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Cluster-Construction Synthesis and Structure of Fe2Co2(CO)11(PC6H5)2 and Fe2Co2(CO)11S2.

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Both ruthenium and cobalt are catalytic elements. The
bimetallic character of the two new clusters and the proven
reactivity of (1) open u p numerous possibilities here. With
sions[’.21.Its application as a synthetic concept calls for
cluster precursors containing appropriate functional ligands. For the synthesis of RP- or S-bridged clusters, suitable precursors are, e . g . , those with P-H or S-S bonds,
which can react directly with carbonylrnetal complexe~[’.~].
We have been able to use this concept for the first time
for the directed synthesis of tetranuclear clusters from two
dinuclear precursors. The reactive educts were the dinuclear complexes ( l a ) and flb). which are predestined by
their functionality and folded
for the addition
of further carbonylmetal units. As expected, their reactions
with carbonylcobalt led smoothly to the new clusters (2a)
and (2b), respectively.
Fig. 1. Molecular structure of (2) in the crystal. Bond lengths [pm]: Ru1-Ru2
278.3(3), R ~ l - C o l 273.1(2), RuI-CO~ 266.0(2), RuZ-COI
R u 2 - C o 2 261.4(3), Col-Co2 248.7(3).
the parent compounds ( I ) and (2) as starting materials, ligand substitution, metal exchange and electron transfer
provide access to a wide field of derivative chemistry.
A suspension of [Ru(CO),CI,], (300 rng, 0.59 mmol) in
50 mL of an aqueous solution of KCo(CO), (500 rng, 2.38
mmol) is stirred for 1 h at room temperature. The black
precipitate which is formed is filtered off, dried in vacuum,
taken up in hexane, filtered, and cooled to -35 “C. (1) separates out as black crystals; 470 mg (76%), m.p. 208°C
A solution of (1) (200 mg, 0.38 rnmol) in hexane (30 mL)
is stirred for 3 d at 35°C and then chromatographed on a
silica gel column (65 x 2.5 cm). Hexane elutes C O ~ ( C O ) ~ ~
and some R U ~ ( C O ) ’Elution
with benzene/hexane (1 :7)
affords 60 mg (46%) of balck (2), rn. p. 182 “ C (dec.).
( l a ) , E’= P P h H
( l h ) , E’= S (with S-S bonding)
(201, E
(Zh), E
The relationship between the two complexes (2) manifests itself in the needle-like shape and black color of their
crystals and in their IR spectra in the v C 0 region (in
CH2C12 [crn-’I, (24: 2080 vw, 2041 vs, 2020 s, 1950 m,
1862 m ; (2b): 2090 vw, 2050 vs, 2039 sh, 2021 sh, 1953 m,
1875 m). They were characterized by crystal structure analysesf5].The molecular structures and most important bond
lengths are shown in Figure 1 and Table 1, respectively.
Received: October 27, 1980 [Z 821 a IE]
supplemented: November 17, 1980
German version: Angew. Chem. 93. 714 (1981)
[I] W. Hieber, H . Lagally, Z. Anorg. Allg. Chem. 251, 96 (1943).
[2] E. Roland. H. Vahrenkamp. unpublished.
131 J. R. Moss, 6’.A. G. Graham, J. Organomet. Chem. 23. C23 (1970).
141 Monoclinic, P2,/c, Z=4, a=928.0(2), b=2364.1(4), c= 1191.8(3) pm,
p= 133.39(1)0; 3011 reflections, R=0.065.
[S] C. H. Wei, Inorg. Chem. 8, 2384 (1969).
161 P. C. Steinhard:, W. L. Gladfelfer,A . D . Harley, J. R . Fox, G. L. Geoflroy.
Inorg. Chem. 19, 332 (1980).
[7] R. E. Benfiefd, B. F. G. Johnson, J. Chem. SOC. Dalton Trans. 1980.
[8] E. Keller, H. Vahrenkamp, 2. Naturforsch. 8 3 3 , 537 (1978).
By Heinrich Vahrenkamp and Edward J . Wucherer[*]
The principle of ligand bridging for the stabilization of
organometal-clusters has been realized o n numerous occa-
Prof. Dr. H. Vahrenkamp, E. J. Wucherer
Institut fur Anorganische Chemie der Universitat
Albertstr. 21, D-7800 Freiburg (Germany)
This work was supported by the Fonds der Chemischen Industrie and
by Rechenzentrum der Universitat Freiburg. We thank Frl. D. Sfeierf for
her valuable help with the preparative work.
0 Verlaq Chemie GmbH. 6940 Weinheim, 1981
Table 1. Values (average) of the most important atomic distances [pm] in the
clusters (2).
Cluster-Construction: Synthesis and Structure of
and Fe2Co,(CO),,S2[**1
Fig. 1. Molecular structures of (20) (E=phosphorus atom of the PCoHs
group) and 126) ( E = S ) in the crystal.
251 3 3 )
227 f2
258 f0.03
(2a) and (2b) belong to the relatively small group of tetranuclear clusters containing planar metal frameworksl6].
Their metal-metal and metal-bridge atom bond lengths lie
in the normal range for such compounds. For both complexes, there exist “pure” cobalt analogues, the clusters
C O ~ ( C O ) ~ (E
~ E=, PPh, S), which were formed by non-specific syntheses and whose structures are known”]. These
clusters also contain rectangular planar arrays of metal
atoms; their C ~ ~ ( C O ) ~ E ~ , ~ - hare
a l vvery
e s similar to those
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Angew Chem. In:. Ed. EngI. 20 ( 1 Y X l ) No. X
of the complexes (21, and their M-M and M-E bond
lengths show the same trend as in (2a) and (2b).
