Insulated Molecular Wires: Dendritic Encapsulation of Poly(triacetylene) Oligomers, Attempted Dendritic Stabilization of Novel Poly(pentaacetylene) Oligomers, and an Organometallic Approach to Dendritic Rods

Abstract

Dendrons 8, 13, and 17 were subsequently attached to (E)-2,3-bis[(triisopropylsilyl)ethynyl]but-2-ene-1,4-diol (18) [4] [21] using the Mitsunobu reaction [22] to give the dendritic silyl-protected monomers 19 ± 21, respectively (Scheme 2). The yield of the third-generation compound 21 was very low (4%), possibly due to steric hindrance of the reacting COOH group by the bulky dendritic wedges in dendron 17. After deprotection with Bu 4 NF in wet THF, the free (E)-enediynes 22 ± 24 were obtained. The dendritic wedges substantially stabilize the usually rather unstable free (E)enediynes [23], and compounds 22 ± 24 can be stored in the air at ambient temperature for months without decomposition. Oxidative Hay coupling [24] of 22 ± 24 in the presence of PhCCH as an end-capping reagent [21] provided the oligomeric PTAs as solids. The first-generation compound 22 afforded separable oligomers up to the pentamer (1a ± e), which extend in length from 19.4 (1a) to 49.4 (1e) [11] [21]. For steric reasons, the second-generation derivative 23 yielded isolable oligomers only up to the trimer (2a ± c). Finally, due to severe steric overcrowding, conversion of the third generation enediyne 24 gave only end-capped monomer and dimer (3a, b) in pure form and sufficient yields.Analytical gel-permeation chromatography (GPC) proved to be extremely useful for monitoring the purification of our compounds. The separation of the oligomers was achieved by preparative GPC (Bio-Beads S-X1; CH 2 Cl 2 ), and the purity of the fractions was determined by analytical GPC because, specifically for the higher oligomers, thin-layer chromatography (TLC) was useless. With other techniques such as 1 H-and 13 C-NMR spectroscopy, we could not detect impurities (lower and higher oligomers) with less than 10% abundance, while analytical GPC was sensitive for impurities with an abundance of less than 1%. The analytical GPC traces of the firstgeneration dendritic oligomers 1a ± e are shown in Fig. 4. Optical detection occurred at 300 nm in the absorption region of the aromatic wedges. GPC Separations of the higher-generation compounds were equally efficient.The molecular constitution of the dendritic rods was confirmed by matrix-assisted laser-desorption-ionization mass spectra (MALDI-TOF-MS; matrix: 9-nitroanthracene), which depicted either the [M Na] or [M K] ions as base peaks, and NMR spectra. In the 1 H-NMR spectra of the centrosymmetrical oligomers, the number of the t-Bu resonances increases with the number of monomeric units ( Table 1). Similar behavior was observed for the aromatic protons positioned between the two alkoxy substituents of the central benzene rings that serve as linkers between PTA backbone and dendritic wedges.

