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-(C 8 H 6 Me), as a mixture of isomers. Formation of both 1-Me and 3-Me isomers of Re(C 8 H 6 Me)(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, Et, i Pr) and subsequent double deprotonation with n BuLi in the presence of DME affords the pentalenyl salts Li 2 (C 8 H 5 R)‚xDME. X-ray crystallographic studies of the dinuclear Mn organometallics anti-[Mn-(CO) 3 ] 2 (C 8 H 5 R) synthesized from the Li salts confirm that these alkylated pentalene ligands are substituted at the 1-position exclusively. The crystal structure of a model hydropentalenyl complex, Re(C 8 H 7 )(CO) 3 , is also reported.

Metal–Metal Electronic Coupling in syn and anti Stereoisomers of Mixed‐Valent (FeCp)2‐, (RhL2)2‐, and (FeCp)(RhL2)‐as‐Indacenediide Ions

“…In complexes in which two transition metals are anchored to two cyclopentadienyl (Cp) rings, a variety of spacers connect the two Cp rings,1d, n in the most prominent of which the two rings are 1) directly linked by a σ bond (fulvalenyl);4 2) separated by saturated linkers XR 2  (X=C, Si, Ge);5 3) connected by unsaturated (CHCH) n 6 or (CC) n 7 chains (molecular wires) or arylene groups Ar;8 and 4) fused in rigid polycyclic aromatic systems (pentalene,1n, 9a–c, g indacene,1n, 9d–h dicyclopentanaphtalene9i–k dianions, etc. ).…”

Synthesis of organometallic pentalenide complexes

“…Jones et al later showed TlOEt in pentane to be equally effective in generating TlPnH from H 2 Pn. 10 The first pK a of H 2 Pn must therefore be below 14, showing it to be slightly more acidic than HCp. 11 Presumably due to charge effects, deprotonation of the second ring in HPn − to furnish the fully 10π delocalised Pn 2− requires a stronger base.…”

“…Treating the gem-dibromo cyclopropane unit in these species with methyllithium furnished 1-alkyl substituted H 2 Pn, which gave high yields of Li 2 [1-alkyl-Pn] upon double deprotonation with n butyllithium (53-70%). 10 Another synthesis of H 2 Pn via carbene rearrangement has been reported by Brinker and Fleischhauer. 29 trans-1,2-Bis(2.2dibromocyclopropyl)ethane, formed by twofold reaction of trans-1,3,5-hexatriene with CHBr 3 and KO t Bu, was found to rearrange to H 2 Pn when treated with methyllithium in diethyl ether.…”

“…10). 10 Reacting this species with methyllithium triggered a carbene-induced rearrangement to give H 2 Pn which was trapped with n butyllithium in DME/pentane to give…”

“…31). 10 Recrystallisation from Et 2 O yielded crystals suitable for XRD analysis. The analogous manganese complex could also be prepared through the reaction of [Mn(CO) 3 ( py) 2 Br] with TlPnH in THF to give the same product of the cyclotetramerisation of acetylene with Mn 2 (CO) 10 (Fig.…”