Neil E. Schore

Donor-acceptor biomorphs from the ionic self-assembly of porphyrins.

Microscale four-leaf clover-shaped structures are formed by self-assembly of anionic and cationic porphyrins. Depending on the metal complexed in the porphyrin macrocycle (Zn or Sn), the porphyrin cores are either electron donors or electron acceptors. All four combinations of these two metals in cationic tetra(N-ethanol-4-pyridinium)porphyrin and anionic tetra(sulfonatophenyl)porphyrin result in related cloverlike structures with similar crystalline packing indicated by X-ray diffraction patterns. The clover morphology transforms as the ionic strength and temperature of the self-assembly reaction are increased, but the structures maintain 4-fold symmetry. The ability to alter the electronic and photophysical properties of these solids (e.g., by altering the metals in the porphyrins) and to vary cooperative interactions between the porphyrin subunits raises the possibility of producing binary solids with tunable functionality. For example, we show that the clovers derived from anionic Zn porphyrins (electron donors) and cationic Sn porphyrins (electron acceptors) are photoconductors, but when the metals are reversed in the two porphyrins, the resulting clovers are insulators.

The polymer-supported Cadiot-Chodkiewicz coupling of acetylenes to produce unsymmetrical diynes

Abstract Cu(II)-catalyzed coupling of polymer-bound ω-haloalkyn-l-ols to terminal alkynes proceeds in moderate yield to give unsymmetrical diynes upon hydrolytic removal from the polymer. Formation of the symmetrical homocoupled byproduct is suppressed relative to conventional Cadiot-Chodkiewicz conditions in homogeneous solution.

A polymer-supported C2-symmetric chiral auxiliary: Preparation of non-racemic 3,5-disubstituted-γ-butyrolactones

A polymer-bound “C2-symmetric” pyrrolidine-based auxiliary is reported and shown to serve an effective control element for a three-step process consisting of N-acylation, Cα-alkylation, and subsequent iodolactonization to deliver optically active 3,5-disubstituted-γ-butyrolactone.

Polymer-supported synthesis as a tool for improving chemoselectivity: Pauson-Khand reaction

Abstract Intermolecular Pauson-Khand (PK) reactions of norbornene-derived substrates have been carried out with several α,ω-alkynols under both normal homogeneous conditions and with the alkynol bound to functionalized Merrifields polymer beads. With 2% crosslinked resin chemoselectivity favoring PK product formation over alkyne trimerization and other related side reactions is enhanced over that found either in solution or on 1% crosslinked polymer. Alkynol chain length and nature of the linker also significantly affect the outcome of the polymer-supported process.

First example of reversal of normal stereoselectivity in the intramolecular Pauson-Khand reaction

Stereoselectivity favoring exo substituent orientation in the intramolecular Pauson-Khand reaction of 3-methyl-4-hydroxy-1,6-heptenynes to form bicyclo[3.3.0]octenones is affected by the relative stereochemistry at C3 and C4. Cycloaddition of one stereoisomer of 3,5-dimethyl-4-propargyl-1,6-heptadiene gives predominantly the bicyclo[3.3.0]octenone isomer containing both substituents in more hindered endo orientations. An explanation based upon the effect of conformational preferences prior to metallacycle formation is proposed.

Efficient synthetic entry to oxygen-bridged lactaranes using organometallic methodology: a short synthesis of furanether B

Abstract A 9-step synthesis of the sesquiterpene furanether B from 2-methylfuran is described; the furan moiety is carried through the last 5 steps, which include Pauson-Khand cycloaddition, the key to the synthesis.

Reaction of dicobalt octacarbonyl with acetylene and carbon monoxide at low temperature and pressure: Formation of cyclic enone products

Abstract Dicobalt octacarbonyl is shown to react with acetylene and carbon monoxide under mild conditions in dimethoxyethane or benzene to produce, in low yields, bicyclo[3.3.0]octa-3,7-diene-2,6-dione, benzoquinone, and the cyclopentadienone-derived products 3a,4,7,7a-tetrahydro-2,7-methanoindene-1,10-dione, 1-indanone, tetracyclo[5.5.2.0 2,6 0 8,12 ]tetradeca-4,10,13-triene-3,9-dione, and tetracyclo[5.5.2.0 2,6 0 8,12 ]tetradeca-4,9,13-triene-3,11-dione. Possible mechanisms for the formation of these products are discussed.

Reduction chemistry of substituted derivatives of cyclopentadienyldicarbonylcobalt. ESR and infrared spectroscopy and their relationship to electronic structure of the dinuclear reduction products

Abstract The reductions of five substituted cyclopentadienyl dicarbonyl cobalt complexes have been carried out. Mixtures of dinuclear radical anions, Ring 2 Co 2 (CO) −• 2 , and ring loss products are obtained with the former predominating except in the case of (C 5 H 4 CO 2 CH 3 )Co(CO) 2 where 85% ring loss is observed. Infrared and electron spin resonance measurements on the radical anions yield the following data: g iso = 2.08 ± 0.01 and g 1 , = 2.18 ± 0.01 for all systems; a iso and a 1 vary over a 10% range, thereby revealing variations in spin density on cobalt over the series. A qualitative electronic picture of the system is presented.

Use of metal complexation in the synthesis of medium-ring acetylenic lactones

The hexacarbonyldicobalt complexes of several appropriately designed acetylenic lactone precursors have been prepared, and lactones containing Co2(CO)6-complexed triple bonds in seven-, ten-, and eleven-membered rings obtained. The latter were best obtained through a retro-Dieckmann fragmentation of 2-(hydroxybutynyl) derivatives of 1,3-clohexanedione. Attempts to extend this reaction to cyclohexanones bearing other anion-stabilizing groups in the 2-position or to 1,3-cyclopentanediones were unsuccessful. Decomplexation afforded the metal-free 11-ring lactone, characterized crystallographically. Treatment of this system with basic reagents led to dimerization. In the case of the smaller rings, cyclization of the complexed acetylenic hydroxyacids under Mukaiyama conditions (2-chloro-N-methylpyridinium iodide, CH2Cl2, reflux) succeeded in modest yields.

Preparation and study of cyclic polynuclear ferrocenes derived from (C6H5)2PCH2CH2Si(CH3)2C5H4Li as a bridging ligand

Abstract The synthesis of the potential bridging ligand (C6H5)2PCH2CH2Si(CH3)2C5H4 (3) is described. The ferrocene (6 derived from 3 has been found to form macrocyclic complexes with metal fragments NiCl2, NiBr2, and Co2(CO)6. Although monomeric, bimetallic products might have been expected based upon the reduced steric demands of ligand 3 relative to an analogous ligand, (C6H5)2PCH2Si(CH)3)2C5H4 (1), it appears that the increased flexibility in 3 is the overriding factor leading to a preference for inter- rather than intramolecular coordination of the second phosphine function in 6.