3MoꢀRu(CO)2Cp (1) are reported and the struc-
tural similarities and differences between the mixed-
metal complexes Cp(CO)3MꢀRu(CO)2Cp (1, 6, 7;
M=Mo, Cr, W) and the mixed-metal mixed-ligand
Cp(CO)3MꢀRu(CO)2Cp+[Ru(CO)2Cp]2
M=Mo (1), Cr (6), W(7)
+[M(CO)3Cp]2
M=Cr, Mo, W
(1)
(2)
Tol, D
[Mo(CO)3Cp]2+[Ru(CO)2Cp]2ꢀꢀꢀꢁ
8
9
Cp(CO)3MꢀRu(CO)2Cp
1
2.2. Synthesis of Cp(CO)3MoꢀRu(CO)2Cp* (2),
Cp*(CO)3MoꢀRu(CO)2Cp (3),
Cp(CO)3MoꢀMo(CO)3Cp* (4) and Cp*(CO)3MoBr (5)
The mixed-ligand complexes 2, 3 and 4 were synthe-
sized by treating the sodium metallates with the appro-
priate bromide complex. It is noteworthy that the
reactions failed when the corresponding iodides were
used, a phenomenon that is also observed in the prepa-
ration of Cp(CO)2FeꢀFe(CO)2Cp* [23]. In all cases only
the formation of the corresponding homometallic dimers
bearing either Cp or Cp* was obtained exclusively. Given
this, a route for the synthesis of Cp*(CO)3MoBr (5) had
to be elaborated. Compound 5 is mentioned in the
literature to be formed from the bromomethyl metal
complex Cp*(CO)3MoCH2Br under reflux in methanol
[24], but no synthesis or analytical data were available
to date. While treatment of [Cp*Mo(CO)3]2 (13) with the
dihalogen I2 yields Cp*(CO)3Mol [25], 5 cannot be
obtained in a similar way due to further oxidation of the
possibly initially formed target compound even when 13
is used in excess [26,27]. The method of choice was a
modified reaction sequence used for the synthesis of
Cp(CO)3MoI [28]. At 0°C the carbonyl metallate
NaMo(CO)3Cp [29] was oxidized with Br2 to yield 5
quantitatively. At higher temperatures initially formed 5
reacts with the not yet consumed NaMo(CO)3Cp to form
the dimer 13 which is subsequently oxidized by Br2 under
multiple bromination.
complexes
Cp(CO)3MoꢀRu(CO)2Cp*
(2)
and
Cp*(CO)3MoꢀRu(CO)2Cp (3) are discussed in detail.
2. Results and discussion
2.1. Metathesis reaction of NaM(CO)3Cp (M=Cr,
Mo, W) with Ru(CO)2CpX (X=Br, I)
Reaction of the anion [Mo(CO)3Cp]− with
Ru(CO)2CpX in tetrahydrofuran (THF) leads to the
elimination of NaX and the formation of orange-red-
crystals which were identified as the heterobimetallic
complexes Cp(CO)3MꢀRu(CO)2Cp (M=Mo, Cr, W) (1,
6 and 7) by IR, NMR, elemental analysis and X-ray
spectroscopy. Further products formed in the reactions
are the homometallic dimers [CpRu(CO)2]2 (9) and the
corresponding [CpM(CO)3]2 (M=Cr, Mo, W) (Eq. (1)).
The yields in these reactions range from 2% for 6 with
the ruthenium iodide compound as the starting material
and 81% for Cp(CO)3MoꢀRu(CO)2Cp (1) when the
ruthenium bromide complex is used. Compound 1 is also
accessible by metal–metal bond metathesis between the
two homometallic dimers 8 and 9 (Eq. (2)) [13,22].
2.3. Preliminary reacti6ity studies of
Cp(CO)3MoꢀRu(CO)2Cp (1)
The reactivity of 1 was tested with several substrates
(Scheme 1) and the reactions monitored by IR spec-
troscopy. The reported products were not isolated. 1 is
stable under reflux in THF for 3 days and thermal
activation of the molecule did not lead to reaction with
PPh3 or CS2, respectively. In this context we tried
unsuccessfully to synthesize Cp(CO)3MoꢀRu(CO)3(h3-
C3H5) (14) with a supposedly higher potential for car-
bonyl replacement, but no complex bearing an allyl
ligand was accessible. Reaction of 1 with AlCl3 or

108
T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
Scheme 1. Reactivity of Cp(CO)3MoꢀRu(CO)2Cp (1).
solutions of Br2 or I2 in THF leads to a metal–metal
bond cleavage and to the expected formation of the
molybdenum and ruthenium halides. The correspond-
ing molybdates and ruthenates are obtained when 1 is
treated with THF solutions of Na(Ph2CO) or
K(Ph2CO) and no further reduction was detected upon
addition of excess Na(Ph2CO) or K(Ph2CO). Further-
more, no reaction was detected with carbon monoxide
or carbon dioxide.
2.4. X-ray crystallographic analysis
The molecular configurations of 1 and 2 are shown in
Figs. 1 and 2, and details of selected bond lengths and
Fig. 1. ORTEP plot of Cp(CO)3MoꢀRu(CO)2Cp (1) with ellipsoids drawn in 50% probability.
Fig. 2. ORTEP plot of Cp(CO)3MoꢀRu(CO)2Cp* (2) with ellipsoids drawn in 50% probability.

