Structure of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene and of 2,4-Di-tert-butyl-1,3-diphosphabenzene: X-ray Analysis, Photoelectron Spectra and Molecular Orbital Calculations

The Low Basicity of Phosphabenzenes: First Examples of Protonation, Alkylation, and Silylation Reactions

“…[10] The identifying 31 P NMR characteristics of 6 are a doublet at d = 304.4 ppm ( 2 J PP = 49 Hz) and a doublet of triplets at d = 85.1 ppm ( 2 J PP = 49 Hz, 1 J PH = 595 Hz). In the 1 H NMR spectrum, the signal for the acidic proton appears appropriately downfield at d = 9.46 ppm with the same large 1 J PH coupling constant (595 Hz) observed in the 31 P spectrum, confirming that the site of protonation is P.…”

The Low Basicity of Phosphabenzenes: First Examples of Protonation, Alkylation, and Silylation Reactions

“…The protonation of 4 at P rather than C was anticipated by density functional theory (DFT) calculations which find protonation at phosphorus to be 40 kJ mol À1 more exothermic in spite of the ring p electrons forming the HOMO of 4. [10] The identifying 31 P NMR characteristics of 6 are a doublet at d = 304.4 ppm ( 2 J PP = 49 Hz) and a doublet of triplets at d = 85.1 ppm ( 2 J PP = 49 Hz, 1 J PH = 595 Hz). In the 1 H NMR spectrum, the signal for the acidic proton appears appropriately downfield at d = 9.46 ppm with the same large 1 J PH coupling constant (595 Hz) observed in the 31 P spectrum, confirming that the site of protonation is P.…”

“…The same effect was observed in the structurally related methyl phosphininium ion reported by Le Floch et al [5] In 6 these two bonds average 1.686(2) ; whereas those remote from the site of protonation average 1.738(3) , close to those in unprotonated 4 (1.727(8) ;. [10] This bond shortening is accommodated by an equalization of the three nearest bond angles. The CÀPÀC bond angle at the site of protonation increases relative to 4 by approximately 138 to 122.4(1)8 while the two adjacent PÀCÀP bond angles decrease by about 138 to an average of 122.5(1)8.…”

New Phosphorus−Carbon Cage Compounds by Diels−Alder and Homo Diels−Alder Reactions of 1,3,5-Triphosphabenzenes with Alkenes

“…[2] Shortly thereafter, a simple one-pot synthesis was developed that also made the isolation of other triphosphabenzene derivatives possible. [3] Although their physicochemical properties (NMR spectroscopic data, [2,3] crystal structure analysis [4] ) as well as theoretical investigations [5] clearly demonstrate the aromatic character of the 1,3,5-triphosphabenzenes 1, the compounds exhibit a surprisingly high reactivity in, for example, 1,2-additions [6] or [4 ϩ 2] cycloaddition reactions. [7] Thus, alcohols undergo addition to the PϪC double bond in alkaline media to furnish the 1,3,5-trialkyloxy-1,3,5-triphosphinanes 4, [6] while alkynes 5 react to afford the novel triphospha cage compounds 7 through a DielsϪAlder/ homo DielsϪAlder reaction sequence (Scheme 1) with the 1,3,5-triphosphabicyclo[2.2.2]octa-2,5,7-trienes 6 as intermediates.…”