Stepwise Assembly of Mixed Metal Dinuclear Carbonyl Complexes

Article abstract of DOI:10.1002/ejic.200300272

The one-pot/three-step solution synthesis of a library of nine directional, dinuclear mixed-metal complexes composed of different metal-carbonyl units (M = Cr, Mo, W) and a bifunctional bridging isocyanide Schiff-base ligand is described. The well-defined

Full text of DOI:10.1002/ejic.200300272

FULL PAPER
Stepwise Assembly of Mixed Metal Dinuclear Carbonyl Complexes
Katja Heinze*[a] and Volker Jacob[a]
Keywords: Heterometallic complexes / Isocyanide ligands / Bridging ligands / Isomers / Group 6 elements
The one-pot/three-step solution synthesis of a library of nine
directional, dinuclear mixed-metal complexes composed of
different metal-carbonyl units (M = Cr, Mo, W) and a bifunc-
Cr, Mo, and W in two positions can be determined post-syn-
thesis by a combination of spectroscopic methods.
tional bridging isocyanide Schiff-base ligand is described. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
The well-defined metal sequence in these complexes with
Germany, 2003)
Introduction
oligonuclear rutheniumϪpyrazine complexes.[15] Sequential
protection/deprotection of a potential coordination site of
a coordinated ligand has allowed a step-by-step synthesis
of oligonuclear ruthenium and osmium polypyridine com-
plexes.[16] Redox activation has been used to construct olig-
One-dimensional materials are interesting with respect to
their exceptional physical and chemical,[1Ϫ3] such as photo-
physical or electrochemical properties.[4] However, the syn-
thesis of metal-containing chain complexes with defined
chain lengths is difficult to achieve. An elegant approach to
overcome the problem of obtaining mixtures of complexes
with different chain lengths is the design and synthesis of
special ligands which allow for only one definite chain
length. This approach has been used, for example, in the
synthesis of oligo-α-pyridylamino ligands which form string
complexes with two, three, four, five, and seven metal
centres depending on the length of the ligand.[5Ϫ8] The
problem is thus transferred to organic synthesis of the li-
gand while metal incorporation is subject to self-organis-
ation processes. A particular drawback of this approach is
the need to synthesise special ligands for each chain length
and the limited control over the metal sequence within the
chain, as usually only homometallic complexes are ob-
tained.
omeric iron/platinum complexes by
a stepwise pro-
cedure.[17]
The repeated alternate addition of metal complex frag-
ments and bridging ligands would be a procedure which
allows full control over chain length, metal, and ligand se-
quence within the backbone. An important prerequisite for
this method is the kinetic stability of the metalϪligand
bonds within the chain so that undesired self-organisation
processes, which would ultimately lead to the thermo-
dynamically most stable species (e.g. scrambled metals, olig-
omer mixtures, or polymers), are suppressed.
The stepwise solution synthesis and characterisation of
nine dinuclear chain complexes composed of different
metalϪcarbonyl units (M ϭ Cr, Mo, W) and a bifunctional
bridging isocyanide Schiff-base ligand is the subject of this
contribution.
The construction of oligonuclear metal complexes may
also be achieved by the stepwise connection of stable metal
complexes through covalent bonds using a protection/de-
protection strategy which has been successfully applied, for
example, to defined ferrocene oligomers[9,10] and oligo-por-
phyrin systems.[11Ϫ14]
A similar, albeit more difficult, approach is the controlled
stepwise assembly of building blocks through coordinative
bonds. Such a procedure should allow the synthesis of com-
plexes with any desired chain length controlled by the num-
ber of repetition cycles. Repeated complex activation and
subsequent addition of a metal-bridging ligand fragment to
a starting complex has been employed for the synthesis of
Results and Discussion
Inert metalϪligand bonds are required for the stepwise
controlled synthesis of multinuclear metal chain complexes.
The coordinative bond between isocyanides and M0 car-
bonyl complexes (M ϭ Cr, Mo, W) is kinetically stable so
that ligand-exchange processes are prevented.[18Ϫ20] Conse-
quently, a suitable bridging ligand with an isocyano group
is used in the assembly of dinuclear metal complexes.