T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
109
Table 1
Crystallographic data for Cp(CO)3MoꢀRu(CO)2Cp (1), Cp(CO)3MoꢀRu(CO)2Cp* (2), Cp(CO)3CrꢀRu(CO)2Cp (6) and Cp(CO)3WꢀRu(CO)2Cp
(7)
1
2
6
7
Empirical formula
Molecular weight
Crystal size (mm)
Crystal system
C15H10MoO5Ru
467.24
0.20×0.20×0.05
Monoclinic
P21/n
C20H20MoO5Ru
537.37
0.30×0.30×0.20
Monoclinic
P21/n
C15H10CrO5Ru
423.30
0.50×0.20×0.10
Monoclinic
P21/c
C15H10O5RuW
555.15
0.30×0.30×0.10
Monoclinic
P21/c
Space group
,
u (A)
Unit cell dimensions
0.71073
0.71073
0.71073
0.71073
,
a (A)
8.3175(2)
11.1579(2)
16.3715(4)
102.540(1)
1483.13(6)
4
2.093
1.883
120(2)
9.6745(2)
26.4386(4)
15.7341(3)
100.8910(10)
3951.98(13)
8
1.806
1.426
120(2)
9.2976(3)
11.5439(2)
14.0692(4)
99.5310(10)
1489.21(7)
4
1.888
1.762
120(2)
9.5378(2)
11.5926(2)
14.1015(2)
101.700(1)
1526.78(5)
4
2.415
8.536
120(2)
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
v (mm−1
T (K)
)
q Range (°)
3.65–26.37
3019
2619
239
0.0221
1.53–27.46
8803
7287
497
0.0268
3.81–27.47
3210
2869
240
0.0238
3.81–25.00
2677
2630
199
0.0193
No. of unique reflections
No. of observed data a
No. of parameters
R1
wR2
0.0480
0.485 and −0.609
0.0506
0.432 and −0.546
0.0598
0.8435 and 0.4728
0.0487
1.200 and −1.089
−3
,
Largest difference peak and hole (e A
)
a I\2|.
angles for 1, 2, 6, 7 and 9 are given in Table 2. The
complexes 1, 6 and 7 consist of M(CO)3Cp (M=Mo,
Cr, W) and Ru(CO)2Cp fragments linked by an unsup-
ported RuꢀM bond. In 2 the Cp ligand is replaced by a
Cp* moiety, but otherwise the bonding situation is
similar to 1. 2 crystallizes in an asymmetric unit, but
one molecule can be neglected for the discussion. The
details are given in Section 5.
pounds [17,30–32]. The MꢀRu bond lengths of
,
2.9435(6) for 6 and 3.0101(3) A for 1 lie in the metal–
ruthenium single bond range. As expected, they are
,
0.04–0.05 A longer than the corresponding bonds in
,
their iron homologues where 2.901(1) and 2.963(1) A
are found for the FeꢀCr [30] bond and the FeꢀMo [31]
bond, respectively. Compound 1 displays a MoꢀRu
,
bond length 0.05 A longer than the corresponding one
in (h7-C7H7)(CO)2MoꢀRu(CO)2Cp [17], which is at-
tributed to higher number of carbonyl ligands. In 2 the
The five carbonyl ligands in 1, 2, 6 and 7 are all
terminal, reflected by M(1)ꢀM(2)ꢀCO angles not
smaller than 65° and MꢀCꢀO angles larger than 168.7°.
However, comparison of 1 and 2 shows that there is a
tendency towards smaller angles for the complex bear-
ing the Cp* ligand. In 2 the Mo(1)ꢀC(3)ꢀO(3) and
Mo(1)ꢀC(4)ꢀO(4) angles decrease by 2.5 and 3.5°, re-
spectively, while the Mo(1)ꢀC(5)ꢀO(5) and Ru(1)ꢀCꢀO
angles remain virtually unchanged. Since also the
MꢀMꢀC(1–5) angles decrease by a maximum of 4.5°
and the change is more pronounced for the molybde-
num fragment, one has to argue that this stronger
‘bending’ of the carbonyl ligands towards the other
metal fragment is a result of the new electronic situa-
tion with a higher electron density rather than of
change in steric requirements which should have the
opposite effect. The Cp/Cp or Cp/Cp* ligands of all the
novel complexes adopt a centric coordination to the
metals and are found in trans position relative to the
MꢀRu vector. Furthermore the Cp and Cp* moieties
exhibit structural properties known from related com-
,
metal–metal bond is determined to be 3.0424(3) A,
constituting an elongation of the MoꢀRu in compari-
son to 1. Similar observations are made for bimetallic
complexes when Cp is replaced by Cp* [32,33]. The
M(CO)3Cp fragments essentially adopt a piano-stool
geometry and a mirror plane through both metal cores
and the Cp or Cp* centroids is inherent in the com-
plexes. While 2 is almost perfect in plane, the other
compounds are also only slightly distorted from it.
2.5. Spectroscopic results
The pattern of the IR absorptions for 1, 6 and 7
compares with that of the corresponding iron homo-
logues [22,31] suggesting a similar structure. The most
significant feature in the IR spectra is the absence of
bands that indicate bridging carbonyl ligands, suggest-
ing an all-terminal carbonyl structure featuring an un-
bridged metal–metal bond (Table 3).

