Synthesis, Characterization, and Structural Studies of Transition Metal Open Fulvalene Complexes

Abstract

Starting from the 3-methylpentadienyl anion, a route to 3,8-dimethyl-1,3,5,7,9-decapentaene has been devised. This pentaene reacts readily with Co(C5H5)(C2H4)2 or [Ru(C5Me5)Cl]4 (2 and 0.5 equiv, respectively) to yield the expected (η4,η4‘-decapentaene)dimetal complexes, in which the two external diene fragments of the pentaene are each coordinated to a metal center, leaving the central CC bond uncoordinated. Subsequent respective two-electron oxidation or reduction then leads to (η5,η5‘-dimethyldecapentaene)MLn species (MLn = Co(C5H5)+ or Ru(C5Me5)). The first three complexes have been found to exist as mixtures of two isomers, and structural studies have confirmed the natures of the two open fulvalene (η5,η5‘) complexes. A related reaction, involving the reduction of [V(C5H5)Cl(PMe3)2]2 and the pentaene with magnesium, has been found to lead to a similar η5,η5‘ complex for which MLn = V(C5H5)(PMe3). Its structural nature has also been confirmed through a diffraction study.