Bisphosphine Dioxides

Although symmetrical bisphosphine ligands of the type Ph2P(CH2)n-PPh2 n = 1-6) can be prepared relatively easily, attempts to synthesize unsymmetrical bisphosphines, in which the two phosphorus atoms have different substituents, have met with little success. However, recently Briggs and Dyer have developed a relatively rapid and efficient synthesis of the unsymmetrical alkane-based bisphosphines / PhP(CH2)nPPh2 n = 3, R = ethyl n = 4, R = methyl or ethyl n = 6, R = methyl, ethyl or cyclohexyl) by the general method shown in Scheme 4, which involves new unsymmetrical biphosphonium salts and bisphosphine dioxides as intermediates. 

Scheme 7,16 Chiral bisphosphine dioxide-catalyzed enantioselective allylation.

Scheme 7,22 Allene-containing chiral bisphosphine dioxide as catalyst.

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