On–off allosteric control of a bifunctional catalyst
A Pt(II) weak-link tweezer and a sulfonate regulator switch a squaramide–amine co-catalyst fully on or off in situ.
Source
A concerted two-prong approach to the <i>in situ</i> allosteric regulation of bifunctional catalysis
What they did
Authors assembled a heteroligated Pt(II) tweezer with a squaramide–tertiary amine ligand and a sodium sulfonate hydrogen-bond acceptor, switched it between semi-open and fully closed states with chloride, measured DMA binding by 1H NMR, and timed the Michael addition of nitroethane to β-nitrostyrene.
What they found
The fully closed Na+ complex binds DMA strongly (Ka ≈ 75 558 M−1) while the semi-open state shows no recognition. Closed-state catalysis gives nearly quantitative conversion (TOF = 2.69 × 10−4 s−1), and chloride toggling reverses activity. Embedding the catalyst in the WLA scaffold improves activity versus free ligand.
The limits
What it doesn't show
Scope beyond a few conjugate additions is proposed rather than demonstrated at scale; polymer-length control of lactide ROP is suggested but not shown here.
Key terms
- Weak-link approach (WLA)
- Hemilabile P,X ligands on d8 metals that open or close a supramolecular catalyst with chemical effectors such as Cl−.
- Hydrogen-bond-donating (HBD) catalyst
- A squaramide that activates electrophiles by dual hydrogen bonds.
- Fully closed (FC) vs semi-open (SO)
- Chelated rigid vs flexible P-only states of the Pt(II) tweezer.
- Bifunctional HBD–Lewis base
- Co-catalyst that activates both electrophile (HBD) and nucleophile (amine).
- Allosteric regulation
- Activity switched by a remote coordination change rather than by modifying the catalytic site covalently.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
The off state of this tweezer catalyst is the:
Common questions
What turns the catalyst off?
The semi-open state lets the sulfonate hydrogen-bond to the squaramide so substrate cannot bind.
What model reaction was timed?
Michael addition of nitroethane to β-nitrostyrene.
Why does Na+ matter in the closed state?
The cation screens the sulfonate so intermolecular ligand–ligand association is minimized.
Can you switch in situ?
Yes: add and abstract Cl− to toggle FC and SO.
More on Catalysis