The bridging Schiff-base ligand (4-isocyanophenyl)pyrid-
ine-2-ylmethylenamine CϵNϪ(NʝNЈ) is accessible by a
two-step procedure starting from 1,4-diaminobenzene
(Scheme 1). Transformation of one amino group into the
desired isocyano group gives 4-isocyanophenylamine in
rather poor yields according to the literature.[21] Optimis-
[a]
Anorganisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax.: (internat.) ϩ49-(0)6221-545707
E-mail: katja.heinze@urz.uni-heidelberg.de
3918
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200300272
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Stepwise Assembly of Mixed Metal Dinuclear Carbonyl Complexes
FULL PAPER
Scheme 1
ation of the purification increased the yield to 45% (see Exp.
Sect.). Schiff-base condensation of the remaining amino
group with pyridine-2-carbaldehyde affords the desired li-
gand CϵNϪ(NʝNЈ) (Scheme 1). CϵNϪ(NʝNЈ) can act
as bridging ligand between two M0-carbonyl units through
i) the chelating Schiff-base moiety, and ii) the isocyano
group.
The trimethylsilyloxy-substituted analogous Schiff-base
ligand TMSOϪ(NʝNЈ)[18] was used as the starting point
for the synthesis of dinuclear complexes. TMSOϪ(NʝNЈ)
reacts with one equivalent of [(CH3CN)3M1(CO)3] (M1 ϭ
Cr, Mo, W) in THF at ambient temperature to give the
reactive intermediate complexes [TMSOϪ(NʝNЈ)-
M1(CO)3thf] (Scheme 2).[18] The labile solvent molecule can
be displaced by the isocyanide ligand CϵNϪ(NʝNЈ) to af-
ford green stable intermediate isocyanide complexes
Scheme 2
Table 1. IR and UV/Vis spectroscopic data of intermediate com-
plexes [TMSOϪ(NʝNЈ)M(CO)3L] in THF (ν˜ in cmϪ1; λmax in nm)
L
Cr
Mo
W
Assignment
[TMSOϪ(NʝNЈ)M1(CO)3CϵNϪ(NʝNЈ)]
(Scheme 2).
ν˜ THF
1805
1906
1826
1860
1915
2074
766
1802
1910
1827
1855
1919
2076
685
1808
1907
1827
1849
1915
2072
705
CO
CO
CO
CO
CO
CN
The potentially chelating Schiff-base site of the coordinated
CϵNϪ(NʝNЈ) ligand is finally coordinated to an M2(CO)4
fragment by reaction with [(CH3CN)2M2(CO)4] (M1 ϭ Cr,
ν˜ CϵNϪ(NʝNЈ)
Mo,
W)
yielding
the
dinuclear
complexes
[TMSOϪ(NʝNЈ)M1(CO)3CϵNϪ(NʝNЈ)M2(CO)4] 1Ϫ9
with the metals Cr, Mo, and W in defined positions of
M1 and M2 (Scheme 2). This reaction sequence may be
performed as a one-pot procedure — isolation of the
λmax THF
λmax CϵNϪ(NʝNЈ)
660
618
628
intermediate complexes is unnecessary
—
provided these two bands with a new set of three νCO bands plus one
that exact stoichiometric conditions are fulfilled. Otherwise, νCN band (Table 1, cf.[18,19,20]). A further proof for isocyan-
side
products
such
as
[XϪ(NʝNЈ)M1,2(CO)4], ide coordination is the shift of the νCN signal by about 50
[XϪ(NʝNЈ)M1,2(CO)3CϵNϪ(NʝNЈ)V (X ϭ OTMS, CN) cmϪ1 to lower energy than the signal of the free ligand
are obtained in larger amounts which have to be removed CϵNϪ(NʝNЈ) (νCN ϭ 2127 cmϪ1). This shift is also ob-
by chromatography. The reactions can easily be monitored served in the IR spectra of the dinuclear complexes 1Ϫ9
by IR spectroscopy due to the characteristic IR absorption (Table 2). Introduction of the M2(CO)4 fragment causes ad-
bands of the intermediate complexes (Table 1).
