Acyclic Pentadienyl Complexes of Transition Elements

Methods of preparation of pentadienyl compounds are summarized in Table II. 

The preparation of pentadienylsodium was being studied at about the same time as ferrocene was discovered. It was not until 1968, however, that the first binary pentadienyl complex of a transition element, bis(pentadienyl)-chromium, was obtained from PINa and CrCl2 (121). This compound forms green, air-sensitive crystals, and like chromocene it has two unpaired electrons (Ht = 2.74 BM). This discovery was shortly followed by that of the curious complex, bis(pentadienyl)dinickel (12) which was prepared from NiCl2 and triethylaluminium in 1,4-pentadiene (122). The pentadienyl ligands in 12 

These compounds remained curiosities for over 10 years until R. D. Ernst obtained open ferrocenes from methyl-substituted pentadienylpotassiums and FeCl2 in thf [Eq. (11)]. The orange-red complexes FePl2 can be sublimed 

Diene + base (M), e.g., 1,4-pentadiene + BuLi-thf, 1,4-pen tadiene + KNH2-NH3, 1,3-pentadiene + BuLi-KOBu -thf II,A 

Chloro- or bromodiene + metal (M), e.g, PlMgCl, PlZnBr, P1jA12CI3 (NOT alkali metals, coupling) II,D 

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