Iron pentacarbonyl, photolytic

In this section, we start by describing the main features of the photolytic chemistry of iron pentacarbonyl and related species, focusing on the experimental data. We then describe our and other people s computational work aimed at understanding the reactivity of the fragments formed upon photolysis, with a focus on the spin-forbidden steps. We consider, in turn, the addition of ligands to Fe(CO)4, Fe(CO)3, and Fe(CO)3L (where L is a ligand such as H2 or ethene). For some of the reactions, we include some new computational results as well as a review of existing work. 

Sarel and co-workers have examined some reactions of alkynylcyclopropanes with iron carbonyl compounds [1]. Treatment of cyclopropylacetylene (5) with iron pentacarbonyl under photolytic conditions gives, after cerium(IV) oxidation, isomeric quinones 6 and 7, derived from two molecules of 5 and two carbonyls with both cyclopropane rings intact [6]. Furthermore, the photoreaction of dicyclopropylacetylene (8) with iron carbonyl gives some ten different products depending on the reagents and the reaction conditions, and some of them have the cyclopentenone skeleton formed by the opening of cyclopropane ring coupled with carbonyl insertion [7] (Scheme 2). 

DIBAL-H/n-butyllithium, in cyclic and acyclic systems with iron pentacarbonyl, in cyclodecanes with lithium dihydrodimethoxyaluminate(III)/copper(I) iodide, and in cyclohexane and cyclopentane systems with NaH/sodium r-butylpentyl/Ni(OAc)2. ° The monoreduction of 1,3-diketones can be carried out under similar conditions, as illustrated by the reaction of a substituted cyclohexane-1,3-dione with oxalyl chloride to give the corresponding 1-chlorocyclohexenone, which was subsequently reduced to the enone with zinc-silver couple (Scheme 45). Kropp et al. have reported the photolytic reduction of vinyl iodides in acyclic systems however, when an a-hydrogen is present, formation of the diene product is a limiting side reaction (Scheme 46). For a more extensive discussion of vinyl halide reductions, see the preceding chapter in this volume. 

An extensive and a systematic photochemical studies had been done on 2-isoxazoline. Photolysis of 2-isoxazolines always result in a mixture of products, depending upon the nature of the substituents. Three possible different pathways of photolytic cleavage are reviewed <9iHC(49)l>. Ultraviolet irradiation of 5-unsubstituted 2-isoxazoline (127) in the presence of iron pentacarbonyl, resulted in ring fragmentation products (a ketone (128) and aldehyde (129)) as well as N—O bond fission products ((130) and (131)) (Scheme 21). The plausible mechanism involves N-donor complexation with photochemically generated pentacarbonyl, prior to N—O and C(3)—C(4) bond fissions <83CL51>. 

Hartwig successfully demonstrated the photolytic activation of the B—B bond in B2cat2, and related substituted catechol derivatives, with iron pentacarbonyl. These oxidative addition reactions of the chborane... 

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