110
T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
the three-absorption pattern is basically retained. The
In contrast to the iron homologues, for the ruthe-
only chemical difference between 1, 2 and 3 is the
change of a Cp to a Cp* and the position of this ligand
in the molecule. So, one can reason that the relatively
large steric requirements of the Cp* in conjunction with
the metal carbonyl fragment to which it is bound to
may prevent rotation around the metal–metal bond.
Consequently one can argue that the sterically more
demanding Mo(CO)3Cp* fragment in 3 promotes the
trans form that is also found in the solid state, while in
2 with the smaller Ru(CO)2Cp* moiety the formation
of conformers is still possible [17]. The IR spectra of
Cp(CO)3MoꢀMo(CO)3Cp* (4) compares nicely with the
spectra of Cp(CO)3MoꢀMo(CO)3Cp (8) and Cp*(CO)3-
MoꢀMo(CO)3Cp* (13), retaining the basic absorption
pattern invoked by the same structural family of com-
plexes and approximately averaging out the wave num-
bers reflecting the new electronic situation.
nium complexes additional weak absorptions are ob-
served that add up to more bands than carbonyl
ligands. For the five carbonyl groups of 1 up to seven
IR-bands are detected depending on the solvent. There-
fore the presence of isomers has to be assumed [22].
Besides the main trans-isomer, cis or anti and gauche
[34] conformers might be formulated. However, there is
no indication of isomeric forms comprising bridging
carbonyl ligands. The ‘mixed-metal mixed-ligand’ com-
pounds 2 and 3 show surprisingly different IR spectra
(Fig. 3).
Compared with 1, the bands of 2 and 3 show a red
shift, which reflects a higher electron density around the
metals [35]. While with basically three bands the IR
patterns for both compounds in THF are essentially the
same, the situation changes in hexane. For 2 the pattern
is almost identical with that for complex 1 while for 3
Table 2
,
Selected bond distances (A) and bond angles (°) for Cp(CO)3MoꢀRu(CO)2Cp (1), Cp(CO)3MoꢀRu(CO)2Cp* (2) Cp(CO)3CrꢀRu(CO)2Cp (6),
Cp(CO)3WꢀRu(CO)2Cp (7) and Cp(CO)2RuꢀRu(CO)2Cp (9) a
1
2
6
7
9
Ru(1)ꢀM(1)
Ru(1)ꢀC(1)
Ru(1)ꢀC(2)
Ru(1)cꢀC(2)
Ru(1)ꢀC(6)
Ru(1)ꢀC(7)
Ru(1)ꢀC(8)
Ru(1)ꢀC(9)
Ru(1)ꢀC(10)
M(1)ꢀC(3)
M(1)ꢀC(4)
M(1)ꢀC(5)
M(1)ꢀC(11)
M(1)ꢀC(12)
M(1)ꢀC(13)
M(1)ꢀC(14)
M(1)ꢀC(15)
3.0101(3)
1.871(3)
1.869(3)
3.0424(3)
1.874(3)
1.863(3)
2.9435(6)
1.874(3)
1.876(3)
2.9974(3)
1.865(4)
1.866(4)
2.7412(4)
1.862(3)
2.037(3)
2.040(3)
2.280(3)
2.297(3)
2.257(3)
2.234(2)
2.280(3)
2.254(3)
2.227(3)
2.233(3)
2.253(3)
2.269(3)
1.968(3)
1.980(3)
1.960(3)
2.347(3)
2.398(3)
2.356(3)
2.312(3)
2.320(3)
2.270(2)
2.299(2)
2.270(2)
2.230(3)
2.235(2)
1.973(3)
1.970(3)
1.944(3)
2.394(3)
2.361(3)
2.314(3)
2.325(3)
2.369(3)
2.256(3)
2.230(3)
2.232(3)
2.255(3)
2.279(3)
1.852(3)
1.831(3)
1.854(3)
2.241(3)
2.211(3)
2.172(3)
2.177(3)
2.218(3)
2.262(4)
2.237(4)
2.244(4)
2.265(4)
2.283(4)
1.968(4)
1.977(4)
1.963(4)
2.314(4)
2.363(4)
2.397(4)
2.362(4)
2.317(4)
Ru(1)ꢀC(1)ꢀO(1)
Ru(1)ꢀC(2)ꢀO(2)
Ru(1)cꢀC(2)ꢀO(2)
M(1)ꢀC(3)ꢀO(3)
M(1)ꢀC(4)ꢀO(4)
M(1)ꢀC(5)ꢀO(5)
Ru(1)ꢀM(1)ꢀC(3)
Ru(1)ꢀM(1)ꢀC(4)
Ru(1)ꢀM(1)ꢀC(5)
M(1)ꢀRu(1)ꢀC(1)
M(1)ꢀRu(1)ꢀC(2)
M(1)ꢀRu(1)ꢀC(2)c
C(1)ꢀRu(1)ꢀMo(1)ꢀC(3)
C(1)ꢀRu(1)ꢀMo(1)ꢀC(4)
C(1)ꢀRu(1)ꢀMo(1)ꢀC(5)
C(2)ꢀRu(1)ꢀMo(1)ꢀC(3)
C(2)ꢀRu(1)ꢀMo(1)ꢀC(4)
C(2)ꢀRu(1)ꢀMo(1)ꢀC(5)
175.8(2)
175.0(3)
176.6(2)
174.8(3)
178.7(2)
176.6(2)
176.8(3)
178.4(4)
178.8(2)
138.2(2)
137.3(2)
172.9(2)
172.2(2)
179.1(3)
70.36(8)
68.63(8)
126.58(8)
82.82(8)
85.94(8)
170.4(2)
168.7(2)
178.0(2)
68.67(8)
65.37(8)
122.09(8)
79.39(8)
84.82(9)
170.5(2)
172.1(2)
179.3(3)
65.01(8)
69.04(8)
119.72(9)
84.15(8)
84.06(7)
173.5(3)
173.9(3)
179.0(3)
70.36(8)
68.63(8)
126.58(8)
82.82(8)
85.94(8)
93.09(8)
47.79(7)
47.71(7)
72.61(11)
−173.05(11)
130.81(12)
165.34(11)
−80.32(12)
−136.46(13)
71.59(11)
−164.25(12)
134.28(12)
163.30(12)
−72.54(12)
−134.01(13)
68.05(12)
−163.16(11)
130.21(12)
159.25(12)
−71.96(12)
−138.59(12)
77.36(17)
−162.36(17)
138.37(18)
169.28(16)
−70.44(17)
−129.71(18)
a M=Cr, Mo, W, Ru.