Organomonophosphines in PtP2Cl2 derivatives: structural aspects

“…, P(C 6 F 5 ) 3 ( Schaefer et al 1992 ), P(OPh) 3 ( Sabounchei and Naghipour 2001 ), P(benzyl) 3 ( Johansson et al 2002 ), P(2-cyanoethyl) 3 ( Khan et al 1993 ), P(NMe 2 ) 3 ( Xi et al 1990 ), P { (MeNCH 2 CH 2 ) 3 N } ( Xi et al 1990 ), P(H) (Bu t ) 2 ( Giannandrea et al 2000 ), P(Bu t ) 2 (cy-C 3 H 5 ) ( Simms et al 1987 ), P(Bu t ) 2 (Pr i ) ( Di Meglio et al 1992 ), P(Bu t ) 2 (Ph) ( Di Meglio et al 1990 ), P(Bu t ) 2 (CH 2 -cy-C 4 H 7 ) ( Simms and Ibers 1987 ), P { (CH 2 C)(CF 3 ) 2 . (OH) } (Ph) 2 ( Montgomery et al 1987 ), P { (F 2 C)(CF 3 ) } (Ph) 2 (at 293 and 173 K; Palcic et al 2004 ), P(benzyl)(Ph) 2 ( Muller 2012b ), P { C 6 H 4 NMe 2 -4 } (cyhexyl) 2 ( Davis and Meijboom 2012 ), P(FC = CF 2 H)(cy-hexyl) 2 ( Barnes et al 2008 ), P(ClC = CF 2 )(Ph) 2 ( Barnes et al 2001 ), P { (CH 2 ) 2 (CF 2 ) 5 (CF 3 ) } 3 ( Stibrany and Gorun 1999 ), P { C 6 H 4 (Pr i )-4 } (cy-hexyl) 2 ( Vuba and Muller 2012 ), P { C 6 H 4 (CH = CH 2 )-4 } (Ph) 2 ( Ogutu and Meijboom 2011 ), P { C 6 H 4 (CF 3 )-2 } (Ph) 2 ( Croxtall et al 2002 ), P { (C 6 H 4 ((CF 2 ) 5 (CF 3 )-2) } (Ph) 2 ( Croxtall et al 2002 ), P(HNNC 5 H 10 )(Pr i ) 2 ( Clarke et al 2003 ), P(C 23 H 21 N 2 O)(Ph) 2 ( Hursthouse et al 2003a ), P(B 10 C 4 H 11 ) (Ph) 2 ( Spokoyny et al 2012 ), P(C 6 H 5 O 2 S)(Ph) 2 ( Velauthamurty et al 2009 ), P(C 7 H 9 )(Ph) 2 ( Massard et al 2012 ( Nagata et al 2003, Tokitoh et al 2004, P(C 21 H 19 O 2 )(Ph) 2 ( Schenning et al 2001 ), P(C 16 H 25 O 2 )(Ph) 2 ( Reznicek et al 2012 ), P(C 8 H 5 S 2 )(Ph) 2 ( Stott et al 2007 ), P(C 12 H 7 S 3 )(Ph) 2 ( Stott et al 2007 ), P { C 6 H 4 P(O)(OEt) 2 } (Ph) 2 ( Ellis et al 2000 ), P(C...…”

Photoisomerization of Enediynyl Linker Leads to Slipped Cofacial Hydroporphyrin Dyads with Strong Through-Bond and Through-Space Electronic Interactions

“…Continuing our studies on the dependence of photophysical properties of strongly conjugated hydroporphyrin dyads on the linking moiety, we intended to prepare a series of arrays where chlorins and bacteriochlorins are connected by a linker comprising alternating carbon–carbon triple and double bonds, i.e., hexa-3-en-1,5-diyne (enediyne) unit. Conjugated chromophores containing this unit possess unusual optical and electrochemical properties, as was demonstrated by Diederich − and others. , The Diederich group also reported a conjugated porphyrin dimer, connected by an enediyne unit . Moreover, conjugated enediynes undergo trans–cis photoisomerization, a trait that has been utilized for the development of photochromic and redox-active molecules. − Overall, we have anticipated that the combination of enediynes with hydroporphyrins will lead to molecules with interesting and useful optical and photochemical properties.…”

Synthesis and Characterization of Multinanometer-Sized Expanded Dendralenes with an iso-Poly(triacetylene) Backbone

“…Apparently, the spacing induced by the four acetylenic C-atoms between the CC bonds is enough to reduce the steric interactions between the peripheral cyclohexylidene moieties, thereby allowing a more-planar p-chromophore. Furthermore, it has been previously shown [18] that effective p-electron conjugation between directly connected CC and CC bonds does not require full planarity of the C 4 fragment in view of the cylindrical p-electron conjugation in the acetylenic bond. Both factors should enhance cross-conjugation in the expanded dendralenes as compared to the parent compounds.…”