Tricarbonyl iron complexes electrophilic attack

Cycloaddition.— Reactions of electrophilic olefins and acetylenes with tricarbonyl-iron complexes of cycloheptatriene and cyclo-octatetraene lead to 1,3-exo-products. Troponetricarbonyliron and tcne, however, have now been found to give complex (20) which results from previously unobserved 1,5-exo-cycloaddition. A dipolar intermediate (21) resulting from initial attack by the electrophile on the hydrocarbon... 

Reaction of tricarbonyl(tropone)iron with tetracyanoethylene gave the 1 1 adduct (602) the similar reaction of the 2-deuteriotropone complex gave exclusively (603). It is concluded that electrophilic attack by TCNE occurs exo to the iron atom and at a non-co-ordinated double bond of the substrate. The tricarbonyl(bicyclo[6,l,0]nona-2,4,6-triene)chromium complex is reported to rearrange at 100 °C almost completely to (604). 2... 

As cations, cobalt tricarbonyl diene complexes 10.86 are also more electrophilic than the iron tricarbonyl complexes (Scheme 10.21). The product of nucleophilic attack is a T -allyl cobalt complex 10.87, which is still electrophilic and may undergo a second attack. 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

Cyclobutadiene-iron tricarbonyl is prepared through reaction of S,4-dichlorocydolmtene and diiron enneacarbonyl. In an analogous manner, one can prepare 1,2-diphenyl- 1,2,3,4-tetramethyl- and benzocyclobutadiene-iron tri-carbonyl complexes. Cyclobutadiene-iron tricarbonyl is aromatic" in the sense that it undergoes facile attack by electrophilic reagents to produce monosubstituted cydo-butadiene-iron tricarbonyl complexes. Functional groups in the substituents display many of their normal chemical reactions which can be used to prepare further types of substituted cyclobutadiene-iron tricarbonyl complexes. 

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