T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
111
Table 3
For none of the compounds signals indicating isomers
were observed, which excludes an intermetallic Cp/Cp*
exchange. Due to the tendency of 6 to homolytic cleav-
age of the metal–metal bond and formation of the
homometallic dimers and Cp(CO)3Cr· [36] it proofed
impossible to obtain a pure analytical sample or a
satisfying NMR of the complex. Due to the presence of
small concentrations of the paramagnetic Cp(CO)3Cr·
usually no signal could be detected in the NMR spec-
tra, with only one exception, where 6 was contaminated
with minor amounts of [CpRu(CO)2]2 (9).
In the carbon NMR spectra, the most prominent
common feature for all the mixed metal complexes as
well as the homometallic mixed-ligand complex 4 is the
single resonance for the carbonyl groups at room tem-
perature which indicates a facile and rapid interchange
of all the carbonyl groups of the molecule in and
between the two metal moieties in solution. The pro-
posed structures are confirmed by the observed addi-
tional resonances. Two doublets around 90 ppm,
characteristic for Cp ligands, are detected for 1 and 7.
The carbon NMR spectra of the mixed-ligand com-
plexes 2, 3 and 4 exhibit a doublet in the same region
for the Cp and a quartet for the methyl groups as well
as a singlet for the quaternary carbon of the Cp*
ligand.
IR data a
Complex
w(CO) (cm−1
)
1
2020 (vw), 2008 (vw), 1965 (vs), 1953 (vs), 1921 (vw),
1902 (w), 1888 (m) b
2022 (vw), 2007 (vw), 1963 (vs), 1953 (vs), 1919 (vw),
1900 (w), 1887 (m) c
2015 (vw), 2004 (vw), 1954 (vs), 1912 (vw), 1877 (m,
br) d
2017 (vw), 2004 (vw), 1955 (vs), 1948 (vs), 1912 (vw),
1890 (sh), 1876 (m) e
2012 (sh), 2007 (vw), 1954 (vs), 1875 (m, br) f
1996 (vw), 1950 (vs), 1944 (vs), 1913 (vw), 1885 (vw),
1870 (w) b
2
1993 (vw), 1940 (vs), 1862 (m, br) d
2000 (vw), 1947 (vs), 1909 (vw), 1880 (m) b
1995 (vw), 1940 (vs), 1869 (m, br) d
1951 (vs), 1913 (s), 1897 (w) b
3
4
2003 (vw), 1945 (vs), 1907 (s), 1889 (m) d
2039 (s), 1967 (vs), 1940 (s) d
5
6
2024 (vw), 2012 (w), 1962 (vs), 1950 (vs), 1912 (vw),
1890 (w), 1877 (m) b
7
2020 (vw), 2006 (vw), 1963 (vs), 1951 (s), 1913 (vw),
1896 (w), 1883 (m) b
8
13
2011 (w), 1956 (vs), 1912 (s) d
1932 (vs), 1989 (m, br) d
a w=weak, vw=very weak, m=medium, s=strong, vs=very
strong, sh=shoulder, br=broad.
b In hexane.
c In cyclohexane.
d In THF.
e In toluene.
3. Conclusions
f In CH2Cl2.
We have successfully demonstrated that the metathe-
sis reaction between NaM(CO)3Cp/Cp* (M=Cr,
Mo, W) with Ru(CO)2Cp/Cp*X (X=Br, I) or
Mo(CO)3Cp*Br is a powerful tool for the synthesis of
unbridged homobimetallic and heterobimetallic com-
plexes of Group 6 metals and ruthenium. For the
molybdenum–ruthenium complexes ligand variation
was feasible, giving rise to the complexes 1, 2 and 3
which reveal intriguing structural similarities and differ-
ences. For the first time comparison of properties of
unbridged bimetallic complexes with molybdenum and
ruthenium metal cores was elaborated. Preliminary re-
activity studies on 1 reveal that carbonyl displacement
is not favored and that reactions occur under cleavage
of the metal–metal bond. Further investigations con-
cerning reactivity and catalytic activity of molybde-
num–ruthenium compounds are underway.