Formation of the intermediate
ditional νCO bands to appear (Table 2) so that the IR spec-
complexes tra of the dinuclear complexes 1Ϫ9 can be described as a
[TMSOϪ(NʝNЈ)M1(CO)3thf] is shown by the appearance superposition of the IR spectra of the corresponding
of two absorption bands in the νCO region (Table 1). Coor- mononuclear
isocyanide
tricarbonyl
complex
dination of the isocyanide ligand CϵNϪ(NʝNЈ) replaces [TMSOϪ(NʝNЈ)M1(CO)3CϵNϪ(NʝNЈ)] and the tetra-
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K. Heinze, V. Jacob
FULL PAPER
carbonyl complex [HO-(NʝNЈ)M2(CO)4][18,19,20] as shown spection reveals that imine protons of the tungsten com-
in Figure 1 for the Cr-W complex 7.
plexes resonate at δ Ն 8.84 ppm while imine protons of the
chromium and molybdenum complexes resonate at higher
fields with δ Յ 8.62 ppm in THF. 13C NMR spectra could
not be obtained due to the low solubility of the complexes.
In the UV/Vis spectra of complexes 1Ϫ9 one or two
MLCT absorption bands are observed in the range
524Ϫ666 nm (Table 4). The low-energy absorption is due to
the (NʝNЈ)M1(CO)3 chromophore, while the high-energy
Table 2. IR spectroscopic data of complexes 1Ϫ9 in THF (ν˜ in
cmϪ1
)
M2 / M1
Cr
Cr
Mo
W
1829
1850
1906
1913
2006
2073
1829
1849
1907
1913 sh
2013
2069
1830
1849
1896
1915
2006
2072
1827
1850
1906
1918
2007
2075
1828
1850
1909
1917
2012
2079
1827
1849
1897
1914
2008
2079
1829
1849
1911 br
absorption
arises
from
the
(NʝNЈ)M2(CO)4
chromophore.[18Ϫ20,22Ϫ24] Like the IR spectra the UV/Vis
spectra can be interpreted as a superposition of spectra of
the individual chromophores, as shown for the ditungsten
complex 9 in Figure 2. These observations demonstrate
that, in each case, the two metal fragments of the dinuclear
system behave as mechanically (IR) and electronically (UV/
Vis) independent units, which appears reasonable in view of
2006
2072
1827
1849
1907
1911 sh
2013
2068
1829
1849
1896
1913
2006
2073
Mo
W
˚
the large metalϪmetal distance of around 10 A (estimated
on model calculations) and the flexible orientation of the
M2(CO)4 fragment with respect to the M1(CO)3 moiety.
Table 4. UV/Vis spectroscopic data of complexes 1Ϫ9 in THF (λmax
in nm; ε in Ϫ1cmϪ1
)
M2 / M1
Cr
Mo
W
Cr
Mo
598 (15200)
557 (8210)
666 (5780, sh)
570 (6030)
594 (9730)
524 (9000)
615 (7250, sh)
562 (9180)
608 (11900)
556 (12210)
609 (11650)
570 (8170)
W
640 (4390, sh)
613 (8600, sh)
600 (7760, sh)
Figure 1. IR spectrum of dinuclear complex 7 and spectra of the
corresponding mononuclear complexes [HO-(NʝNЈ)W(CO)4][20]
and [TMSOϪ(NʝNЈ)Cr(CO)3CϵNϪ(NʝNЈ)] in THF
1
The H NMR spectra of the complexes 1Ϫ9 show broad
and overlapping multiplets in the aromatic region (see Exp.
Section) and are thus not particularly informative. Only the
signals for the imine protons (chemical shift range δ ϭ
8.4Ϫ8.9 ppm) are clearly assignable (Table 3). A closer in-
Figure 2. UV/Vis spectrum of the dinuclear complex 9 and spectra
of the corresponding mononuclear complexes [HOϪ(NʝNЈ)-
W(CO)4] (*)[20] and [TMSOϪ(NʝNЈ)W(CO)3CϵNϪ(NʝNЈ)] (**)
in THF
Table 3. 1H NMR chemical shifts of imine protons of complexes
1Ϫ9 in CD2Cl2
As additional proof for the dinuclear nature of the com-
plexes in solution, and to exclude a simple mixture of
mononuclear complexes, the molecular masses of com-
plexes 1Ϫ9 have been determined by osmometry (see Exp.
