Rational Design and Assembly of M2M‘3L6Supramolecular Clusters withC3hSymmetry by Exploiting Incommensurate Symmetry Numbers

Sun, Xiankai; Johnson, Darren W.; Caulder, Dana L.; Raymond, Kenneth N.; Wong, Edward H.

doi:10.1021/ja0029376

Cited by 108 publications

(54 citation statements)

References 64 publications

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“…In these few cases metal ions were used as structural units in the ligand strands of triple helicates [4] and mesocates. [5,6] In the present paper we would like to report on a novel, noncovalent strategy for the construction of ligand strands for a series of dinuclear double helicates. This strategy utilizes hydrogen bonding between simple pyridine-alcohol precursors to build up the ligand backbone, and we show that the self-assembly of these helicates proceeds with high stereoselectivity.…”

mentioning

confidence: 99%

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Telfer¹,

Sato²,

Kuroda³

2004

Angew Chem Int Ed

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Transition-metal helicates have played a central role in supramolecular chemistry for many years. [1][2][3] The synthetic approach to these structures typically follows a twostep process: 1) The synthesis of a covalent organic ligand using classical methods prior to 2) the reaction of this ligand with suitable metal ions to assemble the desired helicate. The first step in this process is often rather laborious and inefficient, especially compared to the second step which, in general, takes advantage of the kinetic lability of metal-ligand bonds to ensure that the most thermodynamically stable product is formed rapidly and in high yield. Given the obvious advantages of this noncovalent self-assembly step, it is somewhat surprising that noncovalent approaches to step 1, the construction of the ligand strands, have been reported only rarely. In these few cases metal ions were used as structural units in the ligand strands of triple helicates [4] and mesocates. [5,6] In the present paper we would like to report on a novel, noncovalent strategy for the construction of ligand strands for a series of dinuclear double helicates. This strategy utilizes hydrogen bonding between simple pyridine-alcohol precursors to build up the ligand backbone, and we show that the self-assembly of these helicates proceeds with high stereoselectivity.Helicate 1 self-assembles upon mixing commercially available 6-methylpyridine-2-methanol (4) with 0.25 equivalents each of cobalt(ii) chloride and cobalt(ii) acetate in methanol (Scheme 1). Crimson-colored crystals of the complex were obtained in high yield by layering this solution with dioxane. Helicate 2 was prepared from R-6-methylpyridine-2-ethanol (5) in an analogous fashion. This chiral starting material was obtained in 93 % ee by the asymmetric reduction of 2-acetyl-6-methylpyridine using the general method of Ikariya and co-workers.[7] 6-Methylpyridine-2-nitromethanol (7), which serves as the precursor to helicate 3, was generated in situ by the by the Henry reaction [8,9] of 6-methylpyridine-2-carboxaldehyde (6) with nitromethane. This reaction is probably catalysed by the acetate ions that are present as Co(OAc) 2 . Details of all experimental procedures are given in the Supporting Information.The three helicates 1-3 were characterized in the solid state by X-ray crystallography (discussed below), elemental analysis, UV/Vis and IR spectroscopy, and, in the case of 2, solid-state circular dichroism (CD) spectroscopy (see Supporting Information for details). The yield of helicate 1 is high (71 %), however the yields of 2 (27 %) and 3 (18 %) are more modest. Monitoring of the self-assembly process of 2 in solution indicates quantitative formation of the helicate, [10] thus it appears that the crystallization step is responsible for the low yield, and we are currently exploring a variety of methods to improve upon this. It is noteworthy that the presence of a methyl substituent at the 6-position of the pyridine ring appears to be essential for the assembly of the helicates (all experime...

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confidence: 99%

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Telfer¹,

Sato²,

Kuroda³

2004

Angew Chem Int Ed

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“…Raymond and Wong (43)(44)(45) successfully prepared a series of M 2 MЈ 3 L 6 supramolecular clusters where a multifunctionalized ligand (L) was cleverly designed to selectively interact with two types of metal ions (one hard and one soft).…”

