(Li2 [7]), the first oxygenated pentalenide, was cleanly formed in spectroscopically quantitative yield (Scheme 3). H NMR analysis showed that the two electron-donating p MeOPh groups led to a 0.18 ppm difference between the chemical shifts of the wingtip protons H 2 and H 5 in 7, three times the polarisation seen in 5 and 6. Interestingly, its Li NMR chemical shift of -4.78 ppm suggested a stronger interaction of the Li + with the pentalenide than in 2-6, more in the range of a solventshared ion pair (Figures S27─29). To see if the introduction of aryl substituents containing electron-withdrawing groups could lead to further deshielding effects on the pentalenide core, we investigated the deprotonative metalation of an isomeric mixture of ( p FPh)2( p Tol)2PnH2 (8H2). LiHMDS in THF was found to be ineffective in furnishing the corresponding pentalenide salt, implying its pKA to be insufficient for the double deprotonation of a dihydropentalene with either p-tolyl or 4-fluorophenyl in the 1,3-positions (unlike in the preparation of Li2 [2]). Using a mixture of LiHMDS and LiNEt2 showed full consumption of the starting materials by 1 H NMR spectroscopic analysis after 7.5 hours at room temperature, but with a multitude of new, broad signals that could not be confidently assigned. Utilising a heterobimetallic base combination of LiHMDS followed by KH (which had previously proven successful for 2 and 4) ). The weakly electron-withdrawing p FPh groups in 8 led to a marginal 1 H NMR chemical shift difference between H 2 and H 5 of 0.05 ppm, indicating a rather weak influence on the polarisation of the pentalenide core. To increase the electron-withdrawing nature of the substituents on one side of the pentalenide further we also tried to deprotonate the p CF3Ph-substituted dihydropentalene (( p F3C)Ph)2( p Tol)2PnH2. However, in situ NMR analysis showed that bases of higher pKa values than LiHMDS led to unidentifiable heterogeneous mixtures indicative of decomposition (Scheme 4). All attempts of deprotonating a double bond isomer mixture of ( m Xyl)(Ph)( p Tol)(( p F3C)Ph)PnH2, where the CF3 groups were located in para-position but the fluorinated aryl group positioned differently in each dihydropentalene isomer, led to the same observation. Finally, to investigate whether CF3 groups themselves or their location in the aryl substituents of the dihydropentalenes were incompatible with the basic conditions required for their metalation, we tested the deprotonation of (Ph)2(( m F3C)2Ph)2PnH2 (product of the condensation of 1,4-diphenyl-cyclopenta-1,3-diene and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-2-