Self-assembly of triangular metallomacrocycles using unsymmetrical bisterpyridine ligands: isomer differentiation via TWIM mass spectrometry

Abstract

Three unsymmetrical, 60°-bended bisterpyridine ligands with varying phenylene spacer lengths have been synthesized via the Suzuki-Miyaura coupling reactions. Their self-assembly processes were found to be strongly dependent on the ligand geometry. Upon complexation with Zn(II) ions, only 2,4''-di(4'-terpyridinyl)-1,1':4',1''-terphenyl underwent self-selection to give a trinuclear metallomacrocycle with perfect heteroleptic connectivity and the other two afforded a mixture of constitutional isomers. The metallosupramolecular assemblies were characterized by NMR spectroscopy, electrospray mass spectrometry (ESI MS), and single-crystal X-ray diffraction. In particular, the identification of isomeric architecture was accomplished using tandem mass spectrometry (MS(2)) coupled with traveling wave ion mobility mass spectrometry (TWIM MS).

Multicomponent Self‐Assembly of Metallo‐Supramolecular Macrocycles and Cages through Dynamic Heteroleptic Terpyridine Complexation

“…The chemical formula of rhombus [Cd 4 L 1 2 L 2 2 ] was eventually validated by ESI‐MS (Figure a), showing five main signals derived from 4+ to 8+ ions. The ESI‐TWIM‐MS analysis (Figure S70) indicated the absence of other isomers and gave an average collision cross‐section (CCS) of 649.8±21.2 Å 2 , which agreed well with the theoretical values (Table S2). In comparison to the self‐assembly using two 6,6′′‐unsubstituted bistpy ligands with the same geometry, which resulted in a mixture of polygons, the complementary ligand pair efficiently suppressed the formation of the metallo‐triangle assembled from L 2 to afford a stable metallo‐rhombus in quantitative yield.…”

“…Next, the ditopic ligand L 1 , possessing 2,6‐dimethoxyphenyl groups at the terpyridyl 6,6′′‐positions, was synthesized from the Suzuki–Miyaura coupling reaction of the tetrabrominated 120°‐bent bistpy with 2,6‐dimethoxyphenylboronic acid (Scheme S2), and its structure was confirmed by NMR spectroscopy (Figure S3) and high‐resolution mass spectrometry (Figure S14). Ligands L 2 , L 3 , and L 5 were obtained by following the reported procedures . L 4 was synthesized through the Miyaura borylation and Suzuki–Miyaura coupling reactions (Scheme S3), and the structural characterization was based on 1 H NMR spectroscopy (Figure S6) and MALDI‐TOF MS analysis (Figure S15).…”

“…Under similar complexation conditions, the self‐assembly of L 1 with unsymmetrical 60°‐bent bistpy ligands including L 3 , L 4 , and L 6 was examined (Scheme ). Given their unsymmetrical geometry, the complexation may give rise to mismatched cyclic isomers in addition to the expected rhomboidal structures. Notably, it was found that the desired rhomboid was obtained as the only product when the spacer difference between two coordination sites is larger than one phenylene unit.…”

“…ESI mass spectrometry and traveling wave ion‐mobility (TWIM) experiments were conducted with a Waters Synapt HDMS G2 instrument with a LockSpray ESI source using the reported parameters . Matrix‐assisted laser desorption/ionization coupled with a time‐of‐flight detector (MALDI‐TOF) mass spectrometry was conducted with a Bruker autoflex speed MALDI TOF/TOF mass spectrometer with a 355 nm frequency tripled Nd:YAG SmartBeam laser.…”

“…Energy‐minimized structures were obtained by using the reported settings . Calculations were performed with Geometry Optimization and followed by Anneal in Forcite module of Materials Studio version 7.0 program (Accelrys Software, Inc.).…”