The proton NMR spectra of 1, 6 and 7 show two
signals in a 1:1 ratio for the Cp ligands. An unambigu-
ous assignment to the metal centers is possible by
comparing the chemical shifts to related compounds
[17,22] and the complexes 2 and 3. The latter two
exhibit two signals of an intensity of 3:1 which reflect a
Cp* and a Cp ligand, respectively. A comparison of the
proton NMR data of the molybdenum and/or ruthe-
nium containing complexes 1–4, 8, 9 and 13 reveals the
trend to a relative high field shift for the ruthenium
fragments, whereas molybdenum moieties are shifted to
lower field in the mixed metal complexes. This is in
agreement with the finding that in heterobimetallic
complexes a metal fragment usually shows a high field
shift when the introduced other metal fragment bears
carbonyl ligands exclusively and that the opposite effect
is observed for the introduction of fragments with a Cp
ligand [22]. In the mixed metal complexes reported in
this paper the relative number of carbonyl ligands in
Mo(CO)3Cp/Cp* and Ru(CO)2Cp/Cp* is arguably re-
sponsible for the observed trend. The nature of the
Cp/Cp* ligand does not contribute to it significantly, as
derived from the proton NMR data of 4, where the
shift of the two signals is only −0.02 ppm and +0.02
ppm relative to the corresponding complexes 8 and 13.
4. Experimental
4.1. Materials and methods
All manipulations of air-sensitive materials were per-
formed under a nitrogen atmosphere in conventional
Schlenk apparatus. Solvents were distilled from Na/K

112
T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
or Na benzophenyl ketyl under nitrogen. Hexane for
column chromatography was deoxygenated but other-
wise used as received. Deuterated solvents were deoxy-
genated (three freeze–pump–thaw cycles) and stored
under nitrogen over molecular sieves. Cyclopentadienyl
sodium, pentamethyl-cyclopentadienyl sodium, allyl
bromide, M(CO)6 (M=Cr, Mo, W), [Mo(CO)3Cp]2 (8)
(all purchased from Aldrich) and [Ru(CO)3Cl2]2 (John-
son and Matthey) were used as received. Silica gel 60
(0.063–0.200 mm, Merck) for column chromatography
was kept under HV for 5 h and saturated with nitrogen
before use. Column properties: 2×20 cm (if not stated
otherwise), mobile phase at start: hexane. Volume of
reaction mixtures loaded onto the column: max. 2 ml in
THF.
1H- and 13C-NMR are referenced to internal solvent
resonances and are reported relative to tetramethylsi-
lane (l=7.15 ppm and 127 ppm, respectively, for
C6D6). Elemental analysis were performed with an
EA1110 CHNSꢀO analyzer (Carlo Erba instruments).
4.2. Cp(CO)3MoꢀRu(CO)2Cp (1)
At room temperature (r.t.), a solution of 604 mg (2.0
mmol) CpRu(CO)2Br in 20 ml THF was added drop-
wise to 536 mg (2.0 mmol) NaMo(CO)3Cp in 20 ml
THF. After 6 h of refluxing the reaction was termi-
nated, the mixture concentrated and separated into its
components. Fraction 1 (eluent: hexane–THF 25:1):
563 mg (1.2 mmol, 60%) orange needles of
Cp(CO)3MoꢀRu(CO)2Cp (1) (from hexane at −25°C,
NaM(CO)3Cp (M=Cr, Mo, W) [29], NaMo(CO)3-
Cp* [29], CpMo(CO)3] [37], [CpRu(CO)2]2 (9) [37],
[Cp*Ru(CO)2]2 (10) [38], CpRu(CO)2X (X=Br, I) [39],
Cp*Ru(CO)2X (X=Br, I) [25] and (h3-C3H5)Ru-
(CO)3Br (11) [40] were prepared according to methods
reported in the literature.
1
crystals suitable for X-ray crystallography). H-NMR
(ppm): 4.84 (s, 5H, MoCp), 4.57 (s, 5H, RuCp). 13C-
1
NMR (ppm): 219.5 (s, CO), 89.7 (d, JCH=177 Hz,
1
MoCp), 87.5 (d, JCH=177 Hz, RuCp). Anal. Calc. for
Infrared spectra were measured on a Nicolet Magna
705 FTIR spectrometer in hexane or THF solution,
C15H10O5MoRu (FW=467.25): C, 38.56; H, 2.16.
Found: C, 38.94; H, 2.15%. Fraction 2 (hexane–THF
10:1): 190 mg (0.4 mmol, 21%) (1), after crystallization
from small amounts of [CpRu(CO)2]2 (9) (hexane,
−25°C). Fraction 3 (THF): traces of CpRu(CO)2Br, (1),
1
respectively. H- and 13C-NMR spectra were recorded
on a Bruker Avance 250 MHz spectrometer using C6D6
(if not stated otherwise) as solvent. Chemical shifts for
Fig. 3. IR-spectra of Cp(CO)3MoꢀRu(CO)2Cp* (2): (a) in THF; (b) in hexane and of Cp*(CO)3MoꢀRu(CO)2Cp (3); (c) in THF; (d) in hexane.

