Transition metal clusters and colloids of narrow particle size distributions in the range 1-10 nm are currently subject to intense research efforts. 1 From a fundamental perspective, the transition from the properties of the bulk to those of molecular clusters is expected to occur in this size range. A transition metal cluster of 2 nm diameter consists of a few hundred atoms, a large portion of which are located at the surface of the cluster. In view of potential applications, such materials are of interest with regard to for example catalysis 2,3a,f,4c,5b,6d or microelectronics. 1a,b However, increasing the control of particle size and the stability of the metal colloid solutions remain key challenges. Recent approaches to the controlled preparation of metal or semiconductor nanoparticles have utilized surfact-ants 2l,3 or the self-assembled nanostructures of block copolymer micelles, 2t,4 achieving an unprecedented control of particle size and also spatial organization in thin films by the latter method. However, such template structures self-assembled from a larger number of individual molecules are by their very nature dynamic in solution. Thus, their size and aggregation numbers are subject to fluctuations, and such structures can be shear-sensitive. To stabilize micelle-like structures, polymerized micelles 5 and very recently dendrimers 6 have been employed as molecular compartments for the preparation of metal particles. Whereas dendrimers 7 offer the advantage of a well-defined structure, their syntheses are usually tedious. By contrast to the perfectly branched structure of dendrimers, hyper-branched polymers 8 possess a randomly branched structure. They can be prepared conveniently in one-pot procedures; however, usually polymers of extremely broad molecular weight distributions are obtained. In a recent approach, amphiphilic hyperbranched poly-(glycerols) of low polydispersity (M w /M n < 1.7) were prepared by anionic multibranching polymerization of glycidol, 9 followed by partial esterification of the OH functions with long chain fatty acids (Scheme 1). 10 Such amphiphilic macromolecules function as nanocapsules, incorporating individual hydrophilic dye molecules as guests. 10 We now report on the application of these easily accessible, well-defined amphiphilic molecules for the preparation of nanometer-size stable palladium colloids and their application in catalysis. In the following experiments, amphiphilic polymers prepared by esterification of 60-67% of the OH functions of poly(glycerol) scaffolds of different molecular weights with palmitoyl chloride were employed. 11 Solutions of these polymers in apolar organic solvents, such as toluene or chloroform, solubilize PdCl 2 to yield yellow solutions of the otherwise insoluble metal …