The synthesis of solid-state materials is dominated by high-temperature reactions because solid-solid diffusion is the rate limiting step in their formation. This contrasts the solution-mediated synthesis of molecules, and as a result, often limits the formation of solid-state compounds to those that are thermodynamically stable. Intermetallic compounds and alloys of the late transition metals can be particularly difficult to synthesize, yet they possess a wide variety of important physical properties that make them useful for many scientific studies and technological applications. We recently developed a low-temperature solution approach for synthesizing intermetallic solid-state materials that shifts the rate limiting step from solid-solid diffusion to nucleation, and in doing so, allows us to study reaction pathways, isolate solid-state reaction intermediates, and trap kinetically-stabilized phases that are not accessible using traditional high-temperature methods. Our strategy involves the use of readily-available nanoparticles as a toolkit of highly-reactive reagents that can be mixed in known ratios in solution, self-assembled to form nanocomposites, then thermally transformed at low temperatures into pre-designed product phases. This talk will focus on our recent efforts in elucidating reaction pathways and interconverting nanoscale solid-state materials using solution chemistry reactions.