Synthesis, reactivity, and coordination chemistry of secondary phosphines

The coordination chemistry of secondary phosphines is reviewed. Although the number of secondary phosphine complexes is still relatively small, a number of important uses for these complexes have emerged. In particular, they are useful precursors in the synthesis of asymmetric tertiary phosphines, and they are important synthetic intermediates in the preparation of phosphine macrocycles. The use of secondary phosphine complexes in homogeneous catalysis is limited because the complexes are generally unstable under catalytic conditions. The physical properties of secondary phosphines are briefly discussed first, followed by a review of the synthetic routes used to prepare them. The metal complexes of secondary phosphines are then reviewed according to their group in the periodic table. A special focus of this latter section is on secondary phosphine complexes used in the preparation of phosphine macrocycles.