Convenient Solution Route To Alkylated Pentalene Ligands: New Metal Monoalkylpentalenyl Complexes

Abstract

Carbene-induced rearrangement of 8,8-dibromobicyclo[5.1.0]octa-2,4-dienes and subsequent in situ deprotonation of the dihydropentalenes formed represents a straightforward and versatile solution route to pentalene ligands for use in organometallic chemistry. We report here the synthesis of 6-alkyl-substituted 8,8-dibromobicyclo[5.1.0]octa-2,4-dienes and their rearrangement to give correspondingly substituted pentalene ligands. Generation of methyl-substituted dihydropentalenes from 8,8-dibromo-6-methylbicyclo[5.1.0]octa-2,4-diene followed by monodeprotonation with TlOEt gives methylhydropentalenyl salts, Tl(C8H6Me), as a mixture of isomers. Formation of both 1-Me and 3-Me isomers of Re(C8H6Me)(CO)3 from these Tl species shows that monodeprotonation of the dihydropentalenes occurs at the unsubstituted ring. No evidence for the 2-Me isomer is observed, consistent with the rearrangement mechanism reported in the literature. Likewise, rearrangement of 8,8-dibromo-6-alkylbicyclo[5.1.0]octa-2,4-dienes (R = Me, ...