An Efficient, Modular Route to New 2-Acyl-6-aminopentafulvenes and Planar-Chiral [N,O]-Functionalized Pentamethylruthenocenes

A modular, one-pot synthetic protocol was developed for new pentafulvenes containing hydrogen-bridged amino and carbonyl substituents. Starting from sodium cyclopentadienide, first an acyl functionality is introduced by reaction with various carboxylic esters, followed by regioselective iminoacylation with differently substituted imidoyl chlorides, giving access to a first family of 10 different 2-acyl-6-aminopentafulvenes. After deprotonation, these new ambidentate [N,O]H ligands react with early/hard transition metal synthons to give seven-membered metal-chelate κ2-complexes, or with electron-rich late transition metal synthons, e.g., pentamethylruthenium(II) hexafluorophosphate, to give planar-chiral, functionalized η5-sandwich complexes. A second family of 1-acyl-2-imidoylpentamethylruthenocenes is thereby easily accessible as new ruthenocene [N,O]-metalloligands and for further use as planar-chiral synthons. Chemoselective and diastereoselective reduction of the acyl functionality gives imino(pentamethyl)ruthenocene alcohols as a third family of [N,O]H-metalloligands. For one case it is shown that such imino(pentamethyl)ruthenocene alcohols react with oxophilic Zr(IV) under ring closure to a novel pentamethylruthenocene-annelated 2H-pyrrolium salt. All new compounds were fully characterized by spectroscopic methods, and 22 single-crystal X-ray analyses are reported.