Reaction of Unconjugated Dienes with [Fe(R₂P(CH₂)_nPR₂)] Species^†

The effect of varying the bidentate ligand upon the reaction of unconjugated dienes with (R₂P(CH₂)_nPR₂)Fe⁰ species has been investigated. Depending upon the nature of the substituents at phosphorus and upon the length of the hydrocarbon chain joining the phosphorus atoms, either (η²:η²-diene)Fe(R₂P(CH₂)_nPR₂) or (η⁵-dienyl)Fe(R₂P(CH₂)_nPR₂)H species are formed. Extended Hückel MO-calculations have been used to assess the importance of electronic factors in influencing the course of reaction, and it can be shown that distortion of the tetrahedral geometry of the (diene)Fe species causes a destabilization.