Reductive coupling of dimethylfulvene with alkaline earth metals yields inseparable mixtures of the tetramethylethylene-bridged complex Me 4 C 2 (C 5 H 4 ) 2 M and the unbridged metallocene (i-PrCp) 2 M (M ) Mg, Ca, Sr, Ba). In contrast, the reductive coupling of phenylfulvene with activated calcium in THF gives nearly quantitative yields of a mixture of cis-and trans-diphenylethanediyl-bridged ansa-calcocenes. The more soluble cis isomer can be removed by recrystallization, yielding the C 2 -symmetric trans-Ph 2 C 2 H 2 (η 5 -C 5 H 4 ) 2 Ca-(THF) 2 (trans-2). The molecular structure of this ansa-calcocene shows the cyclopentadienyl rings to be bound in an η 5 fashion to the calcium center. This versatile reagent gives high yields of C 2 -symmetric transition metal ansa-metallocene complexes via the facile reaction of trans-2 with metal chlorides (e.g., FeCl 2 and ZrCl 4 ). The molecular structure of the corresponding ansa-zirconocene dichloride complex is described.
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