[(ARENE)(DIENE)FE] AND [(ARENE)(DIAZADIENE)FE] COMPLEXES - PREPARATION, REACTIVITY, AND CATALYTIC PROPERTIES

Two different routes to novel [(diene)(eta(6)-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridin e is essential for the eta(6)-coordination of the heterocycle. investi gations on the reactivity and stability of the [(diene) (eta(6)-arene) Fe] complexes are presented, including those of the benzene, phosphini ne, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron a tom and a pi-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5- cyclooctadiene (GOD) Ligand of [(COD)(eta(6)-arene)Fe] complexes by so me 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of th e benzene or phosphinine arene Ligands, and [(DAD)(eta(6)-arene)Fe] co mplexes are formed, but all DAD derivatives tested so far cause the co mplete disintegration of [(COD) (eta(6)-2,6-dimethylpyridine)Fe]. [(DA D)(eta(6)-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-bu tadiene in the presence of [(Et2AlOEt)(2)] as a co-catalyst. This reac tion yields up to 92% of 1,Ei-cyclooctadiene, and an almost quantitati ve butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N'-bis(cyclohexyl)et hylenediimine) (-eta(6)-toluene)Fe] 5a reveal some details of the Fe-D AD interaction. An effective electron back-donation from occupied iron d-orbitals into the pi-LUMO of the DAD is indicated.