Octadiene iron tricarbonyl

Reaction of n -octadiene iron tricarbonyl (mixed isomers) with tr iphenvlcarbenium tetrafluoroborate ... 

The generic structure is indicative of random incorporation of dienyl iron tricarbonyl moieties, corresponding to 1,3 octadiene-, 2,4 octadiene- and 3 5 octadiene-iron tricarbonyl. We have found that a derivative of constant stoichiometry is obtained ia the thermal decomposition of an excess of Fe(C0)5 dilute xylene solution of c/5-poly(butadiene). The polymer is a bright yellow, air-stable, solid which was conveniently isolated from benzene by lyophilization (see Experimental). The purification procedure detailed in the Experimental Section is a key factor in the stability of the product. 

Figure 4. NMR spectrum of ij -octadiene iron tricarbonyl mixed...

Dihydromesitylene likewise gives a 1,3 complex (34) and 1,4-cyclohexadiene gives 1,3-cyclohexadieneiron tricarbonyl. 1,5-Cyclo-octadiene on treatment with catalytic quantities of Fe(CO)g gives 1,3-cyclooctadiene (35), as the iron tricarbonyl complex is probably not very stable and is continuously displaced by fresh 1,5-diene until isomerization is complete. 

In order to identify the structure of the polymer, we compared the spectral characteristics (IR/NMR) of this product with those of an appropriate octadiene derivative. Based on the work of Pettit, et al.- it would be predicted that octadienes could react with Fe(C0)5 to yield as many as six isomeric dienyl iron tricarbonyl compounds. 

C/5-2,6 octadiene would be the most appropriate small molecular model for the repeat unit in m-poly(butadiene). However, in light of the fact that FeCCO) catalyzes double bond migration and isomerization any isomeric octadiene monomer should serve as an appropriate model for the polymer reaction. We reacted 1,7-octadiene with FeCCO) and obtained a simple infrared spectrum which was nearly identical to that for the reaction product of c/5-poly (butadiene) with Fe(C0)5, i.e., both materials displayed two discrete peaks in the carbonyl region, a sharp peak at 2050 cm and a broad absorption ( "30 cm HWHH) centered at 198O cm" (See Fig. 2). The broad unresolved character of the 1980 cm" band, as compared to that in rj -butadiene iron tricarbonyl which shows discrete sharp peaks at 1980 and 1990 cm in addition to the sharp peak at 2056 cm", can be understood in terms of the variety of isomeric diene iron tricarbonyls which can be formed in the reaction of FeCCO) with either c/5-poly(butadiene) or 1,7-octadiene. 

Figure 2. Isomeric diene iron tricarbonyl expected from the reaction of Fe(CO)5 and octadienes...

The 3c-nmR spectrum of the thermal reaction product between 1,7-octadiene and FeCCO) (Fig. M) is complex and consists of 24 principal peaks which can only be accounted for in terms of the formation of a minimum of the six isomeric octadienyl iron tricarbonyl compounds shown in Fig. 2. While we have not unequivocally assigned each of these peaks, the eleven peaks at high field (14-40 ppm) are due to -CH and -CH2 carbons. The six peaks at (53-66 ppm) are mainly derived from the 1,4 carbons of the diene and the six peaks at 81-93 Ppm may be attributed to the 2,3 carbons of the diene. The low field doublet at 212 and 213 ppm derives from the carbonyl carbons and is indicative of two distinct carbonyl environments. 

Group VIII. Iron. Products of the reaction of tricarbonyl-(l,2,3,6-A -cycIo-octadiene)-iron (8) with phosphines depend on the nucleophilicity of the base. In the case of PPha and P(OPh)3, (9) is formed by carbonyl dissociation followed by addition of the base. This leads to the familiar rate law... 

---