Norbornadiene complexes with iron

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 ... 

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... 

Pyrazoles can be synthesized by thermal cycloreversion of adducts formed in the 1,3-dipolar cycloaddition of alkyldiazoacetates with norbornadiene. The rate of the primary process of cycloaddition is accelerated by iron pentacarbonyl (Scheme 88)155 a similar catalytic effect has been observed during the formation of ethyl 5-phenyl-A2-pyrazoline-3-carboxylate from cycloaddition of ethyl diazoacetate and styrene.155 Reactions of this type are catalyzed presumably because of coordination of one or both reactants to the transition metal, and a wider study of the effect of a variety of complexes on 1,3-dipolar cycloaddition processes would be valuable. 

Cookson and co-workers treated norbornadiene with diiron nonacarbonyl in the dark and isolated five ketones and four dimeric hydrocarbons. The highest-melting dimer, m.p. 163-164°, was isolated easily in 4% yield because it is the first component eluted from a column of silica gel. Lemal and Shim isolated the same dimer from a complex mixture resulting on irradiation of a mixture of norbornadiene and iron pentacarbonyl. Initial characterization excluding alternative structures indicates... 

The use of transition metal complexes as catalysts allows 1,4-cycloadditions to be involved as the major pathway in several cases when conjugated dienes are reacted with norbornadiene. No normal homo-Diels-Alder reaction was observed by reaction of the latter with buta-1,3-diene in the presence of an iron complex catalyst, the main product obtained was such a 1,4-adduct 2f the same adduct 2 was obtained in good yield and selectivity when a catalyst formed from cobalt(II) chloride, diethylaluminum chloride and bis(l,2-diphenylphos-phinojethane was used. ... 

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