No abstract

We describe the synthesis of two cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies by using the breath-figure method. Such breath figures can be washed away with an appropriate solvent. Upon pyrolysis at 500 degrees C under either nitrogen or air, the bubble arrays persist as ceramics and are insoluble in organic solvents or water. The formed pyrolyzed bubble arrays were analyzed by optical and scanning electron microscopy, as well as energy dispersive X-ray microanalysis (EDX). The composition of the ceramic materials is discussed based on EDX and IR data.

Micrometer-sized, spherical, non-fullerene carbon is found in meteorites.[1] Similar spheres have been prepared in the laboratory by pyrolysis of a) polyethylene/poly(vinyl chloride) (PVC) mixtures under high pressure, b) methane over an (undisclosed) mixed metal oxide catalyst, c) aqueous acidic solutions of glucose, d) poly(tetrafluoroethylene) (PTFE) in supercritical water, e) ferrocene, f) hexachlorobenzene with sodium metal in an autoclave, and g) tetrachloromethane with sodium amide. [2±7] In cases where transition metals are involved in the process, metal kernels were observed in the center of the spheres as they seem to function either as a catalyst and/or as a nucleation site. [4] Spheres in which the metal is distributed evenly and homogeneously (either as an alloy or as a carbide/ ceramic) are unknown: [2±7] the high-yield formation of homogeneous cobalt/carbon spheres by pyrolysis of metallated poly(p-phenyleneethynylene) (PPE 7a) is reported.Tetrabenzohexadehydro [20]annulene (1) explodes to form carbon nanotubes and onions.[8] Trisdicobalt hexacarbonyl complex 2, the dicobalthexacarbonyl complex of tolane (3), and a multinuclear cobalt complex of a hexaalkynylated hexabenzocoronene derivative (4) do likewise, but under just conflagration (as opposed to explosion) or even without visible heat evolution.[9±11] The pyrolytic approach works for the ferrocene-ligated dehydroannulene 5, which deflagrates into bagel-shaped, tube-like all-carbon objects. [12] Structures 1±5 are shown in Figure 1. Synthesis and investigation of the thermal decomposition of metallated PPEs 7 was a natural yet promising extension of these reports. Post-functionalization of PPEs [13] is difficult but reduction or appendage of organo±platinum fragments [14,15] has been described. The PPEs 6a±c reacted in good-to-excellent yields (Scheme 1) with dicobalt octacarbonyl in toluene (room temperature) to give the metallated species 7a±c after precipitation into methanol. [13,16] Both IR and NMR spectroscopy indicate complete occupancy of the alkyne sites by dicobalt hexacarbonyl fragments. The organometallic PPE 7a is intrinsically less soluble than its precursor 6a. A sample of 7a of high solubility was produced when PPE 6a of low molecular weight (P n = 15, where P n is the degree of polymerization) was reacted with dicobalt octacarbonyl. The diagnostic signals in the , representing the C±O stretch vibrations of the carbonyl ligands. These C±O stretch vibrations are shifted with respect of those of Co 2 (CO) 8 , assuring that no unreacted cobalt octacarbonyl was left in the product.[17] The reaction of 7a with HCl in chloroform leads to full demetallation and the re-isolation of intact 6a, as expected for a carbonyl complex. Attempts to make 7a more lipophilic by a ligand exchange reaction with triphenylphosphine furnished a material with abysmally low solubility; the use of tributylphosphine should lead to a more soluble polymer. The metallation of 6b and the alkoxy-PPE 6c was likewise facile and gave the polycomplexes 7b and 7c...

No abstract