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Cluster Synthesis by Exchange of Bridge-Forming Carboxylate Ligands.

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spectrum (FD and EI; M + at m/z=282, 70% rel. int.), and
by an absorption at A = 660 nm (E,,, =4060 L/cm mol).
The paramagnetism expected from the empirical formula
is confirmed by a magnetic moment of 2.2 p B (Gouy-balance). From the observed sextet in the ESR-spectrum (acetone solution, -30°C) with a5sM,=5.0 mT one can conclude, that the unpaired electron is localized in a molecular orbital with predominant metal character; no coupling
to N or H nuclei is observed.
Aminyl complexes like 2 are isoelectronic to radical anions of carbene complexes; according to ESR measurements the unpaired electron of the latter is localized
mainly at the carbene ligandL3I.The different electronic
structure of both species is revealed by MO calculations[41
on CSHS(C0)2MnNHCbH5
(2, R=H). The geometry of 2
in the structural formula with planar coordination of the N
atom is found to be the conformation of lowest energy.
The rotational barriers around the N-phenyl and especially
the Mn--N bond, however, are very low. The unpaired
electron is located in an energetically stable molecular orbital (energy difference to the LUMO ca. 3 ev) independent of the conformation; this MO is localized 70-80% in
the CSHs(C0)2Mn-part of the molecule. As shown in
Scheme 1, the SOMO is to be regarded as the antibonding
linear combination of the CSHs(C0)2Mn-HOM0(a") with
the nitrogen p-orbital. At an orthogonal position of the
@NHR ligand the C5H5(C0)2Mn fragment orbital 2a',
nearly degenerate with a", takes over the role of the latter;
for positions in between an appropriate linear combination
of both MO's is utilized.
CpMnICUb
2
@ NHc6 H5
Scheme 1. Simplified interaction diagram for metal complex fragment [5] and
aminyl radical.
Thus, for aminyl complexes like 2 the higher electronegativity of the nitrogen-center compared to carbon causes
localization of two electrons as a lone pair at N (lowest
level in Scheme 1) and of the unpaired electron in the dshell of the metal, in accordance with the rules of the perturbation theory. On the other hand, the d-shell of carbene
complex radical anions (p in Scheme 1 lies at substantially
higher orbital energy) remains fully occupied and the radical electron resides on the ligand-system in the original
LUMO of the neutral carbene complex. In a one-electron
scheme the lowest absorption in the electronic spectrum of
2 corresponds to a transition from the d-shell to the
SOMO with n,*,-character, analogous to the d-x$,-transition in [C5Hs(C0)2Mn]ZN2H2.
Received: April 23, 1982 [Z 19 IE]
German version: Angew. Chem. 94 (1982) 708
A. Neugebauer, Angew. Chem. 87 (1975) 823; Angew. Chem. Inr. Ed.
Engl. 14 (1975) 783.
121 a) Cf. also D. Sellmann, W. Weiss, J. Organomet. Chem. 160 (1978) 183:
b) Procedure- To a stirred solution of 940 mg (3.3 mmol) 1 in 100 mL toluene at - 10°C are added 4 mL of 30% H Z 0 2(-38 mmol). The solution
immediately turns dark blue and, after ra. 5 min, is concentrated to 5 mL.
After addition of 100 mL of hexane the solution is cooled to -25 "C and
filtered. At - 78 "C, 258 mg (27%) of blackish-blue 2 crystallizes within
24 h: the compound is analytically pure after washing with hexane.-For
oxidizing with 02,air is passed through a solution of 1 in toluene at
- 10°C for 2-3 h until the v,,-bands of 1 have disappeared. Work-up
as above.
[3] P. J. Krusic, U. Klabunde, C. P. Casey, T. F. Block, J. Am. Chem. Soc. 98
(1976) 2015.
[4] The calculations are of the Extended Hiickel type: R. Hoffmann, J .
Chem. Phys. 39 (1963) 1397; R. Hoffmann, W. N. Lipscomb, ibid. 36
(1962) 3179, 3489: 37 (1962) 2827. H , , matrix elements: P. Hofmann, Angew. Chem. 89 (1977) 551: Angew. Chem. Int. Ed. Engl. 16 (1977) 536. H,,
matrix elements: J. H. Ammeter, H.-B. Burgi, J. C. Thibeault, R. Hoffmann, J. Am. Chem. Soc. 100 (1978) 3686. Model geometries taken from
structural data of related complexes.