T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
113
[CpMo(CO)3]2 (8), discarded. When Cp(CO)2RuI was
used instead of CpRu(CO)2Br the reaction time in-
creased (up to 4 days), the yield decreased (max. 67%),
and the reaction did not go to completion. 1 was also
isolated in 15% yield from the thermal reaction of
[CpMo(CO)3]2 (8) and [CpRu(CO)2]2 (9) in toluene.
dark red crystals of Cp(CO)3MoꢀMo(CO)3Cp* (4)
1
(from hexane–THF at −25°C). H-NMR (ppm): 4.68
(s, 5H, Cp), 1.73 s, 15H, Cp*). 13C-NMR (ppm): 231.7
1
(s, CO), 104.7 (s, Cp*), 90.6 (d, JCH=178 Hz, Cp), 9.7
1
(q, JCH=128 Hz, Cp*). Anal. Calc. for C21H20O6Mo2
(FW=560.26): C, 45.02; H, 3.60. Found: C, 45.22; H,
3.68%. Fraction 2 (hexane–THF 10:1): [CpMo(CO)3]2
(8).
4.3. Cp(CO)3MoꢀRu(CO)2Cp* (2)
Interestingly, only [CpMo(CO)3]2 (8), [Cp*Mo(CO)3]2
(13) and the halides CpMo(CO)3I and Cp*Mo(CO)3I
were isolated when CpMo(CO)3I was used as a starting
material. At −78°C, 744 mg (2.0 mmol) of Cp-
Mo(CO)3I in 20 ml THF were added to a solution of
676 mg (2.0 mmol) NaMo(CO)3Cp* in 20 ml THF.
NaMo(CO)3Cp and Cp*Mo(CO)3I were formed spon-
taneously. It was allowed to warm to r.t., refluxed for 2
days and stirred under CO atmosphere for 16 h.
Column chromatography lead to the pure compounds
8, 13, CpMo(CO)3I and Mo(CO3)Cp*I. Spectroscopic
data of Mo(CO3)Cp*I: IR (hexane) (cm−1): 2030 (vs),
As described above, a solution of 372 mg (1.0 mmol)
Cp*Ru(CO)2Br in 20 ml THF was added dropwise to
532 mg (2.0 mmol) NaMo(CO)3Cp in 20 ml THF.
After 8 days of refluxing the Cp*Ru(CO)2Br is con-
sumed. The mixture was concentrated and separated
into its components. Fraction 1 (hexane–THF 25:1,
followed by extraction with hexane): 168 mg (0.31
mmol, 31%) orange crystals of Cp(CO)3Moꢀ
Ru(CO)2Cp* (2) (from hexane at +5°C, crystals suit-
1
able for X-ray crystallography). H-NMR (ppm): 4.91
(s, 5H, Cp), 1.62 s, 15H, Cp*). 13C-NMR (ppm): 221.7
1
1
(s, CO), 99.3 (s, Cp*), 89.7 (d, JCH=176 Hz, Cp), 8.9
1962 (vs), 1939 (s). H-NMR (ppm): 1.58 (s). 13C-NMR
(q, 1JCH=128 Hz, Cp*). Anal. Calc. for
C20H20O5MoRu (FW=537.38): C, 44.70; H, 3.75.
Found: C, 44.70; H, 3.78%. No further fractions were
collected.
(ppm): 241.3 (s, CO trans), 223.6 (s, CO cis), 106.2
1
(Cp*), 9.9 (q, JCH=128 Hz, Cp*).
4.6. Mo(CO)3Cp*Br (5)
4.4. Cp*(CO)3MoꢀRu(CO)2Cp (3)
At 0°C, 676 mg (2.0 mmol) of NaMo(CO)3Cp* in 20
ml THF are treated with a solution of bromine in THF.
The reaction is monitored by IR and terminated after
all the starting material is consumed. The reaction
mixture is filtered, concentrated and the product
purified by column chromatography. 5 is eluted as a red
band with THF. 650 mg (1.65 mmol, 83%) orange–red
crystals. 1H-NMR (ppm): 1.46 (s). 13C-NMR (ppm):
244.3 (s, CO trans), 225.2 (s, CO cis), 106.9 (Cp*), 9.4
(q, 1JCH=128 Hz, Cp*). Anal. Calc. for
C13H15BrO3Mo (FW=395.10): C, 39.52; H, 3.83.
Found: C, 39.66; H, 3.84%. For further reactions with
metal organyls 5 was usually used in situ without
further purification.
As described above, a solution of 967 mg (3.2 mmol)
CpRu(CO)2Br in 20 ml THF was added dropwise to
1082 mg (3.2 mmol) NaMo(CO)3Cp* in 20 ml THF.
After 2 h of stirring at r.t. and another 2 h reflux, the
reaction was complete. The mixture was stirred over
night under
a
CO atmosphere (conversion of
[Cp*Mo(CO)2]2 (12) to [Cp*Mo(CO)3]2 (13) and there-
fore easier purification of the desired product), then
concentrated and separated into its components. Frac-
tion 1 (hexane–THF 25:1): 705 mg (1.3 mmol, 41%)
red–orange needles of Cp*(CO)3MoꢀRu(CO)2Cp (3)
1
(from hexane at −25°C). H-NMR (ppm): 4.61 (s, 5H,
Cp), 1.84 s, 15H, Cp*). 13C-NMR (ppm): 224.0 (s, CO),
103.2 (s, Cp*), 87.6 (d, 1JCH=179 Hz, Cp), 9.9 (q,
1JCH=128 Hz, Cp*). Anal. Calc. for C20H20O5MoRu
(FW=537.38): C, 44.70; H, 3.75. Found: C, 44.83; H,
3.81%. Fraction 2 (hexane–THF 10:1): 228 mg (0.57
mmol, 18%) (5). No further fractions were collected.
