INVESTIGATION OF THE INTERMEDIATES IN THE OXIDATION OF A BULKY ARYLPHOSPHINE LIGAND WITH FERRIC-CHLORIDE
Academic Article
Overview
Research
Identity
Additional Document Info
Other
View All
Overview
abstract
The syntheses, spectroscopic properties and structures of iron(II) and iron(III) complexes prepared by reactions of ferric chloride with the tertiary phosphine ligand tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) are described. The novel diferrous chloride salt [H-TMPP]2[Fe2Cl6] (1) was prepared by the reaction of anhydrous ferric chloride with 1 equivalent of TMPP in benzene or diethyl ether. This redox reaction also produces [TMPP-Cl][FeCl4] (2) as the oxidized by-product. The structure of 1, determined by single-crystal X-ray diffraction, revealed that the [Fe2Cl6]2- anion consists of two edge-sharing tetrahedra with two terminal and two bridging chlorides per metal atom. Dissolution of complex 1 in ethanol produces [H-TMPP]2[FeIICl4] (3), which was identified on the basis of a preliminary X-ray investigation. Compound 3, independently prepared by the reaction of [Fe(NCCH3)6][AlCl4]2 with 2 equivalents of TMPP in methanol, reacts with molecular oxygen to initially form [H-TMPP][FeIIICl4] (4) and finally the phosphine oxide species FeCl3(OTMPP) (5). The structure of 4 was determined by single-crystal X-ray diffraction. To test the importance of compound 4 as an intermediate in the production of TMPPO, it was prepared directly by reaction of [Fe(NCCH3)6][SbCl6]2 with 2 equivalents of TMPP in methanol and reacted with oxygen to give 5 in high yield. Compounds 1-5 were further characterized by IR and electronic spectroscopies, as well as by elemental analyses. The reactions of the salts 1, 3 and 4 suggest that the oxidation of tertiary arylphosphines with FeCl3 in alcohols does not proceed via the formation of dioxygen complexes, but rather via quaternarization of the phosphine ligand. 1993.
