The technique of subcomponent self-assembly has been applied to the preparation of a set of copper(I) complexes from diamines and aldehydes in aqueous solution. These complexes may be synthesized alongside one another in solution despite the chemical nonorthogonality of their respective starting materials; thermodynamic equilibration eliminates all mixed products. The reactivity of these complexes has been studied, revealing that in certain cases, the substitution of both ligands and ligand subcomponents could be independently carried out. In one particular case, a complex was shown to be inert to ligand substitution but readily underwent ligand subcomponent substitution, creating the possibility of a previously undocumented kind of cascade reaction: Once ligand subcomponent substitution had occurred, ligand exchange could then happen, allowing both reactions to be triggered by a single chemical event.self-assembly ͉ coordination chemistry ͉ cascade reactions T he generation of complex metal-containing architectures from simple building blocks through self-assembly (1-8) is a compelling means by which to build up functional molecular machines (9-11). Such molecular devices are beginning to give substance to the promises of nanotechnology; recent examples include Mirkin and coworkers' (12) signal-amplifying allosteric catalyst, Nolte and colleagues' (13) ''chain-walking'' epoxidation catalyst, Leigh and coworkers' (14) reversible molecular motor, and the molecular elevator of Stoddart and colleagues (15).A powerful technique in metallo-organic self-assembly consists of the simultaneous formation of covalent (carbonheteroatom) and dative (heteroatom-metal) bonds, bringing both ligand and complex into being at the same time. This ''subcomponent self-assembly'' has its roots in the template synthesis of Busch and coworkers (16) and has recently been used in the synthesis of a wealth of structures, including rotaxanes (17), catenanes (18), helicates (19-22), grids (23-25), and a Borromean link (26). These structures belong to the domains of both dynamic covalent (27) and supramolecular (28) Because subcomponent self-assembly reactions operate on two distinct levels simultaneously, one might expect that these reactions would give rise to mixtures of diverse products or large dynamic combinatorial libraries (30-35), as the multiple components combine in different ways. Although many structures might in theory be possible at both covalent and supramolecular levels, the metal and the subcomponents of the ligand may be chosen such that the thermodynamic preferences of both converge to give rise to a single product or a limited number of products (22)(23)(24)(36)(37)(38). It is important to note that it is the reversible formation of intraligand imine bonds (in addition to the metal-ligand bonds) that allows for this dynamic sorting͞ selection effect to occur.Along similar lines, although the addition of further ligand components might be expected to increase the number of species present in the product mixture, it is non...