Fulvalenes metallocene-derived complexes

While metallocene-derived complexes 103 deserve interest mainly because of their redox properties and applications resulting therefrom, half-sandwich complexes 104 and 105 show more diverse chemical reactions. Based on their synthesis of the fulvalene dianion 102, Smart et al. [99] prepared some molybdenum complexes such as 108 [62% yield based on Na(DME)Cp] by treatment of 102 with molybdenum hexacarbonyl followed by oxidation with bromine. Vollhardt reported the synthesis of a variety of homo- and heterodinuclear fulvalene complexes such as 109-112 by treatment of dihydrofulvalene and respective metal carbonyls. The dichromium complex 110 has some catalytic activity in the hydrogenation of conjugated dienes [110]. The authors report the reaction with iron carbonyls being unsuccessful, whereas the reaction with dicobaltoctacarbonyl resulted in the formation of fulvalene complex 112 lacking a metal-metal bond in 80% yield (Scheme 10.38) [100, 101]. Later, the diiron complex corresponding to 109 was reported [111]. Hermann et al. and Cuenca etal. prepared zirconium(IV) and zirconium(III) fulvalene complexes [112,113]. 

A number of molecular mechanics studies of metal-cyclopentadienyl complexes have been reported recently. The systems studied include linear metallocenes (in particular ferrocene), ferrocene derivatives (such as complexes with substituted cy-clopentadienyl ligands, bis(fulvalene)diiron complexes, ferrocenophanes and mixed-ligand complexes with carbonyls and phosphines), and nonlinear cyclopentadienyl complexes 8,153,221 231]. 

Other derivatives such as CpCo(indenyl) and Co(indenyl)2 have been prepared. These compounds exhibit properties similar to that of cobaltocene but are of lower thermal stability. There have been numerous studies of linked metallocenes with a focus on the nature of metal-metal interactions. The bis(fulvalene)dicobalt complex was found to be diamagnetic, either because of direct metal-metal coupling or by electron coupling through the fluked five-membered ring (Scheme 30). 

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