Angew. Chem. lnt. Ed. Engl. 26 (1987) No. 9 Angen Chem. I n f . Ed. Engl. 26 (1987) No. 9 0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim. 1987 0570-0833/87/0909-0931 $ 02.50/0

On treatment with an organolithium 1,4-diiodocubane generates cubane-1,4-diyl, a highly reactive species, shown here to be a versatile precursor to numerous aryl substituted cubanes, available now for the first time in high yield. The diyl is demonstrated to provide a good route to bicubyl and its derivatives. A kind of “living polymerization” of the diyl is developed to give the p-[n]cubyls. These oligomers are rigid rods made up of cubanes linked together at the 1 and 4 positions, each cubane adding ∼4.15 Å to the length. The properties of these rods, some more than 15 Å long, are discussed, as are methods for modifying their solubility. X-ray crystallographic analyses of some of these compounds are presented, with emphasis on packing parameters.

Rates of intramolecular electron transfer have been measured through cubanes. Pulse radiolysis was used to study the reactions B-CunN (2-naphthyl), and Cu, is the spacer composed of n = 1-3 1,Ccubyl oligomers. Electronic couplings, V, for these reactions were found to decrease exponentially with increasing distance, V(R) = V(R0) exp[-0.5 B-R], with @ = 0.90 A-I. While the electrontransfer rates in these cubanes are a factor of 10 larger than in similar compounds with spacers based on cyclohexane, the distance dependence is almost identical to that for the cyclohexyl-type molecules, @ = 0.94 A-l. The unusual properties of the cubanes enhanced the electron-transfer rates but did not lead to a large difference in distance dependence.BCunN-3 where B = (4-biphenylyl), N IntroductionIn the last decade, numerous compounds have been studied to determine the distance dependence for rates of intramolecular electron-transfer (ET) reactions.'-z1 Generally, the rate was found to decrease approximately exponentially with donor-acceptor (D-A) separation, but this dependence on distance, due primarily to through-bond interactions, varies markedly with the system studied.Previous work from these laboratories' studied the electrontransfer (ET) reactionwhere B = (Cbiphenylyl), N = (Znaphthyl), and S represents spacer groups which varied from 1,3-~yclohexane (4-bonds) to 3,16-androstane (10-bonds). In this paper we report measurements of intramolecular ET rate as a function of distance for a seriesofcubaneoligomers, S = (1,4-cubyl), wheren = 1-3 (Chart I). The results from this study are compared with those for the cyclohexyl-type spacers1 to elucidate the important factors in the distance dependence of ET. These cubanes are rigid, rodlike molecules which accurately fix the donor-acceptor distance and are remarkably stable despite their highly-strained, p-rich C-C bonds.22923 We are interested in studying the cubane spacers because their properties of high connectivity, strong bond-to-bond couplings, and low ionization potential are features expected to enhance long-distance electronic couplings.2c29 The results presented here indicate that, despite the special properties of cubanes, enhancement of the interaction is substantial but not outstanding. Experimental SectionPreparation of the cubane compounds used in this study will be described elsewhere.*' The di-n-hexyl derivative of BCu3N was prepared because precursors to the unsubstituted tercubyl compound were insoluble. The anions were generated by irradiating solutions of the BSN with 30-ps pulses of 20-MeV electrons from the Argonne linac. Irradiation generates solvated electrons (<2 X l e 5 M) which attach to the donor and acceptor Abstract published in Advance ACS Absrrucrs, November 15, 1993. BCu 0 NCU groups to form an equal distribution of B-SN and BSN-. The intramolecular ET reaction is then observed photometrically as it proceeds to equilibrium. Experimental methods for sample preparation and acquisition of transient absorption data and fitting of the data have been desc...

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