Structural Characterization of a Cyclohexamericmeta-Phenyleneethynylene Made by Alkyne Metathesis with In Situ Catalysts

Abstract

Cyclophenyleneethynylenes (CPEs) have recently made a spectacular appearance as a novel class of carbon-rich supramolecular materials. [1, 2] Moore and co-workers have established meta-cyclophenyleneethynylenes (m-CPEs) [1±3] as tubular discotic liquid crystals [3d] and as porous, hydrogenbonded, channel-forming organic solids. [4] Channels in m-CPEs are formed through a combination of hydrogen bonds and the internal cavities of the hexagonally packed m-CPE. However only a low-quality single-crystal X-ray structure of this exciting CPE was obtained [4] and to our surprise, no highquality X-ray structures of m-CPE-derivatives are known. [2b, 5] In the past CPEs have been made by the Pd/Cu-catalyzed coupling of the Heck ± Sonogashira type. Substrates were either a preformed linear oligomer, [3] a half-cycle, [5] or 1-ethynyl-3-halo-substituted benzenes. [6] The latter compounds gave only very low yields of CPEs. Weiss et al., [7] Fürstner et al., [8] and our group [9] have reported that alkyne metathesis either with defined carbyne complexes [7,8] or with in situ catalysts, which are obtained from [Mo(CO) 6 ] and 4-chlorophenol in off-the-shelf 1,2-dichlorobenzene, [10,11] is an excellent method for preparing saturated and unsaturated ring systems. Herein, we report the synthesis of the new hexameric meta-cyclophenyleneethynylenes 2 a, b, d from dipropynylated benzenes 1 by alkyne metathesis as well as the isolation of the corresponding polymers 3 a ± d (Scheme 1). [12] The isolated m-CPE 2 a and its triosmiumdecacarbonyl complex 4 a have been characterized structurally by single-crystal X-ray diffraction analyses.The monomers 1 were prepared from the corresponding diiodides [12] by Pd-catalyzed propynylations. [10] Heating 1 a, [Mo(CO) 6 ], and either 4-chlorophenol or 4-trifluoromethylphenol in off-the-shelf 1,2-dichlorobenzene under a slow stream of nitrogen furnishes a mixture of oligomers and

Alkyne Cross Metathesis Reactions of Extended Scope

“…Only recently it has been shown that this transformation holds great promise for advanced organic synthesis and polymer chemistry. In particular, various applications to ring-closing alkyne metathesis, − alkyne homodimerization, cyclooligomerization, or polymerization reactions 7 display a remarkably wide scope. A largely unexplored field of application, however, is alkyne cross metathesis (ACM).…”