mentioning

confidence: 99%

Self-assembly of nanoscopic coordination cages of D _3h symmetry

Kuehl

Kryschenko

Radhakrishnan

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

155

101

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A family of nanoscale-sized supramolecular cage compounds with a trigonal prismatic framework was prepared by means of spontaneous self-assembly from the combination of a predesigned molecular ''clip'' with tritopic pyridyl subunits. As confirmed by x-ray crystallography, the smallest structure of the reported series is Ϸ1 ؋ 2 nm and possesses a nitrate anion incarcerated inside its molecular cavity. The largest structure has dimensions of Ϸ 1 ؋ 4 nm. T he formation of discrete supramolecular entities driven and held together by metal coordination is an intense new area of investigation at the forefront of supramolecular chemistry (1-10). Because self-assembly is guided by the chemical information encoded into the molecular subunits, diverse structures with predetermined shape, size, and functionality can readily be designed. Indeed, a wide variety of aesthetic structures have been realized, such as molecular grids, helicates, rings, catenanes, tetrahedra, cubes, cuboctahedra, etc. Once assembled, many of the hollow structures have been shown to be capable of encapsulating molecules through electrostatic and͞or dispersion forces. Often times, ions will template the formation of an assembly (11-21). When considering that metal-containing assemblies often possess magnetic, photophysical, and͞or redox properties not accessible from purely organic systems, studies in basic host-guest chemistry hold new promise for technologies in molecular sensing (22-28), separations, and catalysis (29,30).Because lower-symmetry hosts can ultimately be expected to show enhanced guest selectivity, especially toward planar aromatic guests, prismatic cages represent a natural progression in the development of this area. Although M 3 L 2 -type cages are relatively simple three-dimensional constructs, they remain uncommon. Of those that have been reported (31-40), most usually either require the use of templates to assemble in solution, or assemble only in the solid state. Part of the reason for this limitation is possibly the fact that, in most cases, flexible ligands were used. By contrast, structures derived from rigid tritopic linkers with cis-metal ions are either: (i) tetrahedral M 6 L 4 cages (41) where L is a planar ligand, or (ii) double-square M 6 L 4 cages (42) where L is a 109°linker ligand. Construction of the M 3 L 2 , D 3h species is complicated by the fact that rigid tritopic linkers with ideal mutual angles of 60°are not easily accessible. A noteworthy trigonal bipyramidal structure (35), made from Pd(II) ions and a calix[3]arene subunit, was shown to be able to reversibly bind a molecule of C 60 .By exploiting incommensurate symmetry requirements for differing metallic subunits, an alternative approach to structures of this general topology was recently reported. Raymond and Wong (43-45) successfully prepared a series of M 2 MЈ 3 L 6 supramolecular clusters where a multifunctionalized ligand (L) was cleverly designed to selectively interact with two types of metal ions (one hard and one soft).Double oxidative addition ...

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“…[2][3][4][5][6] Cages with lower symmetry and triangular faces have been synthesized only in the past few years. [6][7][8][9][10] Here we report the rational design of a coordination cage with the outer shape of a trigonal bipyramid. The characterization of an intermediate gives insight into the reaction mechanism.…”

Section: Iris M Müller* and Daniela Möllermentioning

confidence: 99%

“…Nevertheless, a few systems have been reported in which the equatorial edges are not covered by ligands, and coordination cages with M 5 L 6 topology resulted (Figure 1 b). [7] A related system is shown in Figure 1 c, d, in which three metal centers (depicted in gray) are coordinated by two ligands with threefold symmetry. Depending on the geometry of the central atom or atom group (usually a phenyl ring) in this ligand, a trigonal bipyramid or a trigonal-prismatic system is formed.…”

Section: Iris M Müller* and Daniela Möllermentioning

confidence: 99%

Rational Design of a Coordination Cage with a Trigonal‐Bipyramidal Shape Constructed from 33 Building Units

Müller

Möller

2005

Angew Chem Int Ed

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Rational Design and Assembly of M₂M‘₃L₆Supramolecular Clusters withC₃_hSymmetry by Exploiting Incommensurate Symmetry Numbers

Cited by 108 publications

References 64 publications

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Self-assembly of nanoscopic coordination cages of D _3h symmetry

Rational Design of a Coordination Cage with a Trigonal‐Bipyramidal Shape Constructed from 33 Building Units

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Rational Design and Assembly of M2M‘3L6Supramolecular Clusters withC3hSymmetry by Exploiting Incommensurate Symmetry Numbers

Cited by 108 publications

References 64 publications

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

Self-assembly of nanoscopic coordination cages of D 3h symmetry

Rational Design of a Coordination Cage with a Trigonal‐Bipyramidal Shape Constructed from 33 Building Units

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Product

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Rational Design and Assembly of M₂M‘₃L₆Supramolecular Clusters withC₃_hSymmetry by Exploiting Incommensurate Symmetry Numbers

Self-assembly of nanoscopic coordination cages of D _3h symmetry