ChemInform Abstract: Coordination Chemistry of Siloles: Synthesis, Reactions, and Stereochemistry of Silicon-Substituted (η4-2,5-Diphenylsilacyclopentadiene)transition-metal Complexes. Crystal Structure of Dicarbonyl(phenyl((η4-exo-1-methyl-2,5-diphenylsilacyclopentadien-1-yl)oxy)# carbene)iron.

ChemInform Abstract

The synthesis of the title complexes derived from the siloles (I), (XII) and (XVII) and the reactivity of these and of (XXII) are described. (VI) and (XIII) are separated from mixtures with the corresponding endo or exo isomer by fractional crystallization. The complexes undergo a variety of substitution reactions at Si in which the exo leaving groups show enhanced reactivity. The derivatives (VIIc) and (VIId) are prepared from (VI) with Co₂(CO)₈ and SbF₅ intercalated in graphite. The stereochemistry of substitution at Si with nucleophiles differs significantly from that established for optically active silanes. The exo- and endo-chloro leaving groups are displaced with retention of configuration at Si. These observations suggest that the stereochemistry is controlled only by electronic factors. The endo-chloro derivative (XIII) reacts with organolithiums (XV) to give new carbene complexes (XVI). (XVIa) is characterized by a crystal structure determination ( P2₁/n, Z=4). In the case of the exo-chloro isomer (VIIa) the reaction course depends on the nature of the Li compound. The reaction of (XVII) with Co₂(CO)₈ and some reactions of (XXII) (with PCl₅ and MeOH to give (XXIVb) and (XXIVc)) are shown in the scheme.