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Crystalline Transition-Metal Complexes with Strongly Anisotropic Physical Properties.

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CONFERENCE REPORTS
Silicon as a Carbanion Substituent in Ylides[**]
By Hubert Schmidbaur“’
From numerous recent publications1’] it appears that
silicon atoms as substituents can stabilize an ylide group
very considerably. The consequence is a much diminished
basicity or nucleophilicity of silylated ylides. Investigations of silyl ylides of phosphorus, arsenic, and sulfur containing various ligands on the silicon atom have shown
that this “silicon effect” is founded in the properties of the
silicon itself and is not caused by inductive, mesomeric, or
steric effects of the ligands.
Possible explanations are concerned with a d-orbital-xinteraction or an altered charge distribution in the 0skeleton. Photoelectron spectra and mass-spectroscopic
determination of ionization potentials[’] do not provide
unambiguous differentiation since the data for the free
ylides and their silyl derivatives show hardly any stepwise
progression.
Extension of the substituents to disilanyl groups, which
would potentially permit a (d-d)rc-interaction,did not lead
to appreciable further stabilization ; on the contrary, considerable steric hindrance occurred, which made syntheses
much more difficult. Investigations were made, not only
with open-chain mono- and di-silanyl ylides, but also
especially with cyclic ylides (1)-(4), in which the steric
/C\SiR2
R”*c,2iR2
/
R3Si
C
I \
R2Si,
,SiR,
5
p R3
7
R3
:R3
fR3
H2
R,?’C\
R2Si+
SiR2
8R3
R,Si%iR,
I
I
R2Si, ,SiR,
F
p R3
factors would be largely eliminated. The tendency for
formation of the latter and their stability were surprisingly
high.
Among the reactions of silyl ylides, trans- and de-silylation
processes are particularly important. The former permit
simple introduction of other substituents, including functional ones, such as Sic!,, SiHCI,, Si(CH,)Cl,, Si(CH,),CI,
Ge(CH,),, Sn(CH,),, PCI,, and As(CH,), groups. Desilylation leads to salt-free pure ylides whose preparation
by other routes is often difficult or impossible. Addition of
reagents such as HF, CH,OH, or CH,SH in situ in connection with desilylations has led to the first syntheses of pentacoordinated tetraorganofluoro-, -alkoxy-, and -mercaptophosphoranes (R,PF, R,POR, and R,PSR)[31. By use of
an excess of the reagent, products of the type R,PF.HF,
R,POR’-ROH, etc., are obtained, in which the anions
contain strong hydrogen bonds.
Lecture at Miinchen on May 9,1972 [VB 345 I€]
German version: Angew. Chem. 84,957 (1972)
[*I
Prof. Dr. H. Schmidbaur
Institut fur Anorganische Chemie der Universitat
87 Wiirzburg, Landwehr (Germany)
Work performed in collaboration with G. Kammel, W Kapp, W
Malisch, K.-H. Mitschke, H . Stiihler, W Tronich, W Vornberger (deceased), and J . Weidlein.
[**I
[l] H. Schmidbaur and W Tronich, Chem. Ber. 100, 1032 (1967); 101,
595,604,3556,3545 (1968); H . Schmidbaur and W Malisch, ibid. 102,83
(1969); 103,97, 3007, 3448 (1970); 104, 150 (1971); H . Schmidbaur and
944
G . Kammel, ibid. 104, 3252 (1971); H . Schmidbaur and W Kapp, ibid.
105, 1203 (1972); H . Schmidbaur, H . Stiihler, and W Vornberger, ibid.
105, 1084 (1972).
[2] Unpublished work in collaboration with H . Bock and S . Elbel,
Frankfurt.
[3] H . Schmidbaur and H . Stiihler, Angew. Chem. 84, 166 (1972); Angew. Chem. internat. Edit. 11,145 (1972); H . Schmidbaur, K.-H. Mitschke, and J . Weidlein,Angew. Chem. 84, 165 (1972); Angew. Chem. internat. Edit. 11, 144 (1972).
Crystalline Transition-Metal Complexes
with Strongly Anisotropic Physical Properties
By H . J . Keller[’l
Square coordination compounds of the transition metals,
which crystallize in columnar stacks, i. e. with formation of
infinite linear metal chains, exhibit strongly anisotropic
physical properties in the solid state. Among these solid
substances there are a few representatives-such as Magnus
salt or the glyoximato complexes of the d8-ions Ni(rI),
Pd(II), and Pt(II)-with only weak intermolecular interactions along the metal chain, which can, however, be
enhanced in various ways:
a) By oxidation of [Pt(NH,),] [PtCl,] or bis(benzi1dioximato)paliadium(rr) an originally fully occupied d, 2
band (valence band) can become partly emptied (conduction band). This results in the partly oxidized complexes
having a metallic luster and increased electrical conductivity.
b) By coordination of d8 metal ions with ligands which
make an overlapping of the energeticallyhigher and empty
dx2-,, band with the fully occupied d22 band possible.
Among these may be mentioned the isonotriles in complexes
of the type PtCl,(CNR), (R=phenyl, p-toluyl, naphthyl,
etc.). A half-occupied conduction band results, which
explains the onedimensional metallic properties of these
compounds.
c) By use of d7 central metal ions, e.g. cobalt(I1). a-Modifications of diiodotetrakis(arylisonitrile)cobalt(II) exhibit,
depending on the type of isonitrile,greatly reduced magnetic
moments (one-dimensional antiferromagnetic behavior)
and remarkable metallic surface luster.
Since lattice defects hinder metallic dc conductivity, for
the identification of strong one-dimensional interactions
in such compounds, resort must be made to either optical
methods, ESR investigations of doped single crystals, or
NMR investigations of the central metal ion.
Compounds of this type are-as suggested by W A . Littlesuitable as high-temperature superconductors. For this
purpose it is necessary to link the one-dimensional metallic
chain with easily polarizable organic groups. Hence, in the
synthesis of columnar complexes of platinum(II), iridium(I),
rhodium(1) or (II), and cobalt(I1) with one-dimensional
metallic properties readily variable organic molecules
(glyoximes or isonitriles) were chosen as ligands in order
to verify Little’s model experimentally.
Lecture at Ludwigshafen, June 14,1972 [VB 353 IE]
German version: Angew. Chem. 84,998 (1972)
[‘I
Prof. Dr.H. J. Keller
Anorganisch-Chemisches Institut der Universitat
69 Heidelberg 1, Im Neuenheimer Feld 7 (Germany)
Angew. Chem. internat. Edit.
Vol. I 1 (1972) 1 No. 10
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