Sect.). In all cases the results agree with the expected mass
within experimental error. This also shows that the com-
plexes remain stable in solution without dissociation, i.e.
the metalϪisocyanide bond remains intact.
M2 / M1
Cr
Cr
Mo
W
8.48
8.54
8.42
8.47
8.54
8.87
8.62
8.49
8.61
8.58
8.51
8.84
8.90
8.48
8.83
8.51
8.90
8.87
Mo
W
The dinuclear species were further characterised by FAB
mass spectroscopy (see Exp. Sect.). Peaks corresponding to
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Stepwise Assembly of Mixed Metal Dinuclear Carbonyl Complexes
ions of the dinuclear complexes and to fragments with loss
FULL PAPER
On the basis of IR (determination of molybdenum con-
of one to seven carbon monoxide ligands but with an intact tent and position), NMR (determination of tungsten con-
{TMSOϪ(NʝNЈ)M1CϵNϪ(NʝNЈ)M2} backbone sub- tent), and UV/Vis (discrimination between 3 and 7) spec-
stantiate the above findings.
troscopy the metal positions in all nine dinuclear complexes
The cyclic voltammograms of complexes 1Ϫ9 in CH2Cl2/ 1Ϫ9 can be unambiguously determined.
(nBu4N)(PF6) show only irreversible and quasireversible
oxidation waves, probably due to the loss of carbon monox-
Conclusion
ide upon oxidation. This behaviour has already been ob-
served for the corresponding mononuclear
complexes.[18Ϫ20]
Dinuclear directional complexes with well-defined metal
sequences have been prepared in solution and characterised.
However, low yields and lengthy purification renders this
solution synthesis unsuitable for trinuclear and higher chain
complexes which could be obtained by repeated chain
With all these spectroscopic data at hand we tried to
answer the following question: Is it possible to determine
(‘‘read’’) the metal sequence in these dinuclear complexes
without any prior knowledge of the synthetic protocol
used? In other words, can these nine complexes be dis-
tinguished with respect to their spectral properties? A closer
growth
cycles
with
[(CH3CN)3M(CO)3]
and
CϵNϪ(NʝNЈ). Currently a new method for the stepwise
assembly of tri- and oligonuclear complexes on a solid
phase is being developed.[18,25,26]
1
inspection of the IR, H NMR, and UV/Vis spectra of the
complexes 1Ϫ9 reveals distinct differences between the indi-
vidual complexes (Tables 2Ϫ4).
The metal sequence of nine dinuclear complexes with Cr,
Mo, and W in two possible positions can be determined
using a combination of standard spectroscopic techniques.
It should be possible to extend the sequence determination
to ‘‘sequencing’’ or ‘‘readout’’ of oligonuclear complexes if
the simulation technique based on spectra of mononuclear
complexes is used in combination with chemometric meth-
ods such as, for example, principal component analysis
(PCA) or partial least-squares (PLS).[29] As the spectro-
scopic determination of the chromium content is rather in-
direct a two letter code with molybdenum and tungsten as
the basis might be advisable in larger chain complexes. The
preparation and characterisation of oligonuclear complexes
built from molybdenum and tungsten fragments is cur-
rently underway.[26]
The IR spectra give three criteria:
(i) ν˜CN Ն 2075 cmϪ1 indicates M1 ϭ Mo (complex 2 or 8)
(ii) νCO,tetra Ն 2012 cmϪ1 indicates M2 ϭ Mo (complex 4
˜
or 6)
(iii) both (i) and (ii) indicates M1 ϭ M2 ϭ Mo (complex 5)
1
The H NMR spectra give two criteria:
(iv) one δH(Imin) Ն 8.84 indicates M1 ϭ W or M2 ϭ W
(3, 6, 7, or 8)
(v) two δH(Imin) Ն 8.84 indicates M1 ϭ M2 ϭ W (com-
plex 9)
Criteria (iii) and (v) completely assign complexes 5 and
9. Taking (i), (ii), and (iv) together complexes 2, 8, 4, and 6
can be unambiguously assigned. For example, (i) and (iv)
1
together indicates complex 8. Combining IR and H NMR
spectroscopy all complexes except the isomeric pair 3/7 can
be unambiguously assigned.
