Takahiro Kusukawa

Cavity‐Directed, Highly Stereoselective [2+2] Photodimerization of Olefins within Self‐Assembled Coordination Cages

Selective encapsulation and isolation of molecules are one of the most attractive features of cagelike molecules.[1] Intermolecular chemical reactions of two or more substrates encapsulated in a molecular cage can be remarkably accelerated and suitably controlled as a result of the dramatically increased concentration and the strictly regulated orientation of the substrates in the cavity.[2] Such systems provide artificial mimics of the sophisticated active site of enzymes.[3] Recently we reported that structurally well-defined coordination cages (1 and 2), which self-assemble from six metal ions and four tridentate ligands, selectively encapsulate large organic molecules at the fixed position of the nanosized cavity.[4, 5] Thus, they are expected to facilitate intermolecular [2 2] photochemical reactions and control the stereoand regiochemistry in stringent geometrical environment. The photodimerization has been studied extensively in some media such as micelles, zeolites, organic hosts (for example, cyclodextrins and cucurbiturils),[6] and crystals.[7] However, a high degree of stereoand regiochemical control is still desired. Here we report remarkably accelerated, highly stereoregulated [2 2] photodimerization of acenaphthylenes (3)[8] and naphthoquinones (4)[9] within the coordination cages (1 and 2) in an aqueous medium that give rise to only syn and head-to-tail isomers. Quantitative formation of a syn dimer of acenaphthylene (3a) within cage 1 was clearly observed in the following experiment: An excess amount of 3a was suspended in a solution of 1 in D2O (2.0 m ) for 10 min at 80 C. Analysis of the D2O solution after filtration of free 3a by 1H NMR spectroscopy showed formation of the encapsulation complex 1 ¥ (3a)2 had occurred (Figure 1a). The signals of 3a were highly upfield-shifted as a result of the efficient encapsulation in the cavity. After the clear solution was irradiated (400 W) for 0.5 h at room temperature, the signals derived from 3a completely disappeared and one set of new signals appeared at 5.84, 5.61, 3.39, and 2.87 (Figure 1b). The signals of 1

Self-Assembly of Nanometer-Sized Macrotricyclic Complexes from Ten Small Component Molecules

Nanometer-sized bowls: six metal centers and four tridentate ligands self-assemble in aqueous solution to give the macrotricycle 1, which has approximate dimensions of 3×2×2 nm. Another macrocycle (not shown), obtained with a different ligand, is of similar size and topology but differs considerably from 1 in its host-guest behavior.

Molecular paneling via coordination

This article deals with a coordination approach to three-dimensional assemblies via ‘molecular paneling’. Families of planar exo-multidentate organic ligands (molecular panels) are found to assemble into large three-dimensional assemblies through metal-coordination. In particular, cis-protected square planar metals, (en)Pd2+ or (en)Pt2+ (en = ethylenediamine), are shown to be very useful to panel the molecules. Metal-assembled cages, bowls, tubes, capsules, and polyhedra are efficiently constructed by this approach.

Encapsulation of Large, Neutral Molecules in a Self‐Assembled Nanocage Incorporating Six Palladium(II) Ions

What a large interior space in a molecule! Self-assembled cage compound 1 has a nanosized cavity (8 Å in diameter) and can encapsulate as many as four molecules of o-carborane. A bulky guest, 1,3,5-tri-tert-butylbenzene, once encapsulated by means of thermally activated slippage, cannot escape from the cavity at room temperature since it is larger than the cavity entrance.

A Discrete Supramolecular Conglomerate Composed of Two Saddle-Distorted Zinc(II)-Phthalocyanine Complexes and a Doubly Protonated Porphyrin with Saddle Distortion Undergoing Efficient Photoinduced Electron Transfer†

Porphyrins (Por) and phthalocyanines (Pc) exhibit lightharvesting efficiency for producing charge-separated states as models of the reaction center in photosynthetic bacteria and photovoltaic cells for energy conversion. The use of supramolecular assemblies to model the functionality of the reaction center is an attractive and fruitful strategy to develop photofunctional materials and devices. Porphyrins exhibit strong Soret bands around 400 to 450 nm, whereas phthalocyanines show strong Q bands around 700 to 800 nm. Thus, the combination of those two p systems can cover nearly the whole range of the visible region and can be a useful strategy for development of photofunctional materials for efficient light-energy conversion. Attempts have so far been made to synthesize covalently linked Por–Pc heterodyad molecules and construct Por–Pc heterosupramolecules. Recently, ZnPor and ZnPc have been reported to form two-dimensional arrays on gold surfaces, and the formation of a cofacial ZnPor–ZnPc coordination tetrad has also been reported. However, a crystal structure determination of a discrete supramolecular assembly composed of both Por and Pc has yet to be reported. In addition, since the Q-band absorption of Pc usually overlaps the wavelength of fluorescence of Por, energy transfer is favored over electron transfer in most heterodyads. We have developed supramolecular assemblies based on a saddle-distorted nonplanar porphyrin, dodecaphenylporphyrin (H2DPP), and its metal complexes. [11–13] The saddle distortion facilitates protonation of pyrrole nitrogen atoms to allow access to a stable diprotonated porphyrin, which can act as an electron acceptor. In addition, the saddle distortion affords higher Lewis acidity at the metal center to maintain axial coordination of ligands, as a result of poor overlap of the pyrrole nitrogen lone pair orbitals with d orbitals of the metal center. In contrast, the Zn complex of the saddle-distorted phthalocyanine 1,4,8,11,15,18,22,25-octaphenylphthalocyanine (H2OPPc) exhibits a lower oxidation potential relative to the corresponding porphyrin complex. To construct supramolecular conglomerates composed of both porphyrin and phthalocyanine in a well-defined manner, we have taken advantage of saddle distortion of both components. Herein, we report formation of a discrete supramolecular assembly composed of H4DPP 2+ and [Zn(OPPc)] connected by 4-pyridinecarboxylate (4-PyCOO ) with coordination and hydrogen bonding (Figure 1). The supramolecular conglomerate [(H4DPP){Zn(OPPc)(k-N-4-PyCOO)}2] (1) was synthesized by reaction of [H4DPP](4-PyCOO)2 (2) and Zn(OPPc) (3) in toluene. We crystallized and isolated 1 in pure form by vapor diffusion of hexanes into solution of the mixture in toluene. X-ray crystallography of 1 unambiguously established its structure (Figure 2a).

