Two routes are described for the synthesis of
(η4-1,5-cyclooctadiene)(η6-phosphinine)iron(0) complexes. A three-component reaction of iron vapor with COD
and 2-(trimethylsilyl)-4,5-dimethylphosphinine at low temperature yields 20%
(COD)(2-(trimethylsilyl)-4,5-dimethylphosphinine)Fe(0) (3), whereas ligand
exchange of one COD ligand of the in situ
prepared metal vapor product (COD)2Fe by
2-(trimethylsilyl)-4,5-dimethylphosphinine or
(η1-2-chloro-4,5-dimethylphosphinine)Cr(CO)5
gives corresponding (COD)(phosphinine)Fe(0)
complexes in more than 80% isolated yield. As the phosphinine
derivatives are prochiral,
complexation leads to the racemate of two enantiomers. Both
enantiomers are found in the
unit cell of single crystalline 3 and are related by an
inversion center. Complex 3 is a novel
room-temperature catalyst for the [2 + 2 + 2] cyclic addition
reaction of one molecule of
butyronitrile with two molecules of methyl propargyl ether giving up to
160 mol of pyridine
derivatives/mol 3. A chemically robust species, 3
is an air-stable crystalline material, but
exposure to oxygen in solution causes slow decomposition.
Efficient synthetic routes are described, leading to novel n^-phosphinine-(1) and n, 6 -l,3-diphosphinine (4,5) iron(0) complexes. 1 is a catalyst for pyridine formation by a [2+2+2]-cyclic addition reaction of nitriles and alkynes and 4 is a useful source of unsaturated free four and six membered organophosphorus rings.
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