4.7. Cp(CO)3CrꢀRu(CO)2Cp (6)
A solution of 604 mg (2.0 mmol) CpRu(CO)2Br in 15
ml THF was added dropwise to 448 mg (2.0 mmol)
NaCr(CO)3Cp in 15 ml THF. It was refluxed for 48 h
and worked up as described above. In addition several
crystallizations were performed. Fraction 1 (hexane–
4.5. Cp(CO)3MoꢀMo(CO)3Cp* (4)
THF
10:1):
yield
ꢀ1%,
red
crystals
of
At −78°C, a solution of 780 mg (2.0 mmol)
Cp*Mo(CO)3Br (5) in 20 ml THF was added dropwise
to 536 mg (2.0 mmol) NaMo(CO)3Cp in 20 ml THF.
The reaction mixture is allowed to warm to r.t. and
stirred for 8 h. After 1 h of refluxing the mixture was
concentrated and separated into its components. Frac-
tion 1 (hexane–THF 50:1): 482 mg (0.86 mmol, 43%)
Cp(CO)3CrꢀRu(CO)2Cp (6) (from hexane at −25°C,
1
crystals suitable for X-ray crystallography). H-NMR
(ppm): 4.51 (s, 5H, Cp), 4.40 s, 5H, Cp). 13C-NMR
1
(ppm): 227.7 (s, CO), 87.6 (d, JCH=180 Hz, Cp), 86.6
1
(d, JCH=177 Hz, Cp). Anal. Calc. for C15H10O5CrRu
(FW=423.30): C, 38.56; H, 2.16%. No further fraction
is collected.

114
T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
4.11. Reacti6ity studies of Cp(CO)3MoꢀRu(CO)2Cp (1)
4.8. Cp(CO)3WꢀRu(CO)2Cp (7)
4.11.1. PPh3
As described above, 523 mg (1.5 mmol) CpRu(CO)2I
in 8 ml THF were reacted with 534 mg (1.5 mmol)
NaW(CO)3Cp in 15 ml THF and kept under reflux for
7 days before standard workup. Fraction 1 (hexane–
THF 10:1): mixture of Cp(CO)3WH, Cp(CO)3Wꢀ
Ru(CO)2Cp (7) and Cp(CO)3WꢀW(CO)3Cp. After re-
moving the solvent the red residue is extracted with
cold hexane (2×10 ml) and the combined yellow hex-
ane solutions are freed from the solvent at high vacuum
to yield 16 mg (0.05 mmol, 3%) Cp(CO)3WH (FW=
333.97) as a yellow solid. Fractionized crystallization of
the red residue from hexane–THF (10:1) at −40°C
yields 207 mg (0.37 mmol, 25%) Cp(CO)3Wꢀ
Ru(CO)2Cp (7) as red–orange crystals. Crystals suit-
able for X-ray crystallography were obtained by recrys-
tallization of 7 from hexane at −40°C. 1H-NMR
(ppm): 4.81 (s, 5H, WCp), 4.64 s, 5H, MoCp). 13C-
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) and 52 mg (0.2 mmol) PPh3 in 15 ml
THF was stirred for 28 days and then refluxed for 1400
min (24 h). There was no change in the IR spectra.
4.11.2. CS2
A solution of 185 mg (0.4 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) and 31 mg CS2 (0.4 mmol) PPh3 in 20
ml THF was refluxed for 7 days and no change in the
IR spectra was detected.
4.11.3. CO2
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 15 ml hexane was stirred under
CO2-atmosphere at r.t. for 3 days and no reaction
could be detected.
1
NMR (ppm): 212.1 (s, CO), 88.1 (d, JCH=179 Hz,
1
4.11.4. CO
WCp), 87.6 (d, JCH=180 Hz, RuCp). Anal. Calc. for
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 15 ml hexane was stirred under
CO-atmosphere at r.t. for 3 days and no reaction could
be detected.
C15H10O5WRu (FW=555.15): C, 32.45; H, 1.82.
Found: C, 33.33; H, 1.91%. The second compound
obtained by the fractionised crystallization from hex-
ane–THF, a red solid, is identified as 110 mg (0.17
mmol, 22%) Cp(CO)3WꢀW(CO)3Cp (FW=665.93).
Fraction 2 (hexane–THF 10:1): 88 mg (0.20 mmol,
27%) [Ru(CO)2Cp]2 (9) (FW: 444.4), yellow–orange
solid. Fraction 3 (THF): 162 mg (0.46 mmol, 31%)
CpRu(CO)2I.
4.11.5. Na(Ph2CO)
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 10 ml THF was stirred vigorously
and titrated with a deep blue solution of Na(Ph2CO) in
THF. The quantitative formation of Na[MoCp(CO)3]
(a) and Na[Ru(CO)2Cp] (b) was detected. IR (THF)
(cm−1): 1901 (vs, a, b), 1823 (m, b), 1796 (s, a), 1747 (s,
a). Upon addition of more Na(Ph2CO) no further
change of the IR spectra was observed.
4.9. [CpRu(CO)2]2 (9)
Yellow rhombs of 9 suitable for X-ray crystallogra-
phy were obtained from crystallization from hexane at
−25°C.
4.11.6. K(Ph2CO)
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 10 ml THF was vigorously stirred
and titrated with a deep blue solution of K(Ph2CO) in
THF. The quantitative formation of K[MoCp(CO)3] (a)
and K[Ru(CO)2Cp] (b) was detected. IR (THF) (cm−1):
1898 (vs, a, b), 1811 (m, b), 1790 (s, a), 1750 (s, a).
