Stereoselective self-assembly of cis- and trans- [Pt2L2] metallacycles via geometrically-asymmetric 90o Pt(II) acceptors

Stereoselective synthesis of cis- and trans- configurations remain challenging in molecular systems. Here, asymmetric 90^o Pt(II) acceptors enable stereoselective coordination-driven self-assembly of configuration-specific [Pt₂L₂] metallacycles. The coordination of trimethylphosphine or triethylphosphine (PR₃) and phosphangulene (Phang) to the Pt(II) centers yielded two asymmetric cis-PtCl₂(PR₃)(Phang) complexes. Upon ligand exchange, these acceptors assemble with the bispyridyl ligands to form statistical mixtures of cis- and trans- metallacycles. Stereoselective self-assembly is achieved by modifying the bis-pyridyl ligand with N-ortho-bismethyl groups, leveraging intramolecular C-H···π interactions with Phang, steric effects, and 90^o Pt(II) heteroligation to selectively generate trans- or cis- isomers. The stereochemistry is confirmed by NMR spectrometry, investigation of the mass spectrometry, density functional theory calculations, and single-crystal X-ray diffraction. Notably, hierarchical self-assembly in the crystalline state revealed stark structural divergences between trans- and cis- metallacycles, offering key insights into stereo-controlled supramolecular design.