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

## TL;DR

This paper describes a new method to create unconventional lithium salts from ortho-phenyl-phosphonate-boranes using dealkylation.

## Contribution

The study introduces a selective dealkylation strategy to synthesize novel lithium salts with high thermal stability and solubility.

## Key findings

- Dealkylation of ortho-phenyl-phosphonate-boranes yields lithium salts with intramolecular P=O···B interactions.
- The lithium salt [Li(MeCN)2][3] shows high thermal stability with decomposition above 200°C.
- The salts exhibit good solubility in organic solvents and weak emissive properties with solvent-dependent dual emission.

## Abstract

Several ortho-phenyl-phosphonate-boranes
1-BR2-2-{P­(O)­(OEt)2}­C6H4 (R =
Cy (cyclohexyl, 2a), Ipc ((+)-isopinocampheyl, 2b), and nHx (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-BR2-2-{P­(O)2(OEt)}­C6H4] (S = MeCN or EtOAc). All
compounds were characterized by multinuclear NMR spectroscopy (1H, 13C­{1H}, and 31P­{1H}). Reactions of 2a with NaI or KI yielded the
respective [Na­(MeCN)]­[1-BCy2-2-{P­(O)2(OEt)}­C6H4] ([Na­(MeCN)]­[3]) and [K­(MeCN)]­[1-BCy2-2-{P­(O)2(OEt)}­C6H4] ([K­(MeCN)]­[3]) salts. Single-crystal X-ray diffraction studies of 2a and [Li­(MeCN)2]­[1-BCy2-2-{P­(O)2(OEt)}­C6H4] ([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·Et2O yielded the new ortho-phenyl-phosphonate-boranes 1-BCy2-2-{P­(O)­(OE)­(OEt)}­C6H4 (E = Me3Si, 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.