Ion Pair Carbon Acidities of Some Silanes in Tetrahydrofuran

Article abstract of DOI:10.1021/jo00059a031

The relative solvent-separated ion pair (SSIP) lithium acidity (pK_Li/THF) and contact ion pair (CIP) cesium acidity (pK_Cs/THF) were obtained for 9-fluorenyltrimethylsilane (1) (21.3, 21.6, respectively) and 9-fluorenyl-tert-butyldimethylsilane (2) (20.3, 20.6, respectively) in THF.Values for pK_Cs/THF were determined at 25 deg C for (p-biphenylylmethyl)-tert-butyldimethylsilane (3), 35.4, benzyltrimethylsilane (4), 37.5, α,α-bis(trimethylsilyl)toluene (5), 34.1, 2-(trimethylsilyl)-1,3-dithiane (6), 33.5, (trimethylsilyl)acetonitrile (7), 28.8, and tris(trimethylsilyl)methane (8), 36.8.Some thermodynamic parameters were determined by measurements at other temperatures, and some ionic acidities (pK(FI)) were determined by conductivity studies.Carbanion stabilization by these silyl substituents varies from about 1 to over 3 pK units in different systems. 9,9-Bis(trimethylsilyl)fluorene (9) was found to undergo silyl transfer on treatment with various carbanions, but this reaction is slower than proton transfer.