Iron complexes, with cycloheptatriene

C7H7)Fe.,(CO)6]+, obtained by reaction of the cycloheptatriene complex with trityl tetrafluoroborate, shows in solution a rapid valence tautomerisrn involving diene bonding to an iron atom and Tr-allylic bonding to the other. 

Diene iron tricarbonyl complexes are prepared by thermal or photochemical reaction of conjugated dienes with iron pen-tacarbonyl in the presence of TMANO, triiron dodecacarbonyl, ()]" -benzylidenacetone)iron tricarbonyl, diiron nonacarbonyl, or diiron nonacarbonyl absorbed on silica gel in the absence of solvent. The latter method is particnlarly usefiil for the preparation of complexes from polar electron-rich dienes and heterodienes. A reductive complexation of cycloheptatrienes using iron tricarbonyl and sodium borohydride to give cyclo-heptadiene iron tricarbonyl has been developed (Scheme 126). 

Various unsaturated cyclic 7t-ligands undergo, within a transition-metal complex, cycloaddition reactions and rearrangements with simultaneous formation of cyclopropane subunits. This is observed with cycloheptatriene ehromium and iron complexes such as 4 which give cycloaddition products, e.g. 

The most facile syntheses of diolefin complexes are those in which the diolefin reacts with a coordinatively unsaturated metal complex without ligand displacement. Thus a unidentate norbornadiene complex of iron, [Fe(f -Cp)(CO)2( 7 -NBD)][BF4], can be prepared by treating [Fe( j -Cp)(CO)2]2 with xs Ph3C[BFJ, followed by quenching with cycloheptatriene prior to addition of norbornadiene . Tetracoordinate complexes of Ir(I) undergo diolefin addition ... 

Two distinct observations are made with respect to the hydrogenation of olefin 7i-complexes with catalysts such as raney nickel. When the olefin is firmly bound to a metal, complete catalytic hydrogenation is prohibited. Thus 7i-cyclopentadienylcobalt cyclooctatetraene (6-22), 7r-cyclopentadienyl tt-cyclopentadiene rhenium dicarbonyl (6-23), and Tr-cycloheptatriene iron tricarbonyl (6-24), each of which contains at least one uncomplexed double bond, readily undergo hydrogenation of the uncomplexed bonds only. The metal-olefin bond is preserved in each case. 

The 7t-(C6)M system is also present in the complexes of cycloheptatriene (C7Hg), when this olefin is bonded to transition metals requiring six it electrons, such as the metals of the chromium subgroup 27) (Table XIX). It should be noted that in its complexes with the iron carbonyls, this ligand is bonded as a 7r-(C4)M system. It was ascertained through chemical and spectroscopic evidence that the third olefinic bond was not participating in coordination to the metal 48) (Table XV). 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

The metal-mediated and metal-catalyzed [6 + 2]- and [6 + 4]-cycloaddition reactions, pioneered by Pettit and co-workers105 106 and Kreiter and co-workers,107 respectively, involve the cycloaddition of metal-complexed cyclic trienes with 7r-systems such as alkenes, alkynes, and dienes. The [6 + 2]-reactions produce bicyclo[4.2.1]nonadiene derivatives and the [6 + 4]-reactions produce bicyclo[4.4.1]undecatrienes (Scheme 32). Trienes complexed to chromium, which can be prepared on large scale (40 g) as reported by Rigby and co-workers,108 react with 7r-systems upon thermolysis or irradiation.109-111 Chromium and iron-catalyzed [6 + 2]-reactions of cycloheptatrienes and disubstituted alkynes... 

A related >/4-norcaradiene tricarbonyliron complex is obtained upon reaction of tricy-clo[4.3.1.0l6]deca-2,4-diene with Fe3(CO)12 in boiling benzene (equation 143). However, the [4.3.1]propellane ring system is not retained in the analogous tricarbonylchromium complex. Instead, as suggested from solution NMR and solid state X-ray analyses, the complex assumes a homoaromatic structure, which is intermediate between a norcaradi-ene and a cycloheptatriene system (equation 144)193,194. It is noteworthy that the Cr(CO)3 group prefers the same conformation as the Fe(CO)3 group in the analogous norcaradiene iron complex. 

Reaction of (CN C—C(CF3)2 with [Fe(cycloheptatriene)(CO)3] yields adduct (39), which under CO pressure gives tricyclic ketone (40) presumably via iron-acyl complex (41 equation 16).47... 

When this hydride abstraction was tried with the iron-cycloheptatriene analog, a carbonium ion complex was formed, but by trityl alkylation. 

Double bonds adjacent to complexed dienes can be cyclopropanated using diazomethane, methyl diazoacetate, or sulfur-based ylids. Cycloheptatriene iron tricarbonyl undergo a [2 -F 2] cycloaddition with chloroketene derived from trichloroacetyl chloride (Scheme 161). 

C7Hg)Fe(CO)3 but also the diene complex (C7Hio)Fe(CO)3 (60) and a trinuclear complex for which structure (110) has been suggested (470). Formation of the diene complex in this reaction obviously involves a rather uncommon intermolecular hydrogen transfer (470). The reaction of Fe2(CO)9 with either 1,3,5-cycloheptatriene or its 7-methoxy derivative yields the complex (triene)Fe2(CO)8 (190), the Mossbauer spectrum of which shows chemically equivalent iron atoms. This, with... 

Cycloheptatriene does not react with Fe(CO)s to give the expected dicarbonyl complex 7i -C7H8Fe(CO)2, but forms instead a mixture of tricarbonyl complexes derived from cycloheptatriene and cyclohepta-1,3-diene (20, 35). This work, together with protonation and related reactions of the free double bond of 7r-C7HsFe(CO)3, have been summarized by Pettit and Emerson (118). More recently, Pettit and co-workers (101) have shown that (7-methoxycycloheptatriene)Fe(CO)3 is protonated by fluoro-boric acid with loss of methanol to give the ir-tropylium-iron tricarbonyl cation. 

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