Experimental Section
The Cr/W isomers 3 and 7 can be distinguished on the
basis of their UV/Vis spectra: the difference of λmax for the
MLCT absorption maxima of the individual chromophores
in the dinuclear species is almost twice as large for complex
7 as for complex 3 (estimated on the basis of the absorption
bands of corresponding mononuclear complexes[18Ϫ20]) so
that for complex 7 a broad absorption with a low-energy
shoulder is observed while complex 3 displays only one
comparatively sharp band (Figure 3).
Unless noted otherwise, all manipulations were carried out under
argon by means of standard Schlenk techniques. All solvents were
dried by standard methods and distilled under argon prior to use.
All other reagents were used as received from commercial sources.
NMR: Bruker Avance DPX 200 at 200.15 MHz (1H), 50.323 MHz
(13C) at 303 K; chemical shifts (δ) in ppm with respect to residual
solvent peaks as internal standards: CDCl3 (1H: δ ϭ 7.24; 13C: δ ϭ
77.0 ppm), [D8]THF (1H: δ ϭ 1.73, 3.58; 13C: δ ϭ 25.5, 67.7),
CD2Cl2 (1H: δ ϭ 5.32; 13C: δ ϭ 53.8 ppm). IR spectra were re-
corded on a BioRad Excalibur FTS 3000 spectrometer using CaF2
cells or CsI disks. UV/Vis/NIR spectra were recorded on a
PerkinϪElmer Lambda 19, 0.2 cm cells (Hellma, suprasil). Mass
spectra were recorded on a Finnigan MAT 8400 spectrometer. El-
emental analyses were performed by the microanalytical laboratory
of the Organic Chemistry Department, University of Heidelberg.
Molecular weight determinations in THF: Knauer vapour-pressure
osmometer No. 7311100000, calibration with benzil.
The ligand TMSOϪ(NʝNЈ) was prepared according to the litera-
ture procedure.[18] The acetonitrile complexes were prepared from
[(cycloheptatriene)M(CO)3] and [(norbonadiene)M(CO)4],[27,28]
respectively, by reaction with CH3CN (M ϭ Cr, Mo, W).
4-Isocyanophenylamine:[21] 1,4-Diaminobenzene (0.28 mol, 30 g)
Figure 3. UV/Vis spectra of the dinuclear Cr/W complexes 3 and 7
was suspended in ethanol (120 mL) and chloroform (400 mL). A
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K. Heinze, V. Jacob
[TMSO؊(NʝNЈ)Mo(CO)3CϵN؊(NʝNЈ)Cr(CO)4] (2):
FULL PAPER
solution of KOH (200 g) in water (800 mL) was carefully added
and the mixture was refluxed for 2.5 h. The organic layer was sepa- C35H27CrMoN5O8Si (821.7): calcd. C 51.16, H 3.31, N 8.52; found
rated and the residue was extracted twice with dichloromethane.
The combined organic phases were washed with water and dried
with MgSO4. After evaporation of the solvent the residue was puri-
fied by flash chromatography (Alox, diethyl ether, Rf ϭ 0.5) giving
the product as yellow needles. Yield: 15 g (0.13 mol, 45%). C7H6N2
(118.1): calcd. C 71.17, H 5.12, N 23.71; found C 71.11, H 5.12, N
C 50.74, H 3.38, N 8.97. Molecular mass found: 846. MS(FAB):
m/z (intensity [%], fragment) ϭ 823 (15) [Mϩ], 711 (100) [Mϩ
Ϫ
4CO], 683 (58) [Mϩ Ϫ 5CO], 627 (40) [Mϩ Ϫ5 CO]. 1H NMR
(CD2Cl2): δ ϭ 0.38 (s, 9 H, SiCH3), 7.02 (d, J ϭ 8.0 Hz, 2 H),
7.2Ϫ7.6 (m, 8 H), 7.8Ϫ8.0 (m, 4 H), 8.49 (s, 1 H), 8.62 (s, 1 H),
9.2Ϫ9.4 (br. s, 2 H) ppm. IR (CsI): ν˜ ϭ 1832, 1911, 2010 (CO),
23.52. MS (EI): m/z (intensity [%], fragment) ϭ 118 (100) [Mϩ], 91 2084 (CN) cmϪ1
(33) [Mϩ Ϫ HCN]. IR (CHCl3): ν˜ ϭ 2129 (s, CN), 3410 cmϪ1 (br.,
.