The intrinsic novelty of the clusters (2) is, therefore, their
systematic preparation. Since numerous functional dinuclear complexes having the butterfly structure shown in
(la) and (lb) and suitable simple carbonylmetals for reaction exist, the route described here to planar tetranuclear
clusters should not be merely limited to (2a) and (2b).
l2a -el
Equimolar amounts (1-2 mmol) of (la) o r (Ib) and
C O ~ ( C Oare
) ~ added to 50 ml of hexane. For the formation
of (2a) the mixture is stored in the dark for 20 d at room
temperature, then chromatographed on silica gel, and finally the product obtained from the third fraction is crystallized from hexane at - 30 “C. The complex (2b) precipitates from the reaction mixture in analytically pure form
after 12 h at 0°C. The yields of(2a) (m.p. 134”C, dec.) and
(2b) (dec. at 100-200°C without recognizable m.p.) are
Received: October 27, 1980 [Z 821 b IE]
German version: Angew. Chem. 93. 715 (1981)
[ I ] D . Seyferth, Adv. Organomet. Chem. 14, 97 (1976).
[2] H . Vahrenkamp, Angew. Chem. 87, 363 (1975); Angew. Chem. Int. Ed.
Engl. 14. 322 (1975).
[3] F. Richter. H . Beurich, H . Vahrenkamp. J. Organomet. Chem. 166, C 5
[4] 6 . K . Teo. M . B. Hall, R. F. Fenske, L. F. Dahl, Inorg. Chem. 14. 3103
[S] (2aj: triclinic, Pi, 2 = 2 , a=962.7(1), b = 1567.8(2), c=960.2(2) pm,
a=91.04(1), B= 109.05(1), y=84.83(1)”; 3190 reflections, R=0.059.(26): monoclinic, P2,/c, Z = 4 , a = 1615.4(5), b=655.6(2), c = 1872.2(5)
pm, B= 115.06(2)”; 2946 reflections, R=0.051.
161 P. Chin;, B T. Heaton. Top. Cum. Chem. 71. 1 (1977).
171 R. C Ryan. L. F. Dahl, J. Am. Chem. SOC.97, 6904 (1975).
As expected, the R,-values of the 5’-0-(4-alkoxytrity1)thymidines (3a-e) on silica gel are somewhat higher
and o n RP-2 somewhat lower than the R,-values of 5 ’ 0
(4,4’-dimethoxytrity1)thymidine. These changes reflect the
reduction in total polarity. The behavior of (3a-e) upon
R P (reversed phase) chromatography on a C,,-phase is,
however, different: here, an apparently specific interaction
New Hydrophobic Protecting Groups for the
Chemical Synthesis of Oligonucleotides‘**]
Fig. 1. Dependence of the Rf-values on the alkyl chain length n of compounds (3) [n=8, 10, 12, 14, 16 = (3a, b, e. d, e)]. 0: silica gel 60 (Merck),
chloroform/methanol 9 : 1; 0 : silica gel RP-2 (Merck), acetone/water
75 : 2 5 ; A : silica gel K C , B(Whatman), acetone/water 75 :25.
By Hans-Helmut Gortz and Hartmut Seliger[*’
In the chemical synthesis of polynucleotide fragments
between the alkyl chains of the sorbent and sorbate leads
by the triester procedure”.*’, chromatographic methods are
to a dramatic reduction of the R,-values with increasing
important for the purification of protected intermediates
chain length upon thin layer chromatography (Fig. 1 ) and
and for the isolation of the unprotected final p r o d ~ c t [ ~ . ~ ~ .
increasing retention times in HPLC (Fig. 2).
The chromatographic behavior of the oligomers can be
The 4-hexadecyloxytrityl (cl6Tr-) derivatives [(6). (8).
varied within certain limits by protecting groups, generally
(11). (13) and (16)] among the oligonucleotide phosphoproducing an unspecific change in the total polarity of the
triesters (4)-(16) (Table 1) exhibit the same characteristic
molecule. We have introduced 4-alkoxytrityl groups as a
behavior as the monomers (3) upon RP-18 chromatogranovel type of hydrophobic protection for the 5’-end of
phy. Of prime interest for preparative application is the
o l i g ~ n u c l e o t i d e s For
~ ~ ~ this
purpose, the 4-alkoxytritanols
magnitude of the R,-difference between the Ci6Tr-deriva(2a-e) were prepared by Grignard reaction from (la-e)
tives and the corresponding compounds having free 5’-OH
and the trityl chlorides reacted with thymidine to produce
groups, which indicates an easy and complete HPLC sepa(3a-e).
ration of both types of components irrespective of the chain
[*] Prof. Dr. H. Seliger, Dr. H.-H. Gortz
Sektion Polymere der Universitat
Oberer Eselsberg, D-7900 Ulm (Germany)
Syntheses with Nucleic Acid Constituents, Part 9.-Par1 8: H. Seliger. B.
Haas. M . Holupirek. T. Knable. G. Todling. M . Philipp. Nucleic Acids
Res. Symp. Ser. 7, 191 (1980).
Angew. Chem In,. Ed. Engl 20 ( I Y U I )
No. 8
length and sequence. This is in contrast to separations
of the 4-methoxy- or 4,4‘-dimethoxytrityl (DMTr) derivatives used so far, in which the starting components with 3’terminal phosphate charge can readily be separated from
the reaction mixture arising from nucleotide condensations, however, good separation of the oligonucleotides
0 Verlag Chemie GmbH. 6940 Weinheim, I981
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structure, synthesis, fe2co2, clusters, 11s2, pc6h5, construction
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