Dealkylation as a Strategy to Synthesize Unconventional Lithium Salts from ortho -Phenyl-phosphonate-boranes

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High Resolution Image Download MS PowerPoint Slide Several ortho -phenyl-phosphonate-boranes 1-BR 2 -2-{P(O)(OEt) 2 }C 6 H 4 (R = Cy (cyclohexyl, 2a ), Ipc ((+)-isopinocampheyl, 2b ), and n Hx ( n -hexyl, 2c )) have been prepared and characterized. Compounds 2a – c can be selectively mono-dealkylated to afford the corresponding lithium ortho -phenyl-boratophosphonate salts [Li(S) n ][1-BR 2 -2-{P(O) 2 (OEt)}C 6 H 4 ] (S = MeCN or EtOAc). All compounds were characterized by multinuclear NMR spectroscopy ( 1 H, 13 C{ 1 H}, and 31 P{ 1 H}). Reactions of 2a with NaI or KI yielded the respective [Na(MeCN)][1-BCy 2 -2-{P(O) 2 (OEt)}C 6 H 4 ] ([Na(MeCN)][ 3 ]) and [K(MeCN)][1-BCy 2 -2-{P(O) 2 (OEt)}C 6 H 4 ] ([K(MeCN)][ 3 ]) salts. Single-crystal X-ray diffraction studies of 2a and [Li(MeCN) 2 ][1-BCy 2 -2-{P(O) 2 (OEt)}C 6 H 4 ] ([Li(MeCN) 2 ][ 3 ]) document the presence of intramolecular P═O···B interactions that form pseudo-heterocyclic rings. In the solid state, [Li(MeCN) 2 ][ 3 ] exists as a lithium-bridged dimer. Thermogravimetric analysis of [Li(MeCN) 2 ][ 3 ] reveals high thermal stability with a decomposition onset above 200 °C. [Li(MeCN) 2 ][ 3 ] displays good to excellent solubility in many organic solvents. Reactions of [Li(MeCN) 2 ][ 3 ] with chlorotrimethylsilane, methyl triflate, and HCl·Et 2 O yielded the new ortho -phenyl-phosphonate-boranes 1-BCy 2 -2-{P(O)(OE)(OEt)}C 6 H 4 (E = Me 3 Si, Me, H). Compounds 2a and [Li(MeCN) 2 ][ 3 ] are weakly emissive in solution and in the solid state, with evidence of solvent-dependent dual emission.

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