151 Valence-MOs of a C5H5(C0)2M-unit: see B. E. R. Schilling, R. Hoffmann, D. L. Lichtenberger, J. Am. Chem. SOC.101 (1979) 585.
Cluster Synthesis by
Exchange of Bridge-Forming Carboxylate Ligands""
By Helmut Werner* and Peter Thometzek
Procedures for the directed synthesis of metal clusters
from smaller mono- and binuclear synthons are still
sparsely documented[']. We have recently shown that dipalladium complexes ( ~ - X ) ( J . L - Y ) P ~ , ( Pare
R ~ obtainable
)~
by "[1+ I]-addition" of a Pdo- and a Pd"-compound, and
that a large variety of bridge ligands, such as C5H5, 2RC3H4, C1, SR, R C 0 2 etc., have proven suitable in such
additions"].
~ I comAccording to MO calculations by H o f m ~ n n [ metal
plex anions [L,M]- should also be capable of bridge formation with the fragment (yY)Pd,(PH,): if they contain
two donor orbitals of symmetry a, and bz which can overlap with the corresponding acceptor orbitals of the Pd2moiety. This prerequisite is fulfilled, e.g., in the case of
the carbonyl(cyc1opentadienyl)metalates [C,H,(CO),,M](M = Ni, Fe, Cr; n = I, 2, 3)l3]. In preliminary experiments
we were able to demonstrate that, as predicted, the complex (C5Hs)(tBuC02)Pd2(PiPr3)21 does in fact react with
[CsHs(C0)3Cr]Na and [C5H5(C0),Mo]Na, and that replacement of the carboxylate by the metalate takes
This exchange process is, however, not restricted to the
anions [C,H,(CO),M]-. Reaction of 1 and [(C0)4Co]Na
(toluene, 25 "C, 24 h) affords the Pd,Co-cluster 2 which
forms dark violet, permanganate-like crystals (yield 78%).
We assume that in 2 the cyclopentadienyl ring and the
(CO),Co-moiety are symmetrically coordinated to the
Pd-Pd bond. The 'H-NMR spectrum (C6D6) shows, aside
from the signals of the iPr,P-ligand, a 1 :2 : 1 triplet for the
CSHSprotons [S=5.74 (t, J,, = 1.9 Hz)], whereas the ,'PNMR spectrum (C,D,) shows a singlet for the two equivalent phosphorus atoms [6=37.78 (s)]. The IR spectrum
(KBr) shows bands for both terminal [2029, 2011, 1990,
1961 cm-'1 as well as bridging CO groups [1858 cm-'1.
I*]
[**I
111 B. C. Saunders: "Peroxidases and Catalases" in G. L. Eichhorn: Inorganic Biochemisrry, Elsevier, Amsterdam, 1973, p. 989; W. C . Danen, E.
692
0 Verlag Chemie GmbH, 6940 Weinheim. loR?
Prof. Dr. H. Werner, P. Thometzek
Institut fur Anorganische Chemie der Universitat
Am Hubland, D-8700 Wiirzburg (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and by gifts of chemicals from BASF
AG, Ludwigshafen, and Degussa AG, Hanau.
0570-0833/82/0909-0692 $ 02.50/0
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 9
oc'
I
IBU
'co
1072; c) H. Werner, Adv. Organomet. Chem. 19 (1981) 155; d) H. Werner,
H.-J. Kraus, P. Thometzek, Chem. Ber. 115 (1982), in press.
[3] P. Hofmann, private communication; Chemiedozententagung Kaiserslautern 1982, Vortragsreferate, p. 113.
[4] M. Pfeffer, J. Fischer, A. Mitschler, L. Ricard, J. Am. Chem. SOC.102
(1980) 6338.
[5] G . Schmid, Angew. Chem. 90 (1978) 417; Angew. Chem. I n t . Ed. Engl. 17
(1978) 392.
2
1
Reaction of 1 with [(CO)SMn]Na does not lead to the
expected Pd2Mn-cluster; instead, C5H5Mn(C0)3 is
formed, so presumably attack of the metalate at the bridging cyclopentadienyl ring takes place.
