Nuwe reaksies van gedeprotoneerde Fischer-tipe karbeenkomplekse
Date
2005-03
Authors
Stander, Elzet
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Journal ISSN
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Abstract
This study comprises the preparation and characterisation of completely new Fischer-type
carbene complexes of chromium and tungsten by deprotonation of (CO)5M=C(NMe2)(Me),
(CO)5M=C(OMe)(Me) or (CO)5M=C(NMe2)C≡CH, and subsequent treatment of the formed
anion with a variety of reagents, including reactive metal complexes.
The deprotonation of the termodynamically stable complexes, (CO)5M=C(NMe2)(Me)
(M = Cr or W) followed by reaction with the sulfonium salt, [Me2(MeS)S][BF4], yielded not
only the expected products (CO)5M=C(NMe2)CH2SCH3, but also thioether complexes,
(CO)5MS(CH3)2, disulfinated complexes (CO)5M=C(NMe2)CH(SCH3)2, S-bridged dinuclear
compounds (CO)5M=C(NMe2)CH2S(CH3)M(CO)5, as well as the unique fourmembered-
C,S-chelate carbene complexes (CO)4Cr=C(NMe2)CH(SCH3)SCH3 and
(CO)4M=C(NMe2)CH2SCH3.
Crystal structure determinations of (CO)5W=C(NMe2)CH(SCH3)2,
(CO)5Cr=C(NMe2)CH2S(CH3)Cr(CO)5, (CO)4M=C(NMe2)CH2SCH3 (M = Cr, W) and
(CO)4Cr=C(NMe2)CH(SCH3)SCH3 were successfully performed. The latter tetracarbonyl
complexes have Cr-S bonding distances of 2.4531(9) and 2.4517(5) Å and a W-S distance of
2.577(1) Å. These relatively weak bonds contribute to the short M-C(O)-distances trans to it.
The formed four membered chelate rings are essentially planar.
The deprotonation of (CO)5Cr=C(NMe2)(Me) and sequential reaction with sulphur and
CF3SO3Me does not yield the expected product, (CO)5Cr=C(NMe2)CH2SCH3, but
(CO)5CrS=C(NMe2)CH3 resulting from a sulphur insertion was isolated. A single crystal
structure determination of the latter complex shows a normal thione carbene complex.
The reaction of methyl(methoxy)carbenepentacarbonylchromium(0) and the tungsten
analogue with n-BuLi, followed by reaction with [Me2(MeS)S][BF4], afforded unexpected
complexes via an unusual addition dissimilar to the above mentioned reactions of
dimethylaminocarbene complexes. The formation of the products,
(CO)5M=C(OMe)[CH=C(Me)NH(Me)] and (CO)4M=C(OMe)[C(SMe)=C(Me)NH(Me)]
(M = Cr, W) can be ascribed to the influence of the heteroatom, oxygen, as well as the
presence of acetonitrile in the sulfonium salt reagent [Me2(MeS)S][BF4]. An unusual
alkylation by Me+ is also affected. The X-ray crystallographic structure determination of the
complexes show hydrogen bonding between the alkoxy oxygen atoms and the protons on the nitrogen atoms. The latter four membered C,S-chelates show bonding distances and angles
similar to these of the previously mentioned four membered chelates.
Deprotonation of the alkynyl carbene complexes, (CO)5M=C(NMe2)C≡CH (M = Cr, W),
with n-BuLi and subsequent reaction with PPh3AuX (X = Cl, NO3), initially afford the
β-transmetalated products (CO)5M=C(NMe2)C≡CAuPPh3. In solution (CH2Cl2) the product
isomerises through metal migration to Ph3PAuC(NMe2)=C=C=W(CO)5. The conversion was
followed by means of 1H-NMR-spectroscopy and it appears that two first order reactions take
place consecutively.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005.
Keywords
Carbenes, Methylene compounds, Complex compounds, Metal complexes, Dissertations -- Chemistry, Theses -- Chemistry