Coordination-Driven Face-Directed Self-Assembly of Trigonal Prisms. Face-Based Conformational Chirality

Abstract

The coordination-driven self-assembly of four different trigonal prisms from three equivalents of one of four different tetrapyridyl star connectors and six equivalents of a platinum linker dication in nitromethane is presented. This face-directed approach affords high yield without template assistance. The prisms have been characterized by multinuclear and DOSY NMR and dual ESI-FT-ICR mass spectrometry. The use of a conformationally chiral star connector leads to a conformationally chiral prism when connector arm ends attached to a vertex have a strongly correlated twist sense and chirality is communicated across polyhedral faces, edges and vertices. Molecular mechanics results suggest that in the smallest prism 3d collective effects dominate and the all-P and all-M conformers are strongly favored. NMR data prove that the two edges of the pyridine rings in the triflate salts of 3a -3d are distinct. An Eyring plot of rates obtained from lineshape analysis and 1-D EXCHSY NMR yields an activation enthalpy ΔH ‡ of ∼12 kcal/mol and activation entropy ΔS ‡ of ∼-15 cal/mol.K for the edge interconversion process, compatible with pyridine rotation around the Pt-N bond. For 3c, this behavior is observed only up to ∼318 K. At higher temperatures, the Eyring plot is again linear but follows a very different straight line, with ΔH ‡ of ∼35 kcal/mol and ΔS ‡ of ∼60 cal/mol.K. This highly unusual result is further investigated and discussed in the following companion paper.

Synthesis and Characterization of Tetra(pyridyl)cyclo­butadiene Iron Complexes [Cp*Fe(C4py4)]– (py = 3‐pyridyl and 4‐pyridyl, Cp* = C5Me5)

“…[4][5][6] More recently, Lee et al used the coordination of the 4-pyridyl-substituted complex C to a diruthenium acceptor to construct a Ru 4 L 2 tetragonal-prismatic cage. [7] This compound was also crystallographically characterized.…”

“…[8] Recently, we obtained the first tetra(2-pyridyl)cyclobutadiene iron complex [K([18]crown-6){Cp*FeC 4 (2-py) 4 }] (1) (Figure 1) by reacting two equivalents of bis(2-pyridyl)acetylene with the iron(0) naphthalene complex [K([18]crown-6){Cp*Fe(η 4 -C 10 H 8 )}] (Scheme 1). [9] Complexation with iron(II) and zinc(II) chloride afforded 1:1 -anion of 1 acts as a bidentade chelate ligand in the molecular structures of these bimetallic compounds.…”

“…[9] Complexation with iron(II) and zinc(II) chloride afforded 1:1 -anion of 1 acts as a bidentade chelate ligand in the molecular structures of these bimetallic compounds. In extension of our previous studies, we now describe the synthesis and characterization of the corresponding 3-pyridyl and 4-pyridyl derivatives [K([18]crown-6){Cp*FeC 4 (3-py) 4 }] (2) and [K([18]crown-6){Cp*FeC 4 (4-py) 4 }] (3). We discuss the structural, spectroscopic and electrochemical properties of these new complexes, which are compared with those of the 2-pyridyl-substituted analogue 1.…”

“…[1] The cobalt complexes [CpCoC 4 (3-py) 4 4 ] (C) (Cp* = C 5 Me 5 ,) was obtained by an analogous route. [2,3] The utility of compounds A-C as tetradentate metalloligands for metallosupramolecular cage compounds was first demonstrated by Brisbois, Grieco et al, who reported the formation of a barrel-shaped Pd 4 L 2 cage upon the reaction of the 3-pyridyl complex A with two equivalents of [Pd(NO 3 ) 2 (en)].…”

“…The groups of Stang and Michl also used B as a building block for large supramolecular cages. They discovered that the self-assembly [2][3][4]7,9] www.zaac.wiley-vch.de…”