The codriven assembly of molecular metalla-links (613, 623) and metalla-knots (41, 31) via coordination and noncovalent interactions

Abstract

Although mechanically interlocked molecules (MIMs) display unique properties and functions associated with their intricate connectivity, limited assembly strategies are available for their synthesis. Herein, we presented a synergistic assembly strategy based on coordination and noncovalent interactions (π–π stacking and CH⋯π interactions) to selectively synthesize molecular closed three-link chains ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mn>6</mml:mn> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mn>3</mml:mn> </mml:msubsup> </mml:math> links), highly entangled figure-eight knots ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>4</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knots), trefoil knot ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>3</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knot), and Borromean ring ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mn>6</mml:mn> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mn>3</mml:mn> </mml:msubsup> </mml:math> link). <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mn>6</mml:mn> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mn>3</mml:mn> </mml:msubsup> </mml:math> links can be created by the strategic assembly of nonlinear multicurved ligands incorporating a furan or phenyl group with the long binuclear half-sandwich organometallic Cp*Rh III (Cp* = η 5 -pentamethylcyclopentadienyl) clip. However, utilizing much shorter binuclear Cp*Rh III units for union with the 2,6-naphthyl-containing ligand led to a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>4</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knot because of the increased π–π stacking interactions between four consecutive stacked layers and CH⋯π interactions. Weakening such π–π stacking interactions resulted in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>3</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knot. The universality of this synergistic assembly strategy for building <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>4</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knots was verified by utilizing a 1,5-naphthyl-containing ligand. Quantitative conversion between the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mn>4</mml:mn> <mml:mn>1</mml:mn> </mml:msub> </mml:math> knot and the simple macrocycle species was accomplished by adjusting the concentrations monitored by NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Furthermore, increasing the stiff π-conjugated area of the binuclear unit afforded molecular Borromean ring, and this topology is a topological isomer of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mn>6</mml:mn> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mn>3</mml:mn> </mml:msubsup> </mml:math> link. These artificial metalla-links and metalla-knots were confirmed by single-crystal X-ray diffraction, NMR and ESI-MS. The results offer a potent strategy for building higher-order MIMs and emphasize the critical role that noncovalent interactions play in creating sophisticated topologies.

Topics & Concepts