P/O Ligand Systems: Synthesis, Reactivity, and Structure of Tertiary o‐Phosphanylphenol Derivatives

Abstract

AbstractReactions of C,O‐dilithium reagents 1 (M = M′ = Li) or C,O‐lithium‐sodium reagents 1 (M = Li, M′ = Na) with chlorophosphanes afford C,O‐disubstitution products 2 or phosphanylphenolates 3 which are treated subsequently with ClSiMe3 to give 4‐methyl‐ and bulky 4,6‐di‐tert‐butyl substituted o‐phosphanylphenol silyl ethers 4. These were applied for the preparation of the corresponding o‐phosphanylphenols 5, mainly P‐asymmetric derivatives. Limitations and side reactions by use of 1 in the above synthesis are discussed. Acid‐base properties, pH‐dependent solubility in water/hexane, and substitution reactions at oxygen and phosphorus of selected representatives of 5 are reported. An example for the separation of enantiomers by esterification with (1S)‐()‐camphanic acid chloride is given. IR studies revealed intramolecular PHO bonds and 2J(PC) the preferred trans arrangement of the phenoxy group in solution. In the solid state, inter‐ and intramolecular PHO bonds were detected by X‐ray structure analysis. The trans arrangement of the phenoxy group is preserved. Because of steric hindrance, the O substituents are tilted towards the phosphorus atom and thus induce large through‐space coupling constants. The PSn distance of 336.9 pm in the bulky substituted OSnMe3 moiety 8h is however too large for the formation of genuine intramolecular coordination. The versatility of o‐hydroxyarylphosphanes and objectives of further studies are shown by preliminary results on complex formation and applications of these phosphanes in catalysis.