[TMSO؊(NʝNЈ)W(CO)3CϵN؊(NʝNЈ)Cr(CO)4]
(3):
NH). IR (CsI): ν˜ ϭ 2129 (s, CN), 3460 cmϪ1 (s, NH). 1H NMR
C35H27CrN5O8SiW (909.6): calcd. C 46.22, H 2.99, N 7.70; found
C 46.32, H 3.47, N 8.02. Molecular mass found: 917. MS(FAB):
(CDCl3): δ ϭ 3.79 (br., 2 H, NH2), 6.62 (d, 2 H, H2,6
,
3JH,H
ϭ
8.5 Hz), 7.17 (d, 2 H, H3,5
,
3JH,H ϭ 8.5 Hz) ppm. 13C NMR
m/z (intensity [%], fragment) ϭ 908 (100) [Mϩ], 797 (66) [Mϩ
Ϫ
(CDCl3): δ ϭ 115.2 (s, C2,6), 128.0 (s, C3,5), 147.8 (s, C1), C4 and
CN not observed ppm.
1
4CO]. H NMR (CD2Cl2): δ ϭ 0.38 (s, 9 H, SiCH3), 7.0 (m, 2 H),
7.3Ϫ7.5 (m, 8 H), 7.93 (br. s, 4 H), 8.48 (s, 1 H), 8.90 (s, 1 H), 9.27
(br. s, 1 H), 9.38 (br. s, 1 H) ppm. IR (CsI): ν˜ ϭ 1828, 1907, 2008
(4-Isocyanophenyl)pyridine-2-ylmethyleneamine CϵN؊(NʝNЈ): A
mixture of 4-Isocyanophenylamine (34.6 mmol, 4.08 g), pyridine-2-
carbaldehyde (52.3 mmol, 5 mL), MgSO4 (5 g), and ethyl acetate
(80 mL) was heated under reflux for 6 h. The resulting brown sus-
pension was filtered and the orange solution was evaporated to
dryness. After recrystallisation from acetone/diethyl ether the
brown solid was dried in vacuo for 4 days. Yield 5.5 g (26.5 mmol,
77%). C13H9N3 (20.7.2)·0.25 H2O: calcd. C 73.74, H 4.52, N 19.85;
found C 73.89, H 4.49, N 19.62. m.p. 84Ϫ85 °C. MS(EI): m/z
(intensity [%], fragment) ϭ 207 (31) [Mϩ], 179 (Mϩ Ϫ HCN, Ϫ H),
79 (100) [C5H5Nϩ]. HR-MS(EI): Calcd. for C13H9N3: 207.07965;
found 207.07663. IR (CH2Cl2): ν˜ ϭ 2127 cmϪ1 (s, CN). IR (CsI):
ν˜ ϭ 2131 cmϪ1 (s, CN). 1H NMR ([D8]THF): δ ϭ 7.39 (d, 2 H,
(CO), 2080 (CN) cmϪ1
.
[TMSO؊(NʝNЈ)Cr(CO)3CϵN؊(NʝNЈ)Mo(CO)4]
(4):
C35H27CrMoN5O8Si (821.7): calcd. C 51.16, H 3.31, N 8.52; found
C 50.73, H 3.40, N 8.68. Molecular mass found: 806. MS(FAB):
m/z (intensity [%], fragment) ϭ 739 (36) [Mϩ Ϫ 3CO], 711 (94)
1
[Mϩ Ϫ 4CO]. H NMR (CD2Cl2): δ ϭ 0.31 (s, 9 H, SiCH3), 6.94
(d, J ϭ 8.0 Hz, 2 H), 7.3Ϫ7.6 (m, 8 H), 7.9Ϫ8.0 (m, 4 H), 8.42 (s,
1 H), 8.47 (s, 1 H), 9.1Ϫ9.3 (m, 2 H) ppm. IR (CsI): ν˜ ϭ 1837,
1912, 2012 (CO), 2082 (CN) cmϪ1
.
