Iron complexes, with cycloheptadiene

Reactions of complexes of 1,2-cycloheptadienes have received only cursory attention. 1,2-cycloheptadiene is readily displaced from bisftriphenyl-phosphine)platinum(O)118 [Eq. (54)], but no reagent has been found that will displace the allene from iron.119 Reaction of the iron complex with alcohol in the presence of base (e.g., 312 — 322) is typical of Fp+ complexes of acyclic allenes.131132 The thermal chemistry of 312 is unusual in its decomposition to 324 (Scheme 41). This is probably attributable to the presence of the triflate counterion, since the corresponding fluoroborate salt is stable when warmed to 40°C for 16 h.119 A mechanism to 324 via carbene complex 321 appears likely. 

High stereospecifity has been found in the reaction of HFA with tricarbonyl (> -cycloheptadiene)iron complexes, 126, 127). 

Cycloheptadienyl-iron complexes. Cyclohcptadienyl-Fe(CO), reacts with nucleophiles to give mixtures of products, usually in low yield. However, complexes 1, in which one CO ligand is replaced by triphenylphosphinc or triphenyl phosphite, react with most nucleophiles at the dienyl terminus and in high yield. Hydride abstraction followed by reaction with a second nucleophile results in a regio- and stereocontrol led substitution at the opposite terminus and again anti to the metal. Decomplexation affords ri.v-5,7-disub-stituted cycloheptadienes. 

The complex functions as a convenient source of the tricarbonyliron moiety by displacement of the unsaturated ketone. For example, reaction with 1,3-cycloheptadiene results in a 78% yield of (//-l,3-cycloheptadiene)tricar-bonyliron. More importantly, it may be used in syntheses of tricarbonyl-(diene)iron complexes where the iron carbonyls are not satisfactory. Several complexes of sensitive heptafulvenes have been prepared in this way, and the reagent has been used in the synthesis of tricarbonyliron complexes of several steroids. 

Tricarbonyl(2,4-cycloheptadiene-l,6-dlone)iron complexes can be alkylated with Grignard reagents to generate tertiary alcohols. Monoalkylated or dialkylated products are obtained depending on the equivalents of the alkylating agent applied. In both cases, a clean anti attack of the nucleophile in respect to the iron center is observed. 

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