DOSY Study on Dynamic Catenation: Self-Assembly of a [3]Catenane as a Meta-Stable Compound from Twelve Simple Components

Synthesis of [2]catenane 6 has been successfully achieved by the combination of Pd complex 1 and pyridines 2 and 3 at a molar ratio of 2:1:1 in D20. A mixture of square molecule 4 (prepared from 1 and 2) and macrocycle 5 (obtained from 1 and 3), in which the final ratio of 1, 2, and 3 was kept 2:1:1 reorganizes in D2O/CD3OD (1:1) to form 6 within one day. However, the same mixture in D2O shows the formation of novel [3]catenane 7 along with the [2]catenane. In order to make 7, the theoretical ratio of components 1, 2, and 3 should be 3:1:2. Thus, deliberately maintaining such ratio of the above-mentioned molecules, a higher proportion of the [3]catenane is observed in D2O as found from 1H NMR spectra of the system. Reorganization of the twelve components to form [3]catenane is supported by studies with the DOSY method. This method is a first attempt to separate, from a mixture, either catenanes or any other supramolecular self-assembly structures. CSI-MS studies further support the assigned catenane super structures 6 and 7. All the results indicate that the [2]catenane is thermodynamically the most stable structure, while the [3]catenane is a meta-stable self-assembly.

Molecular Paneling by Coordination: An M15L6 Hexahedral Molecular Capsule having Clefts for Reversible Guest Inclusion

Only one positional isomer is obtained from the assembly of 21 small components. A triangular molecular panel with five coordination sites is assembled upon complexation with [PdII (en)] (en=ethylenediamine) into a unique M15 L6 hexahedral coordination capsule (see X-ray structure). The capsule can encapsulate/exchange organic guests reversibly through the clefts at the nonbinding sites of the capsule.

Einlagerung von großen, neutralen Molekülen in einem durch Selbstorganisation gebildeten Nanokäfig, der sechs PdII-Ionen enthält

Bis zu vier Gastmolekule (ortho-Carboran oder Adamantan) kann der durch Selbstorganisation gebildete Kafig 1 in seinem Hohlraum aufnehmen, dessen Durchmesser ca. 8 A betragt. Der sperrige Gast 1,3,5-Tri-tert-butylbenzol, der groser als die Hohlraumoffnung ist, kann nur unter Erwarmen der Losung aufgenommen werden, kann dann aber bei Raumtemperatur den Hohlraum nicht mehr verlassen.

The polar effect on the regiochemistry of nucleophilic substitution of trifluoromethylated π-allylpalladium complex

Abstract Allylic nucleophilic substitution of trifluoromethyl-group substituted cinnamyl carbonate with diethyl malonate anion in the presence of palladium complex catalyst gave regio- and stereoselectively the SN2′ product. The regiochemistry caused by the polar effect of trifluoromethyl group was opposite to the methylated cinnamyl substrate in a similar steric environment. The sterically more hindered mesityl and tert-butyl substrates than phenyl derivative also gave the products reacted at the more hindered sites. Although o-substituted substrates expecting intramolecular coordination to affect regiochemistry were examined, no alternative regioisomers were detected.

Alkylative Carbocyclization of ω‐Iodoalkynyl Tosylates with Alkynyllithium Compounds Through a Carbenoid‐Chain Process Leading to (1‐Iodoprop‐2‐ynylidene)tetrahydrofurans and ‐cyclopropanes

Alkylative carbocyclization reactions of omega-iodoalkynyl tosylates with alkynyllithium compounds to give products with incorporated iodine atoms are described. Slow addition of 2-(3-iodoprop-2-ynyloxy)ethyl tosylates to 1-alkynyllithium compounds in tetrahydrofuran at 40 degrees C followed by additional stirring at this temperature gives (Z)-3-(1-iodoprop-2-ynylidene)tetrahydrofurans stereoselectively in good to moderate yields. Under similar conditions at 0 degrees C, 4-iodobut-1-ynyl tosylates react with 1-alkynyllithium compounds to give (1-iodoprop-2-ynylidene)cyclopropanes. The carbocyclization reactions are proposed to proceed through a new carbenoid-chain process involving the exo cyclization of a lithium acetylide intermediate and the vinylic substitution of the resulting TsO,Li-cycloalkylidenecarbenoids (Ts=tosyl) by 1-alkynyllithium compounds.