The carboxylate bridge in compound 3 is also replacable by one of the complex anions [CsH5(CO)3M]- (M=Cr,
Mo, W) and [(CO),Co]-. In toluene (25"C, 24 h) the
Pd2Cr- and Pd,Co-clusters 4 and 7 are formed almost
quantitatively. With a molar ratio of 3 :[CsHs(C0)3M]- of
ca. 1 : 1 the yields of 5 and 6 are considerably lower because the hydrido compounds C5H5(C0)3MH (M = Mo,
W) are formed as well as the trinuclear complex. These can
be separated by column chromatography on silica gel with
pentane and toluene as eluent. In each case, the 'H-NMR
spectra (C6D6) show, in addition to the signals for the cyclopentadienyl and phosphane ligands, a virtual triplet for
the H,,,,-. a broadened singlet for the H,,,,,,-, and a virtual
triplet for the 2-CH3-ally1 protons. After 3'P-decoupling
the virtual triplets transform into a singlets. The IR spectra
(KBr) of 4-6 each show three v(C0) bands at ca. 1840,
1770, and 1725 cm-' which are assigned to the doubly and
triply bridging CO ligands. The IR spectra of 2 and 7 are
very similar. The empirical formulas of the compounds
4-7 are confirmed by elemental analyses and field desorption mass spectra.
Cyclobutadiene: Mesomerism or Valence
Isomerism?**
By Giinther Maier*, Hans-Otto Kalinowski, and
Klaus Euler
Benzene and cyclobutadiene are worlds apart: in benzene the TI electrons are completely delocalized and the
two Kekule structures merely serve to describe the rnesomerically stabilized molecule. In contrast, in cyclobutadiene['] both forms a and b - on condition of a rectangular
singlet ground state-are capable of existing in a dynamic
equilibrium of valence isomers. We report here the first direct spectroscopic evidence[*]for this postulate. Since the
'w====Y
R
H
R
H
equilibrium l a + l b could not be frozen (even at - 185 "C
the olefinic C atoms C-1 and C-3 exhibit a single sharp signal)[3a1,we used the isotopic perturbation method of Saund e r ~ [ ~i.] e.
, we studied the degenerate equilibrium
2a + 2b.
rPrfl-Pd-Pd-P~Prs
c-3 (2)-
+ASP = 0.186 ppm
iPrfl-Pd-Pd-PiPrs
iPrp-Pd-Pd-PiPr3
4 , M = Cr
5, M = Mo
6,M=W
7
The bridge-forming property of the [(C,H,(C:O),M]- and
(C0)4Co-moieties in Pd" complexes has recently been described in the literaturec4];in these cases, however, owing
to the oxidation number I1 of the palladium no Pd-Pd
bonds, and thus no clusters, are strictly present[51.
Received: April 26, 1982 [Z 20 IE]
revised: July 5, 1982
German version: Angew. Chem. 94 (1982) 707
HFig. I. Part (C-1 +C-3) of the 25.2 M H z I3C-NMRspectrum of a mixture of 1
and 2 (1 :9) in deuterated diethyl ether at - 82 "C.
[*] Prof. Dr. G. Maier, Dr. H.-0. Kalinowski, K. Euler
[**I
[I] B. F. G. Johnson: Transition Metal Clusters, Wiley-Interscience, New
York 1980.
121 a) H. Werner, A. Kiihn, Angew. Chem. 8 9 (1977) 427; Angew. Chem. Int.
Ed. Engl. 16 (1977) 412; b) H. Werner, H.-J.
Kraus, Chem. Ber. 113 (1980)
Angew. Chem. Int. Ed. Engl. 21 (1982) No. 9
Institut fur Organische Chemie der Universitlt
Heinrich-Buff-Ring 58, D-6300 Giessen (Germany)
Small Rings, Part 45. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industfie.-Part
44: G. Maier, K.-A. Schneider, K.-D. Malsch, H. Irngartinger, A. Lenz,
Angew. Chem. 94 (1982) 446; Angew. Chem. I n t . Ed. Engl. 21 (1982) 437;
Angew. Chem. Suppl. 1982, 1072.
0 Verlag Chemie GmbH, 6940 Weinheim. 1982
0570-0833/82/0909-0693 $ 02.50/0
693
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