Reactions of Coordinated cyclic polyolefins. The synthesis and cycloaddition reactions of tricarbonyl[(1,2,3,4-η)-3,7,7-trimethylcycloheptatriene]iron

The synthesis of tricarbonyl[(1-4-η)-3,7,7-trimethylcycloheptatriene]iron (III) by two independent routes is reported. The regiospecificity of the reactions is considered in terms of frontier molecular orbitals. Complex III reacts with tetracyanoethylene to form a mixture of 1,3- and 1,6-cycloadducts in 4/1 ratio. Diphenylketene (DPK) forms a 2 + 2 adduct with III at room temperature. At 80°C an acylated addition product is obtained. In general, steric hindrance increases the yield of products formed via bipolar reactions at the expense of those formed via concerted pathways.