Ligand-Controlled Synthesis of [3]- and [4]Cyclo-9,9-dimethyl-2,7-fluorenes through Triangle- and Square-Shaped Platinum Intermediates

The syntheses of [3]‐ and [4]cyclo‐9,9‐dimethyl‐2,7‐fluorenes ([3] and [4]CFRs), cyclic trimer, and tetramers of 9,9‐dimethyl‐2,7‐fluorene (FR), respectively, were achieved by the platinum‐mediated assembly of FR units and subsequent reductive elimination of platinum. A triangle‐shaped tris‐platinum complex and a square‐shaped tetra‐platinum complex were obtained by changing the platinum ligand. The structure of the triangle complex was unambiguously determined by X‐ray crystallographic analysis. Reductive elimination of each complex gave [3] and [4]CFRs. Two rotamers of [3]CFR were sufficiently stable at room temperature and were separated by chromatography. The physical properties of the CFRs were also investigated theoretically and experimentally. Electronic structures: Syntheses of [3]‐ and [4]cyclo‐9,9‐dimethyl‐2,7‐fluorenes, cyclic trimer, and tetramers of 9,9‐dimethyl‐2,7‐fluorene (FR), respectively, were achieved by the platinum‐mediated assembly of FR units and subsequent reductive elimination of platinum through a triangle‐shaped tris‐platinum and a square‐shaped tetra‐platinum complex, respectively. The physical properties of the products were also investigated theoretically and experimentally (see scheme).