Heterogeneous Catalysis in Liquid Phase Organic Synthesis, Promoted by Layered Zirconium Phosphates and Phosphonates

The choice of layered phosphates and phosphonates of tetravalent metals, mainly Zr(IV), plays a key role in the success of liquid phase heterogeneous catalysis for the preparation of useful intermediates in organic synthesis. The preparation, the chemical and thermal stability, and the structural aspects of this emerging class of inorganic and inorgano-organic materials will be reviewed with the aim to clarify their potential in heterogeneous liquid phase catalysis. The possibility of modifying their surface area and porosity and the nature of active catalytic centres by means of ion exchange, intercalation and exfoliation reactions will be also presented. Furthermore, this review will discuss the numerous efforts dedicated to the development of new synthetic methods using acidic or basic Zr(IV) phosphates and phosphonates as valuable alternative solid catalysts compared to other classes of heterogeneous catalysts. The reported methods clearly demonstrated the importance of this type of catalysis, especially for the following features: easy handling, mild reaction conditions, solvent free conditions (in many cases), simple work-up and the recyclable nature of the catalysts. Herein, we present a review of these various types of solid catalysts and their characteristics and applications in organic synthesis.