Scheme showing the electron-transfer nature on selective PR3/P(OR)3 substitution for I-.
Speciation 98: Abstracts
Ling-Kang Liu
Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, ROC
A chelating ligand, the dppe (=
Ph2PCH2CH2PPh2) reaction
with (h5-C5H5)Fe(CO)2I
produced [(h5-C5H5)Fe(CO)(h2-dppe)+][I-].
Forced to behave as a bridging ligand, the dppe reaction with
8-fold activated [(h5-C5H5)Fe(CO)2(acetone)+][ClO4-]
produced [{(h5-C5H5)-Fe(CO)2}2(m,h1:h1-dppe)2+][ClO4-]2.
In our laboratory, we have found that the electron-transfer chain
catalysis could be applied to the selective preparation of either
the chelating dppe product or the bridging dppe product at will,
taking the greatly enhanced reactivity of organometallic 17e-
or 19- radicals in comparison to the 18e-
analogues. Thus, the 2:1 mixture of (h5-C5H5)Fe(CO)2I/dppe
in THF at -78 C, after initiation with diluted MeLi and slow warming
to -50 C, produced [{(h5-C5H5)Fe(CO)2}2(m,h1:h1-dppe)2+][I-]2
precipitates in 93% yield upon addition of n-hexane. The
effect of decreasing the ratio of (h5-C5H5)Fe(CO)2I
to dppe is significant. The 1:1 mixture of (h5-C5H5)Fe(CO)2I/dppe
in THF at -78 C, initialized with diluted MeLi, produced [(h5-C5H5)Fe(CO)(h2-dppe)+][I-]
precipitates in 87% yield after the solution had been slowly warmed
to room temperature.
With trace MeLi, the 1:1 mixture
of (h5-C5H5)Fe(CO)2I/P(OMe)3
in THF at -78 C yielded the phosphonate complex (h5-C5H5)Fe(CO)2P(O)(OMe)2
after an Arbuzov-like demethylation of cationic intermediate [(h5-C5H5)Fe(CO)2P(OMe)3+][I-].
The reaction of one equiv. of MeLi with 1:1 mixture of (h5-C5H5)Fe(CO)2I/P(OR)3
(R = Me, Et, and Ph) in THF at -78 C resulted in the novel complexes
(h4-exo-MeC5H5)Fe(CO)2P(OR)3,
where MeLi is a catalyst initiator and also a methylating reagent
on the (h5-C5H5)-ring.
The stoichiometric amount of MeLi with the phosphine systems produced
similarly the ring-methylation products.
Scheme showing the electron-transfer nature on selective PR3/P(OR)3 substitution for I-.
