A Metalloregulated Four-State Nanoswitch Controls Two-Step Sequential Catalysis in an Eleven-Component System.

The nanomechanical switch 1 with its three orthogonal binding motifs-the zinc(II) porphyrin, azaterpyridine, and shielded phenanthroline binding station-is quantitatively and reversibly toggled back and forth between four different switching states by means of addition and removal of appropriate metal-ion inputs. Two of the four switching stages are able to initiate catalytic transformations (ON1, ON2), while the two others shut down any reaction (OFF1, OFF2). Thus, in a cyclic four-state switching process the sequential transformation A+B+C→AB+C→ABC can be controlled, which proceeds stepwise along the switching states OFF1→ON1 (click reaction: A+B→AB)→OFF2→ON2 (Michael addition: AB+C→ABC)→OFF1. Two consecutive cycles of the sequential catalysis were realized without loss in activity in a reaction system with eleven different components.