Highly selective synthesis and near-infrared photothermal conversion of metalla-Borromean ring and [2]catenane assemblies

Although the selective synthesis of complicated supramolecular architectures has seen significant progress in recent years, the exploration of the properties of these complexes remains a fascinating challenge. Herein, a series of new supramolecular topologies, metalla[2]catenanes and Borromean ring assemblies, were constructed based on appropriate Cp*Rh building blocks and two rigid alkynyl pyridine ligands (L1, L2) via coordination-driven self-assembly. Interestingly, minor differences between the two rigid alkynyl pyridine ligands with/without organic substituents led to products with dramatically different topologies. Careful structural analysis showed that π–π stacking interactions play a crucial role in stabilizing these [2]catenanes and Borromean ring assemblies, while also promoting nonradiative transitions and triggering photothermal conversion in both the solution and the solid states. These results were showcased through comparative studies of the NIR photothermal conversion efficiencies of the Borromean ring assemblies, [2]catenanes and metallarectangles, which exhibited a wide range of photothermal conversion efficiencies (12.64–72.21%). The influence of the different Cp*Rh building blocks on the NIR photothermal conversion efficiencies of their assemblies was investigated. Good photothermal conversion properties of the assemblies were also found in the solid state. This study provides a new strategy to construct valuable half-sandwich-based NIR photothermal conversion materials while also providing promising candidates for the further development of materials science.


General considerations
All reagents and solvents were purchased from commercial sources and used as supplied unless otherwise mentioned.
filtrate. The mixture was stirred at room temperature for 12 h to give a dark green solution. L1 (40.4 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark green solution. The solvent was concentrated to about 8 mL. Upon addition of diethyl ether, a dark green solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (5b). 151.10 mg, yield: 90.0%. Anal. Calcd for C 256

Preparation of complex 6
AgOTf (123.2 mg, 0.48 mmol) was added to a solution of [Cp*RhCl 2 ] 2 (74.4 mg, 0.12 mmol) in CH 3 OH (10 mL) at room temperature. The reaction mixture was stirred in the dark for 12 h and then filtered. 2,5-Dihydroxy-1,4-benzoquinone (16.8 mg, 0.12 mmol) and NaOH (9.6 mg, 0.24 mmol) was added to the filtrate. The mixture was stirred at room temperature for 12 h to give a dark green solution. L2 (33.64 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark green solution. The solvent was concentrated to about 6 mL. Upon addition of diethyl ether, a dark green solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (6

Preparation of complex 7
AgOTf (123.2 mg, 0.48 mmol) was added to a solution of [Cp*RhCl 2 ] 2 (74.4 mg, 0.12 mmol) in CH 3 OH (20 mL) at room temperature. The reaction mixture was stirred in the dark for 12 h and then filtered. 5,8-Dihydroxy-1,4-naphthoquinone (22.8 mg, 0.12 mmol) and NaOH (9.6 mg, 0.24 mmol) was added to the filtrate. The mixture was stirred at room temperature for 12 h to give a dark green solution. L2 (33.64 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark green solution. The solvent was concentrated to about 6 mL. Upon addition of diethyl ether, a dark green solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (7

Preparation of complex 9a
AgOTf (123.2 mg, 0.48 mmol) was added to a solution of [Cp*RhCl 2 ] 2 (74.4 mg, 0.12 mmol) in the mixture solution of CH 3 OH (4 mL) and DMF (16 mL) at room temperature. The reaction mixture was stirred in the dark for 12 h and then filtered. Naphthalenediimide (35.8 mg, 0.12 mmol) and NaOH (9.6 mg, 0.24 mmol) was added to the filtrate. The mixture was stirred at room temperature for 12 h to give a dark brown solution. L1 (40.4 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark brown solution. The solvent was concentrated to about 6 mL. Upon addition of diethyl ether, a dark brown solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (9a

Preparation of complex 9b
AgOTf (123.2 mg, 0.48 mmol) was added to a solution of [Cp*RhCl 2 ] 2 (74.4 mg, 0.12 mmol) in CH 3 OH (20 mL) at room temperature. The reaction mixture was stirred in the dark for 12 h and then filtered. Naphthalenediimide (35.8 mg, 0.12 mmol) and NaOH (9.6 mg, 0.24 mmol) was added to the filtrate. The mixture was stirred at room temperature for 12 h to give a dark brown solution. L1 (40.4 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark brown solution. The solvent was concentrated to about 6 mL. Upon addition of diethyl ether, a dark brown solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (9b). 151.12 mg, yield: 89.

Preparation of complex 10
AgOTf (123.2 mg, 0.48 mmol) was added to a solution of [Cp*RhCl 2 ] 2 (86.8 mg, 0.14 mmol) in CH 3 OH (20 mL) at room temperature. The reaction mixture was stirred in the dark for 12 h and then filtered. Naphthalenediimide (35.8 mg, 0.12 mmol) and NaOH (9.6 mg, 0.24 mmol) was added to the filtrate. The mixture was stirred at room temperature for 12 h to give a dark brown solution. L2 (33.64 mg, 0.12 mmol) was then added. The mixture was stirred at room temperature for another 12 h to give a dark brown solution. The solvent was concentrated to about 6 mL. Upon addition of diethyl ether, a dark brown solid was precipitated and collected. The product was recrystallized from a methanol/diethyl ether mixture to afford block-shaped crystals (10                 6. Near-infrared photothermal conversion research

(b) Details in solid state.
The crystalline compounds 1, 3b, 4b, 5b were grinded well. After that, same weight (30.0 mg) were taken in crystalline state. All these were put a sample cell. And then, they were put under a laser and temperature variation were detected by a same infrared camera as solution compounds. Equations used to calculate near-infrared photothermal conversion efficiency were exhibited as follows:

X-ray crystallography details
Single crystals of 1, 3b, 5b, 7, 8, 9b and 10, suitable for X-ray diffraction study were obtained at room temperature. X-ray intensity data of them were collected at 250, 173, 150, 173, 150, 173 K and 193K on a CCD-Bruker SMART APEX system. In these data, the disordered solvent molecules which could not be restrained properly were removed using the PLATON Squeeze routine.
In asymmetric unit of 1, a solvent mask was calculated and 722 electrons were found in a volume of 2146\%A^3^ in 1 void per unit cell. This is consistent with the presence of 5[CF 3 SO 3 ] per Asymmetric Unit which account for 730 electrons per unit cell.
In asymmetric unit of 3b, a solvent mask was calculated and 462 electrons were found in a volume of 2665\%A^3^ In asymmetric unit of 10, a solvent mask was calculated and 2548 electrons were found in a volume of 14290\%A^3^ in 1 void per unit cell. This is consistent with the presence of 9[CF 3 SO 3 ] per Asymmetric Unit which account for 2628 electrons per unit cell.