Poly(diiodiacetylene), or PIDA, is a conjugated polymer containing the poly(diacetylene) (PDA) backbone but with only iodine atom substituents. The monomer diiodobutadiyne (1) can be aligned in the solid state with bis(nitrile) oxalamide hosts by hydrogen bonds between oxalamide groups and weak Lewis acid−base interactions (halogen bonds) between nitriles and iodoalkynes. The resulting cocrystals start out pale blue but turn shiny and copper-colored as the polymerization progresses. The development of a crystallization methodology that greatly improves the yield of PIDA to about 50% now allows the full characterization of the polymer by X-ray diffraction, solid-state 13C MAS NMR, Raman, and electron absorption spectroscopy. Comparison of a series of hosts reveals an odd−even effect in the topochemical polymerization, based on the alkyl chain length of the host. In the cocrystals formed with bis(pentanenitrile) oxalamide (4) and bis(heptanenitrile) oxalamide (6), the host/guest ratio is 1:2 and the monomer polymerizes spontaneously at room temperature, while in the case of bis(butanenitrile) oxalamide (3) and bis(hexanenitrile) oxalamide (5), where the host and guest form cocrystals in a 1:1 ratio, the polymerization is disfavored and does not go to completion. The topochemical polymerization can also be observed in water suspensions of micrometer-sized 6·1 cocrystals; the size distribution of these microcrystals, and the resulting polymer chains, can be controlled by sonication. Completely polymerized PIDA cocrystals show a highly resolved vibronic progression in their UV/vis absorption spectra. Extensive rinsing of the crystals in organic solvents such as methanol, THF, and chloroform separates the polymer from the soluble host. Once isolated, PIDA forms blue suspensions in a variety of solvents. The UV/vis absorption spectra of these suspensions match the cocrystal spectrum, without the vibronic resolution. However, they also include a new longer-wavelength absorption peak, associated with aggregation of the polymer chains.
In Lewis-basic solvents, alkynyl carbons bonded to iodine have chemical shifts approximately 12-15 ppm higher in frequency than the corresponding shifts in CDCl3. We offer computational evidence that this solvent effect comes directly from polarization of the iodoalkyne triple bond. Hartree-Fock and Density Functional Theory calculations reproduce the change in chemical shift for a gas-phase complex between the iodoalkyne and dimethyl sulfoxide as Lewis base. The amount of spin-orbit coupling from the adjacent iodine does not change appreciably in the complex, according to the calculations.
Recent experiments have demonstrated that the (13)C NMR spectra of iodoalkynes exhibit a strong solvent effect because of complexation with Lewis-basic solvents. This paper describes DFT NMR calculations (B3LYP-GIAO with LanL2DZ or Sadlej pVTZ basis set) of iodoalkynes and their Lewis acid-base complexes, interpreted by using Natural Chemical Shift (NCS) analysis within the framework of the Ramsey formalism for chemical shift. In particular, the paper presents calculations on diiodoethyne and its complexes with one and two ammonia molecules. Examination of the orbital changes upon forming the mono- and bisammonia complexes indicates that mixing of the nitrogen lone pair with the C-I antibonding orbital increases the paramagnetic deshielding at C1. Further increases can be attributed to increased polarization of the iodine lone-pair orbitals onto C1. The haloiodoalkyne series XCCI (X = F, Cl, Br, I) offers additional support for this model of the solvent effect.
A new method to prepare phenanthro[9,10-c]thiophenes has been developed. In the presence of triflic acid, 3,4-diaryl thiophenes undergo 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-promoted cyclo-oxidation. NMR and computational studies indicate that protonation of the thiophene plays a key role in this reaction. The reaction can be used to prepare phenanthro[9,10-c]thiophene, as well as derivatives with alkyl, bromo, and methoxy substituents. However, the yields and selectivity of the reaction depend on both the nature and location of the substituents. Bis(3-methoxyphenyl)thiophene reacts under these conditions to give the desired product in 57 % yield, while bis(4-methoxyphenyl)thiophene gives no product. Bis(3-bromophenyl)thiophene did not react, but cyclo-oxidation of bis(4-bromophenyl)thiophene provides the desired product in 34 % yield.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Diiodobutadiyne forms cocrystals with bis(pyridyl)oxalamides in which the diyne alignment is near the ideal parameters for topochemical polymerization to the ordered conjugated polymer, poly(diiododiacetylene) (PIDA). Nonetheless, previous efforts to induce polymerization in these samples via heat or irradiation were unsuccessful. We report here the successful ordered polymerization of diiodobutadiyne in these cocrystals, by subjecting them to high external pressure (0.3-10 GPa). At the lower end of the pressure range, the samples contain primarily monomer, as demonstrated by X-ray diffraction studies, but some polymerization does occur, leading to a pronounced color change from colorless to blue and to the development of intense Raman peaks at 962, 1394, and 2055 cm-1, corresponding to the poly(diacetylene). At higher pressures, the samples turn black and contain primarily polymer, as determined by solid-state NMR and Raman spectroscopy. Both density functional theory calculations (B3LYP/LanL2DZ) and comparisons to authentic samples of PIDA have confirmed the data analysis.
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The polymerization of simple conjugated dienes has long been of interest: polydienes occur throughout Nature, and polyisoprene and its analogues form the basis of entire industries. In contrast, the polymers of similar small conjugated compounds, diacetylenes, trienes, and triacetylenes, are either unknown or laboratory curiosities. For 40 years, the only viable synthetic method for the 1,4-polymerization of a diacetylene was a topochemical polymerization in a condensed phase. But such an approach is hit or miss: if the diacetylene monomers have a solid-state structure preorganized at distances matching the repeat distance in the final polymer, then thermal or photochemical energy can bring about the polymerization. However, most monomers lack the proper structural parameters and simply do not react. As discussed in this Account, we have developed a supramolecular host−guest strategy that imposes the necessary structural parameters upon a diacetylene monomer that otherwise does not polymerize. We apply this strategy in the synthesis of new types of conjugated polymers made from diacetylenes, triacetylenes, and trienes. To implement the host−guest strategy, we chose a host that would self-assemble into a supramolecular structure with the requisite intermolecular spacing. For diacetylenes, the ideal spacing is 4.9 Å, and the oxalamides, which routinely crystallize with a spacing of 5 Å, make ideal host molecules. We chose specific oxalamide host substituents that bind to the diacetylene guest molecule, typically through hydrogen bonding. We have focused upon the single-crystal-to-single-crystal polymerizations, allowing us to obtain and characterize the polymers in perfect crystalline form and to define and better understand the reaction trajectories. We have prepared several new classes of polydiacetylenes using this strategy, including the first terminal polydiacetylenes and an aryl-substituted diacetylene. Interestingly, to prepare poly(diiododiacetylene), we used halogen bonds to bind the host and guest. The simplest polydiacetylene known, poly(diiododiacetylene), lacks the side chains that complicate the structures of similar previous polymers. Future studies should provide insights into the role of such side chains in conjugated materials. We further demonstrated the strength of the host−guest strategy by moving from the polydiacetylenes to the polytriacetylenes. Although the structural requirements for a triacetylene polymerization had been stated decades ago, no one had ever found a triacetylene with the requisite spacing of 7.4 Å. We designed a series of pyridine-substituted vinylogous amide hosts to achieve this spacing. Cocrystallization of these host molecules with a triacetylene dicarboxylic acid gave us the desired structure. Using thermal annealing, we completed the synthesis of the triacetylene polymer.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
