Iron stereochemistry

Conversion of epoxides into /8-hydroxy isocyanides—preparation of trans-2-isocyanocyclohexanol, using TMSCN to open cyclohexene oxide with irons stereochemistry, followed by KF/MeOH cleavage of the intermediate silyl ether. 

It has been suggested previously (Section 37.3.1) that the relatively short W —OR bond length is indicative of bond order greater than one. If this holds true for the W —OR bonds, then for complexes of the type [WX4(OR)2] the it donor ligands OR will prefer irons stereochemistry since the d electron can be accommodated in the d y atomic orbital hich is orthogonal to the orbitals involved in the bonding of the n donor atom. Indeed, ESR spectra of the dialkoxo complexes are consistent with axial symmetry. This idea has also been put forth to explain the preference of the dioxo complexes with the d electronic configuration for the trans stereochemistry,... 

Reaction of palladium chloride with monooximes yields stable bis complexes of irons stereochemistry (34). Tetrakis(monooxime) complexes may be obtained by reaction with [Pd(acac)2]. ... 

Benzeneselenenyl azide adds to alkenes readily. The addition of the selenenyl azide always occurs with irons stereochemistry. The yield of adducts is reliably high with several different alkenes. Unlike benzeneselenenyl chloride, mixtures of regioisomers are found with simple primary alkenes. No addition occurs between benzeneselenenyl azide and ediyl crotonate. The reagent adds to conjugated dienes in a trans 1,4-fashion which is thought to be due to an initial trans 1,2-addition, followed by a facile 1,3-allylic azide shift (equation 19). Unfortunately, this reagent must be prepared and used in situ ... 

Because of the slightly pyramidal /J-lactam nitrogen bonding, the Irons stereochemistry of the /3-lactam protons, and the 7a-phenyl substituent, no antibiotic activity can be expected in the case of (140). 

Table 25.3 Oxidation states and stereochemistries of some compounds of iron, mthenium and osmium...

Nothing is known about the identity of the iron species responsible for dehydrogenation of the substrate. Iron-oxo species such as FeIV=0 or Fem-OOH are postulated as the oxidants in most heme or non-heme iron oxygenases. It has to be considered that any mechanistic model proposed must account not only for the observed stereochemistry but also for the lack of hydroxylation activity and its inability to convert the olefinic substrate. Furthermore, no HppE sequence homo-logue is to be found in protein databases. Further studies should shed more light on the mechanism with which this unique enzyme operates. 

Treatment of a-alkoxy-substituted iron acyl complexes 20 with bromine in the presence of an alcohol produces free acetals 22 with loss of stereochemistry at the center derived from the a-carbon of the starting complexl2,49. Electron donation from the alkoxy group allows formation of the oxonium intermediate 21, which is captured by the alcohol to generate the product acetal. 

Kimer JF, Dow W, Scheldt WR. 1976. Molecular stereochemistry of two intermediate-spin complexes. Iron(II) phthalocyanine and manganese(II) phthalocyanine. Inorg Chem 15 1685-1690. 

Wilker and Erker92 have studied the stereochemistry of the [4+2] cycloaddition of diarylthioketones and corresponding diaryselenoketones with Irons, trans- and cis,trara,s-2,4-hexadiene, (see later Scheme 30), and found an analogous behaviour between S and Se. 

In 1991, Thomas reported88a that the reaction between vinylketene complexes (221) and several phosphonoacetate anions generated vinylallene complexes (246), in some cases with extremely high stereoselectivity.88,89 This Wadsworth-Emmons type reaction occurs via attack by the phosphonoacetate carbanion at the ketene carbonyl carbon, and product ratios clearly depend on the steric bulk of the R and R substituents. The relative stereochemistry of the major isomers of 246 were determined by X-ray analysis. Upon oxidation of the vinylallene complexes with iron(III) chloride, a range of substituted furanones were isolated.8813,89... 

The stereochemistry is assumed to involve retention of configuration by analogy with the above reaction. The obtained complex appears to be irons by IR spectroscopy. 

The comparison between iron and manganese complexes, despite their electronic and geometrical resemblances, is difficult because of the highly specific hydrogen-silicon interactions in the case of the manganese complexes. The difference in stereochemistry can certainly be attributed to these interactions in the manganese complex. 

Rhodobactin (31) was isolated from Rhodococcus rhodochrous (86). A sequence of four Om units derivatized in different ways is linked together. The nitrogen atoms of the N-terminal Om are substituted with DHB groups, the N-terminal Om is followed by two Om moieties, for which the N -amino groups are transformed into urea units (NH2CONH-), and the C-terminus is cOHOm. The stereochemistry of the Orn units was not determined. Rhodobactin forms a 1 1 Fe /Lig complex. Iron uptake was studied with Fe ". ... 

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