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Fixation of Trimethylsilylnitrene as 3-Trimethylsilylimido(decacarbonyltriiron).

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Fixation of Trimethylsilylnitreneas
p3-Trimethylsilylimido(decacarbony1triiron)
By Ernst Koerner aon Gustorf and Rosemarie Wagner'*]
Trimethylsilyl azide" ( 1 ) exhibits a remarkably higher
degree of thermal stability (b. p.760= 95°C) than organic
azides. due to d, - p, interactions''' between silicon and
nitrogen. A similar stabilization is to be expected for
trimethylsilylnitrene (2) formed from (1) by N, elimination. Very little has been reported hitherto about the
chemistry of (2)
In connection with investigations on
the stabilization of labile intermediates in transition metal
complexes[41we have tried to trap (2) as a carbonyliron
complex during the decomposition of ( I ) .
Like organic a z i d e ~ [ ~( ]1,) already decomposes at room
temperature
in
the
presence
of
Fe,(CO), ;
(CH,),SiNIFe,(CO),o] ( 3 ) is formed as brownish-red
needles which decompose without melting at 110°C. The
mass spectrum of (3) shows, in addition to the molecular
ion, fragments which correspond to successive loss of
10 CO groups. The 'H-NMR spectrum (in benzene) contains a singlet due to a (CH,),Si group at 9.57 T, which is
shifted only slightly downfield compared to that of ( I )
(9.89 T). In the IR spectrum (in n-hexane), which contains
relatively few bands, five stretching vibrations of terminal
CO groups are to be found (in order ofdecreasing intensity)
at 2048, 2019.5, 2014, 1993, and 2088 cm- An intense
band at 1743 cm-' is due to bridging CO[6r71.The symmetrical CH, bending vibration of the (CH.,),Si group in
( 3 ) ,like that in ( I ) , appears at 1255 cm-I (in CCl,).
'.
The data obtained for (3) are consistent with formulation as a trimethylsilylnitrene-[Fe,(CO)lo] complex. Comparison with the known organonitrene complexes of similar configuration, (CH,N), [Fe,(CO),][']
and C,H,N [?T-C,H,N~],''~suggests ( 3 ) as having the
structure proposed below. The trimethylsilylnitrene functions as a 4-electron donor, giving a "closed shell" complex.
I
n'
Si
131
X-ray structural analysis"01 confirms the almost perfect
symmetrical arrangement of the (CH,),SiN group in ( 3 )
and shows that the axial CO group is triply bridging,
in analogy to [Fe,(C0),,]2-f"1.
Hitherto it has not been possible to obtain ( 3 ) by photochemical reaction of Fe(CO), with ( I ) . We are currently
investigating the protolytic cleavage of the (CH,),Si group,
which should lead to a complex of the imine.
Experimental :
A mixture of ( I ) (0.087 mol) and Fe,(CO), (0.028 mol) in
benzene (70 ml) is mechanically stirred under argon for
24 h at 20°C. Approximately 0.01 mol of gas is evolved.
Unchanged Fe,(CO), is filtered off. The residue remaining
[*] Dr. E. Koerner von Gustorf and R. Wagner
Max-Planck-Institut fur Kohlenforschung
Abteilung Strahlenchemie
433 Miilheim-Ruhr, Stiftstrasse 34-36 (Germany)
910
after removal of solvent by evaporation is extracted with
pentane. On cooling the extract to - 78 "C, (3) crystallizes
out ; repeated recrystallization from pentane affords
0.8 mmol of analytically pure (3)"21.
Received. July 16, 1971 [Z 501a IE]
German version: Angew. Chem. 83,968 (1971)
[l] L. Birkofer and P . Wegner, Org. Syn. 50, 107 (1970).
[ 2 ] t.BirkoJer and A . Ritter, Angew. Chem. 77, 414 (1965): Angew.
Chem. internat. Edit. 4,417 (1965).
[3] W Lwowski: Nitrenes. Interscience, New York 1970, p. 423.
[4] E . Koerner lion Gustorf and F.-W Grerels, Fortschr. Chem.
Forsch. 13, 366 (1969).
[S] M . Dekker and G. R . Knox, Chem. Commun. 1967, 1243.
[6] K . Nakamoro in M . Tsursui: Characterization of Organometallic
Compounds, Part I. Interscience, New York 1969, p. 73.
[7] An alternative assigument of this band as a C O stretching vibration
in complexed (CH3)3Si-N=C=0
or (CH,),SI-CO-N<
(both
ligands could be formed by reaction of (2) with CO) can be ruled
out since, in this case, ( 3 ) would have to be coordinatively unsaturated
-which is not compatible with its properties.
[S] R . J . Doedens, Inorg. Chem. 8, 570 (1969).
[9] S. Otsuka, A . Nukainuru, and T Yoshida, Inorg. Chem. 7, 261
(1968); Liebigs Ann. Chem. 719, 54 (1968).
[lo] B. L. Barnetr and C . Kriiger. Angew. Chem. 83, 969 (1971);
Angew. Chem. internat. Edit. 10, 910 (1971).
[ l l ] R . J . Doedens and L. F. Dahl, J. Amer. Chem. SOC.88,4847 (1966).
[12] (CH,),SiN[Fe,(CO),,,]:
the composition has been confirmed
by a complete elemental analysis. MoLwt. (cryosopic in benzene) 538,
calc. 535.
p3-Trimethylsilylimido-p3-carbonyltris(tricarbonyliron)-Crystal and Molecular Structure
By Bobby L. Barnett and Carl Kriiger"]
p, -TrimethyIsilylimido-p, -carbonyltris(tricarbonyliron)
( I ) , a product obtained on reaction of (CH,),SiN, with
Fe,(CO),"], crystallizes from pentane in the acentric
space group Pca2, along [OOI] of the orthorhombic
system. The unit cell (a= 12.853, b=13.316, c=11.488&,
with a calculated density of 1.807 g/cm3, contains four
molecules of the title compound.
The molecular structure was determined from 1639
diffraction data by the heavy atom method. The positions
of the iron atoms were deduced from a sharpened threedimensional Patterson function ; the light-atom positions
were obtained by subsequent Fourier synthesis.Anisotropic
least-squares refinement, in which the anomalous scattering of the Fe and Si atoms was included[21,gave a final
R =4.3 %.
The structure of ( 1 ) (Fig. 1) can be described by a pseudoC, symmetry of the molecular skeleton including a triply
coordinated carbonyl group on the iron cluster as well as a
trimethylsilylimino group. The coordination of the equidistant Fe atoms is characterized by distorted octahedra in
which three carbonyl groups (C,,C5,C8) are slightly
twisted out of the plane of the Fe atoms (see Fig. 2). The
averag Fe-C and C-0 bond lengths are 1.798 and
1.141 A, respectively, and correspond to analogous carbonyl-iron clusters ;the same is trye of the average Fe-Fe
bond lengths of 2.535i0.002A. The linearity of the
carbonyl groups should be noted.
The bond lengths and angles in the symmetrically bound,
triply bridging carbonyl groups Cto-Ol, (see Fig. 3)
[*I
Dr. C. Kriiger and Dr. B. L. Barnett
Max-Planck-Institut fur Kohlenforschung
433 Miilheim-Ruhr, Lembkestrasse 5 (Germany)
Angew. Chem. internut. Edit.
Vof. I0 (1971) 1 No. 12
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trimethylsilylimido, fixation, trimethylsilylnitrene, decacarbonyltriiron
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