Upon addition of more K(Ph2CO) no further change of
the IR spectra was observed.
4.10. Attempted synthesis of
Cp(CO)3MoꢀRu(CO)3(p3-C3H5) (14)
At r.t.,
a
solution of 134 mg (0.5 mmol)
NaMo(CO)3Cp in 5 ml THF, was added dropwise to a
suspension of 177 mg (0.5 mmol) of (h3-
C3H5)ꢀRu(CO)2I in 15 ml THF. The iodide seems to be
consumed already after 5 min. The resulting dark red,
clear solution was stirred for another 2 days and dark-
ens during the course of the reaction. Column chro-
matography yielded the four fractions of [CpMo(CO)3]2
(8), [CpRu(CO)2]2 (9), CpMo(CO)3I, CpRu(CO)2I, re-
spectively. Change of parameters (temperature, use of
(h3-C3H5)ꢀRu(CO)2Br, reaction time) did not give rise
to the desired product 14.
4.11.7. Br2
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 20 ml THF is titrated with a solution
of Br2 in THF until the formation of CpRu(CO)2Br (a)
and CpMo(CO)3Br (b) is complete (IR control). IR
(hexane) (cm−1): 2054 (vs, a, b), 2009 (s, a), 1984 (vs,
b), 1963 (m, b). IR (THF) (cm−1): 2047 (s, a, b), 1993
(s, a), 1969 (vs, b).

T. Straub et al. / Journal of Organometallic Chemistry 612 (2000) 106–116
115
4.11.8. I2
A solution of 94 mg (0.2 mmol) of Cp(CO)3Moꢀ
Ru(CO)2Cp (1) in 20 ml THF is titrated with a solution
of I2 in THF until quantitative formation of
CpRu(CO)2I (a) and CpMo(CO)3I (b). IR (THF)
(cm−1): 2040 (s, a, b), 1991 (s, a), 1963 (vs, b).
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 142814 for 1, 142816 for 2, 142815
for 6, 142813 for 7, 142817 for 9. Copies of this
information may be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
4.11.9. AlCl3
Freshly sublimed AlCl3, 533 mg (0.4 mmol), were
added to a solution of 94 mg (0.2 mmol) of Cp(CO)3-
MoꢀRu(CO)2Cp (1) in 20 ml THF and refluxed for 24
h. CpRu(CO)2Cl (a) and CpMo(CO)3Cl (b) were
formed quantitatively with some decomposition of the
latter. IR (THF) (cm−1): 2047 (s, a, b), 1994 (vs, a),
1952 (m, b).
Acknowledgements
Funding of this project by the European Union
under the TMR Programme, contract ERBFM-
RXCT960091, is gratefully acknowledged.
4.12. X-ray crystallography
References
Single crystals of the air sensitive compounds were
measured in perfluoro polyether RS 3000 (Riedel-de
Hae¨n). X-ray diffraction data were collected at 120 K
with a Nonius Kappa CCD diffractometer using Mo–
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,
Ka radiation (u=0.71073 A) and ƒ-scan data collec-
tion mode with a COLLECT [41] collection program.
DENZO and SCALEPACK [42] programs were used for
cell refinements and data reduction. All structures were
solved by direct methods using SHELXS-97 [43] or SIR-97
[44] programs with the WINGX [45] graphical user inter-
face. A semi-empirical multi-scan absorption correc-
tion, based on equivalent reflections (XPREP in SHELXTL
version 5.1) [46] was applied to Cp(CO)3WꢀRu(CO)2Cp
(7) (Tmax/Tmin=0.4823/0.1839). All structure refine-
ments were carried out with the SHELXL-97 program
[47]. All non-hydrogen atoms were refined anisotropi-
cally. For compounds Cp(CO)3MoꢀRu(CO)2Cp* (2)
and Cp(CO)3WꢀRu(CO)2Cp (7) the hydrogens were
,
constrained to ride on their parent atom (CꢀH=0.95 A
[7] M. Cazanoue, L. Noe¨l, J.J. Bonnet, R. Mathieu, Organometal-
lics 7 (1988) 2480.
and Uiso=1.2 (Ceq) for aromatic hydrogens and
,
CꢀH=0.98 A and Uiso=1.5 (Ceq) for methyl hydro-
[8] (a) D.-K. Hwang, Y.B. Chi, S.-M. Peng, G.-H. Lee
Organometallics 9 (1990) 2709. (b) D.-K. Hwang, Y.B. Chi,
S.-M. Peng, G.-H. Lee J. Organomet. Chem. 389 (1990) C7.
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and Cp(CO)3CrꢀRu(CO)2Cp (6) hydrogens were lo-
cated from the difference Fourier map and refined
isotropically. Although the crystal structure of com-
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contrast to r.t. in Ref. [48b]). The crystallographic
details are available as supporting material and selected
bond lengths and angles are given in Table 2 for ease of
comparison. Crystallographic data of 1, 2, 6 and 7 are
summarized in Table 1 and selected bond lengths and
angles are given in Table 2. The structures and the
numbering schemes for complexes Cp(CO)3Moꢀ
Ru(CO)2Cp (1) and Cp(CO)3MoꢀRu(CO)2Cp* (2) are
presented in Figs. 1 and 2.

116
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