AT the interface between heterogeneous and homogeneous catalysis there is great scope for the development of new materials that combine the advantages and/or minimize disadvantages associated with each of these classes. In particular there is a need for homogeneous catalysts with properties that allow their ready removal from a product-containing solution. One approach to such materials is to anchor homogeneous catalysts to soluble polymer supports(1); we have recently prepared such catalytic materials in which the active centre is an organometallic species(2,3). One disadvantage encountered when anchoring catalytic metal Sites to polymers is the difficulty of accurate control of the number and location of these sites. Here we report an alternative approach-the synthesis of polysilane dendrimers (highly branched macromolecules(4-6)),which are functionalized at their periphery with metal-containing catalytically active sites. These dendrimers show regiospecific catalytic activity for the Kharasch addition of polyhalogenoalkanes to carbon-carbon double bonds. It should be possible to remove the nanoscale catalytic macromolecules of this type from the solution of products using filtration methods.