Synthesis of organometallic pentalenide complexes

Abstract

Challenges and opportunities in the synthesis of pentalenide complexes are reviewed from a practical point of view.

Synthesis of a Tetraphenyl-Substituted Dihydropentalene and Its Alkali Metal Hydropentalenide and Pentalenide Complexes

“…The ease and efficiency of this one step reaction is striking when compared to the difficulties of preparing the unsubstituted and permethylated pentalenide precursors. 17 In addition, while the isomeric mixture of PnH 2 obtained from anaerobic flash vacuum pyrolysis easily polymerizes and is only stable at −78 °C in dilute, anaerobic pentane solution, 30 1,3,4,6-Ph 4 PnH 2 is an air-and water-stable solid that melts at 180 °C without decomposition. The product is formed exclusively as the racemic 1,2-isomer, and attempts to induce isomerization to the 1,5-isomer either through prolonged heating to 200 °C or exposure to silica and acidic alumina (as described for 1,3-Ph 2 PnH 2 ) 26 were unsuccessful.…”

“… The ease and efficiency of this one step reaction is striking when compared to the difficulties of preparing the unsubstituted and permethylated pentalenide precursors . In addition, while the isomeric mixture of PnH 2 obtained from anaerobic flash vacuum pyrolysis easily polymerizes and is only stable at −78 °C in dilute, anaerobic pentane solution, 1,3,4,6-Ph 4 PnH 2 is an air- and water-stable solid that melts at 180 °C without decomposition.…”

“…16 However, both the unsubstituted Pn 2− and the permethylated Pn* 2− are not trivial to synthesize, and there are no examples of well characterized and easily accessible arylsubstituted pentalenides. 17 As demonstrated in the pentaphenyl Cp BIG , 18,19 aryl substituents combine steric bulk with electron withdrawing properties through resonance effects that could prove useful in accessing new pentalenide complexes featuring highly reactive, electron-rich metal centers.…”

“…1,2,3,4,5,6-Me 6 Pn 2– , which can be thought of as the permethylated Cp* equivalent for pentalenides, has also be used to synthesize a range of early and late transition metal complexes. − Silylated Pn 2– derivatives, synthesized by functionalization of unsubstituted pentalenide in the 1 and 4 positions, have also been described . However, both the unsubstituted Pn 2– and the permethylated Pn* 2– are not trivial to synthesize, and there are no examples of well characterized and easily accessible aryl-substituted pentalenides . As demonstrated in the pentaphenyl Cp BIG , , aryl substituents combine steric bulk with electron withdrawing properties through resonance effects that could prove useful in accessing new pentalenide complexes featuring highly reactive, electron-rich metal centers.…”

Connect Four: Tetraarylated Dihydropentalenes and Triarylated Monocyclic Pentafulvenes from Cyclopentadienes and Enones

“…Due to their unsaturated polyquinane framework, 1,2-dihydropentalenes ( PnH 2 ) have been widely utilized in organic photochemistry, cycloaddition reactions, and natural product syntheses − PnH 2 have also found use in organometallic chemistry, where they serve as precursors for dianionic pentalenide ligands . These bicyclic 10 π aromatic compounds have generated interest due to their unique coordination properties, including the formation of electronically coupled bimetallic complexes. , Over the last six decades, few approaches for the synthesis of dihydropentalenes have been demonstrated .…”