The radical reaction between hexaphenylcyclohexaarsine (1) and acetylenic compounds with various substituents (2a-d) using a catalytic amount of AIBN provided the corresponding alternating copolymer, poly(vinylene-arsine). The copolymers obtained were soluble in common organic solvents such as THF, chloroform, benzene, and toluene. From gel permeation chromatographic analysis (chloroform, PSt standards), the number-average molecular weights of the copolymers were found to be several thousands. Structural characterization of the copolymers was provided by 1 H and 13 C NMR spectroscopies. The measurement of the conversion rate of 2a-d during the copolymerization by using gas chromatography gave an evidence to support the assumption that the formation of vinyl radicals by addition of arsenic radicals to acetylenic compounds was the rate-determining step in this copolymerization system. The copolymer obtained showed fluorescence properties which were influenced by the substituents of the acetylenic compounds.

dro-1,4-diarsinines, were synthesized by radical reactions of pentamethylcyclopentaarsine ( 1) and acetylenic compounds. The radical reactions of 1 and acetylenic compounds such as dimethyl acetylenedicarboxylate (2a) and 4-ethynylpyridine (2b) in refluxing benzene with 2,2′-azobis(isobutyronitrile) (AIBN; 5 mol %) under a nitrogen atmosphere proVided the corresponding 1,4-dihydro-1,4-diarsinines (3). Formation of 1,4dihydro-1,4-diarsinine was confirmed by 1 H and 13 C NMR spectra and FAB-mass spectrometry. The structures of 3 were confirmed as cis(e,e) forms by X-ray crystallography. This is a facile synthesis of cyclic organodiarsenic compounds, in which no Volatile toxic intermediates such as arsenic chlorides and arsenic hydrides were used. MoreoVer, this is the first example of the synthesis of 1,4-dihydro-1,4-diarsinines.

Novel 1,4-diarsa-2,5-cyclohexadiene, i.e., 1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(tert-butoxycarbonyl)-1,4-diarsinine, was synthesized by radical reaction of pentamethylcyclopentaarsine (cyclo-(MeAs) 5 ) and di-tert-butyl acetylenedicarboxylate. Two steroisomers, cis-DHDAtBu and trans-DHDAtBu, were obtained as crystals, of which structures were determined by X-ray crystallography. The six-membered ring in cis-DHDAtBu has a boat form, and both the methyl groups on the arsenic atoms are in equatorial positions. Two different polymorphs of trans-DHDAtBu were obtained as a pale yellow platelet crystal and a colorless crystalline fiber. The colorless crystal has a boat-shaped sixmembered ring, and the yellow crystal has a nearly flat chair-shaped ring. The double bonds connected with the two arsenic atoms were longer than that of the boat-shaped DHDAtBu. The UV-vis absorption spectra of cis-DHDAtBu and trans-DHDAtBu in CH 2 Cl 2 showed long-wavelength absorption maxima at 272 and 300 nm, respectively.

Mono- and dinuclear trans-dichloroplatinum(II) complexes, i.e., trans-PtCl2(cis-DHDAtBu)2 and trans,trans-Pt2Cl4(cis-DHDAtBu)2, respectively, using cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(tert-butoxycarbonyl)-1,4-diarsinine (cis-DHDAtBu), which was prepared by the radical reaction of pentamethylcyclopentaarsine (cyclo-(MeAs)5) and di-tert-butyl acetylenedicarboxylate, were obtained individually as only products by stoichiometric addition of cis-bis(benzonitrile)dichloroplatinum to cis-DHDAtBu. Replacement of chloride with iodide by adding KI into acetone solutions of trans-PtCl2(cis-DHDAtBu)2 and trans,trans-Pt2Cl4(cis-DHDAtBu)2 gave trans-PtI2(cis-DHDAtBu)2 and trans,trans-Pt2I4(cis-DHDAtBu)2, respectively. The structures of all the obtained compounds were confirmed by 1H and 13C NMR spectra, X-ray crystallography, and elemental analysis. The interior angles around the arsenic and the As−CC bond angle were significantly varied in a series of the present platinum(II) complexes. These observations suggest that the flexibility of the bond angles around the arsenic center is an inherent property in the present organoarsenic compounds. The intermetallic interaction was induced in the dinuclear platinum(II) “face-to-face” complex using cis-DHDAtBu by the replacement of chloride with iodide. The distance of the Pt−Pt of trans,trans-Pt2I4(cis-DHDAtBu)2 was shortened compared with that of trans,trans-Pt2Cl4(cis-DHDAtBu)2, and the new broad absorption band at around 562 nm was observed in the solution of trans,trans-Pt2I4(cis-DHDAtBu)2. Density functional theory calculations indicate that the frontier molecular orbitals in trans,trans-Pt2Cl4(cis-DHDAOH)2, in which H atom surrogates were used in place of the tBu group, show no d−d interaction orbitals. On the other hand, the HOMO level in trans,trans-Pt2I4(cis-DHDAOH)2 has mainly d xz contributions in the π*-antibonding MO.

We studied ring-collapsed radical alternating copolymerization (RCRAC) of hexaphenylcyclohexastibine (cyclo-(PhSb)6) and several acetylenic compounds in the presence of a catalytic amount of 2,2‘-azobis(isobutyronitrile) (AIBN) in tetrahydrofuran at 70 °C. Although the monosubstituted acetylenic monomers, phenylacetylene (1a), 4-cyanophenylacetylene (1b), and 4-methoxyphenylacetylene (1c), gave low molecular weight poly(vinylene stibine)s, RCRAC of dimethyl acetylenedicarboxylate (1d) and cyclo-(PhSb)6 provided a corresponding poly(vinylene stibine) (2d) of which the number-average molecular weight was 4300 by gel permeation chromatographic analysis. The structure of 2d was supported by 1H and 13C NMR spectra and elemental analysis. The structure and the molecular weight of 2d were insensitive to solvents and the feed ratio of the monomers. When hexaphenylcyclohexaarsine (cyclo-(PhAs)6) was used in RCRAC with 1d, no polymerization proceeded. These results were derived from different reactivity of pnictogen radicals. When the results of RCRAC of cyclo-(PhAs)6 and that of 2 are compared, the arsenic radicals had more reactivity to the ethynyl groups and the antimony radicals had more reactivity toward the vinyl radicals.