[TMSO؊(NʝNЈ)Mo(CO)3CϵN؊(NʝNЈ)Mo(CO)4]
(5):
C35H27Mo2N5O8Si (865.6): calcd. C 48.57, H 3.14, N 8.09; found
C 48.31, H 3.28, N 8.91. Molecular mass found: 841. MS(FAB):
H2,6, 3JH,H ϭ 8.6 Hz), 7.45Ϫ7.49 (m, 1 H, H11), 7.55 (d, 2 H, H3,5
,
3JH,H ϭ 8.6 Hz), 7.90 (dvt, 1 H, H10, J ϭ 7.8, J ϭ 1.2 Hz), 8.26 (d,
1 H, H9, J ϭ 7.8 Hz), 8.62 (s, 1 H, H7), 8.72 (d, 1 H, H12, J ϭ
4.8 Hz) ppm. 13C NMR ([D8]THF): δ ϭ 121.5 (s, C9), 122.5 (s,
C2,6), 125.8 (s, C11), 127.7 (s, C3,5), 136.7 (s, C10), 150.0 (s, C1),
150.2 (s, C12), 152.4 (s, C4), 155.1 (s, C8), 163.2 ppm (s, C7), CN
not observed. All signals were assigned on the basis of DEPT, CH-
COSY, and NOESY experiments. The conformation in solution is
transoid as no cross peak between H7 and H9 is observed in the
NOESY spectrum.
m/z (intensity [%], fragment) ϭ 866 (67) [Mϩ], 782 (67) [Mϩ
Ϫ
3CO], 670 (100) [Mϩ Ϫ 7CO]. H NMR (CD2Cl2): δ ϭ 0.38 (s, 9
H, SiCH3), 7.0 (d, J ϭ 8.4 Hz, 2 H), 7.34 (d, J ϭ 8.4 Hz, 2 H),
7.5Ϫ7.7 (m, 6 H), 7.9Ϫ8.0 (m, 4 H), 8.58 (s, 1 H), 8.61 (s, 1 H),
9.22 (d, J ϭ 3.7 Hz, 1 H), 9.28 (br. s, 1 H) ppm. IR (CsI): ν˜ ϭ
1
1830, 1911, 2016 (CO), 2084 (CN) cmϪ1
.
[TMSO؊(NʝNЈ)W(CO)3CϵN؊(NʝNЈ)Mo(CO)4]
(6):
C35H27MoN5O8SiW (953.5): calcd. C 44.09, H 2.85, N 7.35; found
C 43.34, H 3.22, N 8.01. Molecular mass found: 967. MS(FAB):
Complexes 1؊9: All glassware was passivated with (CH3)3SiCl be-
fore use. [(CH3CN)3M1(CO)3] (1 mmol) was treated with
TMSOϪ(NʝNЈ) (270 mg, 1 mmol) in 40 mL of THF and the solu-
tion was stirred until IR control (see Table 1) indicated complete
formation of [TMSOϪ(NʝNЈ)M(CO)3thf] (at least 15 min).
CϵNϪ(NʝNЈ) (207 mg, 1 mmol) was added as a solid and the
solution turned green immediately. IR control indicated complete
formation of [TMSOϪ(NʝNЈ)M1(CO)3CϵNϪ(NʝNЈ)] after
10 min (see Table 1). A solution of [(CH3CN)2M2(CO)4] (1 mmol)
in THF (10 mL) was then added. The reaction mixture turned
black and was stirred for 30 min. Celite was added and the solution
was evaporated to dryness. The dark residue was chromatographed
on silica gel (T ϭ 0 °C; Et2O, purple fraction; THF, dark-blue
fraction, product complex). The THF fraction was concentrated
and layered with petroleum ether (40/60). The black precipitate was
collected and dried in vacuo. Yields: 20Ϫ55% (0.2Ϫ0.55 mmol).
m/z (intensity [%], fragment) ϭ 955 (17) [Mϩ], 927 (71) [Mϩ
Ϫ
CO], 915 (100) [Mϩ Ϫ 5CO]. 1H NMR (CD2Cl2): δ ϭ 0.31 (s, 9
H, SiCH3), 6.95 (d, J ϭ 8.0 Hz, 2 H), 7.22 (d, J ϭ 8.0 Hz, 2 H),
7.5Ϫ7.7 (m, 6 H), 7.9Ϫ8.0 (m, 4 H), 8.51 (s, 1 H), 8.83 (s, 1 H),
9.12 (br. s, 1 H), 9.31 (br. s, 1 H) ppm. IR (CsI): ν˜ ϭ 1829, 1907,
2016 (CO), 2077 (CN) cmϪ1
.
