The unsymmetrical bidentate phosphine oxides (Me)2PCH2CH2CH2P(iPr)2, (Et)2PCH2CH2CH2P(iPr)2, (Me)2PCH2CH2CH2CH2P(Et)2, and (Me)2PCH2CH2CH2P(Cy)2 were synthesized using air-stable phosphine oxides and 1-chloro-3-bromopropane and 1-chloro-4-bromobutane. The phosphine oxides were used to alkylate the substrates after being deprotonated by sodium bis(trimethylsilyl)amide before following a similar process for the addition of the secondary phosphine oxide. Due to the different substitution rates of bromine and chlorine, the correct intermediates were able to be isolated. All reactions occurred under nitrogen due to the air sensitivity of this reaction. Proton (1H), 13C, and 31P NMR were used to characterize the compounds to ensure that the reactions were successful after each step. These unsymmetrical bidentate phosphine oxides will be reduced and later used as ligands to produce chiral-at-metal complexes to then be used in asymmetric catalysis.

Synthesis of unsymmetrical bisphosphine oxides for future use in chiral-at-metal complexes

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