[TMSO؊(NʝNЈ)Cr(CO)3CϵN؊(NʝNЈ)W(CO)4]
(7):
C35H27CrN5O8SiW (909.6): calcd. C 46.22, H 2.99, N 7.70; found
C 45.41, H 3.29, N 7.88. Molecular mass found: 937. MS(FAB):
m/z (intensity [%], fragment) ϭ 909 (33) [Mϩ], 825 (100) [Mϩ
Ϫ
3CO], 797 (91) [Mϩ Ϫ 4CO]. 1H NMR (CD2Cl2): δ ϭ 0.37 (s, 9
H, SiCH3), 6.99 (m, 2 H), 7.4Ϫ7.6 (m, 8 H), 7.9Ϫ8.0 (m, 4 H),
8.54 (s, 1 H), 8.87 (s, 1 H), 9.30 (br. s, 1 H), 9.39 (br. s, 1 H) ppm.
IR (CsI): ν˜ ϭ 1830, 1907, 2008 (CO), 2080 (CN) cmϪ1
.
[TMSO؊(NʝNЈ)Mo(CO)3CϵN؊(NʝNЈ)W(CO)4]
(8):
[TMSO؊(NʝNЈ)Cr(CO)3CϵN؊(NʝNЈ)Cr(CO)4]
C35H27Cr2N5O8Si (777.7): calcd. C 54.05, H 3.50, N 9.01; found C
(1):
C35H27MoN5O8SiW (953.5): calcd. C 44.09, H 2.85, N 7.35; found
C 43.64, H 2.63, N 7.80. Molecular mass found: 945. MS(FAB):
53.22, H 3.62, N 9.58. Molecular mass found: 765. MS(FAB): m/z
m/z (intensity [%], fragment) ϭ 955 (50) [Mϩ], 927 (100) [Mϩ
Ϫ
(intensity [%], fragment) ϭ 777 (17) [Mϩ], 693 (100) [Mϩ Ϫ 3CO], CO], 870 (50) [Mϩ Ϫ 3CO], 759 (86) [Mϩ Ϫ 7CO]. 1H NMR
581 (94) [Mϩ Ϫ 7CO]. 1H NMR (CD2Cl2): δ ϭ 0.38 (s, 9 H,
SiCH3), 7.0 (br. s, 2 H), 7.2Ϫ7.6 (m, 8 H), 7.9 (br. s, 4 H), 8.48 (s, 7.3Ϫ7.5 (m, 8 H), 7.9Ϫ8.0 (m, 4 H), 8.51 (s, 1 H), 8.84 (s, 1 H),
1 H), 8.54 (s, 1 H), 9.29 (br. s, 1 H), 9.39 (br. s, 1 H) ppm. IR (CsI): 9.2Ϫ9.3 (br. s, 2 H) ppm. IR (CsI): ν˜ ϭ 1823, 1912, 2010 (CO),
ν˜ ϭ 1832, 1908, 2009 (CO), 2082 (CN) cmϪ1 2083 (CN) cmϪ1
(CD2Cl2): δ ϭ 0.31 (s, 9 H, SiCH3), 6.94 (d, J ϭ 8.2 Hz, 2 H),
.
.
3922
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3918Ϫ3923

Stepwise Assembly of Mixed Metal Dinuclear Carbonyl Complexes
[TMSO؊(NʝNЈ)W(CO)3CϵN؊(NʝNЈ)W(CO)4] (9):
C35H27N5O8SiW2 (1041.4): calcd. C 40.37, H 2.61, N 6.73; found
C 40.71, H 2.99, N 7.56. Molecular mass found: 1017. MS(FAB):
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Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. The permanent, generous
support from Prof. Dr. G. Huttner is gratefully acknowledged. We
thank Yasmin Nisar for preparative assistance.
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Received May 7, 2003
Eur. J. Inorg. Chem. 2003, 3918Ϫ3923
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3923